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Dynamic Systems and Control

2010;():1-6. doi:10.1115/ESDA2010-24012.

The main contribution of this paper is to introduce a novel non-Lipschitz protocol that guarantees consensus in finite-time domain. Its convergence in networks with both unidirectional and bidirectional links is investigated via Lyapunov Theorem approach. It is also proved that final agreement value is equal to average of agents’ states for the bidirectional communication case. In addition effects of communication time-delay on stability are assessed and two other continuous Lipschitz protocols are also analyzed.

Topics: Networks
Commentary by Dr. Valentin Fuster
2010;():7-12. doi:10.1115/ESDA2010-24026.

The deployment of multi-agent systems in presence of obstacle deals with autonomous motion of agents toward a specified target by sensing each other and boundaries of obstacles. In this paper, asynchronous, scalable, distributed algorithm is used to deploy agents. Boundaries of obstacles are modeled by virtual agents. Algorithm was implemented by solving continuous n-median problem called generalized Fermat-Weber problem. It is shown that deployment is performed when position of real agents are the geometric median of their Voronoi cells. Simulation results show the validity of the proposed algorithm very well.

Commentary by Dr. Valentin Fuster
2010;():13-20. doi:10.1115/ESDA2010-24076.

This paper presents a simple approach for solving optimal control problems in wheeled mobile robots with bounded inputs. The control objective is to minimize a quadratic index of performance subject to differential constraints (the mobile robot equations of motion). The solution to the problem is obtained by utilizing an explicit trajectory parametrization method, which allows us to establish a sub-optimal control strategy by minimizing a multivariable function subject to a set of algebraic constraints. The approach is based on the flatness property, which allows us to represent the flat output by a polynomial. The bounds on the input signals are taken into consideration in the current analysis.

Commentary by Dr. Valentin Fuster
2010;():21-27. doi:10.1115/ESDA2010-24103.

To obtain economic operation of power plant steam generators, output of mechanical energy must be balanced with the electrical load while maintaining the internal variables within desired ranges. During a boiler unit operation, dynamic variables such as drum pressure, steam temperature and water level of drum must be controlled to achieve an appropriate performance. In this paper, a linear time invariant (LTI) model of a boiler unit is considered where feed-water and fuel mass rates are the control inputs. Due to the inaccessibility of some state variables of boiler system, a robust minimum-order observer is designed to gain an estimate state of the true state. Real dynamic model of boiler unit may associate with parametric uncertainties. In this case, optimum region of poles of observer-based controller are found such that the robust performance of the boiler system against model uncertainties is guaranteed.

Topics: Boilers
Commentary by Dr. Valentin Fuster
2010;():29-33. doi:10.1115/ESDA2010-24105.

Stable control of water level of drum is of great importance for economic operation of power plant steam generator systems. In this paper, a linear model of the boiler unit with time varying parameters is used for simulation. Two transfer functions between drum water level (output variable) and feed-water and steam mass rates (input variables) are considered. Variation of model parameters may be arisen from disturbances affecting water level of drum, model uncertainties and parameter mismatch due to the variant operating conditions. To achieve a perfect tracking of the desired drum water level, two sliding mode controllers are designed separately. Results show that the designed controllers result in bounded values of control signals, satisfying the actuators constraints.

Commentary by Dr. Valentin Fuster
2010;():35-41. doi:10.1115/ESDA2010-24130.

We deal with an initial-boundary value problem describing the perpendicular vibrations of an anisotropic viscoelastic plate free on its boundary and with a rigid inner obstacle. A weak formulation of the problem is in the form of the hyperbolic variational inequality. We solve the problem using the discretizing the time variable. The elliptic variational inequalities for every time level are uniquely solved. We derive the a priori estimates and the convergence of the sequence of segment line functions to a variational solution of the considered problem.

Topics: Vibration , Functions
Commentary by Dr. Valentin Fuster
2010;():43-52. doi:10.1115/ESDA2010-24153.

In this paper, a procedure to analytically develop an approximate nonlinear solution for the prototypic nonlinear mass-spring-damper system based on multi-dimensional convolution expansion theory is offered. An analytical nonlinear step response is also conducted to characterize the overall system response. The developed analytical step response provides an illumination for the source of differences between nonlinear and linear responses such as initial departure time, differences in settling times and steady value, and non-symmetric response. Feasibility of the proposed implementation is assessed by a numerical example. The developed kernel-based model shows the ability to predict, understand, and analyze the system behavior beyond that attainable by linear-based model.

Topics: Dampers , Springs
Commentary by Dr. Valentin Fuster
2010;():53-65. doi:10.1115/ESDA2010-24189.

The work points to study the effects of bodies flexibility concerning the Running Dynamics and Structural requirements and how such aspects could be integrated into a single design process of a mass transit vehicle in terms of Comfort, Safety, Track fatigue and Bogie-frame design. The multi-body system of the vehicle has been developed. The finite element model of the flexible bodies as car-body, wheel-set, bolster-beam and bogie-frame have been implemented. The critical but necessary step, in the integration process of the flexible body into a multi-body system, is the reduction of the finite element model of the body. For that reason an analytical verification in focused to validate the reduced FE-model with respect to the full FE-model has been thought, developed and implemented to provide a useful design tool; such an analytical verification aids the engineer to control and to optimize the reduction technique applied to the full-FE-model of the body. The validation procedure, which has been implemented, consists in developing an alter for the DMAP, Direct Matrix Abstraction Program of the FE-solver, and processing the output into a programming environment.

Topics: Vehicles
Commentary by Dr. Valentin Fuster
2010;():67-74. doi:10.1115/ESDA2010-24247.

Since the piezoelectric actuators have the disadvantages of small travel and hysteretic behavior, a long range friction actuating mechanism was designed. The piezoelectric material is used to generate high frequency oscillation for actuating a finger tip which contacted with a slide to induce the back and forth motion. The LuGre friction model is chosen to simulate the dynamics of this friction actuating mechanism. However, this piezoelectric actuating system has obvious nonlinear and time-varying dead-zone offset control voltage due to the static friction and preload. It is difficulty to establish an accurate dynamic model for model-based precision control design. Hence, the functional approximation (FA) scheme is employed to compensate the system modeling error. The Laypunov-like design strategy is adopted to derive the adaptive laws and the system stability criterion. Different trajectories tracking control are planned to investigate the motion control performance and the steady state error of this adaptive controller. The dynamic experimental results of the proposed controller are compared with that of a model-based PID controller.

Commentary by Dr. Valentin Fuster
2010;():75-83. doi:10.1115/ESDA2010-24264.

Aircraft transmissions have the peculiar characteristics of light structures and high operating speeds, therefore relatively low flexural natural frequencies and high excitation frequencies due to rotation and meshing. Resonance vibrations can create serious problems of malfunctions and even catastrophic failures. A reliable numerical model is surely a convenient means to perform preliminary simulations to identify the most critical resonance conditions and evaluate the effect of structural modifications on the dynamic behaviour of the component in the design development phase. Most numerical investigations found in the literature are carried out on simplified models of the rotating bodies likened to discs to reduce the computational effort. In this work a novel approach based on the application of Duhamel’s integral for the determination of the dynamic behaviour of a rotating gear subject to meshing forces has been developed to obtain more reliable results with a realistic model at an affordable computational cost. The gear response to dynamic excitation is obtained by the determination of its response to impulse using a single 3D finite element transient analysis taking afterwards into account the effect of the gear rotation. Subsequently, the Duhamel’s integral is applied using the tooth load time history in order to simulate as realistically as possible the gear load conditions. This paper presents the case of a real bi-helicoidal gear. A test bench was simulated measuring the displacement observed by some non-rotating virtual displacement sensors, located near the gear rim and disc. The signal was processed identifying the most critical rotating speeds on the basis of its RMS value. The numerical Campbell speed/frequency diagrams are in good agreement with experimental results.

Topics: Simulation , Gears
Commentary by Dr. Valentin Fuster
2010;():85-94. doi:10.1115/ESDA2010-24268.

This work presents the development of a test rig capable of measuring the forces transferred between the blade platforms through the under-platform damper. This test rig is composed of two distinct parts each one representing a platform. The static part contains the load cells, which measure the forces in two perpendicular directions; the moving part controlled using two piezoelectric actuators reproduces any in-plane relative displacement between two adjacent platforms. In this scheme, the damper is placed between these two platforms and loaded by dead weights that reproduce the effects of centrifugal force. The hysteresis cycle, of the damper system, is obtained using the measured forces and the imposed displacement. In addition, two laser beams can be used to measure the damper displacement and its tilt angle, which allows validating dynamic models of the damper. Moreover, the test rig is designed to allow heating the specimens up to temperatures which are normally found in real operation. Finally, the test rig provides necessary variables to study the damper performance and to evaluate some contact models used to simulate under-platform dampers.

Topics: Dampers , Design
Commentary by Dr. Valentin Fuster
2010;():95-104. doi:10.1115/ESDA2010-24272.

A perturbation method is employed in this paper and the problem of model updating in the presence of uncertainty due to manufacturing variability is addressed. Statistical properties of experimental data are considered and updating parameters are treated as random variables. The perturbation equations are used for estimation of means and covariances of updating parameters. The perturbation formulation is included and two approaches of parameter weighting matrix assignments are explained. Results from one of the approaches demonstrate good correlation between the predicted mean natural frequencies and their measured data, but poor correlation is obtained between the predicted and measured covariances of the outputs. In another approach, different parameter weighting matrices are assigned to the means and covariances updating equations. Results from the latter approach are in very good agreement with the experimental data and excellent correlation between the predicted and measured covariances of the outputs is achieved.

Commentary by Dr. Valentin Fuster
2010;():105-114. doi:10.1115/ESDA2010-24275.

A comparative assessment of several vibration based statistical time series methods for Structural Health Monitoring (SHM) is presented via their application to an aircraft scale skeleton structure. A concise overview of some of the main scalar and vector time series methods is provided, encompassing both non–parametric and parametric as well as response–only and excitation–response schemes. Damage detection and identification, collectively referred to as damage diagnosis, is based on single and multiple vibration response signals. The methods’ effectiveness is assessed via multiple experiments under various damage scenarios (loosened bolts). The results of the study confirm the global damage detection capability and effectiveness of scalar and vector statistical time series methods for SHM.

Commentary by Dr. Valentin Fuster
2010;():115-123. doi:10.1115/ESDA2010-24303.

In this paper, a sliding mode control methodology is implemented for the ABS control problem. Tire-road adhesion coefficient is taken as an uncertain parameter within known limits. This allows designing a robust sliding mode controller which does not require utilization of road coefficient of adhesion information, which is difficult to measure. As an improvement over previous studies, the sliding plane is formed to include both integral and derivative terms of the slip ratio error rather than only one of them. A design routine was identified in which the integral term, the derivative term and the relay action replaced by saturation compensate for each other’s drawbacks. Simulations were carried out using a quarter car model, where hydraulic components were assumed to introduce an additional first order dynamics due to hydraulic delay. Results show that, reference tracking performance and stability benefits of the integral term, which allowed for a more flexible relay term, could be used without causing oscillations. Conversely, possible instability at low speeds caused by the derivative term could be prevented by the relaxation of the relay term by means of saturation. As a result, stable controller operation with reduced chattering at both low and high velocities is realized. Finally, the enriched set of parameters involved in the sliding plane is observed to enable the designer to shape different stages of response while maintaining stability and, partly, performance characteristics.

Commentary by Dr. Valentin Fuster
2010;():125-132. doi:10.1115/ESDA2010-24342.

Performance of a haptic device is evaluated based on the concept of transparency which indicates the match between the impedance transmitted to the user and the target virtual impedance. Stability of a haptic device prevalently has been evaluated based on the passivity criterion. Due to conservativeness of passivity, it appears as an obstacle to improve transparency. In this paper, passivity is suggested to be replaced by the complementary stability criterion which accounts for the robust stability of the interaction in the presence of uncertain user hand dynamics. In this respect, an algorithm is proposed which guarantees transparency of the haptic device in a stable manner. Assuming that the dynamics of the device is known, a certain structure of compensators is assigned. This special structure guarantees transparency of the device by compensating for the dynamics of the device and its control loop. The design objective is to obtain a stabilizing controller which achieves robust stability for the interaction of the device in the presence of parametric uncertainties of user hand dynamics and other sources of uncertainties. An iterative method is implemented to derive controller dynamics. The algorithm is applied to a series elastic actuator based haptic device model. Simulation results confirm enhanced transparency and robust stability.

Commentary by Dr. Valentin Fuster
2010;():133-141. doi:10.1115/ESDA2010-24383.

This paper presents an optimal attitude maneuver by Reaction Wheels to achieve desired attitude for a Satellite. At first, Dynamic Equations of motion for a satellite with just three Reaction Wheels of its active actuators are educed, and then State Equations of this system are obtained. An optimal attitude control with the LQR method has exerted for a distinct satellite by its Reaction Wheels. As a result simulation has presented an optimal effort by calculated Gain matrix to achieve desired attitude for chosen Satellite. It shows that satellite becomes stable in desired attitude with a low energy and time consumption. Furthermore equations derivation, coupling of electrical Reaction Wheel equations with dynamic equations of satellite motion, linearizes them and Reaction wheel saturation avoidance approaches are innovative. Simulation results, accuracy of achieving desired attitude and satellite stability support this statement.

Commentary by Dr. Valentin Fuster
2010;():143-150. doi:10.1115/ESDA2010-24426.

Various methods for parametric interpolation of NURBS curves have been proposed in the past. However, the errors caused by the approximate nature of the NURBS interpolator were rarely taken into account. This paper proposes an integrated look-ahead algorithm for parametric interpolation along NURBS curves. The algorithm interpolates the sharp corners on the curve with the Pythagorean-hodograph (PH) interpolation. This will minimize the geometric and interpolator approximation errors simultaneously. The algorithm consists of four different modules: a sharp corner detection module, a PH construction module, a jerk-limited module, and a dynamics module. Simulations are performed to show correctness of the proposed algorithm. Experiments on an X-Y table confirm that the developed method improves tracking and contour accuracies significantly when compared to previously proposed adaptive-feedrate and curvature-feedrate algorithms.

Commentary by Dr. Valentin Fuster
2010;():151-161. doi:10.1115/ESDA2010-24518.

Math models of wheeled ground vehicle dynamics, including flexible body effects, have been the subject of research and development for many years. These models are typically based on a finite system of simultaneous ordinary differential equations (e.g., state-space models). Higher order models that include flexible body effects offer improved accuracy over a wider frequency range than lower order rigid body models; however higher order models are typically more sensitive to uncertainties in the model parameters and have increased computational requirements. Lower order models with the desired accuracy may be achieved by model reduction of higher order models. A more general infinite dimension Laplace transfer function is derived for beam bending governed by a fourth order wave equation. The resulting infinite dimension transfer functions for beam bending are then used to develop a transfer function model of a “half-car” with a flexible body. The infinite dimensional transfer function of the half-car model is then used to assess the accuracy of the state-space models. Differences between the models due to model reduction are compared to theoretical upper bounds.

Commentary by Dr. Valentin Fuster
2010;():163-169. doi:10.1115/ESDA2010-24551.

This paper investigates the chaos synchronization problem for a class of uncertain unified chaotic systems with external disturbances. Based on the proportional-integral (PI) switching surface, a sliding mode controller (SMC) is derived to not only guarantee the occurrence of a sliding motion of error states, but also reduce the effect of external disturbances to an H∞-norm performance. Also, a new reaching law is introduced to reduce the chattering problem that is produced by traditional sliding mode control. The parameters necessary for constructing both PI switching surface and the SMC can be found by the linear matrix inequality (LMI) optimization technique. Finally, a numerical simulation is presented to show the effectiveness of the proposed method.

Commentary by Dr. Valentin Fuster
2010;():171-176. doi:10.1115/ESDA2010-24585.

Ionic polymer metal composite is a class of electro-active polymers that are becoming more significant as smart actuators due to their large bending deflection, mechanical flexibility, low excitation voltage, low density, and ease of fabrication process. These properties make IPMCs suitable for a variety of application fields such as robotics, aerospace, biomedicine etc. There are a lot of linear and nonlinear models which describe actuation properties of IPMC. These models’ parameters may be obtained by various identification methods in which only a very few are nonlinear. Besides, there has been no model that explains all the physical phenomena associated with this actuator. In this paper, a new identification method is presented which incorporates a nonlinear with linear least squares method. This method is implemented on a nonlinear model. This model in comprised of two steps; as a first step, nonlinear relationship between the absorbed current and the voltage applied and as a second step relationship between the absorbed current and the blocked force are determined. The first and second steps are identified using a nonlinear and linear least squares methods, respectively.

Topics: Actuators
Commentary by Dr. Valentin Fuster
2010;():177-184. doi:10.1115/ESDA2010-24593.

Dynamic analysis of variable cross-section beams has been the focus of numerous investigations because of its relevance to aeronautical, civil, and mechanical engineering. In this article, we analyze the case of isotropic Euler-Bernoulli cantilever beams having linearly varying width, constant thickness, and classical boundary conditions. The linear width variation is characterized by a taper parameter, which can be varied between zero and unity. The free transverse vibration problem is cast as a fourth order Sturm-Liouville eigenvalue problem, and numerically solved by using the differential transform technique. A five-parameter exponential fitting model is used to develop novel empirical relations to estimate the first five eigenfrequencies as functions of the taper parameter. The proposed empirical relations are able to predict the eigenfrequencies with an error of less than 0.1% with respect to the simulated values, which make them useful for practical design applications. Using the proposed empirical relations, we then examine the sensitivity of each eigenfrequency to the variation in taper parameter near zero and near unity.

Commentary by Dr. Valentin Fuster
2010;():185-192. doi:10.1115/ESDA2010-24599.

In this paper, a dynamic model of a rotor-ball bearing system is developed in Msc. ADAMS commercial software. Contacts between the balls and the rings are modelled according to Hertzian theory. The bearing model is capable of representing the effects of bearing defects and internal clearances. When they are coupled with the rotor structures, bearings without any defect can also cause excessive vibrations due to the resonance characteristics of the system. In order to demonstrate these characteristics the rotor itself is modelled as a flexible shaft and a disc positioned at the free end of the shaft. The rotor-ball bearing model developed here is capable of representing the gyroscopic effects and the behaviour of the system under different unbalance conditions. Various case studies are performed and Campbell diagrams are obtained by using short-time Fourier transform method. A test rig consisting of two ball bearings, a shaft and a disc is also designed and developed so as to validate the theoretical model using experimental data. The test rig is developed in such a way that all of the elements are easy to assemble/disassamble, allowing quick observation of the system’s dynamic behaviour for different parameters including imbalance, internal clearance and bearing defects. Modal analysis and order tracking analysis were carried out using the test rig. Both the modal results and Campbell diagrams obtained using experimental data are compared with their theoretical counterparts. In the light of the experimental data, the theoretical model is validated for the purpose of further analyses and research.

Commentary by Dr. Valentin Fuster
2010;():193-202. doi:10.1115/ESDA2010-24604.

In this paper, the Differential Quadrature Method (DQM) is used to study the large amplitude free vibration of thin annular sector plates. The geometrical nonlinear governing equations of motion are derived based on the classical plate theory and using the von Karman nonlinear strain-displacement relationships. Following the DQ-procedure and employing the concept of new degrees of freedom a nonlinear eigenvalue problem is obtained which is solved iteratively and nonlinear natural frequencies of the plate are obtained. The results show a very good convergence and they are compared with the available literature for the clamped boundary conditions to demonstrate the validity of the work. The effects of boundary conditions, inner to outer radius ratio and sector angle on the large amplitude free vibration of thin plate are studied.

Commentary by Dr. Valentin Fuster
2010;():203-210. doi:10.1115/ESDA2010-24607.

In the present study, an adaptive sliding mode control method was employed to control a fish robotic system using hardware in the loop methodology. Up to now, few researches have focused on autonomous control of fish robot in dynamic environments which may be the result of difficulties in modeling of hydrodynamic effects on fish robot. Therefore, following the introduction of the nonlinear model for the robot, elongated body theory, suggested by Lighthill, was used to analyze fish movements. Then, kinematics control to track desired trajectories was designed for under-actuated model of robot. Adaptive sliding mode controller, capable of adapting according to changes and uncertainties, was designed and implemented. Using a fabricated stand, experimental tests were performed using hardware in the loop simulation. Computer simulations accompanied by experimental results verify that the presented adaptive controller has two main advantages: first, they make a robot versatile and capable of moving in unknown environments because of system robustness under changes and uncertainties of parameters. Second, they leave out the need for expensive and time consuming experiments to recognize system model and reduce operations for final tuning of controller.

Commentary by Dr. Valentin Fuster
2010;():211-220. doi:10.1115/ESDA2010-24613.

The present work deals with the free vibration control of a simply supported and cantilevered sandwich beam with magnetorheological elastomer (MRE) embedded viscoelastic core and conductive skins subjected to time varying magnetic field. The skins of the sandwich beam are conductive such that magnetic loads are applied to the skins. Considering the core to be stiff in transverse direction, classical sandwich beam theory has been used along with extended Hamilton’s principle and Galarkin’s method to derive the governing equation of motion. The resulting equation reduces to that of a parametrically excited system. Method of multiple scales has been used to study the response and stability of the system. Critical parameters of amplitude and frequency of magnetic field have been determined to actively control the free vibration response of the system. Effects of percentage of iron particles and carbon black in attenuation of vibration of the sandwich beam have been studied. Here the experimentally obtained properties of recently developed magnetorheological elastomers based on natural rubber containing iron particles and carbon blacks have been considered in the numerical simulation.

Commentary by Dr. Valentin Fuster
2010;():221-226. doi:10.1115/ESDA2010-24624.

Ground vibrations generated by high-speed trains are studied in this paper. Open trenches are included in modeling and the problem is formulated using elasticity theory. The ground is modeled by a semi-infinite domain and the embankment with finite layers and the high-speed train is simulated by moving loads. The analytical solution is obtained in frequency domain and the peak particle velocity (PPT) is then achieved for different types of open trenches with different aspect ratios and distance from the track centerline. A parametric study is then carried out and effects of different parameters including the train speed and ground properties on vibration reduction factors are investigated.

Commentary by Dr. Valentin Fuster
2010;():227-231. doi:10.1115/ESDA2010-24629.

Vibration suppression of railway bridges using nonlinear energy sink systems (NES) is studied in this paper. Train is modeled as a set of successive moving loads traveling on an Euler-Bernoulli beam. Energy sink as a new passive control strategy is employed as the suppression system. Galerkin method here is adopted as the solution technique. Within a parametric study, series of numerical simulations are carried out and performance of the passive control system is investigated. It is numerically found that an appropriately designed NES can passively reduce the displacement of the bridge up to 43%.

Commentary by Dr. Valentin Fuster
2010;():233-246. doi:10.1115/ESDA2010-24631.

An interactive software tool based on MATLAB to analyze and design controllers for mechatronic systems is presented in this paper. This toolbox called COMES is a graphical user interface (GUI) to routines for four different control approaches: classical control (lead, lag, PID etc.), preview control, model regulator control and repetitive control. These control approaches have all found widespread use in the practical implementation of controllers for mechatronic systems. The aim is to design a user-friendly toolbox with a well designed graphical user interface (GUI), which hides all calculations from the user as much as possible. Thus, the user can focus on the design and analysis phases through the graphical displays rather than being burdened by the complicated calculations that are involved. The effectiveness of the use of this MATLAB-based toolbox was demonstrated by carrying out some design and simulation studies for several position control applications available in the literature.

Commentary by Dr. Valentin Fuster
2010;():247-254. doi:10.1115/ESDA2010-24669.

Dry friction damping structures are simple and can be used in big range of working temperature, therefore varied kinds of friction contact damping structures have been widely used in turbomachine blades to reduce the forced vibration and improve dynamic stability. However, the dynamic analysis of such structures is still a challenging engineering task because the dry friction damping is a dynamic contact problem with complex boundary condition and strong nonlinear characteristics. A three dimensional numerical model for friction contact has been proposed to investigate the contact kinematics in the contact surfaces between adjacent blade shrouds. Microslip effects taken into account with a discretization of the contact surface with a mesh of contact elements, by altering the number of contact node can consider the effects of the area of the contact surface on forced response of shroud blade. The complex movement in the shroud contact surfaces was described by tracking the trajectory of the relative motion of the contact node. The model can consider the differences between the static friction coefficient and dynamic friction coefficient. The model has the mathematically tractable characteristic and can be easily used, and conforms to the engineering need. In order to decrease time consuming for computing the forced response, a reduced method is employed to condense all nonlinear degrees of freedom (DOF) to the nonlinear DOF on the contact surfaces, hence, iterative procedure of solution is limited in nonlinear degrees of freedoms. An alternating frequency/time domain method (AFT) which takes the advantages of both the time domain method and the frequency domain method is introduced to predict nonlinear vibration of shrouded blade systems. The developed friction model and calculated method of dynamic equation are applied to calculate nonlinear vibration for a real steam turbine blade. The effect of parameters on resonant frequency and response of the blade are investigated and discussed.

Commentary by Dr. Valentin Fuster
2010;():255-261. doi:10.1115/ESDA2010-24675.

Magnetic levitation is an appropriate solution for noncontact 3D manipulation. Workspace of the previously proposed maglev systems are confined to a relatively small cube, and this severely limits application of this technology. In addition, most of the previously given mechanisms require design and application of a subsystem for unifying their magnetic field. In this paper, a moving magnet is implemented which results in horizontally extendable work space; moreover, the field unifying section is not needed since one electromagnet only is used. Further, details of the mechanism and finite element based design procedure of the magnet are presented. Dynamic equations of the system derived by finite element analysis of the magnetic field are highly nonlinear and non-affine with respect to the control input. Two decoupled Fuzzy logic based controllers are used to deal with the 3D manipulation of the ball. The designed controllers provide the system with the precise trajectory tracking capability and robust stability. Simulation results confirm the findings.

Commentary by Dr. Valentin Fuster
2010;():263-270. doi:10.1115/ESDA2010-24729.

In this paper, a practical method to design a robust controller for pressure of boiler in Mashhad Power plant using Quantitative Feedback Theory (QFT) is proposed. In reality fuel flow, air flow and pressure of boiler are three dependent parameters which must control in every power plant. The boiler pressure system has uncertain mathematical model. Uncertainties in mentioned model are caused by lack of knowledge about the dynamics of the system, pay load changes, air flow. Thus, application of robust control methods for high precise control of pressure is inevitable. In the first step plant is converted into a group of linear uncertain plants. Then, a controller is designed for tracking problem and disturbance rejection. Finally, nonlinear simulation has been carried out which indicates successful design of controllers and pre-filters. The research demonstrates that applying the proposed technique successfully overcomes obstacles for robust control of pressure of the Power plant.

Commentary by Dr. Valentin Fuster
2010;():271-280. doi:10.1115/ESDA2010-24752.

In motorcycles and scooters the structural modes of vibration are important because they influence both vehicle’s comfort and vehicle’s stability and handling. Some researchers have shown that instabilities, which may occur when the vehicle is running (weave and wobble), are influenced by the modes of vibration, of the vehicle. At the Motorcycle Dynamics Research Group of Padova University many motorcycles have been tested with the method of modal analysis. The results of this research highlight that the whole motorcycle is a complex system that shows many kinds of modes of vibration: rigid modes, in which the structural components of the vehicle (chassis, fork, handlebars) behave as rigid bodies and deflection is given by tires and suspensions; local modes, in which deflection is concentrated in some subsystem of the vehicle (e.g. handlebars) and the rest of the motorcycle behaves as a system of rigid bodies; global modes with relevant deflection of the whole vehicle. This paper focuses on a specific issue, which is important for motorcycle design: the identifications of the frequencies of the first modes that show relevant deflection of the front fork and swing-arm. First, experimental equipment and testing methods are presented and discussed. Then the modal properties (natural frequencies, damping coefficients and modal shapes) of four motorcycles of different categories are presented, the characteristics of some modes are highlighted. Finally, the paper focuses on the identification of the frequencies that represent the borderline between rigid and elastic behavior of front fork and swing-arm. A method that requires the analysis of the characteristics of a small set of frequency response functions, without carrying out a long and expensive modal analysis of the whole vehicle, is presented. It is based on the properties of rigid modes (variation in vibration amplitude along a set of measurement points).

Topics: Vehicles , Vibration
Commentary by Dr. Valentin Fuster
2010;():281-288. doi:10.1115/ESDA2010-24755.

Majority of researchers’ activities in microrobotics and MEMS fields has been devoted to fabrication processes and design. Lack of work on modeling, simulation and control is considerable. From the viewpoint of motion type, the most significant microrobots are the in-pipe ones. Some of the applications for the in-pipe microrobots are nozzle inspection, endoscopy, colonoscopy etc. IPMC is a new actuator in the class of EAPs. Large bending deflection, mechanical flexibility, low excitation voltage and low density make IPMC a very momentous actuator. This paper presents a new in-pipe microrobot that makes use of IPMC actuators to move the microrobot. Mathematical model of the microrobot is obtained using the extended Hamilton principle. This microrobot motion has four steps in every single movement cycle for which only two feet take part in each step. Thus the modeling process has to be done for the different steps apart. This problem considerably increases the complexity of the model. Another source that complexes the modeling process is due to the nonlinear model of IPMC actuator. Also the influence of IPMC actuators at each other has been examined.

Topics: Actuators , Design , Modeling , Pipes
Commentary by Dr. Valentin Fuster
2010;():289-297. doi:10.1115/ESDA2010-24779.

In this paper, the effects of various parameters influencing on the dynamic response of composite bridge are investigated by FEM method. Herein composite bridge with one, two and four degree of freedom for vehicle has been studied. The corresponding Equations of motion are integrated numerically by applying the Newmark’s method. The models were verified by analytical and numerical solutions available for isotropic bridge. The speed of the vehicle, mass ratio, bridge damping on the dynamic deflection and acceleration and effect of composite bridge layup have been analyzed. Bridge damping can significantly decrease the acceleration of the structure, and it is true particularly for higher values of the speed parameters. Dynamic deflection is not influenced by damping changes; however, it also reduces with the increase of the damping ratio. Bridge damping has negligible effect on the vehicle acceleration. The bridge acceleration generally increases with the mass parameter. The vehicle acceleration increases much steeply and reaches much higher values for large mass parameters.

Commentary by Dr. Valentin Fuster
2010;():299-309. doi:10.1115/ESDA2010-24847.

Spacecraft rendezvous and docking are two processes in which a chaser pursues and meets a leader spacecraft in order to perform several mission based tasks. Although in some preliminary design analysis, these two operations may be pursued independently there could be circumstances in which the spacecraft trajectory and attitudes are coupled and interdependent. The present study is based on the presumption that the often independent translational and rotational motions of the spacecraft are coupled as a result of thrust misalignment. So the thrusters not only contribute to the rendezvous translational motion, but also affect the docking reorientation maneuver through their disturbing effects. In this regard, the coupled spacecraft rendezvous and docking (RvD) maneuver is treated as a multi-objective optimization problem. Multi-objective ant colony optimization (ACOR ) and Genetic algorithm (GA) as new variants of multi objective metaheuristics that have proven to be successful in handling non convex and multi minima problems are utilized to determine the required pareto front. Three design points are selected such that a wide range of mission based operations are covered and the results are compared. It is shown that, despite the presence of the disturbing effects due to the thruster misalignment, the required control commands are reasonable. For a comparative analysis, two different schemes are also utilized to obtain the closed loop control form for the RvD problem under study and their results are compared.

Commentary by Dr. Valentin Fuster
2010;():311-319. doi:10.1115/ESDA2010-24887.

Of the multitude of available control techniques, modal control is a favourite amongst structural dynamicists because of its representation in modal coordinates. The term modal control is used to describe a wide variety of control techniques which find their origin in a description of the system through the main coordinates, defined by the modes of vibration of the system. This approach stems from the consideration that the response of a mechanical system to a disturbance is the sum of the independent responses of its vibrational modes. This motivates the desire to design a control that does not alter these mode shapes, but allows to change the natural frequency and the damping of each mode. In active vibration control the purpose is to increase the damping of modes interested in the vibratory phenomenon. The paper shows how stability, spillover effects, system controllability and sensors and actuators position are all linked to the analysis of the controlled system damping matrix and to the possibility that the forces introduced by the control is non-dissipative. Theoretical aspects are supported by numerical simulations.

Commentary by Dr. Valentin Fuster
2010;():321-330. doi:10.1115/ESDA2010-24902.

A high-speed camera and a Particle Image Velocimetry (PIV) technique are used on a transparent liquid balancing device typical of modern washing machines. Experimental results indicate that the baffles placed inside the ring cavity interact with the fluid for it to develop modes of vibration of circumferential and axial type, thus rendering a complex swirl flow inside the annular cavity comprised of two inertial waves. One of such waves travels backwards relative to the rigid body motion. As as a result, a damping effect is induced and a phase lag with respect to the exciting unbalance occurs. An analytical dynamic model of the unbalanced response is derived and correlated with fluid flow visualization experiments and vibration measurements.

Commentary by Dr. Valentin Fuster
2010;():331-337. doi:10.1115/ESDA2010-24905.

The air fuel ratio (AFR) control is one of the effective methods to reduce emission and fuel consumption in spark ignition (SI) engines. Due to the hard nonlinearities existing in the engine dynamics model, a nonlinear controller should be designed for AFR control. In this Paper, an optimization-based nonlinear control law is developed for injected fuel mass flow to maintain AFR in the stoichiometric value. Simulation results show that the AFR in the controlled system is very close to the desired value, unlike the uncontrolled system in which the AFR has intensive fluctuations.

Commentary by Dr. Valentin Fuster
2010;():339-346. doi:10.1115/ESDA2010-24912.

Receptance coupling substructure analysis (RCSA) is extensively used to determine the dynamic response of milling tool at its tip for the purpose of prediction of machining stability. A major challenge in using this approach is the proper modelling of the joint between the substructures and determination of its parameters. In this paper, an inverse RCSA is developed for experimental extraction of tool-holder frequency response function (FRF) including joint parameters. The accuracy and efficiency of this method is evaluated through an analytical investigation. It is shown that the extracted holder FRF can provide a highly accurate prediction of the tool tip FRF. The developed method is used in prediction of tool tip FRF with different values of the tool overhang. The proposed approach is validated through experimental validation.

Commentary by Dr. Valentin Fuster
2010;():347-355. doi:10.1115/ESDA2010-24948.

In turbomachinery, the complete detuning of turbine blades in order to avoid high cycle fatigue damage due to resonant vibration is often unfeasible due to the high modal density of bladed disks. To obtain reliable predictions of resonant stress levels of turbine blades, accurate modelling of friction damping is mandatory. One of the most common sources of friction damping in turbine blades is the blade root, where energy is dissipated by friction due to microslip between the blade and the disk contact surfaces held in contact by the centrifugal force acting on the blade. In this paper a method is presented to compute the friction forces occurring at blade root joints and to evaluate their effect on the blade dynamics. The method is based on an upgraded version of the state-of-the-art contact model, currently used for the non-linear dynamic analysis of turbine blades. The upgraded contact model is implemented in a numerical solver based on the harmonic balance method able to compute the steady-state dynamic response of turbine blades. The proposed method allows solving the static and the dynamic balance equations of the blade and of the disk, without any preliminary static analysis to compute the static loads acting at the contact interfaces.

Topics: Friction , Damping , Blades
Commentary by Dr. Valentin Fuster
2010;():357-362. doi:10.1115/ESDA2010-24969.

Dynamical systems with contacts are often exposed to wear even under small loads. The wear develops at the micro, macro or global level and changes the contact shape. This changed contact shape alters the dynamics of the system and can further increase the wear. This research presents a numerical investigation of the interaction between the wear at the contacts and the dynamics. The research involves a dynamical model normally used in the research of car-brake dynamics and simulates the run-in wear of the brake pad and the development of waviness on disc. Special attention is given to the real roughness of the contacting surfaces and to on exact numerical simulation; because concurrent contacts between rough asperities occur, a specifically developed multibody dynamics approach is presented. This research shows that after the run-in period a concave pad produces a waviness pattern on the disc. Using a spectral analysis of the disc’s surface it is possible to show the effect of the wear particle-size and the pad-width on the surface waviness.

Topics: Brakes
Commentary by Dr. Valentin Fuster
2010;():363-368. doi:10.1115/ESDA2010-24989.

In this paper, a nonlinear complementary filter is presented to estimate the attitude of a Vertical Take Off and Landing Unmanned Aerial Vehicle (VTOL UAV). The measurements are taken from a low-cost IMU (Inertial Measurement Unit) which consists of 3-axis accelerometers, 3-axis gyroscopes and 3-axis magnetometers. From the proposed estimators, the full orientation matrix R will be retrieved. The proposed observers will estimate the instantaneous quaternions as well as the gyroscope bias. This representation of orientation by the rotation matrix and quaternions allows overcoming the problem of singularities that appear in local parametrization such as Euler angles. Therefore, both estimators may be used to describe any kind of 3-D motion. Convergence of the two observers is theoretically proved and simulations are conducted taking data from a real platform in hovering flight conditions.

Commentary by Dr. Valentin Fuster
2010;():369-378. doi:10.1115/ESDA2010-25090.

Gear transmissions in general and spur gears in particular exhibit a different dynamic behavior depending on the level of the transmitted load. This fact justifies the interest in the study of the role of the load in gear dynamics not only in the context of design, vibration and noise control but also for condition monitoring. This task requires the development of advanced models achieving a compromise between accuracy and computation time. In this work, gear and bearing non-linearities associated with the contact among teeth and roller elements have been included, taking into account the flexibility of gears, shafts and bearings. Besides, parametric excitations coming both from gear and bearing supports, as well as clearance, were also considered. Gear contact force calculations are carried out following a hybrid approach which combines both analytical and numerical tools. This lets to achieve accurate results with an acceptable computational effort and thus dynamic analysis becomes feasible. This approach was improved and the calculation speeded up from the point of view of computational time. This was performed by using a pre-calculated value for gear tooth stiffness as a function of load and the angular position when it operates under stationary conditions. On the other hand, bearings were formulated just as deflections of Hertzian type. This means that bending and shearing of races and rolling elements are neglected. However, the variation in the number of loaded rolling elements as a function of the load and the angular position was taken into account. Shaft flexibilities were added to gear and bearing models to define a simple transmission that was used to study the vibratory behavior under different levels of applied torque. In a preliminary study, this model was linearized for several loads, obtaining the corresponding frequencies and mode-shapes in order to assess their variation with this parameter. Finally, dynamic simulations were carried out, showing the modifications undergone by the orbits, meshing contact forces and transmitted bearing forces.

Commentary by Dr. Valentin Fuster
2010;():379-386. doi:10.1115/ESDA2010-25131.

In this paper the stability and observability of a controlled serial kinematic chain are analyzed with reference to a characterization of observability and stability for a stochastic system grounded in the application of Shannon theory to controlled systems. This approach was proposed in 2004 by H. Touchette and S. Lloyd. In particular it is analyzed in depth the case in which errors on the joints follow (concentrated) Gaussian distributions. In this case the property of Lie Groups (and related tangent space Lie algebra), studied from G. Chirikjian et al., allow to carry out the study of stochastic serial kinematic chains in a simplified way and to properly identify stability and observability conditions from a Shannon information standpoint.

Topics: Stability , Chain
Commentary by Dr. Valentin Fuster
2010;():387-395. doi:10.1115/ESDA2010-25185.

A simulation technology has been developed to predict the transmission efficiency of a metal pushing V-belt and pulleys that make up the drive system of a continuously variable transmission (CVT). When a CVT operates in an actual vehicle, pulley thrust pressure is adjusted by feedback control to maintain a speed ratio. This feedback control has been implemented, for the first time, in an existing simulation that predicts the dynamic behavior of a metal V-belt using explicit structural analysis. The new simulation enables stable control of a target speed ratio when appropriate gains are set for each analysis condition. Using this simulation, the following values can be obtained: 1) pulley thrust pressure that is necessary for maintaining a specified speed ratio but could previously be derived only from physical testing, 2) transmission efficiency of a CVT drive system, consisting of a metal pushing V-belt and pulleys, at each operating condition, and 3) belt friction losses calculated from sliding velocities and friction forces applied to element contact surfaces.

Commentary by Dr. Valentin Fuster
2010;():397-404. doi:10.1115/ESDA2010-25194.

In this research, a new approach for stability analysis of drill string is investigated. To this goal, the potential energy of drill string for axial and lateral vibrations is written in an integral equation. In this equation, the effect of geometrical shortening, which causes nonlinear coupling between axial and lateral vibration, is considered. The work done by WOB force and weight of drill string is calculated. The finite element method is employed to convert the integral potential energy of the continuous system to a discrete one. The effects of stabilizers are modeled by dropping the nodes coincided with them. Dropping and considering third and fourth order tensor of potential energy lead to linear and nonlinear stability analysis, respectively. Taking the first order derivative of discrete potential energy, the equilibrium position of drill string can be found. Taking second order derivative, the stability of the equilibrium position can be analyzed. Illustrated results demonstrate that as the length of hole is increased, the differences between linear and nonlinear cases become larger. This analysis shows the working condition of drill string is stable or not. These results can be used to obtain safe working conditions in drilling progress.

Commentary by Dr. Valentin Fuster
2010;():405-414. doi:10.1115/ESDA2010-25200.

Harvesting of vibration energy has been investigated by numerous researchers over the last decade. The research motivation in this field is due to the reduced power requirement of small electronic components such as wireless sensor networks used in monitoring applications. The ultimate goal is to power such devices by using the waste vibration energy available in their environment so that the maintenance requirement for battery replacement is minimized. Among the basic transduction mechanisms that can be used for vibration-to-electricity conversion, piezoelectric transduction has received the most attention due to the large power densities and ease of application of piezoelectric materials. Typically, a piezoelectric energy harvester is a cantilevered beam with one or two piezoceramic layers and the source of excitation is the base motion in the transverse direction. This paper presents general formulations for electromechanical modeling of base-excited piezoelectric energy harvesters with symmetric and asymmetric laminates. The electromechanical derivations are given using the assumed-modes method under the Euler-Bernoulli, Rayleigh and Timoshenko beam assumptions in three sections. The formulations account for an independent axial displacement variable in all cases. Comparisons are provided against the analytical solution given by the authors for symmetric laminates and convergence of the assumed-modes solution to the analytical solution with the increasing number of modes is shown. Experimental validations are also presented by comparing the electromechanical frequency response functions derived here against the experimentally obtained ones. The electromechanical assumed-modes formulations given here can be used for modeling of piezoelectric energy harvesters with asymmetric laminates as well as those with moderate thickness and varying geometry in the axial direction.

Commentary by Dr. Valentin Fuster
2010;():415-424. doi:10.1115/ESDA2010-25220.

The plant under control is the hydraulic circuit arranged by CNH in a prototype agriculture tractor of medium segment, where instead of the conventional main hydraulic pump, a new device electronically piloted, is installed. The main purpose is basically to obtain some advantages according to the energetic point of view, by means of an appropriate control structure, managing the electronic variable displacement pump. The frontier of the new systems requires the employment of the advanced control techniques, in order to assure the levels of precision, reliability, robustness demanded from systems. The control design methodology employed in the present case is based on robust H∞ optimization techniques, where robust stability properties are guaranteed in presence of unaccountable dynamics and other destabilizing factors. The effectiveness of the proposed control approach is tested on the demonstrative tractor realized from the CNH Agriculture at Modena plants, in all real conditions.

Commentary by Dr. Valentin Fuster
2010;():425-432. doi:10.1115/ESDA2010-25228.

Recently, agricultural tractors fuel consumption is growing, as a consequence of an increased number of components supplied. Otherwise, the increased sensitivity for environmental protection and global market competition are pointing out evermore urgent needs for significant improvement of fuel economy. With normal components of standard production tractors, dimensioned for the worst case operating conditions, is difficult to reduce consumptions. In this study, it is dealt with an innovative configuration where, the main hydraulic pump is substituted with a new electro-hydraulic one, with aim to optimize the operating points. To manage the pump by an appropriate control strategy, is fundamental to understand the characteristics and the dynamic properties of the hydraulic circuit fed by the pump. The purpose of this part of the paper is to describe the modeling activity that cover this necessity.

Commentary by Dr. Valentin Fuster
2010;():433-441. doi:10.1115/ESDA2010-25257.

In this paper, parametric excitation for MEMS gyroscope proposed by Oropeza-Ramos, et al. [1–4] is examined and problems associated with this kind of excitation are shown. It is proved that origin has exponential stability for some sets of parameter values (including those considered in [1–4]). This stability is shown to be global for linearized system and local for the general nonlinear system. Hence, it is concluded that if there would be a periodic orbit, the system has difficulties reaching it. As a solution, a harmonic term to the parametric excitation is added and the new actuation is referred to as parametro-harmonic excitation. It is shown that there are some parameter values for which a stable periodic orbit exists. Finally, stability of periodic orbit of the linear parametro-harmonically excited MEMS gyroscope is analyzed based on Floquet Theory. Figures show that in the non-resonant driving frequencies, only stiffness and damping play important roles in the stability of periodic response and other terms like excitation voltage and imposed external rotation are of less influence on this stability. However, in the parametric resonant regions, not only stiffness and damping affect stability, but also excitation voltage is of great importance.

Commentary by Dr. Valentin Fuster
2010;():443-455. doi:10.1115/ESDA2010-25294.

In turbomachinery applications bladed disks and blisks are subjected to high dynamic loads due to fluctuating gas forces. The dynamic excitation results in high vibration amplitudes which can lead to high cycle fatigue failures (HCF). Herein, the blades are almost identical but differ due to wear or small manufacturing tolerances. These small deviations of the blade properties can lead to a localization of the vibrational energy in single blades and even higher risk of HCF. Intentional mistuning, for example an alternating alignment of two different blades AB around the blisk, has been studied in literature to decrease the sensitivity against statistical mistuning. Using a Component Mode Synthesis (CMS) based mistuning model the influence of intentional mistuning on blisks is analyzed in this paper. Therein, the CMS of the disk is calculated with a fast and accurate cyclic symmetry approach. Therefore, the CMS of the disk can be calculated with one disk segment of the underlying Finite Element Model. The so called Wave Based Substructuring (WBS) is used to reduce the (numerous) coupling degrees of freedom between the disk and the blades with a truncated set of waves. The orthogonal waves are derived with a Singular Value Decomposition or a QR decomposition from the normal modes at the coupling degrees of freedom (DOF) calculated by a cyclic modal analysis of the full structure. In a case study the Reduced Order Model (ROM) of a spatial Finite Element Model is used to determine the influence of intentional mistuning with additional statistical mistuning on the forced response of blisks.

Topics: Blades
Commentary by Dr. Valentin Fuster
2010;():457-463. doi:10.1115/ESDA2010-25306.

In this article, the mathematical modeling of a high pressure regulator with its safety valve is presented. In the first step, the performance of regulator and safety valve are investigated, separately. After that, the safety valve is connected to the output port of air regulator and the output pressure’s variation is investigated. For analyzing of air regulator and safety valve’s operation, the equation of motion of internal parts, continuity equations for chamber and the equations related to mass flow rate which passing from diverse ducts in regulator are derived, respectively. The motion’s equation consists of inertia, controlling spring force, pressurized air force and coulombs friction terms. Because of nonlinearity and coupling, these equations are solved by using numerical methods and the results are presented. Finally, the results obtained in steady state are validated by testing.

Commentary by Dr. Valentin Fuster
2010;():465-473. doi:10.1115/ESDA2010-25309.

In this research, the effects of drilling mud flow and WOB force on the lateral vibration of drill string are investigated. To this goal, the kinetic and potential energy of drill string for axial and lateral vibrations are written in an integral equation. In potential energy equation, the effect of geometrical shortening, which causes nonlinear coupling between axial and lateral vibration, is considered. Drilling mud forces are modeled by Paidoussis formulations. The works done by WOB force, weight of drill string and drilling mud forces are calculated. The mode summation method is employed to convert the continuous system to a discrete one. Dropping and considering third and fourth order tensor of potential energy lead to linear and nonlinear system, respectively. The effects of stabilizers are modeled by a linear stiff spring. The wall contact is modeled by Hertzian contact force. Lagrange equation is employed for finding the equations of motions. First and second natural frequencies of drill string are found for different WOB and drilling mud flow. Also the effects of drilling mud and nonlinear terms on lateral vibration of drill string are investigated. The effect of drilling mud on the post buckling vibration of drill string is also delivered. This formulation can be used for optimization of drilling mud flow, WOB and the number and positions of stabilizer so that the lateral vibration of drill string is minimized.

Commentary by Dr. Valentin Fuster
2010;():475-483. doi:10.1115/ESDA2010-25341.

Simulation is one of the best methods for education and understanding events and used in many fields of science, for example: space researches. For this reason, creating of a frictionless environment that can simulate the operations of satellites will be very usable and appropriate. Spherical air bearings, that we call them TESTBEDs in this paper, are one of the most common devices used in satellite attitude dynamics simulation, because they provide three degrees of freedom rotational motion. They are employed to develop, improve and carry out operational tests of sensors, actuators and attitude control algorithms in experimental framework. An explanation about system engineering tool for testbed design that used by our team in Space Research Lab will be presented in this paper. This systems engineering tool utilizes a testbed-based approach to efficiently track information regarding the mass, cost, operation and volume of simulator subsystems. This subsystem information is derived through a variety of means, including analytical relationships, iterative solvers, and databases of components appropriate for satellite simulators. Finally, a description of 3-DoF satellite simulator and it’s subsystems (manufactured in Space Research Lab) by means of this system engineering tool will be demonstrated as a sample for validating results.

Commentary by Dr. Valentin Fuster
2010;():485-490. doi:10.1115/ESDA2010-25371.

In this paper, an adaptive control scheme for multi-agent formation control is proposed. This control method is based on artificial potential functions integrated with adaptive fuzzy sliding mode control technique. We consider fully actuated mobile agents with completely unknown dynamics. An adaptive fuzzy logic system is used to approximate the unknown system dynamics. Sliding Mode Control (SMC) theory is used to force agents’ motion to obey the dynamics defined by the simple inter-agent artificial potential functions. Stability proof is given using Lyapunov functions, which shows the robustness of controller with respect to disturbances and system uncertainties. Simulation results are demonstrated for a multi-agent formation problem, illustrating the effectiveness of the proposed method. Experimental results are included to verify the applicability of the scheme for a test-bed of six real mobile robots.

Commentary by Dr. Valentin Fuster
2010;():491-498. doi:10.1115/ESDA2010-25395.

In this paper, nonlinear vibration characteristics of a viscoelastic microplate under electrostatic actuation have been obtained. The microplate has been assumed as a CNT-reinforced simply supported square plate and an electrostatic actuation applied on it. The nonlinear equations of motion have been derived and solved, by using combined Galerkin method and indeterminate coefficient procedure. Static pull-in instability of the microplate has been also derived. It has been shown that the pull-in voltage, natural frequency and deflection of the system depend on the value of electrostatic actuation and viscoelastic characteristics of the microplate and differ from those obtained in elastic one. So, good selection of composite components (nanotube, base matrix) can result in better controlling of the microplate due to increasing/decreasing of the pull-in voltage.

Commentary by Dr. Valentin Fuster
2010;():499-508. doi:10.1115/ESDA2010-25436.

Squeeze film dynamical effects are relevant in many industrial components, bearings and seals being the most conspicuous applications. But they also arise in other industrial contexts, for instance when dealing with the seismic excitation of spent fuel racks. The significant nonlinearity of the squeeze-film forces prevents the use of linearised flow models, therefore a fully nonlinear formulation must be used for adequate computational predictions. Because it can accommodate laminar and turbulence flow effects, a simplified bulk-flow model — based on gap-averaged Navier-Stokes equations and incorporating all relevant inertial and dissipative terms — was previously developed by the authors (Antunes & Piteau, 2010), assuming a constant skin-friction coefficient. In this paper we introduce an improved theoretical formulation, fully developed elsewhere (Piteau & Antunes, 2010), such that the dependence of the friction coefficient on the local flow velocity is explicitly accounted for, so that it can be applied to laminar, turbulent and mixed flows. The main part of the paper is then devoted to the presentation and discussion of the results from an extensive series of experiments performed at CEA/Saclay. The test rig consisted on a long gravity-driven instrumented plate of rectangular shape colliding with a planar surface. Theoretical results stemming from both analytical flow models are compared with the experimental measurements, in order to assert the strengths and drawbacks of the simpler original model, as well as the improvements brought by the new but more involved flow formulation.

Commentary by Dr. Valentin Fuster

Micro and Nanotechnology

2010;():509-515. doi:10.1115/ESDA2010-24044.

In order to study the heat transfer behavior of the nanofluids, precise values of thermal and physical properties such as specific heat, viscosity and thermal conductivity of the nanofluids are required. There are a few well-known correlations for predicting the thermal and physical properties of nanofluids which are often cited by researchers to calculate the convective heat transfer behaviors of the nanofluids. Each researcher has used different models of the thermophysical properties in their works. The aim of the present paper is to study the convective heat transfer of nanofluids containing low volume concentration of Al2 O3 nanoparticles with a regard to the migration of nanoparticles due to Brownian diffusion and thermophoresis. To do this, a two-component model has been used and a numerical study on laminar flow of alumina-water nanofluid through a constant wall temperature tube has been performed. Two different models have been adopted for predicting the thermophysical properties of nanofluids. All of the properties are assumed to be temperature as well as particle concentration dependent. The effects of these models on the predicted value of the convective heat transfer of nanofluid and the migration of nanoparticles have been discussed in detail.

Commentary by Dr. Valentin Fuster
2010;():517-523. doi:10.1115/ESDA2010-24107.

In this paper, distributions of velocity and flow rate of micro channels are studied. Moreover, the parameters which influence them were also discussed, as well as their effects and relevant curves. In the Analytical study, the governing equation in specific micro flows is obtained. This equation is specifically investigated for slip flow in two micro parallel plates (micro channel).At the next step numerical representation shows the influence of the related parameters in micro channel flow such as Knudsen number, thermal -accommodation coefficient, mass flow rate ratio and pressure ratio (outlet to inlet), Tangential Momentum Accommodation Coefficient with relative curves, and flow rate distribution in slippery state to no slip state has been compared as the another part of this solution. Finally, the results of investigating parameters and dimensionless numbers in micro channels are reviewed.

Commentary by Dr. Valentin Fuster
2010;():525-532. doi:10.1115/ESDA2010-24176.

Recently, the development of machine tools and sub-micron positioning control systems has brought the minimum thickness of ultra-precision cutting to less than 1 nm. The conventional continuum based method (FEM) becomes impossible to use for numerical analysis. As an alternative method, molecular dynamics (MD) method is significantly implemented in the field of nano-machining to investigate cutting mechanism. In this paper, firstly, molecular dynamics simulations of the nanometric cutting of single-crystal copper were performed applying a pin tool. The model was solved with both Morse and Embedded Atom Method (EAM) potential functions to simulate the interatomic force between the work piece and a rigid tool. The nature of material removal, chip formation, and frictional forces were simulated. In order to investigate the coefficient resistance (the ratio of the cutting force to the thrust force), some MD simulations also carried for various cutting velocity and cutting depths. The results show that the Morse potential and EAM method have some difference to model tool forces and frictional resistance. Also, surface properties and atomic displacement in each of these potential functions have some discrepancy. In addition, cutting and trust forces increase with the cutting velocity and the depth of cut, however the effect of cutting speed is not very significant. Finally the value of frictional resistance is not changed with similar tool for various cutting speeds.

Commentary by Dr. Valentin Fuster
2010;():533-542. doi:10.1115/ESDA2010-24237.

Capillary pressures due to the wetting behaviour of a liquid on a material can be exploited to control the pressure drop of the liquid into microchannels. The pressure can be estimated by the Young-Laplace equation and for a given liquid, high values can be achieved by having small microchannel diameters and high wetting contact angles. An original actuation method for a microvalve can be derived from this, if reversible wettability behaviour can be achieved, i.e. the switching between hydrophobic to hydrophilic states implies that the microvalve can be turned on and off. In the present work a wettability controlled microvalve with UV/dark actuation is proposed. The valve microchannels are obtained by laser microdrilling on commercially pure titanium foil. Then the drilled titanium foil is anodic oxidized to grow on the microchannel surfaces a nanostructured TiO2 layer, which exhibits reversible wettability behaviour upon the alternate application of UV and darkness. Finally, the concept is demonstrated in a prototype microvalve controlled between OFF and ON states by UV light application.

Commentary by Dr. Valentin Fuster
2010;():543-548. doi:10.1115/ESDA2010-24241.

In the present study, an investigation of pressure drop characteristics of CuO-Base oil nanofluid laminar flow inside a horizontal helically coiled tube with constant heat flux boundary condition has been experimentally carried out. The nanofluid is prepared by dispersion of CuO nanoparticles in base oil and stabilized by means of an ultrasonic device. Particle weight fraction is ranging from 0 to 2%. The uniform and constant heat flux produced by an electrical heating coil wrapped around the coiled tube. The required data were acquired for laminar fully developed regime. The effect of different parameters such as fluid temperature, nanofluid particles concentration and mass velocity on the pressure drop characteristics in helically coiled tube for laminar fully developed regime is investigated. The results show that by using the helically coiled tube instead of the straight one, the pressure drop is increased. Also, the pressure drop increasing is happened by using nanofluid instead of base fluid. However, this increase is small compared to the increase resulted by using helically coiled tube. Observations also show that by increasing of mass velocity and concentration of nanoparticles in nanofluid, the pressure drop increasing is more pronounced.

Commentary by Dr. Valentin Fuster
2010;():549-555. doi:10.1115/ESDA2010-24242.

In the present study, an experimental investigation has been carried out to study the heat transfer characteristics of CuO/Base oil nanofluid flow inside horizontal oiled wire inserted tubes (roughed tubes) under constant heat flux. The nanofluids with CuO nanoparticles weight fraction ranging from 0 to 2% are prepared. The oiled wires with different wire wire diameteres and different oil pitches are used as inserts inside a horizontal plain copper tube. The nanofluid flowing inside the tube is heated by electrical heating coil wrapped around it. The convective heat transfer characteristis of the prepared nanofluids are measured during laminar fully developed flow inside horizontal plain and roughed tubes under constant heat flux. The effect of different parameters such as mass velocity, wire wire diameter, oil pith, nanofluid particles concentration and heat flux on heat transfer coefficient is studied. The heat transfer coefficient is increased when a roughed tube is used instead of a plain tube. Moreover, at the same flow conditions, by increasing of wire wire diameter and decreasing of oil pitch, the heat transfer performance is improved. Observations also show that by using nanofluid instead of base fluid, the heat transfer coefficient increases and this increase grows at higher nanoparticles concentrations. As a result, it an be concluded that increasing of wire wire diameter, decreasing of oil pitch and increasing the concentration of nanoparticle, contribute to the enhancement of heat transfer coefficient.

Commentary by Dr. Valentin Fuster
2010;():557-563. doi:10.1115/ESDA2010-24334.

Femtosecond lasers enable materials processing with their notably characteristics, such as precision, high peak density, flexible, and minor thermal affected zone. Applications ranging from high precision micromachining to biological manipulation with no thermal damages are possibly executed via this technology. In this study, the three-dimensional molecular dynamics simulation associated with the parallel computation were utilized to explore the ablation mechanism, the trend between the femtosecond laser fluence density and laser ablation depth as well as affected zone. In addition, we also compared the ablation methods which were single ablation and superposited ablation machining processes. Moreover, the heat-affected zone effect was discussed. Ultimately, a femtosecond laser ablation manufacturing process simulation was implemented by the combination of laser fluence densities to demonstrate the feasibility of fabricating the metallic gratings.

Commentary by Dr. Valentin Fuster
2010;():565-569. doi:10.1115/ESDA2010-24394.

The Atomic force microscope in non-contact mode of operation is modeled as a lumped parameter system. The interaction of the cantilever tip with the sample surface through the van der Waals force introduces the nonlinearity to the model. The model is analyzed by the method of multiple scales and the frequency response equation is obtained. The effects of the nonlinearity, amplitude of excitation, and damping coefficient on the frequency response are studied.

Commentary by Dr. Valentin Fuster
2010;():571-576. doi:10.1115/ESDA2010-24400.

The free vibration analysis of a nano-plate is investigated based on the first order shear deformation theory considering the small scale effect. The governing equations of motion are obtained using Hamilton’s principle by considering the nonlocal constitutive equations of Eringen. These coupled partial differential equations are reformulated into two new equations called the edge-zone and interior equations. Analytical solutions are obtained for a nano-plate with Levy boundary conditions. In order to find the natural frequencies of the nano-plate, the various boundary conditions at one direction of the plate should be imposed. Applying these conditions and setting the determinant of the six order coefficient matrix equal to zero, the natural frequencies of the nano-plate are evaluated. Non-dimensional frequency parameters are presented for over a wide range of nonlocal parameters and different boundary conditions. In addition, the effects of nonlocal parameter on the natural frequency of a nano-plate are discussed in details.

Commentary by Dr. Valentin Fuster
2010;():577-584. doi:10.1115/ESDA2010-24436.

Over the last two decades, explosive boiling has been widely used in industry, many researches have been dedicated to study its aspects. Some applications of explosive boiling are in thermal bubble jet printers, micro-injectors and micro-medicine devices. In such applications ambient pressure is not usually the atmospheric pressure. To have a good design, there is a great need to simulate the bubble growth under non-atmospheric pressure. In this research a three dimensional numerical analysis of growth and collapse of a bubble in a micro-channel under four different ambient pressures is presented. Flow3D package which solves the Navier-Stokes equations with surface tension effects, is used to reach this aim. Leinhard’s equation is used to compute the temperature of explosive boiling in various pressures. It is considered that the internal pressure of the bubble has an exponential form. Bubble dynamics relations have been used to obtain time constant of the bubble. The bubble volume and the flow rates from both ends of the microchannel are obtained. It has been shown that increasing in the ambient pressure causes decreasing in the bubble volume. Numerical results for the growth and collapse of the bubble in the micro-channel are compared with those of experiments under similar conditions. Results of the growth and collapse of the bubble in the micro-channel of a printer, BJ-80, have been used to validation. Comparisons show that the bubble evolution is well predicted by the numerical results.

Commentary by Dr. Valentin Fuster
2010;():585-589. doi:10.1115/ESDA2010-24443.

The object of the present study is to design a micro switch witch activates the airbag of a car when the amplitude of the acceleration of the accident exceeds the critical one. The response time of the micro switch is supposed to be 5 ms. Micro switch consist of a proof mass connected to a clamped-clamped micro beam. The nonlinear partial integro-differential equation of the motion is solved using FEM. According to the results it is recommended to use micro switches instead of accelerometers as airbag activators in car’s safety systems.

Topics: Design , Switches , Airbags
Commentary by Dr. Valentin Fuster
2010;():591-598. doi:10.1115/ESDA2010-24473.

The nonlocal continuum theories are capable to reflect the small length characteristic of nanostructures. In this work, variational principles are presented for the stability analysis of multi-walled carbon nanotubes under various mechanical loadings based on the nonlocal elastic Donnell’s shell by the semi-inverse method. In this manner, a set of proper essential and natural boundary conditions for each layer of the multi-walled nanotube is derived.

Commentary by Dr. Valentin Fuster
2010;():599-606. doi:10.1115/ESDA2010-24499.

Atomic Force Microscope (AFM) is a very strong and beneficial instrument for acquiring images at nanometer scale. Hence, obtaining better image quality and scan speed is a research area of great interest. Improving the dynamic responses of the scanning probe and the vertical motion of the scanner mechanisms are the two major areas of concentration in this sense. Improving the vertical dynamics is achieved either by designing more complex scanner mechanisms with higher bandwidth or designing more sophisticated controllers rather than the PI, PID or PIID types of controllers that are mostly used in practice. In this paper, the authors focus on designing a repetitive control scheme for fast and accurate scanning. It is possible to implement repetitive control to achieve this goal when it is considered that the successive lines of the scan are quite similar due to the very small steps taken to advance on the sample. Repetitive control can reject higher frequency disturbances due to the surface topography in AFM much better than a conventional controller can, as it can drive the error caused by any periodic input signal to zero. Besides increasing the scan speed, it is also important that the phase lag can be compensated perfectly using repetitive control, with the knowledge of the surface topography from the previous period by introducing appropriate phase advance.

Commentary by Dr. Valentin Fuster
2010;():607-614. doi:10.1115/ESDA2010-24504.

A molecular dynamic method was used to simulate the film growth process of ionized cluster beam deposition for Fe clusters depositing on Cu substrate with low energy. The tight-binding many-body potential is used to simulate the interaction between atoms. It will focus on the diverse deposition process parameters including incident energy, and substrate temperature, and it will use atomic stress tensor to obtain the residual stress after the deposition process. During simulations, we will find out the critical value of the incident energy to create epitaxy growth or interfacial intermixing, observe the roughness of epitaxy growth surface to determine the quality of film, and compute the residual stress. From the simulation results, the effects of the deposition process parameters on the morphology of the deposited film could be evaluated.

Commentary by Dr. Valentin Fuster
2010;():615-621. doi:10.1115/ESDA2010-24592.

Carbon nanotubes (CNTs) are expected to have significant impact on several emerging nanoelectromechanical (NEMS) applications. Vigorous understanding of the dynamic behavior of CNTs is essential for designing novel nanodevices. Recent literature show an increased utilization of models based on elastic continuum mechanics theories for studying the vibration behavior of CNTs. The importance of the continuum models stems from two points; (i) continuum simulations consume much less computational effort than the molecular dynamics simulations, and (ii) predicting nanostructures behavior through continuum simulation is much cheaper than studying their behavior through experimental verification. In numerous recent papers, CNTs were assumed to behave as perfectly straight beams or straight cylindrical shells. However, images taken by transmission electron microscopes for CNTs show that these tiny structures are not usually straight, but rather have certain degree of curvature or waviness along the nanotubes length. The curved morphology is due to process-induced waviness during manufacturing processes, in addition to mechanical properties such as low bending stiffness and large aspect ratio. In this study the free nonlinear oscillations of wavy embedded multi-wall carbon nanotubes (MWCNTs) are investigated. The problem is formulated on the basis of the continuum mechanics theory and the waviness of the MWCNTs is modeled as a sinusoidal curve. The governing equation of motion is derived by using the Hamilton’s principle. The Galerkin approach was utilized to reduce the equation of motion to a second order nonlinear differential equation which involves a quadratic nonlinear term due to the curved geometry of the beam, and a cubic nonlinear term due to the stretching effect. The system response has been obtained using the incremental harmonic balanced method (IHBM). Using this method, the iterative relations describing the interaction between the amplitude and the frequency for the single-wall nanotube and double-wall nanotube are obtained. Also, the influence of the waviness, elastic medium and van der Waals forces on frequency-response curves is researched. Results present some useful information to analyze CNT’s nonlinear dynamic behavior.

Commentary by Dr. Valentin Fuster
2010;():623-631. doi:10.1115/ESDA2010-24683.

In this research, the hysteresis in the tip-sample interaction force in noncontact force microscopy (NC-AFM) is measured with the aid of atomistic dynamics simulations. The observed hystersis in the interaction force and displacement of the system atoms leads to the loss of energy during imaging of the sample surface. Using molecular dynamics simulations it is shown that the mechanism of the energy dissipation occurs due to bistabilities caused by atomic jumps of the surface and tip atoms in the contact region. The conducted simulations demonstrate that when a gold coated nano probe is brought close to the Au (001) surface, the tip apex atom jumps to the surface; and instantaneously, four surface atoms jump away from the surface toward the tip apex atom. Along this line, particular attention is dedicated to the dependency of the energy loss to different parameters such as the environment temperature, the tip orientation, the surface plane direction, the system size, the distance of the closest approach and the tip oscillation frequency.

Commentary by Dr. Valentin Fuster
2010;():633-638. doi:10.1115/ESDA2010-24751.

MOEMS (Micro-Opto-Electro-Mechanical System) are MEMS in which the optical part plays a dominant role. The use of MOEMS as scanners and projectors has been studied lately. For high speed scanning applications, electrostatic comb drive actuation has several advantages. In this paper, we demonstrate the application of sliding mode control scheme for amplitude control of comb-actuated resonant microscanners. This method that leads to a simple and practical control function is simply extendable for microscanners with other type of actuation and even for any kind of oscillators that need amplitude control. The functionality and performance of the presented scheme is verified using numerical.

Commentary by Dr. Valentin Fuster
2010;():639-648. doi:10.1115/ESDA2010-24769.

This theoretical investigation intends to study the nano-tunnel problem of the single electron transistor (SET), which is one of the most important components in the nano-electronics industry. With a combined effort of quantum mechanics and similarity parameter, the partial differential equation of transient position-probability density is attained and can be applied to predict the electron’s position inside the nano tunnel. Also, an appropriate set of the initial and the boundary conditions is set up in accordance to the actual electron behavior for solving this PDE of probability density function. Thereafter, a simple, closed-form solution for the probability density is obtained and expressed in terms of the error function for a new similarity variable η. Note that this analytic similarity solution is easy to perform the calculation and suitable for any further mathematical operation, such as the optimization applications. In addition, it is shown that these predications are reasonable and in good agreement to the physical meanings, which are evaluated from both microscopic and macroscopic viewpoints. In conclusions, this is an innovative approach by using the Schrödinger equation directly to solve the nano-tunnel problem. Moreover, with the aids of this analytic position-probability-density solution, it is illustrated that the free single electron in the SET’s tunnel can only appear at some specified regions, which are defined by a dimensionless parameter η within a range of 0 ≤ η ≤ 2. This result can be served as a valuable design reference for setting the practical manufacture requirement.

Commentary by Dr. Valentin Fuster
2010;():649-653. doi:10.1115/ESDA2010-24900.

Particle image velocimetry (PIV) often employs the cross-correlation function to identify average particle displacement in an interrogation window. The quality of correlation peak has a strong dependence on the signal-to-noise ratio (SNR), or contrast of the particle images. In fact, variable-contrast particle images are not uncommon in the PIV community: Strong light sheet intensity variations, wall reflections, multiple scattering in densely-seeded regions and two-phase flow applications are likely sources of local contrast variations. In this paper, we choose an image pair obtained in a micro-scale mixing experiment with severe local contrast gradients. In regions where image contrast is sufficiently poor, the noise peaks cast a shadow on the true correlation peak, producing erroneous velocity vectors. This work aims to demonstrate that two image pre-processing techniques — local contrast normalization and Difference of Gaussian (DoG) filter — improve the correlation results significantly in poor-contrast regions.

Commentary by Dr. Valentin Fuster
2010;():655-662. doi:10.1115/ESDA2010-25095.

In this study, influences of intermolecular forces on dynamic pull-in instability of electrostatically actuated beams are investigated. Effects of midplane stretching, electrostatic actuation, fringing fields and intermolecular forces are considered. The boundary conditions of the beams are clamped-free and clamped-clamped. A finite element model is developed to discretize the governing equations and Newmark time discretization is then employed to solve the discretized equations. The results indicate that by increasing the Casimir and van der Waals effects, the effect of inertia on pull-in values considerably increases.

Commentary by Dr. Valentin Fuster
2010;():663-671. doi:10.1115/ESDA2010-25139.

This study constructs a novel Tapping Mode Atomic Force Microscopy (TM-AFM) model under vibration environment and analyzes the effect of probe size. The TM-AFM measurements are affected by external vibration and the size of the probe. In this study, a sinusoidal external vibration is applied, and TM-AM fixed-amplitude vibration simulated measurements made. The effect of external vibration on the surface profile acquired the simulated measurement of a nano-scale ladder standard sample. The simulated measurements under sinusoidal vibration are compared with actual experimental measurements without vibration isolation facilities, and the corrugations in the two cases were similar, indicating that the simulated measuring model under sinusoidal wave vibration proposed in this study is effective in qualitative analysis. An external vibration during the TM-AFM measurements causes an error between the measured surface profile of the sample and the actual appearance. Additionally simulated measurements are made on the edge of the nano-scale ladder standard sample, and the wave shape is affected by external vibration. The effects of the bevel angle and radius of the sharp end of the TM-AFM probe on the bevel edge effect of the probe and the measured appearance are studied. Qualitative analysis reveals that the bevel angle. Additionally, a smaller probe radius is associated with a simulated result that is closer to the perpendicular side of the ladder standard sample. The results in this study serve as a reference in the selection of probe size and in the qualitative analysis of the effect of external vibration on TM-AFM measurement.

Commentary by Dr. Valentin Fuster
2010;():673-680. doi:10.1115/ESDA2010-25149.

Evaluating the particle location in particle-laden flows is the most important parameter for calculating the two-phase flow parameters and also controls the computational time. In heat conducting nanofluids the volume fraction of particles is typically less than 3%. Nevertheless the their effect on heat transfer is important. In this paper, a new method for coupling thermal effects of dispersed and continuum phases is introduces. The L-N-R search algorithm, which can be used in complex geometries and unstructured grid is used for specifying particle location. For low volume fractions, particles-fluid interaction is considered only for the energy exchange. This exchange is done using a binary search tree. It is shown general usage of nanofluids in microchannels should be done by special considerations.

Commentary by Dr. Valentin Fuster
2010;():681-689. doi:10.1115/ESDA2010-25162.

In this paper, two terminals, doubly clamped, nano-switch has been studied. Here the interest of this study is the situation in which the pull-in and pull-out voltages not be same as each other and the pull-in/pull-out trend follows a hysteresis loop. This property could be used to introduce a double threshold switch with greater stability or noise immunity. With only one input threshold, a noisy input voltage signal near that threshold could cause the output to switch rapidly back. The model comprises a clamped-clamped carbon nanotube (CNT) suspended over a graphite ground electrode plate from which a potential difference is imposed. The actuation is based on DC applied voltages and it is assumed that the neutral axis of bending is stretched when the beam is deflected, and also, due to closeness of the substrate and the CNT, the van der Waals interaction forces between CNT and ground plate is considered. The versatile Galerkin’s method is employed to reduce the nonlinear integral-partial-differential equation of motion to a nonlinear ordinary differential equation in time, and then, the reduced equation is solved by direct numerical integration. The pull-in/pull-out phenomena, hysteresis characteristic are studied. The obtained results are compared to Molecular Dynamic (MD) method. Eventually, a nano-switch immune to input noise is proposed which relies on the hysteresis characteristic of the system. The proposed CNT-based nano-switch can operate in nano-scale electronics similar to the well known Schmitt trigger circuit in classical electronics. When the input voltage is higher than a certain pull-in voltage threshold, the output of the switch is in “ON” state; when the input voltage is below the pull-out voltage threshold, the output is in “OFF” state; when the input voltage is between the two threshold values, the output retains in the previous state.

Commentary by Dr. Valentin Fuster
2010;():691-695. doi:10.1115/ESDA2010-25226.

Due to vast application of silicon wet etching in Micromachining and MEMS structure, investigation about parameters that have more influence on wet etch rate is indispensable. Wet etch rate is dependent to several factor such as temperature, etchant concentration and crystal orientation. Because of temperature and concentration are more controllable therefore the etch rates R{hkl} depend mainly on concentration and temperature of the etchant. Understanding the relation between this parameters and wet etch rate can assist us in order to control and optimization of micromachining process. This paper present a relation between etchant concentration and temperature and wet etch rate on (100) plane, and then identify the etchant concentration in a certain range of temperature as the wet etch rate be in optimal amount. With optimization the etch rate of wafer (100), necessary time for etching process reduces and this reduction of time can lead to reduction of undercutting at convex and concave corners.

Commentary by Dr. Valentin Fuster
2010;():697-702. doi:10.1115/ESDA2010-25234.

Nanomembrane is a very important part of living systems. Alive cells have lipid bilayer nanomembrane in liquid phase. The lateral pressure profile, or stress profile, across a cell nanomembrane is the result of the inhomogeneous nature of the interactions within a nanomembrane. It has been shown that the work exerted by the pressure profile when a protein conformational change takes place is significant, of the order of 10kBT, and that the lateral pressure profile averaged over the whole nanomembrane is modified by the inclusion of a protein. Indeed, understanding the full coupling for stress arising from protein-lipid interactions is of profound importance and calls for elucidation. Here proper ensembles for molecular dynamics simulation of inhomogeneous nanoscale system of nanomembrane-cytotoxin protein are introduced. The Virial pressure theorem together with using molecular dynamics simulation data are proposed to use to calculate pressure filed. The predicted pressure tensor of system without cytotoxin is compared with that of system including this protein. Finally deformation of nanomembrane is related to the variation of pressure tensor.

Topics: Pressure
Commentary by Dr. Valentin Fuster
2010;():703-710. doi:10.1115/ESDA2010-25239.

Recently, micro/nanofabrication technology has been used to develop a number of microfluidic systems. With its integration to microfluidic devices, microchannels and micro scale pin fin heat sinks find applications in many areas such as drug delivery and propulsion in biochemical reaction chambers and micro mixing. Many research efforts have been performed to reveal thermal and hydrodynamic performances of microchannel based micro fluidic devices. In the current study, it is aimed to extend the knowledge on this field by investigating heat and fluid flow in micro heat sinks at high flow rates. Moreover, thermodynamic and thermo-economic aspects were also considered. De-ionized water was used as the coolant in the system. Flow rates were measured over pressures of 20–80 psi. A serpentine heater was deposited at the back of the micro pin fin devices to enable the delivery of heat to these devices. Two micro-pin fin devices each having different geometrical properties (Circular based and Hydrofoil based) were used in this study. In addition, the performances (thermal-hydraulic, exergy, exergo-economic) were also experimentally obtained for a plain microchannel device. Thermal resistances, exergy efficiencies and thermo-economic parameters were obtained from the devices and their performances were assessed.

Commentary by Dr. Valentin Fuster
2010;():711-716. doi:10.1115/ESDA2010-25250.

In this study, the effects of ausforming on the precipitating process and mechanical properties of 17-4PH stainless steel were investigated. For doing ausforming, samples were solution treated at 1050°C for an hour, and then quenched into a salt bath furnace at 400°C. Rolling at 400°C in different percents was done for achieving different mechanical works. After finishing ausforming process, samples were tempered for precipitating at 300,400,500 and 600°C for 1, 2, 4, 8, 16 and 32h. Microstructural studies were done for finding the changes on precipitating process and tensile and hardness test done to study mechanical properties. Scanning electron microscope was used to show precipitates and other phases. Also EDS method used to analyze the elements in each phases.

Commentary by Dr. Valentin Fuster
2010;():717-722. doi:10.1115/ESDA2010-25252.

ECAP is one of the Severe Plastic Deformation methods for reducing the grain size. With this process we can achieve ultrafine grains and consequently high strength. In this study, ECAP process was done on Al-Fe-Si alloy. This alloy was considered because of Fe effect on refining grain size. All samples were ECAPed into 1 pass in ECAP mold with 2 equal channels (1 cm × 1 cm) with 90 degree between them. By this method, around 1.05 as strain was applied on each samples. ECAPed specimens were heat treated (Semisolided) in different times and temperatures for achieving good toughness. Compression and hardness tests were done for finding the mechanical properties. As a result of these test, specimens that tolerate both ECAP and Semisolid have better toughness and strength than received and only ECAPed samples. Based on the microstructural evaluations spheroid solid phase was observed in the Semisolid specimen.

Commentary by Dr. Valentin Fuster
2010;():723-727. doi:10.1115/ESDA2010-25255.

Nanostructured MoSi2 powder has been successfully synthesized by Ball milling of Mo and Si powder mixtures and subsequent self-propagating high-temperature synthesis (SHS) process. It was observed that in comparison with the normally mixed powder, it could be easily ignited and higher combustion temperature was achieved. Based on XRD and SEM, it was confirmed that nanostructure MoSi2 powder could be prepared through self propagating combustion method from the mechanical activated powder mixture.

Commentary by Dr. Valentin Fuster
2010;():729-736. doi:10.1115/ESDA2010-25287.

According to the importance of cooling and heating process of a solid object, entropy generation in confined flow around a block is studied. In the current study, numerical simulation of laminar flow and heat transfer of nanofluids with nanoparticles of different shapes is considered. The nanofluids are water mixture with either Al2O3 nanoshperes or carbon nanotubes (CNTs). The incompressible Navier-Stokes and energy equations are solved numerically in a body fitted coordinates system using a control volume technique. The flow patterns and temperature fields for different values of the particles concentrations are examined in detail. Furthermore, the effects of nanoparticles shape and concentration on the heat transfer are studied. Furthermore the influences of nanofluids on pressure drop and pump power is examined. On the other hand, the entropy generation minimization is considered as the optimization criterion. The results indicate that in most cases the nanofluids enhance the heat transfer as well as pressure drop. It is interesting to note that the shape of nanoparticles is critical in determining the key mechanism of heat transport in nanofluids. Nanofluids with cylindrical nanoparticles exhibit a greater increase in heat transfer compared with nanofluids having spherical shape nanoparticles.

Commentary by Dr. Valentin Fuster
2010;():737-742. doi:10.1115/ESDA2010-25320.

There is substantial interest in using carbon nanotubes (CNTs) to create multifunctional polymer composite materials with outstanding mechanical, electrical, and thermal properties. A difficulty in modeling the behavior of these systems is the non-bulk interphase region in these systems that forms due to nanoscale interactions between the embedded NTs and adjacent polymer chains. However, the mechanical properties of this interphase region are unknown and very difficult to measure directly from experimental testing due to the size scale of this interphase region. Thus a three-phase (nanotube, interphase and matrix) Mori-Tanaka micromechanical model has been developed such that the properties of this interphase region can be inferred from macroscale elastic data. Both as-received and functionalized NTs have been considered in order to investigate the influence of functionalization on predicted mechanical properties of the interphase. A hybrid finite element-micromechanical method is also used to consider the effect of NT waviness in modeling. Results show that the Young’s modulus of interphase region is significantly higher than that of bulk polymer and it must be considered as an independent reinforcement mechanism in CNT/polymer nanocomposites.

Commentary by Dr. Valentin Fuster
2010;():743-749. doi:10.1115/ESDA2010-25370.

In this paper, for the first time, the influence of internal moving fluid on the nonlinear vibration and stability of embedded carbon nanotube is investigated. The Euler-Bernoulli beam theory is employed to model the vibrational behavior of an embedded carbon nanotube. The relationship of nonlinear amplitude and frequency for the single-wall nanotubes in the presence of internal fluid flow is expressed using the multiple scales perturbation method. The amplitude-frequency response curves of the nonlinear vibration obtained and the effects of the surrounding elastic medium, mass and the aspect ratios of nanotubes are discussed. It is shown that beyond the critical flow velocity buckling occurs and surrounding elastic medium plays a significant role in the stability of the carbon nanotube.

Commentary by Dr. Valentin Fuster

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