ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V003T00A001. doi:10.1115/DSCC2017-NS3.

This online compilation of papers from the ASME 2017 Dynamic Systems and Control Conference (DSCC2017) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Vibration in Mechanical Systems

2017;():V003T22A001. doi:10.1115/DSCC2017-5102.

An on-line identification scheme for shear building models using recursive least squares with a matrix parameterized model is presented. Based on Gershgorin circles and tridiagonal matrices properties, the identified model stability is guaranteed in the presence of low excitation or low damping. Stability of the model helps in the design of more robust control laws. The scheme is evaluated in an experimental test-bed with a scaled five stories building where an on-line reduced order model is derived. Results indicate that when employing this matrix parametrization, a significant reduction in the number of calculations involved is achieved, when compared to the standard vector parametrization based schemes, such that real-time applications are feasible to implement. Moreover, the stability on the identified model is preserved.

Commentary by Dr. Valentin Fuster
2017;():V003T22A002. doi:10.1115/DSCC2017-5214.

The behavior of a system comprised of two parallel plates coupled by a discrete, linear spring and damper is studied. Classical Modal Analysis (CMA) is used to illustrate this behavior, while specifically observing the effects of varying the stiffness and damping ratio of the coupling elements. Conditions under which the coupling may be approximated as rigid are identified. Additionally, conditions under which the coupling displacement reaches its maximum and minimum values are identified. This work also lays the groundwork for extending Asymptotic Modal Analysis (AMA) to systems with discrete, elastic, and dissipative coupling.

Commentary by Dr. Valentin Fuster
2017;():V003T22A003. doi:10.1115/DSCC2017-5219.

Although input shaping is an effective approach for vibration suppression in a variety of applications, the time delay introduced is not desired. Current techniques to reduce the time delay can not guarantee zero delay or may cause non-smooth motion, which is harmful for the actuators. In order to address such issue, a modified zero time delay input shaping is proposed in this paper. Experimental results show the advantage of the proposed approach.

Topics: Robots , Delays
Commentary by Dr. Valentin Fuster
2017;():V003T22A004. doi:10.1115/DSCC2017-5312.

In order to attenuate the pulsation of the hydraulic systems, the string hydraulic pulsation attenuator is proposed using the principle of mechanical vibration absorption. We present a new type of mechanical structure that can attenuate the pulsation as well as reduce the noise. Elastic strings and fluid can be seen as a forced vibratory system. Resonant cavities isolated by inner pipes of the string hydraulic pulsation attenuator and the damping orifices on inner pipes constitute the Helmholtz resonant structure. It’s a way to realize the effect of structural resonant and fluid resonant filtering. Based on the dynamic characteristics of the pipeline, the transfer matrix model of the string hydraulic pulsation attenuator is established. The attenuation performance of the string hydraulic pulsation attenuator is evaluated by insertion loss. In MATLAB software, we simulate the pulsating characteristics to analyze the relationship between the main structural parameters and the characteristics of pulsating pressure. The simulated theoretical results are compared and analyzed, which indicates that the string hydraulic pulsation attenuator is very effective for filtering in a very wide frequency range. Pulsation attenuating is good for improving the life of components and the working reliability. Noise reducing is good for people’s health at the working-site. Especially under some secret circumstances, controlling noise is a must.

Topics: Filtration , String
Commentary by Dr. Valentin Fuster
2017;():V003T22A005. doi:10.1115/DSCC2017-5402.

In this paper, we study the linear flexural oscillations of a cantilever beam undergoing chord-wise shape-morphing deformation in a quiescent, Newtonian, viscous fluid. The shape-morphing deformation is prescribed for the beam cross section to an arc of a circle by specifying a periodic maximum curvature continuously along the axis of the structure. This particular strategy is investigated as a possible way to manipulate fluid-structure interaction mechanisms by modifying the hydrodynamic interactions in the vicinity of the submerged structure. Since we focus on the linear vibration of the beam, the fluid flow is described using three-dimensional unsteady Stokes hydrodynamics. By solving the linear unsteady Stokes problem in the frequency domain with a Stokeslet method, we identify the effect of the proposed shape-morphing strategy on the propulsion performance by estimating thrust, lift, and hydrodynamic power dissipation for a range of prescribed deformations. We verify the results obtained from our boundary element method against results from the existing literature. Our findings show a possible improvement in propulsion characteristics and minimization of hydrodynamic power dissipation, for an optimum level of shape-morphing deformation which is aspect ratio-dependent. Results from this study can aid in designing and operating cantilever-based underwater actuation systems for which the multi-objective goal of power losses reduction and propulsion performance improvement is sought.

Commentary by Dr. Valentin Fuster
2017;():V003T22A006. doi:10.1115/DSCC2017-5409.

The paper presents method of the friction coefficient characteristics determination for kinematic pairs in the self-excited vibration conditions occurring in the Froude pendulum. Friction coefficients were calculated by measuring the vibration amplitude of the pendulum. Measurement of this amplitude for kinetic friction coefficient is carried out in the conditions of sliding friction and a static one — when the conditions of stickslip phenomena exist. The proposed method was verified using the LuGre friction model.

Topics: Friction , Vibration
Commentary by Dr. Valentin Fuster

Modeling and Validation

2017;():V003T27A001. doi:10.1115/DSCC2017-5056.

Electromechanical actuators are widely used in miscellaneous applications in engineering such as aircrafts, missiles, etc. due to their momentary overdrive capability, long-term storability, and low quiescent power/low maintenance characteristics. This work focuses on electromechanical control actuation systems (CAS) that are composed of a brushless direct current motor, ball screw, and lever mechanism. In this type of CAS, nonlinearity and asymmetry occur due to the lever mechanism itself, saturation limits, Coulomb friction, backlash, and initial mounting position of lever mechanism. In this study, both nonlinear and linear mathematical models are obtained using governing equations of motion. By using the linear model, it is shown that employing a PI-controller for position and a P-controller for velocity will be sufficient to satisfy performance requirements in the inner-loop control of an electromechanical CAS. The unknown controller parameters and anti-windup coefficient are obtained by the Optimization Tools of MATLAB using nonlinear model. Results obtained from the nonlinear model and real-time unloaded and loaded tests on a prototype developed are compared to verify the nonlinear model.

Commentary by Dr. Valentin Fuster
2017;():V003T27A002. doi:10.1115/DSCC2017-5073.

An accurate building energy forecasting model is a key component for real-time and advanced control of building energy system and building-to-grid integration. With the fast deployment and advancement of building automation systems, data are collected by hundreds and sometimes thousands of sensors every few minutes in buildings, which provide great potential for data-driven building energy forecasting.

To develop building energy forecasting models from a large number of potential inputs, feature selection is a critical procedure to ensure model accuracy and computation efficiency. Though the theory of feature selection is well developed in statistics and machine learning fields, it is not well studied in the application of building energy modeling.

In this paper, a feature selection framework proposed in an earlier study is examined using a real campus building in Philadelphia. This feature selection framework combines domain knowledge and statistical methods and is developed for short-term data-driven building energy forecasting. In this case study, the feasibilities of using this feature selection framework in developing whole building energy forecasting model and chiller energy forecasting model are studied.

Results show that, for both whole building and chiller energy forecasting applications, the model with systematic feature selection process presents better performance (in terms of cross validation error of forecasted output) than other models including that with conventional inputs and that uses only single feature selection technique.

Commentary by Dr. Valentin Fuster
2017;():V003T27A003. doi:10.1115/DSCC2017-5074.

A physics-based control-oriented combustion model is developed to accurately predict in-cylinder pressure and temperature of a diesel engine. The model is under the assumption that the combustion chamber consists of three zones: a liquid fuel zone, a reaction zone, and an unmixed zone. These zones are formulated to account for three key events in diesel combustion: fuel evaporation, chemical reaction, and fuel-air mixing, respectively. The liquid fuel zone is assumed to be of spherical shape. The evaporation of fuel is governed by Fick’s first law of diffusion. The reaction zone is modeled as a reactive system consisting of six species and two reaction steps. The burn rate is calculated based on species concentrations and reaction zone temperature. The unmixed zone contains only air and inert gas. The results of simulations are compared to the test data from a GM 6.7 L 8-cylinder Duramax diesel engine. The multi-zone model is shown to be capable of predicting in-cylinder pressure accurately with more degree of freedoms, compared to the singlezone reaction-based model.

Topics: Combustion , Diesel
Commentary by Dr. Valentin Fuster
2017;():V003T27A004. doi:10.1115/DSCC2017-5113.

A theoretical and computational model has been developed for the nonlinear motion of an inextensible beam undergoing large deflections for cantilevered and free-free boundary conditions. The inextensibility condition was enforced through a Lagrange multiplier which acted as a constraint force. The Rayleigh-Ritz method was used by expanding the deflections and the constraint force in modal series. Lagrange’s Equations were used to derive the equations of motion of the system, and a 4th order Runge-Kutta solver was used to solve them. Comparisons for the cantilevered beam were drawn to experimental and computational results previously published and show good agreement for responses to both static and dynamic point forces. Some physical insights into the cantilevered beam response at the 1st and 2nd resonant modes were obtained. The free-free beam condition was investigated at the 1st and 3rd resonant modes and the nonlinearity (primarily inertia) was shown to shift the resonant frequency significantly from the linear natural frequency and lead to hysteresis in both modes.

Commentary by Dr. Valentin Fuster
2017;():V003T27A005. doi:10.1115/DSCC2017-5134.

The problem of identifying the dispersion number associated with the convective-radiative heat dispersion mechanism in an experimental gasification tubular reactor is addressed. The dependency of temperature response characteristics on the intensity and duration of a heat pulse input are characterized on the basis of a set of off-line experiments, finding that for the range of interest: (i) the coefficient of variation of the temporal temperature response depends almost linearly on the dispersion number, and (ii) the related function is robustly invertible with respect to model and experimental uncertainty. This results establishes the feasibility of identifying the key heat dispersion (inverse Peclet) number from a reasonable on-line heat pulse injection test.

Topics: Uncertainty
Commentary by Dr. Valentin Fuster
2017;():V003T27A006. doi:10.1115/DSCC2017-5142.

This paper describes the definition of the transient model structure for an updraft gasifier and the input variables related to the process and the feedstock quality with the most significant influence on the dynamic models and the transient behaviour.

For such purpose, a set of open-loop dynamics experiments were carried out in the gasifier. Moreover, the output variables performance was recorded together with the composition analysis of the municipal solid waste batch (MSW).

The output and operational variables record was used as base information for performing regressions of transient models with the purpose of determining the model type choice that achieves the largest occurrence frequency of fitting percentage figures above 50%. In addition, the dataset of regression parameters is analysed through feature selection in order to establish the influence of feedstock quality parameters and independent dynamic operational variables in dynamic changes.

The model structure selection determined that underdamped, second order with one zero transfer function (P2ZU) is the most accurate case for updraft gasifiers.

Regarding the influence of feedstock-related information, feature selection results show that ultimate composition is the group of quality parameters with the most significant influence on transient behaviour.

Results also show that recirculation flow rate is the operational variable whose effect in the output variables is the most likely to be predicted and potentially controlled. The results for this variable show that 64.3% of the performed regressions achieved a fitting percentage value above 50%.

Commentary by Dr. Valentin Fuster
2017;():V003T27A007. doi:10.1115/DSCC2017-5171.

Although current state of the art hydraulic variable displacement pumps are highly efficiently at high displacement, they have poor efficiency at low displacement. Besides, different operating speed and load pressure conditions also strongly affect their performance. This paper proposed a novel alternating flow (AF) hydraulic variable displacement pump to 1) eliminate throttling loss by acting as a high-bandwidth pump for displacement control, 2) achieve high efficiency across a wide range of operating conditions and displacements, and 3) allow multiple units to be easily common-shaft mounted for a compact multi-actuator displacement control system from a single prime-mover. This paper presents a simple closed form model for the AF hydraulic pump and shows the model validation with a first generation prototype. The simple closed form model captures input motor energy, output fluid energy and associated energy losses. With the closed form model validated, it can then be used to drive optimal design for future generation prototypes using a dimensionless group method.

Commentary by Dr. Valentin Fuster
2017;():V003T27A008. doi:10.1115/DSCC2017-5212.

This paper describes a numerical technique for simulating the dynamics of constrained systems, which are described generally by differential-algebraic equations. The Projection Method for index reduction of a differential-algebraic equation and a minimal correction procedure are described. This procedure ensures algebraic constraints are satisfied during the numerical integration of the reduced index system of differential equations. Two examples illustrate how the method can be utilized to solve constrained multibody and rotational dynamics problems. The efficiency and accuracy of the proposed index-reduction and minimal correction method are then evaluated.

Commentary by Dr. Valentin Fuster
2017;():V003T27A009. doi:10.1115/DSCC2017-5225.

A significant challenge associated with the development of precision motion control systems is the identification and modeling of friction. In particular, dynamic (presliding) friction is often difficult to accurately model in both the time domain and frequency domain simultaneously. We present a data-based modification to an existing friction model, known as the Dahl Dynamic Hysteresis Model (DHM), which incorporates an empirical friction slope function to provide a more accurate representation of arbitrarily shaped hysteresis curves. This data-based approach avoids the added complexity of identifying or fitting model parameters, and can be implemented with a simple look up table. Simulation results are validated with measured friction data collected from an experimental testbed. We show that the data-based approach significantly improves the friction model accuracy in both the time and frequency domains.

Commentary by Dr. Valentin Fuster
2017;():V003T27A010. doi:10.1115/DSCC2017-5233.

In this paper, we report on a comprehensive experimental study on the fluid-structure interactions of a submerged rigid plate undergoing harmonic oscillations in a quiescent, Newtonian, viscous fluid. We conduct a detailed qualitative and quantitative analysis of the problem for broad ranges of oscillation parameters, including frequency and amplitude, to highlight the fluid-structure interaction mechanisms responsible for the hydrodynamic forces acting on the plate. The primary objective of this study is to understand the effect of the oscillation parameters on the resulting qualitative flow patterns and analyze their relation with vortex shedding and hydrodynamic forces. We classify different flow regimes depending on the behavior of the flow in the vicinity of the structure, with particular focus on vortex shedding and symmetry breaking phenomena, and analyze the forces in each regime by using particle image velocimetry and direct force measurement via a load cell. Comparison of the obtained experimental results against values predicted from numerical and semi-analytical models shows good agreement between our approach and the literature. Fundamental findings from this work have direct relevance to various engineering applications, including energy harvesting devices, biomimetic robotic system, and micro-mechanical sensors and actuators.

Commentary by Dr. Valentin Fuster
2017;():V003T27A011. doi:10.1115/DSCC2017-5238.

Vapor compression systems are widely used as thermal management systems. To satisfy thermal demands, models are used to control and optimize the system’s performance, reliability, and efficiency. Significant effort has been made to model the condenser and evaporator, while there has been minimal focus on control-oriented modeling of the compressor. Initial work illustrates that during transient behavior, the working fluid exhibits a fast dynamic. However, during a startup and shutdown sequence, the working fluid follows a slower dynamic believed to be associated with heat transfer to the shell. To address both thermal dynamics, a graph-based modeling approach is used to incorporate the compressor shell’s thermal capacitance into the model. Experimental and simulation data are compared for a range of operating conditions including shutdown and startup dynamics.

Commentary by Dr. Valentin Fuster
2017;():V003T27A012. doi:10.1115/DSCC2017-5245.

The intricate tendon system of the human muscular-skeletal system contributes to the human hand’s dexterity. A complex bond graph model of the index finger was developed to give insight into this system. Previous validation of this model by use of the ACT hand was difficult due to static joint friction. A new robotic testbed, Utah’s Anatomically-correct Robotic Testbed (UART) finger, has been developed to mitigate this friction. Static force and position experiments were conducted with the UART finger in contact with a surface and were compared to the bond graph model. The results suggest that the model is capable of simultaneously predicting static poses and fingertip force. The average predicted joint angle error was 2.9°. The average fingertip force magnitude error was 7.4%, and the average fingertip force direction error was 4.3°.

Topics: Tendons
Commentary by Dr. Valentin Fuster
2017;():V003T27A013. doi:10.1115/DSCC2017-5284.

Electricity for heating, ventilation, and air condition (HVAC) machines takes up a large percentage of energy consumption in the buildings and thus in turn, a large portion of the energy monetary cost. Optimization of air conditioners use throughout the day will reduce energy consumption and expenditure. This study introduces a second-order differential equation model to capture the indoor temperature dynamics of a building. An experimental test bed is developed to collect a set of indoor/outdoor temperature and sunlight data. Using a least-squares-based system identification process, the model parameters are identified and checked through simulation. Optimization of the room temperature is then determined by solving a mixed-integer quadratic programming problem in relation to the hourly-updated energy prices. Mixed-integer quadratic programming solution is compared to a two-point thermostatic control system. A hybrid solution compromising the quadratic programming algorithm and the conventional thermostatic control scheme is proposed as a tractable approach for the near-optimal energy management of the system.

Commentary by Dr. Valentin Fuster
2017;():V003T27A014. doi:10.1115/DSCC2017-5309.

This paper presents the mechanical modifications and simulation of a bipedal humanoid system actuated with linear springs to produce a standing equilibrium position.

The original humanoid system is comprised of two leg assemblies connected by a hip bracket. Eleven pairs of springs were attached to the system in locations designed to simulate the muscles and tendons in a human body.

The next evolution of the LUIGEE project is the inclusion of three servo motors per leg and a series of elastomeric springs. Although servo motors have been introduced, it is desired to maintain the passive, static aspect of the previous prototype. This paper reports on part modifications to accommodate servo motors and the introduction of polymeric springs that guarantee static stability. ABS plastic and photopolymer resin was used to produce the new model. Due to the size of the motors, some parts of the original robot were redesigned. The new design iteration was stimulated using SimWise 4D®, where the hysteretic effect of rubber was modelled with an equivalent viscous damping.

Topics: Springs
Commentary by Dr. Valentin Fuster
2017;():V003T27A015. doi:10.1115/DSCC2017-5335.

Good understanding of friction in tire-road interaction is of critical importance for vehicle dynamic control systems. Most of the friction models proposed to describe the friction coefficient between tire-treads and road surfaces have been developed based on empirical or semi-empirical relations that are not able to include many effective parameters involved in the tire-road interactions. Therefore, these models are just useful in limited conditions similar to the experiments, and do not accurately represent tire-road traction in numerical tire models. However, in last two decades, a few theoretical models have been developed to calculate the tire-road friction coefficient theoretically by considering both viscoelastic behavior of tire tread compounds and multi-scale interactions between tire treads and rough road surfaces. In this article, a novel physics-based model proposed by Persson has been investigated and used to develop computer algorithms for calculation of sliding friction coefficient between a tire tread compound and a rough substrate. The viscoelastic behavior of tread compound and the surface profile of rough counter surface are the inputs of this physics-based theoretical model. The numerical results of the model have been compared with the experimental results obtained from a dynamic friction tester designed and built in the Center for Tire Research (CenTire). Good agreement between numerical results of theoretical model and experimental results has been found at intermediate range of slip velocities considering the effect of adhesion and shearing in the real contact area in addition to hysteresis friction due to internal energy dissipation in the tire tread compound.

Commentary by Dr. Valentin Fuster
2017;():V003T27A016. doi:10.1115/DSCC2017-5359.

Efficient management of operating room (OR) schedules is of particular interest as this service is the largest cost and revenue center in a hospital and can substantially impact its staffing and finances. A major problem associated with developing OR schedules for elective surgeries is the uncertainty inherent in the duration of surgical services which can disrupt a daily plan. Another problem is the impact of facilities and resources upstream and downstream to the operating room, which affect the performance of the overall system. Using a manufacturing system analytical approach, the peri-operative process is modeled as a transfer line with three machines and two buffers using a discrete time Markov chain. Model predictive control is then applied to control the pace of patient release into the OR rooms. With this model and empirical studies of OR and recovery duration, guidance can be given to OR managers on how to dynamically schedule and reschedule patients throughout an operating room’s day that minimizes cost for a given workload.

Commentary by Dr. Valentin Fuster
2017;():V003T27A017. doi:10.1115/DSCC2017-5388.

In this paper we analyze the steady state dynamic behavior of a nonlinear model of a Proton Exchange Membrane (PEM) fuel cell. This model is used in several theoretical studies and application papers of PEM fuel cells. We indicate limitations and discuss potential constraints of this mathematical model. We establish conditions for the asymptotic stability at steady state by using the first stability method of Lyapunov. We find that the linearized model at steady state is uncontrollable. Specifically, the state variable corresponding to the hydrogen pressure is not controllable. This means that dynamics deviations of the state space variable corresponding to the hydrogen pressure around the steady state equilibrium point cannot be controlled. Due to its stability, the hydrogen pressure we go to the equilibrium point according to its internal (uncontrolled) dynamics so that the model is still applicable for theoretical and practical studies.

Commentary by Dr. Valentin Fuster

Dynamic Systems and Control Education

2017;():V003T31A001. doi:10.1115/DSCC2017-5027.

Single degree of freedom force-feedback mechatronic devices, often called haptic paddles, are used in university curriculum as well as massive open online courses (MOOCs). While devices differ based on the goals of a given course, broadly speaking they provide hands-on learning for students studying mechatronics and dynamics. We introduce the third iteration of the Haptic Paddle at Rice University, which has been modified to improve haptic performance and robustness. The modifications to the design increased device up time as well as the devices Z-width. The performance improvement enables the addition of experimental plants to the haptic paddle base, which can be directed at advanced dynamics and controls courses, or special topics in mechatronics and haptics. The first module, a Haptic Ball and Beam, adds an underactuated plant for teleoperation or more complex control structures, and a testbed for haptic motor learning experiments in undergraduate coursework.

Topics: Haptics , Education
Commentary by Dr. Valentin Fuster
2017;():V003T31A002. doi:10.1115/DSCC2017-5127.

This paper describes ongoing progress in facilitating entrepreneurially minded learning through modifications to an existing senior/graduate level mechatronic design course. The semester-long design experience incorporates a prompted real-world problem intended to motivate the design and construction of a fully autonomous robotic vehicle. Introductory lectures and structured laboratory exercises are provided during the first half of the semester, while the remaining half-semester is allocated to team-based robot design and fabrication. Existing problem-based learning activities have been altered to increase student awareness of economic factors, encourage communication of project issues in economic terms, and promote customer engagement. To this end, project assignments were recast as business problems, with an increased emphasis on prototype and operating costs. Additionally, a customer (represented by the instructor) was created to engage with students. Project success has been indirectly assessed by surveying students as to how their actions align with characteristic entrepreneurial behaviors identified by the Kern Entrepreneurial Engineering Network (KEEN).

Topics: Design
Commentary by Dr. Valentin Fuster
2017;():V003T31A003. doi:10.1115/DSCC2017-5140.

Arduino microcontrollers are inexpensive and easy to program, making them very popular among hobbyists and “makers”. Arduinos are also surprisingly capable when it comes to creating real-time feedback control systems. This paper investigates several facets of using Arduino microcontrollers to teach students to create real-time control systems. A simplified approach to enforcing the real-time execution of a control law is introduced based on the delayMicroseconds function and its accuracy is compared to the standard timer interrupt approach. Initial assessment data is presented on whether or not the delayMicroseconds approach is easier for students to understand. The accuracy of the Arduino’s built-in timing function micros is also investigated.

Commentary by Dr. Valentin Fuster
2017;():V003T31A004. doi:10.1115/DSCC2017-5157.

Control engineering is a cornerstone of most undergraduate engineering programs in colleges and universities around the world. The analysis and synthesis of automatic controllers, in particular, the PID controller, is a central focus of these courses and modules. However, due to its highly abstract nature, students usually find the content challenging and difficult to comprehend. This is aggravated by the employment of traditional lecture/recitation deductive teaching formats as means of delivery of the content. Here, an inductive-based week long design activity strategically held in the middle of the semester was conceived to introduce and motivate the notion of feedback control. During the course of the week, students in teams design, analyze and synthesize automatic controllers to enable a standardized differential wheeled robotic platform to traverse a line circuit autonomously. The strategy to achieve this capability is intentionally left to be open-ended, and students have the design freedom to select and position sensors needed to sense the track, as well as implement and troubleshoot the programming required to enable autonomous control. The activity culminates with a pulsating head-to-head single elimination tournament to decide the overall champion.

Commentary by Dr. Valentin Fuster
2017;():V003T31A005. doi:10.1115/DSCC2017-5226.

Fiber manufacturing process has been an integral part of the optical fiber communications. The optical fiber manufacturing processes involve high precision quality control and large volume production. However, the conventional fiber drawing manufacturing technologies are not flexible and highly specialized. This prevents innovative ideas such as flexible fiber manufacturing and small scale prototypes. A desktop fiber manufacturing kit was designed and tested. The experimental results indicate that diameter can be controlled within 0.02mm with standard deviation of 0.120mm when target diameter was set to be 0.5mm. Proportional control can be used to adjust fiber diameters.

Commentary by Dr. Valentin Fuster
2017;():V003T31A006. doi:10.1115/DSCC2017-5265.

This paper reports the development of an introductory mechatronics course in Mechanical Engineering (ME) undergraduate program at Georgia Southern University. This an updated version of an existing required course in the ABET accredited BSME program. The course covers three broad areas: mechatronic instrumentation, computer based data acquisition and analysis, and microcontroller programming and interfacing. This is a required 3-credit course in the ME program with updated computing application specific content reinforcing theoretical foundation with hands-on learning activities of the existing course. The course has four contact hours per week with two hours of lecture and two hours of interactive session of problem solving and laboratory experiment. For each topic covered, students get the theoretical background and the hands-on experience in the laboratory setting. Both formative and summative assessment of the students’ performance in the course are planned. Both direct and indirect forms of assessment are considered. The paper reports the details of the course materials.

Commentary by Dr. Valentin Fuster

Vibrations and Control of Systems

2017;():V003T32A001. doi:10.1115/DSCC2017-5111.

Electromagnetic (EM) shunt damping has been recently proposed for dual-functional vibration isolation and energy harvesting. This paper proposed two multi-resonant electromagnetic shunt damper configurations, namely in parallel and in series, with application to the building base isolation system. The electromagnetic shunt circuit parameters were optimized based on the H2 criteria to minimize the RMS relative displacement for the concern of building safety subjected to broad bandwidth ground acceleration excitations. The performance of the proposed multi-resonant electromagnetic shunt dampers was compared with traditional multiple tuned mass dampers (TMDs). It shows that, for multiple TMDs and multi-resonant electromagnetic shunt dampers with 5% total stiffness ratio, the parallel electromagnetic shunt damper can achieve the best vibration isolation performance. Case study of a base-isolated structure was analyzed in both the time and frequency domain to investigate the effectiveness of the multimode electromagnetic shunt resonances. It shows that both multimode shunt circuits outperform the single mode shunt circuit by suppressing the primary and the second vibration modes simultaneously. Comparatively, the parallel shunt damper is more effective in vibration isolation and energy harvesting, and is also more robust in parameter mistuning than the series shunt damper. This paper further experimentally validated the effectiveness of the multi-resonant electromagnetic shunt damper on a scaled-down base-isolated building.

Topics: Resonance , Dampers
Commentary by Dr. Valentin Fuster
2017;():V003T32A002. doi:10.1115/DSCC2017-5120.

In this paper, the Method of Multiple Scales is used to investigate the influences of damping and detuning frequency parameters on the amplitude-voltage response of an electrostatically actuated double-walled carbon nanotube. The forces responsible for the nonlinearities in the vibrational behavior are intertube van der Waals and electrostatic forces. Herein, the coaxial case is investigated, which eliminates the influence of the cubic van der Waals in the first-order solution. The double-walled carbon nanotube structure is modelled as a cantilever beam with Euler-Bernoulli beam assumptions since the double-walled carbon nanotube is characterized with high length-diameter ratio. The results shown assume steady-state solutions in the first-order Method of Multiple Scales solution. The importance of the results in this paper are the effect of damping and detuning frequency on the Hopf bifurcations, as these define the intervals of voltage for nonzero amplitudes.

Commentary by Dr. Valentin Fuster
2017;():V003T32A003. doi:10.1115/DSCC2017-5122.

This paper investigates the frequency response of superharmonic resonance of the second order of electrostatically actuated nano-electro-mechanical system (NEMS) resonator sensor. The structure of the MEMS device is a resonator cantilever over a ground plate under Alternating Current (AC) voltage. Superharmonic resonance insinuates that the AC voltage is operating in a frequency near one-fourth the natural frequency of the resonator. The forces acting on the system are electrostatic, damping and Casimir force. For the electrostatic force, the AC voltage is in the category of hard excitation in order to induce a bifurcation phenomenon. For Casimir forces to affect the system, the gap distance between the cantilever resonator and base plate is in the range of 20 nm to 1 μm. The differential equation of motion is converted to dimensionless by choosing the gap as reference length for deflections, the length of the resonator for the axial coordinate, and reference time based on the characteristics of the structure. The Method of Multiple Scales (MMS) is used to model the characteristic of the system. MMS transforms the nonlinear partial differential equation of motion into two simpler problems, namely zero-order and first-order. The influences of parameters (i.e. Casimir, damping, second voltage and fringe) were also investigated.

Commentary by Dr. Valentin Fuster
2017;():V003T32A004. doi:10.1115/DSCC2017-5124.

This paper investigates the dynamics governing the behavior of electrostatically actuated MEMS cantilever resonators. The cantilever is held parallel to a ground plate (electrode) with an AC voltage between the plate and the electrode causing the electrostatic actuation (excitation). For the purposes of this paper this is soft excitation. The frequency of the excitation is near the natural frequency of the cantilever leading to what is known as parametric resonance. The electrostatic force in the problem investigated throughout the paper is nonlinear in nature and includes the fringe effect. Two methods are used in investigating this problem: the method of multiple scales (MMS) and the homotopy perturbation method (HPM). The two methods work well for small non-linearities and small amplitudes. The influence of voltage, fringe, damping, Casimir, and Van der Waals parameters will be investigated in this paper using MMS and HPM as a means of verifying the results obtained.

Commentary by Dr. Valentin Fuster
2017;():V003T32A005. doi:10.1115/DSCC2017-5137.

This paper presents a methodology of designing, modeling, and controlling a fully pneumatic semi-active vibration isolator system. The prototype vibration isolator system consists of an air spring, a variable orifice valve, and an accumulator which has the ability to simultaneously adjust the damping and natural frequency characteristics of the system. This paper presents a comprehensive work of modeling, hardware design, control design, and experimental validation of the proposed semi-active vibration isolation system. A higher fidelity model is obtained by complete characterization of nonlinear relationships between pressure versus volume and effective orifice area versus ride height. The performance of three semi-active controller designs — Linear Quadratic Impulse (LQI), Modified Skyhook, and Relative Displacement — is evaluated and compared experimentally using an OEM Peterbilt cabin suspension unit. The results demonstrate that the properly tuned semi-active suspension provides increased vibration isolation over the traditional passive cabin suspension design.

Commentary by Dr. Valentin Fuster
2017;():V003T32A006. doi:10.1115/DSCC2017-5184.

Selective laser sintering (SLS) is an additive manufacturing (AM) process that builds 3-dimensional (3D) parts by scanning a laser beam over powder materials in a layerwise fashion. Due to its capability of processing a broad range of materials, the rapidly developing SLS has attracted wide research attention. The increasing demands on part quality and repeatability are urging the applications of customized controls in SLS. In this work, a Youla-Kucera parameterization based forward-model selective disturbance observer (FMSDOB) is proposed for flexible servo control with application to SLS. The proposed method employs the advantages of a conventional disturbance observer but avoids the need of an explicit inversion of the plant, which is not always feasible in practice. Advanced filter designs are proposed to control the waterbed effect. In addition, parameter adaptation algorithm is constructed to identify the disturbance frequencies online. Simulation and experimentation are conducted on a galvo scanner in SLS system.

Topics: Lasers , Sintering
Commentary by Dr. Valentin Fuster
2017;():V003T32A007. doi:10.1115/DSCC2017-5186.

This paper deals with two different methods to analyze the amplitude frequency response of an electrostatically actuated micro resonator. The methods used in this paper are the method of multiple scales, which is an analytical method with one mode of vibration. The other method is based on system of odes which is derived using the partial differential equation of motion, as well as the boundary conditions. This system is then solved using a built in matlab function known as BVP4C. Results are then shown comparing the two methods, under a variety of parameters, including the influence of damping, voltage, and fringe.

Commentary by Dr. Valentin Fuster
2017;():V003T32A008. doi:10.1115/DSCC2017-5213.

Vibration-based monitoring of mechanical structures often involves continuous monitoring that result in high data volume and instrumentation with a large array of sensors. Previously, we have shown that Compressive Sensing (CS)-based vibration monitoring can significantly reduce both volume of data and number of sensors in temporal and spatial domains respectively. In this work, further analysis of CS-based detection and localization of structural changes is presented. Incorporating damping and noise handling in the CS algorithm improved its performance for frequency recovery. CS-based reconstruction of deflection shape of beams with fixed boundary conditions is addressed. Formulation of suitable bases with improved conditioning is explored. Restricting hyperbolic terms to lower frequencies in the basis functions improves reconstruction. An alternative is to generate an augmented basis that combines harmonic and hyperbolic terms. Incorporating known boundary conditions into the CS problem is studied.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2017;():V003T32A009. doi:10.1115/DSCC2017-5264.

In this paper, a sliding mode backstepping controller for a pinned-pinned Euler-Bernoulli beam is briefly reviewed and its efficacy in the presence of unknown bounded harmonic disturbances at arbitrary frequencies is analyzed. A brief discussion of the open-loop unstable response to harmonic excitations at resonant frequencies is provided. Motivated by this, particular attention is given to excitations at the natural frequencies of the system. It is shown that in the face of such resonant disturbances, the sliding mode backstepping controller is able to eliminate the vibrations in the beam system where backstepping control alone cannot. Indeed it is shown that if the disturbances are not accounted for, the closed loop system exhibits large (relative to the initial conditions) steady state harmonic vibrations. When the unknown resonant harmonic disturbances are accounted for via the sliding mode backstepping technique, the steady state position is constant and does not exhibit any vibrations, and furthermore it reaches this steady state exponentially at an arbitrarily selected rate.

Topics: Resonance
Commentary by Dr. Valentin Fuster
2017;():V003T32A010. doi:10.1115/DSCC2017-5363.

Delamination is one type of damage that frequently occurs in laminated composite structures, and identification of such damage has been a major research topic in the past few decades. This paper proposes an accurate non-model-based method for delamination identification of laminated composite plates. A weighted mode shape damage index is formulated using squared weighted difference between a measured mode shape of a composite plate with delamination and one from a polynomial that fits the measured mode shape of the composite plate with a proper order. Weighted mode shape damage indices associated with at least two measured mode shapes of the same mode are synthesized to formulate a synthetic mode shape damage index to exclude some false positive identification results due to measurement noise and error. An auxiliary mode shape damage index is proposed to further assist delamination identification, by which some false negative identification results can be excluded and edges of a delamination area can be accurately and completely identified. Numerical examples are presented to investigate effectiveness of the proposed method, and it is shown that edges of a delamination area in composite plates can be accurately and completely identified when measured mode shapes are contaminated by measurement noise and error.

Commentary by Dr. Valentin Fuster

Modeling and Estimation for Vehicle Safety and Integrity

2017;():V003T33A001. doi:10.1115/DSCC2017-5026.

Tests with human drivers in a driving simulator are used for developing dynamic models of drivers during emergency highway steering maneuvers. The maneuvers were required to avoid colliding with suddenly emerging simulated lane-blocking vehicles and objects. The driver models are intended for forming vehicle-driver simulation models that are used in analysis of highway accidents caused by lane obstructions. Four standard driver models are derived based on the test results, ranging from a cautious driver to an aggressive driver. Test data is provided to allow derivation of additional driver models.

Topics: Emergencies
Commentary by Dr. Valentin Fuster
2017;():V003T33A002. doi:10.1115/DSCC2017-5045.

In this paper, we propose a lane changing model based on the collision cone approach. Specifically, we show how a vehicle decides whether to change lanes using the collision cone algorithm based on the information of the velocity and the location of surrounding vehicles. The model compares the current and target lane with a new measure of driving advantages. It determines if there are any existing driving advantages such as free space and speed by lane changing. Moreover, a new methodology of lane changing for collision avoidance, which is based on line of sight (LOS) with a new leader in a target lane, is suggested with a model predictive control (MPC) controller. Additionally, we show that the model makes reliable decisions and generates acceptable lane changing trajectories.

Commentary by Dr. Valentin Fuster
2017;():V003T33A003. doi:10.1115/DSCC2017-5149.

This paper presents a novel mass-center-position (MCP) metric for vehicle rollover propensity detection. MCP is first determined by estimating the positions of the center of mass of one sprung mass and two unsprung masses with two switchable roll motion models, before and after tire lift-off. The roll motion information without saturation can then be provided through MCP continuously. Moreover, to detect completed rollover statues for both tripped and untripped rollovers, the criteria are derived from d’Alembert principle and moment balance conditions based on MCP. In addition to tire lift-off, three new rollover statues, rollover threshold, rollover occurrence, and vehicle jumping into air can be all identified by the proposed criteria. Compared with an existing rollover index, lateral load transfer ratio, the fishhook maneuver simulation results in CarSim® for an E-class SUV show that MCP metric can successfully predict the vehicle impending rollover without saturation for untripped rollovers. Tripped rollovers caused by a triangle road bump are also successfully detected in the simulation. Thus, MCP metric can be successfully applied for rollover propensity prediction.

Topics: Vehicles
Commentary by Dr. Valentin Fuster
2017;():V003T33A004. doi:10.1115/DSCC2017-5154.

In this paper, a novel vehicle lateral stability region estimation method considering both front and rear wheel steering is introduced. Vehicle lateral stability regions are estimated by a local linearization method, which guarantees both vehicle local stability and handling stability. The impacts of front and rear wheel steering angles on stability region estimations are formulated and discussed. To quantitatively explain the shifting feature of stability regions under different front/rear steering angles, an explicit analysis about how the equilibrium points and the geometric centers of stability regions change with respect to different steering angles is formulated. The obtained relationship enables the estimation of stability regions in real time for varying front/rear steering angles. The additional rear wheel steering helps to maintain vehicle states stay within estimated stability regions. To show the effectiveness of the proposed real-time stability region estimation method and stability analysis, a Simulink and CarSim® co-simulation is applied to verify that vehicle states are covered within varying stability regions for a single lane change maneuver.

Topics: Stability , Vehicles , Wheels
Commentary by Dr. Valentin Fuster
2017;():V003T33A005. doi:10.1115/DSCC2017-5255.

For an electric power assist steering (EPAS) control system, it is important to know the rack force information to improve the steering feel control performance. Since there is no direct measurement of rack force in current EPAS system, there have been various rack force estimation algorithms proposed for the control system development. In this paper, two existing rack force estimation methods (based on steering system dynamics and vehicle dynamics) have been implemented in the simulation environment to compare its performance. The effectiveness and limitations of two methods have been analyzed using a simulation of high fidelity EPAS model with various inputs conditions. In addition, new adaptation algorithm is proposed to further improve the estimation performance of the existing methods.

Commentary by Dr. Valentin Fuster
2017;():V003T33A006. doi:10.1115/DSCC2017-5270.

Modeling customer usage in vehicle applications is critical in performing durability simulations and analysis in early design stages. Currently, customer usage is typically based on road roughness (some measure of accumulated suspension travel), but vehicle damage does not vary linearly with the road roughness. Presently, a method for calculating a pseudo damage measure is developed based on the roughness of the road profile, specifically the International Roughness Index (IRI). The IRI and pseudo damage are combined to create a new measure referred to as the road roughness-insensitive pseudo damage. The road roughness-insensitive pseudo damage measure is tested using a weighted distribution of IRI values corresponding to the principal arterial (highways and freeways) road type from the Federal Highway Administration (FHWA) Highway Performance Monitoring System (HPMS) dataset. The weighted IRI distribution is determined using the number of unique IRI occurrences in the functional road type dataset and the Average Annual Daily Traffic (AADT) provided in the FHWA HPMS data.

Topics: Damage
Commentary by Dr. Valentin Fuster

Modeling and Control of IC Engines and Aftertreatment Systems

2017;():V003T34A001. doi:10.1115/DSCC2017-5093.

To meet the more stringent emissions and fuel economy regulations, engine control system has become significantly more complex than before. As a result of this, engine calibration on the dynamometer now occupies one of the longest time sections in the vehicle development process. One strategy automakers have adopted is to use the same engine in multiple applications to reduce the calibration effort. Even then, vehicle design constraints often require changes to be made to the engine’s external components such as the intake and exhaust manifolds. These changes can create variations in the engine combustion behavior so that the engine must be recalibrated on the dyno, resulting in additional cost and effort. This paper explores the potential of reusing existing engine dyno data for a modified engine in these scenarios through the use of the so-called eigenvariable to describe engine operating conditions. Traditionally, engine dyno data is referenced by engine load and speed along with actuator positions (such as camphaser positions). The proposed approach describes dyno data using eigenvariables or variables that describe the engine in-cylinder condition prior to combustion. Eigenvariables are invariant with respect to external engine hardware. This invariance enables the same dyno data to be applied to a modified engine with the same combustion system design.

Topics: Engines , Calibration
Commentary by Dr. Valentin Fuster
2017;():V003T34A002. doi:10.1115/DSCC2017-5095.

Because of its high NOx reduction efficiency, selective catalyst reduction (SCR) has become an indispensable part of diesel vehicle aftertreatment. This paper presents a control strategy for SCR systems that is based on an on-line radial basis function neural network (RBFNN) and an on-line backpropagation neural network (BPNN). In this control structure, the radial basis function neural network is employed as an estimator to provide Jacobian information for the controller; and the backpropagation neural network is utilized as a controller, which dictates the appropriate urea-solution to be injected into the SCR system. This design is tested by simulations based in Gamma Technologies software (GT-ISE) as well as MATLAB Simulink. The results show that the RBF-BPNN control technique achieves a 1–5 % higher NOx reduction efficiency than a PID controller.

Commentary by Dr. Valentin Fuster
2017;():V003T34A003. doi:10.1115/DSCC2017-5101.

A regenerative hydraulically assisted turbocharging system is introduced. A systematic modeling approach for the engine air-path influenced under the influence of the RHAT system is discussed. The proposed modeling approach adopted seeks to reduce model complexity by introducing simple parametric relationships between corrected performance measures and allows smooth extrapolation beyond available hydraulic turbine and pump maps. A lumped parameter model of the hydraulic system is presented. Model validation results are presented for an FTP-75 cycle.

Commentary by Dr. Valentin Fuster
2017;():V003T34A004. doi:10.1115/DSCC2017-5119.

To improve transient torque response of an aggressively downsized turbocharged SI engine a series sequential boosting configuration that utilizes an electrically driven supercharger to assist the main turbocharger compressor is controlled in this paper. A frequency separation controller is designed to decouple the dynamics of the multiple-input-single-output (MISO) system. The controller separates the electric supercharger and turbocharger control actions into different frequency bands that are well suited for the characteristics of each device. The controller can be easily implemented with traditional decentralized single input single output (SISO) control loops.

Significant improvements to the baseline turbocharger only system in transient boost pressure response are observed both in simulation and in vehicle test results. Transitions between the electric supercharger and turbocharger are smooth, without noticeable disturbances, with good coordination between electric supercharger and wastegate control actions.

Commentary by Dr. Valentin Fuster
2017;():V003T34A005. doi:10.1115/DSCC2017-5194.

A novel combustion control, i.e. the trajectory-based combustion control, was proposed previously. This control is enabled by free piston engines (FPEs) and utilizes the FPE’s controllable piston trajectory to enhance thermal efficiency, reduce emissions and realize variable fuels applications. On top of that, a control-oriented model was also developed aimed to implement the trajectory-based combustion control in real-time. Specifically, a unique phase separation method was proposed in the model, which separates an engine cycle into four phases (pure compression, ignition, heat release and pure expansion) and employs the minimal reaction mechanism accordingly. In this paper, the framework of the previous control-oriented model is extended to variable fuels, such as methane, n-heptane and bio-diesel. Such an extension is reasonable since the separated four phases are representative in typical combustion processes of all fuels within an engine cycle. Besides, a least-squares optimization is formulated to calibrate the chemical kinetics variables for each fuel. At last, simulation results and the related analysis show that all the derived control-oriented models have high fidelity and much lighter computational burdens to represent the HCCI combustion of each fuel along variable piston trajectories.

Commentary by Dr. Valentin Fuster
2017;():V003T34A006. doi:10.1115/DSCC2017-5348.

Lean-burn gasoline engines have demonstrated 10–20% engine efficiency gain over stoichiometric engines and are widely considered as a promising technology for meeting the 54.5 miles-per-gallon (mpg) Corporate Average Fuel Economy standard by 2025. Nevertheless, NOx emissions control for lean-burn gasoline for meeting the stringent EPA Tier 3 emission standards has been one of the main challenges towards the commercialization of highly-efficient lean-burn gasoline engines in the United States. Passive selective catalytic reduction (SCR) systems, which consist of a three-way catalyst and SCR, have demonstrated great potentials of effectively reducing NOx emissions for lean gasoline engines but may cause significant fuel penalty due to ammonia generation via rich engine combustion. The purpose of this study is to develop a model-predictive control (MPC) scheme for a lean-burn gasoline engine coupled with a passive SCR system to minimize the fuel penalty associated with passive SCR operation while satisfying stringent NOx and NH3 emissions requirements. Simulation results demonstrate that the MPC-based control can reduce the fuel penalty by 47.7% in a simulated US06 cycle and 32.0% in a simulated UDDS cycle, compared to the baseline control, while achieving over 96% deNOx efficiency and less than 15 ppm tailpipe ammonia slip. The proposed MPC control can potentially enable high engine efficiency gain for highly-efficient lean-burn gasoline engine while meeting the stringent EPA Tier 3 emission standards.

Commentary by Dr. Valentin Fuster

Unmanned Aerial Vehicles (UAVs) and Their Applications

2017;():V003T39A001. doi:10.1115/DSCC2017-5031.

The feasibility of using a constrained Delaunay triangulation method for determining optimal flight trajectories of unmanned air vehicles in a constrained environment is explored. Current methods for developing optimal flight trajectories have yet to achieve computational times that allow for real-time implementation. The proposed method alleviates the dependency of problem specific parameters while eliminating constraints on the Non-Linear Program. Given an input of obstacles with n vertices, a constrained Delaunay triangulation is performed on the space. Converting the vertices of the triangulation to barycentric coordinates on a phased approach defines the state bounds and max time for each phase. With two-dimensional aircraft dynamics, direct orthogonal collocation methods are performed to compute the optimal flight trajectory. Results illustrate computational times and feasibility of Small Unmanned Aircraft System flight trajectories through polygon constraints.

Commentary by Dr. Valentin Fuster
2017;():V003T39A002. doi:10.1115/DSCC2017-5115.

We are interested in the persistent surveillance of an area of interest comprised of stations/ data nodes that need to be visited in a cyclic manner. The data collection task is undertaken by a UAV which autonomously executes the mission. In addition to geographically distributed stations, the scenario also includes a central depot, where data collected from the different nodes must be delivered. In this context, the performance criteria, in addition to a desired minimal cycle time, also entails minimizing the delay in delivering the data collected from each node to the depot. Each node has a priority/ weight associated with it that characterizes the relative importance between timely delivery of data from the nodes. We pose the problem as an average/ cycle reward maximization problem; where the UAV gains a reward that is a decreasing function of weighted delay in data delivery from the nodes. Since we aim to maximize the average reward, the solution also favors shorter overall cycle time. In a cycle, each station is visited exactly once; however, we allow the UAV to visit the depot more than once in a cycle. Evidently, this allows for quicker delivery of data from a higher priority node. We apply results from average reward maximization stochastic dynamic programming to our deterministic case and solve the problem using Linear Programming. We also discuss the special case of no penalty on delivery delay, whence the problem collapses to the well known metric Traveling Salesman Problem.

Commentary by Dr. Valentin Fuster
2017;():V003T39A003. doi:10.1115/DSCC2017-5177.

Simulation environments for Unmanned Aerial Vehicles (UAVs) can be very useful for prototyping user interfaces and training personnel that will operate UAVs in the real world. The realistic operation of such simulations will only enhance the value of such training. In this paper, we present the integration of a model-based waypoint navigation controller into the Reno Rescue Simulator for the purposes of providing a more realistic user interface in simulated environments. We also present potential uses for such simulations, even for real-world operation of UAVs.

Commentary by Dr. Valentin Fuster
2017;():V003T39A004. doi:10.1115/DSCC2017-5210.

This paper focuses on modeling and nonlinear control of in-ground-effect (IGE) on multi-rotor aerial vehicles such as quadrotor helicopters (quadcopters). As the vehicle flies and hovers near obstacles such as the ground, walls, and other features, the IGE which is a function of the distance between the rotor and the obstacle induces a thrust that drastically affects flight behavior. This effect on each rotor can be vastly different as the vehicle’s attitude varies. Furthermore, IGE limits the ability for precision flight control, navigation, and landing in tight and confined spaces. A nonlinear model is proposed to predict the IGE for each rotor. To compensate for the IGE, an adaptive nonlinear disturbance observer (ANDO) is designed to enhance closed-loop PID control. The observer and controller are implemented in a simulation framework, where results show significant improvement in performance compared to the case without observing and compensating for the IGE. In particular, it is shown that the ANDO PID closed-loop controller improves the settling time by approximately 60%.

Commentary by Dr. Valentin Fuster
2017;():V003T39A005. doi:10.1115/DSCC2017-5232.

In this paper, the control maneuvering, and performance analysis of a tilting-rotor quadcopter during autonomous flight is presented. Unlike traditional quadcopters, a tilting-rotor quadcopter provides additional actuated controls as the propeller motors are actuated for tilt which can be utilized to improve efficiency of the aerial vehicle during flight. The tilting-rotor quadcopter design is accomplished by using an additional servo motor for each rotor that enables the rotor to tilt about the axis of quadcopter arm. Here, a detailed control strategy has been discussed to use the propeller tilts for position and orientation control during completely autonomous flights of the quadcopter. In conventional quadcopters, the variation in rotational speeds of the four propellers is utilized for maneuvering. This work incorporates use of varying propeller rotational speeds along with tilting of the propellers for maneuvering the quadcopter during flight. A PD controller is developed to achieve various modes of flight and numerical simulation results are presented demonstrating the performance of the controller. Furthermore, the performance of the tilt-rotor design is compared with respect to the conventional quadcopter in the presence of wind disturbances and uncertainties in the system.

Commentary by Dr. Valentin Fuster
2017;():V003T39A006. doi:10.1115/DSCC2017-5241.

In this paper, we present a feed-forward control approach for complex trajectory tracking by a tilting-rotor quadcopter during autonomous flight. Tilting-rotor quadcopter is a more agile version of conventional quadcopter as the propeller motors are actuated to tilt about the quadcopter arm. The tilt-rotor quad-copter is capable of following complex trajectories with ease. In this paper, we employ differential flatness based feed-forward position control by utilizing a combination of propeller rotational speeds along with rotor tilts. The rotational motion of propellers work simultaneously in sync with propeller tilts to control the position and orientation of the UAV during autonomous flight. The results for tracking complex trajectories have been presented by performing numerical simulations and a comparison is shown with respect to conventional quadcopter for similar flight conditions. It has been found that the tilt-rotor quadcopter is more efficient than the conventional quadcopter during complex trajectory following maneuvers.

Commentary by Dr. Valentin Fuster
2017;():V003T39A007. doi:10.1115/DSCC2017-5278.

This paper presents a novel control approach to perform collaborative transportation by using multiple quadcopter Unmanned Aerial Vehicles (UAVs). In this paper, a leader-follower approach is implemented. The leader UAV uses a Proportional, Integral and Derivative (PID) controller to reach the desired goal point or follow a predefined trajectory. Traditionally, a Position Feedback Controller (PFC) has been used in literature to control the follower UAV. PFC takes the feedback of leader UAVs position to control the follower UAV. Such control schemes work effectively in indoor environments using accurate motion tracking cameras. However, the paper focuses on outdoor applications that requires usage of Global Positioning System (GPS) to receive the positional information of the leader UAV. GPS has inherent errors of order of magnitude that can destabilize the system. The control scheme proposed in this research addresses this major limitation. In this paper, a Force Feedback Controller (FFC) is used to control the follower UAV. An admittance controller is employed to implement this FFC. This controller simulates a virtual spring mass damper system, to generate a desired trajectory for the follower UAV, which complies with the contact forces acting on it. This desired trajectory is then tracked by a traditional PID controller. With the proposed control scheme, the follower UAV can be controlled without using leaders positional feedback and the system can be implemented for real-world applications. The paper presents results of numerical simulations showing the effectiveness of the proposed controller for way-point navigation and complex trajectory tracking.

Commentary by Dr. Valentin Fuster
2017;():V003T39A008. doi:10.1115/DSCC2017-5279.

This paper presents the design and analysis of a pose estimator for quadrotor micro aerial vehicles (MAVs). The proposed design uses the dynamic model of the quadrotor with aerodynamic effects and uses the extended Kalman filter (EKF) formulation for state estimation. Range measurements to known locations, inertial measurements and height measurements are used for the estimation task. The purpose of the study is to evaluate the performance of the estimator when navigating through a changing indoor setting. The study investigates the effect of changing number of rannge measurements, different geometrical arrangements of range sensors and changing availability of confident height information on the performance of the estimator. Performance of the estimator for each scenario is numerically analyzed. Finally a criteria is proposed for selecting the sensors, number of range measurements, geometric location of sensors which facilitates accurate position estimation using the proposed method.

Commentary by Dr. Valentin Fuster
2017;():V003T39A009. doi:10.1115/DSCC2017-5295.

This paper develops a control that combines deterministic and stochastic optimal control solutions to the problem of safe navigation around a spherical obstacle in order to reach a way-point location. The solution for navigation towards the way-point is based on the deterministic minimum time optimal control. Since the intent of the obstacle is unknown to the navigating vehicle, the vehicle anticipates this uncertainty and uses a stochastic optimal control for navigation around the obstacle. The two navigation solutions are combined based on their value functions. Results are illustrated by numerical simulations.

Commentary by Dr. Valentin Fuster
2017;():V003T39A010. doi:10.1115/DSCC2017-5354.

This paper presents a wireless sensor system developed to use RC helicopter dynamics to measure wind turbulence. Wind turbulence is a safety concern for naval helicopter operations due to typical scarcity of landing/takeoff area on naval vessels. Wind turbulence affects the dynamics of helicopters by creating uneven thrust on the rotor blades. The proposed telemetry system, when retrofitted on an RC helicopter, extracts these external disturbances in the helicopter’s dynamics and maps the wind conditions. This study focuses on learning the helicopter’s dynamics in controlled wind conditions using machine learning algorithms. The presented telemetry system uses sensors such as an Inertial Measurement Unit (IMU), optical trackers, and GPS sensors to measure the dynamics of the flying RC helicopter. The system also measures the pilot’s radio inputs to account for pilot inputs in the helicopter’s dynamics. The telemetry system is trained and tested in a large indoor facility where turbulent wind conditions were created artificially using large wind circulation fans.

Commentary by Dr. Valentin Fuster
2017;():V003T39A011. doi:10.1115/DSCC2017-5405.

As the development of computer vision and the popularity of unmanned aerial vehicle, using visual information to control the UAV motion becomes a hotspot. Time-to-contact is one of the concepts that is used to control robot motion such as braking, landing, perching, and obstacle avoidance based on visual information. In this paper, to explore the capability and potential of a direct featureless time-to-contact estimation algorithm for unmanned aerial vehicle motion control, we design an integrated unmanned aerial vehicle system and verify the accuracy of the featureless time-to-contact estimation algorithm. In addition, compressed sensing is combined with the featureless method in time-to-contact estimation to potentially improve the computational speed. The experiment results show that the featureless time-to-contact estimation algorithm, the developed UAV platform and compressed sensing can be readily applied for UAV vision based control.

Commentary by Dr. Valentin Fuster

Dynamics and Control of Renewable Energy Systems

2017;():V003T40A001. doi:10.1115/DSCC2017-5224.

Wind turbine vibrations can result from periodic excitation caused by the wind and by both wind and seas for the case of offshore units. In particular, the turbine drivetrain is subject to torsional vibrations caused by both changes in the wind and grid disturbances. This paper uses a collection of different control schemes to damp the vibrations and seeks the best controller by optimizing each in terms of gain selection. Two 750 kW wind turbine models, one with a DFIG (doubly fed induction generator) and the other with a PMSG (permanent magnet synchronous generator) are used in the investigation. Numerical simulations of the wind turbines using the NREL developed software FAST 8 are the means of conducting the tests. In varying the gains, the work discovers that the best controller for a DFIG differs greatly from the best controller for a PMSG. In addition, the work found that the vibration damping in a DFIG turbine is different when the source of the vibration-causing disturbance is considered. The paper reports both the optimized gains and a set of questions raised by the behavior of the DFIG turbine where the response of the shaft torsion differs according to the source of the disturbance, i.e. either grid side or wind side.

Commentary by Dr. Valentin Fuster
2017;():V003T40A002. doi:10.1115/DSCC2017-5230.

In this paper, we present an online approach for optimizing the 3D layout of an ocean current turbine (OCT) array. Unlike towered turbines, most OCT concepts for Gulf Stream energy harvesting involve tethered systems. The replacement of towers with tethers provides the opportunity for OCTs to adjust their locations within some domain by paying out/in tether to adjust depth and manipulating control surfaces (elevators and rudders) to adjust longitudinal and lateral positions. The ability to adjust the OCT positions online provides the capacity to reconfigure the array layout in response to changing flow conditions; however, successful online array layout reconfiguration requires optimization schemes that are not only effective but also enable fast convergence to the optimal configuration. To address the above needs, we present a reconfigurable layout optimization algorithm with two novel features. First, we describe the location of each turbine through a small set of basis parameters; the number of basis parameters does not grow with increasing array size, thereby leading to an optimization that is not only computationally tractable but is also highly scalable. Secondly, we use Bayesian Optimization to optimize these basis parameters. Bayesian Optimization is a very powerful iterative optimization technique that, at every iteration, fuses a best-guess model of a complex function (array power as a function of basis parameters, in our case) with a characterization of the model uncertainty in order to determine the next evaluation point. Using a low-order analytical wake interaction model, we demonstrate the effectiveness of the proposed optimization approach for various array sizes.

Commentary by Dr. Valentin Fuster
2017;():V003T40A003. doi:10.1115/DSCC2017-5242.

This paper presents a novel data-driven nested optimization framework that aims to solve the problem of coupling between plant and controller optimization. This optimization strategy is tailored towards instances where a closed-form expression for the system dynamics is unobtainable and simulations or experiments are necessary. Specifically, Bayesian Optimization, which is a data-driven technique for finding the optimum of an unknown and expensive-to-evaluate objective function, is employed to solve the nested optimization problem. The underlying objective function is modeled by a Gaussian Process (GP); then, Bayesian Optimization utilizes the predictive uncertainty information from the GP to decide the best subsequent control or plant parameters. The proposed framework differs from the majority of co-design literature where there exists a closed-form model of the system dynamics. We validate the proposed framework for Altaeros’ Buoyant Airborne Turbine (BAT). We choose the horizontal stabilizer area and longitudinal center of mass relative to center of buoyancy (plant parameters) and the pitch angle set-point (controller parameter) as our decision variables. Our results demonstrate that plant and control parameters converge to optimal values within only a few iterations.

Commentary by Dr. Valentin Fuster
2017;():V003T40A004. doi:10.1115/DSCC2017-5262.

Real-time optimization of wind farm energy capture for below rated wind speed is critical for reducing the levelized cost of energy (LCOE). Performance of model based control and optimization techniques can be significantly limited by the difficulty in obtaining accurate turbine and farm models in field operation, as well as the prohibitive cost for accurate wind measurements. The Nested-Loop Extremum Seeking Control (NLESC), recently proposed as a model free method has demonstrated its great potential in wind farm energy capture optimization. However, a major limitation of previous work is the slow convergence, for which a primary cause is the low dither frequencies used by upwind turbines, primarily due to wake propagation delay through the turbine array. In this study, NLESC is enhanced with the predictor based delay compensation proposed by Oliveira and Krstic [1], which allows the use of higher dither frequencies for upwind turbines. The convergence speed can thus be improved, increasing the energy capture consequently. Simulation study is performed for a cascaded three-turbine array using the SimWindFarm platform. Simulation results show the improved energy capture of the wind turbine array under smooth and turbulent wind conditions, even up to 10% turbulence intensity. The impact of the proposed optimization methods on the fatigue loads of wind turbine structures is also evaluated.

Commentary by Dr. Valentin Fuster
2017;():V003T40A005. doi:10.1115/DSCC2017-5275.

In this paper a full nonlinear dynamic control oriented mathematical model of Proton Exchange Membrane (PEM) fuel cell system is developed. The model is structured as a nonlinear five state space model. The derivation of each state equation is based on physics fundamental principles using thermodynamic theory of ideal gas mixtures, conservation of mass law, flow dynamics in serpentine flow channels and diffusion. The output of proposed model, stack voltage, is developed from Nernst equation that includes three main types of losses occurring in the fuel cell. The unknown parameters of the model are estimated and fitted using sets of steady state experimental data. Stack polarization curve of the proposed model is validated by using sets of data for three different values of inlet pressures. Experimental setup used to attain data is the Greenlight Innovation G60 fuel cell test station system and TP50 Fuel Cell stack.

Commentary by Dr. Valentin Fuster
2017;():V003T40A006. doi:10.1115/DSCC2017-5282.

A method for designing and controlling a novel wind turbine blade is presented. The blade is modular, flexible, and additively manufactured. Conventional blades are monolithic and relatively stiff. The conventional method for improving aerodynamic efficiency is through generator torque control. The anisotropic nature of the additive manufacturing (AM) process has the potential to create a flexible blade with a low torsional-to-longitudinal-stiffness ratio. This enables new design and control capabilities that could be applied to the twist angle distribution (TAD). Simulation results suggest this can increase the aerodynamic efficiency during Region 2 operation. The suggested blade design includes a rigid spar with flexible AM segments that form the surrounding shells. The stiffness of each individual segment and the actuator placement define the TAD. In practice, the degree of flexibility for each segment will be established through the design and AM processes. These variations in compliance allow the blade to conform to the desired set of TAD geometries. The proposed design process first determines the TAD that maximizes the aerodynamic efficiency in Region 2. A mechanical design algorithm subsequently locates a series of actuators and defines the stiffness ratio between the blade segments. The procedure is optimized to minimize the amount of variation between the theoretical TAD and that which is obtained in practice. The free-shape TAD is also determined in the final design step. The geometry is chosen to minimize the amount of deflection needed to shape the TAD as it changes with Region 2 wind speed. A control framework is also developed to set the TAD in relation to wind speed. A case study demonstrates the capability of the proposed method. The simulation results suggest that a TAD controlled through five actuators can achieve the full range of required motion. Moreover, the design solution can increase the efficiency at cut-in and rated speeds up to 3.8% and 3.3%, respectively.

Commentary by Dr. Valentin Fuster

Energy Harvesting

2017;():V003T41A001. doi:10.1115/DSCC2017-5034.

In order to reveal the nonlinear response characteristics of asymmetric tristable energy harvesters, this paper originally deduces their complete harmonic balance solutions. In addition, the Jacobian matrix for determining the stability of these analytical solutions is presented. Under different harmonic excitation conditions, the multi-solution response characteristics of asymmetric tristable energy harvesters are analyzed. In detail, asymmetric tristable energy harvesters are found to have seven solutions (four stable solutions) under the appropriate excitation condition. The influence mechanism of asymmetry of potential wells on tristable energy harvesting performance is studied. The results show that the potential barrier is a main factor to influence high-energy interwell oscillation orbit height, which determines the output voltage amplitude and the overall energy harvesting performance. The influence essence of asymmetry for tristable energy harvesters is to change their potential wells and adjust the distribution of their potential barriers.

Commentary by Dr. Valentin Fuster
2017;():V003T41A002. doi:10.1115/DSCC2017-5198.

This paper proposes a novel mechanical-motion-rectifier (MMR) based power-takeoff (PTO) for ocean wave energy harvesting. The proposed PTO directly converts irregular oscillatory wave motion into regular unidirectional rotation of the generator. It is mainly composed of two ball screws, three bevel gears, two one-way clutches, and a generator. The two one-way clutches and the bevel gears change the bi-directional rotation of the two ball screws into unidirectional ration of the generator. The MMR rectifies the irregular reciprocating motion into unidirectional rotation; similar to the way the electric voltage rectifier regulates an AC voltage. The proposed PTO can be integrated into a heaving point wave energy converter (WEC). The dynamics and modelling of the PTO are presented. The frequency-domain dynamics of the WEC are then formulated for operating condition and control. The power generation capability of the proposed WEC has been evaluated in MATLAB and WAMIT. The simulation results demonstrate that the power generation capability can be improved by using the MMR method.

Topics: Wave energy
Commentary by Dr. Valentin Fuster
2017;():V003T41A003. doi:10.1115/DSCC2017-5355.

Maintenance is, amongst others, a key cost driver in aircraft operation. A wireless monitoring device might be able to reduce these costs. However, the supply of energy to such system via power lines would result in additional cabling and battery operation would lead to additional maintenance. Thermoelectric energy harvesting, as a power source for such devices, is considered as one the most promising approaches for autonomous energy conversion onboard fixed wing aircraft. Using thermoelectric generators (TEGs), the temperature difference, between the inside and outside of the cabin, can be used to generate electrical energy.

In this paper an energy harvesting device, for aircraft application needs and requirements, is designed and optimized using modeling and simulation. A variety of models are used for analyzing the static and dynamic behavior of the device. A one-dimensional heat transfer model is used to identify critical parameters, while a detailed three-dimensional heat-transfer and airflow model is used to study realistic operating conditions. The proposed design leads to a significant increase of peak and average output power, specific energy productions and decrease of response time of the harvester.

Commentary by Dr. Valentin Fuster
2017;():V003T41A004. doi:10.1115/DSCC2017-5371.

Neural networks are derived to be used as closed-form representations of mean hydrokinetic turbine performance variables. These representations can be used to obtain estimates of turbine performance when the ambient turbulence characteristics, namely in-flow velocity and turbulence intensity, are given. The neural networks were developed using a detailed hydrodynamic code, which simulates performance of a rigidly mounted hydrokinetic turbine where only rotor rotation is allowed (1-DOF). By varying the in-flow velocity (U) of the water current between 0.4m/s and 2.6m/s with a step of 0.2m/s, as well as Turbulence Intensity (TI) between 5% and 20% with a step of 2.5%, a set of variables including the output shaft power, shaft torque, force on a single blade and drag force were obtained for each case. The obtained data sets were used to train appropriately sized, feed-forward (i.e. without recirculation) neural networks. Four neural networks obtained, one for each output variable of the hydrodynamic code. Each neural net constitutes a closed-form, explicit mathematical relationship (equation) generating estimates for the corresponding dependent variable it has been trained to approximate, when presented with specific values for the independent (input) variables current velocity, U, and turbulence intensity, TI. Four output (dependent) variables of interest of the hydrodynamic code are considered: shaft power, shaft torque, force on a single blade and drag. The dependent variables are actually time-averaged steady-state values derived from each hydrodynamic code run. The results of the neural networks are validated using the background theory, as well as the data generated by the hydrodynamic code. Error of less than 1% has been achieved between the neural net output and the hydrodynamics code data values suggesting that the neural networks and the equations are usable in place of the hydrodynamic code for estimating time-averaged loadings and power production.

Commentary by Dr. Valentin Fuster
2017;():V003T41A005. doi:10.1115/DSCC2017-5396.

Frequency up-conversion is an effective way to increase the output power from a piezoelectric beam, which converts the ambient low-frequency vibration to the resonant vibration of the piezoelectric energy harvesters (PEH) to achieve high electric power output. Frequency up-conversion technologies are realized via impact or non-impact magnetic force to mediate the interaction between the driving beam and the generating beam. Most studies focus on the either linear model prediction or experimental verification of the linear analysis. Few, if any, study the effects of the impact induced nonlinear phenomena on power generation efficiency. In this work, we investigate how to use discontinuous theory to improve the power efficiency of the frequency up-conversion process caused by impacts. The energy harvesting performance of a piezoelectric beam in interaction with a softer beam in periodic motion is studied. The discontinuous dynamical system theory is applied to this problem to study the piezoelectric behavior under periodic motions and its bifurcations.

The beams are modeled with two spring-mass-damper systems, and the analytical model of the piezoelectric beam is created based on the linear mechanical-electrical constitutive law of the piezoelectric material, and the linear elastic constitutive law of the substrate. Based on the theoretical model, the analytical solution of the output power is derived in terms of the vibration amplitude, frequency, and the electrical load. The soft beam is subjected to a sinusoidal base excitation, and the impacts of the more flexible beam excite the piezoelectric beam. The performance of the energy harvesting of period one and period two motions have been studied and bifurcation trees for impact velocities, times, displacements and harvested power versus the frequency of the base excitation are obtained.

Commentary by Dr. Valentin Fuster

Control of Smart Buildings and Microgrids

2017;():V003T42A001. doi:10.1115/DSCC2017-5006.

In this effort, we present a comprehensive comparative study of decentralized and centralized adaptive schemes to control the so-called “Smart Valves” network employed in many applications including, but not limited to, Municipal Piping Systems and oil and gas fields. The network being considered here typically includes scores of coupled solenoid actuated butterfly valves. We here examine the multiphysics network of two interconnected actuated sets. The network undergoes the coupled chaotic and hyperchaotic dynamics subject to some initial conditions and critical parameters. The control schemes’ trade-offs are thoroughly investigated with respect to robustness, computational cost, and practical feasibility of control inputs in the presence of strong nonlinear interconnections and harmful chaotic and hyperchaotic responses.

Commentary by Dr. Valentin Fuster
2017;():V003T42A002. doi:10.1115/DSCC2017-5191.

Load shifting is one means whereby buildings may reduce their peak demand and provide other services to the electric grid. Current rate tariffs penalize facility peak demand, and large commercial and industrial buildings may realize cost savings by reducing this facility peak demand. The successful shifting of electric load requires some knowledge or prediction of the peak demand. This prediction is generally imperfect, and the resulting load shifting control is sub-optimal. This paper develops the optimal load shifting operations using a battery energy storage system under certain assumptions. This optimal solution is then used to develop a generalized strategy for load shifting battery control with the purpose of reducing peak 15-minute demand. This generalized strategy involves a prediction of the target demand level and a prediction of the current 15 minute period. The method whereby these predictions are made is critical to the success of load shifting. The general control logic may be used to analyze the sensitivity of load shifting to prediction error and sampling rate..

Topics: Stress
Commentary by Dr. Valentin Fuster
2017;():V003T42A003. doi:10.1115/DSCC2017-5315.

Model predictive control (MPC) strategies hold great potential for improving the performance and energy efficiency of building heating, ventilation, and air-conditioning (HVAC) systems. A challenge in the deployment of such predictive thermo-static control systems is the need to learn accurate models for the thermal characteristics of individual buildings. This necessitates the development of online and data-driven methods for system identification. In this paper, we propose an autoregressive with exogenous terms (ARX) model of a thermal zone within a building. To learn the model, we present a backpropagation approach for recursively estimating the parameters. Finally, we fit the linear model to data collected from a residential building with a forced-air heating and ventilation system and validate the accuracy of the trained model.

Commentary by Dr. Valentin Fuster
2017;():V003T42A004. doi:10.1115/DSCC2017-5362.

This paper considers islanded microgrids and is motivated by the need for decentralized control strategies with minimal communication among grid components to support a robust and plug-and-play operation. We focus on the problem of power allocation among the distributed generation units (DGs) to maintain low distribution power loss in the grid and develop a communication-free distributed power control approach for power loss minimization based on the extremum-seeking (ES) method. In this approach, the DGs implement ES simultaneously and separately to minimize their current outputs by controlling the active power. The total power loss is thus reduced and no grid structure information or communication is needed in the optimization process. The existence of a Nash equilibrium in the resulting non-cooperative game is proved. Numerical simulations are conducted to demonstrate the performance of the proposed communication-free power control approach and show that it is suitable for maintaining low power loss under different operating conditions in a plug-and-play manner.

Topics: Microgrids
Commentary by Dr. Valentin Fuster
2017;():V003T42A005. doi:10.1115/DSCC2017-5366.

Demand-response programs offer a viable solution for improving the grid efficiency and reliability though the shaping of the consumer’s power demand. For the customers to fully benefit from varying electricity prices, an energy management strategy that coordinates the electrical loads is required. In this framework, this paper uses a Nonlinear Model Predictive Control (MPC) strategy to solve the coupled problem of optimally scheduling home appliances, Heating, Ventilation and Air Conditioning (HVAC) system and controlling electric vehicle charging. Simulation results are presented on selected case studies to demonstrate the ability of the Particle Swarm Optimization (PSO) to solve the optimization problem for a single home faster than real-time. Results show that this strategy is always able to provide near-optimal solutions with limited computation time and no reconfiguration of the control scheme for applications to houses equipped with different technologies.

Commentary by Dr. Valentin Fuster
2017;():V003T42A006. doi:10.1115/DSCC2017-5400.

Microgrids are small-scale power networks where distributed generation and inverter interfaced power sources are common. These networks are faced with more significant control challenges; a smaller system can less effectively dampen and distribute power disturbances or fluctuations, and the system frequency is less robust without synchronous generators to provide rotational inertia. In this paper we will develop optimal control algorithms to control the voltage and frequency in an islanded inverter-based microgrid. The voltages and frequency of this system are controlled using decentralized control. The decentralized controllers operate using only local data, making the control methodolgy scalable. In addition, the studied controllers can be tuned to achieve the desired transient behavior. For voltage and frequency control of microgrids, transient performance is still an area of weakness. The proposed control scheme extends optimal control to the field of microgrid control and can improve the state of microgrid technology.

Topics: Microgrids
Commentary by Dr. Valentin Fuster

Energy Systems

2017;():V003T43A001. doi:10.1115/DSCC2017-5139.

Dynamic characteristics of a proton exchange membrane fuel cell (PEMFC) system can impact fuel economy and load following performance of a fuel cell vehicle, especially if those dynamics are ignored in designing top-level energy management strategy. To quantify the effects of fuel cell system (FCS) dynamics on optimal energy management, dynamic programming (DP) is adopted in this study to derive optimal power split strategies at two levels: Level 1, where the FCS dynamics are ignored, and Level 2, where the FCS dynamics are incorporated. Analysis is performed to quantify the differences of these two resulting strategies to understand the effects of FCS dynamics. While Level 1 DP provides significant computational advantages, the resulting strategy leads to load following errors that need to be mitigated using battery or FCS itself. Our analysis shows that up to 5% fuel economy penalty on New York city cycle (NYCC) and 3% on supplemental federal test procedure (US06) can be resulted by ignoring FCS dynamics, when the dominant dynamics of the FCS has settling time as slow as 8 seconds.

Commentary by Dr. Valentin Fuster
2017;():V003T43A002. doi:10.1115/DSCC2017-5266.

Lithium Iron Phosphate (LiFePO4 or LFP) is a common active material in lithium-ion batteries. It has been observed that this material undergoes phase transitions during the normal charge and discharge operation of the battery. Electrochemical models of lithium-ion batteries can be modified to account for this phenomena at the expense of some added complexity. We explore this problem for the single particle model (SPM) where the underlying dynamic model for diffusion of lithium ions in phase transition materials is a partial differential equation (PDE) with a moving boundary. An observer is derived for the concentration of lithium ions from the SPM via the backstepping method for PDEs in a rigorous way and simulations are provided to illustrate the performance of the observer. Our comments are stated on the gap between the proposed observer and a complete state-of-charge (SoC) estimation algorithm for lithium-ion batteries with phase transition materials.

Commentary by Dr. Valentin Fuster
2017;():V003T43A003. doi:10.1115/DSCC2017-5280.

Accurate control of weight-on-bit (WOB) in oil and gas drilling plays an important role in achieving high rates of penetration (ROP) and minimizing drillstring vibrations. In this paper, we propose a nonlinear, stochastic model of downhole WOB, and provide a framework for estimation, and control of the proposed model. We focus on real-time estimation of modeling and measurement uncertainties, and use these estimates to adapt the controller characteristics accordingly. The presented methodology is simulated for various scenarios, and benchmarked against existing control techniques in the industry.

Commentary by Dr. Valentin Fuster
2017;():V003T43A004. doi:10.1115/DSCC2017-5286.

Conventional closed cycle heat engines — such as Stirling engines — have many advantages, such as high theoretical efficiency and the ability to produce useful work out of any heat source. However, they suffer from low power density due to poor heat transfer capability between the working gas and its surrounding walls. In this work, we proposed a new architecture where the solid displacer of a Stirling engine is replaced with a ferrofluid liquid displacer. In this approach, the relative displacer location with respects to the engine chamber is controlled (and stabilized) through a strong magnetic field generated by a permanent magnet. The liquid nature of the displacer allows the hot and cold chambers of the engine to be filled with porous material, improving the heat transfer by an order of magnitude. Additionally, this engine architecture mitigates sealing issues, can operate at higher pressures, and has naturally lubricating surfaces. A relatively simple configuration of this idea is modeled in this work. Exploratory dynamic simulations of this unoptimized architecture show a thermal efficiency of 21% and a power density of approximately 700W/lit.

Commentary by Dr. Valentin Fuster
2017;():V003T43A005. doi:10.1115/DSCC2017-5316.

Energy systems (e.g. ventilation fans, refrigerators, and electrical vehicle chargers) often have binary or discrete states due to hardware limitations and efficiency characteristics. Typically, such systems have additional programmatic constraints, such as minimum dwell times to prevent short cycling. As a result, non-convex techniques, like dynamic programming, are generally required for optimization. Recognizing developments in the field of distributed convex optimization and the potential for energy systems to participate in ancillary power system services, it is advantageous to develop convex techniques for the approximate optimization of energy systems. In this manuscript, we develop the alternative control trajectory representation — a novel approach for representing the control of a non-convex discrete system as a convex program. The resulting convex program provides a solution that can be interpreted stochastically for implementation.

Commentary by Dr. Valentin Fuster
2017;():V003T43A006. doi:10.1115/DSCC2017-5358.

Directional drilling technology provides more flexibility in the selection of rig locations than conventional vertical drilling. It significantly increases drilling efficiency by avoiding undesirable rock formations. In addition, it maximizes production efficiency by increasing the exposed area of a reservoir and grouping multiple reservoirs. In drilling operations, the analysis of drillstring dynamics is critical to circumvent undesirable vibrations and to improve performance. Linear modeling methods are insufficient to describe the system dynamics because directional drilling, unlike vertical drilling, causes the drillstring and the bottomhole assemble (BHA) to bend with a large curvature. In this paper, a model, based on the finite element method (FEM), is established to characterize the dynamics of a directional drill-string. High computational efficiency is achieved by separating the overall displacement into an initial displacement representing the nonlinear bending and a small deformation linear dynamic model. The proposed model is verified against two case studies from the literature, and the comparisons show accurate results. To demonstrate the utility of the proposed model, a BHA force model is included, which considers bit-rock collision, hydraulic damping of the mud, and the eccentricity of the BHA. The simulation results show the capabilities of the model in describing typical drilling vibrations.

Commentary by Dr. Valentin Fuster

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