ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V006T00A001. doi:10.1115/OMAE2017-NS6.

This online compilation of papers from the ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Ocean Space Utilization: Aquaculture and Related Technology

2017;():V006T05A001. doi:10.1115/OMAE2017-61330.

A net wake shielding and self shielding model has been developed to accurately estimate the hydrodynamic loading on fin-fish aquaculture installations in the dynamics simulation software package ProteusDS. The software was developed to determine the loads and motions of various ocean engineering systems in response to wave, wind and current conditions. The effect of containment net hydrodynamic wake shielding is important to avoid overly conservative estimation of loads on fish farm installations. The reduction in fluid velocity through a net can be significant in many cases, leading to decreased loading and changes in motion on downstream nets and mooring components.

The developed wake shielding model uses a wake volume approach to estimate a reduction in flow velocity and hydrodynamic loading on downstream components within the wake volume. Self shielding effects of adjacent twines within a net are also considered, as interactions between netting twines can reduce hydro-dynamic loading on nets at certain angles of incidence to the oncoming flow. This paper presents the developments both of the wake shielding and self shielding models and demonstrates the capability to accurately predict current forces acting on successive net pens by comparing simulation results with published results from tank tests, as well as a comparison of measured tensions on mooring lines at a full scale fish farm. A method for determining netting drag coefficients based on Reynolds number variations is also presented and compared to experimental drag tests on planar nets to confirm its validity.

Commentary by Dr. Valentin Fuster
2017;():V006T05A002. doi:10.1115/OMAE2017-61519.

This paper presents a study of traditional netting materials subjected to disinfecting chemicals during fish farming and treatment of net cages. A series of tests were performed in order to study the effect of various concentrations of disinfecting chemicals on the tensile strength of Raschel knitted Nylon netting materials.

Simulated spill of diluted hydrogen peroxide to the jump fence during de-lousing did not affect the strength of the applied new and used knotless nylon netting samples. Hydrogen peroxide reacted with biofouling forming gas bubbles, but this did not result in reduced netting strength.

The performed tests did not indicate any effect on netting strength from a simulated single, traditional bath disinfection as performed at service stations applying the disinfectant Aqua Des containing peracetic acid. However, increasing the Aqua Des concentration from 1 to 10 % resulted in a strength reduction of 3–6 %. Simulated spill of concentrated Aqua Des on the jump fence of a net with copper coating residuals resulted in a severe reduction in strength of 45 %. This strength loss was probably a consequence of chemical reaction between copper and Aqua Des, and uncoated netting did not experience any loss in strength subjected to the same chemical exposure. These findings from application of Aqua Des should also apply to other peracetic acid disinfection chemicals with trade names as for example Perfectoxid and Addi Aqua.

Commentary by Dr. Valentin Fuster
2017;():V006T05A003. doi:10.1115/OMAE2017-61531.

This paper addresses the description of exposure from waves and currents in coastal regions for design of marine fish farms. Representative descriptions of environmental conditions are important inputs to the design and dimensioning of reliable fish farm structures. A trend with moving production to more exposed sites and introduction of new and novel fish farm structures increase the need for more precise descriptions of the marine environment to keep control of uncertainties in design. Dedicated field measurements at two exposed aquaculture sites from February to December 2016 are presented. Results from statistical analyses of the measurement data demonstrate that common practice for characterization of exposure in design of fish farms has several deficiencies that should be improved to reduce uncertainties in design.

Topics: Design
Commentary by Dr. Valentin Fuster
2017;():V006T05A004. doi:10.1115/OMAE2017-61631.

Silver salmon is usually cultured around the eastern coast of Tohoku Region in Japan. The smolt of silver salmon begins to be cultured in a cage from November. Currently, the aquaculture of silver salmon is terminated until the end of July due to high water temperature since silver salmon will die in a few days if the diurnal minimum water temperature becomes 21 or 22°C. Live salmon cannot be obtained around August because wild salmon is captured from September or October. In the present study, a submergible cage using flexible tubes is proposed to farm silver salmon in deeper and cooler waters in August. The cage was submerged and floated up by ejecting air from and injecting air into the flexible tubes, respectively. The flexible tubes were inserted into the polyethylene pipes. First, water tank test using the 1/3.64 scaled model was carried out in the Ocean Engineering Basin, Institute of Industrial Science, The University of Tokyo. The cage was submerged or floated up, changing the methods of air ejection or injection. The cage was submerged and floated up faster in case of two vents to increase the rate of air flow than in case of only one vent on flexible tubes. The submersion was also faster if the length of an injection tube between the vents and air compressor was shortened to reduce the pressure loss. However, the maximum inclination angle of the cage was determined by the diameter of the cage and the submerged depth, not depending on the methods of air injection or ejection. Similar results were observed in the field test. Consequently, silver salmon could be farmed in deeper and cooler waters until the middle of August. The inclination of the cage was not the problem for silver salmon, while it may have unfavorable effects on the other species through the deformation of netting. Hence, the methods to reduce the inclination of the cage in submerging or floating up operation should be considered and validated in field test in the future.

Topics: Silver , Water
Commentary by Dr. Valentin Fuster
2017;():V006T05A005. doi:10.1115/OMAE2017-61659.

In Norway there are a total of 1070 registered sites for salmon farming all along the coast. Trends in the aquaculture industry in the recent decade are that salmon farming sites tend to gradually relocate to more wave and current exposed locations. This trend is mainly motivated by the good water quality found in more exposed areas, as well as a lack of available sheltered locations. On the other hand, the increased exposure puts higher loads on the structures and this needs to be addressed by the development of more robust technology. The first step in order to address an increased exposure is to quantify the level of exposure of waves and current, and in this paper a method to easily estimate the level of wind wave exposure on a large number of sites are presented, and subsequently used to analyse all Norwegian sites.

The method can be called fetch analysis, and use long term wind data connected with the fetch length in order to estimate wind wave conditions. The method is divided into four steps: 1) Fetch analysis, 2) Wind data, 3) Estimating wave parameters Hs and Tp and 4) Wave statistics. Significant wave height Hs with return period 1 year and 50 years are estimated for each site. Hs 50 year is often used for design, and the analysis shows that for 38% of the sites Hs 50 year exceeds 1 meter, for 17% of the sites Hs 50 year exceeds 1.5 meter, while 1.4% of the sites have Hs 50 year larger than 2.5 meter. The most exposed site has a Hs 50 year of 2.9 meter. Thus there are large differences in Hs 50 year in the various coastal regions of Norway.

Topics: Wind waves
Commentary by Dr. Valentin Fuster
2017;():V006T05A006. doi:10.1115/OMAE2017-61665.

The aquaculture industry is aiming to move fish farms from near-shore area to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves and current. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from frequency domain analysis. A preliminary mooring system was designed to avoid possible interactions with the fish cages. Time domain simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared in various waves and current conditions. The effects due to misalignment of waves and current directions on the responses were also studied.

Commentary by Dr. Valentin Fuster
2017;():V006T05A007. doi:10.1115/OMAE2017-61824.

Numerical simulation of a motion-controlled ship was conducted. This ship is a catamaran, the motion of which is controlled with motors by an active control system, called Skyhook control. In addition, this ship can harvest wave energy by converting relative displacement between a cabin and floats to rotational motion, and then, to electrical energy by generators. Energy harvesting efficiency can be maximized by a technique, called MPPT (Maximum Power Point Tracking). The model of the ship was constructed on a circuit diagram with SPICE (Simulation Program with Integrated Circuit Emphasis) based on a mechanical-electrical analogy, called Mobility method, because mechanical system and electrical system are coupled through a motor/generator as a transducer in this ship. The results of the simulation based on this model were compared to those of the tank test already done by some of the authors, and its performance was evaluated. The results showed good agreement between the simulation and the experiment qualitatively, while quantitative gap could be found. There are some problems to be solved such as considering precise hydrodynamic force. Thus, the model needs to be improved more. It will be possible to design a new concept of fishery boats using the simulation based on this model in the future. This concept of fishery boats can be aimed at coastal fishery and offshore aquaculture.

Commentary by Dr. Valentin Fuster
2017;():V006T05A008. doi:10.1115/OMAE2017-62030.

Biofouling is a serious problem in marine finfish aquaculture with a number of negative impacts. Marine growth obstructs net openings, thereby reducing water exchange through the net and affecting fish welfare and health, as well as the spreading of dissolved nutrients, particles and pathogens. Furthermore, additional water blockage leads to increased hydrodynamic forces on fish cages, which potentially threaten the structural integrity of the fish farm. However, detailed knowledge about the effects of biofouling on the flow past, and the resulting forces on fish cages, is limited and systematic investigations of the effects of different types of fouling have been called for.

This study investigates the effects of different amounts and sizes of two important fouling organisms in Norwegian aquaculture, blue mussel (Mytilus edulis) and kelp (Saccharina latissima) on the drag on net panels. Drag forces on a number of clean and fouled nets were measured in a flume tank at a flow speed of 0.1 m/s. Net solidity was calculated from images acquired of all nets in the current. The relationship between net solidity and drag was then found for clean nets and for each type of fouling, and biofouling was parameterized by comparing clean and fouled net results: for a given fouled net, a clean net can be found that experiences the same drag. The latter can then be used in numerical models to estimate the effect of fouling on net drag. That means existing models can be used to model the drag effect of fouling. This study found a solidity increase due to mussel and kelp fouling to affect drag roughly at the same rate as an increase in clean net solidity at a flow speed of 0.1 ms−1 and within the tested fouling size range for two net types. Therefore, existing models, describing the relationship between net solidity and drag, can be used directly or with minor alterations (especially at high solidities) to estimate effects of additional mussel and kelp fouling on drag. In contrast, wet weight seems to be unsuitable as a measure to estimate drag on nets fouled with seaweed or mussels. It should be noted that these findings are only valid under similar conditions, and that other fouling types and sizes, as well as test parameters and tank size can affect the relationship between solidity and drag.

Commentary by Dr. Valentin Fuster

Ocean Space Utilization: Coastal Zone Management

2017;():V006T05A009. doi:10.1115/OMAE2017-61142.

In order to simulate the bottom trawl fishery in Ise Bay, a typical semi-enclosed bay in Japan, a fishery simulator has been developed that consists of a fish behavioral model and a fishing operations model. The fish behavioral models are developed for two major target species, conger eel and mantis shrimp, which consider the fish migration as well as the growth and the population change. The fish behavioral models are combined with a fishing operation model, which predicts the behavior of trawling boats based on economic conditions and resource distribution as well as the fish catch amount by each boat. The model is applied to evaluate the effects of fishery management, and it is investigated that how the control of fishing efforts or number of owned fishing boats affects the profit of the target fishery. The mesh size of the trawling net which maximizes the total catch is estimated considering both conger eel and mantis shrimp. At the target ports, reduction of boats number will increase the profit because the effect of fixed cost change exceeds the impact of fish catch decrease. However, the optimum reduction rate is different in each port and interactive effect should be also considered.

Commentary by Dr. Valentin Fuster
2017;():V006T05A010. doi:10.1115/OMAE2017-61618.

Recently, the demanding for effective utilization of marine spaces in forms of oceanic architectures has been rising high by new social requirements as well as other constructions, and the like. Consequently, architecutural characteristics and structural effectiveness of them should be reevaluated accordingly.

Objects of this study are four architectures located in the shallow area of sea around Kyushu Region,namely Marizon, Genkai Sea Hot Spring Palea, Marine Aquarium Sea Doughnut, and Akasaki Elementary School.

Their functions, structures, setting forms, then conditions for situating buidings, processes of construction at sea, and challenges after construction had been clarified by our literature survey, the hearing investigation and the field research.

Our results are as following. Functionally, each above architectures has respective facilities to fully utlize regional marine resources and environment, etc.; Structurally, all of them had premeditated both the bad conditions of coastal environment and providing spaces for water activities. In terms of their construction processes at sea, factors blow had been carefully considered before being sited: limitations of local spatial scale, full utilization of local environmental conditions, measures against disadvantages of sites, the particularities of regional nature, environment, and society.

In conclusion, our findings suggest that planning of the oceanic architecuture should combine the usage, the fuction, and the understructures well with its marine conditions.

Commentary by Dr. Valentin Fuster
2017;():V006T05A011. doi:10.1115/OMAE2017-62596.

The decommissioning of offshore structures around the world will be a persisting problem in the coming decades as many existing structures will exceed their design life, or when the reservoirs are depleted. This paper examines an overview of regulations in countries deemed to be more experienced in decommissioning such as the UK, Norway and the USA. The regulations were identified in terms of three areas: the legal, technical and financial security framework. It is concluded that the majority of the regulations covering the technical section are similar. The major differences are between two overarching philosophies — one that is more prescriptive with stricter requirements and another that is more flexible with a goal-setting regime. Non-technical aspects of decommissioning appear to attract increasing attention from governments, such as decommissioning financial capability, minimisation of costs while meeting regulatory requirements, transfer of liability if other decommissioning options are accepted, and the movement of wastes from offshore to onshore and their subsequent disposal.

Commentary by Dr. Valentin Fuster

Ocean Space Utilization: Deepsea Mining and Ocean Resources

2017;():V006T05A012. doi:10.1115/OMAE2017-61151.

To meet the needs of scientific discoveries in hadal zones, the hadal science and technology center (HAST) of Shanghai Ocean University has made a significant commitment to construct a movable laboratory for hadal trenches in 2013, which includes a mothership, an full ocean depth (FOD) human occupied vehicle (HOV), an FOD Autonomous and Remotely-operated Vehicle (ARV) and several FOD landers. Presently, the HOV is in concept design phase.

Current HOVs in service could only work below 7,000m. To increase the submergence depth from 7,000m to 11,000m for a FOD HOV, the time spending in descent and accent will take a majority part of power endurance and leave little time in scientific studies. Hence, the descent/ascent motion analysis and optimization will play a bigger role in FOD HOV designs contrasting to current HOVs.

In this paper, in order to investigate resistance characteristics and drag coefficients in decent and ascent directions of the FOD HOV, the Reynolds Averaged Navier-Stokes (RANS) equations were solved using computational fluid dynamics. To achieve a faster descent and ascent process, diving and floating with various attacking angles were tried. The numerical analysis for each scenario has been conducted and results were discussed. The method and theory presented in the paper will be applied to the design of a practical deep manned submersible.

Topics: Vehicles , Oceans
Commentary by Dr. Valentin Fuster
2017;():V006T05A013. doi:10.1115/OMAE2017-61238.

Subsea minerals exist in the deep water within Japanese exclusive economic zone. Development of slurry pump passing large particles is required for lifting ore. In design of slurry pump, it is significant to estimate the pressure loss in a riser pipe for large particle slurry transport. Therefore the authors have been studied the slurry flow model for large particle slurry transport. In addition, the authors developed the model for the static pipe including the inclined configurations. Since the lifting pipe will be oscillated due to the connected ship motion and VIV (Vortex Induced Vibration), the authors conducted the scaled model experiment to investigate the effects of pipe oscillation on the pressure loss. The model scale was 1/8. Alumina beads and glass beads were used as solid particles in the experiment. The pipe was vertical, and oscillated in horizontal or vertical direction. The experimental results showed that the horizontal and vertical oscillation had little influence on the static pressure loss in most of the experimental conditions. However the influence was observed for the horizontally oscillating pipe in the low slurry velocity and short oscillation period condition. On the other hand, the significant fluctuation components of pressure loss and flow rate were observed in vertically oscillating pipe. The results also indicated that the density of slurry and amplitude of oscillation had influence on the fluctuation components of pressure loss and flow rate but the particle diameters had little influence on them.

Commentary by Dr. Valentin Fuster
2017;():V006T05A014. doi:10.1115/OMAE2017-61383.

These days, many seafloor massive sulfide (SMS) deposits have been discovered in Japan’s exclusive economic zones. They have many kinds of useful metals, and are expected to be future metal resources. However, SMS mining faces an economic problem for the reason that disposal of unnecessary parts of SMS ores is very expensive in Japan. Adding a function of primary ore separation on seafloor is necessary for economical SMS mining. Some small scale model experiments were conducted by the authors. In this study, CFD analysis is applied for the results of the model hydrocyclone. From the analysis, the fundamental flow condition good for the ore separation in the cyclone is recognized.

Commentary by Dr. Valentin Fuster
2017;():V006T05A015. doi:10.1115/OMAE2017-62272.

The Under-Water TV (UWTV) is used as a reentry support system for the scientific drilling by the drilling vessel “Chikyu”. The “Chikyu” UWTV performs scientific operations cost-effectively where the normal Remotely Operated Vehicles (ROVs) in the market can’t be available. The UWTV in the 2nd generation has been tested in a sea trial and operated in the subsequent scientific drilling project. The shape of the UWTV frame has been modified after the trial and the behavior of the UWTV during its dives has been improved. The tension data in the operations has been measured and the effect of the dynamic behavior is extracted from the data. Then the extracted dynamic effect is used as the indicator to see the UWTV situation under the sea surface and to prevent the UWTV from the operational failure.

Topics: Water
Commentary by Dr. Valentin Fuster
2017;():V006T05A016. doi:10.1115/OMAE2017-62525.

Several hydrothermal vent sites have been discovered along the portion of the Arctic Mid-Ocean Ridge (AMOR) inside the extended Norwegian continental shelf (NCS). Seafloor massive sulfide (SMS) deposits are associated with these hydrothermal vent sites. These deposits contain significant amounts of valuable metals, such as copper, zinc, gold, and silver. Loki’s Castle is one of the most promising sites along the AMOR, with two 20–30 m high and 100 m wide mound-shaped SMS deposits. It is located at a water depth of 2,400 m. A production system concept is proposed for a deep-sea mining operation at Loki’s Castle based on the Nautilus Minerals’ Solwara 1 project. The overall cost structure and design of the Nautilus’ concept is in this study regarded feasible in AMOR in spite of the difference between the operating environment for the two locations. As the only relevant operational experience is De Beers’ shallow-water diamond mining off the coast of South Africa and Namibia, most of the environmental criteria used are taken from offshore drilling. Based on the net operating time, and accounting for scheduled maintenance and waiting-on-weather time, an estimate for annual average production rate and an annual production volume are estimated. Significant downtime is expected in January and July.

Significant uncertainties are associated with early phases of projects. Probabilistic cost, grade and price estimates allow dealing quantitatively with uncertainties by giving input variables as probability distributions. Monte Carlo simulations are in this study run for different sets of variables, and the resulting key performance indicators are given as distributions.

This paper adapts and presents a methodology normally used to assess technological and economic feasibilities of oil and gas projects. The methodology is adapted to the assessment of deep-sea mining projects and is illustrated through the assessment of the case based on Loki’s Castle ore characteristics and technologies planned for the Solwara 1 project with a cost structure adjusted according to AMOR conditions. Costs for processing, refining, waste disposal and logistics after ore arrival at onshore port is not included. The ore uncertainties are huge and the resources are with the present deposit knowledge speculative. Therefore, this study do not attempt to define any reserves.

Commentary by Dr. Valentin Fuster

Ocean Space Utilization: Environmental Assessment for Marine Renewable Energy

2017;():V006T05A017. doi:10.1115/OMAE2017-61622.

Installing devices of marine renewable energy is planned off Kamaishi city, Iwate prefecture, Japan. A device of wave power generation was settled at this site as a test case. It is important to coexist the power generation device and local fishermen. Since Kamaishi is known as a good fishing area, acceptance of fishermen is required to run the wave power generation at the test site. Especially, local fishermen in Kamaishi have a concern about how wave power generation moves along with ocean waves and currents. To acquire an acceptance from local fishermen in terms of setting wave power generation, a model test was conducted to understand the device of wave power generation. It consists of float, spar, middle float, gimbal mechanism and anchor. Middle float, gimbal mechanism and anchor are mooring. The submerged weights of the model almost satisfy the targeted values calculated by the scale ratio and actual submerged weights. The experiment was conducted for 1/125 scale model at a water tank in marine environmental and ecosystem laboratory, the university of Tokyo. We monitored the motion of the model under several conditions of regular waves and currents. The motions of the model were recorded by a video camera and were analyzed. The model was moved with respect to the surface waves and currents. We assessed the motions of the float based on the experiment. The experimental results will be used to explain local fishermen.

Commentary by Dr. Valentin Fuster
2017;():V006T05A018. doi:10.1115/OMAE2017-61627.

Assessment of local ocean environment is significant when devices of marine renewable energy are installed at a demonstration site. A concern about how these devices affect the existence of fish is remained among local fishermen. To confirm variation of fish before and after installing the devices of marine renewable energy, we investigated fish using an underwater camera before installation as a main objective of this paper. First, fish-eye video camera was tested to monitor in a fish cage off Kamaishi city, Iwate prefecture, Japan. We aimed to observe the abundance of fish and to specify the species of fish. The fish-eye video camera is composed of a dome-shaped lens, a container, and a digital video equipped into the container. The recorded video showed outlines of fish, consequently it may be possible to know the abundance of fish. However, specifying the species of fish has a difficulty if we use fish-eye camera since the recorded image is unclear enough to identify correctly. In addition, we examined horizontal transparency of fish-eye camera using a fish-shaped target. Before recording by the video camera, vertical transparency was measured using a white plate. Then we recorded the images by varying the water depth and the distance between the camera and target. When the target was close to the camera, it can be displayed clearly, nevertheless the outline of the target was smeared with increasing the distances between them. Our measurement suggested that the horizontal transparency might be relating to the parameters of water depth and vertical transparency. The investigation was conducted under the one condition, thus we need to obtain further data to understand horizontal transparency qualitatively. Next time, we will conduct another test using additional underwater optical video camera, which is attached on the fish-eye video camera. The combination of these two types of video cameras may enable to observe the abundance of fish as well as to specify the species of fish.

Commentary by Dr. Valentin Fuster
2017;():V006T05A019. doi:10.1115/OMAE2017-62581.

Fukushima nuclear accident of March 11, 2011, soil and water had been contaminated by radioactive cesium. Moreover, radioactive cesium was found in the ocean sludge in Tokyo Bay flowing from rivers. Cesium which is adsorbed to the sludge cannot be easily removed. One of the authors developed decomposition and purification system, a circulation-type system by fine bubbles, that is, by creating aerobic state, aerobic bacteria are activated resulting to decomposition and purification of ocean sludge. Based on the hypothesis that radioactive cesium is adsorbed on the surface of the sludge deposition. It is considered that cesium can be eluted after decomposing the deposited sludge. Once the cesium is eluted in the water, it can fix to a mineral such as zeolite. Eluting and fixing cesium adsorbed on sludge takes so much time. In this case, the concept of removing the left sludge by flocculation method and then followed by coagulating sedimentation method is studied. In this study, our objects are to show the effectivity and efficiency of using flocculation and coagulating sedimentation in removing radioactive cesium. As the results, we pointed out this method is very good.

Commentary by Dr. Valentin Fuster

Ocean Space Utilization: Floating Systems for Renewable Energy

2017;():V006T05A020. doi:10.1115/OMAE2017-61099.

Very large floating structure (VLFS) technology is a novel idea being introduced in ports and harbors, fishing, land reclamation, petroleum product storage facilities and so on. The flexible nature of VLFS makes the response hydroelastic and it is important to have a reduced response of VLFS. The term hydroelasticity refers to the action of hydrodynamic excitation over elastic body limits. The present study tries to examine the combined effect of horizontal loads of wind turbine tower along with the vertical hydrodynamic loads which question the stability of the performance of VLFS. This would lead to better understanding of the hydroelastic response of integrated wind farm-VLFS configuration. To examine the effect of relevant parameters on the VLFS hydrodynamic responses, motion amplitude transfer functions (RAO) for a wide range of wave frequencies are computed.

Pontoon type VLFS are giant platforms resting on the sea surface, which are modeled by very large plates according to the Mindlin thick plate theory. The boundary integral element method (BIEM) is used to solve for the velocity potential using Laplace equation providing suitable boundary conditions. The fluid model is based on linear wave hypothesis. The effect of wind on wind turbines which are located at the edges and corner of the VLFS is investigated in the model. The Kaimal wind spectrum is used to generate time series of wind speed incident on the blades of the turbine and loads are computed using blade element momentum theory as in wind simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence).

The finite element framework is used to develop the model and to find the hydrodynamic loading. Mooring line connections are used to reduce structural instability. In order to reduce the hydroelastic response of VLFS, connection with hinges or semi rigid line connections are observed to be effective. The elastic and dynamic effects of the combined wind-wave loading over the integrated VLFS are being considered. The hydroelastic effects of mooring lines will not be accounted for.

Commentary by Dr. Valentin Fuster
2017;():V006T05A021. doi:10.1115/OMAE2017-61549.

Integrating an array of buoys type converters with a flexible runway can be a viable option for cost-sharing between wave energy capturing devices and ocean space utilization structures, and thus enhance the cost-effectiveness of wave energy utilization. In this study, a configuration of multiple buoys supporting a runway is proposed. Hydrodynamic interactions among the buoys are analyzed using an exact algebraic method based on linear wave theory in the frequency domain. A parametric governing equation of compound wave energy converter referred to as a wave farm is formulated by using Hamilton’s principle which can be discretized by using Galerkin method. The effects of wave condition and the parameters of PTO on the wave energy absorption and dynamic characteristics of a runway are analyzed. This research work is aimed to provide a theoretical guideline for wave energy converters design.

Topics: Wave energy , Buoys
Commentary by Dr. Valentin Fuster
2017;():V006T05A022. doi:10.1115/OMAE2017-61614.

The progress of the global warming is one of our key issue should be overcome in the 21st century. We should balance the energy consumption and reduction of exhausting greenhouse effect gas. The wind energy is expected as one of the key technology for utilizing renewable energy. It is said that as for the efficiency of the electric generation, it is better the wider wind farm with larger wind mill. But, as the land space for the extensive wind farm is quite limited, it will be a candidate how to use the vast ocean space for human activity. So, the construction of an offshore wind farm is one of the solution now. To extend the wind farm widely in the ocean the floating wind turbine system becomes an essential technology. Under such background, there are many researches on the floating wind turbine in waves and in wind. And hydrodynamic response of them in waves is one of the major topics. Many of the researches on the hydrodynamic response, however, deal with the motion of a single floating wind turbine. This report deals with the hydrodynamic response of a wind farm which is consisted of semi-submersible wind turbines. In addition, the investigation of how does the arrangement of the array impact on the hydrodynamic response including the motion of the nacelle is also reported. In the last the example of the change of the expected efficiency of the generator by change of the array arrangement in each sea area around Japan are shown.

Commentary by Dr. Valentin Fuster
2017;():V006T05A023. doi:10.1115/OMAE2017-61656.

A linear electrical generator is a kind of device which can be used to wave energy converter, for directly converting mechanical energy of a floating structure into electrical energy. A wave farm consists of multiple wave energy converters which equipped in a sea area. In the present paper, a numerical model is proposed considering the interference effect in the multiple floating structures, and the controlling force of each linear electrical generator. Especially, the copper losses in the electrical generator is taken into account, when the electrical power is computed. At first, the controlling force coefficients are discussed to find their physical effects on heaving motion. In a case study, the heaving motions and electrical powers of the three floating structures are estimated in the straight arrangement and triangle arrangement. And the average electrical power is analyzed in different distances of the floating structures.

Commentary by Dr. Valentin Fuster
2017;():V006T05A024. doi:10.1115/OMAE2017-61788.

Advanced spar type of the floating wind turbine with a short spar and a cylindrical column floater has been developed and tested recently. However, numerical methods to accurately simulate the interaction between the advanced spar and waves have not been established yet. In this study we simulated the free surface flow around an advanced spar in regular waves using open source computational fluid dynamics (CFD) software OpenFOAM to examine its applicability. We used olaFOAM which equipped with the functions to set the boundary conditions of wave generation at the inlet and wave absorption at the exit. An experiment of the advanced spar model fixed in space in the regular waves with various wave periods was also conducted to obtain an experimental database on the horizontal and vertical forces acting on the structure and pressure distribution on the floater surface. The results of the forces obtained by the numerical simulation, experiment, Morison’s equation were compared to examine the validity of the numerical model. Numerical and experimental results of the horizontal and vertical forces as well as pressure distribution on the floater surface were in good agreement, which confirmed the validity of the present numerical method. Then, we evaluated numerically the effects of the edge of the column by simulating a sharp-edged and a chamfered column floater. The result clarified that a chamfered edge decreased the wake which reduced the forces acting on the floater structure.

Commentary by Dr. Valentin Fuster

Ocean Space Utilization: High Tide and Tsunamis

2017;():V006T05A025. doi:10.1115/OMAE2017-61754.

On the vessels moored at the wharf, the situation such as drifting and wash up on the wharf due to the breaking of the mooring lines is occurred by the tsunami. The authors are clarified for applicability of the proposed floating tsunami protection wharf (FTPW). FTPW is the floating pier for tsunami disaster. The effect of FTPW is most promising as disaster prevention and mitigation measures for the moored vessels. The authors examined large scale FTPW until now. However, when floating body length was longer than a ship breadth, the possibility that disaster prevention performance of FTPW decreased was confirmed. In this study, the examination about the influence that floating body length gives in disaster prevention performance of FTPW is performed using numerical simulation. Therefore, in the range of length of FTPW/breadth of vessel = 1.0 to 8.0, it was confirmed that tsunami protection performance of FTPW was shown enough.

Commentary by Dr. Valentin Fuster
2017;():V006T05A026. doi:10.1115/OMAE2017-62178.

The damage investigations that followed the Great East Japan Earthquake revealed that automobiles, shipping containers, and even ships themselves had been caught up in the resulting tsunami before being hurled into various port facilities, causing immense damage. The damage characteristics of such collisions must be an integral part of disaster mitigation measures aimed at reducing damage due to drifting ships. When considering the impact force of massive vessels on port facilities, it is necessary to take into account the changes in the drift velocity of the vessels due to waves reflected from the facilities and other coastal structures. In previous studies, the moving particle semi-implicit (MPS) method has been adopted to examine cascading tsunami flotsam damage by means of numerical simulations. In the present study, we use the MPS method to examine the drifting behavior and impact force of ships moored to an actual harbor, taking into account waves reflected from coastal area structures. Based on the results, we discuss the applicability of this method to disaster mitigation measures.

Commentary by Dr. Valentin Fuster

Ocean Space Utilization: New Concepts for Ocean Space Utilization

2017;():V006T05A027. doi:10.1115/OMAE2017-61077.

In optimal ship routing, the ship behavior in the ocean is the main concern. However, there is also different type of ship service, namely the short-distance ferry. It is evident that a novel optimal ship routing must be proposed. A ferry service in southern Japan is the focus of this study. This service takes into account the typhoons or atmospheric depressions that influence the ferry ports. The ferry service is sometimes suspended because of the considerable motion of the ships moored in harbors. A wave monitoring system has been operational since 2015; however, the methodology has not been established from the viewpoint of optimal operation. The current situation regarding the ferry service is summarized in detail in this study, and patterns of typhoons and atmospheric depressions are revealed. In particular, it is difficult for ferry users to understand the reason for suspension of the ferry service when typhoons pass several hundred kilometers away with offshore wave heights of less than 2 m. Firstly, the relation between long period waves and the actual operation is clarified. Secondly, moored ship motions are numerically simulated using measured wave data to evaluate mooring criteria. The estimation formula of the mooring criteria is modeled, and the novel concept of optimal routing for the short-distance ferry is proposed.

Topics: Mooring
Commentary by Dr. Valentin Fuster
2017;():V006T05A028. doi:10.1115/OMAE2017-61726.

This study concerns a new concept of floating oil storage facility, to be deployed in coastal waters, in which separate oil storage tanks float in an array, separated by a mooring fender system. In this paper, hydrodynamic properties of a single module are investigated numerically. The effects of different mooring fender parameters including fender stiffness and fender position on the coupled motions are studied. Design criteria and a design approach for the marine fender selection are proposed. Next, time-domain simulations under random waves are performed. Finite water depth effects are taken into consideration. Then a brief parametric study on sloshing phenomenon in fender-supported tanks is conducted. Results show that a carefully designed marine fender will help reduce the roll and pitch motions of the storage tank, and thus function as a stabilizer. This analysis is the basis of a global hydrodynamic response analysis for multiple tanks, including the effects of multibody hydrodynamic interactions between tanks in the future.

Topics: Storage tanks
Commentary by Dr. Valentin Fuster
2017;():V006T05A029. doi:10.1115/OMAE2017-61880.

This paper presents the implementation of a 2D-lidar to a model-scale surface vessel, and the design of a control system that makes the vessel able to perform autonomous exploration of a small-scale marine environment by the use of the lidar and SLAM. This includes a presentation and discussion of experimental results. The completion of this system has involved the development of a suitable control system that merges exploration strategies, path planners, a motion controller, and a strategy for generating controller setpoints. The system was implemented on the Robot Operating System platform, which made it possible to utilize open-source algorithms for state of the art SLAM.

Commentary by Dr. Valentin Fuster
2017;():V006T05A030. doi:10.1115/OMAE2017-61897.

Japan imports coal from Indonesia, the main coal supplier in the Asia-Pacific region. Effective and efficient movement of coal down the Markham River in East Kalimantan, Indonesia, and onto bulk carriers is challenging because the river is shallow and generally cannot accommodate bulk carriers. The primary transportation system comprises small barges that are shuttled back and forth between the inland barge ports along the river and bulk carriers offshore. This system is very time-consuming.

This paper proposes a large-scale floating coal transshipment station (LFTS) for loading, storing, and offloading coal. It will act as a relay base for barges and bulk carriers. Installing an LFTS offshore from East Kalimantan is expected to improve coal transport productivity. The proposed LFTS can store 5 times the capacity of one bulk carrier and can accommodate 2 bulk carriers at the same time during offloading. The LFTS is compartmentalized by bulkheads to segregate coal according to quality. This paper discusses LFTS static stability and its elastic deformation characteristics during coal loading operations.

In this study, linear potential theory and the finite element method (FEM) were used to analyze the LFTS static hydroelastic motion. Due to the compartments, coal loading conditions can vary significantly and affect the local static deflection, so we modeled the overall deformation and rigidity under various operational scenarios. The results were compared to the allowable material stress to identify conditions that will produce material failure. Moreover, we evaluated operation in the shallow Kalimantan River, since the weight of loaded coal deepens the LFTS draft, reducing the clearance between the LFTS and sea bed. We found that this reduced clearance and large added mass impact the natural frequency of the LFTS.

Topics: Elasticity , Coal
Commentary by Dr. Valentin Fuster

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