T. Kelly, I. Zabala, Y. Peña-Sanchez, M. Penalba, J. Ringwood, J. Henriques, J. M. Blanco
Within the wave energy community, hydrodynamic coefficients obtained from boundary element methods (BEMs) are commonly used to predict the behaviour of wave energy converters (WECs) in response to incident waves. A number of commercially-available BEM solvers exist, with a number of open-source alternatives also available. While open-source solvers have an obvious cost advantage compared to their commercial counterparts, the results from such solvers are often susceptible to so-called ‘irregular frequencies’, which arise from ill-conditioning in boundary integral problems, and result in large under- or over-estimation of hydrodynamic parameters at certain excitation frequencies. Furthermore, while commercial solvers may employ techniques to suppress the effects of irregular frequencies, such solvers may, under certain circumstances, exhibit other problems in the hydrodynamic results produced. For example, the results obtained for the added mass at high frequencies, and the infinite frequency added mass for a water column, may be incorrect. The current work first focusses on an approach to remove the effects of irregular frequencies from the results obtained for the radiation damping of a particular WEC geometry. The use of radiation damping results to obtain values for the added mass, through the use of the Ogilvie relations, is then considered.The technique described herein has been implemented in BEMRosetta, an open-source tool which allows a user to view the results from various BEM solvers, as well as converting input files between solvers. The results presented in this paper have been obtained using the BEMRosetta implementation.
{"title":"A post-processing technique for removing ‘irregular frequencies’ and other issues in the results from BEM solvers","authors":"T. Kelly, I. Zabala, Y. Peña-Sanchez, M. Penalba, J. Ringwood, J. Henriques, J. M. Blanco","doi":"10.36688/imej.5.123-131","DOIUrl":"https://doi.org/10.36688/imej.5.123-131","url":null,"abstract":"Within the wave energy community, hydrodynamic coefficients obtained from boundary element methods (BEMs) are commonly used to predict the behaviour of wave energy converters (WECs) in response to incident waves. A number of commercially-available BEM solvers exist, with a number of open-source alternatives also available. While open-source solvers have an obvious cost advantage compared to their commercial counterparts, the results from such solvers are often susceptible to so-called ‘irregular frequencies’, which arise from ill-conditioning in boundary integral problems, and result in large under- or over-estimation of hydrodynamic parameters at certain excitation frequencies. Furthermore, while commercial solvers may employ techniques to suppress the effects of irregular frequencies, such solvers may, under certain circumstances, exhibit other problems in the hydrodynamic results produced. For example, the results obtained for the added mass at high frequencies, and the infinite frequency added mass for a water column, may be incorrect. The current work first focusses on an approach to remove the effects of irregular frequencies from the results obtained for the radiation damping of a particular WEC geometry. The use of radiation damping results to obtain values for the added mass, through the use of the Ogilvie relations, is then considered.The technique described herein has been implemented in BEMRosetta, an open-source tool which allows a user to view the results from various BEM solvers, as well as converting input files between solvers. The results presented in this paper have been obtained using the BEMRosetta implementation.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48183082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Robertson, Gabrielle Dunkle, T. Mundon, L. Kilcher
As the wave energy sector grows and looks to the Blue Economy for commercialization opportunities, there is a distinct and pressing need to clearly understand and quantify the coupled impacts of wave energy converter (WEC) size and wave resource characteristics on the annual energy production, spatial variability and temporal variability. Utilizing generic frequency domain representations of the Oscilla Power Triton WEC and spectral wave conditions at PacWave (Oregon), Los Angeles (California) and WETS (Hawaii), a series of interesting results emerge. Firstly, the ‘optimal’ WEC size, from an energy standpoint, is fundamentally dependent on the frequency distribution of the incoming wave variance density spectrum. Secondly, and from a seasonality perspective, the seasonal WEC energy generation doesn’t necessarily follow the seasonal distribution of gross wave power. Finally, from an hourly power variability perspective, a reduction in WEC size generally decreases variability. However, for each of the locations investigated, there appears to be a WEC size threshold; a threshold where further reducing WEC size results in increased power variability.
随着波浪能行业的发展和蓝色经济的商业化机会，迫切需要清楚地了解和量化波浪能转换器（WEC）规模和波浪资源特征对年度能源生产、空间变异性和时间变异性的耦合影响。利用Oscilla Power Triton WEC的通用频域表示以及PacWave（俄勒冈州）、洛杉矶（加利福尼亚州）和WETS（夏威夷州）的谱波条件，出现了一系列有趣的结果。首先，从能量的角度来看，“最佳”WEC大小从根本上取决于入射波方差密度谱的频率分布。其次，从季节性的角度来看，季节性WEC发电不一定遵循总波浪功率的季节性分布。最后，从每小时功率可变性的角度来看，WEC大小的减小通常会降低可变性。然而，对于所调查的每个地点，似乎都有一个WEC大小阈值；阈值，其中进一步减小WEC大小导致增加的功率可变性。
{"title":"Wave resource spatial and temporal variability dependence on WEC size","authors":"B. Robertson, Gabrielle Dunkle, T. Mundon, L. Kilcher","doi":"10.36688/imej.5.113-121","DOIUrl":"https://doi.org/10.36688/imej.5.113-121","url":null,"abstract":"As the wave energy sector grows and looks to the Blue Economy for commercialization opportunities, there is a distinct and pressing need to clearly understand and quantify the coupled impacts of wave energy converter (WEC) size and wave resource characteristics on the annual energy production, spatial variability and temporal variability. Utilizing generic frequency domain representations of the Oscilla Power Triton WEC and spectral wave conditions at PacWave (Oregon), Los Angeles (California) and WETS (Hawaii), a series of interesting results emerge. Firstly, the ‘optimal’ WEC size, from an energy standpoint, is fundamentally dependent on the frequency distribution of the incoming wave variance density spectrum. Secondly, and from a seasonality perspective, the seasonal WEC energy generation doesn’t necessarily follow the seasonal distribution of gross wave power. Finally, from an hourly power variability perspective, a reduction in WEC size generally decreases variability. However, for each of the locations investigated, there appears to be a WEC size threshold; a threshold where further reducing WEC size results in increased power variability.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42497978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Site development for tidal turbines relies upon a good understanding of the onset flow conditions, with disk averaged velocity typically used as a reference to define turbine power and mean loading. This work investigates the variation of onset flow conditions which occur for the same disk averaged velocity. Analysis builds upon data previously acquired during the measurement campaign conducted for the ReDAPT project using bed mounted ADCPs cite{Sellar2018}. These measurements define the turbulence characteristics and vertical shear profiles over the rotor plane which are incorporated into an efficient blade element method for prediction of unsteady blade loads. This method allows efficient calculation of blade loading for multiple onset shear and turbulence profiles, each with the same disk average velocity, to determine the cyclic loading which contributes towards fatigue. Predictions of fatigue loads from measured profiles are compared with predictions from profiles predicted for the same location with a MIKE3 model cite{Gunn2014}. Within the water depth two vertical positions are analysed, with vertical shear profiles from measurements and a multi-parameter model used to define the onset. For a near-bed location, use of the averaged predicted velocity profiles neglecting variation of turbulence intensity with flow-speed provides fatigue loads to within 1% of predictions obtained using all measured profiles of velocity and corresponding turbulence intensity. For the near-surface location, the same approach under predicts fatigue loads by 16-19%. This is partly due to the occurrence of a wider range of turbulence intensities. Since this is nearly constant with flow-speed a scaling factor is applied to load cycles from predicted profiles to estimate the aggregated fatigue load obtained using all measured conditions, providing confidence that accumulated fatigue loads can be predicted efficiently from velocity profiles obtained from shallow water models.
{"title":"Impact of spatially varying flow conditions on the prediction of fatigue loads of a tidal turbine","authors":"H. Mullings, T. Stallard","doi":"10.36688/imej.5.103-111","DOIUrl":"https://doi.org/10.36688/imej.5.103-111","url":null,"abstract":"Site development for tidal turbines relies upon a good understanding of the onset flow conditions, with disk averaged velocity typically used as a reference to define turbine power and mean loading. This work investigates the variation of onset flow conditions which occur for the same disk averaged velocity. Analysis builds upon data previously acquired during the measurement campaign conducted for the ReDAPT project using bed mounted ADCPs cite{Sellar2018}. These measurements define the turbulence characteristics and vertical shear profiles over the rotor plane which are incorporated into an efficient blade element method for prediction of unsteady blade loads. This method allows efficient calculation of blade loading for multiple onset shear and turbulence profiles, each with the same disk average velocity, to determine the cyclic loading which contributes towards fatigue. Predictions of fatigue loads from measured profiles are compared with predictions from profiles predicted for the same location with a MIKE3 model cite{Gunn2014}. Within the water depth two vertical positions are analysed, with vertical shear profiles from measurements and a multi-parameter model used to define the onset. For a near-bed location, use of the averaged predicted velocity profiles neglecting variation of turbulence intensity with flow-speed provides fatigue loads to within 1% of predictions obtained using all measured profiles of velocity and corresponding turbulence intensity. For the near-surface location, the same approach under predicts fatigue loads by 16-19%. This is partly due to the occurrence of a wider range of turbulence intensities. Since this is nearly constant with flow-speed a scaling factor is applied to load cycles from predicted profiles to estimate the aggregated fatigue load obtained using all measured conditions, providing confidence that accumulated fatigue loads can be predicted efficiently from velocity profiles obtained from shallow water models.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47799003","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Eskilsson, Johannes Palm, P. Johannesson, G. Paredes
There are many uncertainties associated with the estimation of extreme loads acting on a wave energy converter (WEC). In this study we perform a sensitivity analysis of extreme loads acting on the Uppsala University (UU) WEC concept. The UU WEC consists of a bottom-mounted linear generator that is connected to a surface buoy with a taut mooring line. The maximum stroke length of the linear generator is enforced by end-stop springs. Initially, a Variation Mode and Effect Analysis (VMEA) was carried out in order to identify the largest input uncertainties. The system was then modelled in the time-domain solver WEC-SIM coupled to the dynamic mooring solver Moody. A sensitivity analysis was made by generating a surrogate model based on polynomial chaos expansions, which rapidly evaluates the maximum loads on the mooring line and the end-stops. The sensitivities are ranked using the Sobol index method. We investigated two sea states using equivalent regular waves (ERW) and irregular wave (IRW) trains. We found that the ERW approach significantly underestimate the maximum loads. Interestingly, the ERW predicted wave height and period as the most important parameters for the maximum mooring tension, whereas the tension in IRW was most sensitive to the drag coefficient of the surface buoy. The end-stop loads were most sensitive to the PTO damping coefficient.
{"title":"Sensitivity analysis of extreme loads acting on a point-absorbing wave energy converter","authors":"C. Eskilsson, Johannes Palm, P. Johannesson, G. Paredes","doi":"10.36688/imej.5.91-101","DOIUrl":"https://doi.org/10.36688/imej.5.91-101","url":null,"abstract":"There are many uncertainties associated with the estimation of extreme loads acting on a wave energy converter (WEC). In this study we perform a sensitivity analysis of extreme loads acting on the Uppsala University (UU) WEC concept. The UU WEC consists of a bottom-mounted linear generator that is connected to a surface buoy with a taut mooring line. The maximum stroke length of the linear generator is enforced by end-stop springs. Initially, a Variation Mode and Effect Analysis (VMEA) was carried out in order to identify the largest input uncertainties. The system was then modelled in the time-domain solver WEC-SIM coupled to the dynamic mooring solver Moody. A sensitivity analysis was made by generating a surrogate model based on polynomial chaos expansions, which rapidly evaluates the maximum loads on the mooring line and the end-stops. The sensitivities are ranked using the Sobol index method. We investigated two sea states using equivalent regular waves (ERW) and irregular wave (IRW) trains. We found that the ERW approach significantly underestimate the maximum loads. Interestingly, the ERW predicted wave height and period as the most important parameters for the maximum mooring tension, whereas the tension in IRW was most sensitive to the drag coefficient of the surface buoy. The end-stop loads were most sensitive to the PTO damping coefficient.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42011403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pete Davies, N. Dumergue, M. Arhant, E. Nicolas, S. Paboeuf, P. Mayorga
Most tidal turbine blades are currently made from glass or carbon fibre reinforced epoxy composites. These represent a significant part of the turbine cost, but few data are available either to validate current safety factors or to propose alternative more environmentally-friendly materials. This study, performed within the EU H2020 RealTide project, aimed to provide these data. First, a detailed investigation of the static and fatigue behavior was performed at the coupon scale, including not only those materials currently used, but also alternative recyclable thermoplastic matrix composites and natural fibre reinforced materials. Tests were performed before and after seawater saturation, in order to quantify the change in design properties with water uptake. Then a first full scale 5 meter long composite blade was designed and tested to failure. A specific test frame was built, allowing loads up to 75 tons to be applied and simulating the applied moments corresponding to service loads. Static and cyclic loads were applied and extensive instrumentation was used to detect changes in behavior, inluding optical fibres implanted during manufacture, acoustic emission recording, and specific instrumentation developed within the project. The results have enabled numerical simulations to be verified, and this has provided confidence in the modelling tools. These were then employed in order to propose an improved design of a lower cost blade.
{"title":"Material and structural testing to improve composite tidal turbine blade reliability","authors":"Pete Davies, N. Dumergue, M. Arhant, E. Nicolas, S. Paboeuf, P. Mayorga","doi":"10.36688/imej.5.57-65","DOIUrl":"https://doi.org/10.36688/imej.5.57-65","url":null,"abstract":"Most tidal turbine blades are currently made from glass or carbon fibre reinforced epoxy composites. These represent a significant part of the turbine cost, but few data are available either to validate current safety factors or to propose alternative more environmentally-friendly materials. This study, performed within the EU H2020 RealTide project, aimed to provide these data. First, a detailed investigation of the static and fatigue behavior was performed at the coupon scale, including not only those materials currently used, but also alternative recyclable thermoplastic matrix composites and natural fibre reinforced materials. Tests were performed before and after seawater saturation, in order to quantify the change in design properties with water uptake. Then a first full scale 5 meter long composite blade was designed and tested to failure. A specific test frame was built, allowing loads up to 75 tons to be applied and simulating the applied moments corresponding to service loads. Static and cyclic loads were applied and extensive instrumentation was used to detect changes in behavior, inluding optical fibres implanted during manufacture, acoustic emission recording, and specific instrumentation developed within the project. \u0000The results have enabled numerical simulations to be verified, and this has provided confidence in the modelling tools. These were then employed in order to propose an improved design of a lower cost blade.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47716872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zohreh Sarichloo, Pedram Ghorbanpour, F. Salvatore
A computational procedure for the hydrodynamicanalysis and design of horizontal-axis tidal turbinesis presented and numerical applications are discussed. Themethodology combines an original design algorithm and aturbine hydrodynamics model valid for arbitrary 3D flows.Different from standard design methods based on bladeelement models, 3D-flow corrections are not necessary.Blade geometry parameters are determined with the objectiveto maximize power at given design Tip Speed Ratio(TSR), whereas a constraint is introduced in order to limitturbine thrust at TSR higher than the design condition.Numerical applications include the design of a laboratoryscaleturbine and a full-scale turbine for the exploitationof tidal streams in the Messina strait. Alternative designsolutions obtained by varying the design TSR are comparedin terms of energy output as well as mechanical loadstransferred to the powertrain.
{"title":"Horizontal-axis tidal turbine design based on 3D hydrodynamics","authors":"Zohreh Sarichloo, Pedram Ghorbanpour, F. Salvatore","doi":"10.36688/imej.5.77-90","DOIUrl":"https://doi.org/10.36688/imej.5.77-90","url":null,"abstract":"A computational procedure for the hydrodynamicanalysis and design of horizontal-axis tidal turbinesis presented and numerical applications are discussed. Themethodology combines an original design algorithm and aturbine hydrodynamics model valid for arbitrary 3D flows.Different from standard design methods based on bladeelement models, 3D-flow corrections are not necessary.Blade geometry parameters are determined with the objectiveto maximize power at given design Tip Speed Ratio(TSR), whereas a constraint is introduced in order to limitturbine thrust at TSR higher than the design condition.Numerical applications include the design of a laboratoryscaleturbine and a full-scale turbine for the exploitationof tidal streams in the Messina strait. Alternative designsolutions obtained by varying the design TSR are comparedin terms of energy output as well as mechanical loadstransferred to the powertrain.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46363809","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the preliminary design stage of a waveenergy converter (WEC), researchers need fast and reliablesimulation tools. High-fidelity numerical models are usu-ally employed to study the wave-structure interaction, butthe computational cost is demanding. As an alternative,midfidelity models can provide simulations in the order ofreal time. In this study, we operate Uppsala University’sWEC in a relatively mild sea state and model it usingWEC-Sim. The model is verified based on OpenFOAMsimulations. To analyze the ability of the midfidelitymodel to capture WEC dynamics, we investigate the systemseparately with 1, 2, and 3 degrees of freedom. We examinethe contribution of viscous phenomena, and study bothlinear and weakly nonlinear solutions provided by WEC-Sim. Our results indicate that the viscous effects can beneglected in heave and surge motion, but not for pitch.We also find that the weakly nonlinear WEC-Sim solutionsuccessfully agrees with the computational fluid dynam-ics, whereas the linear solution could suggest misleadingresults.
{"title":"Midfidelity model verification for a point-absorbing wave energy converter with linear power take-off","authors":"E. Katsidoniotaki, Yi-Hsiang Yu, M. Göteman","doi":"10.36688/imej.5.67-75","DOIUrl":"https://doi.org/10.36688/imej.5.67-75","url":null,"abstract":"In the preliminary design stage of a waveenergy converter (WEC), researchers need fast and reliablesimulation tools. High-fidelity numerical models are usu-ally employed to study the wave-structure interaction, butthe computational cost is demanding. As an alternative,midfidelity models can provide simulations in the order ofreal time. In this study, we operate Uppsala University’sWEC in a relatively mild sea state and model it usingWEC-Sim. The model is verified based on OpenFOAMsimulations. To analyze the ability of the midfidelitymodel to capture WEC dynamics, we investigate the systemseparately with 1, 2, and 3 degrees of freedom. We examinethe contribution of viscous phenomena, and study bothlinear and weakly nonlinear solutions provided by WEC-Sim. Our results indicate that the viscous effects can beneglected in heave and surge motion, but not for pitch.We also find that the weakly nonlinear WEC-Sim solutionsuccessfully agrees with the computational fluid dynam-ics, whereas the linear solution could suggest misleadingresults.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45870959","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A simple, self-tuning multi-objective controller is demonstrated in simulation for a 3-DOF (surge, heave, pitch) point absorber. In previous work, the proposed control architecture has been shown to be effective in experiments for a variety of device archetypes for the single objective of the maximization of electrical power capture: here this architecture is extended to reduce device loading as well. In particular, PTO actuation forces and the minimization of fatigue damage (determined from the sum of wave-exerted and PTO forces) are considered as additional objectives for the self-tuning controller. Because the power surface is consistently fairly flat in the vicinity of control parameters that maximize power capture in contrasting sea-states (i.e., WECs are often broad banded), it is found to be generally possible to mitigate either fatigue damage or PTO load. However, PTO load is found to contradict with fatigue damage in some sea-states, limiting the efficacy of control objectives that attempt to mitigate both simultaneously. Additionally, coupling between the surge and pitch DOFs also limits the extent to which fatigue damage can be mitigated for both DOFs in some sea-states. Because control objectives can be considered a function of the sea-state (e.g., load mitigation may not be a concern until the sea is sufficiently large) a simple transition strategy is proposed and demonstrated. This transition strategy is found to be effective with some caveats: firstly, it cannot circumvent the aforementioned objective contradictions. Secondly, the thresholds at which objective transitions occur are somewhat exceeded: in this respect they cannot be considered as constraints and must be selected more conservatively. Finally, selection of well-performing transition parameters can be a function of sea-state. While a simple selection procedure is proposed, it is non-optimal, and a more robust selection procedure is suggested for future work.
{"title":"Self-tuning, load-mitigating feedback control of a 3-DOF point absorber","authors":"D. Forbush, G. Bacelli, R. Coe","doi":"10.36688/imej.5.23-35","DOIUrl":"https://doi.org/10.36688/imej.5.23-35","url":null,"abstract":"A simple, self-tuning multi-objective controller is demonstrated in simulation for a 3-DOF (surge, heave, pitch) point absorber. In previous work, the proposed control architecture has been shown to be effective in experiments for a variety of device archetypes for the single objective of the maximization of electrical power capture: here this architecture is extended to reduce device loading as well. In particular, PTO actuation forces and the minimization of fatigue damage (determined from the sum of wave-exerted and PTO forces) are considered as additional objectives for the self-tuning controller. Because the power surface is consistently fairly flat in the vicinity of control parameters that maximize power capture in contrasting sea-states (i.e., WECs are often broad banded), it is found to be generally possible to mitigate either fatigue damage or PTO load. However, PTO load is found to contradict with fatigue damage in some sea-states, limiting the efficacy of control objectives that attempt to mitigate both simultaneously. Additionally, coupling between the surge and pitch DOFs also limits the extent to which fatigue damage can be mitigated for both DOFs in some sea-states. Because control objectives can be considered a function of the sea-state (e.g., load mitigation may not be a concern until the sea is sufficiently large) a simple transition strategy is proposed and demonstrated. This transition strategy is found to be effective with some caveats: firstly, it cannot circumvent the aforementioned objective contradictions. Secondly, the thresholds at which objective transitions occur are somewhat exceeded: in this respect they cannot be considered as constraints and must be selected more conservatively. Finally, selection of well-performing transition parameters can be a function of sea-state. While a simple selection procedure is proposed, it is non-optimal, and a more robust selection procedure is suggested for future work.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46632640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ocean waves provide a vast, uninterrupted resource of renewable energy collocated around large coastal population centers. Clean energy from ocean waves can contribute to the local electrical grid without the need for long-term electrical storage, yet due to the current high cost of energy extraction from ocean waves, there is no commercial ocean wave farm in operation. One of the wave energy converter (WEC) device classes that show the potential to enable economic energy generation from ocean waves is the class of wave terminators. This work investigates the Cycloidal Wave Energy Converter (CycWEC), which is a one-sided, lift-based wave terminator operating with coupled hydrofoils. The energy that the CycWEC extracted from ocean waves was estimated using a control volume analysis model of the 3D wave field in the presence of the CycWEC. The CycWEC was operated under feedback control to extract the maximum amount of energy possible from the incoming waves, and the interaction with different incoming regular, irregular, and short crested waves was examined.
{"title":"Efficiency analysis of the cycloidal wave energy convertor under real-time dynamic control using a 3D radiation model","authors":"A. Mohtat, C. Fagley, Kedar Chitale, S. Siegel","doi":"10.36688/imej.5.45-56","DOIUrl":"https://doi.org/10.36688/imej.5.45-56","url":null,"abstract":"Ocean waves provide a vast, uninterrupted resource of renewable energy collocated around large coastal population centers. Clean energy from ocean waves can contribute to the local electrical grid without the need for long-term electrical storage, yet due to the current high cost of energy extraction from ocean waves, there is no commercial ocean wave farm in operation. One of the wave energy converter (WEC) device classes that show the potential to enable economic energy generation from ocean waves is the class of wave terminators. This work investigates the Cycloidal Wave Energy Converter (CycWEC), which is a one-sided, lift-based wave terminator operating with coupled hydrofoils. The energy that the CycWEC extracted from ocean waves was estimated using a control volume analysis model of the 3D wave field in the presence of the CycWEC. The CycWEC was operated under feedback control to extract the maximum amount of energy possible from the incoming waves, and the interaction with different incoming regular, irregular, and short crested waves was examined.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43563600","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To arrive at a sustainable future we need offshore renewables to succeed, and to do so we need to work together. There have been ecological showstoppers in the past and there will be again in the future unless we can co-design devices, array layouts and site locations of multiple very large-scale developments such that cumulative ecological effects can be assessed and conflicts with ecological laws, local communities and fishing industries be minimized. In order to effectively spatially manage our marine habitats, weigh-up ecological trade-offs and avoid/adapt to the worst effects of climate change, we need all those involved to understand, at some degree of detail, how our marine ecosystems function such that impact mitigation efforts can start at the design stage of devices and developments. This paper outlines a straightforward way to convey the most important environmental issues that are concerning renewables developments, as well as in the context of climate change, and at the scales of individuals and ecosystems. It covers a range of suggestions for the design of data collection, analysis and modelling frameworks to deal with these concerns and finishes with suggestions for potential avenues for future collaboration between ecological and engineering sciences.
{"title":"Ecologically-sustainable futures for large-scale renewables and how to get there","authors":"B. Scott","doi":"10.36688/imej.5.37-43","DOIUrl":"https://doi.org/10.36688/imej.5.37-43","url":null,"abstract":"To arrive at a sustainable future we need offshore renewables to succeed, and to do so we need to work together. There have been ecological showstoppers in the past and there will be again in the future unless we can co-design devices, array layouts and site locations of multiple very large-scale developments such that cumulative ecological effects can be assessed and conflicts with ecological laws, local communities and fishing industries be minimized. In order to effectively spatially manage our marine habitats, weigh-up ecological trade-offs and avoid/adapt to the worst effects of climate change, we need all those involved to understand, at some degree of detail, how our marine ecosystems function such that impact mitigation efforts can start at the design stage of devices and developments. This paper outlines a straightforward way to convey the most important environmental issues that are concerning renewables developments, as well as in the context of climate change, and at the scales of individuals and ecosystems. It covers a range of suggestions for the design of data collection, analysis and modelling frameworks to deal with these concerns and finishes with suggestions for potential avenues for future collaboration between ecological and engineering sciences. \u0000 ","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42100004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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