Jun Umeda, H. Goto, T. Fujiwara, Tomoki Taniguchi, S. Inoue
This paper presents the experimental evaluation results of power production efficiency of model predictive control (MPC) on a wave energy converter (WEC) with a linear generator in regular and irregular waves. A bottom-fixed WEC of point absorber type was subjected to the WEC model in this paper. To compare the power production efficiency, the power production efficiency of the approximate complex-conjugate control with considering the copper loss (ACL) was also evaluated. In regular waves, the MPC performance was comparable to the ACL one in the power-production amount reasonably. In irregular waves which have narrow band spectral distribution, a same trend as the trend in regular waves was obtained. On the other hand, in irregular waves which have broadband spectral distribution, the MPC was more effective than the ACL. Moreover, Experiments in regular and irregular waves were carried out in the MPC under the constraint of the small heave displacement. The constraint of the displacement was approximately satisfied by the MPC. This is useful in practical operation. It is also investigated experimentally how time horizon affects the performance of the MPC. When the time horizon is short, the power production amount of the MPC increases.
{"title":"Experimental Study on Model Predictive Control for a Point Absorber Type Wave Energy Converter With a Linear Generator","authors":"Jun Umeda, H. Goto, T. Fujiwara, Tomoki Taniguchi, S. Inoue","doi":"10.1115/OMAE2018-77724","DOIUrl":"https://doi.org/10.1115/OMAE2018-77724","url":null,"abstract":"This paper presents the experimental evaluation results of power production efficiency of model predictive control (MPC) on a wave energy converter (WEC) with a linear generator in regular and irregular waves. A bottom-fixed WEC of point absorber type was subjected to the WEC model in this paper. To compare the power production efficiency, the power production efficiency of the approximate complex-conjugate control with considering the copper loss (ACL) was also evaluated. In regular waves, the MPC performance was comparable to the ACL one in the power-production amount reasonably. In irregular waves which have narrow band spectral distribution, a same trend as the trend in regular waves was obtained. On the other hand, in irregular waves which have broadband spectral distribution, the MPC was more effective than the ACL. Moreover, Experiments in regular and irregular waves were carried out in the MPC under the constraint of the small heave displacement. The constraint of the displacement was approximately satisfied by the MPC. This is useful in practical operation. It is also investigated experimentally how time horizon affects the performance of the MPC. When the time horizon is short, the power production amount of the MPC increases.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123469467","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 methodology to analyse the influence of power-optimal OWC (oscillating water column) system configurations against the maximum structural response stresses is proposed. Different values of the selected control parameters are considered to represent the power-optimal and non-power-optimal configurations of the system. The wave power extraction and the structural response of the OWC with power-optimal control parameters is compared against those obtained adopting non-power-optimal control parameters. The results reveal that the control parameters have a clear influence on both the wave power extraction and the structural response stresses. This opens a line of research to investigate the trade-off between the wave power extraction and the structural response of the system, hence the potential structural reliability.
{"title":"Influence of the Maximum Wave Power Extraction on the Structural Response of OWC Wave Energy Converters","authors":"M. L. Jalón, F. Brennan","doi":"10.1115/OMAE2018-78536","DOIUrl":"https://doi.org/10.1115/OMAE2018-78536","url":null,"abstract":"A methodology to analyse the influence of power-optimal OWC (oscillating water column) system configurations against the maximum structural response stresses is proposed. Different values of the selected control parameters are considered to represent the power-optimal and non-power-optimal configurations of the system. The wave power extraction and the structural response of the OWC with power-optimal control parameters is compared against those obtained adopting non-power-optimal control parameters. The results reveal that the control parameters have a clear influence on both the wave power extraction and the structural response stresses. This opens a line of research to investigate the trade-off between the wave power extraction and the structural response of the system, hence the potential structural reliability.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123558712","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}
The offshore wind industry continues to grow, but there is still a need for more economical designs. As unavailability conditions can be critical for the fatigue damage in support structures, design standards use conservative values for availability. This leads to most turbines having an unused fatigue capacity at the end of the lifetime. This paper investigates the potential for reducing this unused capacity in order to reduce the capital expenses. The proposed strategy is to design the turbines for a higher availability, closer to the expected value. For individual turbines that experience lower availability than the design value, active load mitigation is imposed to reduce the fatigue damage. The potential of this methods is explored, together with its limitations. It is found that the effect of faults occurring early in the turbines lifetime can be reduced. This is not the case for faults occurring towards the end of the lifetime.
{"title":"Active Load Mitigation to Counter the Fatigue Damage Contributions From Unavailability in Offshore Wind Turbines","authors":"S. H. Sørum, Emil Smilden, J. Amdahl, A. Sørensen","doi":"10.1115/OMAE2018-77962","DOIUrl":"https://doi.org/10.1115/OMAE2018-77962","url":null,"abstract":"The offshore wind industry continues to grow, but there is still a need for more economical designs. As unavailability conditions can be critical for the fatigue damage in support structures, design standards use conservative values for availability. This leads to most turbines having an unused fatigue capacity at the end of the lifetime. This paper investigates the potential for reducing this unused capacity in order to reduce the capital expenses. The proposed strategy is to design the turbines for a higher availability, closer to the expected value. For individual turbines that experience lower availability than the design value, active load mitigation is imposed to reduce the fatigue damage. The potential of this methods is explored, together with its limitations. It is found that the effect of faults occurring early in the turbines lifetime can be reduced. This is not the case for faults occurring towards the end of the lifetime.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122527387","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 this paper a wave energy converter (WEC) based on a segmented floating structure with embedded piezoelectric devices is numerically investigated. To illustrate the idea, a concept design based on assembling existing components is considered. The investigated system is made of three identical box-shaped slender floaters, interconnected by piezoelectric beams, aligned along the wave direction and moored to the seabed. The piezoelectric beams, bent alternatively by the oscillating relative motion of the floaters, constitute the power take-off (PTO) system to generate electricity. The numerical model is divided into two parts: a hydromechanical solver, describing the coupled motion of the floaters and the dynamics of the mooring lines, and a coupled electromechanical solver, which describes the behavior of the piezoelectric benders, including the associated resistive circuit. The coupling between these subsystems is one-way, because the WEC motion deforms the piezoelectric device without any electromechanical feedback on the floating structure. The developed numerical procedure allows for describing the basic features of the WEC response, for estimating the energy that can be generated by the device, and sets the starting point to explore the energy production capability of this kind of device.
{"title":"Energy Harvesting From Waves Using Piezoelectric Floaters","authors":"D. Dessì, G. Leonardi, F. Passacantilli","doi":"10.1115/OMAE2018-78395","DOIUrl":"https://doi.org/10.1115/OMAE2018-78395","url":null,"abstract":"In this paper a wave energy converter (WEC) based on a segmented floating structure with embedded piezoelectric devices is numerically investigated. To illustrate the idea, a concept design based on assembling existing components is considered. The investigated system is made of three identical box-shaped slender floaters, interconnected by piezoelectric beams, aligned along the wave direction and moored to the seabed. The piezoelectric beams, bent alternatively by the oscillating relative motion of the floaters, constitute the power take-off (PTO) system to generate electricity. The numerical model is divided into two parts: a hydromechanical solver, describing the coupled motion of the floaters and the dynamics of the mooring lines, and a coupled electromechanical solver, which describes the behavior of the piezoelectric benders, including the associated resistive circuit. The coupling between these subsystems is one-way, because the WEC motion deforms the piezoelectric device without any electromechanical feedback on the floating structure. The developed numerical procedure allows for describing the basic features of the WEC response, for estimating the energy that can be generated by the device, and sets the starting point to explore the energy production capability of this kind of device.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122147275","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}
Fatigue analysis for floating wind turbines poses a novel challenge to calculation workflows if a probabilistic load environment is to be considered. The increased complexity of the structure itself as well as its interaction with the environment require a coupled and more detailed analysis with respect to resolution of environmental conditions compared to fixed bottom systems. Different approaches to address the computing challenge for floating turbines are possible to support engineering judgement and have been investigated in the past, with conservative binning on the one end of the accuracy scale and computation intensive Monte Carlo simulations on the other end. This study investigates the feasibility of regression based surrogate models based on radial basis functions. The investigation performed here is aligned with work performed in the H2020 project LIFES50+. Consequently, the considered system is the DTU 10MW Reference Wind Turbine installed on the LIFES50+ OO-Star Wind Floater Semi 10MW. The site under investigation is the LIFES50+ Site B (Gulf of Maine) medium severity representative site. Results show a similar convergence of lifetime fatigue load prediction as with Monte Carlo simulations indicating that this technique may be an alternative if a response model of the considered system is of interest. This may be interesting if damage loading is to be calculated at a different site and if a classification of met-ocean conditions is available.
{"title":"A Surrogate Modeling Approach for Fatigue Damage Assessment of Floating Wind Turbines","authors":"K. Müller, P. Cheng","doi":"10.1115/OMAE2018-78219","DOIUrl":"https://doi.org/10.1115/OMAE2018-78219","url":null,"abstract":"Fatigue analysis for floating wind turbines poses a novel challenge to calculation workflows if a probabilistic load environment is to be considered. The increased complexity of the structure itself as well as its interaction with the environment require a coupled and more detailed analysis with respect to resolution of environmental conditions compared to fixed bottom systems.\u0000 Different approaches to address the computing challenge for floating turbines are possible to support engineering judgement and have been investigated in the past, with conservative binning on the one end of the accuracy scale and computation intensive Monte Carlo simulations on the other end. This study investigates the feasibility of regression based surrogate models based on radial basis functions. The investigation performed here is aligned with work performed in the H2020 project LIFES50+. Consequently, the considered system is the DTU 10MW Reference Wind Turbine installed on the LIFES50+ OO-Star Wind Floater Semi 10MW. The site under investigation is the LIFES50+ Site B (Gulf of Maine) medium severity representative site.\u0000 Results show a similar convergence of lifetime fatigue load prediction as with Monte Carlo simulations indicating that this technique may be an alternative if a response model of the considered system is of interest. This may be interesting if damage loading is to be calculated at a different site and if a classification of met-ocean conditions is available.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129948197","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}
The design of floating wind turbines requires both, simulation tools and scaled testing methods, accurately integrating the different phenomena involved in the system dynamics, such as the aerodynamic and hydrodynamic forces, the mooring lines dynamics and the control strategies. In particular, one of the technical challenges when testing a scaled floating wind turbine in a wave tank is the proper integration of the rotor aerodynamic thrust. The scaling of the model based on the Froude number produces equivalent hydrodynamic forces, but out of scale aerodynamic forces at the rotor, because the Reynolds number, that governs the aerodynamic forces, is not kept constant. Several approaches have been taken to solve this conflict, like using a tuned drag disk or redesigning the scaled rotor to provide the correct scaled thrust at low Reynolds numbers. This work proposes a hybrid method for the integration of the aerodynamic thrust during the scaled tests. The work also explores the agreement between the experimental measurements and the simulation results through the calibration and improvement of the numerical models. CENER has developed a hybrid testing method that replaces the rotor by a ducted fan at the model tower top. The fan can introduce a variable force which represents the total wind thrust by the rotor. This load is obtained from an aerodynamic simulation that is performed in synchrony with the test and it is fed in real time with the displacements of the platform provided by the acquisition system. Thus, the simulation considers the displacements of the turbine within the wind field and the relative wind speed on the rotor, including the effect of the aerodynamic damping on the tests. The method has been called “Software-in-the-Loop” (SiL). The method has been applied on a test campaign at the Ecole Centrale de Nantes wave tank of the OC4 semisubmersible 5MW wind turbine, with a scale factor of 1/45. The experimental results have been compared with equivalent numerical simulations of the floating wind turbine using the integrated code FAST. Simple cases as only steady wind and free decays with constant wind showed a good agreement with computations, demonstrating that the SiL method is able to successfully introduce the rotor scaled thrust and the effect of the aerodynamic damping on the global dynamics. Cases with turbulent wind and irregular waves showed better agreement with the simulations when mooring line dynamics and second order effects were included in the numerical models.
浮式风力发电机组的设计既需要仿真工具，也需要规模化的测试方法，准确地整合系统动力学中涉及的不同现象，如气动力和水动力、系泊索动力学和控制策略。特别是，在波浪槽中测试规模浮动风力涡轮机时的技术挑战之一是转子气动推力的适当集成。基于弗劳德数的模型的缩放产生了等效的水动力，但在转子处产生了超出比例的气动力，因为控制气动力的雷诺数没有保持恒定。已经采取了几种方法来解决这一冲突，如使用调谐拖盘或重新设计缩放转子以提供正确的低雷诺数缩放推力。本文提出了一种混合方法，用于在比例试验中集成气动推力。通过对数值模型的校正和改进，探讨了实验测量结果与模拟结果的一致性。CENER开发了一种混合测试方法，在模型塔顶用管道风扇代替转子。风扇可以引入一个可变的力，它代表了转子的总风推力。该载荷来自与测试同步进行的空气动力学模拟，并由采集系统提供的平台位移实时馈送。因此，仿真考虑了涡轮在风场中的位移和转子上的相对风速，并考虑了气动阻尼对试验的影响。这种方法被称为“循环软件”(SiL)。该方法已在Ecole Centrale de Nantes的OC4半潜式5MW风力涡轮机波浪槽的测试活动中应用，比例系数为1/45。利用FAST集成代码将实验结果与浮式风力机等效数值模拟结果进行了比较。仅定常风和定常风下自由衰减的简单情况与计算结果吻合较好，表明该方法能够成功地引入转子尺度推力和气动阻尼对整体动力学的影响。考虑系泊线动力和二阶效应时，湍流和不规则波浪情况与模拟结果吻合较好。
{"title":"Hybrid Scaled Testing of a 5MW Floating Wind Turbine Using the SiL Method Compared With Numerical Models","authors":"F. Vittori, F. Bouchotrouch, F. Lemmer, J. Azcona","doi":"10.1115/OMAE2018-77853","DOIUrl":"https://doi.org/10.1115/OMAE2018-77853","url":null,"abstract":"The design of floating wind turbines requires both, simulation tools and scaled testing methods, accurately integrating the different phenomena involved in the system dynamics, such as the aerodynamic and hydrodynamic forces, the mooring lines dynamics and the control strategies. In particular, one of the technical challenges when testing a scaled floating wind turbine in a wave tank is the proper integration of the rotor aerodynamic thrust. The scaling of the model based on the Froude number produces equivalent hydrodynamic forces, but out of scale aerodynamic forces at the rotor, because the Reynolds number, that governs the aerodynamic forces, is not kept constant. Several approaches have been taken to solve this conflict, like using a tuned drag disk or redesigning the scaled rotor to provide the correct scaled thrust at low Reynolds numbers. This work proposes a hybrid method for the integration of the aerodynamic thrust during the scaled tests. The work also explores the agreement between the experimental measurements and the simulation results through the calibration and improvement of the numerical models. CENER has developed a hybrid testing method that replaces the rotor by a ducted fan at the model tower top. The fan can introduce a variable force which represents the total wind thrust by the rotor. This load is obtained from an aerodynamic simulation that is performed in synchrony with the test and it is fed in real time with the displacements of the platform provided by the acquisition system. Thus, the simulation considers the displacements of the turbine within the wind field and the relative wind speed on the rotor, including the effect of the aerodynamic damping on the tests. The method has been called “Software-in-the-Loop” (SiL). The method has been applied on a test campaign at the Ecole Centrale de Nantes wave tank of the OC4 semisubmersible 5MW wind turbine, with a scale factor of 1/45. The experimental results have been compared with equivalent numerical simulations of the floating wind turbine using the integrated code FAST. Simple cases as only steady wind and free decays with constant wind showed a good agreement with computations, demonstrating that the SiL method is able to successfully introduce the rotor scaled thrust and the effect of the aerodynamic damping on the global dynamics. Cases with turbulent wind and irregular waves showed better agreement with the simulations when mooring line dynamics and second order effects were included in the numerical models.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129250186","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}
Celia Miguel González, Ginés Rodríguez Fuertes, Manuel García Díaz, B. García, F. Castro, J. M. F. Oro
It is well known among the researchers involved in the field of turbines for Oscillating Water Column systems (OWC) that the main problem for Wells turbines is the stall, which appears when the main flow incidence angle exceeds certain value and leads to a sharp drop in the efficiency. It also causes problems during the starting, driving the turbine to not reach the designing rotation speed. Delaying the stall apparition is the key to improve the performance of the Wells turbine. is necessary to delay the flow separation at the trailing edge because it is the reason which leads to the sharp efficiency drop at the stall point. One of the solutions proposed by researchers in this field is using a variable blade profile instead of the traditional ones, built using constant chord and profile from hub to tip. This work tries to dig deeper in this line by analysing a blade with variable chord and shape among the blade span. The work has been developed numerically by using commercial software ANSYS FLUENT®. A CFD code was created in order to obtain the performance curve of the turbine proposed to be compared with those assumed as reference, which were taken from the bibliography and also used to validate the numerical model. The results have shown that an improvement has been achieved. It confirms that using a variable blade profile is a suitable solution to delay the stall apparition.
{"title":"Wells Turbine With Variable Blade Profile for Wave Energy Conversion","authors":"Celia Miguel González, Ginés Rodríguez Fuertes, Manuel García Díaz, B. García, F. Castro, J. M. F. Oro","doi":"10.1115/OMAE2018-78648","DOIUrl":"https://doi.org/10.1115/OMAE2018-78648","url":null,"abstract":"It is well known among the researchers involved in the field of turbines for Oscillating Water Column systems (OWC) that the main problem for Wells turbines is the stall, which appears when the main flow incidence angle exceeds certain value and leads to a sharp drop in the efficiency. It also causes problems during the starting, driving the turbine to not reach the designing rotation speed.\u0000 Delaying the stall apparition is the key to improve the performance of the Wells turbine. is necessary to delay the flow separation at the trailing edge because it is the reason which leads to the sharp efficiency drop at the stall point.\u0000 One of the solutions proposed by researchers in this field is using a variable blade profile instead of the traditional ones, built using constant chord and profile from hub to tip. This work tries to dig deeper in this line by analysing a blade with variable chord and shape among the blade span.\u0000 The work has been developed numerically by using commercial software ANSYS FLUENT®. A CFD code was created in order to obtain the performance curve of the turbine proposed to be compared with those assumed as reference, which were taken from the bibliography and also used to validate the numerical model.\u0000 The results have shown that an improvement has been achieved. It confirms that using a variable blade profile is a suitable solution to delay the stall apparition.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124675146","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}
Rafael d’Amore-Domenech, E. Navarro, Eleuterio Mora, T. Leo
This article illustrates a novel method to produce hydrogen at sea with no carbon footprint, based on alkaline electrolysis, which is the cheapest electrolysis method for in-land hydrogen production, coupled to offshore renewable farms. The novelty of the method presented in this work is the solution to cope with the logistic problem of periodical renewal of the alkaline electrolyte, considered problematic in an offshore context. Such solution consists in the integration of a small chlor-alkali plant to produce new electrolyte in situ. This article describes a proposal to combine alkaline water electrolysis and chlor-alkali processes, first considering both in a separate manner, and then describing and discussing the combined solution, which seeks high efficiency and sustainability.
{"title":"Alkaline Electrolysis at Sea for Green Hydrogen Production: A Solution to Electrolyte Deterioration","authors":"Rafael d’Amore-Domenech, E. Navarro, Eleuterio Mora, T. Leo","doi":"10.1115/OMAE2018-77209","DOIUrl":"https://doi.org/10.1115/OMAE2018-77209","url":null,"abstract":"This article illustrates a novel method to produce hydrogen at sea with no carbon footprint, based on alkaline electrolysis, which is the cheapest electrolysis method for in-land hydrogen production, coupled to offshore renewable farms. The novelty of the method presented in this work is the solution to cope with the logistic problem of periodical renewal of the alkaline electrolyte, considered problematic in an offshore context. Such solution consists in the integration of a small chlor-alkali plant to produce new electrolyte in situ. This article describes a proposal to combine alkaline water electrolysis and chlor-alkali processes, first considering both in a separate manner, and then describing and discussing the combined solution, which seeks high efficiency and sustainability.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124327172","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}
P. Trubat, C. Molins, P. Hufnagel, D. Alarcón, Alexis Campos
Most numerical models for the analysis of offshore wind platforms are based on one of two different approaches, depending on how waves forces are applied to the structure: 1) the potential flow theory, and 2) the Morison equation. Potential flow theory allows to compute the wave forces more accurately when diffraction is relevant. Otherwise, this kind of models assume a fixed position of the floating platform when computing the wave forces. Additionally, second-order effects, as the position and the spin of the structure relative to the incident wave can only be taken into account if second order potential flow is considered. On the other hand, Morison equation can apply the wave forces on a structure based on its spin and position which can be assessed at each time step, but is prone to overestimate the waves forces at the frequencies where diffraction is relevant. In this paper, a modification of the implementation of the Morison equation is presented. This modification allows to reduce the forces in the diffraction frequency range based on the real response from MacCamy and Fuchs’s diffraction theory for cylinders. The implementation can be applied using a frequency-dependent coefficient of added mass, or modifying the amplitudes of the incident waves in the diffraction frequency range in a way that the accelerations derived from the regular wave theory used for the Froude-Krylov wave force computation in Morison equation are equivalent to those computed in the diffraction theory. The implementation is tested in the FloawDyn code, developed at the UPC, and FAST from NREL.
{"title":"Application of Morison Equation in Irregular Wave Trains With High Frequency Waves","authors":"P. Trubat, C. Molins, P. Hufnagel, D. Alarcón, Alexis Campos","doi":"10.1115/OMAE2018-77913","DOIUrl":"https://doi.org/10.1115/OMAE2018-77913","url":null,"abstract":"Most numerical models for the analysis of offshore wind platforms are based on one of two different approaches, depending on how waves forces are applied to the structure: 1) the potential flow theory, and 2) the Morison equation. Potential flow theory allows to compute the wave forces more accurately when diffraction is relevant. Otherwise, this kind of models assume a fixed position of the floating platform when computing the wave forces. Additionally, second-order effects, as the position and the spin of the structure relative to the incident wave can only be taken into account if second order potential flow is considered. On the other hand, Morison equation can apply the wave forces on a structure based on its spin and position which can be assessed at each time step, but is prone to overestimate the waves forces at the frequencies where diffraction is relevant.\u0000 In this paper, a modification of the implementation of the Morison equation is presented. This modification allows to reduce the forces in the diffraction frequency range based on the real response from MacCamy and Fuchs’s diffraction theory for cylinders. The implementation can be applied using a frequency-dependent coefficient of added mass, or modifying the amplitudes of the incident waves in the diffraction frequency range in a way that the accelerations derived from the regular wave theory used for the Froude-Krylov wave force computation in Morison equation are equivalent to those computed in the diffraction theory. The implementation is tested in the FloawDyn code, developed at the UPC, and FAST from NREL.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127778146","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. Windt, J. Davidson, Benazzou Akram, J. Ringwood
To maximise the energy output of wave energy converters (WECs), large structural motions are desired. When simulating WEC performance in Computational Fluid Dynamics (CFD) based numerical wave tanks, these motions must be explicitly accommodated in the computational domain. Using well established mesh morphing (MM) methods, this explicit accommodation results in deformation of control volumes (CVs)/mesh. Thus, large amplitude WEC oscillations may lead to highly distorted CVs and push MM models beyond the limits of numerical stability. While advanced numerical mesh motion methods, such as overset grids, have been developed in commercial CFD codes to overcome these issues, little use of these methods can be found in WEC analysis. However, recently the overset grid method (OSG) has been made available to a wider user community through its release in the open source CFD environment OpenFOAM [1,2]. To evaluate the performance of the OSG, this paper will compare the classical MM method and the OSG against experimental tank test data of the WaveStar device [3].
{"title":"Performance Assessment of the Overset Grid Method for Numerical Wave Tank Experiments in the OpenFOAM Environment","authors":"C. Windt, J. Davidson, Benazzou Akram, J. Ringwood","doi":"10.1115/OMAE2018-77564","DOIUrl":"https://doi.org/10.1115/OMAE2018-77564","url":null,"abstract":"To maximise the energy output of wave energy converters (WECs), large structural motions are desired. When simulating WEC performance in Computational Fluid Dynamics (CFD) based numerical wave tanks, these motions must be explicitly accommodated in the computational domain. Using well established mesh morphing (MM) methods, this explicit accommodation results in deformation of control volumes (CVs)/mesh. Thus, large amplitude WEC oscillations may lead to highly distorted CVs and push MM models beyond the limits of numerical stability. While advanced numerical mesh motion methods, such as overset grids, have been developed in commercial CFD codes to overcome these issues, little use of these methods can be found in WEC analysis. However, recently the overset grid method (OSG) has been made available to a wider user community through its release in the open source CFD environment OpenFOAM [1,2]. To evaluate the performance of the OSG, this paper will compare the classical MM method and the OSG against experimental tank test data of the WaveStar device [3].","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128062070","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：