The reliability of offshore wind turbines is a key factor when estimating maintanence costs, downtime due to component failure and overall efficiency during operational life. Offshore wind turbines have limited accessibility and operate in harsh environments and, as a result, it is difficult to perform frequent checks on electrical and mechanical component. Drivetrain test rigs (DTR) are crucial to the task of: validating the design of new components to avoid early life failure, observe the behaviour of components under load over long periods of time in a controlled environment and produce a maintanence plan that minimize costs and frequency of intervention. In this paper, after a brief introduction on the state of the art in DTR technology, is described a methodology that can be used to create an effective conceptual design for a drivetrain test rig, focusing also on the possible downscaling. The paper starts by analyzing the benefits of the drivetrain use in the wind power industry, bringing examples of real test rigs used in industrial and academical world. Once the topic is mastered it is possible to proceed with a description of the various phases needed to obtain the conceptual design, from the definition of layout to the preliminary 3D modeling. The test rig that is here designed, while inspired from full scale dynamometers used in the industry, is thought as a laboratory tool for academical use that can be used by students to investigate fault detection methods and health monitoring systems of wind turbines. It is also included a section dedicated to the possible techniques for downscaling the test rig, based on simple considerations of the drivetrain mechanical behaviour. Downscaling becomes a key factor when facing the need to test turbine components of ever increasing dimensions in laboratories with limited space and budget. The definition of a procedure to create a scaled version will allow laboratories to build test rigs of smaller dimension but with a damage model for the various components still closely linked to the one in real scale. Downscaling is also a necessity when working with limited power sources, not able to recreate the conditions that the real scale turbine encounters. The ultimate goal is to define a solid base to allow further development in the detailed design phase.
{"title":"On Design and Analysis of a Drivetrain Test Rig for Wind Turbine Health Monitoring","authors":"Lorenzo Balestra, A. Nejad, G. Naldi","doi":"10.1115/omae2019-96721","DOIUrl":"https://doi.org/10.1115/omae2019-96721","url":null,"abstract":"\u0000 The reliability of offshore wind turbines is a key factor when estimating maintanence costs, downtime due to component failure and overall efficiency during operational life. Offshore wind turbines have limited accessibility and operate in harsh environments and, as a result, it is difficult to perform frequent checks on electrical and mechanical component. Drivetrain test rigs (DTR) are crucial to the task of: validating the design of new components to avoid early life failure, observe the behaviour of components under load over long periods of time in a controlled environment and produce a maintanence plan that minimize costs and frequency of intervention.\u0000 In this paper, after a brief introduction on the state of the art in DTR technology, is described a methodology that can be used to create an effective conceptual design for a drivetrain test rig, focusing also on the possible downscaling.\u0000 The paper starts by analyzing the benefits of the drivetrain use in the wind power industry, bringing examples of real test rigs used in industrial and academical world. Once the topic is mastered it is possible to proceed with a description of the various phases needed to obtain the conceptual design, from the definition of layout to the preliminary 3D modeling.\u0000 The test rig that is here designed, while inspired from full scale dynamometers used in the industry, is thought as a laboratory tool for academical use that can be used by students to investigate fault detection methods and health monitoring systems of wind turbines. It is also included a section dedicated to the possible techniques for downscaling the test rig, based on simple considerations of the drivetrain mechanical behaviour. Downscaling becomes a key factor when facing the need to test turbine components of ever increasing dimensions in laboratories with limited space and budget. The definition of a procedure to create a scaled version will allow laboratories to build test rigs of smaller dimension but with a damage model for the various components still closely linked to the one in real scale. Downscaling is also a necessity when working with limited power sources, not able to recreate the conditions that the real scale turbine encounters.\u0000 The ultimate goal is to define a solid base to allow further development in the detailed design phase.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114288086","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 influence of unsteady tidal flow on the flow-induced vibration of a vertical axis tidal turbine blade is investigated numerically in this paper. A 2D CFD model is developed to simulate the blade flow-induced vibration in OpenFoam. The vibration is caused by dynamic loading from the unsteady tide. It is recognized that the unsteady tidal current mainly comes from the changes in tidal velocity magnitude and angle of attack experienced by a tidal turbine blade as it rotates. This paper studies numerically how velocity magnitude and initial angle of attack influence tidal turbine blade vibrations and the effects of the velocity and angle of attack are evaluated separately where the unsteadiness parameters are varied around a set of environmental condition. The vibration is examined through time histories of blade displacement, pressure distribution on the blade surface and the tidal current regime. The blade is assumed to have pitch and heave responses thus the vibration is in the form of transverse and torsional vibrations. The results show that increasing tidal velocity magnitude strengthens the torsional vibration. The increase of angle of attack is likely to generate chaotic motions and enhance both transverse and torsional vibrations.
{"title":"The Influence of Tidal Unsteadiness on a Tidal Turbine Blade Flow-Induced Vibration","authors":"N. Arini, S. Turnock, M. Tan","doi":"10.1115/omae2019-96007","DOIUrl":"https://doi.org/10.1115/omae2019-96007","url":null,"abstract":"\u0000 The influence of unsteady tidal flow on the flow-induced vibration of a vertical axis tidal turbine blade is investigated numerically in this paper. A 2D CFD model is developed to simulate the blade flow-induced vibration in OpenFoam. The vibration is caused by dynamic loading from the unsteady tide. It is recognized that the unsteady tidal current mainly comes from the changes in tidal velocity magnitude and angle of attack experienced by a tidal turbine blade as it rotates. This paper studies numerically how velocity magnitude and initial angle of attack influence tidal turbine blade vibrations and the effects of the velocity and angle of attack are evaluated separately where the unsteadiness parameters are varied around a set of environmental condition. The vibration is examined through time histories of blade displacement, pressure distribution on the blade surface and the tidal current regime. The blade is assumed to have pitch and heave responses thus the vibration is in the form of transverse and torsional vibrations. The results show that increasing tidal velocity magnitude strengthens the torsional vibration. The increase of angle of attack is likely to generate chaotic motions and enhance both transverse and torsional vibrations.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114396612","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}
H. E. Sheshtawy, O. E. Moctar, T. Schellin, S. Natarajan
A tidal stream turbine was designed using one of the optimised hydrofoils, whose lift-to-drag ratio at an angle of attack of 5.2 degrees was 4.5% higher than that of the reference hydrofoil. The incompressible Reynolds-averaged Navier Stokes equations in steady state were solved using k-ω (SST) turbulence model for the reference and optimised tidal stream turbines. The discretisation errors and the effect of different y+ values on the solution were analysed. Thrust and power coefficients of the modelled reference turbine were validated against experimental measurements. Output power and thrust of the reference and the optimised tidal turbines were compared. For a tip speed ratio of 3.0, the output power of the optimised tidal turbine was 8.27% higher than that of the reference turbine of the same thrust.
{"title":"Numerical Investigation of an Optimised Horizontal Axis Tidal Stream Turbine","authors":"H. E. Sheshtawy, O. E. Moctar, T. Schellin, S. Natarajan","doi":"10.1115/omae2019-95722","DOIUrl":"https://doi.org/10.1115/omae2019-95722","url":null,"abstract":"\u0000 A tidal stream turbine was designed using one of the optimised hydrofoils, whose lift-to-drag ratio at an angle of attack of 5.2 degrees was 4.5% higher than that of the reference hydrofoil. The incompressible Reynolds-averaged Navier Stokes equations in steady state were solved using k-ω (SST) turbulence model for the reference and optimised tidal stream turbines. The discretisation errors and the effect of different y+ values on the solution were analysed. Thrust and power coefficients of the modelled reference turbine were validated against experimental measurements. Output power and thrust of the reference and the optimised tidal turbines were compared. For a tip speed ratio of 3.0, the output power of the optimised tidal turbine was 8.27% higher than that of the reference turbine of the same thrust.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127838909","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}
Simulations are conducted in time domain to investigate the dynamic response of a SPAR-type floating offshore wind turbine under the scenarios with freak wave. Towards this end, a coupled aero-hydro numerical model is developed. The methodology includes a blade-element-momentum model for aerodynamics, a nonlinear model for hydrodynamics, a nonlinear restoring model of SPAR buoy, and a nonlinear algorithm for mooring cables. The OC3 Hywind SPAR-type FOWT is chosen as an example to study the dynamic response under the freak conditions, while the time series of freak wave is generated by the Random Frequency Components Selection Phase Modulation Method. The motions of platform, the tensions in the mooring lines and the power generation performance are documented in different cases. According to the simulations, it shows that the power coefficient of wind turbine decreased rapidly at the moment when freak wave acted on the floating structure.
{"title":"Dynamic Response of Spar-Type Floating Offshore Wind Turbine in Freak Wave","authors":"You-gang Tang, Yan Li, Xie Peng, X. Qu, Wang Bin","doi":"10.1115/omae2019-95638","DOIUrl":"https://doi.org/10.1115/omae2019-95638","url":null,"abstract":"\u0000 Simulations are conducted in time domain to investigate the dynamic response of a SPAR-type floating offshore wind turbine under the scenarios with freak wave. Towards this end, a coupled aero-hydro numerical model is developed. The methodology includes a blade-element-momentum model for aerodynamics, a nonlinear model for hydrodynamics, a nonlinear restoring model of SPAR buoy, and a nonlinear algorithm for mooring cables. The OC3 Hywind SPAR-type FOWT is chosen as an example to study the dynamic response under the freak conditions, while the time series of freak wave is generated by the Random Frequency Components Selection Phase Modulation Method. The motions of platform, the tensions in the mooring lines and the power generation performance are documented in different cases. According to the simulations, it shows that the power coefficient of wind turbine decreased rapidly at the moment when freak wave acted on the floating structure.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124064694","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 series of experiments were carried out to investigate the occurrence of the Mathieu-type instability. The main objective of this study is utilization of an auto-parametrically excited oscillation for wave energy converters. In this paper, the subject is the auto-parametrically excited oscillation of a spar-buoy type point absorber with two degrees of freedom. A small spar buoy model with a ballast controlling system was made and the model experiments were conducted to realize the large oscillating motion based on the Mathieu-type instability. The ballast controlling system is installed in the buoy model and the vertical movement of the ballast produces a certain change of the pitching natural period. Using the controlling system, the pitching motion in regular waves under the heave resonant period was measured. In some experiments, it was observed that the large pitching motion occurred suddenly, and the time histories showed different excitation pattern from the theoretical Mathieu-type instability. Based on the model experiments and considerations of the theory of Mathieu-type instability, the occurrence of the large pitching motion is discussed.
{"title":"Experimental Study on Coupled Motions of a Spar-Buoy Under Mathieu Instability","authors":"T. Iseki, Peng Xu","doi":"10.1115/omae2019-95937","DOIUrl":"https://doi.org/10.1115/omae2019-95937","url":null,"abstract":"\u0000 A series of experiments were carried out to investigate the occurrence of the Mathieu-type instability. The main objective of this study is utilization of an auto-parametrically excited oscillation for wave energy converters. In this paper, the subject is the auto-parametrically excited oscillation of a spar-buoy type point absorber with two degrees of freedom. A small spar buoy model with a ballast controlling system was made and the model experiments were conducted to realize the large oscillating motion based on the Mathieu-type instability. The ballast controlling system is installed in the buoy model and the vertical movement of the ballast produces a certain change of the pitching natural period. Using the controlling system, the pitching motion in regular waves under the heave resonant period was measured. In some experiments, it was observed that the large pitching motion occurred suddenly, and the time histories showed different excitation pattern from the theoretical Mathieu-type instability. Based on the model experiments and considerations of the theory of Mathieu-type instability, the occurrence of the large pitching motion is discussed.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"244 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133848886","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}
Shengtao Zhou, Chao Li, Yiqing Xiao, F. Lemmer, Wei Yu, P. Cheng
Due to the non-fully-symmetrical configuration, the platform laying angle of semi-submersible floating offshore wind turbines relative to wind/wave load directions has a noticeable influence on the dynamics characteristics of the whole structure, which indicates that the platform mounting orientation should be carefully considered before installation at sea. The directionality effects of short-term wind/wave loads had been discussed in previous studies, which are, however, insufficient to make a full understanding of the directionality impacts. In our study, based on a 25-year met-ocean database, long-term analysis is carried out by means of an efficient frequency-domain model with eight degrees of freedom. The nonlinear quantities such as aerodynamic loads, aerodynamic damping and mooring stiffness are derived from the time-domain simulation tool FAST, serving as a preprocessing database for the frequency-domain model. A case study is carried out by comparing the long-term responses of a Y-shape semi-submersible floating wind turbine in four mounting orientations. Significant differences can be seen. The platform mounted in the most unfavorable orientation tends to suffer from larger peak nacelle acceleration, which would increase the loads and cause higher tower base fatigue damage. These findings highlight the importance of platform mounting orientations and can serve as a basis for the installation of semi-submersible floating wind turbines.
{"title":"Effects of Platform Mounting Orientations on the Long-Term Performance of a Semisubmersible Wind Turbine","authors":"Shengtao Zhou, Chao Li, Yiqing Xiao, F. Lemmer, Wei Yu, P. Cheng","doi":"10.1115/omae2019-96240","DOIUrl":"https://doi.org/10.1115/omae2019-96240","url":null,"abstract":"\u0000 Due to the non-fully-symmetrical configuration, the platform laying angle of semi-submersible floating offshore wind turbines relative to wind/wave load directions has a noticeable influence on the dynamics characteristics of the whole structure, which indicates that the platform mounting orientation should be carefully considered before installation at sea. The directionality effects of short-term wind/wave loads had been discussed in previous studies, which are, however, insufficient to make a full understanding of the directionality impacts. In our study, based on a 25-year met-ocean database, long-term analysis is carried out by means of an efficient frequency-domain model with eight degrees of freedom. The nonlinear quantities such as aerodynamic loads, aerodynamic damping and mooring stiffness are derived from the time-domain simulation tool FAST, serving as a preprocessing database for the frequency-domain model. A case study is carried out by comparing the long-term responses of a Y-shape semi-submersible floating wind turbine in four mounting orientations. Significant differences can be seen. The platform mounted in the most unfavorable orientation tends to suffer from larger peak nacelle acceleration, which would increase the loads and cause higher tower base fatigue damage. These findings highlight the importance of platform mounting orientations and can serve as a basis for the installation of semi-submersible floating wind turbines.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130900557","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 motivation of the present paper is to show the proof-of-concept of a passive Tuned Liquid Column Damper (TLCD) for floating wind turbines, which increases the platform pitch damping and power production under wind and wave excitations. As the first step, a reliable TLCD model is implemented and coupled with a reduced order floating wind turbine model. Here, the TLCD is modelled as a second order system which is known for ships, whereas the structural model is a coupled aero-hydro-servo-elastic model with five degrees of freedom. The results show that the TLCD is able to damp the platform resonances but to a limited extent, which is inline the findings of previous research. However, the improved platform pitch stability allows a larger blade pitch control bandwidth, which is normally limited by the underdamped soft support platform. Therefore, by introducing the passive TLCD into the floating wind turbine system, a better power production is achieved.
{"title":"Performance of a Passive Tuned Liquid Column Damper for Floating Wind Turbines","authors":"Wei Yu, F. Lemmer, P. Cheng","doi":"10.1115/omae2019-96360","DOIUrl":"https://doi.org/10.1115/omae2019-96360","url":null,"abstract":"\u0000 The motivation of the present paper is to show the proof-of-concept of a passive Tuned Liquid Column Damper (TLCD) for floating wind turbines, which increases the platform pitch damping and power production under wind and wave excitations. As the first step, a reliable TLCD model is implemented and coupled with a reduced order floating wind turbine model. Here, the TLCD is modelled as a second order system which is known for ships, whereas the structural model is a coupled aero-hydro-servo-elastic model with five degrees of freedom. The results show that the TLCD is able to damp the platform resonances but to a limited extent, which is inline the findings of previous research. However, the improved platform pitch stability allows a larger blade pitch control bandwidth, which is normally limited by the underdamped soft support platform. Therefore, by introducing the passive TLCD into the floating wind turbine system, a better power production is achieved.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114712024","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}
This paper deals with the problem of designing an optimal U - Oscillating Water Column (U-OWC) device equipped with a Wells turbine. Specifically, the paper proposes the implementation of a genetic algorithm for designing a U-OWC exposed to the typical sea states available in the Mediterranean Sea. The first challenge encountered in this problem is the efficient calculation of the U-OWC hydrodynamic parameters. The second challenge relates to the fact that the U-OWC dynamics is governed by two coupled nonlinear ordinary differential equations with no closed-form solution. For reducing the computational cost, the genetic algorithm is combined with a semi-analytical approach used for determining the U-OWC hydrodynamic parameters and with a statistical linearization based approximate solution of the equations governing the U-OWC dynamics. Such a procedure allows estimating efficiently, albeit approximately, the power output of the system. Numerical results compare a design based on a conventional “design sea state” vis-à-vis a design based on a “design wave climate”. For this purpose, the case study of the Roccella Jonica marina (Reggio Calabria, Italy) is considered, as relevant wave data are available to characterize the most energetic seas as well as depicting the global wave climate available at that location. The numerical results highlight the fact that an optimization conducted on the basis of a design sea state does not lead to an optimal design in a wave climate.
{"title":"Geometrical Optimization of U-Oscillating Water Columns in Random Waves","authors":"A. Scialò, G. Malara, F. Arena","doi":"10.1115/omae2019-95973","DOIUrl":"https://doi.org/10.1115/omae2019-95973","url":null,"abstract":"\u0000 This paper deals with the problem of designing an optimal U - Oscillating Water Column (U-OWC) device equipped with a Wells turbine. Specifically, the paper proposes the implementation of a genetic algorithm for designing a U-OWC exposed to the typical sea states available in the Mediterranean Sea. The first challenge encountered in this problem is the efficient calculation of the U-OWC hydrodynamic parameters. The second challenge relates to the fact that the U-OWC dynamics is governed by two coupled nonlinear ordinary differential equations with no closed-form solution. For reducing the computational cost, the genetic algorithm is combined with a semi-analytical approach used for determining the U-OWC hydrodynamic parameters and with a statistical linearization based approximate solution of the equations governing the U-OWC dynamics. Such a procedure allows estimating efficiently, albeit approximately, the power output of the system.\u0000 Numerical results compare a design based on a conventional “design sea state” vis-à-vis a design based on a “design wave climate”. For this purpose, the case study of the Roccella Jonica marina (Reggio Calabria, Italy) is considered, as relevant wave data are available to characterize the most energetic seas as well as depicting the global wave climate available at that location. The numerical results highlight the fact that an optimization conducted on the basis of a design sea state does not lead to an optimal design in a wave climate.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127000250","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}
Daniel de Oliveira Costa, Joel Sena Sales Junior, A. C. Fernandes
A non-linear mathematical model is presented for the Equation of Motion of the Water Column inside circular cylindrical structures in different cases, comparing to previous models in literature. Experimental model tests were carried out investigating the water column decay under given initial conditions, and an analysis is performed for each cycle showing the dynamic behaviour of OWC evolving in time. The results show asymmetric pattern in the time series acquired in the decay tests as a consequence of variations of the Added Length and quadratic viscous damping as the direction of the flow changes, as observed in previous studies. A general procedure is proposed to assess the unknown parameters including the quadratic damping viscous coefficients through the concept of “equivalent linear harmonic” as a linearisation of such terms, enlightening its dependence on the motion amplitude as well as the water column draft. Experimental data for the OWC response under a set of incoming regular waves is also presented, comparing the results to numerical simulation through a solver based on the estimation of the damping coefficients obtained in the decay tests.
{"title":"Oscillating Water Column Motion Inside Circular Cylindrical Structures","authors":"Daniel de Oliveira Costa, Joel Sena Sales Junior, A. C. Fernandes","doi":"10.1115/omae2019-96048","DOIUrl":"https://doi.org/10.1115/omae2019-96048","url":null,"abstract":"\u0000 A non-linear mathematical model is presented for the Equation of Motion of the Water Column inside circular cylindrical structures in different cases, comparing to previous models in literature. Experimental model tests were carried out investigating the water column decay under given initial conditions, and an analysis is performed for each cycle showing the dynamic behaviour of OWC evolving in time. The results show asymmetric pattern in the time series acquired in the decay tests as a consequence of variations of the Added Length and quadratic viscous damping as the direction of the flow changes, as observed in previous studies.\u0000 A general procedure is proposed to assess the unknown parameters including the quadratic damping viscous coefficients through the concept of “equivalent linear harmonic” as a linearisation of such terms, enlightening its dependence on the motion amplitude as well as the water column draft.\u0000 Experimental data for the OWC response under a set of incoming regular waves is also presented, comparing the results to numerical simulation through a solver based on the estimation of the damping coefficients obtained in the decay tests.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":" 67","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132187703","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}
This paper uses a coupled FAST-OrcaFlex model in order to explore the impact of simulation duration on model convergence. The work analyses both operational and extreme cases, assessing the estimated fatigue and extreme loads experienced by a floating offshore wind turbine and its mooring system. Considering an OC4 semi-submersible deployed with the NREL 5 MW turbine, the case study performs a parametric sweep over a range of wind speeds, sea states, and simulation durations. Through this sweep, the paper establishes the impact of the simulation duration for this particular floating offshore wind turbine and characterizes the convergence properties of the loads and excursions as a function of the simulation duration. The results inform the selection of simulation durations to be used in coupled aero-hydro models and optimization frameworks for floating offshore wind applications and can be used to aid the development of guidance and standards for coupled floating offshore wind turbine models.
{"title":"Impact of Simulation Duration for Offshore Floating Wind Turbine Analysis Using a Coupled FAST-OrcaFlex Model","authors":"A. Pillai, P. Thies, L. Johanning","doi":"10.1115/OMAE2019-95159","DOIUrl":"https://doi.org/10.1115/OMAE2019-95159","url":null,"abstract":"\u0000 This paper uses a coupled FAST-OrcaFlex model in order to explore the impact of simulation duration on model convergence. The work analyses both operational and extreme cases, assessing the estimated fatigue and extreme loads experienced by a floating offshore wind turbine and its mooring system. Considering an OC4 semi-submersible deployed with the NREL 5 MW turbine, the case study performs a parametric sweep over a range of wind speeds, sea states, and simulation durations. Through this sweep, the paper establishes the impact of the simulation duration for this particular floating offshore wind turbine and characterizes the convergence properties of the loads and excursions as a function of the simulation duration. The results inform the selection of simulation durations to be used in coupled aero-hydro models and optimization frameworks for floating offshore wind applications and can be used to aid the development of guidance and standards for coupled floating offshore wind turbine models.","PeriodicalId":306681,"journal":{"name":"Volume 10: Ocean Renewable Energy","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132952302","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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