Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology最新文献
Global population growth and climate change are driving a need for increased clean renewable energy generation. One such resource is wind energy and while the onshore and fixed offshore wind energy industries are mature, the floating offshore wind energy industry is still at a demonstration phase. Floating wind turbine platforms are generally of a much smaller displacement than the typical offshore structures that have been used in the oil and gas industry. This difference results in changes to the platform dynamics, especially those resulting from second order wave forces. Existing research into low frequency drift motions of small body platforms has been mainly confined to numerical modelling with some experimental work. This work expands on this knowledge by validating numerical modelling with full scale observational data. In this paper, a numerical time-domain model of a relatively small displacement platform is developed. The platform is installed in a relatively shallow water depth of about 110 m and station keeping is provided by four equally spaced catenary mooring chains. The required fidelity for the low frequency response is compared using first order forces only and either a full QTF (quadratic transfer equation) or Newman’s approximation. The model is compared with observation data from the Fukushima FORWARD project’s floating substation, an advanced spar type, which is composed of measurements of multidirectional wave spectra, wind and current as model inputs and six DOF platform motions as outputs. In addition to this the model computational expense is reduced by decreasing the number of wave directions simulated. The accuracy of such reductions is then described. Observation data is grouped according to sea-state data. An empirical drag coefficient formula is proposed. The 50 year return period design sea-state is also modelled using a JONSWAP spectrum and the various numerical models.
{"title":"Numerical Modelling of a Relatively Small Floating Body’s Wave and Low Frequency Motion Response, Compared With Observational Data","authors":"C. Wright, Haruki Yoshimoto, R. Wada, K. Takagi","doi":"10.1115/omae2019-96443","DOIUrl":"https://doi.org/10.1115/omae2019-96443","url":null,"abstract":"\u0000 Global population growth and climate change are driving a need for increased clean renewable energy generation. One such resource is wind energy and while the onshore and fixed offshore wind energy industries are mature, the floating offshore wind energy industry is still at a demonstration phase. Floating wind turbine platforms are generally of a much smaller displacement than the typical offshore structures that have been used in the oil and gas industry. This difference results in changes to the platform dynamics, especially those resulting from second order wave forces. Existing research into low frequency drift motions of small body platforms has been mainly confined to numerical modelling with some experimental work. This work expands on this knowledge by validating numerical modelling with full scale observational data.\u0000 In this paper, a numerical time-domain model of a relatively small displacement platform is developed. The platform is installed in a relatively shallow water depth of about 110 m and station keeping is provided by four equally spaced catenary mooring chains. The required fidelity for the low frequency response is compared using first order forces only and either a full QTF (quadratic transfer equation) or Newman’s approximation. The model is compared with observation data from the Fukushima FORWARD project’s floating substation, an advanced spar type, which is composed of measurements of multidirectional wave spectra, wind and current as model inputs and six DOF platform motions as outputs. In addition to this the model computational expense is reduced by decreasing the number of wave directions simulated. The accuracy of such reductions is then described. Observation data is grouped according to sea-state data. An empirical drag coefficient formula is proposed. The 50 year return period design sea-state is also modelled using a JONSWAP spectrum and the various numerical models.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"23 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":"124485173","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}
Oscillating Water Column (OWC) wave energy device is one of the most studied and applied wave energy converters (WECs). The survivability of WECs is a major concern in the OWC design. In this study, the wave dynamics of a dual-chamber OWC device is numerically and experimentally investigated. The experimental tests were carried out in the wave-current flume at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. A fully nonlinear numerical wave flume based on potential-flow theory and time-domain higher-order boundary element method (HOBEM) is developed and applied to simulate the interaction between air, wave and the dual-chamber OWC device. The numerical model is validated by comparing the simulated wave induced pressure on the barrier walls with the measurements. Then the wave forces and the moment on the device is numerically investigated. The model and experimental results indicate that the horizontal wave force on the front barrier wall is much larger than that on the internal barrier wall. The joint between the back wall and the ground withstands the largest bending moment, therefore, is most vulnerable to structure damage and fatigue.
{"title":"Experimental and Numerical Investigations on Wave Dynamics of a Dual-Chamber OWC Wave Energy Device","authors":"D. Ning, Rongquan Wang, B. Teng, Q. Zou","doi":"10.1115/OMAE2019-95165","DOIUrl":"https://doi.org/10.1115/OMAE2019-95165","url":null,"abstract":"\u0000 Oscillating Water Column (OWC) wave energy device is one of the most studied and applied wave energy converters (WECs). The survivability of WECs is a major concern in the OWC design. In this study, the wave dynamics of a dual-chamber OWC device is numerically and experimentally investigated. The experimental tests were carried out in the wave-current flume at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. A fully nonlinear numerical wave flume based on potential-flow theory and time-domain higher-order boundary element method (HOBEM) is developed and applied to simulate the interaction between air, wave and the dual-chamber OWC device. The numerical model is validated by comparing the simulated wave induced pressure on the barrier walls with the measurements. Then the wave forces and the moment on the device is numerically investigated. The model and experimental results indicate that the horizontal wave force on the front barrier wall is much larger than that on the internal barrier wall. The joint between the back wall and the ground withstands the largest bending moment, therefore, is most vulnerable to structure damage and fatigue.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"84 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":"128004477","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. Eto, S. Togawa, Morikazu Yamamoto, Shintaro Miyasawa, Junko Yamaguchi, T. Ikoma, Y. Aida, K. Masuda, Sena Shimomoto, Yuichi Kitabatake
In 2011, Japan experienced a major catastrophe: The Great East Japan Earthquake and subsequent tsunami. After the tsunami struck, overland transport routes were cut off, and consequently, emergency supplies and people requiring medical attention could not be transported very efficiently. Many hospitals and other emergency facilities were destroyed or were operating with reduced capabilities during this period, meaning victims could not receive treatment within a reasonable timeframe. Therefore, we need to consider emergency facilities, particularly for medical support, which are resilient and versatile for use in such situations. Floating bases for disaster relief and support ships are already available for deployment along coastal regions or on rivers near affected areas. A medical support floating base has also been proposed, which is called the Medi-float hereafter, in preparation for the anticipated Tokyo Inland Earthquake. And it is determined that the primary function of this Medi-float should be as a dialysis treatment center during normal operation and primarily for the treatment of crush syndrome patients during a disaster. But the original proposal was deemed inadequate in terms of facility scale and selection of the suitable site of Medi-float. Therefore, in this research aiming at realization of Medi-float, firstly the number of people who develop crush syndrome in the target area is estimated by GIS based on the damage prediction of the huge earthquake striking Tokyo and the risk of building collapse. Based on the distribution of dialysis treatment facilities and data such as road network data in Tokyo, Voronoi diagrams were created using GIS. And facility scale required for Medi-float and suitable installed site were examined by the distribution of crushed syndrome patients obtained by analysis and Voronoi diagram.
{"title":"On GIS Based Facility Scale and Selection of Suitable Site of Floating Medical Support System on Big Disaster","authors":"H. Eto, S. Togawa, Morikazu Yamamoto, Shintaro Miyasawa, Junko Yamaguchi, T. Ikoma, Y. Aida, K. Masuda, Sena Shimomoto, Yuichi Kitabatake","doi":"10.1115/omae2019-96493","DOIUrl":"https://doi.org/10.1115/omae2019-96493","url":null,"abstract":"\u0000 In 2011, Japan experienced a major catastrophe: The Great East Japan Earthquake and subsequent tsunami. After the tsunami struck, overland transport routes were cut off, and consequently, emergency supplies and people requiring medical attention could not be transported very efficiently. Many hospitals and other emergency facilities were destroyed or were operating with reduced capabilities during this period, meaning victims could not receive treatment within a reasonable timeframe. Therefore, we need to consider emergency facilities, particularly for medical support, which are resilient and versatile for use in such situations. Floating bases for disaster relief and support ships are already available for deployment along coastal regions or on rivers near affected areas. A medical support floating base has also been proposed, which is called the Medi-float hereafter, in preparation for the anticipated Tokyo Inland Earthquake. And it is determined that the primary function of this Medi-float should be as a dialysis treatment center during normal operation and primarily for the treatment of crush syndrome patients during a disaster. But the original proposal was deemed inadequate in terms of facility scale and selection of the suitable site of Medi-float. Therefore, in this research aiming at realization of Medi-float, firstly the number of people who develop crush syndrome in the target area is estimated by GIS based on the damage prediction of the huge earthquake striking Tokyo and the risk of building collapse. Based on the distribution of dialysis treatment facilities and data such as road network data in Tokyo, Voronoi diagrams were created using GIS. And facility scale required for Medi-float and suitable installed site were examined by the distribution of crushed syndrome patients obtained by analysis and Voronoi diagram.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"32 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":"132208694","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}
Y. Nihei, S. Srinivasamurthy, H. Sakamoto, Norikazu Masuda, N. Hara
Aquaculture farms play a vital role for food security in Japan. The cultivation potential is directly related to the quality of the marine environment. Water quality parameters such as dissolved oxygen and temperature need to be measured and monitored regularly throughout the cultivation period. Energy efficiency and ease of navigation are the prime requirements for environmental survey vessels. In this paper, a new and novel automated vessel is introduced and design methodology is explained. Multi-hull innovative vessel is named as ‘Quadmaran’ and developed particularly for carrying out environmental surveys. The vessel consists of four hulls each capable of rotating independently thereby leading to better sailing performance and excellent stability. It is equipped with devices to measure quality parameters at various water depths and includes a dynamic positioning system aiding for the environment data collection. The basic design criteria of the Quadmaran is derived and understood in this study. Scaled model (1/3 scale) is fabricated for tank tests and resistance tests are carried out in a circulating water tank at Osaka Prefecture University, Osaka, Japan. With the knowledge gained from tank tests, multi-hull phenomenon of the Quadmaran is studied and interaction between the hulls is investigated. It is found that wave interference due to hull orientation becomes significant for Froude number greater than 0.5 and resistance of Quadmaran is found to be less than two times the twin hull resistance for same water draft. Further, an attempt is made to understand how the configuration arrangement affects the resistance of the vessel.
{"title":"Design Methodology and Development of an Independently Rotating Multi-Hull Vessel","authors":"Y. Nihei, S. Srinivasamurthy, H. Sakamoto, Norikazu Masuda, N. Hara","doi":"10.1115/omae2019-95401","DOIUrl":"https://doi.org/10.1115/omae2019-95401","url":null,"abstract":"\u0000 Aquaculture farms play a vital role for food security in Japan. The cultivation potential is directly related to the quality of the marine environment. Water quality parameters such as dissolved oxygen and temperature need to be measured and monitored regularly throughout the cultivation period. Energy efficiency and ease of navigation are the prime requirements for environmental survey vessels. In this paper, a new and novel automated vessel is introduced and design methodology is explained. Multi-hull innovative vessel is named as ‘Quadmaran’ and developed particularly for carrying out environmental surveys. The vessel consists of four hulls each capable of rotating independently thereby leading to better sailing performance and excellent stability. It is equipped with devices to measure quality parameters at various water depths and includes a dynamic positioning system aiding for the environment data collection. The basic design criteria of the Quadmaran is derived and understood in this study. Scaled model (1/3 scale) is fabricated for tank tests and resistance tests are carried out in a circulating water tank at Osaka Prefecture University, Osaka, Japan. With the knowledge gained from tank tests, multi-hull phenomenon of the Quadmaran is studied and interaction between the hulls is investigated. It is found that wave interference due to hull orientation becomes significant for Froude number greater than 0.5 and resistance of Quadmaran is found to be less than two times the twin hull resistance for same water draft. Further, an attempt is made to understand how the configuration arrangement affects the resistance of the vessel.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"3 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":"124293291","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}
Xiantao Zhang, S. Draper, H. Wolgamot, Wenhua Zhao, Lifen Chen, Liang Cheng
In this paper, 2D greenwater overtopping of a floating box is numerically investigated using CFD. The incident waves used are compact wave groups which correspond to the maximum relative wave elevation at the edge of the box according to linear theory. The motion of the box for which only heave and pitch modes are considered is calculated using linear potential flow theory and then prescribed in the CFD simulation. It is found that the normalized maximum horizontal momentum flux of greenwater overtopped onto the moving box is consistent with that for a fixed box when the incident wave length is much smaller than the box length. For longer incident wave lengths there is arguably more scatter in the momentum flux compared with that of a fixed box, although the result is still bounded by a value of 1.5 times that predicted by a classical dam break solution. This additional scatter is shown to be due to the effect of box motion.
{"title":"CFD Investigations of 2D Greenwater Overtopping of a Floating Offshore Vessel","authors":"Xiantao Zhang, S. Draper, H. Wolgamot, Wenhua Zhao, Lifen Chen, Liang Cheng","doi":"10.1115/omae2019-95865","DOIUrl":"https://doi.org/10.1115/omae2019-95865","url":null,"abstract":"\u0000 In this paper, 2D greenwater overtopping of a floating box is numerically investigated using CFD. The incident waves used are compact wave groups which correspond to the maximum relative wave elevation at the edge of the box according to linear theory. The motion of the box for which only heave and pitch modes are considered is calculated using linear potential flow theory and then prescribed in the CFD simulation. It is found that the normalized maximum horizontal momentum flux of greenwater overtopped onto the moving box is consistent with that for a fixed box when the incident wave length is much smaller than the box length. For longer incident wave lengths there is arguably more scatter in the momentum flux compared with that of a fixed box, although the result is still bounded by a value of 1.5 times that predicted by a classical dam break solution. This additional scatter is shown to be due to the effect of box motion.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"123 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":"124596433","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}
Along with the development in offshore technology, the offshore platforms are gradually becoming larger and more complex. Recent development of oil and gas field in the deepwater region often involves multiple floating platforms adjacent to each other. Wave free surface associated with the air-gap design is one of the most important issues as the interaction between the platforms can complicate the hydrodynamics further. In this paper, the nonlinearity of incident wave and scattered wave are considered in diffraction analysis based on the potential theory. In addition, the nonlinear incident wave is considered to capture the nonlinear features of free surface due to wave diffraction and radiation. The wave surface amplitude around a multi-body platforms system is numerically analyzed in the frequency domain and compared with the numerical results of a single platform. The distribution of wave surface amplitude with different scatter parameter at different wave steepness is investigated to examine the relationship between the two parameters critical to the nonlinear wave surface elevation.
{"title":"Nonlinear Wave Surface Elevation Characteristics Analysis Around a Multi-Body Offshore Platforms System","authors":"Xiudi Ren, Yibo Liang, L. Tao","doi":"10.1115/OMAE2019-95203","DOIUrl":"https://doi.org/10.1115/OMAE2019-95203","url":null,"abstract":"\u0000 Along with the development in offshore technology, the offshore platforms are gradually becoming larger and more complex. Recent development of oil and gas field in the deepwater region often involves multiple floating platforms adjacent to each other. Wave free surface associated with the air-gap design is one of the most important issues as the interaction between the platforms can complicate the hydrodynamics further. In this paper, the nonlinearity of incident wave and scattered wave are considered in diffraction analysis based on the potential theory. In addition, the nonlinear incident wave is considered to capture the nonlinear features of free surface due to wave diffraction and radiation. The wave surface amplitude around a multi-body platforms system is numerically analyzed in the frequency domain and compared with the numerical results of a single platform. The distribution of wave surface amplitude with different scatter parameter at different wave steepness is investigated to examine the relationship between the two parameters critical to the nonlinear wave surface elevation.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","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":"129842099","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}
L. S. Silva, H. Morishita, C. Pesce, Rodolfo T. Gonçalves
The majority of wave energy devices operate close to resonant conditions to enhance energy conversion resulting in large displacements. As a result, nonlinearities significantly contribute to the dynamics of the system. A typical approach to predict the behavior of the system and power output relies on the derivation of a mathematical model in the time domain to simulate the dynamics through some numerical codes. However, a relatively high computational demand is required for those simulations. In this regard, the present work deals with the nonlinearities in the frequency domain via Statistical Linearization. Two different power-take-off systems are investigated, a linear and a hydraulic one, and their mean power calculations are derived based on the Statistical Linearization. The reliability of the method is verified against the Power Spectrum Density (PSD) of nonlinear time domain simulations. Only the heave motion is analyzed, and several nonlinearities commonly reported for Point Absorbers (PA) were considered, such as cubic stiffness, geometric nonlinearities, drag forces, and Coulomb forces. The approach employed in this work offers a reliable estimation of body dynamics for all nonlinearities considered. In addition, the present method produced a fast estimation, which can be valuable for the assessment of several designs and sea load conditions.
{"title":"Nonlinear Analysis of a Heaving Point Absorber in Frequency Domain via Statistical Linearization","authors":"L. S. Silva, H. Morishita, C. Pesce, Rodolfo T. Gonçalves","doi":"10.1115/omae2019-95785","DOIUrl":"https://doi.org/10.1115/omae2019-95785","url":null,"abstract":"\u0000 The majority of wave energy devices operate close to resonant conditions to enhance energy conversion resulting in large displacements. As a result, nonlinearities significantly contribute to the dynamics of the system. A typical approach to predict the behavior of the system and power output relies on the derivation of a mathematical model in the time domain to simulate the dynamics through some numerical codes. However, a relatively high computational demand is required for those simulations. In this regard, the present work deals with the nonlinearities in the frequency domain via Statistical Linearization. Two different power-take-off systems are investigated, a linear and a hydraulic one, and their mean power calculations are derived based on the Statistical Linearization. The reliability of the method is verified against the Power Spectrum Density (PSD) of nonlinear time domain simulations. Only the heave motion is analyzed, and several nonlinearities commonly reported for Point Absorbers (PA) were considered, such as cubic stiffness, geometric nonlinearities, drag forces, and Coulomb forces. The approach employed in this work offers a reliable estimation of body dynamics for all nonlinearities considered. In addition, the present method produced a fast estimation, which can be valuable for the assessment of several designs and sea load conditions.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"30 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":"116628677","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}
Liu-yi Huang, Yuyan Li, Yin Ni, Hui Cheng, Xinxin Wang, Gang Wang, F. Zhao
The Morison Model is widely applied in the numerical simulation for the hydrodynamics assessment of fish cage. In the Morison model, hydrodynamic forces are calculated based on twines. To reduce the computational time, mesh grouping methods (replacement of multiple meshes with less number of equivalent meshes) have been implemented widely in the calculation. However, as the hydrodynamic equation for a mesh is quite different under wave and current, it is not appropriate to use the classical mesh grouping. On the basis of basic hydrodynamic equations of the meshes with current and wave, this paper carried out the study about theoretical analysis of two methods (the equivalent area method and the equivalent volume method) of the mesh grouping, using main parameters of nets such as the diameter, solidity ratio and elastic modulus related to mesh grouping. A single-point mooring cage, of which tension and displacement could be calculated with finite element method, was selected as a case to carry out the verification of two mesh grouping methods. Flume model experiment was used to validate the accuracy of mesh grouping methods. The results indicated that, the equivalent area method has a higher accuracy in the pure current condition, while the equivalent volume method was more accurate in combined waves and current. The accuracy of results using mesh grouping to analyze hydrodynamics of nets within a certain range of grouping times could be insured with an improved calculation speed. This paper can provide practical advice on the mesh grouping process in the numerical simulation of fish cages and fishing gear.
{"title":"Study on the Influence of Mesh Grouping on Numerical Simulation Results of Fish Cages","authors":"Liu-yi Huang, Yuyan Li, Yin Ni, Hui Cheng, Xinxin Wang, Gang Wang, F. Zhao","doi":"10.1115/omae2019-95706","DOIUrl":"https://doi.org/10.1115/omae2019-95706","url":null,"abstract":"\u0000 The Morison Model is widely applied in the numerical simulation for the hydrodynamics assessment of fish cage. In the Morison model, hydrodynamic forces are calculated based on twines. To reduce the computational time, mesh grouping methods (replacement of multiple meshes with less number of equivalent meshes) have been implemented widely in the calculation. However, as the hydrodynamic equation for a mesh is quite different under wave and current, it is not appropriate to use the classical mesh grouping. On the basis of basic hydrodynamic equations of the meshes with current and wave, this paper carried out the study about theoretical analysis of two methods (the equivalent area method and the equivalent volume method) of the mesh grouping, using main parameters of nets such as the diameter, solidity ratio and elastic modulus related to mesh grouping. A single-point mooring cage, of which tension and displacement could be calculated with finite element method, was selected as a case to carry out the verification of two mesh grouping methods. Flume model experiment was used to validate the accuracy of mesh grouping methods. The results indicated that, the equivalent area method has a higher accuracy in the pure current condition, while the equivalent volume method was more accurate in combined waves and current. The accuracy of results using mesh grouping to analyze hydrodynamics of nets within a certain range of grouping times could be insured with an improved calculation speed. This paper can provide practical advice on the mesh grouping process in the numerical simulation of fish cages and fishing gear.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"5 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":"131423232","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}
L. S. Silva, C. Pesce, H. Morishita, Rodolfo T. Gonçalves
Wave energy converters (WECs) are often subject to large displacements during operating conditions. Hence, nonlinearities present in numerical methods to estimate the performance of WECs must be considered for realistic predictions. These large displacements occur when the device operates on resonant conditions, which results in maximum energy conversion. The system dynamics are usually simulated via time domain models in order to being able to capture nonlinearities. However, a high computational cost is associated with those simulations. Alternatively, the present work treats the nonlinearities in the frequency domain via Statistical Linearization (SL). The SL results are compared to the Power Spectrum Density (PSD) of time domain simulations to verify the reliability of the proposed method. In this regard, the work initiates with the derivation of the governing equations of the air-chamber and the Oscillating Water Column (OWC). Then, the SL technique is presented and applied. The SL results show a satisfactory agreement for the system dynamics, mean surface elevation, mean pressure, and mean power compared to time domain simulations. Also, the SL technique produces a rapid estimation of the response, which is an effective approach for the evaluation of numerous environmental conditions and design, and further optimization procedures.
{"title":"Nonlinear Analysis of an Oscillating Water Column Wave Energy Device in Frequency Domain via Statistical Linearization","authors":"L. S. Silva, C. Pesce, H. Morishita, Rodolfo T. Gonçalves","doi":"10.1115/omae2019-96727","DOIUrl":"https://doi.org/10.1115/omae2019-96727","url":null,"abstract":"\u0000 Wave energy converters (WECs) are often subject to large displacements during operating conditions. Hence, nonlinearities present in numerical methods to estimate the performance of WECs must be considered for realistic predictions. These large displacements occur when the device operates on resonant conditions, which results in maximum energy conversion. The system dynamics are usually simulated via time domain models in order to being able to capture nonlinearities. However, a high computational cost is associated with those simulations. Alternatively, the present work treats the nonlinearities in the frequency domain via Statistical Linearization (SL). The SL results are compared to the Power Spectrum Density (PSD) of time domain simulations to verify the reliability of the proposed method. In this regard, the work initiates with the derivation of the governing equations of the air-chamber and the Oscillating Water Column (OWC). Then, the SL technique is presented and applied. The SL results show a satisfactory agreement for the system dynamics, mean surface elevation, mean pressure, and mean power compared to time domain simulations. Also, the SL technique produces a rapid estimation of the response, which is an effective approach for the evaluation of numerous environmental conditions and design, and further optimization procedures.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"7 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":"132169508","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}
We seek to characterize the behavior of extreme waves in the Gulf of Mexico, using a 109 year-long wave hindcast (GOMOS). The largest waves in this region are driven by strong winds from hurricanes. Design of offshore production systems requires the estimation of extreme metocean conditions corresponding to return periods from 1 year to 10,000 years and beyond. For extrapolation to long return periods, estimation using data for around 100 years from a single location will incur large uncertainties. Approaches such as spatial pooling, cyclone track-shifting and explicit track modeling have been proposed to alleviate this problem. The underlying problem in spatial pooling is the aggregation of dependent data and hence underestimation of uncertainty using naïve analysis; techniques such as block-bootstrapping can be used to inflate uncertainties to more realistic levels. The usefulness of cyclone track-shifting or explicit track modeling is dependent on the appropriateness of the physical assumptions underpinning such a model. In this paper, we utilize a simple spatial statistical model for extreme value estimation of significant wave height under tropical cyclones, known as STM-E, proposed in Wada et al. (2018). The STM-E model was developed to characterize extreme waves offshore Japan, also dominated by tropical cyclones. The method relies on the estimation of two distributions from a sample of data, namely the distribution of spatio-temporal maximum (STM) and the exposure (E). In the current work, we apply STM-E to extreme wave analysis in Gulf of Mexico. The STM-E estimate provides a parsimonious spatially-smooth distribution of extreme waves, with smaller uncertainties per location compared to estimates using data from a single location. We also discuss the estimated characteristics of extreme wave environments in this region.
{"title":"Estimating Extreme Waves in the Gulf of Mexico Using a Simple Spatial Extremes Model","authors":"R. Wada, P. Jonathan, T. Waseda, S. Fan","doi":"10.1115/omae2019-95442","DOIUrl":"https://doi.org/10.1115/omae2019-95442","url":null,"abstract":"\u0000 We seek to characterize the behavior of extreme waves in the Gulf of Mexico, using a 109 year-long wave hindcast (GOMOS). The largest waves in this region are driven by strong winds from hurricanes. Design of offshore production systems requires the estimation of extreme metocean conditions corresponding to return periods from 1 year to 10,000 years and beyond. For extrapolation to long return periods, estimation using data for around 100 years from a single location will incur large uncertainties. Approaches such as spatial pooling, cyclone track-shifting and explicit track modeling have been proposed to alleviate this problem. The underlying problem in spatial pooling is the aggregation of dependent data and hence underestimation of uncertainty using naïve analysis; techniques such as block-bootstrapping can be used to inflate uncertainties to more realistic levels. The usefulness of cyclone track-shifting or explicit track modeling is dependent on the appropriateness of the physical assumptions underpinning such a model.\u0000 In this paper, we utilize a simple spatial statistical model for extreme value estimation of significant wave height under tropical cyclones, known as STM-E, proposed in Wada et al. (2018). The STM-E model was developed to characterize extreme waves offshore Japan, also dominated by tropical cyclones. The method relies on the estimation of two distributions from a sample of data, namely the distribution of spatio-temporal maximum (STM) and the exposure (E). In the current work, we apply STM-E to extreme wave analysis in Gulf of Mexico. The STM-E estimate provides a parsimonious spatially-smooth distribution of extreme waves, with smaller uncertainties per location compared to estimates using data from a single location. We also discuss the estimated characteristics of extreme wave environments in this region.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"25 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":"128317824","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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