Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology最新文献
In Japan, the fundamental disaster management plan was modified after a heavy rainfall event in 2015. According to the updated plan, the transfer of flood disaster risk to non-life insurance is promoted by the Japanese government. Thus, the importance of flood risk modeling for the insurance industry has increased. Winds are expected to become even stronger, resulting in higher storm surges, when the central pressure of the typhoon is intensified. Furthermore, it is possible for an insurance system to experience peak risk when such damage occurs simultaneously. Hence, refining the assessment method of storm surge risk is very important. An insurance company to which storm surge risk is transferred needs to assess not only the infrequent risks, for managing the risk of the company, but also the expected value of the estimated loss, for evaluating the insurance premium. However, only a few studies have assessed storm surges by stochastic approaches. In this study, storm surge losses along the coast of Tokyo Bay are predicted using the output of a stochastic typhoon model for 10,000 years. Storm surge losses due to 600 typhoons potentially causing storm surge damage for 10,000 years are calculated. Exceedance probability curves (EP curves) of estimated storm surge loss for each asset are created. Expected loss and the loss of representative return periods are evaluated based on these EP curves. We successfully determined the expected loss with a small calculation load.
{"title":"Estimation of Expected Loss by Storm Surges Along Tokyo Bay Coast","authors":"Rikito Hisamatsu, Sooyoul Kim, S. Tabeta","doi":"10.1115/omae2019-95336","DOIUrl":"https://doi.org/10.1115/omae2019-95336","url":null,"abstract":"\u0000 In Japan, the fundamental disaster management plan was modified after a heavy rainfall event in 2015. According to the updated plan, the transfer of flood disaster risk to non-life insurance is promoted by the Japanese government. Thus, the importance of flood risk modeling for the insurance industry has increased.\u0000 Winds are expected to become even stronger, resulting in higher storm surges, when the central pressure of the typhoon is intensified. Furthermore, it is possible for an insurance system to experience peak risk when such damage occurs simultaneously. Hence, refining the assessment method of storm surge risk is very important.\u0000 An insurance company to which storm surge risk is transferred needs to assess not only the infrequent risks, for managing the risk of the company, but also the expected value of the estimated loss, for evaluating the insurance premium. However, only a few studies have assessed storm surges by stochastic approaches.\u0000 In this study, storm surge losses along the coast of Tokyo Bay are predicted using the output of a stochastic typhoon model for 10,000 years. Storm surge losses due to 600 typhoons potentially causing storm surge damage for 10,000 years are calculated. Exceedance probability curves (EP curves) of estimated storm surge loss for each asset are created. Expected loss and the loss of representative return periods are evaluated based on these EP curves. We successfully determined the expected loss with a small calculation load.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"81 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123257961","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}
G. McCauley, H. Wolgamot, S. Draper, J. Orszaghova
Water wave propagation over shallowly submerged structures is of much interest in the context of submerged wave energy devices, breakwaters or barrier reefs. This work examines waves passing over a two-dimensional shallowly submerged fixed step extending to the seabed. The problem has been modelled in CFD using the open source toolbox OpenFoam utilising the Reynolds Averaged Navier-Stokes Equations. These simulations are compared to experimental work from a previous study as means of validation and extended to larger amplitude waves for a single incident wave frequency. The flow over the step is characterised and examined in the context of developing an efficient hybrid numerical model for the problem.
{"title":"Wave Interaction With a Shallowly Submerged Step in 2D","authors":"G. McCauley, H. Wolgamot, S. Draper, J. Orszaghova","doi":"10.1115/omae2019-95933","DOIUrl":"https://doi.org/10.1115/omae2019-95933","url":null,"abstract":"\u0000 Water wave propagation over shallowly submerged structures is of much interest in the context of submerged wave energy devices, breakwaters or barrier reefs. This work examines waves passing over a two-dimensional shallowly submerged fixed step extending to the seabed. The problem has been modelled in CFD using the open source toolbox OpenFoam utilising the Reynolds Averaged Navier-Stokes Equations. These simulations are compared to experimental work from a previous study as means of validation and extended to larger amplitude waves for a single incident wave frequency. The flow over the step is characterised and examined in the context of developing an efficient hybrid numerical model for the problem.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"165 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132469520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To investigate the edge effect on numerical calculation of nonlinear forces for a moving body in the time domain, a large body motion model with linear free surface condition is developed with higher-order boundary element method. Five numerical formulations are used to compute the nonlinear radiation forces on submerged surging bodies with sharp edge and a small chamfer radius at the edge. It is found that for those bodies with smooth surface, the nonlinear radiation forces obtained by all of the numerical formulations are close to each other, but large disperses exist for the body with sharp edge. Examination on the vertical nonlinear radiation forces shows that the method on momentum change rate is insensitive to the small edge radius even the chamfer radius is zero, but the other formulations diverse when the edge radius approaches zero. It is suggested that for a body with sharp edge, the method on momentum change rate should be used, or to replace the body surface by the body with a small radius at its sharp edge.
{"title":"Edge Effect on Numerical Calculation of Nonlinear Radiation Forces for a Submerged Body","authors":"Jianye Yang, B. Teng, Y. Gou","doi":"10.1115/omae2019-95421","DOIUrl":"https://doi.org/10.1115/omae2019-95421","url":null,"abstract":"\u0000 To investigate the edge effect on numerical calculation of nonlinear forces for a moving body in the time domain, a large body motion model with linear free surface condition is developed with higher-order boundary element method. Five numerical formulations are used to compute the nonlinear radiation forces on submerged surging bodies with sharp edge and a small chamfer radius at the edge. It is found that for those bodies with smooth surface, the nonlinear radiation forces obtained by all of the numerical formulations are close to each other, but large disperses exist for the body with sharp edge. Examination on the vertical nonlinear radiation forces shows that the method on momentum change rate is insensitive to the small edge radius even the chamfer radius is zero, but the other formulations diverse when the edge radius approaches zero. It is suggested that for a body with sharp edge, the method on momentum change rate should be used, or to replace the body surface by the body with a small radius at its sharp edge.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132148682","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}
Flexible risers are commonly used in ultra deepwater offshore fields to convey fluids from the subsea equipment to the floating production unit. During the development of the production systems, the flexible pipe installation is a critical operation. In this scenario, an operational procedure for the installation frequently used in offshore Brazil is known as Direct Vertical Connection. In this concept, the Vertical Connection Module (VCM) is connected to the flexible pipe through a flanged joint, and lowered in to the subsea equipment with assistance of an installing cable. During the installation procedure, excessive loads may occur in the VCM due to reaction loads induced by the flexible pipe. The present paper aims to describe the Direct Vertical Connection installation and to propose a methodology to study the forces induced by the flexible pipe into the VCM during such operation. For this purpose, a numerical model is developed for the Direct Vertical Connection and it is represented to simulate the installation procedure through a commercial software OrcaFlex. The dynamic behavior of the system is investigated by varying the payout velocity of the installing cable, and the results are shown in terms of bending moment, wall tension and shear forces acting in the flange of the VCM. Numerical simulation result in the present work allows to evaluate the range of loading which acts during the Direct Vertical Connection to help operational design of the installation process, and avoid failure of components during the procedure.
{"title":"Evaluation of Contact Forces in the Vertical Connection of a Flexible Riser in the Subsea Equipment","authors":"Yuri Coelho Del’ Sarto, R. Franciss, C. Morooka","doi":"10.1115/omae2019-95204","DOIUrl":"https://doi.org/10.1115/omae2019-95204","url":null,"abstract":"\u0000 Flexible risers are commonly used in ultra deepwater offshore fields to convey fluids from the subsea equipment to the floating production unit. During the development of the production systems, the flexible pipe installation is a critical operation. In this scenario, an operational procedure for the installation frequently used in offshore Brazil is known as Direct Vertical Connection. In this concept, the Vertical Connection Module (VCM) is connected to the flexible pipe through a flanged joint, and lowered in to the subsea equipment with assistance of an installing cable. During the installation procedure, excessive loads may occur in the VCM due to reaction loads induced by the flexible pipe.\u0000 The present paper aims to describe the Direct Vertical Connection installation and to propose a methodology to study the forces induced by the flexible pipe into the VCM during such operation. For this purpose, a numerical model is developed for the Direct Vertical Connection and it is represented to simulate the installation procedure through a commercial software OrcaFlex.\u0000 The dynamic behavior of the system is investigated by varying the payout velocity of the installing cable, and the results are shown in terms of bending moment, wall tension and shear forces acting in the flange of the VCM. Numerical simulation result in the present work allows to evaluate the range of loading which acts during the Direct Vertical Connection to help operational design of the installation process, and avoid failure of components during the procedure.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122630309","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 work considers the numerical modelling of wave interaction with thin porous structures, based on tests conducted in simplified conditions. Wave flume tests were conducted to measure the wave loads on thin porous sheets extending over the full water column. The porous sheets tested had a range of porosities, hole separation distances and thicknesses. Numerical and analytic models for the wave forces on the porous sheet are formulated under the assumptions of either a linear or quadratic pressure loss across the porous sheet. An iterative boundary element method (BEM) model is formulated to solve the quadratic pressure loss across the porous sheet. It is shown that the assumption of a linear pressure loss at the porous boundary is inadequate to capture the variation in the wave load with both wave frequency and amplitude, but that the quadratic model is in good agreement with the measured forces. The porosity of the sheet is shown to have the dominant effect on the wave loads. The hole separation distance affects the phase of the force on the porous wall, but has only a small effect on the amplitude of the force. The sheet thickness is shown to have a small effect on the amplitude of the force but a significant effect on the phase of the force. The results are of interest for numerical modelling of structures with thin porous boundaries in a wide range of contexts such as breakwaters, aquaculture and offshore structures with porous elements designed to reduce loads.
{"title":"Numerical and Experimental Modelling of Wave Loads on Thin Porous Sheets","authors":"E. Mackay, L. Johanning, D. Ning, D. Qiao","doi":"10.1115/OMAE2019-95148","DOIUrl":"https://doi.org/10.1115/OMAE2019-95148","url":null,"abstract":"\u0000 This work considers the numerical modelling of wave interaction with thin porous structures, based on tests conducted in simplified conditions. Wave flume tests were conducted to measure the wave loads on thin porous sheets extending over the full water column. The porous sheets tested had a range of porosities, hole separation distances and thicknesses. Numerical and analytic models for the wave forces on the porous sheet are formulated under the assumptions of either a linear or quadratic pressure loss across the porous sheet. An iterative boundary element method (BEM) model is formulated to solve the quadratic pressure loss across the porous sheet.\u0000 It is shown that the assumption of a linear pressure loss at the porous boundary is inadequate to capture the variation in the wave load with both wave frequency and amplitude, but that the quadratic model is in good agreement with the measured forces. The porosity of the sheet is shown to have the dominant effect on the wave loads. The hole separation distance affects the phase of the force on the porous wall, but has only a small effect on the amplitude of the force. The sheet thickness is shown to have a small effect on the amplitude of the force but a significant effect on the phase of the force.\u0000 The results are of interest for numerical modelling of structures with thin porous boundaries in a wide range of contexts such as breakwaters, aquaculture and offshore structures with porous elements designed to reduce loads.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125475200","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}
Gang Wang, R. Wan, Liu-yi Huang, F. Zhao, Xinxin Wang, Wenbin Zhu, Wang Lei, Qingchang Xu, Yuyan Li
In this present work, effects of three Euler angles (Angle of Attack (AOA), Angle of Trim (AOT), Angle of Pitch (AOP)) of vertical cambered otter board on hydrodynamic characteristics (drag coefficient (Cd), lift coefficient (Cl), center-of-pressure coefficients (Cp)) were studied based on numerical simulation combined with Kriging Response Surface Methodology (KRSM) and Multi-Objective Genetic Algorithm (MOGA). Wind tunnel experiments were carried out to validate the accuracy of response surface based on numerical simulation. It was demonstrated that AOA had prominent effects on Cd and Cl, while AOT and AOP had less effects. The working posture of otter board were recommended to lean inwards (0°∼6°) and forward (−10°∼0°) to improve the lift-drag ratio without sacrificing Cl. The influences of AOT and AOP on positions of center-of-pressure point were less significant than that of AOA and decreasing with the increase of AOA. In addition, response surface of hydrodynamic coefficients around the critical AOA was a decent indicator of occurrence of stall. Finally, three candidate cases were selected to satisfy the high working efficiency by MOGA, which was consistent with the above recommendations. This study provided a scientific reference of response surface experimental investigations methodology and the configuration of Euler angles of otter board.
{"title":"Effects of Euler Angles of Vertical Cambered Otter Board on Hydrodynamics Based on Response Surface Methodology and MOGA","authors":"Gang Wang, R. Wan, Liu-yi Huang, F. Zhao, Xinxin Wang, Wenbin Zhu, Wang Lei, Qingchang Xu, Yuyan Li","doi":"10.1115/omae2019-95308","DOIUrl":"https://doi.org/10.1115/omae2019-95308","url":null,"abstract":"\u0000 In this present work, effects of three Euler angles (Angle of Attack (AOA), Angle of Trim (AOT), Angle of Pitch (AOP)) of vertical cambered otter board on hydrodynamic characteristics (drag coefficient (Cd), lift coefficient (Cl), center-of-pressure coefficients (Cp)) were studied based on numerical simulation combined with Kriging Response Surface Methodology (KRSM) and Multi-Objective Genetic Algorithm (MOGA). Wind tunnel experiments were carried out to validate the accuracy of response surface based on numerical simulation. It was demonstrated that AOA had prominent effects on Cd and Cl, while AOT and AOP had less effects. The working posture of otter board were recommended to lean inwards (0°∼6°) and forward (−10°∼0°) to improve the lift-drag ratio without sacrificing Cl. The influences of AOT and AOP on positions of center-of-pressure point were less significant than that of AOA and decreasing with the increase of AOA. In addition, response surface of hydrodynamic coefficients around the critical AOA was a decent indicator of occurrence of stall. Finally, three candidate cases were selected to satisfy the high working efficiency by MOGA, which was consistent with the above recommendations. This study provided a scientific reference of response surface experimental investigations methodology and the configuration of Euler angles of otter board.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"293 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131966186","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 rotation on the behavior of a two-dimensional rotating cylinder in flow was investigated by using the discrete vortex method combined with the 4th order Runge-Kutta method. There are three stages for rotational speed dependence of hydrodynamic force on a fixed rotating cylinder, the stage where lift force increases and drag force decreases, the stage where lift and drag forces increase in proportion to the square of rotation ratio, and the stage where lift and drag forces increase in proportion to rotation ratio. As a fixed rotating cylinder begins to rotate and the rotational speed increases, the vortex train that causes VIV weakens and disappears. When the cylinder is mounted on a spring, the vibration frequency of the spring mounted rotating cylinder becomes lower. This indicates that the added mass of the rotating cylinder is increasing as the rotation ratio increases.
{"title":"Investigation of the 2D Behavior of a Rotating Cylinder in Flow Using the Discrete Vortex Method","authors":"C. Rheem","doi":"10.1115/omae2019-95841","DOIUrl":"https://doi.org/10.1115/omae2019-95841","url":null,"abstract":"\u0000 The influence of rotation on the behavior of a two-dimensional rotating cylinder in flow was investigated by using the discrete vortex method combined with the 4th order Runge-Kutta method. There are three stages for rotational speed dependence of hydrodynamic force on a fixed rotating cylinder, the stage where lift force increases and drag force decreases, the stage where lift and drag forces increase in proportion to the square of rotation ratio, and the stage where lift and drag forces increase in proportion to rotation ratio. As a fixed rotating cylinder begins to rotate and the rotational speed increases, the vortex train that causes VIV weakens and disappears. When the cylinder is mounted on a spring, the vibration frequency of the spring mounted rotating cylinder becomes lower. This indicates that the added mass of the rotating cylinder is increasing as the rotation ratio increases.","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":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126518229","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}
Haoyu Ding, J. Zang, D. Ning, Xuanlie Zhao, Qiang Chen, C. Blenkinsopp, Junliang Gao
A new type of coastal structure is proposed to reduce construction-cost and construction-space by integrating wave energy converters (WECs) into breakwater system. To develop this type of system to be more stable and effective, this paper focuses on investigating and improving an existing concept of integrated WEC type of breakwater system using a numerical method based on OpenFOAM®. Validation of the numerical setup is conducted by comparing the numerical predictions with relevant experimental data collected in a wave tank at Dalian University of Technology. The integrated WEC type of breakwater system considered in this paper is a pile-restrained WEC-type dual-floating breakwater system. The two floating breakwaters in this system are constrained to heave motion independently and work as a heaving-oscillating buoy type of WECs driven by a linear power take-off damping system (PTO system). Two parameters including wave transmission factor and capture width ratio (which is defined as the ratio of absorbed wave power to the incident wave power in the device width) are studied and discussed in the paper. The range of effective frequencies (range with wave transmission factor KT < 0.5 and capture width ratio CWR > 0.2) is obtained to evaluate the performance of this system with regard to both breakwater and WEC. These results indicate that damping coefficient of PTO system and gap width between two floating bodies influence wave transmission factor and capture width ratio, and the range of effective frequencies can be improved by the appropriate damping coefficient and gap width.
{"title":"Evaluation of the Performance of an Integrated WEC Type of Breakwater System","authors":"Haoyu Ding, J. Zang, D. Ning, Xuanlie Zhao, Qiang Chen, C. Blenkinsopp, Junliang Gao","doi":"10.1115/omae2019-95739","DOIUrl":"https://doi.org/10.1115/omae2019-95739","url":null,"abstract":"\u0000 A new type of coastal structure is proposed to reduce construction-cost and construction-space by integrating wave energy converters (WECs) into breakwater system. To develop this type of system to be more stable and effective, this paper focuses on investigating and improving an existing concept of integrated WEC type of breakwater system using a numerical method based on OpenFOAM®. Validation of the numerical setup is conducted by comparing the numerical predictions with relevant experimental data collected in a wave tank at Dalian University of Technology. The integrated WEC type of breakwater system considered in this paper is a pile-restrained WEC-type dual-floating breakwater system. The two floating breakwaters in this system are constrained to heave motion independently and work as a heaving-oscillating buoy type of WECs driven by a linear power take-off damping system (PTO system). Two parameters including wave transmission factor and capture width ratio (which is defined as the ratio of absorbed wave power to the incident wave power in the device width) are studied and discussed in the paper. The range of effective frequencies (range with wave transmission factor KT < 0.5 and capture width ratio CWR > 0.2) is obtained to evaluate the performance of this system with regard to both breakwater and WEC. These results indicate that damping coefficient of PTO system and gap width between two floating bodies influence wave transmission factor and capture width ratio, and the range of effective frequencies can be improved by the appropriate damping coefficient and gap width.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"154 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114793991","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}
Artificial reefs (ARs) are structures constructed on the seabed to attract and concentrate fish and to potentially improve and rehabilitate coastal ecosystems. In order to investigate the hydrodynamic characteristics of ARs, a series of model experiments of cubic artificial reefs are carried out in the flume. The model reefs are made of acrylic material with different shapes of opening and various open-area ratios. The hydrodynamic forces of the models are measured in the experiments. The changes of drag coefficient with respect to the open-area ratio and the flow-facing angle of attack are investigated and discussed respectively.
{"title":"Experimental Study on the Hydrodynamic Characteristics of Artificial Reefs","authors":"F. Zhao, M. Ong, Yanli Tang, Xinmeng Wang","doi":"10.1115/omae2019-96019","DOIUrl":"https://doi.org/10.1115/omae2019-96019","url":null,"abstract":"\u0000 Artificial reefs (ARs) are structures constructed on the seabed to attract and concentrate fish and to potentially improve and rehabilitate coastal ecosystems. In order to investigate the hydrodynamic characteristics of ARs, a series of model experiments of cubic artificial reefs are carried out in the flume. The model reefs are made of acrylic material with different shapes of opening and various open-area ratios. The hydrodynamic forces of the models are measured in the experiments. The changes of drag coefficient with respect to the open-area ratio and the flow-facing angle of attack are investigated and discussed respectively.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115982823","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}
Modulational instability of nonlinear waves in dispersive environments is known across a broad range of physical media, from nonlinear optics to waves in plasmas. Since it was discovered for the surface water waves in the early 60s, it was found responsible for, or able to contribute to the topics of breaking and rogue waves, swell, ice breakup, wave-current interactions and perhaps even spray production. Since the early days, however, the argument continues on whether the modulational instability, which is essentially a one-dimensional phenomenon, is active in directional wave fields (that is whether the realistic directional spectra are narrow enough to maintain such nonlinear behaviours). Here we discuss the distinct features of the evolution of nonlinear surface gravity waves, which should be attributed as signatures to this instability in oceanic wind-generated wave fields. These include: wave-breaking threshold in terms of average steepness; upshifting of the spectral energy prior to breaking; oscillations of wave asymmetry and skewness; energy loss from the carrier waves in the course of the breaking. We will also refer to the linear/nonlinear superposition of waves which is often considered a counterpart (or competing) mechanism responsible for breaking or rogue waves in the ocean. We argue that both mechanisms are physically possible and the question of in situ abnormal waves is a problem of their relative significance in specific circumstances.
{"title":"On Signatures and Features of Modulational Instability in Ocean Waves","authors":"A. Babanin","doi":"10.1115/omae2019-95633","DOIUrl":"https://doi.org/10.1115/omae2019-95633","url":null,"abstract":"Modulational instability of nonlinear waves in dispersive environments is known across a broad range of physical media, from nonlinear optics to waves in plasmas. Since it was discovered for the surface water waves in the early 60s, it was found responsible for, or able to contribute to the topics of breaking and rogue waves, swell, ice breakup, wave-current interactions and perhaps even spray production. Since the early days, however, the argument continues on whether the modulational instability, which is essentially a one-dimensional phenomenon, is active in directional wave fields (that is whether the realistic directional spectra are narrow enough to maintain such nonlinear behaviours). Here we discuss the distinct features of the evolution of nonlinear surface gravity waves, which should be attributed as signatures to this instability in oceanic wind-generated wave fields. These include: wave-breaking threshold in terms of average steepness; upshifting of the spectral energy prior to breaking; oscillations of wave asymmetry and skewness; energy loss from the carrier waves in the course of the breaking. We will also refer to the linear/nonlinear superposition of waves which is often considered a counterpart (or competing) mechanism responsible for breaking or rogue waves in the ocean. We argue that both mechanisms are physically possible and the question of in situ abnormal waves is a problem of their relative significance in specific circumstances.","PeriodicalId":120800,"journal":{"name":"Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131797799","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：