We study deep water ocean wind-driven waves in strait, with wind directed orthogonally to the shore, through exact Hassel-mann equation. The strait has “dissipative” shores, there is no any reflection from the coast lines. We show that the wave turbulence evolution can be split in time into two different regimes. During the first regime, the waves propagate along the wind, and the wind-driven sea can be described by the self-similar solutions of Hasselmann equation. The second regime starts later in time, after significant enough wave energy accumulation at the down-wind boundary. Since this moment the ensemble of waves propagating against the wind starts its formation. Also, orthogonal to the wind waves, propagating along the strait, start to appear. The wave system eventually reaches asymptotic stationary state in time, consisting of two co-existing states: the first, self-similar wave ensemble, propagating with the wind, and the second – quasi-monochromatic waves, propagating almost orthogonally to the wind direction, and tending to slant against the wind at the angle of 15° closer to the wave turbulence origination shore line. Those “secondary waves” appear only due to intensive nonlinear wave-wave interaction. The total wave energy exceeds its “expected value” approximately by the factor of two, with respect to estimated in the absence of the shores. It is expected that in the reflective shores presence this amplification will grow essentially. We propose to call this “secondary” laser-like Nonlinear Ocean Waves Amplification mechanism by the acronym NOWA.
{"title":"Nonlinear Laser-Like Ocean Waves Radiation Orthogonal to the Wind","authors":"A. Pushkarev, V. Zakharov","doi":"10.1115/omae2020-19357","DOIUrl":"https://doi.org/10.1115/omae2020-19357","url":null,"abstract":"We study deep water ocean wind-driven waves in strait, with wind directed orthogonally to the shore, through exact Hassel-mann equation. The strait has “dissipative” shores, there is no any reflection from the coast lines. We show that the wave turbulence evolution can be split in time into two different regimes. During the first regime, the waves propagate along the wind, and the wind-driven sea can be described by the self-similar solutions of Hasselmann equation. The second regime starts later in time, after significant enough wave energy accumulation at the down-wind boundary. Since this moment the ensemble of waves propagating against the wind starts its formation. Also, orthogonal to the wind waves, propagating along the strait, start to appear. The wave system eventually reaches asymptotic stationary state in time, consisting of two co-existing states: the first, self-similar wave ensemble, propagating with the wind, and the second – quasi-monochromatic waves, propagating almost orthogonally to the wind direction, and tending to slant against the wind at the angle of 15° closer to the wave turbulence origination shore line. Those “secondary waves” appear only due to intensive nonlinear wave-wave interaction. The total wave energy exceeds its “expected value” approximately by the factor of two, with respect to estimated in the absence of the shores. It is expected that in the reflective shores presence this amplification will grow essentially. We propose to call this “secondary” laser-like Nonlinear Ocean Waves Amplification mechanism by the acronym NOWA.","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129998469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Düz, J. Scharnke, R. Hallmann, J. Tukker, S. Khurana, Kevin Blanchard
The kinematics under spilling and plunging breakers are investigated using both experimental and numerical methods. In a modular laboratory flume, the breakers were generated using dispersive focusing, and the kinematics underneath them were measured utilizing the Particle Image Velocimetry (PIV) technique. Using the state-of-art high-speed video cameras and lasers, the kinematics were measured at a high sampling rate without needing phase-locked averaging. Afterwards, Computational Fluid Dynamics (CFD) simulations were carried out for comparison purposes. These simulations were run in single-phase using a finite-volume based Navier-Stokes solver with a piecewise-linear interface reconstruction scheme. The spilling and plunging breakers from the measurements were reconstructed in the computational domain using an iterative scheme. As a result a good match with the measured waves was obtained in the simulations. Results indicate that even though measured kinematics are somewhat higher than the simulated ones especially in the spilling and overturning regions, the CFD simulations can accurately capture the relevant details of the flow and produce reasonably accurate kinematics in comparison with the PIV results.
{"title":"Comparison of the CFD Results to PIV Measurements in Kinematics of Spilling and Plunging Breakers","authors":"B. Düz, J. Scharnke, R. Hallmann, J. Tukker, S. Khurana, Kevin Blanchard","doi":"10.1115/omae2020-19268","DOIUrl":"https://doi.org/10.1115/omae2020-19268","url":null,"abstract":"\u0000 The kinematics under spilling and plunging breakers are investigated using both experimental and numerical methods. In a modular laboratory flume, the breakers were generated using dispersive focusing, and the kinematics underneath them were measured utilizing the Particle Image Velocimetry (PIV) technique. Using the state-of-art high-speed video cameras and lasers, the kinematics were measured at a high sampling rate without needing phase-locked averaging. Afterwards, Computational Fluid Dynamics (CFD) simulations were carried out for comparison purposes. These simulations were run in single-phase using a finite-volume based Navier-Stokes solver with a piecewise-linear interface reconstruction scheme. The spilling and plunging breakers from the measurements were reconstructed in the computational domain using an iterative scheme. As a result a good match with the measured waves was obtained in the simulations. Results indicate that even though measured kinematics are somewhat higher than the simulated ones especially in the spilling and overturning regions, the CFD simulations can accurately capture the relevant details of the flow and produce reasonably accurate kinematics in comparison with the PIV results.","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122065431","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}
Submerged floating tunnel (SFT) concept has been studied by many researchers as an alternative of conventional or floating bridges, especially in the fjord or as a connection between island and land. One of the major challenges is large dynamic responses under extreme wave and earthquake excitations. In this regard, two different types of SFT, which are mono and dual SFTs, are suggested in this study, and the global performance of them is compared through tunnel-mooring fully-coupled time-domain numerical simulations. The tunnel and mooring lines are modeled by the lumped-mass-based line model. The Morison equation is utilized for hydrodynamic load estimations of the tunnel and mooring lines at their instantaneous positions. To check dynamic response of SFT under operating condition, 10-yr waves with the current are considered as an environmental condition. Dynamic responses, mooring tensions, and inertial and drag forces are systematically compared.
{"title":"Dynamic Response Comparison of Mono and Dual Submerged Floating Tunnels","authors":"W. Chung, Chungkuk Jin, Moo-Hyun Kim","doi":"10.1115/omae2020-18882","DOIUrl":"https://doi.org/10.1115/omae2020-18882","url":null,"abstract":"\u0000 Submerged floating tunnel (SFT) concept has been studied by many researchers as an alternative of conventional or floating bridges, especially in the fjord or as a connection between island and land. One of the major challenges is large dynamic responses under extreme wave and earthquake excitations. In this regard, two different types of SFT, which are mono and dual SFTs, are suggested in this study, and the global performance of them is compared through tunnel-mooring fully-coupled time-domain numerical simulations. The tunnel and mooring lines are modeled by the lumped-mass-based line model. The Morison equation is utilized for hydrodynamic load estimations of the tunnel and mooring lines at their instantaneous positions. To check dynamic response of SFT under operating condition, 10-yr waves with the current are considered as an environmental condition. Dynamic responses, mooring tensions, and inertial and drag forces are systematically compared.","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124377474","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}
Surrogate modeling of the variability of metocean conditions in space and in time during hurricanes is a crucial task for risk analysis on offshore structures such as offshore wind turbines, which are deployed over a large area. This task is challenging because of the complex nature of the meteorology-metocean interaction in addition to the time-dependence and high-dimensionality of the output. In this paper, spatio-temporal characteristics of surrogate models, such as Deep Neural Networks, are analyzed based on an offshore multi-hazard database created by the authors. The focus of this paper is two-fold: first, the effectiveness of dimension reduction techniques for representing high-dimensional output distributed in space is investigated and, second, an overall approach to estimate spatio-temporal characteristics of hurricane hazards using Deep Neural Networks is presented. The popular dimension reduction technique, Principal Component Analysis, is shown to perform similarly compared to a simpler dimension reduction approach and to not perform as well as a surrogate model implemented without dimension reduction. Discussions are provided to explain why the performance of Principal Component Analysis is only mediocre in this implementation and why dimension reduction might not be necessary.
{"title":"Modeling Spatio-Temporal Characteristics of Metocean Conditions During Hurricanes Using Deep Neural Networks","authors":"C. Qiao, A. Myers","doi":"10.1115/omae2020-18989","DOIUrl":"https://doi.org/10.1115/omae2020-18989","url":null,"abstract":"\u0000 Surrogate modeling of the variability of metocean conditions in space and in time during hurricanes is a crucial task for risk analysis on offshore structures such as offshore wind turbines, which are deployed over a large area. This task is challenging because of the complex nature of the meteorology-metocean interaction in addition to the time-dependence and high-dimensionality of the output. In this paper, spatio-temporal characteristics of surrogate models, such as Deep Neural Networks, are analyzed based on an offshore multi-hazard database created by the authors. The focus of this paper is two-fold: first, the effectiveness of dimension reduction techniques for representing high-dimensional output distributed in space is investigated and, second, an overall approach to estimate spatio-temporal characteristics of hurricane hazards using Deep Neural Networks is presented. The popular dimension reduction technique, Principal Component Analysis, is shown to perform similarly compared to a simpler dimension reduction approach and to not perform as well as a surrogate model implemented without dimension reduction. Discussions are provided to explain why the performance of Principal Component Analysis is only mediocre in this implementation and why dimension reduction might not be necessary.","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134634546","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}
Extreme value analysis of significant wave height using data from a single location often incurs large uncertainty due to small sample size. Including wave data from nearby locations increases sample size at the risk of introducing dependency between extreme events and hence violating modelling assumptions. In this work, we consider extreme value analysis of spatial wave data from the 109-year GOMOS wave hindcast for the Gulf of Mexico, seeking to incorporate the effects of spatial dependence in a simple but effective manner. We demonstrate that, for estimation of return values at a given location, incorporation of data from a circular disk region with radius of approximately 5° (long.-lat.), centred at the location of interest, provides an appropriate basis for extreme value analysis using the STM-E approach of Wada et al. (2018).
{"title":"Spatial Features of Extreme Waves in Gulf of Mexico","authors":"R. Wada, P. Jonathan, T. Waseda","doi":"10.1115/omae2020-19190","DOIUrl":"https://doi.org/10.1115/omae2020-19190","url":null,"abstract":"\u0000 Extreme value analysis of significant wave height using data from a single location often incurs large uncertainty due to small sample size. Including wave data from nearby locations increases sample size at the risk of introducing dependency between extreme events and hence violating modelling assumptions. In this work, we consider extreme value analysis of spatial wave data from the 109-year GOMOS wave hindcast for the Gulf of Mexico, seeking to incorporate the effects of spatial dependence in a simple but effective manner. We demonstrate that, for estimation of return values at a given location, incorporation of data from a circular disk region with radius of approximately 5° (long.-lat.), centred at the location of interest, provides an appropriate basis for extreme value analysis using the STM-E approach of Wada et al. (2018).","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125003982","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}
S. Wahls, M. Brühl, Yang-Ming Fan, Ching-Jer Huang
Nonlinear Fourier Analysis (NFA) is a powerful tool for the analysis of hydrodynamic processes. The unique capabilities of NFA include, but are not limited to, the detection of hidden solitons and the detection of modulation instability, which are essential for the understanding of nonlinear phenomena such as rogue waves. However, even though NFA has been applied to many interesting problems, it remains a non-standard tool. Recently, an open source software library called FNFT has been released to the public. (FNFT is short for “Fast Nonlinear Fourier Transforms”.) The library in particular contains code for the efficient numerical NFA of hydrodynamic processes that are approximately governed by the nonlinear Schroedinger equation with periodic boundary conditions. Waves in deep water are a prime example for such a process. In this paper, we use FNFT to perform an exemplary NFA of typhoon data collected by wave buoys at the coast of Taiwan. Our goals are a) to demonstrate the application of FNFT in a practical scenario, and b) to compare the results of a NFA to an analysis based on the conventional linear Fourier transform. The exposition is deliberately educational, hopefully enabling others to use FNFT for similar analyses of their own data.
{"title":"Nonlinear Fourier Analysis of Free-Surface Buoy Data Using the Software Library FNFT","authors":"S. Wahls, M. Brühl, Yang-Ming Fan, Ching-Jer Huang","doi":"10.1115/omae2020-18676","DOIUrl":"https://doi.org/10.1115/omae2020-18676","url":null,"abstract":"\u0000 Nonlinear Fourier Analysis (NFA) is a powerful tool for the analysis of hydrodynamic processes. The unique capabilities of NFA include, but are not limited to, the detection of hidden solitons and the detection of modulation instability, which are essential for the understanding of nonlinear phenomena such as rogue waves. However, even though NFA has been applied to many interesting problems, it remains a non-standard tool. Recently, an open source software library called FNFT has been released to the public. (FNFT is short for “Fast Nonlinear Fourier Transforms”.) The library in particular contains code for the efficient numerical NFA of hydrodynamic processes that are approximately governed by the nonlinear Schroedinger equation with periodic boundary conditions. Waves in deep water are a prime example for such a process. In this paper, we use FNFT to perform an exemplary NFA of typhoon data collected by wave buoys at the coast of Taiwan. Our goals are a) to demonstrate the application of FNFT in a practical scenario, and b) to compare the results of a NFA to an analysis based on the conventional linear Fourier transform. The exposition is deliberately educational, hopefully enabling others to use FNFT for similar analyses of their own data.","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127398752","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}
S. Reijmerink, N. Bruinsma, A. V. D. Hout, M. D. Jong, C. Clément
Moored vessels often experience low-frequency vessel motions when moored in a port due to wave excitation. Under such conditions the loading and offloading of vessels may be hampered when these movements become too large [1,2,3]. Innovative mooring techniques can be used for reducing issues with excessive motions of moored vessels in waves [4,5,6]. Considering applying such techniques as part of the design of mooring facilities and ports is expected to make different approaches to port or mooring facility designs possible. Such techniques, like the ShoreTension (ST) system, are already applied successfully worldwide in ports [7,8,9], however the application and performance limits of such systems under extreme conditions are not well known. This paper describes the results of a research project using physical scale modelling to systematically verify and extend the applicability and performance limits of innovative mooring systems. It resulted in a solid validation database for validating numerical models. The knowledge developed in this research will benefit developers of mooring facilities (including ports) to significantly reduce costs by limiting the need for structures providing shelter from waves. Furthermore, this may also help lowering the impact of port infrastructure on the coastal system when using less invasive infrastructure.
{"title":"Innovative Mooring in the Port of the Future: Scale Model Testing of the ShoreTension System","authors":"S. Reijmerink, N. Bruinsma, A. V. D. Hout, M. D. Jong, C. Clément","doi":"10.1115/omae2020-18167","DOIUrl":"https://doi.org/10.1115/omae2020-18167","url":null,"abstract":"\u0000 Moored vessels often experience low-frequency vessel motions when moored in a port due to wave excitation. Under such conditions the loading and offloading of vessels may be hampered when these movements become too large [1,2,3]. Innovative mooring techniques can be used for reducing issues with excessive motions of moored vessels in waves [4,5,6]. Considering applying such techniques as part of the design of mooring facilities and ports is expected to make different approaches to port or mooring facility designs possible. Such techniques, like the ShoreTension (ST) system, are already applied successfully worldwide in ports [7,8,9], however the application and performance limits of such systems under extreme conditions are not well known.\u0000 This paper describes the results of a research project using physical scale modelling to systematically verify and extend the applicability and performance limits of innovative mooring systems. It resulted in a solid validation database for validating numerical models. The knowledge developed in this research will benefit developers of mooring facilities (including ports) to significantly reduce costs by limiting the need for structures providing shelter from waves. Furthermore, this may also help lowering the impact of port infrastructure on the coastal system when using less invasive infrastructure.","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130650567","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 pump-jet propulsor consists of a duct, a rotor and stators which are installed upstream of the rotor to provide pre-swirl flow or downstream of rotor to absorb the kinetic energy in the flow. The strong interactions between the three components and the vehicle are closely related to their design and exert great effect on noise and hydrodynamic performance. This paper attempts to develop an effective and efficient method for the optimal design of the duct and the pre-swirl stators under the influence of vehicle and rotor via viscous flow CFD simulations. In this paper, the two key parameters, attack angle of the duct and pitch angle of pre-swirl stators, are investigated. The numerical simulations are based on the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations using a two-layer realizable k-ε model for turbulence closure. The computational domain is discretized into mixed unstructured cells. The software package STAR-CCM+ is used for both grid generations and flow simulations. The rotor is replaced by the body-force model which is proposed according to the load distribution of the rotor in pump-jet propulsor. Total thrust of body force balances the resistance of a fully-appended underwater vehicle and its propulsor in the self-propulsion simulations and torque is determined by assuming that the propulsive efficiency is 80%. To the end of the optimal design, the total resistance, as the main consideration, and detailed flow field, such as pressure distribution, are numerically investigated for varied attack angles of the duct and pitch angles of pre-swirl stator. It is shown that the two parameters have significant impact on the performance of the propulsor and the recommended design is given.
泵喷推进器由导管、转子和定子组成，定子安装在转子的上游以提供预旋流或安装在转子的下游以吸收流动中的动能。这三个部件与车辆之间的强相互作用与它们的设计密切相关，并对噪声和水动力性能产生很大影响。本文试图通过粘性流动CFD模拟，建立一种在车辆和转子影响下的风管和预旋定子优化设计的有效方法。本文对风道攻角和预旋定子俯仰角这两个关键参数进行了研究。数值模拟是基于湍流闭合的两层可实现k-ε模型求解reynolds - average Navier-Stokes (RANS)方程。计算域被离散成混合的非结构化单元。STAR-CCM+软件包用于网格生成和流动模拟。根据泵喷推进器中转子的载荷分布，提出了用体力模型代替转子模型。在自推进仿真中，船体力的总推力平衡了全附加式水下航行器与推进器的阻力，在假设推进效率为80%的情况下确定了扭矩。在优化设计的最后，以总阻力为主要考虑因素，对不同风道攻角和预旋定子俯仰角下的流场压力分布等进行了数值研究。结果表明，这两个参数对推进器的性能影响较大，并给出了推荐的设计方案。
{"title":"Numerical Design Study of Duct and Stator for a Pump-Jet Propulsor","authors":"X. Ji, Chen-Jun Yang, Xiaoqian Dong","doi":"10.1115/omae2020-18535","DOIUrl":"https://doi.org/10.1115/omae2020-18535","url":null,"abstract":"\u0000 The pump-jet propulsor consists of a duct, a rotor and stators which are installed upstream of the rotor to provide pre-swirl flow or downstream of rotor to absorb the kinetic energy in the flow. The strong interactions between the three components and the vehicle are closely related to their design and exert great effect on noise and hydrodynamic performance. This paper attempts to develop an effective and efficient method for the optimal design of the duct and the pre-swirl stators under the influence of vehicle and rotor via viscous flow CFD simulations. In this paper, the two key parameters, attack angle of the duct and pitch angle of pre-swirl stators, are investigated.\u0000 The numerical simulations are based on the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations using a two-layer realizable k-ε model for turbulence closure. The computational domain is discretized into mixed unstructured cells. The software package STAR-CCM+ is used for both grid generations and flow simulations.\u0000 The rotor is replaced by the body-force model which is proposed according to the load distribution of the rotor in pump-jet propulsor. Total thrust of body force balances the resistance of a fully-appended underwater vehicle and its propulsor in the self-propulsion simulations and torque is determined by assuming that the propulsive efficiency is 80%. To the end of the optimal design, the total resistance, as the main consideration, and detailed flow field, such as pressure distribution, are numerically investigated for varied attack angles of the duct and pitch angles of pre-swirl stator. It is shown that the two parameters have significant impact on the performance of the propulsor and the recommended design is given.","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133610545","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 present paper is concerned with the accurate prediction of nonlinear wave kinematics underneath measured time histories of surface elevation. It is desired to develop a method which is useful in analysis of offshore measurements close to wind turbine foundations. The method should therefore be robust in relatively shallow water and should be able to account for the presence of the foundation and the shortcrestedness of offshore seastates. The present method employs measurements of surface elevation time histories at one or a small number of locations and solves the associated velocity potential by minimizing the error in the free surface boundary conditions. The velocity potential satisfies exactly Laplace’s equation, the bed boundary condition and (optionally) the boundary condition on the wall of a uniform surface piercing column. This is achieved by associating one wavenumber with every wave frequency thereby sacrificing the possibility of following the nonlinear wave evolution but ensuring a good description of the wave properties locally. For shortcrested waves, the direction of wave component propagation is drawn from a known or assumed directional spectrum. No attempt is made to calculate the directional distribution of the wave field from the surface elevation measurements since this is usually not realistically possible with the available data. The method is set up for analysis with or without a uniform current, for shortcrested or longcrested waves and with or without a surface piercing column in the wave field. It has been compared with laboratory data for steep longcrested and shortcrested waves. The method is shown to be in good agreement with measurements. Since the method is based on a Fourier series of surface elevation, however, it cannot model overtopping breaking waves and associated wave impact loading. For problems where wave breaking is important, the method may serve as a screening analysis used to select wave events for detailed analysis using Computational Fluid Dynamics (CFD).
{"title":"Estimating Wave Induced Kinematics Underneath Measured Time Histories of Surface Elevation","authors":"T. B. Johannessen","doi":"10.1115/omae2020-18727","DOIUrl":"https://doi.org/10.1115/omae2020-18727","url":null,"abstract":"\u0000 The present paper is concerned with the accurate prediction of nonlinear wave kinematics underneath measured time histories of surface elevation. It is desired to develop a method which is useful in analysis of offshore measurements close to wind turbine foundations. The method should therefore be robust in relatively shallow water and should be able to account for the presence of the foundation and the shortcrestedness of offshore seastates.\u0000 The present method employs measurements of surface elevation time histories at one or a small number of locations and solves the associated velocity potential by minimizing the error in the free surface boundary conditions. The velocity potential satisfies exactly Laplace’s equation, the bed boundary condition and (optionally) the boundary condition on the wall of a uniform surface piercing column. This is achieved by associating one wavenumber with every wave frequency thereby sacrificing the possibility of following the nonlinear wave evolution but ensuring a good description of the wave properties locally. For shortcrested waves, the direction of wave component propagation is drawn from a known or assumed directional spectrum. No attempt is made to calculate the directional distribution of the wave field from the surface elevation measurements since this is usually not realistically possible with the available data.\u0000 The method is set up for analysis with or without a uniform current, for shortcrested or longcrested waves and with or without a surface piercing column in the wave field. It has been compared with laboratory data for steep longcrested and shortcrested waves. The method is shown to be in good agreement with measurements. Since the method is based on a Fourier series of surface elevation, however, it cannot model overtopping breaking waves and associated wave impact loading. For problems where wave breaking is important, the method may serve as a screening analysis used to select wave events for detailed analysis using Computational Fluid Dynamics (CFD).","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133016981","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}
Saori Yokota, M. Kuroda, Ryohei Fukasawa, Hiroki Ohba, M. Tsujimoto
Considering the sea conditions in which a large ship encountered in operation, the ship’s behavior in very short waves is important. However, the evaluation of the ship performance in very short waves was not enough validated by tank tests. Because it is difficult to generate waves with enough accuracy due to the performance of the wave generator. In this paper, it is shown that tank tests of added resistance in the regular waves including the very short waves are conducted in the Actual Sea Model Basin at National Maritime Research Institute, MPAT for DTC container ship and accurate results are obtained. The test results are compared with the benchmarks published by SHOPERA (Energy Efficient Safe SHip OPERAtion). In addition, three curves of the added resistance in the regular waves based on the results of the tank test are compared and the sensitivity analysis of energy efficiency is discussed. In the sensitivity analysis, the performance simulator for ships in actual seas (VESTA) is used, and a comparison is carried out for the fuel consumption calculated from the frequency response of each added resistance in waves. As a result, it is found that the tendency in added resistance in very short waves affects the fuel consumption and the decrease of ship speed.
{"title":"Detailed Study on the Behavior of Ships in Very Short Waves","authors":"Saori Yokota, M. Kuroda, Ryohei Fukasawa, Hiroki Ohba, M. Tsujimoto","doi":"10.1115/omae2020-19008","DOIUrl":"https://doi.org/10.1115/omae2020-19008","url":null,"abstract":"\u0000 Considering the sea conditions in which a large ship encountered in operation, the ship’s behavior in very short waves is important. However, the evaluation of the ship performance in very short waves was not enough validated by tank tests. Because it is difficult to generate waves with enough accuracy due to the performance of the wave generator.\u0000 In this paper, it is shown that tank tests of added resistance in the regular waves including the very short waves are conducted in the Actual Sea Model Basin at National Maritime Research Institute, MPAT for DTC container ship and accurate results are obtained. The test results are compared with the benchmarks published by SHOPERA (Energy Efficient Safe SHip OPERAtion). In addition, three curves of the added resistance in the regular waves based on the results of the tank test are compared and the sensitivity analysis of energy efficiency is discussed. In the sensitivity analysis, the performance simulator for ships in actual seas (VESTA) is used, and a comparison is carried out for the fuel consumption calculated from the frequency response of each added resistance in waves. As a result, it is found that the tendency in added resistance in very short waves affects the fuel consumption and the decrease of ship speed.","PeriodicalId":431910,"journal":{"name":"Volume 6B: Ocean Engineering","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114600169","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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