New types of fish farms are often larger and structurally more complex than conventional fish farming structures, and associated challenges concerning safety and costs increase correspondingly. Thus, increased precision in structural design is required, with estimation of hydrodynamic loads on nets as an important topic. Today, both load coefficients for nets and measured netting dimensions are given with relatively high uncertainties. New knowledge for netting materials with high solidities as well as scaled netting commonly applied in model tests are included in the presented study. Results from towing tests and the development of a new mathematical expression for local drag coefficients (for netting twines) indicate that drag coefficients are not only dependent on solidity and Reynolds number, but may also be affected by the velocity reduction and the local velocity at the twines.
{"title":"Load Coefficients and Dimensions of Raschel Knitted Netting Materials in Fish Farms","authors":"Heidi Moe Føre, P. Endresen, Hans V. Bjelland","doi":"10.1115/omae2021-63401","DOIUrl":"https://doi.org/10.1115/omae2021-63401","url":null,"abstract":"\u0000 New types of fish farms are often larger and structurally more complex than conventional fish farming structures, and associated challenges concerning safety and costs increase correspondingly. Thus, increased precision in structural design is required, with estimation of hydrodynamic loads on nets as an important topic. Today, both load coefficients for nets and measured netting dimensions are given with relatively high uncertainties. New knowledge for netting materials with high solidities as well as scaled netting commonly applied in model tests are included in the presented study. Results from towing tests and the development of a new mathematical expression for local drag coefficients (for netting twines) indicate that drag coefficients are not only dependent on solidity and Reynolds number, but may also be affected by the velocity reduction and the local velocity at the twines.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81030364","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 methodology described in this paper is used to reduce a large set of combined wind, waves, and currents to a smaller set that still represents well enough the desired site for ship maneuvering simulations. This is achieved by running fast-time simulations for the entire set of environmental conditions and recording the vessel’s drifting time-series while it is controlled by an automatic-pilot based on a line-of-sight algorithm. The cases are then grouped considering how similar the vessel’s drifting time-series are, and one environmental condition is selected to represent each group found by the cluster analysis. The measurement of dissimilarity between the time-series is made by application of Dynamic Time Warping and the Cluster Analysis is made by the combination of Partitioning Around Medoids algorithm and the Silhouette Method. Validation is made by maneuvering simulations made with a Second Deck Officer.
{"title":"Clustering Applied to Large Sets of Environmental Conditions for Selecting Typical Scenarios for Ship Maneuvering Real-Time Simulations","authors":"F. M. Moreno, E. Tannuri","doi":"10.1115/omae2021-62875","DOIUrl":"https://doi.org/10.1115/omae2021-62875","url":null,"abstract":"\u0000 The methodology described in this paper is used to reduce a large set of combined wind, waves, and currents to a smaller set that still represents well enough the desired site for ship maneuvering simulations. This is achieved by running fast-time simulations for the entire set of environmental conditions and recording the vessel’s drifting time-series while it is controlled by an automatic-pilot based on a line-of-sight algorithm. The cases are then grouped considering how similar the vessel’s drifting time-series are, and one environmental condition is selected to represent each group found by the cluster analysis. The measurement of dissimilarity between the time-series is made by application of Dynamic Time Warping and the Cluster Analysis is made by the combination of Partitioning Around Medoids algorithm and the Silhouette Method. Validation is made by maneuvering simulations made with a Second Deck Officer.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"2009 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86250917","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 wave interaction with cylinders placed in proximity results in significant modification of the wave field, wave-induced processes, and wave loading. The evaluation of such a complex wave regime and accurate assessment of the wave loading requires an efficient and accurate numerical model. Concerning the wave scattering types identified by Swan et al. (2015) and lateral progressive edge waves, this paper presents the application of a two-phase Computational Fluid Dynamics (CFD) model to carry out a detailed investigation of nonlinear wave field surrounding a pair of columns placed in the tandem arrangement in the direction of wave propagation and corresponding harmonics. The numerical analysis is conducted using the Unsteady Reynolds-Averaged Navier-Stokes/VOF model based on the OpenFOAM framework combined with the olaFlow toolbox for wave generation/absorption. For the simulations, the truncated cylinders are assumed vertical and surface piercing with a circular cross-section subjected to regular, non-breaking fifth-order Stokes waves propagating with moderate steepness in deep water. Primarily, the numerical model is validated with experimental data provided by ITTC (OEC)[1] for a single cylinder. Future, the given simulations are conducted for different centre-to-centre distances between the tandem large cylinders. The results show the evolution of a strong wave diffraction pattern and consequently high wave amplification harmonics around cylinders are apparent.
波浪与靠近圆柱体的相互作用会导致波场、波致过程和波载荷的显著改变。要对如此复杂的波浪状态进行评估并准确地评估波浪荷载，需要一个高效、准确的数值模型。针对Swan et al.(2015)确定的波散射类型和横向递进边波，本文采用两相计算流体动力学(CFD)模型，对沿波传播方向串列布置的一对柱及其对应谐波周围的非线性波场进行了详细研究。采用基于OpenFOAM框架的非定常reynolds - average Navier-Stokes/VOF模型，结合olaFlow工具箱进行波浪产生/吸收的数值分析。在模拟中，假设截短的圆柱体是垂直的，表面穿透，横截面为圆形，在深水中以中等陡度传播的规则，非破碎的五阶斯托克斯波。首先，利用ITTC (OEC)[1]提供的单缸实验数据对数值模型进行了验证。在此基础上，对串联大气缸之间不同的中心距离进行了仿真。结果表明，在圆柱体周围形成了强波衍射图样，从而产生了明显的高波放大谐波。
{"title":"Numerical Simulation of Wave Interaction With a Pair of Fixed Large Tandem Cylinders Subjected to Regular, Non-Breaking Waves","authors":"M. Mohseni, C. Guedes Soares","doi":"10.1115/omae2021-62089","DOIUrl":"https://doi.org/10.1115/omae2021-62089","url":null,"abstract":"\u0000 The wave interaction with cylinders placed in proximity results in significant modification of the wave field, wave-induced processes, and wave loading. The evaluation of such a complex wave regime and accurate assessment of the wave loading requires an efficient and accurate numerical model. Concerning the wave scattering types identified by Swan et al. (2015) and lateral progressive edge waves, this paper presents the application of a two-phase Computational Fluid Dynamics (CFD) model to carry out a detailed investigation of nonlinear wave field surrounding a pair of columns placed in the tandem arrangement in the direction of wave propagation and corresponding harmonics. The numerical analysis is conducted using the Unsteady Reynolds-Averaged Navier-Stokes/VOF model based on the OpenFOAM framework combined with the olaFlow toolbox for wave generation/absorption. For the simulations, the truncated cylinders are assumed vertical and surface piercing with a circular cross-section subjected to regular, non-breaking fifth-order Stokes waves propagating with moderate steepness in deep water. Primarily, the numerical model is validated with experimental data provided by ITTC (OEC)[1] for a single cylinder. Future, the given simulations are conducted for different centre-to-centre distances between the tandem large cylinders. The results show the evolution of a strong wave diffraction pattern and consequently high wave amplification harmonics around cylinders are apparent.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"92 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81253698","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}
Filippo Nelli, A. Van Zuydam, K. Pferdekamper, A. Alberello, Marzieh H. Derkani, A. Bekker, A. Toffoli
Sea state conditions can be estimated from the motion of a moving ship by converting its response to incident waves through the response amplitude operator. The method is applied herein to ship motion data from the icebreaker R/V Akademik Tryoshnikov and recorded during the Antarctic Circumnavigation Expedition across the Southern Ocean during the Austral summer 2016–17. The response amplitude operator of the vessel was estimated using two boundary element method models, namely NEMOH and HydroSTAR. An inter-comparison of model performance is discussed. The accuracy of the reconstructed sea states is assessed against concurrent measurements of the wave energy spectrum, which were acquired during the expedition with the marine radar WaMoS-II. Results show good agreement between reconstructed sea states (wave spectrum as well as integrated parameters) and direct observations. Model performances are consistent. Nevertheless, NEMOH produces slightly more accurate wave parameters when quantitatively compared against HydroSTAR.
通过响应幅度算子将运动船舶的响应转换为入射波，可以从运动船舶的运动中估计海况。本文将该方法应用于破冰船R/V Akademik Tryoshnikov的船舶运动数据，这些数据是在2016-17年南极夏季穿越南大洋的南极环游考察期间记录的。采用NEMOH和HydroSTAR两种边界元法模型估计了船舶的响应幅值算子。讨论了模型性能的相互比较。重建海况的准确性是根据在考察期间使用海洋雷达WaMoS-II获得的波浪能谱的同时测量来评估的。结果表明，重建海况(波谱和综合参数)与直接观测结果吻合较好。模型性能是一致的。然而，与HydroSTAR相比，NEMOH在定量上产生的波参数略准确。
{"title":"Reconstructing Sea-States in the Southern Ocean Using Ship Motion Data","authors":"Filippo Nelli, A. Van Zuydam, K. Pferdekamper, A. Alberello, Marzieh H. Derkani, A. Bekker, A. Toffoli","doi":"10.1115/omae2021-62757","DOIUrl":"https://doi.org/10.1115/omae2021-62757","url":null,"abstract":"\u0000 Sea state conditions can be estimated from the motion of a moving ship by converting its response to incident waves through the response amplitude operator. The method is applied herein to ship motion data from the icebreaker R/V Akademik Tryoshnikov and recorded during the Antarctic Circumnavigation Expedition across the Southern Ocean during the Austral summer 2016–17. The response amplitude operator of the vessel was estimated using two boundary element method models, namely NEMOH and HydroSTAR. An inter-comparison of model performance is discussed. The accuracy of the reconstructed sea states is assessed against concurrent measurements of the wave energy spectrum, which were acquired during the expedition with the marine radar WaMoS-II. Results show good agreement between reconstructed sea states (wave spectrum as well as integrated parameters) and direct observations. Model performances are consistent. Nevertheless, NEMOH produces slightly more accurate wave parameters when quantitatively compared against HydroSTAR.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91535164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Daniel de Oliveira Costa, Joel Sena Sales Junior, A. C. Fernandes, Rodrigo dos Santos Corrêa
The problem of water entry of wedges represents one of the most classic research topics in fluid mechanics. Along the past decades, many different analytical methods have been proposed to calculate pressure distribution and peak loads during the water entry, such as Wagner (1932) and Dobrovol’skaya (1969). Zhao and Faltinsen (1993) and Mei (1995) present numerical solutions based on potential theory assumptions (inviscid, irrotational and incompressible flow). For more complex geometries and cases these methods might not be accurate enough due to the simplifications assumed, and in these cases the use of computational fluid dynamics (CFD) might be an interest tool to provide more accurate analysis. This work presents CFD results for different conditions of water entry of 2D wedges. The simulations were performed with a marine dedicated flow solver, FINE™/Marine from NUMECA, which features an unsteady Reynolds-averaged Navier-Stokes (URANS) solver and a finite volume method to perform spatial discretization. The multiphase flow is represented through the Volume of Fluid (VOF) method for incompressible and nonmiscible fluids. Different water entry conditions are explored. The effect of the mesh size, time step and other setup parameters over the results are discussed for simulations with 2D wedges to extend to other studies of water impact. The wedge velocity and hydrodynamic pressure distribution along the model’s face are monitored during the water entry and compared to experimental data from previous publication (Yettou et al, 2006) for water entry of wedges during free fall.
楔体入水问题是流体力学中最经典的研究课题之一。在过去的几十年里，人们提出了许多不同的分析方法来计算进水期间的压力分布和峰值负荷，如Wagner(1932)和Dobrovol 'skaya(1969)。Zhao和Faltinsen(1993)以及Mei(1995)提出了基于势理论假设(无粘流、无旋流和不可压缩流)的数值解。对于更复杂的几何形状和情况，由于假设的简化，这些方法可能不够准确，在这些情况下，使用计算流体动力学(CFD)可能是提供更准确分析的有趣工具。本文给出了二维楔形物不同进水条件下的CFD计算结果。模拟使用NUMECA的船舶专用流动求解器FINE™/ marine进行，该工具采用非定常reynolds -average Navier-Stokes (URANS)求解器和有限体积法进行空间离散化。对于不可压缩和非混相流体，用流体体积法表示多相流。探讨了不同的入水条件。讨论了网格尺寸、时间步长和其他设置参数对二维楔形模拟结果的影响，以扩展到其他水冲击研究。在水进入过程中监测楔形速度和沿模型表面的动水压力分布，并与先前发表的自由落体楔形水进入实验数据(Yettou et al, 2006)进行比较。
{"title":"Hydrodynamic Impact on Wedges During Water Entry","authors":"Daniel de Oliveira Costa, Joel Sena Sales Junior, A. C. Fernandes, Rodrigo dos Santos Corrêa","doi":"10.1115/omae2021-62921","DOIUrl":"https://doi.org/10.1115/omae2021-62921","url":null,"abstract":"\u0000 The problem of water entry of wedges represents one of the most classic research topics in fluid mechanics. Along the past decades, many different analytical methods have been proposed to calculate pressure distribution and peak loads during the water entry, such as Wagner (1932) and Dobrovol’skaya (1969). Zhao and Faltinsen (1993) and Mei (1995) present numerical solutions based on potential theory assumptions (inviscid, irrotational and incompressible flow). For more complex geometries and cases these methods might not be accurate enough due to the simplifications assumed, and in these cases the use of computational fluid dynamics (CFD) might be an interest tool to provide more accurate analysis.\u0000 This work presents CFD results for different conditions of water entry of 2D wedges. The simulations were performed with a marine dedicated flow solver, FINE™/Marine from NUMECA, which features an unsteady Reynolds-averaged Navier-Stokes (URANS) solver and a finite volume method to perform spatial discretization. The multiphase flow is represented through the Volume of Fluid (VOF) method for incompressible and nonmiscible fluids. Different water entry conditions are explored. The effect of the mesh size, time step and other setup parameters over the results are discussed for simulations with 2D wedges to extend to other studies of water impact. The wedge velocity and hydrodynamic pressure distribution along the model’s face are monitored during the water entry and compared to experimental data from previous publication (Yettou et al, 2006) for water entry of wedges during free fall.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75342838","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}
For numerical simulation of structure-wave interaction, the wave generation with high accuracy is prime to analyze the wave loads and motions of the structure. Based on the fifth-order Stokes theory, a two-dimensional viscous wave flume, which was modeled using the commercial CFD solver ANSYS-FLUENT, was applied to the generation and propagation of regular waves in finite water depth. With the user-defined function provided by the solver, the momentum source term and boundary condition, which are used for the wave generation and dissipation, were developed to ensure the accuracy of wave simulation with large steepness. In addition, the wave flume was separated into two regions, which are governed by the laminar model and turbulent model, respectively. The separation of laminar and turbulent regions can alleviate the side effect of turbulence on the accuracy of wave generation. In order to validate the present method, the regular wave propagating with different steepness in finite water depth were simulated. The numerical results were in good agreement with the theoretical ones. The study showed that the present method was effective for the simulation of Stokes wave in finite water depth, especially effective to improve the numerical accuracy in case of large wave steepness.
{"title":"Numerical Simulation of 5th-Order Stokes Wave in Finite Water Depth Based on Momentum Source Method","authors":"Wenjie Wang, Zhi-liang Gao","doi":"10.1115/omae2021-62487","DOIUrl":"https://doi.org/10.1115/omae2021-62487","url":null,"abstract":"\u0000 For numerical simulation of structure-wave interaction, the wave generation with high accuracy is prime to analyze the wave loads and motions of the structure. Based on the fifth-order Stokes theory, a two-dimensional viscous wave flume, which was modeled using the commercial CFD solver ANSYS-FLUENT, was applied to the generation and propagation of regular waves in finite water depth. With the user-defined function provided by the solver, the momentum source term and boundary condition, which are used for the wave generation and dissipation, were developed to ensure the accuracy of wave simulation with large steepness. In addition, the wave flume was separated into two regions, which are governed by the laminar model and turbulent model, respectively. The separation of laminar and turbulent regions can alleviate the side effect of turbulence on the accuracy of wave generation. In order to validate the present method, the regular wave propagating with different steepness in finite water depth were simulated. The numerical results were in good agreement with the theoretical ones. The study showed that the present method was effective for the simulation of Stokes wave in finite water depth, especially effective to improve the numerical accuracy in case of large wave steepness.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"82 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89476703","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}
Guillermo Gallego, A. Yezzi, F. Fedele, A. Benetazzo
We propose a novel remote sensing technique that infers the three-dimensional wave form and radiance of oceanic sea states via a variational stereo imagery formulation. In this setting, the shape and radiance of the wave surface are minimizers of a composite cost functional which combines a data fidelity term and smoothness priors on the unknowns. The solution of a system of coupled partial differential equations derived from the cost functional yields the desired ocean surface shape and radiance. The proposed method is naturally extended to study the spatiotemporal dynamics of ocean waves, and applied to three sets of video data. Statistical and spectral analysis are carried out. The results shows evidence of the fact that the omni-directional wavenumber spectrum S(k) of the reconstructed waves decays as k−2.5 in agreement with Zakharov’s theory (1999). Further, the three-dimensional spectrum of the reconstructed wave surface is exploited to estimate wave dispersion and currents.
{"title":"A Variational Wave Acquisition Stereo System for the 3-D Reconstruction of Oceanic Sea States","authors":"Guillermo Gallego, A. Yezzi, F. Fedele, A. Benetazzo","doi":"10.1115/OMAE2011-49061","DOIUrl":"https://doi.org/10.1115/OMAE2011-49061","url":null,"abstract":"We propose a novel remote sensing technique that infers the three-dimensional wave form and radiance of oceanic sea states via a variational stereo imagery formulation. In this setting, the shape and radiance of the wave surface are minimizers of a composite cost functional which combines a data fidelity term and smoothness priors on the unknowns. The solution of a system of coupled partial differential equations derived from the cost functional yields the desired ocean surface shape and radiance. The proposed method is naturally extended to study the spatiotemporal dynamics of ocean waves, and applied to three sets of video data. Statistical and spectral analysis are carried out. The results shows evidence of the fact that the omni-directional wavenumber spectrum S(k) of the reconstructed waves decays as k−2.5 in agreement with Zakharov’s theory (1999). Further, the three-dimensional spectrum of the reconstructed wave surface is exploited to estimate wave dispersion and currents.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2011-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86558391","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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