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Non-hydrostatic versus hydrostatic modelings of free surface flows

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Journal of hydrodynamics 2014年第4期26卷 512-522页

作者：张景新 SUKHODOLOV Alexander N. 刘桦 MOE key laboratory of hydrodynamics Shanghai Jiao Tong University key laboratory of Estuarine and Coastal engineering Ministry of Transport School of naval architecture Ocean and Civil EngineeringShanghai Jiao Tong University Department of Ecohydrology Institute of Fresh-water Ecology and Inland Fisheries MOE key laboratory of hydrodynamics Shanghai Jiaotong University

The hydrodynamics of geophysical flows in oceanic shelves, estuaries, and rivers are often studied by solving shallow water equations under either hydrostatic or non-hydrostatic assumptions. Although the hydrostatic models are quite accurate and cost-efficient for many practical applications, there are situations when the fully hydrodynamic models are preferred despite a larger cost for computations. The present numerical model is implemented by the finite volume method （FVM） based on unstructured grids. The model can be efficiently switched between hydrostatic and non-hydrostatic modules. The case study shows that for waves pro- pagating along the bar a criterion with respect to the shallowness alone, the ratio between the depth and the wave length, is insufficient to warrant the performance of shallow flow equations with a hydrostatic approach and the nonlinearity in wave dynamics can be better accounted with a hydrodynamic approach. Besides the prediction of the flows over complex bathymetries, for instance, over asymmetrical dunes, by a hydrodynamic approach is shown to be superior in accuracy to the hydrostatic simulation.

关键词： hydrostatic non-hydrostatic TVD scheme non-orthogonal grid

Numerical Analysis on Motion of Multi-column Tension-Leg-Type Floating Wind Turbine Basement

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Transactions of Nanjing University of Aeronautics and Astronautics 2016年第1期33卷 73-79页

作者： Fan Xiang Zhang Jingxin Liu Hua MOE key laboratory of hydrodynamics School of Naval ArchitectureOcean & Civil EngineeringShanghai Jiao Tong University Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration School of Naval ArchitectureOcean & Civil EngineeringShanghai Jiao Tong University

The offshore wind energy presents a good solution for the green energy *** floating offshore wind turbine(FOWT)is one of the most potential choices of the basement construction for offshore wind turbines in deep *** performance of multi-column tension-leg-type floating wind turbine is investigated numerically,particularly at its motion *** on the Navier-Stokes equations and the volume of fluid method,a numerical wave tank(NWT)is established to simulate the floating structure *** analytical relaxation method is adopted to generate regular *** mesh method is used to calculate the motion of the floating *** decay of motion and hydrodynamic forces in the regular wave are *** computation results agree with the experimental data *** results show that the wave force on the lower pontoon of the system is the greatest while that on the center column is the *** information about the changes of the wave forces on different elements of the floating system is discussed.

关键词： numerical wave tank(NWT) wave-floating body interaction fluid-solid coupling offshore wind turbine

Diffraction of Water Waves by A Vertically Floating Cylinder in A Two-Layer Fluid

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China ocean engineering 2008年第2期22卷 181-193页

作者：石强尤云祥缪国平 key laboratory of ocean engineering School of Naval Architecture Ocean and Civil EngineeringShanghai Jiao Tong University

In this paper, the diffraction of water waves by a vertically floating cylinder in a two-layer fluid of a finite depth is studied. Analytical expressions for the hydrodynamic loads on the vertically floating cylinder are obtained by use of the method of eigenfunction expansions. The hydrodynamic loads on the vertically floating cylinder in a two-layer fluid inelude not only the surge, heave and pitch exciting forces due to the incident wave of the surface-wave mode, but also those due to the incident wave of the internal-wave mode. This is different from the case of a homogenous fluid. Some given examples show that, for a two-layer fluid system with a small density difference, the hydrodynamic loads for the surface-wave mode do not differ significantly from those due to surface waves in a single-layer fluid, but the hydrodynamic loads for the internal-wave mode are important over a wide range of frequencies. Moreover, also considered are the free surface and interface elevations generated by the diffraction wave due to the incident wave of the surface-wave and interhal-wave modes, and transfer of energy between modes.

关键词： two-layer fluid vertically floating cylinder hydrodynamic loads surface-wave mode internal-wave hurtle

THE RADIATION PROBLEM OF MULTIPLE STRUCTURES WITH SMALL GAPS IN BETWEEN

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Journal of hydrodynamics 2006年第5期18卷 520-526页

作者： ZHU Ren-chuan MIAO Guo-ping ZHU Hai-rong The State key laboratory of ocean engineering School of Naval Architecture Ocean and Civil Engineering Shanghai Jiaotong University Shanghai 200030 China

Influence of gaps on hydrodynamic interactions of multiple floating structures is considered in the present investigation. Strong and complicate hydrodynamic interactions between the floating bodies are observed and the numerical computations have showed the existence of the sharp peak force response on each floating body at some special resonant wave numbers, which are also proved to be around kL =nπ （n= 1, 2, ...,∞） with a corresponding frequency shift. Width and depth of a gap also give influences on the resonant frequency and resonant amplitude of added mass and damping forces due to the radiation motions of the multiple bodies. The strong hydrodynamic interaction feature may have a big influence on the integrated loads of multiple floating structures system.

关键词： resonance hydrodynamic interaction multiple floating bodies gap influence

Extreme storm surge induced coastal inundation in Yangtze Estuary regions

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Journal of hydrodynamics 2019年第6期31卷 1127-1138页

作者： Zhen-hua Pan Hua Liu key laboratory of hydrodynamics(Ministry of Education) School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China DHI China Shanghai 200235China

Coastal inundation induced by the storm surge belongs to one of the major natural hazards in Shanghai and other regions around the Yangtze *** worst scenarios of coupling the extreme storm and the sea level rise are presented to assess the storm surge hazard in the Yangtze *** numerical model MIKE 21 FM is adopted to implement the numerical study,which includes wind,current,tide and *** storm surge induced by typhoon 9711 is simulated,and the measurements of six tide gauges are used to validate the numerical *** identify the worst case scenario of severe typhoon(9711)and super typhoon(5612),we propose seven typhoon tracks through the Yangtze Estuary and fourteen scenarios of landfall time for each typhoon track,which generates 196 ***,based on the worst case scenario and the relative sea level rise in the range of 0 m to 0.7 m,the coastal inundation maps of Pudong New District and Changxing Island are provided and discussed.

关键词： Storm surge inundation Yangtze Estuary sea level rise numerical simulation

THEORETICAL RESEARCH ON hydrodynamics OF A GEOMETRIC SPAR IN FREQUENCY-AND TIME-DOMAINS

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Journal of hydrodynamics 2008年第1期20卷 30-38页

作者： WANG Ying YANG Jian-min HU Zhi-qiang XIAO Long-fei State key laboratory of ocean engineering School of Naval Architecture Ocean and Civil Engineering Shanghai Jiaotong University Shanghai 200030 China

Considering the coupling effects of the vessel and its riser and mooring system, hydrodynamic analyses of a geometric spar were performed both in frequency- and time-domains. Based on the boundary element method, the 3-D panel model of the geometric spar and the related free water surface model were established, and the first-order and second-order difference-frequency wave loads and other hydrodynamic coefficients were calculated. Frequency domain analysis of the motion Response Amplitude Operators （RAO） and Quadratic Transfer Functions （QTF） and time domain analysis of the response series and spectra in an extreme wave condition were conducted for the coupled system with the mooring lines and risers involved. These analyses were further validated by the physical model test results.

关键词： geometric spar hydrodynamics coupled analysis frequency domain time domain

Forces of fully nonlinear interfacial periodic waves on a cylindrical pile in a two-layer fluid with free-surface boundary conditions

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Journal of ocean engineering and Science 2023年第6期8卷 662-674页

作者： Jiyang Li Zeng Liu Jie Cui School of naval architecture and ocean engineering Jiangsu University of Science and TechnologyZhenjiangJiangsu 212000PR China School of naval architecture and ocean engineering Huazhong University of Science and TechnologyWuhan 430074PR China hubei key laboratory of naval architecture and ocean engineering hydrodynamics(HUST) Wuhan 430074China hubei Provincial engineering Research Center of Data Techniques and Supporting Software for Ships Wuhan 430074PR China

In the frame of fully nonlinear potential flow theory,series solutions of interfacial periodic gravity waves in a two-layer fluid with free surface are obtained by the homotopy analysis method(HAM),and the related wave forces on a vertical cylinder are *** solution procedure of the HAM for the interfacial wave model with rigid upper surface is further developed to consider the free surface *** forces of nonlinear interfacial periodic waves are estimated by both the classical and modified Mori-son *** is found that the estimated wave forces by the classical Morison equation are more conservative than those by the modified Morison’s formula,and the relative error between the total inertial forces calculated by these two kinds of Morison’s formulae remains over 25%for most cases unless the upper and lower layer depths are both large *** demonstrates that the convective acceleration neglected in the classical Morison equation is rather important for inertial force exerted by not only internal solitary waves but also interfacial periodic *** of these should further deepen our understanding of internal periodic wave forces on a vertical marine riser.

关键词： Interfacial periodic waves Wave force Cylindrical pile Homotopy analysis method Morison equation

The research on floe ice force acting on the"Xue Long"icebreaker based on synthetic ice test and virtual mass numerical method

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Journal of hydrodynamics 2021年第2期33卷 271-281页

作者： Wei Guo Qiao-sheng Zhao Yu-kui Tian Wan-chao Zhang State key laboratory of hydrodynamics China Ship Scientific Research CenterWuxi 214082China School of naval architecture and ocean engineering Jiangsu University of Science and TechnologyZhenjiang 212003China

When the ice-going ships advance in the polar region,the navigation in the floe ice region is often encountered,the hull will suffer the high-frequency contact force produced by the floe ice,which will affect the navigation performance of the ***,it is necessary to predict the water and ice force acting on the hull *** this paper,the numerical simulation and experimental verification will be conducted for the polar scientific research ship-"Xue Long".Based on the computational fluid dynamics(CFD)and DEM theory,a virtual mass method is proposed to realize the predicting of the water and ice force and the simulation of the interaction phenomenon between the ice and hull,the numerical method is built to calculate the force acting on the *** the same time,the synthetic ice is used to carry out the experimental research on the advancing straight with different speeds and the oblique navigation with different drift *** optimal virtual mass coefficient is determined through the comparison and analysis of the numerical simulation and test results under typical *** to the optimal virtual mass coefficient,the numerical simulation is carried out with different speeds and drift angles,which is compared with the experiment more *** is found that the virtual mass method based on the combination of CFD and DEM can simulate the overturning and the sliding along the hull of the floe ice vividly,the relative error of the total resistance between model test and numerical method in advancing straight is almost within 10%,while the relative error of the total longitudinal force in oblique navigation is almost within 15%.

关键词： "Xue Long"ship synthetic ice model test computational fluid dynamics(CFD) DEM virtual mass method drift angle

An improved boundary element method for modelling a self-reacting point absorber wave energy converter

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Acta Mechanica Sinica 2018年第6期34卷 1015-1034页

作者： Qian-Long Xu Ye Li Zhi-Liang Lin State key laboratory of ocean engineering Collaborative Innovation Center for Advanced Ship and Deep-Sea ExplorationMuti-function Towing TankKey Laboratory of Hydrodynamics(Ministry of Education)School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China

A numerical model based on a boundary element method (BEM) is developed to predict the performance of two-body selfreacting floating-point absorber (SRFPA) wave energy systems that operate predominantly in *** key numerical issues in applying the BEM are systematically *** particular,some improvements and simplifications in the numerical scheme are developed to evaluate the free surface Green's function,which is a main element of difficulty in the *** a locked SRFPA system,the present method is compared with the existing experiment and the Reynolds-averaged NavierStokes (RANS)-based method,where it is shown that the inviscid assumption leads to substantial over-prediction of the heave *** the unlocked SRFPA model we study in this paper,the additional viscous damping primarily induced by flow separation and vortex shedding,is modelled as a quadratic drag force,which is proportional to the square of body *** inclusion of viscous drag in present method significantly improves the prediction of the heave responses and the power absorption performance of the SRFPA system,obtaining results excellent agreement with experimental data and the RANS simulation results over a broad range of incident wave periods,except near resonance in larger wave height *** is found that the wave overtopping and the re-entering impact of out-of-water floating body are observed more frequently in larger waves,where these non-linear effects are the dominant damping sources and could significantly reduce the power output and the motion responses of the SRFPA system.

关键词： Boundary element method Floating-point absorber Heave Green's function Viscous drag