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Vortex identification methods in marine hydrodynamics

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Journal of hydrodynamics 2020年第2期32卷 286-295页

作者： Wei-wen Zhao Jian-hua Wang De-cheng Wan Computational Marine hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringState Key Laboratory of Ocean EngineeringShanghai Jiao Tong UniversityShanghai200240China

In this paper,several commonly used vortex identification methods for marine hydrodynamics are *** order to extract and analyse the vortical structures in marine hydrodynamics,the Q,λ2-criterion and modified normalized Liutex/RortexΩR method are utilized for vortex identification for propeller open water test,ship drag test,ship propeller-rudder interaction,VIV of a marine riser and VIM of a Spar *** limitation of Q andλ2-criterion is *** Liutex/RortexΩR method is promising for convenient and accurate vortex identification and ***,care should be taken when choosing the small parameter b0 forΩ*** proposed recommended values of b0 for marine hydrodynamic problems.

关键词： Marine hydrodynamics vortex identification Omega Liutex/Rortex naoe-FOAM-SJTU solver OpenFOAM

Effective enhanced model for a large deformable soft pneumatic actuator

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Acta Mechanica Sinica 2020年第1期36卷 245-255页

作者： Qiping Xu Jinyang Liu Department of engineering Mechanics Key Laboratory of Hydrodynamics(Ministry of Education)School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai200240China

Soft pneumatic actuators have been widely used for implementing sophisticated and dexterous movements,due to numerous fascinating features compared with their rigid *** speaking,modeling and analysis of an entire soft pneumatic actuator considering contact interaction between two adjacent air chambers is extremely rare,which is exactly what we are particularly interested ***,in order to establish an accurate mechanical model and analyze the overall configuration and stress distribution for the soft pneumatic actuator with large deflection,we consider the contact interaction of soft materials rather than hard materials,to produce an effective enhanced model for soft contact of a large deformable pneumatic *** this article,a multiple-point contact approach is developed to circumvent the mutual penetration problem between adjacent air chambers of the soft actuator that occurs with the single-point contact approach employed in linear elastic rigid *** contrast to the previous simplified rod-based model that did not focus on contact interaction which was adopted to clarify the entire deformation of the actuator,the present model not only elaborates nonlinear large deformation and overall configuration variations,but also accurately delineates stress distribution law inside the chamber structure and the stress concentration *** means of a corresponding static experiment,a comparison of the simulation results with experimental data validates the effectiveness and accuracy of this model employing a multiple-point contact *** simulation of the actual bending deformation of the soft actuator is obtained,while mutual penetration is successfully circumvented,whereas the model with single-point contact cannot achieve those ***,as compared with the rod-based model,the results obtained using the proposed model are more consistent with experimental data,and simulation precision is improved.

关键词： Soft contact Large deformable pneumatic actuator Mutual penetration problem Multiple-point contact approach Stress distribution

Investigation of the effects of platform motion on the aerodynamics of a floating offshore wind turbine

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Journal of hydrodynamics 2016年第1期28卷 95-101页

作者： Yuanchuan LIU Qing XIAO Atilla INCECIK 万德成 Department of naval architecture Ocean and Marine Engineering University of Strathclyde State key laboratory of ocean engineering School of Naval Architecture Ocean and Civil EngineeringShanghai Jiao Tong University

Along with the flourishing of the wind energy industry, floating offshore wind turbines have aroused much interest among the academia as well as enterprises. In this paper, the effects of the supporting platform motion on the aerodynamics of a floating wind turbine are studied using the open source CFD framework Open FOAM. The platform motion responses, including surge, heave and pitch, are superimposed onto the rotation of the wind turbine. Thrust and torque on the wind turbine are compared and analysed for the cases of different platform motion patterns together with the flow field. It is shown that the movement of the supporting platform can have large influences on a floating offshore wind turbine and thus needs to be considered carefully during the design process.

关键词： floating offshore wind turbine superimposed platform motion aerodynamics Open FOAM

Numerical Prediction of Marine Propeller Noise in Non-Uniform Inflow

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China ocean engineering 2013年第1期27卷 33-42页

作者：潘雨村张怀新 State key laboratory of ocean engineering Shanghai JiaoTong University Department of naval architecture Naval University of Engineering

A numerical study on the acoustic radiation of a propeller interacting with non-uniform inflow has been conducted. Real geometry of a marine propeller DTMB 4118 is used in the calculation, and sliding mesh technique is adopted to deal with the rotational motion of the propeller. The performance of the DES （Detached Eddy Simulation） approach at capturing the unsteady forces and moments on the propeller is compared with experiment. Far-field sound radiation is predicted by the formation 1A developed by Farassat, an integral solution of FW-H （Ffowcs Williams-Hawkings） equation in time domain. The sound pressure and directivity patterns of the propeller operating in two specific velocity distributions are discussed.

关键词： hydroacoustics Detached Eddy Simulation (DES) Ffowcs Williams-Hawkings (FW-It) equation marine propeller non-uniform inflow

Numerical simulations of wake signatures around high-speed ships

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Journal of hydrodynamics 2014年第6期26卷 986-989页

作者：王本龙郭晓宇刘桦何辰 School of naval architecture Ocean and Civil Engineering and MOE Key Laboratory of Hydrodynamics Shanghai Jiao Tong University Xi’an Precision engineering Institute

Navier-Stokes equations are solved to obtain the near field flow and to reveal the generation of droplets due to the breaking of the bow wave. With an adaptive refinement of the Octree mesh, the fine scale flow characteristics, the wave breaking and the splashing are well simulated. For high-speed ships, the V-shape ship wave pattern with the angle smaller than the classical Kelvin angle is confirmed by the present numerical results, which can also be applied to the catamaran. Comparisons of the vertical velocity distributions induced by the mono-hull ship and the catamaran are made at different locations in the wake regions.

关键词： bow wave breaking wave volume of fluid method

Effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks

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Particuology 2020年第2期18卷 159-168页

作者： Wentao Xu Yangbo Tan Meng Li Jianglong Sun De Xie Zeng Liu School of naval architecture Ocean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China School of naval architecture and ocean engineering Huazhong University of Science and TechnologyWuhan 430074China Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai 200240China hubei key laboratory of naval architecture and ocean engineering hydrodynamics Wuhan 430074China ocean engineering.Huazhong University of Science and Technology Wuhan 430074.China

The effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks were *** distribution and power consumption were analyzed by experiments and numerical simulations in both baffled and unbaffled tanks agitated by a Rushton *** unbaffled tanks,a non-aggregation rule was applied and the average dispersion index was found to serve as a reasonable prediction of the full drawdown of floating *** critical impeller speeds in an unbaffled tank were higher than those in a tank with vertical *** each immersion depth in a baffled tank,particles distributed more uniformly and more power was *** of snapshots of the baffled and unbaffled tanks shows that the surface vortex increases the drawdown speed while it decreases the particle distribution uniformity and power ***,the use of baffles to suppress the surface vortex provides for a more uniform particle distribution in stirred tanks.

关键词： Stirred tank Surface vortex Solids drawdown Complete dispersion

Numerical Investigation of Characteristics of Water-Exit Ventilated Cavity Collapse

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Journal of Shanghai Jiaotong university(Science) 2016年第5期21卷 530-540页

作者：秦楠鲁传敬李杰 School of naval architecture Ocean and Civil EngineeringShanghai Jiaotong University MOE key laboratory of hydrodynamics Shanghai Jiaotong University

The collapse of the ventilated cavitation occurring on a cylindrical vehicle during the water-exit is numerically researched. The numerical model employs the finite volume method to solve the multiphase Reynoldsaveraged Navier-Stokes(RNNS) equations and uses the volume of fluid(VOF) method to capture the free surface.A practical water wave environment that the vehicle usually encounters is reproduced in a numerical wave flume,so that the water wave's effect on the cavity collapse flow regime is investigated. The main feature of the waterexit collapse of a ventilated cavity is studied under the wave-free condition. The result indicates that a collapsing ventilated cavity experiences two stages, in which the pattern of cavity evolution is different. In the early stage,the cavity undergoes a rapid shrinkage as a closed body. In the late stage, the cavity releases gas from the front due to the increase of the cavity pressure. The water wave effect is investigated at three typical wave phases: the wave crest, the wave trough and the wave node. Results show that when the vehicle is launched under the wave node, the cavity collapse regime remains fairly axisymmetric and is similar to the wave-free case. However, when the vehicle is launched under the wave crest and trough, the cavity evolution presents highly three-dimensional(3D) features. The results of predicted cavity size, pressure distributions and hydrodynamic forces at different wave phases show that the wave effect is relatively weak at the wave node but becomes apparent at the wave crest and trough.

关键词： water-exit ventilated cavitation cavity collapse water wave effect

An improved series expansion method on the multi-frequency analysis of acoustic boundary element

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Chinese Journal of Acoustics 2016年第3期35卷 241-254页

作者： MIAO Yuyue LI Tianyun ZHU Xiang GUO Wenjie School of naval architecture and ocean engineering Huazhong University of Science &Technology hubei key laboratory of naval architecture & ocean engineering hydrodynamics National key laboratory on Ship Vibration & Noise

For the multi-frequency acoustic analysis, a series expansion method has been introduced to reduce the computation time of the frequency-independent parts, but the Runge phenomenon will arise when this method is employed in high frequency band. Therefore, this method is improved by analyzing the application condition and proposing the selection principle of the series truncation number. The argument interval can be adjusted with the wavenumber factor. Therefore, the problem of unstable numeration and poor precision can be solved, and the application scope of this method is expanded. The numerical example of acoustic radiation shows that the improved method is correct for acoustic analysis in wider frequency band with less series truncation number and computation amount.

关键词： An improved series expansion method on the multi-frequency analysis of acoustic boundary element

Hydrodynamic interaction among hull,rudder and bank for a ship sailing along a bank in restricted waters

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Journal of hydrodynamics 2013年第6期25卷 809-817页

作者：麻绍钧周明贵邹早建 School of naval architecture Ocean and Civil EngineeringShanghai Jiao Tong University State key laboratory of ocean engineering and School of naval architecture Ocean and Civil EngineeringShanghai Jiao Tong University

By applying a CFD tool to solve the RANS equations, the viscous flow around a model of hull-rudder system towed along a bank in shallow water is numerically simulated. Hydrodynamic forces and moments acting on the ship are calculated for different ship-bank distances and rudder angles. A container ship, KCS, is taken as an example for the numerical study. Under the assumption of low ship speed, the influences of free surface elevation and ship squat are assumed to be negligible. Based on the calculation results, the hydrodynamic interaction among the hull, rudder and bank is analyzed.

关键词： hydrodynamic interaction hull-rudder system bank effect CFD