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Study on Far Field Wave Patterns and Their Characteristics of Havelock Form Green Function

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China ocean engineering 2013年第3期27卷 283-298页

作者：许勇董文才肖汶斌 Department of naval architecture & ocean engineering Naval University of Engineering

A new mathematical integral representation including five integrals about the far field wave shape fimction of Havelock form translating-pulsating source is obtained by performing variable substitution. Constant-phase curves and propagation wave patterns are investigated by applying stationary phase analysis method to the new representation. Some findings are summarized as follows：（1） when 0〈r 〈0.25 （where r is the Strouhal number）, three types of stationary phase curves corresponding to three propagation wave patterns such as fan wave pattern, inner V and outer V wave patterns, are found in the integral representation. （2） When r 〉0.25, besides three types of wave patterns such as a ring-faning wave pattern, a fan wave pattern and an inner V wave pattern, a new one called parallel wave pattern is also found which not only exists in the integrals about the ring-fan wave and fan wave, but also in the integrals whose interval is [0, 7＇] ~ In addition, Characteristics about these parallel waves such as mathematical expressions, existence conditions, propagation directions and wave lengths are obtained, and cancellation relationships between these parallel waves are stated, which certificates the fact that there are no parallel waves existing in the far field.

关键词： translating-pulsating source propagation wave patterns constant-phase curves parallel wave pattern

Numerical Investigation of Submarine Hydrodynamics and Flow Field in Steady Turn

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China ocean engineering 2016年第1期30卷 57-68页

作者：曹留帅朱军万文彬 Department of naval architecture and ocean engineering Naval University of Engineering

This paper presents numerical simulations of viscous flow past a submarine model in steady turn by solving the Reynolds-Averaged Navier-Stokes Equations（RANSE） for incompressible, steady flows. The rotating coordinate system was adopted to deal with the rotation problem. The Coriolis force and centrifugal force due to the computation in a bodyfixed rotating frame of reference were treated explicitly and added to momentum equations as source terms. Furthermore, velocities of entrances were coded to give the correct magnitude and direction needed. Two turbulence closure models（TCMs）, the RNG k-ε model with wall functions and curvature correction and the Shear Stress Transport（SST） k-ω model without the use of wall functions, but with curvature correction and low-Re correction were introduced, respectively. Take DARPA SUBOFF model as the test case, a series of drift angle varying between 0° and 16° at a Reynolds number of 6.53×10^6 undergoing rotating arm test simulations were conducted. The computed forces and moment as a function of drift angle during the steady turn are mostly in close agreement with available experimental data. Though the difference between the pressure coefficients around the hull form was observed, they always show the same trend. It was demonstrated that using sufficiently fine grids and advanced turbulence models will lead to accurate prediction of the flow field as well as the forces and moments on the hull.

关键词： submarine hydrodynamics flow field rotating coordinate system Coriolis and centrifugal force

Formulation of Reduction Rate for Ultimate Compressive Strength of Stiffened Panel Induced by Opening

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China ocean engineering 2014年第4期28卷 557-568页

作者：于昌利 LEE Joo-sung School of naval architecture and ocean engineering Harbin Institute of Technology School of naval architecture and ocean engineering University of Ulsan

The main objective of this study is to numerically investigate the characteristics of ultimate compressive strength of stiffened panels with opening and also to fit the design-oriented formulae. For this purpose, three series of well executed experimental data on longitudinally stiffened steel plates with and without opening subjected to the uniform axial in-pane load which is carried out to study the buckling and post-buckling up to the final failure are chosen. Also, a nonlinear finite element method capable of efficiently analyzing the large elasto-plastic deflection behavior of stiffened panels is developed and used for simulation. The feasibility of the present simulation process is confirmed by a good agreement with the experimental results. More case studies are developed employing the simulation process to analyze the influence of various design variables on the reduction rate of ultimate strength of stiffened panel induced by opening. Based on the computed results, two design formulae are fitted and the accuracy of design formulae is studied. Furthermore, the viability of the design formulae for practical engineering is proved.

关键词： stiffened panel opening reduction rate non-linear analysis formulae fitting

Numerical and Experimental Investigation of Interactions Between Free-Surface Waves and A Floating Breakwater with Cylindrical-Dual/Rectangular-Single Pontoon

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China ocean engineering 2018年第4期32卷 388-399页

作者： JI Chun-yan YANG Ke CHENG Yong YUAN Zhi-ming School of naval architecture and ocean engineering Jiangsu University of Science and Technology Department of naval architecture Ocean and Marine Engineering University of Strathclyde

This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics(CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom(3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time *** application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes(sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.

关键词： free-surface floating breakwater three DOF Navier Stokes solver wave structure interaction dynamic full-structured mesh

Study on Characteristics of 3-D Translating-Pulsating Source Green Function of Deep-Water Havelock Form and Its Fast Integration Method

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China ocean engineering 2011年第3期25卷 365-380页

作者：许勇董文才 Department of naval architecture and ocean engineering Naval University of Engineering

The singularities, oscillatory performances and the contributing factors to the 3-＇D translating-pulsating source Green function of deep-water Havelock form which consists of a local disturbance part and a far-field wave-like part, are analyzed systematically. Relative numerical integral methods about the two parts are presented in this paper. An improved method based on LOBATTO rule is used to eliminate singularities caused respectively by infinite discontinuity and jump discontinuous node from the local disturbance part function, which makes the improvement of calculation efficiency and accuracy possible. And variable substitution is applied to remove the singularity existing at the end of the integral interval of the far-field wave-like part function. Two auxiliary techniques such as valid interval calculation and local refinement of integral steps technique in narrow zones near false singularities are applied so as to avoid unnecessary integration of invalid interval and improve integral accordance. Numerical test results have proved the efficiency and accuracy in these integral methods that thus can be applied to calculate hydrodynamic performance of floating structures moving in waves.

关键词： translating-pulsating source Green's function singularity highly oscillatory function integration method

Risk Based Optimal Inspection and Repair Planning for Ship Structures Subjected to Corrosion Deterioration

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海洋工程：英文版 2004年第2期18卷 185-196页

作者：李典庆张圣坤唐文勇 School of naval architecture and ocean engineering

A framework of risk based inspection and repair planning was presented to optimize for the ship structures subjected to corrosion deterioration. The planning problem was formulated as an optimization problem where the expected lifetime costs were minimized with a constraint on the minimum acceptable reliability index. The safety margins were established for the inspection events, the repair events and the failure events for ship structures. Moreover, the formulae were derived to calculate failure probabilities and repair probabilities. Based on them, a component subjected to corrosion is investigated for illustration of the process of selecting the optimal inspection and repair strategy. Furthermore, some sensitivity studies were provided. The results show that the optimal inspection instants should take place before the reliability index reaches the minimum acceptable reliability index. The optimal target failure probability is 10 -3 . In addition, a balance can be achieved between the risk cost and total expected inspection and repair costs by means of the risk-based optimal inspection and repair method, which is very effective in selecting the optimal inspection and repair strategy.

关键词： risk inspection and repair optimization corrosion model ship structures

Hydroelastic Response Analysis of Mat-Like VLFS over A Plane Slope in Head Seas

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海洋工程：英文版 2003年第3期17卷 315-326页

作者：孙辉崔维成刘应中廖世俊 School of naval architecture and ocean engineering

Very large floating structures (VLFS) have an extremely large size of several kilometers in length, thus, the environment at one end of the platform may be different from that at the other end. The importance of such an inhomogeneous environment to the hydroelastic response of a VLFS is of obvious concern for practical application. Some studies have been carried out to investigate the effects of shoreline proximity, breakwaters and harbor walls. In this paper, the impact of the variable depth on the hydroelastic responses of a VLFS is investigated. For simplicity, an ascending plane slope is taken to simulate the varying bottom although the method is capable of treating a bottom of arbitrary variation. The long wave theory and the thin plate theory are employed to model the wave field and the mat-like VLFS respectively. The finite difference method is used to numerically solve the boundary value problem. The results for the zero inclination slope are compared with experimental data and an analytical method to validate the present numerical method. Finally the effect of the inclination of the slope on reflection and transmission coefficients and plate deflections are investigated thoroughly.

关键词： very large floating structures hydroelastic responses inhomogeneous environment variable depth

Application of the generalized body-fixed coordinate system for the wave-body interaction problem of a small-depth elastic structure in head seas

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Journal of Hydrodynamics 2021年第6期33卷 1255-1270页

作者： Kyeonguk Heo Masashi Kashiwagi School of naval architecture and ocean engineering University of UlsanUlsanKorea Department of naval architecture and ocean engineering Osaka UniversitySuitaJapan

The body-fixed coordinate system is applied to the wave-body interaction problem of a small-depth elastic structure which has both rigid and elastic body motions in head *** the weakly non-linear assumption,the perturbation scheme is used and the expansion is conducted up to second-order to consider several non-linear *** solve the boundary value problem,linearization is carried out based not on inertial coordinate but on body-fixed coordinate which could be accelerated by a motion of a *** first,the main feature of the application of body-fixed coordinate system for a seakeeping problem is briefly *** that the transformation of a coordinate system is extended to consider an elastic body motion and several physical variables are re-described in the generalized *** has been found that the deformation gradient could be used for the transformation of a coordinate system if several conditions are *** there are only vertical bending in elastic modes and the structure has relatively small depth,these conditions are generally *** calculate an elastic motion of a body,the generalized mode method is adopted and the mode shape is obtained by solving eigen-value problem of dynamic beam *** the boundary condition of the body-fixed coordinate system,the motion effect reflected to free-surface boundary is considered by extrapolating each mode shape to the horizontal direction from a *** last,simple numerical tests are implemented as a validation *** second-order hydrodynamic force of a freely floating hemisphere is first calculated in zero forward speed ***,motion and added resistance of a ship with forward speed are considered at different flexibility to confirm the effect of an elastic body motion in body-fixed coordinate system.

关键词： Hydroelasticity Higher-order boundary element method(HOBEM) generalized mode method perturbation scheme body-fixed coordinate system wave-body interaction

Review on Tidal Energy Technologies and Research Subjects

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China ocean engineering 2020年第1期34卷 137-150页

作者： Chul Hee JO Su Jin HWANG Department of naval architecture and ocean engineering Inha University

Tidal current power is one of the promising and reliable renewable energies with the advantage of continuous and predictable resource. It can make stable electricity regardless of weather conditions or seasons all year around. The required technologies for tidal current power in the ocean have been developed for years and now recognized that it could be commercialized after intensive field tests and successful demonstrations. There are several tidal farm development projects in the world, such as the MeyGen project in UK with its commercialization at hand. However, various research subjects in the tidal current energy field are seeking improvements and industrialization of tidal current power in terms of economy and technical reliability. This paper introduces the resource assessment procedure of tidal energy that has been applied in Korea coastal regions. The key research subjects for tidal current power together with the interaction effect of multi-arrangement is described. Also, this paper is to introduce the research output of each subject such as turbine design, experimental validation, turbine interaction and wake, multi-array module, FSI (fluid-structure interaction), and duct application.

关键词： tidal current power resource assessment turbine design experimental validation turbine interaction multi arrangement FSI(fluid-structure interaction)