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Application of A Fast Multipole BIEM for Flow Diffraction from A 3D Body

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海洋工程：英文版 2004年第2期18卷 291-298页

作者：滕斌宁德志 State key laboratory of coastal and Offshore Engineering

A Fast Multipole Method (FMM) is developed as a numerical approach to the reduction of the computational cost and requirement memory capacity for a large in solving large-scale problems. In this paper it is applied to the boundary integral equation method (BIEM) for current diffraction from arbitrary 3D bodies. The boundary integral equation is discretized by higher order elements, the FMM is applied to avoid the matrix/vector product, and the resulting algebraic equation is solved by the Generalized Conjugate Residual method (GCR). Numerical examination shows that the FMM is more efficient than the direct evaluation method in computational cost and storage of computers.

关键词： fast multipole method boundary integral equation method generalized conjugate residual method current diffraction

Wave Reflection Coefficient Spectrum

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海洋工程：英文版 2003年第3期17卷 383-396页

作者：俞聿修邵利民柳淑学 State key laboratory of coastal and Offshore Engineering

The wave reflection coefficient frequency spectrum and directional spectrum for concrete face slope breakwaters and rubble mound breakwaters are investigated through physical model tests in the present study. The reflection coefficients of oblique irregular waves are analyzed by the Modified Two-Point Method (MTPM) proposed by the authors. The results show that the wave reflection coefficient decreases with increasing wave frequency and incident angle or decreasing structure slope. The reflection coefficient frequency spectrum and its variation with Iribarren number are given in this paper. The paper also suggests an empirical 3-dimensional reflection coefficient spectrum, i.e. reflection coefficient directional spectrum, which can be used to illustrate quantitatively the variation of reflection coefficient with the incident angle and the Iribarren number for oblique irregular waves.

关键词： wave reflection frequency spectrum reflection coefficient directional spectrum slope breakwater

Torsionally Coupled Response Control of Offshore Platform Structures Using Circular Tuned Liquid Column Dampers

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海洋工程：英文版 2004年第2期18卷 173-183页

作者：霍林生李宏男 State key laboratory of coastal and Offshore Engineering

In this paper, the control performance is investigated of Circular Tuned Liquid Column Dampers (CTLCD) over torsional response of offshore platform structures excited by ground motions. Based on the equation of motion for the CTLCD-structure system, the optimal control parameters of CTLCD are given through some derivations on the supposition that the ground motion is a stochastic process. The influence of systematic parameters on the equivalent damping ratio of the structures is analyzed with purely torsional vibration and translational-torsional coupled vibration, respectively. The results show that the Circular Tuned Liquid Column Damper (CTLCD) is an effective torsional response control device.

关键词： circular tuned liquid column dampers offshore platform vibration control seismic response eccentric structures

Impact Pressure of Incident Regular Waves and Irregular Waves on the Subface of Open-Piled Structures

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海洋工程：英文版 2004年第1期18卷 35-46页

作者：任冰王永学 State key laboratory of coastal and Offshore Engineering

This paper presents the results of comparison of impact pressures on open-plied structures induced by regular waves and irregular waves in a laboratory channel. Regular waves with wave heights ranging from 0.1～0.2 m and periods ranging from 1.0～2.0 s are tested. The target spectrum for the irregular wave is JONSWAP spectrum. Irregular waves with significant wave heights in the range of 0.10～0.25 m and peak periods in the range of 1.0～2.0 s are tested. The relative clearance s/H 1/3(H) is between -0.1 and 0.4, s being the subface level of structure model above the still water level. Time series of impact pressure are analyzed to indicate whether the property of impact pressures induced by the regular wave significantly deviates from that by the irregular wave. The distribution of the impact pressure along the underside of the structure is compared for different types of incident waves. The effects of wave parameters, structure dimension and structure clearance on the impact pressure are also discussed.

关键词： irregular wave regular wave open-piling impact pressure

Simulation of Fully Nonlinear 3-D Numerical Wave Tank

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海洋工程：英文版 2004年第1期18卷 59-68页

作者：张晓兔滕斌宁德志 State key laboratory of coastal and Offshore Engineering

A fully nonlinear numerical wave tank (NWT) has been simulated by use of a three-dimensional higher order boundary element method (HOBEM) in the time domain. Within the frame of potential flow and the adoption of simply Rankine source, the resulting boundary integral equation is repeatedly solved at each time step and the fully nonlinear free surface boundary conditions are integrated with time to update its position and boundary values. A smooth technique is also adopted in order to eliminate the possible saw-tooth numerical instabilities. The incident wave at the uptank is given as theoretical wave in this paper. The outgoing waves are absorbed inside a damping zone by spatially varying artificial damping on the free surface at the wave tank end. The numerical results show that the NWT developed by these approaches has a high accuracy and good numerical stability.

关键词： numerical wave tank full nonlinearity higher order boundary element method three-dimensional time domain

A New Pursuit Mode of Nonlinear Wave Surface

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海洋工程：英文版 2004年第2期18卷 257-266页

作者：孙大鹏李玉成郭海滨 State key laboratory of coastal and Offshore Engineering

The numerical mode of nonlinear wave transformation based on both the Laplace equation for water field and the Bernoulli equation for water surface is a kind of time-domain boundary problem with initial conditions. And the basis for establishing the numerical mode of nonlinear wave in time domain is to trace the position of wave free surface and to calculate the instantaneous surface height and surface potential function. This paper firstly utilizes the ‘0-1' combined BEM to separate the boundary by means of discretization of Green's integral equation based on the Laplace equation, then separates the free surface of wave with FEM and derives the FEM equation of wave surface that satisfies the nonlinear boundary conditions. By jointly solving the above BEM and FEM equations, the wave potential and surface height could be obtained with iteration in time domain. Thus a new kind of nonlinear numerical mode is established for calculating wave transformation. The wave test in the numerical wave tank shows that the numerical simulation with this mode is of high accuracy.

关键词： laplace equation nonlinear wave 0-1 combined type BEM FEM

Fast Evaluation of Time-Domain Green Function for Finite Water Depth

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海洋工程：英文版 2003年第3期17卷 417-426页

作者：滕斌韩凌勾莹 The State key laboratory of coastal and Offshore Engineering

For computation of large amplitude motions of ships fastened to a dock, a fast evaluation scheme is implemented for computation of the time-domain Green function for finite water depth. Based on accurate evaluation of the Green function directly, a fast approximation method for the Green function is developed by use of Chebyshev polynomials. Examinations are carried out of the accuracy of the Green function and its derivatives from the scheme. It is shown that when an appropriate number of polynomial terms are used, very accurate approximation can be obtained.

关键词： Green function time-domain finite water depth

Computation of Viscous Uniform and Shear Flow over A Circular Cylinder by A Finite Element Method

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海洋工程：英文版 2004年第2期18卷 267-280页

作者：赵明滕斌 State key laboratory of coastal and Offshore Engineering

The incompressible viscous uniform and shear flow past a circular cylinder is studied. The two-dimensional Navier-Stokes equations are solved by a finite element method. The governing equations are discretized by a weighted residual method in space. The stable three-step scheme is applied to the momentum equations in the time integration. The numerical model is firstly applied to the computation of the lid-driven cavity flow for its validation. The computed results agree well with the measured data and other numerical results. Then, it is used to simulate the viscous uniform and shear flow over a circular cylinder for Reynolds numbers from 100 to 1000. The transient time interval before the vortex shedding occurs is shortened considerably by introduction of artificial perturbation. The computed Strouhal number, drag and lift coefficients agree well with the experimental data. The computation shows that the finite element model can be successfully applied to the viscous flow problem.

关键词： viscous flow circular cylinder vortex shedding finite element method

Reliability-Based Full-Life Cycle Optimum Design of Offshore Jacket Platform

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海洋工程：英文版 2004年第1期18卷 47-58页

作者：王立成宋玉普 State key laboratory of coastal and Offshore Engineering

Based on the consideration of operation environment and structural property, an optimum design model of offshore jacket platform is developed in this paper, namely, the reliability-based full-life cycle optimum design model. In this model, the time-dependent reliability assessment method for structural members is established by combination of the decrease of sectional size and performance deterioration of material. The initial investment, maintenance cost and failure loss cost are assembled into the model. The total cost of the platform structure system in its full service period is chosen as the objective function, and the initial reliabilities of the layer elements partitioned in advance are taken as the design variables. Different models are obtained, depending on whether the system reliability constraint is considered or not. This optimum design model can result in the lowest full-life cost and the optimal initial layer reliability of an offshore jacket platform in the design of marine structures. The feasibility of this model is illustrated with an actual jacket platform in the Liaodong Gulf as an example.

关键词： offshore jacket platform full-life cycle optimum design model maintenance cost failure loss cost reliability