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Hydrodynamic Characteristics of Square Heaving Plates with Opening Under Forced Oscillation

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China Ocean engineering 2019年第6期33卷 637-648页

作者： CONG Long-fei TENG Bin state key laboratory of coastal and offshore engineering Dalian University of Technology

The existence of the heaving plates can improve the heaving motion performance of an offshore structure significantly by providing both extra added mass and *** the current research,numerical investigation is carried out on the hydrodynamic characteristics of both isolated square heaving plate and double square heaving plates with opening by an immersed boundary-lattice Boltzmann *** effects on hydrodynamic performance of plates due to Keulegan-Carpenter(KC)number,frequency number,opening ratio,opening distribution and spacing of plates are *** is found that the heaving plates with optimized opening ratio can provide additional damping compared with the plates without *** hydrodynamic characteristics of double plates can be obtained with the increase of plate spacing.

关键词： immersed boundary-lattice Boltzmann method square heaving plate opening shape opening ratio opening distribution plate spacing

Bearing Capacity and Critical Punch-Through Depth of Spudcan on Sand Overlying Clay

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China Ocean engineering 2014年第1期28卷 139-147页

作者：刘君于龙周慧孔宪京 state key laboratory of coastal and offshore engineering Dalian University of Technology

Spudcan may experience punch-through failure on strong over weak layered soils, such as sand overlying clay. A large deformation finite element method （LDFE） is used to simulate the penetration process of spudcan into sand overlying clay. The sand is simulated by smoothed hyperbolic Mohr-Coulomb model, and the clay is simulated by a simple elasto-plastic model which obeys Tresca yield criterion. According to the LDFE results of a large amount of cases, the effects of the strength, unit weight and thickness of the top sand layer, as well as the effect of the strength of the underlying clay on the spudcan punch-through behavior, are investigated. The critical depth occurring punch-through and the critical bearing capacity are presented in charts. Fitting equations to calculate the critical punch-through depth and the critical bearing capacity are proposed for the convenience of engineering practice.

关键词： spudcan foundation punch-through sand overlying clay double layer jack-up platform

Adaptive element free Galerkin method applied to analysis of earthquake induced liquefaction

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Earthquake engineering and engineering Vibration 2008年第2期7卷 217-224页

作者：荚颖唐小微栾茂田杨庆 state key laboratory of coastal and offshore engineering Dalian University of Technology

An automatically adaptive element free method is presented to analyze the seismic response of liquefiable soils. The method is based on the element free Galerkin method （EFGM） and the fission procedure that is part of h-refinement, indicated by error estimation. In the proposed method, a posteriori error estimate procedure that depends on the energy norm of stress and the T-Belytschko （TB） stress recovery scheme is incorporated. The effective cyclic elasto-plastic constitutive model is used to describe the nonlinear behavior of the saturated soil. The governing equations are established by u-p formulation. The proposed method can effectively avoid the volumetric locking due to large deformation that usually occurs in numerical computations using the finite element method （FEM）. The efficiency of the proposed method is demonstrated by evaluating the seismic response of an embankment and comparing it to results obtained through FEM. It is shown that the proposed method provides an accurate seismic analysis of saturated soil that includes the effects of liquefaction .

关键词： adaptive element-free Galerkin method soil liquefaction large deformation error estimation seismic response

Numerical Study on the Hydrodynamic Characteristics of Biofouled Full-Scale Net Cage

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China Ocean engineering 2015年第3期29卷 401-414页

作者：毕春伟赵云鹏董国海 state key laboratory of coastal and offshore engineering Dalian University of Technology

The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al.（2006） and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting.

关键词： net cage biofouling drag force flow field numerical simulation

laboratory Study of the Nonlinear Transformation of Irregular Waves over A Mild Slope

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China Ocean engineering 2014年第4期28卷 489-500页

作者：于博马玉祥马小舟董国海 state key laboratory of coastal and offshore engineering Dalian University of Technology

This paper considers the nonlinear transformation of irregular waves propagating over a mild slope （1：40）. Two cases of irregular waves, which are mechanically generated based on JONSWAP spectra, are used for this purpose. The results indicate that the wave heights obey the Rayleigh distribution at the offshore location; however, in the shoaling region, the heights of the largest waves are underestimated by the theoretical distributions. In the surf zone, the wave heights can be approximated by the composite Weibull distribution. In addition, the nonlinear phase coupling within the irregular waves is investigated by the wavelet-based bicoherence. The bicoherence spectra reflect that the number of frequency modes participating in the phase coupling increases with the decreasing water depth, as does the degree of phase coupling. After the incipient breaking, even though the degree of phase coupling decreases, a great number of higher harmonic wave modes are also involved in nonlinear interactions. Moreover, the summed bicoherence indicates that the frequency mode related to the strongest local nonlinear interactions shifts to higher harmonics with the decreasing water depth.

关键词： irregular waves shallow water nonlinear interactions wave height distribution wavelet bicoherence

Hydrodynamic Analysis of Elastic Floating Collars in Random Waves

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China Ocean engineering 2015年第3期29卷 341-356页

作者：白晓东赵云鹏董国海李玉成 state key laboratory of coastal and offshore engineering Dalian University of Technology

As the main load-bearing component of fish cages, the floating collar supports the whole cage and undergoes large deformations. In this paper, a mathematical method is developed to study the motions and elastic deformations of elastic floating collars in random waves. The irregular wave is simulated by the random phase method and the statistical approach and Fourier transfer are applied to analyze the elastic response in both time and frequency domains. The governing equations of motions are established by Newton＇s second law, and the governing equations of deformations are obtained based on curved beam theory and modal superposition method. In order to validate the numerical model of the floating collar attacked by random waves, a series of physical model tests are conducted. Good relationship between numerical simulation and experimental observations is obtained. The numerical results indicate that the transfer function of out-of-plane and in-plane deformations increase with the increasing of wave frequency. In the frequency range between 0.6 Hz and 1.1 Hz, a linear relationship exists between the wave elevations and the deformations. The average phase difference between the wave elevation and out-of-plane deformation is 60° with waves leading and the phase between the wave elevation and in-plane deformation is 10° with waves lagging. In addition, the effect of fish net on the elastic response is analyzed. The results suggest that the deformation of the floating collar with fish net is a little larger than that without net.

关键词： floating collars random waves hydrodynamic characteristics in-plane and out-of-plane deformation net effect

laboratory investigation of the hydroelastic effect on liquid sloshing in rectangular tanks

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Journal of Hydrodynamics 2014年第5期26卷 751-761页

作者：蒋梅荣任冰王国玉王永学 state key laboratory of coastal and offshore engineering Dalian University of Technology

A sloshing experiment is conducted to study the hydroelastic effect in an elastic tank. For this purpose, a translational harmonic excitation is applied to a 2-D rectangular tank model. The lowest-order natural frequencies of the liquid in the tank are determined through the sweep test. The wave elevation and the sloshing pressure are obtained by changing the excitation frequency and the liquid depth. Then the characteristics and the variation of the elevation and the pressure are discussed. The results are compared with the experimental results and the theoretical calculations in a rigid tank. Our analysis indicates that, in the non- resonant cases, the elastic results, the rigid experimental results and the theoretical values are all close to each other. In contrast, under the resonant condition, the elastic experimental result is slightly smaller than the rigid one. Also, the theoretical values are smaller than the experimental results at the resonant frequency.

关键词： liquid sloshing elastic tank wave elevation sloshing pressure

Examination of Extraordinary Transmission of Waves Propagation through Gaps of Vertical Thin Barriers in Channels by A Hypersingular Boundary Element Method

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China Ocean engineering 2019年第5期33卷 509-521页

作者： TENG Bin HUANG Jin state key laboratory of coastal and offshore engineering Dalian University of Technology

The extraordinary transmission (ET) phenomenon is examined for waves propagating through gaps of vertical thin barriers in channels with a hypersingular boundary element method model on the linear potential theory, and an estimate formula based on small gap approximation for predicting the number of ET frequencies is proposed. Numerical computations are carried out to examine the influences of barrier number, barrier interval, gap size, gap position and barrier arrangement on extraordinary transmission and wave height in the channel. It shows that all of those factors evidently affect the extraordinary transmission frequencies. The contours of wave amplitude show that very high waves can be excited in the basins between barriers at the extraordinary transmission frequencies. Proper arrangement of barriers in a channel can avoid the occurrence of ET phenomenon and reduce wave height in the channel.

关键词： extraordinary transmission reflection and transmission coefficients wave height in channels hypersingular BEM

Experimental investigation of motion responses of tunnel element immerging by moored barge

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Journal of Hydrodynamics 2015年第6期27卷 857-864页

作者：左卫广王永学 state key laboratory of coastal and offshore engineering Dalian University of Technology

In this paper, the barge effect on the motion responses of the ttmnel element immerging by the moored barge under waves is investigated experimentally. Both the motion responses of the tunnel element and the moored barge in the experiment are simultaneously acquired by the Untouched 6-D Measurement System. The results show that the sway motion responses of the tunnel element immerging by the moored barge are different from those without the barge. For the system of the tunnel element and the moored barge, the moored barge has two motion components in the sway direction. The high frequency motion of the moored barge has little effect on the high frequency motion of the tunnel element with moored barge. However, the low frequency motion of the moored barge has a significant effect on the sway motion of the tunnel element. The motion responses of the tunnel element and the barge in the heave and roll directions are mainly the high frequency motion.

关键词： tunnel element moored barge motion responses low frequency motion maximum offset