Numerical Simulation of Wave Forces on Seabed Pipelines

A three-step finite element method(FEM)together with Large Eddy Simulation(LES)is ap-plied to incompressible turbulent flow around seabed pipelines at relatively high Reynolds numbers.Bothtwo-dimensional and three-dimensional numerical simulation is carried out to determine thethree-dimensional effect.The results of numerical simulation agree quite well with the wave forces actingon pipeline models measured in physical model test.     

A Coupling Model of Nonlinear Wave and Sandy Seabed Dynamic Interaction

In the paper,a weak coupling numerical model is developed for the study of the nonlinear dynamic interaction between water waves and permeable sandy seabed.The wave field solver is based on the VOF(Volume of Fluid)method for continuity equation and the two-dimensional Reynolds Averaged Navier Stokes(RANS)equations with a k-ε closure.The free surface of cnoidal wave is traced through the PLIC-VOF(Piecewise Linear Interface Construction).Biot's equations have been applied to solve the sandy seabed,and the u-p finite element formulations are derived by the application of the Galerkin weighted-residual procedure.The continuity of the pressure on the interface between fluid and porous medium domains is considered.Laboratory tests were performed to verify the proposed numerical model,and it is shown that the pore-water pressures and the wave heights computed by the VOF-FEM models are in good agreement with the experimental results.It is found that the proposed model is effective in predicting the seabed-nonlinear wave interaction and is able to handle the wave-breakwater-seabed interaction problem.     

海底沉积物实验室剪切波速度及其与沉积物的物理性质之间的关系

采用压电陶瓷弯曲元法和共振柱试验的方法对采自我国海域的一些典型海底浅表层沉积物样品进行了剪切波速测试,获得首批可信数据.两种方法所测得的剪切波速数据具有很好的一致性,且在数赫兹至数十千赫兹频段范围内剪切波速不具明显弥散性.剪切波速与沉积物类型关系密切,不同海区和不同类型海底沉积物的剪切波速有明显差异.近海较细颗粒沉积物粉砂的剪切波速在100m/s左右,细颗粒沉积物的剪切波速在100m/s以下;陆架较粗颗粒沉积物的剪切波速最大,超过100m/s;深海、半深海细颗粒沉积物的剪切波速最低,小于50m/s.剪切波速与含水量、密度、孔隙度、塑限和液限等沉积物物理参数之间具很好的相关性,反映了剪切波速和物理性质之间的密切关系.剪切波速与压缩波速呈正相关性,但在不同的波速范围剪切波速随压缩波速的变化有很大不同.     

Analytical Solution for the Transient Response of A Sloping Seabed Induced by A P-Wave Line Source

Many offshore marine structures are built on the seabed that are slightly or considerably sloping. To study the sloping seabed transient response during marine earthquakes, an analytical solution induced by a P-wave line source embedded in the solid is presented. During the derivation, the wave fields in the fluid layer and the semi-infinite solid are firstly constructed by using the generalized ray method and the fluid-solid interface reflection and transmission coefficients.Then, the analytica...     

Determination of Deformation Modulus for Lower Sands in Nakdong River Delta

The deformation modulus of sands below 30 m in the Nakdong River Delta was estimated by using various in-situ tests, such as the piezocone penetrometer (CPT), seismic dilatometer (SDMT), and pressuremeter tests (PMT). Disturbed sand samples retrieved at several depths of two boreholes were reconstituted to simulate the in-situ deposited condition using a slurry method. Thereafter, the drained triaxial compression (TX) and the resonant column (RC) tests were also conducted. The elastic modulus obtained through the application of the TX and PMT results to conventional methods led to the underestimation of the in-situ values, because the inherent characteristics of the natural sands were not considered. Thus, the non-linear modulus degradation curves were constructed using the modulus degradation from the TX, RC, PMT, and the in-situ maximum shear modulus from SDMT. Thereafter, the modulus at 25% failure stress strength was re-evaluated. The re-evaluated values from the TX were in good agreement with those from the PMT, using the unloading curves and with the existing empirical equation based on the seismic CPT. Finally, a CPT-compatible empirical formula for the deformation modulus at 25% failure strength was proposed.     

3-D Shear Wave Velocity Structure of the Crust and Upper Mantle in South China Sea and its Surrounding Regions by Surface Wave Dispersion Analysis

In this study, we construct a 3-D shear wave velocity structure of the crust and upper mantle in South China Sea and its surrounding regions by surface wave dispersion analysis. We use the multiple filter technique to calculate the group velocity dispersion curves of fundamental mode Rayleigh and Love waves with periods from 14 s to 120 s for earthquakes occurred around the Southeast Asia. We divide the study region (80° E–140° E, 16° S–32° N) into 3° × 3° blocks and use the constrained block inversion method to get the regionalized dispersion curve for each block. At some chosen periods, we put together laterally the regionalized group velocities from different blocks at the same period to get group velocity image maps. These maps show that there is significant heterogeneity in the group velocity of the study region. The dispersion curve of each block was then processed by surface wave inversion method to obtain the shear wave velocity structure. Finally, we put the shear wave velocity structures of all the blocks together to obtain the three-dimensional shear wave velocity structure of crust and upper mantle. The three-dimensional shear wave velocity structure shows that the shear wave velocity distribution in the crust and upper mantle of the South China Sea and its surrounding regions displays significant heterogeneity. There are significant differences among the crustal thickness, the lithospheric thickness and the shear wave velocity of the lid in upper mantle of different structure units. This study shows that the South China Sea Basin, southeast Sulu Sea Basin and Celebes Sea Basin have thinner crust. The thickness of crust in South China Sea Basin is 5–10 km; in Indochina is 25–40 km; in Peninsular Malaysia is 30–35 km; in Borneo is 30–35 km; in Palawan is 35 km; in the Philippine Islands is 30–35 km, in Sunda Shelf is 30–35 km, in Southeast China is 30–40 km, in West Philippine Basin is 5–10 km. The South China Sea Basin has a lithosphere with thickness of about 45–50 km, and the shear wave velocity of its lid is about 4.3–4.7 km/s; Indochina has a lithosphere with thickness of about 55–70 km, and the shear wave velocity of its lid is about 4.3–4.5 km/s; Borneo has a lithosphere with thickness of about 55–60 km, and the shear wave velocity of its lid is about 4.1–4.3 km/s; the Philippine Islands has a lithosphere with thickness of about 55–60 km, and the shear wave velocity of its lid is about 4.2–4.3 km/s, West Philippine Basin has a lithosphere with thickness of about 50–55 km, and the shear wave velocity of its lid is about 4.7–4.8 km/s, Sunda Self has a lithosphere with thickness of about 55–65 km, and the shear wave velocity of its lid is about 4.3 km/s. The Red-River Fault Zone probably penetrates to a depth of at least 200 km and is plausibly the boundary between the South China Block and the Indosinia Block.     

成层海床波浪响应的状态空间解及其应用

针对成层海床的波浪响应问题,采用Laplace-Fourier变换和状态空间法求解控制方程,得到表征该问题基本状态量之间的传递矩阵。利用矩阵递推规律、边界条件及逆变换技术实现成层海床波浪响应的计算。以北海和密西西比三角洲的波浪和海床特征为参数进行算例分析,结果表明该方法具有较高的效率和精度。结合北海的工况指出在砂质海床的表面铺设一层砾石土可以增强海床的抗液化能力,起到保护海床的作用。     

波浪与结构物作用分析的一种高阶边界元方法--自由项和柯西主值积分的直接数值计算

采用直接数值计算方法计算了势流问题高阶边界元方法中的自由项系数和柯西主值积分,建立了波浪与结构物作用的一种高阶边界元方法.通过算例研究了物体表面上固角系数的计算精度和不同网格剖分、不同阶高斯积分点对柯西主值积分的影响.对截断圆柱上的波浪作用力与解析解做了对比,发现本方法具有很高的计算精度,随网格的加密迅速收敛于解析解.     

An Analytical Solution for Dynamic Response of the Plate with Different Impedances Subjected to Underwater Explosion

In this paper, the transmitted part of the incident wave is considered to revise Taylor’s solution, which is used to extend its application for analytical models to predict the response of the plate with different material properties. The influence of the material properties and the boundary condition of the plate on fluid and structural dynamics is systematically investigated. The analytical results are compared with those of detailed dynamic FE simulations and the two are in good agreement. The results indicate that the analytical method is valid and suitable for the plates with different material properties subjected to underwater explosion. It is found that Taylor’s results of the plate with small impedance are invalid, which indicates a potential application field for the analytical method.     

Analytical method of radiation by a wave energy device with dual rectangular floating bodies

The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device on a plane incident wave is solved by the use of an eigenfunction expansion method, and a new analytical expression for the radiation velocity potential is obtained. The wave excitation force is calculated via the known incident wave potential and the radiation potential with a theorem of Haskind employed. To verify the correctness of this method, an example is computed respectively through the bound element method and analytical method. Results show that two numerical methods. are in good agreement, which shows that the present method is applicable. In addition, the trends of hydrodynamic coefficients and wave force are analyzed under different conditions by use of the present analytical method.     

柱对称双浮子波能装置散射问题的解析方法

通过构造绕射势特解的一种新表达式,基于特征函数展开法提出了线性入射波作用下柱对称双振荡浮子波能装置散射问题的一种新的表达式,并在此基础上计算了垂向波浪激励力.从速度势的求解过程可知,绕射势和辐射势的计算量相当,但垂向波浪激励力的计算比采用Haskind关系方法简单得多,两种方法的结果一样.另外对不同工况下垂向波浪激励力的变化趋势进行了分析.     

Comparative Study on Response Surfaces for Reliability Analysis of Spatially Variable Soil Slope

This paper focuses on the performance of the second-order polynomial-based response surfaces on the reliability of spatially variable soil slope. A single response surface constructed to approximate the slope system failure performance function G(X) (called single RS) and multiple response surfaces constructed on finite number of slip surfaces (called multiple RS) are developed, respectively. Single RS and multiple RS are applied to evaluate the system failure probability pf for a cohesive soil slope together with Monte Carlo simulation (MCS). It is found that pf calculated by single RS deviates significantly from that obtained by searching a large number of potential slip surfaces, and this deviation becomes insignificant with the decrease of the number of random variables or the increase of the scale of fluctuation. In other words, single RS cannot approximate G(X) with reasonable accuracy. The value of pf from multiple response surfaces fits well with that obtained by searching a large number of potential slip surfaces. That is, multiple RS can estimate G(X) with reasonable accuracy.     

大深度分层流体中二维淹没浮体的波浪力分析

研究了大深度分层流体中二维任意形状淹没浮体的波浪力特性。首先基于一种合适的格林函数,采用边界积分方程法研究了流体中浮体对水波散射问题,然后通过单个淹没圆柱体的透射能和反射能与解析方法结果的比较,对所提出的方法进行了验证,最后分析了在不同的几何和物理条件下几种形状的浮体对波浪力的特有影响,得到了一些有意义的结果,这对分层海洋中淹没浮体的设计具有重要的参考价值。     

南黄海中部海底沉积物剪切波速度测量及其与物理力学性质参数的关系

采用弯曲元剪切波测试方法对在南黄海中部采集到的沉积物样品进行了剪切波速度测试,基于所获得的剪切波速度数据,分析了研究区沉积物剪切波速度特性及分布规律。分析表明,沉积物剪切波速度为12.05~74.55m/s,总体相对较低。浅表层沉积物剪切波速度呈现出分区域分布特征,可分为东北部低速区、西南部高速区、北西-南东向梯度带以及测区东南部的低速背景上的串珠状高速异常区四个区域。通过回归分析,建立了剪切波速度与密度、含水率、孔隙比、孔隙度、液限、塑限、压缩系数、抗剪强度等沉积物物理力学参数之间相互关系的经验回归公式。回归分析结果表明,海底沉积物剪切波速度与上述物理力学参数之间均具有较好的相关性,相关系数R均大于0.80。     

Comparison of Remolded Shear Strength with Intrinsic Strength Line for Dredged Deposits

Chandler proposed the intrinsic strength line to correlate the undrained shear strength of samples one-dimensionally consolidated from slurry with the void index proposed by Burland. The undrained shear strength on the intrinsic strength line is different from the remolded undrained shear strength that is an important parameter for design and construction of land reclamation. The void index is used in this study for normalizing the remolded strength behavior of dredged deposits. A quantitative relationship between remolded undrained shear strength and void index is established based on extensive data of dredged deposits available from sources of literature. Furthermore, the normalized remolded undrained shear strength is compared with intrinsic strength line. The comparison result indicates that the ratio of undrained shear strength on the intrinsic strength line over remolded undrained shear strength increases with an increase in applied consolidated stress.     

粉沙海床管道在联锁排防护下的冲刷试验研究

采用当地海床的天然粉沙进行试验床面的设计,对海底管道在实际海床受到的极限波浪和最大水流作用进行试验,在管道上方铺设混凝土联锁排,对联锁排块体稳定性和其对管道防护的有效性进行研究。通过物理模型试验,研究了在极限波浪和最大水流作用下,管道在粉沙床面最大冲刷深度。通过不同水深中波流条件下研究了混凝土联锁排防护效果及其周围床面的冲刷变化,观测了联锁排的稳定性。试验结果表明:按半经验半理论简化公式得出的联锁排厚度能满足稳定性的要求,比水利部规范计算的联锁排厚度偏大的公式更加适合应用,试验期间混凝土联锁排的排面稳定,能有效保护管道,在该防护下管道没有冲刷,只在联锁排上下游与床面接触的来流段和尾端有冲刷,但该冲刷深度不影响联锁排整体的稳定性。     

Application of the state space model to the system of wave energy conversion Analytical method for wave forces on single oscillating rectangular buoy

A new analytical method is proposed to analyze the force acting on a rectangular oscillating buoy due to linear waves. In the method a new analytical expression for the diffraction velocity potential is obtained first by use of the eigenfunction expansion method and then the wave excitation force is calculated by use of the known incident wave potential and the diffraction potential. Compared with the classical analytical method, it can be seen that the present method is simpler for a two-dimensional problem due to the comparable effort needed for the computation of diffraction potential and for that of radiated potential. To verify the correctness of the method, a classical example in the reference is recomputed and the obtained results are in good accordance with those by use of other methods, which shows that the present method is correct.     

Numerical Solution of Membrane Forces for A Free-Free Floating Plate with Large Deflection

1 .IntroductionVerylargefloatingstructures (VLFS)haveattractedconsiderableattentionrecentlyduetoitspo tentialuseintheexploitationofoceanresourcesandintheutilizationofoceanspaces (Cui,2 0 0 2 ) .Owingtoitslargesizeandrelativelysmallthickness ,theinfluenceofelasticdeformationonthehydro dynamicresponseisimportant.Thisisknownashydroelasticity .Threedimensionallinear (Wu ,1 984;PriceandWu ,1 985)andnonlinear (Chenetal.,2 0 0 3)hydroelasticityiswellappliedtotheanalysisofthreedimensionalshipsando…     

近岸波浪折射-绕射-破波耗散联合模式的有限元数值研究

建立了近岸波浪折射-绕射-破波耗散的有限元数值模式。采用的有限元方法为改进的混合元法,其中外域开边界条件得到改进,内域有限元为伽廖金有限元。用理论解检验了所建立的数值模式,并将该模式应用到一个模型港湾。     

水深有陡变的人工港域内波高分布的数值计算方法

首次将单源点法应用于水深有陡变的人工港域内波高分布的数值计算,结果与一维理论解符合极好,并与工程实例的物理模型试验结果符合也很好.