共查询到20条相似文献，搜索用时 625 毫秒
1.
A full time-domain analysis program is developed for the coupled dynamic analysis of offshore structures. For the hydrodynamic loads, a time domain second order method is developed. In this approach, Taylor series expansions are applied to the body surface and free-surface boundary conditions, and the Stokes perturbation procedure is then used to establish the corresponding boundary value problems with time-independent boundaries. A higher-order boundary element method (HOBEM) is developed to calculate the velocity potential of the resulting flow field at each time step. The free-surface boundary condition is satisfied to the second order by fourth order Adams–Bashforth–Moultn method. An artificial damping layer is adopted on the free surface to avoid the wave reflection. The mooring-line/tendon/riser dynamics are based on the rod theory and the finite element method (FEM), with the governing equations described in a global coordinate system. In the coupled dynamic analysis, the motion equation for the hull and dynamic equations for mooring-lines/tendons/risers are solved simultaneously using the Newmark method. The coupled analysis program is applied for a truss Spar motion response simulation. Numerical results including motions and tensions at the top of mooring-lines/risers are presented, and some significant conclusions are derived. 相似文献
2.
The performance of regional tide model simulations is examined in relation to the choice of open boundary conditions. Three barotropic open boundary conditions, clamped elevation, clamped normal velocity, and Flather, give similar results when the prescribed values are exact; however, Flather is much less sensitive to errors in the prescribed values. Of particular concern, it was found that with a phase error between the two boundaries, both the clamped conditions resulted in magnitude errors in the unclamped variable (although the simulation remained stable).A modified flow relaxation scheme for the depth-varying prognostic variables is presented. This implementation allows the transmission of a range of vertical modes while retaining realistic topography at the boundary. It was found to be an excellent internal tide boundary condition in tests comparing simulations of different domain length encompassing a ridge and sloping bottom, and in a comparison to an analytical solution. Mass is conserved without any artificial volume constraint. 相似文献
3.
A numerical model for coastal water wave motion that includes an effective method for treatment of non-reflecting boundaries is presented. The second-order one-way wave equation to approximate the non-reflecting boundary condition is found to be excellent and it ensures a very low level of reflection for waves approaching the boundary at a fairly wide range of the incidence angle. If the Newman approximation is adopted, the resulting boundary condition has a unique property to allow the free propagation of wave components along the boundary. The study is also based on a newly derived mild-slope wave equation system that can be easily made compatible to the one-way wave equation. The equation system is theoretically more accurate than the previous equations in terms of the mild-slope assumption. The finite difference method defined on a staggered grid is employed to solve the basic equations and to implement the non-reflecting boundary condition. For verification, the numerical model is then applied to three coastal water wave problems including the classical problem of plane wave diffraction by a vertical circular cylinder, the problem of combined wave diffraction and refraction over a submerged hump in the open sea, and the wave deformation around a detached breakwater. In all cases, the numerical results are demonstrated to agree very well with the relevant analytical solutions or with experimental data. It is thus concluded that the numerical model proposed in this study is effective and advantageous. 相似文献
4.
A time-domain method is applied to simulate nonlinear wave diffraction around a surface piercing 3-D arbitrary body. The method involves the application of Taylor series expansions and the use of perturbation procedure to establish the corresponding boundary value problems with respect to a time-independent fluid domain. A boundary element method based on B-spline expansion is used to calculate the wave field at each time step, and the free surface boundary condition is satisfied to the second order of wave steepness by a numerical integration in time. An artificial damping layer is adopted on the free surface for the removal of wave reflection from the outer boundary. As an illustration, the method is used to compute the second-order wave forces and run-up on a surface-piercing circular cylinder. The present method is found to be accurate, computationally efficient, and numerically stable. 相似文献
5.
A Novel VOF-Type Volume-Tracking Method for Free-Surface Flows Based on Unstructured Triangular Mesh 总被引：4，自引：3，他引：4
A novel VOF-type volume-tracking method for two-dimensional free-surface flows based on the unstructured triangular mesh is presented. Owing to the inherent merit of the unstructured triangular mesh in fitting curved boundaries, this method can handle the free-surface problems with complex geometries accurately and directly, without introducing any complicated boundary treatment or artificial diffusion. The method solves the volume transport equation geometrically through the Modified Lagrangian-Eulerian Re-map （MLER） method, which is applied to advective fluid volumes. Moreover, the PLIC method is adopted to give a second-order reconstructed interface approximation. To validate this method, two advection tests were performed for the establishment of the accuracy and convergence rate of the solutions. Numerical results for these complex tests provide convincing evidence for the excellent solution quality and fidelity of the method. 相似文献
6.
Based on the Rankine source, this paper proposed a time-domain method for analyzing the three-dimensional wave–structure interaction problem in irregular wave. A stable integral form of the free-surface boundary condition (IFBC) is employed to update the velocity potential on the free surface. A multi-transmitting formula, with an artificial wave speed, is used to eliminate the wave reflection for radiation condition on the artificial boundary. An effective multi-transmitting formula, coupled with damping zone method, is further used to analyze the irregular wave diffraction at the artificial boundary. We investigate hydrodynamic forces on floating structure and compare our solution to the frequency-domain solution. It is shown that long time simulation can be done with high stability and the numerical results agree well with the solution obtained under the frequency domain. The efficiency of the proposed multi-transmitting formula and the coupled methods for radiation boundary make them promising candidates in studying the irregular water wave problem in time domain. 相似文献
7.
Hasanuddin Z. Abidin S. Sutisna T. Padmasari K. J. Villanueva J. Kahar 《Marine Geodesy》2013,36(4):291-304
Indonesia has maritime boundaries with 10 countries namely: Australia, Timor Leste, Papua New Guinea (PNG), Palau, Philippines, Vietnam, Thailand, Malaysia, Singapore, and India. Many treaties have been ratified concerning these boundaries. Unfortunately, many coordinates of boundary points mentioned in the treaties are not clear in relation to their geodetic datum. The uncertainty in geodetic datum of boundary points introduces complications and problems in spatial management of Indonesia's maritime boundaries, since it can displace the boundary lines from their assumed true location. This study investigates the possible original geodetic datums for the maritime boundaries between Indonesia and neighboring countries, in the case they are not explicitly stated in the treaties. The displacements of boundaries in WGS84 datum are generally in the order of a few hundred meters, i.e., about 200 to 400 m, depending on the assumed original geodetic datum being considered. These boundary displacements are spatially advantageous for Indonesia in some cases and also disadvantageous in others. The study will sum up with some conclusions and recommendations. 相似文献
8.
In this work, a combined immersed boundary (IB) and volume of fluid (VOF) methodology is developed to simulate the interactions of free-surface waves and submerged solid bodies. The IB method is used to account for the no-slip boundary condition at solid interfaces and the VOF method, utilizing a piecewise linear interface calculation, is employed to track free surfaces. The combined model is applied in several case studies, including the propagation of small-amplitude progressive waves over a submerged trapezoidal dike, a solitary wave traveling over a submerged rectangular object, and wave generation induced by a moving bed. Numerical results depicting the free-surface evolutions and velocity fields are in good agreement with either experimental data or numerical results obtained by other researchers. In addition, the simplification of the initial free-surface deformation used in most tsunami earthquake source study is justified by the present model application. The methodology presented in the paper serves as a good tool for solving many practical problems involving free surfaces and complex boundaries. 相似文献
9.
Hasanuddin Z. Abidin S. Sutisna T. Padmasari K. J. Villanueva J. Kahar 《Marine Geodesy》2005,28(4):291-304
Indonesia has maritime boundaries with 10 countries namely: Australia, Timor Leste, Papua New Guinea (PNG), Palau, Philippines, Vietnam, Thailand, Malaysia, Singapore, and India. Many treaties have been ratified concerning these boundaries. Unfortunately, many coordinates of boundary points mentioned in the treaties are not clear in relation to their geodetic datum. The uncertainty in geodetic datum of boundary points introduces complications and problems in spatial management of Indonesia's maritime boundaries, since it can displace the boundary lines from their assumed true location. This study investigates the possible original geodetic datums for the maritime boundaries between Indonesia and neighboring countries, in the case they are not explicitly stated in the treaties. The displacements of boundaries in WGS84 datum are generally in the order of a few hundred meters, i.e., about 200 to 400 m, depending on the assumed original geodetic datum being considered. These boundary displacements are spatially advantageous for Indonesia in some cases and also disadvantageous in others. The study will sum up with some conclusions and recommendations. 相似文献
10.
Open boundaries are important when simulating water waves. In this study, a transparent boundary condition at an open boundary was developed for simulating nonlinear water waves propagating to a distant area using the Moving Particle Semi-implicit method. The novelty of this study is that the technique of wave analysis used in the experiment was introduced into the particle simulation to absorb incident waves; the simulation cost was reduced by employing inflow and outflow regions instead of a long dissipation region. Incident waves in front of the boundary were evaluated using Fourier analysis, and the particles on the transparent boundary were forced to move at the velocity of the analytical solution for Stokes waves in order to absorb the incident waves. The analysis was restricted to periodic waves. Wave propagation was simulated for two wave periods using the developed transparent boundary condition. The results showed that this transparent boundary transmitted the incident waves with small reflection and the simulation cost was lower than that for wave damping by a conventional highly viscous region. 相似文献
11.
Numerical modeling of coastal circulation encompassing the nearshore requires forcing by tide, surface gravity waves, and possibly other factors. In the nearshore, the wave-induced longshore current and setup are dominant hydrodynamic processes, and lateral boundary conditions representing tide and oceanic forcing typically do not include surface-wave contributions. Without proper boundary conditions, significant gradients in current and water level can occur that contaminate the solution in the internal domain. A standard strategy is to place the boundaries far from the site of interest, but this strategy greatly increases computational demands, and it may not be appropriate for long-term simulations. This paper describes a wave-adjusted boundary condition that accounts for wave-induced water level and current acting in combination with tidal forcing. The wave-adjusted boundary condition is demonstrated for an idealized case of a parallel-contour beach and for an engineering application at Ocean City, MD. 相似文献
12.
SONG Zhiyao XUE Hongchao YAN Yixin
Doctor Senior Engineer College of Harbor Waterway Coastal Engineering Hohai University 《中国海洋工程》1999,(4)
To deal with the problems concerning the shore boundary,moving boundary and engineeringboundary which are encountered frequently in 2D tidal current simulation by the finite difference method,theconcept of line boundary is introduced and studied here,and then the line boundary technique in common useis proposed in this paper.Analysis of some calculation cases shows that this technique is practical,effective,and simple in 2D tidal current simulation involving different boundaries. 相似文献
13.
The paper analyzes the effect which prescribed errors in the cross-shore boundary conditions for a computational domain along a beach have on the flow field predicted inside the domain. This problem is relevant because errors in boundary conditions are unavoidable when modeling limited domains of a nearshore region. For simplicity, we consider a longshore uniform plane beach with monochromatic, obliquely incident waves, and assume depth uniform currents. It is then studied analytically and numerically how small perturbations of the boundary conditions along both upstream and downstream cross-shore boundaries spread inside the computational domain. It is found that the errors at the upstream cross-shore boundary tend to spread over a long distance downstream of the boundary, while the influence of the errors in the downstream boundary condition is limited to the adjacent upstream area of the computational domain. Both the numerical and analytical solutions show that the errors introduced at the upstream boundary decay exponentially in the surf zone at a rate proportional to the bottom friction. A simple formula is developed to estimate the influence distance of the upstream errors. If we consider the mismatch in the volume flux at the upstream boundary, the error merely redistributes in the cross-shore direction to conserve volume. In the case of excessive flux or velocity specified at the cross-shore boundaries, a circulation cell tends to appear in the offshore region where the errors caused by the boundary mismatch increase with the cross-shore width of the model domain. 相似文献
14.
An effective boundary element method (BEM) is presented for the interaction between oblique waves and long prismatic structures in water of finite depth. The Green's function used here is the basic Green's function that does not satisfy any boundary condition. Therefore, the discretized elements for the computation must be placed on all the boundaries. To improve the computational efficiency and accuracy, a modified method for treatment of the open boundary conditions and a direct analytical approach for the singularity integrals in the boundary integral equation are adopted. The present BEM method is applied to the calculation of hydrodynamic coefficients and wave exciting forces for long horizontal rectangular and circular structures. The performance of the present method is demonstrated by comparisons of results with those generated by other analytical and numerical methods. 相似文献
15.
基于GF-1卫星遥感影像的海岸线生态化监测与评价研究——以营口市为例 总被引：1，自引：0，他引：1
海岸线是海洋与陆地的分界线,也是重要的生态交错线。本文采用GF-1卫星遥感影像,通过监测大潮高潮时刻和小潮低潮时刻海岸水陆边界线,构建了潮间带完整性系数,以此为依据将海岸线划分为自然海岸线、具有基本生态功能的人工海岸线、具有部分生态功能的人工海岸线、具有有限生态功能的人工海岸线、具有少量生态功能的人工海岸线和无生态功能的人工海岸线。在此基础上,结合潮间带完整性系数及其毗邻海岸线长度,构建了海岸线生态化指数,用以评价区域海岸线的生态化程度。营口市海岸线以无生态功能的人工海岸线、自然海岸线和具有少量生态功能的人工海岸线为主,分别占到海岸线总长度的45.74%、18.31%和15.53%。营口市总体海岸线生态化指数为0.29,其中西城区、老边区、盖州北、鲅鱼圈区和盖州南分别为0.55、0.17、0.40、0.10和0.55。 相似文献
16.
本文用有限元法配合时步处理来求解三维非线性水波的绕射问题,自由表面条件和物面条件都满足到二阶,采用人工阻尼区来吸收反射波,流场内的速度势通过求解有限元方程得到。对垂直圆柱体的绕射问题进行了计算,得到了自由表面波高时间历程和圆柱所受到的波浪力,计算结果和有关文献的理论计算结果进行了比较。 相似文献
17.
This paper proposes a new approximation to energy dissipation in time domain simulation of sloshing waves by use of a linear potential theory.The boundary value problem is solved by the NURBS(non-uniform rational B-spline) higher-order panel method,in which a time-domain Green function is employed.The energy dissipation is modeled by changing the boundary condition on solid boundaries.Model experiments are carried out in a partially filled rectangular tank with forced horizontal motion.Sloshing-induced internal pressures and horizontal force obtained numerically and experimentally are compared with each other.It is observed that the present energy dissipation approximation can help produce a fair agreement between experimental forces and those of numerical simulations. 相似文献
18.
海底地理实体的划定与命名是当前国际海洋权益领域的热点研究问题之一。然而,由于海底地理实体边界的量化界定技术缺乏,导致其界线确定不可避免地存在人为性,为此,本文提出了一种基于D-P算法和最优路径的海底地理实体边界划定方法。将高分辨率水深模型转换为二维水深矩阵,从横向与纵向进行剖面分析,采用极值点简化和D-P算法进行二次简化的方法,通过坡度变化定位和基部高程定位等基本条件综合判断,从而实现了单体海山的山体与其基部的自动划分;在此基础上,采用路径寻优的方法实现了连体型海山的自动分割。该方法在南海海底地理实体划定中进行了验证,取得了良好的应用效果。 相似文献
19.
In order to fulfill the no-slip condition at the western and eastern boundaries of the ocean basin, introduced ＂effective wind stress＂, which has much larger spatial variations towards the boundaries than in the ocean interior. The effective wind stress can thus be decomposed into spatially slow-varying and fast varying components. Careful scale analysis on the classical Munk winddriven ocean circulation theory, which consists of the interior Sverdrup flow and the western boundary current but of no eastern boundary current, shows that the wind stress curl appearing in the Sverdrup equation must have negligible spatial variations. In the present model the spatially slow-varying component of the wind stress appears in the Sverdrup equation, and the spatially fastvarying component becomes the forcing term of the boundary equations. As a result, in addition to the classical Munk solution the present model has an extra term at the western boundary which （Northern Hemisphere） increases the northward transport as well as the southward return transport, and has a term at the eastern boundary corresponding to the eastern boundary current. 相似文献
20.
闽江口水动力和污染扩散数值模拟 总被引：3，自引：0，他引：3
本文建立了闽江口二维水动力、污染扩散数值模型，模型采用ＡＤＩ双向隐式求解。在水动力模拟中，对岸界的丁坝有用线性边界进行拟合，并考虑到河口区侧向摩擦作用；在污染扩散模拟中，用动态拟合的方法对浓度水边界进行了较为合理的改进。计算结果表明，本模型是成功的。 相似文献