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1 .IntroductionOffshoreplatformsarelargescalesteelorconcretestructures.Theyexperiencevariouskindsofdamagessuchasdents ,corrosionpits ,cracks ,deformation ,etc .,afteryearsofenvironmentalimpactofwinds ,waves ,currents ,soilreactions ,earthquakesandice (DuanandLiu ,1 995) .Thesafetyofthestructureshasalwaysbeenthemostimportantissueconcerned ,anditdependsontheassessmentoftheintegrityofthestructures,orspecificallyontheassessmentofthedamagesinthestructures .Riclesetal.( 1 994)experimentallyinvestig… 相似文献
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This paper analyses nonlinear dynamics of cable towed body system. The cable has been modeled and analyzed using a new nodal position finite element method, which calculates the position of the cable directly instead of the displacement by the existing finite element method. The newly derived nodal position finite element method eliminates the need of decoupling the rigid body motion from the total motion, where numerical errors arise in the existing nonlinear finite element method, and the limitation of small rotation in each time step in the existing nonlinear finite element method. The towed body is modeled as a rigid body with six degrees of freedom while the tow ship motion is treated as a moving boundary to the system. A special procedure has been developed to couple the cable element with the towed body. The current approach can be used as design tool for achieving improved directional stability, maneuverability, safety and control characteristics with the cable towed body. The analysis results show the elegance and robustness of the proposed approach by comparing with the sea trial data. 相似文献
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Nonlinear Finite Element Analysis of Ocean Cables 总被引：1，自引：1，他引：1
Nam-ⅡKIM Sang-SooJEON Moon-YoungKIM 《中国海洋工程》2004,18(4):537-550
This study has focused on developing numerical procedures for the dynamic nonlinear analysis of cable structures subjected to wave forces and ground motions in the ocean. A geometrically nonlinear finite element procedure using the isoparamnetrie curved cable element based on the Lagrangian folmulation is briefly summarized. A simple and accurate method to determine the initial equilibrium state of cable systems associated with self-weights, buoyancy and the motion of end points is presented using the load incremental method combined with penalty method. Also the Newmark method is used for dynamic nonlinear analysis of ocean cables. Numerical examples are presented to validate the present numerical method. 相似文献
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具有链—缆—链结构的复合系泊链缆因其相对于全钢链质量和成本上的优势而在深水系泊中得以广泛应用。基于细长杆理论采用有限差分法建立了可以考虑链—缆—链结构的复合系泊缆数值模型，将其应用于不同工况下全钢链和复合链缆运动的数值模拟中，并开展了验证。首先，将单根钢链顶张力数值模拟结果与不同工况下的模型试验结果进行了对比，验证了数值预报程序应用于全钢链的准确性。然后，对于复合系泊链缆开展了静刚度和动刚度迭代数值模拟，并将模拟结果同已发表文章中的算例结果进行比较，验证了该数值模型在复合链缆模拟上的准确性。发现对于单根钢锚链的验证，激励半径越大，激励周期越小，一个周期内顶张力幅值及其极差越大，钢链运动就越剧烈。对于链—缆—链式复合系泊链缆的验证，发现静刚度迭代中数值模拟结果与算例结果差异较小；对于动刚度迭代，除个别大幅慢漂工况外，两者有较高的吻合；且激励周期越小，激励半径越大，复合系泊链缆顶张力越大，弹性模量越小，运动越剧烈。对于聚酯缆刚度的敏感性分析，发现改变动刚度经验公式参数的情况下，杨氏模量的静刚度迭代和动刚度迭代结果误差分别最大达到了60.81%和68.21%，因此合成纤维材料特性对复合系泊链... 相似文献
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Free vibrations of three-dimensional extensible marine cables with specified top tension via a variational method 总被引：1，自引：0，他引：1
This paper presents a model formulation that can be used for analyzing the three-dimensional vibration behaviours of an inclined extensible marine cable. The virtual work-energy functional, which involves strain energy due to axial stretching of the cable and virtual work done by external hydrostatic forces is formulated. The coupled equations of motion in the Cartesian coordinates of global systems are obtained by taking into account the difference between Euler’s equations and equilibrium equations. The method of Galerkin finite element is used to obtain the mass and stiffness matrices which are transformed into the local coordinate systems. Then the eigenvalue problem is solved to determine its natural frequencies and corresponding mode shapes. The model formulation developed herein is conveniently applied for the cases of specified top tension. The numerical investigations are carried out to demonstrate the validity of the model and to explore in details the influence of various parameters on the behaviours of marine cables. Results for the frequency avoidance phenomenon, maximum dynamic tension and coupled transverse mode shapes are presented and discussed. 相似文献
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A composite numerical model is presented for computing the wave field in a harbor. The mild slope equation is discretized by a finite element method in the domain concerned. Out of the computational domain, the water depth is assumed to be constant. The boundary element method is applied to the outer boundary for dealing with the infinite boundary condition. Because the model satisfies strictly the infinite boundary condition, more accurate results can be obtained. The model is firstly applied to compute the wave diffraction in a narrow rectangular bay and the wave diffraction from a porous cylinder. The numerical results are compared with the analytical solution, experimental data and other numerical results. Good agreements are obtained. Then the model is applied to computing the wave diffraction in a square harbor with varying water depth. The effects of the water depth in the harbor and the incoming wave direction on the wave height distribution are discussed. 相似文献
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A composite numerical model is presented for computing the wave field in a harbor. The mild slope equation is discretized by a finite element method in the domain concerned. Out of the computational domain, the water depth is assumed to be constant. The boundary element method is applied to the outer boundary for dealing with the infinite boundary condition. Because the model satisfies strictly the infinite boundary condition, more accurate results can be obtained. The model is firstly applied to compute the wave diffraction in a narrow rectangular bay and the wave diffraction from a porous cylinder. The numerical results are compared with the analytical solution, experimental data and other numerical results. Good agreements are obtained. Then the model is applied to computing the wave diffraction in a square harbor with varying water depth. The effects of the water depth in the harbor and the incoming wave direction on the wave height distribution are discussed. 相似文献
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James R. Houston 《Applied Ocean Research》1981,3(4):163-170
A two-dimensional finite element numerical model is presented that calculates combined refraction and diffraction of short waves. The wave equation solved governs the propagation of periodic, small amplitude surface gravity waves over a variable depth seabed of mild slope. An efficient computational scheme is employed that allows the solution of practical problems that typically require large computational grids. Comparisons are presented between the finite element model calculations and an analytical solution, a two-dimensional numerical solution, a three-dimensional numerical solution, and measurements from a hydraulic model. 相似文献
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深基坑平面内支撑结构等效刚度的计算常采用有限元等数值计算方法,通过分析深基坑支护结构的4种典型平面内支撑结构型式,探讨了数值计算模型中内支撑结构的单元划分长度、约束弹簧刚度、约束弹簧间距、约束弹簧布置型式等因素对内支撑等效刚度计算结果的影响.经计算分析可知,在其他影响因素不变而只改变某个影响因素时,平面内支撑结构的等效刚度随腰梁单元长度的增加、约束弹簧刚度的增加呈增加的趋势,随约束弹簧间距的增加呈降低的趋势,但基本不受约束弹簧布置型式、除腰梁之外的其他内支撑构件单元长度的影响.在此基础上,得出了数值计算中上述各影响因素的建议取值范围和约束弹簧的布置型式. 相似文献
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An efficient algorithm is presented which simulates the three-dimensional motion of a towed cable. The formulation is based on an implicit, second-order finite difference approximation of the equations of motion. The results of the computation are compared both to those obtained by another numerical model and to experimental measurements. 相似文献
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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 lO0 to lO00. 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. 相似文献
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The experimental and theoretical investigations on the behaviour of pontoon-type floating breakwaters are presented. A two-dimensional finite element model is adopted to study the behaviour of pontoon-type floating breakwaters in beam waves. The stiffness coefficients of the slack mooring lines are idealized as the linear stiffness coefficients, which can be derived from the basic catenary equations of the cable. The theoretical model is supported by an experimental programme conducted in a wave flume. The motion responses and mooring forces are measured for three different mooring configurations, and the results are reported and discussed in detail in this paper. The wave attenuation characteristics are presented for the configurations studied. 相似文献
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Igor Tsukrov Oleg Eroshkin David Fredriksson M. Robinson Swift Barbaros Celikkol 《Ocean Engineering》2003,30(2):251-270
A consistent finite element is proposed to model the hydrodynamic response of net panels to environmental loading. This equivalent net element is constructed to reproduce the drag, buoyancy, inertial and elastic forces exerted on the netting by current and waves. To evaluate the accuracy of the proposed finite element modeling, numerical predictions have been compared with the experimental observations and (simplified) analytical results of other authors. This new modeling technique has been applied to evaluate the performance of a tension leg fish cage in the open ocean environment. 相似文献
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This paper proposes a geometrically exact formulation for three-dimensional static and dynamic analyses of the umbilical cable in a deep-sea remotely operated vehicle (ROV) system. The presented formulation takes account of the geometric nonlinearities of large displacement, effects of axial load and bending stiffness for modeling of slack cables. The resulting nonlinear second-order governing equations are discretized spatially by the finite element method and solved temporally by the generalized- implicit time integration algorithm, which is adapted to the case of varying coefficient matrices. The ability to consider three-dimensional union action of ocean current and ship heave motion upon the umbilical cable is the key feature of this analysis. The presented formulation is firstly validated, and then three numerical examples for the umbilical cable in a deep-sea ROV system are demonstrated and discussed, including the steady configurations only under the action of depth-dependent ocean current, the dynamic responses in the case of the only ship heave motion, and in the case of the combined action of the ship heave motion and ocean current. 相似文献
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This paper proposes a geometrically exact formulation for three-dimensional static and dynamic analyses of the umbilical cable in a deep-sea remotely operated vehicle(ROV) system. The presented formulation takes account of the geometric nonlinearities of large displacement, effects of axial load and bending stiffness for modeling of slack cables. The resulting nonlinear second-order governing equations are discretized spatially by the finite element method and solved temporally by the generalized-a implicit time integration algorithm, which is adapted to the case of varying coefficient matrices. The ability to consider three-dimensional union action of ocean current and ship heave motion upon the umbilical cable is the key feature of this analysis. The presented formulation is firstly validated, and then three numerical examples for the umbilical cable in a deep-sea ROV system are demonstrated and discussed, including the steady configurations only under the action of depth-dependent ocean current, the dynamic responses in the case of the only ship heave motion, and in the case of the combined action of the ship heave motion and ocean current. 相似文献
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In this study, we develop a numerical method for a 3D linear hydroelastic analysis of floating structures with liquid tanks subjected to surface regular water waves and compare the numerical results with experimental tests. Considering direct couplings among structural motion, sloshing, and water waves, a mathematical formulation and a numerical method extended from a recent work [1] are developed. The finite element method is employed for the floating structure and internal fluid in tanks, and the boundary element method is used for the external fluid. The resulting formulation completely incorporates all the interaction terms including hydrostatic stiffness and the irregular frequency effect is removed by introducing the extended boundary integral equations. Through various numerical tests, we verify the proposed numerical method. We also performed 3D hydroelastic experimental tests of a floating production unit (FPU) model in an ocean basin. The measured dynamic motions are compared with the numerical results obtained using the proposed method. 相似文献
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深水动态脐带缆内部结构复杂，其阻尼特性对脐带缆的舞动以及疲劳损伤有着重要的影响。脐带缆在和流体相互作用过程中，脐带缆内部构件可能会产生滑动，进而影响脐带缆的结构阻尼，这也使得真实海况中脐带缆的舞动和疲劳是一项复杂而值得深入研究的课题。为验证有限元模型能够很好地模拟脐带缆的结构阻尼特性，在考虑内部结构单元间摩擦的基础上，利用ANSYS建立了用于中国南海某油田的脐带缆多层滑移接触摩擦模型。同时，采用自由衰减法对该动态脐带缆开展了原型试验，测得了该缆的结构阻尼比与自振周期。通过对比有限元模型计算结果与原型试验结果发现：数值模型获得的该脐带缆的结构阻尼值与试验值非常接近，这为工程中获得脐带缆结构阻尼比的值提供了好的方向。 相似文献
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用于海洋平台的吸力式桩桶基础作为一种新型平台基础正逐渐成为人们研究的重点。为研究吸力式桩桶单桩基础的受力特性，对V-H（竖向—水平）联合荷载作用下的吸力式单桩基础桩土的承载特性进行了数值模拟，并将数值模拟的有限元解通过与API规范中对p-y曲线的计算方法进行对比来验证有限元模型的可行性，最后采用分级作用力的加载方式对其破坏包络曲线进行绘制，并推导出相应的函数表达式。研究表明，采用ABAQUS有限元分析软件对吸力式桩桶进行数值模拟是可行的，随着对吸力式桩桶所施加V-H联合荷载的不断增大，吸力式桩桶所能体现的应力和弯矩极限值也在随之增大，其位移变化主要在施加荷载的区域附近，最后在联合荷载作用下所体现的极限承载状态，即包络曲线大致呈四分之一的椭圆形状。 相似文献
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A model for solving the two-dimensional enhanced Boussinesq equations is presented. The model equations are discretised in space using an unstructured finite element technique. The standard Galerkin method with mixed interpolation is applied. The time discretisation is performed using an explicit three-step Taylor–Galerkin method. The model is extended to the surf and swash zone by inclusion of wave breaking and a moving boundary at the shoreline. Breaking is treated by an existing surface roller model, but a new procedure for the detection of the roller thickness is devised. The model is verified using four test cases and the results are compared with experimental data and results from an existing finite difference Boussinesq model. 相似文献