共查询到20条相似文献，搜索用时 31 毫秒
1.
Under complex currents, the motion governing equations of marine cables are complex and nonlinear, and the calculations of cable configuration and tension become difficult compared with those under the uniform or simple currents. To obtain the numerical results, the usual Newton-Raphson iteration is often adopted, but its stability depends on the initial guessed solution to the governing equations. To improve the stability of numerical calculation, this paper proposed separated the particle swarm optimization, in which the variables are separated into several groups, and the dimension of search space is reduced to facilitate the particle swarm optimization. Via the separated particle swarm optimization, these governing nonlinear equations can be solved successfully with any initial solution, and the process of numerical calculation is very stable. For the calculations of cable configuration and tension of marine cables under complex currents, the proposed separated swarm particle optimization is more effective than the other particle swarm optimizations. 相似文献
2.
Under complex currents, the motion governing equations of marine cables are complex and nonlinear, and the calculations of cable configuration and tension become difficult compared with those under the uniform or simple currents. To obtain the numerical results, the usual Newton?Raphson iteration is often adopted, but its stability depends on the initial guessed solution to the governing equations. To improve the stability of numerical calculation, this paper proposed separated the particle swarm optimization, in which the variables are separated into several groups, and the dimension of search space is reduced to facilitate the particle swarm optimization. Via the separated particle swarm optimization, these governing nonlinear equations can be solved successfully with any initial solution, and the process of numerical calculation is very stable. For the calculations of cable configuration and tension of marine cables under complex currents, the proposed separated swarm particle optimization is more effective than the other particle swarm optimizations. 相似文献
3.
In re-entry,the drilling riser hanging to the holding vessel takes on a free hanging state,waiting to be moved from the initial random position to the wellhead.For the re-entry,dynamics calculation is often done to predict the riser motion or evaluate the structural safety.A dynamics calculation method based on Flexible Segment Model(FSM) is proposed for free hanging marine risers.In FSM,a riser is discretized into a series of flexible segments.For each flexible segment,its deflection feature and external forces are analyzed independently.For the whole riser,the nonlinear governing equations are listed according to the moment equilibrium at nodes.For the solution of the nonlinear equations,a linearization iteration scheme is provided in the paper.Owing to its flexibility,each segment can match a long part of the riser body,which enables that good results can be obtained even with a small number of segments.Moreover,the linearization iteration scheme can avoid widely used Newton-Rapson iteration scheme in which the calculation stability is influenced by the initial points.The FSM-based dynamics calculation is timesaving and stable,so suitable for the shape prediction or real-time control of free hanging marine risers. 相似文献
4.
Dynamic Analysis of Towed and Variable Length Cable Systems 总被引：2，自引：3，他引：2
Towed cable systems are frequently used in marine measurements where the length of the towed cable varies during launch and recovery. In this paper a novel method for modeling variable length cable systems is introduced based on the finite segment formulation. The variable length of the towed cable is described by changing the length of the segment near the towing point and by increasing or decreasing the number of the discrete segments of the cable. In this way, the elastic effects of the cable can be easily handled since geometry and material properties of each segment are kept constant. Experimental results show that the dynamic behavior of the towed cable is consistent between the model and the physical cable. Results show that the model provides numerical efficiency and simulation accuracy for the variable length towed system. 相似文献
5.
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
6.
7.
The key consideration in controlling the dynamic response of an offshore guyed tower subjected to environmental loading is the selection of the stiffness characteristics of the cable mooring array. In the present study, each cable in the array consists of three segments: a leading segment attached to the tower, a short heavy middle segment, and a seabed trailing segment attached at the extremity to an anchor pile. A nonlinear static model is presented in algorithmic form that defines the stiffness characteristics of the cable array. The model involves the inelastic static catenary equations coupled with conditions of geometric compatibility, formulated in terms of seven nondimensional system parameters. The effects of varying each of the system parameters on the stiffness characteristics of example cable arrays are presented and the implications for cable design are discussed. 相似文献
8.
Time-domain numerical simulation of ocean cable structures 总被引：2，自引：0，他引：2
This paper describes the numerical features of WHOI Cable, a computer program for analyzing the statics and dynamics of oceanographic cable structures. The governing equations include the effects of geometric and material nonlinearities, bending stiffness for seamless modeling of slack cables, and a model for the interaction of cable segments with the sea floor. The program uses the generalized-α time integration algorithm, adaptive time stepping, and adaptive spatial gridding to produce accurate, stable solutions for dynamic problems. The nonlinear solver uses adaptive relaxation to improve robustness for both static and dynamic problems. The program solves surface and subsurface single-point mooring problems, multi-leg and branched array systems, and towing and drifting problems. User specified forcing can include waves, currents, wind, and ship speed. 相似文献
9.
海洋路由勘测对海底光缆工程的影响分析 总被引：1，自引：0，他引：1
介绍了水深、海底坡度、土壤剪切强度以及潮流、雷暴等海洋路由各勘测要素及其在海底光缆通信施工中的作用,并对它们在施工中的作用及其必要性进行了评价,从而使海洋路由勘测与施工的需要结合得更紧密,更具有针对性。 相似文献
10.
On the motions of the underwater remotely operated vehicle with the umbilical cable effect 总被引：1，自引：0，他引：1
In this paper, a hydrodynamic model is developed to simulate the six degrees of freedom motions of the underwater remotely operated vehicle (ROV) including the umbilical cable effect. The corresponding hydrodynamic forces on the underwater vehicle are obtained by the planar motion mechanism test technique. With the relevant hydrodynamic coefficients, the 4th-order Runge–Kutta numerical method is then adopted to solve the equations of motions of the ROV and the configuration of the umbilical cable. The multi-step shooting method is also suggested to solve the two-end boundary-value problem on the umbilical cable with respect to a set of first-order ordinary differential equation system. All operation simulations for the ROV including forward moving, ascending, descending, sideward moving and turning motions can be analyzed, either with or without umbilical cable effect. The current effect is also taken into consideration. The present results reveal that the umbilical cable indeed significantly affects the motion of the ROV and should not be neglected in the simulation. 相似文献
11.
12.
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
13.
A numerical approach for predicting motion and tension of extensible marine cables during laying operations in a rough sea is presented here. The solution methodology consists of dividing the cable into straight elements, which must satisfy an equilibrium equation and compatibility relations. The system of nonlinear differential equations is solved by the Runge–Kutta method, taking the effect of regular and/or irregular waves into account explicitly.
Illustrative applications of the method are given for a typical cable laying ship. The results are presented as rms values of the cable dynamic tension and corresponding dynamic factor for two different types of cable and several values of cable stiffness. The effect of axial deformation on the maximum tension at the shipboard pulley location is highlighted. 相似文献
14.
15.
16.
《Applied Ocean Research》2004,26(1-2):23-33
The dynamic behaviour of vertical slender structures for marine applications under parametric excitation is considered. The governing equations are treated using two different numerical schemes. The effect of parametric excitation is examined in cases where the excitation frequency lies in the vicinity of nonlinear resonances. First, the un-damped case is considered and the features of the dynamic response are properly identified and discussed. For explaining the particulars of the un-damped behaviour, the governing equations are treated analytically by applying the method of normal forms. The effect of damping is examined through comparative numerical computations of the system's behaviour. It is shown that the inclusion of hydrodynamic drag in the describing model eliminates the impacts of internal resonances excited due to the parametrically imposed motions. Finally, the paper demonstrates the significance of the terms that describe the coupling between the longitudinal and transverse vibrations. 相似文献
17.
A variational formulation for three-dimensional analysis of extensible marine riser transporting fluid 总被引：1，自引：0，他引：1
Chainarong Athisakul 《Ocean Engineering》2011,38(4):609-620
This paper presents a model formulation for static and dynamic analysis of three-dimensional extensible marine riser transporting fluid. A variational model formulation is developed based on the principle of virtual work-energy and the extensible elastica theory. The virtual work-energy functional is composed of the virtual strain energy due to axial stretching, bending, and torsion and the virtual work done by the external and internal fluid. The governing dynamic equilibrium equations are derived in the Cartesian coordinate. The finite element method is used to obtain the numerical solutions. The numerical examples are provided to demonstrate interesting effects of fluid transportation and axial deformation on large displacements and dynamic properties of the three-dimensional extensible marine riser. 相似文献
18.
流速分布及锚链自身刚度对弹性单锚链系统变形和受力的影响 总被引：1，自引：0，他引：1
在锚链系统中,锚链本身的刚度和水流对其作用是影响锚链变形和受力的主要因素。应用分段外推的数值方法,分别对不同刚度和同一弹性锚链在均匀流作用以及同一弹性锚链在不同流速分布(流速在水深方向呈抛物线分布、对数分布)的水流作用下的变形和受力进行了分析和计算,得出了锚链自身的不同刚度及不同流速对锚链的变形及受力的影响情况。结果表明,刚度对锚链受力及变形影响明显,不同流速分布对锚链的偏移量几乎无影响,但对锚链的受力影响较大,选取抛物线型流速分布对锚链安全有利。 相似文献
19.
20.
痕量元素及其同位素在海洋生物地球化学研究方面扮演着至关重要的角色, 对于认识全球环境变迁具有十分重要的意义[1]。痕量元素及其同位素采集、预处理和分析在海洋研究中具有重要的作用, 是诸多重要科学问题解答的重要数据基础[2]。但是, 当科学家们审慎地评估文献中痕量元素的浓度报道时, 发现海洋中的痕量金属含量发生了数量级水平的下降, 这说明早期文献中报导的痕量金属含量在采样、样品预处理及分析过程中受到了明显的沾污, 其中海洋考察船自身、钢缆、采样设备中的金属器件对于海洋中溶解态痕量金属的沾污显得尤为重要[3]。结合海水痕量元素CTD现场采集工作环境，工作拉力等特殊要求，设计一款敷塑纤维通讯缆，并通过静态拉力试验验证缆绳自身工作拉力；通过成分分析、浸出试验验证敷塑纤维通讯缆最大化降低缆绳对于海中溶解态痕量金属的沾污。 相似文献