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1.
In this study the wave induced surge motion of a twin platform of a pretension leg structural system is investigated. A set of equations along with boundary conditions are derived, and solutions are obtained analytically. The tension-legged twin platform structural system might better represent a platform system in the practical application in either idealized two-dimensional analysis or actual three-dimensional practice than a single platform system. In the analysis the coupling problem of a two-dimensional tension leg twin platform interacting with a monochromatic linear wave train in an inviscid and incompressible fluid is considered. The problem is considered as a combination of the scattering and radiation. These two boundary-value problems are first solved independently and then combined together to resolve for all unknowns. The analysis is focused on the wave induced surge motion of the twin platform and the reflection coefficient. Other than the wave-related parameters, the dimensional effect of the twin platform structure is examined and presented in numerical examples. From the analytical results, it is found that the behavior of the tension-leg twin platform is significantly influenced by dimensional factors of the platform system such as the dimension of each single platform and the spacing between two platforms. It is also realized that to simplify the analysis of a twin platform system into a single platform, it tends to underestimate the wave-induced response and then reduces the safety of the platform system. 相似文献
2.
An analytical solution has been developed in this paper to quantify the flow field and the surge motion of a porous tension leg platform with an impermeable top layer induced by linear waves. The porous layer of the TLP is considered to be anisotropic but homogeneous. The nonlinear form drag in the porous layer is replaced by a linear drag according to Lorentz’s hypothesis of equivalent work. The convergence of the series solution is verified. The dependence of the flow field, the surge motion of the platform, and its resonant frequency on wave and structure properties has been studied. 相似文献
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This paper presents an analytical solution for the dynamic behavior of both the platform and tethers in the tension leg platform system when the platform system is subjected to the wave-induced surge motion and the flow-induced drag motion. Along with the analysis the coupling problem of a two dimensional tension leg platform interacting with a monochromatic linear wave train in an inviscid and incompressible fluid is being considered. The scattering problem and radiation problem are first solved independently and then combined together to resolve for all unknowns. The dynamic behavior of the platform and tethers was further solved based on these solutions. The material property and the dimensional effect for the tether incorporated in the tension leg platform system are both taken into account in the analytical analysis. Corresponding to the variation of material properties and tether dimensions, it was found that the dynamic behavior of both the tether of tension leg platform and the platform itself is closely related to the material property and the dimension of the tether. 相似文献
5.
M. Söylemez 《Ocean Engineering》1996,23(5):423-445
This paper presents the derivation of a general method for calculating wave forces on the cylindrical members of offshore structures. By means of the proposed method one can calculate the wave loading on cylindrical members of fixed or floating offshore structures orientated randomly in waves. This method of calculating wave forces is based on the linear Airy wave theory. Calculation procedure of wave force components is presented in great detail on the basis of wave particle kinematic properties obtained from the linear Airy wave theory. In the procedure of calculating wave forces presented, definitions of the wave reference system for propagating wave, the structure reference system for the platform and the member reference system for the tubular members of the structure are first established, and then the calculation of wave forces is given in terms of its components, which are pressure, acceleration and velocity forces, including current forces. At the end of the paper, expressions of total heave, sway and surge forces and total roll, pitch and yaw moments acting on the platform are given as a sum of these forces acting on each member of the platform. The calculation procedure derived in this paper provides a very efficient means of calculating wave forces and moments during the time-domain simulations of a floating platform experiencing large amplitude motion in intact, progressive flooding and damaged conditions. Comparisons of the predictions with the measurements which will be presented elsewhere reveal that the calculation procedure developed can predict large amplitude oscillatory and steady motion characteristics of an intact and damaged platform in waves with an acceptable degree of accuracy. 相似文献
6.
Hsien Hua Lee Wen-Sheng Wang 《Oceanic Engineering, IEEE Journal of》2005,30(1):59-78
In this paper, a typical tension-leg type net cage system is analyzed, and a set of motion equations for the cage system in the simplified two-dimensional case is derived. Subsequently, a close form analytical solution is obtained when all of the multi-interactions between the top platform structure, the incident wave, and the motion of both the tether and net are considered. The parameter of solidity as a ratio of the twine diameter to the mesh size of the cage is also taken into account in the analysis. The purpose of this paper is to investigate the dragged surge motion of the tension-leg type cage system when subjected to incident waves and flow drags on the net-cages. Furthermore, the dynamic behavior of the platform is compared to the case when the net-cage drag is not considered. Numerical examples are carried out in a range of periods of waves, and the results are discussed focusing on the motion of both the platform and cage. It was found that there is a significant influence of the net-cage drag on the surge motion of the entire structural system. Various parameters such as the material property, twine diameter, mesh size and the dimension of the net-cages were considered. It was found that the vibration of the net-cage system might be significantly overestimated if the drag effect of the net and tethers is neglected. 相似文献
7.
A time-domain simulation method based on potential flow model has been developed to investigate the berthing problem between two floating bodies in wave. The boundary value problem is formulated with respect to an earth-fixed coordinate system because the relative positions of the two vessels continuously change during the berthing operation. The classical finite element method is used to solve the Laplace equation in the fluid domain with moving boundary. The linearized free-surface boundary conditions are integrated in time by applying 4th-order Adams–Bashforth–Moulton method. A simple re-mesh algorithm with local and global mesh systems is introduced to update mesh by considering large horizontal movement of the berthing vessel. The developed numerical method is used to investigate the berthing problem between a FPSO and shuttle tanker in waves. The focus is on the wave-induced motion response during the berthing process. The characteristics of the motion responses in berthing operation are examined with various wave frequencies, berthing speeds and wave headings. 相似文献
8.
Safety is the topmost priority considered by the designers of floating systems or any other structural systems. Reliability, economy and environmental pollutions and the liability of the structure in the case of accidents are also considered by the designers. The paper concentrates on the non-linear behavior of a moored floating platform in stochastic seaway generated using the Pierson–Moskowitz spectrum. Second-order wave forces (slow drift force) acting on the structure is considered as they contribute to a major percentage of the excursion of a large platform. Wave drift damping and skin friction damping have also been considered.It has been shown that the principal frequency of the second-order motion of the platform due to drift forces closely matches the natural frequency of the system in surge motion. This has been subsequently used in tuning a PID (proportionate integral and differential)-based control system for the surge mode, where reduction in the order of 90% has been observed. 相似文献
9.
An autoregressive wave force model is developed which is capable of accounting for localized flow history effects. It was developed in conjunction with the analysis of a series of experiments performed to study the wave-induced forces acting on a free-to-surge vertical cylinder in random waves. The wave force model incorporates a relative motion form of the Morison equation. The formulation presented in this study is quite general, but the filter coefficients in the model must be uniquely determined for each data set. The optimal length of the filter and its sensitivity are illustrated using data from small-scale wave tank tests. A high frequency wave force component observed in the experimental data is reproduced using this model. Lastly, the autoregressive wave force model is used to predict the response of a tension-leg platform to a wave train. A comparison of the results obtained both with and without the filter model are presented. 相似文献
10.
C. J. Garrison 《Applied Ocean Research》1989,11(4):194-201
It is common practice to compute wave-induced loads on the immersed surface of gravity structures exposed to the wave motion and disregard the pore-water pressure variation on the foundation surface. However, when the soil is porous, wave-induced pressures propagate within the soil under the structure and result in a rather significant contribution to overall loads. This paper describes a practical method for numerical modeling of the pore pressure under a gravity platform foundation for compressible water and a rigid, but porous soil. The porous soil may be bounded by an impermeable horizontal layer at some arbitrary depth.
The paper outlines the basic boundary element procedure for pore pressure analysis and presents numerical results for a typical gravity structure as well as results for comparison with an existing analytical solution for a vertical circular cylinder. 相似文献
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The hydrodynamic properties of a dual pontoon floating breakwater consisting of a pair of floating cylinders of rectangular section, connected by a rigid deck, is investigated theoretically. The structure is partially restrained by linear symmetric moorings fore and aft. The fluid motion is idealized as linearized, two-dimensional potential flow and the equation of motion of the breakwater is taken to be that of a two-dimensional rigid body undergoing surge, heave and pitch motions. The solution for the fluid motion is obtained by the boundary integral equation method using an appropriate Green's function. Numerical results are presented which illustrate the effects of the various wave and structural parameters on the efficiency of the breakwater as a barrier to wave action. It is found that the wave reflection properties of the structure depend strongly on the width, draft and spacing of the pontoons and the mooring line stiffness, while the excess buoyancy of the system is of lesser importance. 相似文献
13.
The effect of wave-induced radiation stress on storm surge during Typhoon Saomai (2006) 总被引：5，自引：1，他引：4
The effects of wave-induced radiation stress on storm surge were simulated during Typhoon Saomai using a wave-current coupled model based on ROMS (Regional Ocean Modeling System) ocean model and SWAN (Simulating Waves Nearshore) wave model.The results show that radiation stress can cause both set-up and set-down in the storm surge.Wave-induced set-up near the coast can be explained by decreasing significant wave heights as the waves propagate shoreward in an approximately uniform direction;wave-induced set-down far from the coast can be explained by the waves propagating in an approximately uniform direction with increasing significant wave heights.The shoreward radiation stress is the essential reason for the wave-induced set-up along the coast.The occurrence of set-down can be also explained by the divergence of the radiation stress.The maximum wave-induced set-up occurs on the right side of the Typhoon path,whereas the maximum wave induced set-down occurs on the left side. 相似文献
14.
《Ocean Modelling》2008,20(3):252-269
The effects of wave–current interactions on the storm surge and inundation induced by Hurricane Hugo in and around the Charleston Harbor and its adjacent coastal regions are examined by using a three-dimensional (3-D) wave–current coupled modeling system. The 3-D storm surge and inundation modeling component of the coupled system is based on the Princeton ocean model (POM), whereas the wave modeling component is based on the third-generation wave model, simulating waves nearshore (SWAN). The results indicate that the effects of wave-induced surface, bottom, and radiation stresses can separately or in combination produce significant changes in storm surge and inundation. The effects of waves vary spatially. In some areas, the contribution of waves to peak storm surge during Hurricane Hugo reached as high as 0.76 m which led to substantial changes in the inundation and drying areas simulated by the storm surge model. 相似文献
15.
Hybrid model testing technique is widely used in verification of a deepwater floating structure and its mooring system,but the design of the truncated mooring systems which can reproduce both static and dynamic response same as the full-depth mooring system is still a big challenge,especially for the mooting systems with large truncation.A Cell-Tress Spar operated in 1500 m water depth is verified in a wave basin with 4 m water depth.A large truncation factor arises even though a small model scale 1:100 is adopted.Computer program modules for analyzing the static and frequency domain dynamic response of mooting line are combined with multi-objective genetic algorithm NSGA-II to optimize the truncared mooting system.Considering the asymmetry of layout of mooring hnes,two different truncated mooring systems are respectively designed for both directions in which the restoring forces of the.mooting system are quite,different.Not only the static characteristics of the mooting systems are calibrated,but also the dynamic responses of the single truncated mooting line are evaluated through time domain numerical simulation and model tests.The model test results of 100-year storm in the GOM are reconstructed and extrapolated to a full depth.It is found that the experimental and numerical resuits of Spar wave frequency motion agree well,and the dynamic responses of the full-depth mooring lines are better reproduced,but the low frequency surge motion is overestimated due to the smaller mooring-induced damping.It is a feasible method adopting different truncated mooring systems for different directions in which the restoring force characteristics are quite different and cannot be simulated by one truncated mooring system.Hybrid verification of a deepwater platform in wave basin with shallow water depth is still feasible if the truncated mooring systems are properly designed,and numerical extrapolation is necessary. 相似文献
16.
Experimental and Theoretical Investigation of Wave Forces on A Partially-Perforated Caisson Breakwater with A Rock-Filled Core 总被引：2，自引：0，他引：2
1.IntroductionVertical breakwaters are widely used for harbor and coastline protection in coastal engineering.Recently,perforated breakwaters have been often used in practice as they can effectively reduce thewaveforces actingon,the wave reflectionfromand… 相似文献
17.
大深度载人潜水器低速大漂角模糊滑模航向控制研究 总被引：1，自引：0，他引：1
通过模型试验测量大深度载人潜水器低速大漂角运动时所受到的非线性水动力。基于一种新的模糊滑模控制策略,为潜水器设计了鲁棒航向控制器。在不同的漂角子区间内分别设计局部镇定的滑模控制器,然后通过Takagi-Sugeno模糊推理系统将它们光滑连接,得到模糊滑模控制。仿真计算结果充分显示了该控制策略的有效性。 相似文献
18.
Most previous investigations related to composite breakwaters have focused on the wave forces acting on the structure itself from a hydrodynamic aspect. The foundational aspects of a composite breakwater under wave-induced cyclic loading are also important in studying the stability of a composite breakwater. In this study, numerical simulations were performed to investigate the wave-induced pore water pressure and flow changes inside the rubble mound of the composite breakwater and seabed foundation. The validity and applicability of the numerical model were demonstrated by comparing numerical results with existing experimental data. Moreover, the present model clearly has shown that the instantaneous directions of pore water flow motion inside the seabed induced by surface waves are in good agreement with the general wave-induced pore water flow inside the seabed. The model is further used to discuss the stability of a composite breakwater, i.e., the interaction among nonlinear waves, composite breakwater and seabed. Numerical results suggest that the stability of a composite breakwater is affected by not only downward shear flow generating on the seaward slope face of the rubble mound but, also, a high and dense pore water pressure gradient inside the rubble mound and seabed foundation. 相似文献
19.
A global trajectory tracking controller is presented for underactuated AUVs with only surge force and yaw moment in the horizontal plane. A transformation is introduced to represent the tracking error system into a cascade form. The global and uniform asymptotic stabilization problem of the resulting cascade system is reduced to the stabilization problem of two subsystems by use of the cascade approach. For the stabilization of the subsystem involving the yaw moment, a control law is proposed based on the feedback linearization method. Another subsystem is stabilized by designing a fuzzy sliding mode controller which can offer a systematical means of constructing a set of shrinking-span and dilating-span membership functions. In order to demonstrate the practicability of the proposed controller, control constraints, parameter uncertainties, and external disturbances are considered according to practical situation of AUVs. Simulation results show very good tracking performance and robustness of the proposed control schemes. 相似文献
20.
An analytical solution for the coupling problem of a two-dimensional tension leg structure interacting with a monochromatic linear wave train in an inviscid and incompressible fluid is presented. The tension legs are considered to be linearly elastic. The flow is further assumed to be irrotational and single-valued velocity potentials can then be defined.The boundary value problem is incorporated into a scattering and a radiation problem. The boundary value problems are then solved separately and combined to resolve all unknowns. The complete solutions of the velocity potentials are represented by the series of eigen-functions, and the surge motion of the structure is described in terms of the incident wave properties.The analytical solution is compared with a computer-coded numerical solution utilizing the boundary element method. The solutions agree very well, and both predict a resonant frequency for a specific structure which is different from the natural frequency of the structure due to the presence of the evanescent waves caused by the structure. 相似文献