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1.
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
2.
Floating platform system has been extensively used in ocean exploitation, particularly for a tension-leg platform (TLP) system in deep water. Most of the TLPs are multi-mooring systems, where multi-joints are connected to the tension-legs so that the platform is not allowed to twist freely and may subject to enormous force induced by large incident waves in the weak-direction of the structure. This study aims to exploit a single moored offshore platform system that may attract less force and can be operated with less effort. In our analysis, in addition to mechanical properties of the tether, two important properties are also taken into consideration for the single mooring tether with expanded cross sectional dimension and utilization of stronger material, namely, the sag-extensibility and the flexural rigidity. Finally, the dynamic structural behavior produced by the mechanical effects on the new system is investigated and compared with that of traditional design while the wave-structure interactions of large body are also accounted for. Our study finds that the neglect of sag-extensibility or the flexural rigidity of large, strong mooring cable may result in a conservative but not necessarily safe design. 相似文献
3.
Based on the lumped-mass method and rigid-body kinematics theory, a mathematical model of a gravity cage system attacked by irregular waves is developed to simulate the hydrodynamic response of cage system, including the maximum tension of mooring lines and the motion of float collar. The normalized response amplitudes (response amplitude operators) are calculated for the cage motion response in heave and surge, and the mooring line tension response, in regular waves. In addition, a statistical approach is taken to determine the motion and tension transfer functions in irregular waves. In order to validate the numerical model of a gravity cage attacked by irregular waves, numerical predictions have been compared with the experimental observations in the time and frequency domain. The effect of wave incident angle on the float collar motion, mooring line tension and net volume reduction of the gravity cage system in irregular waves is also investigated. The results show that at high frequencies, the cage system has no significant heave motion. It tends to contour itself to longer waves. The variation amplitude of mooring line forces decreases as the wave frequency increases. With the increasing of wave incident angle, the horizontal displacement of the float collar increases. 相似文献
4.
The large motions that a compliant offshore structure experiences were analysed using Euler parameters. Firstly, the equations of motion of a rigid body undergoing large translations and rotations were obtained using the Lagrangian formulation. Secondly, the hydrodynamic forces acting on the structure were calculated using the modified Morison's equation. A tension-leg platform (TLP) subjected to an oblique incident wave was then analysed using the above formulation. This was followed by an analysis of an articulated tower for comparison with the results of other researchers. An example showing the tower undergoing subharmonic oscillations was also included. 相似文献
5.
针对张力腿结构动力响应特点,提出一套张力腿式浮式风机动力耦合理论模型,编制计算程序,并通过与实验结果的对比,验证理论模型以及程序的适用性。张力腿式系泊系统稳定性好,但张力载荷随平台位移的变化显著;张力腿结构的动态响应与支撑平台和风机系统动态响应存在显著的耦合作用。针对张力腿浮式风机动力耦合特性,采用谱方法对张力腿结构建立耦合动力模型;考虑细长体在波浪中受到的粘性力,通过哈密顿原理推导出张力腿运动控制方程,利用自主开发的计算程序DARwind和数值计算方法求解系统动态响应。最后,将数值计算结果同UMAINE的试验数据进行对比分析,以验证程序的合理性。 相似文献
6.
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
7.
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
8.
Moo-Hyun Kim 《Applied Ocean Research》1992,14(6):353-370
The second-order difference-frequency wave forces on a large three-dimensional body in multi-directional waves are computed by the boundary integral equation method and the so-called FML formulation (assisting radiation potential method). Semi-analytic solutions for a bottom-mounted vertical circular cylinder are also developed to validate the numerical method. Difference-frequency wave loads on a bottom-mounted vertical cylinder and stationary four legs of the ISSC tension-leg platform (TLP) are presented for various combinations of incident wave frequencies and headings. These force quadratic transfer functions (QTF) can directly be used in studying slowly varying wave loads in irregular short-crested seas described by a particular directional spectrum. From our numerical results, it is seen that the slowly varying wave loads are in general very sensitive to the directional spreading function of the sea, and therefore wave directionality needs to be taken into account in relevant ocean engineering applications. It is also pointed out that the uni-directionality of the sea is not necessarily a conservative assumption when the second-order effects are concerned. 相似文献
9.
Numerical Analysis on the Effects of Submerged Depth of the Grid and Direction of Incident Wave on Gravity Cage 总被引：1，自引：0，他引：1
In this paper,the numerical model of the net cage with the grid mooring system in waves is set up by the lumped mass method and rigid kinematics theory,and then the motion equations of floating system,net system,mooring system,and floaters are solved by the Runge-Kutta fifth-order method.For the verification of the numerical model,a series of physical model tests have been carried out.According to the comparisons between the simulated and experimental results,it can be found that the simulated and experimental results agree well in each condition.Then,the effects of submerged depth of grid and direction of incident wave propagation on hydrodynamic behaviors of the net cage are analyzed.According to the simulated results,it can be found that with the increase of submerged depth of grid,the forces acting on mooring lines and bridle lines increase,while the forces on grid lines decrease;the horizontal motion amplitudes of floating collar decrease obviously,while the vertical motion amplitudes of floating collar change little.When the direction of incident wave propagation changes,forces on mooting lines and motion of net cage also change accordingly.When the propagation direction of incident wave changes from 0° to 45°,forces on the main ropes and bridle ropes increase,while the forces on the grid ropes decrease.With the increasing propagation direction of incident wave,the horizontal amplitude of the forces collar decreases,while the vertical amplitude of the floating collar has little variation. 相似文献
10.
11.
In this study a typical tension-leg type of floating platform incorporated with the tuned liquid column damper (TLCD) device is studied. The purpose is to find an effective and economic means to reduce the wave induced vibrations of the floating offshore platform system. The floating offshore platform has been widely applied for the offshore exploitation such as operation station, cross-strait bridges, floating breakwater and complex of the entertainment facilities. For offshore platform being employed as a public complex the stability and comfort to stay will be the major concern besides the safety requirement. Therefore, how to mitigate the vibration induced from waves and similar environmental loading becomes an important issue. The TLCD system utilizing the water sloshing power to reduce the vibration of the main structure, a newly developed device that could effectively reduce the vibrations for many kinds of structure is the first-time employed in the floating platform system. In both the analytical and experimental results it is found that the accurately tuned TLCD system could effectively reduce the dynamic response of the offshore platform system in terms of the vibration amplitude and the resonant frequency. 相似文献
12.
In the present study, the dynamic response of a coupled SPM-feeder-cage system under irregular waves and shear currents is analyzed. A numerical model is developed by using the commercial software Orca Flex. Hydrodynamics coefficients of the vessel are calculated by using a 3D diffraction/radiation panel program. First- and second-order wave forces are included in the calculations. Morison equation is used to compute the drag force on line elements representing the net. Drag coefficients are determined at every time step in the simulation considering the relative normal velocity between the structural elements and the fluid flow. The dynamic response of the coupled system is analyzed for various environments and net materials. The results of the study show the effects of solidity ratio of the net and vertical positions of the cage on the overall dynamic response of the system, confirming the viability of this type of configuration for future development of offshore aquaculture in deep waters. 相似文献
13.
渔用高强度聚乙烯和普通聚乙烯绞捻网片的拉伸力学性能比较研究 总被引：6，自引：0，他引：6
为给深水网箱设计与渔用材料的合理选配提供依据,应用ISO1806等对渔用高强度聚乙烯绞捻网片(以下简称HSPE绞捻网片)和普通聚乙烯绞捻网片(以下简称PE绞捻网片)的拉伸力学性能进行了比较研究。结果表明,(1)在同等条件下,36股HSPE绞捻网片的网目连接点断裂强力和网片单线断裂强力分别比52股PE绞捻网片增加了3.1%,3.7%;而前者的目脚直径和网片阻力可较后者减少19.6%。(2)对网片强力进行了再现性研究,36股HSPE和52股PE绞捻网片网目连接点断裂强力的标准偏差分别为35.93N,25.61N,再现性标准偏差分别为31.07N,36.93N;网片单线断裂强力的标准偏差分别为19.91N,13.49N,再现性标准偏差分别为20.48N,15.49N;网片强力测试数据的变异系数均小于4%;表示测试结果的分散性较小。(3)36股HSPE绞捻网片成本可较52股PE绞捻网片减少38.9%,其在渔业生产中进行推广应用具有可行性。(4)GB/T4925作为一个标准,对绞捻网片来说,存在不足,建议对GB/T4925进行修订。 相似文献
14.
深海极端波浪环境为浮式海洋平台作业时最为关键的海洋动力环境之一。在其作用下,深海浮式平台的运动、气隙以及结构响应等均为近年来的研究热点。然而,在深海环境中,入射波浪环境往往通过X波段雷达进行测量,仅能获得波浪的短时统计值,极大限制了实海域浮动平台动力响应的研究。目前,尚无成熟的方法能够对海洋浮式平台所处海域的入射波时序进行实时测量。针对深远海半潜式平台的波浪时序随船测量问题,结合平台气隙响应与运动响应数据建立基于深层神经网络的波浪非线性解耦模型,准确估计辐射、绕射波浪以及其非线性成分对时序波浪场的影响。研究显示,基于深度神经网络的波浪时序测量技术可以实现从气隙响应到入射波信息的反推,利用该方法计算得到的波浪时序具有较高的精度。 相似文献
15.
F. G. O&#x;Neill 《Ocean Engineering》2003,30(16):2053-2063
A theoretical investigation is carried out of the mesh size measurement of an idealized fishing netting mesh. It is assumed that the bending moment of the netting twine is proportional to curvature and that there is no twine extension and no cross-sectional deformation of the twine. The corresponding momentum and force balance equations are analyzed. The measurement method our analysis most approximates is that of the ICES gauge. The effect on mesh measurement of twine bending stiffness, frictional resistance, boundary slope, gauge force and gauge thickness are all examined. 相似文献
16.
The motion of a tethered spherical buoy subjected to incident regular waves was measured in a wave tank. Transverse instability was observed when the period of the wave generated was close to one-half of the natural period of the buoy. The transverse instability confirmed as Mathieu type was predominant at the surface but diminished with increase in the depth of submergence. The stable and unstable zones were determined on the Mathieu's instability diagram. Experimental results were in agreement with the predicted zone of instability for a two degree of freedom oscillation problem of Mathieu type which has a periodically varying spring constant. 相似文献
17.
Recent field measurements on beaches of different slopes have established that wave motion at periods substantially longer than the incident waves dominates the velocity field close to the shore. Analysis of a number of extensive data sets shows that much of this long wave motion is in the form of progessive edge waves, though forced wave motion, standing edge waves and free waves propagating away from the shore may also contribute to the energy.Theoretically, the drift velocities in bottom boundary layers due to edge waves show spatial patterns of convergence and divergence which may move sediment to form either regular crescentic or cuspate features when only one edge wave mode dominates, or a bewildering array of bars, bumps and holes when several phase-locked modes exist together.Convincing field demonstration of the link between nearshore topography and edge waves only exists for the special case of small-scale beach cusps on steep beaches, formed by edge waves at the subharmonic (twice the period) of the incident waves. At longer periods the link is proving more difficult to establish, due to the longer time-scales of topographic changes, the interaction between pre-existing topography and the water motion, and the observation of broad-banded edge wave motion which is not readily linked to topography with a well-defined scale.These ideas are, however, central to the study of nearshore processes, as most of the plausible alternate hypotheses do not seem to lead to quantitative predictions. Clearly, further theoretical and observational work is essential. 相似文献
18.
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
19.
A numerical study on dynamic properties of the gravity cage in combined wave-current flow 总被引：2，自引：0，他引：2
Yun-Peng Zhao Yu-Cheng Li Guo-Hai Dong Fu-Kun Gui Bin Teng 《Ocean Engineering》2007,34(17-18):2350-2363
Recent work in the area of open-ocean aquaculture-system dynamics has focused either on the response of fish cages in waves or the steady drag response from ocean currents, not on them combined. In reality, however, the forces bearing on these open-ocean structures are a nonlinear, multidirectional combination of both waves and current profiles. In this paper, a numerical model has been developed to simulate the dynamic response of the gravity cage to waves combined with currents. When current flows are combined with regular waves, gravity-cage motion response (including heave, surge, and pitch) and mooring-line forces have been calculated. To examine the validity of simulated results, a series of physical model tests have been carried out. The results of our numerical simulation are all in close agreement with the experimental data. 相似文献
20.
Model experiments of a floating fish cage subjected to waves and current have been performed. The objective was to study the dynamic behaviour of the fish cage model in waves and current. The fish cage model was composed of a model net, a flexible floating collar of the circular plastic type and a weight system. It was found that there are many wave periods in which cancellation of the wave-induced forces on the model occur. These cancellation wave periods are within the range of dimensioning wave periods commonly used for testing of fish farm structures and hence are important to be aware of. Large deformations of the net under realistic wave and current conditions were observed, where contact between the net and other parts of the structure were identified. This may cause damages to the net due to abrasion. 相似文献