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1.
An approximate method is presented to estimate the hydrodynamic loading and associated structural response of each of a pair of free-standing, bottom-nounted, flexible circular cylinders subjected to a regular train of linear surface waves. The cylinders are aligned parallel to the incident wave direction and the response of each is assumed to be one-dimensional and governed by a beam equation. The solution technique for the fluid velocity potential involves replacing scattered waves by equivalent plane waves together with non-planar, first-correction terms, and can be shown to be a large-spacing approximation. Numerical results are presented which show the influence of the various wave and structural parameters on the hydrodynamic loading and dynamic response of the individual cylinders. 相似文献
2.
A numerical procedure is described for predicting the motion and structural responses of tension leg platforms (TLPs) in waves. The developed numerical approach, in a TLP is assumed to be flexible instead of rigid, is based on a combination of the three dimensional source distribution method and the finite-element method. The hydrodynamic interactions among TLP members, such as columns and pontoons, are included in the motion and structural response analysis. Numerical results are compared with the experimental and numerical ones. The results of comparison confirmed the validity of the proposed approach. 相似文献
3.
A.G. Abul-Azm 《Ocean Engineering》1996,23(5):403-422
This paper presents an analytical, computationally efficient method for the wave reflection and dynamic displacement of a submerged flexible breakwater. The solution of the two-dimensional linearized hydrodynamic problem introduced is based on the eigenfunction expansion technique. The breakwater is assumed to be thin, impermeable, flexible, moored to the bed through tethers and kept in tension by means of a floating buoy at its tip. The beam structure is considered to be either clamped or hinged at the sea bed, situated in an arbitrary water depth and subjected to normal linear waves. Numerical examples presented by this method are compared with those obtained by the Boundary Integral Equation Method, presented by Williams et al. Comparisons show an excellent agreement over a wide range of parameters for the wave reflection and the dynamic displacement. Numerical results are presented, mainly to show the effect of the breakwater rigidity and the method of fixation on the wave reflection and the structural displacement over a wide range of wave frequencies. 相似文献
4.
The hydrodynamic response of a porous flexible circular-cylinder in regular waves was analytically studied. To simplify the problem, the cover and the bottom of the cylinder were ignored. Small amplitude water wave theory and structural responses were assumed. The velocity potentials were solved using the Fourier-Bessel series expansion method and the least squares approximation method. The convergence of the series was numerically tested to determine the number of terms in the series expansion. Two types of installations were considered for deformation, hydrodynamic forces, structural flexibility, drafts, and porosity. The present study represented a preliminary step in the study of the fish cage. 相似文献
5.
A. N. Williams 《Ocean Engineering》1988,15(6)
The hydrodynamic interactions due to wave scattering between the numbers of an array of stationary, truncated circular cylinders simulating the columns of an idealized tension-leg platform (TLP) are investigated. The method of solution for the fluid velocity potential involves replacing scattered waves by equivalent plane waves together with non-planar correction terms. This technique is, therefore, essentially a large spacing approximation. Use of this approach makes it possible to determine the hydrodynamic interactions between the array members utilizing only the diffraction characteristics of an isolated cylinder.Numerical results are presented for six array configurations consisting of 2–6 cylinders representing the legs of idealized TLPs. Calculations of the wave loads on these cylinders have been performed for a range of wave and structural parameters. It is found that, for certain parameter combinations, the influence of neighbouring bodies on the total wave field leads to hydrodynamic loading on individual columns which is significantly greater than the loading they would experience in isolation. The presented results demonstrate the significance of hydrodynamic interactions between TLP columns and clearly indicate that these effects should be considered by the designers and researchers associated with TLPs. 相似文献
6.
Many studies have been published concerning the influence of the immersed shape (in still water) of a floating body on its response and power capture from ocean waves. With a few notable exceptions, much of this analysis has assumed small amplitude motion and linear models have been employed to predict response. The form of the upper surface of such a body has received little attention. Here, we show how the shape of the upper (top) surface of a floating body can be designed to ensure that the response amplitude of the body is within a specified value. This is of considerable importance to the survivability of wave energy devices. The approach used is to achieve a large increase of both natural period and hydrodynamic damping for only a small change of float mass. These two factors impose a hydrodynamic limit on the displacement which may be exploited to avoid the ‘end-stop’ problem often encountered in wave device design. To demonstrate the change of response, experimental measurements are presented of the response of an axisymmetric float with rounded base and conical upper surface with rounded perimeter due to a range of regular, irregular and focused wave conditions. Power extraction is not considered since the mechanically undamped response represents the worst case. In contrast to a simple, straight-sided axisymmetric float, a smaller change of mass is required to satisfy a particular response amplitude limit. Although a significant reduction is not expected, hydrodynamic damping may reduce with increasing physical scale, and this remains to be quantified. 相似文献
7.
Steep wave impact pressures and the structural dynamic response of floating production storage and offloading platform (FPSO) bows are studied using 1:80 scale segmented, instrumented models. The construction of these segmented models is discussed. The ‘new-wave’ theory is adopted and extended to generate steep waves and a limiting form of steep wave that might be found in deep water is proposed. A comparison between linear theoretical, experimental and suggested wave models is made. Experimental results with systemically varying parameters are presented. 相似文献
8.
内孤立波中半潜平台动力响应特性 总被引：1，自引：1，他引：0
基于内孤立波mKdV理论,采用时域有限位移运动方程,结合改进的Morison公式,研究了两层流体中内孤立波与带分段式悬链系泊约束半潜平台的相互作用问题。针对东沙群岛南部海域附近某实测内孤立波特征参数,计算分析了在该内孤立波作用下SEDCO-700型半潜平台的内孤立波载荷、运动响应及其系泊张力的变化特性。研究表明,内孤立波不仅会对半潜平台产生突发性冲击载荷作用,使其产生大幅度水平漂移运动,并导致其系泊张力显著增大,因此在半潜平台等深海平台的设计与应用中,内孤立波的影响是不可忽视的。 相似文献
9.
Hydrodynamic modeling of perforated structures 总被引：2，自引：0，他引：2
B. Molin 《Applied Ocean Research》2011,33(1):1-11
A hydrodynamic model of perforated or slotted structures is proposed. It is asymptotic in the sense that the openings are supposed to be infinitely small and numerous, and the wall thickness to be nil. At variance with other work, a quadratic, not linear, law, relating the pressure differential to the traversing velocity, is assumed. As a result the hydrodynamic coefficients (added mass and damping) become amplitude dependent. The model is applied to bodies of various shapes including cylinders, plates and disks, in forced motion or submitted to incoming waves. Good agreement with experimental data is generally observed. 相似文献
10.
Water wave interaction with a floating porous cylinder 总被引：1，自引：0，他引：1
The interaction of water waves with a freely floating circular cylinder possessing a side-wall that is porous over a portion of its draft is investigated theoretically. The porous side-wall region is bounded top and bottom by impermeable end caps thereby resulting in an enclosed fluid region within the structure. The problem is formulated based on potential flow and linear wave theory and assuming small-amplitude structural oscillations. An eigenfunction expansion approach is then used to obtain semi-analytical expressions for the hydrodynamic excitation and reaction loads on the structure. Numerical results are presented which illustrate the effects of the various wave and structural parameters on these quantities. It is found that the permeability, size and location of the porous region may have a significant influence on the horizontal components of the hydrodynamic excitation and reaction loads, while its influence on the vertical components in most cases is relatively minor. 相似文献
11.
The interaction of water waves with arrays of bottom-mounted, surface-piercing circular cylinders is investigated theoretically. The sidewall of each cylinder is porous and thin. Under the assumptions of potential flow and linear wave theory, a semi-analytical solution is obtained by an eigenfunction expansion approach first proposed for impermeable cylinders by Spring and Monkmeyer (1974), and later simplified by Linton and Evans (1990). Analytical expressions are developed for the wave motion in the exterior and all interior fluid regions. Numerical results are presented which illustrate the effects of various wave and structural parameters on the hydrodynamic loads and the diffracted wave field. It is found that the porosity of the structures may result in a significant reduction in both the hydrodynamic loads experienced by the cylinders and the associated wave runup. 相似文献
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14.
箱式超大型浮体结构在规则波中的水弹性响应研究 总被引：3，自引：5，他引：3
利用三维线性水弹性理论研究了箱式超大型浮体结构在正弦规则波中的动力响应，用Bernoulli-Euler梁解析解计算结构在真空中的动力特性，用弹性体三维势流理论计算结构的水动力系数，浮体结构在单位波幅规则波中的刚体运动幅值与DNV／WADAM程序的计算结果进行了比较，并给出了垂向弯曲模态的位移，弯矩随波浪频率的变化规律，由于箱式浮体结构的低阶固有频率很低，相应的弹性振型的响应与刚体运动耦合，结构在波浪中没有发现明显的低阶弹性模态谐振。 相似文献
15.
The interaction of linear water waves with a semi-porous cylindrical breakwater surrounding a rigid vertical circular cylinder mounted on a storage tank is investigated theoretically. The cylindrical breakwater structure is porous in the vicinity of the free-surface, while at some distance below the water surface it becomes impermeable. Under the assumptions of linearized potential flow, the coupled problem of flow in the interior and exterior fluid regions is solved by an eigenfunction expansion approach. Analytical expressions are obtained for the wave motion in both the interior and exterior flow regions. Numerical results are presented which illustrate the effects of the various wave and structural parameters on the hydrodynamic loads and interior and exterior wave fields. It is found that for certain parameter combinations the semi-porous, cylindrical breakwater may result in a significant reduction in the wave field and hydrodynamic forces experienced by the interior structure. 相似文献
16.
建立双臂起重船从运输船上起吊大型稳桩施工平台的吊装系统模型,其中,起重船与运输船呈T型布置。首先基于势流理论,采用专业水动力分析软件AQWA开展了双船系统的频域水动力分析,分析双船起吊系统的水动力干扰特性和遮蔽效应,并对双船间隙自由液面进行黏性修正从而提高频域多体水动力分析的精度。进一步采用频域—时域方法对起吊耦合系统进行参数分析,探究起吊速度、波浪周期等对吊索张力和起重船运动的影响规律。分析多个工况下运输船的遮蔽效应对起吊系统的影响。结果表明,对间隙流体施加阻尼自由液面边界条件可以一定程度提高计算模型的精度,在某些周期的迎浪条件下运输船对起重船的遮蔽效应可以降低吊装系统的响应;起吊速度对时域动力响应的影响较小;周期为8 s的规则波引起过大的动力响应。 相似文献
17.
Analytical and numerical analysis of the dynamics of a marine riser connected to a floating platform 总被引：2，自引：0，他引：2
Forced dynamics of the system comprised of a riser, connected to a floating platform and conveying fluid, is studied in the presence of ocean waves and ocean currents. Shear effects based on nonlinear elastic theory are included in the formulation. The effects of the structural and hydrodynamic parameters on motion amplitude are evaluated and analytically studied based on an approach developed by Butenin. It is demonstrated that when the nonlinearities are small, the solutions obtained using Butenin's method match the numerical results. 相似文献
18.
Floating pontoon breakwaters 总被引：1，自引：0，他引：1
The hydrodynamic properties of a pair of long floating pontoon breakwaters of rectangular section are investigated theoretically. The structures are partially restrained by linear symmetric moorings fore and aft. The fluid motion is idealized as linearized, two-dimensional potential flow. The breakwater motions are assumed to be two-dimensional, in surge, heave and pitch. The solution for the fluid motion is obtained by the boundary integral equation method using an appropriate Green's function. Numerical results are presented that illustrate the effects of the various wave and structural parameters on the efficiency of the breakwaters as barriers to wave action. It is found that the wave reflection properties of the structures depend strongly on their width, draft and spacing and the mooring line stiffnesses, while their excess buoyancy is of lesser importance. 相似文献
19.
The purpose of this paper is to validate a new method that can be used by offshore platform designers to estimate the added mass and hydrodynamic damping coefficients of potential Tension Leg Platform hull configurations. These coefficients are critical to the determination of the platform response particularly to high frequency motions in heave caused by sum-frequency wave forcing i.e. “springing”. Previous research has developed the means by which offshore platform designers can extrapolate anticipated full-scale hydrodynamic coefficients based on the response of individual model scale component shapes. The work presented here further evaluates the component scaling laws for a single vertical cylinder and quantifies the effects due to hydrodynamic interaction. Hydrodynamic interaction effects are established through a direct comparison between the superposition of individual hull component coefficients and those evaluated directly from complete hull configuration models. The basis of this comparison is established by the experimental evaluation of the hydrodynamic coefficients for individual hull components as well as partial and complete platform models. The results indicate that hydrodynamic interaction effects between components are small in heave, and validate component scaling and superposition as an effective means for added mass and damping coefficient estimation of prototype platforms. It is found that the dependency of damping ratio with KC for a TLP is almost identical to that of a single column, thus offering a scaling methodology for prototype damping ratio values. 相似文献
20.
Yung-Chao Wu 《Ocean Engineering》1988,15(6)
The nonlinear hydrodynamic pressures acting on the surface of rigid structures during earthquakes is examined analytically by a two-dimensional potential flow theory. The ground acceleration is assumed to be horizontal and harmonic. When the relative displacement, the ratio of horizontal displacement of structures to the undisturbed water depth, is small. A perturbation method, using the relative displacement as perturbation parameter, is adopted to analyze the nonlinear hydrodynamic pressures. The effect of surface waves on the hydrodynamic pressure distribution is included in this research. Numerical values are given for different wave effect parameters. 相似文献