共查询到20条相似文献，搜索用时 31 毫秒
1.
A procedure to calculate horizontal slow drift excitation forces on an infinitely long horizontal cylinder in irregular beam sea waves is presented. The hydrodynamic boundary-value problem is solved correctly to second order in wave amplitude. Results in the form of second order transfer functions are presented for different two-dimensional shapes. It is concluded that Newman's approximative method is a practical way to calculate slow drift excitation forces on a ship in beam sea and suggested that it may be used in a more general case. Applications of the results for moored ships are discussed. 相似文献
2.
Tom Marthinsen 《Applied Ocean Research》1983,5(3):141-144
A new method for approximating time dependent drift forces in irregular, long or short crested sea is presented. The approximation is based on the assumption that the wave energy spectrum is narrow-banded. The drift forces may be computed from the spectrum or directly from a time record of waves by using Hilbert transforms. Numerical calculations are made for drift forces and corresponding motions of a floating box, and the method is compared to a commonly used method due to Newman. The two methods are found to agree very well. 相似文献
3.
An iterative frequency domain method of analysis is presented for determining the response behaviour of Guyed Offshore Towers to low-frequency, second-order wave drift forces generated in a random sea environment. For the response analysis, the tower is idealized as a shear beam with a rotational spring at the bottom support. The guylines are replaced by a non-linear spring. The second-order drift force is considered to be proportional to the square of the wave elevation and is simulated using a drift force coefficient and the time history of a slowly varying wave envelope in random sea. The responses due to drift forces are obtained in frequency domain by incorporating the non-linearities produced due to non-linear guy lines. An example problem is solved under different random sea states to compare the response behaviour of the tower obtained by the second-order wave force, the first-order wave force and a combination of the two. 相似文献
4.
由于沿海区域的限制以及愈加严重的环境污染,渔业养殖正从近海走向深远海。深远海海域的海况更加恶劣,给养殖装备的设计与性能评估带来新的挑战。为解决该问题,对极端波浪与养殖装备网衣结构的相互作用开展研究。基于waves2Foam建立数值波浪水池,极端波浪模拟采用基于NewWave理论的聚焦波模型,网衣结构模拟采用多孔介质模型,并通过与Morison模型计算的网衣受力等效分析,获得多孔介质模拟网衣结构阻力系数的直接估计方法。然后将多孔介质模型嵌入waves2Foam中,开展聚焦波与网衣结构相互作用的数值模拟,同时开展水槽试验,验证数值模拟的准确性。基于数值模拟结果,系统地分析了不同网衣密实度及不同波浪参数下网衣结构的升阻力特性以及网衣结构对波浪场的扰动规律。研究表明：聚焦波波峰幅值和网衣密实度对网衣结构的升阻力影响较大,且升力峰值出现在阻力为0的时刻;网衣结构对聚焦波的时空演化特性有影响,改变了聚焦波波形。 相似文献
5.
《海洋技术学报》2023,(4)
海上漂浮式光伏在北方冬季面临被海冰破坏的危险,冰期海洋环境对漂浮式光伏的影响尚处于研究初级阶段,因此非常有必要开展相关研究。为了有效防冰与抗冰,本文从水动力、波浪冲击性、支架稳定性、海水腐蚀、锚固方式等方面入手,首先对光伏方阵总环境载荷进行计算与仿真,然后对集装箱式漂浮防波堤、浮体方阵结构、支架、配件材料及锚固系统等进行优化设计,最后在潮汐变化显著的天津南港近海水域进行了冰期试验。试验数据与结果表明：浮式防波堤能有效阻挡围堰外海冰,消浪效果达到设计要求;塑料螺栓不仅可以有效避免因潮汐产生的浮体松动,而且能抵抗来自高盐高雾环境的腐蚀;设计的锚固系统能有效固定光伏方阵,使其漂移在可控范围内。该试验研究成果为优化北方冰期海上光伏技术方案提供了试验依据与理论支持。 相似文献
6.
An analytical solution is presented for calculating the regular wave induced respones of an articulated column in a wave tank. Extension of the procedure leads to calculation of second order mean drift forces and moments. Hydrodynamic interaction between a cylindrical column and the parallel walls of the tank is shown theoretically to be highly significant and experimental data are presented to corroborate this finding. 相似文献
7.
This is a Part I of a paper of nonlinearities of wind waves in the deep open ocean. First, considerations are given in order to verify the theoretical expression for bound waves from observed data. We compare the contribution of bound waves and double Bragg scattering to the second-order scattering, and we show that the contribution of bound waves is larger, and that bound waves can be detected by measuring the Doppler spectra of HF (high-frequency) radio wave scattering from the sea surface. Moreover, if the theory of the HF radio wave scattering from the sea surface is verified, so is the second-order perturbation theory for bound waves. Then, the contributions of bound waves to ocean wave spectra are investigated on the basis of the nonlinear theory. The bound waves are shown to modify frequency spectra and wave directional distributions at higher frequencies, and it is shown that although the modifications of frequency spectra are smaller for a two-dimensional field case than for a one-dimensional field case, they are not negligible at higher frequencies. On the other hand, the modifications of wave directional distributions are shown to be significant at higher frequencies. These discussions become significant only when bound wave predictions are verified in the open ocean. Consequently, it is shown that nonlinearities of water waves are important in considering both radio wave scattering from the sea surface and the detailed structures of ocean wave spectra at high frequencies. 相似文献
8.
The mooring of offshore floating structures, such as offshore platforms, in large waves against drift forces and rotational moments is a challenging problem in offshore engineering. To accurately investigate such problems, called positioning problems, the time-averaged steady forces of the second order known as the wave drift forces must be taken into account. Fortunately, a cloaking phenomenon occurs under certain conditions and dramatically reduces the wave drift force acting on such a floating body, as previously reported by several researchers. In the diffraction problem of water waves, cloaking refers to the condition where there is no scattering in the form of radial outgoing waves. The reduction of wave drift force on a truncated cylinder with the occurrence of cloaking phenomenon has been numerically and experimentally confirmed. In this paper, the arrangement of several small circular cylinders at regular intervals in a circle concentric with a fixed floating body is considered as an effective means of reducing the wave drift force. Using a combination of a higher-order boundary element method (HOBEM) and wave interaction theory, the influences of the geometric parameters of the outer surrounding cylinders on the wave drift force and the total scattered-wave energy are systematically investigated and discussed. A quasi-cloaking phenomenon is first found and reported in the present study, which is beneficial and flexible for application in practical engineering. More than one quasi-cloaking trigger (where a trigger is an occurrence condition) can be found simply by varying the distance between the inner and outer floating bodies. 相似文献
9.
回顾了近几年来深海平台二阶波浪力的研究成果。对几种典型深海平台结构二阶波浪力研究作了详细的阐述,包括理论分析、数值计算和实验验证等。最后指出目前该领域主要研究方向,作为进一步研究的参考。 相似文献
10.
The interaction of a solitary wave with an array of surface-piercing vertical circular cylinders is investigated numerically. The wave motion is modeled by a set of generalized Boussinesq equations. The governing equations are discretized using a finite element method. The numerical model is validated against the experimental data of solitary wave reflection from a vertical wall and solitary wave scattering by a vertical circular cylinder respectively. The predicted wave surface elevation and the wave forces on the cylinder agree well with the experimental data. The numerical model is then employed to study solitary wave scattering by arrays of two circular cylinders and four circular cylinders respectively. The effect of wave direction on the wave forces and the wave runup on the cylinders is quantified. 相似文献
11.
The linear water wave scattering and radiation by an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth is investigated by use of the multipole expansion method. The diffracted and radiated potentials are expressed as a linear combination of infinite multipoles placed at the centre of each cylinder with unknown coefficients to be determined by the cylinder boundary conditions. Analytical expressions for wave forces, hydrodynamic coefficients, reflection and transmission coefficients and energies are derived. Comparisons are made between the present analytical results and those obtained by the boundary element method, and some examples are presented to illustrate the hydrodynamic behavior of multiple horizontal circular cylinders in a two-layer fluid. It is found that for two submerged circular cylinders the influence of the fluid density ratio on internal-mode wave forces is more appreciable than surface-mode wave forces, and the periodic oscillations of hydrodynamic results occur with the increase of the distance between two cylinders; for four submerged circular cylinders the influence of adding two cylinders on the wave forces of the former cylinders is small in low and high wave frequencies, but the influence is appreciable in intermediate wave frequencies. 相似文献
12.
针对混响环境非自由声场中声源测量的问题,本文以消声水池和混响水槽为实验环境,以换能器辐射的声场为研究对象,以水听器阵列为测量前端,进行了混响环境非自由声场中声源对象的测量、分析和重构的实验研究。通过单层水听器阵列对非自由声场进行声压分布测量,并对测量结果作声波分离处理,将分离前后的声压分布和在消声水池中测量的声压分布进行比较,给出了声源频率为5 000 Hz和7 000 Hz时,声场重构的误差分析结果。结果表明,基于单层水听器阵列声压测量的声波分离方法,能够较精确地对混响环境中的声场进行重构。 相似文献
13.
Interactions between water waves and non-wall-sided cylinders are analyzed based on velocity potential theory with fully nonlinear boundary conditions on the free surface and the body surface. The finite element method (FEM) is adopted together with a 3D mesh generated through an extension of a 2D Delaunay grid on a horizontal plane along the depth. The linear matrix equation for the velocity potential is constructed by imposing the governing equation and boundary conditions through the Galerkin method and is solved through an iterative method. By imposing the gradient of the potential equal to the velocity, the Galerkin method is used again to obtain the velocity field in the fluid domain. Simulations are made for bottom mounted and truncated cylinders with flare in a numerical tank. Periodic waves and wave groups are generated by a piston type wave maker mounted on one end of the tank. Results are obtained for forces, wave profiles and wave runups. Further simulations are made for a cylinder with flare subjected to forced motion in otherwise still open water. Results are provided for surge and heave motion in different amplitudes, and for a body moving in a circular path in the horizontal plane. Comparisons are made in several cases with the results obtained from the second order solution in the time domain. 相似文献
14.
The size, complexity and critical operations of many offshore structures, including the mobile offshore bases (MOBs) of current interest, require careful determination of wave forces on the neighboring structures, including their interactions. This paper describes an analytical/numerical approach that determines the wave forces on multiple structures in the vicinity of one another. The method involves the consideration of multiple vessel interaction and scattering in waves. The analysis is an extension of the semi-analytical multiple vertical cylinder analysis published by the author. The analysis is similar to the one proposed by Kagemoto and Yue for axisymmetric bodies.The direct method of linear diffraction, while quite accurate and efficient in solving the hydrodynamic problem, demands a large amount of memory and requires considerable execution time. The present analysis is very efficient in these respects. It is accomplished by marrying the direct method with a semi-closed analytical method of multiple scattering developed for an array composed of vertical cylindrical structures. It is recognized that this analytical method has a limitation owing to the geometry of many offshore structures including MOBs. Therefore, the analysis is extended to an arbitrary geometry. In this method, the direct matrix method of diffraction problem is applied to an isolated module and then extended to structures with the multiple scattering technique to account for the interaction of multiple structures.Comparisons are made of the results from the analytical and conventional numerical diffraction theory with those of the semi-analytical tool using the above-mentioned analysis. 相似文献
15.
The finite element method(FEM) is employed to analyze the resonant oscillations of the liquid confined within multiple or an array of floating bodies with fully nonlinear boundary conditions on the free surface and the body surface in two dimensions.The velocity potentials at each time step are obtained through the FEM with 8-node quadratic shape functions.The finite element linear system is solved by the conjugate gradient(CG) method with a symmetric successive overelaxlation(SSOR) preconditioner.The waves at the open boundary are absorbed by the combination of the damping zone method and the Sommerfeld-Orlanski equation.Numerical examples are given by an array of floating wedgeshaped cylinders and rectangular cylinders.Results are provided for heave motions including wave elevations,profiles and hydrodynamic forces.Comparisons are made in several cases with the results obtained from the second order solution in the time domain.It is found that the wave amplitude in the middle region of the array is larger than those in other places,and the hydrodynamic force on a cylinder increases with the cylinder closing to the middle of the array. 相似文献
16.
《Applied Ocean Research》1987,9(1):2-6
A wave tank test was conducted to measure the forces on a submersible drilling rig model. The results were compared with the analytical results based on linear wave diffraction theory. The test set-up necessitated a small uniform gap between the rig model and the tank floor. Thus, the set-up duplicated an open bottom structure or a structure on a porous foundation. The measured vertical forces experienced a significant reduction due to this gap. The results showed that the measured horizontal forces correlated well with the theory. Because of the small gap, the numerical modeling of the potential theory is difficult and the vertical forces or overturning moment are not expected to correlate. The theoretical values for the vertical forces are based on bottom-seated structure. The theoretical vertical forces were adjusted with the corresponding mean bottom pressure around the structure times the footprint area. The correlation with the adjusted vertical forces were found to be good. Thus, for a small gap at the bottom, the pressure underneath the structure may be well represented by the mean bottom pressures of a sealed structure. Note that the real structure will experience a wave pressure at the bottom due to seepage and thus, the test case is closer to the real situation than the sealed case. The magnitude of this pressure, however, will depend on the type of foundation. 相似文献
17.
This paper deals with the hydrodynamic analysis of an array of Oscillating Water Column (OWC) devices, made up of coaxial cylinders, which are floating either independently or as a unit forming a floating platform. The platform is considered either free – floating or as TLP configuration connected to the sea bottom. Numerical results concerning the three boundary value problems, namely, the diffraction, the motion – and the pressure – dependent radiation ones are given. They have been obtained through an analytical solution method using matched axisymmetric eigenfunction expansion formulations. In all cases the interaction phenomena with neighbouring bodies have been taken properly into account using the physical idea of multiple scattering. Numerical results for the first – and the mean second – order wave forces, the hydrodynamic interaction coefficients along with pressure hydrodynamic parameters, inner air pressure and free–surface oscillation amplitude inside and outside of each device are parametrically evaluated and supplemented by experimental data. 相似文献
18.
在深海中系泊的海洋平台,如Spar平台,水下部分为带有系泊的圆柱结构,其水平方向运动响应往往具有较低的自振频率,容易在低频波浪力(源于非线性的差频效应)作用下发生共振响应,使结构发生大幅水平慢漂。当浮体的瞬时位置大幅偏离初始位置时,基于初始平衡位置的摄动展开法会存在较大误差。针对这一问题,采用两次展开方法,对大幅慢漂运动开展时域模拟研究。对双色波作用下自由漂浮圆柱的大幅运动响应问题进行数值分析,并与采用基于初始平衡位置的摄动展开法的计算结果进行了对比。结果表明,采用新的两次展开法可以计算出波浪遭遇频率的变化和波浪漂移阻尼,而这无法从基于初始平衡位置的常规摄动展开法中得到,体现了两次展开法在分析大幅慢漂问题上的优势。 相似文献
19.
The paper provides a simple analytical method which can be used to give estimates of the Stokes drift based on short-term variation of wave conditions. This is achieved by providing bivariate distributions of wave height and surface Stokes drift as well as wave height and volume Stokes transport for individual random waves within a sea state. The paper presents and discusses statistical aspects of these Stokes drift parameters, as well as examples of results corresponding to typical field conditions. 相似文献
20.
Subrata K. Chakrabarti 《Applied Ocean Research》1981,3(1):2-12
In a wave tank test with vertical tube array arranged transverse to the wave direction, forces on two 1 ft instrumented sections as well as on the tubes are measured. The effect of the spacing of the tubes upon the forces on the tubes are investigated. The mass and drag coefficients are determined from the forces on the instrumented sections of the tubes. They are presented as functions of the Keulegan-Carpenter number (or the period parameter) and the tube spacing. The total forces on the tubes are computed based on the mean values of the hydrodynamic coefficients. The correlation between these calculated values and the measured forces is found to be good. 相似文献