非线性铰接浮体波能转换器的动力学特性研究

针对传统铰接浮体波能转换器捕获效率低、频带窄的瓶颈,提出一种新型高效波能捕获仿生非线性连接结构。该连接结构具有转动负刚度效应,可起到被动相位控制作用,提高系统的波能捕获效率。首先,基于海蛇脊柱骨结构的柔性约束机理,设计了一种高效波浪能捕获仿生连接结构,该结构由球窝结构、球头、翅状突出物和类肌肉柔性结构组成;其次,基于线性波浪理论和Cummins 方程,建立两模块非线性波能转换器的动力学模型,并采用谐波平衡法解析求解非线性控制方程;最后,开展了数值模拟研究,分析了规则波激励下该新型波能转换器的波能转换特性。结果表明：通过引入新型高效仿生连接结构,可有效降低系统的等效固有频率;当连接器的负刚度结构调整到合适参数时,系统的弹性力可以在纵摇相平面上形成一个椭圆势阱,其椭圆势阱的长轴接近铰接浮体系统相对纵摇运动的模态方向,由此驱动两个模块的相对纵摇运动趋于反相,起到被动相位控制的作用。     

Wave-power absorption by a periodic linear array of oscillating water columns

This paper describes a theoretical analysis of the ocean wave energy absorption by a periodic linear array of oscillating water columns (OWCs) of arbitrary planform. The analysis is based on classical linear water wave theory and uses the expressions for the wave field resulting from time-harmonic pressure distributions on the free surface. The water depth is assumed finite and constant. The cases of oblique and normal incidence are analysed. A linear power take-off mechanism is assumed, but a complex characteristic constant (allowing for phase control) and air compressibility are considered. Special analytical expressions are derived for OWCs of rectangular and circular planforms. Numerical results for circular chambers show that the hydrodynamic interaction can substantially change the maximum energy absorption, depending on array and chamber geometry and on angle of incidence.     

Numerical modeling of a wave energy converter based on U-shaped interior oscillating water column

The paper presents a concept of a wave energy converter and the numerical model to calculate the hydrodynamic responses in waves and the power produced by the power take off system. The system consists of an asymmetric floater with an interior U-tank partially filled with water and two lateral air chambers connected by a duct. The motion of the U-shaped oscillating water column, mainly induced by the rolling of the floater, forces the air through the duct where a Wells turbine is installed to absorb the wave energy.The wave-floater hydrodynamics is calculated with a Green's function panel method, while the oscillating water column motions hydro-mechanics are derived from the one-dimensional Euler's equation. The dynamics of the Wells turbine is realistically represented by one additional differential equation on the unknown air pressure fluctuation. This equation is derived assuming small amplitude motions of the water column and assuming the linear isentropic relation is valid for the air thermodynamics in the air chambers. The Wells turbine is characterized by a drastic drop of efficiency above a critical pressure value due to stalling on the blades. The effect of a by-pass valve to prevent stalling is introduced in the numerical model in a simplistic way. The numerical model is implemented and tested for a wave energy converter with a displacement of 1150 t, including 490 t for the interior water column, and an installed turbine with 2.3 m of diameter. An analysis of the influence of changing different design parameters on the system efficiency is also presented.     

半球形多向波聚合波道振荡水柱气室优化设计

为了解决振动水柱式波浪能转换装置收集多向波浪问题,本文设计了半球形多向聚合波道振荡水柱气室结构,以适合远海单点波浪能采集和发电。在规则波正向入射条件下,基于流体仿真分析软件(FLUENT)、流体动力学连续性假设和粘性不可压缩流体动量守恒的运动方程(Navier-Stokes方程)建立半球形振荡气室和三维数值波浪水槽模型。仿真结果表明:增设气室后壁,合理设计波道开口角度实现多向迎波捕获波浪能,优化前壁形状可降低波浪触底反射带来的能量耗散,同时提高了气室内空气压强和出气口速度,有效提升波浪能俘获效率,为后续发电的二次能量转换提供高效的空气动力。     

球坐标系下MASNUM海浪数值模式的建立及其应用

为开展海浪对海洋上混合层的搅拌混合作用及其对海气界面通量的影响等研究,在LAGFD WAM区域海浪数值模式基础上建立了球坐标系下的全球海浪数值模式.重点导出了球坐标系下的海浪能量谱平衡方程及其复杂特征线方程,该组方程包含了背景流场对波动传播的调整、波动沿大圆传播的折射等.数值积分则采用复杂特征线嵌入计算格式.初步数值模拟结果表明,该海浪全球数值模式能够较为精确地刻画海浪的动力过程.     

中尺度地形扰动的非线性问题半解析解

将大气和海洋中f-平面上中尺度地形的扰动问题统一起来作为一个地球物理流体力学问题，应用涡度、能量和经圈动量守恒条件，将原来高度非线性方程变成一个二阶椭园型非线性方程，用数值模拟方法分析了大气中的过山运动和海洋中的沿岸上升流，给出了与观测接近的模拟结果以及运动过程对内部物理参数和外界条件的敏感性分析。所提方法可供进一步的动力学分析和数值研究参考。     

Hydrodynamic Analysis and Power Conversion for Point Absorber WEC with Two Degrees of Freedom Using CFD

Point absorber wave energy device with multiple degrees of freedom (DOF) is assumed to have a better absorption ability of mechanical energy from ocean waves. In this paper, a coaxial symmetric articulated point absorber wave energy converter with two degrees of freedom is presented. The mechanical equations of the oscillation buoy with power take-off mechanism (PTO) in regular waves are established. The three-dimensional numerical wave tank is built in consideration of the buoy motion based upon the CFD method. The appropriate simulation elements are selected for the buoy and wave parameters. The feasibility of the CFD method is verified through the contrast between the numerical simulation results of typical wave conditions and test results. In such case, the buoy with single DOF of heave, pitch and their coupling motion considering free (no PTO damping) and damped oscillations in regular waves are simulated by using the verified CFD method respectively. The hydrodynamic and wave energy conversion characteristics with typical wave conditions are analyzed. The numerical results show that the heave and pitch can affect each other in the buoy coupling motion, hydrodynamic loads, wave energy absorption and flow field. The total capture width ratio with two coupled DOF motion is higher than that with a single DOF motion. The wave energy conversion of a certain DOF motion may be higher than that of the single certain DOF motion even though the wave is at the resonance period. When the wave periods are high enough, the interaction between the coupled DOF motions can be neglected.     

特征线计算格式下共轭方程两种导出途径的比较

共轭方程的导出是建立资料同化模型的关键，其导出方式有两种途径：AFD形式与FDA形式。在特征线计算格式基础上针对一类较广泛海洋动力控制方程分析了其两种共轭方程（AFD形式与FDA形式）之间的关系，并将理论结果应用于波谱共轭方程的讨论。     

Numerical modelling of liquefaction in loose sand deposits subjected to ocean waves

The failure of marine structures is often attributed to liquefaction in loose sand deposits that are subjected to ocean waves. In this study, a two-dimensional integrated numerical model is developed to characterize the liquefaction behaviours of loosely deposited seabed foundations under various types of ocean waves. In the present model, Reynolds-Averaged Navier–Stokes (RANS) equations are used to simulate the surface wave motion, and Biot's consolidation equations are used to link the solid-pore fluid interactions in a porous medium. A poro-elasto-plastic solution is used to reproduce foundation behaviour under cyclic shearing. Unlike previous investigations, both oscillatory and residual soil responses were considered; they are coupled in an instantaneous approach. Verification of the model results to the previous centrifugal wave tests is carried out, obtaining fairly good agreement. Numerical examples show that foundation behaviour under various types of wave loading, particularly standing waves or a solitary wave, embodies a completely two-dimensional process in terms of residual pore pressure development. The parametric studies demonstrate that liquefaction caused by the build-up of pore pressures is more likely to occur in loosely deposited sand foundations with poor drainage and under large waves.     

Study on the dynamic characteristic of a U-type tuned liquid damper

By means of Lagrange's equation, the “coupled” equations of motion for a horizontal plate carrying a U-type tuned liquid damper (TLD) are derived. The “uncoupled” equations of motion for the liquid (in the TLD) and the structural system are then obtained by decoupling the “coupled” ones. Unlike the existing literature to indirectly determine the natural frequencies of a damped vibrating system by using the resonant method, the “complex” eigenvalues of the coupled damped system are obtained directly from the associated eigenvalue equations. Besides, the pressure intensities in the two air chambers and the sizes of the two vertical tanks together with the horizontal conduit are arbitrary in the formulation of this paper. The influence of some key parameters of the TLD on the dynamic responses of the structural system is studied.     

Modelling of the upper turbulent layer in the ocean

A differential model of the upper turbulent layer in the ocean is considered. A closed system of equations includes equations of motion, balance, and dissipation of kinetic turbulence energy. Boundary conditions at the surface are determined using a solution of the atmospheric problem taking into account the interaction between the two media. The formulated algorithm allows for a relationship between turbulent energy dissipation and flux and the parameters of wind disturbance. The vertical profiles of turbulence and drift current characteristics are presented as well as parameters of the ocean-atmosphere interaction for various values of impulse jump within the limits of the wave layer with waves collapsing and not collapsing.UDK 551.456.152     

直驱式波浪能转换系统的研究和性能优化

A direct-drive wave energy conversion system based on a three-phase permanent magnet tubular linear generator （PMTLG） and a heaving buoy is proposed to convert wave energy into electrical energy. Sufficient experimental methods are adopted to compare the computer simulations, the validity of which is verified by the experiment results from a wave tank laboratory. In the experiment, the motion curves of heaving buoy are with small fluctuations, mainly caused by the PMTLG＇s detent force. For the reduction of these small fluctuations and a maximum operational efficiency of the direct-drive wave energy conversion system, the PMTLG＇s detent force minimization technique and the heaving buoy optimization will be discussed. It is discovered that the operational efficiency of the direct-drive wave energy conversion system increases dramatically after optimization. The experiment and optimization results will provide useful reference for the future research on ocean wave energy conversion system.     

Wave propagation in a transversely isotropic porous ocean bottom

Abstract

The equations of wave motion are considered in this article for three-layered medium which consists of liquid and porous layers with finite depth and solid half-space such as ocean bed. By virtue of scalar potential functions for each layer, complicated differential equations of layers are reduced to ordinary differential equations. An analytical method is applied to determine the Green’s functions of media based on an arbitrary shaped time-harmonic excitation at the interface of liquid and porous layers. A Mathcad code is provided to compute the complex integrals. Displacement and stress fields of three layers are discussed. Comparing with special cases, existing answers represent the validity of the proposed method. Numerical results are carried out for circular patch, ring and point loads, and the effects of various parameters on the behavior of the system are plotted. Finally, the achieved results were under discussion.     

Approximation of near-resonant wave motion using a damped harmonic oscillator model

In this work, transient resonant motions excited in linearised scattering interactions are approximated using a simple damped harmonic oscillator model. The scattering interactions considered involve the diffraction of an incident wave-train with a dominant regular time-harmonic component by structures which enclose a portion of the free surface. Provided a single resonant mode only is excited significantly, the fluid oscillation in the vicinity of the structure will primarily be composed of the resonant mode and incident wave mode contributions. The forced damped harmonic oscillator equation is used to predict the fluid motion and, in particular, the elevation of the internal free surface. The predictions are compared to the results from a numerical time-domain solver based on the linearised water-wave equations. It is shown that, given a good estimate of the location of the resonance in the complex frequency plane and a priori knowledge of the form of the incident wave, the model can successfully predict the time-dependent behaviour of the motion. Both two- and three-dimensional scattering problems are considered with a variety of scatterers in each case.     

Dynamical analysis of mesoscale eddy-induced ocean internal waves using linear theories

This study aims to explore generation mechanisms of the ocean internal wave using the dynamical analysis methods based on linear theories. Historical cruise measurements and recent synthetic aperture radar （SAR） observations of mesoscale eddies with diameter of several tens of kilometers to hundreds of kilometers show that the internal wave packets with wavelength of hundreds of meters to kilometer exist inside the mesoscale eddies. This coexistence phenomenon and inherent links between the two different scale processes are revealed in the solutions of governing equations and boundary conditions for the internal wave disturbance with a horizontally slowly variable amplitude in a cylindrical coordinate system. The theoretical solutions indicate that the instability of eddy current field provides the dynamical mechanism to internal wave generation. The derived dispersion relation indicates that the internal wave propagation is modified by the eddy current field structure. The energy equation of the internal waves clearly shows the internal wave energy increment comes from the eddy. The theoretical models are used to explain the observation of the mesoscale eddy-induced internal waves off the Norwegian coast. The two-dimensional waveform solution of the anticyclonic eddy-induced internal wave packet appears as ring-shaped curves, which contains the typical features of eddy stream lines. The comparison of theoretical solutions to the structure of the internal wave packets on SAR image shows a good agreement on the major features.     

On the Vibration Reduction Effect of Offshore Platform Vibration Distribution Structure

Based on the Bohai ocean environment characteristics, a new platform vibration distribution structure is designed to reduce the platform vibration due to flowing ice. The effect of the earthquake wave and ocean wave load on this vibration distribution structure is considered in the design. The principal idea of this new vibration distribution structure is dividing the platform main column into the inner tube and the outer tube. The outer tube is connected with the leg pontoon by braces, while the inner tube is used to support the platform deck. The inner tube and outer tube can be connected or disconneted in the region near the water line. For evaluating the vibration reduction effect of such a structure, tests are carried out on a steel model, and the external load of flowing ice, earthquake wave and ocean wave are simulated by concentated random load applied to different points of the model. The tests are performed in water media and air media respectively. The vibration reduction effect is evaluated     

Some General Properties of Transverse Motions of the Geostrophic Front

Within the framework of the reduced-gravity model of the ocean taking into account the effect of friction in the Rayleigh form, we study the two-dimensional problem of nonlinear motions of a subsurface front of finite width. We consider the conservation laws and the character of motion of the center-of-mass of the cross section of the front and their variations caused by the losses of energy. For fields with special structure, the problem is reduced to the solution of a system of nonlinear ordinary differential equations. It is shown that the initially geostrophic frontal current decays with time according to a power law. The deviations of the initial state of the front from the state of geostrophic balance result in the generation of superinertial oscillations of the hydrodynamic fields.     

畸形波作用下张力腿浮式风力机动力响应特性

针对张力腿系泊浮式风力机的基础运动,忽略柔性构件的影响,建立气动—水动—系泊非线性耦合运动方程。在运动控制方程中包含张力腿系泊系统的非线性回复刚度,桨距角控制以及浮式基础运动对空气动力载荷的影响。在波浪载荷的计算中考虑二阶波浪载荷的作用。采用随机频率相位角调制法生成畸形波波面时历,计算在畸形波作用下张力腿型浮式风力机的动力响应特性。数值模拟结果表明,在畸形波作用下,浮式基础的运动及空气动力性能均受到了显著的影响。其中浮式基础的纵荡和纵摇运动分别受二阶差频与和频波浪力的影响,而垂荡运动的增加则主要是受下沉运动的影响。在畸形波经过的时刻,风力机的功率系数迅速下降,水平方向的风载荷波动先减小,随后其数值急剧下降,而垂直方向的风载荷波动增大。     

利用波能平衡方程研究波浪折射——绕射的数学模型及数值模拟

波能平衡方程是研究风浪要素及波能传播问题的很有效的方法，计算较为简单，在海洋学及海岸动力学中得到广泛的应用。本文采用考虑波能侧向传递机制和耗损制约的波能平衡方程组作为研究波浪折射——绕射变形的控制方程。对数学模型用差分法进行了数值模拟，并用两个例题进行了验证     

Refraction-Diffraction Mathematical Model for Waves With Lateral Energy Transmission Mechanism and Its Verification

To solve problems concerning wave elements and wave propagation, an effective way is the wave energy balance equation, which is widely applied in oceanography and ocean dynamics for its simple computation. The present papaer advances wave energy balance equations considering lateral energy transmission and energy loss as the governing equation for the study of wave refraction-diffraction. For the mathematical model, numerical simulation is made by means of difference method, and the result is verified with two examples.