浮力摆式波浪能装置水动力性能的时域分析

该文采用时域势流模型研究了浮力摆式波浪能装置的水动力性能,通过与频域模型的比较,验证了时域模型,并对比分析了两种典型的PTO阻尼(Power Take-off,能量提取系统)下浮力摆运动和装置转换功率的时间过程、浮力摆摆幅、装置的转换效率等方面,其中恒定阻力矩的选取参照了激振力矩.研究表明:相比采用恒定阻力矩,采用线性阻尼时浮力摆的动力响应更加规则、平稳.两种PTO阻力矩条件下,波浪和摆板参数相同时,装置的最高转换效率基本相同,都能达到100％以上,但转换功率和转换效率的变化趋势有所不同;相应于最佳线性阻尼,采用恒定阻力矩时,装置也存在最佳阻力矩;对于5s左右的波周期,采用不同类型的PTO阻尼,当装置的转换功率相同时,浮力摆的最大转速基本相同,但最大摆幅和最大阻力矩差别则较大.     

Optimization of an annular wave energy converter in a wind-wave hybrid system

A hybrid system of a spar-type floating offshore wind turbine and a heaving annular wave energy converter(WEC)provides a promising solution for collocated ocean renewable energy exploitation.The performance of the hybrid system depends on the dimensions of the WEC.Here an optimization method is proposed to determine the outer radius and the draft of the WEC under the wave condition in a randomly chosen operational site.First,three candidate models are selected based on three operational conditions of energy harvest:(1)The natural frequency of the system is matched with the peak wave frequency in the target site(referred to as synchronized mode),where the wind turbine and the WEC nearly heave together in a near-resonance condition,(2)The natural frequency of the WEC is matched with the peak wave frequency(ring mode),(3)The maximum wave power is harnessed under the peak wave frequency(target mode).Then the candidate modes are evaluated to obtain an optimum.Results show that the extracted wave power under the above operational conditions has an upper bound that can hardly be surpassed by enlarging the dimensions of the WEC only.The optimal annual wave energy production is achieved in the synchronized mode because of the superior performance of WEC over a wide bandwidth of effective energy conversion.     

Numerical examination of wave power absorption by the Edinburgh Duck wave energy converter device

A two-dimensional computational fluid dynamics(CFD)numerical model is developed to study the power takeoff(PTO)efficiency of an Edinburgh duck wave energy conve...     

Numerical study of hydrodynamic behavior and conversion efficiency of a two-buoy wave energy converter

In this paper we propose a two-buoy wave energy converter composed of a heaving semi-submerged cylindrical buoy, a fixed submerged cylindrical buoy and a power take-off(PTO) system, and investigate the effect of the fixed submerged buoy on the hydrodynamics of the heaving semi-submerged buoy based on the three-dimensional potential theory. And the dynamic response of the semi-submerged buoy and the wave energy conversion efficiency of the converter are analyzed. The difference of the hydrodynamics and the wave energy conversion efficiency of a semi-submerged buoy converter with and without a fixed submerged buoy is discussed. It is revealed that the influence of the fixed submerged buoy on the exciting wave force, the added mass, the radiation damping coefficient and the wave energy conversion efficiency can be significant with a considerable variation, depending on the vertical distance between the heaving semi-submerged buoy and the fixed submerged buoy, the diameter ratio of the fixed submerged buoy to the heaving semi-submerged buoy and the water depth.     

Evaluation and optimization of a hybrid wave energy converter using excited motion response in two degrees of freedom

As waves in China seas are not high,a wave energy converter consisting of a coaxial annular buoy and a cylindrical buoy that extracts wave energy using two generators through the relative heave motion between the buoys and the pitch motion of the cylinder could be a more efficient choice.A dynamic model considering constraints and assuming linear power take-off is established to evaluate the power performance of the device.The influences of two key factors,the diameter of the annular buoy and the power take-off stiffness of the pitching generator,and their couplings on the power performance are analyzed.The power of the pitching generator accounts for a major proportion of the total power.An increase in the annular buoy diameter increases the power of the heaving generator while greatly decreases the power of the pitching generator.An increase in the power take-off stiffness of the pitching generator greatly decreases its power while has little influence on the power of the heaving generator.These two factors also influence the peak period of the total power.Based on the findings and practical limitations,an optimization strategy is proposed.Further,the device is optimized based on a real wave environment in Shandong Province,China.     

Flexural-gravity wave resistances due to a moving point source on 2-D infinite floating beam

The flexural-gravity wave responses due to a load steadily moving or suddenly accelerated along a rectilinear orbit are analytically studied within the framework of the linear potential theory. A thin viscoelastic plate model is used for a very large floating structure. The initially quiescent fluid in the ocean is assumed to be homogenous, incompressible, and inviscid, and the disturbed motion be irrotational. A moving line source on the plate surface is considered as a moving point in the two-dimensional coordinates. Under the assumptions of small-amplitude wave motion and small plate deflection, a linear fluid-plate coupling model is established. The integral solutions for the surface deflections and the wave resistances are analytically obtained by the Fourier transform method. To study the dynamic characteristics of the flexural-gravity wave response, the asymptotic representations of the wave resistances are derived by the residue theorem and the methods of stationary phase. It shows that the steady wave resistance is zero when the speed of moving load is less than the minimal phase speed. The wave resistances due to the accelerate motion consist of two parts, namely the steady and transient wave responses. Eventually the transient wave resistance declines toward zero and the wave resistance approaches the steady component as the time goes to the infinity. Furthermore, the effect of the strain relaxation time for this viscoelastic plate is studied and it exhibits more influence for a high-speed motion.     

波浪斜向入射对斜坡作用的研究

目前,国内、外对波浪斜向入射时,斜坡上所受的最大波压力及其作用点的研究,尚未见成果,而工程实践又急需理论指导。鉴于这种情况,本文对此进行了详细的试验研究,拟合出的经验公式和三维曲面图直观地表达了单宽斜坡上最大波压力随入射角的变化规律,以及随波长的变化趋势。     

波浪正向入射对斜坡作用的研究

本文通过大量的室内试验深入研究了波浪正向入射时,光滑斜坡上最大波压力的变化趋势,拟合出的变化规律与前苏联规范公式基本吻合,而且对两者的差别也作了合理的解释。同时,首次找出了最大波压力随波长变化的初步规律。     

直墙波浪力计算中几个问题的探讨

由于近岸波浪动力受地形等主要因素的影响变化剧烈,尤其伴随着波浪破碎,增加了直墙上波浪力确定的困难。直墙上波浪力的确定在现阶段仍以物理模型试验为主。然而,不同的研究者所得的结果往往差异较大。文中通过物理模型试验,对直墙上波浪力计算中几个常见的问题进行了进一步的研究和探讨,提出同时刻压强沿水深的分布型式主要有局部冲击型、均匀分布型和过渡型三种。分析结果可为直墙波浪力更为准确的确定提供依据。     

V形贯底式防波堤上波浪作用力的解析研究

用解析方法计算V形贯底式防波堤在波浪绕射作用下周围流域任意点的速度势,研究波浪作用在V形贯底式防波堤上的波浪力。假定防波堤刚性、薄壁、不透浪、水深恒定。假想的圆柱面将整个流场划分为三个区域,分别在每个区域内将速度势用特征函数展开,然后在公共边界上按照速度连续,速度势连续的原则进行匹配,求得流域中任意一点的速度势和作用在V形贯底式防波堤上的总波力和总波力矩。数值结果给出了作用在防波堤上的波浪力随防波堤张角、入射波波长、入射角变化的曲线。结果表明:作用在V形贯底式防波堤上的波浪力与水深、防波堤的张角、入射波的波长等因素有关。     

多向聚焦波浪作用下直立圆柱受力的实验研究

利用波能聚焦的方法在水池中模拟产生多向聚焦波浪,研究了多向极限大波作用在垂直圆柱上引起的波浪力的特点。实验中研究了不同的波浪参数,如聚焦波幅、谱峰频率、频率宽度和方向分布等多向聚焦波浪对圆柱作用的影响,并将实验结果与二维实验结果进行了比较。结果表明聚焦波浪参数对圆柱作用力具有明显的影响,并且实验结果与二维规则波结果相当,但比二维聚焦波浪实验结果要小。     

极平缓岸坡上的底部波能损耗

本文分别分析与计算了波浪在粉沙质海床、沙纹海床和淤泥质海床上传播时波高的衰减。研究表明,波浪在粉沙质海床上传播的渗透损耗可以忽略不计;波浪在沙纹海床上传播的底摩阻损耗比平滑粉沙底床上传播的损耗大,前者的摩擦系数约比后者值大一个数量级。波浪在淤泥质海床上传播的能量损耗最大,其损耗机遇也很复杂。为了便于比较,将波浪在淤泥质海床上的衰减换算成等价摩擦系数。并运用宾汉模型和波浪作用通量守恒原理计算了波浪在极平缓淤泥质海滩上传播时的衰减及沿程等价摩阻系数。与连云港波浪观测资料对比,符合较好。此外。理论计算发现沿程等价摩阻系数与水深关系较大,由深水至浅水逐渐增大,且水深越浅,增速越快。     

多浮摆式采能装置水动力性能的时域计算及模型试验

该文基于三维时域势流理论,对一种多浮摆式波浪能采能装置的水动力性能进行了时域模拟,获得了单浮摆及双浮摆系统的运动响应、浮摆所受波浪力矩及角速度。根据模拟参数,对单浮摆和多浮摆系统的水动力特性进行了比较。在此基础上,根据几何相似、运动相似等相似准则,进行了单、双浮摆系统的水力模型试验,获得了两种装置的波浪能采集效率。数值模拟及水力模型试验的结果表明,单浮摆的纵摇响应小于双浮摆的情况,浮摆间的相互作用可以提高波浪能的采能效率。     

基于二阶差分法和非结构网格的有限体积法的溃坝模拟

非结构的三角形网格适应于复杂不规则的边界,在此基础上采用有限体积法离散浅水波方程,并结合有限差分法建立了一种新的离散格式,使得界面通量计算达到二阶精度。通过对典型算例的模拟计算,此格式在溃坝计算中能很好地捕捉溃坝波的前进,具有很强的模拟间断的能力,模拟溃坝洪水波间断的形状和位置都能得到很满意结果。     

Effect of a free surface on the formation of a wave bed of a channel flow

Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 5, pp. 50–52, May, 1989.     

Hydrodynamics of the interceptor on a 2-D flat plate by CFD and experiments

Nowadays, the use of interceptor by both partial and total dynamic lift crafts is quite common. In this article, a lot of evidence is given regarding the effectiveness of interceptor. The interceptor, when placed at the stern region, changes the pressure distribution around the craft. Its presence affects drag force, lifting force and the position of pressure's center leading to a new trim. This study focuses on hydrodynamic effects of interceptors on a 2-D flat plate based on both computational fluid dynamic(CFD) and experimental approaches. The Reynolds average Navier-Stokes(RANS) equations are used to model the flow around a fixed flat plate with an interceptor at different heights and attack angles. Based on finite volume method and SIMPLE algorithm which uses static structures, this model can be analyzed and the RANS results can be compared with the experimental data obtained in the current channel of the laboratory of waves and current of COPPE/UFRJ(LOC in Portuguese acronym). According to the results, the increase of pressure at the end of the flat plate was proportional to the interceptor height. In addition, the existence of interceptors can significantly increase the lift force coefficient at high angles of attack also proportional to the interceptor height. The presence of interceptor at the end of the flat plate increased both the lift coefficient and the drag coefficient but hydrodynamic drag did not grow as fast as the lift coefficient did. The lift coefficient increased much more. Furthermore, the results showed that the interceptor effectiveness is proportional to the boundary layer thickness at the end of the flat plate. As the interceptor was inside the boundary layer alterations of flow speed led to changes in boundary layer thickness, directly affecting interceptor's efficiency. Optimum choice of interceptor height had a great effect on its efficiency, and in choosing it the flow speed and length of the boat must be taken into consideration.     

潜体在两层海内波中的波浪力计算

本文以近似潜艇的细长回转体为模型,在两层海模式中三种不同潜深下,利用边界元法计算了内波对潜体的一阶垂荡波浪力和一阶纵摇波浪力矩,作为特例计算了近水面潜体的波浪力及力矩,并与实验结果进行了比较,两者吻合较好。