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.     

二维溃坝洪水波演进的数值模拟

采用基于MacCormack预测-校正技术的隐式数值格式求解控制水流运动的二维浅水方程,建立了模拟大坝瞬间全溃或局部溃倒所致的洪水演进过程数学模型．应用该模型对矩形明渠中缓、急流过渡的水面曲线进行了数值计算,并与理论解进行了比较。最后用该模型预测了矩形河道中大坝瞬间局部溃倒时下游有多个障碍物的洪水演进过程,算例说明该数学模型对模拟溃坝洪水波很有效。     

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。     

椭圆余弦波对V形防波堤绕射波浪力的解析计算

应用椭圆余弦波理论,给出了V形薄壁防波堤的浅水波绕射理论解,对现有Airy微幅波理论进行了有效拓展。通过对V形防波堤的浅水波浪力进行试算,揭示了椭圆余弦波对防波堤的作用规律。计算结果表明:椭圆余弦波理论计算的V形防波堤的最大无量纲波浪力明显大于相同浅水条件下Airy微幅波理论的对应结果,该方法有效拓展了无限长直立薄壁堤的反射波理论。此外,浅水波入射角、V形堤张角和防波堤臂长与水深比等参数的变化均将对V形堤的波浪作用产生相关影响,而V形堤的实际绕射波浪力幅值将随浅水波特征参数值的增大而增大。     

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。     

二维溃坝洪水波的演进绕流和反射的数值模拟

本文采用改进的时空守恒元和解元方法(简称CE／SE法)构造了求解二维浅水方程的数值格式,建立了模拟大坝瞬间全溃和局部溃所致的洪水演进、绕流和反射过程的数学模型。应用此数学模型对局部溃坝的洪水的演进、绕流和反射的情况进行了模拟。算例结果表明CE／SE法精度高、稳定性好,很好的展示了溃坝波的运动特性,是一种研究溃坝洪水波较高精度的数值方法。     

用瑞雷波反演横波操度计算二维抗压强度剖面

在工程地质勘察中,抗压强度是衡量土层抗压能力的重要质量指标.应用τ~p变换提取地震面波,获取高信噪比的频散曲线;采用奇异值分解算法自动反演横波速度,提高横波速度的反演精度,进而计算二维抗压强度剖面.消除了表面波多道分析法所存在的平均效应,提高了瑞雷波纵、横向分辨率和无损检测精度.用上述方法对某高速公路振冲压碾效果进行了无损检测试验,其结果与钻探和试压分析一致.     

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。     

二维溃坝波遇障碍物的水流泥沙数值模拟

本文通过对浅水方程进行Godunov差分离散和对泥沙运动方程进行一阶迎风差分离散,建立了平面l二维溃坝水流泥沙数值模型。在算例中计算了溃坝波遇障碍物后的水流反射、绕射及泥沙冲淤,计算结果表明,溃坝波遇障碍物后会产生明显的反射和绕射,并在障碍物前形成壅水、障碍物的侧面会发生剧烈的冲刷,障碍物前后则会发生局部淤积。本模型能够较好地模拟溃坝间断水流的运动,结果符合水流泥沙运动的基本规律。     

LNG项目取水结构波压力物理模型试验

对某液化天然气(LNG)接收站取水结构采用1∶36.5比尺进行了多种水位(100年一遇高水位,50年一遇高水位,设计高水位,设计低水位和50年一遇低水位)与不规则波组合作用下的波浪物理模型试验.试验过程中测量了取水口戽头及第1节方涵的波压力,分析了取水量对波压力的影响以及不同水位条件下取水口戽头及第1节方涵波压力的变化规律.取水条件按照一期取水量(27 600 m3/h)、二期取水量(55 200 m3/h)与不取水3种工况考虑.试验结果表明,随着水位的降低,各点测得的波压力呈现出明显的增大趋势;不同取水量条件下,各点测得的波压力相差不大,最大相差幅度为5%～8%.     

瑞利阻尼参数对瑞利波作用下场地动力响应的影响

为研究地震中Rayleigh波对地表浅层土体的响应特征,针对Lamb问题的模型工况开展有限元动力分析,验证有限元法精确模拟Rayleigh波作用效应的可行性。以厦门地区浅层的素填土及粉质黏土为研究对象,采用摩尔-库仑本构模型,结合Rayleigh阻尼,并在模型的底部和边界上采用黏性边界,采用有限元法考察Rayleigh阻尼中质量比例阻尼系数α和刚度比例阻尼系数β对响应特征的影响规律。研究表明:有限元动力分析可以模拟Rayleigh波作用下的远场动力问题,能取得与Lamb问题解析解较为一致的解答,同时还可以捕捉P波和S波的到达时间;α的变化对素填土和粉质黏土中Rayleigh波的传播特征基本没有影响;β的变化不会影响传播速度,但影响波的振幅,β是Rayleigh阻尼的主控参数。该结论可为采用有限元法研究Rayleigh波对浅埋结构物的地震动力响应提供理论基础和科学依据。     

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。