不规则波作用下岸基式振荡水柱波能装置的水动力性能研究

为了研究真实海域中振荡水柱（OWC）波能转换装置的水动力性能,本文基于势流理论和高阶边界元方法,建立了不规则波与岸基式OWC波能装置相互作用的二维非线性数值模型,不规则波基于JONSWAP谱生成。为了考虑由于水体黏性引起的能量耗散,在气室内水面边界条件中引入人工黏性阻尼。并在大连理工大学波流水槽中开展了物理模型试验,对数值模型的有效性进行了验证。研究发现,在不规则波作用下,OWC波能装置的水动力效率相较于规则波作用下有所降低,特别是在低频波区域效率差值最大。与规则波相比,不规则波浪作用下装置峰值效率对应的频率变大。气室内的相对水面高程随着有效波高的增加而降低,而气室内相对气压则随有效波高的增加而增大。OWC波能装置的水动力效率受有效波高的影响较小,其峰值效率对应的频率不受波浪非线性的影响。本文可以为OWC波能装置的设计提供参考。     

带纵摇前墙的新型振荡水柱式波浪能装置转换效率以及水动力性能数值研究

提出了一种带纵摇前墙的新型振荡水柱式波浪能(OWC)装置,借助Open FOAM开源代码平台和waves2Foam工具包,数值模拟研究带纵摇前墙OWC装置的水动力性能和转换效率。主要研究前墙吃水d_1、前墙密度ρ、后墙吃水d_2、旋转约束力(用无量纲弹簧系数K表示)对该装置的反射系数C_r、透射系数C_t、耗散系数C_d和波能转换效率ξ的影响规律。结果表明,纵摇前墙能有效减少能量耗散,提高波能转换效率ξ;无量纲弹簧系数K对装置转换效率的影响主要集中在短波区域,且在K为0时装置具有最大的转换效率和最宽的高效频率带;前墙的密度和吃水深度对水动力系数影响不大;后墙的吃水深度对水动力系数影响较大,增加吃水深度能有效提高装置对于中短波和中长波段的波能转换效率,但对系统整体的能量耗散系数影响不大。     

集成于方箱防波堤的双气室振荡水柱波能装置转换效率研究

为实现建造、运行和维护等方面的资源共享,将振荡水柱(oscillating water column,简称OWC)波能转换装置与现有海工结构集成耦合,已成为目前海洋波浪能转换利用的热点问题。以集成于方箱防波堤的双气室OWC装置为研究对象,借助开源代码平台OpenFOAM和造/消波工具箱waves2Foam,采用流体体积法(VOF)捕捉自由面和6自由度(6DOF)动网格求解器模拟垂荡运动响应,对在不同规则波作用下,中墙相对宽度、中墙相对吃水对装置波能转换效率及水动力特性的影响进行数值研究。结果表明,较大的中墙相对宽度能够增强装置的波能转换效率(ξ_total(max)=73%)、降低结构物的相对垂荡位移并对装置前后气室内水柱的振荡幅度与压强变化产生影响;增加中墙相对吃水能显著提高气室在中高频波段波能提取效率(ξ_total(max)=78%),并显著拓宽气室的高效频率带宽(0.9≤ω²h/g≤2.2)。     

非对称垂荡式振荡水柱波能转换装置的水动力性能

为提升波能转换装置的经济竞争力,针对非对称垂荡式振荡水柱（OWC）波能转换装置,基于势流理论和匹配特征函数展开法,通过引入盖根堡多项式近似表征结构尖角附近的流场奇异性行为,深入研究后墙吃水深度（非对称）、墙体厚度和线性弹簧系数对垂荡式OWC装置的波能转换效率、透射系数、气室内平均液面高程等水动力参数的影响规律。研究结果显示,后墙吃水深度及墙体厚度的增加会提升装置在长波区域的高效转换能力,并且显著提高结构物整体阻波防浪性能;线性弹簧的出现,能调节水柱振荡和结构垂荡运动响应之间的相位差,从而有效拓宽垂荡式OWC装置的高效频率带。     

新型沉箱防波堤兼作岸式OWC波能装置的设计及稳定性研究

防波堤与岸式OWC波能装置一直是被独立研究,从未产生交叉,但二者设施布置的条件显然具有关联性。本文根据二者关联的特点,设计出沉箱防波堤兼作岸式OWC波能装置,并通过物理模型试验验证了其可行性。     

振荡水柱波浪能采集气室引浪通道CFD优化设计

振荡水柱(Oscillating water column,OWC)波浪能采集装置气室底部引浪通道对波浪能采集效率具有重要意义。基于流体动力学分析(CFD)技术研究OWC装置气室底部轮廓的优化问题,在ICEM CFD仿真分析系统中建立4种气室底部结构的二维引浪通道模型,应用FLUENT软件流体分相处理及明渠造波法和数值沙滩消波方法建立基于线性波浪理论的二维数值波浪水槽。仿真分析显示,圆形底部轮廓OWC气室较其它3种轮廓结构的气室墙壁受到压力小,形成的反射波小,波能损失小,气室出口速度快由此形成的气室压力大,波能转换效率高。     

基于VOF模型的OWC气室波浪场数值分析

近年来,振荡水柱形式在波能转换装置中得到了广泛应用,由于波况不同,需对气室加以研究并对其形状参量进行优化,从而使空气流速和能量转换达到最大值.利用基于VOF模型建立二维数值波浪水槽,将数值计算的振荡水柱在气室内的升沉运动与物理模型试验进行比较,验证其正确性,并将OWC气室的研究手段予以推广.     

前板可旋转的双垂板结构水动力特性的理论研究

振荡水柱波能转换装置的最大转换效率往往受到腔内水柱共振机制的直接影响。通过对装置的基本结构进行简化,提出了一种前墙可绕固定轴旋转的双垂板式结构系统,旨在通过前墙的旋转运动进一步加剧水柱的振荡,从而对腔内水柱的共振机制进行调节和控制。基于线性波理论,采用匹配特征函数展开法对波浪与双垂板结构的相互作用进行理论研究,针对流场在结构物尖角附近的奇异性特征,将公共界面上的速度分布基于切比雪夫多项式近似展开,并应用区域间的速度与压力连续条件进行求解。通过分析结构的几何参数对反射透射系数、平均波面高程、前墙旋转振幅以及前墙与水面间相位差的影响,深究其共振机理,为振荡水柱波能转换装置的效率优化机制提供理论依据。结果表明,在所研究的波浪频率范围内,前墙的自由旋转运动会加剧板间的平均波面高程,应用于波浪能转换装置中能进一步拓宽高效频率带宽。     

相交圆柱摆式波能装置俘获效率数值分析

摆式波能装置具有结构简单和转化效率高等特点,本文应用AQWA 软件基于势流理论对相交圆柱摆式波能装置进行了数值模拟研究,分析了轴间距比、结构阻尼、净浮力比、水深、波浪特性及吃水深度等主要参数对相交圆柱摆式波能装置俘获效率的影响,并与直板摆式波能装置的俘获效率进行了对比。结果表明：同样条件下,相交圆柱摆式波能装置往往比直板摆式波能装置的俘获效率更高;在研究范围内,轴间距比越大俘获效率越高;潮汐导致的水深变化对底铰摆式波能装置的俘获效率具有明显的影响,在工程应用中应采取适当的措施进行处理。     

基于Simulink的振荡水柱气室优化分析

振荡水柱式(Oscillation Water Column,简称OWC)波浪能采集装置具有结构简单、稳定性好、海洋环境适应性强等优点。为了提高该装置波能采集效率,研究波浪进入气室的振荡水柱气动特性与装置结构参数关系,为系统设计提供理论基础。以振荡水柱式波能转换理论计算分析为基础,采用Simulink软件分别建立前墙处入口压强Pq求解模型、装置气室内压强Po求解模型以及装置内振荡水柱运动方程y求解模型,研究目的是综合分析振荡水柱气室内压强与气室结构、波浪流体动力学参数之间的变化关系。     

Wave power extraction by an axisymmetric oscillating-water-column converter supported by a coaxial tube-sector-shaped structure

An analytical theory is developed to study the effects of a coaxial tube-sector-shaped supporting structure on the conversion efficiency of a suspended, circular OWC converter. An eigen-function expansion method is employed in a cylindrical coordinate system to study wave interaction with an OWC converter in finite depth of water. Effects of the supporting structure, OWC dimensions, wave direction on energy conversion efficiency, and optimization of power-takeoff devices are discussed. Our results show that the coaxial tube-sector-shaped support with an opening in the range of π/2–5π/4 can significantly increase the conversion efficiency and widen the frequency range over which the conversion efficiency is high.     

Comparison between a U-OWC and a conventional OWC

With an additional vertical duct at the wave-beaten side, an OWC is expected to give some much better performances. This is, essentially, due to two reasons. First, an OWC with the additional vertical duct (U-OWC) has an eigenperiod greater than the eigenperiod of a conventional OWC. Second, the amplitude of the pressure fluctuations on the opening of a U-OWC is greater than the amplitude of the pressure fluctuations on the opening of a conventional OWC (the greater the smaller the wave period is). For the first reason, a U-OWC can give performances better than those of a conventional OWC both with swells and large wind waves. For the second reason, a U-OWC can give performances better than those of a conventional OWC also with small wind waves.     

Design and Experimental Study of A Pile-Based Breakwater Integrated with OWC Chamber

A structure scheme of a pile-based breakwater with integrated oscillating water column(OWC) energy conversion chamber was proposed, and four structure forms had been designed. Based on the physical test, the variations of the reflected wave height, the transmitted wave height, the air velocity at the outlet of the chamber, the air pressure and the wave height in the air chamber were studied under the conditions of different wave heights, periods, with or without elliptical front wall and the baffles on both sides of the chamber. Moreover, based on the results, the changes and relationship between the wave-eliminating effect and energy conversion effect of the scheme were analyzed. In general, it turns out, the transmission coefficients of the four structure forms are kept below 0.5. Furthermore, the transmission coefficients of the structural forms G2, G3, and G4 were all smaller than 0.4, and it is only 0.1 at its smallest. Thereinto, in general, the structure form G4 has the best wave-eliminating and energy conversion performance. At the same time, when the wave steepness is 0.066, the energy conversion and wave dissipation effect of the four structure forms is the best. The research results could be provided as the reference for the design structure selection of pile-based breakwater with integrated OWC energy conversion chamber.     

Numerical study of air chamber for oscillating water column wave energy convertor

Oscillating Water Column (OWC) wave energy converting system is one of the most widely used facilities all over the world.The air chamber is utilized to convert the wave energy into the pneumatic energy.The numerical wave tank based on the two-phase VOF model is established in the present study to investigate the operating performance of OWC air chamber.The RANS equations,standard k-ε turbulence model and dynamic mesh technology are employed in the numerical model.The effects of incident wave conditions and shape parameters on the wave energy converting efficiency are studied and the capability of the present numerical wave tank on the corresponding engineering application is validated.     

Experimental hydrodynamic investigation of a fixed offshore Oscillating Water Column device

Oscillating Water Column (OWC) is one of the pioneer devices in harnessing wave energy; however, it is not fully commercialized perhaps due to the complicated hydrodynamic behavior. Previous studies are significantly devoted to OWC devices located in nearshore and coastal regions where incident wave energy would experience dissipation more than offshore. In this paper, a 1:15 scaled fixed offshore OWC model is tested in a large towing tank of National Iranian Marine Laboratory. Wave spectrum shape effect on the efficiency of the OWC model is addressed. Moreover, the paper investigates the effects of the geometric and hydrodynamic factors on OWC device efficiency and uncovers new points in nonlinear interaction occurring inside the chamber; i.e. sloshing. The results indicate that shape of the spectrum inside the chamber is affected by the type of incident wave spectrum, especially for long waves. Pierson–Moskowitz spectrum leaded to higher efficiency rather than JONSWAP spectrum at longer incident wave periods. According to efficiency analysis, increasing wave height may lead to air leakage from the chamber followed by vortex generation, which is a reason for decreasing the efficiency of the OWC device. Furthermore, no shift in the resonant period of the OWC model, due to wave height increase, was observed at the opening ratios equal or smaller than 1.28%. Spectral analysis of water fluctuation inside the OWC chamber illustrates two modes of sloshing. The first mode can be seen at short period waves while the second mode is visible at long period waves. The sloshing modes approximately vanish by increasing draft value.     

Hydrodynamic performance of a pile-supported OWC breakwater: An analytical study

A pile-supported OWC breakwater is a novel marine structure in which an oscillating water column (OWC) is integrated into a pile-supported breakwater, with a dual function: generating carbon-free energy and providing shelter for port activities by limiting wave transmission. In this work we investigate the hydrodynamics of this novel structure by means of an analytical model based on linear wave theory and matched eigenfunction expansion method. A local increase in the back-wall draft is adopted as an effective strategy to enhance wave power extraction and reduce wave transmission. The effects of chamber breadth, wall draft and air chamber volume on the hydrodynamic performance are examined in detail. We find that optimizing power take-off (PTO) damping for maximum power leads to both satisfactory power extraction and wave transmission, whereas optimizing for minimum wave transmission penalizes power extraction excessively; the former is, therefore, preferable. An appropriate large enough air chamber volume can enhance the bandwidth of high extraction efficiency through the air compressibility effect, with minimum repercussions for wave transmission. Meanwhile, the air chamber volume is found to be not large enough for the air compressibility effect to be relevant at engineering scales. Finally, a two-level practical optimization strategy on PTO damping is adopted. We prove that this strategy yields similar wave power extraction and wave transmission as the ideal optimization approach.     

Efficiency of OWC wave energy converters: A virtual laboratory

The performance of an oscillating water column (OWC) wave energy converter depends on many factors, such as the wave conditions, the tidal level and the coupling between the chamber and the air turbine. So far most studies have focused on either the chamber or the turbine, and in some cases the influence of the tidal level has not been dealt with properly. In this work a novel approach is presented that takes into account all these factors. Its objective is to develop a virtual laboratory which enables to determine the pneumatic efficiency of a given OWC working under specific conditions of incident waves (wave height and period), tidal level and turbine damping. The pneumatic efficiency, or efficiency of the OWC chamber, is quantified by means of the capture factor, i.e. the ratio between the absorbed pneumatic power and the available wave energy. The approach is based on artificial intelligence—in particular, artificial neural networks (ANNs). The neural network architecture is chosen through a comparative study involving 18 options. The ANN model is trained and, eventually, validated based on an extensive campaign of physical model tests carried out under different wave conditions, tidal levels and values of the damping coefficient, representing turbines of different specifications. The results show excellent agreement between the ANN model and the experimental campaign. In conclusion, the new model constitutes a virtual laboratory that enables to determine the capture factor of an OWC under given wave conditions, tidal levels and values of turbine damping, at a lower cost and in less time than would be required for conventional laboratory tests.     

Investigation on the Oscillating Buoy Wave Power Device

An oscillating buoy wave power device (OD) is a device extracting wave power by an oscillating buoy. Being excited by waves, the buoy heaves up and down to convert wave energy into electricity by means of a mechanical or hydraulic device. Compared with an Oscillating Water Column (OWC) wave power device, the OD has the same capture vvidth ratio as the OWC does, but much higher secondary conversion efficiency. Moreover, the chamber of the OWC, which is the most expensive and difficult part to be built, is not necessary for the OD, so it is easier to construct an OD. In this paper, a nu-merical calculation is conducted for an optimal design of the OD firstly, then a model of the device is built and, a model test is carried out in a wave tank. The results show that the total efficiency of the OD is much higher than that of the OWC and that the OD is a promising wave power device.