HYDRODYNAMICS OF A DUAL-CHAMBER OWC WAVE ENERGY CONVERTER IN HEAVING MOTION
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摘要: 振荡水柱(OWC)波能转换装置因其结构简单、便于安装维护等特点, 被公认为最具应用前景的波能转换技术. 本研究以垂荡式双气室OWC波能转换装置为研究对象, 借助开源代码平台OpenFOAM及基于interFoam求解器开发的造/消波工具箱waves2Foam, 采用流体体积法(VOF)捕捉自由面和六自由度(6DOF)动网格求解器模拟垂荡运动响应, 数值研究在不同入射规则波作用下, 前后气室相对宽度、弹簧弹性系数对装置捕能宽度比及水动力特性的影响规律. 通过与已有的固定情况下的双气室OWC装置结果对比, 并通过对比自由衰减运动响应验证动网格技术, 揭示了本研究中数值模型的合理性和有效性. 计算结果表明, 较宽的后气室结构布置有利于双气室振荡水柱装置在垂荡状态下的波能提取; 前后气室宽度比为1/2时, 垂荡式双气室OWC装置在测试波频段具有最优的捕能宽度比; 相较于固定状态, 垂荡装置的后气室在中高波频段有着更高的捕能宽度比; 装置前后气室内水柱与OWC装置垂荡运动间存在的相位差使得气室内水面相对振幅和相对压强在测试波频段存在多峰值现象, 进一步发现弹装置通过垂向弹簧进行相位控制, 可显著拓宽高效频谱带, 实现较大的捕能宽度比.Abstract: The oscillating water column (OWC) wave energy conversion device have been recognized as the most promising wave energy conversion technology due to the advantages of its simple structure, convenient assembly and easy maintenance. A heave-only dual-chamber OWC device was numerically investigated by a well-developed open source software OpenFOAM coupled with a wave generation and absorption toolbox Waves2Foam. The volume of fluid (VOF) method tracking the water-air interface and the six-degree-freedom (6DOF) Dynamic Mesh solver duplicating the heave motion of the OWC device were employed to examine the influences of the relative width of the front and rear chambers and the spring elastic coefficient on the energy capture width ratio and hydrodynamic characteristics of the device under the actions of different incident regular waves. Through comparing the present results with the existing ones of a fixed dual-chamber OWC wave energy converter, and examining the free-decay motion of a cylinder, the rationality and effectiveness of the present numerical model has been revealed. The results show that the wider rear chamber can make for the extraction of wave energy of the dual-chamber OWC in heave motion. The heave-only dual-chamber OWC device can improve the device performance as the relative width ratio of the front and rear chambers is 1/2, and the rear chamber has larger capture width ratio in the middle and high frequency wave bands, compared with that of the fixed one. Multiple-peak values of the relative water surface elevation and the relative pressure occur in the whole test wave frequency bands due to the phase gap between the dual-chamber OWC device and the water columns in the front and rear chambers. In addition, it is found that by adjusting the spring stiffness coefficient, the wave-frequency bandwidth of high-efficiency can be significantly broadened and larger energy capture width ratio can be achieved.
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Key words:
- wave energy /
- oscillating water column /
- wave hydrodynamics /
- energy capture width ratio /
- dynamic mesh
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图 1 垂荡式双气室OWC装置数值设置示意图
Figure 1. Schematic diagram of an offshore heave-only dual-chamber OWC system
图 3 结构物周围不同粗细网格
Figure 3. Different spatial resolutions around the dual-chamber OWC system
图 4 不同分辨率网格的气室内水面振幅与压强差历时曲线
Figure 4. Convergence tests of surface elevations and pressure drops in the chambers for grids with different resolutions
图 6 结构物相对振幅
${\eta _{\rm{b}}}/{A_{\rm{i}}}$ 的比较Figure 6. Relative heave amplitude
${\eta _{\rm{b}}}/{A_{\rm{i}}}$ comparison of heave-only box
图 9 相对气室宽度对OWC装置气室内相对波高与OWC装置相对垂荡幅度的影响
Figure 9. Relative surface elevations of the front and rear chamber and the relative dual-chamber OWC device heave amplitude against different relative chamber length
$ {b_1}/h $ 
10 相对气室宽度对垂荡式双气室OWC装置前后气室相对压强、前后气室内水面振荡与OWC自身垂荡相位差的影响
10. Relative pressure drops and the phase difference between the oscillating water column in the chambers and OWC oscillation motion as a function of the dimensionless frequency
${\omega ^2}h/g$ for different relative chamber length$ {b_1}/h $ 
图 10 相对气室宽度对垂荡式双气室OWC装置前后气室相对压强、前后气室内水面振荡与OWC自身垂荡相位差的影响 (续)
Figure 10. Relative pressure drops and the phase difference between the oscillating water column in the chambers and OWC oscillation motion as a function of the dimensionless frequency
${\omega ^2}h/g$ for different relative chamber length$ {b_1}/h $ (continued)
图 11 相对气室宽度对垂荡式双气室OWC装置气室捕能宽度比的影响
Figure 11. Capture width ratio of the heave-only dual OWCs for relative chamber lengths
$ {b_1}/h $ 
图 12 无量纲弹簧弹性系数K对垂荡式双气室OWC装置各气室捕能宽度比的影响
Figure 12. Capture width ratio of the heave-only dual OWCs for different K
表 1 本研究所使用的波浪参数
Table 1. Wave parameters in this study
${{T} }_ { {\rm{s} } }$ ${\omega ^2}h/{\rm{g}}$ $h/ {\rm{m}} $ $H/ {\rm{m}} $ ${\rm{\lambda } }/ {\rm{m}} $ $ H/\lambda $ 1 2.01215 0.5 0.04 1.5130 0.026438 1.1 1.66294 0.5 0.04 1.7813 0.022456 1.2 1.39733 0.5 0.04 2.0483 0.019528 1.3 1.19062 0.5 0.04 2.3118 0.017303 1.4 1.02661 0.5 0.04 2.5712 0.01557 1.5 0.89429 0.5 0.04 2.8265 0.014152 1.6 0.78600 0.5 0.04 3.0781 0.012995 1.7 0.69625 0.5 0.04 3.3266 0.012024 1.8 0.62103 0.5 0.04 3.5722 0.011198 1.9 0.55738 0.5 0.04 3.8153 0.010484 
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表 2 数值波浪水槽边界条件设置
Table 2. Boundary conditions of numerical wave tank
Boundary Velocity field Pressure field Volume phase field inlet wave velocity zero gradient wave alpha bottom fixed value (0,0,0) zero gradient zero gradient atmosphere pressure inlet
outlet velocitytotal pressure inlet outlet outlet fixed value (0,0,0) zero gradient zero gradient front and back empty empty empty
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表 3 不同分辨率网格条件下气室内波面和压强差标准均方根误差
Table 3. NRMSE of surface elevations and pressure drop under different spatial resolutions around the dual-chamber OWC system
Grid resolution NRMSE/% front chamber rear chamber water surface pressure drop water surface pressure drop coarse 0.735 5.443 0.371 6.417 medium 0.279 0.537 0.131 0.763 fine − − − −
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表 4 不同气室宽度参数设置
Table 4. Cases for different front (
${b_1}$ ) and rear (${b_2}$ ) chamber widthsGeometric parameters ($ {e_1}{\text{ = }}{e_1}{\text{ = }}1\% $) $ {d_1}/{\rm{m}} $ ${d_2}/{\rm{m}}$ ${d_3}/{\rm{m}}$ $h/{\rm{m}}$ ${b_1}$ ${b_2}$ ${b_1}/{b_2}$ $ {b_1}/h $ 0.06 0.25 0.25 0.5 0.05 0.25 0.2 0.1 0.06 0.25 0.25 0.5 0.1 0.2 0.5 0.2 0.06 0.25 0.25 0.5 0.15 0.15 1 0.3 0.06 0.25 0.25 0.5 0.2 0.1 2 0.4 0.06 0.25 0.25 0.5 0.25 0.05 5 0.5
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