内波场中圆柱体局部水平力试验研究

发布时间：2018-06-29 04:46

本文选题：分层流体 + 内波　；参考：《中国海洋大学》2014年硕士论文

【摘要】：海洋内波发生于密度分层的海洋中，因为太阳的热辐射等因素造成海水密度分布在垂直方向上形成稳定的层化特性，如果有扰动发生在在密度稳定层化海洋中，就有可能会导致在海水密度跃层处产生内波。由于内波波幅大，波长长，内部蕴含能量巨大。内波发生时，以密度分界面为边界，在上下层形成的波致流方向相反，形成强烈剪切流。这种强烈的作用力作用在海底工程结构物之上，会对其施工安装和安全运营形成潜在威胁。并且内波荷载在垂向分布正负交错，造成海底结构物周期性振动，加速其疲劳破坏。细长圆柱体是组成海洋结构物的基本构件，本文针对内波场中圆柱体进行试验测量，研究其在内波作用下的水平作用力及其影响因素。首先，运用莫里森方程结合mKdv方程估算模型在实验室内波水槽所造内波中的受力情况，根据对内波作用力的粗略估算，选择合适类型传感器以及相应的传感器量程。由于测力传感器在水下工作，受到浮力、水的粘滞作用以及其他因素的干扰，在空气中进行率定的传感器不能真实反映电压信号和圆柱体模型受力之间的关系，因此，传感器的率定需要试验工况下进行。在此基础下，设计传感器的率定系统以及内波水平力的测量系统。然后，设计试验工况，讨论内波波幅以及圆柱体所处深度和圆柱体模型直径对其所受到的水平力的影响，共计二十七种工况，选择三个测力传感器。将选择好的测力传感器在试验条件下进行水下率定，对所得到的的数据进行拟合，得到传感器输出电压信号和力的对应关系。最后，进行内波场中水平圆柱体的水平受力试验。得到的试验数据由于试验装置振动以及电磁干扰会有噪音，将试验数据进行去噪处理后进行时域分析，得到三个变量对圆柱体受力的影响关系。对内波场中不同工况下圆柱体受力进行分析得到圆柱体在内波场中所受到水平作用沿深度的分布规律和圆柱体直径以及内波振幅对圆柱体模型所受水平作用力的影响规律。然后通过傅里叶变换，，得到圆柱体在内波作用下的动力响应频谱图，发现内波对圆柱体顺流向作用力的频率成分除了主频外还存在一个两倍于主频的频率成分，且圆柱体在主频率处的响应比在两倍频率处的响应要大。
[Abstract]:Ocean internal waves occur in a density-stratified ocean because of factors such as solar thermal radiation, which result in a stable stratification of sea water density distribution in the vertical direction, if any disturbance occurs in a density-stable stratified ocean. It is possible to produce internal waves at the density cline of seawater. Because of the large amplitude of internal wave and long wavelength, the internal energy is huge. When the internal wave occurs, the density interface is taken as the boundary, the wave induced flow in the upper and lower layers is opposite, and the strong shear flow is formed. This kind of strong force acting on the structure of submarine engineering will pose a potential threat to its construction installation and safe operation. Moreover, the vertical distribution of internal wave loads is positively or negatively staggered, which results in periodic vibration of undersea structures and accelerates their fatigue failure. Thin and long cylinders are the basic components of ocean structures. In this paper, the horizontal forces and their influencing factors of cylinders in the internal wave field are studied. Firstly, the force of the internal wave produced by the laboratory wave tank is estimated by using the Morrison equation and mKdv equation. According to the rough estimation of the force acting on the internal wave, the appropriate type of sensor and the corresponding sensor range are selected. Because the force sensor works under water and is disturbed by buoyancy, water viscosity and other factors, the sensor with constant rate in the air can not truly reflect the relationship between the voltage signal and the stress of the cylinder model. The rate of the sensor needs to be tested. On this basis, the sensor rate determination system and the internal wave horizontal force measurement system are designed. Then, the effects of the amplitude of internal wave, the depth of the cylinder and the diameter of the cylinder model on the horizontal force are discussed. A total of 27 working conditions are designed and three force sensors are selected. The selected force sensor is used to determine the underwater rate under the experimental conditions, and the corresponding relationship between the output voltage signal and the force of the sensor is obtained by fitting the obtained data. Finally, the horizontal force test of the horizontal cylinder in the internal wave field is carried out. Due to the vibration of the test device and the noise caused by electromagnetic interference, the experimental data are analyzed in time domain after de-noising, and the influence of the three variables on the cylinder force is obtained. The distribution law of the horizontal action along the depth of the cylindrical wave field and the influence of the cylinder diameter and the amplitude of the internal wave on the horizontal force of the cylindrical model are obtained by analyzing the force of the cylinder under different working conditions in the internal wave field. Then, by Fourier transform, the dynamic response spectrum of the cylinder is obtained. It is found that the frequency component of the internal wave acting on the cylinder is two times the main frequency in addition to the main frequency. The response of the cylinder at the main frequency is larger than that at the double frequency.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P731.22

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