摘要
采用FLUENT软件中的用户自定义函数功能和动网格功能进行造波和消波,采用VOF方法捕捉自由液面,开发了一个数值波浪水池,该水池可以生成规则波浪、按照波谱生成不规则波浪以及生成既定的不规则波波列.文中开展了网格和时间步长试验,力图找到经济精确的网格划分方案和高效的时间步长方案.文中按照Jonswap谱进行了不规则波浪的数值模拟,采用了等分能量法分解波谱的频率区间来得到组成波的圆频率,模拟结果显示计算波谱与目标波谱一致,波浪的统计特征得到了很好的体现,模拟不规则波波谱的缺点是耗时过长.由于真实海况下对海洋浮式结构物造成损坏的往往不是整个波浪时间序列,而是少数的几个大波或者波列中的波群.因此采用CFD方法准确模拟出既定的波列将会对了解极端海况下海洋结构物的损坏事故提供极大帮助.采用本文提出的方法成功模拟出了既定的极大波,这个方法的关键在于确定造波板的运动规律.类似按照波谱造波,文中将造波板处的波浪时历进行了分解,得到了若干个小振幅波,通过傅里叶级数法推导出了每个小振幅波的特征参数.同样采用水力传递函数确定每个小振幅波对应的推板振幅,之后将这些组成波对应的推板运动规律进行叠加得到了模拟不规则波波列时需要的推板运动规律.
In this paper,a numerical wave tank （NWT） which is capable of generating regular waves,irregular waves based on wave spectrum and predetermined irregular wave train,is presented. This numerical wave tank integrated with dynamic boundary generating waves,dissipation zone dealing with wave reflection and volume of fluid method capturing free surface,was developed based on secondary development on professional CFD software FLUENT. Grid size test and time step test were performed to acquire accurate and economical mesh resolution and time step benchmark. Simulation of irregular wave was conducted based on Jonswap Spectrum by equally dividing the energy range to get the circular frequency of wave component. Simulated results reveal that calculated spectrum agrees well with theoretical spectrum in terms of statistical characteristics of irregular waves. The deficiency of simulating irregular wave spectrum is the heavy time consumption. In real sea states,damage incidents on offshore floating structures may not due to the whole time series of waves but due to few extreme waves or wave groups in irregular wave train. So,using CFD tools to precisely simulate irregular wave train is of great help in understanding the local characteristics of flow field when the incidents occur to offshore structures. In this paper,an extreme wave was modeled successfully. The key step in this new method of simulating irregular wave train is to determine the wave-maker motion. Similarly,decomposition was made on the wave elevation at the wave-maker into certain number of small amplitude waves. The wave parameters of each wave component were determined by Fourier Series Expansion. The same as simulating irregular wave spectrum a transfer function derived for piston type paddle from potential theory was used to calculate the wave-maker motion corresponding to each wave component. Superposition was made over all the wave components to get the final wave-maker motion.
出处
《中国科学：物理学、力学、天文学》
CSCD
北大核心
2011年第2期112-122,共11页
Scientia Sinica Physica,Mechanica & Astronomica
基金
自然科学青年基金资助项目(批准号:50709019)
