ANSYS声学流固耦合分析时流体部分半径大小的确定
前段时间有朋友问我关于ANSYS声学分析中关于用于模拟无限流体的球体半径问题，当时我也不是很清楚，解释半天也没让人明白。现在搞清楚了，特发此帖，以供新学者参考。ANSYS声学分析中用于确定无限流体球体（FLUID29、FLUID30单元）半径的公式是
球体半径=内部吸声结构最大尺寸（或半径）+0.2×（流体中声速）/（频率）
ANSYS帮助文件中声学流固耦合的第一个例子中提到：In this problem you will determine the first flexural mode (egg mode) frequency of an annular ring submerged in water which extends to infinity. You will perform a harmonic analysis using a frequency sweep between 34 and 38 Hz. The distance from the center of the ring to the infinite elements will at least be equal to (D/2) + 0.2λ where D is the outer diameter of the ring and λ = c/f is the dominant wavelength of the pressure waves. Using 0.26035 for the outer radius of the ring, 1460 for the speed of sound (c), and 36 for the estimated dominant frequency (f), gives (D/2) + 0.2λ = 0.26035 + (0.2)(1460)/36 = 8.37146. However, this is much greater than the distance required when using the acoustic infinite element and a distance of 2 times the outer radius of the ring will be used ( 2 x .26035 = .5207), as shown in the command listing.
可以看出，例子中的声波频率为34Hz~38Hz，公式中取其平均值36Hz。
从红色部分可以看出，从公式所得到的外部球体半径（8.37146）远大于吸声结构尺寸的二倍（0.5207），因此流体半径可以取吸声结构的半径的两倍。
结论：在吸声结构尺寸较小时，通常流体部分半径取其最大尺寸的二倍即可，前提是所取值小于通过公式所得的理论值。
[ 本帖最后由 16443 于 2008-11-10 11:35 编辑 ]
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