电磁力激励水下有限长圆柱壳体振动噪声特征

Vibration and Noise Characteristics of Cylindrical Shell with Finite Length under Electromagnetic Force

针对亲水电机电磁噪声计算与评估的问题,研究了在电磁力作用下和考虑水声负载时有限长圆柱壳体的振动与噪声特性,给出振动、远场声压以及辐射效率的计算公式,并通过数值验证,两者吻合良好。当厚径比较小时,水声负载对于结构的振动与声辐射有很大影响,当h/a≥0.1时,在非共振区域,水声负载的影响可以忽略。ka值较小时,0阶电磁力波作用下的远场声场近似为球面波。这也是电机尺寸小时,可以当作球体计算辐射声功率的主要原因。不同阶数力波的声辐射效率,开始时随着ka的增大而增大,到一定值时趋于平稳。高阶的电磁力波,如超过4阶的,在较大ka值也能产生大的辐射噪声。

With respect to the evaluation of electromagnetic noise of underwater motors, electromagnetic force induced vibration and noise characteristics for a finite cylindrical shell are researched, with water acoustic load considered. Formulae of vibration and far field pressure, and radiation efficiency are presented and validated with numerical simulation. When the ratio of thickness to diameter is small, the acoustic load has great influence on structural vibration and acoustic radiation. When the ratio h/a is bigger than 0.1, the effect of water acoustic load can be ignored except in the resonance region. Under zero order electromagnetic force and with small values of ka, the far field acoustic pressure can be treated as a spherical wave, which is the reason why small motor can use sphere radiation model calculating acoustic power. At the initial stage, acoustic radiation efficiency is increased with ka, but when ka up to a certain value, it tends to be stable. For bigger ka values, high order of electromagnetic force waves, such as more than 4 orders, can produce considerable radiation noise.