Sound power measurements in a non-anechoic tank with random surface
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摘要:
针对非消声水池的声学测量应用, 提出了一种在界面起伏的非消声水池中测量水下声源辐射声功率的方法。基于数值方法分析了在非消声水池中利用起伏界面改善低频声源辐射声功率测量的可行性, 进一步在一个尺寸为1.2 m × 1.0 m × 0.8 m的非消声水池中开展实验研究, 测量了水声换能器的辐射声功率。实验表明, 相对于界面静止的水池, 利用造波装置生成随机起伏界面后, 声场扩散性明显改善: (1) 水池的Schroeder频率从10015 Hz降低到8370 Hz, 辐射声功率的测量范围向低频扩展; (2) 结合空间平均技术测得的频响曲线起伏程度减小, 与自由场值更接近, 辐射声功率的测量结果更为准确。所提方法有助于提高非消声水池中水下目标声学特性的测量能力。
Abstract:A method that uses a random surface to improve measurements of the radiated sound power in a non-anechoic tank is proposed. Based on the finite element method, the feasibility of improving sound power measurements at low frequencies by random surface in a non-anechoic pool is analyzed. The sound power of a spherical source is measured in a non-anechoic tank with a size of 1.2 m × 1.0 m × 0.8 m. Experimental results show that in contrast to a tank with a steady surface, once a random surface is generated using a water pump, the diffusion is significantly improved: (1) the Schroeder frequency is decreased from 10015 Hz to 8370 Hz, indicating the range of measurement is extended to lower frequencies; (2) the frequency response curves measured by spatially averaging techniques have smaller fluctuation and is closer to free-field value, that is, the accuracy of measurement is significantly improved. The proposed method contributes to obtaining more accurate narrowband measurements of underwater target acoustic characteristics in underwater environment environments.
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Key words:
- Radiated sound power /
- Diffuser /
- Non-anechoic tank /
- Reverberation sound field /
- Acoustic measurements
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图 9 声功率级曲线 (a) 工况A; (b) 工况B; (c) 工况C; (d) 工况D; (e) 工况E; (f) 工况F (灰线: 非消声水池测量结果, 黑线: 消声水池测量结果)
表 1 1/3倍频程60 dB混响时间及相应Sabine吸收量
中心频率(Hz) 静止界面 起伏界面 混响时间(s) Sabine吸收量 (m2) 混响时间(s) Sabine吸收量 (m2) 5000 0.298 0.119 0.256 0.138 6300 0.283 0.125 0.231 0.153 8000 0.294 0.120 0.235 0.151 10000 0.277 0.130 0.162 0.219 12500 0.259 0.137 0.146 0.242 16000 0.217 0.163 0.129 0.274 20000 0.207 0.171 0.121 0.293 
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表 2 非消声水池中辐射声功率测量方法
测量方法 实施方法 直接测量 1个水听器在混响控制区内固定位置测量10 s信号 离散空间平均 6个水听器在混响控制区内固定位置测量10 s信号, 6组结果取平均 连续空间平均 1个水听器在混响控制区内随机移动测量10 s信号
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表 4 非消声水池中辐射声功率测量准确性评估
工况 A B C D E F 与自由场值之差 (dB) 4.19 1.90 1.79 1.22 1.24 0.89 频率起伏程度 (dB) 4.36 2.29 2.03 1.60 1.51 0.97
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表 5 重复测量引起的不确定度 (dB)
中心频率 (Hz) 工况 A B C D E F 5000 0.40 0.45 0.43 0.43 0.38 0.26 6300 0.48 0.54 0.46 0.29 0.38 0.26 8000 0.43 0.57 0.44 0.43 0.58 0.41 10000 0.42 0.65 0.43 0.35 0.74 0.31 12500 0.38 0.47 0.38 0.43 0.48 0.29 16000 0.84 0.76 0.24 0.21 0.51 0.49 20000 0.59 0.65 0.53 0.27 0.44 0.33
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