1.Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China 2.Key laboratory of Underwater Acoustics Environment, Chinese Academy of Sciences, Beijing 100190, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No.11904382) and the IACAS Young Elite Researcher Project QNYC (Grant No. 201701)
Received Date:07 August 2019
Accepted Date:21 October 2019
Published Online:20 January 2020
Abstract:The reflection coefficient of the flat sea surface in the ideal condition to the incident sound wave is –1. The perfect reflection effect does not introduce reflection loss. However, the sea surface is usually rough due to the wind. The wind-generated rough sea surface has not only reflection effect, but also scattering effect on the sound wave. At the same time, the wind-generated bubbles layer also has significant effect on the sound propagation. On the one hand, the bubbles layer can change the sound speed profile and result in the refraction of the incident sound wave. On the other hand, the bubbles layer has scattering effect and absorption effect on the incident sound wave and leads to the sound wave to attenuate. In fact, the rough sea surface and the bubbles layer are two main factors affecting the sound propagation in the windy weather at sea. Many researchers have paid much attention to the effect of the wind-generated rough sea surface on the sound propagation, but few of them have considered the effect of the wind-generated bubbles layer on the sound propagation. Based on the Ramsurf sound propagation model under the rough sea surface, the effects of wind-generated bubbles layer underneath rough sea surface on reflection loss and sound propagation with different wind speeds are analyzed. Based on the Hall-Novarini bubbles population model, the sound speed profile in the bubbles layer is modified and the attenuation coefficient due to scattering and absorption of the bubbles layer is calculated. The simulation results shows that when the wind speed is 10 m/s, the effect of the bubbles layer is significant on reflection loss with the frequencies higher than 2 kHz. In the given underwater acoustic environment, for a frequency of 3 kHz, when the source depth and the receiver depth are both 7 m, the enhancement of the transmission loss due to the bubbles layer is 2.6 dB for a wind speed of 13 m/s, and the enhancement is 8.1 dB for a wind speed of 16 m/s. And when the source depth and the receiver depth are both 18 m, the enhancement of the transmission loss due to the bubbles layer is 2.5 dB for a wind speed of 13 m/s and the enhancement is 4 dB for a wind speed of 16 m/s. Keywords:rough sea surface/ bubbles layer/ sound propagation
其中${\phi _j} \equiv {k_j}{h_j}\sin {\theta _j}$是声场穿过厚度为${h_m}$的薄层的路径产生的与角度有关的垂直相移. 其中${k_j}$是第j层的波数, ${h_j}$是第j层的厚度, ${\theta _j}$是第j层的入射波的掠射角. 考虑小掠射角入射的声波, 水中声速为1490 m/s等声速剖面, 分别在风速为7, 10和13 m/s下计算海面反射损失(分别对应图5, 图6和图7), 以$ - \ln \left| {{V_{\rm{c}}}} \right|$计算海面反射损失(单位为奈培). 图 5 风速为7 m/s时起伏海面下气泡层对海面反射损失的影响 (a) 无气泡层; (b) 考虑气泡层对声波的消减效应; (c) 考虑气泡层对声波的折射效应; (d) 同时考虑气泡层对声波的折射效应和消减效应 Figure5. Effects of the bubbles layer underneath the rough sea surface on reflection loss in nepers with a wind speed of 7 m/s: (a) Rough sea surface; (b) rough sea surface + scattering and absorption effect of the bubbles layer; (c) rough sea surface + refraction effect of the bubbles layer; (d) rough sea surface + scattering and absorption effect of the bubbles layer + refraction effect of the bubbles layer.
图 6 风速为10 m/s时起伏海面以及气泡层对海面反射损失的影响 (a) 无气泡层; (b) 考虑气泡层对声波的消减效应; (c) 考虑气泡层对声波的折射效应; (d) 同时考虑气泡层对声波的折射效应和消减效应 Figure6. Effects of the bubbles layer underneath the rough sea surface on reflection loss in nepers with a wind speed of 10 m/s: (a) Rough sea surface; (b) rough sea surface + scattering and absorption effect of the bubbles layer; (c) rough sea surface + refraction effect of the bubbles layer; (d) rough sea surface + scattering and absorption effect of the bubbles layer + refraction effect of the bubbles layer.
图 7 风速为13 m/s时起伏海面以及气泡层对海面反射损失的影响 (a) 无气泡层; (b) 考虑气泡层对声波的消减效应; (c) 考虑气泡层对声波的折射效应; (d) 同时考虑气泡层对声波的折射效应和消减效应 Figure7. Effects of the bubbles layer underneath the rough sea surface on reflection loss in nepers with a wind speed of 13 m/s: (a) Rough sea surface; (b) rough sea surface + scattering and absorption effect of the bubbles layer; (c) rough sea surface + refraction effect of the bubbles layer; (d) rough sea surface + scattering and absorption effect of the bubbles layer + refraction effect of the bubbles layer.