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Underwater reverberation environments that satisfy the conditions of uniformity and isotropy of the diffuse field can be used to measure the acoustic characteristics of underwater targets. This study combines two practical indicators — the standard deviation of the absolute sound pressure field (to indicate uniformity) and the analysis of the wavenumber spectrum in the spherical harmonics domain (to indicate isotropy) — for an accurate evaluation of the diffusion of the sound field in a reverberation tank. A method is proposed that can improve the narrow-band diffusion of the sound field by employing a randomly fluctuating surface. An acoustic experiment was performed in a reverberation water tank (1.2 m×1 m×0.8 m), where a randomly fluctuating surface was generated by making waves. The experimental results show that as the wave motion contributes effectively to the random reflection of sound rays in all directions, the uniformity and isotropy are improved significantly when the surface is fluctuating randomly. This work helps to ensure accurate measurements of the characteristics of underwater targets in reverberation tanks. 相似文献
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在复杂的浅海环境中,水声信道具有强烈的空变和时变特性,致使水声通信系统的鲁棒性很难得到保证.该文不同于依赖复杂信道编码和信道均衡手段的传统水声通信算法,将流形学习思想应用于高维海洋环境参数空间刻画及信号空间映射中,为水下数据传输提出创新方案.从声场角度出发,结合浅海实验数据,分析通信信号时空起伏特性,研究环境参数空间和声场信号空间的内在关系,提出了基于非线性流形学习算法增加合理的物理约束,结合信道稀疏特性,对于高维非线性水声信号系统的冗余维度信息进行维数约简,映射到稳定的低维目标空间,降低信道时空起伏对通信系统的影响.仿真和实验结果验证了算法的可靠性和有效性. 相似文献
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由于海上风速的多变性,同时风机组中存在大量电力电子器件等原因,其并网后所产生的电能质量问题不容忽视。对于离岸较远的大规模海上风电场,基于电压源换流器的高压直流输电(VSC-HVDC)凭借其独特的技术优势未来将成为不可或缺的输电技术。为保证电能质量符合标准,需在并网前对电能质量作出分析。根据风电场等值原理,运用PSACD/EMTDC仿真软件搭建由双馈异步风机组成的大规模海上风电场经VSC-HVDC并网模型,研究其在风速波动下闪变、谐波电压与电流、电压偏差等电能质量问题。结果表明,在风速波动时谐波问题比较严重,实际工程中应充分考虑当地风资源的状况,制定合理的滤波方案,为今后海上风电并网的电能质量分析工作提供借鉴与参考。 相似文献
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