Induced noise of impeller stuck and passive rotation state in multi-stage pump without power drive under natural flow conditions

The natural flow cooling strategy is commonly employed in modem high-speed vessels and nuclear-powered submarines.These vessels rely on the energy generated by their own speed to drive the cooling system and supply cooling water to the condenser.The circulating pump,which operates without a motor drive under natural flow conditions,is a large resistance component in the cooling system.However,it is also the primary noise source,significantly impacting the vessel's safe operation and acoustic stealth performance.This study investigates the induced noise characteristics of a multi-stage pump under natural flow conditions by experiment,computational fluid dynamics(CFD),and acoustic finite element method.The analysis encompasses the distribution of the flow field,variations in acoustic power,spectral features of flow-induced noise,and directivity of external field radiation noise under different natural flow conditions.The results show that the acoustic power distribution is correlated with the flow field.When the impeller is stuck,the noise sources primarily concentrate in the flow separation area at the blade's leading edge,the interface area between the impeller and the guide vane,and the flow shock area inside the guide vane.Conversely,when the impeller rotates passively,the blade wake area has a higher acoustic power.The flow noise spectrum under natural flow conditions mainly exhibits broadband and discrete characteristics.Additionally,the pump structure influences the external field radiation noise,and its directivity varies with different flow rates and characteristic frequencies.This study provides valuable insights into optimal design to reduce the noise of the circulating pump in the vessel's natural flow cooling system.It is essential for ensuring the safe operation and acoustic stealth performance of high-speed vessels and nuclear-powered submarines.     

小球散射超声脉冲声场的指向性

基于对小球散射单频连续声场的研究,利用傅立叶变换对换能器激发的小球散射的脉冲声场进行分析,推导了小球散射脉冲声场的指向性函数计算公式,并计算了指向性函数值。与实验结果对比表明,在换能器中心频率较低、刚性小球半径较小的情况下,所推导的计算公式是可靠的。     

振荡翼型气动及其噪声特性的数值研究

针对低雷诺数下翼型的非定常气动噪声特性,采用计算流体力学(CFD)与Lighthill声类比相结合的方法,分别对俯仰、平振以及俯仰与平振耦合运动的翼型进行了分析,通过自定义程序控制翼型的运动规律,并对其流场及诱导的声场特性进行了数值仿真.结果表明:随着折合频率、振幅的增加,翼型表面升力系数的峰值增大,非定常迟滞效应增强;耦合运动的相位差改变了气动力的响应特性;对于振荡翼型激发的噪声,低频下单极子声源占主要地位;随着声源频率的增大,远场声压指向性逐渐体现出偶极子声源的特性.     

宽带参量阵在浅地层剖面测量中的应用

为了提高宽带参量阵的探测精度,提出参量阵浅地层剖面仪的系统设计. 以换能器阵列作为声发射装置,相较单个换能器能显著提高声源的指向性,有效抑制旁瓣. 利用参量阵的非线性自解调模型,对比分析线性调频信号自解调前、后的波形与频谱变化,分析得出自解调信号的频宽扩展为原信号的2倍,且带宽内信号幅值满足每倍频程12 dB的增长态势. 据此设计改进匹配滤波器来进行脉冲压缩,并通过频谱修正来抑制频谱变化. 仿真结果表明,该宽带参量阵的换能器阵列具有较好的指向性,根据自解调信号和原频信号同指向性的原理,保证自解调信号的高指向性. 提出的改进脉冲压缩技术能进一步提高探测分辨率,通过选择合适的调频范围,距离分辨率可以达到7.5 cm,可以实现高精度的海底地层探测.     

介质透镜操控光电导天线辐射太赫兹波的研究

飞秒激光驱动的太赫兹 (terahertz, THz) 光电导天线是THz时域谱系统中常用的THz源,受全向辐射模式的影响,该光电导天线的天线主瓣小,方向性差。对波束的有效操控将有助于提高光电导天线的发射效率。以低温生长的砷化镓 (LT-GaAs) 作为天线基底材料,通过电磁仿真软件CST对蝶形天线辐射THz波的电磁分布特性进行仿真,研究了介质透镜对蝶形天线辐射出的THz波的操控。通过对透镜扩展厚度的理论与数值分析,得出一定频率下的最佳透镜扩展厚度值。仿真结果表明：随着频率的提高,蝶形天线在加载更小扩展厚度的硅透镜时可获得更好的方向性。     

发射换能器指向性现场测试仪的设计与实现

低频发射换能器的指向性测试一般依靠外场试验进行。为了提高测试效率和测试精度,缩短测试时间,对发射换能器指向性测试方法进行了研究。以多路功放及指向性仪为基础,以通用计算机为平台,添加了同步信号输出卡和多功能信号采集卡,研制了一套发射换能器指向性现场测试设备,开发了多通道同步脉冲信号发生器和自动测试软件。经现场实验证明,该测试设备结构简单、成本低、可维护性好,能够减少测试工作强度和时间。与人工测量结果的对比表明,设备的测量结果更准确、指向性图细节更明显。     

传声器阵列原理与应用

主要介绍了传声器阵列的基本原理、结构组成及声学效果,简要叙述传声器阵列在通信与PC设备中的基本应用与市场发展前景。     

High Performance Piezoelectric Microspeakers and Thin Speaker Array System

This paper reports on an improved piezoelectric microspeaker with a high sound pressure level of 90 dB, a total harmonic distortion of less than 15%, and coherence higher than 0.9. The fabricated Pb(Zr,Ti)O₃ (PZT) microspeakers have a thickness of only 1 mm including the speaker frame and an active area of 18 mm×20 mm. To achieve higher sound pressure and lower distortion, the PZT piezoelectric microspeaker has a well‐designed speaker frame and a piezoelectric diaphragm consisting of a tilted PZT membrane and silicone buffer layer. From the simulation and measurement results, we confirmed that the silicon buffer layer can lower the first resonant frequency, which enhances the microspeaker's sound pressure at a low frequency range and can also reduce useless distortion generated by the harmonics. The fabricated PZT piezoelectric microspeakers are implemented on a multichannel speaker array system for personal acoustical space generation. The output sound pressure at a 30 cm distance away from the center of the speaker line array is 15 dB higher than the sound pressure at the neighboring region 30 degrees from the vertical axis.