间歇性排气嗓声辐射特性的研究

将排气噪声分为三类,研究了间歇性排气过程中的空气动力学和噪声特性,建立了间歇性排气噪声中的单极子源和四极子源所产生噪声的声压级表达式。对气路系统中各参数对噪声的影响进行了全面深入的研究。     

运动型汽车排气系统消声器的研究

为了获得运动型排气噪声,本文研究了汽车排气系统消声器结构对运动声学品质的影响。通过改变消声器的内部结构,建立与之对应的GT-Power模型,利用一维流体动力学原理对排气系统的声学性能进行模拟和仿真,并运用声学测试平台测试节气门全开加速时的尾管噪声。验证了去除排气系统的中排消声器并在后排消声器内加入消声棉的结构,可明显提高噪声的运动性,另外,消音棉的利用可以有效降低高频噪声,消声器进气管处的穿孔结构可以有效消除中低频噪声。     

不同环境下射流辐射噪声特性研究

水下排气噪声形成机理不同于空气排气噪声的产生机理,为了确定水下排气辐射噪声频谱特性及噪声源,进行了水下和空气气体喷射噪声试验研究。分析比较试验结果发现,气泡从管口脱落以及在流场力的作用下气泡体积振动产生的噪声是影响1~4 kHz频段声压的主要噪声源;当水下排气产生的两相流态由气泡流态过渡到射流流态后,气泡辐射噪声峰值与排气速率之间的线性关系消失,1~5 kHz频段内声压值变化较小,而在5 kHz以上的频段声压增幅较其它流量下却明显增大;水下排气由于气流剪切周围水体所引起的湍流噪声要明显低于空气排气产生的湍流噪声。     

小孔喷注消声器在宇航设备上的应用

宇航设备中的供氧排气系统在排气过程中产生了很高的喷注噪声,小孔喷注消声器是控制喷注噪声的有效措施。以喷注噪声理论为基础,利用小孔喷注消声器设计方法,为宇航设备供氧排气系统喷口设计小孔喷注消声器。设计中通过限制孔间距要求,降低孔径,实现了小孔喷注消声器的高降噪效果。加工消声器并测试,降噪效果理想。喷注噪声的计算和实测结果对比显示,两者吻合良好,误差在2 dB(A)左右,但驻压比为4时,计算结果与实测结果相差较大,分析原因是喷口后附加喇叭口结构对喷注噪声中的冲击噪声产生了影响,而经典计算公式并未考虑此种情况。小孔喷注消声器在宇航设备供氧排气系统中应用的可行性和小孔喷注消声器设计方法的可靠性得到了验证。     

水下气体喷射噪声特性研究

水下气体喷射形成了复杂气液流场,同时伴有频带宽、声压大的排气噪声产生。为研究水下排气流动状态与声压频谱之间的关系,建立水下排气噪声测试系统对水下排气形成的两相流场和排气噪声频谱进行了试验研究。结果表明随着排气速度的逐渐增大,排气形成的两相流场由气泡流态过渡为射流流态。伴随着流态的转换,气液边界面附近不稳定,形成大量体积较小气泡,这些小气泡在排气形成的湍流场激振作用下产生共振,从而辐射噪声;另一方面,这些气泡体积小,表面张力大,当多个气泡相互作用以及气泡形态发生变化时将释放出更高的能量,这些能量会辐射形成噪声;喷射流场的流态对水下排气噪声中频段声压峰值有较大的影响。当射流场由气泡流态过渡为射流流态后,2 kHz处对应的声压峰值呈非线性增大。     

尾管中强脉动排气噪声辐射的特征线解

本文应用特征线法，对尾管中的强脉动流的传播问题进行了理论计算．尾管的强脉动排气，在流压超过临界值的情况下，在开口端处的流动将会阻塞，此时应取马赫数等于１代替流压等于大气压作为该处的边界条件．对于强脉动气流，流动的诸参数的起伏量可大于它们各自的时均值，本文将开口端向外的排气气流比作简源，令简源强度与排气气体的体积速度成正比，同时计及湍流噪声的贡献，这样得到的结果与实验可相比较．最后还计算了管长为一定时的噪声辐射与气室压力的关系，气压为一定时的噪声辐射和质量流通量与尾管长度的关系，以及不同气压下噪声辐射与尾管长度的关系，为指导气动声源和往复式发动机尾管的设计提供了计算方法．     

低频噪声的有源控制

本文概述了国内外在噪声有源控制方面的研究情况.随着控制论、数字信号处理技术及微电子学逐步应用于有源控制系统,有源消声的推广价值不断增加.文中介绍了有源控制技术在抵消重复噪声(如柴油机排气噪声)、随机噪声(管道或风洞噪声)及空间噪声(变压器噪声)中的应用实例.     

蓄冷能力对液氢贮箱蒸气冷却屏瞬态特性的影响

蒸气冷却屏可有效降低贮箱漏热,延长低温流体贮存时间。为明确间歇性排气下蒸气冷却屏是否有足够的蓄冷能力能够在短时排气过程中充分蓄存/回收低温气体冷量,本文针对液氢贮箱绝热结构建立了耦合真空多层绝热与蒸气冷却屏的瞬态传热模型,研究了间歇性排气下液氢贮箱外部绝热结构和内部气液相的热力参数变化规律,讨论了绝热结构瞬态温度分布随蒸气冷却屏蓄冷能力的变化特性,对比分析了蓄冷能力对蒸气冷却屏绝热性能的影响。     

空气锤进排气噪声控制用消声器的试验研究

分析了空气锤进排气噪声的特性,全面深入地试验和分析了,不同基本滤波单元及其组合的消声器实际应用在Ｃ４１－１５０型空气锤时对排气噪声的降低功能,并取得了显著的降噪效果。     

四壁倾斜水池点源低频声场特性的理论计算及实验测量

本文对哈船院柴油机水下排气噪声实验用四壁倾斜水池的低频声场特性进行了理论计算和实验测量。在理论上采用边界无法对水池点源声场进行数值模似，并将计算结果与球面波扩展规律进行比较。利用柴油机水下排气管口体积脉动声辐射作为声源在柴油机排气频率范围内和常用测点区域内对水池进行声场特性测量。这一工作对柴油机水下排气噪声的实验研究和理论预报有一定的指导作用。     

Quantitative measurement of pass-by noise radiated by vehicles running at high speeds

It has been a challenge in the past to accurately locate and quantify the pass-by noise source radiated by the running vehicles. A system composed of a microphone array is developed in our current work to do this work. An acoustic-holography method for moving sound sources is designed to handle the Doppler effect effectively in the time domain. The effective sound pressure distribution is reconstructed on the surface of a running vehicle. The method has achieved a high calculation efficiency and is able to quantitatively measure the sound pressure at the sound source and identify the location of the main sound source. The method is also validated by the simulation experiments and the measurement tests with known moving speakers. Finally, the engine noise, tire noise, exhaust noise and wind noise of the vehicle running at different speeds are successfully identified by this method.     

Identification of noise sources on a residential split-system air-conditioner using sound intensity measurements

This paper presents the results of experimental studies of the noise of a residential split-system air-conditioner unit. The compressor and condenser and associated fans were removed from the unit and did not form part of the studies. Care was taken with the unit to separate the inlet and exhaust noise from the noise radiated from the cabinet. The measurements were made with a two-microphone sound intensity probe and these resulted in sound power level data. The sound power levels produced by radiation from the inlet, exhaust and cabinet were obtained for five different volume flow rates. The effect on the sound power generated by removing the coil was investigated. Measurements and subjective studies show that the low frequency sound is predominantly radiated from the exhaust and inlet. At high frequency, the cabinet noise dominates.     

Implementation of active noise control in a multi-modal spray dryer exhaust stack

Tonal noise emitted from large-diameter spray dryer exhaust stacks used in the dairy industry can give rise to complaints from nearby communities. In many cases, the tone at the fan blade passing frequency is characterized by a frequency above the first mode cut on frequency of the exhaust stack and both its amplitude and the frequency are time varying. The variation in amplitude is a result of turbulence and temperature variations in the duct which cause angular variations in the nodal plane of modes with diametrical nodes. This in turn results in large fluctuations in sound pressure with time at any specified location in the duct, thus presenting a significant challenge for an ANC system with fixed control source and error sensor locations. In many food processing industries, the use of sound absorptive materials in silencers is not acceptable and, particularly when the fan speed is variable, it is difficult to achieve an acceptable passive solution at a reasonable cost. Here, the design and implementation of an active noise control system for tonal noise propagating above the cut-on frequency of the first higher order mode in large size cylindrical industrial exhaust stack is discussed, where the frequency and amplitude vary significantly and relatively rapidly with time. Physical system design principles and control algorithm optimization for a practical active noise control system are presented. Finally, real time control results which were achieved by a prototype installation on a large-diameter, in-service exhaust stack are given. Significant noise reductions were achieved in the community.     

Sound propagation through vegetation

The propagation of sound through a large number of scatterers (i.e., trees) is treated in a similar way to a classical diffusion problem. A general differential equation governing the sound intensity is derived which is valid under certain conditions, notably that the depth of the belt of vegetation is large, and absorption small. The predictions of this theory are compared with results derived from a small scale model study, and with some field measurements. They are also compared with published field data. The implications of some of the conclusions reached for the practical achievement of effective sound attenuation are pointed out. In general, it would appear that significant noise reductions may be achieved for a predominantly high frequency source if the existing ground cover is acoustically hard, or if there is no “ground effect” attenuation between source and receiver for some other reason. In other cases, the noise reduction will be much lower and may be negative.     

Multi-mode sound transmission in ducts with flow

Exhaust mufflers, large exhaust stacks, and turbofan engines are common examples of ducted noise. The most useful measure of the sound produced by these noise sources is the sound power transmitted along the duct. When airflow is present, sound power flow can no longer be uniquely determined from the usual measurements of acoustic pressure and particle velocity.One approach to sound power determination from in-duct pressure measurement, and the one discussed in this paper, is to predict the relationship between the sound power and pressure based upon an assumed mode amplitude distribution. This paper investigates the relationship between acoustic pressure and power for a family of idealized source distributions of arbitrary temporal and spatial order. Incoherent monopole and dipole sources uniformly distributed over a duct cross-section can be obtained as special cases. This paper covers the sensitivity of the pressure-power relationship to source multipole order, frequency and, in particular, flow speed. It is shown that the introduction of flow in a hard-walled duct can have a substantial effect on the behavior of the pressure-power relationship for certain source distributions. Preliminary experimental results in a no-flow facility are presented in order to verify some of the main results.     

Expansion-chamber muffler for impulse noise of pneumatic frictional clutch and brake in mechanical presses

A compound expansion-chamber muffler, which consists of a sound absorbing chamber and a switch valve, the chamber integrating structural features of impedance muffler and micropunch plate muffler, is proposed to diminish impulse exhaust noise of pneumatic friction clutch and pneumatic friction brake (PFC/B) in mechanical presses. The structure decreases the impulse exhaust noise of PFC/B over 30 dB(A). A one-dimensional flow model is applied to study the aerodynamic characteristics of compound exhaust process of the single acting cylinder and muffler because the exhaust time is a critical factor for application of muffler in PFC/B. The volume of sound absorbing chamber is found to be an important design parameter to minimize the exhaust resistance of pneumatic cylinder. Experiments are also conducted to validate analytical results. Then the effects of diameter of exhaust ducts and volume of muffler on the exhaust time are discussed in detail. The proposed one-dimensional computational method, which considers the coupling of air-flow field and sound field, gives satisfactory results for the preliminary design of an expansion-chamber muffler. This method has been applied to an existing model HKM3-40MN to reduce its impulse noise.     

海洋信道随机性引起的船舶噪声线谱衰减

阐述准周期性随机声脉冲序列作为船舶噪声模型的普适性,侧重讨论船舶噪声准周期性随机声脉冲序列所产生的线谱经随机海洋信道传输后的变化。指出在大多数工况下,船舶噪声并不是以几种不同频率的加性正弦波直接叠加在宽带连续谱噪声上,而是一类本身并不含有任何有限强度加性正弦波分量的信号。研究结果表明:海洋信道多途效应引起船舶噪声脉冲序列信号时域上时延扩展;海洋信道的随机性使船舶噪声随机声脉冲序列信号准周期性下降,导致船舶噪声线谱相对幅度“额外”快速衰减,对于存在大范围不均匀水团的海洋信道,50 km传播距离上其介质随机起伏引起的船舶噪声线谱“额外”衰减最高可达11 dB。海洋信道随机性引起的船舶噪声线谱衰减不可忽视。      

热粘性对发动机排气管道中噪声传播的影响

声波在气体中传播时,气体的热粘性效应会使声波产生一定程度的衰减,且气体的声吸收系数随温度的升高而增大。由于发动机的排气温度较高,热粘性效应引起的排气管道中的噪声衰减应加以考虑。基于准平面波理论,首次计算了考虑热粘性效应时不同温度、流速和管道尺寸下排气管道中的传递损失,分析了各参数对管道中噪声衰减的影响。结果表明,随着温度和频率的升高热粘性声衰减增强,而气流流速和管道直径的增加会降低直管中的热粘性声衰减。对于简单膨胀腔,传递损失的预测结果表明,热粘性效应使通过频率处的声衰减有所改善。     

Research on the procedure for analyzing the sound quality contribution of sound sources and its application

Transfer path analysis (TPA) plays an important role for identifying and quantifying the contribution by airborne and structure-borne in the automotive industry. The main bottleneck of the TPA method is the test time consumption and complex procedure. It becomes a key target in many applications to find out the source with dominant contribution to overall noise rather than to identify each source. In recent years the contribution pattern of sources to the vehicle overall interior noise has changed with the reduction of engine noise, which masks all other sources. The panel radiation noise of vehicle body could not be ignored. There is an increasing demand for analyzing the sound quality contribution of sound sources in simple ways. The procedure for analyzing sound quality contribution of panel radiation noise is suggested in this study, in which an operational path analysis (OPA) method combined with partial singular value decomposition (PSVD) analysis is applied and sound quality objective assessment is introduced. The experimental research for verifying the procedure is finished, from which the source with largest sound quality contribution is picked up from three sources. For engineering application, the sound quality contributions of panels to the interior noise of a micro commercial vehicle are analyzed by using the procedure. By investigating the contributions of sound sources to each sound quality attribute, the dominant sound source is determined.