An evaluation method for measuring SPL and mode shape of tire cavity resonance by using multi-microphone system

This paper presents an evaluation method for measuring the sound pressure level and mode shapes of tire cavity resonance by using a multi-microphone system. Two commercial tires were evaluated to compare abilities of noise suppression by means of this method in the range of the first resonance from 200 to 260 Hz. One tire was a special tire that suppresses tire cavity resonance with polyurethane foam mounted on the tire’s inner liner. The other tire was a normal tire with no polyurethane foam. The mode shape change from vertical to horizontal direction in both tires. However, the sound pressure level of the special tire was lower than the normal tire at all frequencies.     

Study on the radial composite piezoelectric ceramic transducer in radial vibration

A new type of radial composite piezoelectric transducer in radial vibration is developed and analyzed. The radial composite transducer consists of a piezoelectric ceramic thin ring polarized in the thickness direction and a metal thin circular ring. They are connected together and excited to vibrate in the radial direction. The radial vibrations of a piezoelectric ceramic thin ring and a metal thin circular ring are analyzed, respectively. Their radial electro-mechanical equivalent circuits are obtained. Based on the electro-mechanical equivalent circuits and using the boundary conditions between the piezoelectric ceramic thin ring and the metal thin circular ring in the radial direction, the electro-mechanical equivalent circuit of the radial composite piezoelectric transducer is derived out and the resonance frequency equation is obtained. The relationship between the resonance frequency and the geometrical dimensions of the transducer is analyzed. Some radial composite piezoelectric transducers are designed and manufactured. The resonance frequencies and the anti-resonance frequencies, the electro-mechanical equivalent circuit parameters are measured. The effective electro-mechanical coupling coefficient and the mechanical quality factor are calculated. It is illustrated that the measured radial resonance frequencies are in good agreement with the theoretical results from the resonance frequency equation.     

Parametric study on sound radiation from an infinite fluid-filled/semi-submerged cylindrical shell

This work presents the parametric study on the far-field sound pressure radiated from an infinite fluid-filled/semi-submerged cylindrical shell excited by a radial point load. Here, the exterior fluid is non-viscous, isotropic and irrotational coaxial flow. The formula of the radial velocity of the shell in wave-number domain is developed by using the wave-number domain approach (WDA). Then, the analytic expressions are derived for the far-field sound pressure radiating from the shell by using the same method presented in Salaün [Journal of the Acoustical Society of America 90 (1991) 2173]. The influences of parameters such as fluid velocity, structural damping, position of the force, and structural thickness on the far-field sound pressure are investigated. The sound pressure is shown to be very different from the one in the case of a fluid-filled/full-submerged cylindrical shell. Furthermore, it is shown that the pressure and the resonance frequency would increase with the fluid velocity increasing for downstream propagation. The reverse is true for upstream propagation. Moreover, the far-field sound pressure is related to the position and frequency of the excited force. In addition, the influences of structural damping and thickness are shown to be very important.     

压电陶瓷复合换能器固有频率的有限差分法*

为丰富换能器固有频率的研究理论，以及提供一种新的计算方法供工程人员选择，提出了计算其固有频率的有限差分法。以由径向极化的压电陶瓷圆管与金属预应力管沿径向复合而成的二元压电陶瓷复合换能器为例，建立并推导了其向振动的数学模型及其有限差分形式，给出了换能器径向振动的特征方程。利用MTALAB对计算实例的径向振动的固有频率进行编程计算，理论计算结果与已有实验结果符合很好，验证了有限差分法计算压电陶瓷复合换能器固有频率的可行性及准确性。通过仿真计算，给出了换能器径向振动固有频率与其结构尺寸的影响关系：换能器径向振动的固有频率随压电陶瓷圆管内径的增大而降低，随换能器壁厚比的增大而降低。该文所建立的换能器径向振动固有频率的有限差分法同样适用于结构形式相近的换能器及其他元器件。     

Identification of winter tires using vibration signals generated on the road surface

During the winter, traffic regulations state that automobile drivers must use winter tires on unsafe roads such as snowy expressways. The present report is concerned with the development of an automatic tire identification system that can discriminate winter tires from summer tires with high accuracy. The system detects the impact vibration signal that is specifically generated by winter tires when tread blocks with wide grooves strike the road surface during rolling. The signal is picked up by a commercially available vibration sensor. If the signal contains specified impact frequency components, the tire is judged to be a winter tire. Compared with the previous identification system, which used airborne tire/road noise, the proposed system has two advantages. First, it is unaffected by meteorological factors such as wind noise. Second, the proposed system performs well even when the target vehicle is traveling at low speed. We evaluate the performance of the system outdoors using a number of vehicles with various tires and demonstrate an overall improvement in identification accuracy for vehicles traveling at low or moderate speeds.     

热扩散效应在热声分离中的作用机理

在充满二元混合气体的声波谐振管中,振荡的气体会在径向上建立振荡的温度梯度,径向的温度梯度会引起两种组分的分子沿着不同方向进行扩散,在这种热扩散效应和热声效应的共同作用下,声波能够把混合气体中的两种组分分别带向谐振腔的速度节点和压力节点,使得混合气体在声波传播方向上逐渐分离。为了研究热声分离过程的机理,本文对一个半波长的声波谐振管进行了二维的建模,并基于可压缩的SIMPLE算法,通过求解He-Ar混合气体的速度场、温度场和一种组分的浓度场,对谐振腔内的传热传质过程进行了详细的数值模拟研究。数值模拟结果与文献的理论计算值进行了比较,结果符合良好。随后,通过研究一个周期内径向上的温度、速度和Ar的摩尔分数分布,揭示了径向上的热扩散过程,以及中间气体与边界层内气体之间的热质交换过程,完整地解释了热声分离过程的发生机理。     

AERODYNAMIC DAMPING OF RANDOMLY EXCITED PLATES IN STATIONARY AND MOVING AIR

An experimental study of the aerodynamic damping of oscillating plates has been undertaken. Plates of various shapes were placed into an air flow normal to the plate and excited to oscillate parallel to the flow direction by electromagnetic forces of equal amplitudes and random frequencies. The aerodynamic damping of oscillating plates, evaluated in terms of a quality Q-factor from a frequency response resonance curve, was found to vary linearly with the absolute pressure in stationary surrounding air and with the air flow velocity in moving air. The flow velocity was also found to affect the aerodynamic damping more than the absolute pressure. A simple empirical model has been developed to predict the variation of the aerodynamic damping with the flow velocity.     

4单元矩形径向线螺旋阵列天线的理论分析和数值模拟

 提出了一种便于组合的矩形径向线螺旋阵列天线。介绍了该矩形阵列天线的提出背景以及工作原理，分析了L型电磁组合探针的耦合特性，设计并数值模拟了中心频率为4.0 GHz的4单元矩形径向线螺旋阵列天线。模拟结果表明：该天线易于实现单元天线激励幅度和相位的均匀性及其随频率变化的平坦性。该口径为90 mm×90 mm 的天线在中心频率4.0 GHz 下，方向性系数为12.57 dB，轴向轴比值1.55；在3.60～4.05 GHz的频率范围内方向性系数大于11.6 dB，轴比小于1.55，反射系数小于0.2。     

矢量拖线阵水听器流噪声响应特性

针对传统拖线阵流噪声理论的局限性, 建立了完善的矢量拖线阵流噪声理论分析方法, 可全面准确地揭示矢量拖线阵流噪声响应特性. 基于细长圆柱的湍流边界层压力起伏Carpenter模型, 采用波数-频率谱分析方法对矢量拖线阵流噪声响应特性进行了理论研究, 导出了圆柱形矢量水听器流噪声响应的声压和振速自功率谱及其互功率谱的解析表达式, 定量分析了流噪声响应功率谱与拖曳速度、水听器尺寸、套管尺寸和材料等参数之间变化规律; 另外, 还讨论了圆柱形矢量水听器偏离护套轴线时矢量拖线阵流噪声响应, 导出了流噪声响应的声压、径向和轴向振速自功率谱及其互功率谱的解析表达式, 数值计算结果表明: 轴线偏移距离对声压和轴向振速的高频噪声的影响要大于对低频噪声的影响, 而对径向振速的全频段噪声都有明显影响, 且对振速分量影响要远大于对声压影响.     

Thermoelastic damping effect on in-extensional vibration of rotating thin ring

Sensitive devices such as resonant sensors and radio frequency micro-electro-mechanical system (RF-MEMS) filters etc., require high Quality factors (Q-factors) defined as the ratio of total system energy to dissipation that occurs due to various damping mechanisms. Also, thermoelastic damping is considered to be one of the most important factors to elicit energy dissipation due to the irreversible heat flow of oscillating structures in the micro scales. In this study, the Q-factor for thermoelastic damping is investigated in rotating thin rings with in-plane vibration. First, in order to obtain the temperature profile of the model, a heat conduction equation for the thermal flow across the radial direction is solved based on the bending approximation so-called in-extensional approximation of the ring. Using the temperature distribution coupled with a displacement, a governing equation of the ring model can then be derived. Eventually, an eigen-value analysis is performed to obtain the natural frequency of rotating thin rings, and the analytical and numerical values of Q-factors can then be determined by the definition. Furthermore, the effects of rotating speed, dimensions of the ring, mode numbers and ambient temperatures on the Q-factor are discussed in detail.