Papers by Keyword: Acoustic Radiation

Abstract: An advanced method named hybrid FE-SEA method was introduced to study the acoustic radiation characteristic for cylindrical structure with elastic plate cap in medium-frequency region. This method consists of the finite element method (FEM) for low-frequency region and the statistical energy analysis (SEA) for high-frequency region, which can be employed to deal with the problem of acoustic radiation result from model coupling of elastic connection effectively. According to the FE-SEA theory, a hybrid model of cylindrical structure with elastic plate cap was built to validated whether the hybrid method was feasible to calculate the acoustic radiation in the medium-frequency region. Moreover, the acoustic radiation characteristic of such model under the single point force excitation was studied. The result of numerical calculation agreed well with that of experiment, which validated the accuracy and validity of the hybrid FE-SEA method in solving the medium-frequency acoustic radiation of the cylindrical structure with elastic plate cap.

Abstract: To adopting means to reduce power radiated from the hull, power injected by the shaft system and that radiated by the hull are analyzed for an underwater cylinder excited by the propeller/shaft system. As the power is injected by combination of the solely acting loads on the junction and there concurrent, power transmitted by each solely acting load, radiated by the hull and the concurrent power are compared to understand the mechanism of power transmission and transformation. In the comparisons, quantities are decomposed according to circum orders to understand the radiation modes. The conclusion drawn in the paper will provide some guidance for acoustic reduction by shaft isolation design.

Abstract: The far-filed approximation solution was derived in a closed formula by using Fourier transform method. Two kind of possible concentrated forces, a line force, a point force, were included in the analysis. Moreover, a parametric study was carried out to clarify the effect of the incentive loading position and the various physical characteristics parameters of the rectangular plate. Conclusion is drawn that, the far-filed pressure level decreased with external excitation approached to the edge. Through analysis on far-filed sound pressure level, that can give foundation of designing acoustical elements and active noise control.

Abstract: This work proposes to study the effects of physical parameters and loading conditions on both dynamic and acoustic responses of a brake system subjected to squeal. A simplified brake system model composed of a disc and a pad is investigated. The friction interface is modeled by introducing linear and non-linear stiffnesses at several local nodes to model contact. The classical Coulomb law is applied to model friction and the friction coefficient is assumed to be constant. A stability analysis of this system is performed with respect to the friction coefficient and the hydraulic brake pressure. Then self-excited vibrations are investigated for two cases of loading conditions: static loading and ramp loading. Time responses for these cases are significantly different: the case with ramp loading presents higher amplitude of velocity than the static loading case. For the case with ramp loading, the spectrum analysis performed by the Continuous Wavelet Transform, shows the appearance of the fundamental frequencies of unstable modes but also their harmonics and combinations frequencies. Sound pressures radiated during squeal event present different peculiar patterns of directivity for both cases and for a progressive load, the levels are significantly higher.

Abstract: The acoustic radiation of submerged damped cylindrical shell is investigated by combining with thin shell theory and elasticity theory. The classical integral transform technique is used to derive the solutions of coupled equations. Numerical computations show the correctness of the proposed method, and also conclude the influence of thickness of inner shell and coated layer to acoustic radiation. The conclusions may be valuable to the application of damping material on noise and vibration control of underwater pipes.

Abstract: Based on the previous study, the coupling analysis for a submerged active constrained layer damping (i.e. ACLD) cylindrical shell with ring ribs is developed in this paper. Firstly, the governing equation for this kind of shell is proposed. Then, a multi-virtual-point-sound-source wave function superposition method combing the transfer matrix method is proposed to obtain the acoustic pressure level. Later, numerical results are given to verify the developed method. Finally, the damping effect for the ACLD treatment on the ring-stiffened cylindrical shell is discussed.

Abstract: The characteristic of the acoustic radiation of vibrating structure is the important factor in valuing its performance. This paper puts forward a visualization system of the acoustic radiation based on NAH which combines the measurement, data management and visualization. The visualization technology it adopts point a new way to the observation of the acoustic radiation. Experiments have shown that this system can offer a complete solution for the measurement and research of the radiation field.

Abstract: The cylinder for experiment has been excited by steady sinusoidal and random white noise excitation forces and the acceleration responses are measured. The frequency response functions of two excitation ways agree well. The reciprocity law and the linearity are certified by exchanging the excitation and measurement spots and increasing input voltage continuously respectively. The influence of mesh size to calculated time and precision of vacuum vibration mean square velocity and underwater vibration mean square velocity and acoustic radiation are investigated. Results show that time consumed mounts with the mesh size gets smaller, and the vibroacoustic results is less influenced at lower frequencies but much more at higher frequencies.

Abstract: To overcome the non-uniqueness of solution at eigenfrequencies in the boundary integral equation method for structural acoustic radiation, wave superposition method is introduced to study the acoustics characteristics including acoustic field reconstruction and sound power calculation. The numerical method is implemented by using the acoustic field from a series of virtual sources which are collocated near the boundary surface to replace the acoustic field of the radiator, namely the principle of equivalent. How to collocate these equivalent sources is not indicated definitely. Once wave superposition method is applied to sound power calculation, it is necessary to evaluate its accuracy and impact factors. In the paper, the basic principle of wave superposition method is described, and then the integral equation is discretized. Also, the impact factors including element numbers, frequency limitation, and distance between virtual source and integral surface are analyzed in the process of calculate the acoustic radiation from the simply supported thin plate under concentrated force. The extensive measures of acoustic field at the thin plate are compared with results obtain using different numerical methods. The results show that: (a) The agreement between the results from the above numerical methods is excellent. The wave superposition method requires fewer elements and hence is faster. But the extensive numerical modeling suggests that as long as the volume velocity matching yields more than adequate accuracy. (b) The equivalent sources should be collocated inside the radiator. And the accuracy of a given Gauss integration formula will decrease as the source approaches the boundary surface. (c) The numerical method is applicable to the acoustic radiation of structure with complicated shape. (d) The method described in this paper can be used to perform effectively sound power calculation, and its application range can be extended on the basis of these conclusions.

Abstract: Vibration and radiated sound of Air Conditioning are harmful to environment and safeness. Air Conditioning Compressor is its major part bringing vibration. To lower noise of a compressor and to improve its sound characteristic, the paper probes into a method indirect measurement of vibration, which both vibration and radiation behavior is represented using acoustic signal and theory of radiation modes. The paper investigates on the basic coupling relationship between structural vibration and acoustic radiation by means of the real modal analysis theory. Besides, the vibration and acoustic radiation characteristics of the rotary compressor are identified through the experiment method. According to the experimental results, between the vibration modes and the acoustic radiation modes have the comparability about the parameters. Therefore, this paper put forward a new method to the Active Structural Acoustic Control (ASAC), and provides the theoretical foundation of indirect measurement of vibration by using acoustic signal.