Search

A combined approach based on finite element method and genetic algorithm (FEM-GA) is proposed for optimizing the natural frequencies of plate structures. This approach can identify the optimal boundary conditions so that the plate's natural frequencies can be adjusted simultaneously to their corresponding target values. In this approach, the natural frequencies of plates with arbitrary boundary conditions are calculated by FEM, while GA is employed for searching the optimal solutions of the multiple-objective optimization problem. The FEM is validated by comparing with previous results. The proposed approach is illustrated by numerical examples. The results demonstrate the effectiveness of this approach.

This paper presents a theoretical study of the dispersion characteristics of sound wave propagation in a periodic ducted Helmholtz resonator (HR) system. The predicted result fits well with a numerical simulation using a finite element method. This study indicates that for the same system, no matter how many HRs are connected or what the periodic distance is, the area under average transmission loss T L¯ curves is always the same. The broader the noise attenuation band, the lower the peak attenuation amplitude. A noise control zone compromising the attenuation bandwidth or peak amplitude is proposed for noise control optimization.

This paper presents a theoretical study of a duct loaded with identical side-branch resonators. The Bloch wave theory and the transfer matrix method are used to investigate wave propagation in the duct. It is found that this duct-resonator system has a unique attenuation characteristic brought about by structural periodicity. Three types of stop-bands are discussed and their bandwidths are predicted. All of the results predicted by the theory fit well with a computer simulation using a three-dimensional finite element method. Compared to a single resonator, this structure may have a potential application in broadband noise control.

Helmholtz resonator is often used to reduce noise in a narrow frequency range. To obtain a broader noise attenuation band, combing several resonators is a possible way. This paper presents a theoretical study of sound propagation in a one-dimensional duct with identical side-branch resonators mounted periodically. The analysis of each resonator was based on a distributed-parameter model that considered multi-dimensional wave propagation in its neck-cavity interface. This model provided a more accurate prediction of the resonant frequency of the resonator than traditional lumped-parameter model. Bloch wave theory and the transfer matrix method were used to investigate wave propagation in these spatially periodic resonators. The results predicted by the theory fit well with the computer simulation using a three-dimensional finite element method and the experimental results. This study indicates that the wave coupling in this periodic system results in the dispersion of the frequency band into the stop and the pass bands. The long-term significance is that periodic resonators may more effectively control noise in ducts by broadening the bandwidth they attenuate and increasing the magnitude of sound attenuation., (© 2012 Acoustical Society of America)

The transient vibration and sound radiation (TVSR) of plate-like structures with general elastic boundary conditions was investigated using the time-domain finite element method (TDFEM) and time-domain boundary element method (TDBEM). In this model, the structure can have arbitrary elastic boundary conditions and hence the effects of the boundary conditions on the TVSR can be effectively studied. The predicted results agreed well with existing experimental data using two classical boundary conditions: simply supported at all edges and clamped-free-free-free. The TVSR of a single panel with a more general boundary condition in two connected chambers was also measured. The predicted results agreed well with these experimental results. The prediction method was subsequently applied to evaluate the effects of elastic boundary supports on the TVSR of a window caused by a sonic boom. Loudness, non-audible acoustic perception, and tactile vibration thresholds were analyzed for different boundary conditions (varying between clamped and simply supported). The possibility of improving the transient vibration and noise isolation performance by selecting an appropriate boundary condition was thereby demonstrated.

Several prediction methods have recently been developed for systematically studying the effects of general boundary conditions on the sound transmission loss (STL) of plate-like structures. But corresponding experimental validation studies remain scarce owing to the difficulty of obtaining accurate boundary conditions for practical structures. This paper presents a convincing experiment conducted on a baffled plate system to validate the STL prediction model in a previous paper by Yu et al. [Noise Control Eng. J. 58(2), 187-200, 2010]. A method is proposed to determine the boundary conditions of this system, and experimental STL compares well with the predictions based on the identified boundary condition., (© 2011 Acoustical Society of America)

A theoretical study of the multi-coupling flexural and longitudinal waves that propagate in a periodic dual-beam-type waveguide with structural connection branches is conducted. The analytical equations of the transfer matrix method are derived for the wave transmission with consideration given to the fully flexural and longitudinal motions that are tri-coupled at each connection. Based on this transfer matrix method, numerical calculation is performed to investigate the characteristic wave-types that propagate in a semi-infinite periodic structure. The complex wave-coupling phenomena in the periodically connected dual-beam waveguide are then analyzed numerically. Remarkably, it is found that three symmetric and three antisymmetric types of characteristic coupled waves propagate in a periodic structure. The numerical results show that the energy contribution of the coupled waves with respect to the source excitation depends on the forbidden band of the wave-types and on the energy ratios and combination of wave-types. This study promotes the fundamental understanding and prediction of coupled acoustic waves in multi-layered frame structures. The long-term significance is that it may lead to a more effective control method for structure-borne sound transmission in a multi-layered coupling structure.

Measurements of flow noise produced by strip spoilers in the air duct of a ventilation system and radiated from an open exhaust termination unit into a reverberation chamber have been made. The results agree with the previous work of Nelson and Morfey [J. Sound Vib. 79, 263-289 (1981)]. Prediction of flow noise produced by multiple spoilers requires the values of the ratio of the mean drag forces that act on the spoilers, the phase relationship between the fluctuating drag forces that act on the spoilers, and the coherence function of the noise sources. The latter is empirically derived from the measured results, where the predicted results agree well with the experimental results within 3 dB at most frequencies except for very high frequencies.