Advanced Materials Research Vols. 479-481

Abstract: The research on enclosure noise control is caused more and more attention. The key of noise control is to grasp physical essence about enclosure sound-structure coupling field. The research work has been carried out on a enclosure model of two simly supported flexible plate and four rigid plates. The research is focused on sound –structure coupling field analysis of the enclosure when applying primary forces on two flexible plate simutaneously. At the constraint condition of average acoustic potential energy(AAPE) formulars of enclosure sound–structure coupling field is derivated. The simulation show the follow conclusion: first, the wave energy transfer path is from primary force flexible plate to acoustic cavity, then to another flexible plate, and then feedback to acoustic cavity. Second, when structural natural frequences are the same as acoustic natural frequencies of the enclosure, the noise reach the maximum value. The third, when applying primary force on Plate a and on Plate b simutaneously, the wave energy transfer path and The relation of sound-structure coupling are more complex than only applying force on one plate.

Abstract: To identify the fatigue crack propagation of tubular joints in the offshore platform, we applied the wavelet coefficient energy theory to monitor and analyze the acoustic emission(AE) signal of marine structures with typical fatigue crack propagation. Based on typical tubular joints model fracture experiments of the offshore platforms, we successfully extracted the characteristics of AE signals during crack propagation. Further analysis results demonstrated that the elastic wave generated by the crack extension was superimposed by a variety of high frequency signals, and it changed with the evaluation of crack. The variation of wavelet coefficient energy and the change of crack propagation state showed a strong correlation. Thus the characteristics of AE signals can be used to identify different stages of crack propagation accurately, intuitively, and clearly, so as to label the development process of crack.

Abstract: According to the phenomenon that the increasing noise of the ventilator in Longyan Beishan Coal Mine are caused by the bearings, this paper starts analyzing the reasons for the noise of the ventilator bearing, and thinks that the noise is mainly the active noise from the air and noise from the machines which are caused by vibrations. The noise of the ventilator bearing is related to such factors as its size, material, structure design, processing, assembling, loading, and lubrication. So it puts forward that workers should try to choose light, small-sized bearings so as to improve the quality of assembly, adjust the space and apply preloaded force; the workers should strengthen maintenance, use proper lubrication and enhance the monitoring.

Abstract: In order to solve the problem of error and abstract in the identification process caused by current wavelet methods using grayscale to identify noise sources, a cabin noise source identification method based on wavelet transform(WT) was proposed. Firstly, multi-wavelet reconstruction signals were constructed from original time-domain signals through Matlab Wavelet Toolbox. Secondly, the eigenvectors were defined by calculating the energy value of reconstructed signals at all levels. And the correlation coefficients between cabin noise signal and other signals were obtained by these eigenvectors. Then the extent of vibration or noise energy radiation influence on the cabin noise was estimated by the size of correlation coefficients. Finally, an example was also given to show the effectiveness of the method.

Abstract: Based on the lumped parameter modal, the modal shape characteristics of the tuned free bladed disk and the random mistuned bladed disk was studied. It can be concluded that the vibration energy is evenly distributed in the tuned free system, but in the mistuned system, the modal localization dose exist. And the localization degree gets stronger while the mistuning strength is bigger .Then based on the finite element model of a bladed disk. The intentional mistuning technology’s role in reducing the sensitivity of the bladed disk to random mistuning was studied in this paper. The blades vibration response characteristics and the intentional mistuning technology was also studied through magnification factor for amplitude and localization factor. The result shows that the mistuning sensitivity level can be reduced by adding the quantity of intentional mistuning, and intentional mistuning has an important meaning to reduce the adverse effect of the random mistuning to the blades vibration response.

Abstract: Vehicle suspension is a MIMO coupling nonlinear system; its vibration couples that of the tires. When magneto-rheological dampers are adopted to attenuate vibration of the sprung mass, the damping forces of the dampers need to be distributed. For the suspension without decoupling, the vibration attenuation is difficult to be controlled precisely. In order to attenuate the vibration of the vehicle effectively, a nonlinear full vehicle semi-active suspension model is proposed. Considering the realization of the control of magneto-rheological dampers, a hysteretic polynomial damper model is adopted. A differential geometry approach is used to decouple the nonlinear suspension system, so that the wheels and sprung mass become independent linear subsystems and independent to each other. A control rule of vibration attenuation is designed, by which the control current applied to the magneto-rheological damper is calculated, and used for the decoupled suspension system. The simulations show that the acceleration of the sprung mass is attenuated greatly, which indicates that the control algorithm is effective and the hysteretic polynomial damper model is practicable.

Abstract: The bearing of rotating machine often fails due to the frictional forces of rolling element, such frictional forces often generate a series of ultrasound, and that is to say, there must be some necessary relationships between the faults of rotating machinery equipment and the ultrasound from the equipment. In this paper, the histogram method which is the simplest method in statistics is used to analyze the ultrasonic signals. Through the analysis, the bearing faults could be preliminarily diagnosed. A verification research with respect to vibration method is carried out to analyze the effectiveness and superiority of ultrasonic method by using the histogram. Extensive experiments have been performed in a bearing vibration measuring instrument, and the results indicated that the fault diagnosis method based on the ultrasonic amplitude histogram is more useful than the method based on the vibration amplitude histogram. In addition, it is more sensitive and more effective than the method based on vibration amplitude histogram.

Abstract: The vibroacoustic phenomena for the slender elastic thin shell filled with water by finite element method is introduced in this paper. The unsymmetric (u, p) variational formulas and finite element procedures are implemented for 3 dimensional structures of vibroacoustic environment based on the displacement field u and the fluid acoustic pressure field p. As illustrated by numerical examples, the longitudinal acoustic pressure eigenmodes will be occurred besides the transverse bendable eigenmodes of the slender shell, nonetheless the eigenvalues and the order of eigenmodes for the fluid acoustic pressure field can only be determined by the flexibility and geometry stiffness of the slender shell.

Abstract: Vibration slot, which is connected by the framework welded by the angle and the u-shaped slot formed by the stainless steel plate bending with fasteners, is an important part of the vibrating conveyor. The major function of vibration slot is carrying and conveying material. Due to vibration slot owning the thin plate structure and the flat large feature of surface, it is the primary noise source of vibrating conveyor. Therefore, it is very important to research and control the surface radiation noise of the vibration slot for reducing the noise of vibrating conveyor. This paper, through combining the finite element and the boundary element, researches noise radiation of vibration slot and understands the main noise source of vibration slot and radiation condition. The natural frequency of vibration slot, the vibratory response of vibration slot and the noise radiation of vibration slot are researched by inputting different structure parameters. Through analysis and comparison, some regularity conclusions that will provide a basis for the noise reduction of vibration slot are summarized .

Abstract: As the seat frame is an essential structure of bulldozer's cab, dynamic characteristics of the structure are particularly important. The finite element model of the seat frame was established by CATIA software, and then modal analysis was carried out in absolute freeness. After investigating inherent frequency and vibration mode of several typical modes seriously, dynamic characteristics of the frame were clear. Weak links of the structure were obtained on the basis of analysis result, and structure improvement was conducted. Finally, the comparison and analysis was carried out between the unmodified seat frame and the modified one, the result shows that the dynamic characteristic of seat frame is optimized.