Stiffness is one of the main performance parameters of bellows which depends on the geometric dimensions, especially shell thickness of the bellows. U-shaped bellows,the most wildly used kind in engineering is commonly hydraulic pressure formed, and the deformation in board-ring is much greater than that in shell-ring. Considering that shell thickness is decreasing with increase of its radius in forming process. ,the thickness variation with redius can be described by a power function which is used to modify the commonly used empirical formula for axial stiffness calculation. Through comparison of the computational results by FEM simulation using MSC Nastran and the results by experiments the effectiveness of the method presented in this paper is verified.

Gas-and-liquid double-phased flow in pipelines generates noises. In this work, the double-channel data collector and spectrum analysis instrument were applied for data collection and processing of the noise of the pipelines. By changing the experiment conditions, the noises of the pipelines with different gas and liquid ratios were measured, and the corresponding frequency spectra of the noise were obtained. Through statistical analysis of the noise frequency spectra, the noise characters were summarized. It is concluded that noise testing is an effective method to confirm that whether the gas pipeline contains liquid and whether the liquid plug appears.

In order to increase the lifespan and efficiency of micromotors, the damping effect of the metal brushes of micromotors is studied. The relationship between Rayleigh damping model and dissipation factor of materials is established. The location of rubber damper in the structure is simulated and optimized by means of the transient dynamic analysis module of MSC.Marc. Meanwhile, the vibration magnitudes of the metal brushes are measured with Polytec Scanning Vibrometer when the rubber damper attached at the original and optimal locations respectively. The results show that the vibration magnitude of triple frequency after the optimization can be reduced to 12.1 % (clockwise rotation) and 11.2 % (counterclockwise rotation) respectively. This method can improve the vibration performance of metal brushes. It is of significance for engineering practice.

During the detection of automobile chairs’ electric slides, the characteristic signals related to the comfort characteristic have been extracted from the vibration signal, and its power spectrum density is chosen as one of the criteria for quality control of products. Based on the demodulation of the second-order circulation statistics of cyclic spectrum density (CSD), the CSD slice chart of the vibration signal of the products is analyzed. And the characteristic modulation signals are obtained. As a result, the defect frequencies which effect the riding comfort are obtained according to their respective power, and the products quality can be well evaluated

Spacecraft will suffer the complex and severe dynamic environment loads during its launching stage. These environment loads are mostly composed of acoustic excitation due to very high sound pressure level in the payload fairing and structural excitation due to vibrations and shock transmitted through the payload attach fitting. The very high sound pressure level in the payload fairing is caused by the transmitted sound and structural acoustic radiation. In the last decade, various control techniques of dynamic environment loads has received a great deal of attention. The improving of the dynamic environment would allow more sensitive equipment to be included in missions, and reduce the risk of equipment or component failure as well as spacecraft structural weight and cost. In this paper, the status and development of active and passive noise control techniques of payload fairing is mostly summarized.

The finite element method is used to analyze the acoustic characteristics of an expansionchamber muffler with its inlet and outlet pipes being coaxial. Its transmission loss (TL) is calculated. The result is compared with that of the onedimensional solutions based on planar wave theory. The limitation of onedimensional planar wave theory is discussed. The acoustic characteristics of eccentric outlet muffler, doubleoutlet muffler and doublecavity muffler are analyzed. The result indicates that the position and the number of outlet can affect the acoustic characteristic of a muffler for higher and medium frequencies; while the doublecavity muffler has high noiseelimination efficiency for lower and medium frequencies.

Engine failuremode vibration and partial abrade are the most bothersome problems for engine enterprises. In this paper, some helpful experiences for solving these issues are summarized for an engine. Combining the experiences with theoretical analysis, the efficient method on process of design, fabrication and test is provided.

The acoustic performances of Yshaped, multiwedgeshaped, and Tshaped structures of noise barrier are simulated by using acoustic softwareRAYNOISE. In the region of 30m height and 50m width behind the sound barrier, the simulation result of noise reduction effect is obtained. The result indicates that the multiwedgeshaped structure is the best for noise reduction. Its insertion loss can reach 14.5dB in the region of 2m height and 50m width behind the noise barrier. The noise barrier of the Tshaped structure has good acoustic performance in the region of lower height behind the noise barrier. The insertion loss of the Yshaped structure decreases slightly when the height of the measurement point increases. The influence of sound absorption material on noise reduction is studied. The result indicates that the distribution of sound absorptionmaterial has no influence on the noise reduction effect in the region just behind the barrier. The possible reason is that the reflection between the barrier and the vehicle is not considered in the simulation.

Based on the finite element model of acousticstructure coupling field in a sealed cavity and the improved Senthares nonharmonic psychoacoustics model, the sound pressure level of the internal radiating sound due to the excitation of the harmonic force exerted on the shell of the cavity is calculated. The acousticstructure coupling effect is considered. The sound roughness caused by the rapid modulation at the evaluation point is analyzed. Moreover, the effects of the sound pressure level of the modulated sound, the frequency of the modulated sound and the stiffness of the shell on the radiating sound roughness are studied. This work provides the data and method for determination of the internal radiating sound roughness in the cavity caused by the rapid modulation of the other sound sources.

Exhaust noise of marines diesel engines is strongly related to rotating speed. Thus, the active noise control can be realized by composing secondary sound sources with the rotating speed signals as the base frequencies. But the difficulty lies on the determination of the weights of different sound sources. An arithmetic based on calculating the best errorweights is presented to overcome the difficulty. The results indicate that the method can effectively control exhausting noise and trace the change of diesel engines rotating speed. It adapts to the working conditions of marine propelling engines, whose rotating speeds are changing frequently.

By using equivalent linearization technique, the response computation of a single degree of freedom dry friction damped system with velocity_dependent exponentially variable coefficient of sliding friction under harmonic excitation is discussed. The amplitude_frequency equation is also derived. Each parameter’s influence to the response of the dry friction damped system is analysised by numerical results.