Applied Mechanics and Materials Vols. 226-228

Abstract: Based on Hertz-Mindlin contact model in software EDEM by discrete element method, using linear vibrating screen 360 mm×600 mm, movement characteristics of particle group on sieve plate and law of particles going through sieve plate were studied in screening process of coal in certain conditions, which were as follows: dip angle was 0 °, amplitude was 5 mm, frequency was 11 Hz. The simulation test results show that there are important influences of vibration direction on screening process. And influence law of vibration direction on screening effect was revealed finally. The paper also gained mathematical model between particle group’s screening efficiency and vibration direction angle, and mathematical models of particles easy or hard to sieve and material between average movement speeds and vibration direction angle.

Abstract: This paper studies the vibration localization of fluid-loaded irregularly ribbed plate analytically. The modal expansion method was adopted to solve the multi-coupled system, the ribs were considered as Timoshenko beams attached to the plate. The localization mechanism was investigated by comparing different coupling effect at the plate-beam interface, it was found the ribs space irregularity only localize the modes associated with the shear force coupling. Both the light and heavy fluid loading pressure were concerned by Rayleigh integral , the study showed that obvious vibration localization phenomenon can be achieved by the ribs space irregularity, and the localization effect was weakened by the long range interaction through the heavy fluid, although the response amplitude of the modes decreased obviously. The investigation may be quite significant for vibration confinement and noise control in engineering.

Abstract: A mathematical model of a single degree of freedom air spring vibration isolation system is established. The model analyzes the influence of structural damping in the air spring vibration isolation system based on the traditional model. This paper establishes the relationship between the working pressure p, the volume ratio of n and system vibration transmissibility T under forced vibration. The experimental results are verified on different working pressure. The results showed that working pressure p has little effect on the resonant frequency of the system and the system vibration transmissibility. The smaller the ratio n, the lower the resonant frequency of the system and the system vibration transmissibility. The environmental excitation frequency range must be taken into account in designing.

Abstract: The ultrasonic transducer converts electrical energy into mechanical vibration, and its vibration characteristics have a great effect on the bonding quality. Bond grid arrays (BGA) application and the ability to decrease the temperature of the wire bonding process urgently demand higher bonding frequencies. The ultrasonic transducer working at 135 KHz has been designed, simulated and tested. Based on electromechanical equivalent circuit theory, the dimensions of the transducer were designed. Through finite element method (FEM), the dynamic characteristics of the transducer were investigated. The 5th order axial mode of the transducer resonating at 133 KHz is the working mode. The undesirable modes near the working mode have a great influence on the quality of bonding and must be considered carefully in system design. At last, the experimental testing was conducted for verifying the design and simulation results of the transducer.

Abstract: This paper presents a passive method to control low-frequency noise in a cylindrical structure by using multi-modal T-shaped acoustic resonators. The feasibility of noise transmission control on the cylindrical structure is investigated, including a detailed experimental evaluation of the control performance using a single resonator and a resonator array consisted of different resonators. Finally, six long T-shaped acoustic resonators are used to target the first four lowest cylindrical cavity resonances, and up to 9 dB noise reduction is achieved, and broadband improvement of noise reduction is also observed.

Abstract: Multi-wavelet has many excellent properties that single wavelet cannot satisfy simultaneously, such as symmetry, orthogonality, compact support and high vanishing moments etc. It contains several scaling functions and wavelet functions, which can make it match different characteristics of analyzed signal. Therefore, it is always used in bearing fault diagnosis. However, multi-wavelet is multi-dimensional and vibration signal is one-dimensional, so the 1-D vibration signal should be preprocessed before being decomposed with multi-wavelet. It means that the initial data need to be converted to r-dimensional data, and then is input to a tower algorithm. If preprocessing is done, multi-wavelet properties will be destroyed. Due to balanced multi-wavelet has unique properties, the preprocessing can be omitted. In this paper, a balanced multi-wavelet called CL4BAL is designed through balancing original CL4 multi-wavelet and is applied in the vibration signal processing. Comparing the frequency band index after decomposition and reconstruction of CL4BAL and CL4 multi-wavelet, it can be proved that CL4BAL is much better than that of CL4 multi-wavelet in bearing fault diagnosis.

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: Based on the actual structure of the motor,the model of rotor system has been established. Horizontal electromagnetic vibration problems of the rotor system are researched under the situation of asynchronous motor running in symmetrical steady state.Calculate the electromagnetic energy and electromagnetic force of the three-phase asynchronous motor (p=4). Study the electromagnetic characteristics and nonlinear electromagnetic vibration problems of the motor rotor system. Taking the gyroscopic effect into account, when analysing the rotor. Calculate the natural frequencies of the system and study double resonances problem caused by the electromagnetic force. Rotary speed, support rigidity all have certain influences upon natural frequencies of the system. Consider these factors for obtaining some regular curves. The first approximate solution and steady response curve of the system were obtained by analysing the double resonances caused by corresponding electromagnetic force.

Abstract: Vibration responses of the water wall of coal gasifier under impact loads were investigated. The influences of different diameters of water walls and impact loads on the effectiveness of ash removal were further considered. The results showed that the peak acceleration along the axial direction of the water wall is greater than 80% of the peak acceleration at the impact point when rapping devices are installed at the 1/4, 1/2 and 3/4 heights. Moreover, rapping devices should be staggered 30 degree in the hoop direction at different heights to avoid the dead zone of ash removal. Furthermore, vibration accelerations increase with increasing the diameter of water wall, while the impact time should be as short as possible for higher efficiency of ash removal.

Abstract: In order to improve thin circular saw blade’s cutting stability, it’s nonlinear dynamic incremental equilibrium equation was obtained according to nonlinear vibration theory and D’Alembert principle. It could be concluded from the above equation that cutting several radial slots on the circumference of the saw blade will cause significant change of dynamic characteristics of the saw blade. This thesis, employing the finite element method and matrix perturbation principle, calculated and studied respectively the effect of number, length and width of the radial slots on natural frequencies of the saw blade. Results show that number and length have distinct influence on natural frequencies but hardly does width have. So proper choice of number, length and width of the radial slots can improve effectively the dynamic characteristics of the saw blade.