The frequency-domain analysis is the most important and applicable signal processing technology in fault diagnosis for machinery. In the literature, a number of frequency-domain-based methods have been applied to detect faults in machinery and each method has its special features. Therefore, selecting appropriate method plays a pivotal role in inspecting defects based on vibration signals. Characteristics of fault-caused vibration signals and frequency-domain-based methods are summarized in this paper using representative examples, so as to establish a rule of selecting appropriate signal methods of extracting vibration features for different mechanical equipments. The results can be used to improve the precision and reliability of many kinds of fault diagnoses for key components in different machinery.

This paper describes an investigation about the frequency characteristics of the various types of vehicles in different speed. The noise samples were recorded to analyze the spectrum and the energy ratio of different frequency bands. The results showed that most of the vehicle noise energy was mainly located between 400Hz and 2.5kHz. The noise energy distribution of small cars was almost from 1kHz to 2.5kHz, the noise energy of large cars was evenly distributed from 400Hz to 2.5kHz and the noise energy distribution of middle cars was in between. Most of buses noise energy was located in low-frequency band from 10Hz to 315Hz. As the speed increased, the energy distribution of small cars and middle cars was more concentrated, the noise frequency of large cars has no significant relationship with speed and the ratio of bus noise energy in low-frequency band was increased.

Electric Vehicles have been serving as taxis and public buses in many cities. The subject of this paper are electric and fuel vehicles. An analysis and comparison of the maximum A sound level and spectrum of electric and fuel cars and buses under different speed is provided in this paper. The aim is to offer some references to the prevention of transport noise in cities.

Negative stiffness mechanism can be used to isolate the low frequency vibration of the system. In this paper, an analytical expression of the force and stiffness was derived by using the equivalent magnetic charge method. Meanwhile, the optimal arrangement and magnetization of the rectangular permanent magnets were obtained to accomplish the negative stiffness. Finally, the trimagnets quasi-zero-stiffness vibration isolation was designed. The simulation results proved that the correctness of the theoretical analysis and the excellent low frequency vibration isolation performance was achieved without affecting the load ability.

The noise of wind tunnels sharply decreases the reliability and precision of wind tunnel experiments. Thus to decrease noise of wind tunnels has become a key technical issue of wind tunnel construction. This paper put forward 1-D discrete noise by ANC based on Fx-LMS. The results indicate that it can minimize the error caused by microphone mismatch, decrease the effects of the changing of weight coefficients on the system, and then increase the system convergence speed. According to the experiments on the duct by active noise control technical after optimized algorithm parameters in anechoic chamber of 0.55m×0.4m aero-acoustic wind tunnel, it has good effects on noise decreasing.

In the case of resonant suppression of the servo system, the depth and width of the notch filter are unreasonable and the resonance suppression is not ideal, so optimization method of resonant suppression parameters of notch filter is proposed in paper. The resonant spectrum is obtained by FFT transformation of velocity deviation, and the notch frequency is determined by the frequency at the maximum amplitude. The depth parameter is determined by the ratio of the amplitude of the curve to the maximum amplitude on the spectrum, and the width parameter is determined by width between the corresponding frequency and the resonant frequency. In order to ensure the rationality of the parameters, the amplitude at the resonant frequency after filtering is used as the fitness, and the notch depth and width parameters are optimized by improved particle swarm optimization (PSO) algorithm. This method avoids the trap parameters into local optimum due to noise interference and load change. The experimental results show that the method can analyze the mechanical resonance and match the optimal parameters on the line. It can significantly reduce the mechanical resonance.

A simplification computation method of the high-order harmonic solution of nonlinear ordinary differential equation was discussed. The Fourier coefficient expansion procedure of nonlinear ordinary differential equation with quadratic or cube term is improved and simplified. The procedure is composed of two steps of matrix operation with the same computation process so that the algorithm is easier to program than previous. Results for the Duffing equation show high-order harmonic solution in line with numerical solution but more efficient.

Least-squares complex frequency-domain (LSCF) method developed to be implemented in modal parameter estimation recent years. An expect result was received either in the system of weak damping or heavy damping. An User Interface was designed based on Matlab consisting of the LSCF method. Different parameters were set based on different coefficient matrixes and solution modification of the pole of the system was given. A test was used to validate the consistency of the different coefficient matrixes and that the User Interface was correct.

A survey on the research of the unbalanced magnetic pull(UMP) in the motors is given in the paper. The mechanism of UMP is analyzed and summarized. The developing status of the research of UMP, especially the nonlinear UMP, is also introduced. The ways to preventing and reducing UMP are also summarized. Finally, the future research orientation of UMP is also discussed.

Abstract: Based on the theory of Improved Fourier Series Method (IFSM), the vibration characteristic of rectangular thin plate with arbitrary boundary condition is studied. Besides, sine function term is introduced to modify the discontinuity of boundary condition. What’s more, through changing the values of the restraint stiffness k and the rotational restraint stiffness K, arbitrary boundary conditions can be simulated. Therefore, defects of the ordinary method dealing with structure vibration that could only be solved under some simplified boundary conditions have been overcome. The effectiveness of this method has been verified by comparing with the results of Literature and FEM software. Based on large amount of calculation, we found natural frequency differs greatly in varied boundary conditions. Besides, natural frequency of rectangular thin plate decreases with the growth of aspect ratio.

Operational transfer path analysis is an effective in-situ method for measuring the vibration transmission path. OTPA requires only operational measurements of the path references and target response(s) to establish a transmissibility matrix between references and target(s) from operational data under different test conditions. There is no need to measure operational forces and transfer function comparing to traditional method. It is easier and can operate in-situ. This article analyzes the basic theory of the operational transfer path analysis and the cause of the error. A car’s vibration analysis is given as an analysis example. The implementation procedures of operational transfer path analysis are given in detail. The noise sources were found out, and reasonable noise and vibration reduction suggestion was given.

Taking the common monolithic track bed, type Ⅲ damping fastener, polyurethane damping pad and steel spring floating plate track of subway line as the research objects, the damping effects of track structures under different damping measures were compared and analyzed through on-site driving vibration tests. Meanwhile, the frequency response and attenuation characteristics of track structure under different damping measures were studied by hammering test. The results show that there is little difference in the rail vibration acceleration among the four types of tracks, and the tunnel wall vibration acceleration of steel spring floating slab track is the smallest, and the high frequency damping effect of all kinds of track damping is better than that of low frequency damping, and type Ⅲ damping fastener, polyurethane damping pad and steel spring floating plate reduce tunnel wall vibration by 2.9 dB,13.7 dB and 22.4 dB, respectively. The decrease of the stiffness of damping fasteners leads to the obvious decrease of the resonance mode of the rail and the attenuation ability of the rail vibration along the longitudinal direction. Polyurethane damping pad and steel spring floating plate track are consistent in the variation of rail frequency response characteristics and vibration attenuation characteristics.

As for M1 class vehicle sound quality, this paper first proposed subjective evaluation test by considering the subjective feelings. First, collected a large number of sound signals of vehicles as for the database of sound quality evaluation, collected a large number of sound signals as for the database of sound quality evaluation, according to different frequency bands of sound signals show different characteristics, sound signals were divided to different frequency band. Then determined the best proportion of male and female while do subjective evaluation test. And then did sound quality subjective evaluation test by specific paired comparison. Finally, analyzed the test results and obtained: M1 class vehicle sound characteristic is most influenced by the frequency band 500-4000Hz, followed by 20-150Hz, the frequency band above 4000Hz has minimal impact.

By measurement of a laptop thermal system, the noise characteristics are obtained. The fan outlet is confirmed as the major noise source. Mathematical relationship of the fan rotating speed and noise of the fan outlet is set up. Through simulation of the airflow field, fin arrangement angle is found out effected to the outflow quantity and pressure, but much less effected to the noise. The fin is redesigned, which leads to a big increase of the cooling efficiency, so that the fan rotating speed is decreased, as a result noise of the thermal system is lowed. The experimental results show that the rotating speed can get a reduction of 16.8 % and noise is 2.0 dB(A) lower than the original one.

Abstract:In this paper,a study on an inline-four diesel engine mounting system is conducted.Using the dynamics simulation software for internal combustion engine named GT-CRANK,a virtual ptototype model of engine mounting system is set up.Then the vibration isolation performance of the mouting system is simulated under differernt schemes of mount stiffness.The law that how the variation of mount stiffness in differert directions influences the vibration isolation performance of the mounting system is found after analyzing the simulation result.Ultimately,combined with the influence law ,the optimization of the mount stiffness is conducted to improve the mounting system performance of vibration isolation.