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.

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.

The main noise source of the metro is the wheel-rail noise. This noise will generate a reverberation sound field in the tunnel after reflecting from the tunnel’s wall and then passed into the carriage through the carriage’s structure which will affect the riding comfort. In this paper, the qualitative analysis about the influence fact of the wheel-rail noise in classical theories and relevant standards were studied. Using the date tested in the domestic metro line to make a quantitative analysis on each factor’s specific impact on the noise inside the carriage. On this basis, comprehensive control suggestions on the noise inside the metro were put forward to provide conference for the subway route planning.

A dynamic vibration absorber with frequency adjustment installed in the maximum resonance displacement point of the pipeline which plays an role in reducing the piping vibration under different natural frequencies by moving the position of mass block on the leaf spring has been designed based on the principle of anti-resonance.A space pipeline has been built.The ability of designed dynamic vibration absorber to damp the pipelines which possess different natural frequencies within the available range of frequency has been validated via finite element analysis and pipeline vibration test.The result shows that the best damping effect of dynamic vibration absorber through adjusting the position of mass block on the leaf spring. And the best installation location is the maximum resonance displacement of the pipes.The application value of the designed dynamic vibration absorber has been indicated.

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.

During the design of Propeller Shaft, CAE method is used to simulate the mode and check the vibration. There is a Propeller Shaft that the first mode has met the target, but having resonance problem on full vehicle when test. In this paper, the CAE method was improved, and the structure was optimized to remove the problem mode. According to the test result and subject evaluation, a favorite effect was reached.

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.

Numerical modeling on a scaled shaft-hull model is made using the finite element method firstly. Then the experimental data is used to verify and modify the dynamics model. Direct boundary element method is applied to compute the acoustic radiation signature of the hull when subjected to the propeller exciting force in both transverse and longitudinal direction. The acoustic pressure and far-field pressure distribution is obtained. The energy method is also used to compare the acoustic power under different loading conditions.

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: 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.

Abstract: Aerodynamic characteristics and vibration characteristics of a micro quad-rotor aircraft were studied based on finite element method. A three dimensional physical model of the fluid fields was established. By adding boundary conditions, the fluid fields were analyzed numerically using the finite volume method and the aerodynamic characteristics were obtained. Then the aerodynamic force was loaded to the aircraft structure to get the stress distribution and find out where the maximum stress is. At last, the first six vibration modes and their vibration characteristics were obtained after the modal analysis of the micro quad-rotor aircraft.

With the vigorous development of civil aviation, the development trend of large passenger aircraft airworthiness noise, the average every 10 years, Airworthiness noise reduction 6EPNdB. ICAO is studying the more stringent noise standards, 2016, large passenger aircraft the airworthiness noise than the fourth phase noise is expected to limit the low 10EPNdB above. To make the design and manufacture of civil aircraft meet the noise standard international practice, the need to update the noise certification standards, this article studies the noise certification standards for aircraft engine project.

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.

This paper describes the method of subjective evaluation and objective tests on impact shake when vehicle passing the typical speed bumper. By analyzing the impact hardness and impact shake response signal and further study on the the signal characteristics a Neural Network is setup to build the correlation between subjective rating and test results. The feasibility of this method applying on small sample group is also been studied.

Abstract: In views of the aerodynamic noises generated by axial fan, a three-dimensional model of this kind of fan is built. Lighthill acoustic analogy theory, FW-H acoustic wave equation and FLUENT numerical simulation are used to analyze the characteristics of aerodynamic noises arisen from the axial fan’s rotating blades. The simulation result shows that the static pressure of rotating blades is mainly distributed on the front side of blades. However, the fluctuating pressure is distributed on both sides and mainly in the margin of blades, which is caused by the severe air turbulence from the vortexes in the outer edge of blades. The acoustic power of blades is also distributed in the margin of blades, but its characteristic of distribution is different from that of fluctuating pressure, indicating that the aerodynamic noises of rotating blades are not all produced by fluctuating pressure. In addition, the faster the blades rotate or the larger the blade’s diameter is, the more intense the aerodynamic noise is.

The friction-induced brake noise has important influence on the riding comfortableness and urban environment. The investigations on the mechanisms of friction-induced brake noise are significance to determine the control measures. The literature survey on the progress of the mechanisms and control measures of friction-induced brake noise during the past thirty years is briefed. The mechanisms of the noise are divided into three classes; they are self-excited vibration, structure instability, and “hot spot” theory. The control measures are analyzed from the structural design optimization and modify the material performance. In order to acquire better understanding of the formation mechanism and the control methods of friction-induced noise, the further study on friction-induced brake noise should be carried out by combining the inter-disciplines including tribology, dynamics and heat transfer.