Abstract: Active vibration isolation technology can overcome the defects of passive vibration isolation technology that the poor vibration isolation performance in low and resonant frequencies. Compared with other active vibration isolation technologies, magnetic suspension isolation technology has shown useful characteristics, such as wide response frequency range, fast response, high reliability and long-life. However, the control of MSVI is still one of the areas that require further investigation. This paper presents a Fuzzy Neural Networks(FNN) control algorithm for a magnetic suspension isolation vibration system, which is optimized by improved Genetic Algorithm(GA). The output force responses of the FNN and passive vibration isolation system under same excitation are simulated. The simulation results show that the fuzzy control system has much better performance in vibration isolation.
Abstract: In the process of running-in vibration signal denoising for remanufacturing engine based on wavelet transform, there are relatively large differences in denoising results when different wavelet bases are used, so the selection of wavelet bases affect the consequent of de-noising processing. On the base of analyzing the characteristics of the commonly used wavelet bases, the paper has compared the impact of the wavelet base on signal denoising. Using SNR(Signal to Noise Ratio) and RMSE(Root Mean Square Error) as criteria, and combined with the characteristics of the running-in vibration signal of the remanufacturing engine, the wavelet base coif4 has been selected as the optimistic base, which has relatively better denoising effect, and improves the SNR and resolution, so it can be used in actual practice.
Abstract: A reliable condition monitoring system is very useful in a wide range of industries to detect the occurrence of incipient defects so as to prevent machinery performance degradation, malfunction and sudden failure. Among the rotating machinery, many mechanical problems are attributed due to bearing failures. So implementing condition monitoring for bearing is critically needed. Considering that most research for condition monitoring only focus on detecting the existing fault, this paper add degradation tendency prognostics into the condition monitoring process. The kernel of bearing condition monitoring method presented in this paper is related to condition features extraction and remaining useful life prediction. The former is realized by the comprehensive vibration analysis for specific fault frequencies. The latter is achieved by adaptive neuron-fuzzy inference system based on extracted degradation signal. For illustration purpose, a bearing case from NASA data repository is used to validate the feasibility of the proposed method. The result indicates that the performance degradation of bearing can be effectively monitored and the predicted remaining useful life with 5.6% relative error can be the important reference for maintenance decision making.
Abstract: Various failures in electronic systems, particularly in the connections between the printed circuit board (PCB) and components, are due to mechanical shock and vibration. The vibration characteristic of a plug-in PCB in an airborne electronic case (AEC) was studied first by finite element modeling (FEM) and experimental techniques. The coupling method and torsional spring elements were used in FEM to better simulate the PCB’s realistic boundary condition. A reasonable correlation between simulation and test results was obtained. Since the fundamental frequency is one of the most important dynamic characteristics of PCB, the orthogonal design and variance analysis, as well as FEM method, were discussed subsequently to investigate the effects of different factors. Analysis results demonstrate a good correlation with current studies. Finally, a general design guideline was presented to maximize the PCB’s fundamental frequency.
Abstract: Field measurements of dynamic characteristics of the multi-storey reinforced concrete frame structure buildings were carried out, by using the ambient vibration test technique, and structural modal parameters were extracted. The measured results and calculated results in accordance with current design specifications were compared. Results show that for multi-storey reinforced concrete frame structure, the measured vibration period of structure is close to the natural period calculated in accordance with the empirical formula of the “Load Code for the Design of Building Structures”. In the actual project, when the designer calculate the natural period if considering only the quality of the infill walls, without considering the stiffness of the infill walls, the period should be shortened. In this paper, the recommended period shortening factor for the multi-storey reinforced concrete frame structure is gave 0.4~0.5.
Abstract: As a new wind-break and dust-control technology, the wind fence is widely used at storage yards in factories and ports. The wind fence structure is a new high-rise wind-resistant structure with light damp and very heavy wind load, and the wind-induced vibration response is unknown and equivalent static wind load is hard to determine in design. Based on the Davenport spectrum, wind-induced vibration of the plane frame structure was analyzed with frequency domain method and the response spectrum of displacement and acceleration were obtained. The equivalent static wind load was studied and the wind-induced vibration coefficient and gust loading factor were gained. The results show that the wind-induced vibration response of the structure is significant, and it should be taken into consideration in structural design.
Abstract: An approach combining FEM with BEM is adopted to calculate the structural vibration and sound radiation of an underwater cylindrical shell. By using FORTRAN codes to compute the added mass and added damping matrices, DMAP codes to add them to structural mass and damping matrices, the problem of fluid-structural interaction was solved. Through comparing the mean square normal velocity level and sound radiation power level of ring-stiffened cylindrical shell with different inertia moment of stiffeners, the results can be acquired: with the moment of inertia gets bigger, the peak frequency of the frequency-response curves increases while the peak value of vibration and sound radiation decreases. The number of strengthened stiffeners has the same effect on peak frequency as the moment of inertia, but has no effect on peak value.
Abstract: The monorail truss structure natural vibration characteristics affect the performance of monorail in the work, this paper apply finite element method to carry out monorail truss natural vibration characteristics research. Considering the engineering practice, research and development two groups of monorail truss structure, calculated strength for two kinds of structural, two groups of truss structure strength meet the requirements, then used Guyan reduction theory to carry out modal analysis for the two trusses. From the modal analysis result can be found that the two groups of truss each order natural vibration period are not significant, structure natural frequency is intensive distribution, truss 2 dynamic rigidity is better, so was selected as the final structure scheme. The design ideas and methods provide a useful reference.
Abstract: Based on the open-jet aero-acoustic wind tunnel, an experimental study was made to research the effects of the jet-flow on sound propagation. This study is focused on the changes of the direction of the sound propagation, the changes of the sound pressure level, the phenomenon of tone broadening and the availability of the existing prediction method for sound propagation in jet-flow. The results indicate that the influence of the jet-flow on the value of the noise source shift varies along the direction of the jet-flow and there is no regular influence on the sound pressure level. In addition, the flow around the test sample has affected the sound propagation, and the phenomenon of tone broadening exists when high frequency signal is used. The study also reveals the limitation of the application of the existing prediction method, because the model it used is too simple.
Abstract: The exciting source of ground vibration from urban rail generally consists two parts, a quasi-static load moving through the railway, and a dynamic interaction between wheel and rail. The latter is caused mainly from the wheel-rail unevenness, and usually described by a power spectral density function, PSD in brief. From the three dimensional point of view, this kind of exciting source can hardly be measured directly. A procedure is proposed to invert the source function from the ground vibrations observed at array. A dynamic coupled train-track-3D ground model is adopted to calculate the vibrations from given PSD. The Micro-Genetic Algorithm including the operators of the tournament selection, the uniform crossover and the re-initialization together with an elitist strategy is schemed to the inversion. The object function is designed as minimum of the sum of residua between calculated and observed ground vibration acceleration levels of 18 center frequencies, at 4 ground points and twice trains. The result shows that the ground vibration acceleration levels calculated from the obtained excitation source function agree with those from the observed data quite well, even for an additional point where the observed data have never been adopted in the inversion process.