Abstract: In order to extract effectively detection signals in the noise background for non-stationary signal.On the basis of EEMD, improved EEMD is put forward, the improve EEMD threshold noise reduction is researched in this paper.The simulation signal compared the noise reduction effect of the wavelet,EMD,EEMD,and the improved EEMD. The improved EEMD threshold noise reduction have the best noise reduction result , the highest signal-to-noise ratio, the smallest standard deviation error.After the improved EEMD threshold noise reduction , the measurement signal time domain waveform smooth. More high frequency noise was obviously reduced in Hilbert time- frequency spectrum. Signal-to-noise ratio significantly improve, and signal characteristics are very clear.
Abstract: A ship is a large and multifunctional marine structure operating on the sea. In practice, the environmental noise on a ship has many complicated components and they influence the vibration of the ship structure. Besides the stochastic excitations such as waves and winds, there are also propeller- and host-induced harmonic excitations. In this paper, NExT/ERA algorithm program and a ship model have been made to realize the modal parameters identification of ship structure in the presence of both white noise and harmonic excitations. Moreover, whether the signal filtering technology has a great effect on the results of modal analysis is discussed. In order to study and analyze the influence of the harmonic excitations, experiments under different signal-to-noise ratio (SNR) conditions have been carried out. This has a guiding significance to the engineering practice.
Abstract: After a short introduction about vehicle wind buffeting noise generation mechanisms, sunroof buffeting characteristics of a production sedan under different wind speeds and operating modes are investigated through full-scale aeroacoustic wind tunnel tests. As sunroof fully open, the severest buffeting effect occurs at wind speed 50kph, with the peak SPL 122dB and the corresponding resonance frequency 18Hz for the test point at the front row. From ca. 60kph it seems that the buffeting effect disappeared. As sunroof tilt, the severest buffeting effect occurs at wind speed equal or less than 30kph, the resonance frequency equal or less than 15Hz. From ca. 40kph the buffeting effect almost disappeared. Whether sunroof fully open or tilt, the resonance frequency increases all along as wind speed goes up till the buffeting effect disappeared (less than 20Hz). Different test positions at the front row or back row show very similar buffeting characteristics.
Abstract: The feasibility of using shape memory alloy (SMA) as actuators to control the vibration of a double-decker cantilever beam is demonstrated in the paper. A new and reliable form of SMA actuator is proposed in this study that no debonding and softening occurs even the maximum shear is generated by recovery force of the SMA wires. The magnitude and stability of the recovery force are tested when the SMA wires with the prestrain are heated cyclically. According to the simulation results, the four vibrational modes (three bending and one torsional) of cantilever beam can be changed simultaneously. Finally the vibrational response excited by pulsing and sinusoidal signal is successfully suppressed by using the SMA actuators in the experiments.
Abstract: The low-pressure spool in a high-bypass ratio turbofan engine has its unique characteristics. The slightness rotor and the large lumped mass in blade and disk are the structural characteristics while the dynamic coupling between bladed-disk and shaft is the mechanical characteristic. This paper studies on the modeling technology of a flexible rotor system based on the finite element method (FEM). The equivalent-disk method, an equivalent principle of finite element modeling, is put forward. The blades are equivalent to a disk which can not only retain the structural and mechanical characteristics but also control the scale of the model and convert the periodic geometry into axisymmetric geometry. The results show that the equivalent-disk method is helpful to improve the modeling techniques of rotor system and can be used in engineering.
Abstract: In this paper, the vibration characteristics of the rotating thin circular cylindrical shell subjected to the radial excitation are presented. Based on the Love’s shell theory, the governing equation of the rotating thin circular cylindrical shell is derived by using the Hamilton’s principle. Then, the amplitude-frequency responses for traveling wave vibration of the circular cylindrical shell are investigated. The results indicate that there exists the traveling wave vibration for the rotating thin circular cylindrical shell, namely: the forward wave and the backward wave. The effects of the damping and excitation on the amplitude-frequency response are analyzed.
Abstract: Measurement accuracy of rotor unbalance in different speeds is affected by the nonlinearity of the vibration signal processing channel. Support Vector regression (SVR) is proposed to use for channel modeling and compensation, which performance is far superior to the traditional look-up table method. First the amplitude-frequency and phase-frequency characteristics models based on SVM regression are made using frequency response data of standard signal passing to measuring-channel as training samples, then the measurement signal is compensated according to the model obtained. Simulation and experimental results show that this method has higher accuracy, better generalization ability than the traditional BP neural network modeling method.
Abstract: As space industry and technology develop, the spacecraft structure systems become increasingly complex and the scales become much larger. Early in the project stage, finite element analysis is required to rapidly and accurately analyze and forecast dynamic characteristics of spacecraft. Based on this, the optimized structural design of spacecraft is then determined. Theoretical analysis done, the effect of both the type and size of shell elements and solid elements on calculation result is discussed during the dynamic analysis process. Shell elements and solid elements are respectively used for the study on load-bearing structure of spacecraft payload instrument. The purpose is, based on meeting the requirement of accuracy, to quickly conduct finite element dynamic analysis of the structure in the early payload structural design and provide a reference for the optimized design of spacecraft structure.
Abstract: The rotational frequency of large scale wind turbine is very low, so low order modal of drive-train in a horizontal-axis Wind turbine generator system (WTGS) needs special attention to avoid structural resonance. In this paper, with Lagrange’s equation, a three-mass drive-train dynamics of WTGS is modeled and analyzed. After comparing with the results by GHbladed4.1 and SIMPACK, we found that those results show little differences clearly. So the drive-train dynamics above is rational and the accurate analyses are fit to identify the crucial low order torsional modal of drive-train rapidly in WTGS. In addition, the anti-resonance frequency of the gear-train found by frequency response method can be very significant for vibration isolation of drive train in the wind turbine system.
Abstract: The dynamic characteristics of machine tool may directly affect its machining capability, which is analyzed to improve the machining precision and efficiency. In this paper, the 3D finite element model of main components turn-milling center is established by using ANSYS software, and then spindle box of turn-milling center is analyzed and optimized; the natural frequencies and vibration models are obtained after analysis, which guarantee the design requirement of the machining center. Therefore it is significant to improve the design quality of machining center by using FEA software in the design process.