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Dynamical analysis of a thin-walled rectangular plate with preload force
Get PDFFinite element (FE) models are utilized to investigate the influence of preload force and the stress stiffening on the dynamic characteristics of a thin-walled rectangular plate. An experimental platform system is established to obtain the dynamic characteristics of the specimen using the resonance method. Simulation and experimental results agree well with each other, which validates the effectiveness of the FE model. The results show that the preload force not only improves the overall dynamic performances of the thin-walled plate but also contributes to the local stiffness of the loading position because of the generation of stress
Modal analysis of HPGe detector assembly in gamma-ray spectrometers
Get PDFThe HPGe detector assembly of gamma-ray spectrometer cooled by Stirling cycle cryocooler is under consideration. Modal analysis based on the compiled dynamic model was carried out. The natural frequencies and modes shapes for HPGe detector with relative efficiency 15 % mounted by supports made from composite G-Etronax and CESTILENE HD 1000 were calculated by Solidworks simulation. The frequencies of the axial mode are in range of 200-600 Hz where electrical interferences caused by mechanical vibrations (so-called microphone noise) has a large impact on the resolution of spectrometer. It is shown that for cryostat cap the lowest natural frequencies determined by the thickness of input window lay in higher frequency range. The validity of the adopted model was confirmed by the experiments. The calculated natural frequencies of the detector assembly are compared to the harmonics of cryocooler’s vibration. The results obtained are useful to identify the interferences source in electrical circuits of spectrometer at its adjusting
The fabrication of electrochemical geophone based on FPCB process technology
Get PDFThe subject of the studies presented in this paper is the fabrication of electrochemical geophone, especially the electrochemical transducer with symmetrical four-electrode cell by FPCB process technology. The geophone assembled by transducer, dumbbell-shaped tube, highly-flexible membranes, electrolyte solution and signal-amplification circuit, is calibrated using a standard vibration platform, and the results show a good consistency of each geophone parameters. Coupled with low cost, the electrochemical geophone by FPCB shows a good potential application prospect
Analysis acoustic target strength of anechoic coatings in low frequency based on equivalent parameter inversion
Get PDFIt’s generally different to predict the acoustic target strength of a submarine with anechoic coatings by conventional finite element method (FEM). Parameter inversion is a common method to solve this problem. Some researchers have studied the parameter inversion about normal incidence of anechoic coatings. In this paper, the FEM of impedance tube is used to obtain acoustic reflection coefficient of anechoic coatings. Then the genetic algorithm is applied to acquire the physical parameters of viscoelastic material which is equivalent to anechoic coatings. The LMS Virtual Lab is used to construct finite element model of the anechoic coatings to validate the parameter inversion with normal incidence
Hybrid residual fatigue life prediction approach for gear based on Paris law and particle filter with prior crack growth information
Get PDFGear has been widely used in the modern industry, and the gear reliability is important to the driving system, which makes the residual fatigue life prediction for a gear crucial. In order to realize the residual fatigue life of the gear accurately, a hybrid approach based on the Paris law and particle filter is proposed in this paper. The Paris law is usually applied to predict the residual fatigue life, and accurate model parameters allow a more realistic prediction. Therefore, a particle filtering model is utilized to assess both model parameters and gear crack size simultaneously. As a data-driven method, particle filter describes the dynamical behavior of model parameters updating and gear crack growth, whereas the Paris law, as a model-based method, characterizes the gear’s crack growth according to the physical properties. The integration of the Paris law and particle filter is proposed as a hybrid approach, which is suitable for nonlinear and non-Gaussian systems, and can update the parameters online and make full use of the prior information. Finally, case studies performed on gear tests indicate that the proposed approach is effective in tracking the degradation of gear and accurately predicts the residual gear fatigue life
Study on active vibration isolation system using neural network sliding mode control
Get PDFIn this paper, an active vibration isolation system based on hybrid algorithm is presented in a wide frequency band. Initially, a nonlinear magnetostrictive actuator model is used to establish the appropriate parameters by experiments, which make the actuator using in vibration isolation system work in a better linear dynamic performance, then the sliding mode algorithm modified by neural network, a hybrid algorithm is proposed as the active control controller, and its stability is also analyzed by Lyapunov theory. Furthermore, a dynamic virtual prototype model of active vibration isolation is established to carry out the co-simulation with Adams and Matlab/Simulink, and the results show that under the difference excitations, the neural network sliding mode controller exhibits a good control performance, and the active vibration isolation can effectively improve the vibration isolation effect, reduce the force transmitted to the base and broaden the vibration isolation bandwidth
Influence of support stiffness on aero-engine coupling vibration quantitative analysis
Get PDFThis paper investigates the whole aero-engine coupling vibration, as a rotor tester to be the research object. The rotor tester system is composed of two mountings, stator system, support structures and the rotor system. The modal experiment of the whole tester under the condition of mounting in the test room is carried out. The finite element (FE) model of the rotor tester is built, and the model was modified and validated according to the modal test results. A rotor-stator coupling factor and a section rotor-stator rubbing risk coefficient are proposed, the influence of the support stiffness values on the engine vibration characteristics, such as natural frequencies, modal shapes, rotor-stator coupling degree, and stator-rotor rubbing risk degree at compressor and turbine section is quantitative studied. Results show that the support stiffness contributes to the rigid body modal shapes greatly and to the rotor bending ones slightly. The factor and coefficient defined in this study are both reasonable, and they can reflect the corresponding characteristics exactly. Moreover, the effect of the supports stiffness values on the rotor-stator coupling degree and the rotor-stator rubbing risk degree is nonlinear. The rotor-stator coupling factor and the section stator-rotor rubbing risk coefficient proposed in this study provide a new way to quantitatively research the whole engine coupling vibration
Numerical study on axial vibration of water-lubricated small thrust bearing considering grooved pad
Get PDFThis paper presents the effect of pad with transverse grooves on the axial vibration for a small thrust bearing under water lubricated. Due to downsizing of electronic devices, the component part such as the thrust bearing in the micro fabrication becomes small size. Therefore, to study the characteristic of vibration for a small thrust bearing under water lubricated is significant for high precision machining. The hydrodynamic lubrication model was used to predict the water film thickness, the water pressure profile, and the bearing stiffness. A finite difference method (FDM) and a Newton-Raphson scheme are employed to achieve numerical results, i.e. the water pressure distributions, the water lubricating film thicknesses and the bearing stiffness under the variation of groove depths. The grooved shape of pads, that examined in this paper, was elliptical shape. The equation of motion under the impulse excitation considering in the axial vibration for a small thrust bearing was solved by using a Runge-Kutta method. The numerical results showed that the use of elliptical transverse grooves is effective to increases the fluid film stiffness and the maximum displacement in the axial vibration is able to be reduced
Rolling bearing health status assessment based on ITD-GMM method
Get PDFThis paper proposed a Rolling bearing health state assessment based on ITD-GMM method to fully dig the favorable information of the vibration signal from the rolling bearing with decline trend. By data analytic, the six components of vibration signal were calculated, and each component has three feature vectors. Finally, the performance of rolling bearing was quantified, and the curve of performance was acquired. The experimental results indicate that the method is feasible and effective for the assessment of rolling bearing
Study on coupling effect between the time-varying gear backlash and the different time-varying mesh parameters on the gear system
Get PDFThe vibration excitation of the rolling mill mainly comes from the gearbox in the process of rolling strip, and the meshing excitation is the main excitation factor of the gearbox. And the gear backlash plays an important role in the meshing excitation. However, the backlash is inevitable in the process of designing the gear system. Therefore, it is important to select the appropriate gear backlash to reduce the vibration amplitude of the gearbox, to improve the rolling speed and the quality of the steel strip. So, in this paper, the effect of the different variation amplitudes for the time-varying gear backlash (TVGB) on the vibration characteristics of the gear system under various mesh parameters is studied. A new formulation for calculating nonlinear damping and time varying meshing stiffness is applied in this coupling model. The results show that increasing of the load torque, the damping ratio, the system parameter or decreasing the directional rotation radius variation or kinematic transmission error caused the effects of variation amplitudes for the (TVGB) on the dynamic characteristics of the gear system to decrease. Test data from a gearbox experimental table verifies the accuracy of the model. The model is shown to be capable of simulating the mutually coupled effect between the backlash and the different parameters on the gear system. So, the new coupled model can be used as guide to select the appropriate gear backlash values for the rolling mill under different operating conditions