Applied Mechanics and Materials Vols. 105-107

Abstract: Support vector regression is used to establish a kind of patch near-field acoustic holography. The regression functions are constructed by treating the measured data on the patch holography as training samples, and then the data outside the measurement aperture are extrapolated. The experimental results show that the extrapolation of the sound pressure outside the smaller initial hologram aperture may be realized easily and effectively, and the reconstruction accuracy is satisfactory.

Abstract: For the relatively strong vibration caused by a three-wheeled motorcycle exhaust system and raised the level of the noise in the whole motorcycle, this paper combines the experimental modal analysis method and finite element analysis (FEA) method, establishes finite model of the exhaust system, finishes the experimental modal analysis and transient response analysis based on Hyperworks software and laboratory equipment, and obtains six natural frequencies and mode shapes. Comparison has been made between acceleration RMS changes before and after the mounting points changed with the transient excitations. At the end, the document also verifies better results after the improvement and found the basement of reducing noise in the next step.

Abstract: The vibration is a high-precision machine tool components in the design of the major issues, facing its precision has a great influence, so column parts of its modal analysis is necessary. Creating three-dimensional finite element model of the column, using finite element analysis software ANSYS modal analysis of the column, which can reached the first five natural frequencies and mode shapes. Column Part of our understanding of dynamic performance and improve the machining accuracy is helpful. Modal analysis method is the dynamic performance of the column on the main approach, which mainly is to determine the vibration characteristics of the column that is the natural frequency and vibration mode, which we can determine the modes of processing accuracy, and thus the relevant parts of the machine column can be optimized so that it meet the requirements.

Abstract: A calculation model for Truss Spars motion response is established under the wave action by combing the potential flow theory and the modified Morison equation. The high order boundary element method is used to acquire the wave exciting force and the relevant hydrodynamic information. By numerical simulation, the surge, heave and pitch s are obtained, and the parameter analysis for influence of Morison drag coefficient on responses are conducted. The calculated results indicate that the surge and pitch motions are only sensitivity to the drag coefficient in the low frequency range, and consequently the viscous damping would play an important role when the platform undergoes 2nd order wave slow drift force. For the heave response, the heave plates installed on the Truss Spar provide large vertical viscous damping which distinctly affects the heave .

Abstract: In the paper the shear wave velocity and Poisson’s ratio profile are studied using the MASW test. Slant stacking was adopted in experimental dispersion curve constructing. Theoretical dispersion curve can be constructed by thin layer stiffness matrix method. A real-parameter genetic algorithm is required to minimize the error between the theoretical and experimental dispersion curves. Test results show that spectrum using slant stacking shows the fundamental mode of Rayleigh wave in the frequency range from 15 Hz to 50Hz. To reduce the error of experimental and theoretical dispersion curve using real-parameter genetic algorithm is feasible. The results also show that the strata of Lu-Liao-His Earth Dam can be modeled as 3 soil layers with an underlying half space.

Abstract: Thin-walled structures of future hypersonic flight vehicles will encounter complex loadings and exhibit obvious nonlinear responses. The thermal loads from high speed flow or engine jet flow can cause thermal buckling of thin-walled structures, such as Thermal Protection System (TPS). If the structures are loaded with intense acoustic loads simultaneously, large deflection nonlinear response, including snap-through, can be induced. Snap-through will give rise to large amplitude stress cycles and non-zero mean stress, which can lessen the fatigue life markedly. Starting from Hooker’s Law with thermal components, the large deflection governing equations of motion for simply-supported plate under thermo-acoustic loadings are derived. The partial differential equation (PDE) of motion which is difficult to solve is then transformed with Galerkin’s method to the system of ordinary differential equations (ODE) under modal coordinates. The displacement responses under different combinations of temperature increments and sound pressure levels are calculated by employing Runge-Kutta method. Typical thermo-acoustic responses are predicted: 1) random vibration around pre-buckled equilibrium position, 2) persistent snap-through between post-buckled positions, 3) intermittent snap-through, 4) vibration around one of the two post-buckled positions. By dividing the restoring force term in the equation into linear term and nonlinear one, the evolutions of each term are obtained to illustrate the mechanism of thermo-acoustic response and the contributions of each force, including shear force, thermal force and membrane force. Thus a further insight into thermo-acoustic response has been achieved.

Abstract: The hydraulic suspension system is an important system of modular assembled trailer, which is used to turn trailer, control chassis frame height and make trailer comfortable. Therefore, the parts durability of suspension system has been required for service life and safety starting in design. Durability analysis on the parts of hydraulic suspension system is performed in this paper, including linear static analysis and fatigue life analysis. The vibration characteristics of finite element model are determined, which is verified by vibration measuring experiment. The fatigue life of suspension system parts is calculated by stress-life method with the effects of the road roughness and trailer speeds are considered.

Abstract: As the capacity and water head of large hydropower projects become higher and higher, the flow-induced structural vibration of powerhouse becomes a very important problem for the design and operation process. Especially as the water head and the running speed are much higher for the pump-turbine than the general turbine, the hydraulic exciting vibration is very remarkable. In this paper the simulation results of free-vibration characteristics of powerhouse structure for different types were concluded and the frequency behavior of the pressure fluctuation in spiral case and draft tube were discussed. The structural dynamic responses under hydraulic exciting were presented including the dynamic responses of displacement, velocity, acceleration and stresses. Based on the vibration criterion of the powerhouse structure, the vibration evaluation was made.

Abstract: The accurate identification of modal parameters is the core content in the experiment modal analysis of structure. The effective and accurate collection of vibration dates comes to be as the premise of high precise identification. This paper presents a new method of data collection in modal parameter identification. By high-speed camera, time series images of vibration were obtained; Then, the images collected were processed using digital image correlation method, and the time-displacement graphic on vibration direction of some pixels selected was got; Finally ,the time-domain signal was post-processed based on the complex Morlet wavelet transform, and the modal parameters were got. By a specific experiment, the method was proved feasible and effective.

Abstract: The paper describes modal analysis of lifting platform usually used in theatre technologies. The platform itself consists of several components mutually connected by joints. The behavior of particular joints can be linear or nonlinear. The connection of two main parts - tables and pillars of lifting platform-must be considered as nonlinear because the force transfer between these parts can occur only in one direction. Since standard modal analysis is in principle linear, the method of linear description of nonlinear behavior has to be proposed. The contribution presents such method using application of three different boundary conditions which allow describing the nonlinear behavior of system by tools of linear analysis. Consequently, the modal analysis of the entire system is performed for all three types of boundary conditions. On the base of mode shapes visualization the proper mode shapes are extracted which satisfy the real behavior of the lifting platform.