Abstract: In order to know the vibration characteristics of the vehicle body in white, the experimental modal analysis was performed by using LMS modal equipment. The basic principle of experimental modal analysis was introduced. Then, the first ten order modes were obtained within 100 Hz. The front several main modes were analyzed. The test results fully show that the car body in white has excellent first order torsional, bending and overall vibrational characteristics.
Abstract: Based on Kirchhoff hypothesis, the vibration equations of constrained damping plate are established and the equations are solved. Influence of the thicknesses of constrained layer and viscoelastic layer on structural vibration character are analyzed, the curves of natural frequency and loss factor with different thicknesses of viscoelastic layer and constrained layer are obtained. The figures indicated that it is not the more thickness of the viscoelastic layer and constrained layer the higher of the loss factor. Both of the thicknesses have optimum values, which are interact. The relationship between of loss factor and added mass is investigated. The results show that various thickness plans can obtain the same loss factor but very different added mass. So it is very necessary to optimize the thickness of viscoelastic layer and constrained layer to obtain the best damping effect.
Abstract: Based on fiber optic gyroscope technique new method of rotation angle testing in three-axis vibration is proposed in this paper, and the theory of fiber optic gyroscope is introduced as well. According to the measurement accuracy requirement, the angle testing system of FOG is designed by analyzing the environment of three-axis vibration. It was applied in experimental investigation of rotation angle in three-axis vibration with the FOG testing system and the real-time angular rate signal was processed by frequency analysis. The results of practical application show that it is feasibility and validity of angle testing method by means of FOG technique.
Abstract: As cars become more and more quiet the sound quality of rotary components such as car compressor becomes more important in the customer’s subjective perception of passenger car quality. This needs a new evaluation method which is not only the traditional method like sound pressure level but also Psychoacoustic Metrics to focus the specification of component sounds. This paper on one hand analyzed one car’s abnormal noise reason through the tests, found the main problem frequency band of the compressor, and on the other hand studied the compressor’s psychoacoustic metrics. In this paper the countermeasure of solving this problem was also given, and then noise level and psychoacoustic parameters are compared. Both objective evaluation and subjective evaluation showed that the compressor with the solution not only reduced the sound pressure level, but also improved the car sound quality greatly.
Abstract: The generalized elasticity is presented where a modified constitutive relation for the couple stress is proposed. A rigid-flexible coupled model is set up where three types of additional inertia forces along with their increments are elucidated in the model. The finite element formulation is developed with the use of the constrained variational principle. As an example, a dynamic analysis on a rotating cantilever is numerically carried out. The dynamical responses of the displacement and rotational angle at the free end, the stress and couple stress at the fixed end of cantilever are presented. An idea of critical angular velocities is proposed to insure system stability. The displacement trajectory of the free end of cantilever is approached and the dynamic stiffening problem is discussed.
Abstract: This paper presents experimental results for the hydrodynamic forces on several different bodies oscillating in the vicinity of the free surface. Firstly, results for two horizontally symmetric bodies, a flat plate of finite thickness and a cylinder, are presented. Results show that these two different shaped bodies react in different ways with the free surface and are likely to have different added mass associated with them. Secondly, results for two thrusting bodies, a NACA0012 symmetrical foil and a NACA4415 cambered foil, show that the free surface amplifies the thrust produced by a vertically oscillating foil. Results showing the effects of spanwise flow are also presented and indicate spanwise flow is negligible at zero translational velocity and so the use of endplates of the foils was unnecessary. The conclusion of these experiments is that a submergence of 5 chord lengths is sufficient for the horizontal and vertical forces on the vertically oscillating objects to be unaffected by the free surface.
Abstract: Finite difference method and transfer matrix method were used to get spectrum response curve of unit impulse function signal to research the spectrum characteristics of acoustic traveling though the drill string. Similarities and differences of the two methods were discussed through analysis of spectrum curve get from the two approaches. The results show that: The distribution of band-pass and band-stop get by the two calculating methods is basically the same, some transmission coefficient of finite difference method is less than 1, is not completely transmission phenomenon. Analysis of the reason for this is that the transfer matrix method is an analytic method, finite difference method is a numerical algorithm. From the calculation precision of speaking, analytic algorithm is higher than that of numerical algorithm. But to verify the reliability of two methods needs based on laboratory experiment or field test.
Abstract: An acoustic wave propagation simulating method based on semi-symplectic theory is developed. The acoustic wave equations with n degree of freedom in space domain of Lagrange System which are obtained in FEM are converted to equations with 2n degree of freedom in Hamiltonian System with the Legendre’s Transformation. These equations are then integrated with the Precision Integration algorithm in time domain. The algorithm is employed to simulate the acoustical wave propagation in two dimensional medium. We demonstrate the remarkable stability of the presented algorithm by comparison of the results of the FEM and that of the Semi-Sympectic Theory under different time steps. The results presented in this paper show that the proposed algorithm is effective, accurate, and not sensitive to time step.
Abstract: In the present paper, we investigate an impulsive predator-prey model of integrated pest management(IPM) strategy. Other than the general Holling's functional response, an S-shaped mixed functional response is considered, simultaneously, we model this system assuming that the releasing of nature enemies and spraying of pesticides are impulsive at different fixed moment, which is more realistic comparing with at the same time. With the help of Floquet's theorem, small amplitude perturbation skills and comparison theorem involving multiple Liapunov functions, we show that under some sufficient conditions, the system exists an oscillative pest eradication periodic solution, which is local stable and globally attractive. Otherwise, the system is permanent. This result(threshold) provides us a very useful information for the control of ecosystem.
Abstract: The present paper focuses on the fluid-structure interaction of flexible marine propellers. The aim is to develop a simulation method to predict the hydro-elastic performance. To compare with the experimental results, the geometry of propeller DTMB4119 is used. The solution procedure first computes the hydrodynamic pressures due to rigid-blade rotation via the BEM (Boundary Element Methods, BEM). The hydrodynamic pressures are then applied as external normal surface traction for the FEM (Finite Element Methods, FEM) solid model to obtain the deformed geometry. The commercial FEM code is then used to solve the equation of motion in the rotating blade-fixed coordinate system. User-defined subroutines are developed to generate FEM models using 8-node linear solid volumetric elements. Iterations are implemented between BEM and FEM solvers until the solution converges. This study shows that the simulation method developed in this paper is reasonable.