Theoretical And Experimental Research On Vibration Properties Of Composite Foundations

The prediction and control of noise and vibration is a very important field in ship engineering. The research and application of related technology in this field is very significant to improve the quality and safety of merchant ship, or battle effectiveness and survival capability of military ship. The research on the control of ship vibration and sound radiation in the water caused by mechanical excitation has a long history and a lot of results all over the world. In order to improve the effect of vibration and noise reduction, it is very attractive to develop new vibration isolation technology based on composite structures dynamic characteristics.Marine mechanical equipment foundation is the most important mechanical vibration transferring route to ship hull structures. In order to improve the effect of foundation on vibration and noise reduction, the composite foundation, which is different from traditional steel foundation, is designed in this paper. And its vibration properties are studied by theoretical and experimental methods. The paper consists of the following aspects:(1) A literature review of the related researches—The whole frame of mechanical noise control are given based on acoustic concepts. The theories of flexible vibration isolation systems are presented based on mechanical design concepts. The theories of structure-borne sound propagation are also presented based on structure design concepts. Finally, the researches on damping of fiber reinforced polymer composite are reviewed.(2) Investigation on dynamic characteristics of two pole elements by matrix description approach—Relationships between input state vectors and output state vectors of continuous elements (Euler-Bernoulli beam, rod) and discrete elements (mass, spring, damper, rigid body) are deduced respectively in element coordinating system. Analytical formulae of forward transfer matrix, reverse transfer matrix, impedance matrix and mobility matrix are derived separately when the positive definition of state vectors are assumed the same. The characteristics of the four matrices are studied. Analytical formulae of the four matrices of a general beam are given by combining the corresponding formulae of Euler-Bernoulli beam with those of the rod. Numerical examples show that the results respectively by the present method and those of the finite element method are nearly the same. When frequency is close to zero, the relationship between the displacement impedance matrix and the static stiffness matrix are established. The relationship between dynamic matrix description method and static matrix description method is discussed.(3) The impedance synthesis method of built-up structures—The basic and generalized definitions of mechanical impedance are given. The four poles parameters matrices and algorithm of passive linear vibration mechanical systems are also given. The impedance synthesis method is introduced. The analytical formulae of simple model are deduced by transfer matrix method. The longitudinal vibration equations of the anti-vibration foundation are achieved both by transfer matrix method and mobility matrix method. The analytical formula for the longitudinal force transmissibility is given. Two approaches yields similar results, but the process of transfer matrix method is simpler. The transverse vibration equations of the anti-vibration foundation are also deduced using transfer matrix method. The analytical formula for the transverse force transmissibility is consequently given. It is showed that matrix description methods facilitate solving dynamic questions using computer programming. Analytical formulae in this paper can be applied in dynamic design of the anti-vibration foundation to achieve good precision with less computation.(4) Dynamic experiment and analysis of a composite rod—The formulae of driving point impedance and transfer impedance of the rod under different boundary conditions are deduced. The influences of damping and material parameters to the impedance are analyzed. The composite rod is tested on an impedance platform facility with single point excitation and the mechanical impedance data are obtained. It shows that theoretical results agree with the experimental data when excitation frequency is higher than 100Hz, which also validate the measurement method. The initial modal parameters are then identified with the experiment method, analytical method and hybrid method. After these, the optimal modal parameters are identified by two nonlinear least square methods called Levenberg-Marquardt and Trust region algorithms respectively. Research work show that the mechanical impedance data, which are calculated from the discrete system modal with single degree of freedom and based on optimal modal parameters, coincide well with the experimental result, and this modal can describe the dynamic properties of the composite rod within testing frequency range very well. (5) Dynamic experiment and analysis of a composite T joint—The typical marine T joint is designed. The T joint is tested on the impedance platform facility with the help of special designed tools and the positive and negative mechanical impedance data are obtained. The discrete system mathematical modal of T joint is obtained using the method developed in the fourth chapter.(6) Dynamic properties of the adhesive joint—The linear dynamic properties of the adhesive joint in normal direction are studied with theoretical and experimental compound method. The impedance matrix can be numerically simulated using the combination of three"bush"elements based on viscoelastic theory. Numerical example shows that the results from FEM method coincide with those from transfer matrix method. The parameters of"bush"elements are used in the seventh chapter.(7) Experimental and simulation researches on dynamic properties of the composite foundation—The dynamic properties of two systems, that is, the composite foundation installed in a framed cylinder, and equivalent steel foundation installed the same cylinder, are studied respectively with experimental and FEM method. Results show that the computer and test aided modeling method of the composite foundation are reasonable. The vibration isolation effect of the composite foundation is better than that of the equivalent steel foundation.(8) Summary and forecast—The research contents in the dissertation are summarized. The future research contents of related fields are proposed.The innovation research works in the dissertation are primarily as follows:(1) To improve the efficiency of mechanical vibration isolation, a new idea of using composite foundation in place of steel foundation is presented.(2) The composite mechanical equipment vibration isolation foundation, which is a combination of composite web plate and steel anti-vibration mass, is presented.(3) Based on the wave theory, the four poles parameters matrices of the Euler-Bernoulli beam and rod are deduced using the shape functions related to frequency. The computer programs are made to calculate special numerical examples. The results of the programs are almost the same with those of ordinary FE programs. For the simplified theoretical model, with the deduced four poles parameters matrices of the Euler-Bernoulli beam, rod, rigid body and mass, the system formulae of anti-vibration foundation are deduced, which provide simple tools for the design of anti-vibration foundation. (4) Based on the computer and test aided modeling idea, the dynamic modeling method of the composite foundation is presented. The ordinary FE programs are used to model non adhesive parts. The experimental data in frequency domain are obtained from an impedance platform facility. Then two nonlinear least square methods called Levenberg-Marquardt and Trust region algorithms are used to carry out parameter identification. The reasonable system formulae of specimen are achieved. The impedance matrixes of the adhesive parts, which are obtained from the system formulae of rod and T joint, are numerically simulated using a combination of three"bush"elements in Nastran program.(5) The composite foundation and steel foundation are researched using experimental and FEM methods. The results show that the dynamic modeling method of the composite foundation is reasonable. Compared with steel foundation, the vibration isolation effect of the composite foundation is very good.