Tian Yun Li

The Vibro-Acoustic Characteristics of the Cylindrical Shell Partially Submerged in the Fluid

The characteristics of the sound radiation and vibrational power flow of the partially submerged cylindrical shell under a harmonic excitation are studied. The approximate acoustic boundary of the free surface is used to solve the fluid domain. The structure-fluid coupling equation is established based on the Flügge and Helmholtz theories. The far-field sound pressure is calculated and compared with that in infinite field. It is found that the far-field sound pressure presents large gap in different immersion status in the presence of the free surface while the results of the input power flow in these cases have less differences.

Flow-Induced Noise Simulation Based on LES/Lighthill Hybrid Method

A hybrid numerical method of combining Large Eddy Simulation (LES) and Lighthill’s acoustic analogy theory is utilized to simulate the flow-induced noise at low Mach numbers. The aerodynamic noise generated by flow through a cavity, which is similar to a valve, is simulated and the results are validated by comparing with the open literature. In the simulation, the turbulent flow is computed with LES. After this, the flow field simulation results are used to compute the flow-induced noise with Lighthill’s acoustic analogy theory based on the commercial software ACTRAN. Finally, the simulation results of the flow-induced noise, including the sound pressure level and the peak frequencies, are analyzed and compared with experimental data. It is validated that the hybrid method of combining LES and Lighthill’s acoustic analogy theory used in this paper is feasible and reliable in engineering applications.

Free Vibration Analysis of Fluid-Filled Elliptical Cylindrical Shells

A method is presented for the free vibration analysis of finite fluid-filled elliptical cylindrical shells with variable curvature. Based on the Goldenveizer thin-shell theory, the vibration equations have been expressed as a matrix differential equation by using the transfer matrix and the fluid-loading term is represented as the form of Mathieu function, the transfer matrix is determined by use of the mid-Magnus series method. The natural frequencies are calculated numerically in terms of the matrix elements with a combination of appropriate initial guess and Lagrange interpolation method. The results of the degradation model obtained by the present method are compared to those of existing literatures. It is shown that the present method is highly accurate and the results are reliable. The sensitivity of the frequency parameter to the ellipticity parameter and the length of the shell are investigated respectively.

Vibration Isolation Characteristics of Euler Strut Spring Used in Low Frequency Vibration Isolation System

Recently, the Euler strut is used as the supporting spring in the low frequency isolation. An Euler spring is a column or strut of steel material which is compressed elastically beyond its buckling load, which makes the ratio of the isolated mass to the mass of the supporting spring maximum, and greatly increasing the internal resonant frequencies of the isolator. In this research, the unique mechanical properties and the expressions of the displacement transmissibility of the Euler strut are deduced. The influences of structural parameters of the strut on the stiffness and vibration isolation characteristics are investigated in detail. The results show that the Euler strut has the potential in low frequency vibration isolation, and the length and breadth of the strut can influence the stiffness, transmissibility and critical loading mass respectively.

Vibration Characteristics Research of Finite Cylindrical Shells Semi-Submerged

A significant amount of research on the vibration and sound radiation of the cylindrical shell has been carried out and reported. The cylindrical shell was usually assumed to be submerged in an infinite fluid. However, the fluid region surrounding the cylindrical shell is bounded. Free vibration and forced vibration characteristics of finite cylindrical shells semi-submerged are studied in this paper, based on energy functional variational principle. The combined form of the triangular series and the Fourier series is used for the displacement of the cylindrical shell, then the orthogonality can be used to eliminate the other two directions after the variation, and only the radial displacement is kept. The relationships between the amplitudes of fluid load and the amplitudes of the radial displacement are established by the orthogonal processing of the continuous conditions of the solid-liquid coupling contact surface and the boundary conditions of the free liquid surface. Finally, the fluid structure coupling control equation is obtained. The results show that the method is correct and effective, in addition, providing a new thought for solving similar problem.

Vibrational Frequencies Calculation of Fluid Conveying Pipes Based on Fluid-Structure Coupling and Acoustic-Structure Coupling Models

Two coupling models, the fluid-structure coupling and the acoustic-structure coupling, have been studied in this paper, in order to describe the free vibration of a fluid-filled cylindrical shell under internal pressure from two different angles. For both models, a new approach to solve the characteristic equation is presented, using the Galerkin method to obtain the natural frequency of each mode. The comparison shows the results of two models are in good agreement. Although the two models are based on different mechanical theories, the mathematic essences are confirmed to be the same, both derived from Bessel functions.

Nonlinear Input Power Flow Analysis of a Plate with a Breathing Crack

Plates are commonly used in engineering structures. However crack is the most common form of damages in the plate structures. The crack in the plate will open and close during vibrational cycle, making the cracked structure with nonlinear dynamic characteristics. Based on vibrational power flow theory, the nonlinear dynamic analysis of a plate structure is carried out. The contact elements are used to simulate the nonlinear behavior of the breathing crack. Aiming to study the input power characteristics and the super harmonic resonance of a breathing cracked plate which is under the resonant excitation. By the finite element calculation, the structural input power curve is analyzed, which provides a theoretical basis for the damage identification of cracked structures.

Active Control of Input Power Flow to the Cylindrical Shells Based on Piezoelectric Actuator

The dynamic models of the infinite cylindrical shell with integrated piezoelectric actuator are derived firstly in this paper, then, the total input power flow is calculated and expressed as the Hermitian quadratic form to act as the objective function to implement the control. The optimum set of secondary force is obtained by using feed-forward quadratic optimal theory, and the total input power flow with control was calculated for different locations of the actuator. The results show that different axial and circumferential locations will induce different influences on the control effect, and the results are greatly related to the vibration type and the circumferential mode.

Optimization of Pendulum for a High-Impact Shock Testing Machine with Medium Weight

Collision impulse to pendulum shaft is tend to be generated when hammer impacting the anvil. In order to eliminate the collision impulse and find a preferential size of the pendulum, based on the rigid body dynamical model, the conditions of the coincidence of the center of strike and the center of percussion are established; calculation formula of the distance between the axis of the pendulum shaft and the center of percussion is derived. By selecting certain geometric parameters of the pendulum as design variables and transferring the multi-objective nonlinear optimal design problem into single objective problem, a mathematical model of the optimal design of the pendulum is established. Matlab optimization toolbox is utilized to calculate the model, and a reasonable result is obtained. The work of this paper has considerable significance in the far field of engineering design.

Vibrational Power Flow Analysis of Stiffened Plate and Shell Structures

In this paper, the vibration and power flow characteristics of stiffened plate and cylindrical shell structures are investigated by using finite element method. The power flow formulas of basic shell structural elements are given at first. Then a simply supported plate and stiffened plate’s input power flow characteristics and power flow vectors are investigated. The effects of stiffeners in plates are discussed. For a simply supported cylindrical shell, the influence of the structural damping, viscous damper and stiffeners on the cylindrical shell’s input power flow characteristics and propagated power flow characteristics are discussed in detail. The power flow vectors are visualized to reveal the distribution of energy in the shell structures. Some useful conclusions are drown and helpful for the vibration control of plate and shell structures.