Method for forecasting inherent frequency of liquid-filled cylindrical shell

Abstract

The invention aims to provide a method for forecasting the inherent frequency of a liquid-filled cylindrical shell. The method comprises the following steps: establishing a free vibration equation ofthe cylindrical shell by adopting a Kennard thin shell theory; solving a Helmholtz wave equation under a cylindrical coordinate system, fluid acts on a cylindrical shell as a radial load, and a hydrodynamic model of the cylindrical shell is established; selecting an improved state vector; obtaining the relationship between the element displacement, the rotation angle, the force and the like of thetraditional state vector and the middle surface displacement according to the Kennard thin shell theory, so as to establish a conversion matrix between the improved state vector and the traditional state vector; introducing boundary conditions at two ends of the liquid-filled cylindrical shell to forecast the inherent frequency of the liquid-filled cylindrical shell. According to the method, thederivation workload of the first-order derivative equation and the transfer matrix and the possibility of derivation errors are reduced, the application range is wide, the implementation process is simple and convenient, and programming calculation is facilitated. The prediction precision is high, the whole solving process does not cause increase of the variable freedom degree number, and high prediction efficiency is ensured.

Description

technical field [0001] The invention relates to a natural frequency prediction method. Background technique [0002] Fluid-filled cylindrical shell structures are ubiquitous in buildings and ship piping systems, and there are many methods for predicting their natural frequencies. The transfer matrix method has become a common method for solving chain structure dynamics problems because of its advantages of less variable degrees of freedom and easy and quick solution. There are many applications in the problem. [0003] If the structural governing differential equations are written in the form of first-order differential equations, a simple relationship can be established between the state vectors of the starting point and the ending point using the transfer matrix, and the natural frequency prediction of the liquid-filled cylindrical shell can be performed by using the boundary conditions. Therefore, the calculation accuracy of the transfer matrix method mainly depends on ...

AI Technical Summary

Problems solved by technology

However, with the application of the transfer matrix method in the multi-degree-of-freedom system, the derivation of the first-order equation of the state vector becomes more and more difficult

The traditional state vector is generally composed of displacement, velocity, force, moment, etc., but the state vector cannot be directly obtained from the vibration equation, which makes the derivation process of the state vector first-order differential equation very complicated, not only increases the workload, but also often makes mistakes

[0004] Luo Wen (Luo Wen, Computational Research on Fluid-Structure Interaction of Conveying Pipelines. Master Thesis of Harbin Engineering University. 2014.) applied the transfer matrix method to solve the dimensionless natural frequency of the liquid-filled cylindrical shell, but its state vector first-order differential equation The derivation process is more complicated, and its transfer matrix is ​​a circumferential transfer matrix, which is different from the general transfer matrix along the length direction of the chain structure

[0005] Wan Haochuan et al. (Wan Haochuan, Li Yinong, Zheng Ling, Improved Structural Vibration Transfer Matrix Method, Vibration and Shock, 2013,32(1):173–177.) proposed a method using the improved transfer matrix method to calculate the Compared with the traditional solution method, the derivation and solution process of the solution proposed by them is simplified, but the influence of the internal liquid filling on the improved transfer matrix and natural frequency of the cylindrical shell is not considered.

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