Damage Identification Of Storage Tanks Based On Additional Virtual Masses

In recent years,with the rapid development of world economy,demand s for Petroleum,natural gas and other chemical products have increased rapidly.And more and more tanks are in service,which makes the damage identification of storage tanks have received widely concern.Aiming at storage structure characterized by space symmetry,dense low modes and insensitivity to the local damage,the damage identification method of additional virtual mass was proposed using the idea that additional physical parameters increase the test data of frequency and improve its sensitivity.In this paper,the basic idea of the virtual deformation method(VDM)was introduced,and then the frequency response formula after putting the additional virtual mass was deduced.Then,this method was used combined with the spatial symmetry of the storage tank structure to preliminary determine the location of the damage by the distribution pattern of the frequency after putting the additional virtual mass.Furthermore,the sensitivity analysis of the finite element model was used to solve the damage degree by supposition.Secondly,the finite element model of the steel upright cylindrical tank with fix ends was simulated to illustrate and verify the effectiveness of the additional virtual mass method.Then the finite element model of the storage tank was established by ANSYS software,from which the element stiffness matrix and mass matrix were extracted.Then the MATLAB software was used to assemble the global matrix and model condensation was conducted by the Guyan condensation method where the normal degree of the tank wall was the major degree of freedom.Then,the relationship between the added virtual mass and the sensitivity of the tank model was analyzed,and the optimal mass of the added mass and the frequency with the corresponding highest sensitivity were determined by the relation curve and the sensitivity curve.Finally,the location of the damage was preliminary identified by the comparison of the damage identification coefficients,and the damage degree of the tank structure was identified by the sensitivity optimization method and the FE model.Then the experiment was carried out using the tank structure model.On the basis of the above theory,the damage location of the tank was judged in the empty tank.Then,the tank was filled with water of different height to study the relationship between the modal information and the liquid level height.Then,the frequency information was compared with the real mass and virtual mass,and the virtual deformation method was proved to be applicable in the liquid-stored state.Finally,the damage location of the tank structure model with different liquid level height was identified by the method used in empty tank damage identification,and the applicability of the method was also verified.