Research On Structure Damage Identification Method Of Additional Mass Considering The Effct Of Fluid

Fluid-structure interaction(FSI)is a kind of phenomenon of interaction between movable or deformable structures and internal or surrounding fluid flows.Structural engineers pay more attention to fluid-structure coupling vibration in dams,bridges,tanks,ships and other structures.The vibration mechanism of these structures is complex,and structural health monitoring for these structures has always been a hot topic in the field of civil engineering.Damage identification is an important part of structural health monitoring.Vibration-based damage identification method is the most commonly used method to characterize structural damage status by selecting reasonable structural physical parameters.In this paper,a damage identification method based on additional mass and virtual mass is adopted for structures with fluid-structure coupling vibration.The main research contents are as follows:(1)Firstly,the vibration mechanism of structure with solid-liquid coupling effect is introduced.The vibration equation of immersed structure is deduced by fluid finite element method combined with structural finite element method.The effect of fluid on structure can be equivalent to "additional mass".Then,the numerical simulation model of the immersed cantilever beam is established,the additional mass matrix of the immersed cantilever beam is derived and calculated,and the frequency of the immersed cantilever beam is calculated.Finally,the sensitivity-based method is used to identify the damage of the numerical simulation model.The results show that the additional mass can well consider the influence of immersion on the structure.The results of damage identification at different immersion heights are very accurate,which shows that the damage identification method has high applicability and reliability.(2)Using a submerged beam test model,the damage identification of each substructure is carried out by adding mass to each substructure.Firstly,the natural frequencies of the immersed cantilever beam are tested,and then compared with the numerical simulation results to ensure that the finite element model of the immersed cantilever beam agrees with the dynamic characteristics of the experimental model.Then the damage identification is carried out under the four conditions of 0.2m-0.8m immersion.The experimental results show that the damage location of immersed cantilever beam can be accurately identified by using additional real mass,regardless of whether the immersion height is low or high.At the same time,the experimental results and damage identification results show that the additional mass damage identification method proposed in this paper is effective in numerical simulation and test.(3)Additional mass damage identification method is further developed.Additional virtual mass method is used to identify the damage of liquid storage tank structure.Firstly,using the software ANSYS and its internal FSI,the finite element model of the tank and the internal liquid are established.By using the fluid element to simulate the internal water of different heights,the change of natural vibration frequency is studied.Then,using a tank structure test model,the frequency results of the test model and the ANSYS finite element model are compared according to the same working conditions as the numerical simulation,so as to ensure the numerical value of the tank.The dynamic characteristics of the simulation model and the experimental model are in good agreement.Then,the damage identification of the test model is carried out by means of additional virtual mass method.The experimental results show that the method has good feasibility at all liquid level heights,and can accurately locate the damage location.At the same time,combined with ANSYS finite element model,the damage degree can be identified.