Building Structure Dynamic FEM Based On Optimization Of Mass Distribution

Vibration system modeling is the basis of structural dynamic analysis. Finite Element Method (FEM) is used most widely to model a structure. This method will first discretize the continuum elastic medium, and then establish a principle of the overall energy equation, using numerical methods to solve the parameters of structure of at last. It is very difficult to build a dynamics finite element model for large and complicated structure exactly, because it needs engineers spent a lot of time and effort to build and iterative update by the result of mode test. The static's finite element model is always built early in the process of structure finite element analysis, so the dynamic FEM can be obtained by updating some static's finite element model. If the mass distribution and damping property established suitably, we can update static's finite element model to dynamics model with relatively less workload and greatly save time and funding.This paper presents a calculation procedure, which is transforming static mechanical model into dynamic model according with the result of mode test, based on optimizing the distribution of mass. By calculating the sensitivity coefficients of mass of every node to mode frequencies and shapes, an optimization model can be established, and its objective function is minimizing each node mass changes, and the constraints are the system's weight, the position of center of gravity, each I-Principal, and mode frequencies and shapes by mode test. Examples of a standard aircraft model and a complicated structure of wing certificate this method and shows that this quickly modeling method for structural dynamics FEM and analysis has important engineering value.