Tóm tắt:

In finite element method (FEM), the selection of boundary condition types will affect on the results of a model. The boundary condition depends on the type of boundary elements. In the wave propagation in rock/soil medium such as blast vibration in tunnel blast, fixed or roller or non-reflecting boundary conditions can be used. The boundary element, used fixed or roller boundary conditions, is finite elements. The wave may be reflex when propagating to boundary. NonReflecting Boundary Conditions (NRBCs) are used to model a problem with an infinite domain by using a finite model. Many types of NRBCs are available, but, in general, they all act to prevent energy radiating toward infinity from being reflected back into the model at the finite boundary of the model. Infinite elements are another method of imposing a NRBC in a finite element method model. The concept of infinite elements is to use finite elements to define a semi-infinite domain at the boundary which is desired to be a NRBC. In this paper, the finite element method is used to study the blast wave propagation by using two types of boundary conditions: fixed condition and nonreflecting boundary condition. In the first model, there are only finite elements (FE). On the contrary, both finite and infinite elements (FE+IE) are used in the second model. The comparison of the results of these models is presented to show the effect of used element type.