The Sufficien Condition of Virtual Transmitting BoundaryStability and Near Source Instability Mechanism

• 1、School of Architecture Engineering, Northeast Dianli University, Jilin, Jilin 132012

Abstract：Give a simple example and illustrate the near source instability mode of 2-order transmitting boundary and near source without instability behavior of 2-order best-fitting transmitting boundary. Combining virtual wave frequency concept with relevant theory and numerical analysis results, under precondition of time-space discrete step satisfy the inner domain wave computation method stability criteria, following basic conclusions are deduced: 1、The sufficien condition of virtual transmitting boundary have not high frequency oscillation instability and low frequency drift instability are: the maximum virtual wave frequency of opened system less than the highest natural frequency of relevant closed system and the minimum virtual wave frequency of opened system greater than basic natural frequency of relevant closed system. 2、The mechanism of virtual transmitting boundary instability is: the constant valuation apparent wave velocity in the normal direction Ca to transmitting of arbitrary normal outgoing wave have certain frequency-selecting affects, only by harmonic wave in narrow-band of Cxk and Ca sufficien close can get ideal transmitting, the amplitude of other harmonic wave of far from this narrow-band is continuous superimposed amplification by virtual reflect wave, and finally lead to instability. 3、The mechanism of virtual best-fitting transmitting boundary restrain instability is always guarantee harmonic wave in incident wave close to predominant frequency get ideal transmitting, and almost completely restrain near source instability phenomena.

Keywords： computational solid mechanics near source wave transmitting boundary instability mechanism virtual wave frequency sufficien condition of stability best-fitting transmitting boundary.