Tracked with pneumatic stiffness, transfer equation of external pressure to internal and Helmholtz frequence, frequence-shift characteristics for roof structures with idealized closed wall and with wall having opening, and similarity criterion theory for pneumatic stiffness are discussed, the key action of wall flexibility in theoretical study is considered.

Based on the sound absorption mechanism of Helmholtz Resonator,the advantage of soft tube length is fully used in the new structure,and thus the low-frequency noise can be controled easily.

A new structure which lays sound absorption materials on the surface of Helmholtz resonator with extended necks is proposed in this paper,and then the theoretical analysis and numerical simulation of its sound absorption characteristics are done.

According to the special no-zeros structure matrix derived from the Helmholtz equation,an effective ILU decomposition method is presented.

Based on 2-deminsion wave equation using Fourier transform this paper gives Helmholtz equation and the generalized WKB,which is a new approximation method for solving difficulties in wave field analogy and difficulties of inversion in seismic exploration.