NUMERICAL SIMULATION OF THE UNIT IMPULSE FUNCTION ACOUSTIC SIGNAL PROPAGATION IN DRILL STRING STRUCTURE USING FINITE DIFFERENCE METHOD

In order to realize transmission underground information, using acoustic as the carrier and using the drill string as the transmission channel, it is necessary to understand the transmission characteristics of different types acoustic wave transmited in drill string. The drill string is simplified as ideal periodic tube structure. Finite-difference method is employed to simulate and analyse the unit impulse function acoustic signal propagation in periodic tube structure. Based on the obtained time domain and frequency domain distribution of the signals, the following conclusions are given. The output end will receive a relatively long time signal under the excitation of the unit impulse function acoustic signal, the signal will decay with the increase of time, and maximum amplitude is less than the input signal; drill string channel structure is the comb filter structure; pass band exists resonant peak, peak number is associated with the number of drill pipe and joints. The simulation results have good consistency with similar research results and verify that the feasibility and validity of the mathematical model and numerical method adopted.