ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

1pPA13. Comparison of computer codes for propagation of sonic booms through the atmosphere.

James P. Chambers

Henry E. Bass

Richard Raspet

Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677

Robin O. Cleveland

Mark F. Hamilton

David T. Blackstock

Univ. of Texas, Austin, TX 78713-8029

NASA initiated an exercise to compare sonic-boom propagation codes. Three different codes developed at our two universities are compared here: SHOCKN (Mississippi), THOR (Texas), and ZEPHYRUS (Texas; developed by L. D. Robinson). Each code includes nonlinear steepening, absorption and dispersion (relaxational and thermoviscous), geometric spreading, and atmospheric stratification. All three codes calculate steepening in the time domain. The main difference is in the calculation of absorption and dispersion. SHOCKN and ZEPHYRUS use the frequency domain; the FFT is used to transfer back and forth between the time and frequency domains. ZEPHYRUS employs weak shock theory to reduce the number of FFT operations. All of THOR's calculations are done in the time domain. Code accuracy and effectiveness is judged by comparing ground level predicted waveforms (input waveforms are specified by NASA). The codes are capable of dealing with arbitrary atmospheric data. Results are presented here for uniform and isothermal atmospheres, with and without the effects of molecular relaxation. Early comparisons revealed discrepancies, which led to improvement of codes. Current comparisons show excellent agreement. Ground waveforms show surprising sensitivity to input stratification data. Some comparisons of code running time have been made. The FFT operations apparently make SHOCKN and ZEPHYRUS run more slowly than THOR. [Work supported by NASA.]