Zhernokletov et al. approximation

This is an approximation of shock wave velocity - particle velocity dependences for shock Hugoniots of substances with normal density. It is given by:

D = a₀ + a₁U + a₂ / (1 + a₃U), up to 3 parts.

where D - shock wave velocity, U - particle velocity, a₀, a₁, a₂, a₃ - the coefficients. The approximations are constructed for more than 80 substances. There are 3 general types of approximations:

1. The dependence consists of 1 part (Pade approximation).
2. The dependence consists of 2 parts: lower (linear) and upper (Pade).
3. The dependence consists of 3 parts: lower (linear), middle (constant) and upper (linear).

Full reference: M. V. Zhernokletov, V. N. Zubarev, R. F. Trunin, V. E. Fortov, Experimental data on shock compressibility and adiabatic expansion of condensed substances at high energy densities, Chernogolovka (1996)