An Asymptotic Derivation of Weakly Nonlinear Ray Theory
نویسنده
چکیده
Using a method of expansion similar to Chapman Enskog expansion, a new formal perturbation scheme based on high frequency approximation has been constructed. The scheme leads to an eikonal equation in which the leading order amplitude appears. The transport equation for the amplitude has been deduced with an error O(ǫ2) where ǫ is the small parameter appearing in the high frequency approximation. On a length scale over which Choquet Bruhat’s theory is valid, this theory reduces to the former. The theory is valid on a much larger length scale and the leading order terms give the weakly nonlinear ray theory (WNLRT) of Prasad, which has been very successful in giving physically realistic results and also in showing that the caustic of a linear theory is resolved when nonlinear effects are included. The weak shock ray theory with infinite system of compatibility conditions also follows from this theory.
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