for example

Axel Vogt — Fri, 19 Feb 2010 01:18:09 Z

I do not know what you mean by sum of Bessel functions or what you expect to see, but for example you can go as follows:

  sin(t);
  convert(%, hypergeom, include=all, only=sin);
  convert(%, Bessel);

which expresses sin as BesselJ(1/2,t)*sqrt(t*Pi/2)

Perhaps the following is your desired monster:

  myExpr:=sin(c + I * (sin (d + k * sin(t))));
  convert(myExpr, hypergeom, include=all, only=sin);
  convert(%, Bessel);
  convert(%, BesselJ);

MaplePrimes - answers and comments on Question, Bessel simplification?