In this paper, by means of the developed two dimensional radiation magneto-hydrodynamic Lagrangian code, the dynamic hohlraums, which are consisted of tungsten plasma shell and low density foam cylinder with or without an embedded hard foam layer on the cylinder and a capsule in the center, are simulated. We understand the effects of the hard foam layer on the hohlraum radiation field, and the coupling of capsule and hohlraum for the capsule fusion, by comparing the simulated results of different configuration hohlraums. After applying a hard foam layer on the low density foam cylinder, the time, uniformity, and the first peak value of radiation field, receipted by the capsule, is delayed, increased, and reduced, respectively. Furthermore, the radiation temperature on the capsule surface is increasing smoothly, and the dwelling time of the hohlraum is prolonged. For a driven current of peak 50 MA and full rise time 300 ns, the dwelling time can be longer than 10 ns, and the radiation temperature at the late time can be higher than 350 eV. The time variation of the radiation temperature is close to that measured in American National Ignition Facility (NIF) hohlraum in which the capsule was imploded and the fusion energy of 1.37 MJ was released. After embedding a capsule into the center of low density foam cylinder, the radiation temperature receipted by the capsule during the late process increases. This implies that both the hard foam layer and the coupling of the capsule and the dynamic hohlraum are good for the capsule ablating implosion.