Conservation Laws in Smooth Particle Hydrodynamics: The DEVA Code

We describe DEVA, a multistep AP3M-like-SPH code particularly designed tostudy galaxy formation and evolution in connection with the global cosmologicalmodel. This code uses a formulation of SPH equations which ensures both energyand entropy conservation by including the so-called $\bn h$ terms. Particularattention has also been paid to angular momentum conservation and to theaccuracy of our code. We find that, in order to avoid unphysical solutions, ourcode requires that cooling processes must be implemented in a non-multistepway. We detail various cosmological simulations which have been performed to testour code and also to study the influence of the $\bn h$ terms. Our resultsindicate that such correction terms have a non-negligible effect on somecosmological simulations, especially on high density regions associated eitherto shock fronts or central cores of collapsed objects. Moreover, they suggestthat codes paying a particular attention to the implementation of conservationlaws of physics at the scales of interest, can attain good accuracy levels inconservation laws with limited computational resources.Comment: 36 pages, 10 figures. Accepted for publication in The Astrophysical Journa