SPH is now widely used in several high strain-rate and large-deformation problems which may otherwise be difficult to simulate when using traditional mesh based approaches. LS-DYNA allows mesh-based and mesh-free techniques such as SPH to exist and interact in one simulation allowing users to take advantage of both procedures. The interaction or coupling between the SPH and other elements can be defined using traditional tied or penalty based contact definitions. Since there is no mesh connectivity for the SPH particles, it is imperative that only one-way type of contact defintions are applicable in which the SPH is always defined to be the slave and the elements are defined to be master. LS-DYNA has several types of one-way based contact definitions which are identified by the presence of the string NODES_TO_SURFACE or ONE_WAY in any of the contact keyword.

Contact thickness for the SPH particles
When using automatic or non-automatic type one-way contacts, the SPH particles have no associated contact thickness. The recommended way to define the particle contact thickness is to use the ‘SST’ parameter in the *CONTACT keyword or by using ‘OPTT’ parameter in the *PART_CONTACT keyword. If the SPH particles are representing a volume, then it may be suggested to use a resonable thickness to avoid any nodal release due to excessive penetration. Typical values of particle contact thickness when representing a volume is 0.8-1.0mm. If the SPH particles are representing a shell type structure, then the thickness of the shell can be used as the contact thickness.

It must be noted that there is no need for SINGLE_SURFACE type contacts for defining the self interaction of SPH particles as they are accounted for by the SPH formulation.