Gravity Analysis in LS-DYNA
Gravity load (or preload) in LS-DYNA is applied using *CONTROL_DYNAMIC_RELAXATION. In addition, *LOAD_BODY_Z is used to apply gravity load in Z direction. Note that *LOAD_PARTS can be activated to apply load on selected parts instead of whole model. As in LS-DYNA performs explicit analysis by default, it needs a curve to be defined through *DEFINE_CURVE that is used in *LOAD_BODY_Z to apply gravity loads. The curve can be a very small duration ramp loading, followed by constant load for a long duration.
Dynamic relaxation is invoked either by:
1) IDRFLG flag in *CONTROL_DYNAMIC_RELAXATION
2) SIDR flag in *DEFINE_CURVE
LCID must be defined to apply gravity load through *LOAD_BODY_Z. LCIDDR is an optional curve, which is used when a different load curve than LCID needs to be used for dynamic relaxation phase.
The binary output database that contains results of dynamic relaxation phase is obtained through *DATABASE_BINARY_D3DRLF (similar to D3PLOT). LS-DYNA creates dump file (d3dump01, d3dump02, ..) at the successful termination of an analysis. This dump contains all the information required to start a subsequent analysis (e.g., Seismic Analysis) using *RESTART. Three types of restart options are possible depending on changes required in the subsequent analysis. Information on these options can be found here.
For nonlinear response-history analysis (or soil-structure-interaction), a full-deck restart is required. This is done through activating the card *STRESS_INITIALIZATION.
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