XSTEP

Bulk Data Entry Defines explicit analysis control.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)
XSTEP	`SID`	`TA0`	`DTA`	`DTTH`	`NPRINT`	`RFILE`	`NITER`	`NPAMS`
	`DTSCA`	`DTMIN`	`TSTYP`	`TACT`
	`TYPE1`	`TSC1`	`DT1`	`DTM1`	`ESID1`	`AMST1`
	`TYPE2`	`TSC2`	`DT2`	`DTM2`	`ESID2`	`AMST2`
	etc.

Example

(1)	(2)	(3)	(4)	(5)
XSTEP	2
	0.9		DETAIL
	GRID	CST	0.9	0.1e-6

Definitions

Field	Contents	SI Unit Example
`SID`	Set identification number. (Integer > 0)
`TA0`	Start time for writing animation files. Default = 0.0 (Real > 0)
`DTA`	Output time step for animation files. If zero, no output. 3 Default = 0.01*TTERMS(Real > 0)
`DTTH`	Output time step for time history files. If zero, no output. 3 Default = 0.001*TTERMS(Real > 0)
`NPRINT`	Print every `NPRINT` iteration. If negative, to .out and standard output; if positive, only to .out file. Default = -1000 (Integer)
`RFILE`	Cycle frequency to write restart file for nonlinear iteration. Default = 5000 (Integer > 0)
`NITER`	Maximum number of iterations in conjugate gradient. Only valid when `TSTYP`=GRID and `TACT`=AMS. Default = 1000 (Integer > 0)
`NPAMS`	Frequency (number of cycles) for writing additional output about the number of iterations before convergence in the conjugate gradient. Default = blank (Integer > 0)
`DTSCA`	Default scale factor on explicit time step for all elements. Default = 0.9 (Real > 0)
`DTMIN`	Default minimum explicit time step. Default = 0.0 (Real > 0)
`TSTYP`	Time step control type. 2 ELEM Elemental time step. GRID (Default) Nodal time step. CONTACT Contact interface time step. DETAIL Definition in continuation lines. (Character)
`TACT`	Action if minimum time step is reached (For `TSTYP`=GRID, ELEM, CONTACT. 3 DEF Default (`TSTYP`=GRID, CONTACT - Do nothing, ELEM (Shells) = DEL, ELEM (Solids) = STOP DEL Delete (`TSTYP`=ELEM and CONTACT only). STOP Stop run. CST Standard mass scaling. Continue with constant time step. AMS Advanced mass scaling. Continue with constant time step (`TSTYP`=GRID and CONTACT only).
`TYPEi`	Entity type selection. 4 GRID CONTACT SHELL SOLID No default (Character)
`TSCi`	Time step control method. 4 STOP Stop after reaching `DTMi`. A restart file will be written. This option is the default for brick and quad elements. DEL Element deletion. Elements reaching `DTMi` are removed. This option is the default for shell elements. For `TYPEi`=CONTACT, the impacted grid that fixes the time step will be removed from the interface. CST Constant time step after reaching `DTMi`. For `YPEi`=SHELL, SOLID (except 8 integration points hexas) the formulation switches to small strain for each element that reaches the `DTMi`. For `TYPEi`=GRID, CONTACT, the mass of the grid that reaches `DTMi` is increased. You should check the evolution of the mass of the model. AMS Advanced mass scaling. Constant time step after reaching `DTMi`. Advanced Mass Scaling does not modify the global mass so that the global momentum of the related nodes is conserved. More accurate than `TSCi`=CST (`TYPEi`=GRID and CONTACT only). SET Forces are reduced to keep constant time step (`TYPEi`=GRID only). Default = according to table (blank or Character)
`DTi`	Time step scale factor for entity type. 4 Default = 0.9 (Real > 0.0)
`DTMi`	Minimum time step for entity type. Default = 0.0 (Real > 0.0)
`ESIDi`	GRID SET identification number (For `TYPEi`=GRID, but `TSCi` ≠ AMS). No default (blank, Integer ≥ 0)
`AMSTi`	Tolerance for advanced mass scaling convergence (Only for `TYPEi`=AMS). Default = 10^-4 (Real > 0.0)

Comments

The XSTEP Bulk Data Entry is selected by the Subcase Information command XSTEP = option. It is only used in explicit analysis (ANALYSIS = EXPDYN); it is ignored in other analyses.
Any number of continuation lines can be used.
Time step control for explicit analysis.

GRID

Elements

Default

Do Nothing

Options

AMS, CST, STOP

ELEM: Shells

Default

DEL

Options

CST, STOP

ELEM: Solids

Default

STOP

Options

CST, DEL

TSTYP=GRID

The nodal time step is used. With this option, the computation of each cycle is slightly more expensive, but the time step can be higher, mainly for non-optimized meshes and therefore the overall runtime shorter.

TSTYP=GRID

TACT=CST, the mass of the grid that reaches DTMIN1 is increased. You should check the evolution of the mass of the model.

TSTYP=ELEM

TACT=CST, the element formulation switches to small strain for each element that reaches the DTMIN1.

Overview of default settings and options for TYPEi:

	Do Nothing	STOP	DEL	CST	AMS	SET
SHELL	N/A	Optional	Default	Optional	N/A	N/A
SOLID	N/A	Default	Optional	Optional	N/A	N/A
CONTACT	Default	Optional	Optional	Optional	Optional	N/A
GRID	Default	Optional	N/A	Optional	Optional	Optional

TYPEi=GRID: The nodal time step is used. With this option, the computation of each cycle is slightly more expensive, but the time step can be higher, mainly for non-optimized meshes and; therefore, the overall runtime shorter.
TYPEi=GRID and TSCi=CST: DTi=0.67 is recommended.
TYPEi=CONTACT and TSCi=DEL: The impacted node which fixes the time step is removed from the interface.
TYPEi=SOLID and TSCi=CST: Only active for solid elements with the flag ISMSTR=2 set on PSOLIDX. This option is not available for 8 integration points.

For more information about nonlinear analysis, refer to Explicit Dynamic Analysis (Radioss Integration) in the User Guide.
TSTYP=NODA and TACT=AMS can activate elementary time step for Advanced Mass Scaling, as well as TYPEi=NODA and TSCi=AMS.
NITER and NPAMS are only valid for Advanced Mass Scaling (AMS). If more NITER iterations have been performed before convergence of the conjugate gradient, the computation stops and error out. If NPAMS is specified, at each NPAMS cycle an additional output is provided including: the number of iterations before convergence of the conjugate gradient at this cycle, the final residual norm and the force vector norm.
This card is represented as a loadcollector in HyperMesh.