XSTEP

Bulk Data Entry

XSTEP – Parameters for Explicit Analysis Control

Description

Defines explicit analysis control.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
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.-

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
XSTEP	2
	0.9		DETAIL
	GRID	CST	0.9	0.1e-6

Field

Contents

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. See comment 3.

Default = 0.01*TTERMS (Real > 0)

DTTH

Output time step for time history files. If zero, no output. See comment 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. See comment 2.

ELEM is the elemental time step

GRID is the nodal time step

CONTACT is the contact interface time step

DETAIL is from definition in continuation lines

Default = GRID (Character = GRID, ELEM, CONTACT or DETAIL)

TACT

Action if minimum time step is reached (For TSTYP = GRID, ELEM, CONTACT, see comment 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. See comment 4.

No default (Character = GRID, CONTACT, SHELL, or SOLID)

TSCi

Time step control method. See comment 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 TYPEi = 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 = STOP, DEL, CST, AMS, or SET)

DTi

Time step scale factor for entity type. See comment 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

1.	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.

2.	Any number of continuation lines can be used.

3.	Time step control for explicit analysis

TSTYP	Elements	Default	Options
GRID		Do nothing	AMS, CST, STOP
ELEM	Shells	DEL	CST, STOP
	Solids	STOP	CST, DEL

With 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.

For 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.

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

4.	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

With 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.

With TYPEi = GRID and TSCi = CST, DTi = 0.67 is recommended.

With TYPEi = CONTACT and TSCi = DEL, the impacted node which fixes the time step is removed from the interface.

TYPEi = SOLID and TSCi = CST is only active for solid elements with the flag ISMSTR = 2 set on PSOLIDX. This option is not available for 8 integration points.

5.	For more information about geometric nonlinear analysis, refer to Geometric Nonlinear Analysis in the User's Guide.

6.	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.

8.	This card is represented as a loadcollector in HyperMesh.