XSTEP

Bulk Data Entry 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.                

Example

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

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.
    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.
  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
    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.
  5. For more information about nonlinear analysis, refer to Explicit Dynamic Analysis (Radioss Integration) in the User Guide.
  6. TSTYP=NODA and TACT=AMS can activate elementary time step for Advanced Mass Scaling, as well as TYPEi=NODA and TSCi=AMS.
  7. 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.