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/DT/Eltyp/Keyword3/Iflag

/DT/Eltyp/Keyword3/Iflag

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/DT/Eltyp/Keyword3/Iflag

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Engine Keyword

/DT - Time Step with Entity Selection and Time Step Control

Description

Time step with entity selection and time step control.

Format

/DT/Eltyp/Keyword3

 

Or

/DT/INTER/AMS/1

Tol_AMS

Or

/DT/BRICK/CST/1

ASP_min VDEF_min

Data

Description

Eltyp

Entity selection:

BRICK - Brick elements

QUAD - Quad elements

SHELL - Shell elements

SH_3N - Triangular shell elements

TRUSS - Truss elements

BEAM - Beam elements

SPRING - Spring elements

AIRBAG - Airbag

INTER - Interfaces (Type 7, 10, 11, 19, and 20 only)

/INTER/STOP is available for interface Type 21, also.

NODA - Nodes

Keyword3

Time step control type:

STOP - The run will stop if the time step reaches and a restart file will be written. This option is the default for brick and quad elements.

DEL - The element which fixes the time step is removed. This option is the default for shell elements. (see Comment 1)

CST - The time step becomes constant after reaching . This option only works if “Eltyp” is BRICK, SHELL, or INTER.

For shell or brick elements (except Isolid = 12 AND /TEGRA with Itetra > 0) the formulation switches to a small strain formulation for each element that reaches the .

For interfaces, the nodal mass of the node that reaches is increased. Thus the momentum is not conserved. You should check the evolution of the mass of the model.

AMS - Stands for Advanced Mass Scaling. It is only available if “Eltyp” = INTER.

The stability of penalty springs related to impacts is insured through Advanced Mass Scaling so that the time step becomes constant, equal to

SET - Is only available if  “Eltyp” = NODA; forces are reduced in order to keep a constant time step.

Scale factor on time step for the option defined by “Eltyp”.

Default = 0.9

Minimum time step

Tol_AMS

Tolerance for AMS convergence -only used when “Keyword3” = AMS.

Default = 10-4

Iflag

Node group flag (Comment 13)

ASP_min

Minimum Aspect ratio (Tet collapse); Solid elements for which aspect ratio < ASP_min will be switched to small strain formulation to keep constant time step. (Comments 14 and 15)

Default = 0

VDEF_min

Minimum Volume ratio (V/Vo); Solid element for which Volume change < VDEF_min will be switched to small strain formulation to keep constant time step. (Comments 14 and 15)

Default = 0

Comments

1.If “Keyword3” = DEL and “Eltyp” = INTER, the impacted node which fixes the time step is removed from the interface.
2.Advanced Mass Scaling does not modify the global mass, so that the global momentum of the related nodes is conserved. Therefore, /DT/INTER/AMS is more accurate than /DT/INTER/CST.
3.The option /DT/BRICK/CST is only active if the brick elements have the flag Ismstr=2 in Type definition. This option is not available if Isolid = 12.
4.The table below lists the different available combinations of  “Eltyp” and “Keyword3”.

 

STOP

DEL

CST

AMS

QUAD

Default

Optional

 

 

BRICK

Default

Optional

Optional

 

SHELL, SH_3N

Optional

Default

Optional

 

BEAM, TRUSS, SPRING

Optional

Optional

 

 

INTER (Types 7, 10, 11, 19 and 20)

Optional

(/INTER/TYPE21 also)

Optional

Optional

Optional

AIRBAG

Optional

 

 

 
5.For each "Eltyp" value, only one option /DT/Eltyp/Keyword3 is available at the same time, except that it is possible to use /DT/INTER/DEL or STOP at the same time as /DT/INTER/AMS.
6.DT/INTER/AMS is compatible with the following kinematic conditions: boundary conditions, imposed velocities, imposed displacements, imposed accelerations, tied interfaces (/INTER/TYPE2), rigid bodies, fixed rigid walls, rigid links and cylindrical joints.
7./DT/INTER/AMS does not work if applied to nodes involving: rivets (/RIVET), rigid elements (/RBE2), interpolation constraint elements (/RBE3), moving rigid wall, Lagrange multipliers (/MPC and /GJOINT). In such cases, an error is output by RADIOSS Engine.
8.The rigid bodies which are connected to nodes where AMS applies can be activated/deactivated during RADIOSS Engine run through /RBODY/ON and OFF, but not with sensors.
9./DT/INTER/AMS is compatible with dynamic relaxation (/DYREL) and Rayleigh damping (/DAMP)
10./DT/INTER/AMS always applies to the whole model, except that it is possible to use Elementary time step for AMS (/DT/AMS) on a part group and to use /DT/INTER/AMS at the same time: /DT/INTER/AMS will then apply to nodes which are not belonging to the part group.

For example:

/DT/AMS/1

Tol_AMS

 

/DT/INTER/AMS

 

11.Elementary time step for Advanced Mass Scaling will apply on the part group declared in /AMS of the RADIOSS Starter Input deck, but /DT/INTER/AMS will apply to nodes which do not belong to the part group.
12.All options of /DT/Eltyp/Keyword3, (except /DT/INTER/AMS) can be combined with /DT/NODA or /DT/NODA/CST.
13.“Iflag” can be only used with Eltyp = NODA.
•If Iflag =1, only the nodes belonging to the node group grnd_ID are affected
•If Iflag =0 or blank, all nodes are affected
14./DT/BRICK/CST/1 is only active if Ismstr=2 or 4 and is compatible with /TETRA4 with Itetra=0, /TETRA10, and /BRICK solid elements with Isolid=1, 2, 14, 17, or 24.
15.When using /DT/BRICK/CST/1, elements will be switched to small strain formulation when one of the two minimum values for ASP_min or VDEF_min have been reached. ASP_min uses the same tetra collapse calculation as HyperMesh element quality check.  Elements failing the ASP_min criteria will be switched to the small strain formulation at the beginning or during a simulation.  VDEF_min can be used to switch highly deformed or compressed elements to the small strain formulation during the simulation thus avoiding negative volume issues that can arise.