TSTEP
Bulk Data Entry Defines time step parameters for control and intervals at which a solution will be generated and output in transient analysis.
Format
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) |
---|---|---|---|---|---|---|---|---|---|
TSTEP | SID | N1 | DT1 | N01 | W3,1 | W4,1 | |||
N2 | DT2 | N02 | W3,2 | W4,2 | |||||
etc. | |||||||||
TINT | TMTD | TC1 | TC2 | TC3 | TC4 | Alpha | Beta | ||
TSTEP | MREF | TOL | TN1 | TN2 |
Example
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) |
---|---|---|---|---|---|---|---|---|---|
TSTEP | 2 | 10 | .001 | 5 | |||||
9 | 0.01 | 1 |
Definitions
Field | Contents | SI Unit Example |
---|---|---|
SID | Set identification
number. No default (Integer > 0) |
|
N# | Number of time steps of
value DT#. No default (Integer ≥ 1) |
|
DT# | Time increment. No default (Real > 0.0) |
|
N0# | Skip factor for output.
Every N0i-th step will be saved for
output. Default = 1 (Integer > 0) |
|
W3,# | The frequency of interest
in radians per unit time; used for the conversion of overall
structural damping into equivalent viscous damping. 3 Default = blank (Real > 0.0, or blank) |
|
W4,# | The frequency of interest
in radians per unit time; used for the conversion of element
structural damping into equivalent viscous damping. 3 Default = blank (Real > 0.0, or blank) |
|
TINT | Continuation line flag indicating the parameters for time integration are to follow. | |
TMTD | Time integration
method. For Linear Direct Transient Analysis:
For Nonlinear Direct Transient Analysis:
(Integer > 0) 6 |
|
TC1 | Time integration
parameters for transient subcases. Default = -0.05 (-1/3 < Real < 0) 6 |
|
TC2 | Time integration
parameters for transient subcases. Default= 0.25*(1-TC1-TC4)2 (Real ≥ 0.25 - 0.5*(TC4 + TC1)) 6 |
|
TC3 | Time integration
parameters for transient subcases. 6 Default = 0.5-TC1-TC4 (Real) |
|
TC4 | Time integration
parameters for transient subcases. 6 Default = 0 (-1 < Real < 0.5) |
|
Alpha | Rayleigh damping
coefficient for transient subcases. 7 Default = 0.0 (Real) |
|
Beta | Rayleigh damping
coefficient for transient subcases. 7 Default = 0.0 (Real) |
|
TSTEP | Continuation line flag indicating the parameters for time stepping are to follow. | |
MREF | Controls activation of
automatic time-stepping for structural linear transient, structural
nonlinear transient, linear transient heat transfer, and nonlinear
transient heat transfer analyses. Structural Linear direct
transient analysis (Newmark-Beta method) 8
Structural Nonlinear direct transient analysis
(Generalized alpha method) 8:
Structural Nonlinear direct transient analysis
(Backward Euler method) 8: Linear and nonlinear transient heat transfer analyses
8, 9:
(Integer) See Comment 8 |
|
TOL | Tolerance for automatic
time stepping in transient subcases. Default = 1.0 (Real > 0) 8 |
|
TN1 | Control parameter for
automatic time stepping in transient subcases. It specifies the
maximum number of cut-backs in a single time step. Default = 5 (Integer > 0) 8 |
|
TN2 | Control parameter for
automatic time stepping in transient subcases. It specifies the
minimum number of time step enlargement requests required before the
solver enlarges the next time step. Default=1 (Integer > 0) 8 |
Comments
- TSTEP entries must be selected with the Subcase Information command TSTEP=SID.
- The entry permits changes in the size of the time step during the course of the solution. In the example shown, there are 10 time steps of value .001, followed by 9 time steps of value .01. Also, in the case of this example, you have requested that the output be recorded for t = 0.0, .005, .01, .02, .03, and so on.
- W3 and W4 define frequencies used in linear transient analyses to convert structural damping to equivalent viscous damping. The W3 and W4 fields on TSTEP are not supported for Nonlinear Transient Analysis. For Nonlinear Transient, PARAM, W3 and PARAM, W4 can be used.
- Different values for W3 and W4 may be set for each set of time increments. If any of the fields are left blank then the value is taken from the PARAM, W3 or PARAM, W4 definition.
- Transient Response Analysis using Fourier Transformation cannot be used in a model, which also contains a Modal Frequency Response Analysis subcase. OptiStruct will error out in such cases.
- Time integration method.The TMTD field can be used to control the time integration scheme for both linear transient and nonlinear transient analysis.
- Linear Transient Analysis
If TMTD field is blank for linear transient analysis, the traditional time integration scheme is used. Automatic time-stepping (MREF=1) is not supported for traditional time integration.
If TMTD=1, the Newmark-Beta Integration scheme is used for linear transient analysis. Automatic time-stepping (MREF=1) is supported for Newmark-Beta time integration.
For more information, refer to Linear Transient Analysis in the User Guide.
- Nonlinear Transient Analysis
If the TSTEP entry is not referenced or present in the input deck, or if the TMTD field is blank, the Generalized Alpha method (more specifically, the HHT- method) will be used by default.
When TMTD =1, coefficients of Generalized Alpha method are specified using TC1, TC2, TC3, and TC4, for four non-dimensional parameters ( and ), respectively. In general, the Generalized Alpha method should be used for most nonlinear transient analyses. In this method, numerical damping can be adjusted through the parameters and . In particular, non-zero and introduces damping for high-frequency response components. On the other hand, Backward Euler method can be used for quasi-static analysis, such as post-buckling problem, since this method is dissipative, and therefore stable.
When TMTD =2, the backward Euler method does not require the input of the TCi fields. The Alpha and Beta fields introduce subcase-dependent Rayleigh damping, so the viscous damping matrix in a particular subcase is .
For more information, refer to Nonlinear Transient Analysis in the User Guide.
- Linear Transient Analysis
- Subcase-dependent Rayleigh damping for nonlinear direct transient subcase is issued using Alpha, and Beta. Alternatively, they can be specified using PARAM, ALPHA1 and PARAM, ALPHA2, respectively.
- Automatic time-stepping is applicable
for structural linear transient, structural nonlinear transient, linear
transient heat transfer, and nonlinear transient heat transfer analyses. It is
controlled using the MREF field.
- MREF=0
- Indicates no automatic time stepping.
- MREF=1
- Automatic time stepping is activated.
- TOL
- Specifies the tolerance for time step adjustment error control.
- TN1
- Specifies the maximum number of cutbacks in a single time step.
- TN2
- Specifies the minimum number of time step enlargement requests required before the solver enlarges the next time step.
If DTMIN and DTMAX are specified on the NLADAPT entry for Nonlinear Transient Analysis, they have highest priority over the time-stepping process and they are always respected.
- The TSTEP entry is
also used to define the time-step control for linear transient heat transfer and
nonlinear transient heat transfer analysis. Automatic time-stepping can be
turned on using MREF=1 (see the Linear Transient Heat Transfer Analysis and Nonlinear Transient Heat Transfer Analysis
User Guides for more information). Manual time-step control
(MREF=0) is the default for transient
heat transfer. The recommended time-step to set for transient heat transfer
is:Where,
- Time-step.
- Smallest dimension of any element in the model.
- Highest thermal diffusivity.
Where,- Thermal conductivity.
- Density.
- Specific heat.
- This card is represented as a load collector in HyperMesh.