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TSTEP |
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TSTEP |
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TSTEP |
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TSTEP |
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Bulk Data Entry
TSTEP – Transient Time Step Parameters
Description
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 |
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N2 |
DT2 |
N02 |
W3,2 |
W4,2 |
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-etc.- |
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TMTD |
TC1 |
TC2 |
TC3 |
TC4 |
Alpha |
Beta |
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MREF |
TOL |
TN1 |
TN2 |
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Field |
Contents |
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. See comment 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. See comment 3. Default = blank (Real > 0.0, or blank) |
TMTD |
Time integration method for nonlinear direct transient subcases. Default = 1 (Integer > 0). See comment 6. |
TC1 |
Time integration parameters for nonlinear transient subcases. Default = -0.05 (−1/3 < Real < 0). See comment 6. |
TC2 |
Time integration parameters for nonlinear transient subcases. Default= 0.25*(1−TC1−TC4)2 (Real ≥ 0.25 − 0.5*(TC4 + TC1)). See comment 6. |
TC3 |
Time integration parameters for nonlinear transient subcases. See comment 6. Default = 0.25−TC1−TC4 (Real) |
TC4 |
Time integration parameters for nonlinear transient subcases. See comment 6. Default=0 (-1 < Real < 0.5) |
Alpha |
Rayleigh damping coefficient for nonlinear transient subcases. See comment 7. Default = 0.0 (Real) |
Beta |
Rayleigh damping coefficient for nonlinear transient subcases. See comment 7. Default = 0.0 (Real) |
MREF |
Reference displacement method for automatic time integration in nonlinear transient subcases. Default = 1 (Integer = 0, 1 or 2). See comment 8. |
TOL |
Tolerance for automatic time integration in nonlinear transient subcases. Default = 1.0E-2 (Real > 0). See comment 8. |
TN1 |
Control parameter for automatic time integration in nonlinear transient subcases. Default = 5 (Integer > 0). See comment 8. |
TN2 |
Control parameter for automatic time integration in nonlinear transient subcases. Default=5 (Integer > 0). See comment 8. |
| 1. | TSTEP entries must be selected with the Subcase Information command TSTEP = SID. |
| 2. | Note that the entry permits changes in the size of the time step during the course of the solution. Thus, 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. |
| 3. | W3 and W4 define frequencies used in transient analyses to convert structural damping to equivalent viscous damping. See the Reference Guide entries for PARAM,W3 and PARAM,W4 for more details. |
| 4. | 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. |
| 5. | 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. |
| 6. | The TMTD field specifies the time integration scheme for nonlinear direct transient subcases. If TSTEP entry is not referenced or present in the input deck, then the Generalized Alpha Method (more specifically, the HHT-a method) will be used by default. |
TMTD=1: Generalized alpha method.
When TMTD=1, coefficients of generalized alpha method are specified using TC1, TC2, TC3, and TC4, for a, β, γ, and am, respectively. In general, the generalized alpha method should be used for most transient analysis. In this method, numerical damping can be adjusted through the parameters a, β, γ and am. In particular, non-zero a and am 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.
TMTD=2: Backward Euler method.
The backward Euler method does not require the input of TCi fields. The Alpha and Beta fields introduce subcase-dependent Rayleigh damping, so the viscous damping matrix C in any particular subcase is [C] = Alpha * [M] + Beta * [K].
7. 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.
8. Automatic time stepping for nonlinear direct transient is specified using MREF > 0.
MREF =0: indicates no automatic time stepping.
MREF =1 or 2: indicates the options of reference displacement in automatic time stepping.
When MREF =1 or 2, the tolerance for time step adjustment error control is specified by TOL.
TN1: specifies the maximum number of cut-backs in a single time step.
TN2: specifies the minimum number of time step enlargement requests required before the solver actually enlarges the next time step.
| 9. | This card is represented as a loadcollector in HyperMesh. |
See Also:
