Time_scaling_factors
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Data Structure: Time_scaling_factors |
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Time (Mass) scaling data structure |
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Time_scaling_factors NUM=ival where ival is the data structure number |
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Overview The Time_scaling_factors data structure is used to automatically adjust the element mass in the explicit geomechanical solver to optimise the time step in quasi-static problems (see also Initial_mass_scaling_constant in the Material_data structure manual page). The algorithm is based on a user specified target time step together with a maximum allowable increase/decrease in the mass. It is an alternative/complementary approach to the material based mass-scaling to reduce inertia effects and optimize the time step (see Initial_mass_scaling_constant in the Material_data structure manual page).
Notes •Optimal_time_step is the simplest method to define automatic mass-scaling to achieve a uniform critical time step for all all elements in a mesh that corresponds to a target time step. It is therefore generally recommended •Mass-scaling may also be specified on the material data structure (see Initial_mass_scaling_constant in the Material_data structure manual page). If both algorithms are specified they are used together with the material based mass-scaling being applied first. Then time based mass-scaling will override the material based mass-scaling to further change the applied mass-scaling. •If in Time_scaling_factors the Model_type is set to "Absolute_target" the mass-scaling constant is automatically evaluated and the Initial_mass_scaling_constant does not have any effect. •One data structure is required but may be respecified at any stage in the analysis
Examples demonstrating the usage of Time_scaling_factors include: •inc_2d4n_004a1.dat •elt_2d4n_002.dat •elt_2d4n_004.dat |
 | Optimal_time_step Optimised Target time step for mass-scaling |
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Optimal_time_step is the simplest method to define automatic mass-scaling to achieve a uniform critical time step for all all elements in a mesh that corresponds to a target time step. If the optimised time step is specified then the model type ( Model_name) is set to "Absolute_target" with no restriction on the maximum allowable time step change ( Max_step_change_flag = 0) and the Target time step is set to the optimised time step.
Notes •If in Optimal_time_step is used (the Model_type is set to "Absolute_target") the mass-scaling constant is automatically evaluated and the Initial_mass_scaling_constant would not have any effect at all (no material based mass-scaling will be performed). •Optimised time-scaling is recommended. In this case mass-scaling is applied to all elements, whether their critical time step is above or below the target time step. In this case all elements will have a mass-scaling appropriate for the target time step defined via Optimal_time_step.
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| Model_type Target time step model type |
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Specifies the number of the target time step model. Valid values are: •1 - "Upper_target" - Increase time step only (default) •2 - "Absolute_target" - Increase/decrease time step
Notes •"Absolute_target" is recommended •For transient solver algorithms (Solution_algorithm =1 or 4) the Model_type will have effect. •For incremental steady stage algorithms (Solution_algorithm =2, 3 or 5) the "Absolute_target" will always be used. •If "Upper_target" is used to achieve transient steady-state simulations care should be taken to ensure that the element masses are approximately equal for all elements in the problem. This often requires scaling-down the mass of some materials so that the element critical time step (before applying Time_scaling_factors) is below the target time step. This is best achieved by running a single step and checking the computed element critical time step before defining the Time_scaling_factors data. •If Model_type is specified then Model_name should not be defined as both keywords are interchangeable
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| Model_name Target time step model type |
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Specifies the target time step model name. Valid names are: •"Upper_target" - Increase time step only (default) (Model 1) •"Absolute_target" - Increase/decrease time step (Model 2)
Notes •If Model_name is specified then Model_type should not be defined as both keywords are interchangeable
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| Target_time_step Target time step for mass-scaling |
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Defines the target time step value for mass-scaling.
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| Max_step_change_factor Maximum factor for scaling of time step for mass scaling |
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Defines the maximum factor for scaling of time step for mass scaling. Consequently, the ratio between the original and scaled time step after mass scaling cannot exceed this value.
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| Max_step_change_flag Flag indicating that maximum change restriction is active |
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Flag indicating that maximum change restriction is active (defined via Max_step_change_factor ). Valid values are: •0 - No restriction on maximum change •1 - Apply restriction to maximum change (default)
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