Solver Settings - Dynamics
Settings → Solver → Dynamics
Dynamic simulations are transient or time-varying simulations used to investigate the movements of parts over time; these movements result from the combined effects of forces and constraint relationships. You can perform dynamic simulations on models that have any number of Degrees of freedom (DOF).
It is computationally more efficient, however, to perform Kinematic simulations on models with zero DOF and to perform dynamic simulations only on models with one or more DOF. For dynamic simulations, Adams Solver can use several numerical algorithms to calculate an approximate solution to the equations of motion it formulates for your mechanical system.
Learn more About Dynamic Simulations.
For the option: | Do the following: | ||
|---|---|---|---|
Category | Set to Dynamic. | ||
Integrator | Select an integrator (the integrators HASTIFF, HHT and Newmark are only available with Adams Solver (C++)). For more on the integrators, see Comparison of Integrators and the: ■INTEGRATOR statement in the Adams Solver (FORTRAN) online help ■INTEGRATOR statement in the Adams Solver (C++) help Note: Unknown appears if your model uses an integrator that is not used or no longer supported. For example, if you import a dataset (.adm) file that contains the statement "INTEGRATOR/HASTIFF", which is discontinued, Adams View displays Unknown. If you try to select Unknown, Adams View defaults to GSTIFF. | ||
Formulation | If you selected the integration method GSTIFF, WSTIFF, HASTIFF or Constant BDF, select a formulation for the integrator: ■I3 ■SI2 ■SI1 - only available in Adams Solver (FORTRAN) See Equation Formulation Comparison and the INTEGRATOR statement in the Adams Solver online help, for more on the integrators. Note: Unknown appears if your model uses an integration method that is not used or no longer supported. If you try to select Unknown, Adams View defaults to I3. | ||
Corrector | Specify the corrector algorithm that is to be used with the currently selected Integrator. The corrector in a stiff integrator ensures that all the unknowns satisfy the equations of the system. The algorithms, original and modified, differ primarily in the algorithm that they use to define when the corrector iterative process has converged. ■Original - Specifies that the corrector available in the previous releases of Adams Solver be used. This is the default. This implementation of the corrector requires that at convergence, the error in all solution variables be less than the corrector error tolerance. Note that sometimes when achieving convergence becomes difficult during a simulation, Adams Solver will switch to the Modified corrector and mention this in the message file (.msg). ■Modified - Specifies that a modified corrector is to be used. This implementation of the corrector requires that at convergence, the error in only those variables for which integration error is being monitored, be less than the corrector error tolerance. This is a slightly looser definition of convergence, and you should use proper care when using this. The modified corrector is helpful for models containing discontinuities in the forcing functions. Problems with contacts belong in this category. ■Original (Constant) - Specifies that during the simulation Adams Solver cannot switch from the original corrector to the modified corrector. For additional information, see Extended Definition in the INTEGRATOR statement in the Adams Solver online help. | ||
Error | Specify the relative and absolute local integration error tolerances that the integrator must satisfy at each step. For BDF, HHT, and Newmark integrators, Adams Solver monitors the integration errors in the displacement and state variables that the other differential equations (differential equations, linear state equations, general state equations, and transfer functions) define. ABAM, SI1, and SI2 formulations also monitor errors in velocity variables. The larger the error, the greater the error per integration step in your solution. Note that the value for error is units-sensitive. For example, if a system is modeled in mm-kg-s units, the units of length must be in mm. Assuming that all the translational states are larger than 1 mm, setting ERROR=1E-3 implies that the integrator monitors all changes of the order of 1 micron. The error tolerances (e) are enforced as: || Yc - Y || < MAX (e, e * ||Y||) where: ■Yc is the column matrix of computed values for the unknowns, Y. ■The symbol || . || indicates the root-mean-square of the array of numbers. | ||
Hmax | Enter the maximum time step that the integrator is allowed to take. When setting the Interpolate option, the integration step size is limited to the value that is specified for Hmax. If Hmax is not defined, no limit is placed on the integration step size. If you do not set the Interpolate option, the maximum step size is limited to the output step. Range is 0 < Hmin  Hinit Hmax. | ||
More | Click to set more advanced options. | ||
Hmin | Specify the minimum time step that the integrator is allowed to take. Default is 1.0E-6*HMAX for GSTIFF and WSTIFF integrators, and machine precision for ABAM, SI1, and SI2 formulations and HHT and Newmark integrators. Range is 0 < HMIN HINIT HMAX. | ||
Hinit | Enter the initial time step that the integrator attempts. The default is 1/20 of the output step. Range is 0 < HMIN HINIT HMAX. | ||
Adaptivity | All of the BDF integrators (GSTIFF, WSTIFF, HASTIFF and Constant BDF) use Newton-Raphson iterations to solve the nonlinear Differential-Algebraic equations of motion. This iteration process is referred to as correcting the solution. The adaptivity value modifies the corrector error tolerance to include a term that is inversely proportional to the integration step size. This is intended to loosen the corrector tolerance when the step size gets small (many corrector failures occur because of small step size). If the integration step size is equal to h, Adaptivity/h is added to the corrector tolerance. When setting a value for Adaptivity, begin with a small number, such as 1E-8. Note that this relaxes the tolerance of the corrector, which can introduce additional error into the dynamic solution. The corrector tolerance must be at least a factor of 10 stricter than the integration tolerance. The ratio advocated in theoretical literature ranges from .1 to .001 and is a function of the integrator order and step size. The ratio that Adams Solver uses varies with the integrator chosen, but is within the range specified above. If you use an Adaptivity value to relax the corrector tolerances, be sure to validate your results by running another simulation using a different integration error tolerance. The Adaptivity value affects only the GSTIFF, WSTIFF, and Constant BDF integrators. An Adaptivity value is typically required to overcome corrector convergence difficulties and you should not use it in normal situations. The default is 0, and the range is Adaptivity  0. | ||
Interpolate | Set to Yes when you don't want the integrator to control the integration step-size to precisely hit an output step. The integrator might then overshoot an output point and in this case an interpolation algorithm will provide an approximation of the solution at the output point. This approximate is then refined to provide for the consistent solution at the output point. | ||
Kmax | Specify the maximum order that the integrator can use. The order of integration refers to the order of the polynomials used in the solution. The integrator controls the order of the integration and the step size, and, therefore, controls the local integration error at each step so that it is less than the error tolerance specified. For problems involving discontinuities, such as contacts, setting Kmax to 2 can improve the speed of the solution. However, we do not recommend that you set the Kmax option unless you are a very experienced user. Any modification can adversely affect the integrator’s accuracy and robustness. Kmax's default and range depend on the integrator you selected: | ||
For the integrator: | The default is: | The range is: | |
ABAM | 12 | 1 Kmax 12 | |
GSTIFF, WSTIFF, HASTIFF, Constant BDF | 6 | 1 Kmax 6 | |
RKF45, HHT, Newmark | Not applicable | Not applicable | |
Note: KMAX is irrelevant (ignored) if the integrator selected is HHT or Newmark. Both these integrators are constant order (order 2 and 1, respectively) and, therefore, the order does not change during simulation as is the case for the rest of the integrators available in the solver. | |||
Maxit | Enter the maximum number of iterations allowed for the Newton-Raphson iterations to converge to the solution of the nonlinear equations. The correctors in GSTIFF and WSTIFF use the Newton-Raphson iterations. ABAM also uses Newton-Raphson iterations to solve for the dependent coordinates. We recommend that you do not set Maxit larger than 10. This is because round-off errors start becoming large when a large number of iterations are taken. This can cause an error in the solution. The default is 10, and the range is Maxit > 0. | ||
Scale | Enter the sum of the relative and absolute error tolerances. If T is the sum of the relative and absolute error tolerances applied to the state vector, then the following tolerance is applied: r1 * T to the translational displacements r2 * T to the angular displacements r3 * T to the modal coordinates The scale applies to only WSTIFF and ABAM. It is does not apply to GSTIFF and Constant BDF. The use of scale factors is not supported in Adams Solver (C++). | ||
Beta | One of the two defining coefficients associated with the Newmark method. Learn more about the Newmark integrator with INTEGRATOR statement help. Default value is 0.36. Range is defined in conjunction with Gamma. Together they must satisfy the stability condition.  | ||
Gamma | One of the two (together with Beta) defining coefficients associated with the Newmark method. Default value is 0.7. Range is defined in conjunction with Beta. Together they must satisfy the stability condition. | ||
Alpha | Defining coefficient for the HHT method. Default value is -0.3. Range is -0.333333 <= ALPHA <= 0 | ||
Fixed Iterations | Specify the number of iterations per integration step for the GSTIFF and HHT method. Valid values: off, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Default value is off. Learn more about the Fixed Step Integrator Option in the INTEGRATOR statement help. | ||
Hratio | Specify the number of times the step size goes into the output sampling rate (that is, hratio=dtout/h) for the GSTIFF and HHT method. Hratio is relevant if fixed_iterations is specified. Default value is 1. Learn more about the Fixed Step Integrator Option in the INTEGRATOR statement help. | ||
Max Error | Specifies the amount of error above which the user would like Adams Solver to stop trying to solve the problem for the GSTIFF and HHT method. Value is positive real and it is relevant if fixed_iterations is specified. Learn more about the Fixed Step Integrator Option in the INTEGRATOR statement help. | ||
Advanced Rotation | Use a singular-free rotation representation to solve the dynamic equations of motion. This option is supported by the GSTIFF, WSTIFF, HHT and NEWMARK integrators. Default value is on. This setting can improve solver efficiency for rotation-dominant models. | ||