About the DASSL Integrator

The DASSL integrator computes force trajectories during a dynamics simulation by interpolating the user values specified at specific time steps. The integrator is available by default.

Recommendation: Use the DASSL integrator to run a dynamics simulation.

This page discusses:

See Also
About the Surfacic Contact Model
In Other Guides
Managing Contacts

Characteristics

During a dynamics simulation, the DASSL integrator calculates system equations generated from the mechanism model. It also computes force trajectories by interpolating the values specified by the user at specific time steps. The DASSL integrator is available.

Recommendation: Use the DASSL integrator to run a dynamics simulation.

The selection of an integrator depends on various simulation criteria, including the simulation stability, the integrator performance, and the accuracy of results. For more information on the Symplectic Euler integrator, see About the Symplectic Euler Integrator.

Time Step Parameters

To specify the parameters, do one of the following:

The TimeStep Max and TimeStep Min parameters are not visible to the user. The values are defined by default and you cannot modify them:

  • TimeStep Min: 1e-10s (1e-2s for a contact specification)
  • TimeStep Max: 1 (if there is no contact specification)
The internal time step is variable and adapts to the complexity of the simulation.

During a kinematics or a dynamics simulation, the value of the Result Time Step determines the result sampling. The quality of the animation and the accuracy of the result depend on the result sampling.

Adapt the value of the Result TimeStep to make sure that all contacts are detected, and to prevent a tunneling effect.

Tolerance Parameters

Tolerance parameters for a dynamics simulation are defined in the Play Parameters. For more information, see Playing Mechanism Using the Compass.

You can specify a relative and an absolute tolerance for the following errors:

Error type Description Default values
Position error Absolute: 1.e-2mm, Relative: 1.e-7
Angle error Absolute: 1.e-5rad, Relative: 1.e-7
Linear velocity error Absolute: 1.e-1mm/s, Relative: 1.e-2
Angular velocity error Absolute: 1.e-4rad/s, Relative: 1.e-2

The error computed for each variable is compared to the tolerance Tol = TolAbs + q * TolRel, where TolAbs is the Absolute Tolerance, q is the Evaluated Variable, and TolRel is the Relative Tolerance.

Note: No unit is associated with a relative tolerance.

Contact Management

The DASSL integrator is adapted to the computation of a continuous contact between two surfaces. The quality of the generated results does not depend on the time step value specified by the user.

During a dynamics simulation, contacts are computed using the Surfacic Contact Model. For more information, see 3D Modeling | Mechanical Systems | Mechanical Systems Experience | Running a Simulation | Managing Contacts | About Contacts and .

Note: If a motor drives the command of a mechanism along a given direction and if a contact opposing this direction is detected during the simulation between this product and another, the contact is not taken into consideration.
Important: Before launching a dynamics simulation, specify a mass and an inertia for every product that is not fixed.