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After   RecurDyn Contact - Becoming an Experienced User, 1st Episode in this episode, we will look at solid contact objects and geo contact objects, which are the most widely used contact objects in RecurDyn.

Note: Contact objects can be used in a variety of ways depending on the elements in the model, such as its geometries and parameters. Therefore, the following information should be used as a basic guide to working with contact objects. In actual models, the contact objects may behave differently than described in this guide.

Solid Contact

Solid contact objects are useful when contact occurs between two convex surfaces or between a flat surface and a convex surface.

The following examples show simplified models that are suitable for simulation using solid contact objects. For models in which the two convex surfaces are in direct contact, a solid contact object can provide satisfactory results in terms of speed and accuracy.


If the results are not satisfactory even when the contact occurs between convex surfaces, refer to the  manual   and modify the contact parameters.

As described in the manual, however, when contact occurs between flat surfaces or contact occurs over a large area between a convex surface and a concave surface, geo surface contact objects work better. (You can still adjust the parameters of the model to use solid contact objects for these cases. However, it is easier to use geo surface contact objects.)

The following example shows a model in which several small spheres exist inside a larger sphere. In this example, contact occurs between the convex surfaces of the small spheres and the concave surface of the larger sphere. However, as the contact occurs only in small portions of the spheres rather than large areas, solid contact objects may still be applied successfully.


When you define the contact inside a shape, as shown above, you may need to adjust the Normal Direction in the Solid tab of the Properties dialog box.

Geo Surface Contact (Geo Contact)
Geo surface contact objects can be applied to almost any form of contact. If the contact occurs between two convex surfaces, however, a solid contact object will produce faster analysis results than a geo surface contact object. As we stated before, a geo surface contact object works better than a solid contact object when contact occurs between flat surfaces or contact occurs over a large area between a convex surface and a concave surface. The following example shows one such case, which is simplified to highlight when it is best to use a geo surface contact object.

If a model does not produce satisfactory results using solid contact objects, we recommend using geo surface contact objects.

Please refer to the below figure to understand how the contact force is calculated in RecurDyn. (Simplified explanation)

Standard contact force formulation in RecurDyn (Multi-Body Dynamics software)

If you want to know more about RecurDyn Contact, please refer to the below articles