About Clamps

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Generally a clamp represents a surface that is welded, bolted, or otherwise connected to a larger part; although it might also be used to represent a large resisting force. Clamped surfaces maintain their original shape during a simulation, though the unclamped surfaces around them can stretch, bend, and deform as appropriate.

From a simulation standpoint, clamping a surface completely defines the response of that surface during a simulation: it will not move. Therefore, you should not apply additional features to a clamped surface.