11.2.1 Applied Loads

Using generalized coordinates has almost no effect on the modeling of applied loads. The standard Mech load functions Force, Moment, Gravity, and GyroMoment are used to apply loads to a generalized coordinate slave body in exactly the same way as they are used with standard bodies. The one load function that is affected by the use of generalized coordinates is Load, which is used to apply a load directly to a specified coordinate.
Since Load references the coordinates in a model directly by their symbolic name, it can be used to apply a load directly to a generalized coordinate. Conversely, Load cannot be used to apply a load directly to a Cartesian coordinate of a slave body because a slave body doesn't have any explicit Cartesian coordinates.
For example, suppose a model has two bodies, 2 and 3, and body 3 is a slave to body 2. The two bodies are joined by a revolute joint and the symbol alpha represents the rotation of the slave, relative to the master. The Force function may be used to apply a force in the global X direction to the slave, but the Load function may not.

This loads the Modeler2D packages and defines names for bodies 2 and 3.

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Here is a load object that applies a 10-unit force to the slave body.

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This load object does not apply the 10-unit force to the slave body, because X3 is not a coordinate in the model.

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However, the Load function can be used to apply a moment to the slave body because the generalized coordinate alpha is an angular coordinate. A load applied directly to alpha essentially applies a counterclockwise moment to the slave body, and a clockwise moment to the master.

Here is a load object that applies a 10-unit moment to the slave, and an equal and opposite moment to the master.

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Here is a simpler load object that applies the same 10-unit couple between the slave and master.

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In general, the Load function should be used instead of Force or Moment whenever possible because the resulting algebraic expressions that are added to the model can be much simpler.