7.2.2 Applying Loads

SetLoads is the core function for applying loads to a Mech model. SetLoads takes load objects that represent the physical loads applied to the model and builds them into a global load vector that represents the total force and moment applied at the origin of each body in the model.

The load application function.

Mech uses a Lagrange multiplier method to resolve the static and dynamic forces on a model, which will be discussed further in Section 7.3. It is usually not necessary to specify initial guesses for the Lagrange multipliers, because the equations of motion are linear in the Lagrange multipliers unless friction forces are applied. If initial guesses are needed, they can be specified with the LambdaGuess option for SetLoads.

An option for SetLoads.

Because forces and moments are additive quantities, it is not necessary to apply all of the loads to the model simultaneously. With the AddLoads option, loads can be applied to the model sequentially.

An option for SetLoads.

Loads for the Model

Three loads are defined for the model developed in Section 7.2.1.

Here are the load objects for the ladder-on-wall model.

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Initially, only the two Force objects are applied. SetLoads incorporates the loads into the model.

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By using the AddLoads option for SetLoads, additional loads can be applied to the model at any time. Thus, the Moment can simply be added to the current loading.

This adds the Moment object to the ladder-on-wall model.

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Mech load objects can contain dependencies on other dependent variables. For example, to model the force applied by a linear spring, it is necessary to have the magnitude of the force be a function of the distance between two points.
The Force of an extension spring with a free length of 2 units and a spring constraint k attached between the top of the ladder and the top of the wall could be modeled as follows.

Here is a spring force.

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