# Pendulum-like effect

In modeling a wing with the finite element method, I am asked to consider an engine (approximated as a lumped force and moment) and it's mass, inertia, prestress and gravity contributions.

So the engine contribution (in terms of mass and inertia) to the Virtual Work is:

$$\delta \mathcal{W}_{engine} = - \delta s^{T} M \ddot{s} - \delta \theta^{T} J \ddot{\theta}$$

where $$s$$ is the displacement of the engine.

How should I add the prestress and the pendulum-like contribution?

• That would depend on your model. Does your model has rotational degrees of freedom? Jun 13, 2019 at 15:06
• yes, the wind can rotate and bend. Jun 14, 2019 at 16:57
• Not the whole thing. Each single node of your model. Jun 14, 2019 at 17:01