I would like to analyze the structure of the UAV that I have for different loading conditions. It is a simple quad-copter with co-axial motors at each motor arm (I have 2 motors at each arm, so 8 motors in total). I have a global FEA model where I have all of the structure meshed with proper properties assigned to the elements and also ensuring element quality and connectivity. I have difficulties in choosing the right boundary conditions.
I ran a few test cases to understand the behaviour of the FEA model (basically, checking the reaction loads at constraint points). Among these test cases, the boundary condition which fit right was where I constrained the 3 translational degrees of freedom at the motor-points and applied mass elements for the motor, payload (5 kg), and the battery and ran ‘gravity load analysis’. The reaction forces at the constraint points were equal to the thrust I would require to hover.
Now, I would like to understand how will the structure behave for the one-motor-failed condition. What boundary condition can I go for this case? Say, if what I have so far is incorrect and I need to assign loads at the motor points, where do I constrain my model?
Any help is highly appreciated. Thanks in advance!
Maybe this old workshop helps you in setting up boundary conditions for your case? Step-by-Step Tutorial: Homework of Session 2- Level 1 - you could even use one arm in the first step as suggested in the step-by-step tutorial.
It sounds like you are just trying to model a hovering condition. In that case you approach sounds good but I would make one change. I would only fix one point in the XYZ directions and the other three points I would only fix in the vertical direction.
If you performed an analysis with only three points constrained (two motors out), could you get what you want from this worst case condition?
What I thought initially was, constraining all 3 translational DoF would give me the reactions at the motor points. For the motor failed condition, I removed all 3 DoF constraints at one of the motor-booms. Does this approach make sense?
I was also thinking of using elements like CBUSH (as we have in Nastran) at the motor points, and constrain these points so that they will help me in restricting the forces through the elements and get appropriate reaction forces.
