How to create a drop test using Event Simulation in Fusion 360

Solution:

Due to the nature of event simulation, the simulation needs to have a small duration (such as 0.001 seconds). With this being said, a full drop test cannot occur with this duration. Instead, the item of interest is the impact. The initial conditions can be set to simulate that aspect. 

 

1. Calculate the velocity of the falling object just before impact. The equation to solve is as follows: V=SQRT(2*GRAVITY*DISTANCE) where DISTANCE is the free-fall distance.
2. Position the dropped object a small gap away from the floor. If the impact is to occur at 1/50 of the duration, the gap can be calculated from the duration and velocity: GAP = V*DURATION/50. 
3. Apply an initial velocity to the falling object equal to V.
4. Activate Gravity.
5. Use the Contacts Manager ("Contacts > Manage Contacts") to define Separation contact between the appropriate bodies.
6. Set the duration: "Manage > Settings > General > Total Event Duration". The "Number of Result Intervals" only changes how many results are saved over the duration. The result interval does not change the internal time step size used by the solver. (See details that follow.)
7. Set up any other requirements such a bonded contact between parts, constraints, rigid bodies for any part that can be idealized as perfectly rigid, material properties, other live loads, and so on.

 

Details on Event Simulation

 

• The solver calculated the time step size based on the mesh size and the material properties. You have no direct control over the time step size.
• The time step size is typically on the order of 1E-6 to 1E-10 seconds! This is why the duration needs to be short. A duration of 1 second with a time step size of 1E-10 would require a long run time.
• The maximum runtime permitted is limited. (As of this writing, the time limit is 12 hours.)
• The time step size is based on the dimensions of the smallest elements in the entire model. (Technically, in the parts that are not rigid bodies.) Therefore, remove small rounds or fillets from elastic parts that are not critical to the analysis.