I'm hoping to gain a better understanding of inputs and settings for a linear transient dynamic analysis using modal superposition with this shell plate example model. The two load cases I'm attempting to run are:
Load Case 1 (LC1): acceleration shock
- input peak acceleration: 15.2 g's
- 11 ms terminal peak sawtooth shock pulse
Load Case 2 (LC2): velocity shock
- initial velocity: 68 in/s
- 11 ms terminal peak sawtooth shock pulse
These are some assumptions and outputs I'd like to have represented:
- time step must capture critical shock input response and the peak structure response after the input finishes
- input shock pulse at same location as SPC
- output displacement with respect to SPC
- 10% global structural damping
- distance units are in inches
Here are some issues and questions from the example model in its current state:
- LC1 results show a displacement "drift" in the direction of acceleration application throughout the time history. Why is this and what can I do to prevent it?
node 613337 is on the cantilevered end of the plate
node 610154 is one of the four SPC/shock input nodes at the center of the rigid elements. I expected this displacement value to be equal to 0 throughout the time history, but it changes based on the time step input.
2. The time step input for both load cases currently has two stages: 0.001 s increments for the first 0.1 s and 0.005 s increments for the remaining time. The severity of the results increases during the second time step stage. I was expecting to see the deflections and stresses continue to oscillate and decrease, but with increased time between results reports. Recommendations or guidance on this?
3. Viewing worst case results: what is the method for locating the peak stress that occurs throughout the transient response?
Model and results files (.fem, .h3d, .out, and .mvw for the Hypergraph images above) are attached. Thanks!
