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Overview
This page explores the parameters defining the nature and behavior behaviour of collision objects in our impact analysis. The goals of this investigation are listed below.
Gain a better understanding of the real-life representation of the collision objects in order to accurately model their behavior behaviour in collision scenarios
Verify the size, geometry and material of collision objects and ensure they meet ASC regulations
Re-evaluate contact types and fixed supports used in the current simulation setup
Propose new simulation setups that can model the behaviour of the chassis and collision objects more realistically
Ensure models are sufficiently constrained and can be solved by running test cases in Ansys
Left To Do:
double check the automatic contacts in the current model
finish defining set up cases
run in ansys
compare to existing results (stresses, model behavior)
ideal result = lower stresses but still realistically modelled
1.0 ASC Regulations Regarding Collision Objects
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This page summarizes all collision scenario cases: MS14 Simulations Overview
Sample CAD model with chassis and collision objects: https://workbench.grabcad.com/workbench/projects/gcwijX10VhtEeZ8mtyGdmiV5BQItzO7K-9PXmyIs5vRPFL#/file/544822163
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Information on our current collision objects setup is summarized in the table below.
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3.0 Model Setup
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3.1 Existing Set-up
See this page for details on the current Ansys Workbench Setup: MS14 Workbench Setup
“11. Add
afixed support to the back face of your impact object”
“12. Add acceleration to your model, in the direction away from the impact object. For every G of force you want to simulate, add 9.8m/s^2 to acceleration (i.e. for 5Gs, acceleration should be 49m/s^2).”
3.2 Proposed Set-up
See slide 3 in the attached slides in section 4.0 below.
3.3 Old Notes on Proposed Set-up:
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There are 3 main iterations for each collision scenario. V1 - evaluate the effect of the contact type parameter ONLY V1.2 - change fixed supports on collision body V2 - potentially change the frame of reference - accelerate the chassis into the fixed object instead V3 - evaluate the material choice note: accelerating objects into chassis is simpler. chassis is a more complex structure so it is easier to keep it fixed, ie simulation is more likely to converge this way 3.2 Front/ Side Bar Collisions Setup
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1 of 2 cases we can model
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bar object represents car bumpers so constraining the sides and allowing for bowing (previously discussed) doesn’t make sense…
instead, go back to the fixed support on the back face
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3.3 Rollover (Wall) Collisions Setup
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4 Top (Pucks) Collision Setup
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4.0 Simulation Results
Show results based on setups defined in 3.0
take note of any modifications / iterations required
4.1 Case 1 Results
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Version
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Changes/Notes
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Result (images)
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V1
4.2 Case 2 Results
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Version
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Changes/Notes
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Result (images)
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V1
4.3 Case 3 Results
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Version
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Changes/Notes
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Result (images)
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V1
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5.0 Conclusions and Next Steps
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In general, the “DOF errors” kept appearing on different tubes of the chassis in UX, UY and UZ.
These tubes were constrained (fixed or displacement constraint) in order to help with convergence. However, this method was not efficient as the errors continued to show up in other areas.
Eventually, this method led to a point where constraining elements any further would lead to inaccurate modelling in the behaviour of the chassis. (i.e. fixing all tubes will allow the sim to solve)
Due to limited time constraints, the convergence issues that arise from the non-linear contacts were not able to be resolved.
Moving forward, it is best to continue using the bonded contact type only.
6.0 Other Resources:
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Ansys static structural: ANSYS - Static Structural Analysis
analysis settings
types of loads
types of supports
types of results