Week 11 Car Crash simulation

Objective: A parametric study using 3 different values of thickness for the car body.

Model:

Definition of a Car body:

Implicit vs Explicit Analysis:

Implicit and Explicit analysis differ in the approach to time incrementation. In Implicit analysis each time increment has to converge, but you can set pretty long time increments. Explicit on the other hand doesn’t have to converge each increment, but for the solution to be accurate time increments must be super small.

How Implicit Analysis Works:

First of all, implicit seems to be a more “basic” solution. In essence, it works just as you would think it should!

Firstly, in each time increment, the “global equilibrium” in the model is established. This means that each increment has to converge (this is happening in iterations).

After global equilibrium is ok, the solver calculates all the local finite element variables (stresses, etc.) for this increment.

Benefits: Since global equilibrium is verified at each time increments, those increments can be BIG!

Drawbacks: Each time increment computes slowly since iterations are needed to get to the global equilibrium.

How Explicit Analysis Works:

It works in a way, that you don’t have to converge each step! There are no convergence criteria to check and… no iterations! Instead of verifying the “global equilibrium” solver assumes that the equilibrium “simply exists”. This means that the solver goes straight into the calculation of local finite element variables! As such procedure has only one step:

Calculate all of the local finite element variables for the given increment, and move to the next one!

Benefits: Each increment calculates extremely fast!

Drawbacks: For this to work, the time step has to be EXTREMELY small. Otherwise, it’s impossible to maintain this equilibrium that is assumed to “simply exist”. To achieve this, users do not have direct control over how big-time increments explicit solver will take. Solver itself calculates how small timesteps are still ok. And those acceptable time increments are SUPER SMALL!

This is why explicit problems should last fractions of the second! If they would last seconds… you would need millions of increments!

Symmetry:

Mesh sizing and methods:

Final Mesh:

Analysis Settings:

Fixed support:

Displacement:

Solution:

Total Deformation:

Equivalent stress:

Total stress of the system:

Equivalent stress in the car body:

Parametric Data for different thickness:

Benefits of Parametric Design Analysis:

- Parametric analysis is an excellent way to get accurate information about the influence of all parameters on the design objectives, such as system performance with respect to stress,

heat flow, mass flow, and other variables.

- With this information, the design team can make informed decisions throughout product development, especially in the early conceptual stage.

- As a consequence of the parametric analysis, the design team also can react quickly to any modification due to external constraints (for example, manufacturing) and can easily answer

any “what if” questions.