Crash CAE Flashcards
Who said: “All models are wrong, but some are still useful.”
“All models are wrong, but some are still useful.”
George Box, University of Wisconsin-Madison
Who said: “A simulation is reliable if the differences between numerical and test results are small enough to lead to the same design conclusions”
“A simulation is reliable if the differences between numerical and test results are small enough to lead to the same design conclusions”
Paul du Bois, independent consultant in the automotive industry
Explain difference between verify and validate in the context of FEM.
It is important to verify and validate models:
– Are the mathematical equations correctly implemented? (Verify)
– Are results close to experimental observations? (Validate)
Which are the Guidelines for model development?
Guidelines for model development
- Define the objective(s) of the model
- Don’t make the model more complicated than what is required for its application(s)
- Use experience from earlier model development efforts
- Implement as much as possible model parts which have been validated on a component level
- Make model validation an essential part of your strategy
How to Developing a predictive model.
Explain Optimum of Model Refinement
Visual difference of Multi Body Models and FE models
Compare MBD, FEM and Testing.
Which are the major simulation softwares?
Major Simulation Softwares
Multi Body Dynamics
MADYMO
CAL3d
Finite Element Method
LSDYNA,
RADIOSS,
PAMCRASH(VPS),
ABAQUS(Explicit)
What is Finite Element Method?
Explain Discretization in the context of FEM.
Explain the different Mesh Types.
Explain Shell Element.
Explain Numerical Quadrature
In numerical analysis, a quadrature rule is an approximation of the definite integral of a function, usually stated as a weighted sum of function values at specified points within the domain of integration. An n-point Gaussian quadrature rule, named after Carl Friedrich Gauss, is a quadrature rule constructed to yield an exact result for polynomials of degree 2n − 1 or less by a suitable choice of the points xi and weights wi for i = 1, …, n.
Explain Hourglassing.
Hourglass (HG) modes are nonphysical, zero-energy modes of deformation that produce zero strain and no stress. Hourglass modes occur only in under-intetgrated (single integration point) solid, shell, and thick shell elements. LS-DYNA has various algorithms for inhibiting hourglass modes. The default algorithm (type 1), while the cheapest, is generally not the most effective algorithm.
A way to entirely eliminate hourglass concerns is to switch to element formulations with fully-integrated or selectively reduced (S/R) integration. There can be a downside to this approach. For example, type 2 solids are much more expensive than the single point default solid. Secondly, they are much more unstable in large deformation applications (negative volumes much more likely). Third, type 2 solids have some tendency to ‘shear-lock’ and thus behave too stiffly in applications where the element shape is poor.
Why can you use Under-integrated elements?
Explain Mesh Convergence in Practice.
Explain Isoparametric Elements.
Isoparametric Elements
As mentioned above, to form a mesh over a general region the elements must be allowed to take more general shapes. This is done by using the parent elements and transforming them by some mapping. The essential idea underlying this centres on the mapping of the simple geometric shape in the local coordinate system into distorted shapes in the global Cartesian coordinate system. The mapping from local to global coordinates will take the form
Give some examples of Mesh quality requirements.
Explain Static versus Dynamic FE.
Give examples of Static versus Dynamic FE.
Meaning on nonlinear analysis in terms of FE?
Explain Equation of motion.
Explain Explicit FE analysis.
Explicit analysis handles nonlinearities with relative ease as compared to implicit analysis. This would include treatment of contact and material nonlinearities.
In explicit dynamic analysis, nodal accelerations are solved directly (not iteratively) as the inverse of the diagonal mass matrix times the net nodal force vector where net nodal force includes contributions from exterior sources (body forces, applied pressure, contact, etc.), element stress, damping, bulk viscosity, and hourglass control. Once accelerations are known at time n, velocities are calculated at time n+1/2, and displacements at time n+1. From displacements comes strain. From strain comes stress. And the cycle is repeated.
Difference between Static and Dynamic FE.
In static analysis, there is no effect of mass (inertia) or of damping. In dynamic analysis, nodal forces associated with mass/inertia and damping are included.
Static analysis is done using an implicit solver in LS-DYNA. Dynamic analysis can be done via the explicit solver or the implicit solver.
Describe Critical Time Step
When would you use mass scaling?
When is Self-Contact important?
Which type of contact is the most common one?
Why are contacts computationally demanding?
What are contact segments?
Where does contacts take place?
What is important to review when setting up your model?
Crash Simulation Automotive Specific Challenges
