Assignment 3-2D Element Formulation Challenge

Crashworthiness Analysis using HyperMesh and Radioss

#Assignment 3-2D Element Formulation Challenge

AIM: Comparison of results with base simulation and improved shell element properties

OBJECTIVES:

(1). Changing the runtime to 55 ms. of crash beam file.

(2). Changing the number of animation steps during simulation to a minimum of 25 and maximum of 60.

(3). Running the base simulation without any modification to element properties.

(4). Checking and determining the energy error and mass error at the end of the simulation, whether results will be acceptable or not.

(5). If acceptable, Plot-- Rigid wall forces, Internal energy, Hourglass energy, Contact energy and Total energy of the simulations.

(6). Changing all the shell elements properties to given recommended properties, saving that as separate, rad files and running the simulation.

(7). Following steps 4 and 5 after changing recommended properties.

(8). Comparing all the results of both the cases simulations.

(9). Briefing changes in the results of both cases.

component:

PROCEDURE FOR OBJECTIVE 1 : Changing the runtime to 55 ms. of crash beam file.

STEP 1: Open Hyperworks in Radioss solver.

STEP 2: Import Solver desk runname_0000.rad file (starter input desk).

STEP 3: Follow following commands

• Going to model tab
• Click on Cards collector
• Click on ENG_RUN card
• Change Tstop to 55

PROCEDURE FOR OBJECTIVE 2 : Changing the number of animation steps during simulation to a minimum of 25

STEP 1: Follow following commands

• Going to model tab
• Click on Cards collector
• Click on ENG_ANIM_DT card
• Change Tstart to 25

PROCEDURE FOR OBJECTIVE 3 : Running the base simulation without any modification to element properties.

STEP 1: Set eng_run and eng_anim_dt cards as we did in objective 1 and 2.

STEP 2:

• Analysis>Radioss>save as input runname_0000.rad file
• Checkbox include collectors
• Write (-nt 4) in options (increasing speed of simulation -number of threads 4cpu ).
• Click Radioss

STEP 3: Switch to Hyper view

STEP 4: select local model and result runname..h3d file

• Simulation Started from 25 and Ending View

PROCEDURE FOR OBJECTIVE 4 : Checking and determining the energy error and mass error at the end of the simulation, whether results will be acceptable or not.

• Opening runname_0001.out file, we can see energy error percentage and mass error at the end of computation.

• As we know, Energy error must be negative and decreasing, the error must be less than 15% at the end of computation, we find -10.3% energy error and mass error is 0.1659*10^-0.3
• So results are acceptable.

PROCEDURE FOR OBJECTIVE 5 : Plot-- Rigid wall forces, Internal energy, Hourglass energy, Contact energy and Total energy of the simulations.

STEP 1: Toolbar>select bropbox list>click Hypergraph 2D

STEP 2: Select data file tab > give file path of runname_T01.file

STEP 3: Global variables>select internal energy,hourglass energy,contact energy and total energy>select MAG>apply

• Graph of Internal energy, Hourglass energy, Contact energy and Total energy.

STEP 4: Select new plot.

STEP 5: Select rigid wall/R wall forces>4 rigid wall>select resultant normal force, resultant tangent force, total resultant force>apply

• Graph of Rigid wall forces

PROCEDURE FOR OBJECTIVE 6 : Changing all the shell elements properties to given recommended properties, saving that as separate, rad files and running the simulation.

STEP 1: Making a new folder to save all new property changed files.

STEP 2: Go to model tree>select properties

STEP 3: Select Hat section and Close out panel property one by one and change --

• Ishell to 24
• Ismstr to 2
• Ish3n to 2
• N to 5
• Ithick to 1
• Iplas to 1

PROCEDURE FOR OBJECTIVE 7 : Following steps 4 and 5 after changing recommended properties.

• Repeat Procedure of objective 1 to 6 again for this case.
• Simulation Started from 25 and Ending View

RESULTS OF SECOND CASE:

• Energy error percentage and mass error at the end of computation.

• Graph of Internal energy, Hourglass energy, Contact energy and Total energy.

• Graph of Rigid wall forces

PROCEDURE FOR OBJECTIVE 8 and 9 : Comparing all the results and Briefing changes of both the cases simulations.

	Case 1 Base Simulation	Case 2 Property changed element Simulation
Internal energy	Increases as time increases	Increases as time increases
Hourglass energy	Increases as time increases	Remains Zero as time increases
Contact energy	Remains Zero as time increases	Remains Zero as time increases
Total energy	Decreases as time increases	Remains constant as time increases
Energy error %	-10.3 %	-0.1 %
Mass error	0.1695*10^-03	0.1695*10^-03
Rigid wall forces	Total resultant force and resultant normal force remains almost similar and fluctuates more w.r.t time. Resultant tangent force increases then decreases at last	Total resultant force and resultant normal force remains almost similar and decreases w.r.t time. Resultant tangent force decreases then increases at last

Conclusion : Energy error decreases and hourglass remains constant after improving shell elements’s property.

LEARNINGS:

Details on hourglass energy and modes

• Hourglass Energy and Modes.

Hourglass energy :It is work done by the forces calculated to resist hourglass modes, takes away from physical energy of the system.

Hourglass modes are zero energy modes of deformation that produce zero strain and no stress. Hourglass mode occurs only in under integrated solid, shell and thick elements.

• Causes

While post processing results we can see a false deformation with zig zag lines such phenomena is called Hourglass Effect.

Generally this does not happen in experiment but in FEA it happens, this is just a non energy mode which leads to excessive element distortion. More structured and less distorted elements are better for the results.

• Steps to avoid hourglass deformation
• Perturbation (Viscous) Method (Q4 Elements): Ishell 1,2,3,4 -

When hourglass deformation is happening there is some damping can applied and because of that damping the deformation will be stabilized and that way it will try to control the speed at which it is deforming is happening. When we apply daming it is going to oppose only velocity but not the force. To apply that velocity a force is getting generated by it is going to affect only the speed at which this deformation is happening and that is why while this force is being introduced it is going to add some stiffness (stiffness is added to the element’s node) and this stiffness in the end is going to cause hourglass to be controlled.

Because this force is externally applied but not in natural FEA means this force constituting another energy type is called hourglass energy that is why it is called an artificial energy because it does not exist in nature .

• Physical Stabilization (QEPH Elements): 24(QEPH)

In this case the stiffness is artificially added on the element and to add this it is going to affect the material’s property directly, so here stiffness is added right to the material.

• Using fully integrated elements, hourglass deformation can be avoided.
• Mesh refinement will also helps to avoid hourglass deformation

_____________________________________________________________________________________________________

• Importing starter file runname_0000.rad file
• Using Radioss command
• Running .h3D file in Hyperview to see animation
• Reading runname_0001.out file
• Using Hypergraph 2D
• Reading Energies and Forces graph
• Changing property parameters