Comparing default shell properties with recommended properties by plotting graph in HyperGraph
OBJECTIVE:To compare the results with base simulation and improved shell elements properties by performing energy, mass error checks, plotting graph in HyperGraph and animating in HyperView.
SIMULATION 1: With default Shell Properties.
Imported Element_Formulation-Shell-3_assignment_0000.rad file. Property was not changed.
Changed Runtime to 55milli seconds and animation frequency to 2.2 to get 25 animation files.
SIMULATION 2: With recommended shell properties, same Runtime and animation frequency as above.
After assigning recommended properties:
ENERGY ENERGY AND MASS ERRORS:
Energy error must be negative and decreasing. The error must be less than 15% at the end of simulation (5% for a good model). If error increases a little, and then decreases it may be acceptable.If the error increases, this means that a problem has occoured.Then the error may grow to 99.9% with computation failure message.
So ideally the error should be atmost -15% and better to have -5%.The closer to 0% error the better.For QEPH shell formulation or fully integrated elements, the error can be slightly positive since there is no hourglass energy and computation is much more accurate.An error of 1-2% is acceptable.Otherwise any positive error means which means energy has been created and it is a model issue.
Opened Element_Formulation-Shell-3_assignment_0001.out file to check the energy error and mass errors.
At the end of simulation1 error is shown below:
ENERGY ERROR AND MASS ERROR:Simulation 1
-10.3% AND MASS ERROR 0.1659E-03
Since energy error is negative it indicates energy has been dissipated from the system.
Also since energy error is less than -15%, so model is ACCEPTABLE for further calculations.
ENERGY ERROR AND MASS ERROR:Simulation 2
-0.1% and 0.1659E-03
ELEMENT QEPH(4node) Ishell 24 has inbuilt Hour Glass stablization due to which there is reduce in energy errors in second simulation.
PLOTTING OF VARIOUS GRAPH:
SIMULATION 1 AND 2 : HOURGLASS
From above plot we can see HG in simualtion 2 is constant and zero. This is mainly due to selection of QEPH element.
HG energy is controlled by two method.
HG PERTURBATION METHOD: For element suspected to HG modes, internal HG forces are applied to resist the HG mode deformation.
Stiffness Method: Here Extra stifness is applied on material itself even before HG error can appear so there is HG energy generation in this method. QEPH elements uses this method.
SIMULATION 2 AND 1:INTERNAL ENERGY
SIMULATION 2 SIMULATION 1
Internal energy is sum of kinetic and potential energy. In simulation 1 change in internal energy is almost linear and in 2 we see a curve. At the beginning KE was high and IE was zero due to zero deformation and at the end KE goes to zero and IE becomes high and constant but still less than KE mainly due to energy error. we can see zero KE only if we increase run time more than 55ms.
If we increase runtime to 85ms, KE become zero and IE become maximum and remain constant.
SIMULATION 2 AND 1:CONTACT ENERGY
SIMULATION 1 SIMULATION 2
In both cases, we see around 17ms, sudden increase in contact energy. This is mainly due to buckling. In simulation2, this was captured better.
SIMULATION 1 AND 2:TOTAL ENERGY
SIMULATION 1 SIMULATION 2
Total energy is decreasing almost linearly, this may be due to incomplete capture of deformation, element may not be able to completely transfer force and stresses to neighbouring element or may be due to default element properties.
SIMULATION 1 AND 2:RIGID WALL FORCES
SIMULATION 1 SIMULATION 2
Initially, there was huge force, but due to internal deformation this force gradually decreased and friction force aslo got generated. Total resultant force is sum of normal force and tangential force.
SIMULATION 1 AND 2:VON MISES STRESS
SIMULATION 1 SIMULATION 2
Both simulation shows same value of VON MISES stress but node at which max force is acting got changed. The reason could be due to recommended properties applied for 2nd simulation. At 716 node there is no stress in both simulations.
CONCLUSION:
With default properties, element deformation does not look natural. To overcome this shell properties was changed according to recommendations.QEPH ISHELL 24, with inbuilt HG stablization was used to capture deformations and transfer of stresses more effectively.
Radioss file link:
https://drive.google.com/file/d/1gmZ4m4_4lIipgBnZP38uyTw71gZlxmKQ/view