Comparing the simulation results of the base setup and improved shell element properties for Crash Tube Analysis.
Aim : The task was to compare the simulation results of the base setup and improved shell element properties for Crash Tube Analysis.
Description :
1st the simulation was conducted on crash tube with base setup i.e without any modification to element properties.
The output report file presenting errors screenshot is given below.
As we can see the max energy error that occurs is -11% . Energy errors should be negative and up to 15% negative error is accepted. So these simulation is good enough to get further results. Here The Hourglass energy is not counted in this energy balance, so that a negative energy error generally occurs.
Energy error is negative represents that energy is dissipating.
The mass error is 0.165*10^ -3.
The report plot from hyerpview and hypergraph are given below.
Here as we can see in the first image , it represents vonmises stress contour (Average method), The maximum stress occurs at node no 705 of magnitude 349 Mpa and min stress occurs at node no 716 of 0 magnitude.
The 2nd Image represents various Energy v/s time plot.
As we can see Kinetic energy initially is very high because tube initially collides the wall with high velocity. Now since it collides at high speed the internal energy starts opposing and hence starts increasing along with time. The hourglass energy that is not taken into account of energy errors and it explains negative energy error.
The 3rd and 4th image represents force v/s Time
The Resultant force is almost similar to Resultant Normal force as we can see in the images. The frictional force (Tangential) slightly goes on increasing with time as the crash tube opposes the collision so frictional force increases.
2. Simluation of the crash tube after changing the shell elements properties to recommended properties.
The following properties were applied to property cards - Hat section and close out panel.
Then after running simulation with the above properties , the output file representing errors screenshot is given below
As we can see the maximum energy error is only 0.1 % and the mass error is similar to previous one. In case of using QEPH shell formulation, the Energy Error can be slightly positive since there is no Hourglass energy and the computation is much more accurate.
The report from Hyperview and Hypergraph are given below.
As we can see 1st image shows Contour plot of vonmisses stress. The maximum stress occurs at node no 168 which is of magnitude 346.15 Mpa and minimum stress occurs at node no 716 which is of magnitude 0. The animation time was set to 60.
Image 2 shows various energy v/s Time graph plot
Here also since collision at the beginning is with high velocity kinetic energy is high and thus it gives rise to internal energy as it is opposing the collision. The total energy is constant.
The interesting curve here is the hourglass curve which is completely straight line on horizontal (X –axis) representing that as we have applied QEPH it does not consider Hourglass energy.
3rd Image is of Forces V/S Time
Here also Resultant and Resultant normal force are almost similar. Tangential force is the effect of collision of crash tube to wall and hence it increases with time.
Conclusion : After application of the property card, Hourglass energy has completely become zero because of the use of QEPH shells. These elements increases the number of Integration points and as the no of intergration points increases the element gets more stiffer thus resulting in less deformation.
The important conclusion is that setting up correct elemental property is very important in the preprocessing step, otherwise the results will be devaited from the actual results and will lead to wrong results.