Assignment 3-2D Element Formulation Challenge

IMPORT:-

. The given rad file is imported to hyperwork and is displayed as below.

. The element view is st to shaded elems view which displays the elements as follows.

. Changung run time to 55ms:

. In model tree, under CARDS collector, ENG_RUN card have a tstop of 60, ehich is changed to 55.

. Changing animation steps to 40:

. To have 40 animation steps, the frequency should be RUN time/animation steps = 55/40 = 1.375

. In model tree, under CARDS collector, ENG_ANIM_DT card have a Tfreq of 1.0, which is changed to 1.375.

. The base simulation is run without any modification to element properties using radioss under analysis tab.

. Create a folder to save the rad file in local directory.

. edit option providing number of threads as ''-nt4''.

. After analysis the OUT file is viwed to check whether the energy error and mass error fall within the aceptable range.

. The energy errors start from 0% to 10% which is within acceptable range.

. Masss error stays constant throughtout the simulation at 0.1659e-03 which is aslo within the acceptable range.

. Since the error value are acceptab;e, rigid wall forcae, internal energy, hourglass energy, contact energy, total energy of the simulation are plotted with the help of hypergraph 2-D

. hyperview is opened to view the simulation (deformation of the crush tube).

. model and result (h3d file) anre loaded from the newly created folder

. animation shown how the crush tube deformes (displacement) under the action of force.

. to plot the specific graph, hyper graph 2-d is selected.

. file named element_formulation-shell-3_assignment T10 is opened.

. specified energies are plotted against time on the same plot as shown below:

. from the plot obtained for base simulation without any modification be element properties following observation are made;

. internal energy increase throughout the simulation which is due to the force developed on tube due to deformation.

. there is a slight increase in hourglass energy throughtout the simulation.

. contact energy remain zero throughout the simulation.

. total energy of the system has a slight decrease from the start to end of the simulation.

total resulant force and resultant normal rigid wall force are plotted against time as shown above.

. the rigid wall force curve is of a non-linear behaviuor, which is due to the variation in the force exerted by the crush tube on the wall throughout the simulation.

. contouyr plot of hourglass energy is obatined using contour option under hyperview.

Contour plot of displacement is obtained using contour option under hyperview,

CHANGING THE SHELL ELEMENTS PROPERTIES TO RECOMMENDED PROPERTIES:-

Recommended properties;

parameters

commant

Ishell = 24

QEPH 4 node shell are best combination of cost and accuracy

Ismstr = 1

full geometric nonlinearities with possible smell strain forulation activation in RADIOSS engine.

Ish3n = 2

standard 3 noded shell (co) with modification for large rotation (default)

n = 5

number of intergration point set to 5 for accuracy bending.

Ithick = 1

Thickness change is taken into account for accuracy.

Iplas = 1

Iterative plasticity for good accouracy.

the shell element properties are modified to recommenede property values.

. changing run time to 55ms.

. In model tree, under CARDS collector, ENG_RUN card have a Tstop of 60, which is changed to 55.

. changing animation steps to 40.

. to have 40 animation steps the frequancy should be run time/animation step = 55/40 = 1.375

. in model tree, under CARDS collector, ENG_ANIM_DT card have a Tfreq of 1.0, which is changing to 1.375.

. Runing the simulation with the newly defined recommended properties using radioss option under analysis tab.

.create a folder to save the rad file in local directory.

. edit option provieded number of threads as ''-nt4''.

. After analysis the OUT file is viewed to check whether the energy error and mass error fall within the aceptable range

. the energy error start from 0% to -0.10% which is within acceptable range

. mass error stays constant throughout the simulation at 0.1659e-03 which the error value are acceptable range.

. since the error value are acceptable, rigid wall forces internal energy, hourglass energy, contact energy, total energy of the simulation are plotted with the help of hypergraph 2-D

. file named elemnt _formulation -shell-3_assignment T01 is opene.

. specified energies are plotted againest time on the same plot as shown below.

. from the plot obtained for simulation after modification to element propertes following observation are made.

. internal energy increase throught the simulation which is due to the force developed on tube due to deformation

. total energ remain same throughout the simulation.

. hourglass energy and contact energy remain zero and follows the origin throughout the simulation.

A new plot is create to plot the rigid wall forces.

total resultant force and resultant normal rigid wall force are plotted against time as shown above.

the rigod wall force curve is of a non-linear behaviour, which is due to the variation in the force exerted by the crush tube on the wall throughout the simulation.

COMPARISON:-

Default

RECOMMENDED PROPERTIES

when recomeded properties are change from the base values, simulation results shown that

1. total energy remain constant rather decreseing which is clear from the energy error which went till-10% now changed to -0.1%.

2. Hourglass energy which was increase changed to zero throughout the simulation.

3. contact energy characteristics are same in both cases,.

4. Internal energy is having a gradual increasing characateristics in both the cases.

5. rigid wall force also decresed to a lower value than that of default value rigid wall force value

6. contour plots shows that there is a slight increae in maximum displacement of element with recommended property values.

Hourglass energy:-

1. In FEA, the hourglass mode is also known as the ''zero energy mode'' because deformation energy of elements under hourglassing mode is zero. but the hourglass energy is not equal to zero

2. in a shell element which have a number of integration points for reduce compulation effort, a reduced intergration which uses a single integration point is used in such case the deformation mode from the analyisis results will be false. this is called hourglass phenomanon.

3. This is just a non physical zero energy mode which lead to excesssive element distortions. the more structured and less distorted your element are the better the results.

To solve this problem,

1. Mesh refining is a solution. Hourglassing is more prone in coarse mesh.

2. Fully integrated element are better through computational time increase vastly and integrated are prone to shear locking.

3. providing a small arbitrary stiffness in the mode in which hourglass deforms. this is only a FEA pont of view and in actual physical system, there is no such stffness. this is whst is called as built in hourglass controls.

4. Viscous damping.