Assignment 3-2D Element Formulation Challenge

AIM:--

1) Run the simulation with the default property card (CASE 1)

2) Changing the property card ( CASE 2)

3) Comparing CASE 1 & CASE 2

PREREQUISITE:--

ELEMENT FORMULATION

1D:- Includes SPRING, TRUSSES, BEAMS.

2D:- Includes shell elements like QUADS, TRIAS.

3D:- Includes solid elements such as HEXA, TETRA elements.

Hourglass:

"Hourglass is a deformation, that is noticed when an element is deformed due to the applied load. But the strain energy due to this deformation is not recorded for that element". It is also known as "Zero energy deformation modes" where an element is seen deformed.

• It indicates instability.
• It is also said to be as, non-physical mode of deformation, that occurs in reduced or under integrated elements & produces no stress.
• Usually, it can be seen in the post-processing stage, where the elements will have zig-zag formation.

BEFORE HOURGLASS EFFECT

AFTER HOURGLASS EFFECT

METHODS TO CONTROL THE HOURGLASS:--

1. Perturbation method(viscous method)
2. Physical stabilization method (stiffness method)

Perturbation method(Viscous method):-

• This method is generally used for the elements with Ishell: 1,2,3,4 or Q4 elements.

• The process how this method work is: When the hourglass deformation occurs---> There will be some damping applied, which is stabilizes the deformation, which results in controlling the speed of deformation.

• But this damping opposes only the velocity, But not the force. So, the force is introduced, which results in adding some stiffness to the elements. This stiffness helps in controlling the hourglass.

• The force is applied externally, by some other means. But not from FEA nature. This force constitutes energy called "Hourglass energy", Which is artificial energy(neither Kinetic nor internal energies). It is a loss of both energy types.

• If the hourglass energy is added along with the kinetic energy & Internal energy, A balance system is obtained.

• Recommended for high velocity or high strain rate problems. Example: Involving high explosives.

• A huge amount of hourglass energy is generated.

Physical stabilization method (stiffness method):--

• In this method, the stiffness is getting added right from the material level. This will have a large effect on our component.

• It is recommended for fewer velocity problems.
• used for QEPH elements.
• Less amount of hourglass energy is needed. Because it is going to be controlled before it arises.

Q4 element:

• It is an under(or) reduced-integrated element. Because it has only 1 integration point for an element.
• It is represented in the radioss solver by an entity named "Ishell(1,2,3,4)".
• Usually Ishell:1, Ishell:4 elements are used, when no more velocities are to be found.
• By default, the solver takes as Ishell:1.
• As it has only 1 integration point, the time required to solve the problem with this type of element is relatively less.
• The cost required to solve this type of element is relatively low.
• But there will be no accuracy in the results.

QBAT element:

• It is a fully integrated element, Which means it comprises 4 integrated points. Each point is near to each node.
• It is represented in the radioss solver by an entity named "Ishell: 12".
• Because of these 4 Gaussian integration points, there will be no Hourglass deformation.
• Using this element is not economical. But the achieved results are more accurate than the remaining Ishell elements of quads.

QEPH element:

• It is an improved under-integrated element with physical hourglass stabilization within itself.
• It is represented in the radioss solver by an entity named "Ishell:24".
• This type of element is mostly used recently. Because of its best compromise between the cost, quality& accuracy in results.
• It is widely used in the automotive industry.

CO element:

• It is a standard co-rotational triangle, with modification for large rotations.
• Usually, it helps in representing the tria elements with the entity named "Ish3n:2".
• It consists of 1 integration point.
• No hourglass deformation.
• Low CPU cost.
• Results may not be accurate.

Key parameters in /PROP/SHELL:-

Ishell:-To select the element formulation for 4-noded shell elements.
Ish3n:-To select the element formulation for 3-noded shell elements.
N:- To choose the number of integration points through the thickness
Ismstr:- To specify whether the strain formulation is small or large.
Iplas:- To choose method for the calculation of post-yield strain.
Ithick:- To determine if the thickness is constant under load or if the element thins.

PROCEDURE--

CASE 1:-- WITHOUT ASSIGNING THE RECOMMENDED PARAMETER IN THE PROPERTY

1) Import the model in RADIOSS user interface

2) Import the file as SOLVER DECK

3) Model will look like this

4) Now next step is to assign the value of time step in ENG_RUN cars as 55ms as per question

5) Now we have assign the number of animation steps. I choose 50ms as number of animation step as per the question.

Tfrequency= TIME STEP/NUMBER OF ANIMATION STEP = 55/55 = 1

6) In the property card every parameter property is by default shown below.

7) Now we will run the simulation ANALYSIS--RADIOSS

8) In the RUN OPTION panel it is recommended to write -nt 4. not stands for number thread it assigned to do the simulation at faster rate.

9) Click RADIOSS and it will show JOB IS COMPLETED

10) Now click on RESULT, it will directly take you to hyperview where we can see the animation of the simulation. Animation file are in name of h3d

11) Click apply

12) Now switch to contour mode

13) After switching choose the RESULT TYPE to see the deformation. I choose VON MISSES and click apply.

14) we can see animation

15) Now we can see the output of simulation in 0001.out file

SAFE TOLERANCE IS -15% TO +5%

16) Graphs for plotted for this various energy. For plotting graph we have to switch to hypergraph tab and import file T01 which is stands for time history

CASE 2:-- ASSIGNING THE RECOMMENDED PARAMETER IN THE PROPERTY

1) Assign all the parameter property

2) After assigning run the simulation same as above simulation

3) von misses deformations is

4) Now we can see the output of simulation in 0001.out file

SAFE TOLERANCE IS -15% TO +5%

5) Graphs for plotted for this various energy. For plotting graph we have to switch to hypergraph tab and import file T01 which is stands for time history

COMPARISON BETWEEN THE CASE 1 & CASE 2

CONCLUSION:--

1) Learned how to carry out simulation

2) Learned about property card

3) Learned how to use hypergraph

4) Leaned about hourglass and how to remove these