Assignment 3-2D Element Formulation Challenge

Objectives:

1. To Change the run time to 55 ms for the Crash Beam file.

2. To Change the number of animation steps during Simultions to  minimum of 25 and maximum of 60.

3. To  Run the base simulation without any modification to element properties.

4. To Carry out enrgy error mass error checks for the simulation carried out.

5. To Plot rigid wall forces,Internal enrgy,hourglass energy, contact energy & total energy of the simulations.

6. To carry out the all the above exercises by changing the shell elements properties to the recommended values given below and saving it as a seperate read file.

1.  I_shell =24   (QEPH 4 nodes shells are best combination of cost and accuracy)
2.  I_smstr=2     (Full geometric nonlinearities (default)with possible small strain formulation activation in RADIOSS Engine)
3.  I_sh3n=2      (Standard 3 noded shell (C0)with modification for large rotation(default))
4.  N=5            (Number of integration points set to 5 for accuracy bending)
5.  I_thick=1       (Thickness change is taken into account for accuracy) 
6.  I_plas=1        (Iterative plasticity for good accuracy)

7. To Determine any changes in the results if any & reasons for the same.

 Fig 1 Given Model File

Procedure:

1. Changing the run time to 55ms

            The Change in the value of  run time to 55 ms is made in the engine file.i.e.Element_Formulation-Shell-3_assignment_0001.

2.Changing the number of animation steps during simulation to minimum of 25 & maximum of 60.

            Since the animation steps can be minimum of 25 and maximum of 60, we can choose it to be 50. Hence, the Tfreq in the engine file should be (Total run time / no of animation steps) i.e 55/50= 1.1 ms.

Fig 2 Making changes in the engine File for run time & Animation steps

3.To import the Stater file

              The radioss starter file is imported using the import tool from the standard tool bar. The import solver deck option is chosen and the starter file is chosen for importing and the import button is hit.

 Fig 3 Importing the Starter file

4.Running the base simulation without any modification to element properties

          The radioss tool from the analysis tools panel are selected. The Default properties are as follows:

1. I_shell =0
2. I_smstr=0
3. I_sh3n=0
4. N=5
5. I_thick= 1
6. I_plas=1

             The radioss tool in the analysis tools panel, the path where in the analysis files are to be stored are entered and 4no of threads are entered in the options so that 4 no of processors can work simultaneously for faster analysis. On hitting the Radioss button, the analysis starts.

 Fig 4 Running the analysis by default values

 Fig 5 Analysis being Run

 5. Checking the .Out file for energy error and mass error

         The Eenrgy error in the .Out file is 10.3% which is less than 15% and hence accepteable.The Mass error is found to be constant at 0.1659E-03 without any addition to the mass.

Fig 6 Checking for the Energy and Mass error

6. Plotting the rigid wall forces without any Changes to the Element Properties

            The client selector is changed from Hypermesh to Hyperview.

 Fig 7 Changing from Hyperworks to Hyperview

                 The .h3d file is uploaded and the play button is hit for the animation to start. 

Fig 8 Uploading the .h3d file for the animation

         The Page window layout is changed in order to split the windows into two windows and the Client selector is changed from the hyperview to the hypergragh in the second the window.

Fig 9 Creating the Hypergraph Window

         The X- axis is set as the Time and the Y-axis is set as the Total Resultant Rigid wall forces. 

Fig 10 Plotting the rigid wall forces

 7.Plotting the internal energy without any Changes to the Element Properties

 The X- axis is set as the Time and the Y-axis is set as the Internal energy. 

 Fig 11 Internal Energy Plot without changing Properties

  8.Plotting the Kinetic energy without any Changes to the Element Properties

           The X- axis is set as the Time and the Y-axis is set as the Kinetic energy. 

Fig 12 Kinetic Energy Plot without changing Properties 

9.Plotting the Hourglass energy without any Changes to the Element Properties

           The X- axis is set as the Time and the Y-axis is set as the Hourglass energy.

Fig 13 Hourglass Energy Plot without changing Properties

10.Plotting the Contact energy without any Changes to the Element Properties

                The X- axis is set as the Time and the Y-axis is set as the Contact energy.

Fig 14 Contact Energy Plot without changing Properties

11.Plotting the Total Energy of the Simulation without any Changes to the Element Properties

                       The X- axis is set as the Time and the Y-axis is set as the Total energy of the simulation.

  Fig 15 Total Energy without changing Properties   

12.Changing the Element properties and running the base simulation

       The following changes are made to the element properties:

•  I_shell =24   
•  I_smstr=2     
•  I_sh3n=2     
•  N=5            
•  I_thick=1        
•  I_plas=1        

           The base simulation is run and the energy error and the mass error are checked in the .out file.

 Fig 16 Energy error and mass error after changing the properties    

     The energy error is found to be only -0.1% at last cycle ascompared to -10.3% when the base simulation was run without making any changes to the properties.

Hourglass  : The Hour glass  is the deformation mode in the under integrated elements where in there is no stress produced hence, the strain produced is an inaccurate one.

Causes for the Hourglass : The hour glass ususally occurs due to the  Underintegrated Elements .

Ways to avoid Hourglass : The ways to avoid the hourglass are through the following methods:

   a) Perturbation method : An opposing force is applied on the node based on the material applied,young's modulus,Yield stress & Plastic tangent in order to stablize the deformation. This method is generally employed by using the Shell element Ishell=1,2,3,4(Q4).The energy produced due to the opposing force is called as the Hourglass Energy.

   b)Physical stablization Method : In this method, the hourglass is controlled at the material level when the element Ishell=24(

13.Comparing the Rigid wall forces,internal energies,Kinetic energies ,Hourglass energies & total energy after changing the element properties with the same without changing element properties

    i) Comparisons of the Rigid wall Forces

  Fig 17 Comparison between Rigid Wall forces

               The Maximum force and the minimum force values were found to be higher after change in the elemment properties.

ii)Comparison of the  internal energies

 Fig 18 Comparison of Internal Energies        

                 The Change in the Internal energy without any changes to the element properties is More linear where as with the Change in the element properties ,the change in the Internal energies is more exponential. 

 iii)Comparison of the  Kinetic energies

Fig 19 Comparison of Kinetic Energies

        The Decrease in the Kinetic Energy when there is no Change in the Element Properties is Linear with time where as the decrease in the Kinetic energy when there is change in the Element properties is Exponential with time. 

 iv)Comparison of the  Hour glass energies

  Fig 20 comparison of Hour glass energies

       The Hour Glass energy changes with the progression of the time when there is no change in the element properties whereas once the element properties are changed to the Specified values , it is obeserved that the Hour glass energy remains zero & it doesn't change with time.

vi)Comparison of the Total energies

Fig 22 Comparison of Total Energies

            The total energy falls below the value of 5.5E+07 N-mm when there is no change in the element properties where as there is total energy doesn't fall below 6.125E+07N-mm when the element properties are changed to the required values.

Reasons for the Changes in the plot of Rigid Wall forces,Interrnal energies,Kinetic Energies,Hourglass Energies and Total Energies:

  The Element type employed without any changes to the Property Element is Ishell=0 where as the element type employed after the changes to the element properties is Ishell=2,4( QEPH) which leads to the physical stablization of the Hourglass deformtion at the material level hence leading to better accuracy.

Fig 23 Comparison of the Results

Results:

1. The run time for Simulation was changed to 55 ms Sucessfully.
2. The number of animation steps during Simultions was changed Successfully to 50.
3. The base simulation was run successfully without any modification to the element Properties.
4. The Comparison of the Rigid wall forces plot,internal energy plots,Hourglass energies,Contact Energies & total energies in both the cases i.e,without modification to the element properties and with the specified modification to the Element properties was carried out comprehrehensively.
5. The reasons for the Changes in Plots were determined.