3D Meshing and Editing Starter and Engine Files

Objective:

1. Check the material properties of the rail component and calculate the speed of sound in steel rail.
2. The length of the rail is about 1000 mm. Calculate the time takes for a shock wave to travel from one end of the rail to the other.
3. Time for sound to travel length of rail.
4. Edit the engine file so that the stress wave can be monitored, moving from one end of the rail to the other during impact - this will require a termination time equal to the time it takes for the sound to travel the length of the rail(set on/RUN card).
5. Set the frequency of animation output to a time that will give 20 animation steps (/ANIM/DT).
6. Change /print -10.
7. 3d meshing tetra mesh and hex mesh

• Repeat class examples and, maintain the quality.
• Target tet size=5mm, hex size=10mm, tet collapse=0.15.

Introduction:

• There are two parts to the Radioss simulation, the Starter and Engine. The Starter is an input data check and must successfully complete without errors before the simulation can be completed in the Engine.
• Starter files consists all the input parameters required for the Radioss for analysis and simulation such as the unit system, material properties, etc.
• The Radioss Starter takes as input the model or commonly called Starter input file runname_0000.rad and creates the Starter output file runname_0000.out.
• The Radioss Engine files describe the solution control and output for the simulation. While the Radioss Engine is running, an Engine output file, runname_0001.out, is created which contains statistics about the simulation including time, time step, current system energies, energy error, and mass error.
• 1D elements: 1D elements are used to connect two components or surfaces where the load or other forces would be acting. The forces which are supposed to act on a body or the loads which would cause the body to undergo deformation are applied on these elements. These include elements like, rods, bars, beams, springs, welds, etc.
• 3D elements: to mesh a solid body, 3D elements are used. 3D elements can be created either by converting 2D shells into 3D, or by volumetric meshing, or by quick tetra method. 3D elements are of various types such as 4 noded linear tetrahedron (TETRA4), 8 noded thick shell (BRICK/HEXA), 6 noded thick shell (PENTA6).

Calculations:

• From the starter file provided (FIRST_RUN_0000.rad), following parameters were identified:

Modulus of Elasticity (E) = 210000 MPa or 210000 N/mm².
Density of steel, Rho (ρ) = 0.0078 g/mm³.

Length of rail (L) = 1000mm.

• The image below shows the values in the starter file
  
  

To identify the above given entities, following calculations were made:

1. Speed of sound in steel (C) :

From the standard formulae,

`c = √ E/ ρ`

upon substituting,

`c = √ 210000 /0.0078`

We get 5188.745 mm/ms or 5188.745 m/s.

2. Time taken by shock wave to travel length of rail

Since the length of rail is 1m, time taken for shock wave to travel the length would be,

`1/5188.745` = 0.0001927 s
or 0.1927ms.

3. Time for sound to travel length of rail

Since the shockwave travels at the speed of sound irrespective of the medium, therefore, the time for sound to travel the length of rail would also be 0.1927ms.

4. Termination time = time required for sound to travel length of rail =1927ms.
   
   
5. Frequency of animation output (T_freq)
   
   Here the animation steps are given as 20. So, T_freq = (Termination time)/(animation steps)
   T_{freq = `0.1927/20`}
   = 0.009635

Procedure:

• All the values calculated above have to be replaced in the engine file, FIRST_RUN_0001.rad with the initial values. This can be done simply in the notepad or by importing the file in the RADIOSS using the import solver deck option.
• In this case, it is done in notepad. The value of termination time of termination time specified under /RUN/FIRST_RUN/1/ was changed from 60.000000000000 to 0.1927000000000, and the Frequency of animation output (T_freq) was changed from 1.0000000000000 to 0.0096350000000.
• The following image shows the changes made in the engine file.
  
  
• For the 3D meshing operation, the model of the housing was provided in the .hm format which was directly imported in the HyperMesh using the ‘import geomtery’ command. The image below shows the model as provided in the assignment.
  
  
• The hub component of the model was meshed first. 3D meshing in the housing model was done by converting the 2D tria elements into 3D tetra elements.
• 2D elements were created by using the ‘automesh’ option by keeping the ‘elem size’ as 5mm, and the ‘elem type’ as ‘tria’. This created a tria mesh on all the surfaces of the housing which were checked for the minimum and maximum length using the ‘check elem’ option from the ‘tools’ tab.
  
  
• This mesh was converted into 3D by the ‘3D>tetramesh>Tetra mesh’ option by selecting the surfaces to be meshed. Along with this the specified parameters specified such as target size, and tet collapse were mentioned beforehand in the ‘Tetramesh parameters’ from the same menu.
• This created uniform tetra mesh pertaining to the quality criteria as shown below.
  
  
• After this, the ‘housing’ component was meshed. But for this, the method of volumetric meshing was opted. The ‘volume tetra’ option from ‘3D>tetramesh’ was used by selecting all the surfaces of the housing, and keeping ‘2D type’ as ‘trias’ and ‘3D type’ as ‘tetras’, and the ‘elem size’ as 5mm.
• This created tetra mesh on the housing within few seconds. The ‘volume tetra’ is time saving technique of 3D meshing, but the user does not have any control on the quality of the mesh.
• After creating the mesh for both the components, the model was checked for ‘tet collapse’ from the ‘check elem>3D’ as per the given value of 0.15. 0 failed elements were found in the model, and the mesh was finalized as shown below.
  
  
• After finalizing the mesh, the 2D shell elements were deleted using the ‘delete>elem>by config>QUAD4’ command.
• Later, another model ‘arm bracket’ had to be 3D meshed. It consisted of 4 components. First the base component was meshed. For this, all the components except this were hidden and the base component was initially meshed with 2D shell elements using the ‘automesh’, keeping the ‘elem type’ as ‘mixed’ and the ‘elem size’ as 10mm (specified in the question). The mesh was refined by remeshing the component again to remove the tria elements.
• These 2D elements were converted into 3D using the same previous method of ‘3D>tetramesh>Tetra mesh’ option by selecting the surfaces to be meshed. The image below shows the 3D mesh of the base.
  
  
• The second component, ‘arm_curve’ had to be meshed. Since the component had a curved geometry, the elements had to be spun around it. For this purpose, the ‘spin elems’ command from the ‘3D>spin’ option was selected. In this, the 2D elements of the lower face geometry residing on the ‘base’ component were selected.
• To specify the direction, a center of the curve was obtained from the ‘distance>three points’ option by selecting three random points on the curve. This center along with random N1,N2, and N3 nodes was selected and the elements were spun across of geometry keeping the ‘arm_curve’ as the current component. This created 3D along the curve as shown in the image below.
  
  
• The ‘arm_straight’ component was meshed later, using the ‘linear solids’ command. A 2D mesh was created on the other side of this component which had same number of elements as that on the face of the ‘arm_curve’ component. The faces of the arm curve were shown using ‘tools>faces’ option.
• From the ‘3D>linear solids’ option the elements on the face of the ‘arm_curve were selected in the ‘from’ and the elements from the ‘arm_straight’ were selected in the ‘to’. Three equivalent nodes N1, N2, and N3 were selected to define a plane on both the elements. By hitting ‘solids’ button, 3D hexa elements were created across the geometry of the component as shown in the figure.
  
  
• To mesh the ‘boss’ component, all the components and their meshes were hidden except the boss component. One side of the boss which was split into different surfaces was 2D mesh using the ‘automesh’ option. The number of nodes on the outer curve was matched with those on the inner curve to create uniform mesh. The number on the outer curve was set equal to that on the ‘arm_straight’ component as shown in the image below.
  
  
• These 2D elements were then converted into 3D using the ‘3D>solid map>general’ option. The ‘source geom’ was selected as the surface which was meshed before, while the ‘dest geom’ was selected as surface on the opposite side of the boss.
• The ‘elems to drag’ were selected as those of the mesh and the ‘along geom’ option was set on ‘mixed’. In this option, the lines, and the node path was selected to specify the path of the 3D mesh, which created 3D mesh along the boss, with a separate component for the solid mesh for the boss as shown below.
  
  
• Along with this, another model for 1D elements was provided in the assignment. In this model, the components were to be connected using different types of 1D elements like bars, rods, beams, welds, springs, etc.
• As seen in the image below, ‘rigid’ (rbe2) was created from the 1D tab by selecting one node from both the surfaces.
  
  
• Similarly, ‘beam’, ‘2 noded spring’, ‘3 noded spring’ was created between the two components.
  
  
• On the other side, ‘seam weld’ of ‘type 2 (spring single row) was created from the ‘connectors’ option from ‘1D’ panel, by selecting the node path, setting the spacing equal to the element size (5mm), and selecting the components.
  
  
  
  
• Similarly another type of seam welds, ‘quads’ was created on the other side of the components as shown in the image below.
  
  
  
  

Result and Conclusion:

• In this assignment, basics of RADIOSS required for analysis of every component were studied, along with the different types of 3D meshing like 2D to 3D mesh, Volume tetra, and Utility check tetramesh (quick tetra) were understood.
• This challenge gave an insight about the RADIOSS analysis part and their starter and engine files, and how to edit them.
• Different commands used in 3D meshing were practiced and used for the components provided in the assignment.
• Apart from this, 1D elements which is a crucial part of HyperMesh were used to connect the components provided. Iterations of different 1D elements such as bars, beams, rods, springs, spotwelds, seam welds, etc were practiced, and the assignment was completed successfully.

Additional link for the model and files : Models and files