Assignment 2 Time Step Calculation
1. Check the material properties of the rail component and calculate the speed of sound in steel rail=_______
Ans:
In the data we have two files
1.FIRST_RUN_0000.rad (starter input file): Which has all data required for the slover such as model information, elements, nodes, loads, boundary condition etc.
2.FIRST_RUN_0001.rad (engine input file): Which has all data required for the radioss engine i.e speed , time step, run time, what all data we want as output.
Import the runname_0000.rad file in to hypermesh:
To import file,
a. change user profile to radioss Because we are using slover as Radioss
b. File>Import>Solver deck. we can see the new tab where options are available for browse file. Browse the file FIRST_RUN_0000.rad (starter input file),
c. Click on import so we can see imported files required for the solver such as model information, elements, nodes, loads, boundary condition etc.
d. To calculate the speed of sound in steel rail we need material properties (Density and young's modulus), first check for unit system used in the model by clicking on moel>cards>BEGIN_CARD it's in g-mm-ms
Browse material data from model>materials shown in the fig below
e. To calculate Speed of sound 'C' we have
`C=sqrt(E/rho)` m/s..................(eq1)
C is speed of sound m/s
E is Young's modulus GPa
`rho` is Density in `(M kg)/(mm^3)`
since following unit system shown
we have E = 210000 `N/(mm^2)`, convert to GPa,`
`210X10^9 `N/(m^2)` = 210 GPa..................(eq2)
`rho = 0.0078 g/(mm^3)` = `7.8X10^-6 (M kg)/(mm^3)`..................(eq3)
substitute eq2 and eq3 in eq1
`C=sqrt(211/(7.8X10^-6)` m/s`
c = 5188.7 m/s ..................(eq4)
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=______
Ans:
For time step we have
'`Delta=l/C` s
l is length in m which is 1m
C is speed of soun in m/s
`Delta=1/5188.75`
`Delta`=0.193ms
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)
Change the time stop to shock wave to travel from one end of the rail to the other which is 0.193 ms
5.Set the frequency of animation output to a time that will give 20 animation steps(/ANIM/DT)
Ans:
ANIM/SD (Frequency)= Time for sound to travel length of rail/number of animation steps
=0.193/20
=0.0095 ≈ 0.01 ms
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.
3D Meshing
Introduction on 3D Meshing:
3D elements are usually used to mesh volumes. They are derived from 2D elements that are used when the problem is unable to be simplified. 3D solid elements only account for translational displacements.
These elements are suitable for three-dimensional analysis. uses for solid parts and sheets of thickness more than 5mm, Transmission castings. engine blocks etc
Example- Tetra elements and hexa elements.
Tetra element is the 4 noded with 4 triangle faces are formulated in three-dimensional space with three degrees of freedom per node. These are the translational degrees of freedom in the X, Y and Z directions, respectively. In the figure Tetra element is shown for 4 nodes and 10 nodes.
4 nodes Tetra element 10 nodes Tetra element
Hexa element is the 8 noded with 6 triangle faces are formulated in three-dimensional space with 6 degrees of freedom per node. These are the translational and rotational degrees of freedom in the X, Y and Z directions, respectively. In the figure the Hexa element is shown for 8 nodes and 20nodes.
8 nodes Hexa element 20 Hexa Tetra element
1. Create Teramesh for Housing
2. For the given models, Create 3D tetramesh with 6mm element size.
Aim: To create the 3D tetra meshing for the Housing & Hexa Mesh for Arm Bracket by eliminating geometrical errors and considering the given element quality criteria using Hypermesh
Element Quality Criteria:
| S.No | Quality Criteria | Value |
| 1 | Target/Average length | 5 |
| 2 | Tetcolapse | 0.15 |
| 3 | Hexa mesh size | 10 |
Procedure:
1. Import Housing.stp in to Hypermesh
2. CAD Geometry clean up and topology
3. Defeaturing
4. Tria shell meshing
5. Tetra meshing
6. Check for tetcolapse
1. Import Housing.stp in to Hypermesh : Import the given Housing.IGSand arm bracket in to the Hypermesh Shown in the fig.1.1
Steps to import
a. Click on import geometry select type of file (IGS or Stp). If we want to open the Hypermesh file just click on the open model.
b. Browse the file and open. it will appear in the file selection table
c. click on import. Show in the fig 1.1A
Fig.1.1A: Import file
Fig.1.1: Imported file
2. CAD Geometry clean up and topology: In this step the given model undergoes geometry check. Where all the defects such as collapsed faces, cracks, free edges, T-edges are clear. In the fig.2.1 show description on surface.
Fig.2.1: Description on surface.
Tools used in topology
Tools>Edge Edit Panel
A. Equivalence (multiple edges at a time): Search surfaces for pairs of free edges and combine into shared edges
B. Toggle (edge pair at a time): Select an edge; equivalences with other free edges found within a user specified tolerance
C. Replace (1 edge pair at a time): Select 2 edges to equivalence together. Control which edge to retain and which to move.
D. Geom>Surfaces>Ruled or Geom> Quick edit > filler surface or 2d> spline> surfaces only (to create missing surfaces) .
3) Defeaturing: Update the Criteria length as per given element Quality criteria which is Target/Average length 5 For Housing.
Tools used in Defeaturing
A. Toggle edge: Left-click a free edge (red) to make it shared (green), or a shared edge to make it suppressed (blue).
Right-click a suppressed edge to make it shared, or a shared edge to make it free.
In either case, the edge must meet the criteria for the type of edge you wish to change it to. For example, toggling a free edge to a shared edge requires the presence of a similar edge within the distance you specify in the tolerance field.
B. Replace (1 edge pair at a time) Select 2 edges to equivalence together. Control which edge to retain and which to move.
C. Geom> Quick edit > filler surface (to create missing surfaces) .
4. Tria shell meshing:
Before meshing Assign given element Quality criteria in to hypermesh by Preferences>criteria file setting
Start meshing Process by Automesh (2D>Automesh )
steps to mesh
a. Select surfaces for initial mesh and for remesh select elements.
b. select size and bias abd select mesh size which is Target/Average length 5.
c. Select type of mesh as mixed (Quad, Tria, mixed, R tria etc) here tria is selected and click on alin and size in order to get proper mesh near features.
click on mesh or middle mouse button
Modify mesh flow by changenging surfaces to elements and select the elements then mesh . Make sure that while doing mesh all the element Quality criteria must be satisfied. Avid maximum opposite traits and. In fig.5.2, 5.3 and 5.4 show the mesh flow for all the models
Fig.5.2: Housing 1
5. Tetra meshing: Tetra meshing is the 3D meshing process where the tetra elements are used to fill the volume. In hypermesh we can done tetra mesh by 3 methods
1. Tetra mesh panel: Convert 2d tria mesh to tetra mesh
2. quick tetra mesh on close surface or components
3. Volume tetra mesh by selecting solids in the model.
here all the models are done by tetra mesh panel that is Convert 2d tria mesh to tetra mesh
Start Tetra meshing Process by Automesh (3D>Tetramesh > tetramesh )
steps to mesh
a. Select Elements option in panel and select elements for tetra mesh
b. tick on Fix comp boundaries and update input shells
c. Click on the mesh or middle mouse button shown in the figure 6.1 panel for tetra mesh. We can tetra mesh in the figure 6.2
Fig.6.1: Tetra mesh anel
Fig.6.2: Tetra mesh
6. Check for tetcolapse: tetcolapse is the quality parameter for tetra elements.
It can be calculated by measuring the distance of a node from the opposite face, then each of the four values will be divided by the Square root of the opposite face’s area. The minimum of four resulting values is then normalized by dividing it by 1.24.
Generally tet collapse can be calculated by the formula = Min of (h/√A) ÷ 1.24 Referred form
To clear the tetcolapse
1.increase the minimum height of node from opposite plane until it reaches 0.15 as per the quality criteria
2. Remesh the component by providing remesh parameters shown in the fig. 6.3
Fig.6.3: remesh parameters
In the figure 6.4 shows tetcolapse for all models
Fig.6.4:tetcolapse for all models
7. Hexa Meshing: Hexa element is the 8 noded with 6 triangle faces are formulated in three-dimensional space with 6 degrees of freedom per node. Hexa meshing is the 3D meshing process where the Hexa elements are used to fill the volume.
steps to mesh
a. Create 2D mesh on all quads on one side of the surface using 2D>Automesh.
b. Drage the elements from top to bottom, 10 is the elements size using drag (3D>drag). we can see hexa elements created.
c. Drag the elements of feature which is in curve shape using line drag (3D>line drag)
select elements>select line which is guide to the elements>give no. of elemental rows required>press on drag
d. To create Map b/w two faces of same shape but different size, extract 2D elements from 3D elements by tools>faces>select elements>find faces, so we can see faces
e. Create same no. elements on other face with
f. Using linear solid (3D>linear solid) create hexa elements b/w them
g. For Cylinder
create 2D mesh on top surface and solid map (3D>Solid Map). do slide map by using node list option as path for the hexa mesh and make sure that connectivity of each Hexa element.
Fig.6.1: Tetra mesh anel
Result: Tetra and hexa meshing is done successfully for all 3 model by eliminating geometrical errors and considering the given element quality criteria using Hypermesh
In the fig. bellow show results images for all 3 model
