Hypermesh Report on - Performing 3D Meshing using tetra mesh and hex mesh elements

Hypermesh Report on: -

Performing 3D Meshing using tetra mesh and hex mesh elements.

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• Introduction: 

Hypermesh has several functions that require the definition of a volume, such as creating tetrahedral and hexahedral meshes. This can be done either with surfaces that enclose the volume or with solved geometry entities. Working with solids provides a couple of advantages over surfaces. Selecting the volume for the function requires only a single click because solids represent the volume with a single entity, as opposed to surfaces. sold that are topologically connected to each other also allow the functions being used to recognize the connection. Creating the mesh in these cases allows the mesh in adjacent volumes to automatically have proper connectivity. In 3D meshing, there are 3-dimensions that means we have to consider the volume of the solid entity. 

• 3D elements should be used when all dimensions are comparable.

 x-y-z

Element shape: tetra, penta, hexa, pyramid.

Additional from user: nothing

Element type: solid

Practical application: Gearbox, engine block, crankshaft, etc.

• About different types of 3D elements:

• Tetra: The tetra elements also known as tetrahedron elements. The tetrahedron elements consist of four triangular faces, six straight edges, and four vertex corners.
• Hexa: The hexahedron is any polyhedron with six faces. A hexahedron is a regular cube with all its faces square and there squares around each vertex.
• Penta: It is also known as a triangular prism. This Penta element has 5-faces, 9-edges & 6-vertex. 
• Pyramid: The square pyramid is a pyramid having a square at the base and four triangular faces perpendicular around it.

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3D Meshing procedure for Part-1:

Step 1: Import the geometry 

1. Go to the files/import sub-panel.
2. Select the \'.hm\' import translator.
3. In the filename field, enter [housing.hm] or use the browser to find the
file.
4. Click import.

Step 2: Model evaluation

This model has two components first is cover and the other is a hub. We will start with meshing the hub body and then we will mesh the cover body by applying both the bodies with 3D tetra meshing as the geometry is complex.

Step 3: Component 2D meshing.

• Hub Body

This image shows 2d tria meshing of the hub body by allowing mesh size of 5mm. This process necessary as we have to convert 2d trias into 3d tetras.

Process:

• Goto 2D page
• then click on >  Automesh command 
• then select >  surface to have meshed
• then select  >  element size (5mm)
• then select  >  element type (trias - as we have to do 3d tetra mesh further)
• then click on > mesh

Step 3: Component 3D of hub body meshing.

This image shows the isometric view of the hub body with masking some elements to view the 3D tetra meshing of the body.

Process:

• Goto 3D page
• then clicks on >  tetramesh command 
• then select option >  tetramesh parameters to allot tet collapse & min. tetra size
• then give tet collapse value >  0.150 
• then give a min. tetra size  >  3.00 mm
• then click on > tetramesh option
• then select  >  elements you want to convert from 2d to 3d.
• then clicks on >  mesh

Step 4: Volumetric meshing of the Cover body.

Volumetric meshes are a polygonal representation of the interior volume of an object. Unlike polygon meshes, which represent only the surface as polygons, volumetric meshes also discretize the interior structure of the object.

This image shows the isometric view and front view of the cover body with masking some elements in isometric view to clear a look of the 3D tetra meshing elements of the body.

Process:

• Goto 3D page
• then clicks on >  tetramesh command 
• then select option >  tetramesh parameters to allot tet collapse & min. tetra size
• then give tet collapse value >  0.150 
• then give a min. tetra size  >  3.00 mm
• then select option > volume tetra to alloted to this body
• then select >  surf/solid  you want to mesh
• then select  > 2D type: trias as option
• then select  > 3D type: tetras as option
• then clicks on >  mesh.

(Note: While doing this meshing you can also use proximity meshing, which refines the mesh in areas where the features are small and closer together. And using curvature options will place elements along curved surfaces on user-specified settings.) 

Step 5: Quality check

This image shows the selectional view of the 3D meshing of the cover body using tetra elements. And the image below that shows the number of element and Zero % failure in tet collapse.

Tet collapse: The height of the tetra element is measured from each of the four nodes to its opposite face, and then divided by the square root of the face area.

Process:

• Press function key F10
• then clicks on >  3-d option
• then click on >  tet collapse to check error.

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3D Meshing procedure for Part-2:

Step 1: Import the geometry 

1. Go to the files/import sub-panel.
2. Select the \'.hm\' import translator.
3. In the filename field, enter [arm_bracket.hm] or use the browser to find the
file.
4. Click import.

Step 2: Model evaluation

This model has four components base, arm_curve, arm_straight & boss. We will start with meshing the base body and then we will mesh the other bodies one by one applying all the bodies with 3D Hexa meshing as the geometry is simple to mesh.

Step 3: Base Component 2D meshing. 

This image shows the 2D meshing of the top surface of the base body.

Process:

• Goto 2D page
• then click on >  Automesh command 
• then select >  surface to have meshed
• then select  >  element size (10 mm)
• then select  >  element type (quads - as we have to do 3d Hexa mesh further)
• then click on > mesh

Step 4: Base Component 3D meshing. 

This image shows step by step procedure of doing offset mesh to create Hexa mesh elements.

Process:

• Goto geom page
• then click on >  nodes command 
• then select >  line node option
• then create  >  4-nodes 
• then click on >  create
• Goto 3D page
• then click on >  element offset command 
• then select >  solid layers option
• then select  >  2D elements, 4-nodes and side surfaces of the base
• then enter no. of layers >  4
• then click on >  offset-

Step 5: Arm_curve Component 3D meshing. 

This image shows step by step procedure of doing spin mesh to create Hexa mesh elements on arm_curve body.

Process:

• Press function key F4
• then click on >  three nodes option 
• then select >  any three-node 
• then create a center point for the curve by selecting >  circle center
• Goto 3D page
• then click on >  spin command 
• then select >  spin element option
• then select  >  2D elements, 3-nodes from the curve and select center point node.
• then enter angle > 90 deg and enter the spin 25
• then click on >  spin-

Step 6: Arm_straight component 3D meshing

This image shows step by step procedure of doing linear solid mesh to create Hexa mesh elements on arm_curve body.

Process:

• Goto 2D page
• then click on >  Automesh command 
• then select >  surface to have meshed
• then select  >  element size (10 mm)
• then select  >  element type (quads - as we have to do 3d Hexa mesh further)
• then click on > mesh
• Goto 3D page
• then click on >  linear solid command 
• then select >  elements from arm_curve face to have meshed
• then select  >  3-nodes from the same face
• then select  >  2D elements as you can see in the image.
• then click on >  Select equivalent 3-nodes from the 2D mesh face
• then type  >  density=12 
• then click on > solids

Step 7: Boss component 3D meshing.

This image shows step by step procedure of doing solid mapping mesh to create Hexa mesh elements on the boss body.

Process:

• Goto 2D page
• then click on >  Automesh command 
• then select >  surface to have meshed
• then select  >  element size (10 mm)
• then select  >  element type (quads - as we have to do 3d Hexa mesh further)
• then click on > mesh
• Goto 3D page
• then click on > none option at source geom
• then select >  2D elements on boss surface
• then select  >  opposite side of 2d mesh surface as destination geom. (10 mm)
• then select  >  element, line, nodes & surfs as per the availability at that point. 
• then select  >  element size (10 mm)
• then click on > mesh.

Step 8: Quality check

This image shows the isometric view of the 3D meshing of the arm_bracket (part-2) body using Hexa elements. 

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Conclusion:

We understood the concept of 3D meshing. Here we learn about the 3d meshing commands for tetra meshing and hexa meshing of an component. The following given below reasons let us know about when to use which mesh:

• Hexahydral mesh: less elements = faster solution time with better accuracy. when the geometry or solid is a simple structure we go for hexa meshing.
• tetrahedral mesh: easier to mesh more complex geometry - mesh quality is often easier to achieve with tetrahedral (or poly) mesh.

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Questions and answers:

1. Check the material properties of the rail component and calculate the speed of sound in steel rail

ans.

young\'s modulus = 210000 g/mm^2

density = `rho` = 0.0078 g/mm^3

Speed =

2. The length of the rail is about 1000 mm.calculate the time it takes for a shock wave to travel from one end of the rail to the other.

ans.

lenght, l = 1000 mm

Speed, c = 5188.74 mm/sec

3.Time for sound to travel the length of rail = 0.192 sec.

4.Edit the engine file so that the stress wave can be monitored, moving from one end of the rail to the other during an 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)

ans.

5.Set the frequency of animation output to a time that will give 20 animation steps(/ANIM/DT)

ans.

frequency of animation, f

6.Change /print -10.

ans.

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