Week- 5 - Solid meshing

Aim: To perform solid mesh or volume mesh for given Rear View Mirror component in ANSA.

Check Geometrical errors and mesh the Surfaces with the given 2D element Quality criterias given below.

S.No	Quality Criteria	Value
1	Target/Average length	1
2	Minimum Length	0.5
3	Maximum Length	2

Use tetra elements to mesh the Volumes defined in the model and check for the below quality after Volume meshing.

S.No	Quality Criteria	Value
1	Tet collapse	0.2

Introduction:

3D geometries are needed to perform 3D mesh and they come from CAD models, which take longer and more effort to produce. Furthermore, analysis containing 3D elements usually contains more nodes and elements thus would take longer to solve. 2D analysis, however, requires less time to mesh and less time to solve. The 2D analysis also provides a more sufficient amount of structural information than 1D analysis and produces results close to 3D analysis. However, 2D analysis can only replace 3D analysis when structures can be represented by plate elements. When a structure is more complex, 3D elements need to be used.Engineers sometimes model structural elements using combined 1D/2D/3D mesh to take advantage of the benefit of each type of element while saving analysis time.

3 D elements are mainly used to mesh volumes they are converted from 2 D elements when the model has thickeness more than 6 mm.

tetrahedron has 4 nodes and is the most basic 3D finite element. Figure (b) shows a pentahedral (pyramid) element, figure (c) shows an 8 node rectangular solid element , and figure (d) shows an 8 node hexahedral isoparametric element

Tetrahedral Mesh:

A tetrahedral mesh is a 3D generalization of a 2D triangular mesh. Tetrahedral elements are commonly constructed as equilateral, such as in systems with circular curvature, or they could be constructed as isosceles tetrahedra when a system has asymmetry. Tetrahedral elements could also be totally unstructured and adapted to arbitrary geometries with high accuracy. The accuracy would be much higher than a simple cubic grid applied in 3D or a square grid applied in 2D.

Tet collapse=Min of (h/√A)/1.24

Tet colapse is equal to the distance of node from opposite face,the each value is divided by the square root of the opposite face's area then minimum of four resulting value is divided by the factor 1.24.

Procedure:

Open the Rear View Mirror component igs file in ANSA .Since there are single cons found in the part faces are not joined properly

• Geometrical cleaning in order to remove geometrical errors exist in the part do geometric check and apply fix will remove single cons and faces will join with double cons
• or else we can apply topo to fix the geometrical errors .

• Go to mesh module and set the perimeter length as 1.
• Set the target length and min and max length for model.
• Set the given quality criteria from quality tool bar.

• Min length is 0.5 and max length is 2, for 2D mesh and for volume mesh Tetra collapes value is 0.2.

• click on the orient command if orientation of inner and outer surafce is not uniform.

• Go to measure tool and check the distance between two curves.

• As the distance between two double cons found less than the min length quality criteria it is needed to be suppressed one of the double cons. or also say that defeaturing the contruction line in order to maintain the minimum gap.

• Again the distance between the next contruction line is 0.568 which is above the minimum legnth criteria.

• Now after switching to mesh module go to mesh generation best mesh command apply trai for flat surface and Ortho Tria for curved surface.

• Next step is to clear quality as criteria is set for min and max length only it will show in mesh with respective color code.

• To fix the quality shell mesh >Reconstruct and select the area where quality has to fix.

• it will show no off mesh we have to clear the quality until no of off become zero or dissapear.

• Now 2d mesh is complete then switch the moudle to volume mesh and Define> manual

• In list command next to the define command one PID has been generated

• Now it has to be remeshed and define the type as tetra rapid, the solid mesh will be generated.

• Tetra element has formed as show in below fig.

• Now that the solid mesh have formed we have to check quality criteria for solid mesh tetra collapse that is highlited in its respective color code.

• In order to clear tetra collapse we hae to apply fix quality in volume mesh module improve>fix quality.

• after fix quality option the tetra collapse quality has been clear form the model.

Ball

• The above procedure have to repeat for all the remaining property IDS.

Mirror

Mirror Holder

Hanging Arm

Learning Outcomes:

• For solid meshing first need to do 2D meshing and then convert it into 3D meshing.
• For flat surfaces Tria elment mesh is used and for Curved or Spherical surface Ortho tria mesh method has to be used
• Tetra Elements are perfered over hexa elements for complex geometry and has less kinks and dipss on the surface of component hence achived smooth surface.
• learn to clear quality in solid mesh.

Conclusion:

Solid meshing has been performed on Rear View Mirror component in ANSA interface and quality criteria has been maintained for given component.