2D Meshing of an Automobile Hood model using ANSA
AIM
*To mesh a Hood model after cleaning up geometry and generating a midsurface of the model.
STEPS FOLLOWED
*The CAD model has to be pre-processed before solving and ANSA software is used here to mesh the model.
*Model dimension, Geometry editing and complexity reduction is done in ANSA.
1.GEOMETRY CLEANUP
*Import the model using file_open.
*The given model should be analysed properly.
*The model can be disassembled with the help of properties for better understanding.
*Disassemble the portions according to the model and lock each views.
*Apply topo on the selected view and check up the geometry.
*Correct all triple cons using release in CONS and apply TOPO from faces to convert it to double cons.
*Unchecked faces and needle faces should be removed.
*Geometry cleanup should be conducted to all the views of the model as it is checked in the inner extract of the model as shown above.
2.MIDSURFACING
*Midsurface can be obtained manually and automatically by using Midsurf command.
*On generating automatic midsurface, the parent geometry will be deleted.
*Here, midsurface is generated manually by using OFFSET.
*After generating midsurface , check for geometry once again.
*To eliminate triple cons present, use DELETE in FACES.
*Hide the parent geometry and obtain the midsurface plane.
*Go to orient and change the model into same colour if it is differing.
*Set PID and it will be saved in properties.
INNER EXTRACT
OUTER EXTRACT
HINGES & LATCH
3.MESHING
*A mesh is a network that is formed of cells and points. It can have almost any shape in any size and is used to solve Partial differential equation.Each cell of the mesh represents an individual soultion of equation which, when combined for whole network,results in a solution of entire mesh.
*On meshing the model element size must be consistent and so set element length in perimeters. Here as per the given details, it is 5.
*Quality criteria and meshing parameters should be entered according to the given values.
*In quality criteria aspect, skewness, angle, minimum length, maximum length and jacobian is considered here as shown below.
*In presentation parameters of Quality criteria, tick the elements % and all details.
*If diamond structure or any other feature is available in the model, run the number in perimeters and select the structure.
*By making sure it is even number, slide the structure according to the way of meshing.
*Check all the fillets before meshing to make sure it is under the minimum length given for meshing.
*Mesh the features initially and the construction lines can be altered without effecting the fillets of the features for a better mesh.
* As it is shown above in meshing mode, the element length is entered initially and the best mesh is provided when 'best' is applied from mesh generation.
*In shell mesh there is an option of reconstructing the best mesh. It is better to go with reconstructng because it applies a better mesh according to the periphery of the selected area satisfying the quality criteria.
*In some cases when an element fails in satisfying quality criteria, split and swap command is used from elements to either split the element into a better way or by skipping the edge to form a quadrangle.
*As it is shown below the construction lines can be altered without effecting any fillets or features if present.By making it in an appropriate manner, best mesh can be provided minimizing the trias formed and satisfing in quality.
*Cut and proj cut from macros is used to cut the surface according to the way of meshing.
ERRORS AND CORRECTION
* After providing the best mesh to the midplane, each element should be examined wheather it is satisfying the quality criteria.
*The error faced here was the failure of skewness, angle and minimum length together as shown below
* The only error area is showed up as shown above and it was failing for three of the criteria.By reconstructing and and improving the mesh didnt make any change.
*Later on checking the topo mode it was found that a small construction line was removed near to a fillet and due to it sharp edge formation happened in that particular area.
* Due to the sharp edge formation, it was continously failing.
*The construction line was retained at that particular area and mesh was provided once again satisfying all the qualities.
CONCLUSION
*In preprocessing meshing is significant as it helps in the flow of stress evenly throughout the model.
*A smooth mesh is better in weight distribution analysis.
*Meshing is done in the midplane of the model and not in the parent geometry.
*Initially mesh the features available in the model to reduce the complexity.