Finite element Pre Processing: Siemens Femap vs. MSC Patran
There have been quite a few market whispers about MSC Software and its products since the company’s acquisition by Symphony Technologies few years back. It’s flagship pre-processing tool called MSC Patran has been under spotlight since the introduction of new equivalent tool by MSC Software (now Symphony) called MSC Apex. MSC Software adopted a similar strategy during 2008-09 by introducing a bunch of multi-disciplinary pre-processing tools such as MD Patran and later SimExpert. All these products had a very long gestation period with little luck in making a long term market presence.
Many veteran FEA analysts, particularly in aerospace domain are well familiar with the pains of using MSC Patran in geometry cleaning, meshing and composite modeling environments. The objective of this blog is to take a deep dive into these issues and demonstrate how an alternative product called Femap from Siemens can alleviate many of these unaddressed issues.
Femap has been a part of FEA community since more than 30 years and it was developed with the mission of having a dedicated PC based pre and post processor for engineering FEA. It is solver neutral as well as CAD independent solution that offers high performance modeling and analysis capabilities to solve toughest engineering problems.
- Mid surface extraction
Almost all FEA pre-processors have this embedded tool but as the geometry becomes more and more complex, many of them fail to extract mid surfaces correctly. The automatic feature of Femap makes this job not only easy with minimum number of clicks but offers higher fidelity as well. User does not need to select opposite faces multiple times in case thickness changes in space. Just enter the maximum thickness value a part has and Femap does the rest for you. Its further possible to combine the mid surfaces so they appear as a single entity in the history tree.
- Tools in the meshing toolbox
Before creating a mesh, the meshing toolbox offers multiple value added features to clean and modify the underlying geometry for a better mesh.
- Project curve:
This features splits the extracted surface at the boundary of thickness transition so that the underlying elements are able to update the shell thickness property as the thickness changes on either side of the split.
- Feature removal options
There are many features in CAD that may not be needed in FEA analysis and holes are the prominent ones. It is possible to close holes and similar geometries with just a click, if needed. By default, a point entity is created at the geometric center of the closed holes to make sure a kinematic constraint can be applied at those points, if needed.
- Pad and washers
These features allow for mesh refinement in the vicinity of holes and depending on the geometry of holes, either a washer (circular) or a pad (square) option may be chosen. The feature creates iso-parametric meshes around the holes based on the distance of influence defined by the user. This is an “on the fly” feature that updates an existing mesh every time this feature is executed instead of creating a new mesh.
- Dynamic node repositioning
This is a very handy feature to improve mesh quality on the fly. With the mesh quality contour option active, user can dynamically move any node of the mesh either on surface or on a curve until its quality improves which is instantly perceived by the user as element color changes from red to green. The effect of this tool is very local and only a few elements in the vicinity of selected node are considered at a time.
- API’s for automating repetitive tasks
Most of Nastran based BDF’s include multiple RBE’s. Femap understands the pain of creating these RBE’s manually and applying boundary conditions to them. The custom tools provide an option to create RBE’s by selecting peripheral curves or nodes. The independent nodes are created automatically. Using API’s it is further possible to completely automate the RBE generation process.
The grouping options in custom tools provide an option to automatically define a group for independent nodes of all the RBE2’s in the model. This group can later be used to create constraints on RBE’s without picking each independent node individually.