Posts Tagged "Femap"

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.

 

Siemens PLM‘s robust FEA solver NX Nastran is offered in multiple flavors. At first, it is associated with multiple graphical user interfaces, and the right choice depends on the user’s existing inventory as well as technical resources available. There are three options to explore:

  • Basic designer-friendly solution: In this bundle, basic NX Nastran capabilities are embedded in the NX CAD environment. The environment also offers stress and frequency solution wizards that provide direction to the user throughout the workflow. This solution is primarily meant for designers who wish to perform initial FEA inquiry on simple models. Advanced solver and meshing functionalities are not available.
  • Advanced solution for analysts: This solution offers more features with more complexity, so it is not meant for novice users and requires prior understanding of FEA technology. There are two separate GUIs associated with this type of NX Nastran.
  • NX CAE based solver: This is a dedicated pre/post processor for FEA modeling that has its own look and feel. It looks different from NX CAD but it is tightly coupled with NX CAD in terms of associativity – hence any updates in the CAD model are quickly updated in the FEA model as well through synchronous technology. If required, it is possible to associate this solution with Siemens Teamcenter for simulation process management.
  • FEMAP based solver: This is yet another dedicated PC based pre/post processor from Siemens with its own look and feel. FEMAP offers a CAD neutral and solver neutral FEA environment. It is tightly coupled with the NX Nastran solver but it is also possible to generate input decks for Abaqus, ANSYS, LS-Dyna, Sinda, etc.

This explains all the possible GUI offerings for NX Nastran. Now let’s have a look at what functionalities are available within the NX Nastran solver. Veteran Nastran users know very well that various physics-based solver features of Nastran are called solution sequences and each one of those is associated with a number.

  • Solution sequence 101: This is the most popular sequence of Nastran family. It primarily offers linear static functionalities to model linear materials, including directional materials such as composites for small deformation problems. Basic contact features such as GAP elements are also included. This sequence is widely used in T&M and aerospace verticals.
  • Solution sequence 103: This is yet another popular solution sequence that extracts natural frequencies of parts and assemblies. Multiple algorithms are available for frequency extraction such as AMS and Lancoz. This sequence serves as a precursor for full-blown dynamics analysis in Nastran.
  • Solution sequence 105: This sequence offers linear buckling at the part and assembly level. A typical output is buckling factor as well as buckling eigen vector. The buckling factor is a single numerical value which is a measure of buckling force. Eigen vectors predicts the buckling shape of the structure.
  • Solution sequence 106: This sequence introduces basic non-linear static capabilities in the solution and Nastran 101 is a prerequisite for this sequence. It supports large deformations, metal plasticity as well as hyper elasticity. Large sliding contact is also available but it is preferable to limit the contact modeling to 2D models only; it is tedious to define contact between 3D surfaces in this sequence.
  • Solution sequences 108,109,111,112: All these solution sequences are used to model dynamic response of structure in which inertia as well as unbalanced forces and accelerations are taken into consideration. These solution sequences are very robust, which makes Nastran the first choice dynamic solver in the aerospace world. Sequences 108 and 111 are frequency-based, which means that inputs/outputs are provided in a frequency range specified by the user. The solution scheme can be either direct or modal. Sequences 109 and 112 are transient or time-based which means inputs/outputs are provided as a function of time and scheme can be either direct or modal.
  • Solution sequences 153, 159: These are thermal simulation sequences: 153 is steady state and 159 is transient. Each one of these takes thermal loads such as heat flux as inputs and provides temperature contours as outputs. They do not include fluid flow but can be used in conjunction with NX flow solver to simulate conjugate heat transfer flow problems.
  • Solution sequence 200: This is a structural optimizer that includes topology and shape optimization modules for linear models. An optimization solver is not an FEA solver, but works in parallel with the FEA solver at each optimization iteration, hence sequence 101 is a prerequisite for NX Nastran optimization. Topology and shape optimizations often have different objectives; topology optimization is primarily used in lightweight design saving material costs while shape optimization is used for stress homogenization and hot spot elimination.

Questions? Thoughts? Leave a comment and let me know.

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