Posts Tagged "FEA"

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.

As an FEA analyst, you are likely losing too much of your time in CAD repair.

If you are an experienced FEA analyst, you must have come across following types of situations often while meshing your models:

“I create 3D geometries in CAD uniting together several surfaces so that the CAD modeler itself sees one unique surface; however, whenever I export it as a .sat, .stp or even binary file for Parasolid and then import it into the FEA pre-processor, I again see all those surfaces that are not supposed to be there.”

“For some parts I am extruding surfaces to solids, and for some parts I am building solids out of intersecting surfaces. All in all, it is a kind of a box structure with a hole on one side. I started importing it to GUI part by part, and as soon as I have top and bottom plate and two sides, the meshing fails. How did you exactly resolve this meshing problem?”

The FEA user community knows that most of the user interfaces available for finite element analysis are good for FE modeling only – they are not expert CAD modelers. It often happens that the CAD model created is not free from defects from a meshing perspective. The most common problems are duplicate edges, gaps, silver surfaces, unnecessary patches, etc. The problem is often more severe if a CAD model is first translated to a neutral format such as .sat, .iges, .step files before being imported into the FEA pre-processor; the defects are generated during the translation. In many other cases, the repairs made in the CAD model are not propagated into FEA modeler. The only option left is to repair the geometry in the FEA model itself, but the repair tools required often don’t exist in these user interfaces.

One-click model transfer from CAD to FEA without any neutral file format

For Abaqus users, there is great news: the Abaqus CAE pre-processor now has associative interfaces for CATIA, ProE and SOLIDWORKS.

The CATIA V5 Associative Interface allows you to transfer CATIA V5 Parts and Products into Abaqus/CAE using associative import. Materials and publications assigned to the CATIA V5 model are also transferred to the Abaqus/CAE model as material and set definitions respectively. In addition to associative import, the CATIA V5 Associative Interface allows you to directly import the geometry of CATIA V5 models in .CATPart and .CATProduct format into Abaqus/CAE without any intermediate neutral files. The following options are available with CATIA V5 associative interface: […]

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