Scope of PATRAN and NASTRAN in FEM and FEA for Aircraft Structures

Presently, PATRAN is the most widely used tool for pre and post-processing purposes in the world. It provides meshing, the analysis set up, and more for the solver, NASTRAN.

This article is an overview of how PATRAN and NASTRAN can be used effectively in creating aircraft structures. But before we look at the applications of these tools, let us start with a brief introduction of FEM and FEA

FEM and FEA

You might be aware of why we are using the Finite Element Method (FEM) and Finite Element Analysis (FEA) instead of the closed-form or closed-loop solution methods like those of mechanics of materials (MoM) and strength of materials (SoM).

If you look at the closed-loop solutions of MoM and SoM, all of them use the simplified assumptions that work particularly well for simplified geometries and not for complex geometrical shapes.

MoM, SoM, and theory of elasticity (ToE) deal primarily with one-dimensional and two-dimensional geometries. But in FEM and FEA, we have the luxury of analyzing complex geometries with various boundary conditions and loads in three dimensions.

Some of the pioneers who developed FEM and FEA in the mind-1900s are:

• Zienkiewicz
• Clough
• Argyris
• Martin

Finite Element Methods is an approximate numerical method where a larger domain is broken down into smaller domains called 'elements,' which are then assembled in the form of a matrix. Each of these elements is interconnected at points known as 'nodal points' where the stresses and strains can be computed using Hooke's Law and then averaged over all the elements.

These are solved using the following formula:

where,

• K = Property or Stiffness
• u = Behaviour or Distance
• F = Action or Force

Why FEA?

In general, FEA offers the following benefits:

• Can be used on complex geometries
• Three dimensional
• User interactive
• Saves time
• Applications in different industries
• Huge post-processing capabilities

A downside to FEM and FEA is the high processing time. The processing time of the software tools increases along with the size of the model, or as the size of elements decreases.

MSC PATRAN and MSC NASTRAN

There are many simulation and analysis software in the market, like Ansys, when it comes to FEM and FEA. However, started in 1965 by McNeal Schwedler, PATRAN and NASTRAN are the leading software tools in the aerospace industry.

NASTRAN, the solver, was initially developed for NASA by MSC for internal projects. However, because of the scope of this product, it soon became commercially available and expanded into the world of consumerism.

Structure of PATRAN and NASTRAN

PATRAN and NASTRAN are used in a variety of applications, including for primary structures, secondary structures, helicopter structures, and more. PATRAN is the pre/post processor, while NASTRAN is the solver.

The NASTRAN file input is arranged in five sections, as shown below:

• NASTRAN Statement
• File Management Section
• Executive Control Section
• Case-Control Section
• Bulk Data Section

Commonly Used NASTRAN Elements

The NASTRAN element library contains over 50 finite elements.

• Zero-dimensional
• One-dimensional
• Two-dimensional
• Three-dimensional
• Scalar
• Axisymmetric
• Rigid
• Heat transfer
• Fluid-structure
• P-version
• Contact
• "GENEL" user-supplied element

The image below shows the analysis of a sample model. The results are displayed on the right-hand side as a NASTRAN input file, thereby giving you an insight into the organizational structure of NASTRAN and its input file.

Input File

Here the input file is shown.

Once the model is completed in PATRAN, it generates a .dat file upon saving it. This file will have all the information regarding the model, the materials, their properties, loads, forces, and more. This gives complete freedom to the user to edit or amend any of the values to run a new study.

After running the solver, i.e., NASTRAN, two files are generated:

1. .f06
2. .op2

Since FEM is primarily based on the displacement method where you solve problems based on static and equilibrium boundary conditions, NASTRAN prints all the resultant forces, boundary conditions, and more in the .f06 file. The .op2 files are used mainly for post-processing purposes.

Below are some snapshots from PATRAN and NASTRAN.

You will find the model of a wing in the top left corner where you can see the FEM model and results. The right-hand side picture shows the different packages of MS:

• MSC PATRAN
• MSC NASTRAN
• MSC Fatigue – Exclusively for fatigue
• MSC Dytran – For dynamics
• MSC Marc – For implicit dynamics
• MSC ADAMS – For multibody dynamics
• MSC SOFY

Opportunities in Aero Structures

As mentioned before, there are numerous commercial packages available online such as:

Out of all the aforementioned software tools, you can get a lot of flexibility editing models of aircraft structures through MSC PATRAN and NASTRAN without even opening the pre-processor and post-processor.

Some of the job roles that you can get into as a FEM analyst are:

• FE Engineer
• FE Analyst
• Stress Engineer
• Stress Analyst
• Structural Engineer

Some renowned government organizations in India using PATRAN and NASTRAN are:

• DRDO
• NAL, HAL, CABS
• ISRO

Some significant players that use PATRAN and NASTRAN for aerostructures in the private sector are:

• Airbus
• Boeing
• Bombardier
• Embraer
• Safran
• Collins Aerospace
• Spirit Aerospace

PATRAN and NASTRAN were exclusively developed for the aerospace industry. Hence, they are largely used for:

• Aircraft primary structures
• Secondary aircraft structures
• Satellite structures
• Landing gears of different aircraft

Conclusion

To summarise, FEM is mostly used for complex 3D geometry as it enables us to perform analysis for different materials and properties conveniently.

PATRAN and NASTRAN are primarily used in the aviation and aerospace sectors worldwide. They generate .dat, .f06, and .op2 files after modeling and running an analysis after saving. The .dat file is the input file, while the other two are generated after running the solver.

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