Northrop Grumman Mission Systems

uses MSC Apex’s Hex meshing to cut workflow time

in half By James Pura, Product Marketing Manager

Volume XII - Winter 2020 | mscsoftware.com | 89

90 | Engineering Reality Magazine

Many structural analysts favor the Hexahedral mesh (Hex mesh) because it requires fewer elements, results in less simulation time and produces more accurate results than a tetrahedral mesh. However, Hex elements are not widely used due to the extra cost (often measured in engineering working hours) needed to create them.

For the engineers at Northrop Grumman Mission Systems in San Diego, CA, this couldn’t be more true, since their legacy tool (Patran) had multiple limiting factors that made the use of hexahedral elements impractical.

As anyone who has created a hex mesh FEA model knows, regardless of what tool they used to build it, defeaturing geometry and preparing it for a hex mesh is the first major hurdle to creating mesh-ready geometry. Before a tet mesh or a hex mesh is constructed, the geometry must be idealized first.

In the legacy workflow (Patran), Northrop Grumman’s users lacked a way to quickly and easily identify and defeature their geometry, which required them to use a separate software application, CATIA v5, to perform the defeaturing. This then led to a back-and-forth workflow between the geometry software and meshing tools, making the entire process inefficient and time-consuming (not to mention extremely frustrating).

The next commonly experienced limiting factor in building a hex mesh is the complexity of the step-by-step meshing process itself. The hex meshing process involves partitioning the complex geometry into simpler 3D geometry blocks that are “hex mesh friendly.” Regardless of what tool you use, the hex meshing process is sometimes prohibitively time-consuming since it requires a one-by-one, cell-by-cell hex meshing process. This impracticality prevents users from widely creating hex mesh for simulations and therefore, this often leads users to use the less-preferred tetrahedral mesh.

MSC Apex benchmark geometry

MSC Apex’s Automatic Defeaturing tool

The Northrop Grumman engineers performing this task reviewed and benchmarked MSC Apex versus their legacy workflow and tools and found quite a few benefits from using the new workflow. The first benefit they found was the Geometry Cleanup & Defeaturing toolset available in MSC Apex, which allowed users to do both generic and detailed defeaturing in preparation for creating a solve-ready mesh. Two differentiators

Volume XII - Winter 2020 | mscsoftware.com | 91

New Hex Mesh created in Apex

Benchmark Geometry that is mesh-ready

Legacy Mesh created in Patran

“After the benchmark was complete and we were looking

at the results, we realized that the 16-hour workflow for building a

Nastran model went down to 7 hours with MSC Apex.”

– Jamie Kofoid, Electromechanical Technical Fellow, Northrop Grumman Mission Systems

that users preferred were the integration of the Parasolid geometry kernel into the MSC Apex platform (adapted and developed specifically to meet the needs of structural analysis engineers) and the other was the automatic defeaturing method which made defeaturing quick and easy and allowed users to use fewer tools to finish the task, thus saving time in the overall analysis workflow.

The second benefit they found was the suite of generative updates and meshing toolsets in MSC Apex that allowed for a fully connected, solve-ready hex mesh to be achieved much faster. The Hex Mesh Diagnostic Tool was especially helpful since it gave them immediate feedback on any issues with the geometry and how to remedy the situation so a hex mesh could be achieved – something that can’t be found in any other FEA pre-processor. Additionally, the Feature Mesh Settings Tool allowed users to automatically create washer meshes, and MSC Apex’s meshing algorithms allowed users to drag a box around the whole model (instead of clicking one cell at a time), and a fully-connected hex mesh would be created. And then finally, when changes to the geometry were made after the mesh was already created (such as going back to defeature a fillet or pinhole that was missed), the mesh would automatically update to the new geometric feature.

The final benefit Northrop Grumman’s engineering team identified during the benchmark was the Analysis Readiness capability in MSC Apex. Once a hexahedral mesh was produced, it could immediately be verified for continuity and solver validity. Since a run-ready MSC Nastran solver deck was the “finish line” for each of the finite element models that they built, the Analysis Readiness tool helped users quickly detect and fix potential issues in the solver deck before running in MSC Nastran, and thus gave them “first-run success” for simulations.