Analysis of Large Assemblies Using Superelements in ANSYS Workbench

The 2011 earthquake and Tsunami in Japan led to severe loss of many structures and equipment. Can engineering simulations make us better prepared for such natural calamities?

Most organizations analyze the different components with great details for various failure conditions. But, seldom do they do a complete system analysis due to enormous computational requirements. With robust system level design the complex/large equipment could have survived the earthquake better.

Even with ever increasing computational power, solving larger FE models remains a challenge. Analyzing the complete system, like vibration analysis of a full-vehicle or full data-center-rack remains out of scope due to their enormous model sizes. At ANSYS, we focus at all levels of engineering analyses and help our customers achieve robust system level design.

Figure 1 large assemblies

Figure-1: Some Large Assemblies

Typically engineers perform system level analyses using lumped mass type techniques and “assumed” boundary conditions. A better approach is the use of “Superelements”. The Superelements can be created by regular Substructuring or by Component Mode Synthesis (CMS). The behavior of various component [called superelements] is captured with lesser number of degrees of freedom [called master nodes]. The characteristics of the full system model are achieved by enforcing equilibrium and compatibility along the interfaces of these superelements. This reduction in model provides an efficient solution for large assemblies without losing accuracy.

Figure-2: Defining Superelements

Figure-2: Defining Superelements

Defining multiple superelements (may be nested) with their respective master nodes and connections with rest of the model can still be complex for large assemblies. Using an ACT extension [called ExtCMS] makes it very simple to solve superelements in the Workbench Mechanical. This extension helps user to define/organize the superelements, export/reuse in different analyses and expand to visualize the results.

Figure-3: ExtCMS toolbar and objects in model tree

Figure-3: ExtCMS toolbar and objects in model tree

Here is an example of automobile suspension system solved using the ExtCMS extension.

Figure-4: Project Schematic

Figure-4: Project Schematic

Setting up this analysis involving the three superelements takes only a few seconds, then solving the solution is a single-click action.

Validation of the superelement approach for accuracy and speedup compared to the full finite element simulation approach:

superelement validation

figure 5 response plot

In conclusion, using superelements makes large system-level simulations possible. It achieves the model size reduction for fast simulation without losing accuracy. It also allows reuse of unchanged & repetitive components. The ExtCMS extension makes it easy for users to use superelements for complete system level analysis and design more robust systems.

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About Rajiv Rath

Principal Technology Specialist, Rajiv obtained his MTech in 2000 from the IIT, Kanpur, one of the top engineering schools in India. He has been with ANSYS ever since and has specialized in customizing various ANSYS products. He is helping the customer worldwide achieve workflow streamlining and productivity gains in both Fluids and Mechanical domains.