Adaptive Mesh Refinement for Civil and Structural Designs
Staff posted on October 15, 2014 |
Scia Engineers helping Civil and Structural Engineer Design Faster

More and more civil and structural engineers are being asked to work iteratively with designers and architects.  As timelines shrink, and projects become more complex, engineers are looking for ways to increase efficiency and work smarter.

Integrated Structural Design software like Scia Engineer from Nemetschek are helping engineers to do just that. 

In the latest release, Scia Engineer introduces Adaptive Mesh Refinement technology, a feature normally reserve for high-end 3D Finite Analysis programs, to the structural and civil engineer for building and infrastructure design.

One Problem with Manual Meshing; Time


A local Edge Refinement manually defined by the engineer.
A question that needs to be asked at the beginning of every Finite Element analysis is how to set a mesh size.  Manually setting and refining a mesh is tedious and time consuming. The trial and error involved can easily zap an engineer’s productivity. This is a problem, as an engineer’s time could be better spent making important design decisions as opposed to pre-processing their analysis.

Think of it: to manually mesh a design, engineers have to create a mesh, test it, determine areas of refinement (lines, nodes, and 2D spaces) and repeat until their errors are within spec.

“Engineers will typically ask us what mesh size to use. Truthfully, the answer depends on your design and experience. We can make rough suggestions but no mesh is perfect the first time around,” said Cyril Heck. Mr. Heck uses his civil engineering background to serve as Sales & Marketing Manager at Nemetschek Scia. “We want a fine enough mesh to give accurate answers, but not too fine as you don’t want a solution to take 10 hours. You need a good mesh that is precise where it needs to be but quick to run as well.”

The adaptive meshing in Scia Engineer solves this trial and error process by letting the software improve the mesh and add local refinements where necessary. For the tool to run, engineers input an acceptable error tolerance, a representative load case, and then let Scia Engineer do all the heavy lifting.

To better illustrate this process, let’s take a look at the practical example shown below.


The automatic adaptive meshing process.

Step 1:
The user enables automatic mesh refinement in Scia Engineer and establishes the average size of a 2D element. In this example a value of 3ft is used.  The mesh is then generated and the analysis is run to determine the accuracy and necessary refinement of the initial setup.  In this first step, the estimation of the global mesh error remains high, as shown by the colors red, yellow and green.

Step 2:
In the second step, the user regenerates the mesh according to the recommended refinement.  Then the structure is analyzed in order to generate results on the new mesh.  In this result, the suggested mesh refinement is localized at the column-to-slab connection points (as shown in dark blue and purple).  In addition, the global mesh error has been significantly reduced, with peak values only at the locations of additional suggested refinement.

Step 3:
In the final step, the mesh is further adapted with additional localized refinements as shown by the finer mesh at the column-to-slab connections and wall-to-slab connection points. While additional mesh refinement is suggested, the peak values of global mesh error are no longer apparent as shown with the majority of the slab colored dark blue and purple.  At this point, an ideal mesh has been defined and the refinement process is complete. The engineer can utilize this ideal mesh for analysis and design.

How Adaptive Meshing Solves Your Time Crunch

“In theory you can spend ages making the perfect mesh manually. But you will not be able to influence every point, only your chosen refinement zones. This means you will not have control on every sweet spot. Additionally, many will not have the knowhow to produce such a mesh in a reasonable time,” said Heck.

Scia Engineer’s adaptive mesh, however, is able to refine every cell individually. It works by comparing FEA calculated stress values with theoretically calculated stress/gradient values across the mesh.

These theoretical values are determined using the superconvergent patch recovery method. This method is based on energy balances and is outlined in detail in this journal article written by Zienkiewicz and Zhu.

Based on these two values Scia Engineer calculates an error estimate for each cell. Using further research by Zienkiewicz and Zhu cells with unacceptable errors are refined. The calculations are then reassessed and iterated until all the error values are within tolerance. This cell by cell analysis will ensure the level of refinement needed to hit all those problem areas.

“Essentially, the tool starts with a coarse mesh and will subdivide each mesh element where needed,” explained Heck. “It will also smooth out the mesh to ensure it is consistent and geometrically satisfying for FEA analysis.”

For more detailed information on Nemetschek Scia, Scia Engineer, and their adaptive mesh technology, visit their website, watch the video below, or read the following journal articles: Superconvergence and the superconvergent patch recovery and The superconvergent patch recovery (SPR) and adaptive finite element refinement.

Nemetschek-Scia has sponsored promotion of their Scia Engineer software on ENGINEERING.com.

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