Shorter Solve Times with QUAKE/W

by Nate Hekman on June 2, 2009

Last year while discussing hardware recommendations for getting the most out of GeoStudio 2007, I mentioned that the solvers are multi-threaded, “meaning [they] will take full advantage of multiple CPUs or cores.”

But a QUAKE/W user showed me that’s not true in all cases.  He had a QUAKE/W analysis that was only using one of his four cores, and asked me why that was, or what he could do to change it.

That was news to me, and at first I thought it was a bug, but after some digging through the code and discussing with other engineers in the group, I learned a valuable lesson.

It turns out QUAKE/W will take full advantage of multiple CPUs when using the Parallel Direct Solver option but only for Initial Static and Nonlinear Dynamic analyses.  The Equivalent Linear analysis types are not currently formulated in a way that lends itself to parallelization, and thus even if you choose the “Parallel Direct Equation Solver” option, they will only use a single core while solving.

QUAKE/W analysis types - only the first and last lend themselves to multi-threading.

We did have some other suggestions, however, for how this customer could greatly speed up solving his analysis.  Some of these may help you as well.

Shorten the Earthquake Record

This customer had over 12,000 data points in his earthquake record.  That means over 12,000 finite-element analyses for each iteration. 

Much of this is unnecessary.  The first thing to do is to lop off the ends.  Normally in an earthquake record the beginning and end can be lopped off, as the vibrations are small enough as to not affect the final solution. 

In this case we suggested getting rid of the first five seconds and the last 25 or so, which I’ve highlighted here.

Focus on the important part of the quake by getting rid of the 'noise' at the beginning and end.

We’ve just cut down the number of data points to 5000, less than half.  That cuts the solve time less than half too.

Resample the Earthquake Record

This record’s data points are 4/1000 sec apart.  That kind of precision is likely not necessary for a geotechnical analysis. 

Use Excel to remove every other data point, then re-scale the record so it still has the same peak accelerations, and you’ve reduced the number of equations by half again, still likely without affecting your results.

Understand the Equivalent Linear Method

Remember what the EL method is all about.  You are looking for only one number for each element and taht is the maximum dynamic shear stress.  This usually occurs at one of the peaks.  All analyses after the peak has been established are irrelevant to the analysis.

Simplify the Mesh

Especially in the early stages of an analysis, when you’re trying to answer some initial questions, use a simple mesh.  For example:

  • if you know all the important activity will be in one area, get rid of mesh detail a long way from that area;
  • stick to just a few materials and a couple of regions;
  • try a 1D column to start with.

Besides making for shorter solve times, a simpler geometry and simpler mesh also makes it easier to understand and interpret the answers you’re getting.  You can add complexity later and watch how (or if) it affects what you’ve understood so far.

Happy meshing!

{ 4 comments… read them below or add one }

1

Rafael 06.04.09 at 10:20 am

Just an additional note. After resampling and re-scaling the earthquake record it is always good practice to do at least two very important verifications:
1. Verify that the acceleration spectra of the final and initial records are comparable. Now use your engineering judgment to decide what falls in the “comparable category” 😉
2. Verify that the displacement spectra returns to zero.
Finally, I’ve had good experience with records digitized to 0.02 and 0.025 seconds.
All the best!

2

Nate 06.15.09 at 10:55 am

Thanks for the additional points, Rafael.

3

S.Srinivasa Rao 08.20.09 at 6:00 am

Hi Sir,

This is Srinivas doing M.Tech Geotechnical engineering in National Institute of Technology, Warangal(NITW), India. I downloaded your GEostudio2007 7.14 version and i want to learn this software, to learn this i tried to download your Resource CD but i didnt get that. So send me that Resource CD and help me to learn this software. This is purly for educational purpose only.

Thanking you,

Yours faithfully,
S.Srinivasa Rao.

4

Nate 08.20.09 at 3:04 pm

If you are not already a licensed user of one of our products, then the best way to get the Resource CD is to order the Student Edition CD (scroll to the very bottom) from our web site for $10 USD, as this includes the Resource CD.

However, you can get all the resources free from our web site even without downloading the entire CD. The CD contains sample gsz files, all of which can instead be searched and downloaded individually from here. And it contains tutorial movies which can be viewed or downloaded from here.

I hope this helps.

Leave a Comment

You can use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>