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What you asked us in January 2020

By Chloe Allison 17 February 2020

Each month our application engineers respond to a large number of support requests, and sometimes we see the same questions coming up again and again. This has inspired a brand-new feature for our blog: a monthly review of common support questions!

To start us off, here are some of the questions we received in January.

What values should I use for hourglass suppression?

You can enable hourglass suppression using the matr hrgl command. Hourglass suppression should only be used when you experience hourglassing in the mesh or instability in some extreme cases. There are default values for the bb and fb options, as described in the Command Reference. fb/bb can be used for linear elastic and nonlinear materials. The visc option can be used for liquids: start at 0.1. The goal is to minimize the amount of hourglass suppression used in the model as much as possible because it is another form of loss that is non-physical.

What is the difference between frequency of interest and frequency of damping?

The frequency of interest is used as a parameter to control mesh resolution. We recommend 15 elements per wavelength to resolve the waves sufficiently. This is typically set to the center of your operating frequency band. For example, if you are interested in data up to 2 MHz, your drive frequency should be around 1 MHz, assuming your time-domain input signal has enough energy to cover this frequency range. Remember we are operating in the time domain, so you can FFT the time trace to determine if this covers your frequency range of interest.

For frequency of damping, again we set this to the center of the operational frequency band to ensure our damping models are accurate over this frequency range. If your drive signal is at the center of the operational band, then you should set both to the same frequency value.

What units are my graph in?

OnScale operates in SI units. For example, distance is in meters, pressure in Pascals, force in Newtons, frequency in Hz and so on.

How do I radially pole a material?

Check out this article!

How do I overlap shapes in Analyst mode?

When defining shapes using the site command in Analyst mode, any shapes that overlap existing ones will overwrite the material assignment in areas where they intersect. For example, if object1 and object2 overlap in some region then the region will be given the material of whichever object is defined last.

Scenario 1

Object1 and object2 overlap from $i2->$i3. Object2 is created after object1, so $i2->$i3 will be object 2.

site

          regn object1 $i1 $i3

          regn object2 $i2 $i4

 

Scenario 2

The order is reversed, so $i2->$i3 will be object1.

site

          regn object2 $i2 $i4

          regn object1 $i1 $i3

 

How can I transmit and receive in the same model?

If you wish to transmit and receive in a model you must have a receive circuit. You can create one using the Circuit tool, which is found in the Tools tab.

Questions

After transmission in the prcs command, you can switch to this circuit to receive on the chosen electrode. Here is a simple example of a pulse echo model using an Rx circuit.

How can I achieve finer mesh density in one area of my model?

When you have fine details in your model it can be costly to mesh for these details as this drives the time step down, which means the model requires more computation. However, using a refined grid method you can choose to mesh two areas of the grid differently and glue them together. Here is an example of this. We are also in the process of developing general connectivity (GCON) meshes, which provide capability to mesh with triangular, quadrilateral, tetrahedral and hexagonal elements. Check out this basic wave propagation example of a plate with a hole meshed with triangular elements.

 

Chloe Allison
Chloe Allison

Chloe Allison is an Application Engineer at OnScale. She received her MA in Electrical and Electronics Engineering from the University of Strathclyde. As part of our engineering team Chloe assists with developing applications, improving our existing software and providing technical support to our customers.