All posts by Walter Frei

Walter Frei | April 14, 2014

One of the questions we get asked all the time is: “Can I use COMSOL Multiphysics for solving my fluid-structure interactions problems?” Of course the answer is yes, so let’s talk a little about the various fluid-structure interaction (FSI) modeling techniques. Along the way, we will introduce the add-on modules you will need for these various types of analyses.

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Walter Frei | April 9, 2014

In a previous posting, we looked at computing and controlling the volume of a cavity filled with an incompressible fluid, which solved for the static deformation of a fluid-filled rubber seal. In that example, we did not explicitly model the fluid, but added an equation to solve for the pressure, assuming incompressibility of the fluid. Here, we will extend this approach and include the hydrostatic pressure of the fluid in the deforming container.

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Walter Frei | March 25, 2014

It is well-known that you can use the RF Module to compute the impedance of lossless transmission line structures, such as coaxial cables of uniform cross section. But did you know that you can also compute an effective impedance for waveguides with non-uniform cross section? Let’s find out how!

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Walter Frei | February 17, 2014

COMSOL’s Optimization Module is a powerful tool for improving the performance of your devices and systems. Here, we will look at optimizing the power applied to two heaters in a flow channel with the objective of heating up the fluid as much as possible as it passes through the channel, while constraining the peak temperature at the heaters themselves. One application of this technique is improving the efficiency of thermal processes.

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Walter Frei | February 11, 2014

When solving a thermal processing problem, such as the heating or cooling of a part, it is desirable to change the heating, or cooling, based upon the computed solution. That is, we may want to include a feedback loop into our model. In this article, we will set up a feedback loop using a component coupling to turn a heat load on or off depending upon the temperature of the part being heated.

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Walter Frei | February 3, 2014

There are various ways of handling interactions between fluids and solids in COMSOL. You can, for example, explicitly model the fluid using the full Navier-Stokes equations for the pressure and fluid velocity fields. Although that can be a very accurate approach, it’s much more expensive than is needed for certain types of Fluid-Structure Interaction (FSI) problems. Here, we’ll introduce a method for modeling enclosed volumes containing incompressible fluids, under the additional assumption that the momentum and energy transfer via the […]

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Walter Frei | January 17, 2014

We often want to model an electromagnetic wave (light, microwaves) incident upon periodic structures, such as diffraction gratings, metamaterials, or frequency selective surfaces. This can be done using the RF or Wave Optics modules from the COMSOL product suite. Both modules provide Floquet periodic boundary conditions and periodic ports and compute the reflected and transmitted diffraction orders as a function of incident angles and wavelength. This blog post introduces the concepts behind this type of analysis and walks through the […]

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Walter Frei | January 8, 2014

When you are working with foreign CAD data, such as files in STEP or IGES file formats, you may think that you need to re-import a new CAD file and start your modeling over from scratch if you want to study a change in size or shape. But, in fact, you can modify the geometry that you’ve imported with some clever usage of the Deformed Geometry interface in COMSOL Multiphysics. Here, we will look at how this can be done.

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Walter Frei | December 27, 2013

One of the perennial questions in finite element modeling is how to choose a mesh. We want a fine enough mesh to give accurate answers, but not too fine, as that would lead to an impractical solution time. As we’ve discussed previously, adaptive mesh refinement lets the software improve the mesh, and by default it will minimize the overall error in the model. However, we often are only interested in accurate results over some subset of the entire model space. […]

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Walter Frei | December 26, 2013

One of the questions we get asked often is how to learn to solve multiphysics problems effectively. Over the last several weeks, I’ve been writing a series of blog posts addressing the core functionality of the COMSOL Multiphysics software. These posts are designed to give you an understanding of the key concepts behind developing accurate multiphysics models efficiently. Today, I’ll review the series as a whole.

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Walter Frei | December 23, 2013

In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. Here, we will examine techniques for accelerating the convergence of these two methods.

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