##### 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!

Read more ⇢##### 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.

Read more ⇢##### 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.

Read more ⇢##### 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 […]

Read more ⇢##### 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 […]

Read more ⇢##### 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.

Read more ⇢##### 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. […]

Read more ⇢##### 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.

Read more ⇢##### 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.

Read more ⇢##### Walter Frei | December 16, 2013

Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. So far, we’ve learned how to mesh and solve linear and nonlinear single physics finite element problems, but have not yet considered what happens when there are multiple different interdependent physics being solved within the same domain.

Read more ⇢##### Walter Frei | December 12, 2013

Whenever we are solving a thermal problem where radiation is significant, we need to know the emissivities of all of our surfaces. Emissivity is a measure of the ability of a surface to emit energy by radiation, and it can depend strongly upon the wavelength of the radiation. This is very relevant for thermal problems where the temperature variation is large or when there is exposure to a high-temperature source of radiation such as the sun. In this post on […]

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