## Implementing the Weak Form with a COMSOL® App

##### Chien Liu | April 16, 2015

Previously in our weak form series, we discretized the weak form equation to obtain a matrix equation to solve for the unknown coefficients in our simple example problem. Following the same procedure as in this previous blog post, we will implement the equation in the COMSOL Multiphysics® software with additional steps included to examine the matrices. We will find it more convenient to use a COMSOL® software application to display all relevant matrices at once, arranged logically on one screen.

##### Walter Frei | April 13, 2015

High-intensity lasers incident upon a material that is partially transparent will deposit power into the material itself. If the absorption of the incident light can be described by the Beer-Lambert law, it is possible to model this power deposition using the core functionality of COMSOL Multiphysics. We will demonstrate how to model the absorption of the laser light and the resultant heating for a material with temperature-dependent absorptivity.

##### Walter Frei | March 27, 2015

Often, the most tedious step of finite element modeling is subdividing your CAD geometry into a finite element mesh. This step, usually just called meshing, can sometimes be fully automated. More often, however, the careful finite element analyst will want to semi-manually create their meshes. Although this does require more work, sometimes there are significant advantages in doing so. In this blog entry, we will look at one of the key manual meshing techniques: the concept of geometric partitioning.

##### Pär Persson Mattsson | February 20, 2015

We have previously written about HPC with the COMSOL Multiphysics® software, clusters, and hybrid computing. But not all of us have a cluster available in the office (or the hardware to build a Beowulf cluster). So what possibilities do we have if we really need that extra compute power that a cluster can give us? One solution is to utilize cloud computing, a service that provides compute power on a temporary basis, to give our computations and productivity a boost.

##### Walter Frei | February 16, 2015

One of the more common questions we are asked is about the modeling of periodic, or pulsed, heat loads. That is, a heat load that turns on and off repeatedly at known times. Modeling such a situation accurately and efficiently in COMSOL Multiphysics is quite easy to do with the Events interface. The techniques we will introduce are applicable to many classes of time-dependent simulations in which you have changes in loads that occur at known times.

##### Lexi Carver | February 2, 2015

In recent postprocessing blog posts, we’ve demonstrated different plot types that are typically used for common fluid, mechanical, chemical, and electrical applications. In the next several parts of this series, we’ll introduce a few more unusual plot types that are specific to unique applications and discuss some other tools that you can use to change the feel of your visualization. Here, we highlight polar, far-field, and particle tracing plots.

##### Chien Liu | April 1, 2015

Over half a century ago, Mark Kac gave an interesting lecture on a question that he had heard from Professor Bochner ten years earlier: “Can one hear the shape of a drum?” He focused on the (then undetermined) uniqueness of the set of eigenvalues given the shape of a vibrating membrane. The eigenvalue problem has since been solved and here we explore the “hearing” part of the question by considering some interesting physical effects.

##### Walter Frei | March 19, 2015

We often need to work with experimental data in COMSOL Multiphysics, usually to represent material properties or other inputs to our model. However, experimental data is often noisy; it contains experimental errors that we do not want to introduce into our simulations. In this blog post, we will look at how to fit smooth curves and surfaces to experimental data using the core functionality of COMSOL Multiphysics.

##### Walter Frei | February 19, 2015

A thermostat is a device that senses the temperature of a system and uses this information to control the system’s heaters, or coolers, to keep the temperature close to a desired setpoint. While there are many different types of thermostats, we will focus today on one that turns a heater either on or off based upon two setpoints. This is known as an on-off or a bang-bang controller, and it can be implemented with the Events interface in COMSOL Multiphysics.

##### Chien Liu | February 9, 2015

This post continues our blog series on the weak formulation. In the previous post, we implemented and solved an exemplary weak form equation in the COMSOL Multiphysics software. The result was validated with simple physical arguments. Today, we will start to take a behind-the-scenes look at how the equations are discretized and solved numerically.

### Using Perfectly Matched Layers and Scattering Boundary Conditions for Wave Electromagnetics Problems

##### Walter Frei | January 28, 2015

When solving wave electromagnetics problems, it is likely that you will want to model a domain with open boundaries — that is, a boundary of the computational domain through which an electromagnetic wave will pass without any reflection. COMSOL Multiphysics offers several solutions for this. Today, we will look at using scattering boundary conditions and perfectly matched layers for truncating domains and discuss their relative merits.