## Part 2: Modeling the Harmonic Excitations of Nonlinear Systems

##### Walter Frei | August 11, 2016

Extending our discussion on modeling the harmonic excitations of linear systems, we will now shift focus to nonlinear systems. We will look at problems where the loading on the system has some sinusoidal components as well as cases where the material properties or loads and constraints depend directly on the solution. As you will see, COMSOL Multiphysics can address these apparently nonlinear cases with some very efficient solution algorithms. Let’s find out how.

Read More##### Walter Frei | August 10, 2016

In many engineering situations, we can assume that excitations on the system of interest and the responses are sinusoidal over time. When this assumption holds, we can use a so-called frequency-domain analysis, which leads to some very efficient solution techniques. Let’s go over a few basic concepts and the conditions under which we can make this assumption, while exploring various solution approaches to take.

Read More##### Walter Frei | June 22, 2016

Have you ever wanted to quickly predict the temperature of an enclosed structure, such as your house, that is exposed to ambient environmental conditions? The temperature inside depends on the surrounding air temperature, wind speed, and solar loads, all of which have significant variability. For simplicity, we often also want to approximate the inside air as well-mixed. Today, we will discuss the tools in COMSOL Multiphysics that help you quickly build such thermal models.

Read More##### Walter Frei | March 30, 2016

Whenever solid materials are heated enough, they will melt and then vaporize to a gas. Certain materials will even go directly from the solid to the gas phase, a process referred to as sublimation or ablation. If the material is heated strongly enough, there will be significant material removal. Today, we will look at how you can model this process in COMSOL Multiphysics.

Read More##### Walter Frei | March 22, 2016

Whenever you are modeling coils with the AC/DC Module in COMSOL Multiphysics, you need to consider what type of boundary conditions to use to truncate your modeling domain. In this blog post, we will introduce the different boundary conditions that you can use and how to choose between them.

Read More##### Walter Frei | March 8, 2016

Have you ever had a set of nonuniformly distributed points in a Cartesian plane that sample a surface height, such as points on the contours of a map or data points representing some material property data? If so, you probably also wanted to reconstruct, or interpolate, a continuous and smooth surface between these points. You can construct such a surface using the core capabilities of COMSOL Multiphysics by using Radial Basis Functions. Let’s find out how…

Read More##### Walter Frei | June 30, 2016

Thermostats are used in most homes for controlling furnaces and air conditioners to maintain a comfortable interior temperature. A simple thermostat controlling a heater will have on and off setpoints. Such a control scheme is easy to implement within COMSOL Multiphysics using the Events interface, as presented in a previous blog post. Today, we will expand this technique to include a delay, a time lag between turning the heater on or off, in a thermostat simulation.

Read More##### Walter Frei | April 6, 2016

Have you ever wanted to write out mesh and analysis data from COMSOL Multiphysics into a text file? You may want to do this when passing information to another software program or even just into a spreadsheet. You often want to customize the exact format in which such data is written, depending upon the needs of the other tools with which you are working. This is very easy to do with the Application Builder. Let’s find out how!

Read More##### Walter Frei | March 24, 2016

In today’s blog post, we will introduce a procedure for thermally modeling a material with hysteresis, which means that the melting temperature is different from the solidification temperature. Such behavior can be modeled by introducing a temperature-dependent specific heat function that is different if the material has been heated or cooled past a certain point. We can implement this behavior in COMSOL Multiphysics via the Previous Solution operator and a little bit of equation-based modeling. Let’s find out how…

Read More##### Walter Frei | March 16, 2016

Thermal curing is the process of temperature-induced chemical change in a material, such as the polymerization of a thermoset resin. This process is relevant, for example, when a precursor resin is heated and hardens during the manufacturing of composites. You can often assume that the material does not flow during curing, which simplifies the analysis. Thermal curing is very easy to model within the core functionality of COMSOL Multiphysics, as we will show in this blog post.

Read More##### Walter Frei | March 3, 2016

One of the most common uses of the AC/DC Module is for modeling electromagnetic coils and the interactions with their surroundings. Today, we will look into one of the key concepts to keep in mind when modeling coils: closing the current loop. If your work involves modeling coils, you will need a complete understanding of this topic.

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