## 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##### Amelia Halliday August 3, 2016

When you are creating a model, it can sometimes be difficult to keep track of all the parts in the geometry, including the conditions or constraints that apply to each section. This is especially true when dealing with large, complex geometries and multiple physics interfaces. In COMSOL Multiphysics, tools like named selections help maintain your model setup and streamline your workflow. Here’s a look at three tutorial videos demonstrating how to create and utilize Explicit, coordinate-based, Boolean, and adjacent selections.

Read More##### Kateryna Vyshenska July 27, 2016

Archimedean spirals are often used in the analysis of inductor coils, spiral heat exchangers, and microfluidic devices. Today, we will demonstrate how to build an Archimedean spiral using analytic equations and their derivatives to define a set of spiral curves. Based on these curves, we will then create a 2D geometry with specific thickness, extruding it to a full 3D geometry.

Read More##### Caty Fairclough July 12, 2016

You’ve generated your simulation results and you want to communicate your findings with other people. To do so clearly and effectively, you will need to create easy-to-understand, eye-catching visualizations. Therefore, as of COMSOL Multiphysics® software version 5.2a, you now have six new color tables to further enhance your postprocessing. Let’s learn about the inspiration behind these color tables and take a look at a few specific use cases.

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##### Amelia Halliday June 28, 2016

Simulation is a powerful tool that enables you to obtain a holistic view of your design’s performance. While the physics you are studying may be complex, the environment in which you run such studies doesn’t have to be. This rationale has served as the logic behind continuously optimizing the user interface (UI) in the COMSOL Multiphysics® software for ease-of-use. Several tutorial videos, three of which are highlighted here, guide you on how to navigate the environment and utilize its tools.

Read More##### Henrik Sönnerlind June 27, 2016

Say you are working on a modeling case where loads are moving in such a way that they cross over different mesh elements and boundaries during the simulation. In these cases, among other instances, you may want to apply a boundary condition to only part of the geometrical boundary or only under certain conditions. In this blog post, we’ll discuss how you can utilize the flexibility of COMSOL Multiphysics to handle such situations.

Read More##### Yosuke Mizuyama May 30, 2016

In a previous blog post, we discussed simulating focused laser beams for holographic data storage. In a more specific example, an electromagnetic wave focused by a Fourier lens is given by Fourier transforming the electromagnetic field amplitude at the lens entrance. Let’s see how to perform this integral type of preprocessing and postprocessing in COMSOL Multiphysics with a Fraunhofer diffraction example.

Read More##### Caty Fairclough May 9, 2016

Have you ever wondered how tigers develop their stripes? Alan Turing’s theory of morphogenesis offers one possible explanation for this occurrence, suggesting that patterns, such as stripes, develop naturally from initially homogeneous states. Today, we’ll take a closer look at Turing’s theory and explore some modern research on this topic, including the modeling of branching morphogenesis in COMSOL Multiphysics.

Read More##### Magnus Ringh April 27, 2016

You can use the residual operator, new with COMSOL Multiphysics version 5.2, to evaluate and plot your model’s algebraic residual in order to troubleshoot convergence issues. This blog post demonstrates the use of the residual operator for visualizing and understanding the convergence properties of a turbulent flow simulation.

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