## Exploiting Periodicity in Models with High Péclet Numbers

##### Walter Frei November 18, 2015

When solving a chemical species transport problem, we are often dealing with cases that have a high Péclet number, where the ratio of the advection to diffusion is very high. We may also be dealing with such problems in structures that are periodic along the flow direction, and where the flow field itself is periodic. Using COMSOL Multiphysics, we can greatly reduce our computational requirements for such problems by using General Extrusion component couplings and the Previous Solution operator.

Read More##### Walter Frei September 8, 2015

Good competitive paddling requires strength, timing, consistency, and teamwork. Initially, this may seem quite easy. Simply stick your paddle in the water and make the water go backward so that the boat moves forward. As it turns out, there are actually many different paddling strokes you can use depending on the situation.

Read More##### Walter Frei September 7, 2015

When using the finite element method, we often want to model solid objects that are rotating and translating within other domains. The deformed mesh interfaces in COMSOL Multiphysics can be used to model these movements. In this blog post, we will look at the modeling of large linear translations and rotations of domains within other domains, while introducing efficient modeling techniques for addressing such cases.

Read More##### Walter Frei September 4, 2015

COMSOL Multiphysics includes two interfaces for manually defining the deformation of finite element mesh, the Deformed Geometry interface and the Moving Mesh interface. In this blog post, we will address when to use these interfaces and how to use them to efficiently model translational motion.

Read More##### Walter Frei September 2, 2015

Modeling geometries with high aspect ratios can be one of the more challenging tasks for the finite element analyst. You want to have a mesh that will accurately represent the geometry and the solution, but you do not want too many elements, as solving your models would then require excessive computational resources. Here, we will look at using swept meshing to generate efficient and accurate finite element meshes in the context of some common modeling cases.

Read More##### Walter Frei August 11, 2015

In the course of building multiphysics models, we often encounter situations in which the solution to one physics is periodic — or very nearly so — while the solutions to other physics of interest are nonperiodic. If we know this ahead of time, it is possible to exploit the periodicity to reduce computational requirements. Here, we will demonstrate how to accomplish this using the General Extrusion component couplings in COMSOL Multiphysics.

Read More##### Walter Frei August 5, 2015

One useful — but in my experience, rarely used — capability available within COMSOL Multiphysics is the ability to compute design sensitivities. Assuming that you have a single objective function that is computed based on your finite element model, you can easily compute how sensitive this objective function is with respect to any model input, using only the core COMSOL Multiphysics package. In this blog post, we will look at how to use this functionality.

Read More##### Walter Frei July 21, 2015

When modeling a manufacturing process, such as the heating of an object, it is possible for irreversible damage to occur due to a change in temperature. This may even be a desired step in the process. With the Previous Solution operator, we can model such damage in COMSOL Multiphysics. Here, we will look at the “baking off” of a thin coating on a wafer heated by a laser.

Read More##### Walter Frei June 30, 2015

Over the last several weeks, we’ve published a series of blog posts addressing the various domain and boundary conditions available for wave electromagnetics simulation in the frequency domain; as well as modeling, meshing, and solving options. In this blog post, I will tie all of this information together and provide an introduction to the various types of problems that you can solve in the RF and Wave Optics modules.

Read More##### Walter Frei June 25, 2015

COMSOL Multiphysics version 5.1 includes a Previous Solution operator within time-dependent studies. This operator allows you to evaluate quantities at the previous time step when using the default implicit time-stepping algorithm. Let us take a look at how this operator is implemented and then examine how it can be used for various modeling needs.

Read More##### Walter Frei June 22, 2015

A question that we are asked all of the time is if COMSOL Multiphysics can model laser-material interactions and heating. The answer, of course, depends on exactly what type of problem you want to solve, as different modeling techniques are appropriate for different problems. Today, we will discuss various approaches for simulating the heating of materials illuminated by laser light.

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