# COMSOL Blog

## Plotting Spatial Derivatives of the Magnetic Field

##### Marc Fernandez Silva | March 5, 2014

Being able to compute the spatial gradients of the magnetic field or magnetic flux density is needed in areas such as radiology, magnetophoresis, and geophysics. One of the most important applications is in the design of magnetic resonance imaging machines, where it’s important to analyze not only the field strength, but also the spatial variation of the field. Today’s blog will demonstrate how to compute and plot the gradients of the magnetic field in 3D electromagnetic simulations in COMSOL Multiphysics.

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### Analyze your Simulation Results with Projection Operators

##### Clemens Ruhl | February 12, 2014

Have you ever used your hands to make shadow puppets on the wall? By shining a light behind your (three-dimensional) hands, you create two-dimensional projections on the wall. When analyzing your simulation data in COMSOL Multiphysics, you can do something similar with your model using projection operators.

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### Size Parameters for Free Tetrahedral Meshing in COMSOL Multiphysics

##### Andrew Griesmer | January 30, 2014

Meshing a geometry is an essential part of the simulation process, and can be crucial for obtaining the best results in the fastest manner. However, no one wants to be bogged down figuring out the exact specifications for their mesh. To help combat this problem, COMSOL Multiphysics has nine built-in size parameter sets when meshing. Here, we’ll discuss size parameters for free tetrahedral meshing. Swept meshing with prismatic and hex elements, and other types, will be covered in future postings.

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### Using the General Extrusion Coupling Operator in COMSOL: Dynamic Probe

##### Chandan Kumar | January 28, 2014

Here is an interesting question: How can we easily probe the solution at a point that is moving in time, but associated with a stationary geometry? One option is to use the General Extrusion coupling operator. In this blog post, we will take a look at how to use the General Extrusion coupling operator to probe a solution at a point in your geometry, and illustrate how to implement a dynamic probe using an example model.

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### Solving Algebraic Field Equations

##### Bjorn Sjodin | January 14, 2014

Many of our users are well aware of the fact that COMSOL Multiphysics can be used to solve partial differential equations (PDEs) as well as ordinary differential equations (ODEs) and initial value problems. It may be less obvious that you can also solve algebraic and even transcendental equations, or in other words, find roots of nonlinear equations in one or more variables with no derivatives in them. Are there real applications for this? Absolutely!

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### Visualization for 2D Axisymmetric Electromagnetics Models

##### Chris Pinciuc | December 31, 2013

Today we’ll look at how to make 3D plots of vector fields that are computed using the 2D axisymmetric formulation found in the Electromagnetic Waves, Frequency Domain interface within the RF and Wave Optics modules.

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### Using Adaptive Meshing for Local Solution Improvement

##### 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. […]

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### Learning to Solve Multiphysics Problems Effectively

##### 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.

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### Improving Convergence of Multiphysics Problems

##### 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.

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### Simulating Viscous Fingering Using Equation-Based Modeling

##### David Kan | December 18, 2013

A prospective user of COMSOL approached me about modeling viscous fingering, which is an effect seen in porous media flow. He hadn’t found a satisfying solution elsewhere, so he turned to COMSOL. I’d like to share with you some of my insight on how to go from idea to model to simulation by taking a “do-it-yourself approach” and utilizing the equation-based modeling capabilities of COMSOL Multiphysics.

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### Solving Multiphysics Problems

##### 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.

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