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Physics Solutions

1128: Thermoacoustics interface yields unexpected results

I tried the thermoacoustics physics interface in a model where I use the material properties of water. I used the COMSOL Material Browser to get the properties. The solution is not what I expect. I suspect there is...
Version: 4.3b - Platform:

1043: Equilibrium reactions in Reaction Engineering Lab

I have set up a couple of equilibrium reaction in Reaction Engineering Lab. The results look strange, and I don't even seem to get convergence. The Reaction Engineering Lab together with COMSOL Multiphysics allows you...
Version: 3.5a - Platform: Windows

1038: Using symmetries in COMSOL Multiphysics

How do I take advantage of the symmetries in my COMSOL model? ##Using Symmetries to Reduce Model Size By using symmetries in a model you can reduce its size by one-half or more, making this an efficient tool for...
Version: All versions - Platform: All Platforms

1031: Flux through interior boundaries

When plotting the normal flux through the boundaries in my model, I am surprised to see that two adjacent boundary segments have opposed flux. This is clearly not physically possible. Why does this happen and what can...
Version: 3.5a - Platform: All Platforms

1009: How do I model materials with gain/losses?

I am using a time-harmonic application mode to solve an electromagnetics problem. If I want to introduce lossy materials, or materials with gain, what are my options? COMSOL Multiphysics uses the time-harmonic...
Version: 4.0,4.0a,4.1 - Platform: All Platforms

1004: Resolving the Skin Depth

Why do the currents in my metal look strange? How can I get a realistic solution at high frequencies? Not resolving the skin depth is one of the more common modeling mistakes in AC and RF applications. Luckily, in most...
Version: 4.0,4.0a,4.1,4.2 - Platform: All Platforms

973: My flux calculation seems wrong

I am solving a diffusion-like problem in COMSOL Multiphysics and discovered that boundaries that are defined with insulation/symmetry conditions have an integrated value of the normal component of the flux that is far...
Version: All versions - Platform: All Platforms

952: Avoiding negative concentrations

Why do I get negative values of the concentration in my diffusion/convection model? It is clearly unphysical. There are several possible reasons for negative concentrations: ## Numerical errors The most common reason...
Version: 3.5a,4.0,4.0a,4.1,4.2,4.2a,4.3,4.3a - Platform: All Platforms

939: Can COMSOL Multiphysics handle polar, spherical, and cylindrical...

Can COMSOL Multiphysics handle polar, spherical, and cylindrical coordinates? And how can I define these coordinates? ##COMSOL 4 To add another coordinate system to the **Model Builder**, right-click...
Version: All versions - Platform: All Platforms

916: Electromagnetic coils: multi-turn with fixed total current and skin...

How can I model a multi-turn current-carrying circular or cylindrical coil with skin effect? How do I specify a fixed total current in each winding while leaving the spatial distribution of the current density free?...
Version: 3.5a,4.0,4.0a,4.1,4.2 - Platform: All Platforms