# Support Knowledge Base

## Physics

1172: Solving time dependent models with inconsistent initial values

A common mistake when setting up transient models is to have initial conditions that are inconsistent with the loads and boundary conditions. This occurs most often when running transient fluid flow studies, but the...
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1104: Stabilization schemes in COMSOL

How can I see which stabilization schemes are used by COMSOL Multiphysics in transport physics interfaces such as Single-Phase Flow and Transport of Diluted species? Numerical solutions of transport equations can...
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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...
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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...
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952: Avoiding negative concentrations

Why do I get negative values of the concentration in my diffusion, convection and reaction model? Why do I see values that go below, or above, their lowest, or highest, possible values based upon the boundary...
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913: Computing Time and Space Integrals

How do I compute integrals over space or time? What if I want to use the result of these integrals elsewhere in my model? The COMSOL Multiphysics architecture allows you to evaluate integrals in both space and time in...
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905: Modeling of step transitions

You may want to define loads, material properties, or boundary conditions that vary abruptly with respect to the solution, or with respect to time. This can, however, lead to a solution which is discontinuous in space...
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878: Should I use the RMS, the peak, or the instantaneous value to...

Should I use the RMS, the peak, or the instantaneous value to specify sources for electromagnetic fields? How can I specify the phase angle? The COMSOL Multiphysics formulation uses complex fields when solving...
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875: What does degrees of freedom (DOFs) mean in COMSOL Multiphysics?

What does degrees of freedom (DOFs) mean in COMSOL Multiphysics? The solution time and memory requirements are strongly related to the number of degrees of freedom in the model. It is often desirable to be able to...
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816: How do I solve a PDE with space derivatives of order higher than two?

How do I solve a PDE with space derivatives of order higher than two? For example, the equation for a function . Introduce names for the second derivatives of u, say . Then the equation can be written . You can...
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