Help with Magnetic Dipole Moment

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Discussion Overview

The discussion centers on the calculation of the resultant magnetic dipole moment of a permanent magnet situated within a steel housing. Participants explore the effects of the steel on the magnetic field and the implications for numerical modeling using Comsol software. The scope includes theoretical considerations of magnetization and practical challenges in simulation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks to determine the total magnetic dipole moment of a permanent magnet within a steel housing, noting that the remnant flux density is altered by the housing.
  • Another participant suggests that numerical modeling is appropriate for this scenario, emphasizing the relationship between magnetization, magnetic induction, and magnetic fields in ferromagnetic materials.
  • A participant expresses confusion over the results obtained from Comsol, noting that the magnetic moment increases when the steel housing is added, which contradicts their expectation that it should decrease.
  • There is a question raised about whether the magnetic moment routed through the steel would detract from the effective magnetic moment.
  • One participant agrees that the magnetic moment should not appear larger and highlights the complexity of diagnosing simulation issues without detailed knowledge of the geometry and assumptions involved.

Areas of Agreement / Disagreement

Participants express a shared understanding that the magnetic moment should not increase with the addition of the steel housing. However, there is no consensus on the reasons for the unexpected results in the simulation, and multiple viewpoints regarding the modeling approach and assumptions remain unresolved.

Contextual Notes

Limitations include potential misunderstandings of the simulation setup, the complexity of the geometry involved, and the accuracy of the initial magnetic moment value used for comparison.

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Im looking to find the resultant magnetic moment of a permanent magnet inside of a steel housing. Some of the remnant flux density is absorbed by the magnet and the field is altered. I want to figure out the total magnetic dipole including the presence of the steel housing. I've been using Comsol but I am new to that program and I am unsure of how to work the formulas
 
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Magnetic fields in the presence of iron are not readily soluble analytically, so numerical modeling is the right way to go. I don't understand what you mean by "how to work the formulas." Have you taken an advanced undergrad E&M class? You'll see how magnetization, magnetic induction and magnetic fields are related, and how a ferromagnetic material doesn't "absorb" flux but rather reroutes it (the relevant properties are permeability and reluctance). I'm not familiar with Comsol but would be surprised if it requires formulas--don't you mesh up your geometry and solve it with finite elements or some similar technique?
 
Well, I'm a mechanical engineer but this is part of a project I have to do. Yes I am just meshing it in comsol. I am then using the the software to calculate magnetization of the entire volume. What I am confused about is that when I have the permanent magnet alone I get the correct Magnetic moment, however when I add the steel housing around the Magnet I get higher Magnetic Moment which doesn't make sense. If I want to find the magnetic moment to simplify this assembly into its equivalent singular magnet to use in another more complex model I think I should expect the Magnetic moment to drop a little with the addition of the steel housing.
 
Can I expect the magnetic moment that's routed through the steel to take away from the effective magnetic moment in this case?
 
Agreed, moment shouldn't look bigger. Without knowing details of your problem, geometry, etc., it's impossible to know where you went wrong. Simulation codes can be tricky, especially regarding meshing and boundary conditions. The best approach would be to sit down with someone experienced in COMSOL who can review your model and assumptions. A couple of other questions they can address: How do you know that the dipole moment of the permanent magnet is "correct"? Why do you assume that your larger system will be accurately modeled if you replace a complex geometry by a simple dipole?

Sorry, this is not the sort of problem that I could diagnose over internet even if I were familiar with COMSOL.
 

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