Dear everyone,
I'm currently in need of calculating magnetic attracting force between two magnetic components and hope to have your advices.
Let's consider a magnetic circuit consisting of a permanent magnet (say Alnico), soft magnetic alloy arms with a movable part, an air gap and leakage at magnet. (Please refer to the attached image)
I need to calculate the magnetic force between two magnetic arms A and B.
Currently, I use two methods to calculate this force, achieving two different results. I wonder which method is correct. Please kindly enlighten me if you have a better approach as well. Thanks everyone.
1. Method 1: magnetic force = d(total co-energy, including each and every parts of circuit)/dx
- Solve magnetic field distribution (H and B) in every parts of the circuit corresponding to each position of movable arm A.
- Calculate co-energy for each and every parts of the circuit, including permanent magnet, leakeage, soft magnetic alloy, and air gap.
- Calculate total co-energy of the system at each position of movable arm A.
- Calculate differentiation of total co-energy with respect to position x.
- Magnetic force = differentiation of total co-energy with respect to position x.
2. Method 2: magnetic force only involves flux density across the air gap at the instance of consideration
- Solve magnetic field distribution (H and B) in every parts of the circuit.
- Magnetic force between arm A and B = 1/2mu0 * Bgap^2 * Agap (in which Bgap is the flux density across airgap and Agap is the cross section of the airgap).
Lastly, how can we model the leakage at magnet as a regular magnetic element (with which cross section area, length, permeability)?
Thanks everyone.
Regards,
Kien-Cuong
Hi Kien-Cuong Pham I can do a computer simulation of the construction of your figure in FEMM 4.2 software and send you the results. This will allow you to compare them with those calculated by you. Will this be useful to you?
Hi Iosko Balabozov. That is very nice of you. Yes, that would certainly be very useful. Which format of the drawing do you need for the simulation? Do you need a 2D drawing or a 3D CAD file?
Hi Kien-Cuong Pham the 2D drawing is enough, but if you already have 3D model, sent it to me and I then I will use COMSOL to make 3D application, that would be more useful for you.
Hi Iosko Balabozov , Thank you very much for your kind help. I have sent you the necessary files via message.
Hi Kien-Cuong Pham
I would also like to calculate the problem numerically. It would be interesting to compare the results with the proposed analytical calculations. If not difficult, send me the geometry and properties of the material.
Hi Ekaterina Kurbatova,
Thank you very much for your offer to help. Please find in the attached files: - Explanation of problem - 3D model - Magnetisation data of materials
If possible, please kindly help me to solve the magnetic force versus a few displacement positions of the part. Two cases for the magnet include a linear model and a real non-linear demagnetisation curve of Alnico5.
Thank you very much for your kind help. Your help is much appreciated.
Hi Kien-Cuong Pham , I was very busy last few weeks. I saw the files that you sent me in a message. I used them to make a 2D and 3D COMSOL models for you.
In the PDF file are Force - Stroke(displacement) characteristics for the two variant that you describe. Also some visualization (figures) of the magnetic field are included in the PDF.
The COMSOL files are with big size, because of the saved db with results, so if you need also COMSOL files, please write me a message and I will sent them through download link.
Hi Prof Iosko Balabozov ,
Thank you very much for your devoted answers. Your kind help is very much appreciated.
Yes, COMSOL files would be extremely helpful as well. Thank you.
Hi Kien,
If you still need assistance about your question, please see my paper:
"Design a new high intensity magnetic separator with permanent magnets for industrial applications", K Arab-Tehrani, A Colteu, I Rasoanarivo, F Michel-Sargos
International Journal of Applied Electromagnetics and Mechanics 32 (4), 237-248
It can help you.
Best regards,
Kambiz TEHRANI
The electromagnetic force can be easily obtained from the co-energy. first, you have to developpe the explicit expression of the magnetizing inductance then calculate its derivative regards to the linear displacement of the mobile part.
(you have to substitute the permanent magnet by its corresponding coil (equivalent ampere-turns), which generates the same MMF) using the demagnetizing curve. I can provide you more explicit clarification if you wanted too.
- Badges
- Science topic