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Levitating Ring Magnet

Posted Mar 11, 2020, 7:35 a.m. EDT Low-Frequency Electromagnetics Version 5.4 3 Replies

Muhammad Zeeshan
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Hello everyone i am new to COMSOL and trying to plot distribution of force on a permanent ring magnet levitating over another at certain height, i am using AC/DC module =>magnetic field no currents and using 2-D axisymmetric geometry. i gave equal but opposite magnetization to the magnets, now i am confuse how to use weight of levitatiing magnet in calculation of net force. Kindly help me how to get magnetic forces due to both magnet and weight of lifted magnet also net force(magnetic +gravitational ) acting on magnet it.

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3 Replies Last Post Mar 12, 2020, 7:03 a.m. EDT
Lars Dammann COMSOL Employee

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Posted: 5 years ago Mar 11, 2020, 10:59 a.m. EDT

Hi, you may find this example model interesting: https://www.comsol.com/model/an-electrodynamic-levitation-device-14221

You can compute the force on one magnet using a Force Calculation node. The above mentioned model uses that as well. Here is another, easier model that shows how to use Force Calculation: https://www.comsol.com/model/permanent-magnet-78

Both of these models are also part of the Application Library. Please find File > Application Library in the menu in COMSOL Multiphysics and find the models AC/DC > Verification Examples > electrodynamic_levitation_device and AC/DC Module > Magnetostatics > permanent_magnet

Best regards, Lars

Hi, you may find this example model interesting: https://www.comsol.com/model/an-electrodynamic-levitation-device-14221 You can compute the force on one magnet using a **Force Calculation** node. The above mentioned model uses that as well. Here is another, easier model that shows how to use Force Calculation: https://www.comsol.com/model/permanent-magnet-78 Both of these models are also part of the Application Library. Please find **File > Application Library** in the menu in COMSOL Multiphysics and find the models **AC/DC > Verification Examples > electrodynamic_levitation_device** and **AC/DC Module > Magnetostatics > permanent_magnet** Best regards, Lars
Muhammad Zeeshan
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Posted: 5 years ago Mar 12, 2020, 6:54 a.m. EDT
Updated: 5 years ago Mar 12, 2020, 6:55 a.m. EDT

Thankyou sir Lars, i will check these modals, at the time i want to knoow how to give gravitational force (weight) to levitating magnet, should i use its equation in variables or i have to use another study ?? need you kind suggestion

Thankyou sir Lars, i will check these modals, at the time i want to knoow how to give gravitational force (weight) to levitating magnet, should i use its equation in variables or i have to use another study ?? need you kind suggestion
Lars Dammann COMSOL Employee

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Posted: 5 years ago Mar 12, 2020, 7:03 a.m. EDT

You will have to model the movement of your device somehow, in the "Electrodynamic Levitation Device" model that I mentioned this is done by a moving mesh interface and two global equations, one for the position and one for the velocity in y-direction of the moving piece. If you look at the equation for the velocity, you will find this expression:

d(v,t)+(F_g-mf.Forcez_0)/M_disc

This expression is implicitly zero, so you can understand it as "the acceleration is equal to the sum of the forces F_g (the gravitational force) and mf.Forcez_0 (the electromagnetic force) divided by the objects mass". If you are simulating a stationary problem, you do not need an equation for the velocity, but just for the position, where you can specify that the sum of all forces should be zero.

You will have to model the movement of your device somehow, in the "Electrodynamic Levitation Device" model that I mentioned this is done by a moving mesh interface and two global equations, one for the position and one for the velocity in y-direction of the moving piece. If you look at the equation for the velocity, you will find this expression: > d(v,t)+(F_g-mf.Forcez_0)/M_disc This expression is implicitly zero, so you can understand it as "the acceleration is equal to the sum of the forces F_g (the gravitational force) and mf.Forcez_0 (the electromagnetic force) divided by the objects mass". If you are simulating a stationary problem, you do not need an equation for the velocity, but just for the position, where you can specify that the sum of all forces should be zero.

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