Discussion Forum

Posted: 1 decade ago Jun 18, 2012, 8:48 a.m. EDT

Hi you need to tell us which version, and which physics you consider (3D MF I suspect, with V4) there are different ways to simulate a coil, in full 3D it requires a high mesh density hence quite some RAM and time to solve, it's much quicker in 2D-axi with or without the advanced coils domains. One way you select the wire section and define a current density J0/Awire [A/m^2] (where J0 is the current in one wire and Awire is the wire section (not the coil) But you can also in 3D select your twisted coil domain and impose a current of the type J0/Awire in a predefined Cylindrical Coordinate system for the "sys2.phi" direction or as you do it in x and y (check the sign and plot the current vector to be sure it loops around) You can find some example hereby (4.2a) -- Good luck Ivar

Posted: 1 decade ago Jun 19, 2012, 12:45 a.m. EDT

Respected Dr. Kjelberg, Thank you for your response. I can find myself better now. We are using Comsol 4.2a in 3D, Cartesian coordinate system. We have tried with 2D Axi symmetric model and it is matching with the experimental results. I would like to rectify my errors and hence the correct form (of the helix) is: Jx = J0*y/sqrt(x^2+y^2) Jy = -J0*x/sqrt(x^2+y^2) Where J0 = N*I / A, where A is the cross sectional area of the wire (not the coil) = pi*r^2, where r is the radius of the wire. N being the no. of turns and I is the current (Amp). In experiment we are using N =40, but due to computing constraint, we had to use N =24 in 3D simulation. The difference between the simulated and experimental B Field flux density is around 3-5 Gauss, would it be because of the no. of turns which we had to choose less because of the constraint of computing resources? Thanks. Uttam M. Pal

Posted: 1 decade ago Jun 19, 2012, 3:17 a.m. EDT

Hi I suspect its more an meshing density issue, in 3D you need a very fine mesh, take a look at this 2D/3D case to make my model very small I had to reduce the number of 3D turns, but normally if you rerun it it will wind up again -- Good luck Ivar

Attachments:

• CoilTst3D2D_1.mph

Posted: 1 decade ago Jun 21, 2012, 7:53 a.m. EDT

Hello M. Pal, I'm currently using Comsol 4.2 in 3D, cartesian coordiante system, and I've got a problem concerning the value of J0. When I apply the formula J0= N*I/A with N the number of wires of my real coil, the result is wrong. It's seems that you choose a different number of wires in your simulation.Why? So, I'd like to know what you mean by the constraint of computing ressources. Thanks. Mathilde Bongrain [QUOTE] Respected Dr. Kjelberg, Thank you for your response. I can find myself better now. We are using Comsol 4.2a in 3D, Cartesian coordinate system. We have tried with 2D Axi symmetric model and it is matching with the experimental results. I would like to rectify my errors and hence the correct form (of the helix) is: Jx = J0*y/sqrt(x^2+y^2) Jy = -J0*x/sqrt(x^2+y^2) Where J0 = N*I / A, where A is the cross sectional area of the wire (not the coil) = pi*r^2, where r is the radius of the wire. N being the no. of turns and I is the current (Amp). In experiment we are using N =40, but due to computing constraint, we had to use N =24 in 3D simulation. The difference between the simulated and experimental B Field flux density is around 3-5 Gauss, would it be because of the no. of turns which we had to choose less because of the constraint of computing resources? Thanks. Uttam M. Pal [/QUOTE]

Posted: 1 decade ago Jun 21, 2012, 8:46 a.m. EDT

Dear Bongrain, If I am not wrong, number of wires means no. of turns. The actual experiment was having 40 turns, but in simulation we had to choose 24, because when we use more than 24 in simulation, we were facing meshing difficulties. Meshing difficulties means: the meshing would stay in 3% for long period of time, without showing any progress. Also I would wish to mention a point of using Cartesian (global) co-ordinates or cylindrical co-ordinates: -In Cartesian Co-ordinates, I had to keep N in the formula J0=N*I/A , while in the cylindrical co-ordinates, i could only use J0=I/A in phy direction, where A is the cross sectional area of the wire(=pi*r^2). The mph model attached in the last message of Dr. Kjelberg is very helpful, do go through it and try to obtain the results modifying it. With Regards, Uttam M. Pal

Posted: 1 decade ago Jun 21, 2012, 9:12 a.m. EDT

Thanks so much for your answer, I didn't expect to receive it so quick. I've got another question to you. I've got a multi-layers coil and I would like to know if the formula J0=N*I/A is still viable. Is N the total number of turns of the coil or the number of turn for one layer? I didn't succeed to open the Dr Kjelberg's model. Thank a lot again. Mathilde Bongrain

Posted: 1 decade ago Jun 21, 2012, 9:31 a.m. EDT

I believe, N will be the total number of turns in the coil (including all the layers), while A would remain same (pi*r^2). You can verify the results by using 2D Axi symmetric model. The 2D Axi-symmetric. and 3D model would give the B flux density of the same order. What is the error that you are getting while you try to open the model posted. I was able to open it in Comsol 4.2a. Uttam M. Pal

Posted: 1 decade ago Jun 21, 2012, 10:31 a.m. EDT

Thanks for your answer. I've just had the answer from the comsol support about the problem concerning the choice of J0 and they told me that the formula is wrong in the case of a multi-layered coil (the real formula is much more complicated). The only way to make it easily in a 3D is to use the COMSOL 4.3 version. In this version, the multi-turn coil module is available in 3D as it was in 2D-axis in the COMSOL3.2a version. Concerning the problem of opening the Dr Kjelberg's model, the message "this file requires license for the CAD import module" appears although I've got that module. I hope my message help you thanks. Mathilde Bongrain

Posted: 1 decade ago Jun 22, 2012, 5:42 a.m. EDT

Hi i see the CAD Kernel module is on, but I'm using here the COMSOL Kernel module, I'll upload the file again (if my browser allows me to -- Good luck Ivar

Attachments:

• CoilTst3D2D_1_42a.mph
• CoilTst3D2D_1_43.mph