AC/DC Currents flowing through air region
Posted Aug 22, 2024, 10:37 a.m. EDT Electromagnetics, Materials, Results & Visualization Version 6.2 6 Replies
Please login with a confirmed email address before reporting spam
I'm pretty new to COMSOL but have been required to use it for an assignment, so I'm not fully aware of how to problem solve when I get strange things happening like this!
I am building a model using the AC/DC module with frequency domain analysis. I have a homogenised coil with many turns situated above a 1.5mm layer of CFRP, then underneath that there is a 3mm layer of Aluminium. The aluminium layer has a cuboid region cut out of it, which one half of the coil is located above. The cuboid region was created by subtracting a cuboid from the plate, which then leaves a region that isn't allocated as aluminium and therefore defaults to air. I have double checked and the region is indeed air and is not overriden by any other material.
However, the Eddy currents produced in the Al layer are clearly just flowing straight through this air region as if it wasn't there and it was all just part of the Al sample. In the screenshot attached, the slice runs directly through the centre of the coil and air region, which is the square directly under one half of the coil. It clearly shows the current just flowing straight through it, which isn't physical. The "n-shaped" object to the left of the air region is a Ti rivet, which should also have some impact on the current, but it doesn't seem to.
It looks like COMSOL is considering the entire sample to just be one solid block of conductive material, but I've checked and double checked my material assignment and I can't see why this should be the case. Can anyone offer a possible solution please? Thanks in advance!
The COMSOL version I'm running is V6.2.
Attachments:
Please login with a confirmed email address before reporting spam
Hi Luke,
that is indeed a little mysterious.
I added an Ampere's Law node that overrides all the Free Space assignments and set the conductivity for air and the dielectric to 1 S/m for solver stability. Now the result looks realistic.
I think the Free Space thing is relatively new and I never used it. I always use Ampere's law with suitable material assignments. Free space is essentially equivalent to air. The Free Space node should actually just add the stabilization conductivity that is needed to get the solver to converge. But maybe I am missing something.
I would be curious about comments from other people.
Cheers Edgar
-------------------Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Please login with a confirmed email address before reporting spam
Hi Luke, Thanks for reaching out!
The reason for the lack of material contrast, is that everything is free space. Adding materials to the model gives COMSOL access to the necessary material data, but it does not specify how to treat the domains. In the physics, the default node is "Free Space" (vacuum/air), this node serves as a canvas. You can add an "Ampère's Law in Solids" node to indicate that your metals are solid (basically; what Edgar says -- see attached).
The reason for this design is that for electromagnetical phenomena (in particular related to anisotropic material properties and eddy currents) the behavior of liquids and solids is conceptually different. Since making everything liquid or solid by default would result in models that are wrong in one way or another, we decided to start with empty space and encourage the end user to make a decision.
On top of this, the free space node comes with built-in stabilization. That is the reason why you got some current in your initial model (although a very small amount). On the forum you may have seen the general advice to use "1 S/m in the air". The free space feature determines an appropriate amount of stabilization conductivity automatically, by looking at the local skin depth.
We've been experimenting with this design for about one release now and your feedback shows that for some use cases this can lead to confusion. We will look into this and improve the usability in this regard.
Thanks for reporting! Kind regards, Durk
Attachments:
Please login with a confirmed email address before reporting spam
Hi Luke,
The Free Space is the default domain feature in the Magnetic Fields interface since version 6.2. It is there to automate the modeling of free space (non-conducting media with relative permittivity and relative permeability of unity). Depending on the frequency, some artificial conductivity is needed in such domains and the Free Space feature is there to automate that.
The Free Space feature must be overridden by the user in domains having a (non-free space) material by adding Ampère's Law in Solids or Ampère's Law in Fluids - otherwise the entire simulation domain will be treated as free space.
The reason for having two flavors of the Ampère's Law feature is to be able to correctly handle models with moving parts/mesh as then solids and fluids must be treated differently.
When adding Ampère's Law in Solids to your non-air domains (above the Coil as the Coil also overrides Free Space and is overridden by Ampère's Law in Solids), the solver warned for some missing material properties in the CFRP_homogenised material (permittivity and conductivity) so I added, hopefully intelligent, guesses for those see the attached version.
I hope this helps.
-------------------Magnus
Attachments:
Please login with a confirmed email address before reporting spam
Durk and Magnus,
thanks for your comments. In earlier versions the default node was Ampere's Law and all domains were treated according to their material settings. Now we need additional Ampere's law nodes for everything that is not free space. That is fine for me. Is the automatic stabilization conductivity in the Free Space node available in the model variables? I didn't find it in the equation view. And I guess I need to do some reading about the differences of solid and fluid Ampere's law nodes.
Cheers Edgar
-------------------Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Please login with a confirmed email address before reporting spam
Hi Edgar,
It shows up in equation view in the regular tensor conductivity variables, e.g: mf.sigmaxx The equivalent skin depth that is aimed for in the frequency domain when using "Automatic" is 100 times the linear size of the geometry.
From the manual: "A suitable rule of thumb for choosing the stabilization conductivity is given by the skin depth, as compared to the overall geometry size. The assumption is that if the skin depth in Free Space is around one hundred times the device size, the resulting loss and the impact on lumped device properties are insignificant. At the same time, the model will still be sufficiently stable. What is considered a good value will differ per model, though. It is therefore recommended to double-check the free space loss as compared to other loss terms in the model. If the stabilization conductivity has a negative impact on the overall model accuracy, consider lowering it."
Best regards,
-------------------Magnus
Please login with a confirmed email address before reporting spam
Thank you all so much for your help and explanations - makes perfect sense now that I know what the problem was.
Reply
Please read the discussion forum rules before posting.
Discussion Forum Rules and Guidelines
The goal of COMSOL Access is to provide a forum for you to communicate effectively with COMSOL as well as your colleagues within the multiphysics simulation community. This involves providing you with access to technical support and downloads of the latest {:comsol} software releases, as well as the ability to share your comments and work with other users of the {:comsol} software through forums such as the blog, discussion forum, and Application Exchange. In order to make this an efficient and pleasant experience for you and other members of COMSOL Access, we ask that you follow a few rules and guidelines.
When registering for COMSOL Access, you agree to provide your complete and truthful information for all fields requested on your COMSOL Access account registration page. You also agree to maintain the accuracy of all information associated with you on your COMSOL Access account. You agree to maintain your COMSOL Access account for use solely by you, not to share your username and password with anyone else, and to take appropriate precautions to restrict access to your username and password from others. Furthermore, you agree not to submit any information relating to your employer through your COMSOL Access account without your employer’s authorization. Should you use a COMSOL Access account associated with an employer, you agree to immediately discontinue using that account upon termination of that employment.
The moderators of the forums will remove any generally objectionable material as quickly as possible. You acknowledge that all posts made to these forums express the views and opinions of the author and not the administrators, moderators, or webmaster (except for posts by these people). Hence, they will not be held liable.
You agree not to post or link to any material that is abusive, obscene, vulgar, slanderous, hateful, threatening, sexually oriented, or that infringes upon or violates any third-party rights or any other material that may violate any applicable laws. You agree that you will not otherwise use your COMSOL Access account to violate or to assist anyone in violating any law. Engaging in any activity in violation of these COMSOL Access rules and guidelines may lead to you being immediately and permanently banned from COMSOL Access. The IP address of all posts is recorded to aid in enforcing these conditions. You agree that the webmaster, administrator, and moderators of the forums have the right to remove, move, or close any topic at any time as they see fit. As a user of COMSOL Access, you agree to any information you have entered into any of the forums being stored in a database.
You agree that you will not use your COMSOL Access account in violation of any applicable export control laws. You represent and warrant that you are not subject to any comprehensive sanction or embargo by the U.S. or any other country, nor are you identified on any list maintained by the U.S. government that identifies persons for which the U.S. maintains restrictions. Further, you represent and warrant that you are not subject to any restriction on the receipt of technology or products under the export control laws of the U.S. or any other country.
Basic Rules
- Flaming: Do not post any messages that harass, insult, belittle, threaten, or flame another member or guest. Debates are fine, but argue with the point, not the person.
- Trolling: Do not post with the purpose of starting a dispute. Note that a person disagreeing with your opinion is not considered trolling; keep it civil, even if you are sure that the other person is wrong. Anything seen as trolling will result in you being banned.
- Spamming: Posts without content or containing nonsense waste space and everyone's time. Spam will be removed from the forum.
- Offensive Posts, Links or Images: Do not use profanity, racial, ethnic, religious, or other slurs or any other offensive material.
- Advertising: Posting of advertisements for products or services, links to auctions, affiliate links, links to promote websites, and so forth is not allowed.
- Disclosure of Personal Information: Do not disclose any other member's email, real name, address, phone number, IP address, or other personal information. This includes posting contents of emails and private messages without the sender's consent. Do not bring personal disputes into the forums. Bans and warnings issued to other users are considered personal information.
- Misleading Titles: The subject line of the post should be as informative as possible about the content of the post. This also reduces the amount of duplicate posts.
- Thread Hijacking: Taking a thread off-topic to pursue one's own agenda is not permitted.
- Piracy: Do not upload, post, email, transmit, or otherwise make available any content that infringes upon any patent, trademark, trade secret, copyright, or other proprietary rights ("Rights") of any party. This includes COMSOL model files created by a forged or illegitimate license.
- Honesty: Users must provide truthful information in creating their COMSOL Access account.
These rules are subject to change. The moderators reserve the right to remove, edit, or move posts at their discretion. The COMSOL Access administrators will reserve the right to permanently remove a user account without notice if any of the rules are not followed. Particular services accessible with your COMSOL Access account may be subject to additional rules. You agree to comply with all rules applicable to each service you access through your COMSOL Access account.
Posting Guidelines
When posting, understand that you are trying to communicate with other people. Although many COMSOL Access members are not fluent in English, the official language of this forum is English.
Here are some important guidelines of language:
- Write in English.
- If you are familiar with LaTeX, please use this to write mathematical equations.
- Always do a quick check for spelling/grammar mistakes.
- Format your post in a legible manner. Use the Preview button often.
- Be concise and articulate as much as possible.
- Use the Enter key to create paragraphs.
- Capitalize correctly. It is difficult to read posts that are written entirely in uppercase or lowercase.
- Use correct punctuation. Avoid run-on sentences.
- Try to avoid using “text speak”, “net speak”, or slang. The purpose of language is to be understood.
- Never invent acronyms and use as few acronyms as possible. For example, write "COMSOL Multiphysics" and not "CMP".
- Review your post before publishing it. Try to catch typos.
- Please check to see if a topic has already been posted. Do not post multiple threads on the same topic.
Disclaimer
By submitting content to the forums, you hereby grant COMSOL a nonexclusive, royalty-free, perpetual, worldwide, and unrestricted license to reproduce, publicly display, publicly distribute, and prepare derivative works of the content. COMSOL hereby grants you a license to copy and/or use content from the forums solely for your own internal purposes. COMSOL provides the forum service for the benefit of our users to share content with the community. All content is provided "as is" without warranty of any kind, express or implied, including without limitation, warranties of merchantability, noninfringement, design, operation, and fitness for a particular purpose, and the entire risk as to the quality and performance of the programs is with you.
Neither COMSOL, the authors, nor the copyright owners of submitted materials warrant that the programs will be error-free, uninterrupted, virus-free, secure, and suitable for your needs, produce specific results, or that errors or failures will be corrected. Comments on supplied content should be sent to the author or copyright owner through the tools provided in the forums.
Please log in to post a reply.
Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.
Suggested Content
- KNOWLEDGE BASE Set Up Access to a COMSOL Server Installation
- BLOG Modeling Coils in the AC/DC Module
- KNOWLEDGE BASE The Magnetic and Electric Fields Interface with Electrical Circuit Gives an Unexpected Error for Transient Studies
- BLOG Computing the Inductance of a Straight Wire
- FORUM Calculation of the total current flowing through a conductor