Continuity between two domains with different physics

Posted Jul 8, 2025, 1:21 p.m. EDT Computational Fluid Dynamics (CFD), Porous Media Flow, Physics Interfaces Version 6.0 2 Replies

Sayee Srikarah Volaity

Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hello all,

I am developing a model for the combustion of a fuel pellet placed inside a furnace. There is air flow enabled in the furnace, which I would think "seeps" oxygen inside the porous pellet. Before I went into the complete heat, mass and reaction coupling, I just wanted to to run a study with just fluid flow interfaces defined. I am using the laminar flow interface for the furnace domain and brinkman equations for the porous pellet domain.

Since I defined the geometry as a union, I would assume that COMSOL automatically treats internal boundaries with continuity conditions, however, when I checked the results I see that the continuity is not maintained.

Currently, the interfaces between the pellet and the furnace are defined as walls, which I assumed would be overridden automatically. Now I think I need to add some additional B.Cs to let COMSOL know that there is an interface between the pellet and the furnace where continuity needs to be maintained. Or do I need to define identity pairs? Or is there anything else that I am missing. I am also having some trouble determining the source and destination boundaries while defining identity pairs.

I am attaching an annotated image with some information that might be useful.

Any help is much appreciated, thank you!

Attachments:

Picture1.png

Reply

2 Replies Last Post Oct 15, 2025, 7:01 p.m. EDT

COMSOL Moderator

Hello Sayee Srikarah Volaity

Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.

If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.

Martin Czornik

Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 15 hours ago

Hi, Sayee

I´m currently working on a simulation of a channel with laminarflow over a well with a hydrogel. Using laminar flow physics an brinkmann for the hydrogel and having a similar issue regarding die boundary between those. I m able to simulate something, but not it wont take the hydrogel correctly. Did u find a solution jet ?

Best regards, Martin

Robert Koslover Certified Consultant

Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 minutes ago

If you are employing different physics in two different but adjoining domains, then it seems to me that you need to tell the model how you want these two domains to be related. I usually do other kinds of physics problems than your example, but analogous situations arise in my work. Anyway, I think you need to set up a "multiphysics" configuration. You need to ensure that the boundary condition, between the domains, that is enforced on the flow-like variable (sorry that I don't know what it is called, in your model) when solving the physics in at least one of those two domains, is assigned to be equal to (or otherwise related to) whatever is the corresponding variable for that quantity from the other domain. You need to decide if this should be a self-consistent calculation (where both domains have their physics solved, while interacting with each other) or simply one where you solve the physics in one domain and then use it to determine a flow (or whatever) boundary condition into the other domain, which is then also solved separately.

Anyway, if: (1) you post your .mph model to the forum, and (2) you explain the exact nature of the physical coupling between these two domains that you are trying to realize, then you may just receive some useful advice from other folks here. Comsol is a math and physics code. When you set up different physics (not merely different material properties) in different domains, it is typically impossible for the code (that is, the people who wrote it) to guess how you want to couple those systems. So you need to specify the right physics/relationships at the boundary, whether you want them calculated self consistently or first one then the other, etc. There can be a number of subtleties to doing this. If what you want to do is a common example that the Comsol folks have already studied and documented, you might find ready-to-go examples in the Application Library or elsewhere. If not, then you need to understand more about the details of your particular multiphysics problem. Finally, if you succeed, and if you think this is a worthy/important problem that others may also want to solve, then I encourage you to post your solved example to the Application Exchange: https://www.comsol.com/community/exchange/ .

-------------------
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara

If you are employing different physics in two different but adjoining domains, then it seems to me that you need to tell the model how you want these two domains to be related. I usually do other kinds of physics problems than your example, but analogous situations arise in my work. Anyway, I think you need to set up a "multiphysics" configuration. You need to ensure that the boundary condition, between the domains, that is enforced on the flow-like variable (sorry that I don't know what it is called, in your model) when solving the physics in at least one of those two domains, is assigned to be equal to (or otherwise related to) whatever is the corresponding variable for that quantity from the other domain. You need to decide if this should be a self-consistent calculation (where both domains have their physics solved, while interacting with each other) or simply one where you solve the physics in one domain and then use it to determine a flow (or whatever) boundary condition into the other domain, which is then also solved separately. Anyway, if: (1) you post your .mph model to the forum, and (2) you explain the exact nature of the physical coupling between these two domains that you are trying to realize, then you may just receive some useful advice from other folks here. Comsol is a math and physics code. When you set up different physics (not merely different material properties) in different domains, it is typically impossible for the code (that is, the people who wrote it) to guess how you want to couple those systems. So you need to specify the right physics/relationships at the boundary, whether you want them calculated self consistently or first one then the other, etc. There can be a number of subtleties to doing this. If what you want to do is a common example that the Comsol folks have already studied and documented, you might find ready-to-go examples in the Application Library or elsewhere. If not, then you need to understand more about the details of your particular multiphysics problem. Finally, if you succeed, and if you think this is a worthy/important problem that others may also want to solve, then I encourage you to post your solved example to the Application Exchange: https://www.comsol.com/community/exchange/ .

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.

Discussion Forum