# How to define BC for internal layers

• kamran46
In summary, the purpose of defining boundary conditions (BC) for internal layers is to specify how the layer interacts with the surrounding environment and how it affects the overall behavior of the system. BCs are crucial in accurately modeling the physical processes within a system and predicting its behavior. There are several methods for defining BCs for internal layers, including analytical, numerical, and experimental approaches. When defining BCs, factors such as the type of material, physical properties, surrounding environment, and intended purpose must be considered. The accuracy of a model is highly dependent on the defined BCs. BCs can be changed or updated, but caution must be taken to avoid compromising the model's reliability. Testing and validation of the updated BCs is recommended before using
kamran46
Hi all,

I am new to this forum and COMSOL. I want to define the temperature at the common surface of two cylinders in contact. When I model the cylinders, the common surface (middle surface) is not active for defining any BC. Please tell me how can I do this in COMSOL. Thanks.

Last edited:
go to Physics->Boundary setting->mark the interior boundaries checkbox.
and then you can set BC.

Thank you very much.

## 1. What is the purpose of defining BC for internal layers?

The purpose of defining boundary conditions (BC) for internal layers is to specify how the layer interacts with the surrounding environment and how it affects the overall behavior of the system. BCs are crucial in accurately modeling the physical processes within a system and predicting its behavior.

## 2. How can BCs be defined for internal layers?

There are several methods for defining BCs for internal layers, including analytical, numerical, and experimental approaches. Analytical methods involve solving mathematical equations to obtain BC values. Numerical methods use approximations and algorithms to determine BC values. Experimental methods involve conducting physical experiments to measure BCs.

## 3. What factors should be considered when defining BCs for internal layers?

When defining BCs for internal layers, it is important to consider the type of material, the physical properties of the material, the surrounding environment, and the intended purpose of the BCs. Other factors such as boundary conditions at the interface of different layers and the overall system boundaries should also be taken into account.

## 4. How do BCs affect the accuracy of a model?

The accuracy of a model is highly dependent on the BCs that are defined. Inaccurate or inappropriate BCs can lead to incorrect predictions and unreliable results. It is essential to carefully consider and accurately define BCs to ensure the reliability of a model.

## 5. Can BCs be changed or updated after they have been defined for internal layers?

Yes, BCs can be changed or updated after they have been defined for internal layers. However, any changes should be made with caution and after careful consideration to avoid compromising the accuracy and reliability of the model. It is recommended to thoroughly test and validate the updated BCs before using them in the model.

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