How Can I Set Boundary Conditions?

How Can I Set Boundary Conditions?#

Date	Category
2025-06-17 15:50:52	Heat

Boundary conditions for heat simulations are defined using the HeatChargeBoundarySpec class, which has two required fields: condition and placement.

condition: Specifies the boundary condition to impose. It accepts one of the following types: - TemperatureBC - HeatFluxBC - ConvectionBC

placement: Specifies where the boundary condition should be applied. Available options include:

- [StructureBoundary](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.StructureBoundary.html)
  The boundary of a structure. Only the portion of the boundary not covered by subsequent structures is considered.

- [StructureStructureInterface](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.StructureStructureInterface.html) 
  The interface between two structures. Specifically, this refers to the boundary of the succeeding structure that lies within the preceding structure.

- [MediumMediumInterface](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.MediumMediumInterface.html)
  The interface between two media.

- [SimulationBoundary](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.SimulationBoundary.html)
  The boundary of the heat simulation domain. You can specify particular surfaces using the `surfaces` field. By default, all surfaces are selected.

- [StructureSimulationBoundary](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.StructureSimulationBoundary.html)
  The portion of the heat simulation domain boundary that is covered by a structure. As with `StructureBoundary`, only regions not covered by subsequent structures are included.

You can check out this HeatSolver notebook for an example of how to use it in practice.