Weak Form Equation

As described in Equations, you need a Weak Form Equation () (a differential equation using a weak formulation) for all features that contribute to the governing equations.

To add a Weak Form Equation, first add a Component node under Building Blocks>Components, then:

•	On the Component 1 toolbar, click Weak Form Equation ().

•	Right-click the Component node and select it from the Equations submenu.

The Settings window has the following sections:

Integrand

The content of the Expression field adds up as a weak form contribution to the system of equations that you later solve for in the Model Builder.

Selection

The options in the Selection list and Output entities list define the selection where this variable definition is valid. See Specifying Selections for more information.

Preferences

Clear the Use volume factor in axial symmetry and for non-orthonormal systems check box if you want to skip any volume factors in the weak form equation. In axial symmetry this means that you do not get the factor 2πr. For more information on non-orthonormal systems.

Advanced

If you want to use a different base vector system than the parent feature or property, you can choose a different system in the Base vector system list.

• Specifying Selections • Entering Names and Expressions • Using Coordinate Systems • The Weak Form PDE in the COMSOL Multiphysics Reference Manual