This lesson covers the process of defining the domain of a boundary value problem using a 2D axisymmetric section of a vessel with Ansys Workbench™ simulation integration platform. The lesson explains how to model the vessel, set the analysis type to 2D, and adjust the units and grid spacing. It also provides a step-by-step guide on how to sketch the geometry of the vessel, ensuring the correct orientation and dimensions. The lesson concludes with the transformation of the sketch into a 3D model and saving the project. For instance, the lesson demonstrates how to create an L-shaped geometry with specific dimensions and constraints.