Abstract: Systems and methods for manipulating boundary conditions are described, including rendering at least a portion of a model of a mechanical thing. The model includes mesh data and boundary condition data, which may be rendered with contour lines. User input is received indicating changing at least a segment of at least one of the contour lines. The user input may be input using a graphical user interface to produce a graphical representation of a new contour line to replace at least a segment of one of the contour lines. At least the new contour line may be outputted and/or stored as modified boundary condition data to represent the replaced segment.