Create a boundary condition that fixes one end of the beam.
- Select Main Menu > Preprocessor > Loads > Define Loads > Apply > Structural > Displacement > On Areas.
- From the Graphics Window, select the end surface of the double cantilever (shown below) and click OK in the Apply U,ROT on Areas dialog box.
- In the dialog that appears, select ALL DOF and enter a displacement of 0 and click OK.