A pendulum subjected to the uniform gravitational field of the Earth1 is analyzed using a coupled Multibody Dynamics and Finite Element Method (MbDFEM) framework. The purpose is to evaluate the stresses induced in the material of the parts. These stresses arise from the dynamic forces generated by the motion of the assembly.
The two videos presented below illustrate the isometric view of the pendulum assembly. The pin is constrained to the ground, and the connection between the pin and the pendulum is modeled as a hinge joint. In the left video, the pendulum motion is shown together with the hinge joint force vector, expressed in the reference frame of the pendulum (by convention, the action force). In the right video, the hinge joint force is depicted in the reference frame of the pin (corresponding to the reaction force). At the center of mass of the pendulum, the d'Alembert force can be seen in red, the d'Alembert torque in double-headed blue arrow, and the weight vector in white. Since the pin is grounded (not accelerating), it's d'Alembert force and torque are zero, and only the weight vector can be seen ai its center of mass.
Two markers can be appreciated for each part. The first two represent the mass-markers, which are attached to each part center of mass and have their there axes aligned with the corresponding principal axes of inertia. The second two are the part origin markers, attached to each part coordinate system2.
In both videos, the direction of the gravitational acceleration is indicated by a white arrow, while the coordinate system located at the base of this arrow denotes the orientation of the global inertial reference frame. All the coordinate system axes are color-coded as follows: X in red, Y in green, and Z in blue. Gravity is aligned along the negative global Y-axis.
The pin axis is aligned with the global Z-axis, ensuring that the hinge joint is not subjected to torque. At the initial configuration (time t=0), referred to as the initial assembly, the pendulum is oriented parallel to the global X-axis. Consequently, the oscillatory motion commences from a "horizontal" position.