Dynamic Transient Analysis: Sudden drop in initial angular velocity using RBE2 (Disc Brake)

Hi everyone,

I am working on a transient dynamic disc brake simulation in Marc, and I’m running into an issue with the initial free rotation of the disc prior to brake contact.

My goal is to have the disc spin freely at a constant initial angular velocity of 104.72 rad/s (1000 RPM) before the brake pads engage to stop it. However, the disc is not maintaining this constant speed. The angular velocity suddenly drops from 104.72 rad/s to a negative value, and then ramps back up to stabilize around 32–34 rad/s.

Here is the breakdown of my model setup:

Geometry & Material:

• Dimensions: Hollow disc with OD 100 mm, ID 50 mm, Thickness 10 mm.

• Material: Steel (Linear Elastic) — E = 210 GPa, Poisson’s ratio = 0.3, Density = 7850 kg/m³.

Kinematics & Boundary Conditions:

• Connections: Using RBE2 elements tied to the inner bore of the disc. All DOF (X, Y, Z, Rx, Ry, Rz) at the inner bore are tied to a single central Master Node.

• Boundary Conditions: Fixed displacement applied to the Master Node in space. X, Y, Z, Rx, and Rz are fixed (0). Only the axis of rotation (Ry) is left free.

• Initial Conditions: An initial angular velocity of 104.72 rad/s is applied to the Master Node about the Y-axis.

Loadcase Setup:

• Type: Structural Dynamic Transient.

• Time Stepping: Adaptive time control.

My primary concern: I need the disc to hold its constant 104.72 rad/s rotation without dropping until the contact friction from the brake is introduced.

Has anyone experienced this sudden velocity drop with rotating RBE2 setups in dynamic transient runs? Could this be an artifact of my adaptive time stepping, numerical damping, or how the initial velocity is being transferred from the master node to the RBE2 tied nodes?

Any insights or suggestions would be greatly appreciated!

Thanks in advance.