<p>Electrorheological (ER) and magnetorheological (MR) dampers, which are active damping devices, stand out for their exceptional performance in mitigating vibrations in mechanical systems and construction engineering. Their prowess lies in the inherent ability of ER/MR fluids to change their mechanical properties, particularly viscosity and shear stress, in response to the influence of electric or magnetic fields. In this study, a damper filled with Giant-ER (GER) fluid, a modified product of ER fluid, is employed in the rotor system for vibration suppression. This damper operates in a Cut submode derived from the conventional working modes. This mode results in an effective enhancement of the damping performance by integrating the advantages of these modes, thereby achieving a damping force density of 1.2 × 10⁴ N/m² and a modulation coefficient of 15 within a multi-layered cylindrical damper. Whereafter, the dynamics of the rotor system are modeled and analyzed based on the Jeffcott rotor model, which incorporates a parallelogram-structured motion decoupling mechanism equipped with the proposed Cut submode dampers that are introduced to reduce the vibration of the transmission shaft in the rotor system. Furthermore, to evaluate the damping effect, a vibration-damping performance validation testbed is constructed. The results are noteworthy, demonstrating that by leveraging the superior properties of the GER fluid, the Cut submode damper effectively suppresses the vibrations of the transmission shaft, particularly at the resonant frequencies, achieving an impressive 88.9% reduction when subjected to an electric field of 3 kV/mm compared to the action of 0 kV/mm. This performance highlights the exceptional effectiveness of the proposed Cut submode, underscoring its vast potential for various engineering applications.</p>