Rotating machinery, and rotorcraft in particular, are inherently affected by high vibration levels, which can compromise structural integrity, reduce component life, and degrade onboard comfort. Traditional passive vibration absorbers, while simple and reliable, operate effectively only within a narrow frequency range and become inadequate for modern helicopters, where the main rotor speed is no longer constant. Fully active solutions, on the other hand, offer excellent performance but introduce substantial cost, complexity, and maintenance requirements. The aim of this thesis is to transform a passive Tuned Mass Damper (TMD) into a semi--active device with variable effective mass, referred to as VMAVA (Variable Mass Active Vibration Absorber), thereby extending its operational bandwidth and enabling tuning across the varying excitation frequencies associated with rotor speed changes.