ANALYSIS AND CONTROL OF THE TRANSIENT SHIPBOARD ENGAGEMENT BEHAVIOR OF ROTOR SYSTEMS

The transient coupled aeroelastic flap-lag-torsion response of an articulated rotor during simulated rotor engagements is examined. The rotor is modeled using the finite element method and aerodynamics are modeled using a nonlinear quasi-steady blade element theory for a 360° angle of attack range. The blade equations of motion are time integrated in modal space for a specified rotor speed profile. The airwake around a simple ship geometry is calculated using the Parallel Unstructured Maritime Aerodynamics code. Two rotor locations on the flight deck are examined. Predicted aeroelastic results for the calculated ship airwakes are compared to previous results, which assumed simple airwake models. Tip deflections and blade bending moments using the calculated airwakes are two to three times greater than for the simple airwake models. The reduction of excessive tip deflections by increasing the collective pitch setting in the vulnerable period of the engagement is examined. It was found that the maximum downward tip deflections could be reduced by as much as half, but the blade bending moments could not be reduced due to excessive upward flapping of the rotor.