Compact Hydropneumatic Heave Compensator

Passive and semi-active heave compensator: Project design methodology and control strategies

“…The cylinder area must be the minimum possible, in order to provide small accumulator volume. This volume is a critical point in the design of PHC, since the required volume is usually considerably large to ensure the desired performance ([ 17 ] and [ 2 ]). However, the cylinder area has minimum limit, because the accumulator pressure is inversely proportional to this parameter.…”

“…The SAHC frequency response is satisfactory, but the compensator accumulator volume is much larger (99 m 3 and 138 m 3 ) than usual values employed in such applications about 13 m 3 . In [ 17 ], the damping is calculated in function of displacement and drill string mass, getting an acceptable frequency response with a commercial volume accumulator of 14 m 3 . The control diagram of SAHC is shown in the Fig 4 .…”

“…Firstly a strict requirement (3dB of maximum gain and cutoff frequency of 0.056 Hz ), then a less strict requirement (10dB of maximum gain and cutoff frequency of 0.056 Hz ). The strict requirement is used in [ 17 ] and [ 27 ], to obtain a flat passband. The less strict requirement is applied in [ 2 ] and reproduced here for comparison purposes.…”

“…The servo-valve modifies the damping ζ in function of displacement and sprung mass. In [ 17 ] the following control law is used: …”

“…Semi-active magnetorheological actuators are used in these fields, theirs controllers are designed considering an unknown disturbance, uncertain parameters and actuator limitations [ 15 ] and [ 16 ]. Examples of SAHC in the offshore drilling can be found in [ 13 ] and [ 17 ].…”