Operations
Resonance Avoidance
Keep the suspended-load system detuned from the wave period — so motion is damped, not amplified, and the lift stays inside its window.
Resonance avoidance means keeping the suspended-load system's natural period clear of the dominant wave period. When the two coincide, a heave compensator does the opposite of its job — load motion is amplified rather than reduced, and amplification of several times the input is possible. Norwegian Dynamics sizes the gas spring and damping so the compensated system operates above resonance, in the motion-isolation region, with margin held across the full load range. The payoff is a load that stays controlled in a wider band of sea states — a longer weather window and a de-risked lift.
What we control
Detune the natural period
The compensator's natural period is set by load mass and gas-spring stiffness. Sufficient gas volume gives a soft spring and a long natural period, pushing the system well above the wave-period band. RIGEL sizes this for the fixed design case; CYGNUS carries the same detuning to heavy subsea lifts at lower equipment weight.
Hold margin across the load range
The lightest load gives the shortest natural period and the highest resonance risk, so the system is checked across the full load range, not just the design point. ANTARES adjusts its gas-spring characteristics as conditions change, holding the natural period away from the wave period over a wider operating range.
Cap the response with damping
Even a well-tuned system can be pushed toward its natural frequency by long-period swell. Hydraulic damping in RIGEL, ANTARES and CYGNUS limits peak response and provides a safety margin when the excitation period drifts closer to the natural period.
Account for the coupled system
At depth the crane wire's elasticity couples with the compensator, creating resonance modes that differ from either part alone. Compensator sizing is verified with coupled dynamic analysis using site wave data and vessel RAOs, so resonance is avoided across foreseeable conditions.
Choose the right compensator
The engineering behind it
For the full method and worked examples, see the engineering guide — forces are sized to DNV-RP-N103 and checked against the crane’s derated capacity.
Worried about resonance on an upcoming lift?
Send SWL, stroke, sea state, payload and operation sequence. We’ll come back with a recommended compensator, an operating-window view and the next engineering step.