Adaptive Passive Heave Compensation

What's the difference between an adaptive PHC and a basic PHC?

Typically an adaptive PHC is a more expensive and higher performing compensator. The main differences are summed up in the below table:

Feature Basic PHC Adaptive PHC
Cost1×2–3×
Gas to oil ratio3–48–16
Stroke equilibrium control❌✅
Adjustable stiffness during use❌✅
Adjustable damping during use❌✅
Quick lifting❌✅
Temperature compensation❌✅
Weight compensation❌✅
Depth compensation❌✅
Battery operation❌✅
Data logging❌✅
Rod locking❌✅

What does the adaptive PHC solve?

The adaptive PHC has many positive contributions:

  1. Filling and preparation of the PHC is done with software control that monitors that the filling is done according to the lifts parameters.
  2. Piston rod locking reduce required lifting height (the rod doesn’t extend when the payload is lifted).
  3. The weight of the payload is measured by the PHC (when it is attached) and gas pressures can be adjusted in case of an error (adjusted on the fly, the adaptive PHC doesn’t need to be brought back to deck).
  4. Splash zone settings are applied to ensure suitable dynamics during the crossing of the splash zone, which typically includes a higher stiffness setting, higher damping (extension and retraction) as well as equilibrium adjustments to compensate for buoyancy effects.
  5. When the adaptive PHC enters the seawater it will rapidly cool and hence the gas pressure will drop. This effect is compensated for using onboard high pressure gas which is injected to maintain pressure at the correct level.
  6. As the adaptive PHC is lower into deeper waters the external pressure will build up and cause significant forces that will tend to push the compensators piston rod inwards. This effect is compensated for by adjusting gas pressure down. Special techniques are used for extremely deep waters with lighter payloads. Contact us for more information about those.
  7.  During landing or for avoiding resonance it is often required with low stiffness. The adaptive PHC has a low stiffness mode that increases performance in those scenarios (bigger gas volume is connected to the cylinder).
  8. The adaptive PHC can be used for shock absorption utilizing it’s adjustable damping which will limit extension damping and have higher retraction damping.
  9. The adaptive PHC can be used for quick lifting (multiple times is possible) which initially keeps tension below the weight of the payload and then quickly increases it causing retraction of the piston rod in a controlled manner.
  10. Data logging can be used to post process a lift to see stroke usage, DAF, landing speeds, etc.

When should an adaptive PHC be used instead of a basic PHC?

  1. If the performance of a basic PHC is insufficient (for landing mostly).
  2. If the equilibrium position will drift too much with a basic PHC (can be offset partly by using longer stroke) for example due to buoyancy or water depth.
  3. If different settings are required to achieve required dynamics (different splash zone to subsea settings).