Balanced heave compensation

Balanced heave compensation is a technology engaging the principle of a balanced-arm lamp for offshore motion compensation.

The technical working principle can be summarized as converting the non-linear force of a gas spring or hydro-pneumatic spring into an adjustable, substantially linear force, by several mechanical measures. The technology comprises a series of patented inventions by NHLO licensed to and marketed by Seaqualize.

In cooperation with IHC and research partners MARIN and ECN a scale model of a first device comprising the technology, an offshore access bridge has been tested. Seaqualize is currently working on a full-scale prototype of the access bridge. The project has been subsidized by the Dutch Ministry of Economical affairs as a Renewable Energy project.

The research project indicates balanced heave compensation enables a range of potential benefits compared to currently available solutions. This may lead to improvements and cost savings in (engaging) heave compensation systems.

Balanced heave compensation (BHC) differs from traditional (spring based) Passive Heave Compensation (PHC) and Active Heave Compensation(AHC) in several ways.

In traditional spring based heave compensation systems the movement of the mass is parallel to the movement of the spring cylinder. A passive heave compensation system is in effect a mass spring system, it stabilizes a certain mass in a single position of the spring, in that position only the spring and the mass are balanced. In other positions of the spring the mass and the spring are not balanced and the mass will tend to start moving towards the stabilized position due to residual forces in the spring. Therefore, only in certain (preset) conditions a mass spring system can be beneficial for heave compensation. In other (unexpected) conditions, mass spring systems may experience unwanted effects such as load amplification. An active heave compensation system adds an active component to a passive heave compensation system in order to counteract these residual forces.

In BHC systems the movement of the mass is not parallel to the movement of the spring cylinder, leading to significantly lower residual forces, and therefore lower requirements on the active components. In BHC systems, load amplification is unlikely to occur since the mass is balanced in two positions and substantially balanced around these two positions. Residual forces are minimized and therefore unexpected conditions such as variations in the wave pattern have a negligible effect on the working principle. BHC is therefore best characterized as an AHC with a lower power requirement.

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