Heave Compensation
Heave compensation is technology applied to minimising the vertical movement of a load supported by lifting gear mounted on a heaving platform. There are two basic types: * Active heave compensation, has a control system that uses power to drive the lifting gear to keep the load stabilised along the vertical axis to compensate for any movement of the platform specific point, using power to gain positional accuracy. * Passive heave compensation uses a relatively soft spring which isolates the load from most of the vertical force variation to reduce transmissibility of transient loads. **Balanced heave compensation Balanced heave compensation is a technology engaging the principle of a balanced-arm lamp for offshore motion compensation. Working principle The technical working principle can be summarized as converting the non-linear force of a gas spring ...

Passive Heave Compensation
Passive heave compensation is a technique used to reduce the influence of waves upon lifting and drilling operations. A simple passive heave compensator (PHC) is a soft spring which utilizes spring isolation to reduce transmissibility to less than 1. PHC differs from AHC by not consuming external power. Principle The main principle in PHC is to store the energy from the external forces ( waves) influencing the system and dissipate them or reapply them later. Shock absorbers or drill string compensators are simple forms of PHC, so simple that they are normally named heave compensators, while " passive" is used about more sophisticated hydraulic or mechanical systems. A typical PHC device consists of a hydraulic cylinder and a gas accumulator. When the piston rod extends it will reduce the total gas volume and hence compress the gas that in turn increases the pressure acting upon the piston. The compression ratio is low to ensure low stiffness. A well designed PHC device can ...
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Heave (translational Motion)
Ship motions are defined by the six degrees of freedom that a ship, boat or any other craft can experience. Reference axes The '' vertical/Z axis'', or ''yaw axis'', is an imaginary line running vertically through the ship and through its centre of mass . A yaw motion is a side-to side movement of the bow and stern of the ship. The '' transverse/Y axis'', ''lateral axis'', or ''pitch axis'' is an imaginary line running horizontally across the ship and through the centre of mass. A pitch motion is an up-or-down movement of the bow and stern of the ship. The '' longitudinal/X axis'', or ''roll axis'', is an imaginary line running horizontally through the length of the ship, through its centre of mass, and parallel to the '' waterline''. A roll motion is a side-to-side or port-starboard tilting motion of the superstructure around this axis. Rotational There are three special axes in any ship, called longitudinal, transverse and vertical axes. The movements around them ...
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Active Heave Compensation
Active heave compensation (AHC) is a technique used on lifting equipment to reduce the influence of waves upon offshore operations. AHC differs from Passive Heave Compensation by having a control system that actively tries to compensate for any movement at a specific point, using power to gain accuracy. Principles The purpose of AHC is to keep a load, held by equipment on a moving vessel, motionless with regard to the seabed or another vessel. Commercial offshore cranes usually use a Motion reference unit (MRU) or pre-set measurement position detection to detect the current ship displacements and rotations in all directions. A control system, often PLC or computer based, then calculates how the active parts of the system are to react to the movement. The performance of an AHC system is normally limited by power, motor speed and torque, by measurement accuracy and delay, or by computing algorithms. Choice of control method, like using preset values or delayed signals, may affect ...
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