NEXT GENERATION DRIVE AND CONTROL SOLUTIONS FOR OIL AND GAS OPERATIONS
Apart from its normal operation, the winch is provided with additional controls to realize the compensation functions
AHC solution requires specific control devices and instrumentation: -A motion reference unit (MRU) to measure actual vessel motions in all degrees of freedom -A load sensing device (load-cell or load-pin) to measure actual wire tension
Rotary Active Heave Compensation Lastly, active heave compensation can be accomplished in several different ways, which can be generally grouped into Rotary Active Heave Compensation (RAHC) and Linear Active Heave Compensation (LAHC). The Rotary Active Heave Compensation RAHC solution is based on rotary hydraulic drives providing all functionality for the lifting device. In almost all cases the lifting device is a winch for wire rope (steel, polyester, Dyneema™, etc.) or umbilical lines which are used as hoisting. Especially for offshore winch drives in rotary AHC systems, Bosch Rexroth offers the DS2R electrohydraulic controller with proportional valve. In fact, the controller is an upgrade to the electrohydraulic controller used on the company’s A4VSO and A4VSG hydraulic axial piston components, which function as secondary control units in the Rexroth Active Heave Compensation (AHC) system for offshore winching applications. The controller is fitted directly to the secondary control unit – axial piston equipment that can serve both as a pump or motor to manage effectively variations in torque on winch drives in rotary AHC systems. As part of the overall AHC system, the secondary control unit utilizes either a Rexroth A4VSO (open loop control) or A4VSG (closed loop control) axial piston unit to provide the winch torque control when the AHC system is engaged. The new DS2R controller comes with the Rexroth 4WRPH high-response proportional valve and offers several key engineering and operational advantages, including: •H igh dynamic response, which is crucial in continuously varying wave motion conditions. •P recise, accurate motion so that the loaded winch cable remains continuously ‘idle’ – moving up and down only according to the winch, not the surface wave motion •E nergy efficiency - through better control of hydraulic components, including the ability to use hydraulic accumulators to recover and re-use up to 70% of the secondary control unit’s installed power •M ore reliability and easier maintenance, with a simpler design that eliminates a sandwich filter and is less prone to contamination. In addition, the Rexroth proportional valve included with the DS2R is capable of handling
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HOIST WINCH WITH AHC
a greater range of fluid viscosities and requires less pressure drop to maintain control.
Linear Active Heave Compensation The Linear Active Heave Compensation LAHC solution is based on a linear hydraulic actuator or cylinder providing all functionality related to heave compensation of the lifting device. There are two types of applications: 1. T he cylinder arrangement acts directly on a structural arrangement (e.g. boom or lever) of the lifting device, while the lifting operation is performed by a normal hoist winch 2. T he cylinder arrangement operates in
BOOM WITH AHC (ACTUATED BY CYLINDER)
combination with a winch, which provides for the normal hoisting functions and also accommodates for the wire rope storage (on the winch drum). In almost all cases hoisting is done using wire rope or umbilical lines.
AHC CYLINDER RIGGING ARRANGEMENT
Combined Passive and Active Heave Compensation In a number of applications both passive and active heave compensation are applied to: –A ccount for large loads: the passive compensation accounts for the static part of the load, thus reducing the installed power requirement. – I ncrease accuracy: the active compensation accounts for the required compensation accuracy using measured vessel motions as a reference.