Performance Evaluation of Active Heave Compensator in Deepwater Installation Operation
- Young-Myung Choi (Korea Research Institute of Ships and Ocean Engineering) | Bo Woo Nam (Korea Research Institute of Ships and Ocean Engineering) | Sa Young Hong (Korea Research Institute of Ships and Ocean Engineering) | Jong Wook Kim (Advanced Technology Institute, Hyundai Heavy Industry)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- March 2018
- Document Type
- Journal Paper
- 31 - 39
- 2018. The International Society of Offshore and Polar Engineers
- numerical simulation, lifting operation, KEY WORDS: Active heave compensator, model test, deepwater installation, subsea structures
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- 33 since 2007
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In this study, a series of model tests were carried out to evaluate the performance of an active heave compensator (AHC) in deepwater installation operations. In the tests, a crane vessel and three different subsea structures were examined during deepwater crane lifting operations with an AHC. To validate the experimental results, time-domain numerical simulations were performed with the same AHC control algorithm. First, free-decay tests were conducted to identify the added mass of the subsea structure and the natural period of the hoisting system. Then, the performance of the AHC was evaluated for regular and irregular wave conditions. The effects of winch capacity and installation water depth on AHC performance are discussed.
To install various subsea equipment or structures in deep water, safe and economic installation methods should be taken into account. Among various installation methods for subsea equipment, the conventional crane-wire installation method has been widely used in real-sea operations. Safe crane lifting operations require checking the crane capacity, rigging design, and structural strength of the lifted object. If the weight of the lifted object is considerable, the coupled dynamics of the crane vessel and the lifted object with crane wire become quite important. In particular, it is well known that vertical oscillation of the lifted object can be a significant factor during deepwater crane installation operations, especially for the landing phase. In addition, the resonant vertical motions of the lifted object can cause large dynamic tension of the hoisting wire during the lifting operation.
In the field of subsea installation, as installation depth and weight of installation objects increase, the needs of the heave compensation system increase. Heave compensators can be categorized into two types. One is the passive heave compensator (PHC), which is a kind of spring-damper system that shifts the resonant frequency of the vertical motion of the hoisting wire system. The PHC is also designed to reduce impacts on offshore cranes by adding damping in the hoisting wire. However, it depends on the types of subsea structure and sea conditions. The other type is the active heave compensator (AHC), which compensates for the vertical motion of a lifted object by using either controlled winches or hydraulic pistons with reference signals. The AHC systems generally use information from a vessel motion reference unit (MRU) to control the payout length of the winch line. The AHC system is rather complex and expensive but it is relatively unaffected by the subsea structure type and sea conditions. Also, the control mode can be changed adaptively for varying installation stages.
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