Introduction of Detachable WTIV and its Operability Study to Optimize Installation Cost of Offshore Wind Farm
Sunghun Jung, Myunghwan Kim, Jungin Choi, Sunjung Kim
Samsung Heavy Industries, Seongnam-si, Republic of Korea
In this paper the patented Samsung D-WTIV concept is introduced which can reduce construction cost for OWF installation by overcoming disadvantages of the conventional WTIVs with its unique functions and optimized operating model. Generally, the conventional WTIVs are jacked-up and fixed in location every time for the installation; an entire vessel topped with multiple OWT has to be lifted - to install a single OWT and cannot be utilized to any other operations during the installation of OWTs. To maximize the overall efficiency, D-WTIV design is comprised of the two detachable parts depending on their independent functional; a CU and a MS. CU is designed for OWT installation and consists of the jacking legs and main crane systems so it is a relatively compact structure compare to conventional WTIV. The MS is the self-propelled vessel for transit, fitted with DP thrusters and can be utilized to performing other tasks while CU is conducting installation works, such as O&M, commissioning and accommodation support. D-WTIV also has dedicated features; a unique Coupling and a Refilling system to enhance the inter-operations between CU and MS. A comparison of cost for installation was made between conventional WTIV and D-WTIV for a virtual OWF project based on typical specific site conditions. The underlying assumption and formula of the installation cost calculation are made based on SHI's ITEM that includes an operational algorithm for D-WTIV and Markov Chain's Theory to compute weather windows from observed metocean data.
A novel concept operating optimization model for D-WTIV, coded in Python 3.5.1, has been developed by combining an operational algorithm for D-WTIV and an SHI's ITEM to optimize construction duration of OWF. To consider the site dependent weather condition more accurately, a Markov chain model is implemented to generate synthetic weather model from observed time series from NOAA. Systematic case studies and parametric studies have been carried out to establish an optimal installation cost model for utilizing D-WTIV by changing major installation parameters such as number of turbine(s) in the farm, site distance from the shore, number of chartered vessel(s), number of loaded turbine(s) on deck, loading time, installing time and limiting condition of Coupling system and Refilling system.
By utilizing D-WTIV, it is shown that the installation cost of the OWF can be reduced to 16.1% with initial estimations. From the systematic parametric studies, it is found that the installation cost can be further reduced to 23.7% in case of the loading time per turbine and installation time per turbine is 36 hours and 54 hours, respectively, which is proven to be within a reasonable range from the available literature review. It is also found that to secure cost efficiency of D-WTIV, the operability of Coupling and Refilling systems have to be designed with at least an equivalent level of jacking system that significant wave height of operating condition within the range of above 1.5m.
Recently, many developers and engineers involved in the offshore wind industry have focused on optimizing expenditure of OWF to ensure economic efficiency. The newly developed D-WTIV by SHI can be a feasible solution to achieve this goal by reducing the installation time and cost of OWF with its dedicated operation philosophy and functionality. Not only on OWF installation, utilization of D-WTIV can be a cost effective solution for various offshore construction works such as refurbishment and decommissioning of OWT at the end of their service life in the future. Alternative operational modes that are adaptable to the show the cost benefits for vessel business planning will be further discussed in our separate technical paper in the near future.
By reducing and optimizing the constructional expenditure of the OWF with the newly developed D-WTIV, it could lead to reduce the COE of the whole offshore wind industry and can present the future direction of WTIV design concept. With the SHI's ITEM, it is our conclusion that it can contribute to establishing a development plan of OWF for developers and vessel owners considering the environment condition during installation.
COE Cost of Energy
CU Crane Unit of D-WTIV
DP Dynamic Positioning
D-WTIV Detachable Wind Turbine Installation Vessel
ITEM Installation Time Estimation Model
MS Mother Ship of D-WTIV
NOAA National Oceanic and Atmospheric Administration
OWF Offshore Wind Farm
OWT Offshore Wind Turbine
SHI Samsung Heavy Industries
WTIV Wind Turbine Installation Vessel