Validation of the HVS (Heave and VIM Suppressed) semi-submersible’s global performance is carried out through wave basin model tests and correlation with numerical analysis. As an application for a wet-tree floater, Technip designed the HVS semisubmersible to have reduced heave and VIM (Vortex Induced Motion) response. The HVS semisubmersible has blisters attached to the columns. The blister breaks the coherence of the vortex shedding along the length of the column and as a result reduces the VIM response. The redistribution of pontoon volume because of the blister reduces the heave excitation loading. The blister also provides adequate buoyancy for quayside integration. To validate the improved hull global performance, the wave basin model tests were performed. In the tests, collinear hurricane environments of the Gulf of Mexico were considered for two different headings. Truncated mooring was applied to simulate prototype mooring system. Wind loading was applied by means of a dynamic controlled wind winch. Current was generated by a wire attached to a system of pulleys. The measured hull responses were correlated with MLTSIM, a Technip in-house time-domain nonlinear motion analysis program. Through the correlation with model test results, the improved HVS semisubmersible global motion in hurricane environments is validated.
Prelude floating liquefied natural gas (FLNG) facility reached a significant milestone in June 2018 when gas was introduced onboard for the first time as part of the facility startup process, loaded from an LNG Carrier (LNGC) moored in side-by-side (SBS) configuration. This first offshore LNG SBS operation allowed Prelude’s utilities to switch from running on diesel to running on gas. SBS mooring is the base case configuration for offloading both LNG and Liquefied Petroleum Gas (LPG) into product carriers using Marine Loading Arms (MLA) once the Prelude FLNG facility is fully operational. These complex and weather sensitive operations are expected to take place on a weekly basis. This means critical decisions about weather-window and timing should be supported as much as possible by predictive analysis and modelling of forecast environment to reduce the risks. There are multiple criteria for evaluating the operability of LNGC or LPGC SBS offloading. These criteria cover the various phases of an operation, such as personnel transfer to the visiting carrier, Terminal Team Leader (TTL) transfer, spool fitting and fender lowering, approach and mooring, connection and testing of the loading arms, ramp-up of product transfer, full rate cargo transfer, loading arm purging and recovery, de-berthing, and people and hardware recovery. The criteria have been tailored to be appropriate to the phase of the operation. They comprise both environment-based criteria (maximum acceptable wind and waves conditions), and criteria related to motion or mooring (carrier roll, MLA envelope, mooring line tension, fender deflection). Motion and mooring criteria are evaluated through dynamic time-domain simulations. This allows an accurate modelling of non-linear effects, including mooring characteristics and partially filled cargo tanks. Thrusters can be used to control Prelude FLNG facility position if needed. The required thruster force to maintain the selected heading is calculated with frequency-domain calculation for all possible headings. This paper presents a visual reporting tool, developed by TechnipFMC in partnership with Shell. This tool has been used to support operational decisions during commissioning and startup, for SBS LNG and LPG import to Prelude FLNG facility. The daily reports used weather forecasts, in combination with numerical simulations, to predict the maximum motion and mooring criteria which contribute to determine both the timing and the decision to proceed with the operation. The format of the report has been designed to be user friendly for offshore operational staff, summarizing efficiently and in a visual manner the usage factors for each criterion separately. An overall operability is also presented for a quick overview. This paper also presents the details of numerical simulations, summarizes the different studies carried out to ensure the reliability of these simulations and discusses the possibilities for future development.
Coral South Floating Liquefied Natural Gas (FLNG) unit is designed to offload its product to LNG Carriers (LNGC) moored in a Side-by-Side (SBS) configuration, using Marine Loading Arms (MLA) technology. With such a method, multiple design aspects require accurate hydrodynamic simulations at an early stage of engineering phase for a large number of environmental conditions, including wind sea and swell: sizing of FLNG mooring outfitting, design of the MLAs for the candidate LNGC fleet and availability of LNG offloading. Complex phenomena like multi-body hydrodynamic coupling and LNG sloshing in partially filled tanks must be accounted for, and non-linear berthing characteristics require time-domain simulations. However the computing time for all the environmental conditions described in the available 23-year hindcast databases combined with all the possibilities of FLNG heading obtained with thruster assistance, for multiple LNGC and loading conditions, is not compatible with the project engineering phase timeframe, so the simulations must be first performed on a suitable-size sample of environmental conditions, creating a database which can then be used for predicting the data related to any environment. The selected sample of environmental conditions must meet the constraints of computing time while keeping a sufficient resolution to be reliable. In other projects, the time-domain quantities subject to operability criteria, derived from this limited number of simulations, were used to predict the behavior for any unknown environment by interpolation. This approach presented some limitations like the overfitting of maxima dependent on the wave realization (seed), which is seen as a noise, and was not best suited for generalizing the results to non-simulated environments out of the sample. In this paper, the improved methodology used for the Coral South FLNG project is presented. A Radial Basis Function (RBF) Artificial Neural Network (ANN) is used to model the variables impacting the SBS offloading operability. The ANN learns from the results of simulations performed on a sample defined with a K-means clustering algorithm. The RBF is modified to be adapted to the specifics of the driving parameters, of which some are periodic (wave direction) and the rest non-periodic. A proper smoothing of seed-dependent maxima and accurate estimations for unknown environments (generalizations) are achieved. The learning process does not require significant computing time and fewer preliminary time-domain simulations are needed. This design methodology represents a significant improvement for the calculations performed during the project's engineering phase, but it may also be applied later once offshore, to assist in decision making relative to the weekly forecasted SBS LNG offloading operations. When Coral South FLNG operates, the learning database may be completed with on-site measurements to further improve its accuracy. The principle may also be extended to other offshore operations constrained by environmental conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.