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The operator has developed a floating substructure technology for offshore wind farms known as HexaFloat. This concept uses a minimal floating hexagonal tubular substructure supporting wind-turbine tower and providing necessary floatability. The substructure is connected by tendons to a basket counterweight filled with solid ballast providing stability with pendulum-restoring forces. The assembly of the basket and the substructure behaves as a rigid body if all tendons are loaded. This assembly provides flotation with excellent stability thanks to the distance between the center of gravity and the center of buoyancy. Because this stability is provided by weight, large hydrostatic stiffness is unnecessary. As a result, only the central cylinder is exposed to the wave energy. The whole floating system can be anchored with three to six low-tension mooring lines, depending on environmental conditions.
The operator has developed a floating substructure technology for offshore wind farms known as HexaFloat. This concept uses a minimal floating hexagonal tubular substructure supporting wind-turbine tower and providing necessary floatability. The substructure is connected by tendons to a basket counterweight filled with solid ballast providing stability with pendulum-restoring forces. The assembly of the basket and the substructure behaves as a rigid body if all tendons are loaded. This assembly provides flotation with excellent stability thanks to the distance between the center of gravity and the center of buoyancy. Because this stability is provided by weight, large hydrostatic stiffness is unnecessary. As a result, only the central cylinder is exposed to the wave energy.
In 2017 the authors conducted an experimental hydro-aero-dynamic (station-keeping) campaign in MARIN's Offshore Basin aimed at validating its floating offshore wind turbine simulation tools. Since wind turbine dynamics cannot be readily downscaled in presence of Froude-scaled hydrodynamics, a bespoke coupling approach was developed. This was based on real-time load actuation using a winch system jointly with simulation software running on a data feed from the basin acquisition system. The result was a softwarein-the-loop experimental setup allowing to introduce controlled aerodynamic loading in the tests based on both the model's live response and simulated turbine physics. The software involved in this campaign, specifically developed for this task, is a customised version of NREL FAST, a standard open-source wind turbine simulator. Software-in-the-loop strategy emerges as a viable option to introduce multi-physical coupling in floating wind turbine tests in a controlled way.
Driven by the evidence of climate change many governments have decided to reduce carbon emissions associated with the production of electricity. Hence, there has been an increase in the use of renewable energy. Additional benefits include moving towards an energy supply which is more sustainable and more distributed. International targets for decarbonisation of the economy have been agreed at COP21 meetings in Paris in 2015. Of the renewable electricity technologies available, offshore wind allows electricity to be generated at scale and at a reasonable price (as can be seen from the second round of UK contract for difference see [
Offshore Wind (OSW) is rapidly maturing sector and is increasingly seen as a major contributor to electricity supply in states with coastal demand centres and good wind resource. While there is a 28-year history and set of experiences that has been learned in the European theatre, the U.S. is only recently beginning to move forward with grid scale projects. The U.S. Department of the Interior's Bureau of Ocean and Energy Management (BOEM) has, to date, leased fifteen Wind Energy Areas (WEAs) to developers along the eastern continental shelf of the U.S which to date have auctioned for a total of over $472 million [
The history of offshore wind power has included some notable hurdles and set-backs. Where these were due to fundamentals of design or analysis, large fleets of offshore assets were affected. Examples include failures of gearboxes, grounted connections and accelerated blade surface erosion. As floating wind is scaled up, to minimise similar exposure to technical risks, formal processes will help to identify the novel features, novel applications and components with the highest risk. Assumptions about suitability of existing onshore or offshore technical solutions must be challenged. Also care must be taken when using demonstration projects comprising single units as the basis for scaling up technologies. Currently, although monitored and scrutinised so as to be proven technically, these have comprised small-scale wind farms, under experimental conditions.
Mauries, Benjamin (Saipem SA) | Arcangeletti, Giorgio (Saipem S.p.A.) | Colmard, Christophe (Saipem SA) | Di Felice, Annalisa (Saipem S.p.A.) | Delahaye, Thierry (Saipem SA) | La Sorda, Enrico (Saipem S.p.A.) | D'Amico, Amerigo (Saipem S.p.A.) | Temeng, Kofi-George (Saipem SA)
Oil and Gas Operators are moving active production and injection equipment onto the seabed with the aim of reducing CAPEX and/or topside space requirements. Moreover, they want to minimize new production floating facilities (e.g. through tieback to existing FPSO/Floaters). Given this scenario, the overall electric power needs may become an issue because of the extra power demand due to the increasing number of electric consumers placed subsea. These electric loads may include the subsea boosting (pumps or compressors) operations, pipeline heating or the typical subsea water, chemical injection and valves actuation (in the case of all electric control systems), just to mention some of potential subsea power consumers, and may exceed the existing FPSO/Floater power production capacity. A potential solution to overcome this issue consists of the deployment of wind generators combined with topside Island power generation. Offshore wind power is indeed more and more considered for shore power supply, but also by the Oil and Gas industry with the objective of reducing the carbon footprint of their facilities. High power marine wind generators are already consolidated technologies for near coast, and today they are evolving in the short-term to floating solutions for the open sea. Saipem has developed its own floating wind turbine solution, called Hexafloat, consisting in a pendular floating foundation made of tubular elements and connected through tendons to a counterweight. This solution is particularly cost-competitive for deepwater locations (thanks to the low mooring costs) even for harsh environmental conditions (thanks to an excellent stability), and will unlock the possibility to deploy large wind power generators far from the coastline in deep water.
In 2017 the authors conducted an experimental hydro-aero-dynamic (station-keeping) campaign in MARIN's Offshore Basin aimed at validating its floating offshore wind turbine simulation tools. Since wind turbine dynamics cannot be readily downscaled in presence of Froude-scaled hydrodynamics, a bespoke coupling approach was developed. This was based on real-time load actuation using a winch system jointly with simulation software running on a data feed from the basin acquisition system. The result was a software-in-the-loop experimental setup allowing to introduce controlled aerodynamic loading in the tests based on both the model's live response and simulated turbine physics. The software involved in this campaign, specifically developed for this task, is a customised version of NREL FAST, a standard open-source wind turbine simulator. Software-in-the-loop strategy emerges as a viable option to introduce multi-physical coupling in floating wind turbine tests in a controlled way.
Multi-turbine floating offshore platforms (MUFOPs) are emerging as a viable concept for reducing levelized cost of energy in offshore wind developments. If properly designed, the cost per megawatt of electric power generated can be lower compared to single-turbine platforms. To maximize yield, minimize cost and ensure a safe design, the spacing between rotor-nacelle assemblies (RNAs), must be carefully considered. This spacing (R), is the sum of the platform column spacing (c), and tower horizontal projected length (h). Rotor diameters pose considerable challenges to the arrangement of multiple wind turbines on one platform; challenges pertaining to safe operations, feasibility of construction and transportation. Specific insights are necessary to facilitate the development of viable concepts. The parametric study presented in this paper discusses the optimization of MUFOPs using tower inclination and column spacing.
Representative configurations (adjusting tower inclination and / or column spacing) are developed with a multi-turbine semi-submersible-type platform and analyzed in time domain using coupled analysis. The configurations consist of two 5 WM reference turbines of the National Renewable Energy Laboratory (NREL), U.S.A. A non-dimensional parameter (R/c), is used to characterize the configurations. Wind, wave, and current loads are applied in analysis to assess the behavior of the system holistically. Hydrodynamic, aerodynamic, elasto-dynamic, servo-dynamic and mooring-dynamic effects are captured interactively at each time-step of analysis. An operational turbine condition is simulated in analysis using full-field turbulent wind to capture spatial variations of wind loads acting on each turbine of the system.
Characteristic responses of the nacelle, tower and platform are assessed to determine the optimal combination which avoids both inadequate and excessively conservative designs of multi-wind-turbine platforms. By analyzing the spectral densities of the responses, the potential impact of the observed responses on fatigue design is qualified. Optimal configurations from the scenarios considered, allow minimal or no wake interactions, tolerable towerbase loads and acceptable accelerations and motions of the nacelle and platform. Results indicate that optimal solutions exist at R/c ratios greater than 1.0.
An assessment of a range of tower inclinations and column spacing for optimal design of multi-wind-turbine platforms is a study that has not been documented in literature, and deserves attention considering current industry trends for floating offshore wind turbines. This paper offers significant insights on the characteristics of optimal tower and column arrangements for such platforms and provides reliable benchmarks for future designs.
Offshore Floating Wind is finally emerging as a promising source of Renewable Energy, but the Industry still faces important challenges. Among these, the impact the floater's motions have on the product life-cycle performance still requires evaluation and validation. In this sense, the industry has struggled to define an approach that minimizes the Levelized Cost of Energy (LCOE). The reasons for this, among others, are that each floater typology induces different motions on the nacelle equipment, each metocean site conditions are different, and the wear at the nacelle depends on the turbine model and manufacturer. Hence, the industry recommendations have so far usually limited the maximum longitudinal accelerations at the nacelle to 0.3-0.4g, and the maximum roll-pitch combination is set below 10°.
The induced motions add dynamic loading, wear down the mechanical equipment, produce fatigue damage on the structural members and are a source of potential downtimes, due to machine failures or simply due to unacceptable accelerations at the nacelle. Therefore, the different components of the turbine should be reinforced, increasing the CAPEX; or the maintenance and repair activities with its associated costs should increase; being both a possible combination.
The purpose of this paper is to analyze the different costs items associated with more or less conservative approaches with regards to the motions at the nacelle highlighting the combination of accelerations, operational weather windows, construction and maintenance strategies that can lead to the optimum LCOE.
Several response spectra of accelerations at the nacelle will be obtained for two different floaters, namely; a spar and barge preliminary sized for the DTU-10MW reference wind turbine. The effect of the turbine controller on the motions is not considered. For different acceleration cutoff values, the energy produced is estimated.
Li, Jiawen (Dalian Maritime University) | Hu, Guanqing (Dalian University of Technology) | Jin, Guoqing (Dalian University of Technology) | Sun, Zhendong (Dalian University of Technology) | Zong, Zhi (Dalian University of Technology) | Jiang, Yichen (Dalian University of Technology)
A novel semi-submersible platform, referred to as HexaSemi, is proposed with a completely new designed heave plate. Compared with the WindFloat-type design, the new heave plate has a single hexagonal shape with a moonpool. From a structural point of view, its integral design can increase the integrity of the structure. In this paper, we mainly study its hydrodynamic performance for an offshore wind turbine. A numerical model is set up to simulate the motion characteristics of the floating wind turbine system, based on WADAM, Star-CCMC, and FAST. The comparative analysis of HexaSemi and WindFloat-type platforms under the storm condition is conducted and discussed. It is found that the integral design can increase the viscous hydrodynamic damping and reduce the heave response and the mooring cable force.
Offshore wind energy is a kind of clean, abundant, and renewable resource, and it has become one of the most promising power generation methods in new energy (Karimirad, 2013). Compared with the land and shallow water, the deep-water areas have the advantages of steadier and stronger wind speed. Therefore, it is an inevitable trend for future wind farms to develop from the fixed type in shallow water to the floating type in deep sea (Gao et al., 2010). The semi-submersible platform is characterized by its small draft combined with hydrostatic stability during installation and substantial waterplane restoring. The structure stability is the foundation of the safe operation of the floating offshore wind turbine. One of the common challenges to the design of floating offshore wind turbine (FOWT) is the ability to predict the dynamic load responses of the coupled wind turbine and platform system, which usually combines a wind loading wave and a stochastic wave (Jonkman, 2010; Tran and Kim, 2015). It is necessary to study the dynamic response of the floating platform under the loading of the marine environment.