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Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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Overview of FOWT Demo Projects Cost and Analyses of Hull
Design Features
Glib Ivanov, I-Jen Hsu and Kai-Tung Ma
National Taiwan University, Taiwan
Abstract The potential of many novel concepts in any industry goes unnoticed when nobody invests their
time and money in them. However, some Floating Offshore Wind Turbines (FOWT) have gathered attention
and persuaded investors due to the successful completion of a demonstration project. This paper provides
an in-depth analysis of how demo projects around the world were born, what made them successful, and
proposes ideas for a demo project in Taiwan. The TaidaFloat, a semi-submersible FOWT floater with slight
innovations, requires a demo project to showcase its potential. The paper presents an example platform with
a parametric design approach, addressing the problem of scaling down the project to demo size and
constraining heave and pitch motions. The floating turbine is designed with a local supply chain capability
in mind and a mooring system is proposed with a line weight reduction priority due to the limited anchor
handling tugs in Taiwan. This paper provides insight into how a demonstration project can be carried out
in Taiwan or locations with similar conditions across Asia-Pacific.
Keywords Floating Wind· FOWT · demonstration· Semi-submersible· natural period· stability · cost ·
Taiwan· renewable · energy · project
Fig. 1.1 Timeline of FOWT demo projects around the world
1 Overview of the FOWT demo projects
Land-based wind turbines have been around since James Blyth generated electricity with them in 1887.
They become popular and are widely installed for power generation since the 1990s. In 2009, the first
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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Floating Offshore Wind Turbine (FOWT) demo was installed by Statoil (now Equinor). Since then, there
were extensive trials and demo projects in the few countries taking part, sometimes predating the actual
farm construction by a decade. A lot was learned from the demonstration project, and the designs were
adjusted. Table 1.1 shows all public demonstrator projects launched on the water before September 2022
in chronological order.
Table 1.1 Comparison of ever-deployed FOWT demo projects
PROJECT
Year
(on water)
2009
2011
2013
2013
2015
2016
2013
2017
2018
2021
2021
2022
2022
2023
Power, MW
2.3
2.0
2.0
2.0
7.0
5.0
0.012
2.0
3.2
5.5
3.6
2.0
6.2
7.25
Project
Name
Hywind
WindFloat 1
Goto
Mirai
Shinpuu
Hamakaze
Volturn US
demo
Floatgen
Hibiki
SanXia
TetraSpar
Sath
FuYao
Guan Lan
Design
Company
Statoil
(Equinor)
Principle
Power
TODA
Corporatio
n
Fukushima
Forward
Fukushima
Forward
Fukushima
Forward
DeepCwind
Ideol
Ideol
Three
Gorges
Stiesdal
Saitec
CSSC
CNOOC
Country
Norway
Portugal
Japan
Japan
Japan
Japan
USA
France
Japan
China
Denmark
Spain
China
China
HULL
Type
Spar
Semi
Spar
Semi
Semi
Spar
Semi
Barge
Barge
Semi
Spar
Barge
Semi
Semi
Length, m
n/a
33.0
n/a
57.2
75
59.0
11.3
36.0
45.0
79.0
56.5
64.0
72.0
77
Breadth, m
n/a
46.2
n/a
64.2
149
51.0
12.8
36.0
45.0
91.0
67.0
30.0
80.0
88.9
Draught, m
100
13.7
76.0
16.0
17
33
2.9
7.0
7.5
13.5
14.0
10.0
33.0
8
Displ., t
5433
2800
4408
-
26K
8000
40
7500
10K
13K
5036
-
15.6K
11K
MOORING
Water
Depth, m
200
45
100
120
120
120
27
33
33
30
200
85
65
120
Mooring
Layout
3x1
cat.
1+1+4
cat.
3x1
cat.
2x3
2x3
+1x2
cat.
6x1
cat.
3x3
cat.
synth.
3x3
cat.
chain
3x3
cat.
3x3
cat.
3x1
cat.
single
point,
6x1
3x3
cat.
3x3
cat.
Anchor
drag/suct
drag
drag
drag
drag
drag
drag
drag
drag
suct.
drag
drag
driv.
suct.?
OVERALL
Certification
DNV
ABS
NK
NK
NK
NK
ABS
BV
NK
CCS
DNV
DNV
CCS
CCS
Status
Power
Power
Power
Decom
Decom
Decom
Decom
Power
Power
Testing
Testing
Testing
Testing
Testing
Estimated
Project
Cost,
$US
millions
78
25
61
25
-
-
5
20
8
33.7
50
17
-
48.5
Suct. – suction pile anchor; Driv. – driven pile anchor; Decom – decommissioned; light colour – excluded from comparison.
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
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1.1 Hywind and TetraSpar in Scandinavia
Norway achieved a breakthrough by pioneering the earliest Floating Offshore Wind Turbine (FOWT)
demonstration project in 2009, solidifying its position as a leader in renewable energy [1]. The successful
demonstration provided confidence in the feasibility of FOWT, empowering Norway to emerge as a
prominent player in this field. It is worth noting that a considerable amount of work was undertaken between
the initial demo and the development of full-scale Hywind spars, emphasizing the extensive efforts required
to establish the viability of large-scale offshore wind farms. While financing was challenging for many
projects, Hywind, founded by Statoil—an oil and gas company committed to clean energy—enjoyed
relatively favorable conditions. The demonstration facility continues to generate power until 2029 [2] and
has paved the way for the world's largest floating wind farm, Hywind Tampen, featuring 11 spars that supply
electricity to oil and gas platforms.
Figure 1 highlights another noteworthy Scandinavian project, TetraSpar [3]. The most recent demonstrator,
launched in 2021, incorporates a 3.6 MW turbine, representing a full-scale platform rather than a demo.
The design aims for small-scale production and has incurred a cost of approximately $50 million, financed
by a consortium of leading energy companies. The renowned designer, Henrik Stiesdal, aimed to
differentiate the TetraSpar platform from its competitors, presenting an innovative solution. Interestingly,
following the demo launch, an alternative pure semi-submersible design, TetraSub [4], was introduced,
indicating the evolving nature and novelty of the TetraSpar concept.
While most fixed offshore wind turbines in Europe were erected in the calm Baltic Sea, allowing for
comfortable installation and lower extreme loads, the focus has now shifted to the North Sea, where mean
wave heights can reach up to 11 meters [5], accompanied by more frequent storms. This poses new
challenges for ensuring structural survivability but provides access to higher-quality wind areas. As the
global wind industry expands, Asia has emerged as a prominent region, with Japan becoming the first
country to complete a large-scale FOWT project in 2015, and Taiwan making significant investments in the
wind industry. However, Asian developments face the unique weather phenomenon of typhoons, which,
combined with constant monsoons in autumn and winter, occasionally ravage East and South Asia during
summer and autumn. Therefore, wind turbines and platforms in these regions must be designed to withstand
the forces induced by typhoons. Additionally, frequent and powerful earthquakes pose another factor to
consider, as they can lead to failures in anchor and mooring lines [6].
1.2 WindFloat in Portugal/USA and VolturnUS
The WindFloat project [7] stands out as a crucial demonstrator and a precursor to commercial Floating
Offshore Wind Turbines (FOWT). Over a span of three years, the USA-designed prototype underwent demo
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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operations off the coast of Portugal, encountering storm events that exceeded expectations. It successfully
withstood record-breaking 17-meter waves, surpassing the design wave height. This highlights the
significance of considering extreme conditions in addition to predominant wave characteristics. Despite
reaching the end of its five-year operational life [8], the prototype was sold and relocated to Kincardine,
Scotland. The success of the WindFloat demo led to the implementation of two small-scale pre-commercial
wind farms: WindFloat Atlantic, consisting of three semis offshore Portugal, and WindFloat Kincardine,
comprising five semis offshore Scotland. Principle Power, based in the USA [9], secured $25 million in
funding for the prototype's design, fabrication, and installation off the Portuguese coast. Funding sources
included the Portuguese government, the WindPlus joint venture involving Energias du Portugal, Repsol (a
Spanish oil company), A. Silva Matos (a Portuguese manufacturer), Vestas, and government innovation
funds.
In contrast to most commercial projects, the Volturn US demo [10] provided comprehensive data, which
was not only shared but also utilized for validating simulation software predictions [11]. The results
demonstrated the reliability of simulations in producing accurate outcomes. The demo also extensively
explored towing operations. However, due to the utilization of an extremely small turbine, despite its
success, it did not immediately spur the development of full-scale FOWT projects in the US. Even a decade
later, no active projects have emerged, and the Volturn demo was decommissioned and disassembled after
18 months.
1.3 Japan
Fukushima Mirai [12], part of the Fukushima Forward project [13], featured a 2 MW turbine and
successfully demonstrated various customized technologies developed by different Japanese institutions,
including custom mooring chains with specialized steel grades. The Fukushima Forward project stands out
as the largest-scale and longest-duration demonstration project, with a total funding of $115 million [14].
While the project faced challenges in securing company participation and raising funds, valuable lessons
were learned from deviations from the original plan. Fukushima Hamakaze, with a 5 MW turbine, provided
data for software validation [15]. However, during towing in 2016, the platform experienced a 45-degree
tilt due to ballasting issues, leading to its disassembly [16]. Shinpuu, featuring a 7 MW turbine, showcased
an innovative L-shaped semi-submersible design but was salvaged due to profitability concerns. The
decommissioning works for Mirai, Hamakaze, and their offshore power substation were tendered for $48
million [17], highlighting the significance of considering decommissioning costs in the initial assessments.
The Goto Demo [18], a spar-type platform similar to Hywind, demonstrated its stability by withstanding
two severe typhoons without any structural damage or cracks. After three years of operation, it was
relocated to Fukue Island for further demonstration and possible expansion into a floating offshore wind
farm. The construction of the 16.8 MW Goto floating wind farm offshore Japan is set to begin in September,
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
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with commissioning expected in January 2024 [19].
On a different note, Skwid [20], the first vertical wind turbine tested in Japan, sank during the installation
process off the coast of Kabe Island in 2014, highlighting the importance of proper sea bottom investigation,
installation procedures, and thoughtful design considerations for routine operations such as anchoring. The
platform was eventually salvaged [21].
In total, Japan had five large-scale built prototypes, placing it at the forefront in terms of this metric. This
was attributed to the close integration between academia and industry, with consortiums formed by
numerous companies and universities. The creativity and innovation of Japanese universities complemented
the resources and expertise of industrial partners. Additionally, strong government political support and
funding played a crucial role, with the Fukushima Project serving as a reconstruction effort for the affected
province and aligning with green energy transition goals [14]. In contrast, the US faced limitations in project
funding, lengthy permission processes, and a lack of political focus on green energy at the time, resulting
in private companies like Principle Power testing and installing their platforms in Europe instead of
developing them domestically.
1.4 Fuyao and Sanxia in China
A design that challenges conventionality: SanXia [22], was installed and connected to the grid in the South
China sea in 2021. The project "Sanxia" (meaning Three Gorges) is China's first FOWT, with a capacity of
5.5 MW. Next, with a large design displacement of 15,600 tons, it may be difficult to call FuYao [23]
FOWT a ”demo”, however, this 6.2 MW platform is planned to serve as a technology demonstration before
the even bigger turbines are built for commercial use in China. As is often the case with many Chinese
projects in any industry, the scale is unparalleled, despite FuYao being a rather conventional configuration
(3 columns, off-centre turbine, boasting both pontoon and bracing).
Their third and most recent FOWT is China National Offshore Oil Corporation’s Guan Lan [24], with the
turbine in the centre, it embodies all the experience learned from the previous Chinese projects. Albeit its
construction cost of 6.63 $/W is slightly higher than SanXia’s 6.08 $/W [25], it’s lighter than Fuyao by 800
ton. One of the most lightweight by among competitors, with an only 4000-ton hull supporting a 1200-ton
turbine [26], this is due to its many connection bracings, that provide strength with smaller expense that
increasing shell thickness [27, 28]. All of them are deployed in the South China Sea, but not much technical
information or papers could be found in the public domain.
1.5 Floatgen and Sath in Southern Europe
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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A French company, Ideol, advocates for concrete as a construction material due to its cost-effectiveness,
while the Japanese hold a different perspective [29]. In 2018, they launched two sister demonstration
projects: concrete Floatgen in France [30] and steel Hibiki in Japan [31]. Interestingly, it appears that a steel
barge in Japan is still less expensive to build compared to a concrete barge in France. These projects
showcase adaptations in various details such as turbine blade count (3 vs. 2), mooring system type (synthetic
vs. chain), hull material (concrete vs. steel), and classification society (BV vs. ClassNK). Barge-type
platforms, despite facing typhoons, have shown susceptibility to significant turbine loads in cases of pitch
motion resonance with incident waves [32]. It is intriguing to explore how engineers of the Hibiki project
have addressed these concerns and how fatigue damage may manifest over time. In France, the project
receives support from the European Union through the FP7 program, the French Environment and Energy
Management Agency as part of the national Investments for the Future Program, and the regional
government. After project completion, it was decided to extend their energy production, leading Ideol to
sign an investment agreement with several companies aiming to finance innovative infrastructure projects
funded by the Investment for the Future Program. Notably, in 2023, Floatgen reported a 60% capacity factor
throughout the year [33], surpassing the typical planned efficiency of 40%. The fundraising stage required
several years to convince investors, and BW Ideol's press releases provide detailed information on the
process and funding amounts [34].
The Sath project, [35] initiated by a Spanish design company in 2020, involves a concrete twin-hull barge
structure. In 2022, a 2 MW unit was installed in a test field offshore Spain. The Sath design incorporates
prefabricated concrete components and a single-point-mooring system, enabling the floating structure to
yaw around its mooring and passively align itself with wave and current directions.
2 Demo Projects Analysis
To determine TaidaFloat demo design parameters, and compare it to other projects, a literature study on
demo projects was conducted.
Of these demo projects, their principle dimensions, turbine ratings, cost and other data are compiled and
listed in Table 1.1. Data sources include press releases, scientific publications and news articles. The grey
colour in the Table signifies concrete structure. The readers are referred to another conference paper by the
same authors in 2021 for a similar comparison of full-scale semi-sub FOWT projects [34]. From Table 1, a
few observations about the current state of FOWT demonstrators can be made.
Semi-submersible type floaters are in the absolute majority, 7 out of 14 belonging to this category, while
3 of these 14 are barge type, which are a kind of semi-sub. The remaining 4 are spar type, and no TLP
demonstrators were launched so far, except for a tiny 80 kW prototype done in Italy [36]. Spar-type FOWT
don’t vary much from one another, and as a direct successor of fixed-bottom columns, they are easier to
design, therefore the development of this FOWT type has already moved to industrial scale and away from
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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demo projects, while semi-submersibles concepts vary greatly and therefore new innovative concepts are
being actively tested and demonstrated. The widely discussed TLP technology seems not to be field-ready
yet, or no interested parties are funding it.
Fig. 2.1 Floater type and current stage of FOWT demo projects
Funding is a crucial part of demo projects. Among the successfully completed projects, only a small part
was retired, while most projects are connected to the grid after test and continue to produce power – this is
a key point for investors, as demo projects deemed unprofitable had been cancelled. These trends are
visualized in Figure 2.1.
An increase in floater displacement and power rating can be seen as new demonstrators have to keep up
with smaller turbines being phased out of production. While 2 MW turbines were the standard for early
projects, fixed and floating offshore wind turbines were growing in size [37], as shown in Figure 2.2.
Turbine manufacturers react to the demand and produce larger turbines, phasing out the smaller ones. An
offshore 2 MW turbine can only be custom-made in 2022 and no longer mass-produced, forcing
demonstration projects to adopt higher power ratings. Another factor here is the expectation from investors
not only to gain technical data but also get sell the electricity provided by the demo, while in the early
projects revenues from electricity were rarely considered.
As the platform’s dimensions are governed mainly by stability and seakeeping requirements, and not by
turbine weight, a big increase in turbine power will only lead to a small enlargement of a floater. Bigger
turbines are only available for offshore projects, as a hundred meters long the blades and nacelles could not
pass through most roads, tunnels and bridges. Fueled by the desire for efficiency, even offshore turbines
have grown so large that they can’t be handled by most port cranes, and almost no factories can produce
nacelle bearings of diameters about 10 meters, that’s why in 2023 Vestas CEO halted many people’s dreams
of 30 and 50 MW turbines, saying the 15 MW turbines are big enough for now and will not grow soon
[38].
For the subsea parts (i.e. mooring components), all demos have been exclusively using drag anchors before
both Chinese projects’ experiments with suction and driven piles. It is reasonable as drag anchors are the
cheapest choice, but there are many potential benefits accessible to other anchor types, such as anchor
sharing, precise anchoring location, fast and easy installation with small vessels etc. Mooring layout is
usually a 3x3 catenary chain, while some designs opt for 3x2 or even 3x1 using large-diameter chains.
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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Using fewer chains, but bigger chains help reduce installation time, saving vessel hiring costs, which is one
of the major concerns in the whole industry. However, 3x1 or single point moorings provide no redundancy
in one-line damaged condition, and thus no reliability in case of a mooring failure [39].
Fig. 2.1 Trend of FOWT demo size
2.1 Developments for Taiwan
In Taiwan, wind energy has been a development focus, since the political decision to phase out nuclear
power plants, as other sources of renewable energy are hardly accessible here [33]. Floating wind research
has also started to gain traction. Recently, a wave tank test of a barge-type FOWT was conducted [34]. The
authors also participated in an indigenous design of DeltaFloat semi-submersible [40]. Another notable
design in Taiwan may arguably be the TaidaFloat semi-submersible [29], which was designed by a team
including both authors. The team from National Taiwan University was sponsored by Taiwan’s government
agency, the Ministry of Science and Technology, to come up with a reference platform, best suitable for
Taiwan’s local environment and manufacturing conditions, and possibly to serve as a workable design for
wind energy developers. A smaller version of TaidaFloat and DeltaFloat is currently being designed as a
prototype for technology readiness demonstration.
The amount of financing required for such a project is hotly debated. According to Table 1, the average
FOWT demo project cost (excluding VolturnUS mini project and SATH for which no full data was found)
amounts to $38.7 mil, and the projects get cheaper with time due to the learning curve [41]. Please keep in
mind that this Figure is for reference only, as the costs shown in Table 1.1 compare different projects based
on limited data available in the media.
3 Principal Dimensions
With the aim of local manufacturing, TaidaFloat’s design basis is the dimensions that allow for
manufacturing in Keelung shipyard, in the north of Taiwan. It was chosen as it is close to initially proposed
project site and isn’t overloaded with orders. Its main limitations are 42 m drydock width, and 300-ton
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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crane capacity. To reduce project’s initial costs, and in line with earlier demonstrator’s choices, a 2 MW
power rating was selected for platform’s turbine, but the platform could support a bigger turbine if required.
As the manufacturers moved on to bigger turbines and no data for a marine-grade 2 MW turbine was found
in open source, data shown in Table 3.1 was obtained by scaling down the 5 MW turbine that comes with
OrcaFlex.
Usually, floaters in demo projects are scaled down with a scaling factor λ, all principal dimensions are
directly downscaled, while turbine power is scaled down as λ3.5, the method described in detail in [10].
According to this practice, metocean conditions like wave height and period also have to be scaled down
for a fair comparison. Forces (waves, turbine thrust, current drag) are to be scaled down as λ3, while Velocity
(wind speed, current) as λ0.5. Since it’s not a tank test but a long operational test, and naturally
environmental parameters can’t be controlled in the sea, a site with metocean conditions closest to those
obtained by scaling down, needs to be found. Unfortunately, due to administrative reasons, the only possible
locations for TaidaFloat demo were Taiwan National Ocean University’s wave test zone near Keelung and
the areas for designated sites [42] for Offshore Wind Energy development near Taichung port, where
installation of the full scale TaidaFloat’s turbine is planned.
Table 3.3 Correlation factors between floater parameters and heave period
d
B
∆
Heave
Pitch
Draught
1.00
Width
0.00
1.00
Displacement
0.63
0.78
1.00
Heave peak
0.11
0.99
0.84
1.00
Pitch peak
0.11
0.99
0.84
1.00
1.00
As it turned out, due to grid overuse and administrative problems, the turbine couldn’t be connected to the
grid at Keelung site, so turbine would have to be connected to a heating element submerged in water to
generate load. As seen from the other demo projects experience, the turbine can provide power for many
years after testing has finished, and it’s important that it provides power to attract investment. Therefore,
the more probable site will be in offshore Changhua, Taiwan.
Fig. 3.3 Array of design parameters investigated
The metocean conditions in both sites are the same as for the big TaidaFloat, and decision was made that
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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TaidaFloat demo will not be a scaled down model, but rather a smaller version instead. With same
manufacturing constraints in mind, platform’s natural period became the biggest challenge, as waves in
Taiwan strait are quite high during Typhoon season, reaching 14.3 m amplitude. As some wave’s period
approaches the natural period of heave and pitch of draft design – 13.5 s, it should be changed to prevent
resonance and subsequent mooring or structural failures. Column’s dimensions were chosen according for
manufacturing ease, ballast and equipment requirements, length maxed out to drydock dimensions, so the
two parameters left to vary were draught and pontoon width. A parametric study was conducted in ANSYS
AQWA to determine the relationship between those 2 parameters and movement RAO eigenperiods; 98
different combinations were considered. Extreme shapes are shown in Fig. 3.3, while the 15 m draught 5
m pontoon width version is the original draft. The parametric study results are presented in Figure 3.4.
An important observation can be made if we take a look at correlation factors in Table 3.3, we can see how
increasing both draught and width increases displacement almost equally fast, width causing slightly larger
displacement change. At the same time, increasing draught only slightly increases heave and pitch
eigenperiod, while increasing width has a much stronger effect on eigenperiod increase. The same can be
clearly seen from the surface slopes in Figure 3.4. Aforementioned applies not only to heave, but to all 6
DOF.
Suitable candidates are all the platforms in the green area in Figure 3.4, to save material cost and allow
for shallower berths, the shallowest draft was chosen, final principal dimensions are shown in Table 3.4.
Fig. 3.4 Heave eigenperiod, pontoon width and floater depth contour plot for TaidaFloat demo
Table 3.4 TaidaFloat demo principal dimensions
Length, m
40.8
Breadth, m
47.1
Height, m
29
Draught, m
15
Pont. Width, m
9
Displacement, t
3895
Hull weight, t
±1000
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Fig. 3.5 Left: Old 20 m draught overflows at 23.3 deg. Right: Adjusted 15 m draught doesn’t overflow.
As AQWA parametric study was conducted with low fidelity to save computational time, final configuration
was tested in OrcaWave, it and subsequent mooring design will be explained in the next section. It should
be noted, that in this parametric study, only wave period range between 10 and 20 was considered, of course
there is a another larger eigenperiod peak down the line, but it’s that period is large it’s of no concern for
seakeeping.
OrcaFlex Simulation showed that in extreme survivability case platform tilt can reach 21 degrees. Platform
with 20 m draught overflows at 23.3 degrees, as seen in Fig. 3.5, which is unacceptable for stability reasons,
discussed in chapter five. Platform with 15 m draught choice is confirmed as it only reaches overflow at 33
deg.
Following principle can be used for future designs of similar tri-column floaters with ring pontoons: To
increase natural period, pontoon width can be increased. Draught should not be increased more than
necessary to reduce wave loads, as high draught to freeboard ratio has a devastating effect on survival
stability, material cost and berth depth requirement.
4 Stability
Environmental conditions and RNA operating modes are to be considered in calculating the overturning
moment are specified in 9-2/5.1.1 ABS rules [43] for assessing the intact stability. Figure 4.1 illustrates the
variation in wind moment due to changes in wind speed, two types of wind load, the thrust generated by
the rotor, and wind pressure. During wind turbine operation, the rotor thrust is the dominant factor, but
when wind speed reaches the cut-out speed, the rotor will shut down and the blade pitch will change to
approximately 90 degrees, causing wind pressure to become the dominant factor in wind moment. The
maximum wind moment occurs when wind speed reaches the 50-year return wind speed, which is 57 m/s
at the assumed operation location. Therefore, the 50-year return wind speed was deemed the most dangerous
condition and used for calculating intact stability in the subsequent analysis. Additionally, the roll stability
is inferior to pitch stability due to the smaller side column cross-area. As a result, all calculations of intact
stability are based on roll motion.
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Fig. 4.1 Contribution of rotor thrust and vessel/tower drag moment as a function of steady wind speed. The rated wind speed
moment (DLC 6.1) may dominate, which is the normal turbine operating range.
Static stability curve in Figure 4.2 depicts the relationship between the moment and the inclination angle.
There are two types of moments that balance each other and cause the platform to tilt: the righting moment
and the overturning moment. The righting moment is calculated using ORCA3D and the overturning
moment is calculated following the procedure in the ABS-published paper [44]. The formula for the
overturning moment is:
But as previously stated, the maximum value of overturning moment is determined by the 50-year return
wind speed so the formula is simplified to:
The intact stability criteria following the FOWT rule 9-2/5.1.1 [43], the first intercept and the
minimum second intercept can be obtained using the area-ratio-based criterion from Figure 4.2, to achieve
the area ratio greater than 1.3, the downflood angle must be greater than 23.3 degrees, which is completely
fine with all openings upon deck are still far away from the sea water level after platform tilted 23.3 degrees
(shown in Figure 3.5).
The intact stability is determined by an area-ratio criterion shown in Table 4.1, and the downflood angle
must be larger than 23.3 degrees, although the detailed design of opening has yet to be determined, there is
a large tolerance between the lowest point of deck and SWL after platform tilts 23.3 degrees, therefore, the
platform is in full compliance with intact stability criteria set by ABS rules.
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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Fig. 4.2 Static Stability Curve. The area-ratio-based criterion
Table 4.1 Intact stability calculation
First intercept (deg)
9.24
*
Downflood limit (deg)
23.3
Area ratio*
1.300
Fig. 5.1 Final TaidaFloat Demo render
5 Conclusions
5.1 Demo Projects
After analysing previous demo projects, several key points were learned for designing a new prototype
demonstrator:
First, funding is the essence of a successful demo program. The Japanese government is willing to spend
an enormous amount of money on FOWT projects. European projects are usually private-government
partnerships, while the US only most recently decided to develop floating wind at all [45]. Recently, the
UK decided to invest 31.6 million pounds into FOWT demo projects [46]. The progress of different
countries in FOWT technology is clearly seen from the above analysis, so for a new country, such as Taiwan,
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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to enter the industry and catch up with the current players, a clear policy must be outlined by the government,
with regulations facilitating wind sites lease, governmental funding of both research and demo projects, as
well as a free energy market to encourage private investment in the sector. A key to a successful and swift
demo project erection is amassing a large number of interested stakeholders. A good point to make with
them is that the demo FOWT keeps producing energy and is not thrown away after a couple of years. Most
of the initially decommissioned platforms were repurposed to keep power production going for years.
Second, construction and development costs vary greatly by country, for example, a steel barge in Japan
costs less than a concrete one in France, where concrete was used intentionally to cut costs. Every country
or region deciding to commence its FOWT project should develop a design fitting its own industrial
situation, and not necessarily buy a foreign design. The demo floater dimensions, materials and other design
choices should originate from the local industry compatibilities and infrastructure. The average FOWT
demo project cost found was $38.7 mil USD.
Third, interesting enough, every project mentioned had some degree of academic collaboration. Student
researchers and professors from the University of Tokyo, Massachusetts Institute of Technology, Danish
Technical University, Centrale Nantes, and many other renowned and smaller institutions were directly
involved in the design of the floaters, with master’s and Ph.D. theses defended as a result. As FOWT are a
very new and unexplored technology domain, only with the help of researchers, companies can ensure their
design will be advanced, safe and reliable.
5.2 Floater Design
International demo projects experience was combined with Taiwan’s local conditions to design the most
suitable Floater and mooring system for use in Taiwan Strait. As a small demonstration floater still
encounter from the same big waves a big platform would encounter, stability and natural period become
the critical design factors.
Following principle was devised to be used for future designs of similar tri-column floaters with ring
pontoons: To increase natural period, pontoon width can be increased. Draught should not be increased
more than necessary to reduce wave loads, as high draught to freeboard ratio has a devastating effect on
survival stability, material cost and berth depth requirement.
Also, it’s more challenging to design a mooring system for a small floater. For similar areas prone to
typhoons, at least 3x2 mooring arrangement is necessary to guarantee survivability in case a typhoon
exceeds expectations and leads to one of the line’s failures. If the mooring system of one floater fails, the
floater might collide with other floaters in the farm and lead to the whole wind farm’s collapse. This will
be explored in future research.
Presented by Ivanov Glib on 29th August 2023 at the 3rd World Conference on Floating Solutions
(WCFS2023), Tokyo, Japan
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Acknowledgements
Many thanks to my colleague Chang Hung Chun for helping with the Chinese reports.
Many thanks to Dr Jer Fang Wu, advisor at NTU ESOE, for guidance on ABS practice.
Thanks to my colleague Yuki Igarashi for previous research on TaidaFloat mooring.
Many thanks to Taiwan’s National Science & Technology Council and Ministry of Education’s
Yushan Fellow Program for supporting FOWT research at our lab.
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