US 20130272846A1(19) United States(12) Patent Application Publication (10) Pub. No.: US 2013/0272846A1(43) Pub. Date:

Inoue

Publication Classification(54) TURNING/OSCILLATING MOTIONSUPPRESSINGAPPARATUS OF WIND
POWER GENERATING FACILITY AND
FLOATING OFFSHORE WIND POWER
GENERATING FACLITY

Oct. 17, 2013(51) Int. Cl.
F3B I7/06(2006.01)(52) U.S. Cl.

CPC ...................................... F03B 17/06 (2013.01)(75) Inventor: Shunji Inoue, Tokyo (JP)USPC ........................................................... 415/31(57)(73) Assignee: NATIONAL MARITIMERESEARCH INSTITUTE, Tokyo (JP)(21) Appl. No.:

13/883,560(22) PCT Filed:Nov. 4, 2011(86). PCT No.:

PCT/UP2011/006177

S371 (c)(1),(2), (4) Date: Jun. 30, 2013(30)
Foreign Application Priority Data
Nov. 5, 2010

(JP) ................................. 2010-2485.11

ABSTRACTThe present invention provides a floating offshore wind tur
bine capable of Suppressing yawing of a nacelle caused by agyro effect which is a cause of adverse influence of power
generating efficiency of a wind turbine and endurance ofdevices thereof. The floating offshore wind turbine includes arotor which is rotated by wind, a nacelle in which a rotation
shaft of the rotor is accommodated, and a tower including aturning seated bearing which Supports the nacelle Such thatthe nacelle can turn with respect to a sea surface to exert aweathercock effect. The tower is provided with yawing Suppressing means which Suppresses yawing of the nacelle.
According to this, it is possible to Suppress the yawing of thenacelle generated by a gyro effect caused by yawing gener
ated in the floating body by waves of the sea surface.

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US 2013/0272846 A1TURNING/OSCILLATING MOTIONSUPPRESSINGAPPARATUS OF WIND
POWER GENERATING FACILITY AND
FLOATING OFFSHORE WIND POWER
GENERATING FACLITYTECHNICAL FIELD

0001. The present invention relates to a floating offshore
wind turbine capable of efficiently Suppressingyawing (turningfoscillating motion) of a nacelle in which a rotation shaftof a rotor is accommodated and yawing of a floating body.
BACKGROUND TECHNIQUE
0002. In conventional wind turbines, to change an orien
tation of a wind turbine in accordance with change in a winddirection, an active control apparatus which is combined witha wind direction sensor is used. For example, there isemployed a configuration that a wind turbine is turned by apower apparatus in accordance with a result of measurementof the wind direction sensor, and the wind turbine is held at a
position suitable for the wind direction. To simplify a systemof the entire wind turbine, the active control apparatus isomitted in Some cases. When the active control apparatus is tobe omitted, a rotation shaft of a rotor of the wind turbine is
Supported on a horizontal plane Such that the rotation shaft
can freely turn, and the orientation of the wind turbine ischanged by a weathercock effect to follow the change in thewind direction.

0003. In the wind turbine, the rotor receives wind androtates, thereby generating electric power. If moment in a
vertical direction is applied to a rotation axis of rotation of therotor, gyro moment is generated in a direction cross at rightangles to both the direction of the moment and the rotation
axis of the rotor by a so-called gyro effect. For example, in a
floating offshore wind turbine provided on a floating bodywhich is floating in water, moment in the vertical direction is
generated due to influence of waves. Hence, gyro moment isgenerated in a horizontal direction cross at right angles to therotation axis of rotation of the rotor by the gyro effect.
0004. In a floating offshore wind turbine including theactive control apparatus, a nacelle is held by a floating body at
a position matching with a wind direction. Therefore, rotation
motion of the floating body rotating around a central axis of
the floating body is generated by gyro moment caused by the
gyro effect generated in the nacelle in which the rotation shaftof the rotor of the wind turbine is accommodated. Here, sincemotion of waves is repetitive motion, the floating body moves
repetitively (yawing) together with the nacelle.
0005. In a floating offshore wind turbine in which theactive control apparatus is omitted, a rotation shaft of a rotorof a wind turbine is supported such that the rotation shaft canfreely turn with respect to a floating body. Hence, yawing ofa nacelle is generated by gyro moment caused by a gyro effectgenerated in the nacelle.
0006. The present inventor found that moment caused bythis gyro effect was a cause of an adverse influence exerted on
power generating efficiency of the floating offshore windturbine and endurance of devices thereof.

0007 To prevent vibration generated in a wind turbine
apparatus, it is proposed to employ various configurations(patent documents 1 to 3).
0008 Patent document 1 describes a wind turbine apparatus. The wind turbine apparatus includes, as an active control

Oct. 17, 2013

apparatus of a nacelle, a whirling driving source which whirls
a platform Supported on an upper end of a tower and fixing
means in a whirling direction. In this wind turbine apparatus,
to suppress vibration generated in the tower or the like byresonance of a blades and resonance wind speed, patent docu
ment 1 describes a configuration that a vibration Suppressing
apparatus is provided.
0009. In a wind turbine, to attenuate vibration action in anedge direction of blades of a rotor, patent document 2
describes a configuration that oscillation action attenuatingmeans is disposed in a nacelle.
0010. In a wind turbine device, to prevent vibration frombeing transmitted to a nacelle frame through a speed increas
ing gearbox and to prevent vibration from being transmitted
from the nacelle frame to the speed increasing gear box,
patent document 3 describes a configuration that a vibration
isolation damper is provided between the speed increasinggear box and the nacelle frame.
PRIOR ART DOCUMENT
Patent Document

0011

Patent Document 1 Japanese Patent Publication

No. 2003-176774

0012 Patent Document 2 Japanese translation of PCT
International Application, Publication No. 2002-5 17660
0013 Patent Document 3 Japanese translation of PCT
International Application, Publication No. 2008-546948
SUMMARY OF THE INVENTION

Problem to be Solved by the Invention
0014. Such a conventional wind turbine has a problem ofvibration generated by rotation itself of the rotor and the like,but there are no conventional wind turbines which focus

attention on oscillation of a nacelle generated by gyro
moment caused by the gyro effect. Hence, the vibration
motion Suppressing means used in the wind turbine appara
tuses described in these patent documents can not prevent
yawing of the nacelle and the floating body generated by gyro
moment caused by the gyro effect when the floating offshore
wind turbine receives influence of waves.

0015 Hence, it is an object of the present invention toprovide a floating offshore wind turbine capable of prevent
ingyawing of the nacelle and the floating body generated by
gyro moment caused by the gyro effect, and capable of Suppressing adverse influence on power generating efficiency of
the wind turbine and endurance of devices thereof.

Means for Solving the Problem
0016 A first aspect of the invention provides a floating
offshore wind turbine which generates electricity using afloating body as a portion of a structure body on ocean com
prising a rotor which is rotated by wind, a nacelle in which atleast a rotation shaft of the rotor is accommodated, the structure body including turning means which Supports the nacelle
Such that the nacelle can turn with respect to a water Surface,and yawing Suppressing means which suppresses yawing of
the nacelle with respect to the water Surface and using ahydrodynamic damper which suppresses yawing by mutualinterference between a shape or a structure of the structure
body and peripheral fluid as the yawing Suppressing means.
According to this aspect, the yawing Suppressing means canUS 2013/0272846 A1

Suppress the yawing of the nacelle caused by a gyro effect.
Also, the yawing Suppressing means can Suppress yawing of
the nacelle which is induced by the gyro effect caused by
pitching of the floating body on the ocean. According to thestructure using this hydrodynamic damper, resistance to yaw
ing is varied by resistance to water of the underwater hydrodynamic damper in accordance with a turning speed of thenacelle or the floating body, and it is possible to suppress theyawing.
0017. According to a second aspect of the invention, in the
floating offshore wind turbine of the first aspect, the nacelle isprovided on a windward side as compared with the rotor.
According to this aspect, the nacelle can be turned withrespect to a water surface by a so-called weathercock effect,
and an orientation of the rotation shaft can be made to con
form to a wind direction.

0018. According to a third aspect of the invention, in the
floating offshore wind turbine of the second aspect, a coning
angle is given to the rotor. According to this aspect, it ispossible to further enhance the so-called weathercock effect.
0019. According to a fourth aspect of the invention, in the
floating offshore wind turbine of the first aspect, a hydraulicdamper is further provided as the yawing Suppressing means.
0020. According to a fifth aspect of the invention, in the
floating offshore wind turbine of the first aspect, a friction
damper is further provided as the yawing Suppressing means.
If the hydraulic damperor the friction damper is used as theyawing Suppressing means, resistance for Suppressing theyawing of the nacelle can be varied in accordance with aturning speed of the nacelle.
0021. According to an eighth aspect of the invention, in the
floating offshore wind turbine of the first aspect, the floating
body is moored by mooring lines.
0022. According to a ninth aspect of the invention, in the
floating offshore wind turbine of the eighth aspect, the float
ing body is formed into a Substantially cylindrical shape, apair of mooring lines composed of two mooring lines whose
one ends are connected to two points on a circumference of acircle of the substantially cylindrical shape when the floating
body is projected onto a horizontal plane is used as the moor
ing method, and the two mooring lines are formed into Sub
stantially tangent lines of the circle and extend on the sameside. According to these aspects, it is possible to suppress
rotation around a cylindrical center axis of the floating body.
0023. According to a tenth aspect of the invention, in the
floating offshore wind turbine of the first aspect, the nacelle issupported by the structure body such that a predetermined
angle is formed between a horizontal plane and the rotation
shaft of the rotor in a state where wind is not received so thatthe rotation shaft of the rotorina state where wind is received

becomes parallel to a wind direction. According to this
aspect, the predetermined angle can be set while taking, into
account, a fact that the wind turbine inclines when the rotor

receives wind. Therefore, when electricity is generated, therotation shaft of the rotor can be made parallel to a winddirection. Here, “a state where the rotor receives wind and thewind turbine inclines' means a state where the wind turbine isinclined by receiving wind of a typical wind speed which isassumed at a place where the wind turbine is installed.
Examples of the typical wind speed are an average annual
wind speed and a wind speed at which power generating
efficiency becomes maximum.

Oct. 17, 2013

Effect of the Invention

0024. According to the floating offshore wind turbine ofthe present invention, since the yawing Suppressing means
can Suppress yawing caused by a gyro effect, it is possible toSuppress adverse influence by the yawing on the power gen
erating efficiency of the wind turbine caused and enduranceof devices thereof.

0025 If the nacelle is provided on a windward side ascompared with the rotor oraconing angle is given to the rotor,
the nacelle can be turned by a so-called weathercock effect,
the rotation shaft can be made to conform to a wind direction
and the front face of the rotor can be in contradiction to thewind direction. Therefore, it is possible to enhance the power
generating efficiency of the wind turbine. Further, it is pos
sible to Suppress yawing and to reduce a load of the yawing
Suppressing means.
0026. If the hydraulic damper or the friction damper isused as the oscillating control means, resistance of the oscil
lating control means can be varied in accordance with aturning speed of the nacelle. Therefore, it is possible to Suppress fast yawing of the nacelle caused by a gyro effectwithout Suppressing slow yawing of the nacelle caused by aweathercock effect.

0027. If the hydrodynamic damper which suppresses yaw
ing by interference with Surrounding fluid is used, resistancecan be varied in accordance with a turning speed of thenacelle, the yawing generated in the nacelle or the floating
body due to the gyro effect can be Suppressed, pitching of thefloating body can be suppressed, and power generating effi
ciency and endurance of devices can be enhanced.
0028. The floating offshore wind turbine of the invention
includes the yawing Suppressing apparatus. Therefore, it ispossible to enhance the power generating efficiency andendurance of the devices by Suppressing the yawing of thenacelle caused by the gyro effect. It is also possible to Suppress pitching of the floating body by reaction of the gyro
effect.

0029. If the floating body is moored by a mooring method
which Suppresses rotation motion of the floating body aroundits center axis, it is possible to effectively suppress yawing of
the nacelle and pitching of the floating body caused by a gyro
effect, and it is possible to enhance power generating effi
ciency and endurance of the devices.
0030) Ifa predetermined angle is provided between a hori
Zontal plane and the rotation shaft of the rotor in a state where
the rotor does not receive wind, a side view direction of therotation shaft of the rotor and a side view direction of windcan be substantially parallel to each other and can be made to
Substantially conform to each other when electricity is gen
erated. Therefore, a rotation plane of the rotor can be madeperpendicular to a wind direction Substantially at rightangles,
and it is possible to enhance power generating efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS

0031 FIG. 1 is a schematic perspective view showing a
configuration of a floating offshore wind turbine according toa first embodiment of the present invention;
0032 FIG. 2 is a side view of essential portions showing a
structure of ayawing Suppressing apparatus of a wind turbine
according to the first embodiment of the invention;
0033 FIG. 3 shows a relation between change in a winddirection on the ocean and a deflection angle of a floating
body on water caused by influence of waves, wherein (a) is a

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Oct. 17, 2013graph showing change in a wind direction and (b) is a graphshowing change in a deflection angle;
0034 FIG. 4A is a schematic perspective view showing a
configuration of a hydraulic damper,0035 FIG. 4B is a schematic front view showing a con
figuration of the hydraulic damper;0036 FIG.4C is a sectional view taken along a line A-A in

0067 C. coning angle
0068 B predetermined angle

FIG. 4B;

described below with reference to FIGS. 1 to 8. In this0037 FIG. 5A is a schematic perspective view showing a
configuration of a friction damper,
0038 FIG. 5B is a schematic front view showing a con
figuration of the friction damper,0039 FIG. 6A is a plan view showing a configuration of amooring apparatus of the floating body according to the first
embodiment of the invention;

0040 FIG. 6B is a side view showing a configuration of
the mooring apparatus of the floating body according to thefirst embodiment of the invention;

0041 FIG. 7 is a diagram showing a configuration of a pairof mooring lines in the first embodiment of the invention;
0042 FIG. 8A is a plan view showing a configuration of aconventional tension mooring method;0043 FIG. 8B is a side view showing a configuration of
the conventional tension mooring method;0044 FIG.9 is a side view of essential portions showing a
structure of ayawing Suppressing apparatus of a wind turbine
according to a second embodiment of the invention;
0045 FIG. 10A is a schematic side view showing a con
figuration in a state where the yawing Suppressing apparatus
possessed by a floating offshore wind turbine according to thesecond embodiment of the invention receives wind;0046 FIG. 10B is a schematic side view showing a con
figuration in a state where the yawing Suppressing apparatus
possessed by the floating offshore wind turbine according to
the second embodiment of the invention does not receivewind;0047 FIG. 11 is a schematic perspective view showing a
configuration of a floating offshore wind turbine according toa third embodiment of the invention;

0048 FIG. 12 is a schematic perspective view showing a
configuration of the floating offshore wind turbine according
to the third embodiment of the invention; and0049 FIG. 13 is a schematic perspective view showing a
configuration of a floating offshore wind turbine according toa fourth embodiment of the invention.
EXPLANATION OF SYMBOLS

0050. 10, 40, 50, 60 floating offshore wind turbine0051) 11 rotor
0052 12 rotation shaft
0053 13 nacelle

0054
0055
005.6
0057.
0058
0059
0060
0061
0062
0063
0064
0065
0066

14 turning seated bearing (turning means)
15 tower (structure body)
16 yawing suppressing means
160 hydraulic damper
165 friction damper
20, 30 yawing suppressing apparatus
31 floating body
32 mooring line
41 structure body
42 turning means
44, 64 hydrodynamic damper
51A structure body upper portion
51B structure body lower portion

MODE FOR CARRYING OUT THE INVENTIONFirst Embodiment0069. A first embodiment of the present invention will beembodiment, a case where the invention is carried out as afloating offshore wind turbine will be described.
0070 FIG. 1 is a schematic perspective view showing a
configuration of the floating offshore wind turbine 10 accord
ing to the first embodiment. As shown in FIG. 1, the floating
offshore wind turbine 10 includes a floating body 31 provided
with a yawing Suppressing apparatus 20. The floating body
31 is moored to anchors 33 provided on a sea bottom B
through mooring lines 32. A line coming out from a lower
portion of the floating body 31 is an electric feederline 34. A
structure of the yawing Suppressing apparatus 20 possessedby the floating offshore wind turbine 10 of the embodimentwill be described with reference to FIG. 2.

0071 FIG. 2 is a side view of essential portions showing a
structure of the yawing Suppressing apparatus 20 of the windturbine 10 according to the first embodiment. As shown in
FIG. 2, the yawing Suppressing apparatus 20 is composed ofa rotor 11 which is rotated by wind, a nacelle 13 in which a
rotation shaft 12 of the rotor 11 is accommodated, a tower(structure body) 15 having a turning seated bearing (turningmeans) 14 which supports the nacelle 13 such that the nacelle
13 can turn with respect to a water Surface or a ground Surface,and a yawing Suppressing means 16 which Suppress yawingof the nacelle 13 with respect to the water surface.
(0072. The rotor 11 includes a hub 17 which is radiallyprovided with a plurality of blades 18, and the rotation shaft
12 connected to the hub 17. The rotation shaft 12 is rotatably
supported in the nacelle 13. If the rotor 11 receives wind, therotation shaft 12 rotates and a generator (not shown) provided
in the nacelle 13 generates electricity. A hollow arrow w in
FIG. 2 shows a wind direction. In the yawing Suppressing
apparatus 20 of the embodiment, the rotor 11 is provided ona leeward side as compared with the nacelle 13. According tothis configuration, it is possible to effectively generate a socalled weathercock effect in which a side view direction of therotation shaft 12 conforms to a wind direction by yawing of
the nacelle 13 provided on the turning seated bearing 14.
0073. The rotation shaft 12 rotates upon receiving wind W.
and the rotation shaft 12 is accommodated in the nacelle 13.

The nacelle 13 also includes electricity generating means (notshown). Such as a gear box (not shown) which increases a
rotation speed of the rotation shaft 12 and transmits the rotation to the generator, possessed by a wind turbine device. The
nacelle 13 is supported by the turning seated bearing 14
provided on the tower 15 such that the nacelle 13 can turn ina direction parallel to a sea surface P. According to this con
figuration, a direction of the rotation shaft 12 can be varied byyawing of the nacelle 13 in accordance with change in a winddirection W. and a rotation plane of the blades 18 of the rotor
11 can be in contradiction to wind.

0074. When a force in the vertical direction is applied bywaves while the rotor 11 is rotating, the yawing Suppressingmeans 16 Suppresses yawing of the nacelle 13 generated by agyro effect. Attention is paid to the yawing of the nacelle 13
caused by the gyro effect, the yawing Suppressing means 16 isprovided. Since the yawing Suppressing means 16 can Sup

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press the yawing of the nacelle 13, it becomes possible toenhance power generating efficiency of the floating offshore
wind turbine 10 and to enhance endurance of devices thereof.

Although the tower 15 is provided with the yawing suppress
ing means 16 in this embodiment, instead thereof, the nacelle
13 may be provided with the yawing Suppressing means 16.
0075 When the yawing suppressing apparatus 20 is pro
vided on a wind turbine apparatus on land instead of thefloating offshore wind turbine 10, the nacelle 13 is supportedby the turning seated bearing 14 Such that it can turn withrespect to a ground Surface. If moment in the vertical direction
is applied for any reason, the yawing Suppressing means 16
can suppress yawing of the nacelle 13. The above-describedweathercock effect is also of assistance in reducing a load of
the yawing Suppressing means 16.
0076 Next, a mechanism for generating yawing in thenacelle 13 of the floating offshore wind turbine 10 by the gyro
effect on the ocean will be described with reference to FIGS.

1 and 3. If a rotating object (Substance) rotates in a direction
cross at right angles to a rotation axis, moment acts in direc
tions intersecting with each other at right angles. This
moment is called gyro moment. An effect for generating the
gyro moment is called a gyro effect.
0077(2xL=T

0078 S2: angular velocity of pitching motion
0079 L: angular momentum of rotating object
0080 T. gyro moment0081. When the rotor 11 is rotating motion L, if motion
generating a restoring force via yawing of the floating body
31 by waves of a sea surface P is generated, whereby apitching S2 is generated, the rotor 11 yaws in the verticaldirection cross at rightangles to the rotation axis S. According
to this, gyro moment acts in the horizontal direction cross atright angles to both the rotation axis S of the rotor 11 and thevertical direction. In the floating offshore wind turbine 10,
since the nacelle 13 can turn by the turning seated bearing 14.
yawing of the nacelle 13 is generated in a direction shown by
T in FIG. 1 by this gyro moment.
0082 FIG. 3 shows a relation between change in a winddirection on the ocean and a deflection angle of the floating
body on water caused by influence of waves, wherein (a) is agraph showing change in a wind direction and (b) is a graphshowing change in a deflection angle. Portions surrounded bybroken lines in the graph (a) as well as the graph (b) showchange during one hour. If the graphs (a) and (b) of FIG.3 arecompared with each other, it can be found that change in awind direction is generated while taking a long time, andchange in a deflection angle caused by influence of waves isgenerated in a short time. That is, a turning speed of thenacelle 13 caused by change in a wind direction is slow, anda speed of yawing of the nacelle 13 caused by a gyro effectcaused due to influence of waves and so on is fast.

0083. Since the deflection angle caused by the influence ofwaves is varied with the short period, yawing of the nacelle 13
is induced by the gyro effect. The yawing of the nacelle 13
adversely affects the power generating efficiency of the windturbine and endurance of the devices.

0084. To selectively suppress yawing of the nacelle 13
caused by the gyro effect while allowing the nacelle 13 to turn
as a wind direction is varied, it is preferable that means whose
resistance is varied in accordance with a turning speed of thenacelle 13 is used as the yawing Suppressing means 16.
According to this, a so-called weathercock effect can beexerted without generating an attenuation effect for slow

Oct. 17, 2013

yawing of the nacelle 13 Supported by the turning seatedbearing 14 caused by change in a wind direction which isvaried while taking a relatively long time. It is possible toallow an attenuation effect to exert for yawing of the nacelle
13 which is caused by waves with a short period, and thus, it
is also possible to selectively inhibit yawing of the nacelle 13.
I0085. Since the floating offshore wind turbine 10 of theembodiment can suppress the yawing of the nacelle 13 by the
yawing Suppressing means 16, it becomes possible to Suppress the adverse influence.
I0086. If the yawing suppressing apparatus 20 including
the yawing Suppressing means 16 is used, it is possible torestrain yawing from generating in the nacelle 13 by a gyro
effect caused by pitching of the floating body 31 caused bywaves. Further, by Suppressing the yawing of the nacelle 13,
it is also possible to Suppress pitching of the floating body 31
caused by reaction of the gyro effect.
I0087 FIGS. 4A to 4C schematically show a configurationof a hydraulic damper, wherein FIG. 4A is a perspective view,
FIG. 4B is a front view and FIG. 4C is a sectional view taken

along an arrow A-A in FIG. 4B. As shown in these drawings,
the hydraulic damper 160 includes a rotation body 163 and oil
164 in its interior surrounded by a body case 161 and a cap
162. The hydraulic damper 160 utilizes a braking force gen
erated by viscosity resistance of the oil 164. By adjusting a
gap between the body case 161 and the rotation body 163, a
contact area of the oil 164 and viscosity of the oil 164, it ispossible to vary a braking torque (resistance) with respect torotation of the rotation body 163. There is such a relation
between a rotation speed and a braking torque of the rotationbody 163 that if the rotation speed is increased, the braking
torque is increased, and if the rotation speed is reduced, thebraking torque is also reduced.
I0088. If the hydraulic damper 160 is used, since it utilizes
the viscosity resistance of oil 164, there is a merit that changewith time of characteristics Such as wearing is Small. It is
possible to reduce influence of change in Viscosity caused bya temperature by selecting a kind of oil 164, but it is possiblethat when wind is strong, heat of oil 164 is lost, its viscosity is
increased and the braking torque is increased by taking a
constitution of cooling oil 164 by wind as an example.
I0089 FIGS. 5A and 5B schematically show a configuration of a friction damper, wherein FIG. 5A is a perspective
view and FIG. 5B is a front view. As shown in these drawings,
the friction damper 165 includes afriction material 167 whichis in contact with an outer surface of a rotation shaft 166, arotation shaft-connecting material 168 which surrounds thefriction material 167, and an elastic body 169 which pushes
the rotation shaft-connecting material 168 in a predetermined
direction. The friction damper 165 utilizes a braking force
generated by friction resistance between the rotation shaft
166 and the friction material 167. By adjusting friction resis
tance and contact areas between the rotation shaft 166 and thefriction material 167, it is possible to vary a braking torque(resistance). There is such a relation between a rotation speed
and a braking torque of the rotation shaft 166 that if therotation speed is increased, the braking torque is increased,
and if the rotation speed is reduced, the braking torque is also
reduced.

(0090. When the friction damper 165 is used, there are
merits that a sealing portion is unnecessary and thus theconfiguration can be simplified, and in an environment that an
ambient temperature is largely varied, characteristics canrelatively stably be maintained. Even if a size of the friction

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material 167 is varied due to wearing, a braking force canconstantly be maintained correspondingly by means of a bias
ing force of the elastic body 169. That is, even if the size of thefriction material 167 is varied due to friction, the elastic body
169 biases the friction material 167 and friction resistance
between the rotation shaft 166 and the friction material 167

can constantly be maintained.
0091. The floating body 31 is moored to the anchors 33
provided on the sea bottom B by means of the mooring lines
32 in water by a mooring method of restraining the floating
body 31 from rotating around the center axis. Hence, rotationof the floating body 31 in water is suppressed. This mooring
method will be described later.

0092. There is a floating offshore wind turbine including
an apparatus which actively controls rotation of the nacelle toconform to a wind direction. In this facility, a wind turbine is
temporalily fixed to the floating body and held at a position
conforming to the wind direction, i.e., a position where arotation plane is in contradiction to wind. Hence, the floating
body tries to rotate around a vertical rotation axis by gyro
moment caused by a gyro effect of the rotor of the windturbine. Therefore, a mooring method which suppreses rotation motion of the floating body around its center axis Suppresses this yawing. According to this, it is possible to Suppress the adverse influence on the power generating efficiencyof the floating offshore wind turbine and endurance of thedevices thereof.

0093. However, there is another floating offshore windturbine of a method in which the apparatus which actively
controls rotation of the nacelle is omitted and a nacelle ismade to conform to a wind direction by a weathercock effect.
In such a facility, a rotation shaft of a rotor of a wind turbine
is supported such that the rotation shaft can freely turn withrespect to a floating body. Hence, even if yawing of thefloating body is Suppressed, yawing caused by a gyro effectgenerated in the nacelle can not be suppressed. Therefore, inthe floating offshore wind turbine 10 of this embodiment, theyawing Suppressing means 16 is provided, thereby Suppress
ing the yawing generated in the nacelle 13 by the gyro effect.
0094. The mooring method of restraining the floating
body 31 from rotating around its rotation axis will be
described with reference to FIGS. 6A, 6B and 7.

0095 FIGS. 6A and 6B show a configuration of a mooringapparatus of the floating body according to the first embodi
ment, wherein FIG. 6A is a plan view and FIG. 6B is a sideview. Here, in FIG. 6A, the mooring apparatus of the floating
body is projected onto a horizontal plane. One ends of theplurality of mooring lines 32 are connected to the floating
body 31. The other ends of the mooring lines 32 are connectedto the anchors 33 provided in water.
0096. The floating body 31 is formed into a substantially
cylindrical shape. A pair of mooring lines composed of thetwo mooring lines 32 is used. One ends of the two mooringlines 32 are connected to two points on a circumference of acircle of the substantially cylindrical shape when the floating
body 31 is projected onto the horizontal plane. The two moor
ing lines 32 are formed into Substantially tangent lines of thecircle, and the mooring lines 32 extend on the same side.
According to this, it is possible to avoid a case where when theyawing Suppressing means 16 Suppresses yawing, a force isapplied to the floating body 31 and yawing is generated in the
floating body 31.
0097 FIG.7 shows a relation between the floating body 31
and the two mooring lines 32 connected to lower rightOct. 17, 2013

anchors 33 in the plan view (projection view on horizontal
plane) of FIG. 6A. One ends of the two mooring lines 32 areconnected to points A and B on the circumference of thefloating body 31. The mooring lines 32 are formed into tan
gent lines L1 and L2 in the points A and B.
0098. In this configuration, when rotation around a center
C of the floating body 31 is generated in the floating body 31,
one of the two mooring lines 32 extends and a tensile force
acts. When a radius of the floating body 31 is defined as randa rotation angle of the floating body 31 is defined as A0, an
extension amount AL of the mooring line 32 on the extension
side in this plan view is obtained by the following equation(1):
AL=rxA0(1)0099. In this case, if a spring rate of the mooring line 32 isdefined as k, a tensile force T of the floating body 31 in atangential direction is obtained by the following equation (2)by Hooke's law:
0100. A torque N generated by this extension is obtainedby the following equation (3):
N=T.

(3)

0101 If configurations of the two mooring lines 32 are asshown in FIG. 7, a torque which rebels against rotation can begenerated irrespective of a rotation direction. Hence, rotationof the floating body 31 is suppressed.
0102) In FIGS. 6A and 6B, the mooring lines 32 areformed into the tangent lines L1 and L2 in FIG. 7. However,
it is apparent that even if the mooring lines 32 are formed into
L3 and L4 (broken lines) in FIG. 7, the same effect can beexerted.

0103 FIGS. 8A and 8B show a configuration of a conventional simple tension mooring method. It is apparent that
motion (floating motion) of the floating body 31 in the hori
Zontal direction is Suppressed by mooring lines 32 whichradially extend in three directions shown in FIG.8. However,in the plan view (FIG. 8A), since an angle formed between arotation direction (circumferential direction) of the floating
body 31 and the mooring line 32 is substantially 90°, it isdifficult to Suppress the rotation. Hence, the mooring method
shown in FIGS. 8A and 8B does not suppress rotation of thefloating body 31 around its center axis.
Second Embodiment

0104. A second embodiment of the invention will be
described below with reference to FIG.9. Ayawing suppress
ing apparatus of a wind turbine of the second embodiment isdifferent from the yawing Suppressing apparatus of the first
embodiment in a configuration where a coning angle is given
to a rotor. The same numbers are allocated to the members

described in the first embodiment, and explanation thereof
will be omitted in the second embodiment.

0105 FIG. 9 is a side view of essential portions showing a
structure of the yawing Suppressing apparatus 30 of the windturbine according to the second embodiment. As shown in
FIG.9, according to the yawing Suppressing apparatus 30 of
the embodiment, a nacelle 13 is provided on a windward side
as compared with a rotor 11. A coning angle C. is given to therotor 11. Here, the coning angle C. is an angle between astraight line which connects a connected portion 18A of ablade 18 with respect to a hub 17 and a tip end 18B and whichUS 2013/0272846 A1

is shown by an alternate long and short dash line and a verticalline V shown by an alternate long and short dash line in thedrawing.
0106. According to this configuration, the nacelle 13 Sup
ported by a turning seated bearing 14 is automatically turnedin accordance with change of a wind direction W in a state
where the nacelle 13 can freely turn in the horizontal direction, and a weathercock effect for conforming a rotation shaft
12 of a rotor 11 to the wind direction can be enhanced. Whenan axial direction of the rotation shaft 12 and a wind direction

conform to each other, a rotation plane of the rotor 11, i.e., aplane formed by a locus of the tip end 18B of the blade 18 isperpendicular to the wind direction Substantially at rightangles. If the weathercock effect is enhanced, a load of yaw
ing Suppressing means 16 is further reduced.
0107. When the present invention is carried out as thefloating offshore wind turbine (see FIG. 1) including theyawing Suppressing apparatus 30, it is preferable to employ
such a configuration that the rotation shaft 12 of the rotor 11
in an electricity generating state where the rotation shaft 12
receives wind and inclines is located on a horizontal plane H.
This configuration will be described with reference to FIGS.
10A and 10B.

0108 FIGS. 10A and 10B schematically show a configu
ration of the yawing Suppressing apparatus 30 provided in the
floating offshore wind turbine of the embodiment, wherein
FIG. 10A is a side view in a state where wind is received and
FIG. 10B is a side view in a state where wind is not received.

As shown in FIG. 10A, according to the yawing Suppressing
apparatus 30 of the embodiment, the rotation shaft 12(straight line in the axial direction is shown by S) of the rotor
11 in the electricity generating state where the rotation shaft
12 receives wind and inclines is located on the horizontal

plane H. According to this, a direction of the rotation axis of
the rotation shaft 12 can conform to the wind direction W(both of them can be parallel to each other). Hence, in the state
where wind is not received as shown in Fig. 10B, the nacelle
13 is supported by a tower 15 such that the rotation shaft 12(straight line S) of the rotor 11 forms a predetermined angle B
with respect to the horizontal plane H.
0109 The predetermined angle B may be set based on themost general wind speed so that power generating efficiencyof the floating offshore wind turbine becomes excellent. Further, control means of the predetermined angle B which varies
the predetermined angle B such that the predetermined angle
B becomes the optimal angle in accordance with a wind speed
may be provided.
0110. The configuration described with reference to FIGS.
10A and 10B can also be used in the floating offshore windturbine using the yawing Suppressing apparatus 20 describedin the first embodiment.
Third Embodiment0111. A third embodiment of the invention will be
described below with reference to FIGS. 11 and 12. In thethird embodiment, a case where the invention is carried out asa floating offshore wind turbine will be described. The same
numbers are allocated to the members described in the first or

second embodiment, and explanation thereof will be omitted
in the third embodiment.

0112 FIG. 11 is a schematic perspective view showing a
configuration of a floating offshore wind turbine 40 according
to the third embodiment. As shown in FIG. 11, the floating
offshore wind turbine 40 is configured such that a nacelle 13

Oct. 17, 2013

and a structure body 41 are integrally formed together so thatthe nacelle 13 does not turn with respect to the structure body
41. The structure body 41 floats on water, the nacelle 13 is
fixed to an upper end of the structure body 41, and a lower endof the structure body 41 is connected to anchors 43 provided
on a sea bottom B through turning means 42. The turningmeans 42 is for connecting the structure body 41 to theanchors 43 such that the structure body 41 can turn in accor
dance with change in the wind direction W. and the turningmeans 42 makes the structure body 41 exert a weathercock
effect.

0113 Hydrodynamic dampers 44 are provided on an outerside of the structure body 41. The structure body 41 is mooredby a mooring method which does not suppress rotation of thestructure body 41 around its center axis. By locating thehydrodynamic dampers 44 in water, a function as yawing
Suppressing means can be exerted. That is, resistance of eachof the hydrodynamic dampers 44 having a blade shape against
water becomes smaller with respect to slow yawing of thestructure body 41 and becomes greater with respect to fast
yawing. Hence, it is possible to selectively attenuate andSuppress the yawing of the structure body 41 caused by a gyro
effect which is fast yawing. By providing the structure body
41 with the hydrodynamic dampers 44 in this manner, it ispossible to Suppress yawing of the structure body 41 caused
by a gyro effect. To Suppress yawing of the structure body 41,
the structure body 41 may be provided with the hydraulicdamper 160 (see FIGS. 4A to 4C) or the friction damper 165(see FIGS.5A and 5B). It is also possible to moor the structure body 41 also using another mooring method which does
not suppress rotation of the structure body 41 around its
center axis by means of mooring lines.
0114. Although the hydrodynamic dampers 44 are applied
to the floating offshore wind turbine in the third embodiment,
it is also possible to apply the hydrodynamic dampers 44 to awind turbine installed on the ground for example. In this case,turning means is Supported in a state where the structure body
floats in water in a pool such that the structure body can turnwith respect to a ground Surface, and the water in the poolprovided in a periphery and the hydrodynamic dampers 44 aremade to mutually interfere. According to this, the hydrody
namic dampers 44 can exert function as yawing Suppressingmeans also in the wind turbine installed on the ground.
0115 FIG. 12 is a schematic perspective view showing a
configuration of a floating offshore wind turbine 50 having a
configuration different from that of the floating offshore windturbine 40 according to the third embodiment. As shown in
FIG. 12, in the floating offshore wind turbine 50, an upper
portion 51A of a structure body 51 and the nacelle 13 areintegrally formed together, and the turning means 42 is pro
vided between the structure body upper portion 51A and astructure body lower portion 51B. The structure body lower
portion 51B located lower than the turning means 42 is fixed
to the anchors 43 on the sea bottom B through a plurality ofmooring lines 54.
0116. According to this configuration, since the structure
body upper portion 51A can turn in accordance with changeof the wind direction W by the turning means 42, it is possible
to exert a weathercock effect. The yawing Suppressing means
16 provided in the structure body 51 can suppress yawing of
the nacelle 13 by a gyro effect. It is also possible to moor the
structure body upper portion 51A also using another mooring
method which does not suppress rotation around a center axisby means of mooring lines.

US 2013/0272846 A1

Oct. 17, 2013

be described. The same numbers are allocated to the members

restrain the floating body 31 from generating yawing by thehydrodynamic dampers 64. The hydrodynamic dampers 64
generate a hydrodynamic effect by interference with surrounding fluid and exert a function as yawing Suppressingmeans. Hence, a shape of a cross section of the structure bodyitself may be an angular shape or a shape having many con
cavo-convex portions.

described in the first to third embodiments, and explanation

INDUSTRIAL APPLICABILITY

Fourth Embodiment0117. A fourth embodiment of the invention will be
described below with reference to FIG. 13. In the fourth

embodiment, a configuration in which a floating offshore
wind turbine is moored by a mooring method that does not
Suppress rotation of a floating body around its center axis will
thereof will be omitted in the fourth embodiment.

0118 FIG. 13 is a schematic perspective view showing a
configuration of a floating offshore wind turbine according to
the fourth embodiment. As shown in FIG. 13, a floating body
31 of a floating offshore wind turbine 60 of the fourth embodi
ment is moored to a sea bottom B by mooring lines 32 bymeans of a so-called catenary method. Therefore, the floating
body 31 can yawing around its center axis to some extent.
That is, the floating body 31 is moored by a mooring method
not Suppressing rotation around its center axis. Hence, even if
the yawing Suppressing means 16 constrains yawing of anacelle 13 with respect to the floating body 31 generated by agyro effect, the floating body 31 can yawing around its center
axis to some extent. As a result, the mooring lines 32 can not
suppress the yawing of the nacelle 13. However, the floating
body 31 of the floating offshore wind turbine 60 is provided
with a plurality of blade-shaped hydrodynamic dampers 64.
The hydrodynamic dampers 64 can restrain the floating body
31 from generating the yawing.
0119 When the floating offshore wind turbine is mooredby the mooring method which does not suppress rotation of
the floating body around its center axis, if the yawing Suppressing means 16 which is for Suppressing yawing of thenacelle 13 in the turning seated bearing 14 and the hydrody
namic dampers 64 which are for Suppressing yawing of thefloating body 31 are combined with each other, it is effective
for Suppressingyawing of the nacelle 13 and the floating body
31 caused by a gyro effect.
0120. In the floating offshore wind turbine 60 of the fourth
embodiment, the two hydrodynamic dampers 64 are disposed
Such that they are opposed to each other through the floating
body 31. That is, a line connecting mounted portions of thetwo hydrodynamic dampers 64 to the floating body 31 passes
a Substantially center of a cross section which is parallel to ahorizontal plane of the floating body 31. This is because thatthe hydrodynamic dampers 64 are provided not for Suppress
ing pitching of the floating body 31 but for Suppressing yaw
ing of the floating body 31. That is, the hydrodynamic damp
ers 64 of the floating offshore wind turbine 60 are provided sothat the hydrodynamic dampers 64 interfere with outside
water and become resistance of yawing of the floating body
31. Therefore, it is unnecessary to provide three or morehydrodynamic dampers 64 unlike a case where the hydrody
namic dampers 64 are provided for Suppressing the pitching.
Hence, even if the number of hydrodynamic dampers 64 isone, the same function is exerted. However, since the samefunction is exerted eve if the number of the hydrodynamic
dampers 64 is three or more, the number of the hydrodynamic
dampers 64 may be three or more.
0121. In the fourth embodiment, even if an apparatus
which actively controls rotation of the nacelle is provided
instead of the yawing Suppressing means 16, it is possible to0.122 The present invention can be utilized as an apparatus
for enhancing power generating efficiency of a wind turbine
and endurance of devices thereof. Especially, the invention isuseful for enhancing power generating efficiency of a floating
offshore wind turbine and endurance of devices thereof.

1. A floating, offshore wind turbine which generates elec
tricity using a floating body as a portion of a structure body on
Ocean,

comprising a rotor which is rotated by wind, a nacelle inwhich at least a rotation shaft of the rotor is accommo

dated, the structure body including turning means which
Supports the nacelle Such that the nacelle can turn withrespect to a water Surface, and yawing Suppressingmeans which Suppresses yawing of the nacelle withrespect to the water Surface andusing a hydrodynamic damper which suppresses yawing
by mutual interference between a shape or a structure of
the structure body and peripheral fluid as the yawing
Suppressing means.
2. The floating offshore wind turbine according to claim 1
wherein the nacelle is provided on a windward side as com
pared with the rotor.
3. The floating offshore wind turbine according to claim 2,
wherein a coning angle is given to the rotor.
4. The floating offshore wind turbine according to claim 1,
wherein a hydraulic damper is further provided as the yawing
Suppressing means.
5. The floating offshore wind turbine according to claim 1,
wherein a friction damper is further provided as the yawing
Suppressing means.
6. (canceled)
7. (canceled)
8. The floating offshore wind turbine according to claim 1,
wherein the floating body is moored by mooring lines.
9. The floating offshore wind turbine according to claim 8.
wherein the floating body is formed into a substantially cylin
drical shape, a pair of mooring lines composed of two moor
ing lines whose one ends are connected to two points on acircumference of a circle of the substantially cylindricalshape when the floating body is projected onto a horizontal
plane is used as the mooring method, and the two mooringlines are formed into Substantially tangent lines of the circle
and extend on the same side.

10. The floating offshore wind turbine according to claim
1, wherein the nacelle is supported by the structure body suchthat a predetermined angle is formed between a horizontal
plane and the rotation shaft of the rotor in a state where wind
is not received so that the rotation shaft of the rotor in a state

where wind is received becomes parallel to a wind direction.
k

k

k

k

k