U.S. patent application number 09/804887 was filed with the patent office on 2001-09-20 for frictional resistance reducing vessel and a method of reducing frictional resistance of a hull.
This patent application is currently assigned to Ishikawajima-Harima Heavy Industries Co., Ltd.. Invention is credited to Takahashi, Yoshiaki.
Application Number | 20010022152 09/804887 |
Document ID | / |
Family ID | 27531447 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022152 |
Kind Code |
A1 |
Takahashi, Yoshiaki |
September 20, 2001 |
Frictional resistance reducing vessel and a method of reducing
frictional resistance of a hull
Abstract
The object of the present invention is to provide a frictional
resistance reducing vessel and method of reducing the frictional
resistance of a hull that are able to effectively conserve energy
consumed during operation by reducing frictional resistance at a
low level of energy consumption. In the present invention, a
negative pressure region (51), which is at low pressure relative to
a gaseous space, is formed in the water accompanying operation of a
hull (30), and together with bubbles being guided to this negative
pressure region (51) in the water from the gaseous space, the state
of this negative pressure region (51) is changed based on changes
in vessel velocity.
Inventors: |
Takahashi, Yoshiaki; (Tokyo,
JP) |
Correspondence
Address: |
PEARNE & GORDON LLP
526 SUPERIOR AVENUE EAST
SUITE 1200
CLEVELAND
OH
44114-1484
US
|
Assignee: |
Ishikawajima-Harima Heavy
Industries Co., Ltd.
|
Family ID: |
27531447 |
Appl. No.: |
09/804887 |
Filed: |
March 13, 2001 |
Current U.S.
Class: |
114/67A |
Current CPC
Class: |
B63B 1/34 20130101; Y02T
70/10 20130101; B63B 1/38 20130101 |
Class at
Publication: |
114/67.00A |
International
Class: |
B63B 001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2000 |
JP |
P2000-071213 |
May 22, 2000 |
JP |
P2000-150654 |
May 31, 2000 |
JP |
P2000-163610 |
Sep 5, 2000 |
JP |
P2000-269281 |
Sep 8, 2000 |
JP |
P2000-274068 |
Claims
What is claimed is:
1. A frictional resistance reducing vessel that reduces frictional
resistance of a hull by releasing bubbles onto the submerged
surface of a hull, provided with: a negative pressure forming
portion arranged protruding from said submerged surface that forms
a negative pressure region in the water which is at low pressure
relative to a gaseous space; an air outlet for releasing bubbles
towards said negative pressure region; a flow path of which one end
is open to a gaseous space and the other end is open into the water
via said air outlet; and, a drive mechanism that changes at least
one of the protruding state of said negative pressure forming
portion from said submerged surface, the opening surface area of
said air outlet, and the flow path cross-sectional surface area of
said flow path.
2. The frictional resistance reducing vessel according to claim 1
that is also provided with a control apparatus that controls said
drive mechanism based on changes in vessel speed.
3. A method of reducing frictional resistance of a hull by
releasing bubbles onto the submerged surface of a hull; wherein, a
negative pressure region at a low pressure relative to a gaseous
space is formed in the water accompanying vessel operation, and
together with a gas being led from the gaseous space to the
negative pressure region in the water, the state of said negative
pressure region is changed based on changes in vessel speed.
4. A frictional resistance reducing vessel that reduces the
frictional resistance of a hull by releasing bubbles onto the
submerged surface of a hull, provided with: an outer cylindrical
portion of which one end is open to the atmosphere and the other
end is open in the water; an inner cylindrical portion, which
together with being installed in the state of being inserted into
the outer cylindrical portion, one end is open to the atmosphere
and the other end is open into the water; and, an asymmetrical air
blowing portion provided on the other end of said inner cylindrical
portion protruding from said submerged surface, the protruding
state of which is in the lengthwise direction of the hull.
5. The frictional resistance reducing vessel according to claim 4
that is also provided with a protrusion adjustment means for
adjusting the protruding state of said air blowing portion.
6. The frictional resistance reducing vessel according to either of
claims 4 of 5 wherein, the cross-sectional shapes of said outer
cylindrical portion and said inner cylindrical portion are
isosceles triangles.
7. A frictional resistance reducing vessel that reduces the
frictional resistance of a hull by releasing bubbles onto the
submerged surface of a hull, provided with: a negative pressure
forming portion arranged protruding from said submerged surface so
that cavitation occurs in the water behind it due to the relative
flow of water with respect to the hull during operation; a
discharge outlet provided behind said negative pressure forming
portion; and, a flow path of which one end is open to a gaseous
space and the other end is open into the water via said discharge
outlet.
8. A frictional resistance reducing vessel that reduces the
frictional resistance of a hull by releasing bubbles onto the
submerged surface of a hull, provided with: an indentation formed
so as to be recessed from the submerged surface; a negative
pressure forming member, which together with being supported to as
to rotate freely inside said indentation, forms a negative pressure
region in the water at a low pressure relative to a gaseous space
by having at least a portion protrude from said submerged surface;
a flow path for guiding air from the gaseous space to the negative
pressure region in the water, one end of which being open to the
gaseous space, and the other end being open into said indentation;
and, an angle adjusting mechanism for causing at least a portion of
said negative pressure forming member to protrude in a prescribed
state from said submerged surface that supports said negative
pressure forming member and adjusts the angle of said negative
pressure forming member.
9. A frictional resistance reducing vessel that reduces the
frictional resistance of a hull by releasing bubbles onto the
submerged surface of a hull, provided with: an indentation provided
in said submerged surface; a flow path of which one end is open to
the atmosphere and the other end is open to the inside of said
indentation; a wing body having a wing that is arranged within said
indentation; and, a positioning mechanism that supports said wing
body in a prescribed direction while allowing to move freely and
positions said wing at a prescribed position; said positioning
mechanism positioning said wing so that the inside of said
indentation is open relative to the flow of water and results in
negative pressure relative to the atmosphere during reduction of
frictional resistance.
10. The frictional resistance reducing vessel according to claim 9
wherein, said positioning mechanism positions said wing so that the
lower surface of said wing is at roughly the same height as said
submerged surface during times other than when reducing frictional
resistance.
11. The frictional resistance reducing vessel according to either
of claims 9 or 10 wherein, said switching mechanism has an
operational means that allows the position of said wing to be
freely manipulated from the deck.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a frictional resistance
reducing vessel that reduces the frictional resistance of the hull,
and more particularly, to improving the total energy efficiency by
efficiently releasing bubbles into the water.
[0003] 2. Description of the Prior Art
[0004] A method has been proposed in the prior art for the purpose
of conserving energy consumed during operation of marine vessels
and so forth that consisted of reducing frictional resistance
between the hull and the water by feeding a gas into the water and
juxtaposition of a large number of microbubbles in the vicinity of
the surface of the hull shell plate (submerged surface).
[0005] Technologies for generating microbubbles in water are
proposed in Japanese Unexamined Patent Application, First
Publication No. 50-83992, Japanese Unexamined Patent Application,
First Publication 53-136289, Japanese Unexamined Patent
Application, First Publication 60-139586, Japanese Unexamined
Patent Application, First Publication 61-71290, Japanese Unexamined
Utility Model Application, First Publication No. 61-39691 and
Japanese Unexamined Utility Model Application, First Publication
No. 61-128185.
[0006] In these technologies, air pressurized by a pump, blower or
other pressurization apparatus is blown into the water from a
plurality of holes or a porous plate provided in the hull.
[0007] The present applicant has proposed a technology for
juxtaposition of microbubbles on the shell plate of a hull by
feeding a gas (such as air) into the water from a delivery outlet
provided in, for example, the vicinity of the bow, as such a
technology pertaining to reducing frictional resistance. This
technology attempts to cover the hull shell plate with microbubbles
as a result of dispersing microbubbles along the lines of flow of
water over the hull shell plate by feeding a gas from a delivery
outlet. When this gas is fed into the water, a gas supply apparatus
such as a blower is used as the motive power source.
[0008] However, in the case of blowing a gas into water using such
an apparatus, since a new motive power is required to operate the
apparatus, the amount of motive power conserved during operation as
a result of reduction by microbubbles ends up being lost. At
locations of comparatively large water depths, such as the bottom
of a large ship, in particular, it is necessary to pressurize the
gas to a high pressure corresponding to the water pressure
(hydrostatic pressure) when blowing the gas into the water, thereby
resulting in the consumption of a large amount of energy. In
addition, in the installation of the apparatus in the hull, huge
costs are incurred, such as equipment costs and installation costs.
Moreover, since the composition of the apparatus is comparatively
complex, the apparatus is expensive and its maintenance and
inspection are not easy.
[0009] In consideration of the above circumstances, the objects of
the present invention consist of the following:
[0010] (1) to effectively conserve energy consumption during
operation by reducing frictional resistance with a low level of
energy consumption;
[0011] (2) to effectively reduce frictional resistance by
efficiently mixing bubbles into the water;
[0012] (3) to reduce hull construction costs; and,
[0013] (4) to simplify maintenance and inspection.
SUMMARY OF THE INVENTION
[0014] The present invention employs the following means to achieve
the above objects.
[0015] Namely, the present invention is characterized by being a
frictional resistance reducing vessel that reduces frictional
resistance of a hull by releasing bubbles onto the submerged
surface of a hull; provided with a negative pressure forming
portion arranged protruding from the submerged surface that forms a
negative pressure region in the water which is at low pressure
relative to a gaseous space; an air outlet for releasing bubbles
towards the negative pressure region; a flow path of which one end
is open to a gaseous space and the other end is open into the water
via the air outlet; and, a drive mechanism that changes at least
one of the protruding state of the negative pressure forming
portion from the submerged surface, the opening surface area of the
air outlet, and the flow path cross-sectional surface area of the
flow path.
[0016] This frictional resistance reducing vessel is also
preferably provided with a control apparatus that controls the
drive mechanism based on changes in vessel speed.
[0017] In addition, the method of reducing frictional resistance of
a hull as claimed in the present invention is characterized as
being a method of reducing the frictional resistance of a hull by
releasing bubbles onto the submerged surface of a hull; wherein, a
negative pressure region at a low pressure relative to a gaseous
space is formed in the water accompanying vessel operation, and
together with a gas being led from the gaseous space to the
negative pressure region in the water, the state of the negative
pressure region is changed based on changes in vessel speed.
[0018] In addition, the present invention is characterized by being
a frictional resistance reducing vessel that reduces the frictional
resistance of a hull by releasing bubbles onto the submerged
surface of a hull; provided with an outer cylindrical portion of
which one end is open to the atmosphere and the other end is open
in the water; an inner cylindrical portion, which together with
being installed in the state of being inserted into the outer
cylindrical portion, one end is open to the atmosphere and the
other end is open into the water; and, an asymmetrical air blowing
portion provided on the other end of the inner cylindrical portion
protruding from the submerged surface, the protruding state of
which is in the lengthwise direction of the hull.
[0019] This frictional resistance reducing vessel is also
preferably provided with a protrusion adjustment means for
adjusting the protruding state of the air blowing portion.
[0020] In addition, the cross-sectional shapes of the outer
cylindrical portion and inner cylindrical portion are preferably
isosceles triangles.
[0021] In addition, the present invention is characterized by being
a frictional resistance reducing vessel that reduces the frictional
resistance of a hull by releasing bubbles onto the submerged
surface of a hull; provided with a negative pressure forming
portion arranged protruding from the submerged surface so that
cavitation occurs in the water behind it due to the relative flow
of water with respect to the hull during operation; a discharge
outlet provided behind the negative pressure forming portion; and,
a flow path of which one end is open to a gaseous space and the
other end is open into the water via said discharge outlet.
[0022] In addition, the present invention is characterized by being
a frictional resistance reducing vessel that reduces the frictional
resistance of a hull by releasing bubbles onto the submerged
surface of a hull; provided with an indentation formed so as to be
recessed from the submerged surface; a negative pressure forming
member, which together with being supported to as to rotate freely
inside this indentation, forms a negative pressure region in the
water at a low pressure relative to a gaseous space by having at
least a portion protrude from the submerged surface; a flow path
for guiding air from the gaseous space to the negative pressure
region in the water, one end of which being open to the gaseous
space, and the other end being open into said indentation; and, an
angle adjusting mechanism for causing at least a portion of the
negative pressure forming member to protrude in a prescribed state
from the submerged surface that supports the negative pressure
forming member and adjusts the angle of the negative pressure
forming member.
[0023] In addition, the present invention is characterized by being
a frictional resistance reducing vessel that reduces the frictional
resistance of a hull by releasing bubbles onto the submerged
surface of a hull; provided with an indentation provided in the
submerged surface; a flow path of which one end is open to the
atmosphere and the other end is open to the inside of said
indentation; a wing body having a wing that is arranged within said
indentation; and, a positioning mechanism that supports said wing
body in a prescribed direction while allowing to move freely and
positions the wing at a prescribed position; said positioning
mechanism positioning the wing so that the inside of the
indentation is open relative to the flow of water and results in
negative pressure relative to the atmosphere during reduction of
frictional resistance.
[0024] This positioning mechanism preferably positions the wing so
that the lower surface of the wing is at roughly the same height as
the submerged surface during times other than reduction of
frictional resistance.
[0025] In addition, the above switching mechanism preferably has an
operational means that allows the position of the wing to be freely
manipulated from the deck.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a drawing that explains the principle of the
method of reducing frictional resistance as claimed in the present
invention.
[0027] FIG. 2A is a side view schematically showing one embodiment
of a frictional resistance reducing vessel as claimed in the
present invention.
[0028] FIG. 2B is an enlarged cross-sectional view of the vicinity
of a bubble generator schematically showing one embodiment of a
frictional resistance reducing vessel as claimed in the present
invention.
[0029] FIGS. 3A, 3B and 3C are drawings showing the cross-sectional
shape of an air induction pipe.
[0030] FIGS. 4A and 4B are drawings for explaining the manner in
which the protruding height of the air induction pipe from the
submerged surface is changed.
[0031] FIG. 5 is a flow chart showing an example of a procedure for
changing the state of the negative pressure region in the
water.
[0032] FIG. 6A is a side view schematically showing one embodiment
of a frictional resistance reducing vessel as claimed in the
present invention.
[0033] FIG. 6B is an enlarged cross-sectional view of the vicinity
of a bubble generator schematically showing one embodiment of a
frictional resistance reducing vessel as claimed in the present
invention.
[0034] FIGS. 7A and 7B are drawings for explaining one example of a
method of reducing the frictional resistance of a hull by a
frictional resistance reducing vessel as claimed in the present
invention.
[0035] FIG. 8 is a perspective view showing the structure of
negative pressure forming portion 23 in FIG. 6B.
[0036] FIG. 9A is a side view of the starboard side in the vicinity
of the bow schematically showing one embodiment of a frictional
resistance reducing vessel as claimed in the present invention.
[0037] FIG. 9B is an overhead view as viewed from below of the
bottom of a vessel in the vicinity of the bow of the frictional
resistance reducing vessel shown in FIG. 9A.
[0038] FIG. 9C is a cross-sectional view taken along line A-A in
FIG. 9A.
[0039] FIG. 10A is a side view schematically showing one embodiment
of a frictional resistance reducing vessel as claimed in the
present invention.
[0040] FIG. 10B is an enlarged cross-sectional view of the vicinity
of a bubble generator schematically showing one embodiment of a
frictional resistance reducing vessel as claimed in the present
invention.
[0041] FIGS. 11A and 11B are drawings for explaining an example of
a method of reducing frictional resistance of a hull by a
frictional resistance reducing vessel as claimed in the present
invention.
[0042] FIG. 12 is a cross-sectional view taken along line B-B in
FIG. 10B.
[0043] FIG. 13A is a side view schematically showing one embodiment
of a frictional resistance reducing vessel as claimed in the
present invention.
[0044] FIG. 13B is an overhead view of the vessel bottom as viewed
from in the water schematically showing one embodiment of a
frictional resistance reducing vessel as claimed in the present
invention.
[0045] FIG. 14A is an enlarged cross-sectional view of the vicinity
of a bubble generator schematically showing one embodiment of a
frictional resistance reducing vessel as claimed in the present
invention.
[0046] FIG. 14B is an overhead view of the vessel bottom as viewed
from in the water showing the constitution of a wing body in a
frictional resistance reducing vessel as claimed in the present
invention.
[0047] FIGS. 15A and 15B are drawings for explaining an example of
a method of reducing the frictional resistance of a hull by a
frictional resistance reducing vessel as claimed in the present
invention.
[0048] FIG. 16 is a perspective view showing the constitution of a
wing body.
[0049] FIG. 17A is an overhead view of the vessel bottom as viewed
from in the water showing another embodiment of a frictional
resistance reducing vessel as claimed in the present invention.
[0050] FIG. 17B is a cross-sectional view taken along line C-C in
FIG. 17A.
BEST MODE FOR CARRYING OUT THE INVENTION
[0051] To begin with, an explanation is provided of the theory of
reducing the frictional resistance of a hull by the technology
claimed in the present invention with reference to FIG. 1. Here,
for the sake of convenience, the method of reducing frictional
resistance of a hull of the prior art in which a gas is pressurized
and blown into the water is referred to as the "positive pressure
method", while the method utilizing negative pressure as claimed in
the present invention is referred to as the "negative pressure
method". In addition, the same reference symbols are used for those
portions that are the same in the remaining drawings, and an
explanation of those portions will be omitted.
[0052] FIG. 1 is a drawing schematically showing frictional
resistance reducing vessel 10 as claimed in the present invention.
Reference symbol 11 indicates a hull shell plate (submerged
surface), 12 a negative pressure forming portion, 13 an air outlet,
14 a flow path and 15 the water surface (draft line).
[0053] When frictional resistance reducing vessel 10 operates at a
prescribed velocity V, water flow 20 is formed relative to the
hull. Moreover, this frictional resistance reducing vessel 10 forms
negative pressure region 21, which is at low pressure (negative
pressure, vacuum pressure) relative to a gaseous space (air), in
the water during operation. Namely, negative pressure region 21 is
formed in the water as a result of the flow state of the water
being changed by negative pressure forming portion 12 that
protrudes from hull shell plate 11. At this tine, the pressure of
air outlet 13 that faces negative pressure region 21 becomes lower
than the gaseous space (air), and the force of the pressure
gradient acts on the fluid (sea water and air) within flow path 14.
As a result, together with sea water being discharged from flow
path 14, air that has flowed in from the atmosphere flows through
flow path 14, and is fed into the water in the form of microbubbles
22.
[0054] When bubbles having a volume Qv are released at a location
at depth D (m) from a liquid surface in a static liquid of density
.rho. (the density of the bubbles is assumed to be zero), the
energy required for their release is represented with the following
equation:
E=(P-Pa)Qv (1)
[0055] where, Pa is the pressure of the gaseous space (atmospheric
pressure) and P is the pressure at the location where the bubbles
are released (=.rho.gh, where g is gravitational acceleration).
[0056] At this time, if the flow rate in the vicinity of air outlet
13 on the vessel bottom is taken to be V.sub.1, then the pressure P
at that location is represented with the following equation:
P=Pa-.rho.(V.sub.1.sup.2-V.sup.2)/2+.rho.gD (2)
[0057] Furthermore, although flow rate V.sub.1 changes according to
the release of bubbles to a boundary layer, this change is ignored
here.
[0058] As is clear from equation (1), in the case pressure P at the
location where bubbles are released is low in comparison with
atmospheric pressure Pa, namely when P<Pa, energy becomes
negative (E<0), and additional energy is not required for moving
air to the vessel bottom. Furthermore, in addition to the bubbles
that move from the atmosphere to the vessel bottom via flow path
14, the bubbles in the vicinity of air outlet 13 also include
bubbles generated when the pressure of negative pressure region 21
becomes low in comparison with saturated vapor pressure as a result
of cavitation and separation action that occur due to negative
pressure forming portion 12.
[0059] In this manner, in frictional resistance reducing vessel 10
as claimed in the present invention, by changing the flow state of
water by negative pressure forming portion 12 and forming negative
pressure region 12 in the water, bubbles can be generated in the
water with less energy than pressurization methods.
[0060] Next, an explanation is provided of the relationship between
the shapes of the constituents for forming a negative pressure
region in the water (each of the shapes, etc. of negative pressure
forming portion 12, air outlet 13 and flow path 14), and frictional
resistance reduction effects of the hull.
[0061] Here, each parameter is defined as shown below.
[0062] h: Mean negative pressure (Pa) at negative pressure region
21
[0063] v: Mean flow rate of air inside flow path 14 (m/sec)
[0064] Q: Quantity of air fed into water (m3/sec)
[0065] d: Protruding height of negative pressure forming portion 12
from submerged surface 11 (m)
[0066] V: Vessel velocity (m/sec)
[0067] V': Flow rate of gas-liquid two-phase flow in vicinity of
air outlet 13
[0068] .DELTA.F: Amount of reduction of frictional resistance
(kgf)
[0069] .DELTA.R: Amount of increase in resistance due to negative
pressure forming portion 12 (kgf)
[0070] .DELTA.N=.DELTA.F-.DELTA.R: Frictional resistance reduction
effect (Net Gain (kgf))
[0071] Here, Net Gain is equivalent to the increase in vessel
velocity obtained as a result of reducing frictional resistance
when converted to "kgf".
[0072] .DELTA.NV: Net Gain when vessel velocity V is constant
[0073] .DELTA.Nd: Net Gain when height d of negative pressure
forming portion 12 is constant
[0074] .alpha.: Resistance increase coefficient when vessel
velocity V is constant (kgf/m)
[0075] .beta.: Frictional resistance reduction coefficient when
vessel velocity V is constant (kgf/m)
[0076] .epsilon.: Resistance increase coefficient when height d of
negative pressure forming portion 12 is constant
(kgf/(m/sec).sup.2)
[0077] .gamma.: Frictional resistance reduction coefficient
relative to square of vessel velocity V when height d of negative
pressure forming portion 12 is constant (kgf/(m/sec).sup.2)
[0078] .delta.: Frictional resistance reduction coefficient
relative to vessel velocity V when height d of negative pressure
forming portion 12 is constant (kgf/(m/sec).sup.2)
[0079] [Relationship Between Mean Negative Pressure h (m) and Air
Quantity Q (m.sup.3/sec)]
[0080] The mean negative pressure h (m) in negative pressure region
21 is proportional to the square of the flow rate v (m/sec) of air
inside the air induction pipe (AIP) (h.alpha.v.sup.2). In addition,
when the flow path cross-sectional area of the flow path is
constant, the quantity of air Q (m.sup.3/sec) fed into the water is
proportional to the flow rate v of the air (m/sec) (Q.alpha.v).
[0081] Namely,
h.alpha.v.sup.2.alpha.Q.sup.2
[0082] and air quantity Q increases by the square root relative to
increases in mean negative pressure h.
[0083] Q.alpha.{square root}h (3)
[0084] [Relationship Between Air Quantity Q (m.sup.3/sec) and
Vessel Velocity V (m/sec)]
[0085] The following results if hypothesized that height d (m) of
the negative pressure forming portion is constant, and that mean
negative pressure h is proportional to the flow rate V' (m/sec) of
gas-liquid two-phase flow in the vicinity of the air outlet (around
the AIP):
h.alpha.V'.sup.2 (4)
[0086] Therefore,
Q.alpha.V' (5)
[0087] In addition, since flow rate V' (m/sec) of gas-liquid
two-phase flow in the vicinity of the air outlet is considered to
be nearly proportional to vessel velocity V (m/sec), the following
results from equation (5):
Q.alpha.V'.alpha.V (5')
[0088] [Relationship Between Amount of Reduction of Frictional
Resistance .DELTA.F (kgf) and Air Quantity Q (m.sup.3/sec)]
[0089] The following is considered to be valid based on the
findings thus far:
.DELTA.CF.alpha..DELTA.F/V.sup.2.alpha.Q/V
[0090] From this, the following can be derived:
.DELTA.F.alpha.QV (6)
[0091] In addition, the following can be derived from equations (5)
and (6):
.DELTA.F.alpha.V.sup.2 (7)
[0092] On the other hand, if it is assumed that air quantity
Q(m.sup.3/sec) is nearly constant, then the following equation can
be derived from equation (6):
.DELTA.F.alpha.V (8)
[0093] [Frictional Resistance Reduction Effect Relative to Change
in Height d (m) of Negative Pressure Forming Portion when Vessel
Velocity V (m/sec) is Constant (Net Gain)]
[0094] In the following example, the width of the negative pressure
forming portion in the direction of vessel width is constant, and
the surface area of the region opposing the flow of water is
proportional to its height d. At this time, as shown in equation
(9), air quantity Q (m3/sec) is proportional to the product of the
flow rate v (m/sec) of the air in the flow path and the height d of
the negative pressure forming portion.
Q.alpha.vd.alpha.Vd.alpha.{square root}hd (9)
[0095] Furthermore, although the negative pressure region changes
accompanying changes in height d of the negative pressure forming
portion, that change is ignored here. The following equation is
derived from equations (6) and (9) when vessel velocity V is
constant:
.DELTA.F.alpha.d (10)
[0096] Moreover, since the width of the negative pressure forming
portion is constant, the amount of increase in resistance .DELTA.R
(kgf) is proportional to height d of the negative pressure forming
portion.
.DELTA.R.alpha.d (11)
[0097] In other words, when the width of the negative pressure
forming portion is constant, if the value of
.DELTA.NV=.DELTA.F-.DELTA.R reaches a maximum, maximum frictional
resistance reduction effects are obtained. Here, when the following
equations are used:
.DELTA.F=.beta.d
.DELTA.R=.alpha.d,
[0098] then the following equation results:
.DELTA.NV=.DELTA.F-.DELTA.R=.beta.d-.alpha.d
[0099] Moreover, the following equation results if .DELTA.NV=y and
d=x:
y=(.beta.-.alpha.)x (12)
[0100] and when y.gtoreq.0, a net gain is obtained. However, the
maximum value of height d of the negative pressure forming portion
is not determined from equation (12).
[0101] [Frictional Resistance Reduction Effects Relative to Changes
in Vessel Velocity V (m/sec) when Height d (m) of the Negative
Pressure Forming Portion is Constant (Net Gain)]
[0102] The following equation is derived from equations (7) and
(8):
.DELTA.F=.gamma.V.sup.2+.delta.V (13)
[0103] In addition, when height d of the negative pressure forming
portion is constant, the amount of the increase in resistance
.DELTA.R is proportion to the square of vessel velocity V.
.DELTA.R=.epsilon.V.sup.2 (14)
[0104] The following equation is derived from equations (13) and
(14):
.DELTA.Nd=.DELTA.F-.DELTA.R=(.gamma.-.epsilon.)V.sup.2+.delta.V
(15)
[0105] Moreover, the following equation results when .DELTA.Nd=y,
V=x, A=.gamma.-.epsilon. and B=.delta.:
y=Ax.sup.2+Bx (16)
[0106] Here, as is clear from the derivation process, parameter
.alpha. and parameter .beta. in equation (12) are dependent on the
shapes of each constituent for forming the negative pressure region
(protruding shape of the negative pressure forming portion, opening
surface area of the air outlet, flow path cross-sectional surface
area of the flow path and so forth). In addition, .gamma. and
.epsilon. that compose parameter A in equation (16) are dependent
on the characteristics of the hull (such as its output and hull
shape), while .delta. that composes parameter B is dependent on the
state of each constituent for forming the negative pressure
region.
[0107] In other words, frictional resistance reduction effects
fluctuate according to each of the parameters of equations (12) and
(16), the protruding height d of the negative pressure forming
portion and vessel velocity V. Thus, as in the manner of the
frictional resistance reducing vessel as claimed in the present
invention, by changing at least one of the states of each
constituent consisting of the protruding state of the negative
pressure forming portion from the submerged surface, the opening
surface area of the air outlet, and cross-sectional surface area of
the flow path, the state of the negative pressure region in the
water can be changed according to the characteristics of the hull,
thereby making it possible to realize effective reduction of
frictional resistance. Moreover, by controlling a drive mechanism
based on changes in vessel velocity with a control apparatus, the
state of the negative pressure region in the water can be
controlled so as to maximize frictional resistance reduction
effects.
EMBODIMENT 1
[0108] Next, the following provides an explanation of an embodiment
of the frictional resistance reducing vessel as claimed in the
present invention with reference to the drawings.
[0109] In FIG. 2A, reference symbol M indicates a frictional
resistance reducing vessel, 30 a hull, 31 a bubble generator, 32 a
hull shell plate (submerged surface), 33 a propeller, and 34 a
rudder.
[0110] Frictional resistance reducing vessel M is a large ship in
the manner of, for example, a Very Large Crude Oil Carrier (VLCC).
In comparison with other types of vessels, the surface area of the
bottom of a large ship in hull shell plate 32 below draft line 15
is formed to be large relative to the side of the vessel.
Furthermore, the type of vessel to which the present invention is
applied is not limited to this large ship, but the hull may also be
of another form such as that of a high-speed vessel or fishing
vessel.
[0111] As shown in FIG. 2B, bubble generator 31 is equipped with
air induction pipe 40, which is arranged inside opening 32a
provided in the bottom of the vessel, drive mechanism 41, which
drives air induction pipe 40 while supporting it so as to move
freely in the vertical direction, and control apparatus 42, which
controls drive mechanism 41.
[0112] Air induction pipe 40 is composed mainly of a cylindrical
member, and has inside a space that serves as a flow path (flow
path 43). The lower end of air induction pipe 40 is in the form of
inclined surface 44, which is inclined relative to the axial
direction, and the lower end of flow path 43 opens into the water
via air outlet 45 provided in this inclined surface 44 and facing
toward the rear (stern). On the other hand, the upper end of flow
path 43 opens into a gaseous space (atmosphere) via air intake port
40a.
[0113] Cross-sectional shapes of air induction pipe 40 are shown in
FIGS. 3A through 3C. In frictional resistance reducing vessel M of
the present embodiment, a plurality of types of air induction pipe
40 having different cross-sectional shapes are used selectively,
examples of which include the round cylindrical shape shown in FIG.
3A, the square cylindrical shape shown in FIG. 3B, and the
semi-circular cylindrical shape shown in FIG. 3C.
[0114] Returning to FIG. 2, drive mechanism 41 is equipped with
drive motor 47, cylindrical housing pipe 48, which guides air
induction pipe 40 in the vertical direction, and a transmission
unit not shown which moves air induction pipe 40 up and down inner
cylindrical housing 48 by transferring the drive power of drive
motor 47. Furthermore, a rack and pinion mechanism, direct drive
mechanism using a linear guide and so forth are applied for the
transmission unit. In addition, the upper end of housing pipe 48 is
preferably arranged so that it is positioned above the draft line
(water level 15). Moreover, it is preferable to provide an
attachment adapter that matches each of the cross-sectional shapes
of air induction pipe 40 in order to selectively house a plurality
of types of air induction pipes 40 inside housing pipe 48.
[0115] Control apparatus 42 comprehensively controls the entire
hull, and is composed of a microcomputer (or mini-computer)
containing a central processing unit (CPU), read-only memory (ROM),
random access memory (RAM) and so forth.
[0116] Next, an explanation is provided for the method of reducing
the frictional resistance of hull 30 by a negative pressure method
in the frictional resistance reducing vessel M having the above
structure.
[0117] When the vessel is stopped, water (sea water) enters flow
path 43 to nearly the same water level as that surrounding hull 30.
When hull 30 enters the operating state due to the thrust of
propeller 33, as shown in FIG. 4A, relative water flow 50 is formed
relative to hull 30.
[0118] When hull 30 reaches a prescribed vessel velocity, as shown
in FIG. 4B, control apparatus 42 adjusts the position (height) of
air induction pipe 40 using drive mechanism 41, and causes lateral
surface 40b (negative pressure forming portion) of air induction
pipe 40 to protrude by a prescribed height d from hull shell plate
32.
[0119] At this time, the water flow path is narrowed by lateral
surface 40b of air induction pipe 40. As a result, together with
the flow rate of water flowing along hull shell plate 32
increasing, a breakaway region is formed in the water due to the
sharp angle of the protruding end of air induction pipe 40.
Moreover, due to the decrease in pressure accompanying increased
flow rate (based on Bernoulli's theorem), and the breakaway action
and cavitation in the breakaway region, hydrostatic pressure
decreases locally in the water on the side of inclined surface 44
of air induction pipe 40, resulting in the formation of negative
pressure region 51 that is at low pressure relative to the
atmosphere.
[0120] At this time, due to the pressure of air outlet 45 facing
negative pressure region 51 being lower than the pressure at air
intake port 40a, pressure gradient force acts on the fluid (sea
water and air) in flow path 43, which together with causing sea
water to be discharged from flow path 43, air that has entered from
air intake port 40a is fed into the water from flow path 43.
[0121] Air that has been fed into the water mixes into the water in
the form of microbubbles 52, and the frictional resistance of hull
30 is reduced due to the presence of a large number of bubbles 52
in the vicinity of hull shell plate 32.
[0122] Here, as was previously mentioned, the energy required for
feeding air into the water is obtained by changing the flow state
of the water by air induction pipe 40, and this energy is less than
a conventional positive pressure method. Consequently, in the
frictional resistance reducing vessel M of the present embodiment
which uses a negative pressure method, bubbles are generated in the
water with less energy consumption than conventional positive
pressure methods, thereby enabling frictional resistance during
operation to be efficiently reduced.
[0123] Moreover, as was previously described, frictional resistance
reduction effects fluctuate according to the characteristics of
hull 30 (such as output and hull shape), the shape of air induction
pipe 40 that forms negative pressure region 51 (such as the
protruding shape of air induction pipe 40 from hull shell plate 32,
the opening surface area of air outlet 45, and the surface area of
flow path 43), and vessel velocity. Therefore, in the frictional
resistance reducing vessel M as claimed in the present invention,
at least one of the shape of air induction pipe 40, the protruding
height of air induction pipe 40 from hull shell plate 32 and vessel
velocity is changed by drive mechanism 41 so that maximum
frictional resistance reduction effects are achieved. FIG. 5 is a
flow chart showing an example of this procedure.
[0124] As shown in this flow chart, the shape of air induction pipe
40 is first selected (Step 100). For example, the shape of air
induction pipe 40 that is effective for reducing frictional
resistance is determined by selectively using a plurality of air
induction pipes 40 having different shapes and comparing the
changes in vessel velocity at those times.
[0125] More specifically, air induction pipes 40 having different
cross-sectional shapes as shown in, for example, FIGS. 3A through
3C are sequentially installed on drive mechanism 41 and the ends
(lower end) of air induction pipes 40 are protruded by the same
height d from hull shell plate 32 either manually or by a drive
mechanism not shown with the rotating speed of propeller 33
constant. At this time, since the opening surface area of air
outlet 45 and the surface area of flow path 43 differ according to
the shape of the air induction pipe 40 that is installed, the state
of negative pressure region 51 changes. Therefore, the changes in
vessel velocity (increases or decreases) at that time are compared,
and the air induction pipe 40 for which vessel velocity increased
the most is selected based on the results of that comparison.
Furthermore, although three types of air induction pipes 40 having
mutually different cross-sectional shapes are shown in FIGS. 3A
through 3C, the shape of air induction pipe 40 is not limited to
these, but rather the shape and number of air induction pipes that
can be selected are random.
[0126] When the shape of air induction pipe 40 has been selected,
the optimum protruding state of air induction pipe 40 is determined
by control apparatus 42 (Steps 101 and 102). More specifically,
control apparatus 42 controls drive mechanism 41 to change the
protruding height d of air induction pipe 40 from hull shell plate
32 with the rotating speed of propeller 33 constant (for example,
at the rotating speed corresponding to the standard cruising
velocity). The optimum protruding height d of air induction pipe 40
relative to a prescribed vessel velocity is then determined from
the change (increase or decrease) in vessel velocity at this time
(Step 101). Furthermore, the optimum protruding height d may also
be determined based on the above-mentioned equation (12) by
resolving parameters .beta. and .alpha. in equation (12) using the
method of least squares and so forth and calculating that
solution.
[0127] In addition, control apparatus 42 determines the optimum
vessel velocity relative to the prescribed protruding height d from
the change (increase or decrease) in vessel velocity when the
rotating speed of propeller 33 is changed with the protruding
height d of air induction pipe 40 (for example, the protruding
height determined in Step 102) constant. Furthermore, the optimum
vessel velocity may also be determined based on the above-mentioned
equation (16) by resolving parameters A and B in equation (16) and
calculating that solution based on data on the increase or decrease
in vessel velocity when the rotating speed of propeller 33 (vessel
velocity) is changed.
[0128] The closer the optimum vessel velocity calculated at this
time is to the current vessel velocity, the more effective the
current protruding height d is on reducing frictional resistance.
Thus, control apparatus 42 repeatedly changes protruding height d
of air induction pipe 40 and vessel velocity within a prescribed
range to search for the maximum increase in vessel velocity
(frictional resistance reduction effect: .DELTA.N) (Step 103). As a
result, air induction pipe 40 is controlled at the optimum
protruding state relative to a desired vessel velocity.
[0129] In this manner, in the frictional resistance reducing vessel
M of the present embodiment, by changing the shape of air induction
pipe 40 (cross-sectional shape and protruding height from hull
shell plate 32) based on the change in vessel velocity, the state
of negative pressure region 51 in the water can be controlled so as
to maximum frictional resistance reduction effects for a desired
vessel velocity. Thus, the frictional resistance of hull 30 can be
effectively reduced by juxtaposition of a large number of bubbles
on hull shell plate 32 while consuming little energy, thereby
making it possible to effectively conserve energy consumed during
vessel operation.
[0130] Moreover, since bubble generator 31 employs a simple
composition and eliminates the need for an apparatus for
pressurizing the gas, it goes without saying that the construction
cost of hull 30 can be held to a low level.
[0131] The size, number and location of bubble generator 31 should
be determined based on the results of flow field analysis and
operational testing, etc. obtained by computational fluid dynamics
(CFD) so that the flow of water in the vicinity of opening 32a of
hull shell plate 32 during operation is of the desired state.
[0132] In addition, the method of changing the state of the
negative pressure region in the water is not limited to the method
explained in the above embodiment, but rather should be changed by
changing at least one of the protruding state of the negative
pressure forming portion (lateral surface 40b of air induction pipe
40) from hull shell plate 32, the opening surface area of air
outlet 45, or the cross-sectional surface area of flow path 43.
Moreover, in the above embodiment, although the opening surface
area of air outlet 45 and cross-sectional surface area of flow path
43 are changed by selectively using a plurality of air induction
pipes 40 having different shapes, an opening and closing mechanism
that changes the cross-sectional surface area of flow path 43 may
be provided, and this may be driven according to changes in vessel
velocity.
[0133] In addition, in the above embodiment, since the end of air
induction pipe 40 having an apical shape is made to protrude from
hull shell plate 32, cavitation occurs easily behind it. This
results in the advantages that, when this cavitation occurs, gas
and water are aggressively mixed at the interface between the gas
and water due to its agitation effects, which together with
promoting the release of bubbles 52 from the gas-liquid interface,
causes a large amount of gas to be introduced into the water via
flow path 43 due to the strong negative pressure action generated
by cavitation, resulting in a large number of bubbles 52 being
mixed into the water. However, the shape of air induction pipe 40
is not limited to that shown in FIG. 2B, but rather is arbitrarily
determined so that a negative pressure region is effectively formed
in the water. In addition, with respect to the shape of air
induction pipe 40, the cross-sectional area of flow path 43 is
preferably as large as possible so as to take in as much air as
possible, and the resistance added by lateral surface 40a as the
negative pressure forming portion that protrudes from hull shell
plate 32 is preferably as low as possible.
EMBODIMENT 2
[0134] The following provides an explanation of another embodiment
of the frictional resistance reducing vessel as claimed in the
present invention with reference to the drawings. FIG. 6A shows an
example of arranging bubble generator 111, instead of bubble
generator 31, on the bottom of frictional resistance reducing
vessel M shown in FIG. 2A.
[0135] As shown in FIG. 6B, this bubble generator 111 is equipped
with outer cylinder 121, which extends in the vertical direction
and is fixed to hull 30, inner cylinder 122 in the form of an air
induction pipe (AIP) that is housed within outer cylinder 121 while
being able to be attached and removed and being able to move freely
along the axial direction of outer cylinder 121 (vertical
direction), negative pressure forming portion 123 provided on the
lower end of inner cylinder 122, and position adjustment unit 124
for adjusting the position (height) in the axial direction of inner
cylinder 122 relative to outer cylinder 121.
[0136] Outer cylinder 121 has a cylindrical shape, and is installed
by passing through hull 30 so that both ends are open above and
below draft line 15. Inner cylinder 122 is a cylindrically shaped
member of a size that is able to be inserted into outer cylinder
121, and is inserted into outer cylinder 121 through an opening
formed in the upper end of outer cylinder 121. Although
corrosion-resistance surface-treated steel or aluminum and so forth
is used for the material of outer cylinder 121 and inner cylinder
122, resin having corrosion resistance relative to sea water
(synthetic resin) is preferably used for the material of inner
cylinder 122 for the purpose of reducing weight.
[0137] Negative pressure forming portion 123 has a box shape in
which one face is open, and the open end is coupled while
maintaining airtightness to the lower end of inner cylinder 122 so
that a projection is formed from the lower end of inner cylinder
122 in the downward direction. More specifically, negative pressure
forming portion 123 has forward inclined surface 123a, which
extends on an incline relative to the axial direction of inner
cylinder 122 and faces toward the front (bow) of the direction of
progress Dv, and backward inclined surface 123b positioned on its
back side and facing toward the rear (stern) of the direction of
progress. A roughly apically shaped projection is formed that
protrudes from hull shell plate 32 perpendicularly relative to the
direction of progress Dv of hull 30 by mutually joining the edges
of these inclined surfaces 123a and 123b. Furthermore, discharge
outlet 123c, which is continuous with the opening formed in the
lower end of inner cylinder 122, is provided in backward inclined
surface 123b.
[0138] In addition, as a result of inner cylinder 122 being
arranged inside outer cylinder 121, flow path 130 is formed inside
inner cylinder 122 and negative pressure forming portion 123. In
addition to one end of flow path 130 opening into a gaseous space
(atmosphere) via opening 122a formed in the form of an air intake
port in the upper end of inner cylinder 122, the lower end of flow
path 130 opens into the water via discharge outlet 123c of negative
pressure forming portion 123.
[0139] Position adjustment unit 124 is equipped with a drive
apparatus not shown such as a motor for moving inner cylinder 122
to a prescribed position, and a locking mechanism and so forth not
shown for locking inner cylinder 122 at that prescribed position,
and causes negative pressure forming portion 123 to protrude from
hull shell plate 32 to a prescribed position corresponding to the
operating state of hull 30.
[0140] The shape and locations of each composite member of bubble
generator 111 are designed based on the results of flow field
analysis and operational testing, etc. obtained by computational
fluid dynamics so that the flow of water behind (on the stern side)
of negative pressure forming portion 123 during operation is of the
desired state. Here, the height H of negative pressure forming
portion 123 is determined so that cavitation and separation occur
in the water behind negative pressure forming portion 123 itself
due to the flow of water relative to hull 30. For example, height H
of negative pressure forming portion is set to be as large as
possible within the range of diameter D.sub.1 of inner cylinder
122. Furthermore, one or a plurality of bubble generator 111 are
arranged according to the size of the vessel bottom.
[0141] The following provides an explanation of a method of
reducing the frictional resistance of hull 30 by the frictional
resistance reducing vessel having the structure described above
with reference to FIGS. 7A and 7B.
[0142] When the vessel is stopped, water (sea water) enters flow
path 130 to nearly the same water level as that surrounding hull
30. When hull 30 enters the operating state due to the thrust of
propeller 33, relative water flow 140 is formed relative to hull
30.
[0143] When a prescribed vessel velocity V is reached in the
operating state, as shown in FIG. 7A, positioning adjusting unit
124 adjusts the position (height) in the axial direction of inner
cylinder 122 relative to outer cylinder 121 so that negative
pressure forming portion 123 protrudes by a prescribed height H
from hull shell plate 32.
[0144] At this time, the water flow path is narrowed by forward
inclined surface 123a of negative pressure forming portion 123. As
a result, together with the flow rate of water flowing along the
vessel bottom increasing, cavitation and separation occur in the
water behind negative pressure forming portion 123 due to the sharp
angle of its protruding end. Consequently, hydrostatic pressure
decreases locally in the water behind negative pressure forming
portion 123, and negative pressure region 141 is formed at a lower
pressure than the atmosphere. At this time, since the pressure of
outlet port 123c facing negative pressure region 141 is lower than
the pressure at opening 122a formed in the upper end of inner
cylinder 122, pressure gradient force acts on the fluid (sea water
and air) in fluid path 130, which together with causing sea water
to be discharged from flow path 130, air that has entered from
opening 122a formed in the upper end of inner cylinder 122 is fed
into the water by flowing through flow path 130.
[0145] Air that has been fed into the water mixes into the water in
the form of bubbles 142, and as a result, the frictional resistance
of hull 30 is reduced due to the presence of a large number of
bubbles 142 in the vicinity of hull shell plate 32.
[0146] At this time, the energy required for feeding air into the
water is mainly the energy for changing the location of the gas.
This energy is obtained by changing the flow state of the water by
negative pressure forming portion 123, and this energy is less than
the energy consumed in the case of pressurizing a gas and blowing
it into the water. Namely, according to the present invention,
energy consumption during vessel operation is effectively conserved
by reducing the frictional resistance of hull 30 with a lower level
of energy consumption.
[0147] In addition, in the present embodiment, negative pressure
forming portion 123 in the form of a roughly apically shaped
projection is arranged protruding from hull shell plate 32, and
aggressively forms cavitation and separation. Consequently, due to
the resulting agitation effects, a large amount of gas is
introduced into the water via flow path 130 resulting in the
generation of a large number of bubbles. At this time, although
drag relative to water flow 140 increases since negative pressure
forming portion 123 is arranged protruding from hull shell plate
32, the Reynold's number on an actual hull 30 is comparatively high
due to the surface roughness of hull shell plate 32. Moreover,
since a large number of bubbles are generated in the water, the
increase in drag has little effect on frictional resistance
reduction effects.
[0148] Moreover, in the present embodiment, the protruding state of
negative pressure forming portion 123 from hull shell plate 32 is
controlled by adjusting the position (height) of inner cylinder 122
relative to outer cylinder 121 according to the vessel's operating
state. Thus, in the case, for example, the vessel has not reached a
prescribed vessel velocity V, or in the case frictional resistance
reduction effects produced by bubbles cannot be expected due to
inclement weather, as shown in FIG. 7B, by moving negative pressure
forming portion 123 to the inside of hull shell plate 32 by
position adjustment unit 124 so that negative pressure forming
portion 123 is no longer protruding, the increase in drag relative
to water flow 140 is suppressed making it possible to reduce energy
consumption. Moreover, by adjusting the protruding height of
negative pressure forming portion 123 according to the operating
velocity, bubbles 142 can be controlled to be effectively released
into the water.
[0149] The main governing factors for the formation of negative
pressure region 141 are the shape of negative pressure forming
portion 123, its protruding height from hull shell plate 32, and
the Reynold's number. Since the present invention is not considered
to be susceptible to disadvantages caused by water depth, the
technology as claimed in the present invention is also advantageous
for application to large ships.
[0150] In addition, since bubble generator 111 has a simple
composition and eliminates the need for an apparatus for
pressurizing the gas, it goes without saying that the construction
cost of hull 30 can be held to a low level.
[0151] Furthermore, the various shapes and combinations, etc. of
each composite member shown in the embodiment described above refer
to only a single example, and can be altered in various ways based
on design requirements and so forth within a range that does not
deviate from the purport of the present invention. In addition,
although the above embodiment indicated an example of applying the
present invention to a large ship, the present invention is not
limited to large ships, but can also be applied to other vessels
such as high-speed vessels and fishing vessels. Furthermore, the
size, number and location of bubble generator 111 should be
suitably determined according to the shape of hull 30. However, as
was previously mentioned, since the Reynold's number on an actual
hull 30 is already comparatively high due to the surface roughness
of hull shell plate 32 resulting in the action of diffusion
effects, it is not necessary to provide an excessively large number
of bubble generators 111.
EMBODIMENT 3
[0152] The following provides an explanation of still another
embodiment of the frictional resistance reducing vessel as claimed
in the present invention with reference to the drawings. FIG. 9A is
a side view of the starboard side in the vicinity of the bow of
frictional resistance reducing vessel M shown in FIG. 2A that shows
an example in which bubble generator 201 is arranged on the bottom
of frictional resistance reducing vessel M shown instead of bubble
generator 31. In addition, FIG. 9B is an overhead view as viewed
from the bottom of vessel M, while FIG. 9C is a cross-sectional
view taken along line A-A in FIG. 9A. In these drawings, reference
symbol 202 is an outer cylinder, 203 an inner cylinder, 204 a
stopping mechanism (protrusion adjustment means) and 205 a cover.
Among these, outer cylinder 202, inner cylinder 203 and stopping
mechanism 204 compose bubble generator 201 in frictional resistance
reducing vessel M.
[0153] Outer cylinder 202 is a through path that passes vertically
through the inside of hull 30, its upper end (one end) 202a opens
to the atmosphere, and its lower end (other end) 202b is welded to
hull 30 so as to open into the water. The cross-sectional shape of
this outer cylinder 202 is an asymmetrical shape in the lengthwise
direction L of frictional resistance reducing vessel M consisting
of, as shown in FIG. 9C for example, an isosceles triangle of which
the bottom side a is perpendicular to lengthwise direction L. Inner
cylinder 203, having an outer diameter slightly smaller than the
inner diameter of outer cylinder 202, is inserted into this outer
cylinder 202. The cross-sectional shape of at least the portion of
this inner cylinder 203 that protrudes into the water is in the
form of an isosceles triangle having an outer diameter slightly
smaller than outer cylinder 202 so that inner cylinder 203 is able
to freely move vertically within outer cylinder 202.
[0154] Upper end (one end) 203a of inner cylinder 203 is open to
the atmosphere, while air spraying portion 206 is provided in the
lower end (other end) 203b of inner cylinder 203. As shown in FIG.
9B, together with obstructing lower end 203b of inner cylinder 203,
this air spraying portion 206 is composed of isosceles triangle
face plate 206b in which circular spray outlet 206a is formed in
its center, and half-dome-shaped protruding plate 206c that
protrudes from face plate 206b and covers spray outlet 206a from
the front (bow side) of hull 30.
[0155] Namely, in the case of setting to a position along the
vertical direction of inner cylinder 203 so that face plate 206b is
located roughly in the same plane as hull shell plate 32, this air
spraying portion 206 protrudes from hull shell plate 32. In
addition, since half-dome-shaped projecting plate 206c covers the
front half of spray outlet 206a from the front side of hull 30, the
protruding shape of air spraying portion 206 is asymmetrical in
lengthwise direction L of hull 30.
[0156] In addition, inner cylinder 203 installed in outer cylinder
202 is stopped and prevented from moving further by stopping
mechanism 204, and the vertical position of inner cylinder 203
relative to outer cylinder 202 is set by stopping mechanism 204.
Stopping mechanism 204 is able to stop inner cylinder 203 inside
outer cylinder 202 at least in the state in which face plate 206b
and hull shell plate 32 are roughly in the same plane (State A),
and in the state in which protruding plate 206c is not protruding
from hull shell plate 32 as shown in FIG. 9A.
[0157] In addition, cover 205 occludes upper end 202a of outer
cylinder 202 open to the atmosphere when frictional resistance
reducing vessel M is stopped, and prevents, for example, water from
being blown up through outer cylinder 202 during inclement weather
and so forth.
[0158] The following provides an explanation of the method of
reducing frictional resistance of hull 30 by frictional resistance
reducing vessel 30 having the structure described above.
[0159] In the case of this frictional resistance reducing vessel M,
inner cylinder 203 is set in state B when the vessel is stopped. At
this time, sea water enters inner cylinder 203 to the same height
(water level) as draft line 15. In the operating state, inner
cylinder 203 is set in state A. When the vessel is operating,
atmosphere (air) that has been taken in from upper end 203a of
inner cylinder 203 is sprayed into the water from air spraying
portion 206, and this air is dispersed in the direction of the
stern in the form of microbubbles by the flow of water (turbulent
flow).
[0160] Namely, in the case frictional resistance reducing vessel M
is operating at cruising velocity in state A, the flow path of
water that flows from the direction of the bow to the stern in the
vicinity of air spraying portion 206 is locally narrowed by the
presence of protruding plate 206c. As a result, the static pressure
of water at air blowing portion 206, or in other words at lower end
203b of inner cylinder 203, decreases below atmospheric pressure,
or in other words the pressure at upper end 203a of inner cylinder
203, resulting in a state of negative pressure. As a result, air
taken in from upper end 203a is sprayed into the water from spray
outlet 206a. Air that has been sprayed into the water in this
manner takes on the form of bubbles as a result of being finely
dispersed by water flow from the bow to the stern. Bubbles
generated in the vicinity of the bow are sequentially dispersed and
move towards the stern along the lines of water flow and broadly
cover the vessel's bottom, thereby reducing the frictional
resistance between hull shell plate 32 and the water at the
vessel's bottom.
[0161] In addition, together with the cross-sectional shape of
inner cylinder 203, which is installed so as to engage while moving
freely with outer cylinder 202, being in the form of an isosceles
triangle, since the vertical position of inner cylinder 203 can be
changed by stopping mechanism 204, inspection and maintenance of
bubble generator 201 as well as testing of friction reduction
effects and so forth can be performed easily.
[0162] Moreover, since the cross-sectional shapes of outer cylinder
202 and inner cylinder 203 are set to the shape of an isosceles
triangle, in the case inner cylinder 203 is extracted from outer
cylinder 202 during maintenance and inspection, the orientation of
air spraying portion 206, which has an asymmetrically protruding
shape in the lengthwise direction of hull 30, can be made to be the
normal orientation, namely the orientation such that
half-dome-shaped protruding plate 206c covers spray outlet 206a
from the front side of hull 30, simply inserting inner cylinder 203
into outer cylinder 202 without paying attention to the orientation
of air spraying portion 206. Thus, installation of inner cylinder
203 in outer cylinder 202 during maintenance, inspections and so
forth can be performed easily as compared with the case of the
cross-sectional shapes of outer cylinder 202 and inner cylinder 203
having a symmetrical shape in the lengthwise direction L (such as a
circular or oval shape).
[0163] In addition, the vertical position of inner cylinder 203 can
be changed between state A and state B by stopping mechanism 204 in
this frictional resistance reducing vessel M, differences in
frictional reduction effects due to the presence or absence of
protrusion of protruding plate 206c relative to hull shell plate
32, namely due to the presence or absence of the spraying of air
into the water, can be tested easily.
[0164] Furthermore, the present invention is not limited to the
above embodiment, but also can be modified, for example, in the
manner described below.
[0165] (1) Although the cross-sectional shapes of outer cylinder
202 and inner cylinder 203 were in the form of an isosceles
triangle in the above embodiment, air spraying portion 206 is
always at the normal orientation when inner cylinder 203 is
inserted into outer cylinder 202 if they have an asymmetrical shape
in the lengthwise direction of frictional resistance reducing
vessel M. Thus, the above cross-sectional shape may be another
shape such as a pentagon or heptagon. However, an excessively
complex shape is undesirable in terms of production cost. From the
viewpoint of production cost, the cross-sectional shape of outer
cylinder 202 and inner cylinder 203 is preferably an isosceles
triangle, which is asymmetrical in lengthwise direction L of
frictional resistance reducing vessel M, and is also the simplest
shape.
[0166] (2) Although half-dome-shaped projecting plate 206c is
provided over face plate 206b so as to cover roughly half of spray
outlet 206a in air spraying portion 206 of the above embodiment,
the present invention is not limited to this. Protruding plate 206c
may also be provided so as to cover less than half or more than
half of spray outlet 206a. However, the extent to which protruding
plate 206c covers spray outlet 206a is, as a general rule,
determined from the viewpoint of whether or not spray outlet 206a
most efficiently forms a negative pressure state.
EMBODIMENT 4
[0167] The following provides an explanation of still another
embodiment of the frictional resistance reducing vessel as claimed
in the present invention with reference to the drawings. In FIG.
10A, reference symbol Ma indicates a frictional resistance reducing
vessel, 60 a hull, 62 a hull shell plate (submerged surface), 63 a
propeller, 64 a rudder and 311 a bubble generator.
[0168] As shown in FIG. 10B, bubble generator 311 is equipped with
indentation 320 formed so as to be recessed from hull shell plate
62 of the vessel bottom, flow path 321 which passes through hull 60
and is open above and below draft line 15, and negative pressure
forming member 322 arranged inside indentation 320.
[0169] Indentation 320 is formed by chamber 330 attached to hull
shell plate 62 from the inside of hull 60. Namely, chamber 330 is
formed into the shape of a box of which one face is open, and that
open end is connected to hull shell plate 62 from the inside of
hull 60. Furthermore, chamber 330 is comprised of an integrally
molded article made of hard polyurethane, and is removably attached
to hull shell plate 62.
[0170] Flow path 321 is a space formed inside air induction pipe
(AIP) 331 connected to chamber 330. Namely, discharge outlet 330a,
for releasing bubbles into the water, is located in the back of
indentation 320 in chamber 330, and air induction pipe 331
comprised of a tubular member is connected to discharge outlet
330a. As a result, one end of flow path 321 is open to a gaseous
space (atmosphere) via air intake port 331a of air induction pipe
331, while the other end is open into the water via discharge
outlet 330a of the above chamber 330. In addition, the internal
cross-sectional area and shape of air induction pipe 331 are
determined so that a desired flow volume of liquid flows through
flow path 321 with low pressure loss.
[0171] Negative pressure forming member 322 is arranged so that at
least a portion protrudes from hull shell plate 62, forms a
negative pressure region in the water behind itself (on the stern
side) that is at a lower pressure than the gaseous space
(atmosphere) at a prescribed vessel velocity Vs by using the
relative flow of water with respect to hull 60 during vessel
operation, and is supported while allowing to rotate freely
centering around stainless steel support shaft 332.
[0172] In addition, negative pressure forming member 322 is
comprised of a member in which the cross-sectional shape in the
direction perpendicular to support shaft 332 is roughly that of an
isosceles triangle, and has a plurality (here, three) of faces
322a, 322b and 322c parallel to support shaft 332. Moreover,
negative pressure forming member 322 is at a prescribed angle
centering around support shaft 332 due to the action of angle
adjustment mechanism 323 that controls the rotation of support
shaft 332. As a result, a portion of prescribed faces 322a and 322b
protrude from hull shell plate 62, and from a different angle,
prescribed face 322a is positioned roughly in the same plane as
hull shell plate 62. Furthermore, negative pressure forming member
322 is comprised of a molded article made of hard polyurethane.
[0173] As shown in, for example, FIG. 12, angle adjustment
mechanism 323 is equipped with bearings 333 and 334, which support
support shaft 332 while allowing to rotate freely and which are
supported in chamber 330, levers 335 and 336 fixed to support shaft
332 on the outside of chamber 330 for assisting in the rotation of
support shaft 332, and locking portion 337 for locking the rotation
of support shaft 332. In this example, the arrangement angle of
negative pressure forming member 332 is changed centered about
support shaft 332 by an operator rotating support shaft 332 by
means of levers 335 and 336, and the arrangement angle of negative
pressure forming member 332 can be set by locking support shaft 332
with locking portion 337.
[0174] Furthermore, angle adjustment mechanism 323 is not limited
to the structure by which the arrangement angle of negative
pressure forming member 322 is adjusted by the above manual
operation, but rather a structure may also be employed in which,
for example, the arrangement angle of negative pressure forming
member 322 is driven automatically by having a driving motor and so
forth. Furthermore, bearings 333 and 334 have a sufficiently sealed
structure so as to prevent the entrance of water into the hull from
the water.
[0175] In addition, the shapes and locations of each constituent
member of bubble generator 311 are designed based on the results of
flow field analysis and operational testing, etc. obtained by
computational fluid dynamics so that the flow of water behind
(stern side) of negative pressure forming member 322 during
operation is of the desired state. For example, the height of
negative pressure forming member 322 and the shape of chamber 330
are determined so that a negative pressure region is formed in the
water behind negative pressure forming member 322 that is at a
lower pressure than the gaseous space (atmosphere) during operation
at prescribed vessel velocity Vs.
[0176] Furthermore, in addition to the hard polyurethane previously
mentioned, a material such as corrosion-resistant metal or plastic
that has surface corrosion resistance primarily with respect to sea
water and is also resistant to adherence to the surface by marine
organisms is preferably used for the material of negative pressure
forming member 322, chamber 330 and air induction pipe 331. In
addition, one or a plurality of bubble generators 311 may be
arranged corresponding to the size of the vessel bottom.
[0177] The following provides an explanation of the method of
reducing frictional resistance of hull 60 by frictional resistance
reducing vessel Ma having the above structure with reference to
FIGS. 11A and 11B.
[0178] When the vessel is stopped, water (sea water) enters flow
path 321 to roughly the same water level as that surrounding hull
60. When hull 60 enters the operating state due to the thrust of
propeller 63, relative water flow 340 is formed with respect to
hull 60. When the vessel reaches a prescribed velocity V, as shown
in FIG. 11A, by adjusting the angle of negative pressure forming
member 322 by angle adjustment mechanism 323, a portion of negative
pressure forming member 322, namely a portion of prescribed faces
322a and 322b of negative pressure forming member 322, protrudes
from hull shell plate 62.
[0179] At this time, as a result of the water flow path being
narrowed by face 322a of negative pressure forming member 322,
together with the flow rate of water flowing along the vessel
bottom increasing, due to the sharp angle of its protruding end, a
separation region is formed in the water, and due to the presence
of this separation region, hydrostatic pressure in the water behind
face 322a of negative pressure forming member 322 locally
decreases, resulting in the formation of negative pressure region
341 at a lower pressure relative to the atmosphere.
[0180] This being the case, the pressure of discharge outlet 330a
facing negative pressure region 341 becomes lower than the pressure
at air intake port 331a. As a result, a pressure gradient acts on
the fluid (sea water and air) inside flow path 321, and together
with sea water being discharged from flow path 321, air that has
entered from air intake port 331a is fed into the water via flow
path 321.
[0181] Gas that has been fed into the water mixes into the water in
the form of bubbles 342 after being released from gas-liquid
interface 343, and the frictional resistance of hull 60 is reduced
due to juxtaposition of a large number of bubbles 342 in the
vicinity of hull shell plate 62.
[0182] At this time, the energy required to feed air into the water
is mainly the energy for changing the location of the gas. This
energy is obtained by changing the flow state of the water by
negative pressure forming member 322, and is lower than the energy
consumed in the case of pressuring a gas and spraying it into the
water. Namely, according to the present embodiment, energy
consumption during vessel operation is effectively conserved by
reducing the frictional resistance of hull 60 with a low level of
energy consumption.
[0183] In addition, in the present embodiment, the protruding state
of negative pressure forming member 322 from hull shell plate 62 is
controlled by adjusting the angle of negative pressure forming
member 322 with angle adjustment mechanism 323 according to the
vessel operating state. Namely, in the case, for example, the
vessel has not reached a prescribed vessel velocity V or in the
case frictional resistance reduction effects produced by the
bubbles cannot be expected due to inclement weather, as shown in
FIG. 11B, by adjusting the angle of negative pressure forming
member 322 with angle adjustment mechanism 323, and positioning
prescribed face 322a of negative pressure forming member 322 in
roughly the same plane as hull shell plate 62 so that negative
pressure forming member 322 is not protruding, the increase in drag
relative to water flow 340 is inhibited, thereby making it possible
to reduce energy consumption. Moreover, by adjusting the protruding
height of negative pressure forming member 322 according to vessel
velocity, bubbles in the water are controlled so as to be
effectively released.
[0184] In this manner, in the present embodiment, the frictional
resistance of hull 60 can be effectively reduced by effectively
releasing bubbles into the water according to operating velocity or
inhibiting excessive increases in the drag of hull 60 as a result
of controlling the protruding state of negative pressure forming
member 322 from hull shell plate 62 according to the vessel
operating state.
[0185] Moreover, since the protruding state of negative pressure
forming member 322 from hull shell plate 62 is controlled by
adjusting the angle of negative pressure forming section 322,
bubble generator 311 can be composed simply and in a compact form,
enabling bubble generator 311 to be easily additionally attached to
the existing hull.
[0186] In addition, in the present embodiment, since negative
pressure forming member 322 is prevented from protruding by
arranging prescribed face 322a of negative pressure forming member
322 in roughly the same plane as hull shell plate 62, the opening
of indentation 320 is broadly obstructed by its face 322a which
reduces the surface irregularity in hull shell plate 62, and
thereby effectively inhibits the increase in drag relative to water
flow 340.
[0187] In addition, together with bubble generator 311 having a
simple composition, since an apparatus for pressurizing a gas is
not required, it goes without saying that the construction cost of
hull 60 can be held to a low level. Moreover, since chamber 330 and
negative pressure forming member 322 shown in FIG. 10B are molded
articles made of hard polyurethane, it is easier to achieve cost
reductions through mass production. In addition, since chamber 330
is removably attached to hull shell plate 62, less manpower is
required during maintenance.
[0188] Furthermore, the various shapes and combinations, etc. of
each of the constituent members shown in the above embodiment
merely represent one example, and can be altered in various ways
based on design requirements and so forth within a range that does
not deviate from the purport of the present invention. The present
invention also includes, for example, the variations described
below.
[0189] Although angle adjustment mechanism 323 is operated manually
based on the operating velocity and weather conditions in the above
embodiment, the present invention is not limited to this, but
rather angle adjustment mechanism 323 may be driven automatically
on the base of operating velocity and other data so as to adjust
the arrangement angle of negative pressure forming member 323.
[0190] In addition, although the above embodiment indicated an
example of applying the present invention to a small fishing
vessel, the present invention is not limited to this, but rather
can also be applied to other vessels such as tankers, container
ships and other large ships as well as high-speed vessels.
Furthermore, the size, number and location of bubble generator 311
are suitably set according to the shape of the hull.
EMBODIMENT 5
[0191] The following provides an explanation of still another
embodiment of the frictional resistance reducing vessel as claimed
in the present invention with reference to the drawings. FIG. 13A
shows an example of arranging bubble generators 411 on the bottom
of frictional resistance reducing vessel M shown in FIG. 10A
instead of bubble generator 311. In addition, as shown in FIG. 13B,
a plurality of bubble generators 411 are arranged in a row in the
direction of vessel width on the vessel bottom near the bow in the
present embodiment.
[0192] As shown in FIGS. 14A and 14B, bubble generator 411 contains
indentation 420 formed so as to be recessed from hull shell plate
62 of the vessel bottom, flow path 421, one end of which is open to
the atmosphere, while the other end is open to the inside of
indentation 420, wing body 422 having a wing and arranged inside
indentation 420, and positioning mechanism 423 that supports wing
body 422 while allowing to move freely along the lateral surface of
indentation 420, and positions the wing in a prescribed
position.
[0193] Indentation 420 is formed by chamber 430 having a
rectangular shape that is coupled to hull shell plate 62 from the
inside of hull 60. Namely, chamber 430 is formed into the shape of
a box of which one face is open, and the open end is coupled from
the inside of hull shell plate 62.
[0194] Here, flow path 421 is a space formed inside air induction
pipe (AIP) 431 connected to chamber 430. Opening 430a for
introducing a gas into the water is provided in chamber 430, and
air induction pipe 431 is connected to this opening 430a.
Furthermore, as shown in FIG. 14A, the installation space of air
induction pipe 431 can be used more efficiently by using a flexible
tubular member for air induction pipe 431.
[0195] As shown in FIG. 16, wing body 422 is mainly composed of
base 435, struts 436 and 437, and wing 438. Base 435 has a chamber
structure, and has inclined surface 435a on the bottom. This
inclined surface 435a here is formed into an upward curved shape,
and is formed so that its height gradually becomes higher towards
the front in direction of progress Dv (bow side). The ends of each
of the above struts 436 and 437 are respectively coupled to both
ends in the direction of width of this inclined surface 435, and
the other end of each strut 436 and 437 is respectively coupled to
both ends in the direction of width of the above wing 438. Struts
436 and 437 and wing 438 are respectively formed into a prescribed
wing form, and the leading and trailing edges are arranged to as to
face direction of progress Dv of hull 60. In addition, wing 438 is
arranged so the convex wing surface is facing upward. Furthermore,
an NACA wing form, an Ozibal wing form or various other wing forms
can be applied for the shapes of wing 438 and struts 436 and 437,
and are set according to the shape and velocity of the hull
(standard cruising velocity).
[0196] In addition, base 435, struts 436 and 437, and wing 438 are
mutually assembled to form a cylindrical shape in wing body 422,
and form curved water channel 439 in which a convex portion faces
upward in the vertical direction on the inside. In addition,
openings 435b and 435c are formed in the upper and lower (inclined
surface 435a) surfaces of base 435, and the above water channel 439
is connected with the space located above base 435 through these
openings 435b and 435c.
[0197] Returning to FIG. 14A, positioning mechanism 423 is in the
form of a linking mechanism that slides wing body 422 vertically
along the lateral surface of indentation 420, and the height of
wing 438 from hull shell plate 62 can be varied by operating lever
440. Furthermore, lever 440 is arranged on the deck, and its
operating position is maintained by a stopping means such as a
hook. In addition, flexible cover 441 in the form of a bellows and
so forth is arranged on positioning mechanism 423 which isolates
the above indentation 420 from the deck while adapting to the
movement of lever 440.
[0198] The following provides an explanation of the method of
reducing frictional resistance of hull 60 by frictional resistance
reducing vessel Ma having the structure described above with
reference to FIGS. 15A and 15B.
[0199] When the vessel is stopped, water (sea water) enters
indentation 420 to about the same water level as that around hull
60. When hull 60 enters the operating state due to the thrust of
propeller 63, relative water flow 450 is formed with respect to
hull 60. When the vessel reaches a prescribed velocity (for
example, the standard cruising velocity), as shown in FIG. 15A,
wing body 422 is moved downward by positioning mechanism 423 as a
result of operating lever 440, causing wing 438 to protrude to a
prescribed height from hull shell plate 62. At this time, the
inside of depression 420 is open to water flow 450, and a
separation region is formed in the water due to the level
difference of the entrance of indentation 420. Due to this
separation region, water pressure (hydrostatic pressure) in water
channel 439 decreases. In addition, since the flow path of water
along inclined surface 435a gradually narrows in water channel 439,
the flow rate of water flowing through water channel 439 increases
towards the back and water pressure decreases further. As a result,
the water pressure in water channel 439 forms a locally negative
pressure relative to the atmosphere.
[0200] Due to this pressure difference relative to the atmosphere,
pressure gradient Pf acts on the fluid (sea water and air) inside
flow path 421 and indentation 420, and air flows from the
atmosphere into flow path 421 and indentation 420. This air is then
fed into the water in water channel 439 via openings 435b and 435c
of wing body 422.
[0201] Air that has been fed into the water mixed into the water in
the form of bubbles 452, and the frictional resistance of hull 60
is reduced due to the juxtaposition of a large number of bubbles
452 in the vicinity of hull shell plate 62.
[0202] At this time, the energy required for feeding air into the
water is mainly the energy for changing the location of the gas.
Since this energy is obtained by changing the flow state of the
water by indentation 420 and wing body 422, this energy is less
than the energy consumed in the case of blowing pressurized gas
into the water. Namely, according to the present embodiment, energy
consumption during vessel operation is effectively conserved by
reducing the frictional resistance of hull 60 with a lower level of
energy consumption.
[0203] In addition, in the present embodiment, a separation region
and cavitation occur due to the level difference formed at the
entrance of indentation 420. Consequently, gas and water are
aggressively mixed at the interface of the gas and water due to the
agitation effects produced by this separation region and
cavitation, thereby promoting the release of bubbles 452 from
gas-liquid interface.
[0204] Moreover, due to circulating flow .GAMMA. that occurs around
wing 438 (because the flow rate over the upward facing wing surface
is greater than that over the downward facing wing surface), a
pressure difference occurs above and below wing 438, and upward
lift acts on hull 60 by means of wing 438. Consequently, the bow in
particular of hull 60 is raised up due to this lift, the submerged
surface area of hull 60 decreases, and the friction resistance of
hull 60 is further reduced. In addition, since this circulating
flow .GAMMA. that occurs around wing 438 acts in the direction that
increases the flow rate inside water channel 439, a decrease in the
water pressure inside water channel 439 is promoted, and the
suction force on bubbles 452 into the water increases.
[0205] Moreover, this circulating flow .GAMMA. also occurs around
struts 436 and 437 that support wing 438, and these circulating
flows .GAMMA. cause the formation of an eddy in the water behind
them. The eddy formed by circulating flow .GAMMA. changes the eddy
structure in the turbulent boundary layer in the vicinity of the
wall surfaces involved in frictional resistance, thereby dispersing
the amount of water movement within the boundary layer and
contributing to reduction of the frictional resistance of hull
60.
[0206] Furthermore, since adequate circulating flow .GAMMA. is
generated even during low-speed operation (for example, at about 10
knots), the above-mentioned friction resistance reduction effects
are demonstrated over a wide range of operating velocities.
[0207] In addition, in the present embodiment, the protruding
height of wing 438 is adjusted by positioning mechanism 423
according to the operating velocity and other operating conditions,
and is controlled so that bubbles are effectively released into the
water. This adjustment can be performed easily by a crew member by
operating lever 440 arranged on the deck.
[0208] In addition, in the present embodiment, in the case, for
example, the vessel has not reached a prescribed vessel velocity or
in the case frictional resistance reduction effects produced by the
bubbles cannot be expected due to inclement weather, as shown in
FIG. 15B, the wing 438 is positioned by positioning mechanism 423
so that the lower surface of wing 438 is roughly at the same height
as hull shell plate 62. Consequently, an increase in drag with
respect to water flow 450 is inhibited. Namely, by positioning the
lower surface of wing 438 so as to be roughly in the same plane as
hull shell plate 62, together with the opening of indentation 420
being blocked, since the surface irregularities in hull shell plate
62 are reduced, the increase in drag with respect to water flow 450
is effectively inhibited.
[0209] In this manner, in the present embodiment, the energy
consumption during operation can be reduced by effectively
releasing bubbles into the water according to operating velocity or
inhibiting excessive increases in the drag of hull 60 as a result
of controlling the protruding height of wing 438 from hull shell
plate 62 according to the vessel operating conditions.
[0210] In addition, since bubble generator 411 employs a simple
composition and eliminates the need for an apparatus for
pressurizing the gas, it goes without saying that the construction
cost of hull 60 can be held to a low level.
[0211] Furthermore, the various shapes and combinations, etc. of
each composite member shown in the embodiment described above refer
to only a single example, and can be altered in various ways based
on design requirements and so forth within a range that does not
deviate from the purport of the present invention. For example,
although positioning mechanism 423 is operated manually by means of
lever 440 based on operating conditions in the above embodiment,
the present invention is not limited to this, but rather the
protruding height of wing 438 may also be adjusted by driving
positioning mechanism 423 automatically based on operating velocity
and other data.
[0212] In addition, although the above embodiment indicated an
example of applying the present invention to a small vessel, the
present invention is not limited to large ships, but can also be
applied to other vessels such as tankers, container ships and other
oversized and large ships as well as high-speed vessels. The size,
number and location of bubble generator 411 should be suitably
determined according to the shape of the hull.
[0213] In FIGS. 17A and 17B, recesses are formed in hull shell
plate 62 (the vessel bottom here) to serve as bubble generators in
addition to depressions 420 in which the above wing body is
arranged. Here, a plurality of recesses 70 having a prescribed
depth are formed between a plurality of depressions 420 arranged in
a row in the direction of width and to the outside of a plurality
of depressions 420. As shown in FIG. 17B, these recesses 70 are
formed so that their depth from hull shell plate 62 gradually
becomes shallower towards the direction of the stern (towards the
back in the direction of progress). In addition, inclined surface
71, which protrudes at a prescribed height from hull shell plate
62, is formed in the area in front of (bow side) and adjacent to
each recess 70. The angled portion of this inclined surface 71
causes the occurrence of separation and cavitation for the purpose
of newly generating bubbles in the water and guiding bubbles
released from the above indentation 420 into recess 70 by creating
a state of low pressure inside recess 70. In this case, a portion
of the bubbles released from indentation 420 fill the inside of
recess 70 and are dispersed in the direction of vessel width. As a
result, a broad range of hull shell plate 62 is covered by dense
bubbles which is able to promote frictional resistance reduction
effects.
[0214] Furthermore, the various shapes and combinations, etc. of
each composite member shown in the embodiment described above refer
to only a single example, and can be altered in various ways based
on design requirements and so forth within a range that does not
deviate from the purport of the present invention. The shapes of
bubble generator 411 and recess 70 are designed using various types
of analysis such as flow field analysis by computational fluid
dynamics so as to minimize resistance (drag) relative to the flow
of water accompanying operation of hull 60 as well as change that
flow of water to a desired state.
[0215] Furthermore, since bubbles 22, 52, 142, 342 and 452 that are
mixed into the water in the above embodiments 1 through 5 are
formed at an internal pressure lower than the hydrostatic pressure
corresponding to water depth, when the above bubbles move at a
constant water depth (for example, when the bubbles are moving
along the vessel bottom), large water pressure acts on the bubbles
the farther they move away from the negative pressure region,
thereby causing the size of the bubbles to gradually become
smaller. According to research conducted thus far by the present
applicants, comparatively small bubbles are preferable for reducing
the frictional resistance of hull 60. Thus, bubbles generated by
negative pressure also act advantageously for reducing frictional
resistance with respect to this point as well.
* * * * *