船底気泡流観察用曳航式水中航走体

船底気泡流状況を確認するために、観測用の曳航式水中航走体を新たに開発した。Fig. E.4 に観 測用の曳航式水中航走体を示す。本船の船首部から曳航した曳航式水中航走体は、Fig. E.5に示す ように船速を利用して船底部へ潜り込ませる。船速が速くなると曳航式水中航走体が浮上してくるため、

稼動式の水平翼により深度をコントロールして、船底との距離を維持できるようにした。また、船首部か らの曳航索長を調整することにより、船体長手方向の位置を調整可能とした。曳航式水中航走体の内 部にはVTRカメラおよび光源を装備し、船底状況を観測可能とした。

Fig. E.4 Towed vehicle for ship bottom observation.

Fig. E.5 Observation using towed vehicle.

表図題一覧

Table 1.1 Drag reduction by passive means. ... 5

Table 1.2 Drag reduction by active means. ... 5

Table 2.1 Boundary conditions. ... 35

Table 2.2 Mesh division of the wall direction in the prior examination calculation. 36 Table 2.3 Principal paticulars of calculated ship. ... 45

Table 2.4 Boundary conditions. ... 45

Table 2.5 Parameter of mesh for the proof calculation of ship hull. ... 46

Table 2.6 Comparison of drag coefficient. ... 62

Table 2.7 Comparison of CPU time. ... 63

Table 2.8 Principal particulars of ship. ... 65

Table 2.9 Energy saving effect. ... 66

Table 2.10 Energy saving effect (F.O. consumption). ... 67

Table 3.1 Experimental conditions of visualization of bubbly flow. ... 79

Table 3.2 Observation results of bubble flow. ... 85

Table 3.3 Observation results of bubble flow. ... 86

Table 3.4 Principal particulars of tested propeller. ... 91

Table 3.6 Bubbly flow conditions. ... 92

Table 3.5 Propeller open water test conditions. ... 92

Table 4.1 Experimental conditions. ... 100

Table 4.3 Principal particulars of model propeller B. ... 104

Table 4.2 Principal particulars of model propeller A. ... 104

Fig. 1.1 Resistance components of ships. ... 2

Fig. 1.2 Energy loss components of ships. ... 2

Fig. 1.3 Classification of energy saving device for ships [1]. ... 3

Fig. 1.4 Conceptual turbulent boundary layer near-wall phenomenology [16]. ... 7

Fig. 1.5 Riblet [1]. ... 8

Fig. 1.6 Image for LFC mechanism [22]. ... 10

Fig. 1.7 Spatiotemporal scales of coherent structure in real application [31]. ... 11

Fig. 1.8 Feedback control system for wall turbulence [31]. ... 11

Fig. 1.9 Feedback control system for wall turbulence with 192 wall shear force sensors and 48 shell-deformation actuators [31]. ... 12

Fig. 1.10 Photograph of air behavior [42]. ... 14

Fig. 1.11 The principal of the air cavity system. ... 14

Fig. 1.12 Till Deymann, full-scale test ship of SMOOTH. ... 14

Fig. 1.13 The bubble injectors [7]. ... 17

Fig. 1.14 3%power saving at about 14kn [7]. ... 17

Fig. 1.15 General arrangement of equipments [9]. ... 17

Fig. 1.16 Shear force sensor [70]. ... 18

Fig. 1.17 Example of time history of shear force measurement [70]. ... 18

Fig. 1.18 Image of MALS. ... 21

Fig. 1.19 Modular carrier ship “YAMATAI”. ... 21

Fig. 2.1 Calculation flow. ... 26

Fig. 2.2 Sketch of the air injection model. ... 31

Fig. 2.3 Calculation area. ... 35

Fig. 2.4 Air injection model. ... 35

Fig. 2.5 Void fraction profile in One-way calculation (Dzmin=1.0mm). ... 36

Fig. 2.6 Void fraction profile in Two-way calculation (Dzmin=1.0mm). ... 37

Fig. 2.7 Void fraction profile in Three-way calculation (Dzmin=1.0mm). ... 37

Fig. 2.8 Comparison of the void fraction profile in One-, Two-, Three-way calculations (Dzmin=1.0mm). ... 38

Fig. 2.9 Each sectional air mass flow in One-, Two-, Three-way calculations (Dzmin=1.0mm). ... 39

Fig. 2.10 Comparison of void fraction profile in Two-way calculation (x=100m). ... 40

Fig. 2.11 Each sectional air mass flow in Two-way calculation (Qa=0.049m³/s). ... 40

Fig. 2.12 Relation between smallest mesh size and drag coefficient on wall surface in Three-way calculation ( mm). ... 41

Fig. 2.13 Void fraction profile in Two-way calculation (x=100m). ... 42

Fig. 2.14 Each sectional air mass flow in Two-way calculation (Qa=0.049m³/s). ... 42 Fig. 2.15 Relation between smallest mesh size and drag coefficient on wall surface in

 7

t

a

Three-way calculation. ... 43 Fig. 2.16 Relation between and frictional drag reduction in Model-B

(Dzmin=20mm, ). ... 44 Fig. 2.17 Relation between and frictional drag reduction in Model-B

(Dzmin=20mm, mm). ... 44 Fig. 2.18 Arrangemens of air injectors. ... 46 Fig. 2.19 Mesh of hull surface. ... 47 Fig. 2.20 Wake distribution at propeller plane in single-phase flow calculation

(Mesh-A, Model-A). ... 48 Fig. 2.21 Wake distribution at propeller plane in single-phase flow calculation

(Mesh-B, Model-A). ... 48 Fig. 2.22 Wake distribution at propeller plane in single-phase flow calculation

(Mesh-A, Model-B). ... 49 Fig. 2.23 Wake distribution at propeller plane in single-phase flow calculation

(Mesh-B, Model-B). ... 49 Fig. 2.24 Distribution of skin friction coefficient on hull surface in single-phase flow calculation (Mesh-A, Model-A). ... 50 Fig. 2.25 Distribution of skin friction coefficient on hull surface in single-phase flow calculation (Mesh-B, Model-A). ... 50 Fig. 2.26 Distribution of skin friction coefficient on hull surface in single-phase flow calculation (Mesh-B, Model-A). ... 51 Fig. 2.27 Distribution of skin friction coefficient on hull surface in single-phase flow calculation (Mesh-B, Model-B). ... 51 Fig. 2.28 Void fraction distribution at midship section in One-way calculation

(Mesh-A, Model-A). ... 52 Fig. 2.29 Void fraction distribution at midship section in One-way calculation

(Mesh-B, Model-A). ... 52 Fig. 2.30 Void fraction distribution at midship section in One-way calculation

(Mesh-A, Model-B). ... 53 Fig. 2.31 Void fraction distribution at midship section in One-way calculation

(Mesh-B, Model-B). ... 53

t

a

0 .

 1 A

wf

A

wf

 7

t

a

Fig. 2.32 Void fraction distribution at propeller plane in One-way calculation

(Mesh-A, Model-A). ... 54

Fig. 2.33 Void fraction distribution at propeller plane in One-way calculation (Mesh-B, Model-A). ... 54

Fig. 2.34 Void fraction distribution at propeller plane in One-way calculation (Mesh-A, Model-B). ... 55

Fig. 2.35 Void fraction distribution at propeller plane in One-way calculation (Mesh-B, Model-B). ... 55

Fig. 2.36 Distribution of ta in One-way calculation (Mesh-A, Model-A). ... 56

Fig. 2.37 Distribution of ta in One-way calculation (Mesh-B, Model-A). ... 56

Fig. 2.38 Distribution of ta in One-way calculation (Mesh-A, Model-B). ... 57

Fig. 2.39 Distribution of ta in One-way calculation (Mesh-B, Model-B). ... 57

Fig. 2.40 Distribution of skin friction coefficient on hull surface in Three-way calculation (Mesh-A, Model-A). ... 58

Fig. 2.41 Distribution of skin friction coefficient on hull surface in Three-way calculation (Mesh-B, Model-A). ... 58

Fig. 2.42 Distribution of skin friction coefficient on hull surface in Three-way calculation (Mesh-A, Model-B). ... 59

Fig. 2.43 Distribution of skin friction coefficient on hull surface in Three-way calculation (Mesh-B, Model-B). ... 59

Fig. 2.44 Wake distribution at propeller plane in Three-way calculation (Mesh- A, Model-A). ... 60

Fig. 2.45 Wake distribution at propeller plane in Three-way calculation (Mesh-B, Model-A). ... 60

Fig. 2.46 Wake distribution at propeller plane in Three-way calculation (Mesh-A, Model-B). ... 61

Fig. 2.47 Wake distribution at propeller plane in Three-way calculation (Mesh-B, Model-B). ... 61

Fig. 2.48 Comparison of frictional resistance ratio ( ) in Three-way calculation. ... 63

Fig. 2.49 Flow of energy-saving effect prediction by air lubrication system. ... 64

/

_f1

f

C

C

Fig. 2.50 Results of speed trial. ... 66

Fig. 2.51 Comparison of F.O. consumption. ... 67

Fig. 2.52 Trend data of shear force and water speed (Results of ship bottom observation) ... 68

Fig. 2.53 Results of ship bottom observation (Vs=9.8kn, ALS-ON→OFF) and location of shear force sensors. ... 69

Fig. 2.54 Local skin friction reduction with ALS operation. ... 70

Fig. 2.55 Correlation between drag reduction and air layer thickness [95]. ... 70

Fig. 2.56 Void fraction distribution prediction on the bottom. ... 71

Fig. 2.57 Void fraction distribution prediction at the propeller position (port side). . 71

Fig. 2.58 Distribution of computed skin friction on the bottom. ... 72

Fig. 2.59 Comparison of computed and measured local skin friction reduction at positions of shear force sensors in 14.9kn and 13.5kn. ... 73

Fig. 2.60 Schematic view of changes from air film to bubbles. ... 74

Fig. 2.61 Comparison of computed total frictional drag reduction. ... 75

Fig. 3.1 An image of visualization of bubbly flow on ship bottom. ... 78

Fig. 3.2 Layout of visualization test for bubbly flow on ship bottom. ... 79

Fig. 3.3 Photographs of bubble flow visualizations on ship bottom (in still water). .. 80

Fig. 3.4 Photographs of bubble flow visualizations on ship bottom (constant heel angle=2.4deg.). ... 80

Fig. 3.5 Photographs of bubble flow visualizations on ship bottom (in oblique flow, drift angel=3deg.). ... 81

Fig. 3.6 Photographs of bubble flow visualizations on ship bottom (in oblique flow, drift angel=8.6deg.). ... 81

Fig. 3.7 Photographs of bubble flow visualizations on ship bottom ... 82

Fig. 3.8 Photographs of bubble flow visualizations on ship bottom ... 82

Fig. 3.9 Photographs of bubble flow visualizations on ship bottom ... 83

Fig. 3.10 Patterns of bubble flow on ship bottom. ... 83

Fig. 3.11 Bubble flow into propeller. ... 85

Fig. 3.12 Distribution of the void fraction on the hull surface. ... 87

Fig. 3.13 Comparison of the void fraction distribution. ... 87

Fig. 3.14 Air blow for full-scale ship. ... 88

Fig. 3.15 Bubble flow at ship bottom for full-scale ship. ... 88

Fig. 3.16 Experimental result of air blow in cavitation tunnel. ... 89

Fig. 3.17 Results of ship bottom observation (Vs=7.3kn, ALS－ON). ... 90

Fig. 3.18 Layout of propeller open water test in bubble flow. ... 91

Fig. 3.19 Bubble generation nozzle (Circular diffusion type). ... 92

Fig. 3.20 Bubble flow position. ... 92

Fig. 3.21 Propeller open water characteristics in bubbly flow (Slip=0.4). ... 94

Fig. 3.22 Photographs of propeller open water characteristics (Center distribution： Slip=0.4). ... 95

Fig. 3.23 Photographs of propeller open water characteristics (Upper distribution： Slip=0.4). ... 95

Fig. 4.1 Layout of propeller pressure fluctuation measurements. ... 99

Fig. 4.2 Bubble injector. ... 99

Fig. 4.3 Bubble flow position. ... 100

Fig. 4.4 Photographs of cavitation tests in bubble flow (Slip=0.4). ... 102

Fig. 4.5 Results of propeller pressure fluctuation measurements in bubble flow. ... 102

Fig. 4.6 Photograph of cavitation test in bubble flow (Propeller A). ... 104

Fig. 4.7 Photograph of cavitation test in bubble flow (Propeller B). ... 104

Fig. 4.8 Results of propeller pressure ... 105

Fig. 4.9 Results of propeller pressure ... 105

Fig. 4.10 Calculation Model. ... 107

Fig. 4.11 Comparison of reduction effect of sound pressure between calculation and experiment from Ref.[94]. ... 107

Fig. 4.12 Calculation model for pressure fluctuation of propeller. ... 108

Fig. 4.13 Comparison of reduction effect of pressure fluctuation by change of average void fraction for the 1D theory (rg=0.5mm, BL=1m). ... 109

Fig. 4.14 Comparison of reduction effect of pressure fluctuation by change of bubble radius for the 1D theory (α=0.2%, BL=0.5m). ... 109

Fig. 4.15 Comparison of reduction effect of pressure fluctuation by change of bubble layer thickness for 1D theory (α=0.2%, rg =0.5mm). ... 110

Fig. 4.16 Comparison of reduction effect of pressure fluctuation by change of average

void fraction for 3D-FEM (rg=0.5mm, BL=1m). ... 111

Fig. 4.17 Comparison of reduction effect of pressure fluctuation by change of bubble layer thickness for 3D-FEM (α=0.2%, rg=0.5mm). ... 111

Fig. 4.18 Distribution of void fractions used for 3D-FEM. ... 113

Fig. 4.19 Comparison of reduction effect of pressure fluctuation by change of bubble layer thickness for 3D-FEM (α=2.25%, rg=0.5mm). ... 113

Fig. 4.20 Comparison of reduction effect of pressure fluctuation by change of bubble layer thickness for 3D-FEM (α=4.5%, rg=0.5mm). ... 114

Fig. 4.21 Distribution of pressure fluctuation between with and without bubble layer at 1.5Hz (rg=0.5mm, BL=1.35m). ... 114

Fig. 4.22 Comparison of reduction effect of pressure fluctuation by change of average void fraction for 3D-FEM (rg=0.5mm, BL=0.45m). ... 115

Fig. 4.23 Comparison of pressure wave between with and without bubble layer. ... 116

Fig. 4.24 Calculated local void fraction on ship bottom and at the position of propeller. ... 118

Fig. 4.25 Calculated void fraction α2 on center line at the position of propeller. ... 118

Fig. 4.26 Bubble flow around a propeller with ALS-on for full-scale ship. ... 119

Fig. 4.27 Bubble flow around a propeller with ALS-off for full-scale ship. ... 119

Fig. 5.1 Bubble flow calculation result of ALS with stern bubble suction chamber.126 Fig. C.1 Outline of the bubble flow analysis around ship in waves. ... 146

Fig. C.2 Dynamic mesh for forced excitation of ship. ... 148

Fig. C.3 Outline of wave and flow in consideration of forward ship speed. ... 149

Fig. C.4 Calculation area... 149

Fig. C.5 Wave pattern around hull in regular head waves. ... 150

Fig. C.6 Void fraction distribution on ship bottom in regular head waves. ... 151

Fig. C.7 Void fraction distribution at propeller plane in regular head waves. ... 151

Fig. D.1 The mock-up of air chamber and recess. ... 155

Fig. D.2 Air velocity at chamber outlets. ... 156

Fig. D.3 Photograph of the experiment. ... 156

Fig. D.4 Air blow for mock-up model (Heel angle is 0deg.). ... 157

Fig. D.5 Air blow for mock-up model (Heel angle is 3deg.). ... 158

Fig. D.6 Comparison of valve opening and flow rate (without heeling). ... 159

Fig. D.7 Comparison of valve opening and power of blower. ... 160

Fig. D.8 Comparison of valve opening and flow quantity (Heel angle is 1.8deg. toward starboard). ... 161

Fig. D.9 Air blow of full-scale ship. ... 161

Fig. D.10 Flow diagram. ... 162

Fig. D.11 Calculation model for Fluent. ... 163

Fig. D.12 Comparison of flow rate distribution. ... 163

Fig. D.13 Relation between pressure loss and vale opening angle. ... 164

Fig. D.14 Analytical result of flow rate distribution (All valves are fully opened). . 165

Fig. D.15 Analytical result of flow rate distribution (Flow rate is equally distributed under minimum valve pressure loss). ... 166

Fig. D.16 Analytical result of flow rate distribution (Heel angle is 3deg. (port side down)). ... 167

Fig. D.17 Analytical result of flow rate distribution (Valve opening is adjusted as the distribution of flow rate becomes even). ... 167

Fig. D.18 Analytical result of flow rate distribution (All valve openings are O2 deg.). ... 168

Fig. D.19 Analytical result of flow rate distribution (Valve opening are linearly varied from starboard to port). ... 169

Fig. D.20 Analytical and measured result of flow rate distribution. ... 169

Fig. D.21 Simulated result of void fraction in seachest. ... 170

Fig. D.22 Velocity distribution and void fraction in seachest. ... 171

Fig. E.1 Shear force sensor. ... 174

Fig. E.2 Sensor arrangement on ship bottom. ... 174

Fig. E.3 Positions of shear force sensors. ... 174

Fig. E.4 Towed vehicle for ship bottom observation. ... 175

Fig. E.5 Observation using towed vehicle. ... 175

記号一覧

A

m ： プロペラ作動円面積 [m²] Awf ： 摩擦抵抗低減モデルにおける定数 [1/mm]

a

i ：

i

方向の船体重心の運動振幅 [m]

B ： 船幅 [m]

B

a ： 空気吹出部の船幅方向幅 [m]

B

L, BL ： 気泡層の厚さ [m]

C ： 水中音速（気泡無状態） [m/s]

C1 ： 水中音速 [m/s]

C2 ： 気泡流中音速 [m/s]

C

D ： 気泡の抗力係数 [ - ]

Cf , Cf ： 摩擦抵抗係数 [ - ]

0

Cf ^{, Cf0} ： 摩擦抵抗係数（ALS 非作動時） [ - ]

1

Cf , Cf1 ： 摩擦抵抗係数（単相流） [ - ]

Cm ： 水中の音速（気泡有状態） [m/s]

C

L ： 気泡の揚力係数 [ - ]

C

TD ： 気泡の乱流拡散係数 [ - ]

C

TL ： 気泡の乱流揚力係数 [ - ]

Cvp, Cvp ： 粘性圧力抵抗係数 [ - ]

1

C

vp , Cvp1 ： 粘性圧力抵抗係数（単相流） [ - ]

C ： 標準壁関数における定数（=0.09） [ - ]

Db ： 気泡直径（気泡径） [mm]

Dzmin : 壁面垂直方向の最小格子間隔 [mm]

d

^{： 喫水 [m]}

E ： 標準壁関数における経験定数（=9.793） [ - ]

EHP ： 有効馬力 [kW]

ep ： プロペラ効率 [ - ]

ep0 ： プロペラ効率（気泡無状態） [ - ] FB

： 気泡に働く浮力 [N]

FD

： 気泡に働く抗力 [N]

FL

： 気泡に働く揚力 [N]

FTD

： 気泡に働く乱流拡散力 [N]

FTL

： 気泡に働く乱流揚力 [N]

F 

S

： 気泡に働く表面力 [N]

F 

W

： 気泡に働く壁面反発力 [N]

g

,

g 

： 重力加速度 [m/s²]

H

^{： 波高 [m]}

H

a ： 空気吹出直後の気泡存在高さ [m]

Hn ： 気泡放出の深さ方向位置 [mm]

K ： プロペラ面内への気泡流入率 [ - ] or [%]

KQ , KQ ： トルク係数 [ - ]

KQ0 ： トルク係数（気泡無状態） [ - ]

KT , KT ： 推力係数 [ - ]

KT0 ： 推力係数（気泡無状態） [ - ] k ： 乱流エネルギー [m²/s²]

k

m ： 気泡を含む水中での音波の波数 [1/m]

k

s ： 気泡を含まない水中での音波の波数 [1/m]

L ： 船長（代表長さ） [m]

L

^{： 規則波の波長 [m]}

Loa ： 船長（全長） [m]

L

PP ： 船長（垂線間長） [m]

L

x ： 空気吹出部の船長方向長さ [m]

n ： プロペラ回転数 [1/s]

n

b ： 単位体積あたりの気泡個数 [ - ] nｇ ： 摩擦抵抗低減モデル（Model-A）の定数 [ - ]

P0 ： 大気圧 [Pa]

P

B ： 気泡を船底に送り込むのに必要なエネルギー [kW]

p

_{： 圧力 [Pa]}

Q

a ： 単位時間あたりの空気吹出量 [m³/s] or [L/min]

Re ： レイノルズ数 [ - ]

ReB ： 気泡運動に対するレイノルズ数 [ - ]

Rf ： せん断力計出力 [N]

rg ： 気泡半径 [m]

S

^{： 浸水表面積} [m²]

Ss ： せん断力計の検力部面積 [m²]

tB

S ： 気泡運動に対するストークス数 [ - ]

T

： 流れに対する相対座標系での波周期 [s]

TL ： 音波の透過損失 [dB]

t

： 時間 [s]

ta ： 相当空気膜厚さ [mm]

t

b ： 相当空気膜厚さ（空気吹出部の船幅方向幅基準） [mm]

U,

U

_ ： 一様流の流速 [m/s]

U* ^{： 無次元速度 [ - ]}

u

,

u

_x : 主流方向速度 [m/s]

u ： 摩擦速度 [m/s]

V,

V

： 船速 or 一様流速 [m/s]

Vg ： 気泡体積 [m³]

V

m ： 流速（曳航速度） [m/s]

V

s ： 船速 [m/s] or [kn]

V

T ： 気泡の終端速度 [m/s]

v

： 壁面に垂直な方向の速度 [m/s]

w ： 伴流率 [ - ]

x

i ：

i

方向の船体重心の変位 [m]

Y

k,

Y

_ ： 乱流による

k

と



^{の散逸率 [m]}

y

w ： 壁面からの距離 [m]

y ： 壁面からの無次元距離 [ - ]

z

： 水面からの距離 [m]



,



_g ： ボイド率 [ - ] or [%]



1 ： ボイド率（プロペラ単独特性試験時） [%]



2 ： ボイド率（キャビテーション試験時） [%]



g _{： 実効ボイド率} [ - ] or [%]



： 付加質量係数 [ - ]

ドキュメント内 空気潤滑法による船舶の摩擦抵抗低減技術に関する 研究 (ページ 182-194)