Practical Ship Hydrodynamics

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70 Practical Ship Hydrodynamics for both the ‘naked’ hull and the hull with appendages). Propulsion tests are performed with an operating propeller and other relevant appendages. A problem is that the forces on appendages are largely driven by viscosity effects with small to negligible gravity effects. As Reynolds similarity is violated, the forces cannot be scaled easily to full scale. For ships with large and unusual appendages, the margins of errors in prediction are thus much larger than for usual hulls where experience helps in making appropriate corrections. The model is towed by weights and wires (Fig. 3.5). The main towing force comes from the main weight G1. The weight G2 is used for fine tuning: RT D G1 š G2 sin ˛ V R T Course keeper G 1 Sand strip (turbulence stimulator) Measuring mass R T Figure 3.5 Experimental set-up for resistance test G 2 Measuring scale The sign is positive if the vertical wire moves aft. The angle ˛ is determined indirectly by measuring the distance on the length scale. Alternatively, modern experimental techniques also use strain gauges as these do not tend to oscillate as the wire-weight systems. The model test gives the resistance (and power) for towing tank conditions: ž (usually) sufficiently deep water ž no seaway ž no wind ž fresh water at room temperature This model resistance has to be converted for a prediction of the full-scale ship. To do this conversion several methods are outlined in the following chapters, namely: ž Method ITTC 1957 ž Method of Hughes/Prohaska ž Method ITTC 1978 ž Geosim method of Telfer The most important of these methods in practice is the method ITTC 1978. Resistance tests are also used to measure the nominal wake, i.e. the wake of the ship without propeller. Measurements of the nominal wake are usually G 2
Resistance and propulsion 71 limited to the propeller plane. The local velocities were traditionally measured by pitot tubes. Currently, Laser-Doppler velocimetry also allows non-intrusive measurements of the flow field. The results are usually displayed as contour lines of the longitudinal component of the velocity (Fig. 3.6). These data play an important role in the design of a propeller. For optimizing the propeller pitch as a function of the radial distance from the hub, the wake fraction is computed as a function of this radial distance by integrating the wake in the circumferential direction: w⊲r⊳ D 1 � 2 0w⊲r, ⊳ d 2 0.8 0.7 0.6 90° 90° 0.9 Figure 3.6 Results of wake measurement 0.4 180° 180° 1.275 R 1.275 R 0° 0° 0.5 V/V o The wake field is also used in evaluating propeller-induced vibrations. 3.2.3 Method ITTC 1957 The resistance of the hull is decomposed as: RT D RF C RR RF is the frictional resistance, RR the residual resistance. Usually the resistance forces are expressed as non-dimensional coefficients of the form: ci D Ri 1 2 V2 s S
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Practical Ship Hydrodynamics
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Butterworth-Heinemann Linacre House
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3 Resistance and propulsion .......
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5.4.5 Interaction of rudder and shi
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Preface The first five chapters giv
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1 Introduction Models now in tanks
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Introduction 3 certain investigatio
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Introduction 5 there have been prop
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Introduction 7 is a material consta
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Introduction 9 margin may make a di
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Introduction 11 solution either. Ev
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Introduction 13 in naval architectu
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Introduction 15 ž Finite differenc
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Introduction 17 makes seakeeping pr
Page 29 and 30: Introduction 19 ship. Inner flow co
Page 31 and 32: Introduction 21 performed on workst
Page 33 and 34: Introduction 23 experts, while boun
Page 35 and 36: Introduction 25 two more decades be
Page 37 and 38: Introduction 27 Figure 1.3 A cylind
Page 39 and 40: Introduction 29 resolved by conside
Page 41 and 42: Introduction 31 ž LSOR (line succe
Page 43 and 44: Introduction 33 flow direction. CDS
Page 45 and 46: Introduction 35 equation, i.e. the
Page 47 and 48: 2 Propellers 2.1 Introduction Ships
Page 49 and 50: Propellers 39 ž rake iG The face o
Page 51 and 52: KT KQ h 10 . K Q K T Figure 2.3 Pro
Page 53 and 54: Propellers 43 methods or panel meth
Page 55 and 56: Propellers 45 This formula can be i
Page 57 and 58: Propellers 47 power. The earliest l
Page 59 and 60: Propellers 49 corrected subsequentl
Page 61 and 62: Propellers 51 flow computations are
Page 63 and 64: Propellers 53 occurs earlier, as ca
Page 65 and 66: Propellers 55 2.5.2 Open-water test
Page 67 and 68: Propellers 57 the traditional prope
Page 69 and 70: Propellers 59 (model/full-scale shi
Page 71 and 72: Propellers 61 represents the cavity
Page 73 and 74: Resistance and propulsion 63 1. The
Page 75 and 76: Resistance and propulsion 65 3.1.2
Page 77 and 78: Figure 3.3 Double-body flow y Wave
Page 79: Resistance and propulsion 69 course
Page 83 and 84: Table 3.1 Recommended values for CA
Page 85 and 86: Resistance and propulsion 75 3.2.6
Page 87 and 88: P B ⋅ 10 3 (kW) 40 30 20 10 0 n P
Page 89 and 90: Resistance and propulsion 79 t is t
Page 91 and 92: Resistance and propulsion 81 are no
Page 93 and 94: 3.4 Simple design approaches Resist
Page 95 and 96: Resistance and propulsion 85 of the
Page 97 and 98: Resistance and propulsion 87 non-li
Page 99 and 100: Resistance and propulsion 89 resist
Page 101 and 102: Resistance and propulsion 91 (doubl
Page 103 and 104: Resistance and propulsion 93 only b
Page 105 and 106: Resistance and propulsion 95 resist
Page 107 and 108: Resistance and propulsion 97 1°. S
Page 109 and 110: Ship seakeeping 99 3. Addition of t
Page 111 and 112: Ship seakeeping 101 1. No recording
Page 113 and 114: Ship seakeeping 103 Re denotes the
Page 115 and 116: Ship seakeeping 105 the ship axis x
Page 117 and 118: Ship seakeeping 107 The procedure t
Page 119 and 120: Ship seakeeping 109 If several ω r
Page 121 and 122: a 0.015 0.010 0.005 0 1 2 3 4 5 Uc/
Page 123 and 124: Ship seakeeping 113 The (only stati
Page 125 and 126: Ship seakeeping 115 height H1/3 for
Page 127 and 128: Ship seakeeping 117 using data of B
Page 129 and 130: Ship seakeeping 119 for each strip
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Ship seakeeping 121 between near fi
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Ship seakeeping 123 wave length of
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Ship seakeeping 125 The elements of
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Ship seakeeping 127 4.4.3 Rankine s
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Ship seakeeping 129 to zero. Then t
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Ship seakeeping 131 for commercial
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Ship seakeeping 133 Since the spect
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Ship seakeeping 135 ž The ωj are
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Ship seakeeping 137 changing sea sp
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Ship seakeeping 139 The wave impact
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Ship seakeeping 141 pressure gauges
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v(t) h(x,t) y u(x,t) Figure 4.23 On
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Ship seakeeping 145 computations wi
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Ship seakeeping 147 4. Derive the p
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Ship seakeeping 149 The free consta
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5 Ship manoeuvring 5.1 Introduction
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Ship manoeuvring 153 ž yaw rate (r
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Ship manoeuvring 155 Table 5.2 Non-
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Ship manoeuvring 157 but also the i
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C y 1.50 1.25 1.00 1.75 0.85 0.80 0
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Ship manoeuvring 161 section. The l
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Ship manoeuvring 163 methods have b
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esistance R is proportional to spee
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Ship manoeuvring 167 accuracy, but
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Ship manoeuvring 169 the difference
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Ship manoeuvring 171 it is importan
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d, y 20° 10° 0° −10° −20°
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Distance Lateral deviation Length o
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Ship manoeuvring 177 also performed
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Ship manoeuvring 179 ž Rudders out
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ehind the leading edge (nose) is: c
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Ship manoeuvring 183 the rudder. In
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Ship manoeuvring 185 attack ˛ of n
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V a /V 0.4 0.3 0.2 0.1 V a /V 2.0 1
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Ship manoeuvring 189 ž Rudder with
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average between VA and V1: � �
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C L (V corr ≠ V A ) C L (V corr =
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Ship manoeuvring 195 hull influence
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Ship manoeuvring 197 - Estimate the
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Ship manoeuvring 199 rudder tip vor
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Ship manoeuvring 201 (1993) uses de
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Ship manoeuvring 203 ž Profiles wi
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Ship manoeuvring 205 The ship perfo
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6 Boundary element methods 6.1 Intr
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C ⊲t1n3 C n1t3⊳⊲t3 xxz C s3 x
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xx D ⊲ 3 x⊲x xq⊳ ⊳/r 2 xy D
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The velocity in the x direction is:
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∂ ∂z Boundary element methods 2
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Boundary element methods 217 2. Thr
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and ⊲ , ⊳ is: r D � ⊲x ⊳
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⊲1⊳ y D � d 2 y d r 2 f ⊲c
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Boundary element methods 223 the so
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2 0 8xz D 2 2 0 8xxz D 2 2 0 8xzz D
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Figure 6.9 Velocities induced by po
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It is convenient to write ϕ as:
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Boundary element methods 231 usuall
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Boundary element methods 233 From t
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with: Boundary element methods 235
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Numerical example for BEM 237 S is
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Numerical example for BEM 239 In ea
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Numerical example for BEM 241 Once
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Numerical example for BEM 243 ž Tr
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Numerical example for BEM 245 that
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Numerical example for BEM 247 is ch
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Table 7.1 Sign for derivatives of p
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z y Figure 7.5 Coordinate system us
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the contour (Fig. 7.5): n� iD1 i
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Numerical example for BEM 255 Let E
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Numerical example for BEM 257 At th
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Numerical example for BEM 259 This
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Numerical example for BEM 261 The i
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Numerical example for BEM 263 The e
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References Abbott, I. and Doenhoff,
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References 267 Morgan, W. B. and Li
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Index Actuator disk, 44 Added mass,
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Practical Ship Hydrodynamics

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