Offshore and Coastal Modelling

388 Pages·13.001 MB·English

Lecture Notes on
Coastal and Estuarine
Studies
Managing Editors:
RichardT. Barber Christopher N. K. Mooers
Malcolm J. Bowman Bernt Zeitzschel
12
Offshore and Coastal Modelling
Edited by
RRG. Dyke, A.O. Moscardini, and E.H. Robson
Springer-Verlag
Berlin Heidelberg New York Tokyo
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Copyright American Geophysical Union. Transferred from Springer-Verlag in June 1992.
Lecture Notes on Coastal
and Estuarine Studies Offshore and Coastal Modelling Vol. 12
PREFACE
The paper s containe d i n thi s volum e wer e presente d orall y a t th e sevent h
POLYMODLE conference , hel d a t Sunderlan d Polytechni c i n th e Unite d King -
dom i n May 198 4 an d sponsore d b y Barclay s Bank PLC an d Imperia l Chemica l
Industrie s Ltd . The conference s ar e organise d annuall y b y th e Nort h Eas t
of Englan d Polytechnic' s Mathematica l Modellin g an d Compute r Simulatio n
Group - POLYMODE.L The Grou p i s a non-profi t makin g organisatio n base d
on th e mathematic s departmen t o f th e thre e polytechnic s i n th e regio n
and ha s membershi p draw n fro m thos e educationa l institution s an d fro m
regiona l industry . It s objectiv e i s t o promot e researc h an d collaboratio n
in mathematica l an d computer-base d modelling .
Afte r a shor t introductor y chapter , th e volum e may b e considere d a s
dividin g naturall y int o fou r parts . Chapter s 2 t o 5 c onstitut e th e firs t
part o n Tides , Stor m Surge s an d Coasta l Circulation s whic h deal s wit h th e
hydrodynamic s o f coasta l seas . Chapter s 6 t o 11 concer n Coasta l Engine -
erin g Modellin g an d discus s suc h coasta l phenomen a a s beac h erosion ,
sedimen t transport , an d non-linea r waves . The thir d par t (Chapter s 12
to 16 ) o n Offshor e Structure s consider s se a structure s i n genera l an d
the connection s betwee n th e structure s (hoses , moorings , pipelines ) i n
particular . The las t tw o chapter s focu s o n Offshor e Corrosio n problems .
The editor s woul d lik e t o tak e thi s opportunit y t o than k al l o f th e
participant s o f POLYMODLE 7 fo r makin g th e conferenc e s o successfu l an d
particularl y thos e who presente d th e papers . The editor s ar e especiall y
indebte d t o Avri l Barto n an d Barbar a Fould s who no t onl y type d thi s
manuscrip t bu t als o gav e valuabl e secretaria l assistanc e durin g th e
organisin g o f th e conference . The hel p o f Nei l Purve s who re-dre w some
of th e diagram s i s als o acknowledged .
P.P.G. Dyke ,
A. 0 . Moscardini ,
E. H. Robson .
Sunderlan d Polytechnic , Octobe r 1984 .
Copyright American Geophysical Union. Transferred from Springer-Verlag in June 1992.
CON T E N T S
PAGE
CHAPTER1 MODELLINGI N OFFSHORE AND COASTAL ENGINEERING:
P. P. G. Dyke
CHAPTER2 TIDES, STORM SURGES AND COASTALC IRCULATIONS:
3
N. S. Heaps
2.1 Bathymetry 3
2.2 Tides and Tidal Currents 3
2.3 North Sea storm Surges 10
2.4 Two-dimensionalN umericalS torm-surgeM odels 15
2.5 Surge Forecasting
26
2.6 Three-dimensionalM odels
40
2.7 VerticalS tructureo f Current
42
CHAPTER3 MODELLING STORM SURGE CURSRTERNUTC TURE:
55
A. M. Davies
3.1 Introduction 55
3.2 SpectralM odel Formulatoin 55
3.3 Form of Vertical Eddy Viscosity 58
3.4 A 3-D SimulationM odel of Surge Currentso n the
65
North-WestE uropeanS helf
3.5 A MechanisticM odel of Wind Induced Current
71
Profiles
3.6 Concluding Remarks 77
CHAPTER4 Optimally Controllde Hydrodynamicsf or Tidal
Power from the Severn Estuary: 83
s. C. Ryrie
4.1 Introduction 83
4.2 Hydrodynamics 83
4.3 Optimal Control 85
VI
PAGE
CHAPTER 5 NUMERICAL MODELLING OF STORM SURGES IN RIVER
ESTUARIES:
E. H. Twizell
5.1 Introduction 93
5.2 Points to note in Modelling 93
5.3 The Aims of a Mathematical Model of Storm 95
Surges
5.4 The Differential Equations of the Model 98
5.5 Computational Aspects 102
5.6 Numerical Results : The Storm of 1953 105
5.7 Summary 107
CHAPTER 6 COASTAL SEDIMENT MODELLING:
1nq
B. A. O'Connor
6.1 Introduction 109
6.2 Need for Computer Models 109
6.3 Model Types 111
6.4 Conclusions 132
CHAPTER 7 THE APPLICATION OF RAY METHODS TO WAVE REFRAC-
TION STUDIES:
I. M. Townend and I. A. Savell
7.1 Introduction 137
7.2 Ray Models 139
7.3 Application of the Ray Model, a Simple Case 146
7.4 A Study including Wave Breaking 154
7.5 A Study including Diffraction and Reflection 161
7.6 Future Developments 163
CHAPTER 8 A MODEL FOR SURFACE WAVE GROWTH: 165
A. J. Croft
8.1 Introduction 165
8.2 Formulation of the Problem 166
8.3 First Order Solution 170
8.4 Second Order Solution 172
8.5 Third Order Solution 173
8.6 Wind Shear Stress 179
8.7 Conclusion 184
VII
PAGE
CHAPTER 9 POWER TAKE-OFF AND OUTPUT FROM THE SEA-LANCHESTER
1g7
CLAM WAVE ENERGY DEVICE:
F. P. Lockett
9.1 Introduction 187
9.2 Experimental Tests 187
9.3 Power Take-off Simulation 188
CHAPTER 10 NUMERICAL MODELLING OF ILFRACOMBE SEAWALL:
201
P. Hewson and P. Blackmore
10.1 Introduction 201
10.2 Finite Element Modelling of Ilfracombe Seawall 201
10.3 Need for a Finite Element Model Approach 202
10.4 Conclusions 215
CHAPTER 11 MODELLING THE PLAN SHAPE OF SHINGLE BEACHES:
21g
A. H. Brampton and J. M. Motyka
11.1 Introduction 219
11.2 General Considerations when Modelling Beach 221
Changes
11.3 Derivation of an Alongshore Transport Formula 225
11.4 Incipient Motion of Shingle 228
11.5 Discussion 231
11.6 Conclusions 232
CHAPTER 12 MATHEMATICAL MODELLING APPLICATIONS FOR OFFSHORE
STRUCTURES:
P. J. Cookson
12.1 Introduction 235
12.2 Operational, Environmental and Foundation 235
Condition
12.3 Structural Concepts 2 37
12.4 Fabrication 242
12.5 Construction 2 43
12.6 Load Out 244
12.7 Tow Out 246
12.8 Installation 247
12.9 Mathematical Modelling in Platform Design 247
12.10 Conclusions 250
VIII
PAGE
CHAPTER 13 MATHEMATICAL MODEL OF A MARINE HOSE-STRING AT A
BUOY : PART 1, STATIC PROBLEM:
M. J. Brown
13.1 Introduction 251
13.2 Assumptions 254
13.3 Equations 255
13.4 Boundary Conditions 256
13.5 Hose Radius 257
13.6 The Load 258
13.7 Method of Solution 259
13.8 Analytical Solutions for Simplified Models 261
13.9 Results 262
13.10 Applications 268
13.11 Conclusions 274
Appendix 1 2 77
CHAPTER 14 MATHEMATICAL MODEL OF A MARINE HOSE-STRING AT A
BUOY : PART 2, DYNAMIC PROBLEM: 279
M. J. Brown
14 . 1 Introduction 279
14 .2 Equation of Motion 279
14 .3 Boundary Conditions 281
14 .4 Method of Solution 282
14 .5 Flanges 284
14 .6 Comparison of Analytical and Numerical Results 288
14 .7 Numerical Results 289
14 .8 Conclusions 298
Appendix 1 301
CHAPTER 15 THE DESIGN OF CATENARY MOORING SYSTEMS FOR
OFFSHORE VESSELS: 303
A. K. Brook
15.1 Introduction 303
15.2 Representation of the Environment 305
15.3 Mathematical Model of Moored Vessel 307
15.4 Calculations of Environmental Forces and Moments 308
15.5 Calculation of Mooring Forces and Moments 314
15.6 Static Analysis 319
15.7 Response of Vessel to Wind Gusting and Wave
Drift Action
15.8 Conclusions 320
IX
PAGE
CHAPTER 16 SOME PROBLEMS INVOLVING UMBILICALS, CABLES
323
AND PIPES:
D. G. Simmonds
16.1 Introduction 323
16.2 The Statics of Cables and Pipes 323
16.3 Hydrodynamic Forces 329
16.4 Analytical Solutions 333
16.5 Typical Problems and Numerical Solutions 338
16.6 Final Comments 348
CHAPTER 17 MATHEMATICAL MODELLING IN OFFSHORE CORROSION:
353
A. Turnbull
17.1 Introduction 353
17.2 General Mass Transport Theory 355
17.3 Mathematical Modelling of the Electrochemistry
356
in Cracks
17.4 Mathematical Modelling in Cathodic Protection
371
Offshore
17.5 Mathematical Modelling of Crevice Corrosion
372
and Protection
17.6 Mathematical Modelling of Corrosion in Concrete 372
17.7 Conclusions 374
CHAPTER 18 FATIGUE CRACK GROWTH PREDICTIONS IN TUBULAR
377
WELDED JOINTS:
S. Dharmavasan
18.1 Introduction 377
18.2 Fatigue Crack Growth Behaviour of Tubular
377
Joints
18.3 Theoretical Analysis of Crack Growth 385
18.4 Conclusions 392
Subject Index 394
Lecture Notes on Coastal
and Estuarine Studies Offshore and Coastal Modelling Vol. 12
1. MODELLING IN OFFSHORE AND COASTAL ENGINEERING
P.P.G. Dyke,
Department of Mathematics and Computer Studies,
Sunderland Polytechnic,
Green Terrace,
Sunderland.
As a branch of engineering, offshore engineering is probably one of
the newest. On the other hand, coastal engineering is one of the
oldest, yet each has benefited from the other. Offshore engineering
has had to grow up very quickly and has relied on the expertise of
coastal engineers when data and knowhow have been sadly lacking.
Coastal engineering, an altogether less glamorous and one can almost
say overlooked, branch of engineering, has received a welcome shot in
the arm from all the exploration and production now occurring in
coastal waters throughout the world. The major difference between
them, besides their pedigree, is that Offshore Engineering tends to
be related to the extraction of hydrocarbons from continental shelf
seas and hence can be seen as a net contributor to the Gross National
Product. Coastal Engineering, however, is an expense justified only
by the promise of an incursion of much greater expense if the effects
of waves, wind and currents on coastal structures and the coast
itself are ignored. This difference is a very important one to
industry and research grant awarding bodies, especially when they are
spoilt for choice on how to distribute,monies amongst researchers,
and has lead many erstwhile coastal engineers to conduct research in
the field of offshore engineering.
Parallel with the rapid rise of offshore engineering has been the well
publicised increase in accessibility of computers. The important
aspect of this for the engineer is the improvement in the data hand-
ling speed and the ease with which very large programs can now be
processed by even modest computers. The computer is now an essential
tool for the engineer to use in design, and the mathematical model
has become as commonplace in the everyday work of the engineer as the
laboratory model. In fact the mathematical model, if well enough
constructed, has the advantage over the laboratory model of relative
cheapness and greater flexibility. In the last twenty years, off-
shore engineering has given birth to many interesting and challenging
Copyright American Geophysical Union. Transferred from Springer-Verlag in June 1992.