Page 17 - Pipelines and Risers

XIV Contents

9.5.2 Single Span Modal Analysis ........................................................................................................ 130
9.5.3 Multiple Span Modal Analysis ..................................................................................................... 130
9.6 Example Cases ..................................................................................................................................... 131
9.6.1 General ......................................................................................................................................... 131
9.6.2 Fatigue Assessment ...................................................................................................................... 133
9.7 References ............................................................................................................................................ 135
Chapter 10 Force Model and Wave Fatigue 137
10.1 Introduction .......................................................................................................................................... 137
10.2 Fatigue Analysis ................................................................................................................................... 138
10.2.1 Fatigue of Free-spanning Pipelines .............................................................................................. 138
10.2.2 Fatigue Damage Assessment Procedure ...................................................................................... 140
10.2.3 Fatigue Damage Acceptance Criteria ........................................................................................... 141
10.2.4 Fatigue Damage Calculated using Time-Domain Solution .......................................................... 142
10.2.5 Fatigue Damage Calculated Using Frequency Domain Solution ................................................. 142
10.3 Force Model ......................................................................................................................................... 144
10.3.1 The Equation of In-line Motion for a Single Span ....................................................................... 144
10.3.2 Modal Analysis ............................................................................................................................ 145
10.3.3 Time Domain Solution ................................................................................................................. 147
10.3.4 Frequency Domain Solution ......................................................................................................... 150
10.4 Comparisons of Frequency Domain and Time Domain Approaches ................................................... 152
10.5 Conclusions and Recommendations ..................................................................................................... 153
10.6 References ............................................................................................................................................ 154

Chapter 11 Trawl Impact, Pullover and Hooking Loads 155
11.1 Introduction .......................................................................................................................................... 155
1 1.2 Trawl Gears ..............................................................................................
1 1.2.1 Basic Types of Trawl Gear .......................................................................................................... 155
1 1.2.2 Largest Trawl Gear in Present Use .............................................................................................. 156
1 1.3 Acceptance Criteria .............................................................................................................................. 156
11.3.1 Acceptance Criteria for Impact Response Analyses .................................................................... 156
11.3.2 Acceptance Criteria for Pullover Response Analyses .................................................................. 157
11.4 Impact Response Analysis ................................................................................................................... 157
11.4.1 General ......................................................................................................................................... 157
11.4.2 Methodology for Impact Response Analysis ............................................................................... 157
11.4.3 Steel Pipe and Coating Stifmess .................................................................................................. 160
11.4.4 Trawl Board Stiffness, Mass and Hydrodynamic Added Mass .................................................... 163
11.4.5 Impact Response ............................................................................
11.5 Pullover Loads .......................................................................................
11.6 Finite Element Model for Pullover Response Analyses ....................................................................... 168
11.6.1 General ......................................................................................................................................... 168
11.6.2 Finite Element Models ................................................................................................................. 168
11.6.3 Analysis Methodology ................................................................................................................. 169
1 1.7 Case Study ........................................................................................................................................... 170
11.7.1 General ......................................................................................................................................... 170
11.7.2 Trawl Pull-Over For Pi on an Uneven Seabed .................................................................. 170
1 1.8 References ........................... ..................................................................................................... 175
Chapter 12 Installation Design 177
12.1 Introduction .......................................................................................................................................... 177
12.2 Pipeline Installation Vessels ................................................................................................................ 178
12.2.1 Pipelay Semi-submersibles .......................................................................................................... 178
.............................................................................................................. 182
12.2.2 Pipelay Ships and B~g