SWAN
SCIENTIFIC
AND
TECHNICAL
DOCUMENTATION
SWAN Cycle III version 40.91ABC
SWAN
SCIENTIFIC AND TECHNICAL
DOCUMENTATION
by
: The SWAN team
mail address
: Delft University of Technology
Faculty of Civil Engineering and Geosciences
Environmental Fluid Mechanics Section
P.O. Box 5048
2600 GA Delft
The Netherlands
e-mail
home page
:
:
swan-info-citg@tudelft.nl
http://www.swan.tudelft.nl
Copyright (c) 1993-2013 Delft University of Technology.
Permission is granted to copy, distribute and/or modify this document under the terms of
the GNU Free Documentation License, Version 1.2 or any later version published by the
Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-
Cover Texts. A copy of the license is available at http://www.gnu.org/licenses/fdl.html#TOC1.
iv
Contents
1 Introduction
1.1 Historical background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Purpose and motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 Readership . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.4 Scope of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.5 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.6 Acknowledgements
2 Governing equations
2.2.1 Wave kinematics
2.2.2
2.1 Spectral description of wind waves
. . . . . . . . . . . . . . . . . . . . . .
2.2 Propagation of wave energy . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Spectral action balance equation . . . . . . . . . . . . . . . . . . . .
2.3 Sources and sinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.1 General concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.2
Input by wind (Sin) . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.3 Dissipation of wave energy (Sds) . . . . . . . . . . . . . . . . . . . .
2.3.4 Nonlinear wave-wave interactions (Snl) . . . . . . . . . . . . . . . .
2.3.5 First- and second-generation model formulations in SWAN . . . . .
2.4 Wave damping due to vegetation . . . . . . . . . . . . . . . . . . . . . . .
2.5 The influence of ambient current on waves . . . . . . . . . . . . . . . . . .
2.6 Modelling of obstacles
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6.1 Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6.2 Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6.3 Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7 Wave-induced set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Numerical approaches
3.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Discretization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.1 Discretization in geographical space . . . . . . . . . . . . . . . . . .
3.2.2 Note on the choice of geographic propagation schemes . . . . . . . .
3.2.3 Discretization in spectral space
. . . . . . . . . . . . . . . . . . . .
v
1
1
2
2
2
4
4
7
7
10
10
10
12
12
17
19
25
31
33
35
35
36
37
37
39
41
41
43
43
46
47
vi
3.3 Solution algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 An illustrative explanation of the sweeping approach . . . . . . . . . . . .
Implementation of DIA within the four-sweep technique . . . . . . . . . . .
3.5
3.6 Convergence-enhancing measures
. . . . . . . . . . . . . . . . . . . . . . .
3.7 Stopping criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8 Governing equations in curvilinear co-ordinates
. . . . . . . . . . . . . . .
3.9 Computation of force in curvilinear co-ordinates . . . . . . . . . . . . . . .
3.10 Numerical treatment of obstacles
. . . . . . . . . . . . . . . . . . . . . . .
3.11 Crossing of obstacle and grid line . . . . . . . . . . . . . . . . . . . . . . .
3.12 Integration over σ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.13 Transformation from relative to absolute frequency . . . . . . . . . . . . .
3.14 Interpolation of spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.15 Computation of breaking source term . . . . . . . . . . . . . . . . . . . . .
3.16 On the approximation of refraction on coarse grids in large-scale SWAN
applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.16.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.16.2 The problem with refraction on coarse grids and how to deal with it
3.16.3 A historical overview of limitation on cθ
. . . . . . . . . . . . . . .
4 Wave boundary and initial conditions
5 Implementation of 2D wave set-up
5.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2 Analysis and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2.1 Discretization of the 2D setup equation . . . . . . . . . . . . . . . .
5.2.2 The iterative solver for the linear system . . . . . . . . . . . . . . .
6 Iterative solvers
6.1 Strongly Implicit Procedure (SIP) . . . . . . . . . . . . . . . . . . . . . . .
6.2 Successive Over Relaxation (SOR) technique . . . . . . . . . . . . . . . . .
7 Parallel implementation aspects
7.1 Load balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2 Parallelization of implicit propagation schemes . . . . . . . . . . . . . . . .
8 Unstructured mesh implementation
8.1 Description of an unstructured grid . . . . . . . . . . . . . . . . . . . . . .
8.1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.2 Relations between number of cells, vertices and faces
. . . . . . . .
8.1.3 Conditions imposed to the grid . . . . . . . . . . . . . . . . . . . .
8.2 Some notes on grid generation . . . . . . . . . . . . . . . . . . . . . . . . .
8.3 Numerical method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.1 Discretization procedure . . . . . . . . . . . . . . . . . . . . . . . .
48
51
54
54
56
58
60
61
63
63
64
65
66
68
68
68
72
75
77
77
78
78
84
87
87
88
89
89
90
93
93
93
94
94
95
95
95
8.3.2 The sweeping algorithm . . . . . . . . . . . . . . . . . . . . . . . .
99
Interpolation at user-defined locations . . . . . . . . . . . . . . . . . . . . . 100
8.4
8.5 Computation of wave-induced force . . . . . . . . . . . . . . . . . . . . . . 102
8.6 Calculation of diffusion-like terms . . . . . . . . . . . . . . . . . . . . . . . 104
vii
9 The overall solution algorithm
Bibliography
Index
105
107
123
viii