source: anuga_work/production/onslow_2006/report/anuga_setup.tex @ 4228

Last change on this file since 4228 was 4228, checked in by sexton, 17 years ago

(1) add building damage scripts for the study areas and update project.py (2) update report generation scripts (3) update Gantt chart (4) report updates to reflect URS input

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1The following information is required to undertake the
2inundation modelling;
3
4\begin{itemize}
5\item onshore and offshore elevation data (topographic and bathymetric data,
6see Section \ref{sec:data}),
7\item initial conditions, such as initial water levels (e.g. determined by tides),
8\item boundary conditions (the tsunami source as described in
9Section \ref{sec:methodology}), and
10\item computational requirements relating to the mesh construction.
11\end{itemize}
12 
13The initial conditions used for this scenario are MSL, HAT and LAT which were
14defined in Section \ref{sec:data}. Figure \ref{fig:IC} shows the MSL, HAT and
15LAT contours to illustrate the water level for each of these inial conditions.
16The dynamics of
17tidal effects (that is, the changes in water height over time for
18the entire study area) are not currently modelled.
19Sea floor friction will generally provide resistance to the water flow
20and thus reduce the impact somewhat. However, limited
21research has been carried out to determine
22the friction coefficients, and
23thus it has not been incorporated
24in the scenario. The
25results are therefore likely to be over estimates.
26
27\begin{figure}[h]
28
29  \centerline{\includegraphics[width=\paperwidth]{../report_figures/onslow_dli_contour.jpg}}
30
31  \caption{Onslow region showing the initial conditions used for the study;
32  -1.5m AHD (LAT), 0m AHD (MSL) and 1.5m AHD (HAT) contour lines.}
33  \label{fig:IC}
34\end{figure}
35
36
37To set up a model for the tsunami scenario, a study area is first
38determined. Preliminary investigations have indicated that the
39output from MOST or URS should be input to ANUGA
40at the 100m water depth. Historical run-up heights are
41of the order of 10 m and we would expect that a tsunami wave
42would penetrate no higher for this scenario, hence we have
43bounded our study region at 10m elevation.
44Current computation requirements define a coastline
45extent of around 100 km. Therefore, the study area of around 6300 km$^2$ 
46covers approximately 100 km of
47coastline and extends offshore to the 100m contour line and inshore to
48approximately 10m elevation.
49
50The finite volume technique relies on the construction of a triangular mesh which covers the study region.
51This mesh can be altered to suit the needs of the scenario in question. The mesh can be refined in areas of
52interest, particularly in the coastal region where complex behaviour is likely to occur.
53In setting up the model, the user defines the area of the triangular cells in each region of interest\footnote{Note that the cell
54area will be the maximum cell area within the defined region and that each
55cell in the region does not necessarily have the same area.}.
56The cell areas should not be too small as this will cause unrealisticly long computational time,
57and not too great as this may inadequately capture important behaviour.
58%There are no gains in choosing the area to be less than the supporting data.
59Figure \ref{fig:onslow_area} shows the study area with regions of difference cell areas. The total number
60of cells is 401939.
61Lateral accuracy refers to the distance at which we are confident in stating a region is inundated.
62Figure \ref{fig:onslow_area} shows the maximum triangular cell area and lateral accuracy for each region.
63Therefore we can only be confident in the calculated inundation extent in the Onslow town centre to within 30 m.
64
65
66\begin{figure}[hbt]
67
68  \centerline{ \includegraphics[scale=0.125]{../report_figures/onslow_resolution_zones.jpg}}
69
70  \caption{Study area for Onslow scenario highlighting four regions of increased refinement.
71Region 1: Surrounds Onslow town centre with a cell area of 500 m$^2$ (lateral accuracy 30 m).
72Region 2: Surrounds the coastal region with a cell area of 2500 m$^2$ (lateral accuracy 70 m).
73Region 3: Water depths to the 50m contour line (approximately) with a cell area of 20000 m$^2$ (lateral accuracy 200 m).
74Region 4: Water depths to the boundary (approximately 100m contour line) with a cell area of 100000 m$^2$ (lateral accuracy 445 m).
75}
76  \label{fig:onslow_area}
77\end{figure}
78
79
80The final item to be addressed to complete the model setup is the
81definition of the boundary condition. As
82discussed in Section \ref{sec:methodology}, a series of events corresponding
83to a range of return periods are selected as the tsunami sources.
84The resultant tsunami wave is made up of a series
85of waves with different amplitudes which is affected by the energy
86and style of the event as well as the bathymetry whilst it travels
87from its source to Onslow. The amplitude and velocity of each of these
88waves are then provided to ANUGA as boundary conditions and propagated
89inshore.
90
91The tsunami generation and propagation modelling uses the URS paradigm.
92The URS output is saved every 2.5 seconds and with a spatial resolution
93of two arc minutes.
94
95Sea floor friction will generally provide resistance to the water flow
96and thus reduce the impact somewhat. Initial experimental results
97indicate that the friction coefficient shoudl be 0.017.
98The following table summarises the modelling parameters;
99
100\begin{table}
101\begin{center}
102\caption{Parameters used in ANUGA for the Onslow scenario.}
103\begin{tabular}{|l|l|l|}\hline
104Mesh & & \\ \hline
105& resolution in Region 1 & 500 m$^2$ \\ \hline
106& resolution in Region 2 & 2500 m$^2$ \\ \hline
107& resolution in Region 3 & 20000 m$^2$ \\ \hline
108& remaining resolution & 100 000 m$^2$ \\ \hline
109Model parameters & & \\ \hline
110& friction & 0.017 \\ \hline
111& minimum stored height & 0.1 m \\ \hline
112\end{tabular}
113\end{center}
114\end{table}
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