Report: the end?

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Edgar P. Burkhart 2022-02-01 02:01:15 +01:00
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@ -103,7 +103,7 @@ turbulence: the $k-\varepsilon$ model and the $k-\omega$ sst model. The
$k-\omega$ sst model should provide better results in situations where strong
pressure gradients are present, at the cost of computing power.
For the purposes of this initial sensibility study, the $k-\omega$ model will
be used.
be used, as it will allow for faster computation times.
\subsection{Domain}
The studied domain will be a two-dimensionnal vertical slice going through the
@ -115,7 +115,7 @@ inside of the Saint-Jean-de-Luz bay, as shown in \autoref{fig:map}.
\begin{figure}
\centering
\input{fig/map.pgf}
\caption{Studied domain.}\label{fig:map}
\caption{Studied domain and bathymetry (\cite{shomsjl}).}\label{fig:map}
\end{figure}
The bathymetry was generated using bathymetric data from the SHOM
@ -154,6 +154,11 @@ $H=\SI{7.5}{\m}$. The wave equation is the following:
\eta=H\left[\sech\sqrt{\frac 34\frac Hh\frac{x-ct}h}\right]^2
\end{equation}
The setup will be run for a duration of \SI{60}{\s}, using an adjustable
timestep according to the cfd criteria. The results will be outputed at an
interval of \SI{0.5}{\s}, which will provide enough accuracy to represent the
studied case while providing a usable amount of data.
\subsection{Porosity setup}
The goal of the study is to find out the influence of the porosity parameters
on the model results. Porosity in the olaFlow model is goverened by five
@ -184,9 +189,69 @@ being the value that yielded the lowest error in the model calibration.
\caption{Parameter values.}\label{tab:params}
\end{table}
\subsection{Post-processing}
The results from the olaFlow model will be post-processed using Python. In
order to analyze the sensibility of the model to the studied parameters,
velocity and pressure sensors will be considered on the boundary of the
porous part of the breakwater.
\section{Results}
\subsection{Pressure}
\begin{figure}
\centering
\input{fig/p.pgf}
\caption{Dynamic pressure computed using olaFlow.}\label{fig:p}
\end{figure}
Dynamic pressure was computed by olaFlow on the entire domain. The dynamic
pressures obtained on the top side of the breakwater armour at
$x=\SI{79.75}{\m}$ and $x=\SI{99.75}{\m}$ is plotted in \autoref{fig:p}.
These results show that the porosity parameters that were modified have a minor
influence on the dynamic pressure generated by the water flow. The maximum
difference between the peak pressure for all cases is \SI{2}{\percent},
which confirms the negligible impact of the porosity parameters on dynamic
pressure.
\subsection{Velocity}
\begin{figure}
\centering
\input{fig/U.pgf}
\caption{Flow velocity computed using olaFlow.}\label{fig:u}
\end{figure}
The flow velocity was plotted at the same positions as dynamic pressure in the
previous section. The results are visible in \autoref{fig:u}.
Immediatly, it is apparent that the conclusion for flow velocity will not be
the same as for dynamic pressure. The difference between the velocity peaks for
all cases reaches \SI{65}{\percent}, showing the importance of selecting
adequate porosity parameters.
The graphs also show that the most influencial parameter in this case seems to
be porosity. The difference in peak flow velocity generated by the change in
mean diameter is of around \SI{26}{\percent}, while a change in porosity yields
a difference of around \SI{53}{\percent}.
Contrarily to dynamic pressure, flow velocity computations are strongly
impacted by changes in the porosity parameters.
\cite{poncet2021characterization} showed that attempting to calibrate those
results does not always yield the expected results, showing the necessity for
additionnal measurement campaigns, or for a large enough calibration database
to ensure the accuracy of a numerical model.
\section{Conclusion}
This project has shown that although the influence of porosity parameters on
flow pressure is fairly minor, their influence on flow velocity is major.
This shows the importance of using adequate values for these parameters in
order to ensure an accurate representation of reality.
Nevertheless, this study only focused on the mean diameter and porosity
parameters, but several other model parameters may have an influence on the
results. In particular, the friction parameters from the porosity model were
not studied -- default values were used -- and the influence of the
turbulence model was not considered. More work is still needed to evaluate the
influence of those parameters on the accuracy of the model.
\printbibliography
\end{document}