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Example of the use of the principle of linear superposition.

$\phi _i (\vec{x})$ is a unit-source flow located at $\vec{x}_{i}$.


\begin{alignat}{2}
\phi_{i}(\vec{x}) = & = \frac{1}{2\pi }\ln \vert\vec{x}-\vec{...
...\vec{x}-\vec{x}_{i}\vert \right)^{ - 1} & \mbox{\ (in 3D),} \notag
\end{alignat}

A more general potential function can be written as the linear superposition of the unit-sources, as follows:


\begin{displaymath}\phi(\vec{x}) = \sum_{i} m_{i}\phi_{i}(\vec{x}) \notag
\end{displaymath}  

where the value of the constants $m_{i}$ are found such that:


\begin{displaymath}\phi = \sum_{i} m_i \phi_i (\vec{x}) \mbox{ \ satisfies the KBC on the boundaries } \notag
\end{displaymath}  

Caution: $\phi(\vec{x})$ must be regular for $x \in V$ (fluid domain), so it is required that $\vec{x} \notin V$.


 
Figure: Note: $\vec{x}_{j}, j=1,\ldots,4$ are not in the fluid domain $V$.
\begin{figure}
\centering\epsfig{file=lfig105.eps,height=2in,clip=}
\end{figure}



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