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Global reference frame

The global coordinate system $O(\vec{e_1},\vec{e_2},\vec{e_3})$ is as follows:

• The point $O(0,0,0)$ is on the mean free surface,

• the vector $\vec{e_1}$ defines the $X$ coordinate,

• the vector $\vec{e_2}$ defines the $Y$ coordinate,

• the vector $\vec{e_3}$ defines the $Z$ coordinate and is upward.