Coefficient of proportionality between the hydrodynamic pressure force or moment on a rigid body in the $i$ direction due to unit acceleration of the rigid body in the $j$ direction ( $i,j=1,\ldots,6$, where $1,2$ and $3$ stands for translation in the $x, y$ and $z$ directions and $4, 5$ and $6$ stands for rotation with respect to the $x, y$ and $z$ axis respectively).

From the physical standpoint the added-mass coefficients represents the amount of fluid accelerated with the body. However, the added-mass coefficients for translation generally differ depending on the direction of the body motion, as opposed to Newton's equation $F = ma$ where the body mass $m$ is independent of the direction of the acceleration $a$. Also, in the absense of body symmetry, the cross-coupling coefficients such as $m_{12}, m_{13}$ and $m_{23}$ are non-zero, implying that the hydrodynamic force differs in direction from the acceleration.


Timothy S Choe
2003-03-15