AddedMass:

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   Generate the added mass for various geometric shapes. At this point
   only 'prolate spheroid' is included.
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   Form:
   [mAdded, rOrigin, volume, m] = AddedMass( type, rho, d )
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   ------
   Inputs
   ------
   type        (1,:)  'prolate spheroid'
   rho         (1,1)   Density of surrounding fluid
   d           (1,1)   Data structure depends on body
                       .x    (1,1) x length
                       .y    (1,1) y length

   -------
   Outputs
   -------
   mAdded      (6,6)  Added mass
   rOrigin     (3,1)  Origin
   volume      (1,1)  Volume
   m           (6,6)  Generalized mass

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