Stalking The Mythical Hydro-Validation Beast of Yore
- Sean M. Kery (CACI) | Pauk Bragulla (CSRA LLC)
- Document ID
- The Society of Naval Architects and Marine Engineers
- SNAME Maritime Convention, 24-27 October, Providence, Rhode Island, USA
- Publication Date
- Document Type
- Conference Paper
- 2018. The Society of Naval Architects and Marine Engineers
- 13 in the last 30 days
- 26 since 2007
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Validating a seakeeping code for a modern ship requires precise numerical simulations and / or model testing and / or full scale testing data to compare the computational data against. At best that validation will be limited to that ship class and the range of operating conditions contained in the research.
When researching an older modern vessel like El Faro, or a historic vessel like Titanic, the traditional methods of validation are unattainable because the necessary data does not exist. If money were no object, such a validation might be attempted, however with many older ships the technical record contains insufficient detail to support a rigorous effort. On the recent CSRA El Faro Investigation, the author, has had to approach the problem from other directions due to limited input information of less than ideal credibility.
Five major groups of information will affect the response of any ship to waves to a greater or lesser extent, but the roles and relative importance of the different factors is not well explored in the technical literature:
- Mass, added mass and the translational and rotational inertia (gyradius) terms
- Damping, including roll damping but also damping related to the heave, pitch and yaw degrees of freedom.
- The large angle stability restoring forces which are effected by cargo loss, cargo shift and downflooding.
- The choice of wave spectral properties used in the model
- The effect of nuances of the model setup including the length of simulation problem.
The first 4 terms correspond to the standard differential equation of Motion:
MXdd + C1Xd +C2 Xd^2 +KX = F
M are the various mass terms including body fixed mass, and added and entrained water
C1 are the linear damping terms
C2 are the non-linear damping terms
K is the instantaneous righting moment or lack there of
F represents the fluid forces in general which includes wind, waves and forward and leeward speeds.
The author has systematically explored the input parameter space in each of these areas and some of the insights gained may be of use to other investigators.
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