The determination of hydrodynamic coefficients of full scale underwater vehicles using system identification (SI) is an extremely powerful technique. The procedure is based on experimental runs and on the analysis of on-board sensors and thrusters signals. The technique is cost effective and it has high repeatability; however, for open-frame underwater vehicles, it lacks accuracy due to the sensors’ noise and the poor modeling of thruster-hull and thruster-thruster interaction effects. In this work, forced oscillation tests were undertaken with a full scale open-frame underwater vehicle. These conducted tests are unique in the sense that there are not many examples in the literature taking advantage of a PMM installation for testing a prototype and; consequently, allowing the comparison between the experimental results and the ones estimated by parameter identification. The Morison’s equation inertia and drag coefficients were estimated with two parameter identification methods, that is, the weighted and the ordinary least-squares procedures. It was verified that the in-line force estimated from Morison’s equation agrees well with the measured one except in the region around the motion inversion points. On the other hand, the error analysis showed that the ordinary least-squares provided better accuracy and, therefore, was used to evaluate the ratio between inertia and drag forces for a range of Keulegan–Carpenter and Reynolds numbers. It was concluded that, although both experimental and estimation techniques proved to be powerful tools for evaluation of an open-frame underwater vehicle’s hydrodynamic coefficients, the research provided a rich amount of reference data for comparison with reduced models as well as for dynamic motion simulation of ROVs.

References

References
1.
Smallwood
,
D.
, and
Whitcomb
,
L.
, 2003, “
Adaptive Identification of Dynamically Positioned Underwater Robotic Vehicles
,”
IEEE Trans. Control Syst. Technol.
,
11
(
4
), pp.
505
515
.
2.
Caccia
,
M.
,
Indiveri
,
G.
, and
Veruggio
,
G.
, 2000, “
Modelling and Identification of Open-Frame Variable Configuration Underwater Vehicles
,”
IEEE J. Ocean. Eng.
,
25
(
2
), pp.
227
240
.
3.
Ridao
,
P.
,
Tiano
,
A.
,
El Fakid
,
A.
,
Carreras
,
M.
, and
Zirilli
,
A.
, 2004, “
On the Identification of Non-Linear Models of Unmanned Underwater Vehicles
,”
Control Eng. Pract.
,
12
, pp.
1483
1499
.
4.
Avila
,
J. P.
, 2008, “
Modelling and Identification of Hydrodynamic Parameters of an Underwater Robotic Vehicle
” (in Portuguese), Ph.D. thesis, Polytechnic School of the University of São Paulo, Brazil.
5.
Patel
,
M. H.
,
Dynamics of Offshore Structures
, (
Butterworth
,
London
, 1989, Chap. 5.
6.
Wolfram
,
J.
, and
Naghipour
,
M.
, 1999, “
On the Estimation of Morison Force Coefficients and Their Predictive Accuracy for Very Rough Circular Cylinders
,”
Appl. Ocean Res.
,
21
, pp.
311
328
.
7.
Chakrabarti
,
S.
, 2005,
Handbook of Offshore Engineering
,
Elsevier Science
,
Amsterdam, The Netherlands
, Chap. 4.
8.
Sarpkaya
,
T.
, and
Isaacson
,
M.
, 1981,
Mechanics of Wave Forces on Offshore Structures
,
Van Nostrand
,
New York
, Chap. 3.
9.
Sarpkaya
,
T
., 1981, “
A Critical Assessment of Morison’s Equation and Its Applications
,”
Proceedings of the International Conference on Hydrodynamics in Ocean Engineering
,
Trondheim
,
Norway
, pp.
447
467
.
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