0
Research Papers: Structures and Safety Reliability

New Methodology for the Determination of the Vertical Center of Gravity of In-service Semisubmersibles: Experimental Assessment

[+] Author and Article Information
Ivan N. Porciuncula

Petróleo Brasileiro S.A.,
UO-BC/IPP/EN—Naval Engineering,
Macaé CEP 27.923-510, Rio de Janeiro, Brazil
e-mail: ivann@petrobras.com.br

Claudio A. Rodríguez

LabOceano,
Department of Naval Architecture
and Ocean Engineering,
COPPE—Federal University of Rio de Janeiro,
Caixa Postal No. 68.508,
Rio de Janeiro CEP 21.945-970,
Rio de Janeiro, Brazil
e-mail: claudiorc@laboceano.coppe.ufrj.br

Paulo T. T. Esperança

LabOceano,
Department of Naval Architecture
and Ocean Engineering,
COPPE—Federal University of Rio de Janeiro,
Caixa Postal No. 68.508,
Rio de Janeiro CEP 21.945-970,
Rio de Janeiro, Brazil
e-mail: ptarso@laboceano.coppe.ufrj.br

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received April 21, 2016; final manuscript received August 28, 2016; published online October 20, 2016. Assoc. Editor: Xi-Ying Zhang.

J. Offshore Mech. Arct. Eng 139(2), 021601 (Oct 20, 2016) (9 pages) Paper No: OMAE-16-1044; doi: 10.1115/1.4034762 History: Received April 21, 2016; Revised August 28, 2016

Recently, the authors have proposed a new methodology for the vertical position of the center of gravity (KG) estimation of semisubmersibles at its production location. The procedure, called the Zero GM method, is based on the identification of a characteristic behavior of the floater around an induced neutral equilibrium condition. The proposed methodology has been already numerically explored in terms of stability and practical feasibility based on real data of an offshore production semisubmersible. As the procedure implies in temporarily taking the vessel to neutral–unstable upright equilibria (both considered unsafe conditions), experimental tests appear as a physical mean of demonstrating the procedure's practical application and safety. The objective of this paper is to present the results of a model test campaign where the Zero GM method has been experimentally investigated on an offshore semisubmersible. The model and its ballast weight distribution were especially designed to simulate the path of the KG in the process of finding the neutral equilibrium, both in calm-water and in waves. The effect of mooring lines was also assessed. The experimental results showed that around the neutral equilibrium a jump in the loll angle and a peak in the roll oscillation period appear, so that KG can be accurately estimated, even in the presence of (mild) waves and mooring. Capsize or risk of capsize has not been observed during the tests, even when relatively large unstable conditions were tested in waves.

Copyright © 2017 by ASME
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Fig. 1

Semisubmersible model at LabOceano's ocean basin

Grahic Jump Location
Fig. 2

Hydrostatic roll restoring moment (numerical model)

Grahic Jump Location
Fig. 3

Model's deck ballast system: rods locations on the deck

Grahic Jump Location
Fig. 4

Ballast positions on the rods with respect to deck (in mm, model scale)

Grahic Jump Location
Fig. 5

Model calibration measurement: XG and ZG coordinates

Grahic Jump Location
Fig. 6

Model calibration measurement: pitch inertia

Grahic Jump Location
Fig. 7

Mooring system layout

Grahic Jump Location
Fig. 8

Mooring restoring curves in surge and sway

Grahic Jump Location
Fig. 9

Spectra of tested waves

Grahic Jump Location
Fig. 10

Conventional inclining test results

Grahic Jump Location
Fig. 11

Measured equilibrium/loll angle in decay tests

Grahic Jump Location
Fig. 12

Measured natural roll period in decay tests

Grahic Jump Location
Fig. 13

Roll decay time series: free-floating

Grahic Jump Location
Fig. 14

Roll decay time series: moored condition

Grahic Jump Location
Fig. 15

Roll time series under wave W01 (T = 8 s, H = 1.44 m, beam waves)

Grahic Jump Location
Fig. 16

Roll time series under wave W02 (T = 10 s, H = 2.47 m, beam waves)

Grahic Jump Location
Fig. 17

Roll time series under wave W03 (T = 10 s, H = 2.47 m, bow quartering waves)

Grahic Jump Location
Fig. 18

Roll time series under wave W04 (T = 10 s, H = 3.67 m, beam waves)

Grahic Jump Location
Fig. 19

Mean roll in waves around neutral equilibrium

Grahic Jump Location
Fig. 20

Roll response spectra under wave W01 (T = 8 s, H = 1.44 m, beam waves)

Grahic Jump Location
Fig. 21

Spectral peak periods of roll responses in waves around neutral equilibrium

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In