EXPERIMENTAL STUDY ON VORTEX-INDUCED MOTIONS (VIM)          OF A LARGE-VOLUME SEMI-SUBMERSIBLE PLATFORM           Rodolfo ...
Outline     •    Introduction     •    Objective     •    Experimental Setup     •    HHT for Signal Analysis     •    Res...
Introduction •    The VIV is usually studied for rigid and      flexible cylinders with large aspect                      ...
Objectives     • Model test experiments       were performed to check       the influence on VIM,       such as:          ...
Experimental Setup     •    Experiments performed at the Institute of          Technological Research (IPT) at São Paulo, ...
Hilbert-Huang Method for the                         Signal Analysis                                                      ...
Results:                                                       Transverse Characteristic Amplitudes                       ...
Results:                                            Yaw Characteristic Angles                             5,00            ...
Yaw Characteristic Angle                                                                                    5,00    •   By...
Comparing Time Histories                 Vr=3.78                              Vr=6.76                                Vr=12...
Conclusions     • The VIM phenomenon was experimentally observed       for a Large-volume Semi-submersible Platform     • ...
Conclusions     • Considering the headings, an important asymmetry       was observed by comparing the 0 and 180 degrees  ...
Ongoing Results     • How do the waves concomitant with current influence the       VIM?     • What is the procedure to co...
See you in RIO next year!!                                                                            THANKS              ...
Upcoming SlideShare
Loading in …5
×

OMAE2011-4910: Experimental Study on Vortex-Induced Motions (VIM) of a Large-Volume Semi-Submersible Platform

1,115 views

Published on

A great deal of work has been developed on the spar and monocolumn vortex-induced motion (VIM) issue. However, there are very few published works concerning VIM of semi-submersible platforms, partly due to the fact that VIM studies for this type of platform recently became interesting particularly due to the increasing semi-submersible dimensions (columns diameter and height. In this context, a meticulous experimental study on VIM for this type of platform concept is presented here. Model test experiments were performed to check the influence of many factors on VIM, such as different headings and hull appendages. The results comply with in-line, cross-flow and yaw motion amplitudes, as well as with combined motions in the XY plane.

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,115
On SlideShare
0
From Embeds
0
Number of Embeds
12
Actions
Shares
0
Downloads
46
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

OMAE2011-4910: Experimental Study on Vortex-Induced Motions (VIM) of a Large-Volume Semi-Submersible Platform

  1. 1. EXPERIMENTAL STUDY ON VORTEX-INDUCED MOTIONS (VIM) OF A LARGE-VOLUME SEMI-SUBMERSIBLE PLATFORM Rodolfo T. Gonçalves Guilherme F. Rosetti TPN – Numerical Offshore Tank Department of Naval Architecture and Ocean André L. C. Fujarra Engineering Escola Politécnica – University of São Paulo Kazuo Nishimoto São Paulo, SP, Brazil Allan C. OliveiraRotterdam| The Netherlands | June | 2011June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 1
  2. 2. Outline • Introduction • Objective • Experimental Setup • HHT for Signal Analysis • Results – Transverse Characteristic Amplitude – Yaw Characteristic Angle – Time History • Conclusions • Ongoing ResultsRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 2
  3. 3. Introduction • The VIV is usually studied for rigid and flexible cylinders with large aspect Analytical ratio (L/D), for example in a riser dynamic scenario • VIM is investigated for rigid VIV VIM bodies with low aspect ratio, e.g. spar, MPSO and slender buoys Numerical Experimental • The current dimensions of the new semi-submersible platforms have increased, therefore VIV on: VIM on: promoting VIM Flexible Risers Spar platforms • The geometry of the semi- Steel Catenary Risers Monocolumn platforms Umbilical submersible implies more Slender buoy Every slender body operating Large-volume Semi-submersible complex VIM than that single at offshore scenario platforms column platformsRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 3
  4. 4. Objectives • Model test experiments were performed to check the influence on VIM, such as: – different current incidence angles (or headings) – hull appendages • Hard pipes in columns (black) • Fairleads and mooring chains in columns (red) • Riser supports in pontoons (green)Rotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 4
  5. 5. Experimental Setup • Experiments performed at the Institute of Technological Research (IPT) at São Paulo, Brazil • Small-scale tests (1:100) of a Large-volume Semi-submersible platform: – Four rounded-square columns – Rectangular closed-array pontoon – Only the hydrodynamic important appendages were represented (riser support, hard pipe and mooring lines running above the columns) • Equivalent mooring system: – Approximately parallel to the water surface – Linear and symmetric stiffness • Current velocity emulated by the towing carriage: • Different headings: – From 0.044m/s to 0.292m/s (model-scale) – 0, 15, 30, 45, 180, 195, 210 and 225 degrees – These velocities were suitable to investigate the entire range of synchronization for the VIM in the y- • Measurements: direction (cross-flow) • 6DOF motions using a commercial system for acquiring and processing • Forces at the 4 equivalent mooring linesRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 5
  6. 6. Hilbert-Huang Method for the Signal Analysis E H E ω t Time History t ω Instantaneous Marginal Energy Level Hilbert-Huang EMD Spectrum Spectrum IMFs Hilbert Transform Characteristic motion amplitude Hilbert Spectrum H (ω,t) Characteristic motion See Gonçalves et al. (OMAE2010) for details frequencyRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 6
  7. 7. Results: Transverse Characteristic Amplitudes 0,50 0,50 0,45 0,45 Nondimensional Amplitude (Ay/L) Nondimensional Amplitude (Ay/L) 0,40 0,40 0,35 0,35 0,30 0,30 0,25 0,25 0,20 0,20 0,15 0,15 0,10 0,10 0,05 0,05 0,00 0,00 0,00 5,00 10,00 15,00 20,00 0,00 5,00 10,00 15,00 20,00 Reduced Velocity (Vr) Reduced Velocity (Vr) 0º 15º 30º 45º 180º 195º 210º 225º • The characteristic amplitude is • Except for the headings of 0 and 180 nondimensionalized by the column face length, L. This choice permits to directly degrees, all other incidences showed a compare results from different incidence synchronization at 4 < Vr <10 conditions • It is not possible to define one • The reduced velocity is defined as: – Vr = (U.T0) ⁄ D oscillation frequency for Vr > 14 – T0 is the transverse natural period in calm water • The appendages influence on VIM can – D=L(|sin ∅|+|cos ∅| ) be verified by comparing the headings: – 0 and 180 degrees • According to those results, the 30, 45, – and also 15 and 195 degrees 210 and 225 degrees showed the largest • Differences may be attributed to the VIM amplitudes in the transverse presence and position of the hard pipes direction in the columnsRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 7
  8. 8. Results: Yaw Characteristic Angles 5,00 5,00 4,50 4,50 4,00 4,00 Yaw Amplitude [degree] Yaw Amplitude [degree] 3,50 3,50 3,00 3,00 2,50 2,50 2,00 2,00 1,50 1,50 1,00 1,00 0,50 0,50 0,00 0,00 0,00 5,00 10,00 15,00 20,00 0,00 5,00 10,00 15,00 20,00 Reduced Velocity (Vr) Reduced Velocity (Vr) 0º 15º 30º 45º 180º 195º 210º 225º • Considering the TRANSVERSE-T0, a • Again, it is possible to observe the synchronization range of the yaw is appendages influence by comparing identified for Vr > 10 the 0 and 180 degrees, and also 15 • Possible existence of “Vortex- and 195 degrees heading induced Yaw Motion (VIY)” • In previous work, Waals et al. (2007) proposed that the yaw oscillation was a consequence of a galloping phenomenon • The same behavior has not been observed in the present workRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 8
  9. 9. Yaw Characteristic Angle 5,00 • By using the natural period of yaw 4,50 (model test value), T6, to calculate the 4,00 Yaw Amplitude [degree] 3,50 reduced velocity, a typical VIM 3,00 behavior, for this degree of freedom, is 2,50 observed 2,00 1,50 – Vr=U T6 / D 1,00 • The largest yaw angles occur in Vr = 8, 0,50 0,00 a very similar result to that usually 0,00 5,00 10,00 15,00 20,00 obtained for VIM in the transverse Reduced Velocity (Vr=U T6 / D) 0º 15º 30º 45º 180º 195º 210º 225º direction • The amplitudes decrease for a high value of Vr, characterizing a auto- controlled phenomenon, like VIVRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 9
  10. 10. Comparing Time Histories Vr=3.78 Vr=6.76 Vr=12.06 • Time history of motions in the in-line (x/L), transverse direction (y/L) and yaw motion for the heading of 45 degrees • Vr=3.78 corresponds to a region at the beginning of the transverse synchronization • Vr=6.76 corresponds to the peak of oscillation inside the region of the transverse synchronization. The yaw motion presents frequency similar to the transverse oscillation • Vr=12.06 corresponds to the peak of yaw motion, i.e. in the region of the yaw synchronization. The frequency of the yaw motion is clearly definedRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 10
  11. 11. Conclusions • The VIM phenomenon was experimentally observed for a Large-volume Semi-submersible Platform • The largest VIM in the transverse direction was observed at 30, 45, 210 and 225 degrees of heading • In general, the VIM in the transverse direction occurs in a range of 4.0<Vr<14.00 with peaks around 7.0<Vr<8.0. The largest amplitudes obtained were Ay/L=0.4 (where L is the characteristic dimension of the rounded-square column)Rotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 11
  12. 12. Conclusions • Considering the headings, an important asymmetry was observed by comparing the 0 and 180 degrees incidences. Among other appendages, the hard pipes may be the reason for the differences observed • Considerable yaw motion oscillations were verified in these tests and a synchronization region could be well identified, herein named as “Vortex-Induced Yaw Motion (VIY)” • The largest yaw motions were verified for the 0 and 180 degrees of incidence, corresponding to angles around 4.5 degrees.Rotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 12
  13. 13. Ongoing Results • How do the waves concomitant with current influence the VIM? • What is the procedure to consider the VIM (current + waves) in the fatigue analysis? PRELIMINARY RESULTS Regular waves Sea conditionsRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 13
  14. 14. See you in RIO next year!! THANKS rodolfo_tg@tpn.usp.brRotterdam| The Netherlands | June | 2011 30th International Conference on Ocean, Offshore and Arctic Engineering 14

×