This presentation presents a new analysis and a comparison of results obtained from Vortex-Induced Motion (VIM) model tests of the MonoGoM platform, a floating unit designed for the Gulf of Mexico. The choice of scale between the model and the platform in which the tests took place was a very important issue that took into account the basin dimensions and mooring design. The tests were performed in three different basins: the IPT Towing Tank in Brazil (September 2005), the NMRI Model Ship Experimental Towing Tank in Japan (March 2007) and the NMRI Experimental Tank in Japan (June 2008. The objective of this work is to discuss the most relevant issues regarding the concept, execution and procedures to analyze comparatively the results obtained from model tests. The approach employed in the tests was designed to build a reliable data set for comparison with theoretical and numerical models for VIM prediction, especially that of Monocolumn platforms.

1. VORTEX-INDUCED MOTION OF A MONOCOLUMN
PLATFORM: NEW ANALYSIS AND COMPARATIVE
STUDY
Rodolfo T. Gonçalves¹
André L. C. Fujarra¹
Guilherme F. Rosetti¹
Kazuo Nishimoto¹
Marcos Cueva²
Elizabeth F. N. Siqueira³
¹ Department of Naval Architecture and Ocean Engineering
University of São Paulo, São Paulo, SP, Brazil
² Ocêanica Offshore, São Paulo, SP, Brazil
³ Research and Development Center (CENPES)
Petrobras, Rio de Janeiro, RJ, Brazil
Honolulu, Hawaii
June 2009

2. Summary
 Introduction
 Experimental setup
 Analysis Procedure
 Results
 IPT-Brazil (2005)
 NMRI-Japan (2007)
 NMRI-Japan (2008)
 Conclusions

3. Introduction
 This paper presents a new analysis
and a comparison of results obtained
from Vortex-Induced Motion (VIM)
model tests of the MonoGoM platform;
 The tests were performed in three
different basins;
 The objective of this work is to discuss
the most relevant issues regarding the
concept, execution and procedures to
analyze comparatively the results
obtained from model tests;
 The approach employed in the tests
was designed to build a reliable data
set for comparison with theoretical
and numerical models for VIM
prediction, especially that of
Monocolumn platforms.

5. Experimental Setup
 The experimental setup is characterized Breadth at the bottom 118.85 m
by a scale model of the MonoGoM floating
Main Breadth 100.00 m
(monocolumn platform) unit, supported by
a set of equivalent horizontal moorings, in Depth 58.00 m
three different basins: Draft test 39.50 m
 Towing Tank of the Instituto de Pesquisas
Tecnológicas do Estado de São Paulo Displacement 262,000 ton
(IPT), Brazil, in September 2005;
 Model Ship Experimental Towing Tank
(Middle Towing Tank) at the National
Maritime Research Institute (NMRI),
Japan, during March 2007, and;
 400 meter Experimental Tank of NMRI,
Japan, during June 2008
 The instrumentation was dedicated to
monitoring:
 Movements in the 6 degree of freedom;
 Accelerations on the XY plane;
 Forces in the springs (only in NMRI);
 Towing velocity.

6. Experimental Setup
1 2
 The main characteristics of IPT (Brazil)
the tests are: 3 4 3 3
NW
SE
incidence incidence
Dimensions Number
Model Total of Y Y
Tank LxWxD of Reynolds Number Vrn 2 1
Scale runs U U
[m] Springs
X X
IPT - Brazil 280.0 x 6.6 x
1:200 4 or 2 2x104 – 1x105 2.5 – 13.5 63
(2005) 4.0 Mooring Line
NMRI - Japan 150.0 x 7.5 x Mooring Line 4 4
1:90 3 5
1.5x10 – 3.5x10
5
6.0 – 11.0 41
(2007) 3.5
NMRI - Japan 400.0 x 18.0 x Low 1.5x105 – 3.5x105 7.0 – 11.5 57
1:90 3
(2008) 8.0 5
High 5.5x10 1x10
6
3.5 – 9.5 14
NMRI (Japan)
 Basically the difference are: CCD camera
 Dimensions of the basin; Spring
 Model scale;
1
180 degree 0 degree
incidence
 Number of springs;
incidence
3 Y Spring
Reynolds number.
U U
 X Spring
Mooring Line Wire
MPSO
2

7. Analysis Procedure
 The standard procedure of results  Non-Dimensional Motion Amplitudes
analysis intends to be robust and was  A/D is defined by the authors as the average
structured based on the current of the 20% highest peaks of the motion
signal
literature regarding fluid structure
interaction, in particular, the VIV and
VIM phenomenon.
 Restoration Forces
 Hydrodynamic Forces
 The linear rigid body motion equations for a
platform with two uncoupled DOF. are
represented by Sarpkaya, T. (2004) as shown
below:
 The restoration forces are measured in the
springs
 Then the lift and drag coefficients can be
write:

8. Analysis Procedure
 Added Mass  Reduced Velocity
 Fujarra, A.L.C. and Pesce, C.P.  The reduced velocity is
(2002), proposes a classical defined for each drift level,
analysis on the frequency taking into account the
domain for estimating the eventual alteration on the
added mass coefficient. added mass and restoration,
 According to that analysis, the thus:
following relation can be
stated:
 And:

9. Results – IPT (2005) 3
Y
SE
incidence
U
2
3
Y 1
NW
incidence
U
X X
Mooring Line
Mooring Line 4 4
 The results for the different
headings are similar until
Vrn = 10 for all the non-
dimensionals;
 The non-dimensional
motions increase in a
greater speed from Vrn =
10 , mainly on the NW
heading;
 In the Vrn = 10 region, the
in-line motion in the double
frequency of the motion
coexists with the transversal
motion;
 In the same region, there is
a high level of dynamic
amplification;

10. Results – IPT (2005)
 A new class of suppressor
of innovative geometry was
tested aiming to attenuate
VIM effects;
 The motions due to VIM are
mitigated in the region of
Vrn < 10. In region of Vrn >
10 nothing could be
concluded;
 Regarding added mass a
great decrease can be
observed in this region, due
to the change in the
pressure field which
resulted from the change
caused by the spoiler plates
on the flow.

11. Results – IPT (2005)
90 90 90
SE NW spoiler
2 2 2
120 60 120 60 120 60
1.5 1.5
plates 1.5
150 30 150 30 150 1 30
1 1
0.5 0.5 0.5
180 0 180 0 180 0
210 330 210 330
210 330
240 300 240 300
240 300
270 270
270
 The polar motion graphics on the XY plane have  Concerning the use of
clearly shown the presence of the coexistence spoiler plates, the
of the inline and cross-flow motions in both result of the motion on
cases. On the NW heading, the formation of the the XY plane, shows
typical eight shape trajectory is clear. that there is no
presence of any usual
observed shape.

12. Results – NMRI (2007)
 The non-dimensional
amplitude has shown
maximum values for of
about 0.9; these values are
closer to those verified in
the IPT tests;
 A great dispersion can be
observed. This can be
explained by the reduced
acquisition time. Due to the
length of the tank, L =
150m and the model scale
(1:90), a short running time
was possible, hence few
cycles were verified on the
motion registry.

13. Results – NMRI (2008)
 The execution of the same tests
in a new basin aimed at
obtaining a temporal series with
more cycles in fully developed
condition as well as higher
Reynolds number, obtained by
the increase of the carriage
speed;
 The non-dimensional amplitude
shows a similar pattern as those
obtained in the previous tests;
 The results regarding the drag
coefficient were practically
constant Cd = 0.7. The
difference occurs where the
dynamic amplification
phenomenon for values Vrn >
10 was verified.

14. Conclusions
 The present paper has presented an extensive database on the
effects of VIM of monocolumn platforms which can be used
advantageously for the initial design of such platforms;
 The results coming from different basins can be considered similar,
exempting their own peculiarities;
 When dimensioning VIM experiments, it is necessary to choose the
model scale in such a way as to allow for the greatest acquisition
time to improve statistics;
 Tests for Vrn > 12 are necessary to allow not only the identification
of the lock-in region, but also better behaved motions with clear
observations of double frequency and eventual motion drop;
 The paper that will be presented in the next aims to complement
the previous work in the literature and mainly to provide continuity
to this present work, in the way VIM tests are made for a new
configuration of a monocolumn platform.

15. Thank You!
Rodolfo T. Gonçalves
(rodolfo_tg@tpn.usp.br)