Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
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HYDRODYNAMIC INTERACTION BETWEEN FLOATING STRUCTURES DURING
HEAVY LIFT OPERATIONS – IS IT WORTH ANALYSING?
Z Ayaz, M Safsafi, A Slyozkin and N Xie, Saipem Ltd., UK
SUMMARY
This paper assesses a series of typical multi-body interaction cases for heavy lift operations; installation or lift onto
FPSO, spar platform, heavy transport vessel (HTV) and floating launched jacket with the DP semi-submersible crane
vessel (SSCV). The operability parameters for heavy lift/installation operations are assessed with and without
considering hydrodynamic interaction effects. The operational stages most affected by the interaction effects are
identified and the conclusions are drawn with respect to analysis and operational guidance.
Keywords: Floating multi-body interaction, FPSO, spar, semi-submersible crane vessel, dynamic-positioning
NOMENCLATURE
DP
DOF
FPSO
Hs
HTV
RAO
SSCV
S7000
Tz
Tp
Dynamic positioning
Degrees-of-Freedom
Floating Production, Storage and Offloading
Significant wave height (m)
Heavy Transport Vessel
Response Amplitude Operator
Semi-Submersible crane vessel
Saipem 7000
Zero-crossing period(s)
Wave peak period (s)
1.
INTRODUCTION
The heavy lift vessels and floating platform/vessels that
are being worked on can exert hydrodynamic loads on
each other, whether they are connected through mooring
system or operating in a dynamic positioning (DP) mode,
due to proximity. These loads are mainly caused by
diffraction and radiation wave fields which are
propagating from each body and influence the motion of
the neighbouring body. Traditionally, hydrodynamic
modelling of multi-body interactions during lifting
operations has been carried out independent of this
influence of disturbed wave fields between the bodies,
[1]. Instead, the interaction between the floating bodies
has been taken into account via crane hoisting and
rigging wires, mooring lines or in the case of the DP
operations the forces applied to the DP system through
the crane loads, [2], (mechanical coupling). This has,
however, proven to be an acceptable method based on
the studies carried out for crane vessel-cargo barge
coupled motions [3], [4], [5]. These studies showed that
barge motions may be affected by some 20% to 30% due
to proximity to the SSCV, however these hydrodynamic
interaction effects are an order of magnitude smaller than
the mechanical coupling effects, [3], [5]. Nevertheless, it
has been noted that hydrodynamic interaction effects can
only by analysed properly by means of a complicated
diffraction analysis which have proven to be an
expensive task when the early studies, which formed the
standard industry practise, were conducted, [3], [4].
Furthermore, the sea states experienced in practise are
considerably less severe than those used in the analysis
© 2014: The Royal Institution of Naval Architects
or model tests. It is also a well-known fact that for any
particular weather conditions, the experience and skill of
the offshore personnel responsible for the operation serve
to minimise the response, [4].
With advancement of multi-body diffraction solvers and
computational fluid dynamic tools (CFD), radiation and
diffraction forces through the interaction of multi-bodies
and other interaction effects such as shielding can now be
taken into account in the analysis process. These tools
have become an indispensable part of most multi-body
interaction analyses involving cargo transfer, [5], [6], 7],
[8]. The analyses can be carried out both in frequency­
domain, [6], [7] or in time-domain which takes non­
linearities due to coupling between SSCV, adjacent body
(or two interacting vessels) and cargo into account, [2],
[5], [8]. They are now being used to model operational
methods which are being employed by the offshore
personnel based upon the experience such as using SSCV
as a shield to reduce the motions of vessel/platform. The
increasing presence of deep-water floating platforms
such as FPSO, spar or semi-submersibles, have also
resulted significant portion of the DP SSCV operations
involve cargo transfer onto such platforms in which
hydrodynamic interaction between similar size of
structures could be important, [2], [5].
(a)
(b)
(c)
(d)
Figure 1: Installations with SSCV from (a) FPSO, (b)
Spar, (c) Cargo barge and (d) Jacket Installation
Therefore, in order to shed new light into the influence of
hydrodynamic interaction effects on typical multi­
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
floating body heavy lift operations, of which the
examples are shown in Figure 1, the numerical analyses
are presented in this paper using state-of-art numerical
analysis tools.
structures is handled creating a mesh (panel) or “freesurface lid” in the gap in which spurious waves are
partially suppressed by tuning damping parameters, [5],
[9].
2.
The hydrodynamic database including hydrodynamic
reaction (radiation), diffraction and drift forces of the
coupled system as shown in Figure 2 is then provided to
6-DOF non-linear time domain analysis software which
can handle hydrodynamic and mechanical coupling of
multiple floating structures and cargo, [10], [11]. An
illustration of numerical models for the coupled system is
shown in Figure 3.
NUMERICAL ANALYSIS
The numerical assessment consists of modelling coupled
body hydrodynamics, 6-DOF coupled non-linear time
domain simulations and the critical stages in which
operability can be affected due to hydrodynamic
interaction.
2.1
NUMERICAL MODEL
The hydrodynamic interaction between two floating
bodies is calculated using DIFFRAC software package,
[9]. DlFFRAC solves the linearized velocity potential
problem using a three-dimensional source distribution
technique (Green Function), [5], [9].
If it is assumed that there exist M independently moving
bodies, various quantities of potential, ϕ, can be
separated into various quantities due to the linearization:
M
6
  0  7   mj
(1)
m1 j1
where ϕ0 is incidental wave potential, ϕmj is potential due
to motion m of a body and ϕ7 is diffracted wave
potential. These sources are distributed over the wetted
hull surface which is modelled by a number of panel
elements (See Figure 2). As shown in (1), the program is
capable of handling the hydrodynamics of any number of
independently moving bodies. The following then can be
computed in relation to the analysis described in this
paper:
 Added mass and damping coefficients;
 Wave forces and wave moments;
 Wave induced motions;
 Wave heights in the waterline or in arbitrary off­
body points;
 Water velocities over the body surface or in
arbitrary off-body points;
 Pressure distribution over the body surface;
 Second-order wave drift forces.
Figure 2: Example of multi-body mesh for DIFFRAC
The well-known problem of overprediction of wave
forces and wave drift forces in the gap between two
Figure 3: SSCV- Floating Body (Spar) and Cargo
Hydrodynamic and Mechanic Coupled Numerical
Model, [2]
2.2
ANALYSIS DATA
The heavy lift operations assessed in this paper were
carried out by the Saipem’s SSCV “S7000”. The
following structures were assessed for the analysis;
FPSO, Spar Platform, HTV and a floating launch Jacket.
The principal particulars of each structure are given in
Table 1.
Table 1: Principal particulars of the analysed floating
structures
Parameter
Length (m)
Width (m)
Draught (m)
Displacement
(t)
S7000
175
87
27.5
165540
FPSO
258
41
15.5
119618
SPAR
173
25.9
154
83500
HTV
159
42
5.3
23320
Jacket
140
88
110
22100
The numerical models used for each analysis are shown
in Figure 4. The hydrostatic and hydrodynamic models
were validated using the available model test and design
information. Note that the analysis involving FPSO,
Spar and HTV represent typical multi-body diffraction
analysis models while the Jacket has also been modelled
as panels along with more appropriate Morison element
modelling for truss type structures. The reason for this is
explained in Section 2.3. The viscous damping terms
have been added to the models separately.
© 2014: The Royal Institution of Naval Architects
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
SSCV-FPSO: The analysis covers the installation of a
module onto FPSO, as shown in Figure 1(a), which is
guided by installation aids (bumper-guide). A
conventional approach as shown in Figure 3 has been
followed for the modelling of the module rigging,
bumper and guide system, and it will not be described in
detail in this paper. The hydrodynamic database was
created considering the interaction effects as explained in
Section 2.1 and as a companion to the traditional
approach with no interaction (i.e. when only phasing and
vessel relative positions are considered), was also
investigated.
The analysis was performed using LIFSIM [10]
simulation software package. The Figures 5 and 6 below
present two typical relative positions of the SSCV and
FPSO for the module installation. The distance between
bodies was approximately 35m. Hence, the
hydrodynamic properties were derived based on the
vessel relative positions and then used for the analysis.
The module installation analysis considered the pre­
setdown hovering of the module above the installation
area on the FPSO, see Figure 1(a), and the final
engagement with the guidance system. The analysis
presented here focused on the latter stage as it was found
to be the most governing stage of the operation and was
also challenging in terms complexity of the simulation.
The acceptable criteria were based on module motions,
rigging and guide/bumper system loads and there were
monitored throughout the simulation in order to identify
the environmental limits of the operation.
Figures 7 and 8 present the two examples showing the
numerical model of the module installation onto the
FPSO.
Figure 4: Hydrodynamic interaction analysis models of
installation between SSCV and FPSO, Spar, HTV and
Jacket, from top to bottom, respectively.
These terms have also been calibrated against the model
test data or software considering viscous damping on
truss members (e.g. the strake on the spar or Jacket
tubular and plate members), [11].
2.3
Figure 5: SSCV – FPSO relative position – side by side
ANALYSIS STAGES
In order to investigate the effect of hydrodynamic
interaction, the critical stages in each heavy lift
operation, where the operability is deemed significantly
governed by the motions of vessels in proximity, are
identified. The analyses then were performed using state­
of-art tools incorporating hydrodynamic interaction
effects shown in Section 2.1 to compare against
traditional analysis methods.
© 2014: The Royal Institution of Naval Architects
Figure 6: SSCV – FPSO relative position – bow on
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
Bumper system
Guide system
Figure 9: Topside set-down onto Spar numerical model
Figure 7: Module Installation onto FPSO – Simple model
Bumper system
SSCV-HTV: While the first two cases involved
mechanical coupling of two floating bodies through
rigging as well as bumper-guide system (FPSO), this
case covered the condition in which relative motions
between two bodies are governing the operation only. In
this condition, the SSCV crane hooks were lowered to
the rigging platform prior to connection to the module
which was on the HTV, Figure 10, see also Figure 1(c).
The distance between bodies was 9.5m.
Guide system
Figure 8: Module Installation onto FPSO – Complex
Model
Figure 7 presents the relatively simple system with two
tubulars representing the guide system and horizontal
tubular with a “cowhorn” representing a bumper system
on the module. Figure 8 presents a more complex system,
when the bumpers are installed at two sides of the
module in order to fit it inside the guide system as
shown.
SSCV-Spar: This analysis covered the installation of
Topside section onto a Spar. It is similar in principle to
the FPSO analysis. The module was held above the
installation position and then setdown onto the Spar. The
alignment of the cranes was maintained by DP controlled
movements of the SSCV as well as rapid ballasting and
lowering of hooks to keep track of the sinking the Spar.
The analysis model is shown in Figure 9, see Figure 1(b)
also. The distance between bodies was approximately
35m. As the criteria, the module, Spar motions, SSCV
crane vertical motions, and rigging loads are monitored
throughout the simulation in order to identify the
environmental limits of the operation.
Figure 10: The pre-rigging hovering of crane hooks
above HTV/module.
As the criteria, relative horizontal and vertical motions of
hook (SSCV) / rigging platform (HTV) are monitored to
provide the safe operation limits for rigging crew who
will make the rigging connection.
SSCV-Launch Jacket: The first three cases cover typical
operations which are suited to the diffraction tools (panel
methods) for the analysis of hydrodynamic floating
structures. Launch Jackets are made up of truss members
on which hydrodynamic forces (inertia and drag) can be
analysed by the well-known Morison formula, [2] and
[5]. However, the forces on the Jacket structure could
also be influenced by the disturbed wave field (shielding)
by the SSCV. The floating launch Jackets often have
relatively large buoyancy tanks which are attached to the
Jacket structure to achieve self-floatation following the
launch from barge (Figure 11).
© 2014: The Royal Institution of Naval Architects
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
3.
THE EFFECT OF HYDRODYNAMIC
INTERACTION ON OPERABILITY
ASSESSMENT
The numerical methods, analysis stages and criteria
described in Section 2.0 are used to derive the
operability. The important aspects of this assessment are
highlighted in the following sections.
Figure 11: Post-launch
numerical model
SSCV-Jacket
connection
The Jacket position should achieve a “head-up” position
which ensures the rigging platform on top of Jacket is
above the water. Subsequently, rigging crew can be
transferred to the Jacket for the connection of rigging
with the SSCV cranes. This stage could be expected as
most restrictive phase of the installation operation as
relative vertical motions between the transfer positions
on rigging platform and water line must be sufficiently
small to ensure safe personnel transfer.
As the Jacket legs and buoyancy tanks are the largest
wave-load induced members, these elements are
modelled as panels to create wave diffracted members in
both in time-domain solver [11] and in hydrodynamic
interaction solver [9], Figure 12. Due to their large
diameters, they are most likely to be subject to wave
diffraction.
Figure 12: MOSES model including Morison elements
(left) and DIFFRAC panel model (right)
The Jacket-SSCV relative motion analysis was carried
out using MOSES software which was calibrated against
DIFFRAC. The time-domain solver, MOSES, model of
the Jacket also includes smaller “Morison” elements
which can take into account the buoyancy and damping
effects in the analysis. Therefore, the hydrodynamic
coefficients (added mass and damping) are adjusted in
DIFFRAC to calibrate the Jacket RAOs with those
calculated by the MOSES. Once the combined
hydrodynamic model is created (Figure 4) then MOSES
modelled RAOs are calibrated against those obtained by
the DIFFRAC for the subsequent time-domain analysis
with the calibrated model. The distance between bodies
is 16m.
© 2014: The Royal Institution of Naval Architects
The installation of Modules onto FPSO: Figure 13 to 18
provide the FPSO RAO plots for head and beam seas for
no interaction case (denoted here as ‘1BODY’) and two
vessels configurations (denoted ‘2BODY:side and :bow
corresponding to Figures 5 and 6, respectively) when the
hydrodynamic interaction is considered.
As can be seen from Figures 13 to 18, the interaction
causes increased motions normal to the direction of
waves. The motions in parallel plane to the direction of
waves are not shown since the differences in amplitudes
are small. The reflection and diffraction of waves along
the FPSO and SSCV hulls cause asymmetry to motions
in horizontal plane for head seas onto the FPSO (Figures
13-15) and vertical plane for beam seas onto the FPSO,
respectively (Figures 16-18). The standing waves
between SSCV columns cause these changes in FPSO
motions as shown previously in numerical models and
model tests for barge motions, [4], [6].
Figure 13: FPSO Roll RAO in Head Seas onto FPSO
Figure 14: FPSO Yaw RAO in Head Seas onto FPSO
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
of waves between the SSCV columns and the FPSO hull
due to positioning.
Figure 15: FPSO Sway RAO in Head Seas onto FPSO
Figure 18: FPSO Surge RAO in Beam Seas
The similar trend is also seen for SSCV motions although
the impact is less severe. The yaw motion is affected in
both FPSO positions due to coupling effect as shown in
Figure 14 and Figure 19 below.
Figure 16: FPSO Pitch RAO in Beam Seas
Figure 19: FPSO Yaw RAO in Beam Seas onto FPSO
Figure 17: FPSO Heave RAO in Beam Seas
The motion amplitudes peak at resonance frequency as
motions parallel to wave direction. Although, the
amplitudes are still relatively small 50% to %60
increases around natural period can be observed, Figures
16 to 18. For horizontal plane motions (sway, roll and
yaw) ‘FPSO bow onto SSCV’ condition represents
higher motions, while the motions in vertical plane are
more onerous in ‘side-by-side’ case again with reflection
The comparisons in Figures 13 to 19 are shown for a
linear model. The non-linearities, through a ‘non­
stationary or transient’ analysis were taken into account
in the actual time-domain analysis to derive the
operability. A Monte-Carlo simulation was applied by
running the full module installation analysis in a number
of different wave trains. A probability of exceedance
value was then applied to maximum operable values
from each run which are obtained based on the criteria
defined as explained in Section 2.3. The exceedence
criterion was applied to take human factor (crane driver’s
ability) into account.
The operability plots for the two FPSO installation
positions are produced accordingly. Figure 20 presents
the plots of operable Hs in different heading and wave
periods (Tp between 6s to 12s) for the condition when
© 2014: The Royal Institution of Naval Architects
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
SSCV is in “bow on” configuration relative to the FPSO
(Figure 6). Similarly, Figure 21 presents the operability
when vessels are in “side by side” configuration.
SSCV, is also observed (Figure 21). These effects are
lessened when the waves coming onto the SSCV from
the opposite directions (Figures 20-21).
Figure 20: Operability for module installation onto FPSO
– “bow on” – with Hydrodynamic Interaction
Figure 22: Operability for module installation onto FPSO
– “bow on” – without Hydrodynamic Interaction
Figure 21: Operability for module installation onto FPSO
– “side by side” – with Hydrodynamic Interaction
Figure 23: Operability for module installation onto FPSO
– “side by side” – without Hydrodynamic Interaction
In order to assess the impact of hydrodynamic interaction
on operability, an identical analysis is also performed
without consideration of the interaction in the
hydrodynamic properties, i.e. a single hydrodynamic
database has been created for each floating body which
are then simply “merged” together. The operability
rosettes for these analyses are given in Figures 22 and 23.
The interaction effect can be clearly seen from these
operability plots. Figure 20 shows the shielding effect of
the FPSO when the waves head onto the SSCV. The
pitch and heave of the SSCV reduce thus any mechanical
coupling (rigging motions) are damped. When the
incident waves come from starboard beam onto the
SSCV similar behaviour, this time shielding by the
When the same analyses conducted without considering
effect of interaction, the operability rosettes look more
symmetrical (Figures 22-23). The impact of shielding
and coupled motions cannot be seen when the waves are
coming onto bow or starboard beam to the SSCV. On the
other hand, the exclusion of wave interaction between the
vessels implies increase in operability for beam seas
(Figure 23). This is mainly due to increased yaw motion
of FPSO due to interaction with the SSCV as shown in
Figures 14 and 19. This could not be captured by the
traditional analysis method (Figures 22-23).
© 2014: The Royal Institution of Naval Architects
Furthermore, the similarity of overall limiting
environmental limits indicates that mechanical coupling
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
are more governing than hydrodynamic interaction. The
operability is reduced, as expected, with longer periods
as wave periods are closer to natural periods of the
vessels.
Installation of the Module onto the Spar: The platform is
bow onto the DP SSCV as shown in Figures 4 and 1(b).
The hydrodynamic reaction forces (added mass and
damping) and wave excitation forces, all non­
dimensionalised, of the spar platform are shown in
Figures 24 and 25.
The surge and pitch modes of
hydrodynamic reaction forces for the longitudinal waves
onto the SSCV (head/aft) are shown as they will be
subject to wave reflection and shielding effects with the
SSCV hull in these conditions.
Spar are then produced. The analysis method and criteria
are similar to ones for the FPSO.
Figure 26 presents the plots of Hs limits for different
heading and wave periods (Tz from 4s to 8s) considering
hydrodynamic interaction between two bodies. Figure 27
presents the same analysis without hydrodynamic
interaction effects considered. The comparison of Figures
26 and 27 indicate that the operability is improved in
longitudinal direction due to the shielding and additional
damping effect from wave reflection between two
bodies. These effects are less prominent as the wave
periods getting closer to natural periods of the SSCV.
Figure 24: Hydrodynamic reaction forces (non­
dimensionalised) on the spar with and without
hydrodynamic interaction for modes in longitudinal
direction to the SSCV
The other modes of motions are not shown in Figures 24
and 25 since the differences are very small. As can be
seen from Figure 24, the added mass and inertia are not
greatly affected while the damping force is increased
with interaction for higher periods. This is due to fact
that the SSCV motions thus wave reflection and damping
in the gap between the SSCV and spar increase in longer
wave periods which are closer to the SSCV natural
period. Equally, the wave excitation forces on the spar
increase in these longer periods while the shielding
provides reduction in shorter wave periods for the waves
coming from aft of the SSCV.
The operability plots for the module installation onto the
Figure 25: Wave excitation forces (non-dimensionalised)
of the spar with (top) and without (bottom)
hydrodynamic interaction for modes in longitudinal
direction to the SSCV
© 2014: The Royal Institution of Naval Architects
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
Lift of the Module from the HTV: While the first two
analyses involve also the mechanical coupling (via
rigging and installation aids), this case covers mainly
hydrodynamic interaction of two floating structures in
proximity. The HTV is brought bow onto the DP SSCV
as shown in Figures 10 and 1(c). Figure 28 to 30 provide
the HTV RAO plots for all 360 environmental rosette for
no interaction case (denoted here as ‘1BODY’) and two
vessels configurations (denoted ‘2BODY) when the
hydrodynamic interaction is considered.
As in the previous cases, the modes of motion in which
larger differences are observed due to hydrodynamic
interaction are plotted here. As can be seen, the shielding
effect on the HTV due to the SSCV is clear (Figures 28­
30).
Figure 26: Operability (Hs-Tz) for module installation
onto Spar with Hydrodynamic Interaction
The operability for pre-rigging of Topside to the SSCV
cranes (See Figure 10) with and without hydrodynamic
interaction effects is shown in Figures 31 and 32. The
trends seen here in the operability similar to the previous
cases.
Figure 28: HTV Sway RAO
Figure 27: Operability (Hs-Tz) for module installation
onto Spar without Hydrodynamic Interaction
The asymmetry due to installation position as well as
rotation in horizontal plane caused by the hydrodynamic
interaction is captured for the analysis with
hydrodynamic interaction effects (Figure 26). While, this
asymmetry cannot be seen for the analysis without
hydrodynamic interaction effects which shows
improvement in operability in beam seas onto the SSCV
(Figure 27). As also seen in FPSO analyses, limiting Hs
values overall remain similar with and without
considering hydrodynamic interaction effects. This also
confirms mechanical coupling between the structures are
more governing for the operability compared to
hydrodynamic interaction.
© 2014: The Royal Institution of Naval Architects
Figure 29: HTV Heave RAO
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
Figure 30: HTV Roll RAO
The asymmetry due to lifting position with respect to the
SSCV and HTV orientation and hull forms are captured
by the model including hydrodynamic interaction effects
(Figure 31). When these effects excluded (Figure 32)
there is more optimistic estimation for operability for
longer wave periods which are closer to natural periods
of the vessels.
Figure 31: Operability (Hs-Tz) for pre-rigging of a
Topside to SSCV cranes with Hydrodynamic Interaction
Figure 32: Operability (Hs-Tz) for pre-rigging of a
Topside to SSCV cranes without Hydrodynamic
Interaction
The shielding between the vessels does not significantly
effect the operability due to strict criteria (normally
relative horizontal and vertical motions of 1m between
hook/rigging platform is not allowed), small gap (less
than 10m) and typical installation sea states wave periods
analysed (Tz up to 8s or around Tp 11s) which are
generally below typical natural periods of the SSCV.
While the mechanical coupling does not exist in this
case, since the topside and rigging platform motions are
fully controlled by the HTV, the operability is mainly
governed by the HTV motions.
Installation of the Jacket by the SSCV cranes: As
explained in Section 2.3, this case covers the connection
of rigging on the Jacket in free-floating condition to the
SSCV cranes (Figure 11). Therefore, it is similar to
HTV/SSCV interaction in terms of analysis method and
governing criteria. The absolute and relative wave
elevation RAOs at ladder on the side of the top of Jacket
(See Figure 11) are plotted in Figures 33-34 for period
ranges (Tp) 5s to 12s. The wave elevation RAOs are
plotted for waves coming from aft and aft quartering to
the SSCV (between 315°-0°-45°, see operability rosettes
in Figures 35-36) which will create highest shielding
© 2014: The Royal Institution of Naval Architects
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
effect on the Jacket motions based on the position given
in Figure 11 (denoted here as ‘1BODY’ for Jacket and
‘2BODY’ for Jacket and SSCV combined).
Figure 33: Absolute wave elevation RAOs at Jacket
Ladder
Figure 35: Operability (Hs-Tz) for pre-rigging of a
floating Jacket to SSCV cranes with Hydrodynamic
Interaction
Figure 34: Relative wave elevation RAOs at Jacket
Ladder
The shielding effects are clearly seen in shorter wave
periods when the hydrodynamic interaction effects taken
into account (Figures 33-34). These effects are less
significant with longer wave periods as the periods are
closer to SSCV natural periods thus the SSCV/Jacket
begin to move with incoming waves. This also highlights
the fact that waves do diffract around the larger diameter
buoyancy tanks and legs of a launch Jacket in shorter
period installation sea state waves.
Subsequently, the operability plots with and without
considering the interaction effects are shown in Figures
35 and 36, respectively. The impact of the shielding at
shorter periods can be clearly seen (Figure 35).
© 2014: The Royal Institution of Naval Architects
Figure 36: Operability (Hs-Tz) for pre-rigging of a
floating Jacket to SSCV cranes without Hydrodynamic
Interaction
Since creating panel method of Jacket and then calibrate
this model may be numerically more expensive process,
analysing disturbed wave fields around the SSCV can
also be carried out to identify the actual wave amplitude
coming onto the Jacket from the SSCV shielded
directions.
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
4.
CONCLUSIONS
While the impact of hydrodynamic interaction between
floating structures during heavy lift and installation
operations is an indisputable fact, due to its relatively
smaller impact compared to mechanical coupling and the
complication in working it out, it has been ignored in
common analysis approach within the industry.
Therefore, the study presented in this paper has been
conducted with a new state-of-art analysis tools covering
different analysis scenarios to validate this approach. The
significant points of this analysis are summarized as:
interaction i.e. environmental limitations, gap between
the floating structures etc. would be required for further
validation of some of the points given above.
5.
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August, 1991
The mechanical coupling when two structures are
connected via rigging or installation aids is the biggest
governing factor in determining the operability.
However, in cases where this coupling is not present the
operability does not drastically change overall with and
without considering interaction effects. This is due to the
relatively benign sea states chosen for the installation
operations, and experience of installation crew (analysed
here as probability of exceedence) to control the
operation.
5.
MARIN
(Maritime
Research
Institute,
Netherlands)
‘Hydrodynamics of Floating
Offshore Structures’, Industry Training Course,
Wageningen, the Netherlands, March, 2007
6.
CLAUSS, G.F., and STUTZ, K.S., ‘Interaction
of Coupled Floating Structures in Waves’, In:
Proceedings of 12th. International Offshore and
Polar Engineering Conference, pp. 271-280,
Kitakyushu, Japan, May, 2002
Nevertheless, analysis tools for hydrodynamic interaction
effects have significantly advanced over the last two
decades and provide ease-of-use in combination with
more established coupled time-domain multi-body
motion analysis tools.
7.
CLAUSS, G.F., and JACOBSEN, K., ‘Multi­
body Systems in Waves – Impact of
Hydrodynamic Coupling on Motions’, In:
Proceedings of 12th. International Congress of
the International Maritime Association of the
Mediterranean, Lisbon, Portugal, September,
2005
8.
DE JONGE, J.B., PETERS, O.A.J. and
HUIJSMANS, R.H.M., ‘An Accurate and
Efficient Hydrodynamic Analysis Method for
Offshore
Discharge
Operations’,
In:
Proceedings of 2nd. International Marine Heavy
Transport & Lift Conference, pp. 93-100, Royal
Institute of Naval Architects, London, UK,
February, 2008
The analysis considering hydrodynamic interaction
successfully captures the asymmetric nature of
operability with respect to incoming wave headings,
installation positioning and shielding between the
floating structures. The impact from shielding captured
by the analysis validates the operational methodology
followed by the offshore crew (i.e. using SSCV as a
shield for incoming wave direction to vessel/platform
etc.). This could be a significant advantage compared to
a traditional approach for a more realistic assessment of
the installation conditions.
The impact of hydrodynamic interaction is similar for
different types of floating structures considered here;
FPSO, spar platform, HTV and Jacket structure.
However, the impact of the hydrodynamic interaction on
the motions of floating structures with comparatively
smaller displacements to the SSCV is higher for shorter
wave periods.
Furthermore, the shielding and damping effects due to
reflected waves between the floating structures which are
often utilised in practise by the installation vessel crew,
can be more realistically represented for engineering
stage for structures even not fully conforming to the
applicability of hydrodynamic interaction analysis tools
i.e. Jacket-type structures.
More detailed analyses covering parametric assessment
of some of the important aspects of the hydrodynamic
© 2014: The Royal Institution of Naval Architects
Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
9.
MARIN
(Maritime
Research
Institute,
Netherlands)
‘Reference
Manual
for
DIFFRAC’, www.marin.nl
10.
MARIN
(Maritime
Research
Institute,
Netherlands) ‘Reference Manual for LIFSIM’,
www.marin.nl
11.
Bentley Systems Inc., ‘Reference Manual for
MOSESMulti-Operational
Structural
Engineering Simulator’, www.ultramarine.com
6.
AUTHORS BIOGRAPHY
Dr. Zafer Ayaz, BSc, CEng, MRINA, is principal naval
architect at SAIPEM Ltd. He is a member of the naval
analysis department since 2006 responsible for naval
analysis of offshore heavy lift and pipelay installation
projects. He has also been involved with offshore
execution of projects in North Sea and GoM. Dr. Ayaz
graduated from Department of Naval Architecture and
Marine Engineering of Technical University of Istanbul
in 1998 with BSc in Naval Architecture and Marine
Engineering. He then obtained his PhD in 2003 at the
Ship Stability Research Centre, Department of Naval
Architecture and Marine Engineering, University of
Strathclyde where he also worked as Research Fellow
until 2006.
Mohamed Safsafi, Naval Architecture and Offshore
Structure Engineer, graduated from the National School
for Advanced Technologies (ENSTA ParisTech) in 2008.
He has previously worked in Bureau Veritas (student
trainee), Saipem Paris as Naval Architect involved in
FPSO, FLNG & Pipelay vessel design and platform
installation projects, Gaz Transport and Technigaz
(Subdivision of Total and GDF Suez) as Project
Engineer. In 2013 he joined Saipem London as a Naval
Architect. He has been involved in different Platform and
subsea installation projects in the North Sea and Caspian.
Antons Slyozkin, MSC, AMRINA, AMSNAME,
graduated from the Newcastle University in 2011. He
joined Saipem’s 2 year Graduate Training Scheme in the
same year, as a Graduate Naval Architect. During that
time he was involved in different Platform installation
projects in the North Sea including jacket, pile and deck
installations. Recently, he has finished the Training
Scheme and now works as a Naval Architect in Saipem.
Dr. Nan Xie, holds the current position of senior naval
analysis engineer at the naval analysis department of
Saipem Ltd. He is responsible for naval architect
analysis of offshore transportation and installation
projects. He was previously a research fellow at
Department of Naval Architecture and Marine
Engineering of University of Strathclyde and senior
engineer at Department of Marine Hydrodynamics of
China Ship Scientific Research Centre.
Presentation
© 2014: The Royal Institution of Naval Architects
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Marine Heavy Transport & Lift IV, 29-30 October 2014, London, UK
© 2014: The Royal Institution of Naval Architects