Post on 14-Oct-2014
Modeling the effect of sloshing on
ship motions
Tim Bunnik, MARIN
2ComFLOW-3 meeting, San Francisco, November 9, 2009
Contents
– Problem definition
– Linear diffraction method for sloshing effect on
ship motions
– ComFLOW coupling to ship motion code for
sloshing effect on ship motions
– Conclusions
3ComFLOW-3 meeting, San Francisco, November 9, 2009
Problem definition
Francescutto and Contento, ISOPE 1994
4
Problem definition
R0 R1
R2
R3
Gaillarde, RINA 2004
ComFLOW-3 meeting, San Francisco, November 9, 2009
5
Problem definition
Molin, OMAE 2008. This dataset was used for validation.
2 3 4 5 6 7 80
0.5
1
1.5
2
2.5
3
3.5
4
frequency [rad/s]
roll
RA
O [ra
d/m
]
closed tank
open tank
ComFLOW-3 meeting, San Francisco, November 9, 2009
6
Linear Diffraction Method
• Potential flow
• Small ship motions and waves
• Boundary element method
• MARIN program DIFFRAC
ComFLOW-3 meeting, San Francisco, November 9, 2009
7
Linear Diffraction Method
• Water in the tank is modeled as
1. Rigid mass+
2. Frequency dependent added mass+
3. Hydrostatic restoring force (GM free-surface correction)
• There is no damping force from the tank since there is no
radiation of waves
• Computation on model scale
ComFLOW-3 meeting, San Francisco, November 9, 2009
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Linear Diffraction Method
Sloshing modes n=1
n=2
ComFLOW-3 meeting, San Francisco, November 9, 2009
Odd sloshing modes
unbounded in linear diffraction
theory
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Linear Diffraction Method
0 2 4 6 8 10 12-5
0
5
10
15
20
frequency [rad/s]
roll
ad
de
d m
ass/r
oll
ine
rtia
[-]
barge with open tank containing 29 cm of water
DIFFRAC =0
DIFFRAC =0.01
DIFFRAC =0.02
0i12
xg
xz
Additional damping
on free surface
ComFLOW-3 meeting, San Francisco, November 9, 2009
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Linear Diffraction Method
Roll RAO with
closed water tank
Very good!
ComFLOW-3 meeting, San Francisco, November 9, 2009
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Linear Diffraction Method
Roll RAO with
open tank
Reasonable, but
far from perfect
ComFLOW-3 meeting, San Francisco, November 9, 2009
12
ComFLOW coupling for ship motions
Sloshing loads
Pre-defined motions
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 10 20 30 40 50 60 70 80 90 100
Old situation:
Comflow.exe
ComFLOW-3 meeting, San Francisco, November 9, 2009
13
ComFLOW coupling for ship motions
Sloshing loads
New situation:
Comflow.lib
Body motion program
F=m * a
Motions
Velocities
Accelerations
ComFLOW-3 meeting, San Francisco, November 9, 2009
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ComFLOW coupling for ship motions
• STEP_IN_TIME()
• get_time(T_comflow,TMAX)
• set_moving_frame(T_next, motion, velocity, acceleration)
• get_force_FRCBX(iBOX, FORCE, MOMENT, x, y, z)
Interface routines:
Coupling made with aNySIM: In-house code for time-domain
simulation of ship motions
ComFLOW-3 meeting, San Francisco, November 9, 2009
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• Linear diffraction analysis for the barge
• The sloshing tank is modeled with ComFLOW
• 2D 1-phase simulations (1 cell in longitudinal direction)
• Simulations on model scale
• 400 seconds irregular beam waves to determine roll RAO
Hs=0.06 m Tp=1.6 s
ComFLOW coupling for ship motions
ComFLOW-3 meeting, San Francisco, November 9, 2009
16
ComFLOW coupling for ship motions
Very coarse grid (20x12) ~ hours
Coarse grid (40x23) ~ 1 day
Fine grid (80x46) ~ 3 days
ComFLOW-3 meeting, San Francisco, November 9, 2009
17
ComFLOW coupling for ship motions
3 4 5 6 7 80
0.5
1
1.5
2
2.5
3
3.5
4
frequency [rad/s]
roll
RA
O [ra
d/m
]
Closed tanks seastate irr1.
aNySIM-ComFLOW verycoarse
Molin [2008]
ComFLOW-3 meeting, San Francisco, November 9, 2009
•Closed tank
•Water modelled with
ComFLOW
•No free surface
18
ComFLOW coupling for ship motions
ComFLOW-3 meeting, San Francisco, November 9, 2009
• Open tank, airgap 16 cm
• Good agreement
• Small grid effects
3 4 5 6 7 80
0.5
1
1.5
2
2.5
3
3.5
4
frequency [rad/s]
roll
RA
O [ra
d/m
]
Flat roof 16 cm above still water level. Seastate irr1.
aNySIM-ComFLOW very coarse
aNySIM-ComFLOW coarse
aNySIM-ComFLOW fine
Molin [2008]
19
Conclusions
• Coupling between ComFLOW and ship motion code (aNySIM) is
working well
• Reasonable results Molin dataset with linear diffraction method
• Good results Molin dataset with ComFLOW/aNySIM method
• ComFLOW library with interfaces will be made available in the first
deliverable of ComFLOW-3, so users can couple it to their own
simulation programs
ComFLOW-3 meeting, San Francisco, November 9, 2009
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The end
Next JIP week
19-23 April 2010 - Aberdeen
Dinner
Gather 19.00 in lobby
ComFLOW-3 meeting, San Francisco, November 9, 2009