Sloshing Effect on Ship Motions

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


6

Linear Diffraction Method

• Potential flow

• Small ship motions and waves

• Boundary element method

• MARIN program DIFFRAC


7


• 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


8


Sloshing modes n=1

n=2


Odd sloshing modes

unbounded in linear diffraction

theory

9


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


10


Roll RAO with

closed water tank

Very good!


11


Roll RAO with

open tank

Reasonable, but

far from perfect


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


13


Sloshing loads

New situation:

Comflow.lib

Body motion program

F=m * a

Motions

Velocities

Accelerations


14


• 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


15

• 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



16


Very coarse grid (20x12) ~ hours

Coarse grid (40x23) ~ 1 day

Fine grid (80x46) ~ 3 days


17


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]


•Closed tank

•Water modelled with

ComFLOW

•No free surface

18



• 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]

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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


20

The end

Next JIP week

19-23 April 2010 - Aberdeen

Dinner

Gather 19.00 in lobby


Sloshing Effect on Ship Motions

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