1 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Predictions of a
Semi-Displacement Vessel
Including Applications to
Calm-Water Broaching
www.cesos.ntnu.no CeSOS – Centre for Ships and Ocean Structures
Babak Ommani
CeSOS Conference
29-May-2013
Potential-Flow
2 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Semi-Displacement Vessels
Fabbri et al. 2009, INSEAN
0.4 ~ 1.2Fn
/Fn U Lg
3 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Semi-Displacement Vessels
Increase in the Role of Hydrodynamic Force Comparing to Hydrostatic
Conventional Semi-Displacement Planning Hydrofoil
Dynamic instability !!
Hydrostatic Hydrodynamic
Force
Submerged
Volume
Velocity
squared
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General types of instability
Increasing Froude number
Broaching
Non-oscillatory
Cohen and Blount, 1986
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Calm-Water Broaching
Lugni et al. 2004, INSEAN
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Equations of Motion
𝑋 𝑌 𝑍
𝑥 𝑦
𝑧
𝐶𝐺
U
Sway
22
24
26
42
44
46
62
64
66
B
B
B
B
B
B
B
B
B
22
24
26
42
44
46
62
64
66
A
A
A
A
A
A
A
A
A
18 Coeffs.
acc. vel.
Roll
Yaw
Linear
decomposition
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Overview
• Introduction
• Numerical Implementation
• Advancing and Oscillating Flat Plate
• Linear Dynamic Stability Analysis
• Conclusions
8 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Numerical Implementation
• Potential flow
• Neumann-Kelvin Linearization
– Linearized Body Boundary Condition
• Mean body position
– Linearized Free-Surface Boundary Condition
• Mean free surface
– Initial Condition, Radiation Condition
• Linearized pressure on the body
• Forces and moments
Ux
2 0
p U gzt x
j j
S
F pn ds
9 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Numerical Implementation
• Rankine Panel Method
• Collocation Method
• Discretization
,( )
( )
,( )
S
S
G p qC p p q ds
n q
qG p q ds
n q
10 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Simplification
𝑋 𝑌 𝑍
𝑥 𝑦
𝑧
𝐶𝐺
• Transfer to center plane – Semi-Displacement vessel to a Flat Plate
𝐿
𝐻
U
11 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Oscillatory motion of a Plate
VS
BodyFS
XY
Z
x
y
z
Conservation of
Vorticity
• Time-domain solver – Fourth order Runge-Kutta
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Sway Motion
0.32
=H/L=0.2
Fn
0.96
=H/L=0.2
Fn
/L g
/L g
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Vessel Model
• Vessel M
Lugni et al. 2004, INSEAN
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Dynamic Stability Analysis
• Back to the simplified
model – Surface piercing flat plate
– Advancing and oscillating
• Hydrodynamic coefficients – Sway-yaw (8 coeffs.)
– Sway-yaw-roll (18 coeffs)
• Frequency and Froude
number dependent
Computed
Extrapolated
0 0( , )Fn
( , )Fn plane
15 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Yaw analysis, Computational
Domain
0 0( , )Fn
22
26
62
66
A
A
A
A
22
26
62
66
B
B
B
B
Stable
every where
st
ae
ia Harmonic
Motion
Sway-Yaw Free-system
response frequency
16 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Roll-Yaw analysis, 22
24
26
42
44
46
62
64
66
B
B
B
B
B
B
B
B
B
22
24
26
42
44
46
62
64
66
A
A
A
A
A
A
A
A
A
18 Coeffs.
0 0( , )Fn
Computational
Domain
4 3 2
4 3 2
1 0 0
C s C s C s
C s C
*
1 1,s s *
2 2,s s
Two Frequencies? Time-Domain
analysis is needed
17 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Roll-Yaw analysis, 22
24
26
42
44
46
62
64
66
B
B
B
B
B
B
B
B
B
22
24
26
42
44
46
62
64
66
A
A
A
A
A
A
A
A
A
18 Coeffs.
0 0( , )Fn
Computational
Domain
4 3 2
4 3 2
1 0 0
C s C s C s
C s C
*
1 1,s s *
2 2,s s
Sway-Yaw Free-system
response frequency
Two Frequencies? Time-Domain
analysis is needed
18 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Roll-Yaw analysis, 22
24
26
42
44
46
62
64
66
B
B
B
B
B
B
B
B
B
22
24
26
42
44
46
62
64
66
A
A
A
A
A
A
A
A
A
18 Coeffs.
Computational
Domain
4 3 2
4 3 2
1 0 0
C s C s C s
C s C
*
1 1,s s *
2 2,s s
Roll Free-system
response frequency
Stable
every where
Sway-Yaw Free-system
response frequency
Two Frequencies? Time-Domain
analysis is needed
19 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Roll-Yaw analysis, sensitivity
• Many uncertain parameters – Hydrodynamic coefficients
• Due to simplification
– Vessel geometrical properties
• Due to insufficient data GM KM KG
KGKM
GM
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Dynamic Stability
• Sway-Roll-Yaw analysis, sensitivity
(1 )A v A
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Dynamic Stability
• Sway-Roll-Yaw analysis, sensitivity Unstable
roots
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Dynamic Stability
• Sway-Roll-Yaw analysis, Computational
Domain
0.675KG
D
Computational
Domain
0.5KG
D
23 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Roll-Yaw analysis,
Computational
Domain
0.5KG
D
Sway-Yaw Free-system
response frequency
24 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Roll-Yaw analysis,
Computational
Domain
0.5KG
D
Sway-Yaw Free-system
response frequency
Roll Free-system
response frequency
25 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Roll-Yaw analysis,
Computational
Domain
0.5KG
D
Sway-Yaw Free-system
response frequency
Roll Free-system
response frequency
Unstable
System
11 0a
1Re( )s
*
1 1,s s
1Im( )s
Recorded Instability
26 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Dynamic Stability
• Sway-Roll-Yaw analysis,
Computational
Domain
0.5KG
D
Sway-Yaw Free-system
response frequency
Roll Free-system
response frequency
Unstable
System
11 0a
1Re( )s
*
1 1,s s
1Im( )s
27 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Conclusions
• A simplified hydrodynamic model is used for semi-
displacement vessel.
• Roll motion influences the dynamic stability in sway and
yaw.
• Cross coupling hydrodynamic coefficients matter.
• It seemed that high stiffness in Roll can cause instability in
sway-yaw!!
• It was not possible to capture instability induced by Loss
of restoring moment in Roll
• Simplified hydrodynamic model may be the reason
28 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
Thank you!
29 www.cesos.ntnu.no 29-May-2013, CeSOS Conference Babak Ommani
References
• Chapman, R. (1975), Numerical solution for hydrodynamic forces on a surface-piercong plate oscillating in yaw and sway, in
`Proc. 1st International Conference on Numerical Ship hydrodynamics', Bethesda, MD,USA, pp. 330-350.
• Fabbri, L., Di Memmo, A., Palini, M. and Lugni, C. (2009), Prova di manovrabilit�a su uno scafo semidislocante, Technical
Report 2009-084rt, INSEAN, Rome, Italy.
• Faltinsen, O.M. (2005). Hydrodynamics of High-Speed Marine Vehicles. New York: Cambridge University Press.
• Lugni, C., Colagrossi, A., Landrini, M. and Faltinsen, O. (2004), Experimental and numerical study of semi-displacement mono-
hull and catamaran in calm water and incident waves, in `Proc. of 25th Symposium on Naval Hydrodynamics', Canada.
• Ommani, Babak, and O. M. Faltinsen. 2011. “Study on Linear 3D Rankine Panel Method for Prediction of Semi-Displacement
Vessels’ Hydrodynamic Characteristics at High Speed.” In Proceedings of the 11th International Conference on Fast Sea
Transportation (FAST 2011). Honolulu, HI, USA.
• Ommani, Babak, O. M. Faltinsen, and C. Lugni. 2012. “Hydrodynamic Forces on a Semi-Displacement Vessel on Straight
Course with Drift Angle.” In Proceedings of the 10th International Conference on Hydrodynamics (ICHD). St. Petersburg,
Russia.
• Ommani, Babak, O. M. Faltinsen, 2013. “Linear dynamic stability analysis of a surface piercing plate advancing at high forward
speed.” Accepted for publication in, Proceedings of the ASME 2013 32nd International Conference on Ocean, Offshore and
Arctic Engineering(OMAE2013). Nantes, France.
• van den Brug, J. B., Beukelman, w. and Prins, G. J. (1971), Hydrodynamic forces on a surface piercing at plate, Technical
Report 325, Delft University of Technology, Ship Building Labratory.
