This document summarizes a study on simulating the motion response of an intact and damaged ship in head waves using computational fluid dynamics (CFD). It describes setting up CFD cases to analyze the heave and pitch motions of an intact ship model in regular head waves of varying wavelengths. The study also simulates a damaged ship condition and compares the motion responses to the intact case. Areas identified for future work include modeling water intrusion during flooding and simulating more complex sea states with irregular waves.

1. Motion response of an intact and damaged
vessel in head waves
Sainath Atul Nashikkar
B.Tech Naval Architecture and Ocean Engineering
Indian Maritime University

2. INTRODUCTION
• The design for marine structures requires a lot of understanding
about the behaviour and characteristics of the ship at sea .
• Once in the water the ship has to meet its operational
requirements , structural strength requirements and also its
environmental and safety of the passengers and crew on board
.
• The uncertain behaviour of the sea adds to the efficient design
of ship for various sea conditions .A wide and reliable study of
the characteristics of the ship help the designers in designing an
efficient ship .
• Towing tanks ,wind tunnels ,cavitation tunnels and wave basins
have been considered as reliable inputs of the knowledge of
ship characteristics at sea. But they are expensive so only ship
owners with big budgets opt for it.

3. The Use Of CFD in Marine
• Résistance and wave prediction .
• Manoeuvring and seakeeping analysis
• Propulsion system flow analysis
• Ship motion in waves
• Flow over control devices in a ship
• Movements of fluid within internal tanks of a ship
• Using CFD results for structural analysis .

4. Ship Motions
Number Degree of freedom
Force and
moments
Linear and angular
velocity
Position/
Euler angle
1 Motions in the x- direction (Surge) X u x
2 Motions in the y-direction (Sway) Y v y
3 Motions in the z- direction (Heave) Z w z
4 Rotation about x-axis (Roll) K p ϕ
5 Rotation about y-axis (Pitch) M q θ
6 Rotation about the z-axis (Yaw) N r Ψ

5. Translatory motions

6. ROTATORY MOTIONS

7. INTACT SHIP
In this condition the ship does not have any leakages or any ingress of wa
into the hull.
DAMAGED SHIP
In this condition the ship has an opening in the hull because of collision w
another ship, grounding or explosion .
HEAD WAVES
When the waves approach the ship opposite to the direction of the head
the ship .
Terms used

8. IMPORTANCE OF THE MOTIONS
Heave Motion : The heave motion of the ship leads to increase and
decrease in the hydrostatic pressure around the vessel . The cases of
hogging and sagging occur because of this .Heaving plays an
important role in drill ships and also for helicopters landing on vessels
.
.

9. Pitch motion : The pitch motion of the ship is responsible for slamming
or pounding and an idea of the pitching motion helps in identifying
the forces acting on the bow

10. Roll Motion : The roll motion in a ship is particularly important
because excessive rolling may lead to capsizing of the ship . In
passenger ships rolling leads to a very uncomfortable ride and
causes sea sickness.

11. Ship damages

12. IMPORTANCE OF THE STUDY
The study of ship motion is very important as it helps the designers
and vessel operators.
• To understand the behaviour of the ship in various sea states .
• Designing of roll damping devices with adequate strength and
efficiency .
• Calculating the forces that would be generated by these motions
helping in proper strengthening of ship.
• Damaged Ship responses are particularly important to passenger
vessels which have to comply with the International Maritime
Organization (IMO) Safe-Return-to-Port (STRP) requirement .
• Damaged ship responses also help naval vessels to understand
the ship motions after damage.

13. Paper and Geometry
• Experimental Ship Motion and Load Measurements in Head and
Beam Seas
Authors :
E.Begovic –Department of Naval Architecture and Marine
Engineering , University of Naples Federico II , Napoli , Italy
A.H.Day , A.Incecik –Department of Naval Architecture and
Marine Engineering ,
University of Strathclyde , Glasgow ,UK
• The geometry used is an unappended hull of DTMB 5415 ,a
benchmark model of ITTC . Full scale dimensions of the ship are
taken into the computation.

14. GEOMETRY DETAILS

15. SETTING THE CASE
• The case was setup in EHP
(Estimate Hull Performance) and
modifications to the setup were
done as required .
• EHP sets up the case for half
model but the half model was
then replaced with a complete
one as a complete model is
required for roll response .
• The case was first run with Flat
waves as for testing the setup .

16. MESHING
• The cell count was one
million cells.
• Thickness of Near Wall
Prism Layer is Changed for
each wave to keep the
Wall Y+ value within the
range of 100-150.

17. VOLUME MESH
REPRESENTATION

18. PHYSICS SETUP
• The EHP sets up a flat wave . It
was later changed to a Fifth
order wave .
• Rest all models were the same .

19. Fifth Order Wave specifications
• Four different wavelengths were chosen randomly from a set of
twenty one waves .
• The wavelength was calculated from the Wavelength to Ship
length ratio .
• The wave height was calculated according to the steepness
ratio given .
• The sea wave period of the waves were given from which the
wave speed was calculated .
• The water depth was taken as the depth of the domain.

20. DFBI Solver
• The hull mass for the full ship was
inserted manually as EHP inserts
the mass of half ship.
• The Centre of Mass was also
calculated by EHP which also
matched with the original data.
• EHP only calculates Moment of
Inertia in the Y-axis ,the Z and X
axis Moment of Inertia was
calculated manually using
empirical formulas .

21. CALCULATION OF MOMENT
OF INERTIA
I = m*r^2
Rx = 0.33B
Ry =0.26Lpp
Rz =Ry
Where m = mass
B = width
Lpp = length between perpendiculars

22. SOLVING CONDITIONS
• The implicit unsteady solver time step was kept at 0.1
seconds
• The maximum inner iterations were kept to 15.
• All Cases were run for a maximum physical time of 350
seconds
• Computing time was nearly 3 days for each wavelength
case using 4 processors .

23. WAVE DATA
1st Case
Wavelength = 44.5086m
Wave height = 0.890172m
Wave period = 5.336 s
Velocity of wave = 8.3411 m/s
2nd Case
Wavelength = 146.466m
Wave Height = 2.929 m
Wave period = 8.3726 s
Velocity of wave = 16.785 m/s
3rd Case
Wavelength = 62.1414 m
Wave height = 1.243 m
Wave period = 17.452 s
Velocity of wave = 3.576 m/s
4th Case
Wavelength = 72 m
Wave height = 1.44 m
Wave period = 6.784 s
Velocity of wave = 10.61 m/s

24. Intact Heave RAO
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.2 0.4 0.6 0.8 1 1.2
HEaveRAO
λ/L
RAO – Response amplitude operator ( Heave amplitude / Wave
amplitude )

25. HEAVING

26. Intact Pitch RAO
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.2 0.4 0.6 0.8 1 1.2
λ/L

27. PITCHING

28. DAMAGED CONDITION
In this case the damaged condition has been simulated by
simulating the final condition of the ship after damage .

29. DAMAGED HEAVING

30. DAMAGED PITCHING

31. FUTURE WORK
• Modelling water intrusion into the ship and simulating flooding
into the compartment . Accurate modelling of the internal of
the ship would be an added advantage.
• The present work is performed on an unappended hull but in
reality the ship has many appendages such as the bilge keels ,
fin stabilizers ,rudder , propeller ,etc. Superstructure of the ship is
also not considered .
• Higher sea state conditions can be simulated to know the
survivability of the ship .
• The current work simulates regular waves but in reality the sea
waves are mostly irregular .So simulations with irregular waves
can be a major breakthrough.