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DESCRIPTION
NutsTRANSCRIPT
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CFD Applications in Ship Design
Optimization
1
Khairul Hassan
Doctoral student in Department of Maritime Engineering
Graduate School of Engineering, Kyushu University, Japan
Maurice F. White
Professor of Marine Engineering
Department of Marine Technology
Norwegian University of Science and Technology (NTNU) Norway
Cosmin Ciortan, PhD, Consultant
Dept. of Ship Hydrodynamics, Det Norske Veritas (DNV),
Oslo, Norway
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2 Introduction
Brief description of the CFD procedure
CFD application
CFD application in ship design optimization
CFD application in drag analysis for different wind directions
Limitations of the CFD simulation
Conclusion
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3During design optimization the important considerations
ship capacity and Ship stability
Ship Hull
Hydrodynamic
resistance
Aerodynamic
resistance
CFD simulation in Ship design optimization
Ship design optimization
Dimensions optimization
Shape optimization
CFD simulation can be used for
both of the
optimizations
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4For wind resistance simulations, only the part above the waterline is
considered
Ship Hull
Geometry of the problem
Principle particulars
Length water line, LWL=221.65m
Breadth=32.2m
Depth=18.5m
Draught=10.78m
Block coefficient, CB=0.674
Deadweight, DWT=40900tonnes
Cargo capacity: 2800TEU containers;
Design speed: 23 knots
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Boundary conditions and simulation conditions
Simulation Space 3 dimensional
Motion stationary
Time steady
Flow materials Gas / air
Air density 1.18415 kg/m^3
Dynamic viscosity 1.85508E-5 Pa-s
Flow type Couple
Equation of state Constant density
Viscous Regime Turbulence (Reynolds
averaged Navier-Stokes)
Reynolds averaged
turbulence
K-Epsilon turbulence
Ship speed 23knots
CFD simulation conditions for above water hull
analysis:
Mesh size: On container stacks and deck house- target
size 0.6m and minimum size 0.2m, on the deck and on the
above water hull- target size 0.8m and minimum size 0.2m.
The total boundary length is 1000m, and breadth also is 1000 m, the height is 245m
and the ship position at the centre of the
bottom surface. The length and the breadth
are the same because the ship is rotated
from 0 deg to 180deg. 5
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Mesh/grid generation
Grid/mesh generation is the mostimportant task and valid mesh generation is
the most time consuming part in CFD
analysis.
The quality of the CFD analysis mostlydepends on the quality of generated mesh.
Mainly three types of mesh: structured,unstructured and hybrid. Here the
unstructured mesh and hybrid mesh are
used.
Generating the mesh type for CFDanalysis by Starccm+ is Polyhedral. In
analysis the volumetric control density is
2.5m.
The used numbers of prism layers are 4for 3 cm
6
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Graphical presentation of CFD Simulation Result
The simulation results can be presented by
1. graphical from
2. tabular form
In graphical form the streamlines represent the air
flow and help to give us a
better understanding of the
numerical results
Gaps between container stacks can have a significant
influence on the resulting
forces
Graphical presentation of the
simulation result
7
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Simulation Result as Tabular Form
The result of the pressure and shear forces on different stacks arepresented in the following table (ship speed 23 knots in head wind 20 knots)
The drag force acting on the different parts of the ship hull and container stacks
Part Pressure(N) Shear(N) Net(N)
------------------------------ ------------- ------------- -------------
DH -2.068550e+04 -1.023979e+02 -2.078790e+04
hull -1.369280e+04 -2.036224e+03 -1.572903e+04
Stack_1 -7.055177e+03 -5.296690e+01 -7.108144e+03
Stack_2 -4.209718e+02 1.244562e+01 -4.085262e+02
Stack_3 -2.034496e+04 -1.264827e+01 -2.035760e+04
Stack_4 1.518748e+04 -3.620133e+01 1.515128e+04
Stack_5 -1.888242e+04 -3.576994e+01 -1.891819e+04
Stack_6 1.559257e+04 -4.994998e+01 1.554262e+04
Stack_7 -2.733035e+04 -4.540582e+01 -2.737576e+04
Stack_8 2.933077e+03 -8.248552e+01 2.850592e+03
Stack_9 1.596127e+02 -8.651351e+01 7.309917e+01
Stack_10 -5.175854e+02 -8.462801e+01 -6.022134e+02
Stack_11 -7.120480e+03 -8.316351e+01 -7.203644e+03
Stack_12 -2.639828e+03 -7.487794e+01 -2.714706e+03
Stack_13 1.671533e+03 -4.370696e+00 1.667162e+03
Stack_14 9.267767e+02 2.337641e+00 9.291143e+02
------------------------------ ------------- ------------- -------------
Total: -8.221904e+04 -2.772820e+03 -8.499186e+04
Monitor value: -84991.85938N
Assign the container
stacks, deck house and
the hull
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9Above water hull optimization
The forecastle deck is removed during the simulation in order to
investigate the stacks effect on the aerodynamic resistance properly.
The ship speed is 23 knots and wind speed is 20knots with
head wind condition.
The internal spaces among the stacks are 0.6 and 1.2m
The simulation results are taken from the M. Sc. project work done under Marine Technology, NTNU, Norway and partially financed by DNV
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Comparison By applying:-
1.General form of stacks
2. By modifying 3 rear container stacks, for
considering accommodating the available spaces due
to remove the stacks
3.The 45o drag reduction surface with the front edge
of the first stack, with modifying rear stacks
4.Sloping upper surface including above modification
The simulation results are taken from the M. Sc. project work done under Marine Technology, NTNU, Norway and partially financed by DNV
Air resistance(KN)
1 103.6
2 96.84
3 85
4 69.86
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Final drag force curve
0
50000
100000
150000
200000
250000
300000
350000
400000
0 20 40 60 80 100 120 140 160 180
Angle betweent the ship sailing direction and the wind direction
Dra
g f
orc
e
Full loaded conditionPartially loaded condition
Full loaded means all of the container stacks are present during simulation
Partially loaded means the container stacks 9 and 10 are removed during
simulation
For the angle between wind direction and the ship advance 140 and 30 the
drag forces are highest.
Streamlines & pressure of air on stacks
and on hull when incidence angle 0
Streamlines & pressure of air on stacks
and on hull when incidence angle 90
and the stacks 9 and 10 are removed
CFD simulation for different wind flow direction
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Results of container stacks modification
For the reduction of the produced emission gases the counteraction may create other severe problems
This paper reviews the reduction in the production of the emission gases which is achievable by reducing the fuel consumption.
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Due to optimization of the container stacks for 1000
nautical miles distance
Reduction of fuel consumption 2.83 tonnes
Reduction of emission gas CO2 about 6.6 tonnes
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Conclusions
By applying the design optimization:-
The aerodynamic drag force can be reduced by attention to the layout and steamlineing of the container stacks
Due to increase in the spaces between containers the drag forces will also increase
The emission of exhaust gases produced from the fuel can be reduced by design optimization
The most important things are the proper knowledge and understanding about ship design optimization and that CFD simulation is
used properly. Interesting questions are:-
- Verification of the CFD results
- Size and resolution of the model
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Summary of CFD results for this case study:-
A drag reduction surface at 45 on front row of containers reduced air flow resistance by 11.5%
By sloping the upper surface of the container stacks and avoiding large
gaps between stacks the air resistance could be reduced by about 15%
Streamlining of containers on the after deck behind the deck house
reduced the air resistance by about 6.5%
By design optimization a reduction of air resistance of about 33% was
achieved.
The air resistance was 3.2% of the total resistance for this design and
speed of ship leading to fuel and emissions reductions of ~ 1% .
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Thank you for your attention !