-
ADVANCES IN COMPUTATIONAL AND EXPERIMENTAL MARINE
HYDRODYNAMICS
VOL. 2 CONFERENCE PROCEEDINGS
(ISBN: 978-93-80689-22-7)
OF
International Conference On Computational and Experimental
Marine Hydrodynamics (MARHY 2014)
DECEMBER 3 - 4, 2014 AT IIT MADRAS, CHENNAI, INDIA
ORGANISED BY
Department of Ocean Engineering
INDIAN INSTITUTE OF TECHNOLOGY MADRAS
&
The Royal Institution of Naval Architects
PKKText Box Editors P. Krishnankutty, Rajiv Sharma, V. Anantha
Subramanian and S. K. Bhattacharyya
-
i
ORGANISING COMMITTEE
PATRONS
Prof. Bhaskar Ramamurthi, Director, IIT Madras Mr. Trevor
Blakeley, Cheif Executive, Royal Institution of Naval Architects
Prof. V. Anantha Subramanian, Head, Department of Ocean
Engineering, IIT Madras (Chairman) Prof. S.K. Bhattacharyya,
Department of Ocean Engineering, IIT Madras (Secretary) Prof. P.
Krishnankutty, Department of Ocean Engineering, IIT Madras
(Secretary) Prof. S.A. Sannasiraj, , Department of Ocean
Engineering, IIT Madras Dr. R. Panneer Selvam, , Department of
Ocean Engineering, IIT Madras Dr. Rajiv Sharma, , Department of
Ocean Engineering, IIT Madras Dr. V. Sriram, , Department of Ocean
Engineering, IIT Madras
TECHNICAL COMMITTEE
Prof. Manhar Dhanak, Florida Atlantic University, USA Prof. Raju
Datla, Stevens Institute of Technology, USA Prof. Pierre Ferrant,
Ecole Centrale de Nantes, France Prof. Kostas Belibassakis,
National University of Athens (NTUA), Greece Prof. P.
Ananthakrishnan, Florida Atalntic University, USA Prof. D. Sen, IIT
Kharagpur, India Prof. C.P. Vendhan, IIT Madras, India Prof. Shekar
Majumdar, Nitte Meenakshi Institute of Technology, Bangalore,
India
-
ii
About the Conference
Marine hydrodynamics deals with flow around marine vehicles,
such as surface ships, submarines, AUVs
and ROVs, and offshore structures, both fixed and floating ones.
Some of the important topics are
marine vehicle resistance and propulsion, controllability, wave
loads, wave induced motions, and energy
and ecology considerations. Correct understanding and
application of hydrodynamics on marine vehicles and structures are
vital in their design and operation.
Computational methods in marine hydrodynamic problems are
applied to solve a wide range of
maritime applications. Significant progress has been made over
the recent past towards the
development of the 'numerical towing tank' and 'virtual basin or
cavitation tunnel'. Research and
development work is still ongoing to enhance their stability,
accuracy, computational speed and its
integration into the overall design process. While the
computational hydrodynamics can provide
important insights into physical flow characteristics and offers
an economic way to investigate a range of
design options, it may still lack the accuracy to match results
obtained in real-life experiments. This
obviously points to the fact that the computational methods do
not replace the experiments completely.
The development of non-invasive flow measurement and
visualization techniques such as particle image
velocimetry (PIV) has resulted in better understanding and
quantifying the complex hydrodynamic
behavior such as wake in ship propeller region, flow around
appendages and vortex shedding from
risers.
The aim of the conference and the pre-conference workshop is to
provide a venue for disseminating
advances made in computational and experimental marine
hydrodynamics and explore outstanding and
frontier problems in marine hydrodynamics for further research
and applications.
-
iii
INTERNATIONAL CONFERENCE ON COMPUTATIONAL AND EXPERIMENTAL
MARINE HYDRODYNAMICS
(MARHY 2014)
PAPER INDEX
-
iv
Paper No. Title/Authors 1 Effect of Structural Deformation on
Performance of Different Marine Propellers
HN Das, ChSuryanarayana , B TejoNagalakshmi, P VeerabhadraRao 2
CFD Simulation Of Ship Maneuvering
K RavindraBabu, VF Saji, HN Das 3 Spatial-Spectral Hamiltonian
Boussinesq Wave Simulations
E. van Groesen, R Kurnia 4 Validation Studies for the Scaling of
Ducted Propeller Open Water Characteristics
A. Bhattacharyya, V. Krasilnikov 5 Hydrodynamic Analysis Of
Podded Propeller Using CFD
NishantVerma , Om PrakashSha 6 Predicting the Impact of Hull
Roughness on the Frictional Resistance of Ships
PA Stenson, B Kidd, HL Chen, AA Finnie, R Ramsden 7 Numerical
Wave Tank Studies for Floating Wind Turbines
ShivajiGanesan, DebabrataSen 8 Sea Trials of a Water Jet
Propelled High Speed Craft
K.O.S.R. Ravisekhar Radhakrishna, R. Panneer Selvam 9
Biomimetically Inspired Autonomous Ocean Observation System
AquaBot
Prasad Punna,JagadeeshKadiyam, D.Gowthaman, R.Venkatesan 10
Numerical Study of Self-Propulsion andManeuvering Characteristics
of 90t AHTS
Vessel, Praveen Kachhawaha,P Krishnankutty 11 Investigation on
Effect of Skew on Natural Frequency for a MarinePropeller Blade
in
Water Using F.E.M;Md. Ayaz J. Khan, Sanjay D. Pohekar, Ravindra
B. Ingle 12 Effect of Environmental Loads on the Maneuverability of
a Tanker
Deepti B. Poojari,Saj A.V, Sheeja Janardhanan, A R Kar 13 Heave
Damping Characteristics of a Buoy Form Spar by CFD Simulation
and
Experimental Studies; N. senthilkumar, S. Nallayarasu 14 CFD
simulation and experimental studies on frequency andamplitude
dependency of
heave damping of Spar hull with andwithout heave plate; J.
Mahesh, S. Nallayarasu, S. K. Bhattacharyya
15 Reduction in Ship's Resistance by Dimples on the Hull? A
Complementary CFD Investigation, S. C. Sindagi, Md. A. J. Khan,
A.S. Shinde
16 Hydrodynamic Analysis Of Flapping Foils For Near Surface
Vehicles P.Ananthakrishnan
17 Application of Direct Hydrodynamic Loads in Structural
Analysis YogendraParihar, S. K. Satsangi, A. R. Kar
18 Ship scale CFD self-propulsion simulation and its direct
comparison with sea trials results, Dmitriy Ponkratov,
ConstantinosZegos
19 Wake Estimation: A Comparative Study Between Different
Solvers Jai Ram Saripilli, Prasada Naidu Dabbi, Ram Kumar , Sharad
S Dhavalikar, ApurbaRKar
20 Experimental and CFD Simulation of Roll Motion of Ship with
Bilge Keel IrkalMohsin A.R. , S. Nallayarasu , S.K.
Bhattacharya
21 Pitch and Heave Control of Swath using Passive Fins
AzaruddinMomin, V. Anantha Subramanian.
22 Numerical Evaluation of Sloshing Pressure in a Rectangular
Tank Fitted in a Barge Subjected to Regular Wave Excitation;Jermie
J Stephen, S.A Sannasiraj, V Sundar
-
v
23 Numerical Investigation of Ship Airwake over Helodeck for
Different Configurations of Hangar Shapes of a Generic Frigate;B
Praveen, RVijayakumar, SN Singh,VSeshadri
24 CFD Analysis for the Configuration of the Hydrodynamic
Depressor SenthilPrakash M N , Jithin P N
25 Numerical & Experimental Investigation on
Semi-submersible Platform for Offshore Desalination Plant;
AshwaniVishwanath, PurnimaJalihal
26 Behaviour Of Ship Under Sloshing,
AbhijeetSajjan,A.P.Shashikala 27 Estimation of Submarine
Hydrodynamic Coefficients from Sea Trials Data using EKF
Amit Ray, DebabrataSen 28 Assessment of Slamming Dynamics on
High Speed Vessel
Deepak Bansal, V. Anantha Subramanian 29 Estimation of Hull -
Propeller System Performance for Variation in Pitch- Diameter
(P/D) RatiosMd.Kareem Khan, Amit Kumar, PC Praveen, Manu Korulla
, PK Panigrahi. 30 The Effect of Moonpool and Damping Plate on
Damping Characteristics of Spar Hulls
Using CFD Simulation;Tom P.M. , S. Nallayarasu 31 Hydrodynamic
Analysis of Self Installing Mono Column Wind Float During
Transition
Phase, UtkarshRamayan, R. PanneerSelvam, NaganSrinivasan 32
Experimental and Computational Study of Lift - Based Flapping Foil
Propulsion System
for Ships;Naga Praveen BabuMannam, Krishnankutty P 33
Investigation on the Effect of Fineness Ratio on the Hydrodynamic
Forces on an
Axisymmetric Underwater Body at Inclined Flow;Praveen PC ,
Krishnankutty P, Panigrahi PK
34 Flapping Flexible Foil Propulsion Sachin Y. Shinde,Jaywant H.
Arakeri
35 Estimating Manoeuvring Coefficients of a Container Ship in
Shallow Water Using CFD AnkushKulshrestha , P Krishnankutty
36 Analysis and Design of Geotube Saline Embankment S.
SherlinPremNisholdR. Sundaravadivelu , NilanjanSaha
37 Numerical and Experimental Determination of Velocity
Dependent Hydrodynamic Derivatives of an Underwater Towed Body;
Roni Francis , K sudarshan , P Krishnankutty & V. Anantha
Subramanian
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
EFFECT OF STRUCTURAL DEFORMATION ON PERFORMANCE OF DIFFERENT
MARINE PROPELLERS HN Das, NSTL, Defence Research and Development
Organisation, India
Ch Suryanarayana, NSTL, Defence Research and Development
Organisation, India
B Tejo Nagalakshmi, NSTL, Defence Research and Development
Organisation, India
P Veerabhadra Rao, NSTL, Defence Research and Development
Organisation, India
ABSTRACT
Propeller geometry is very crucial for its performance and a
little deviation in shape can cause changes in its
hydrodynamic performance. Hydrodynamic loading causes
deformation to the propeller blades, which leads to
change in shape. The change in shape is particularly of concern
when new designs use different composite materials
instead of conventional metals. Effect of this change of shape
on hydrodynamic performance of a propeller is being
studied in the present paper. A five bladed bronze propeller
from an existing ship is analysed to examine effects in
conventional propeller. Its open water efficiency was estimated
for original and deformed shape. Pressure based
RANS equation was solved for steady, incompressible, turbulent
flow through the propeller. Numerical solution was
obtained using Finite Volume Method within ANSYS Fluent
software. FEM based solver of ANSYS Mechanical
APDL was used to make the structural calculations.
Fluid-structure interaction was incorporated in an iterative
manner.
Additionally a five bladed composite propeller was analysed for
hydrodynamic performance. Its deformation was
estimated under hydrodynamic loading for different fibre
orientations. Hydrodynamic performance of the deformed
propeller was compared with that of the original one.
NOMENCLATURE
All Dimensions are in SI Units
1. INTRODUCTION
Geometry of propeller is very crucial for its
performance. A little deviation in its geometry may
largely influence the performance of a propeller. A
previous study reveals that some deviation in geometry
of a propeller during fitting into a ship caused variation
in its performance from its original design [9]. This
raised curiosity about performance of any propeller
when it is deformed under hydrodynamic loading.
Composite materials being more flexible, deformation
of composite propeller becomes more crucial and
hence its performance will be more interesting. The
present study concentrates on open water performance
of a metallic propeller vis--vis a composite one. At
first stage a five bladed metallic propeller was
analysed. CFD analysis was carried out for pre-
deformed geometry of the propeller to obtain
hydrodynamic pressure. This pressure was then applied
to the propeller to estimate its deformations. A FEM
code ANSYS Mechanical APDL was used for this. A
further CFD analysis was carried out with this
deformed shape to get the hydrodynamic performance
of the deformed propeller. This process was repeated
for few times to arrive at hydrodynamic load and a
compatible deformed shape of the propeller. At second
stage analysis of a five bladed composite
propeller is carried out in similar way.
2. LITERATURE REVIEW
Computation of viscous flow through propeller was
demonstrated in 22nd
ITTC conference in Grenoble,
France in 1998[10, 11 etc.]. In the last decade, Das et.
al. has carried out CFD analysis of contra-rotating
C D
E1,E2,E3
G12, G31, G23
J
Kt Kq k
n
p
Q
S
T
U Xt
Yt
Xc
Yc
12, 13, 23
Coefficient in k- turbulence model Diameter of Propeller
Youngs Modulus
Modulus of Rigidity
Advance Ratio
Coefficients of thrust
Coefficients of torque
Kinetic Energy of Turbulence
Revolution per second for
propeller Pitch
Torque of Propeller
Shear Strength
Thrust of Propeller
Free-stream Velocity
Tensile Strength in direction of fibre
Tensile Strength in direction normal
to the fibre
Compressive Strength in direction of
fibre
Compressive Strength in direction
normal to fibre
Dissipation rate of Turbulence
Kinetic Energy
Efficiency
Coefficient of Viscosity
Poissons Ratio
Density of Water.
1
PKKText Box
PKKText Box
PKKText BoxAdvances in Computational and Experimental Marine
Hydrodynamics (ACEMH 2014)Proc. of Conf. MARHY-2014 held on 3&4
Dec. , 2014 at IIT Madras, India - Vol.2 (ISBN:
978-93-80689-22-7)Editors: P. Krishnankutty, R. Sharma, V. Anantha
Subramanian and S. K. Bhattacharyya
PKKText Box
PKKText Box
PKKText BoxCopyright 2014 by IIT Madras, Chennai, India and the
RINA, UK
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
propeller [3], hull-propeller interaction [4] and study of
propeller noise [5]. Many studies on static analysis of
propeller blades are available in literature. Stress
analysis for isotropic material by Sudhakar M [7] and
study for composite propeller by Y. Seetharama Rao
et. al. [8] is few examples.
Towards the end of last century, analysis of
composite propeller was started to exploit the
advantage of its flexibility [13]. In recent times,
Blasques et al. [14], Mulcahya et al. [15], Motley et al.
[16] and Liu and Young [17] reported study of
composite marine propeller for static deformation,
dynamic analysis and hydrodynamic performance.
3. GEOMETRY OF THE PROPELLER
3.1 METAL PROPELLER
A five bladed propeller is considered for the present
study (Fig. 1). Considering its diameter to be as D,
other geometrical parameters are expressed. The hub
diameter is 0.313D. Pitch ratio (p/D) of its blades at
radial section of 0.7D is 1.547. The propeller was
modelled using Catia V5 software.
3.2 COMPOSITE PROPELLER
Geometry of marine propeller is very
complex. An actual ship propeller, for which
experimental results are already available, is already
described in para 3.1. However, to ascertain the effect
of fibre orientation in a composite propeller, study is
done for a propeller with simple geometry which is
specially designed for this purpose.
A wing of uniform aerofoil section is chosen
to be propeller blade. This wing is placed over a hub of
1.314 m diameter. The length of wing is taken as
1.443m, which makes the diameter of the propeller as
4.2m. A constant pitch is maintained throughout the
blade. Pitch ratio (p/D) becomes 1.547 which was the
pitch ratio at a radial section of 0.7R of the actual
metallic propeller-blade. Blade thickness, thus, varies
in only one direction, from leading edge to trailing
edge and does not vary from root to tip. The maximum
thickness of blade is so decided that stress remains
within the allowable limit. This simple blade becomes
a wing with uniform cross-section. For analysis, the
blade is modelled in XY plane and its thickness run in
Z direction.
The geometrical description of the simple
propeller is given in Fig. 2. Surface model of the
propellers were made in CATIA V5, R9 software.
4. GRID GENERATION
4.1 GRID FOR FLUID STUDY
The surface model of propeller was imported from
Catia to ANSYS ICEM CFD 12.0. A suitable domain
size was considered around the propeller to simulate
ambient condition. A sector of a circular cylindrical
domain of diameter ~4D and length of ~7D was used
for flow solution. The sector of 72 was so chosen that
only one blade is modelled in the domain. Periodic
repetition of this sector simulates the whole problem. A
multi-block structured grid was generated for the full
domain using ICEM CFD Hexa module. The grid thus
generated was exported from ICEMCFD to ANSYS
Fluent 12.0 solver. Extent of domain and grid over the
blade is shown in Figs. 3 and 4. A grid with total 0.268
million cells were employed to descritise the flow
field.
4.2 GRID FOR STRUCTURAL ANALYSIS
The grid from only the blade surface was imported to
ANSYS mechanical APDL software. A view of
imported mesh is shown in Fig 5. Total 361 elements
(around 400 Nodes) were used over the blade. Fig. 6
shows grid and boundary condition for composite
propeller.
5. SETTINGS UP THE PROBLEM
5.1 FLOW SOLUTION
The problem was solved using the segregated solver of
ANSYS Fluent 12.0. In brief the code uses a finite
volume method for discretization of the flow domain.
The Reynolds Time Averaged Navier-Stokes (RANS)
Equations were framed for each control volume in the
discretised form. For the present solution,
STANDARD scheme is used for pressure and a
SIMPLE (Strongly Implicit Pressure Link Equations)
procedure is used for linking pressure field to the
continuity equation. The detailed formulation of
numerical process is given in Ref [6]. The
computations were carried out on an Eight Core Dell
Precision T7500 Workstation (64bit Xeon E5640
Processor @2.67 GHz, 4GB RAM, 64 Bit Windows
XP OS). The flow is treated as incompressible and
fully turbulent. Standard K- model has been used for modelling
turbulence. The near wall turbulence was
modelled using standard wall functions and the free
stream turbulence has been prescribed as follows
K = 10
-4* U
2
The continuum was chosen as fluid and the properties
of water were assigned to it. A moving reference frame
is assigned to fluid with different rotational velocities
to simulate appropriate advance ratio. The wall
forming the propeller blade and hub were assigned a
relative rotational velocity of zero with respect to
adjacent cell zone. A constant uniform velocity was
prescribed at inlet. At outlet outflow boundary
condition was set. The farfield boundary was taken as
inviscid wall.
The following boundary conditions are used in this
analysis [Fig. 2]:
5
2
KC
2
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
(i) Velocity Inlet, (ii) Outflow, (iii) Moving Wall
(iv) Inviscid Wall, (v) Periodic
5.2 DEFORMATION STUDY
Metal Propeller
The deformation of the metal propeller blade was
estimated using ANSYS Mechanical APDL 12.0
software. The solver used Finite Element Method
(FEM) for descritisation. For structural analysis, only
one surface of the blade was modelled. The pressure,
estimated from flow solution, was applied to this blade
surface. Fluents output of pressure distribution over two
surfaces of blade, face and back, was written to a
file. A program picked up the pressure values from this
file and put to the nearest node points over the single
surface of the blade, to be used in Mechanical APDL
software. An four nodded shell elements i.e., SHELL
181, available with ANSYS solver were chosen for the
analysis. Propeller blade was considered as cantilever.
The root of the blade was considered as fixed,
restraining all degrees of freedoms there.
The blade was made of Aluminium Nickel Bronze,
which has Youngs Modulus 1011 N/m2 and Poissons Ratio of 0.34. A
constant thickness of 0.1 m was
applied for the blade. This makes the volume of the
blade approximately same to the actual blade. Mesh
and boundary condition for FE solver is shown in Fig
5.
Composite Propeller
The deformation of the propeller blade was estimated
using ANSYS Mechanical APDL 12.0 software. One
surface of the blade was considered for analysis.
Geometry with mesh was imported from ANSYS
Fluent software (where CFD study was done). The
pressure over both face and back was written to a .cdb
file from ANSYS Fluent. The same .cdb file was read
in ANSYS Mechanical APDL 12.0 software to get the
loading over the blade. Properties of Graphite Epoxy
Composite Lamina with volume fraction 0.3 were
obtained from Jones [18]. Properties are given below.
Stiffness:
E1=207 GPa E2=E3=5.0 GPa G12=G31=2.6 GPa G23=2.87 GPa 12=
13=0.25 23=0.33
Strength:
Xt= 1035 GPa Yt= 41 GPa Xc= 689GPa Yc= 117 GPa S = 69GPa
Mesh and boundary condition for FE solver is shown
in Fig 6.
5.3 FLUID-STRUCTURE INTERACTION
The deformed shape of the propeller blade under each
operating condition was transferred to ICEM-CFD
software. After developing the actual blade around this
deformed surface, mesh was again generated. This
mesh was exported to Fluent and corresponding
operational conditions in terms of propeller rpm and
linear velocity was assigned in the solver. The
hydrodynamic results obtained from flow solution
represent the behaviour of the deformed propeller. A
new pressure distribution now develops over the blade
due to the change in geometry. The new load is again
exported to ANSYS APDL software for deformation
analysis. The original blade geometry is considered for
this. The process is repeated iteratively till the time
when pressure distribution does not change any further
between two successive iterations.
6. RESULTS
6.1 METAL PROPELLER
Analysis is carried out for the hydrodynamic
performance of the propeller. Open water
characteristics i.e., thrust (Kt) and torque coefficients
(Kq) as well as efficiency () were computed at different advance
ratios (J), defined as
KT = , KQ =
= , nD
UJ (1)
According to the convention, thrust and torque are
expressed as non-dimensional quantities which remain
same under similar operating condition.
The propeller was analysed under a constant linear
velocity of inflow (U). Its rpm was varied to obtain
different values of the advance ratio. Analysis was
done for five advance ratios, ranging between 0.6 and
1.3. Pressure distribution over the propeller blade for J
= 0.6 is plotted in Fig 7.
Von-Mises stress over propeller blade for operating
condition J=0.6 is shown in Fig 8. The deformed shape
of the blade is shown in Fig. 9 and 10. The maximum
deformation is observed as 0.006428D. This
deformation is corresponding to an Advance Ratio of
0.6.
The open water characteristics for original and
deformed propeller geometry are shown in Fig 11.
Experimental results were available for a scaled down
propeller model [12]; so CFD results could be
compared with observations from experiment. From
Table 1, it is observed that change in hydrodynamic
efficiency due to deformation is very small (around
0.01).
6.2 COMPOSITE PROPELLER
Analysis was made for composite propeller to
get the deformed shape of the propeller blade with
different Laminates. Strength was checked from Tsai-
42 Dn
T
52 Dn
Q
2
J
Q
T
K
K
3
PKKText Box
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
Hill Criteria. Deformation and stress levels of the
propeller blade for different composite materials are
given in Table 4 to 6.
Propeller was run at different rpm and
advance velocities to produce advance ratio in the
range of 0.6 to 1.3. Amongst all the conditions, case
corresponding to 200 rpm and 30 Knots velocity of
advance gave the maximum structural loading. So all
the structural results corresponding to this case are
only reported here. Different thicknesses were tried out
and table 2 shows the deformation and stresses
developed within the propeller-blade. The minimum
required thickness is found out to be 80mm, where
stresses are within allowable limits and maximum twist
angle is 0.448. Table 2 shows that 80mm thick
laminate with 90/0/0/90/90 stacking satisfies the failure
criteria.
Final stacking sequence of composite layers is
arrived to 90/0/0/90/90 to avoid failure. Results for
other stacking sequences are given in Table 3. It is
observed that fibres need to be oriented at 90 at least
at the outermost layers to get the stress within
allowable limits. Other orientations of fibre lead to
higher deformation and stress which causes failure.
Table 4 shows that a suitably designed graphite- epoxy
composite laminate (90/0/0/90/90) could withstand all the load
cases with 80mm thickness. Maximum
deformation of such propeller blade is observed to be
32mm with twist in blade as 0.4 (Table 2).
To keep the volume of the paper short,
hydrodynamic performance for only 80mm thick
propeller blade with graphite epoxy is reported. Open
water characteristics of deformed and pre-deformed
propeller with blade thickness 80mm are shown in Fig.
12. It is observed that its hydrodynamic performance
remains almost unchanged before and after
deformation. However, a meagre 0.85% improvement
is obtained after deformation for operation at J= 0.6.
The change in pressure distribution due to deformation
of blade marginally alters the stress level.
7. CONCLUSIONS
The present study indicates that capability of
computational methods to solve complex engineering
problem like fluid-structure interaction for a propeller-
flow.
CFD results agreed well with experimental
observations (Fig. 11) giving good validation of this
study.
Study shows that a bronze propeller is rigid
enough to hold its shape under operational conditions,
so that its hydrodynamic performance is not affected
due to structural deformations.
Shape change in composite propeller alters its
hydrodynamic performance. Further studies may be
carried out to examine if this can be used for
improvement of design.
8. REFERENCES
1. Edward V. Lewis, Principles of Naval Architecture Volume II,
Published by The
Society of Naval Architects and Marine
Engineers, Jersey City, NJ, 1988
2. JP Ghosh and RP Gokarn, Basic Ship Propulsion, Allied
Publishers Pvt Ltd., 2004
3. H.N.Das and Lt.Cdr.P.Jayakumar, Computational Prediction and
Experimental Validation of the Characteristics of a Contra-
Rotating Propeller", NRB seminar on Marine
Hydrodynamics, Feb 2002
4. Commodore N Banerjee, HN Das and B Srisudha Computational
Analysis And Experimental Validation of Hull Propulsor
Interaction For An Autonomous Underwater
Vehicle (AUV) Seventh Asian CFD Conference 2007, Bangalore,
India, November
26-30, 2007
5. GV Krishna Kumar, VF Saji, HN Das and PK Panigrahi Acoustic
Characterization of a Benchmark Marine Propeller Using CFD National
Symposium on Acoustics (NSA-
2008), NSTL, Visakhapatnam, 22 - 24 Dec
2008.
6. ANSYS FLUENT 12.0 Documentation 7. Sudhakar M, Static &
Dynamic Analysis of
Propeller Blade M Tech Thesis submitted to Andhra University,
2010.
8. Y.seetharama Rao, K. Mallikarjuna Rao, B. Sridhar Reddy,
Stress Analysis of Composite Propeller by Using Finite Element
Analysis, International Journal of Engineering Science
and Technology (IJEST), Vol. 4 No.08 August
2012
9. HN Das CFD Analysis for Cavitation of a Marine Propeller 8th
Symposium on High Speed Marine Vehicles, HSMV 2008, Naples,
Italy, 22-23 May 2008
10. KN Chung, Fedric Stern and KS Min, Steady Viscous Flow Field
Around Propeller P4119,
Propeller RANS/ Panel Method Workshop,
22nd
ITTC Conference in Grenoble, France,
1998
11. A Sanchez Caja, P 4119 RANS Calculations at VTT, 22nd ITTC
Conference in Grenoble,
France, 1998
12. NSTL Internal Report on Hydrodynamic Model Tests For New
Design Frigate (Open
Water, Self Propulsion & 3d Wake Survey
Tests); Report Number NSTL/HR/HSTT/221/2 November 2010
13. Lin G. Comparative Stress-Deflection Analyses of a
Thick-Shell Composite Propeller
4
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
Blade. Technical Report, David Taylor
Research Center, DTRC/SHD-1373-01, 1991
14. Blasques JP, Christian B, Andersen P. Hydro-elastic analysis
and optimization of a
composite marine propeller, Marine Structures
2010; 23: 22-38.
15. Mulcahya NL, Prustyb BG, Gardinerc CP. Hydroelastic
Tailoring of Flexible Composite
Propellers. Ships and Offshore Structures
2010; 5/4: 359-370.
16. Motley MR, Liu Z, Young YL. Utilizing Fluid-Structure
Interactions to Improve Energy
Efficiency of Composite Marine Propellers in
Spatially Varying Wake. Composite Structures
2009; 90: 304-313.
17. Liu Z, Young YL., Utilization of Bend-Twist Coupling for
Performance Enhancement of
Composite Marine Propellers, Journal of Fluids
and Structures 2009; 25: 1102-1116.
18. Jones R M, Mechanics of Composite Materials, Scripta Book
Company, 1975
Fig 2 Geometry & Solid Model of Composite Propeller
Fig 1 Solid Model of Metal Propeller
5
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
Fig 3. Extent of Domain and Boundary Conditions
for Flow Analysis
Fig 4. Surface Grid over Metallic and
composite Propeller
Fig 5. Grid, Boundary Conditions with Applied
Pressure for Structural Analysis (Metal propeller)
Fig. 6 Mesh and Boundary Conditions with Loading for
Structural Analysis over Composite Propeller
(SHELL 181 Element)
6
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
(a) Face
(b) Back
Fig. 7 Pressure Distribution over Face & Back J=0.6
Fig. 9 Deformed Shape at J=0.6
Fig. 10 Deformed Shape at J=1.2
Fig. 8 Von Mises Stress(N/m2) over
Propeller Blade, J=0.6
7
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
8
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
0
0.1
0.2
0.3
0.4
0.5
0.6
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
Co
-eff
icie
nt
of
Thru
st ,
To
rque
and
Eff
icie
ncy
Advance Ratio, J
Fig. 12Open Water Charateristics : Before & After
Deformation
Kt After Deformation
Kq After Deformation
efficinecy After Deformation
Kt
Kq
efficiency
Table 1 Open Water Characteristics for Metal Propeller : Before
and after Deformation
Before Deformation Deformed Difference
J kt kq
kt kq
Kt
(%)
Kq
(%)
0.6 0.471 0.097 0.4649 0.463 0.097 0.4562 -1.71 0.16
-0.00867
0.8 0.368 0.079 0.5905 0.366 0.081 0.5800 -0.54 1.24
-0.01039
1 0.268 0.063 0.6803 0.269 0.063 0.6835 0.66 0.19 0.003251
1.2 0.162 0.043 0.7139 0.164 0.044 0.7004 0.90 2.86 -0.0135
1.3 0.105 0.033 0.6692
9
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
Table 2: Stress Level & Deformation for Composite Propeller
Blade with different thicknesses
Propeller rpm=200; Material: GRAPHITE EPOXY, Laminate
(90,0,0,90)
Thickness
(mm)
Maximum
Deformati
on
(mm)
Twist
Angle
() Extreme Normal Stress (MPa)
Extreme
Shear
Stress
(MPa)
Failure Condition
t x (min)
x (max)
y (min)
y (max)
z (min)
z (max)
xy Layer Tsai-Hill Index (Max)
100 16.30 0.240 -32.3 30.1 -328 316 -0.47 0.861 83.3
90 0.066
0 0.014
0 0.0844
90 0.554
90
21.78
0.315
-39.8
37.2
-405
386
-0.638
0.945
103
90 0.098
0 0.025
0 0.141
90 0.851
88
23.17
0.33
-41.6
39
-424
403
-0.679
0.966
107
90 0.107
0 0.028
0 0.157
90 0.932
85
25.51
0.3628
-44.6
41.8
-454
430
-0.748
0.1
115
90 0.123
0 0.034
0 0.187
90 1.073
80 31.96 0.448 -54.6 40.4 -613 454 -1.07 0.845 146
90 0.3465
0 0.0399
0 0.365
90 0.277
90 1.00
10
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
Table 3: Stress &Deformation for Composite Propeller Blade
with different fibre orientation
Plate Thickness=80mm; Propeller rpm=200
Maximum
Deformation
(mm)
Twist
Angle
() Extreme Normal Stress (MPa)
Extreme
Shear
Stress
(MPa)
Failure Criteria
Laminate x (min)
x (max)
y (min)
y (max)
z (min)
z (max)
xy Layer Tsai-Hill (Max)
(90/0/0/90) 30.19 0.4126 -50.3 47.2 -513 482 -
0.883 1.07 129
90 0.157
0 0.0485
0 0.251
90 1.369
(45/-
45/45/-45) 54.41 0.355 -99.2 159 -422 332 -1.26 4.15 -182
45 1.2918
-45 0.159
45 33.0611
-45 6.076
(120/30/75
/30/
-15/30)
100.55 0.709 -174 105 -776 1110 -43.8 20.9 288
120 1.69144
30 5.985
75 97.741
30 62.224
-15 16.597
30 237.402
(302/902/30
2/902/302)
67.28 0.6322 -106 71.2 -302 803 -6.4 9.02 233
30 1.6964
30 1.0175
90 0.708
90 0.2454
30 12.581
30 24.437
90 2.663
90 5.9468
30 83.732
30 111.250
11
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
Table 4: Stress & Deformation for Composite Propeller Blade
, rpm 200
Laminate Thickness
(mm)
Maximum
Deformation
(mm)
Twist
Angle
() Extreme Normal Stress (MPa)
Max
Shear
Stress
(MPa)
Failure Criteria
t
x
(min)
x (max)
y (min)
y (max)
z (min)
z (max)
xy Layer Tsai-Hill
(Max)
(90/0/0/90/90) 50 119.68 1.58
(+) -139 104 -1550 1090 -3.27 1.78 370
90 2.2733
0 0.613
0 3.574
90 1.9814
90 6.678
(90/0/0/90/90) 40 221.582 2.904
(+) -215 162 -2380 1620 -5.53 3.11 571
90 5.524
0 2.209
0 11.274
90 5.092
90 16.093
12
PKKText Box
PKKText Box
-
International Conference on Computational Experimental Marine
Hydrodynamics
MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
CFD SIMULATION OF SHIP MANEUVERING
K Ravindra Babu, NSTL, Defence Research and Development
Organisation, India
VF Saji, NSTL, Defence Research and Development Organisation,
India
HN Das, NSTL, Defence Research and Development Organisation,
India
ABSTRACT
International Maritime Organization (IMO) sets the standard for
ship maneuverability. Naval ships needs even better
maneuverability. Accurate prediction of ships maneuverability is
very important even at the early stage of design. Basic step
towards finding the maneuvering characteristic of any vessel is to
find the hydrodynamic derivatives. There
are many methods available for hydrodynamic derivatives
prediction such as free running model test, captive model test
etc. However these methods are expensive and time consuming.
Predictions based on semi-empirical or empirical
methods are not accurate. Whereas, accurate estimation of
hydrodynamic derivatives is essential for evaluation of
maneuverability and directional stability.
RANS based CFD code are becoming popular as an alternative
method to determine hydrodynamic derivatives. This
paper presents prediction of hydrodynamic derivative for static
maneuvers using SHIPFLOW software. CFD results in
terms of hydrodynamic forces, moments and derivatives are
compared with experimental results for a naval vessel and
showed good agreement.
1. INTRODUCTION Predictions of ship-maneuvering performance
have
been one of the most challenging topics in ship
hydrodynamics. Due to the lack of analytical methods
for predicting ship maneuverability, maneuvering
predictions have traditionally relied on either empirical
method or experimental model tests.
Recently, computational fluid dynamics (CFD) based
methods have shown promise in computing complex
hydrodynamic forces for steady and unsteady
maneuvers. Significant progress has been made
towards this goal by applying Reynolds-averaged
Navier-Stokes (RANS) based CFD codes to static
maneuvers and dynamic maneuvers with generally
good agreements with experimental data.
The CFD simulations provide more insight into the
entire flow structure around the hull, and the
simulation results can be used to compute the forces
and moment acting on the hull and also to determine
hydrodynamic derivatives of the ship hull. Although
RANS methods are considered promising, many
difficulties associated with time accurate schemes, 6
DOF ship motions, implementations of complex hull
appendages, propulsors and environmental effects such
as wind, waves, and shallow water remain challenges. Captive
model test and free running test require large
set up and are time consuming, whereas in practices, both time
and cost are limited. Thus the execution of
extensive model tests for every ship is practically
beyond possibility. Results of semi-empirical or
empirical methods are not very accurate. RANS based
CFD are hence becoming popular for calculation of
derivatives. Present work employs a RANS based CFD
tool (SHIPFLOW 5.1) for the calculation of
hydrodynamic derivatives.
2. SIMULATION OF SHIP MANEUVERS Two simulations corresponding to
straight line test and
rotating arm test have been performed using the
SHIPFLOW software for finding derivatives. An actual
ship has been considered for this purpose. Fig 1 shows
the model of the ship. Total length of the ship is 151.5m
with beam 17.71m. For this analysis 4.9m of draft was
used. Derivatives calculated using forces and moments
obtained by SHIPFLOW are compared with
experimental results.
Fig 1 Ship model
13
PKKText Box
PKKText BoxCopyright 2014 by IIT Madras, Chennai, India and the
RINA, UK
PKKText BoxAdvances in Computational and Experimental Marine
Hydrodynamics (ACEMH 2014)Proc. of Conf. MARHY-2014 held on 3&4
Dec. , 2014 at IIT Madras, India - Vol.2 (ISBN:
978-93-80689-22-7)Editors: P. Krishnankutty, R. Sharma, V. Anantha
Subramanian and S. K. Bhattacharyya
PKKText Box
PKKText Box
-
International Conference on Computational Experimental Marine
Hydrodynamics
MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
For a bare model without propellers or rudders, the
Abkowitzs mathematical models for hydrodynamic forces and moment
can be reduced to eqn (2.1) and
(2.2) by dropping the terms related to rudder angle ( ).
For the straight line test (static drift):
2
3
3
vv
v vvv
v vvv
X X X
Y Y Y
N N N
(2.1)
For the rotating arm test (steady pure yaw):
2
3
3
rr
r rrr
r rrr
X X X r
Y Y r Y rv
N N r N r
(2.2)
3. CFD MODELING To solve the flow around the hull two
different
approaches, i.e. global and zonal approaches are
available in SHIPFLOW. A global approach means
that the Navier-Stokes equations are solved in the
whole flow domain. A zonal approach means that the
flow domain is divided into different zones based on
the flow characteristics inside. Global approach has
been used here. Experimental results are already
available for a model scale of 1:19.2 [5]. The present
simulations are also carried out for same model
scale, so that the results can be compared and
validated.
3.1 FLOW SOLUTION
The potential flow analysis was carried out under the
XPAN module of SHIPFLOW. This estimates the
wave resistance. However flow near the stern end is
completely viscous. Therefore a RANS solver
XCHAP is used to resolve viscous effects. XCHAP
has been used in the analysis. It is a finite volume
code that solves the Reynolds Averaged Navier
Stokes equations.
3.2 MESH GENERATION
The total number of elements generated was 858400.
The total number of panels generated was 2834 and
nodes generated were 3086. For potential flow
calculations, required mesh was generated by
XMESH module and for RANS calculations, grids
were created by XGRID module. The mesh was
generated automatically by giving XMAUTO in
XMESH. The type of the mesh used in XGRID was
medium. Figure 2 & 3 shows generated mesh on ship
hull body.
4 RESULTS
4.1 POST PROCESSING OF RESULTS
USING SHIPFLOW
Pressure distribution for Froude number of 0.23 is
shown in fig 4. The wave height variation along the
length of the ship is plotted. This is obtained from
the potential flow analysis done in SHIPFLOW.
The variation in the wave height at Froude number
Fig 3 Mesh
Fig 2 Grids of domain
around the ship hull
14
PKKText Box
PKKText Box
-
International Conference on Computational Experimental Marine
Hydrodynamics
MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
(Fn) =0.23 can be clearly visualized from the fig 5
and 6 shown below.
Fig.5 Wave height along hull (from free surface) for a
velocity 1.646m/s
Fig.6 Free surface elevation for a velocity 1.646m/s
4.2 SIMULATION OF STRAIGHT LINE TEST
The velocity-dependent derivatives Yv and Nv of a
ship at any draft and trim can be determined from
measurements on a model of the ship, ballastard to a
geometrically similar draft and trim, towed in a
conventional towing tank at a constant velocity, V,
corresponding to a given ship Froude number, at
various angles of attack, to the model path shown in
fig 7
V = -V sin
Where the negative sign arises because of the sign
convention adopted.
A straight line test was carried out in a towing
tank to determine the sway velocity dependent
derivative. The test condition is simulated for a naval
ship model using SHIPFLOW software at different
drift angles. Hydrodynamic derivatives are
calculated using the forces and moments obtained by
SHIPFLOW.
Fig 7 Straight line test
Hydrodynamic Derivatives
Hydrodynamic derivatives are calculated using the
least square method using forces and moment
obtained by SHIPFLOW. These hydrodynamic
derivatives are compared with experimental results
and presented in Table 1.
Plots of Y vs. v and N vs. v are presented (Fig 8 and
Fig 9 respectively)
Table 1 Non-dimensionalised
sway force & yaw moment
y = 0.0030x - 0.0000
0.00015
0.00025
0.00035
0.00045
0.06 0.11 0.16 0.21
Y'
v
Yv'
Yv'
Derivative Computed
value
Experimental
value
-Yv 0.003 0.00285
-Nv 0.0092 0.017
Fig 4 Pressure Distribution
15
PKKText Box
PKKText Box
-
International Conference on Computational Experimental Marine
Hydrodynamics
MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
Fig 8 Y vs. v plot
Fig 9 N vs. v plot
4.3 SIMULATION OF ROTATING ARM TEST
This is carried out to measure the rotary derivatives Yr
and Nr on a model, a special type of towing tank and
apparatus called a rotating-arm facility is occasionally
employed.
An angular velocity r given by u
rR
The only way to vary r at constant linear speed is to
vary R. The derivatives Yr and Nr are obtained by
evaluating the slopes at r = 0. Because of ship
symmetry, the values of Yr and Nr at the negative
values of r are a reflection of their values at positive r
but with opposite sign. This test condition is simulated
using SHIPFLOW software for different radius of
rotation. Hydrodynamic derivatives are calculated
using the forces and moments obtained by
SHIPFLOW.
Fig 10 Rotating arm test
Hydrodynamic Derivatives
Hydrodynamic derivatives are calculated using least
square method using forces and moment obtained by
SHIPFLOW. These hydrodynamic derivatives are
shown in Table 2.
Graph has been plotted between Y vs. r and N vs. r which shown
in Fig 11 and Fig 12 respectively.
Table 2 Non-dimensionalised sway force
& yaw moment
Derivative Computed
value
Experimental
value
Yr 0.0206 0.026
Nr 0.065 0.069
Fig 11 Y vs. r plot
Fig 12 N vs. r plot
4.4 TURNING CIRCLE SIMULATION Introduction
Sea trial and free running model tests are
straightforward methods to obtain IMO
maneuverability criteria. However the free running
model test is not practical due to limitations of towing
tank and it is also expensive.
Computational simulations are advantageous than free
y = 0.0092x - 0.0001
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0 0.05 0.1 0.15 0.2
N
v
Nv'
Nv'
y = 0.0206x - 0.0015
0.0009
0.0029
0.0049
0.0069
0.0089
0.05 0.25 0.45
Y
r
Yr'
Yr'
y = 0.065x - 0.0049
0.0025
0.0075
0.0125
0.0175
0.0225
0.0275
0.0325
0 0.2 0.4 0.6
N
r
Nr'
Nr'
16
PKKText Box
PKKText Box
-
International Conference on Computational Experimental Marine
Hydrodynamics
MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
running model tests for assessing vessel
controllability and maneuvering performance. Once
the hydrodynamic derivative are calculated using the
captive model test or theoretical method or using
RANS based CFD, almost any maneuver or ship
operation can be simulated without additional model
tests. The simulation model can be readily and
economically modified to determine the effect of
changes, such as increasing of rudder size.
The linear equations of motion have only limited use.
If a vessel is straight - line stable, they can be used,
in principle, for maneuvering prediction, if the
considered maneuvers are not too tight. If they are
tight, the result will not be accurate enough, as
contributions of nonlinear terms become significant
and they could no longer be ignored. If a vessel
is path-unstable, the linear system of equations
cannot be applied at all, as the solution will have a
tendency of unlimited increase and only nonlinear
terms could stop its growth.
A nonlinear system is derived from nonlinear terms
in the Taylor series expansion of usually it is
expanded up to the third power, as the terms of
higher order are small in most cases. In general,
which terms will be retained is determined by both
theoretical consideration and practical experience.
Numerical values of hydrodynamic derivatives come
from model tests with planar motion mechanism
(PMM), rotating arm, a free running model, empirical
formulas or RANS based CFD. There are numerous
formulations of the nonlinear equations, but the most
common are the cubic and quadratic nonlinearity.
The quadratic nonlinearity be used here because of
the availability of a complete set sample data.
However, cubic nonlinearity may also be used.
Simulation Program
The system of equations used here is given in ABS
Rule for Vessel maneuverability, which is a more
simplified form. The system of equation is integrated
with respect to time using MATLAB (2012 b)
software to get the trajectory for turning circle
maneuvers.
In the input block, the code will read the input data
such as rudder angle and hydrodynamic coefficients.
These input data will then be used in the process
block in order to calculate the hull, rudder and
propeller forces.
Hull modules are divided into three sub-blocks
called surge, sway and yaw sub-block. Surge, sway
and yaw acceleration are calculated using the
nonlinear equation.
The equation of motion was double integrated to
obtain the translation of motion in the x and y
direction. Fig 11 shows the predicted turning circle.
Fig 11 Turning circle plot
The steady turning diameter has been found to be
27.615m
Calculation of tactical diameter according to abs
guidelines
0.910 0.424 0.675SVTD STD
L L L
Eqn 4.1 shows the calculation of tactical diameter
Where,
TD = tactical diameter in m,
Vs = test speed in knots
L = length of the vessel in m, measured
between perpendiculars,
STD = standard tactical diameter in m
Tactical Diameter = 35.27 m < 5L. Hence IMO criteria
have been satisfied.
Table 3 gives the comparison between turning circles
calculated in different ways.
Table 3 Comparison of tactical diameter in ships length
Parameter ABS
guidelines
Present
result
Sea trial
result
Tactical
diameter in
ships length 5 4.47 3.8
(4.1)
17
PKKText Box
PKKText Box
PKKText Box
PKKText Box
-
International Conference on Computational Experimental Marine
Hydrodynamics
MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT
Madras
(m)
The difference between computational and sea trial
results may be attributed to the nonlinear terms of
hydrodynamic coefficients, which were neglected in
the present analysis. In spite of the inaccuracy of
present linear analysis, the predicted tactical diameter
qualifies the ABS criteria in a very similar way as the
actual sea trial result does .
5 CONCLUSIONS In view of the present state of art, successful
analysis for computational estimate of Tactical
Diameter for ship, as reported in the present work
is very encouraging.
Velocity dependent variables were calculated using static
maneuvers.
Stability condition was checked.
Turning circle maneuver has been simulated using ABS guideline
for maneuverability. Results
agreed well with sea-trial observations.
As the results obtained are in good agreement with the sea-trial
results, RANS based CFD tool
can be used for calculation of turning
circle/hydrodynamic derivative calculation at early
design stage to predict maneuvering characteristic
of vessel.
6 REFERENCES 1. American Bureau of Shipping, 2006, Guide for
Vessel manoeuvrability, American Bureau of
Shipping.
2. Fossen, T. I., 1999, Guidance and Control of Ocean Vehicles,
University Of Trondheim,
Norway.
3. Lewis, E. V., 1988, Principles of Naval Architecture, The
Society of Naval Architects and
Marine Engineers, Jersey city, NJ.
4. SHIPFLOW 5.0 Users Manual, 2013, Flowtech International AB,
Sweden.
5. NSTL Report Number NSTL/HR/HSTT/203 A Hydrodynamic Model
Tests For P-15 Vessel-Mar 2008.
18
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India
2014: The Royal Institution of Naval Architects and IIT
Madras
1
SPATIAL-SPECTRAL HAMILTONIAN BOUSSINESQ WAVE SIMULATIONS
R. Kurnia, University of Twente, The Netherlands E. van Groesen,
University of Twente, The Netherlands & Labmath-Indonesia,
Email: [email protected], [email protected]
ABSTRACT This contribution concerns a specific simulation method
for coastal wave engineering applications. As is common to reduce
computational costs the flow is assumed to be irrotational so that
a Boussinesq-type of model in horizontal variables only can be
used. Here we advocate the use of such a model that respects the
Hamiltonian structure of the wave equations. To avoid
approximations of the dispersion relation by an algebraic relation
that is needed for finite element/difference methods, we propose a
spatial-spectral implementation which can model dispersion exactly
for all wave lengths. Results with a relatively simple
spatial-spectral implementation of the advanced theoretical model
will be compared to experiments for harmonic waves and irregular
waves over a submerged trapezoidal bar and bichromatic wave
breaking above a flat bottom; calculation times are typically less
than 25% of the physical time in environmental geometries. 1.
INTRODUCTION The dynamic equations for incompressible, inviscid
fluid flow have a well-known Hamiltonian structure in the surface
potential and elevation as state variables [1, 2, 3, 4]. The
dimension reduction is obtained by modelling instead of calculating
the interior flow, as in Boussinesq equations. A spectral
implementation makes it possible to treat the non-algebraic
dispersion relation in an exact way above flat bottom; a
quasi-homogeneous approximation makes it possible to deal with
varying bathymetry. As a consequence, waves with a broad spectrum,
such as short crested irregular waves in oceans and coastal areas,
can be dealt with. By truncating the required Dirichlet-to-Neumann
operator at the surface to a desired order of nonlinearity,
nonlinear long and short wave interactions and generation can be
calculated exactly in dispersion to the order of truncation. In our
research over the past years, difficulties with spectral modelling
when spatial inhomogeneities are present have been overcome by
using Fourier Integral Operators leading to hybrid spatial-spectral
implementations. Then waves above varying bottom, waves colliding
to (partially) reflecting walls or run-up on coasts can be
simulated. Using a kinematic initiation condition, a breaking
algorithm (of eddy viscosity-type) has been implemented [5]. Waves
can be initiated by a prescribed initial wave field or generated
from given elevation at points or lines.
Comparing simulations with experimental data shows that the
simulations are of high quality, typically the correlation with
experiments is above 0.9, and are numerically efficient with
calculation times typically less than 25% of the physical time in
environmental geometries. In the present contribution examples of
simulations for long crested waves will be shown: high frequency
wave generation for harmonic and irregular waves running over a
bar, and extensive frequency down-shift in bi-chromatic breaking
waves above a flat bottom. With a good quality transfer function
from wave elevation to wavemaker motion, the simulations can be
used to design experiments in wave tanks in an efficient way [6].
2. BASIC EQUATIONS Waves on a layer of incompressible, inviscid
fluid can be described for irrotational internal fluid motion by
variables depending on the horizontal variables only, namely the
surface elevation and the fluid potential at the surface. The
structure of the equation is special: it is a dynamical system as
in classical mechanics, with a Hamiltonian structure. This was
described by Zakharov [2] and Broer [3], and follows from Lukes
variational principle [1] as was shown by Miles [4]. The equations
are completely determined by the Hamiltonian (, ) and read (using
partial variational derivatives denoted by ! , and ! )
19
PKKText Box
PKKText Box
PKKText Box
PKKText BoxAdvances in Computational and Experimental Marine
Hydrodynamics (ACEMH 2014)Proc. of Conf. MARHY-2014 held on 3&4
Dec. , 2014 at IIT Madras, India - Vol.2 (ISBN:
978-93-80689-22-7)Editors: P. Krishnankutty, R. Sharma, V. Anantha
Subramanian and S. K. Bhattacharyya
PKKText BoxCopyright 2014 by IIT Madras, Chennai, India and the
RINA, UK
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India
2014: The Royal Institution of Naval Architects and IIT
Madras
2
! = ! , ! = !(, ) The Hamiltonian is the sum of the kinetic
energy (, ) and the potential energy (). Unfortunately cannot
easily be expressed in the basic variables since it requires to
solve the interior fluid potential (, , ) to determine the
Dirichlet-to-Neumann operator ! = () at the surface: = 12 ! = 12 In
[5] the operator is constructed up to 5th order in the surface
elevation . Here we will only describe the 2nd order method since
this case is especially simple. Introduce the tangential fluid
velocity = ! for simplified notation. Then is a quadratic
expression in , and it can be written as = 12 ()! where is some
operator. In fact has a clear physical interpretation (when the
gravitational acceleration is taken out of the integrand). In two
limiting cases is easily determined to be (related to) the phase
velocity. One limiting case is the shallow water equations, which
are above bathymetry with depth () obtained for !" = () + . The
other limiting case is the linear wave theory, for infinitesimal
small waves above constant depth ! . Then the Laplace problem can
be solved in the strip with Fourier expansion and becomes a
pseudo-differential operator ! = (,!)()!"# /2 with = () !!"# the
Fourier transform of and ,! = tanh ! . Note that ,! is the usual
phase velocity that corresponds in linear theory with the
dispersion relation ! = tanh ! . Above varying bottom () this
generalizes in a quasi-homogeneous way to ,() = tanh ()
which is a Fourier integral operator. Even more so, by taking
the total depth , = + (, ) , the expression ,(, ) = tanh (, ) leads
to a second order correct approximation for nonlinear wave
propagation above varying bottom. Observe that the limiting cases
(shallow water and linear theory) are obtained in a consistent way.
For higher order approximations the expression becomes a bit
different but with a similar structure. For details we refer to
[7]. These models are part of HaWaSSI software (Hamiltonian Wave
Ship Structures Interactions) that has been developed over the past
years. 3. SPATIAL-SPECTRAL IMPLEMENTATION Most important in the
result above is that using the phase velocity operator provides the
correct dispersive properties without any restriction on the
wavelengths, a substantial improvement above other Boussinesq
models. However, in order to retain this property in a numerical
implementation, Fourier truncation has to be used; with finite
elements or finite differences, the non-algebraic expression in has
to be approximated by an algebraic expression, leading to
restrictions on the wavelengths that are propagated with the
correct speed. A technical problem arises in the use of (adjoints
of) Fourier integral operators that appear in the explicit
expressions of the right hand sides of the Hamilton equations. To
facilitate the use of fast (inverse) Fourier transform, the
spatial-spectral phase velocity (,(, )) has to be simplified. That
can be done by a piecewise constant approximation, or by a
interpolation method; see [5, 8] for more details. 4. TEST CASES In
this section we will illustrate the simulation capacity of the
HaWaSSI code for various different cases. 4.1 HARMONIC WAVE OVER A
TRAPEZOIDAL BAR Beji and Batjess [9, 10] conducted a series of
experiments to investigate wave propagation over a submerged
trapezoidal bar. The experiments correspond to harmonic and
irregular waves for either non-breaking, spilling breaking and
plunging breaking cases. These test cases are very challenging
since they involve a number of complex processes such as the
amplification of the bound harmonics during shoaling process, wave
breaking on the top of the bar and wave decomposition in the
downslope part.
20
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India
2014: The Royal Institution of Naval Architects and IIT
Madras
3
The simulation for harmonic wave plunging breaking case has been
shown in [5]. In this section we will show results for the
non-breaking harmonic wave with frequency f = 0.5 Hz, wave height H
= 2 cm. In Figure 1, the bathymetry is presented; the water depth
varies from 0.4 m in the deeper region to 0.1 m above the top of
the bar. In the experiment at seven position the wave height is
measured: s1, s2, , s7 at positions x = 5.7, 10.5, 12.5, 13.5,
14.5, 15.7, 17.3 m. The measured wave surface elevation at s1 is
used as influx signal for our simulation.
Figure 1: Lay out of the experiment of Beji and Battjes [10].
The locations of the wave gauges are indicated.
Figure 2: Shown are at the top elevation time traces and at the
bottom, normalized amplitude spectra at positions s2 to s7 for the
non-breaking harmonic wave case, the measurement (blue, solid) and
the simulation with the HaWaSSI code (red, dashed-line). In Figure
2 we compare at all measurement points the elevation time traces in
the time interval (60;95) s and the spectra of the measurements and
simulations. It shows that the simulated surface elevation is in
good agreement with the measurement: the wave shape is well
reproduced and in phase during the shoaling process at up-slope,
the wave amplification at the top and the wave decomposition at the
down-slope. The corresponding normalized amplitude spectra describe
the generation of bound harmonic at the upslope and
annihilation at the downslope. Good agreement between
measurement and simulation is obtained, except for a slight
underestimation of the amplitude spectra of third and fourth
harmonics at s5, s6, s7. 4.2 IRREGULAR WAVES OVER A TRAPEZOIDAL BAR
In this section we show results of propagation of non breaking
irregular waves over the same trapezoidal bar.
21
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India
2014: The Royal Institution of Naval Architects and IIT
Madras
4
The input signal consist of irregular waves with JONSWAP type of
spectrum with peak frequency f = 0.5 Hz, significant wave height Hs
= 1.8 cm. For this test case the simulated surface elevation is
also in good agreement with measurement, as shown in Figure 3 at
the top. The wave shape is well reproduced and in phase, with a
slight underestimation of the wave crests at s4 and s5. The
generation of high frequency wave components due to nonlinear
interaction occurs when the wave propagates over the bar in
reasonable good agreement with measurement is shown in Figure 3 at
the bottom; the generation of high frequency waves is observed as
the appearance of a second peak frequency near f = 1 Hz. 4.3
BICHROMATIC WAVE BREAKING OVER A FLAT BOTTOM In this section we
show simulation results for a bichromatic wave with initial
steepness kp.a = 0.18, amplitude a = 0.09 m, periods T1 = 1.37 s,
T2 = 1.43 s
over a flat bottom with depth D = 2.13 m. This test case is one
of a series of wave breaking experiments that have been conducted
in the wave tank at TU Delft and registered as TUD1403Bi6 [6]. In
the experiment at six position the wave height is measured: W1, W2,
, W6 at x = 10.31, 40.57, 60.83, 65.57, 70.31, and 100.57 m. The
measured surface elevation at W1 is used as influx signal in our
simulation. In this simulation we use a third order Hamiltonian
model with extended wave breaking as described in [5]. In Figure 4
at the top we show the good agreement of the time traces of
elevations of simulations and measurements at W2 to W6. The wave
shape is well reproduced and the breaking position is well
predicted; the breaking takes place at multiple positions starting
at W3. In Figure 4 at the bottom we show the corresponding
normalized amplitude spectra; high frequency wave generation and
downshift in the spectra are observed.
Figure 3: Same as in Figure 2. Now for irregular waves with peak
frequency f = 0.5 Hz and significant wave height Hs = 1.8cm.
22
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India
2014: The Royal Institution of Naval Architects and IIT
Madras
5
Figure 4: Same as in Figure 2. Now for bichromatic wave breaking
over a flat bottom (TUD1403Bi6) .
Table 1: Correlation between simulations and measurements at
measurement positions and the relative computation time (Crel) for
the test cases.
No Case s2 (W2) s3 (W3) s4 (W4) s5 (W5) s6 (W6) s7 Crel 1
Harmonic waves over a bar 0.99 0.99 0.97 0.96 0.96 0.96 1.44 2
Irregular waves over a bar 0.97 0.96 0.93 0.89 0.88 0.89 0.78 3
Bichromatic wave breaking 0.98 0.94 0.92 0.90 0.86 - 1.89
In Table 1 we give quantitative information of the correlation
and the computation time for the test cases that have been
presented. The correlation between the measurement and the
simulation is defined as the inner product between the normalized
time signals. Deviations from the maximal value 1 of the
correlation measures especially the error in phase, a time shift of
the simulation. The relative computation time is defined as the
cpu-time divided by the total time of simulation. Since the
laboratory experiments are scaled with a geometric factor of
approximately 50, the relative computation time for real scaled
phenomena is a fraction of 7 of the test relative time; hence our
simulations at geo-scale run in less than 25% of the physical time.
All the calculations were performed on a desktop computer with CPU
i7, 3.4 Ghz processor with 16 GB memory.
4. CONCLUSIONS The accuracy of the code as shown above makes it
possible to use simulations in the design of experiments in wave
tanks as was shown in [6] for a series of breaking waves of
irregular, bi-chromatic and focussing type. Since in the present
code waves are generated based on a time trace at an influx
position, a high-quality transfer function is needed that
transforms the influx signal to the corresponding wave maker
motion. An extension to a fully coupled Hamiltonian-Boussinesq
wave-ship model is presently being implemented as part of
HaWaSSI.
23
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India
2014: The Royal Institution of Naval Architects and IIT
Madras
6
ACKNOWLEDGEMENTS We thank Prof. S. Beji for providing the
experimental data over the bar. This work is funded by the
Netherlands Organization for Scientific Research NWO, Technical
Science Division STW, project 11642. REFERENCES 1. J. C. Luke. A
variational principle for a fluid with
a free surface. J. Fluid Mech. 27, 395-397. 1967. 2. V. E.
Zakharov. Stability of periodic waves of
finite amplitude on the surface of a deep fluid. J. Appl. Mech.
Tech. Phys. 9, 190-194. 1968.
3. L. J. F. Broer. On the Hamiltonian theory of surface waves.
Appl. Sci. Res. 29, 430-446.
4. J. W. Miles. On Hamiltons principle for surface waves. J.
Fluid Mech. 83, 153-158. 1977.
5. R. Kurnia, E. van Groesen. High order Hamiltonian water waves
models with wave breaking mechanism. Coast. Eng. 93, 55-70.
2014.
6. R. Kurnia, et al. Simulation for design and reconstruction of
breaking waves in a wavetank. 2014. (to be published).
7. R. Kurnia, E. van Groesen. Accurate dispersive Hamiltonian
wave Boussinesq modelling and
simulation for coastal wave applications. 2014. (to be
published).
8. E. van Groesen, I. van der Kroon. Fully dispersive dynamic
models for surface water waves above varying bottom, Part 2: Hybrid
spatial spectral implementations. Wave Motion. 49, 198-211.
2012.
9. S. Beji, J. A. Battjes. Experimental investigation of wave
propagation over a bar. Coast. Eng. 19, 151-162. 1993.
10. S. Beji, J. A. Battjes. Numerical simulation of nonlinear
wave propagation over a bar. Coast. Eng. 23, 1-16. 1994.
AUTHORS BIOGRAPHY Ruddy Kurnia holds current position of Ph.D
student at Department of Applied Mathematics, University of Twente,
The Netherlands. His research focuses on modelling and simulation
of accurate dispersive wave for coastal wave applications. E. van
Groesen is professor of Applied Mathematics at the University of
Twente, and scientific director of Labmath-Indonesia, Bandung,
Indonesia. His main research area is the variationally consistent
modeling and simulation of water waves, recently also including the
interaction with ships.
24
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT Madras
1
Validation Studies for the Scaling of Ducted Propeller Open
Water Characteristics
A. Bhattacharyya, Department of Marine Technology, NTNU,
Trondheim, Norway; V. Krasilnikov, MARINTEK, Trondheim, Norway
ABSTRACT
This paper presents the results of validation studies for the
open water characteristics of a four-bladed controllable pitch
propeller operating inside two ducts of different designs. The
results of numerical calculations by CFD are compared with model
test results in terms of propeller and duct thrust, propeller
torque and efficiency, and also in terms of velocity field
downstream of propulsor. In order to quantify the scale effects on
open water characteristics, CFD calculations are also carried out
at Reynolds numbers corresponding to full scale conditions, and
comparisons between the propulsor characteristics in model scale
and full scale are presented for the range operating conditions
from bollard to free sailing.
NOMENCLATUTRE
J : Advance Coefficient
KTD : Duct Thrust (N)
O : Open water efficiency D : Propeller Diameter (m)
KTP : Propeller thrust (N)
KQ : Propeller torque (Nm)
KT_Tot : Total thrust (N)
INTRODUCTION
The analysis of scale effects on open water characteristics of
marine propellers is important to have accurate full scale power
prognoses based on model test results. The flow around a rotating
propeller is highly three-dimensional, and it involves high degree
of swirl, adverse pressure gradients and, in some cases, flow
separation and associated vortex shedding. For a ducted propeller,
the propeller-duct interaction at different Reynolds numbers is of
prime importance and has a strong influence on the corresponding
thrust and torque characteristics and propulsor efficiency. The
scale effects depend on the propeller and duct geometries as well
as the loading conditions.
With advanced CFD techniques, robust flow solvers have been
developed to resolve viscous turbulent flows, and they have become
essential tools used in the marine industry to analyse complex flow
around ship propellers. In this study, the scale effects on the
open water characteristics of a four-bladed controllable pitch
propeller operating with two different duct designs (a standard
Wageningen 19A duct, and the Innoduct designed by Rolls Royce) have
been investigated. The results of model tests performed at China
Ship Scientific Research Center (CSSRC) and CFD simulations done
with the commercial CAE software STAR-CCM+ are used for comparisons
in model scale conditions, while full scale calculations are
performed by CFD.
The strong duct-propeller interaction demands a separate scaling
procedure for the open water characteristics of ducted propellers,
where the simpler scaling methods developed for open propellers
will not be applicable. In spite of the studies conducted earlier
on scale effects on ducted propellers, the development of a
universal procedure has not been possible due to complexity of
interactions and geometry dependencies. In this study, it has been
found that the trend of scale effects for the propeller working
inside the two investigated ducts are similar. The detailed flow
physics at different Reynolds numbers should be considered, in
order to develop an efficient scaling procedure for the estimation
of full scale open water characteristics of ducted propellers.
25
PKKText Box
PKKText BoxCopyright 2014 by IIT Madras, Chennai, India and the
RINA, UK
PKKText BoxAdvances in Computational and Experimental Marine
Hydrodynamics (ACEMH 2014)Proc. of Conf. MARHY-2014 held on 3&4
Dec. , 2014 at IIT Madras, India - Vol.2 (ISBN:
978-93-80689-22-7)Editors: P. Krishnankutty, R. Sharma, V. Anantha
Subramanian and S. K. Bhattacharyya
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT Madras
2
BACKGROUND
The capability of performing efficient full scale simulations
has made CFD a powerful tool for the investigation of scale effects
of propellers. In most of the published CFD studies on scale effect
on propeller characteristics, the RANS method is used with an
isotropic turbulence model, the SST k- model (Menter, 1994) being
the most common choice in the recent works. Most of the works are
based on fully turbulent flow assumption (Stanier, 1998), Maksoud
and Heinke (2002), (Krasilnikov et al, 2007), and only a few of
them employ the recent extensions of the SST k- model to consider
the laminar-turbulent transition flow regime (Mller et al,
2009).
Maksoud and Heinke (2002) performed systematic investigations
into the scale effects on the open water characteristics of a
Wageningen Ka 5-75 propeller fitted with a 19A duct at four values
of propeller diameters and thrust loading coefficients.The increase
of Reynolds number in full scale resulted in reduction of propeller
thrust and increase of the duct thrust. Krasilnikov et al. (2007)
presented a hybrid mesh generation technique for the steady RANS
analysis of a series Ka propeller fitted with different duct
designs using the SST k- model. This study shows that scale effects
on the characteristics of ducted propellers depend on duct design,
propeller design and loading conditions. Different ducts can
produce different flow accelerations, which leads to variations in
effective loading for the same propeller operating inside those
ducts. This, along with different separation patterns on the duct
in model scale and full scales, influences the magnitude of scale
effect. The common conclusion from these studies is a larger
reduction of propeller torque in full scale compared to that of an
open propeller under equivalent operating conditions. This is due
to the combined effect of the decrease of blade section drag and
higher duct induced velocities on propeller. The Specialist
Committee on Unconventional Propulsors of the 22nd ITTC (ITTC,
1999) have considered the three extrapolation methods proposed in
(Stierman, 1984) for powering prognoses for the ships with ducted
propellers. In this work, the most commonly used method 2 is
followed, in the sense that the chosen approach implies that the
resistance test is done for the naked
hull, while the open water tests are performed with the
propeller operating in the duct.
TEST CASES
In this paper, flow analyses are performed for a 4-bladed
controllable pitch propeller working within a standard 19A duct,
using the RANSE flow solver implemented in STAR-CCM+. Comparisons
of open water characteristics and induced velocities downstream of
the propeller are made with model test results. The dependence of
the propeller and duct forces on simulation methods and turbulence
modelling is studied. Finally, the scale effects are investigated
using CFD calculations of a full scale propeller, having the
diameter 20 times of model scale and rate of revolution scaled
according to the Froude number identity. The predicted changes with
scale in propeller thrust and torque, duct thrust and propulsor
efficiency for this propeller are compared with those obtained for
the same propeller operating inside the Innoduct.
In Fig. 1 the profiles for the two ducts subject to
investigation are shown with the mesh around the duct and blade
tip.
CFD SIMULATION SET-UP
The propeller and duct are defined by their respective
geometries which are used to generate
Fig. 1: Duct profiles including mesh
19A duct
Innoduct
26
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT Madras
3
local grids in STAR-CCM+. Two different solution methods were
used for the simulations. In the Moving Reference Frame (MRF)
method the propeller is fixed while its rotation is taken into
account by a local reference frame rotating at the desired speed.
The stationary position of the duct is ensured by an appropriate
setting of the zero rotation rate of the duct boundary. The
additional acceleration terms from the rotating frame are
incorporated into the modified equations of motions. This approach
has been found to be suitable in the range of regular operation
conditions (J= 0.2 to 0.6) where the interactions between moving
and stationary parts can be approximated with sufficient accuracy
by the quasi-steady solution. The Sliding Mesh (SM) model is used
to resolve strictly the relative motion of stationary and rotating
components and to account for all unsteady interactions. The
bollard condition (J= 0) is a typical example where unsteady
interactions are important, and where the MRF method is not
sufficient to resolve the flow accurately. The simulation domains
used with these two methods are shown in Figs. 2 and 3, and the
details of mesh and solution settings are explained below.
One-block, One-blade passage:
(a) Only one fluid region whose rotational motion is considered
in rotating reference frame. (b) Domain corresponds to one blade
passage with periodic boundaries (c) Prismatic mesh in the boundary
layers, and polyhedral mesh in the rest of the domain. (d) Mesh
refinement by means of volumetric controls and local surface cell
size near the leading and trailing edges of propeller and duct, in
the region of tip clearance and in the propeller slipstream. (e)
Methods used: MRF, steady. (f) Cell count is about 7.5 million per
one blade passage.
Two-blocks, Whole domain:
(a) Whole domain divided into two fluid regions connected by the
two internal interfaces. (b) Hexahedral trimmed cells in the outer
fluid region, and polyhedral mesh in the propeller region. (c)
Prismatic boundary layer mesh on the duct and propeller blade
surfaces (d) Mesh refinement similar to one-block set-up. (e)
Methods used: steady MRF to initialize the solution, and unsteady
SM to iterate until convergence. (f) Cell count per blade passage
is approximately the same as in the steady MRF method. (g) The
time-accurate SM solution is done according to implicit unsteady
algorithm, using the first-order temporal discretization scheme and
time step corresponding to 2 degrees of propeller rotation.
For the model scale simulations with the 19A duct, solutions
with the three different turbulence models have been compared,
including k--SST model, k- realizable model, and Reynolds Stress
model (linear pressure strain). For both two-equation models all y+
treatment has been used. The full scale simulations have been done
using only the k--SST model.
The details of the near-wall mesh at the duct trailing edges are
shown in Fig. 4.
Fig. 2: 1 block - 1 blade passage simulation set-up
Fig. 3: 2 blocks - whole domain simulation set-up
19A duct
27
PKKText Box
PKKText Box
PKKText Box
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT Madras
4
The boundary layer mesh of prismatic cells plays a very
important role in providing adequate levels of the wall y+ function
on simulated bodies, as well as in resolving accurately the
velocity profiles in the boundary layer. In the present
simulations, the values of wall y+ < 5 have been maintained on
the blade and duct surfaces in both the model scale and full scale
simulations (see Fig. 5 for the 19A duct). This has been achieved
by reducing the total relative thickness for the prism mesh in full
scale (0.002D, D being propeller diameter) compared to that in
model scale (0.0025D) along with a higher stretching factor (1.4)
for the prism layer mesh in full scale compared to that in model
scale (1.2) The number of prism layers (20) has been same at both
scales.
In the course of the studies it was also confirmed that a
sufficiently smooth transition between the prism mesh and core mesh
in terms of cell size change is essential for achieving physically
correct flow picture, in particular, in the zones of larger
velocity gradients, such as duct trailing edge and tip
clearance.
The test calculations show that, in full scale simulations, one
can employ the high Reynolds near-wall resolution (wall y+ >30)
without reducing the accuracy of numerical predictions. However,
for consistency of analyses, in the present study both the model
scale and full scale simulations were performed with low Reynolds
near-wall resolution (wall y+
-
International Conference on Computational and Experimental
Marine Hydrodynamics MARHY 2014
3-4 December 2014, Chennai, India.
2014: The Royal Institution of Naval Architects and IIT Madras
5
Turbulence Model J KTP KTD KQ
SST
k-
m
odel
0.01 0.361 0.375 0.072 0.26 0.329 0.218 0.067 0.60 0.263 0.075
0.056 0.94 0.131 -0.024 0.035
Rea
lizab
le
k- m