CFD Analysis of Resistance Characteristics of High-Speed

CFD Analysis of Resistance Characteristics of

High-Speed Displacement Hull Forms fitted

with Hull Vane®

by

Venkata Karthik Avala

Bachelor of TechnologyNaval Architecture and Ocean Engineering

Indian Maritime University, Visakhapatnam 2013

A thesissubmitted to the College of Engineering at

Florida Institute of Technologyin partial fulfillment of the requirements

for the degree of

Master of Sciencein

Ocean Engineering

Melbourne, FloridaMay 2017

COPYRIGHT

In presenting this thesis in partial fulfillment of the requirements for an ad-vanced degree at the Florida Institute of Technology, I agree that the libraryshall make it freely available for reference and study. I further agree that per-mission for copying of this thesis for scholarly purposes may be granted by theHead of my department or by his or her representatives. It is understood thatcopying or publication of this thesis for financial gain shall not be allowed with-out my written permission.

Venkata Karthik AvalaOcean Engineering and SciencesFlorida Institute of TechnologyMelbourne, Florida

May 2017

© Copyright 2017, Venkata Karthik AvalaAll Rights Reserved

Signature

We the undersigned committee hereby recommendthat the attached document be accepted as fulfilling in

part the requirements for the degree ofMaster of Science in Ocean Engineering.

“CFD Analysis of Resistance Characteristics of High-Speed Displacement HullForms fitted with Hull Vane® ”,

a thesis by Venkata Karthik Avala

Dr. Prasanta K. Sahoo, Ph.D.Associate Professor, Ocean Engineering and SciencesCommittee Chair

Dr. Stephen Wood, Ph.D.Department Head, Ocean Engineering and Sciences

Dr. Chelakara Subramanian, Ph.D.Professor and Chair, Mechanical and Aerospace Engineering

Dr. Ronnal Reichard, Ph.D.Professor, Ocean Engineering and Sciences

Abstract

TITLE: CFD Analysis of Resistance Characteristics of High-

Speed Displacement Hull Forms fitted with Hull Vane®

AUTHOR: Venkata Karthik Avala

MAJOR ADVISOR: Dr. Prasanta K. Sahoo, Ph.D.

Improving the performance and resistance of a high-speed monohull forms has

been of interest to Naval Architects for several decades. A considerable amount

of research has been carried out in this area by using stern flaps and other

appendages.

This research thesis investigates the resistance characteristics of high-speed

round bilge hull forms fitted with a Hull Vane® in the stern region of the vessel.

The Hull Vane® is a fixed foil located below the waterline at the aft of the stern

of the vessel. The Hull Vane® reduces the generation of waves at the aft and

improves the vessel's motions. This thesis investigates the drag reduction by

fitting a Hull Vane® in the stern region of a select few of Australian Maritime

Engineering Cooperative Research Center (AMECRC) systematic series hull

forms, originally developed as High-Speed Displacement Hull Forms (HSDHF)

series at MARIN, The Netherlands.

The aim of this research is to:

- Validate the total resistance of AMECRC series models #3, #4, #8, #11,

#13 for the Froude numbers 0.5, 0.6, 0.7 in CFD against the experimental

data available.

iii

- Attach a Hull Vane® of NACA 4412 profile at the aft region of the above

hull forms at the same Froude numbers and determine reduction in resis-

tance if any.

Hull Vane® used for this analysis has a profile similar to NACA 4412 and prin-

cipal dimensions such as span has been varied according to the breadth of the

models tested. The flap angle and chord length have been kept constant.

Figure 1: Hull-form fitted with Hull Vane® (with permission from businesspresentation)

The CFD research is carried out on STAR CCM+, a CFD package used to

simulate the drag characteristics. Models #8, #11 and #13 have shown a

significant reduction in the total resistance varying from 7% to 29% with an

average reduction of 17.3% when fitted with a Hull Vane® . Model #3 and

#4 did not show any significant improvement in the resistance. In fact, model

#4 has shown an increase in resistance when fitted with a Hull Vane® . It

is expected that the results of this research would hopefully lay the ground

work for further studies and comparative analysis. The conclusions would be

beneficial for anyone interested in the Hull Vane® research.

iv

Nomenclature

Acronyms

AMECRC Australian Maritime Engineering Cooperative Re-

search Center

CAD Computer Aided Drafting

CFD Computational Fluid Dynamics

HSDHF High-Speed Displacement Hull Forms

IGES Initial Graphics Exchange Specification

ITTC International Towing Tank Convention

JONSWAP Joint North Sea Wave Project

LCB Longitudinal center of buoyancy

MARIN Maritime Research Institute Netherlands

NACA National Advisory Committee for Aeronautics

NURBS Non-uniform rational B-spline

RANS Reynolds-averaged Navier Stokes

VOF Volume of Fluid

WSA Wetted surface area

v

Greek Symbols

α Hull Vane® inflow angle

β Hull Vane® angle

∆ Mass Displacement

λ Wave length

∇ Volume displacement

ρ Density

θ Trim angle

Latin Symbols

CD Drag coefficient

CL Lift coefficient

Fn Froude Number

L/∇1/3 Slenderness Ratio

A Area

B/T Breadth to Draft ratio

D Drag force

L Length

L/B Length to Breadth Ratio

S Wetted Surface Area

V Velocity

vi

Contents

Abstract iii

Nomenclature v

List of Figures ix

List of Tables xi

Acknowledgment xiii

Dedication xiv

1 Introduction 1

1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Scope of Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Background 3

2.1 Literature Survey . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3 Components of Total Resistance . . . . . . . . . . . . . . . . . . 9

2.4 STAR CCM + . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 AMECRC Series 13

4 Hull Vane® 20

4.1 Thrust force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.2 Trim correction . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.3 Reduction of waves . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.4 Reduction of motion in waves . . . . . . . . . . . . . . . . . . . 26

vii

4.5 Hull Vane® - Profile . . . . . . . . . . . . . . . . . . . . . . . . 27

5 Geometry 28

5.1 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.2 Mesh Generation . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.3 Boundary Condition and Solution Setup . . . . . . . . . . . . . 31

6 Validation of CFD 33

6.1 Statement of Uncertainty . . . . . . . . . . . . . . . . . . . . . . 34

7 Results and Discussion 40

8 Conclusion 47

8.1 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Bibliography 50

A Sensitivity study 54

viii

List of Figures

1 Hull-form fitted with Hull Vane® (with permission from business

presentation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

2.1 Transom Wedge and Stern Flap Karafiath et al., (1999) . . . . . 4

2.2 Integrated Wedge-Flap Karafiath et al., 1999 . . . . . . . . . . . 5

2.3 Interceptor at the stern of the ship Karimi et al., (2013) . . . . 6

3.1 Lines Plan of the Parent Hull of the AMECRC Series . . . . . . 14

3.2 Body Plan of five selected models of the AMECRC Series . . . . 17

3.3 Change in Hull Shape of AMECRC Series [Sahoo and Doctors

(1999)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.4 AMECRC Systematic Series models #3, #4, #8, #11 and #13

Parameter Space . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.1 Schematic representation of the forces on the Hull Vane® Uithof

et al., (2014) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.2 Pictorial representation of Hull Vane® (with permission from

business presentation) . . . . . . . . . . . . . . . . . . . . . . . 23

4.3 Pictorial representation of trim correction at the Stern (with per-

mission from business presentation) . . . . . . . . . . . . . . . . 24

4.4 Wave pattern on a 55-metre supply vessel without Hull Vane®

(top) and with Hull Vane® (bottom) at 20 knots. From CFD

computations (blue portrays a wave trough and red a wave crest)

Uithof et al., (2014) . . . . . . . . . . . . . . . . . . . . . . . . . 25

ix

4.5 Comparison of the wave profile of the 55 metre supply vessel

without Hull Vane® (left) and with Hull Vane® (right) at 13

knots. As seen from the aft deck during sea trials Uithof et al.,

(2014) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.6 Comparison of the motions of AMECRC series model #13 fitted

with and without Hull Vane® . . . . . . . . . . . . . . . . . . . 26

5.1 Geometry of Model 11 with Hull Vane® in Star CCM+ . . . . . 29

5.2 Volumetric mesh of Model 11 fitted with Hull Vane® . . . . . . 31

6.1 CFD and Experimental data for bare hull [Model 3] . . . . . . . 35



6.4 CFD and Experimental data for bare hull [Model 11] . . . . . . 38

6.5 CFD and Experimental data for bare hull [Model 13] . . . . . . 39

7.1 Resistance data for the Model 3 with and without Hull Vane®

using CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42


using CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43


using CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

7.4 Resistance data for the Model 11 with and without Hull Vane®using

CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45


using CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

A.1 Resistance data for model 13 at different Hull Vane® positions

in x-axis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

x

List of Tables

3.1 Parameter range of the models Sahoo and Doctors (1999) . . . 15

3.2 Parameters of the five models used for this analysis, Sahoo and

Doctors (1999) . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3 Parameters which are constant for the models, Sahoo and Doctors

(1999) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.1 Fluid properties of fresh water . . . . . . . . . . . . . . . . . . . 31

5.2 Boundary condition and solution method . . . . . . . . . . . . . 32

6.1 Resistance data Validation [Model 3] . . . . . . . . . . . . . . . 35





7.1 Resistance data of Model 3 with and without Hull Vane® using

CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42


CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43


CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44


CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45


CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

xi

A.1 Sensitivity study of AMECRC model #13 fitted with Hull Vane®

for Fn 0.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

xii

Acknowledgement

I would like to express my deepest appreciation to Dr. Prasanta Sahoo who

read my numerous revisions and critiqued patiently. Without his guidance and

persistent help, this would not have been possible. He has been so generous

and patient during this research. I would also like to thank Dr. Wood, Dr.

Subramanian and Dr. Reichard for their valuable time.

I would like to extend my sincere thanks to my Naval Architecture laboratory

fellow mates for being with me and helping me out with this research.

I would like to thank Van Oossanen Naval Architects for their encouragement

and support.

I would also like to express my deepest gratitude to my family and friends for

their love, affection and for being my source of inspiration and support.

xiii

Dedication

To my late Father, my Mother and my Sister.

xiv

Chapter 1

Introduction

1.1 Motivation

The idea of high-speed ships emerged in 1870 when naval forces began using

torpedo boats, development of which followed as a result of the invention of the

torpedo in 1860 by Giovanni Luppis of Austria-Hungary, DeJong (2011). The

naval forces started using torpedo boats because they are relatively cheaper and

faster than the heavily armoured battleships of the time which could easily be

outrun and outmaneuvered. In the late 19th and the early 20th century, ships

began to move at higher speeds due to the invention of steam turbine and in-

ternal combustion engines.

The drag force on the hull is an important factor to deal with in the process

of ship design. Researchers around the world have developed various devices

designed to improve drag reduction and also generate lift. Some of these are

directed to the stern of the ship such as stern wedges, stern flaps, trim tabs and

vanes . Experimental model testing involves extensive cost and time but gives

1

reliable results in the preliminary design stage. As computer simulation tech-

niques have improved over the years, many stages of design could be simulated

with a reasonable accuracy, thus enabling the testing of improved designs with

lesser cost and time.

The evolution of the stern devices can be challenging to track as their design is

often specific for a given stern type and vessel characteristics. Hull Vane® is a

stern device known for reduction of total resistance and suitable for round bilge

hull forms.

1.2 Scope of Work

This research primarily focuses on resistance prediction of high-speed round

bilge hull forms by fitting them with a Hull Vane® .

This research would comprise of the following steps:This research would com-

prise of the following steps:

A. Hull forms were developed from NURBS curves for models #3, #4, #8,

#11 and #13 of AMECRC series.

B. CFD analysis was performed for resistance of the bare hull models at

Froude numbers 0.5, 0.6, 0.7 and validated against the model tank test

data.

C. Hull Vane® location both in longitudinal and vertical direction was varied

but angle of attack was kept constant during simulation when attached to

the bare hull models at Froude numbers of 0.5, 0.6 and 0.7.

D. Results were obtained, analyzed and discussed.

2

Chapter 2

Background

2.1 Literature Survey

The dynamics of high-speed vessels is an important parameter in the design pro-

cess. Inadequate attention to this aspect will impact unavoidable penalty during

the vessel's life. One aspect of this endeavor is the reduction of drag. Naval Ar-

chitects have over the years developed different appendages to reduce the drag

component by creating a lift component. A study conducted by Karafiath and

Fisher (1987) on stern wedges mentions that the concept of the stern wedges is

not new and quotes a notable reference to German, Italian and the US Navies,

where the appendage has proven to reduce the resistance of the ship up to 6%

at maximum speed. It was also shown that a reduction of running trim (trim

observed when the vessel is in motion) of up to 2.0 degrees could result in 2%

of saving in fuel consumption.

3

Figure 2.1: Transom Wedge and Stern Flap Karafiath et al., (1999)

An investigation by Cusanelli and Cave (1993) on the application of stern flaps

as a retrofit on the vessels of US Navy found a reduction in power, which resulted

in reduced fuel consumption and increased top speed. Cusanelli and Karafiath

(1997) in their research explained the power saving aspect of the wedges and

flaps. Their study was conducted on U.S. Navy ships, including frigates and

destroyers. In their study on integrated wedge-flap design, Karafiath and Cu-

sanelli (1997) mentioned that a reduction in power of 11.6% was observed, while

a wedge only configuration lead to a power reduction of 6.2%.

4

Figure 2.2: Integrated Wedge-Flap Karafiath et al., 1999

Tsai et al., (2004) studied interceptors and found that these can be used to

reduce the resistance of planning hulls. Application of wedge flap and transom

flap includes both increasing the performance of small craft and reduction of

resistance in large fast displacement ships. Studies on the effect of wedge flaps on

the trim and resistance of fast displacement ships was carried out by Kapsenberg

et al., (2012).

5

Figure 2.3: Interceptor at the stern of the ship Karimi et al., (2013)

Van Oossanen (1992) invented the Hull Vane® (figure 4.2) which is a fixed,

resistance-reducing foil situated below the waterline, aft of the stern of the

ship. The application of the Hull Vane® can be traced back to 1992 when the

first full-scale Hull Vane® was fitted on a catamaran vessel. However, the

catamaran did not achieve the expected speed due to excessive trim and wave

generation. “Placing a foil in the steepest part of the interacting wave system

aft of the midship of the catamaran proved to reduce the bow-up trim and the

resistance significantly” as mentioned in Uithof et al., (2014).

The Hull Vane® was then applied on the 2003 America's cup French challenger

“Le Defi Areva”. “During model tests a resistance reduction of 5% was found

6

at model scale for a full-scale speed of 10 knots” as mentioned in Uithof et al.,

(2014).

In addition to the above, research focused on the working principles of the Hull

Vane®, and a number of applications were tested, mostly by computational

analysis using CFD. Further tests have been conducted on models ranging from

sailing yachts and motor yachts to more commercial vessels, such as supply ves-

sels, containerships, cruise ships and Ro-Ro vessels and the influence of the Hull

Vane® on total resistance was found to have varied between -26.5% and +9.5%,

exhibiting that the fuel saving device is not suitable for all cases as mentioned

in Uithof et al., (2014).

In 2014, two ships equipped with Hull Vane® were launched. The first one is a

55-metre supply vessel Karina, which had its required engine power reduced by

15% during sea trials after a Hull Vane® was retrofitted to the transom. The

second vessel was a 42-metre displacement yacht for which the Hull Vane® was

incorporated during the design phase, which showed a resistance reduction of

up to 23% as mentioned in Uithof et al., (2014). Uithof et al., (2014) concluded

that extensive research has been carried out by employing CFD computations,

numerous model tests and sea trials were conducted, and the reduction in resis-

tance was found to be up to 26.5% on ships running at Froude numbers between

0.2 and 0.7 which is effective Froude number range for the Hull Vane® .

7

2.2 Theory

Predicting the resistance characteristics of a ship has always been a difficult

task as it is associated with three prominent factors namely accuracy, time and

application cost. There are two basic ways of predicting the wave resistance

followed by the Naval Architects.

Towing tank test: This method is considered to be the most reliable method

which yields accurate resistance results by using geometrically similar models

for testing. The objectives of measurement in towing tank resistance tests are

to obtain the relationship between residuary resistance coefficient and Froude

number of a ship model and if required, the form factor. The direct measure-

ment of the tests is the total resistance as well as the running attitudes of a ship

model at each speed.

CFD method: This is a numerical simulation of the model which behaves just

like a numerical towing tank and predicts the resistance data. The time pe-

riod for completing a simulation is based on the parameters of the model, other

attributes, and conditions which would be given as input by the user. This

method may seem economically feasible when compared to the towing tank test

but is not as accurate.

The prediction of resistance characteristics of hull forms can be done in several

ways:

- Extrapolation from geometrically similar models

8

- Dedicated model tests

- Series data based on systematic model tests

- Regression based procedures and

- Computational fluid dynamics.

Resistance is the driving force which is responsible for the uniform rectilinear

motion of the ship with a constant speed in a calm sea. The total resistance

is divided into two components namely viscous resistance which is associated

with the friction experienced by the body with respect to the fluid medium, and

the other is wave making resistance which causes the generation of waves. The

wave making resistance is the resultant force created by the pressure changes

due to the atmosphere on the free surface, which results in waves on the sur-

face. As the speed and form of the ship has a profound effect on wave making

resistance that eventually increases the total resistance experienced by the ship,

it is essential to find out ways of reducing it so that better drag characteristics

could be achieved. To accomplish this, high values of slenderness ratio (L/1/3)

or increasing the dynamic lift of the hull are required. Wave making resistance

is also influenced because of the interference between the separate hull wakes in

multihull forms like catamarans and trimarans.

2.3 Components of Total Resistance

The ITTC-78 method suggested the total resistance components of mono-hull

should be expressed by equation:

9

CT = (1 + k)CF + CR + CA + CAA (2.1)

Where (1+k) is the form factor determined from resistance tests. CF is the fric-

tional resistance coefficient, which is always calculated according to the ITTC-57

ship model correlation line and is given by:

CF =0.075

(log10Rn − 2)2(2.2)

CR is the residuary resistance coefficient and is expressed by the equation:

CR = CT − (1 + k)CF (2.3)

CA is the correlation allowance given by:

CA = (5.68− 0.6 logRe)× 10−3 (2.4)

CAA is the air resistance coefficient given by:

CAA =AV T

1000S(2.5)

where AV T is the projected face area of the ship above waterline

CT is the total resistance coefficient and is calculated by the formula:

CT =RT

12ρSV2

(2.6)

CW is the wave resistance coefficient and is calculated by the formula:

10

CW =RW

12ρSV2

(2.7)

whereas in CFD the total drag is measured as a direct physical measurement of

resistance components and is given by equation:

CT = CV + CP (2.8)

Where CV is viscous resistance coefficient and CP is pressure resistance coeffi-

cient.

The total resistance coefficient can also be expressed as:

CT = (1 + k)CFITTC + CWexp (2.9)

where the wave resistance coefficient is obtained by experimental data. The

frictional resistance coefficient is calculated by using the form factor and ITTC-

57 correlation line.

2.4 STAR CCM +

STAR CCM+, a CFD tool a user friendly software when compared to other CFD

packages. It is a Multidisciplinary, timely and affordable simulation tool backed

by experts as mentioned in http://mdx.plm.automation.siemens.com/star-ccm-

plus. Estimating Hull Performance (EHP), an add-on of STAR CCM+ used

for these simulations, provides naval architects with a streamlines graphic user

interface driven process for estimating the hull performance in calm water.

“EHP has been tailored for analyses of unappended displacement hulls. With

11

its automatic set-up and intuitive, user-friendly GUI, EHP can be used by

all naval architects, including those with very little CAD or CFD experience.

EHP guides users from CAD import, through solution of single or multiple

speeds in a single session, to automatic PowerPoint generation with images

and reports of the results. You can even use your own company template.

After model setup, EHP gives optional direct access to the sim file, which

can easily be adapted to more complex geometries and/or specific conditions,

thereby allowing more experienced users to harness the full power of STAR-

CCM+ to deliver high-quality predictions for various scenarios”, as mentioned in

http://mdx2.plm.automation.siemens.com/brochure/estimating-hull-performance-

brochure-ehp.

One user from www.cfd-online.com mentions that, “There are benefits for both

ANSYS and Star-CCM+. Sophisticated geometry and meshing is not a problem

for either software package. One of the primary distinctions is the performance

and accuracy of the flow solver. At present, industry folks prefer the reliability

and robustness of the ANSYS fluid dynamics solvers over Star-CCM+.”

Another user from www.reddit.com quotes that, “I feel like Star-CCM+ is

slightly faster and converges a little better, mainly due to the higher qual-

ity prism + polyhedral elements mentioned elsewhere. It's not something I've

bothered to benchmark though.”

12

Chapter 3

AMECRC Series

Australian Maritime Engineering Co-operative Research Center (AMECRC) se-

ries is based on High speed displacement hull form (HSDHF) series. The HSDHF

series project was started in 1979 at the Marine Research Institute Netherlands

(MARIN) to improve the performance of high-speed displacement vessels, es-

pecially their seakeeping qualities. The 14 models depicted by the AMECRC

have been illustrated in the article by Sahoo and Doctors (1999).

These models were tested in the Ship Hydrodynamics Center at Australian Mar-

itime College. All the models were of length 1.6 m. The CB of 0.396 to 0.5,

L/B ratios of the models were in the range of 4.0 to 8.0 and B/T ratios were

between 2.5 to 4.0. Calm water tests were conducted at speeds in the range

of 0.4 to 4.0 m/s with respect to Froude numbers 0.1 to 1.0. The models were

free to sink and trim. Figure 3.1 shows the lines plan of the parent hull of the

AMECRC series. Figure 3.3 represents the change in Hull shape of AMECRC

series. Figure 3.4 represents the parameter space of the selected AMECRC se-

13

ries models.

Body plan

Profile

Half-breadth

Figure 3.1: Lines Plan of the Parent Hull of the AMECRC Series

AMECRC series has a total of 14 models and the parameter ranges of all the

14

models are mentioned in Table 3.1. For the purpose of this study, out of the 14

models of the AMECRC series five models were chosen and the parameters of

the five models are mentioned in Table 3.2. The body plans of the five models

are shown in Figure 3.2 (Sahoo and Doctors, 1999). The parameters of the

models which are kept constant are given in Table 3.3

Table 3.1: Parameter range of the models Sahoo and Doctors (1999)

Parent model AMECRC

L/B 8.0 4-8

B/T 4.0 2.5 - 4.0

CB 0.396 0.396-0.50

Table 3.2: Parameters of the five models used for this analysis, Sahoo andDoctors (1999)

Model L/B B/T CB Model Disp.(kg) L/∇ 13 WSA (m2)

3 8 2.5 0.447 11.454 7.098 0.3626

4 8 4 0.447 7.158 8.302 0.3064

8 4 2.5 0.5 51.197 4.308 0.7552

11 4 4 0.5 32.006 5.039 0.6318

13 6 3.25 0.45 15.784 6.379 0.4384

15

Table 3.3: Parameters which are constant for the models, Sahoo and Doctors(1999)

CP 0.626

CWP 0.796

AT/AX 0.296

BT/BX 0.964

CM CP × CB

LCB 44.6% LPP from transom

The models selected for the resistance characteristics study when fitted with

Hull Vane® are models #3, #4, #8, #11 and #13. These models were selected

as they represent the overall parameter space of the AMECRC series models.

Their body plans are given in figure 3.2

16

Model #3 Model #4

Model #8 Model #11

Model #13

Figure 3.2: Body Plan of five selected models of the AMECRC Series

17

Figure 3.3: Change in Hull Shape of AMECRC Series [Sahoo and Doctors(1999)]

18

Figure 3.4: AMECRC Systematic Series models #3, #4, #8, #11 and #13Parameter Space

19

Chapter 4

Hull Vane®

A Hull Vane® is a wing-shaped fixed-foil structure, horizontally placed below

the waterline near the stern of the vessel. When the stern wave flows over the

Hull Vane® , a hydrodynamic lift is created. The lift generated by the Hull

Vane® can be broken down into two forces, one in the x-direction and one in

the z-direction. Hull Vane® has four distinct effects on vessels namely, a thrust

force, a trim correction, the reduction of waves, and the reduction of motions in

waves (Uithof et al., 2014). The effect of a Hull Vane® on thrust force can be

explained by basic foil theory and Figure 4.1 shows the schematic representation

of the forces on the Hull Vane® .

20

Figure 4.1: Schematic representation of the forces on the Hull Vane® Uithof etal., (2014)

4.1 Thrust force

Figure 4.1 shows a schematic representation of the transom stern of a vessel at

zero trim fitted with a Hull Vane® (aft). In this Figure 4.1, represents the angle

between the inflow and the chord line of the Hull Vane® ; represents the angle

between the chord line and the body-fixed x-axis of the Hull Vane® . When the

stern flow meets the Hull Vane® , it creates two vectors, the lift force vector,

LHV and the drag force vector DHV . The sum of these vectors can be broken

down into an x-component and a z-component.

~LHV + ~DHV = ~FHV = ~Fx,HV + ~Fz,HV (4.1)

21

A thrust force will be generated if the x-component of the drag vector is smaller

than the x-component of the lift vector. The lift and drag forces are given by

the following equations:

LHV = CL ∗1

2ρV 2A (4.2)

DHV = CD ∗1

2ρV 2A (4.3)

The value of CL and CD depends on on factors like shape of the Hull Vane®

and the proximity of the free surface. If represents the trim angle, then the

thrust force generated in the x direction can be derived by the following equation

(Uithof et al., 2014):

Fx,HV = sin(α + β + θ) ∗ LHV − cos(α + β + θ) ∗DHV (4.4)

22

Figure 4.2: Pictorial representation of Hull Vane® (with permission from busi-ness presentation)

4.2 Trim correction

The resultant force in the z-direction affects the trim of the vessel at high

speeds which in turn affects the total resistance of the vessel. The force in the

z-direction can be derived by the following equation (Uithof et al., 2014):

Fz,HV = cos(α + β + θ) ∗ LHV + sin(α + β + θ) ∗DHV (4.5)

The influence of Hull Vane® on the running trim can be estimated by the

equation (Uithof et al., 2014):

δθ =trimmingmoment

rightingmomentperdegreeoftrim≈ FZ ∗ armGML ∗∆ ∗ g ∗ sin(1◦)

(4.6)

23

The trim affects the angle of attack of the flow on the Hull Vane® and is shown

to have an influence on the thrust force generated by the Hull Vane® .

Figure 4.3: Pictorial representation of trim correction at the Stern (with per-mission from business presentation)

4.3 Reduction of waves

The flow past the top surface of the Hull Vane® creates a low-pressure region

which interferes with the transom waves, resulting in a significantly lower wave

profile. Figure 4.4 shows the wave profile in a CFD simulation before and after

attaching a Hull Vane® . Figure 4.5 shows the wave profile during sea trial of

a supply vessel.

24

Figure 4.4: Wave pattern on a 55-metre supply vessel without Hull Vane®

(top) and with Hull Vane® (bottom) at 20 knots. From CFD computations(blue portrays a wave trough and red a wave crest) Uithof et al., (2014)

Figure 4.5: Comparison of the wave profile of the 55 metre supply vessel withoutHull Vane® (left) and with Hull Vane® (right) at 13 knots. As seen from theaft deck during sea trials Uithof et al., (2014)

25

4.4 Reduction of motion in waves

During bow-down pitching motions, the stern of the vessel is lifted but the ver-

tical lift on the Hull Vane® is reduced by the reduced angle of attack of the

flow thereby counteracting the pitching motion. Also, when the stern goes down

into water, the vertical lift is increased, which again counteracts the pitching

motion. The added resistance is reduced due to this and thus a Hull Vane® is

comparatively more effective in waves than in calm water.

Figure 4.6: Comparison of the motions of AMECRC series model #13 fittedwith and without Hull Vane®

26

4.5 Hull Vane® - Profile

The Hull Vane® profile selected for this research was similar to NACA 4412.

This was suggested by the Van Oossanen Naval Architects to be an efficient

foil for use as a Hull Vane at the aft of the transom stern below the waterline.

Particulars of Hull Vane® selected are:

• Profile NACA 4412

• Chord length of 1m

• Max. camber: 0.04 m (4% of 1m)

• Location of max camber: (40% of chord length from leading edge) i.e. 0.4

m aft of leading edge (0.4 x 1m)

• Max thickness: 0.12m (12% of 1m)

• Located at -1m from the stern in x-direction and -4.5m from the waterline

in z-direction

27

Chapter 5

Geometry

5.1 Geometry

Generating an extensive CFD solution is a must when the results are used to

interpret the actual solution for a problem. So, significant attention is required

in the setup process and the subsequent analysis. CFD analysis of any prob-

lem consists three main steps namely pre-processing, analysis of the problem

and post-processing (Mahmood, 2011). Pre-processing involves creating and

importing the model geometry, domain creation, precise model meshing and

setting up the required boundary conditions. The analysis was carried out by

the CFD program based on the inputs from the user. Post processing is the

visualization and analysis of the data produced.

The AMECRC models were initially created as NURBS curves using Maxsurf

modeler. Then the models have been converted into 3DM file format, to import

them into a 3D modeling software. Using Rhinoceros 3D modeler, surfaces have

28

been created and joined to create a closed poly surface, a representation of the

solid body.

This solid body model was imported to Star CCM+ in IGES format as a ge-

ometry and the domain is created. The domain is the boundary within which

the analysis would be carried out and also acts as a towing tank where the fluid

medium flows for an accurate representation of real world scenario. The domain

size is determined by the length of the model hull and is taken as one model

length forward and three model lengths aft of the model hull. The breadth of

the domain is of one model length on port side and one model length on the

starboard side of the hull form. The height of the domain is of one model length

and depth of the domain is of two model lengths.

Figure 5.1: Geometry of Model 11 with Hull Vane® in Star CCM+

CFD packages take long durations for a simulation to complete. So, one should

29

have an insight into the methods available for reduction of computational time.

Since the models are symmetric in nature, they could be modeled as a half-

domain along the central longitudinal axis to save the computational time.

The domain was divided into zones which were defined as inlet, outlet, symme-

try, top, bottom and side. Inlet was specified at the front side of the domain

where there is an inflow of the fluid and outlet was named at the rear of the

domain where there is an outflow.

5.2 Mesh Generation

After the domain is created, a Boolean operation was performed to subtract

the model from the domain which represents the whole domain as a single body

rather than two different parts. The next step was to generate a fine meshing

over the created half of the domain. For a detailed mesh, the trimmed cell

meshing method was used. It provides a greater mesh quality and delivers a

superior solution as suggested by STAR CCM+.

30

Figure 5.2: Volumetric mesh of Model 11 fitted with Hull Vane®

5.3 Boundary Condition and Solution Setup

In this research, the flow simulation of the model was conducted with the

commercial software STAR CCM+. The system was considered as a three-

dimensional implicit unsteady, incompressible, multi-phase, viscous and turbu-

lent flow. The fluid properties of water are given in Table 5.1.

Table 5.1: Fluid properties of fresh water

Kinematic Viscosity, υ 1.004 x 10−6m2/s

Dynamic Viscosity, µ 0.001 pa-s

Density, ρ 998.46 kg/m3

The motion of the free surface is driven by the gravitational force so the gravity

effects should be taken into consideration in the boundary conditions. VOF

31

formulation is applied in CFD to solve multiphase free surface flows, consider-

ing the volume of fluid (VOF) method suitable for modeling free surface flow

such as ship motion through the open water, filling the tank and sloshing (Jones

and Clarke, 2010). For the computation of turbulence flows, there are differ-

ent turbulence models by default in the CFD package such as Standard and

Realizable k- models. The turbulence model of realizable k- two-layer method

has been applied for computation since it is expected to provide superior per-

formance compared with the standard k- two-layer model for flows involving

the boundary layer and it accurately predicts the spreading rate of planar jet.

For a realistic scenario, multi-phases are chosen for the fluid condition, which

is defined as air and water.

The primary phase is set to water which has higher density, while the secondary

phase is the air which has the lowest density. The couplet of inlet and outlet

was set up for velocity inlet and pressure outlet to calculate the pressure and

viscous forces on the free surface flow of the ship. The boundary condition and

solution method used in this study are given in Table 5.2.

Table 5.2: Boundary condition and solution method

Inlet/Outlet Velocity Inlet/Pressure Outlet

Pressure Field Function

Velocity Field Function

Volume Fraction Composite

Turbulent Kinetic Energy Constant

32

Chapter 6

Validation of CFD

Power prediction of high speed displacement hull forms has always been a chal-

lenge due to lack of data since it involves varying hull form parameters. The

results from the CFD analysis should be validated against the experimental

data to determine if the model is an accurate representation of the actual ves-

sel. It has to also be validated to justify the comparison of the bare hull model

and Hull Vane® fitted model. 5 of the AMECRC series hull forms have been

selected and the CFD analysis was carried out for 3 different Froude numbers.

The validation was carried out by performing resistance analysis on the round

bilge displacement hull form models #3, #4, #8, #11 and #13 for the Froude

numbers 0.5, 0.6 and 0.7. The results were compared against the available ex-

perimental data of the AMECRC models. The total resistance compared from

CFD and experimental data for round bilge hull forms are given in Table 6.1,

6.2, 6.3, 6.4 and 6.5.

33

6.1 Statement of Uncertainty

The uncertainty sources for the experimental data were not available. It could

be speculated that the blockage effects for the towing tank experiment have

not been considered which means that the interaction of the waves generated

by the hull form with the walls of the towing tank could have accelerated the

flow around the model. This may give a partial explanation for the under pre-

diction of resistance from CFD analysis. The grid and the cell size may not

be fine enough for capturing all the flow scales around the hull form. There

could be an error in the determination of convergence criteria depending on the

averaged or final value of the total resistance that is considered. The waterline

of the hull form selected for the analysis could also have an error in the actual

measurement which affects the wetted surface area of the model hull. There

could also be an error in the boundary conditions of the domain such as wall

and symmetry, created for the CFD analysis. The turbulence model selected

may not be appropriate for the present analysis. These may be some of the

factors accounting to the error in validation results of STAR CCM+ against

experimental data.

34

Table 6.1: Resistance data Validation [Model 3]

Fn 103RT/∆(Experiment) 103RT/∆(CFD) Error%

0.5 58.0 51.7 11%

0.6 78.2 59.6 24%

0.7 94.7 80.3 15%

Figure 6.1: CFD and Experimental data for bare hull [Model 3]

35



0.5 58.1 43.9 24%

0.6 78.7 55.1 30%

0.7 99.3 82.5 17%


36



0.5 85.9 83.0 3%

0.6 95.4 107.6 -13%

0.7 104.6 116.5 -11%


37



0.5 92.1 79.3 14%

0.6 118.7 106.8 10%

0.7 130.2 115.1 11%


38



0.5 65.3 52.5 19%

0.6 87.9 76.8 12%

0.7 102.6 88.9 13%


39

Chapter 7

Results and Discussion

STAR CCM+ has been used to predict the resistance characteristics of hull

forms fitted with and without Hull Vane® for models #3, #4, #8, #11 and

#13. The simulations were carried out for speeds corresponding to Froude

numbers 0.5, 0.6 and 0.7 to predict the difference in resistance of the high-speed

displacement hull forms fitted with Hull Vane® . The computed resistance

characteristics for the five models of the AMECRC series with and without

Hull Vane® have been shown in the graphical representation in Figures 7.1 to

7.5 for the analyzed models. The results suggested that the analysis from STAR

CCM+ showed reduction in resistance for the models fitted with Hull Vane®

when compared to bare hull. Analysis conducted in chapter 6 clearly showed

that the CFD validation results does not hold good for all speeds. From the

results obtained through CFD analysis, it was obvious that there is a difference

in the total resistance, but in order to rely on these CFD results, STAR CCM+,

the CFD tool, has to be validated against experimental results. The percentage

difference in resistance for model #3 varied from -12% to 1% with an average

40

of 4% reduction in resistance. The percentage difference in resistance for model

#4 varied from -4% to 26% with an average of 10% increase in resistance which

was not desired. The percentage difference in resistance for model #8 varied

from -26% to -7% with an average of 18.3% reduction in resistance. The per-

centage difference in resistance for model #11 varied from -29% to -16% with

an average of 21.3% reduction in resistance when fitted with Hull Vane® . The

percentage difference in resistance for model #13 varied from -17% to -8% with

an average of 12.3% reduction in resistance.

41

Table 7.1: Resistance data of Model 3 with and without Hull Vane® using CFD

Fn 103RT/∆(withoutHullV ane®) 103RT/∆(withHullV ane®) % Reduction

0.5 51.7 51.1 -1%

0.6 59.6 60.3 1%

0.7 80.4 72.1 -12%

Figure 7.1: Resistance data for the Model 3 with and without Hull Vane® usingCFD

42



0.5 43.9 42.2 -4%

0.6 55.1 74.0 26%

0.7 82.5 89.4 8%


43



0.5 83.1 77.5 -7%

0.6 107.6 88.0 -22%

0.7 116.5 92.7 -26%


44

Table 7.4: Resistance data of Model 11 with and without Hull Vane® usingCFD


0.5 79.3 61.4 -29%

0.6 106.8 89.7 -19%

0.7 115.2 99.4 -16%

Figure 7.4: Resistance data for the Model 11 with and without Hull Vane®usingCFD

45

Table 7.5: Resistance data of Model 13 with and without Hull Vane® usingCFD


0.5 52.5 47.1 -12%

0.6 76.9 65.8 -17%

0.7 88.9 82.0 -8%

Figure 7.5: Resistance data for the Model 13 with and without Hull Vane®

using CFD

46

Chapter 8

Conclusion

The objective of this research is to predict any favorable reduction in the re-

sistance characteristics of high-speed displacement hull forms when fitted with

Hull Vane® . 5 models of the AMECRC systematic series hull-forms based on

the HSDHF series have been chosen for CFD simulations as a part of this study.

MAXSURF has been used to generate the required curved surfaces (NURBS) of

AMECRC hull forms and Rhinoceros 3D has been used to convert the required

curved surfaces (NURBS) into a solid body. Hull Vane® was generated using

Rhinoceros and then the geometry has been imported into STAR CCM+, a

CFD tool. The objective of this thesis could be fulfilled with the existing CFD

tool, but the results obtained cannot be relied upon. In order to have complete

confidence in the CFD results, it is necessary to validate the CFD tool. For this

purpose, the CFD tool was used for the resistance prediction of bare hull and

the results were compared against the experimental data that had already been

established for the respective models of the AMECRC series. STAR CCM+, a

CFD tool has been used for the analysis purpose. We can conclude from this

47

work that:

• CFD results obtained were not accurate when compared to the experimen-

tal results but the curves show a similar trend as the experimental data,

thus providing encouragement that CFD tool could be used for resistance

prediction. The validation of results for the models showed a similar curve

trend between the experimental results and the resistance predicted using

STAR CCM+ except for model #3 and #8.

• The results obtained for models #8, #11 and #13 showed a significant

reduction in resistance of the hull forms fitted with Hull Vane® . There

was no considerable reduction in resistance for model #3, and an increase

in resistance for model #4 was observed when fitted with Hull Vane® .

• This could be the result of poor Hull Vane® optimization.

• It can be concluded that the results obtained from STAR CCM+ needed

more validation.

• Sensitivity analysis of AMECRC model #13 (Table A.1) shows that chang-

ing of the Hull Vane® position in x-direction does not account to a con-

siderable resistance reduction.

• Optimization of the Hull Vane® for different models and Froude numbers

would improve the resistance reduction. This research is intended to serve

as a foundation for future studies on Hull Vane® .

48

8.1 Future Work

• The research work carried out as a part of this thesis is limited to the

investigation of only 5 models of the AMECRC series hull forms. The

investigation can further be expanded to all the models of the AMECRC

series.

• The analysis could also be carried out with other systematic series of high

speed hull forms such as NPL series, Series 64 etc.

• Different NACA profiles could be selected for the Hull Vane® and rigor-

ous optimization (Longitudinal and vertical position of the Hull Vane® ,

wingspan) could be carried out for better results.

• In this study, only the calm water resistance has been considered. The

investigation could also be extended to the resistance in waves.

• STAR CCM+ was used for the resistance prediction. These results could

also be validated by conducting towing tank experiments or using other

CFD tools.

• Furthermore, the present study investigated only three Froude numbers

i.e. 0.5, 0.6, and 0.7. The analysis could be carried out for a wider range

of Froude numbers.

49

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53

Appendix A

Sensitivity study

Table A.1: Sensitivity study of AMECRC model #13 fitted with Hull Vane®

for Fn 0.6

Fn 0.6 No Hull Vane® Hull Vane® at 0m

(x-axis)

Hull Vane® at -1m

(x-axis)

Hull Vane® at -2m

(x-axis)

103RT/∆ 76.9 66.1 65.8 64.7%

% Difference -16% -17% -19%

54

Figure A.1: Resistance data for model 13 at different Hull Vane® positions inx-axis

55

Documents

CFD Analysis of Resistance Characteristics of High-Speed