i

RESISTANCE REDUCTION THROUGH AIR LAYER FORMATION BENEATH

A VESSEL

FATIMAH AMIRAH BINTI JAAFAR

A thesis submitted in fulfilment of the

requirements of the award of the degree of

Master of Engineering (Marine Technology)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

JUNE 2015

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“For my beloved father and mother,

who all have given full support and love;

To my dedicated lecturer,

for the encouragement and guidance,

and for those who seeks for knowledge,

I dedicate this work with great respect and honour.”

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ACKNOWLEDGEMENT

First of all, I would like to praise for Allah. In this opportunity I would like to

express the finest gratitude for those who involved in the completion of this research

either directly or indirectly. The sincerest gratefulness to my scholarship, Majlis

Amanah Rakyat (MARA) for being my sponsor in my study.

I am also grateful to Marine Technology Centre staffs and technicians for

their continuous help and guidance in completing this project. Their kind guidance,

support, criticism and respect throughout the research until the very end. In addition,

special gratitude to Mr. Arif, a technician from Electrical Engineering Faculty (FKE)

for giving me the opportunity to use equipment from Electrical Laboratory.

A special appreciation and compliment also is dedicated to family, supervisor

and friends, who have granted the fullest support, love and patience from the

beginning. In addition, special gratitude to my respect lectures from Mechanical

Engineering Faculty (FKM), especially under Department of Marine Technology

who were directly or indirectly involved. My appreciation goes to other individuals

whose names are too many to mention who have contributed directly or indirectly in

the completion of this thesis. Thank you.

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ABSTRACT

Air bubble lubrication system is one of the techniques for ship energy saving

in lowering ship frictional resistance. Air lubrication technique can reduce the skin

friction using air layer or artificial air cavity generated beneath a vessel by air

injection. This research presents the study on resistance reduction on a displacement

hull model with microbubble generated beneath the vessel. Microbubble barriers

were made in order to trap the generated microbubble more effectively beneath the

vessel model. The subject of the study was a tanker model (MTL 036) with main

dimension: L = 2.956 m, B = 0.436 m and T = 0.174 m. Resistance test was carried

out at Marine Technology Centre, Universiti Teknologi Malaysia. The experiment

conducted in two different conditions: resistance test without microbubble and

resistance test with microbubble. The model was towed using the towing carriage

and the resistance force (x-axis) and side force (y-axis) were recorded from 0.704

m/s to 1.14 m/s (equivalent to 10 knots to 16 knots in full scale). The model test

results show that the total resistance with microbubble is lowered by 6 % to 13.9 %

at the speed of 0.704 m/s and 0.849 m/s. The rate of resistance reduction decreases

when the speed of the model increases. The highest resistance reduction was

obtained at the speed of 0.849 m/s where 13.9 % reduction in resistance is achieved.

The micro-bubble barriers are found to be able to effectively trapped the air beneath

the model and reduce the total resistance effectively

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ABSTRAK

Sistem pelinciran gelembung udara adalah salah satu teknik untuk penjimatan

tenaga kapal dalam mengurangkan rintangan geseran kapal. Teknik pelinciran udara

boleh mengurangkan geseran kulit menggunakan lapisan udara atau rongga udara

tiruan yang dihasilkan di bawah kapal melalui suntikan udara. Kajian ini adalah

untuk menkaji kesan gelembung udara yang dijana pada badan kapal model anjakan

dan keberkesanan halangan. Subjek kajian adalah model kapal tangki (MTL 036)

model dengan dimensi utama: L = 2,956 m, B = 0,436 m dan T = 0,174 m. Ujian

rintangan air telah dijalankan di Pusat Teknologi Marin, Universiti Teknologi

Malaysia. Eksperimen dijalankan dalam dua keadaan yang berbeza: ujian rintangan

tanpa microbubble dan rintangan ujian dengan microbubble. Model ini telah ditarik

menggunakan pengangkutan tunda dan daya ketahanan (x-paksi) dan daya sisi (y-

axis) diukur pada kelajuan penundaan 0.704 m/s hingga 1.14m/s(bersamaan dengan

10 knot hingga 16 knot pada skala sebenar). Dari kajian, ia menunjukkan bahawa

rintangan dengan gelembung udara adalah lebih rendah berbanding dengan rintangan

tanpa gelembung udara 6% hingga 13.9%. Berdasarkan keputusan itu juga

menunjukkan bahawa pengurangan rintangan adalah berkesan . Penghadang

gelembung udara adalah berkesan untuk mengurangkan geseran kapal.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

TABLE OF CONTENTS vii

LIST OF FIGURES x

LIST OF TABLES xii

LIST OF APPENDICES xiii

CHAPTER 1 INTRODUCTION 1

1.1 Background 1

1.2 Problem statements 3

1.3 Objectives of study 4

1.4 Scope of Study 4

1.5 Research Planning 5

CHAPTER 2 LITERATURE REVIEW 7

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2.1 Introduction 7

2.2 Skin Friction Resistance 7

2.3 Air Lubrication Method 9

2.4 Microbubbles Properties 9

2.5 Microbubbles Parameter 10

2.5.1 Microbubble size 10

2.5.2 Location of microbubbles injection 12

2.6 Microbubbles generation methods. 14

2.6.1 Porous 14

2.6.2 Venturi Tube Type Bubble Generator 15

2.6.3 Electrolysis 16

2.7 Summary 20

CHAPTER 3 METHODOLOGY 21

3.1 Introduction 21

3.2 Research Flow Chart 22

3.3 Experimental Variables 23

3. 4 Experimental Design (Model Testing) 24

3.4.1 Model prepraration 24

3.5 Microbubbles Generation Mechanism 25

3.5.1 Installation of Microbubbles Generator 26

3.5.2 Simple Test of Electrolysis Method : 27

3.6 Test Protocol 28

3.6 Summary 29

CHAPTER 4 RESISTANCE TEST 30

4.1 Introduction 30

4.2 Experiment Facilities and Equipment 30

4.2.1 Towing Tank 31

4.2.2 DAAS Software (Data Acquisition System) 32

4.2.3 Towing Carriage 32

4.2.4 Air Struct 32

4.2.5 DC Power Supply 32

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4.3 Experimental Procedure 33

4.4 Water Leakage Inspection 34

4.5 Model Test Equipment Calibration 34

4.6 Experimental Result 35

CHAPTER 5 DATA ANALYSIS AND DISCUSSION 36

5.1 Introduction 36

5.2 Data Analysis 36

5.3 Discussion 38

CHAPTER 6 CONCLUSION AND

RECCOMENDATIONS 41

6.1 Conclusion 41

6.2 Recommendations For Future Study 42

REFERENCES 44

APPENDIX A 46

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Mitsutbishi Air Lubrication System (MALS) Pump

Air Bubble 2

2.1 Drag reduction ratios with different porous plates

(Tsai and Chen, 2011) 11

2.2 Drag reduction and Froude number at different

bubble injection locations 12

2.3 Air Outlet Location Viewed From The Bottom

(Mitsubishi Heavy Industries, 2010) 13

2.4 Schematic drawing of the microbubbles generation

through porous medium 15

2.5 Schematic sketch of the venturi tube type bubble

generator 15

2.6 Schematic diagram of hydrogen microbubbles

experiment 17

2.7 Produced hydrogen flow according to time and

electrodes materials. 18

2.8 The effect of voltage to the rate of hydrogen produce 19

3.1 Research flow 22

3.2 Barrier design beneath the vessel 25

3.3 The Installation of Microbubbles Mechanism and

Barrier 27

3.3 The Simple Electrolysis Test 28

4.1 Side view of towing tank 32

4.2 Plan view of towing tank 32

4.3 The model test without microbubles running at speed

0.849 m/s 37

5.1 Model Test Result With and Without Microbubble 38

5.2 Model Test Drag Reduction 39

5.3 Raw Data Recorded Resistance and Time During

Model Speed 1.068 m/s 39

5.4 Raw Data Recorded During Model Speed 1.068 m/s 40

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LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 Gantt chart for Project 1 and 2 5

3.1 Ship and Model Particular 24

3.2 Test protocol for condition 1 (without

microbubble). 29

3.3 The test protocol for second condition 2

(microbubbles generated with barrier) 30

4.1 Data recorded for calibration test 36

4.2 Resistance test without microbubbles beneath the

vessel 37

4.3 Resistance test with microbubbles beneath the

vessel 37

5.1 Drag reduction of the air layer formation 38

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LIST OF APPENDIX

APPENDIX NO. TITLE PAGE

A

Raw Data of Calm Water Resistance Test

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1

CHAPTER 1

INTRODUCTION

1.1Background of Research

Throughout history the oceans have been important to people around the world

as a means of transportation. Twenty-four hours a day and all year round, ships carry

cargoes to all corners of the globe. That’s make maritime transport like a backbone of

world trade and globalization. In order to continue as one of the most effective ways in

carrying goods around the world, there will be improvement in the vessel efficiency

performance.

Ship efficiency is related to low fuel consumption. Ship resistance is the most important

factor in fuel consumption and the major factor in ship resistance is skin friction resistance.

Frictional resistance is a major resistance component of the ship resistance which is

approximately 60% to 70% of the total resistance. By reducing the frictional resistance will

affect to the total resistance, consequently the fuel consumption will decrease.

Previously, a few methods of drag reduction had been introduced to reduce vessel skin

friction resistance. The air lubrication system is one of the techniques for ship energy saving by

reducing the skin friction. The air lubrication technique can reduce the skin friction using air

layer or artificial air cavity generated beneath the vessel by air injection [Buhnell and Hefner,

1990].

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Thus the vessel is floating on a thin layer of air bubbles generated beneath of the vessel,

which help to reduce resistance between the hull and water. Recently, Mitsubishi Heavy

Industries developed MALS (Mitsubishi Air Lubrication System), which has been applied to two

module carriers of NYK-Hinode Line, a coal carrier built by Oshima Shipbuilding, a ferry of

Japan's A-Line Ferry. It was announced that net power savings up to about 13% were obtained

from the sea trials of the module carriers (Mizokami et al.,2010; Mizokami et al., 2011; Tanaka,

2011).

Figure 1.1: Mitsutbishi Air Lubrication System (MALS) Pump Air Bubble onto The Bottom of

a Ship’sHull to Reduce Frition (Mitsubishi Air Lubrication System)

Air layering is formed when air is injected into the boundary layer of the wetted surface.

Then an air-water mixture flow containing both air bubbles and water is formed. If the amount

of the air injected increase, an air bubble will combine and form a layer that covers the surface.

The frictional drag on the surface covered with a continuous air layer can be reduced effectively

as if the wetted surface area was reduced because the friction with water may change into that

with air (Bushnell and Hefner, 1990).

Therefore, on the surface covered with a transitional air layer, it is expected that both air

bubbles and patches of continuous air contribute to the frictional drag reduction (Elbing et al.

2008) described that a reduction in the local frictional drag can be achieved from about 20% to

80% on the surface covered with a transitional air layer.

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1.2 Problem Statement

Economy is one of the factors need to be considered in ship design. In terms of economy

the vessel needs to improve their efficiency. Ship efficiency is related to low fuel consumption.

Ship resistance is the most important factor in fuel consumption and the major factor in ship

resistance is skin friction resistance. There are a few methods of drag reduction had been

determined to reduce the skin friction resistance of the vessel.

In order to reduce the friction without changing the existing hull of the vessel is by

introducing an air layer method on the vessel hull. This method is suitable for the practical user

for a vessel as the reduced rate can reach as high as 80% (Madavan et al. 1983). It's had proved

by a previous study by Mc Cormick and Bhattacharyya in 1973.So by designing or introducing

the air layer that can generate beneath of the vessel has a great potential for power saving as the

resistance also will reduce.

However, it is difficult to trap the air layer beneath the ship's hull. Based on a previous

study, the air layer generated is more effective located after the mid-ship. So, it had been

assumed that the generated air layer might be dispersed with the wave making by the vessel. In

order to avoid the air layer from disperse is by adding barrier. Previously, set up consisting of

two counter-rotating cylinders were used to remain trapped the air layer (Van Gils et al. 2011).

Thus, this project is conducted to determine how the air layer with barrier can be design beneath

the vessel and to identify the amount of resistance reduction with the generated air layer.

1.3 Research Objective:

1) To design barrier that can trap air layer beneath the vessel.

2)To determine the amount of resistance reduction of a tanker model with the trapped air layer

beneath a vessel.

4

1.4 Scope of Research

1) Study and propose various methods of air generation.

2) A displacement hull to be used as the subject of the study.

3) Propose and modify existing hull design to maximize air layer beneath a vessel.

4) Model resistance test to be conducted at Marine Technology Centre.

5) Compare model test results before and after air layer formation.

5

1.5 Project planning

Master project 1

No Task Week

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 Background of study

2 Problem identification

3 Identification of objective and scope of study

4 Literature review

i) Ship Resistance Component

ii) Drag Reduction

iii)Method to reduce drag reduction

iv) Method to generate air bubble for air layer

v) Characteristic of microbubbles for air layer

5 Finalizing Research Methodology

6 Experimental design

M1

7 Experimental equipment preparation

8 Research proposal write-up and presentation

M2

M1 : Completing Experimental Design

M2: Submittion of research proposal

6

Master project 2:

No Task Week

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 Model Testing Preparation

2 Resistance Test

M3

3 Data processing and analyzation

M4

4 Recommendation and Conclusion

5 Result : Report Writing

6 Final Presentation and Thesis preparation

7 Thesis submission

M5

M3: Completing the resistance test M4: Complete data Processing and analyzation

M5: Submit Complete thesis

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