Energy Saving Technology by Proper Remodeling of Hull

Jun MIYOSHI

Regional Training Workshop on Optimizing Energy and Safety at Sea for Small-Scale Fishing Vessels, SEAFDEC

Feb. 47, 2013, Bangkok

National Research Institute of Fisheries Engineering, FRA

PresenterPresentation NotesI am Jun Miyoshi from the National Research Institute of Fisheries Engineering, or FRA.I will be talking about Energy Saving Technology by Proper Remodeling of Hull.

Introduction

2

National Research Institute of Fisheries Engineering, FRA

Shipbuilding Company

Hokkaido Univ.

Fishing vessel performanceFleet planning for proper fishing management

Basic design, sea trials, etc.

Maneuvering performance and mathematical model construction of hydrodynamic forces acting on a ship hull

Born in 1972

PresenterPresentation NotesFirst, let me introduce myself.I was born in 1972; I graduated from Hokkaido University, where I studied the maneuvering performance of a ship and the construction of a mathematical model of hydrodynamic forces acting on a ship hull.I then worked at a shipbuilding company and was engaged in basic design and sea trials, especially those of commercial ships and battleships.Currently, I am studying and researching fishing vessel performance and fleet planning for proper fishing management by using the system engineering method.

Table of Contents

3

1. About Resistance

2. Proper Remodeling of a Hull

3. Summary

2.1 Installation of the bulbous bow2.2 Fins fitted forward of the propeller2.3 Shape refinement of the appendages of a hull

Types of resistance, Scale effect

4. Future topics

PresenterPresentation NotesHere is the table of contents for this presentation.First, I will talk about resistance by reviewing the types of resistance and scale effect which are important to think of technology for energy saving. I will then describe the proper remodeling of a ship hull. This topic mainly involves hardware improvements to a fishing vessel. I will focus on three topics in particular: installation of a bulbous bow, fins fitted forward of a propeller, and shape refinement of the appendages of a hull.I will then provide a summary of the presentation.Finally, I will talk about future topics.

1. About Resistance

4

Types of Resistance Acting on a Ship Hull

5

Two types of resistances act on a ship hull.

Pressure Resistance Viscous Pressure ResistanceWave-making Resistance

Frictional Resistance

Total ship resistance = Frictional Resistance + Viscous Pressure Resistance + Wave-making Resistance

PresenterPresentation NotesTwo types of resistances act on a ship hull: frictional resistance and pressure resistance. The pressure resistance can be divided into viscous pressure resistance and wave-making resistance. The total ship resistance consists of frictional resistance, viscous pressure resistance and wave-making resistance.

Relations of Forces

6

Direction of forces

Magnitude of forces

Pressure

Friction

Thrust Inertia force for ship motion

Frictional R. Pressure R.

PresenterPresentation NotesI now talk about the relations of forces, such as their direction and magnitude.When a ship is moving forward by the thrust force from a propeller, the tangential stress, or friction, and normal stress, or pressure, work on a ship hull.The friction and pressure generate frictional resistance and pressure resistance. The directions of these resistances are opposite to that of the thrust.The ship moves forward by the inertia force.The relations of the magnitude are shown here.The thrust minus the frictional resistance and pressure resistance is the inertia force.Thus, to save energy, we must reduce the frictional resistance and pressure resistance as much as possible.

Frictional Resistance

7

Boundary layer

Flow velocity Flow velocity

Rf

SmoothSurface of a ship hull

CoarseNo slip Rf

Gradient of velocity Viscous stressFrictional resistance

OutsideInviscid

Viscous

PresenterPresentation NotesI describe the frictional resistance here.The surface condition of a dirty ship hull is very coarse with no slip condition.When the flow is running at this velocity magnitude, the velocity is very low owing to friction near the surface. Gradually, the magnitude of the velocity becomes higher and finally becomes the same as that of the velocity in the far fluid area.The gradient of the velocity is the viscous stress and generates the frictional resistance.For a clean surface condition, as the surface is smooth, the velocity magnitude is larger than that of the coarse condition. Thus, the gradient of the velocity is lower, and the frictional resistance also becomes lower.The field with the gradient for the velocity is said to be the boundary layer.In the boundary layer, the fluid condition is viscous. Outside, the fluid condition is inviscid.

8In order to reduce the frictional resistance, the surface should be smooth.

Energy Saving through Frictional Resistance

From the hardware viewpoint, smooth paintingand a small surface area are required.

Viscous Pressure Resistance

9

Boundary layerVortex

The vortexes absorb large amounts of energy from a ship.A ship consumes large amounts of energy in order to generate vortexes.

The boundary layer is detached as the pressure becomes higher around the aft of a ship.

PresenterPresentation NotesI now talk about the viscous pressure resistance, which is one of the pressure resistances. When a ship is running, a boundary layer is formed on the surface. Around the aft of a ship hull, many vortexes are generated.Around the aft, the flow velocity changes suddenly, and the pressure distribution also changes. Thus, the boundary layer detaches, and vortexes are generated. The vortexes absorb large amounts of energy from the ship. Thus, the ship consumes large amounts of energy in order to generate vortexes.These actions become the viscous pressure resistance.

Energy Saving through Viscous Pressure Resistance

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Boundary layerVortex

The boundary layer does not detach as the pressure gradually changes around the aft of a ship.

PresenterPresentation NotesTo save energy with regard to the viscous pressure resistance, it is important to avoid the generation of vortexes. If an object like this is made or attached, the boundary layer does not detach, because the pressure changes gradually around the aft of a ship body.

Wave-making Resistance

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The waves absorb large amounts of energy from a ship.A ship consumes large amounts of energy in order to make waves.

PresenterPresentation NotesI now describe the wave-making resistance, which is one of the pressure resistances.When a ship is running, waves such as those shown in these pictures are formed.The waves absorb large amounts of energy from a ship.Thus, the ship consumes large amounts of energy in order to make waves. These actions become the wave-making resistance.

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Ship motion

Pressure

Pressure R.

A smaller entrance angle for the ship hull generates lower wave-making resistance; the total form is also important.

Entrance angle of a hull

Energy Saving through Wave-making Resistance

This pressure resistance and gravity are associated with the formation of waves.

PresenterPresentation NotesThis slide is on saving energy by reducing the wave-making resistance.When a ship is running, a pressure force acts on a ship hull in the normal direction.The pressure resistance is generated in the direction opposite to the ships motion.This pressure resistance and gravity are associated with the wave formation.As the waves are generated mainly at the bow of a ship, the entrance angle of the ship hull is a key factor to reducing the wave making. A smaller entrance angle of a ship hull generates lower wave-making resistance. The overall form of the ship hull is also important.

Summary of Kinds of Resistance and Improvements Possible

13

Pressure Resistance Viscous Pressure Resistance

Wave-making Resistance

Frictional ResistanceEnsure a smooth paint of the surface of a shipDesign a ship with a small surface area.

Design the curvature of the aft of a ship hull or object to be gradual so as to not detach the boundary layer and prevent the generation of vortexes.

Design the entrance angle of the bow of a ship hull to be small so as to not change the curvature dynamically.

Type of Force and Order of Magnitude

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Inertial

Viscous

Type of Force Order of Magnitude of Force

U 2 2

Gravitational g 3 U

[N]

[N]

[N]

When considering the fluid characteristics and resistance scaling, the force type and order of magnitude are important.

Where velocity = U (m/s), length = (m), density = (kg/m3), viscosity = (kg/(m s)), gravitational acceleration = g (m/s2)

PresenterPresentation NotesI now describe the types of force and orders of magnitude.There are three type of forces: inertial force, viscous force, and gravitational force.The order of each magnitude is as follows. The forces are expressed by using the density, ship velocity, ship length, viscosity of water, and gravity.The inertial force is associated with the ship mass and acceleration by a propeller.The viscous force is especially associated with the viscosity of water.The gravitational force is especially associated with gravitational acceleration.

Scale Effect of Viscous Resistance

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Inertial

Viscous

(Frictional resistance and viscous pressure resistance)

U 2 2

U

U

Re

Reynolds number

The characteristics of the boundary layer on the surface of an object are governed by viscosity.Scaling is associated with inertial and viscous forces.

The frictional resistance and viscous pressure resistance depend on the Reynolds number.

Scale Effect of Wave-making Resistance

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Inertial U 2 2 U2

g

The wave-making resistance depends on the Froude number.

Gravitational g 3

FnFroude number

Ug

The characteristics of the waves are governed by gravity.Scaling is associated with inertial and gravitational forces.

Summary of Principal Force and Scale Effect of Resistance

17

Pressure Resistance Viscous Pressure Resistance

Wave-making Resistance

Frictional ResistanceThe principal force is the viscous force.Scaling depends on the Reynolds number.

The principal force is the viscous force.Scaling depends on the Reynolds number.

The principal force is the gravitational force.Scaling depends on the Froude number.

2. Proper Remodeling of Hull

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2.1 Installation of Bulbous Bow

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Bulbous bow A bulb-type object attached to the fore part of a ship hull.

PurposeReduce wave-making resistance

Bulbous bow of Japanese fishing vessels that have lengths of less than 15 m

Role of Bulbous Bow

20

Attach a bulbous bow

Bulbous bow itself makes a wave

The purpose of a bulbous bow is to reduce wave-making resistance.

Wave becomes small from wave interference

Wave-making resistance is generated

PresenterPresentation NotesWhen a ship moves forward, a wave is made like this, and wave-making resistance is generated. This resistance is proportional to the square of the wave height.When a bulbous bow is attached, the bulbous bow itself makes a wave.Owing to wave interference, the wave around the ship hull becomes smaller.The purpose of a bulbous bow is to reduce wave-making resistance by inducing wave interference.

Improvement Method using a Ship Model

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Summary of the Installation of Bulbous Bow

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The wave-making resistance is reduced by wave interference.

The main resistance to be reduced by using a bulbous bow is wave-making resistance.

2.2 Fin-fitted Forward Propeller

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FinsPlates fitted on the aft of a ship hull. Many types of fins are produced by shipbuilding companies.

PurposeImprove the wake pattern (i.e., flow pattern past a hull) in order to achieve high propeller efficiency.

Role of Fins

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Rearrangement of the flow (wake) pattern

PresenterPresentation NotesThe flow pattern at the aft of a ship hull is like this. Because of the vortexes, the flow becomes turbulent.The purpose of the fins is to rearrange the flow pattern and achieve high propeller efficiency.

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Improvement around the Aft of a Hull

Smooth the shape of the aft of a hull in order to improve propeller efficiency

PresenterPresentation NotesThis is one improvement to the aft of a ship hull.This is a Thai fishing vessel.When a propeller is running, thrust force is produced.If the form becomes smooth or fins are attached, the propeller efficiency is improved, and a larger thrust force is produced.

Summary of Fin-fitted forward Propeller

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The fins rearrange the flow pattern and achieve high propeller efficiency.

The main resistance to be reduced by using fins is viscous pressure resistance.

2.3 Shape Refinement of Appendages of a Hull

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AppendageObject attached to a ship hull: 1) skeg, 2) bilge keel, 3) sonar cover, 4) structures around a rudder, and 5) anodes

PurposeReduce mainly viscous pressure resistance

Appendages of a Thai fishing vessel (SEAFDEC excursion 2010)

1) Skeg

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Flat plate of the aft of the keel plate

PresenterPresentation NotesI now talk about the skeg.

Role of Skeg

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Wind, WaveMaintain course

Same effect as feathers on an arrow

The skeg is used to maintain course.

Viscous pressure resistance

PresenterPresentation NotesThe skeg is used to maintain course.When wind or waves are hitting a ship in this direction, the course of the ship changes. When the course changes, viscous pressure resistance acts on the skeg, and the course is then maintained.This effect is the same as that of feathers on an arrow.

Skeg of a Thai Fishing Vessel

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Vortexes are generated by the skeg.The viscous pressure resistance is large.

Skeg of a Thai fishing vessel

PresenterPresentation NotesThis is the skeg of a Thai fishing vessel.Vortexes are generated by the skeg, and the viscous pressure resistance is large.

Improvement of the skeg

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Vortexes are generated.

Viscous pressure resistanceis reduced.

PresenterPresentation NotesThis is an improvement of the skeg in order to reduce the viscous pressure resistance.As the vortexes are generated from this part, small fins are attached here.This reduces the viscous pressure resistance.

2) Bilge Keel

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Plates attached to both sides of the bilge of a hull.

Bilge keel of a Thai fishing vessel

PresenterPresentation NotesI next discuss the bilge keel.

Role of the Bilge Keel

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Direction of viscous pressure resistance

The rolling of a ship is reduced by using the viscous pressure resistance.

Viscous pressure resistances work in the direction opposite to ship motion.

The bilge keel is used to reduce rolling.

PresenterPresentation NotesThe bilge keel is used to reduce the rolling of the hull.When a ship rolls, vortexes are generated around the bilge keel, and the viscous pressure resistance works in the direction opposite to the ship motion. The rolling of the ship is reduced by using the pressure resistance.

Improvement of the Bilge Keel

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Picture quoted by NRIFE, FRA

The flow pattern underwater is similar to the wave pattern on the surface

PresenterPresentation NotesThis is one improvement to the bilge keel.The flow pattern underwater is similar to the wave pattern on the surface.If possible, the bilge keel should be along the stream line.

Improvement of the Bilge Keel

35

Shave the corner smooth in order to reduce the viscous pressure resistance

Bilge keel of a Thai fishing vessel

PresenterPresentation NotesThis is another improvement to the bilge keel.An airfoil cap is attached to the tip of the bilge keel and smoothed by shaving of the corners of the wooden keel in order to reduce the viscous pressure resistance.

3) Sonar Cover

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The sonar cover or echo-sounder cover is used to protect against bubbles and obstacles.

Sonar cover of a Japanese fishing vessel (trawler)

PresenterPresentation NotesNext, I discuss the sonar cover.

Observation of Flow around a Sonar Cover

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Stream linesRe = 1.0 105

PresenterPresentation NotesThe stream lines past a sonar cover are very complex.As the vortexes are generated, the viscous pressure resistance becomes large.

Improvement of a Sonar Cover

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Photo by Kawashima

Observation of Flow around Different Types of Sonar Covers

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Original shape of cover

Improved shape of cover

Flow

Re = 1.0 105(sonar cover level)

Flow pattern of the bottom of a ship

PresenterPresentation NotesThis slide shows the observed flow around different types of sonar covers. This picture is the flow pattern of the bottom of a ship. The flow is running from left to right. This is the original shape of the cover. The other is the improved shape of the cover. The original sonar cover has a square shaped in the aft, while the improved sonar cover has a smooth shape. When the flow goes past the original sonar cover, the strings are swinging. In contrast, when the flow goes past the improved sonar cover, the stream line is smooth.The vortexes, or viscous pressure resistance, are the main reason for the resistance.This picture clearly indicates that the improved design can reduce resistance.

4) Structure around Rudder and an Improvement

40Airfoil cover

Rudder structure of a Thai fishing vessel

Shoe Piece and an Improvement

41

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5) Anode Protections

A steel ship has many anode protections on the hull, rudder, bilge keel, and sonar cover in order to avoid steel corrosion.

The resistance of each anode protection is small for a ship, but many anode protections cannot be ignored as resistance objects.

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Anode Protections on a Rudder

Anode protections on a rudder experience high-speed flow velocity from the propeller.

The resistance is proportional to the square of velocity; rudder anode protections, in particular, should not be ignored as resistance objects.

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Comparison of ResistancesR

esis

tanc

e

0.0

0.5

1.0

1.5

Results of Model Testing at FRA

Re = 1.5 105(aft propeller)

45

Improvement of Arrangement of Anodes on a Rudder

Improvement of Arrangement

46Improved arrangement

Original arrangement

Observation of flow pattern

PresenterPresentation NotesThis slide shows examples of rearranged anodes.The black objects are anodes. This is the stream line. In order to reduce the viscous pressure resistance, anodes are attached along the stream line.

47

Improvement of Anode Shape

Original

Improved

48

Rudder Shape

Airfoil type

Plate type

Plate type

PresenterPresentation NotesRefinement of the rudder shape is useful for energy saving.There are many types of rudder shapes.

Relations among Forces Acting on the Airfoil-type Rudder

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Flow

Flow

Drag

Lift

Propeller

ThrustResistance

Rudder

The airfoil of a rudder generates thrust force. The total resistance of a rudder is reduced by the thrust force.

PresenterPresentation NotesI now discuss the relations among forces acting on the airfoil-type rudder.When the propeller is running, the circulating flow acts in this direction on a rudder. The drag force and lift force are generated in these directions. Then, the resistance and thrust forces are produced in these directions. Finally, the total resistance works at this magnitude and in this direction.

Relations among Forces Acting on the Plate-type Rudder

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Flow

FlowDrag

Propeller

Resistance

Rudder

The plate-type rudder does not generate thrust force.The resistance of this rudder is larger than that of the airfoil-type rudder.

Improvement of Rudder Shape

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Attach an airfoil or round-shaped cover.

3. Summary

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53

Main Resistances

Bilge keelViscous pressure

resistance

Sonar coverViscous pressure

resistance

Anode protections Viscous pressure

resistance

Bulbous BowWave-making

resistance

Rudder structures Viscous pressure

resistance

SurfaceFrictional resistance

PresenterPresentation NotesThe main resistance to be reduced using the bulbous bow is the wave-making resistance. The main resistance to be reduced by the surface is the frictional resistance. Finally, the main resistance to be reduced using the bilge keel, sonar cover, anode protections, and rudder structures is the viscous pressure resistance.

54

Scaling

Bilge keelRe, Fn

Sonar coverRe

Anode protections Re

Bulbous BowFn

Rudder structures Re

SurfaceRe

55

Improvements

Bilge keelAlong stream line

Sonar coverAirfoil shape

Anode protections Airfoil shape,

Along steam line

Bulbous BowWave interference

Rudder structures Airfoil shape

SurfaceSmall area,

smooth painting

56

Estimation of Energy Saving

Bilge keel2%3%

Sonar cover2%3%

Anode protections 1%

Bulbous Bow2%5%

Rudder structures 1%

Totalabout 10%

Clean surface2%3%

PresenterPresentation NotesThis slide is on the estimated saved energy.The effect of each measure is small, but the total effect reduces fuel consumption by a useful amount.

4. Future Topics

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2. Modeling on computer

3. Calculate the resistance by the computational fluiddynamics (CFD) method

1. Capture the form of a fishing vessel

Analysis of fluid for Energy Saving

3D modeling tool, Rhinoceros

3D Camera of FRA

ANSYS FLUENT, OpenFOAM

We are considering fluid simulation of fishing vessels from member countries

4. Conduct experiments of the resistance by the model testing

FRA Basin

59

Optimization of form and size of an individual fishing vessel and the fleet

Optimize the ship form considering the result of the analysis and the operation of a fishing vessel.

Optimize the fleet size and total gross tons,considering the fish resources and economicmanagement.

Thank you for your attention

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Energy Saving Technology by Proper Remodeling of HullIntroductionTable of Contents1. About ResistanceTypes of Resistance Acting on a Ship HullRelations of ForcesFrictional ResistanceEnergy Saving through Frictional ResistanceViscous Pressure ResistanceEnergy Saving through Viscous Pressure ResistanceWave-making ResistanceSlide Number 12Summary of Kinds of Resistance and Improvements PossibleType of Force and Order of MagnitudeScale Effect of Viscous ResistanceScale Effect of Wave-making Resistance Summary of Principal Force and Scale Effect of Resistance2. Proper Remodeling of Hull2.1 Installation of Bulbous BowRole of Bulbous BowImprovement Method using a Ship ModelSummary of the Installation of Bulbous Bow2.2 Fin-fitted Forward PropellerRole of FinsImprovement around the Aft of a HullSummary of Fin-fitted forward Propeller2.3 Shape Refinement of Appendages of a Hull1) Skeg Role of SkegSkeg of a Thai Fishing VesselImprovement of the skeg2) Bilge KeelRole of the Bilge KeelImprovement of the Bilge KeelImprovement of the Bilge Keel3) Sonar CoverObservation of Flow around a Sonar CoverImprovement of a Sonar CoverObservation of Flow around Different Types of Sonar Covers4) Structure around Rudder and an ImprovementShoe Piece and an Improvement 5) Anode ProtectionsAnode Protections on a RudderComparison of ResistancesImprovement of Arrangement of Anodes on a RudderImprovement of ArrangementImprovement of Anode Shape Rudder ShapeRelations among Forces Acting on the Airfoil-type RudderRelations among Forces Acting on the Plate-type RudderImprovement of Rudder Shape3. SummaryMain ResistancesScalingImprovementsEstimation of Energy Saving4. Future TopicsAnalysis of fluid for Energy SavingOptimization of form and size of an individual fishing vessel and the fleetThank you for your attention