An estimation tool of long term benefits of auxiliary wind propulsion by means of a traction kite including the effect of route optimization

Date February 2009

Author Naaijen, Peter, Wel Shi and J-G. Kherian AddSS Deift University of Technology

Ship Hydromechanics Laboratory

Mekelweg 2, 2628 CD Deift

TU Deift

DeIft University of Technology

An estimation tool of long term benefits of auxiliary

wind propulsion by means of a traction kite including

the effect of route optimization

By

Peter Naaijen, Wel Shi and ean-Gregoire Kherian

Report No. 1650-P 2009

Proceedings of the i.e Workshop on "Development of Advanced Ship Support System using Information Technology" Tokyo University of Marine Science and

February 5, 2009

Etchujima Hall, Etchujirna Campus,

Tokyo University of Marine Science and Technology

Tokyo, Japan

Proceedings of The lS Workshop

on

"DEVELOPMENT OF ADVANCED SHIP

SUPPORT SYSTEM

Program

Opening 13:00-13:10

Sessioni: Maritime Broadband Communication System 13:10-14:10

> Development of Maritime Broadband Communication / Kohei Ohtsu and Run Shoji,

Tokyo University of.Marine Science and Technology

> An Estimation Tool of Long Term Benefits of Auxiliar Wind Propulsion by Means of a Traction Kite Including the Effect of Route Optimization / Peter Naaijen, Wei Shi, Deift University of Technology, and Jean-Gregoire Kherian, Gusto MSC

Session2: Electronic Navigation System 14:10-15:10

> Development of an e-Navigation Strategy in IMO and Study on Navigational Intention Exchange Support System / Yasuyuki Niwa, National Maritime Research

Institute

> A Scaled-down version of the Integrated Navigational Information Systemon Seascape Image for the training ship SIIIOJJEMARU / Takahiko Fujisaka, Tokyo University of Marine Science and Technology

Coffee Break 15:10-15:20

Session3: Advanced Operation Control System 15:20-16:20

> Practical Education for Marine Control Engineering Using an Actual Training Ship / Jun Kayano, Tadatsugi Okazaki, Hayato Kondo, Hitoi Tamaru and Kohei Ohtsu, Tokyo University of Marine Science and Technology

> On the Development of Decision-support and Guidance System for Ships Operating in Close Proximity / Egil Pedersen, Norwegian University of Science and Technology

Session4: Advanced Management System for Marine Engineer 16:20-17:20

> Knowledge Bank System for Marine Engineering Operation / Sachiyo Horiki and Masahiro Osakabe, Tokyo University of Marine Science and Technology

Recording System of Seamless Work-log With a Wearable device and its Application to an Education Support System / Katsunori Matsuoka, National Institute of

Advanced Industrial Science and Technology

TABLE OF CONTENTS

Foreword to the Textbook 3

Maritime Broadband Communication System 5

Development of Maritime Broadband Communication 7

An Estimation Tool of Long Term Benefits of Auxillar Wind Propulsion

by Means of a Traction Kite including the Effect of Route Optimization 21

Electronic Navigation System ₃₅

Development of an e-Navigation Strategy in IMO and Study on Navigational

Intention Exchange Support System 37

A Scaled-down version of the Integrated Navigational Information System

on Seascape Image for the traiiiing ship SBIOJIMARU 47

Advanced Operation Control System 57

Practical Education for Marine Control Engineering

Using an Actual Training Ship 59

On the Development of Decision-support and Guidance System

for Ships Operating in Close Proximity 69

Advanced Management System for Marine Engineer 75

Khowledge Bank System for Marine Engineering Operation 77

Recording System of Seamless Work-log With a Wearable device

Foreword to the Textbook

The Information Technology (IT) has found its way into shipping to achieve safe and efficient marine transportation as is exemplified by the IMO e-Navigation Strategy. In order to lead the way in this new field, the Tokyo University of Marine Science and Technology (TUMSAT) launched a new research and development project in 2008 on advanced IT-based ship operation technologies such as Maritime Broadband Communication System, Electronic Navigation System, Advanced Ship Operation and Control System and Advanced Management System for Marine Engineering. The TUMSAT also intends to integrate the outcome of this project into its

currinulum to provide young professionals with sufficient knowledge in advanced

marine-related IT technologies to the broad maritime community including the maritime industry, maritime education and training institutions and maritime authorities.

The project is run by the following 4 groups:

The Maritime Broadband Communication System Group attempts to develop a maritime broadband communication system, which enables ships at sea and land-based personnel to share

ship operation information.

The Electronic Navigation System Group aims at developing a navigation assistance system following the E-Navigation Strategy proposed by the IMO.

The Advanced Ship Operation and Control System Group focuses on ship control

technologies such as ship to ship operation, tracking control, and automatic berthing.

The Advanced Management System for Marine Engineering Group endeavors to develop a knowledge bank system for marine engineering operation.

We hope that this workshop will become a milestone in the development of advanced ship support systems for safe and efficient ship operation.

Hideo Yabuki Proj ect manager Professor

An Estimation Tool of Long Term Benefits ofAuxiliar Wind

Propulsion by Means of a Traction Kite Including the Effect of

Route Optimization

Peter Naaijen, Wei Shi, Deift University of Technology, theNetherlands Jean-Gregoire Kherian, GustoMSC, the Netherlands

SUMMARY

This paper describes an estimation tool to assess long-term benefits of auxiliary wind propulsion means of traction kites. Methods are described to estimate kite propulsion force, ship and resistance and propulsion performance without using any specific experimental data of the considered ship and kite system. A voyage optimization/simulation tool is presented that has been developed in order to assess the effect of route optimization. Results of the performance prediction for the 52560 tons displacement bulk carrier Jin Hui is presented.

INTRODUCTION

Although the recent drop in oil price

dramatically decreases the direct financial

benefit for ship owners of reducing fossil fuel consumption, there is still enough reason to search for sustainable alternatives if the long

term is considered: sooner or later, the oil price will increase again. Besides, there is an ongoing process to regulate emissions in the UN-based

International Maritime Organization (IMO).

which is based on Art. 2.2 of the Kyoto Protocol.

EU has stated that international shipping to the

EU region may be regulated by EU by linking, it

to EU ETS from 2012 unless aglobal regulatiàn

is established [1]. Either way, polluting will

have to !be paid for in the near future.

Shipping is the most energy-efficient mode of

transport which is probably why the sector has

got away with doing veiy little

to reduce

emissions until now. The fact that shipping

(responsible for transporting more than 90 % of

world trade) accounts for approx. 3-5 % of

global CO2 emissions is

more and more

considered to be a good reason to change this.

One way to achieve this is to reintroduce wind power. Having some advantages compared to

conventional sails, a traction kite propulsion system for commercial ships is an interesting concept which is being worked on by various

parties in industry

This paper describes an accurate method to assess the long term benefit of wind assisted

propulsion, applied on the specific concept of a high performance (high lift to drag ratio) kite for traction force generation.

Attached tc a single tow line via a steering

gondola, these kites can be actively controlled in

order to create high flying speeds resulting in

high traction force. Figure 1 depicts such a

-Figure 1, Ship with kite (courtesy: Skysails)

Compared to more conventional wind

propulsion by sails, there are some benefits

involved with applying kites:

a kite can be actively controlled in order

to create

its own flying speed thus

increasing its apparent wind speed and the traction force: more traction power

can be created with less 'sail' area this

way.

due to the fact that a kite can fly at

higher altitudes it is exposed to higher

wind speed

due to the low attachment point of the

tow line the roll heeling moment is

considerably smaller

there are no masts taking deck space

A logical

first step when quantifying the

benefits of such a system is to analyze its

perfonnance for a range of environmental

conditions. A detailed description of such an

analysis can be found in Naaijen et.al. [8].

When considering the area of operation of the

specific

ship of which the performance is

knQwn, average long-term wind and wave data

can be used to estimate the long term fuel

saving potential. This kind of analysis has been

presented by Jager [2].

However, since the environmental conditions

play such an important role in the case of wind

propulsion, it can be expected that the efficiency

increase that can be obtained by applying

weather routing is even more pronounced than is the case for conventional propulsed ships, and therefore should be taken into account to come

towards a fair and accurate estimate of

long-term fuel saving.

In the following, the estimation of the

performance of a kite equipped ship, based on

some general input parameters is briefly described. Results for case study are presented.

Next, the tool is

described that has been

developed to include the effect

of route

optimization of long-term fuel saving.

Performance analysis

introduction

This section describes how the performance of the ship - kite system is analyzed. First the kite traction force calculation is explained followed by a description of how kite, hull, propeller and

engine interact fmally resulting in fuel

consumption and forward speed that can be

obtained in prescribed wind conditions.

Kite traction

A kite can be considered as a wing surface

which enables the application

of existing

aerodynamic concepts: the resulting force acting

on a kite j5 determined by calculating lift and drag on a 3D wing surface being governed by relative wind speed and angle of attack. The

main assumption for the model is instantaneous

equilibrium between the direction of the tow

line and the direction

of

the resultant

aerodynamic force on the kite. For a kite, this

equilibrium is depending on its position in space

which will be described using the so-called

flight envelope (FE). The apparent wind speed, experienced by the kite is a combination of true

wind, ship speed and the kite's own flying

speed. Depending on the position, the kite will develop its flying speed in such a way that the resulting force is parallel to the tow line. It's the

calculation to determine this equilibrium speed

and the resulting towing force.

Flight Envelope

The set of possible positions in space of a kite, attached to a tow line with length r, is described

by a quarter sphere with radius r, which is called

the flight envelope (FE). See Figure 2 where the

direction of the true wind is indicated. True

wind speed is defined by W. Point F is the

attachment point of the tow line. The half circle LUR is called the edge of the FE. P is the centre

of the so-called power zone. When assuming

uniform inflow over the altitude in the FE, P is the point where the highest speed and traction of the kite are obtained. The boundary layer for the wind speed in which wind speed increases with

altitude will result in an maximum speed and

traction force occurring at a certain altitude

above the mentioned point P.

All half circles parallel to LUR are called

iso-power lines: kite speed and traction are constant on these lines. All circle segments from P to the

edge are iso-gradient lines: the gradient of speed

and power has a constant maximum value on

these lines.

The position of the kite within the FE, indicated

by K is described by two angles (See Figure 2):

- 9 is the inclination of the tow line FK with

respect to the line FP

- _{is the inclination of the plane FKP with}

respect to the horizontal plane

In order to describe the flying direction of the kite, a kite reference system XK, YK, ZK is defmed

having its origin at K. The XK axis is tangential to the iso-power line through K pointing from L

to R, while the y axis is tangential to the iso-gradient line through K pointing towards P. The

ZK axis is parallel to the tow line, pointing

outwards the FE.

v is the angIe between the flying direction of the

kite and the positive

XK axis. See Figure 3 showing a top view (looking in negative ZK

direction) on the kite.

Figure 2, Flight Envelope (FE)

YK

Figure 3, Kite in projected plane of FE

Having defmed how the kite's position and

flying direction are described, this defmition is

used now to formulate the apparent wind

experienced by the kite.

First, the apparent wind is split up into a part

tangential to the FE (Vt) which is a combination

of tangential velocities and v, in XK and y direction respectively, and a radial part parallel

The tangential velocity is caused by a

combination of true wind and kite speed. The part due to the kite speed can be split up into a

part tangential to the iso-power lines in the

direction of XK (v..k) and a part tangential to the iso-gradient lines in the direction of YK (vyk). Ifl YK direction, there is a contribution by the true

wind (v) as well. With the above mentioned definitions, the following formulae for these

velocities can be found:

Vt_y =-rO±Wsin(0)=vYk _'y-' (1) = -rsin(0). q3 = v, (2)

Combining these two contributions to the total tangential velocity yields:

(v-k

y=arctanl

t\Vx_k

(5)

The radial velocity is caused by true wind only:

Vr_z=WCOS(0) (6)

With the above defmed velocities, a formula for the total relative velocity Vrel and the angle of attack a experienced by the kite can be derived: (See Figure 4 which depicts a cross section of

the kite and the involved angle of attack.)

Perpendicularto towline

Chordline

\\

Relativew,ndN/\

Figure 4, Kite Angle of Attack

a = arctan _L (8)

I' v,

To fmd the effective angle of attack, ae, the angle at which the kite is attached to the tow

line, ak, has to be subtracted from a. (Figure 4)

ow line Vrz \ D

\"N

_N N N N N \ N

\

Lift and Drag

To determine the resulting force on the kite, first

lift and drag of the 2D airfoil are determined.

Corrections to this 2D lift and drag coefficients

are made in order to take into account 3D

induced drag and the curvature of the kite.

Furthermore some additional contributions to the drag are considered which take into account

line drag, inlet drag, and drag due to

irregularities and surface roughness.

2D lift and drag coefficients are calculated by

the free available panel method program XFOIL

by Drela & Youngren [3]. The inviscid flow calculated by the program is constructed by a

superposition of three potential flows being the free stream, a flow created by a vortex sheet on

the airfoil surface and a source sheet on the.

airfoil surface and wake. Vt =(v,_) +(v,_,)1 2 2

(3)

For the flying speed vk and direction y of the kite follows:

Vk=\fVy_k+Vx_k - .(4)

ae = a - ak (9)

The viscous part of the solution resulting in frictional resistance is described by boundary

layer shape parameter equations. For a detailed

description of XFOIL reference

is made to

Drela & Youngren [3] and Drela [4].

The obtained 2D lift and drag coefficients have

to be corrected in order to include 3D effects

This is done based on Prandtl's lifting line

theory assuming elliptical lift distribution over

the wing span.

The fact that a kite has a certain span wise

curvature will also effect the lift of the whole

kite. Resolving the lift force perpendicular to the

curved kite into the ZK direction results in the following fonnulation for the lift on the curved

kite according to Lingard [6]: (See Figure 5).

Lc=GLcos'(C) (10)

where:

CL = 3D Lift coefficient of straight wing CL, = 3D Lift coefficient of curved wing

= angle of curvature (See Figure 5.)

._- curved kite

i controlling gondola

Figure 5, lines between gondola and kite

The lines between steering gondola and kite,

where the speed is assumed to equal the speed

of the kite itself, appear to generate a

considerable amount of drag. The drag

coefficient of all these lines together can be determined using the formulation of Prakash

[7]:

C_0,i nR.dcos3(a,) (11)

where:

CD,! = drag

coefficients

of lines

between gondola and kite

n = number of lines

R= length of lines between gondola and kite

d = diameter of individual lines

= angle of attack between relative speed and

kite line S = kite area

According to Prakash [7], the number of lines

depends on the kite aspect ratio as follows

n=8+l6AR

(12)

The diameter of the individual lines between

gondola and kite is chosen such that their total cross sectional area equals that of the tow line

between gondola and ship.

For determining the line drag the part of the tow

line underneath the gondola and the

part

between gondola and

kite are considered

separately. For the lower part it appeared that

even when taking into account a line drag

coefficient of 3, the drag of the tow line did not exceed 1% of the total drag (partly because the

speed of the tow line itself is low). Therefore the

lower tow line drag is neglected. (It must be

noted however that an increase in line drag can

be expected due to vortex induced vibrations

which is not taken into account here.)

Other additional drag coefficients come from

the air

inlet, and surface irregularities and

surface roughness. The air inlet is an opening at

the nose of the kite enabling air flow into the

inflatable kite. Approximations for drag

coefficients of these components given by

Prakash [7] have been used.

As mentioned,

the key assumption of the

presented approach to calculate the kite traction

is the resultant force on the kite being parallel to

the tow line. When assuming that the Reynolds

number (based on which the 2D lift and drag

coefficients are calculated) is independent of the instantaneous relative kite velocity Vrej and as a

consequence independent of the position of the

kite in the FE, the Lift to Drag ratio (L/D) is

also independent of the kite position. This

means that the direction of the resultant kite

force depends on the angle of attack only. With

a known L/D, the required angle of attack for

tow line is easily determined and also

independent of the kite position. Equation (8) gives the relation between angle of attack and

radial and tangential relative velocity of the kite, The radial velocity v,-., is. a result of true wind only (equation (6)) and depends on the position of the kite on the FE. The tangential velocities and v however are strongly dependent of the kite's own speed in terms ofq3 and O. So for

a given flying direction y and a given position

on the FE (defmed by and 9), the required

angle of attack for which the resultant force on the kite is indeed parallel to the tow line can be

obtained by tuning the kite's own speed in terms

of qS and _:

By combining equations (1), (2) and (5) can be expressed as follows:

=sin(9).tan(y)

(13)

By substituting equation (13) and equations (1) and (2) in the expression for, the angle of attack

(8), a quadratic equation for can be obtained:

2 (r2 sin2 (9). (i+ _(r))) q(2rsin(8)tan(y)).Wsin(0)

=W2sin2(0),+10s(0)')

tan(a))

(14)

Having solved from equation (14), 9 follows

from equation (13).

Knowing the kite velocities the instantafleous

relative velocity Vrelof the kite is known which

enables the calculation of the resultant force on the kte from the lift and drag force

L=pv,,'S.Cj (15)

D=PVrI2SCD (16)

As mentioned calculation of lift and drag

coefficients is based on a constant Reynolds

number (independent of 'location in the FE and)

independent of the instantaneous relative

velocity of the kite. Therefore the lift to drag

ratio is also independent of the location on the FE and only depending on the angle of attack.

The angle ak between kite cord 'line and tow line

has been chosen such that the angle of attack for

which the resultant force is parallel to the tow

line is giving the maximum lift to drag ratio. For

the kite considered during the case study that

will be described in the 'last paragraph, this L to

D ratio amounts to 3.5.

As mentioned, one of the benefits of a kite is that its relative velocity can be increased by

actively maneuvering it on a desired track on the

FE.

-Such a track could be an orbit shaped as

depicted in Figure 6.

0

300 -200 -100 0 Figure 6, possible kite track on FE

100 200

When a certain track is prescribed, total relative kite velocity and traction force at a finite number of points on the track can be

determined. The average traction force and its direction can be calculated by a time integration over the chosen orbit. In the present study an orbital shape as depicted in Figure 6 is

considered. The mathematical expression of the selected type of orbit is presented in Wellicome

[911.

In case of a kite towing a ship, the wind that

enters the FE (being called 'true' wind until

now) is in fact a combination of true wind and

wind created by the

ship's own speed. In

general the direction of these two will not

coincide. The FE is positioned on the ship in

such a way that its edge is perpendicular to the direction of combined true wind and ship speed at the average flying altitude of the kite. As the kite's flying altitude is supposed to be within the

so-called surface layer of the atmosphere, where

the occurring wind is dominated by pressure

differences and no geotropic winds occur, the variation of wind speed with altitude can be

expressed by a logarithmic profile (Troen [5]):

W(z)=Ciog1n[_) (17)

where:

W(z) Wind speed at altitude z above sea surface

log

InifL

L

Uref known wind speed at reference level Zref reference level (10 m)

= surface roughness (depending on wave height)

Figure 7 depicts a top view on ship and FE for a

stem quartering wind condition. The hatched

area represents a likely area for positioning the

kite track.

App. wind direction at

r' s

Figure 7, FE on ship for bow quartering wind

For a given ship course and wind direction, a

range

of tracks

having similar horizontal

amplitude as shown in Figure 6 are tested. The

track generating the highest force in the ship

direction is selected. The horizontal and vertical

amplitudes of the kite track are kept constant

and were chosen so as to represent a realistic

kite flying behavior.

Concerning the vertical position of the kite

orbit, an optimum can be found resulting in the highest mean traction force in the ship's sailing

direction.

This optimum flying altitude is 'governed by:

the variation of traction force over the

FE

the

variation of wind velocity over

altitude

variation of 'horizontal traction force with inclination of tow line

To assess the effect of the flying altitude on the kite force in the direction of the forward speed Xkjte, and' to fmd the optimum' flying altitude in terms of maximum_Xjijte, simulations of the kite,

flying along an orbital track, have been made

for various flying altitudes during a case study.

(Details about this case study are presented later

on.) For three different towing line lengths, 150

m, 350 m and 550 m and three different wind

speeds, the traction force in the direction of the

forward ship speed (time-averaged over one

revolution on the orbit) has been calculated for

various flying altitudes.

It appears that the altitude at which maximum forward towing force occurs amounts to 27 to

33 % of the towing

line length, slightly

decreasing with increasing wind speed.

Above presented results are for a wind direction of 0 degrees off the stern. Similar calculations

have been made for different wind directions

resulting in optimum flying altitudes in the same range.

The properties of the kite that has been applied

for the current case study are as follows: Kite area:

Lift coefficient: Drag coefficient: LID ratio: Line length:

Average flying altitude:

S = 400 m2 CL=0.73 C=0.21 LID=3.5 r=300m 100 m

The lift and drag coefficients determined as

described above have been used. Wind tunnel measurements reported by Gernez [10] resulted

in lift and drag coefficients of 0.70 and 0.1,8

showing that the calculated values can be

considered to be realistic.

For a constant ship speed of 15 kn the resulting kite force in the direction of the forward speed

of the ship is presented in Figure 8

0 50 100 150

True wind direction [deg

Figure8, Kite force IkN] against true wind speed [knj and direction [deg] for'ship forward speed of 15.0 kn

An operational limit in terms of a maximum

wind speed at which the kite can be applied has

been assumed. Both apparent wind speed and true wind' speed are capped at 20 mIs for kite

application.

Wind drag

Apart from the wind driven force generated by the kite a second wind force has to be taken into account that results from the air flow around the

hull part above the water line and the

superstructure. To approximate this force the

method of Isherwood [11] is applied, which is

based on regression analysis of wind tunnel

measurements. This method provides drag

force coefficients in longitudinal and transverse

direction and a yaw moment coefficient that can

be obtained by substituting some main

characteristics concerning the ship's

superstructures. As will be explained in the next

paragraph, only the longitudinal drag is relevant

for the current study.

The input parameters that govern the drag force

coefficient C given by Isherwood for the

longitudinal force are given in Table 1.

Coefficient C and corresponding force

are related as follows:

c

F

-

_paiYr4

Where Vr indicates the

experienced by the ship. The

dependent of the

apparent relative to the ship.

(18)

apparent wind

coefficient Cx j5

wind direction

Table 1, parameters used for Bulk Caner to determine

C1 wind coefficient

Calculation of Fuel Consumption and

ship speed

In this section the method used to determine the

performance of the existing propulsion system.

As will be explained in the next section, the ship

operation scenario to be considered

is the

constant propeller revolutions scenario: given a

certain fixed propeller speed, ship speed and fuel costs engine are to be determined. Since

ships hull resistance, provided thrust by the

propeller and kite force are all depending on

LOA, Length o.a. [ml 189.99

B, Breadth [m 32.26

AT, Transverse projected wind

area [m2]

756 AL, Lateral projected wind area

[m2]

3570 S, Length of perimeter of lateral

projection [ml

(Excluding waterline and slender bodies)

300.00

C, Distance from bow to centroid of lateral projected area [ml

115.00

M, Number of distinct groups of

masts or king posts [-]

2 0 700 S 600 600 a 15 0) 400 C)) 300 25 0) 200 30, 100 35 0

forward speed, the determination of the forward

speed is an iterative process. Once the ship

speed has been solved, corresponding engine

power and fuel consumption can be determined.

A detailed

description

of the calculation

methods can also be found in Shi [12]

In this section the following nomenclature is

used:

D diameter of the propeller, m

J

advanced ratio

F,, engine brake power, kW

Fe effective towing power, kW F,,, thrust power, kW

Fir transmission power, kW

Qprop torque of propeller, Nm

RA model-ship correlation resistance, kN RAPP resistance of appendages, N

RB additional pressure resistance of bulbous

bow near the water surface, kN

RF frictiOnal resistance according to the ITFC-1957 friction fonnula, kN

R Iota! total ship resistance, kN

additional pressure resistance of immersed transom stem, kN

Rw wave-making and wavebreaking resistance,

kl'l

Tprop thrust of propeller, N

V3hIp ship speed, rn/s 0 relative quality

1 +/cj form factor describing the viscous resistance of the hull form in relation of R1

flprop propeller speed, rad/s

t thrust deduction factor

w wake factor

'Ia' hull efficiency

?lo open water efficiency 7r relative rotative efficiency

'hr transmission efficiency

p seawater density, kg/rn3

Power Transmission

From the propulsion system point of view, the main engine generates amount of power, known

as the engine brake power, transferred by the transmission system, (gearbox and' shaft, the

power propels the propeller, generating amount

of thrust to overcome the ship resistance. See

Figure 9 for the power transmission through the propulsion system and the consequent efficiencies

4-

4

I-

D

Figure 9, Propulsion chain

Ship Resistance

In general, the ship resistance 'is determined by the sailing speed, the shape of the hull and the wave conditions. In the ship design phase, there

are different kinds of methods to predict ship

resistance and other factors, such as the thrust deduction factor (t) and the wake factor (w), on the basis of ship dimensional parameters. The

Holtrop and Mennen method, presented

in

Holtrop [121 & [13], has been implemented to

calculate ship resistance.

According to the Holtrop and Mennen method, the total ship resistance is divided into six parts,

as shown in (20):

1?totai = (1 + k1 )RF + + R. + RB + Rfl, + R4 (20)

In Holtrop [12] & [13], a statistical method,

which resulted into a set of prediction formulas,

was presented for the determination of each

component of the resistance. This method was based on regression analysis of random model and full-scale test data. By running this part of

simulation program with the input of ship

design data and ship speed, an accurate value of ship resistance, as well as the thrust deduction

factor (t) and the wake factor (w), are generated.

Thus, the effective towing power and the hull

efficiency are calculated:

F - R10:,,V,1p (2)

1H

/(lw),

(3)

Hull Hydromechanics

As was concluded by Naaijen et. al. [8], the drift angle of the hull and required rudder angles resulting from the transverse force and yaw moment caused by applying a kite as auxiliary propulsion are very small. The effects on the

overall efficiency appeared to be negligible. For this reason, in the current study only the

longitudinal force balance is considered. No additional resistance components due to drift and rudder are taken into account.

Propeller

In order to balance the moving force acted on the ship body, an estimate of the performances

of the propeller is required. The Wageningen

B-Screw Series are used to predict the thrust, the delivered torque and the open water efficiency

of the propeller.

Concerning with the steady-state shipping

operation conditions, the ship speed remains constant, by means of the balance of the ship

resistance, the wind force and the propeller

thrust.

The thrust and torque performance of propeller

of the Wageningen B-Screw Series are

represented by the standard open water curves

using J, KT and KQ On the basis of experimental

data, refer to Kuiper , the Maritime Research

Institute Netherlands ''0

developed K,

KQ versus J diagram to describe open water diagram of propellers within Wageningen

B-Screw Series, see Eq. (21), (22) and (23) Also, fig. 2 illustrates the KT, KQ versus J diagram of

the reference bulk carrier.

(2pmp1)pmp)

T/

2D 4) K - / (pnpmp prop Qprop1/ 2D 5) KQ =

/

(pn

Since the open water diagram is based on the open water ,test, during which the flow in

front of the propeller is uniform, the open water propeller efficiency is introduced, as shown in

(24),

as well as the

versus J diagram

illustrated in Fig. 2:

b0

_KTJ/

/(2nKQ) (24)

Figure 10. open water propeller diagram of the

considered bulk carrier

When calculating

V4 from ship speed, the

effective wake factor (w) according to Holtrop [13] is used. The same source gives values for

the thrust dedUction factor (0 and relative

rotative efficiency (pr) are used to correct the open water thfltst Tprop

and torque

Afterward, the demanded power in propelling

the propeller is: Ir

/ølr7lo) (8)

Transmission system & Main Diesel Engine With the assumption of j = 0.97, the demanded

engine brake power at specific ship speed is achieved:

b (9)

Concerning with the fuel consumption, a

simpliifled calculation method, based on engine

brake power and engine rotation speed,

is

implemented. As a shown in Brussen [15], the

algorithm can be expressed as:

FC = (a + bF* + c(P )2)(d -i-

+ f(fl°

)2₎₍₂₅₎

According to Eq. (26), there are 6 parameters

which determine the trend of engine

fuel

consumption. By combining typical operation conditions, Table. 1 illustrate a f coefficients,

of the main diesel engine of the reference bulk

r

Table 2, typical engine operation point and coefficients

Table 3, main particulars, engine and propeller characteristics of considered bulk carrier

Overall propulsion performance Bulk

Carrier

The overall performance of the bulk carrier due to kite application and wind drag is presented here. For an appropriate range of wind

conditions the force balance of propeller thrust,

kite force and wind drag and hull resistance (all speed dependent) is solved iteratively. The resulting ship speed and fuel consumption are

stored in two dimensional lookup tables in order to avoid time consuming iterative calculations

during the route optimization / simulation

described in the next section. These iookup tables are visualized in Figure 11 and Figure 12.

In both figures the nominal operation

performance (without wind influence) is shown by the single contour line and indicated value of fuel consumption and forward speed.

10

500

Fuel consumption Iton/hr

Effect kite

Ship Speed Iknl

bs:

50

0 50 100 150

True wind direction Idegi

Figure 11, Fuel consumption for given true wind speed and direction

:

1.62 1.5 1.48 1.46 1.44 1.42 1.4 1.38 1.36 17.5 17 16.5 16 15.5 15 14.5 14 13.5 60 100 150

True wind direction (dog]

Figure 12, Ship speed at constant propeller rate for given true wind speed and direction

Route optimization

As mentioned, the added value of the developed

tool above existing estimation methods is to

include the effect of route optimization which

might be of significant impact in case the

performance strongly depends on environmental conditions.

Route optimization Algorithm

The method used for the actual route

optimization is the so-called modified isochrone

method that was developed at Delfi University

of Technology by Hagiwara [16].

Instead of a spatial grid, a time grid is applied in

this method. See Figure 13 from the starting

Sulzer 6RTA48TB Op.point 1 2 3 4 5 Pb (kW) 8203 0 0 6152 4102 n,,,5(rpm) 118 118 35 107 94 FC(gfs) 389.7 31.1 23.3 283.1 188.1 a 0.0908200 b 1.0532000 c -0.0045346 d 0.6783600 e -0.1477300

f

0.3463700 Bulk carrier General Name: Jiii Hui Classification: ABS Al DWT, ton: Displacement, m': 52559 Design speed, knot: 14.8 Principal dimensions Length o.a., m: 189.99 Length p.p., m: 182 Beam mid, m: 32.26 Draught, m: 10.75 Depth, m: 16.69 Cb: 0.802 cw: 0.84 Cp: 0.818 Engine Main engine: SUizer Type: 6RTA48TB No: Power, kW: 8203 Speed, rpm: 118 Fuel type: HFO Propeller No: 1 Diameter, m: 6.35 Type: fixed pitch PID: 0.59 AE/AO: 0.55 No. of blades: 4 Speed, rpm: 118

point the ship is navigated for a preset time

interval At with a certain heading.

ti

Departure point

Sub-sector angle

Ce

I

Great circles departing from X0

Sth-aector S, (k)

Great circle route free to

For several reasons, an interesting scenario for

kite application is that of constant speed with

varying thrust (and corresponding varying

propeller speed):

increasing the ship speed by auxiliary

kite propulsion will decrease the

operability and efficiency of the kite: a 'slow'

ship benefits more from kite

propulsion than a fast one due to the

more favourable apparent wind direction

for slower ships

varying speed may result

in earlier

arrival but since arrival time remains

uncertain due to uncertainty in predicted

wind conditions, the question is how

favourable this possible early arrival will

be

For these reasons, the constant speed scenario is an attractive one which unfortunately cannot be

dealt with by the

isochrone method: the

isochrones are known in advance for

this

problem and the resulting possible tracks will

diverge from the great circle track until the fmal isochrone and then converge to the destination.

The minimum time route is per definition the

shortest route between departure and destination location. The minimum fuel route however may

not be found this way.

However, the scenario of constant propeller

speed is likely to benefit significantly from kite

propulsion as well. Both ship speed and fuel consumption will be affected in a similar way

by kite application as was shown in the previous

section: the kite's driving force results in both increased speed and as a consequence earlier

arrival and less overall fuel consumption due to

less engine, operation hours. Besides, the fuel

consumption per hour decreases due to the kite

in this scenario as can 'be seen in Figure 11.

Environmental data

The environmental data to be used in

combination with the developed tOol is provided'

in so-called ww3-type grib files by the National

Oceanic' and Atmospheric Administration

(NOAA). These files contain so-called records

Figure 13, Construction of isochrones (Source:

Hagiwara 1161)

This is done for a range of n headings. Doing so,

a number of positions is obtained that can be reached by the ship at ti. From each of these reached positions, the procedure is repeated resulting in possible arrival points after 2At.

Form these n arrival points a selection is made

by choosing in every sub-sector (as depicted inFigure 13) that one having the largest great circle distance from the starting point. This

selection of points defrnes the so-called

isochrone at

t2. The points on the previous

isochrone from which the new found isochrone

points can be reached are memorised.

By repeating this procedure,

a number of

isochrones and the possible tracks between them

are constructed between starting point and fmal destination. As soon as the minimum distance

from the latest constructed isochrone is less than the expected distance that can be covered during

At hours, the ship is navigated from each of the points on the fipal isochrone to the destination along a rhumb line. This method is particularly

suitable for minimum passage time

optimizations

When it comes to minimum fuel optimization

there are some restrictions to the applied

of various environmental quantities such as

wind speed and wind direction, significant wave

height, period and direction. Records for 0 hours

forecast up to 180 hours forecast with 3 hours

intervals are provided in the grib files that are

updated with the latest forecasts every 6 hours.

Optimization vs. Simulation

The developed tool provides the possibility to

both optimize and simulate voyages

in a realistic way: when analyzing a certain voyage, the first step is to fmd the optimal route between departure location and destination. This is done as described above using only the latest grib file available at the entered departure date and time. Once the optimal route is found, Simulation of the journey for At hours (the time between the

isochrones) along the optimal course is carried out, using only the 0 hours forecast values of

several grib files. Considering the location

reached after At hours as a new departure point, the optimization pro ces is. repeated to find the updated optimal route from the reached location to the destination. .This process can be repeated until the destination is reached.

This way, the minimum At that can be applied

using the described grib.files, is 6 hours.

An example of the graphical output of the first

optimization step

for an east bound North

Atlantic crossing from New York to the English

Channel is shown. Isochrones and

interconnecting tracks are depicted in black. The

wind field shown by the blue arrows

corresponds with the forecast for the last part of

the

voyage. The minimum distance

route

deviates from the great circle since the great

circle crosses some pieces of land (Nova Scotia and New Foundland) in this example. As can be

seen the minimum fuel route hardly deviates

from the minimum distance route in this case.

However this will strongly depend on the

predicted wind conditions.

6 4 3

.'\\\ \'\\\\\\\\

-

'/J(\\\\\\\\ \\\\\\\\ Iii

.,\

\\\\

-"/_

Figure 14, example of optimlation of east bound North Atlantic crossing

Future work

Added resistance in waves has not been taken into account in any of the presented results. It

will

be implemented by means of using

quadratic RAO's for the added resistance in

waves resulting from calculations with existing

strip theory software.

Having developed the described tool, it will be

used to optimize and simulate a

sufficient

number of voyages for different ocean areas and seasons, with and without kite propulsion and

compare those to great circle (or shortest

distance) crossings in order to obtain statistics

on the long term benefits of applying kite

propulsion and the effect of route optimization

on it.

Acknowledgements

Ashish Tha and Anoop Mohan contributed to the development of the presented simulation tool for which they are gratefully acknowledged.

The authors thank Prof. Hideki Hagiwara for providing parts of the original code of the modified isochrone method.

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