Proceedings of the Symposium Aspects of Navigability of Constraint Waterways, Including Harbour Entrances, Volume 2, Delft, The Netherlands

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lume

SYMPOSIUM

TECHNISCHE UNIVERSITEIT Laboratorium voor Scheepshydromechanica Archief Mekelweg 2, 2628 CD Delft Tel.: 015- 786873 - Fax: 015- 781838

delft 1978

P1978-5

aspects of "12

navigability of

constraint waterways,

including

harbour entrances

delft ,the netherlands,april 24-27,1978

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SYMPOSIUM

aspects of

navigability of

constraint waterways,

including

harbour entrances

(3)

olume

coed

o

...

nas

delft 1978

aspects of

navigability of

constraint waterways,

including

harbour entrances

delft ,the netherlands,april 24-27,1978

volume 2

papers 1-15

(4)

aspects of

navigability of

constraint waterways,

including

harbour entrances

of

the mathematical model.

But the main limitations of the model arise from

- the determinative _{representation of environmental factors} : although

the influence of human factor can be assessed by repeated _runs

perfor-med with different pilots, the mathematical model does _{not reproduce}

presently the natural fluctuating character of environmental _factors

like current or wind. The fact that the _{same orders induce the same}

trajectory can always lead to satisfactory results during _entrance

manoeuvres ; this disadvantage can be reduced by changing the

hydro-dynamic _{conditions between two following tests (entrance with} diffe-rent curdiffe-rent pattern) or adding random fluctuations.

- the time step for entering the pilot's orders : it is desirable to

shorten this step but the cost of the manoeuvre would rise and the

number of possible tests would decrease ; an another disadvantage

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-5-1

arises from the fact that the pilot has presently unlimited time to formulate his next orders but this disadvantage can be easily

correc-ted by fixing a determined time scale which can be unity.

But the mathematical model has the advantage of not introducing scale effect (but the pilots don't realize the scale effects of the physical model) and in spite of the limitations described above test results

show the capabilities of the mathematical model and probably the greatest benefit resulting from the use of this model is that a large number of

alternate harbour designs can be processed in a short time and at a

rela-tively low cost.

III - MATHEMATICAL MODELS OF THE SHIP'S VERTICAL MOTIONS 111.1 -Brief description

The three-degree and six-degree-of-freedom models determine the ship

movements under waves by solving at each time step the equations of the

mechanical system constituted by the ship, the closed conduit fluid under the hull and the open channel fluid around.

So the important effect of shallow water is taken into account but the

ship hull is schematized by a parallelepiped. A detailed description of

these models can be found in (6). 111.2 -Main results

The results show that under regular waves the ship has oscillatory

move-ments round a position slightly different from the position in still

water. The difference on the average is proportional to the square of

wave height but remains small for wave heights less than about 4 m. The

amplitude of movements is proportional to the wave amplitude for small

movements but in case of heavy waves, the movements increase less than the wave amplitude.

Roll, heave and pitch amplitudes depend on

the ratio of the apparent wave period depending on the ship speed and

the natural periods of the ship movements

the ratio of the wave length and a characteristic dimension of the ship (length for pitch and heave).

The natural periods and damping of the ship movements are appreciably

increased by the confined fluid effect under the hull with respect to

their values in deep water.

Figure 8 shows an example of computed heave, roll and pitch amplitudes

as a function of wave period for a loaded ship. The draught is 20 m, the waves come from astern (450) and the wave height is 2 m. The calculations are made for two different underkeel clearances. The maximum sinkage of

(6) XVIe I.A.H.R. CONGRESS proceedings volume 1 p. 43-50

"Approche des grands navires dans les chenaux d'acces au port"

par M. DAVESNE et A. WARLUZEL, Laboratoire National d'Hydraulique,E.D.F.

FRANCE.

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-6-water.

A very simplified model for computing the vertical movements of the ship has been developed. This model allows explanation of the results in terms of transfert functions. These functions can be considered as the

product of two functions : the first represents the relation between

the exciting forces and the ship movements and depends mostly on the ratio of the force period and the natural periods of the ship movements and on the ship movements damping. The second represents the relation between waves and exciting forces. This latter relation mostly depends on the ratio of the wavelength and ship dimensions. It has zeros for

precise values of this ratio. 111.3 -Calibration of the models

There are practically no measurements in situ concerning vertical ship movements with a small underkeel clearance and few experimental studies

have been carried out. Sogreah in FRANCE studied these movements with a

radioguided ship model in the cases of the harbour of LE HAVRE-ANTIFER and LE VERDON. These studies have been used to compare the mathematical

model and the physical model results.

Such a comparison remains difficult due to the fact that it is not easy

to reproduce well defined test conditions with the physical model mostly

regarding reproduction of perfectly regular waves.

Nevertheless the comparison shows a good agreement between measured and computed results in the case of a 215 000 t ship subjected to astern

waves (15°) with regard to the very damped movements (heave and pitch).

On the contrary, the computed roll amplitude seems to be less important

than the observed one.

Roll is characterized by a small damping even in shallow _{water, which}

induces particular movements under random waves : the records of tests

show a mixing of various oscillatory periods and particularly _strong

movements at the natural period of roll.

Such movements under random waves were reproduced by the

three-degree-of-freedom model for the case of beam waves but could _{not be studied by}

the six-degree-of-freedom model owing to its complexity and cost.

In Sogreah physical model, waves were not perfectly regular _{and induced}

this characteristic behavior of roll. For the _{two methods the lack of}

data about the roll damping makes the extrapolation of _{model results to}

nature uncertain.

It is very desirable to undertake measurements in situ in _{order to check}

physical and mathematical models.

111.4-Application of the model

It is unsatisfactory to fix the underkeel _{clearance in still water to}

an empirical value often given as a percent of the ship draught. _The

choice of the channel dredging depth must take into account the local

wave conditions and the maximum ship sinkage predicted in _{the limiting}

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-7-1

wave conditions. The models developed by the L.N.H. allow prediction

of the ship sinkage under waves (the squat due to the ship speed which is determined by empirical laws or experimental tests must be

added to the vertical movements of the hull). But the results must be compared to in situ tests and the use of the complex model requires a

long computational time.

In order to have a tool usable in situ to forecast the ship movements under given waves action, Bureau Veritas is developing for the Port Autonome de Bordeaux a linear simplified model using partly the L.N.H.

results. This model should allow giving the pilot of a given ship (characterised by a small number of parameters) information concerning risks of bumping under the waves conditions measured in situ just before

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Drag force = F. = k2EFixi 1

F.

= pSC (V.cos

a)

1 2 x 1 Rudder forces

Force opposite to ship's forward motion

1 R = pV2 L (h + 2) (k1 Cf + Acf + Cs) Propeller thrust T = pn2 D4 CT T = pD2 (1 LO)2 V2 KT

if

n little

Propulsion machinery forward

Gx = T(1 cos ((S (S0) ) 2

G = T sin (8

(50)

k V sin 8

Propulsion machinery backward

Gx = 0

G

= -

kV2 sin - k T

Values of coefficients fixed after calibration (case of a 213 000t tanker)

k = 105 = 1.1 k, = 0.52 80 = 0

Cx = 1.5

k' = 0.7 }(o = to,, ky = 1) _{kp = 0.3}

Fig.1 FORMULATION OF DIFFERENT FORCES

APPLIED TO THE SHIP

--Y- = + F M -=',,

''

' = = TRGx+0.25T/1.25

if T C

= T/1.25 R Gx if T > = G + FT

y

G X + MT v G 0 0 (1 + k+o)m M (1 + k' )

I

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1 6 5 4 3 2 1 2000 1000 0 Stopping distance (km) 0

2 4 6 8 10 12 Initial speed (knots)

Fig.2(a) STOPPING DISTANCE VERSUS SHIP SPEED

Stopping time (s)

2 4 6 8 10 12 Initial speed knots

Fig.2 (b) STOPPING TIME VERSUS SHIP

SPEED

A

Mathematical I

model curve

/

A0n(d,v) in situ test points

/

d =depth (meter)

/

v =wind velocity (knots)

/

7 /

/

A08 (25m x , 30nd)

/

xA06(33m, 15nd)

/

_{004(40m , 18nd)}

/

x A02 (deep water,8nd)

/

x A03(deep water ,4 nd)

z

)005 (42m, Und)

x7

A04 (27m, 30nd) ---- . A07 (36m,17nd)1

V

..."'

.,"

.---

...- ..----xA04(40m,18nd )

/

ir xA02 (deep water 8 nd )

x x I A06( 33m,15nd)

/

A08(25m 30nd)

/

x A03 (deep water 4nd)

/

xA09 (27m, 30 d)

xA07 (3 m, 17nd) 1

/

xA05 42m ,14n

/

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20

15

10

5

Fig.3 ENTRANCE INTO GIRATION WITH A 15 KNOTS

SPEED

(CASE OF A 213 000t SHIP)

i

/

/helm

20°

i

/

A

/

_/helm

100 /

/

I

_//

/

_/

/

I

/

_/

I

_//

I

/

_//

/

_/

/

helm

_5°

/

_/

//

/

_/

/

_/

/

in situ test

--

mathematical model

/

1 /

_=1.105

/

'.

0.7

/

---

../

0 30 60 90 120 150

_{time (s)}

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1

Current direction

Current velocity 3 knots

ship's speed,'

= 6 Knots,a *45°

/water

no current

number of propeller turns and

rudder angle

Scale: 1/20000

Fig.4 : SHIP COMING INTO A CROSS CURRENT

1

Path of the shin meas;:ad

on the nhysical scale model

(2 tests)

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. turning and

.stopping area

-.

,

Strong flow current

(between 3 and 4 knots)

46 0

number of propeller turns

positive value: propulsion machinery forward negative value: propulsion machinery backward rudder on

le(in d

rees)

positive value: helm starboard negative value: helm port area with weak current.

Scale

:

1P0 000

Fig.5:

APPROACH CHANNEL TO THE VERDON HARBOUR

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1

channel centerline

Fig.6.STAT 1ST ICAL ANALYSIS OF ENTRANCE MANOEUVRES

FOR THE FINAL PROJECT OF LE VERDON HARBOUR

(tests performed with a 213000t ship and with springtidat

currents )

I 1

\so

(a) plan of LE VERDON harbour

10m Success 100 SO 60 40 20 40 100 $O 60 3

\.

N 20

6

4

2

HT +2 +4 +6 Tidal hours

(b) mathematical model

(about 10 tests per tidal hour)

halfsuccess failure

0

6

4

2

HT +2 +4 +6

Tidal hours

(b) Statistical results

Fig.7 STATISTICAL ANALYSIS OF ENTRANCE MANOEUVRES

FOR THE FIRST STAGE OF DEVELOPMENT OF LE VERDON HARBOUR

(tests performed with a 15 600 t ship and with springtidat currents )

6

4

2

HT +2 +4 +6

Tidal hours

(a) physical model

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41 (degrees) 0.7 4 (degrees) 0 (meter) 0.75 1 1 1 1 1 1 1 9.6 12.8 15.2 17.6 20.0 22.4 24.8

Apparent wave period (s)

(b) TRANSFER FUNCTIONS ( MODULUS) (meter) 2.5 2.0 1.5 1.0 0.5 0

/310m

,/'dent

wave height :2 m 25t Ship draught :20 m UNDERKEEL CLEARANCE: 3.50m UNDERKEEL CLEARANCE: 2,50m

(in stilt water)

(0) COMPUTATIONAL DATA

7 10 15 20

Wave period (s)

(c) MAXIMUM SHIP SINKAGE

(WITHOUT SQUAT)

Fig. 8- CALCULAT ION OF A 250 000 t

_{SHIP MOVEMENTS}

WITH A SMALL UNDERKEEL CLEARANCE

11 1111

1111

PITCH

Ai

rAll

Will,

A

Ag.

II

7 III

1111

I I

IIII

I I

11 /

/

.

1

1111

'

/

1111

ROLL'1

1111

A

I

61 "

IIIr

1

I

Ili

Il Tv

HEAVE

A

0 7 10 15 20 Wave period (s) 0.6 0.5 0.3 0.2 0.1 0.5 0.25 1.5 0$

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PHYSICAL MODEL STUDY OF THE NAVIGATION CONDITIONS OF HARBOUR APPROACHES AND ENTRANCES

BY MM. BARBIER (1), QUATRE (2), LEPETIT (3), DAVESNE (4)

Abstract

During harbour approach and entrance manoeuvres, large ships must navigate in restricted waterways while being subject to generally difficult environmental

conditions (waves and tidal currents, wind and poor visibility, etc...). Two methods have been tested to simulate the path of the ship and optimize

harbour definition and entrance

mathematical modeling described in a second paper (5)

physical modeling at small scale with a radioguided ship model, presented in this paper.

After a brief description of the physical method, the paper presents two

recent applications (study of the new outer harbour of DUNKERQUE and the

new harbour of LE VERDON near the mouth of the Gironde Estuary) and discusses the capabilities and limitations of the method which appeared during the tests. The professional pilots' opinion about the physical tool has been specially taken into account. Finally, the paper presents the first results of a compa-rison between ship's trajectories measured in nature and in the physical model in the case of DUNKERQUE harbour.

Director of the Gironde estuary development (BORDEAUX PORT AUTHORITY -FRANCE).

Director of studies and exploitation (DUNKERQUE PORT AUTHORITY - FRANCE). Head of the Maritime Hydraulics Division (LABORATOIRE NATIONAL

Engineer in the Maritime Hydraulics Division (LABORATOIRE NATIONAL

Mathematical modeling of paths and motions of a shin during port apnroach under current, wind and wave actions by MM. BARBIER, LEPETIT, DAVESNE, Mme GRAFF (Delft, avril 1978).

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During harbour approach and entrance _{manoeuvres, large ships must navigate in} restricted waterways while being subject to generally difficult environmental conditions : waves and tidal currents, wind and poor visibility, etc... The

very weak power of the ship's propulsion machinery compared _{to its mass} results in poor manoeuvrability and makes the vessel very sensitive to the action of external forces. Consequently each harbour project for the reception of large ships must be examined by fundamental studies concerning

navigabi-lity conditions in harbour channel and entrance in order to receive ships with the maximum safety under limiting conditions _{fixed by the designer for}

harbour utilization.

Two kinds of prediction methods have been tested _{to study the path of the} ship during entrance manoeuvres and to improve the navigation _{channel and} harbour entrance geometry

mathematical modeling as described in a second paper (1),

physical modeling at small scales (1/150 to 1/200) with a radioguided ship model presented in this paper.

After a brief description of the physical method, the paper presents the main

results obtained in two recent applications

new outer harbour of DUNKERQUE in the North of France,

new harbour of LE VERDON near the mouth of the GIRONDE estuary in the West of France.

The paper discusses the capabilities and limitations of the method which

appeared during the tests. For this discussion, the professional pilots' opinion has been especially taken into account.

Finally since DUNKERQUE outer harbour is now in actual use, the paper presents the first results of a comparison between large ship trajectories measured in situ with those obtained on the physical model.

II - DESCRIPTION OF THE PHYSICAL MODELING 11.1 - Physical model

The method consists of steering a radioguided ship model on an

undis-torded small scale (1/150 to 1/200) model representing the study area (navigation channel, harbour entrance and stopping area) and

repro-ducing tidal currents and waves in the case of approach manoeuvres in

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In the case of harbours located in a tidal sea, the current _pattern influence is the main parameter for the loaded ship. Since the harbour structures change the natural currents, the current pattern encountered by a ship during approach and entrance manoeuvres is _{very variable and} so it is necessary to reproduce in detail these tidal currents.

In fact, for the physical model representing a restricted area, its boundary conditions depend on the harbour structures and so it must be calibrated from the currents measured on a smaller scale model. The similitude problems raised by using a small scale ship model are

difficult to solve. The main difficulty arises from the fact that

Reynolds number similarity is not maintained. Consequently the viscous

friction stresses are too important in the model. To correct this diver-gence, it is necessary to increase the propeller thrust when the machine runs forward and reduce it when the machine runs astern with respect to

its value deduced from the Froudian similitude rules.

The modification of the thrust can be obtained either _{by additional}

forces for example owing to aerial _{screws tied to the ship speed on}

water, or by an increase of the propeller turning speed when running

forward and a decrease when running astern. This _{more simple solution} has been chosen here.

The distorsion of the propeller speed is calibrated _{to reproduce at the}

best the ship speed in still water as a function of the number of turns

of the propeller and the stopping distance for _{a given initial ship}

speed (crash-stop manoeuvre).

Different opposite scale effects can change the rudder action and its

surface must be adjusted to reproduce the correct turning conditions of the ship.

The accelerations and deccelerations of the ship model _{are greater than} those for the real vessel.

These different scale effects introduce limitations in steering the

radioguided ship model : the pilot must steer at a speed _{near the one}

used for calibrating _{the stopping distance (but for other ship speeds} the differences concerning stopping distances between the model and the real ship remain small) and at slowly varying working _conditions.

11.2 - Tests methodology

The method consists of performing a high number _{of approach and entrance}

manoeuvres in the most severe conditions (biggest ship able _{to enter the}

harbour, springtidal currents), then statistically _{interprating these}

tests according to a given criteria. The chosen criteria _{consists of} computing for each tidal hour the percent of "successful" tests (good trajectory of the ship, stop in the harbour limits), _{"half-successful"} (successful entrance but having a trajectory too close to channel banks or harbour structures) or "failures" (the ship hits the _{channel banks} or one harbour structure).

Such results give

- a comparison according to a quantitative criteria _{between the} naviga-tional conditions for different harbour designs and therefore an improvement of the channel and harbour entrance geometry. This method

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the extrapolation of results from model to nature was valid

- qualitative information on the navigation conditions of the new

harbour, on the pilot manoeuvres to b p flndertaken according: to the external conditions oc currents, and on usefulness of navigation aids.

III - EXAMPLES OF APPLICATIONS AND RESULTS

The simulation of the path of a 240 000 t ship with a radioguided model has been applied to the studies of

the new outer harbour of DUNKERQUE for Port Autonome de Dunkerque

the project of LE VERDON harbour for Port Autonome de Bordeaux near the mouth

of the Gironde estuary.

111.1 -Navigational tests on the physical scale model of LE VERDON harbour

The undistorted physical model at scale 1/200 represents the end of the

navigation channel, the harbour entrance and stopping area (see

figure 2). The model was calibrated from springtidal currents measured on a smaller scale model reproducing the lower part of the Gironde

estuary (horizontal scale : 1/600 ; vertical scale : 1/60).

The tidal range is about five meters ; the spring tidal currents are parallel to the navigation channel and the maximum depth averaged

velo-cities are between 2 and 3 knots. But during the entrance the ship must navigate with cross currents and the current -)atternsencountered near the entrance change quickly.

The first experiments have been performed with a basic harbour design

optimized from the flow pattern results obtained on the smaller scale model (see figure la). Then the navigational tests have shown that

modifi-cations of the harbour entrance geometry allow an improvement of the nau-tical conditions in comparison with the initial project (see figure lb).

The final entrance geometry avoids the sharp curve of the channel axis

with cross currents and increases the entrance area sheltered from

strong estuarine currents.

With the final design, an example of an entrance manoeuvre performed

with a strong backward flcw current is given in figure 2.

Figure 3a presents the statistical results of tests carried out for the

same final harbour geometry but by two different pilots : a pilot not

accustomed to steering the radioguided ship model and a more experienced one. The results are different and stress the fact that it is necessary

to carry out a large number of tests with different pilots and in parti-cular with professional ones because these pilots can really sense the

natural navigation conditions (limitations on the rudder and engine

operation, maximum permissible drift angle, etc...).

The human factor influence can be reduced by averaging the results obtai-ned by different pilots as shown in figure 3b.

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-4-The results show that failures occur mainly during flow currents because the ship manoeuvrability is poorer with backward currents than with

front ones since its speed with regard to the current velocity is small. It seems that these results depend mainly on the natural estua-rine currents and little on the harbour geometry.

111.2 -Navigational tests on the physical scale model of DUNKERQUE outer harbour

The new outer harbour of DUNKERQUE located in the North Sea is destined

to receive large displacement ships up to 450 000 tons and to allow the development of a new 8 000 ha industrial and portuary area.

Near the new harbour, the tidal currents are parallel to the coast

the tidal range is about 6 meters and the maximum spring tidal current (about 0,90 m/s) occurs one hour before high tide. Water slacks occur about three hours before and after high tide.

The approach channel is parallel to the coast while the entrance channel is oriented towards the South-East. In this part of the channel, the

ship must navigate with an oblique current coming from astern during

flow.

The final project (see figure 4) has been optimized from physical model studies in order to assure a good protection against _{waves and to offer} satisfactory _{nautical conditions determined from the flow pattern} observations.

This project is characterized by a large stopping area ; consequently

the ship can enter the outer harbour with a 5 or 6 knots speed giving a better manoeuvrability.

But the only analysis of the current pattern was very insufficient to

predict the percent of time the ship can enter the harbour with _safety

conditions. This study has been made on the undistorded scale model (1/150) equiped with a radioguided model of the "MAGDALA" 213 000 t tanker and calibrated from current patterns measured _{on a smaller scale} model (1/400 and 1/60).

The statistical analysis of entrance manoeuvres (see figure 5) shows that the ship can enter the harbour with the maximum safety _{from 2 hours and} half after to 2 hours before high tide in the most severe conditions.

The number of tests performed with _{waves was not sufficient to give}

precise conclusions but it seems that the difficulties encountered during entrance manoeuvres are a little increased by the influence of waves. These difficulties are due mainly to the ship's vertical _motions

which hinder on the scale model a good appreciation _{of the horizontal}

movements.

IV - CAPABILITIES AND LIMITATIONS OF THE MODEL

The physical model has the main advantage of giving the pilot _{a concrete}

repre-sentation of the ship and the harbour. Moreover the use of a model allows the pilot to relax and to try different

types of manoeuvres, which he would not do in nature.

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made

The physical model has the disadvantage of contracting time (14 times for a

1/200 scale) which forces the pilot to react more quickly than in situ.

The steering of the radioguided ship model by remote control changes the

conditions for pilot's orders. It is obvious that the use of large scale models with an embarked pilot better represents real conditions (cf. Port

Revel in France) ; such a model is necessary for pilot training. On the

contrary for testing the navigation entrance conditions into a new harbour in a tidal sea, a small scale model allows a more precise study owing to the better reproduction of complex currents near the harbour structures.

Moreover the greater time contraction allows the performance of a greater number of tests, which is necessary for statistical assessment of results

to account for variations due to human factors.

With the model, the pilot does not sense immediatly as in nature very small

movements of his ship particulary with respect to ship head ; this leads him

to react with delay. The simulation can be considered pessimistic for this point of view.

After a great number of manoeuvres have been performed by the same pilot, he

gets accustomed to the physical tool and the percentage of succeeded manoeuvres increases as has been shown before. This remark stresses once more the fact that it is necessary to carry out tests with different pilots

and in particular with professional ones.

All the manoeuvres have been performed under the most severe conditions

(spring tidal currents, biggest loaded ship). The results cannot be easily extrapolated to other types of ship or tidal ranges ; nevertheless in the

case of DUNKERQUE study the extrapolation to neap tides was carried out taking into account the following assumption : the difficulties encountered

during entrance manoeuvres are mainly linked to the ratio of the tidal current velocity and the maximum ship's velocity.

V - RESULTS IN NATURE

The exploitation of the new outer harbour of DUNKERQUE began one year ago and

it is very interesting to know the pilots' opinion and to compare the first

trajectories measured in situ with the model results.

According to the pilots' opinion

"The natural currents near the harbour structure are in good agreement with those predicted by the phpsical model, which is extremely important for the safety of the first entrances into the new harbour ; moreover different types of entrance manoeuvres deduced from experimental tests have been corroborated by the manoeuvres in situ".

Figure 6 presents three trajectories recorded in situ with the portuary radar during entrances of 20 m draught ships, two hours after high tide but for different tidal coefficients. During neap and mean tides, the cross currents are weak and the observed trajectories are almost straight, the ship drift angle remaining near zero. On the contrary in spring tide, it is obvious that the difficulties encountered by the pilot are more important due to the cross currents velocity (0,40 m/s) : the vessel drift angle is about 100 and the

ship deviates from the channel axis.

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-6-The statistical analysis deduced from the model tests (see figure 5) shows effectively that the entrance manoeuvres present difficulties for this tidal

hour.

Figure 7 presents in detail two examples of trajectories performed on the

physi-cal model and the envelope of curves obtained for the same hour (about 10 tests). The comparison of these results with the only trajectory available in nature is obviously inaccurate but it is possible to make some remarks

the ship drift angle is comparable to that observed in nature

the deviation from the channel axis seems to occur later on the physical model than in nature, so that the ship passes near the west jetty head.

This difference can arise from the facts that the curve of the approach channel is not reproduced on the scale model and that the departure position is perhaps

too near the harbour entrance, the current effect reacting with delay. VI - CONCLUSION

In spite of unavoidable imperfections, the physical method with the use of

a radioguided ship model at small scale is a very effective tool for predicting the background flow pattern induced by the harbour structure and for optimizing the navigation channel and harbour entrance geometry. For determining the

navi-gability conditions in a given harbour design, the mathematical model presented

in a second paper is also used and gives results comparable with _{those of the}

physical model test.

The statistical analysis requires a great number of tests but gives very

impor-tant qualitative and quantitative information. These tests must be performed

by different pilots and in particular professional ones.

The professional pilots' contribution from the beginning of the project up to

the final design is absolutely necessary and is one of the main reasons for the success of the method.

(28)

4 ---____,.. -... ..----r _{- ...F} _-19.5 co ---...,-,-._ ok - --- ....

r-,,r

---.\ .-r-rfr

--r'r>---c-rr'>.--

_{----..._,...._"---} _{r-r-l-r r}

--

rrrr---, 1 --,,Tr ' ---trajectory axis

(b) FINAL

PROJECT

)\

e, CP.> /

F\ -21.5

\

00 950m I

\

\ Stopping area

//

,

///

///, / ///

(a) INITIAL PROJECT

Dg 105 Om .4

///

//

/

/// //// ///, /

// / /// /// ///

0 590 1000m --19.5

/

Fig.1 THE NEW HARBOUR OF LE VERDON AND-1.1.5 ACCESS CHANNEL

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point CD 4 000 -3000- terminal1 .terminal 2 point C) 1 st light

2 nd light

paint entrance

o arrival

T: starboard

B: port

3 HOURS BEFORE HIGH TIDE

(strong backward current)

Fi9.2 EXAMPLE OF A 240000t. SHIP ENTRANCE MANOEUVRE

ON THE VERDON PHYSICAL SCALE MODEL

SCALES

Plan/Nature

0 200 400 600 m 1 1 i 1

i1

ship speed 0 1 2 3 4 5 6 7 8 9 ioknots 1111111'1i Iiillt11111

2

speed orders 5 halm angle orders 02 5 _102T 5 o° 5 30°8 0° 5 10°B 5 0° 10°8 5 4 102B 02 4 3 1021 02 3 3 3028 3 30211 3 02 3 3027 0 302 T AR.3 3021

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0 -6

Fig.3

0 , , 41/,

&'

//71MINNV, //// //// 110 60 40 20 0 MANOEUVRES NOTATIONS

The ship runs closer than SOm by the channel

bank or a portuary structure

Success

ra Half success

Failure

-4 -2 HT +2 +4 +6

Tidal hour

Beginner pilot

Experienced pilot

(a)Ranges of about 10 tests per tidal hour performed on physical model by two different pilots

(%)loo

SO

-6 -4 -2 HI +2 +4 +6

Tidal hour

(b) Physical model tests carried out by 4 different pilots

STATISTICAL ANALYSIS OF ENTRANCE MANOEUVRES

EXAMPLE OF RESULTS FOR THE VERDON HARBOUR

STUDY

(experiments carried out with a 240.000t. ship and with

springtide currents)

-6 -4 -2 HT +2 +4 +6 Tidal hour SO 60 40 20 60 40 20

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80 60

40

20

THE NEW OUTER HARBOUR OF DUNKERQUE AND ITS ACCESS CHANNEL

Fig.4

Success percentage 100 % 0 400 1200 2000m

ilt4%

WWIWW.A11111

Nkh,

90% Threshold

_1111h.

A. Wit&

STATISTICAL ANALYSIS OF ENTRANCE MANOEUVRES ON THE PHYSICAL MODEL

(experiments carried out with a 240000t. ship and with springtide currents)

Fig.5

2

HT. +2 +3 +4 +5 +6 -4 -3 -2 -1 H.1.

I I

Tidal hour

(32)

'\.

1 knot

(spring tide)

0 ship's speed (knots)

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.

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(spring tide

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tide)-

fr

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I 9 _ 2 _1977

spring tide

BERGEHUS 26_3_1977 mean tide WORLD MITSUBISHI 27_ 3_1977

neap tide

\

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-....

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--Fig.6

TRAJECTORIES MEASURED IN SITU

DURING SHIP ENTRANCE INTO DUNKERQUE OUTER HARBOUR

( 2 hours after high tide)

/7

// // //

(33)

Navigational channel

CDL

Oshies speet (knots)

2 examples of tests

envelope of curves obtained for the same hour

STOPPING AREA

I.

Fig.7 TRAJECTORIES MEASURED ON THE PHYSICAL

MODEL

OF DUNKERQUE OUTER HARBOUR

(2hours after high tide)

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DESIGN OF NAVIGATION CANALS

BY I W DAND* AND W R WHITE**

Principal Scientific Officer, National Maritime Institute, Feltham, U.K. Principal Scientific Officer, Hydraulics Research Station, Wallingford, U.K.

SYNOPSIS

The paper describes model experiments carried out to investigate the navigation of ships in a canal and the effect of the passage of these ships on the canal itself. The application of results from these experiments to the design of the canal cross-section are indicated with particular attention being paid to the problems of siltation and ship handling. Finally a design scheme is outlined and suitable design criteria are discussed.

1. INTRODUCTION

As part of a wide-ranging techno-economic study, led by Maunsell Consultants Ltd., of the feasibility of widening and deepening the Suez Canal to accommodate large ships, Sewell(1), the United Kingdom's National Maritime Institute (NMI) and Hydraulics Research Station (HRS) jointly studied the hydrodynamic problems associated with navigation and canal erosion. As a result of this, information was gathered which allowed a basic design of canal to be obtained.

The overall design of a canal is a complex process involving many disciplines each dependent on the other for information. The overall approach adopted in the study in question is shown diagrammatically in Figure 1, but this paper is concerned solely with the technical aspects of the cross-section and canal curve design. The availa-bility of the inputs from other disciplines is assumed.

2. GENERAL APPROACH

In designing the test programme it was necessary to restrict the number and range of the variables considered such that the work could be carried out within the financial restraints placed upon the study. Variables which were not considered to have a major influence on navigation or erosion such as the side slopes of the canal and the water temperature were ignored. The final test programme could be regarded as a basic research exercise in which the major geometrical and dynamic factors were varied in a systematic way.

The major factors covered were as follows:

Size of the canal relative to the ship (blockage ratio).

Width of the canal relative to the beam of the ship (width ratio). Depth of the canal relative to the draught of the ship (draught ratio). Geometry of the canal cross-section adjacent to the banks.

Ambient currents within the canal (tidal influences). Types of ship.

Speed and alignment of transits. Emergency stopping procedures.

At the outset it was clear that experiments whose results might be subject to scale effect should be carried out at as large a scale as possible. In order to gain some insight in the simplest possible manner into the effect of a human controller on navigation during steady state and transient manoeuvres, a free-running manned ship model was used (model A). This yielded information on propulsion, squat, handling and stopping in a straight canal, results being non-dimensionalised for application to a range of ship/canal combinations.

Experiments in which scale effect was thought to be negligible _{were carried out at a smaller size using a} free-running radio-controlled geosim (model B) of the larger model. These experiments were concerned mainly with the handling of ships in a curved canal in which the behaviour of the model _{under various conditions, such as}

1. Sewell T F D, 'Towards new transit regulations on an enlarged Canal', Dock & Harbour Authority, July 1976, pp 80-82.

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3

a change in severity of the canal curve, was used as a measure of this change rather than a definite prediction of the behaviour of any particular ship under given conditions.

The hull form chosen for most of the model experiments _{was that of a full-form single-screw tanker. It was in} fact a model of a VLCC that had been in service for some years and was typical of the type. Any choice of hull form must of necessity be a compromise, but at the outset it seemed appropriate _{to choose a VLCC hull} as it was felt that its handling, powering and stopping problems might be severe so that it _{was the most likely} ship-type around which to design a safe and economical canal.

Some experiments were also carried out with a smaller ship model (model C) which represented a vessel such as a tug which might transit the canal at high Froude length numbers thereby creating an appreciable free _wave system. This model was radio-controlled but carried no on-board recording equipment.

3. DESCRIPTION OF MODELS

3.1 _{Straight canal model}

The canal model used for experiments with ship models A and C, _{was contained within a tank 10 m wide by} 0.9 m deep by 90 m long. The general layout is shown in Figure 2 and typical cross-sections _{are shown in} Figure 3.

Four centrifugal pumps gave flow velocities of up to 0.15 m/s through the largest canal cross-section. Full width

manually operated flap gates controlled the water level at the downstream end of the tank and these also served

the purpose of partially absorbing any waves generated by the acceleration of the ship from rest and travelling ahead of the ship. For this purpose gates were also fitted at the upstream end of the tank for use when the ship model was travelling against the flow.

The moulded canal was 70 m long leaving a full depth area 10 m long at both ends of the tank to accommodate the pump inlet diffusers and to allow the ship model to be turned around as required. The invert of the canal was laid with cement mortar and screeded level to an accuracy of ± 2 mm. The canal sides and berms were then moulded in cement mortar using permanent wooden templates. The upstream end of the canal was faired into the tank sides with quadrants.

The land-borne instrumentation of the model was located within a 10 m long test section at the longitudinal centre of the canal.

Four water level followers were mounted on a transverse beam cantilevered out over the deep water channel. One follower was mounted as close to the track of the ship as was safely possible, a second near to the junction of the 1 on 4 side slope of the canal and the horizontal berm and the remaining two over the berm itself. A second beam carried four directional miniature propeller meters. Two twin wire wave recorders were mounted adjacent to and in line with the two water level followers located over the berm. The output from each group of instru-ments was fed to an ultra-violet (UV) chart recorder.

At each end of the 10 m test section light beams were projected across the canal to receivers on the opposite bank. Fins mounted on the ship models interrupted the light beams and activated an electronic timer from which the speed of the ship was calculated. Two additional light beams linked to the timer and mounted 10 m either end of the test section monitored the uniformity of the speed of the ship. When a light beam was interrupted, each UV recorder chart was automatically marked to correlate the position of the ship model with the UV trace.

Each test run was photographed by twin ovrhead cameras whose combined field of view covered the test section and further 8 m lengths of canal upstream and downstream. Small lights at 2 m intervals on datum lines either side of the tank located the canal and two lights on each ship model recorded its course. The lights on model A were mounted on the starboard bow and the port quarter and showed as parallel tracks on the photograph when the model was running straight. Interrupters on the cameras split the light traces into a series of timed dashes and this provided a back-up indication of speed.

The experimental canal was too short for model A to accelerate to steady speed and come to rest under its own power. Acceleration was therefore assisted by a catapault system and deceleration by a hydraulic arrester.

3.2 Curved canal model

A smaller scale curved canal model was constructed in a large manoeuvring tank using bank sections manufactured from glass-reinforced plastic. These were connected together to form curved canals of a constant radius but

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or following current was simulated. Experiments using ship model B were run in this canal model.

3.3 Ship models

The model was constructed from rigid polyurethane foam and measurements were made on board of the

following:

propeller torque propeller thrust

propeller shaft revolutions

underkeel clearance at four points under the hull rudder angle

backflow beneath the model amidships.

A diagrammatic view of the model and the equipment carried on board is given in Figure 4. Signals for all transducers were suitably conditioned and recorded in analogue form on a 14 channel magnetic tape instrumenta-tion recorder for subsequent analysis by computer.

The operator controlled the model from a position such that his height-of-eye was correct to scale. A console was provided which enabled control of rudder and shaft revolutions, both controls being suitably damped to give a more realistic 'feel'. The operator was also able to operate the underkeel clearance probes and two fans fixed to the model which allowed simulation of a cross-wind. The aft fan could be turned through 900 to provide a known thrust to the model thereby offsetting the non-scale propeller loading inherent in free-running ship model experiments. Further displays on the control console gave information on rudder angle and shaft revolutions; tape recorder controls and a device enabling synchronisation with the shore-based measuring equipment were also

provided.

3.3.2 Model B _{This model was geometrically similar to model A but had a length of 3.675 m. It was fitted} with a radio-control system allowing full control of motor and rudder. Rudder angle and shaft revolutions were

recorded throughout each run on a two-channel battery-powered pen recorder mounted in the model. The on-board equipment was completed by a motorised camera used to track the model position by photo-graphing, at known time intervals, previously-surveyed marker posts positioned on the banks of the canal bend model. Computer analysis of the resulting photographs yielded position information while analysis of _{the chart} records gave rudder angle statistics.

3

As in model B control of rudder angle and shaft revolutions _{was achieved using radio-control equipment.} 3.3.4 Operational methods Both models A and B were controlled by the operators on preset target courses using the minimum amount of rudder angle compatible with control. The positional information obtained from the tracking photographs gave statistical information _{on the width of navigation lane used by the model and the} deviation of the mean course from the target course.

To determine the best stopping techniques in a canal, however, an experienced pilot was carried on board who gave helm and engine orders to the operator, the experiments continuing on a trial and error basis until a suitable

stopping method was found. Stopping techniques are not discussed in this paper.

3.3.1 Model A This was a model of a VLCC to a scale of 1:40.5. It had the following principal particulars: Length between perpendiculars, Lpp 8.069 m

Beam, moulded, B 1.264 m Load draught, TL 0.488 m Block coefficient 0.831 Rudder area/(Lpp TL) 0.020 Number of propellers 1 Number of blades 6 Diameter D 0.217 m

3.3.3 Model C This was a model of a small single screw coastal vessel with the following principal particulars: Length between perpendiculars, Lpp 1.429 m

Beam, moulded, B 0.447 m Load draught amidships 0.166 m Block coefficient 0.45

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3

4. TYPICAL RESULTS

4.1 Effects on the canal of vessels in transit

4.1.1 Drawdown Water level followers indicated changes in water level as vessels passed the measurement section. In general the maximum drawdown occurred approximately amidships and water levels could be assumed constant across the width of the canal at this point. It was shown that the fall in water level, Ah, could be related to the depth of water in the canal, h, the speeds of the vessel, Vs, and the ambient current, Vc, and the blockage ratio, BR. A general expression for the drawdown was established as

2

_ 8.8 x (Vs Vc)

BR' '4 2g

and this relationship is plotted on Figure 5 together with the experimental points.

4.1.2 Return current _{Directional current meters provided a continuous record of flow patterns around the} vessel. Typical results are shown in Figure 6 which illustrates the temporary migration of water from the horizon-tal berm of the present Suez Canal as a vessel passes.

4.1.3 Surge waves resulting from drawdown effects The present western side of the Suez Canal has a horizontal berm which runs out from the bank at a level between 1 m and 2 m below water level. One disadvantage of a horizontal berm (as incorporated in cross-section No. 1, see Figure 3) is that under certain circumstances surge

waves can be created by vessels in transit. Conditions which increase the likelihood of surge waves include shallow depths of water over a berm, hb, high speeds of transit and significant drawdown of the water surface caused by the passing ship.

At slow speeds of transit there is a gradual and small fall in water level as the bow of the vessel passes and a gradual increase as the stern reaches the point under consideration. As the speed of transit increases, the amount of drawdown increases and at some stage a weak undular disturbance is initiated over the berm. At _{even higher} speeds this weak undular disturbance is transformed into a surge wave which travels along the berm roughly in line with the stern of the vessel.

It is unwise to design new banks which will induce damaging surge waves under the operating conditions antici-pated for the new canal. Hence it was desirable to be able to predict when these effects would occur and to develop design criteria which would avoid them.

A semi-empirical approach to the problem, utilising the observed drawdown characteristics, indicated a general relationship between the Froude number (based on the speed of the ship and the undisturbed depth over the berm), the blockage ratio and the type of wave disturbance. The plot is given in non-dimensional form in Figure 7. 4.1.4 Ship waves The potential erosion caused by large vessels in transit through the canal results from the bulk movement of water around the hull of the vessel. The return currents can cause movement of sediment on the sloping banks and the drawdown of water amidships may cause damaging currents and surge waves adjacent to the banks of the canal. At normal convoy speeds large vessels move at low Froude numbers based on ship length; they do not therefore make prominent free wave patterns. Smaller ships moving at the same absolute speed have higher Froude numbers due to their smaller lengths and thus produce more prominent wave patterns which will

impinge upon the canal banks. Large surface waves could be a potential source of damage to the banks. Ship waves are influenced by many factors, the major ones being the speed of the ship, the length of the ship, the shape of the hull (particularly the forward sections) and the depth of water through which the ship is pass-ing. It was not possible to cover all these variables in the present investigation but the results using a single vessel served as a general guide to the likely magnitude of ship waves in the canal. Typical results obtained using model C in the straight canal model are shown in Figure 8.

4.1.5 Stability of canal cross-section Maintenance dredging within a canal forms a significant part of the annual operating costs. Although these costs are fairly small in comparison with the revenue from ships using the canal

it is important to assess the operational problems which may arise in the future and the maintenance fleet which will be required for an enlarged canal.

The movement of sediment caused by the passage of ships through a restricted waterway is a complex hydro-dynamic process which is not fully understood. The approach used for the non-cohesive sediments (D35 > 0.1 mm) of the middle reaches of the canal was to develop a calculation technique, based on existing knowledge of sedi-ment transport phenomena, and to test the validity of the technique against maintenance dredging rates for the

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Deposition caused by a single transit was calculated using the total bed material load sediment transport theory of Ackers and White(2) and the principles described by Fredsoe(3) to determine components of movement down the side slopes of the canal.

To compute the total annual infill it was necessary to split the total number of transits into categories, each category of transit being composed of ships of equal size travelling at equal speeds. The calculations were carried out for each category and infill volumes were multiplied by the number of ships within the category. It was then possible to sum the infill volumes of all categories to determine the maintenance dredging commitment. Furthermore the relative contributions of each category could be studied.

Table 1 shows computed results for the existing Suez Canal where the estimated maintenance commitment is between 24 tri3/m run and 35 m3/m run per annum. It can be seen that the large vessels, even though theyare

few in number, have a disproportionate effect on siltation.

TABLE 1: Sediment infill rates, pre-1967 Suez Canal

Results obtained with model A related to navigation in a straight canal only and provided the basic data for cross-section design. Experiments with model B furnished additional data to enable any necessary modifications to be made to the basic section design in a bend. We consider here results obtained from model A.

4.2.1 Resistance and powering _{Typical measurements of shaft power Ps are shown in Figure 9. Such} measure-ments were combined with estimates of effective power, PE, to obtain _{a propulsive coefficient, 77p, for the ship} model from

np ' PE/Ps

....(2)

The effective power was obtained from total hull resistance estimated using an extension of Landweber's

method(4). Once the variations of rip with blockage ratio and Froude depth number were known it was possible to produce design charts for the shaft power of a family of tankers, _{an example of which is given in Figure 10.} This shows the variation of Ps (given as a percentage of installed _{power Pi) with blockage ratio and water depth/} at rest draught ratio h/T. Indications of whether propeller cavitation is likely (L)due to increased thrust loading on the blades or unlikely (U) are also shown on Figure 10, the cavitation check being made using the method of

Burrill(5) together with values of thrust _{identity wake faction and thrust deduction obtained from model A.} Ackers P and White W R, 'Sediment transport: New approach and analysis', Journal of Hydraulics Division, ASCE Paper No. 10167, 1973.

Fredsoe J, 'Levelling of side slopes in river navigation channels', Institute of Hydrodynamics and Hydraulic Engineering. Technical University of Denmark, Progress Report No. 38, Lyngby 1976.

Landweber L, 'Tests of a model in restricted channels', DTMB report 460, Washington, May 1939. Burrill L C, 'Developments in propeller design and manufacture for merchant ships', Institute of Marine Engineers, London, August 1943.

5 Type of Length of transit ship

(n)

Beam of ship 070 Draught of ship

(n)

Speed of transit (m/s) Number of ships in type Annual infill per m run (ms) 1 140 _19.0 _8.5 _3.89 ₉₅₀₀ _0.06 2 170 22.0 8.5 3.89 4500 0.18 3 200 26.0 8.8 3.89 2500 0.72 4 220 30.0 10.0 3.89 3000 6.81 5 235 33.0 11.0 3.89 1000 8.54 6 260 37.0 11.5 3.89 500 13.07 Totals 21000 29.38

Proceedings of the Symposium Aspects of Navigability of Constraint Waterways, Including Harbour Entrances, Volume 2, Delft, The Netherlands

lume

SYMPOSIUM

delft 1978

P1978-5

aspects of "12

navigability of

constraint waterways,

including

harbour entrances

delft ,the netherlands,april 24-27,1978

SYMPOSIUM

aspects of

navigability of

constraint waterways,

including

harbour entrances

olume

coed

o

nas

delft 1978

aspects of

navigability of

constraint waterways,

including

harbour entrances

delft ,the netherlands,april 24-27,1978

volume 2

papers 1-15

aspects of

navigability of

constraint waterways,

including

harbour entrances

Contents

of

F.

a)

if

n little

Gx = 0

= -

Cx = 1.5

Fig.1 FORMULATION OF DIFFERENT FORCES

APPLIED TO THE SHIP

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if T C

y

I

Fig.2(a) STOPPING DISTANCE VERSUS SHIP SPEED

Fig.2 (b) STOPPING TIME VERSUS SHIP

SPEED

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