Experimental facilities of the CTU ship hydrodynamics laboratory

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4 DEC. 1919

ARCHIEF

Experimental Facilities of the CTU Ship

Hydrodynamics Laboratory

By

C. P. Sheng and B. L. Wang

Shanghai Chiao-Tung University

May 1979

Lab, y. Scheepsbouwktince

Technische Hogeschool

Deift

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Experimental Facilities of the CTU Ship

flydrodynamks Laboratory

By

C. P. Sheng and B. L. Wang

Introduction

The Ship Hydrodynamics Laboratory of the Department of Naval Architecture of the

Shanghai Chiao-Tung University (OTU) has been established for 20 years. At present,

the laboratory comprises two parts: ship model towing tank and cavitation tunnel. The

features of the facilities are briefly outlined in this paper.

i CTU Ship Model Towing Tank

The ship model towing tank, completed in 1958, is intended for carrying out model

resistance tests, open water propeller and self-propulsion tests in calm water and in waves.

Ship motions in regalar waves are also investigated.

1.1 Towing Tank (Fig 1)

The tank is built of reinforced concrete and divided into five intermediate sections

(15m each) and two end sections by transverse expansion joints. The principal dimensions of the tank are

Length 110m

Width 5m

Depth _3.5m

Depth of water 3m

The tank contains a trimming dock and two atorage docks at the south end. A

detachable end wave absorber is installed in front of the docks and small wave dampers

(curved plastic plate) are fitted along the tank side. A plunger type wave generator is

equipped at the north end of the tank.

Two rails are installed on adjustable bed-pieces with supports fixed to the tank walls

permitting vertical

rail adjustment up to

± 12mm and in horizontal direction up to

± 2mm. On top of the side walls, small water channels are built close by the rails. The

water surface in the channels is taken as reference for rail height adjustment. The rather

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Iig i.

Sketch

f the Towing Tank

trimming dock storage dock expansion joint end wave absorber side wave damper wave generator

7

rail

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Pig 2 Towing Carri2ge

1.2 Towing Carriage (Fig 2)

The towing carriage, suppUed by kempf Renimers, is of platform construction with

a measuring frame and other struc-tures. The observation platform can be lowered down for shallow water tests.

The carriage is supported on

four

_{wheels (0.6m dia.),}

_each

driven by a D. C. motor. Eight guide wheels are fitted on the port

side of the carriage to control its

longitudinal alignment of motion. The carriage is started

manu-ally with the desired speed

set

beforehand. In case the carriage is not manually stopped in timo, one

of the braking devices is _{automatically brought in action in approaching the end of the}

tank. _{The technical particulars of the towing carriage are}

Length _7m

Breadth 6.8m

Total wt. ht 6T

Max. speed _6m/seo

Min. possible speed O. 04m/seo

For high speed range (0.5-6m/see), the carriage is driven by 4 D. C. motors, 5 kW

each, with an accuracy of 0. 59 in speed control.

For low speed range (0. 04-0. 6 m/sec), the earriage is driven by i D. C. motor,

1.1 kW.

Breaking systems: Electrical and Mechanical.

The original electronic control generator-motor system, owing to the limitation óf its

accuracy, stability and acceleration, was replaced by a transistor SOR generator-motor system in 1970. For further improvement of the carriage performance, _{a SOR power}

supplied digital-analogue control servo-mechanism system is now in progress.

1.3 Wave Generator and Wave Absorber

A Kempf & Remmer wave generator _{of the plunger type is provided, which is}

driven by a T HP DO motor. _{The wave length and height are continuously adjustable.}

After careful calibration, the regular waves generated _{can be represented by Fig 3 or the}

following formulae with reasonable accuracy.

-=l.050.203T2 (For?<6m)

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--1.O5Ù.13X

where,

h - wave height (cm)

s - stroke or travel of

the plunger (cm)

T - wave period (Eec)

02

X - wave length (m)

o

In order to produce two

di-mensional irregular waves, ref

it-ting of the control system of the

wave generator is now in progress. Fig 3

It is hoped that the new control system will be

The end wave absorber (Fig 4) has the shape of a wide, curved

three sections meeting the water surface at an angle of 12°. These seetions can be

thscon-nect&I to allow passage of the ship model. The small side wave dampers can be turned

up for model experiments in waves.

0.8

Fig 4 Ed Wave Absorber

1.4 Instrumentation

The ship model towing tank is provided with the neeessary measuring instruments for resistance, open water, S. P. experiments and ship motions in regular waves.

Kempf & Remmers resistance dynamometer up to 10kg. Resistance dynamometer for submerged bodies up to 10kg. Propeller dynamometers with different measuring capacities. For S. P. experiments:

Kem1:f & Remmers Jo5 dynamometer, thrust up to 3kg, torque up to 4kgcrn,

max. rpm=3000.

Kempf & Remoners Jo4 dynamometer, thrust up to 10kg, torque up to 10, 20

or 4okgcm, max. rpm= 2000. Foi' open water experiments:

4---.

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tI

...__.L

-V.8 0.91.0 2.1 12 8.3 1.4 1.5 1.6 17 18 1.9

T (ser-)

put into operation in the near future.

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Kempf & Remmers Ail dynamometer, thrust up to 20kg, torque up to 120 kg cm, max. rpm=1500.

Kempf & Remmers J08 clynamometer, thrust up to 80 kg, torque up to 360 kg

em, max. rpm=2000.

Duct thrust dynamometer up to 10kg.

CPP blade spindle torque dynamometer, torque up to i Ookgcm, max. rpm 600, blade setting angle range ± 45°.

Rudder dynamometer, torqueup to 5kgcm, lift up to 5kg, drag up to 2kg.

Apparatus for measuring heave, pitch and roll of ship model in waves.

Devices for measuring velocity fields and wake survey: blade wheels, Prandtl pitot

tubes, 5-hole tubes and o on.

Wave probes: for measuring wave profiles produced by wave generator. Besides, a

capacitance type wave probe is installed at a suitable place in the towing tank for the

longitudinal cut wave measurement.

1.5 Workshops

Workshops are equipped with a set of machine tools for manufacturing ship models, propeller models and various model appendages.

Hull models are made of paraffin wax or wood, worked on a tracer milling machine (Kempf & Remmer), which can also be used for measuring ship models.

Propeller models are made of white metal or bronze, worked on a drill machine (Kempf & Remmers) by spot drilling the casting. It can also be used for measuring

propeller models.

Generally, the model size used in the towing tank is:

Length of ship models: 3-5 m,

Diameter of propeller models: 0.12-0.15 m (for S. P. models)

0.25-0.30 m

(for open water models)

1.6

Comnparative Experrnents

Comparative experiments are taken as a part of the activities

of the

laboratory.

Since 1958 a number of comparative experiments, some of them were directly related to

the recommended works of ITTO or OTTO, have been carried out in the towing tank.

For resistance, open water and S. P. comparative experiments, models of different types were employed, such as the Victory geosim family, standard model, B4-40 series, lOA ±

Ka4 - TO and so on. A parent model of series 60 with L= 2. 258m, _°b= 0. 1 was used for seakeeping comparative experiments. Some of the experimental results are given in

Fig 5Fig 10.

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5-0.6 05 0.4 0.3 02 o1 Q 04 0.6 U5 10 12 1 1

Fig 5 Resistance Tests

aaiimuaui

ullillini

RURIV1RR

"Ji'

R

a

R /

'IRR

Tr a

R,R.

ni:::

2 1.

-rl

(Ks) c2 1O CS(Sc.,) 08 4

e--cru 14SM8

Fig 6 Open Water Tests (=5Q Victory Model)

.7 0.9V .1 1,

Yn(i/.)

Fig 7 Self-Propulsion Tests (a=5O Victory Model)

VCtG?j MI1 -so c-ru

-y

j

7,

I

/

15 13 9

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X. 6 0.8 06-1.2 08 -06 04 02 Fn 0.20

-7-Fig 9 Seakccping Comparative Tcts

0.9 80 X, I 1,2 2.3 LI 1.5 10 1.7 18 _iy

Fig B Sekeeping Coniparitivc Tests

0

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o - 20 20 -1.0 - 20 2.0 .0 G -10

20

20 g.0

s

iiIF'

0.22 »

,,

'N ..

/

__//

-I A

I

--

1n0,30 \ -'J 1 2 8

56

:is 11 12 1.3 14 15 ie Fig 1.0 Resistance Tests of CTTC Standard Model

- - - . -. - - relative errors between each test and year average

relative errors between the average of 4 tests and year average

- relative errors between CTU yea.r average and average of 14 CT'I. models

-20 2° g. o o -ID

20

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9

Fig 11 Sketch of Tuniel Circuit

2 CTU Cavitation Tunnel

Recently, the laboratory has built a cavitation tunnel, which is primarily intended for carrying out propeller experiments in uniform and nonuniform flow fields. Other

investigations such as special-type propellers, hydrofoils, axisymmetrical bodies, rudders,

cavitation damage, cavitation noise etc. are also contemplated..

2.1 Tunnel

The tunnel, built by Shanghai Kiang-Nan Shipyard, is made of mild steel and ha a

closed loop circuit in the vertical plane. A sketch of the circuit is shown in Fig 11. The

technical particulars of the tunnel are as follows:

Distance between vertical limbs, C. to C. 11m

Height between horizontal limbs, C. to C. 10m

Water content about 50 in3

Length of test section

2m

Diameter of test section 0.6 m

Max. model diameter 0.3 rn

Max. water velocity 15 rn/s (20m/s)

Contraction ratio 6.25:1

Angle of diffuser To

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The test section is fitted with eight rectangular plexiglas windows (680 x 310mm)

along its sides to permit visual oi)servation and photograph. An interchangeable flow

regulator section is provided for simulating wake field by means of wire mesh grid. The model to be tested is mounted on the upstream shaft. It makes possible to study

hub vortex cavitation and rudder performance behind the propeller. The shaft (6m long,

40mm dia.) has a shrouded tube with an outer dia.

of 98mm, in which is fitted with

six polytetrafluoroethylene bearings. The shaft system is cooled andlubricated continuously

by filtered water, supplied by a special pump. The general view of the working part is

shown in Figl2. Figl3 shows the photo of a propeller model testing in the OTU

cavita-tion tunnel.

Fg 12

Preliminary calibrations indicate that a minimum

cavitation number min 0. 15

and a power factor

P. F =0. 318 can be achieved at the Max. water veloci-ty i 5m/s. Pitot traverse measurement at the propeller

position has been carried out. The velocity

distribu-tion at water speed V =4. 0 rn/sec and 8. Om/sec is

given in

Figl4 and Figl5

respectively. In these

figures, the outer circle of 3 00mm in diameter

repre-sents

the maximum size of propeller disc and the

inner circle with diameter of 60mm represents the

hub size.

10

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Fig 14 Velocity Distdbu.

iloti at V4Om/sec

Fig 15 Velocity Distribu

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It shows that the velocity distribution a the propeller position is satisfactory and

only a small variation of 2-39, caused by the upstream shaft

supports,

exists in a

quite narrow region near the hub.

2.2

Propeller Dyuam.ometer

The propeller dynarnomeer drive system is of special designed variable-frequency

alternating

current type with speed

range 0-5000rpm. Its speed can be regulated continuously by varying the frequency and voltage of the alternating current supplied to the T5kw driving motor.

Torque Measurement.

The stator of the driving motor is freely suspended ort

ball bearings and connected to the automatic torque-balance through a lever system. The

propeller torque is indicated numerically by the automatic torque-balance. The measurable torque is 15kg-m.

Thrust Measurement. The propeller thrust is transmitted through a thrust

bear-ing and a lever system to the automatic thrust-balance. The propeller thrust is indicated

numerically by the automatic thrust-balance. The measurable thrust is 300kg.

RPM Measurement.

The propeller RPM is indicated by a digital

frequency

meter, which is connected to a photoelectric impulse converter mounted on the shaft end

of the driving motor.

2.3

Velocity and Pressure Measurements

The water velocity at the

test section is measured by U-type manometers. A

mercury manometer is provided for high speed measurement and a water manometer is

for low speed measurement.

The pressure difference between the test section and atmosphere is measured by a

mercury manometer. Thus the absolute pressure in the test section is determined in

con-nection with the atmospheric pressure indicated by a barometer. The pressure in test section can be regulated in a range of 2 atm. to near vacuum by the use of an air com-pressor and a vacuum pump.

By means of differential pssure transducers, the water velocity and pressure in the

test section can be manually or automatically regulated and controlled to any desired value within the range.

2.4

Auxiliary Equipment

A stroboscope with a short flash of

i 0s is provided for

visual observation and photographic purpose. Two impulse long-arc xenon lamps are used as the light source of the stroboscope.

To regulate the air content in the tunnel water, a deaerator of 4m in height, i . 5m

in diameter filled with plastic wavy sheets is installed. Normally, it takes about 30

minutes to deaerate the water to an air content ratio of 0. 3 compared with the staidard

air content. A modified Van-Slyke type meter is provided for measuring the contents of

air in the tunnel water.

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-A storage tank of 9m3 is at cisposal w1en thè wter level is lowered tor changing

models or other apparatus in the test section.

It should also be mentioned that the tunnel is equipped with a special designed filter system to keep the tunnel water clean and transparent.

2.5 Experimental Results of ITTC Standard propeller

As the cavitation tunnel was just completed,. it is considered necessary to carry out calibrations for the whole system. A bronze standard propeller model, recommended by

the 9th ITTO cavitation committee, has been manufactured and tested in the CTU

cavitation tunnel and ship model towing tank so as to compare the experimental results with other establishments. The principal dimcnsions of the standard propeller model

employed are

Diameter D= 300mm, Pitch P= 300mm,

Pitch ratio

_=1.0,

Disc area ratio D. A. R=fl.6

Boss diameter ratio = 0.2, Number of blade Z= 4,

Blade thickness fraction B. T. F=0.05.

The range of the local Reynold's number at 0. 15R is

R00.7V20.T52

_{(0.9-3.19)x 106}

The experimental results are plotted in Figl6.

os 0.4 1OKQ 0.3 C 2 o. i o

-

13

-CTIJ rt1oel Re.SLJI+S fispherc)

CTL) Tun,d Re5uI+$(4.0)

CTL) TU,inJ P05Ui4-3 (2.0)

CTU Turei ResuI+5(=f.0)

CTU Tor'k PesuI+s

X S R C w 41.. ... o -4-

_____

A'

I --.

-

..S... 03 0.5 06 0.7 0.9 10 I.,

J

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The dotted lines in FigI 6 represent the _{range of the experimental results of SSPA}

(Sweden), Mitsubishi (Japan), Newcastle (England), EL. Pardo (France) and Brodarski

(Yugoslavia) cavitation tunnels. It can be .een that there is remarkably good agreement