Manoeuvring test facilities in the ship hydrodynamics laboratory of the Helsinki University of Technology

Onde rafde DATUM: OOCIJ4INTATiE ibliotheek van

nische Hoccho

DOCUMENAjT1: Ké'c_ 4? 'i3/

V. Kostilainen, I.J. Sukselainen

MANOEUVRING TEST FACILITIES IN THE SHIP HYDRODYNAMICS LABORATORY OF THE HELSINKI UNIVERSITY OF

TECHNOLOGY

L-'431

sbouwkunde

13th INTERNATIONAL TOWING TANK CONFERENCE 1972

SUBJECT-NANOEUVRABILITY

MANOEUVRING TEST FACILITIES IN THE SHIP HYDRODYNAMICS LABORATORY OF THE HELSINKI UNIVERSITY OF TECHNOLOGY By V. Kostilainen and I.J. Sukselainen

Abstract

A new building for the Ship Hydrodynamics and Ship Structural Laboratories of the Helsinki University of

Technology was completed in December 1970. It comprises

two larger basins, manoeuvring and seakeeping basin of

mx

mx 3 mwith a towing basin of 130 mxli mx

5,5

m attached to it. The manoeuvring test facilities

have been completed (finished) first, and are now in full

working order. These facilities include ultrasonic tracking system, model autopilot with several fixed

steering programs and necessary telemeter transmitting

and data logging systems.

Introduction

The original plans of the Ship Laboratories of the Helsinki University of Technology consisted of a conventional

towing basin of abt 200 m length. _{Later, plans were}

changed to correspond to the requirements of actual

research projects. _{The length of the tank was reduced to}

130 m and a manoeuvring and seakeeping basin was included

to the final plans. In addition to these, the facilities

will comprise an atmospheric circulating water channel of composite concrete-steel construction with _{a measuring} section of 1,5 m x i in.

Until now model tests have been made with _{free running}

models of 3,2 - 3,5 in length. This model size seems to

-2-for measuring equipment and batteries and the limitation of scale effects. On the other hand, this model size has

proved to be the maximum with respect to the size of the

basin. Thus, in the light of experiments made this far, the size of the manoeuyring basin, 40 in x 40 m x 3 m,

appears to be a suitable solution both from the economical and model testing technical points of view.

Arrangement of the basin

General arrangement of the basin is as shown in Fig. 1. The manoeuvring basin 40 m x 4O ni is connected to the

towing basin by an approachway of 6 mbreadth. Water level at maximum depth of 3 m is the same as the normal water level in the towing tank. When manoeuvring tests

in shallow water are made, the approachway is closed by a floodgate of floating type and the water level in the towing basin can be kept unchanged.

The bottom of the basin was precisely levelled for _shallow

water experiments. _{An ordinary reinforced concrete bottom} was cast abt ₃ cm below the designed bottom level. By means of a net of precisely levelled brass studs _{a layer} of concrete of low cement percentage was then laid and

finished to the exact level. _{The evennies of the bottom was} checked by systematically running a model very slowly at shallow water. Clearance between the bottom of the model

and tank was measured by means of a modified ultrasonic

wall thickness gauge. _{According to these measurements 95 %} of the area of the bottom is at the _{same level within}

accuracy of 1 mm. Maximum deviations in the::'rest _{5 %} are of the order of _{2 mm and these areas will be levelled} in connection with the next emptying of _{the basin. Though}

the tracking of the model is carried _{out in the first place} by ultrasonic method, there' is a photographing platform

13.6

in above the tank bottom. _{The rails of the overhead} crane of the model work shop have been extended _{3 in over}

structures used in the tests.

A plunger type deep water wave maker of 4O in length iil be built on one side of the tank. A removable flap-type shallow-water wave maker, which has a maximum length of 20 in, is now under construction.

Model Position Plotter System

The system determines the rectilinear coordinates of a

free sailing ship model the maneuvering basin by

ultrasonic distance measements, using a digital

coordinate computer. The path of' the model is plotted

on a X-Y-plotter and simultaneusly recorded on punched

tape by the data logging system of the tank. Tha basic

design was done by K. Luukkonen when working at the

Applied Electronics Laboratory of the University. He was also responsible for constructing the original equipii'ent.

By measuring the distance to a model from three or four

corners of a square basin with a side length a, the

expressions for the X- and Y-coordinates can easily be computed without using trigonometric functions. Thus

r r

a"3"+a

X

2a 2a

r r

a r xj a

The distances r1 are measured by using ultrasonic pulse, which is transmitted at known instant from _{a model borne} ultrasonic transmitter and received by four appropriate receivers situated in the corners of the 0 in by 40 in

manoeuvring basin. The transmitter is sending pulses on

radio command from the centx"al unit ashore. At the

instant when the pulse is sent, the computing of the square of' the distance in units of 2.a at a frequency

z'

flow structure of which is shown in Fig. 2. When the

ultrasonic pulse reaches anyone of receivers; UR, the

contents of 12 most significant bits of the distance in

SQR is transferred to the corresponding register DR. The initial values of XR and YR are set by the LCU to be

equal to 210. Three of four distances in DR are selected so that the longest distance is rejected. The

data selector directs the two necessary square distances

for each coordinate to XR and YR respectively. The LCU

controls the additions and subtractions in the XR and YR

registers according to the equations. For an analogue

X-Y-plotter the computed coordinates are converted to

analogue voltages. The coordinates are simultaneously

recorded by a data logger on punched tape.

The position plotting can occure at frequencies of 4,2,1

arid 1/2 Hz. _{The Working frequency of the ultrasonic part} is 124 kHz. The transmitter and the receivers use

piezoelectric radially polarized ceramic tubes (Brush

Clevite PZT-5 H) located vertically. The receiver signals

are amplified at tank corners by 80 db amplifiers feeding

long transmission lines to the central unit. The error

in the positioning is suppdsed to be within ± 20 mm.

Model Autopilot System

For precise and repeatable model manoeuvring an automatic rudder control unit is desirable. In our labòratory the

problem has been solved by constructing a special digital

control unit actuating the rudder by a stepping motor.

Mr. J. Kangas from the Applied Electronics Laboratory has been responsible for the design and construction of

the unit.

A functional block diagram of the system can be seen in Fig. 3. The automatic steering modes are as follows:

5

- trapezoidal steering

-

Z-marìeuver

-

constant heading constant course rate - Nomoto parallel shift

In addition, a hand control mode is provided. The program

required is pre-selected before each run and the model is launched under

manual

radio control. The ptogram is then

started by radio and after the experiment the model is returned to dock by hand steering. All program parameters

are pre-set by digital selector switches at the front

panel. The rudder is turned in steps of 0.08 deg. During a run the rudder can be centered automatically at will.

General instrumentation

The models, which use NiCd-batteries as power suppliers, can be equipped with all necessary gear. The instrument-ation

includes

coLrse-, course-rate-, heel-, and trimgyros,

propeller dynamometers, speed logs, echo sounders for

shallow water etc. The measured data is transferred to the data logging station ashore by a 8-channel

FM-FM-telemetry system. The received data is normally scanned

along with the model position coordinate values by a

data logger. The data is then punched on paper tape at

a maximum rate of 75 characters per second. For higher

data rates the telemetry system also allows the measured values to be recorded as FM-multiplex on magnetic tape

for subsequent processing. The reduction and analysis of the experimental data is accomplished by an Univac 1108

computer in the State Computing Center. The computer is

also accessible through a slow time-sharing terminal in

GATE

r

1L

L.J

MODEL ORK SHO

MANOEUViÑG BAS

I ¿0m

i'

O 10m

SID (2)

-UR1 UR2 SIR 24 bits

-'

SQR

24bitsF-DR i DR 2 DR3 0R4

LOGIC CONTROL UNIT

IXR

h-j XBR

2bits

_j D/tA converter YR LC U I YBR 12 bits I

D/A converter

I

6i

'V- LIMIT FOR Z - STEERING

0

SUMMATION _{SW ITCH} 6max 'V- 'Po Q - .4 COMPARATc* L FIG 3. MODEL MANEUVERING AUTOPILOT BLOCK DIAGRAM S IGN _SENSOR

I

RUDDER ANGI.E COU N T ER STEPPIN6 MOTOR

i..

I. LIMIT SWITCHES 4 PERIODIC STEERING

-FREQUENCY FREQUENCY SWITCH

DIRECTION SW ITCH

M ANUA L STEERING BY R,'

SINE AMPLITUDE

A

_J AMPL

r

SINE MEMORY SWITCH

i

BRM MEMORY CONTROL INITIAL MODE S

OFFSET DUR ATIO__

i CONTROL F R 0M RADIO CONTROL

Q-..

10Hz M1 12 BIT 'V MASTER s

LOW PASS FILTERS

-

('P) AID C ON VER TE R (Q) 'Vo ('ii)) CLOCK PROGRAM SELECTOR Tp p Kp SUMMATION

I

COMPAR ATOR