NSMB - Research Report

The Netherlands Ship Model Basin (NSMB) in

Wageningen and Ede is an independent foundation

working on a non-profit base. The objective of

NSMB is to perform scientific research in h y d r o

-mechanics, in particular with respect to marine

technology.

The N S M B was f o u n d e d in 1929 by the Dutch

Government and four large shipping c o m p a n i e s .

Work started in Wageningen in 1932. In the

beginning, the development of N S M B originated in a

large and increasing number of industrial orders for

the optimization of hull form and propulsion devices

by means of model tests in a deep-water basin. In its

endeavours towards providing a high scientific level

of industrial service, and in order to operate on an

independent base, N S M B has continuously looked

for new fields of specialized service to the s h i p

-building, shipping and offshore industries. These

specialized services are of such a nature that they

are often not carried out within these industries

themselves.

As a consequence of this philosophy, a continuous

development of special-purpose laboratories has

taken place, resulting in the building of cavitation

tunnels, the sea-keeping basin, the shallow water

basin, the high speed towing tank, the wave and

current basin, the de-pressurized towing tank and

the ship-manoeuvring simulator. This c o m p l e x of

laboratories required an investment of 60 million

Dutch guilders (not corrected for inflation).

At the present time (1979), the staff at N S M B

consists of about 400 persons, of w h o m 90 have

had a higher professional education.

The annual turnover of scientific industrial orders

amounts to about 30 million Dutch guilders, of which

approximately 60 per cent comes from a b r o a d .

The activities of NSMB can be broadly divided as

follows:

• ship powering (45%);

• ocean engineering ( 4 0 % ) ;

« ship handling ( 1 0 % ) ;

• computing services f o r t h e shipbuilding and

shipping industries ( 5 % ) .

W a g e n i n g e n

Netherlands Ship Model Basin (NSMB)

Head Office

Postal Address

Telephone

Cables

Haagsteeg 2, Wageningen

P.O. Box 28

6700 A A Wageningen,

The Netherlands

+ 8 3 7 0 - 1 9 1 4 0

Modeltank

Ship Powering

Work in tlie Sliip Powering Department of NSMB

comprises:

• model tests to determine the resistance and

propulsion in calm water;

• h y d r o d y n a m i c aspects for the design of hull forms,

hull a p p e n d a g e s and propulsion devices;

• the o c c u r r e n c e of cavitation on propulsion devices

and hull a p p e n d a g e s ;

• the detrimental effects associated with the

occurrence of cavitation, such as cavitation

erosion, vibration and noise;

• full scale measurements to check the validity of the

c o r r e s p o n d i n g model predictions.

iï'Etaiatöoni sff n««? tiiulll d^mgas

To evaluate the speed-power performance of a new hull design, NSMB carries out:

• resistance tests;

• self-propulsion tests with stock propellers;

Cavitation on a propeiier model • comparisons of the results of fitted behind a ship model in the these tests with those of Depressurized Towing Tank c o m p a r a b l e ships tested

Typical bow forms of present-day merchant ships: photographs of some 12-metre models tested in the Depressurized Towing Tank

previously;

• observations, by means of p h o t o g r a p h s and films, of the f o r m a t i o n of waves at various speeds of the m o d e l . Besides the s p e e d - p o w e r p e r f o r m a n c e of a new ship hull, optimization of the flow around the stern of the vessel is required to avoid serious flow separation which can be detrimental for the propeller. To this end NSMB carries out:

• flow visualization tests by means of a paint-smear technique, with and without operating propeiier; • flow visualization tests by means of wool-tufts attached to the hull, with and without operating propeller.

The above tests can be carried out in deep water as well as in shallow water.

Evaluation of hull appendage

designs

To optimize ttie design of hull appendages such as bilge keels, stabilizer fins, shaft bossings, shaft brackets, struts, sonar d o m e s , etc., NSMB carries out:

9 resistance tests to establish the

effects of appendages on resistance;

s self-propulsion tests to establish the effects of appendages on speed-power p e r f o r m a n c e ; • flow visualization tests to

establish the correct orientation and location of appendages for least resistance, with and without propeller;

• strut orientation tests by electronic flow-direction sensors, with and without operating propellers;

• strut orientation tests by means of swivel flags;

© cavitation observation tests on stabilizers, struts and other appendages to establish correct orientation of appendages; 8 measurement of forces acting on

appendages such as stabilizer fins to establish the zero-lift orientation.

Stern arrangement of a new minehunter for the French, Beigian and Netherlands Navies. fJlain and secondary propulsors were designed by NSMB. A

comprehensive series of model tests were carried out to determine the resistance, propulsion, cavitation, radiated noise and manoeuvring properties.

Propulsor-rudder configuration of a pushboat tested in the Shallow Water Laboratory

Arrangement drawing ot the laser-Doppier velocimeter used for the measurement of the wal<e field in the propeller plane behind a ship model, with or without the operating propeiler

Flow field measurement and

calculations: wake surveys for

propeller design

To obtain the required flow field information for a propeller design, NSMB oan carry out:

» wake field measurements at the location of the propeller by means of two-hole and five-hole Pitot tubes and a laser-Doppler velocimeter;

9 calculations of the possible scale

effect on the measured wake field;

• harmonic analyses of the wake field for facilitating the choice of the number of propeller blades.

2 stepping motors Mirror Beam Rotating Displacer Grating Laser

leller design

NSMB has well-developed capabilities to design conventional and unconventional propellers. Based on preliminary resistance and propulsion tests and wake surveys, various c o m p u t e r p r o g r a m m e s are adopted for the design and analyses of propellers and propeller performance, including off-design p e r f o r m a n c e .

Ship Powering

4578B

Models of three different aft bodies, designed for the same vessel, ready for testing in the Depressurized Towing Tank

Evaluation of propeller

designs

The s p e e d - p o w e r - r e v o l u t i o n relationship of a specific propeller design is ascertained by carrying out:

• o p e n water tests in n o n -cavitating a n d / o r -cavitating conditions;

• self-propulsion tests in w h i c h , if r e q u i r e d , cavitation is taken into account;

• measurement of thrust and t o r q u e in all 4 q u a d r a n t s in addition to standard open-water tests, to evaluate stopping and acceleration manoeuvres. These tests are carried out for both forward and astern speed and for f o r w a r d and astern propeller rotation.

Model of an azimuthing thruster

For the propellers of tugs, trawlers, pusher craft, etc. additional tests can be carried out such as: • overload tests to determine

propeller thrust and t o r q u e at various towing speeds; • bollard pull tests to determine

propeller thrust and t o r q u e at zero forward s p e e d .

For controllable pitch propellers, additional tests are carried out such as:

• measurement of the h y d r o -dynamic c o m p o n e n t of the spindle t o r q u e on one blade or for the complete propeller, with or without the effect of cavitation; • measurement of propeller thrust,

t o r q u e and spindle t o r q u e In 4 quadrants In addition to standard open-water tests, to evaluate crash astern, crash ahead and stopping manoeuvres, at various f o r w a r d and astern pitch settings;

• measurement of transient effects on propeller thrust and t o r q u e behind the hull or in open water while reversing or changing pitch settings.

To evaluate the p e r f o r m a n c e of azimuthing thrusters, N S M B carries out s o m e addltonal tests, viz.:

• thrust and t o r q u e measurements, and the measurement of the thrust provided by the nozzle in oblique flow (from 0 to 360 degrees) at various f o r w a r d speeds.

Model fitted with a stern paddle wheel during a propulsion test in the Shallow Water Laboratory

Models of overlapping propeller arrangement, twingondolar stern arrangement and nozzle propeller arrangement, tested in the Depressurized Towing Tank

Ship Powering

Influence of cavitation as

measured during propulsion tests in the Depressurized Towing Tank

at atmospheric ( )and scaled ( ) pressure

condition.

Evaluation of cavitation

performance of propsSisrs

To assess the cavitation

performance of a specific propeller design, NSMB can carry out: • cavitation observation tests In a

cavitation tunnel in which the axial c o m p o n e n t of the wake field can be simulated; • cavitation observation tests in a

cavitation tunnel in which all 3 c o m p o n e n t s of the wake field can be simulated by means of the d u m m y techniques; • cavitation observation tests in

which the propeller is tested behind a complete ship model In a vacuum towing tank, thereby facilitating the proper simulation of the wake field and propeller-hull interaction effects; • cavitation-inception

measurements to determine cavitation-inception ship speeds and to assess the f r e e d o m from pressure side, suction side, bubble and tip vortex cavitation; • thrust and torque measurements

for heavily cavitating propellers to determine the f r e e d o m f r o m thrust breakdown.

Assessment of level of

propelter-inelyeeiD] viE: •.öjieiïöng ïorjiwo

To determine wtietlier or not the proposed hull and propeller design will give rise to vibration of the ship structure, the vibration-exciting forces Induced by the propeller can be ascertained f r o m measurements. In more than 20 locations on the aft part of the hull, the pressure fluctuations can be measured and integrated over the hull surface to yield the 6

c o m p o n e n t s of the total excitation force.

In carrying out these tests at scaled pressure, the Important Influence of cavitation on the propeller is taken Into account.

These tests can be carried out for various ship draughts, ship speeds and propeller loadings.

Hull-pressure test Forward

Port _STBD

Looking from above

Grid on tiie aft body of a sfiip modeishowing the iocations where pressure signais are measured. By integration, the six components of the totai vibration-exciting force on the aft body are obtained

Assessment of

propeller-indueed shaft forces and

moimeiiiiio

A 6-component d y n a m o m e t e r for the measurement of dynamic shaft forces and m o m e n t s Induced by the propeller is available for measurement in cavitating and non-cavitating conditions. A c o m p u t e r p r o g r a m m e for the calculation of these forces and m o m e n t s Is also available.

Six-component dynamometer used for measurement of the fiuctuating forces and moments on a modei propeiier in cavitating or non-cavitating condition Driving shaft Driving belt Fly-wheel Pick-up -6 Measuring Channels -2 Puis Channels

Puis unit (Gurley) 2 Puis Amplifiers

Rotary Transformer

Ship Powering

Assessment of noise caused

by cavitating propellers

In certain cases it is necessary to ascertain the inboard and o u t b o a r d noise radiated by cavitating propellers. In particular, this is the case for ships and floating structures which have a dynamic positioning system based on an acoustic sensoring system, and for ships which use sonar e q u i p m e n t , e.g. naval vessels.

Cross-section of Depressurized Towing Tanl< sfiowing location of permanent hydrophone arrangement for measurement of noise radiated by cavitating propellers

To determine the acoustic signature of cavitating propellers, NSMB carries out the following tests:

• far-field noise measurements, adopting a series of stationary hydrophones below and abeam of the path of the m o d e l ; • near-field noise measurements,

adopting hydrophones which are flush-mounted In the hull of the model, or h y d r o p h o n e s which are attached to the model In some way, close to the cavitating propeller;

• acoustic source level measurements (for low frequencies), adopting the reciprocity principle which allows the transfer function between the propeller and the space inside the hull to be d e t e r m i n e d , using a reciprocal sound source located inside the hull and measuring the response at the location of the non-operating propeller. Measurement of the noise inside the hull due to the cavitating propeller, using the sound source as a receiver, leads to the determination of the acoustic source level of the propeller. Predictions of noise on full-scale are based on the results of the above-mentioned tests and derived scaling laws which have been extensively correlated with the results of full-scale noise measurements.

Arrangement adopted for the measurement of noise radiated from a cavitating azimuthing-thruster model in the Depressurized Towing Tank

Ocean Engineering

The activities of the Ocean Engineering Department

of N S M B cover:

0 model testing of ships, offshore structures and

mooring facilities in waves, wind and current;

• computation of wave-induced pressures and

overall forces and wave-induced motions for ships

and other fixed or floating bodies.

Testing of a spread mooring system

Sea-keeping

Sea-keeping investigations on ships comprise the study of: • ship motions;

• wave-induced loads on the hull;

9 local Impacts due to 'slamming';

• shipping of water;

» speed loss, either voluntary or involuntary;

9 optimization of anti-rolling

devices.

Sea-keeping tests are also carried out for towed barges, where the main Interest lies in the determination of sea-fastening positions and dimensions. For the design of fairways, both 'squat' and vertical motions in shallow water are of interest in order to determine under-keel clearance requirements. For sea-keeping studies, facilities for model experiments are available for regular and irregular wave conditions. Computer p r o g r a m m e s are also available.

Measurement oi wave-induced forces and moments on a modei of a fast cargo sfiip

Ocean Engineering

Fixed structures

Fixed structures are in use mainly in connection with the recovery of proven recoverable oil and gas reserves in both shallow and moderate w a t e r d e p t h s .

Jackets

S p a c e - f r a m e structures, made up of a c o m p o s i t i o n of tubular m e m b e r s , either as jackets 'piled' to the bottom or as gravity-type platforms, u p o n which the deck structure and 'topside facilities' are Installed.

Transport of a jacket on a barge Launching of a jacket from a barge

The following p r o b l e m s are studied at N S M B :

• effect of wave loads on the complete structure and on structural m e m b e r s , both under survival conditions and moderate sea states;

• transport f r o m construction yard to site. Model tests are

conducted to determine the required power of tugs and also wave loadings. If the structure Is towed on a barge, the barge motions are studied In order to determine the dimensions and positioning of sea-fastenings, either by model tests or by c o m p u t e r calculations; • launching f r o m a barge; • ' u p - e n d i n g ' , determination of the

o p t i m u m sequence for filling the ballast tanks. Stability during u p -ending. Determination of wave-induced motions (e.g. with respect to bottom clearance). Also, personnel who will be controlling such operations in reality are often trained in a laboratory, using a small-scale m o d e l .

Large-volume structures

The best-known examples are the large, concrete, gravity-type platforms. A typical representative of this class of structure consists of a large volume caisson standing on the s e a - b e d , on top of which a number of c o l u m n s are placed to support the deck structure. Tasks involved and associated problems studied at NSMB are typified below:

a wave-induced pressure distribution for structural analysis purposes; overall wave loads with respect to the stability of the structure; wave

deformation above the caisson for the determination of necessary air gaps between the deck structure and still-water level. These items are investigated both by means of model tests and by calculations (using the three-dimensional diffraction theory);

® most of the construction takes place in a more or less sheltered deepwater site (fjord or estuary), during which t i m e the g r o w i n g structure is kept afloat. Certain problems, such as t e m p o r a r y m o o r i n g , deck mating etc., may also require model testing; o transport to the installation site:

determination of towing power, wave motions (because bottom clearance may be a p r o b l e m underway), wave loads and accelerations for structural analysis purposes; 0 immersion of the structure,

stability, sequence of ballasting, influence of waves during i m m e r s i o n ;

• positioning during the final phase of i m m e r s i o n . The structure must be positioned by tugs within a close distance of the target 'landing' position. In Wageningen, real-time simulation is used to train tow masters who will be in c o m m a n d of such operation.

Measurement of wave loads on a concrete gravity-type platform

Experiments on the tow-out of a concrete gravity platform

Ocean Engineering

Semi-permanent fixed

structures: jack-up rigs

Tasks involved and p r o b l e m s studied include the following: • wave-loads on legs; • overall stability; • towing;

• t o u c h - d o w n (termed 'landing') when lowering the legs (of the j a c k - u p ) .

Compliant structures

These structures, while not completely f i x e d , have less than six degrees of f r e e d o m . Examples are the articulated c o l u m n s used as a production p l a t f o r m , flare structure or m o o r i n g tower and the tethered buoyant platform or tension-leg p l a t f o r m .

Tasks involved and associated problems studied at N S M B are: • wave loads, motions and forces

induced in universal joints and tension legs, both under survival and normal operating conditions; • towed t r a n s p o r t and installation

stages.

Floating structures

In the offshore industry, floating structures are generally used for such operations as transport, drilling, a c c o m m o d a t i o n of production facilities, storage and construction activities, such as derrick barges and pipelaying barges.

In the case of stationary floating structures, NSMB not only studies the environmental loads and induced motions under survival conditions but also under normal operating conditions, so as to determine the 'workability' of the structure.

Model tests provide the most c o m m o n tool for studying these items; theoretical methods of analysis are also available, such as:

• strip theory for ships or other slender bodies;

• three-dimensional diffraction theory for structures of an arbitrary shape;

• methods developed especially for s e m i - s u b m e r s i b l e structures.

Model of a tension leg platform in waves

In addition to wave loads and various motions, attention must be paid to the need for position-keeping:

• anchoring systems:

determination of loads applied to the chains;

• dynamic positioning systems: determination of low-frequency environmental loads needed for the design of D.P. systems, performance of t h r u s t e r s , etc.

Determination of tfie operational cfiaracteristlcs of a

Experiment on pipe-iaying Testing of a semi-submersibie driii rig in transit condition

In most cases, the activities carried out on a floating structure require that, in addition to possible anchor chains, other structural m e m b e r s are attached to the floating structure, these m e m b e r s being generally of a m o r e or less flexible character, as for instance with: • risers, connected to drillshlps or

drilling platforms;

» the stinger of a pipelaying barge, together with the pipe that is being laid.

Generally spealdng, c o m p l e t e systems are evaluated during model testing operations, including 'drillship-plus-riser and anchor systems' or 'lay-barge-plus-stlnger-plus-pipe' extending to the s e a - b e d .

During model tests, the elastic properties of such m e m b e r s are simulated to scale. Problems of interest here are motion behaviour and loads induced in the riser or pipe.

Mode/ of aspeciai-purpose vessei

for the construction of a storm-surge barrier

Ocean Engineering

Mooring facilities

Many special m o o r i n g facilities fiave been d e v e l o p e d for offshore loading and the discharging of oil or gas. The most c o m m o n system Is the single-point m o o r i n g (S.P.M.) for e x p o s e d locations; also jetties for sites operating under m o d e r a t e w/eather

conditions. Other systems, e.g. the 'spread m o o r i n g ' system, are also tested at N S M B .

Side-by-side mooring of a tanl<er to a singie buoy storage vessei

A tanl^er moored to a singie point mooring system

Single-point mooring systems

These systems are characterized by the fact that a ship is m o o r e d by means of a bow hawser or a rigid arm to a single m o o r i n g point. The m o o r i n g point c o m p r i s e s a buoy, connected to the sea-bed by means of a t e n s i o n e d anchor chain (single anchor leg m o o r i n g ) or by a n u m b e r of conventional anchor chains (catenary anchor leg mooring), or an articulated spar buoy. Usually, oil is transferred f r o m the wellhead on the sea-bed to the buoy by means of a flexible underwater hose and f r o m the buoy to the tanker by means of a floating hose.

Conditions involved and p r o b l e m s studied at N S M B are:

• for m o o r i n g systems under survival c o n d i t i o n s : motion behaviour of the buoy and underwater hose, loads on the anchor leg(s) or m e m b e r s of an articulated spar and loads on hoses;

• for normal operating conditions: motion behaviour of the m o o r e d ship under the influence of waves, wind and current, motion behaviour of the buoy and hoses, loads in the bow hawser (or rigid arm and its connections to buoy and ship) and loads on the anchor leg(s).

Underwater picture of

instrumented anchor chains and underwater hose system

Most experiments on S.P.M. systems are carried out in tlie unique wave and current basin, in which both current and irregular wave conditions can be generated at any angle of incidence and in which enough space is provided for the large horizontal motions of the moored vessel.

Various types of singie point mooring systems

Experimentai study on ttie reiative motions between a moored bull< carrier and a barge-mounted grain eievator

Jetties

These are f i x e d - m o o r i n g structures used in shallow waters under moderate wave conditions. The ship is m o o r e d against fenders or flexible 'breasting dolphins' by means of m o o r i n g lines, thus being rather restricted in its horizontal movements. With this method of mooring, 'weathervaning', as occurs with S.P.M. systems, is not possible.

Investigations at NSMB usually c o m p r i s e :

• motions of the m o o r e d ship and loads on fenders and mooring lines under various weather conditions;

® impact loads on the fenders during the berthing procedure. Model testing is the technique used most frequently at NSMB, although recently a c o m p u t e r simulation t e c h n i q u e has also become available for the theoretical p r e d i c t i o n of motion behaviour of the m o o r e d ship, fender and m o o r i n g line loads.

Ocean Engineering

Systems for ttie extraction of

energy from waves

Following the oil crisis, interest in the possibility of extracting energy from wave motions has increased considerably. Structures designed for this purpose need to be checked with regard to wave loads, mooring forces a n d , in particular, operating efficiency.

Ocean thermal energy

conversion (OTEC) systems

It is possible to make use of the temperature gradient in the ocean to generate energy. The main c o m p o n e n t s of such systems (of interest to hydrodynamicists) are a barge, a very long tube or hose hanging down f r o m the barge, and an anchoring or positioning system. The p r o b l e m s involved are very similar to those encountered in deepwater drilling (i.e. ship or barge motions, m o o r i n g , 'loads on' and 'behaviour o f the riser).

Testing of a model of a multi-purpose semi-submersible cutter suction dredger

New developments

In addition to the search for h y d r o c a r b o n s and their c o m m e r c i a l exploitation, other activities are currently being developed In the o c e a n . It Is expected that these will be of growing i m p o r t a n c e in the future. The structures used for these activities and the p r o b l e m s involved are generally quite similar to those previously discussed In relation to the offshore oil and gas industry.

S o m e e x a m p l e s of such activities, the p r o b l e m s involved and the investigations that can be carried out by N S M B are given below:

Offshore dredging

The d r e d g i n g of hard soil and rock in exposed locations, an operation which requires special e q u i p m e n t having g o o d motion behaviour. Special d r e d g e r s e m p l o y i n g jack-up or s e m i - s u b m e r s i b l e concepts are currently being developed for this purpose.

Offshore plants

Offshore power plants, chemical plants or gas liquefaction plants are no longer in the realms of science fiction.

Such plants are usually mounted on moored floating structures. In addition to studying the usual problems, special attention must be paid to acceleration effects on the structure, which may induce undesirable loads on machinery components. Mooring of ships to the barge may be a necessity from time to time, thus raising the p r o b l e m of the interaction of two adjacent floating bodies.

Deep-sea mining

At the moment, five major international consortia are preparing operations to harvest the large amounts of manganese nodules lying on the ocean bed. Several systems for such deep-sea mining are being developed, but ali have the following c o m p o n e n t s in c o m m o n : a ship and an apparatus on the sea-bed which collects the nodules and is coupled to a flexible riser or continuous bucket system in order to bring the nodules to the ship on the surface.

The p r o b l e m s involved are not new in themselves, but they are still extremely difficult to solve because of the t r e m e n d o u s waterdepths involved, which average about 5,000 meters.

Ship Handling

The Ship Handling Department of NSMB provides

the following services:

o model tests on the manoeuvring characteristics of

ships;

• real-time simulation for the evaluation of nautical

aspects of fairways and harbours, and for training;

0 full-scale observations of ship manoeuvres.

Very large crude carrier passing througii tiie Suez Canal

Standard manoeuvi-ing trials

In order to assess the

manoeuvrability characteristics of ships in waters that are

unrestricted in w i d t h , N S M B carries out tests using free-sailing ship models:

e zigzag manoeuvring tests;

• turning-circle tests; « s p i r a l / r e v e r s e d - s p i r a l tests; e b r o a c h i n g ;

• other f r e e - r u n n i n g manoeuvres in both calm and s t o r m y conditions, in deep or shallow water.

Free-running manoeuvring tests on a radio-controiied modei

Ship Handling

static and dynamic force

m s a s y r s m s n t a

In order to determine the data for a mathematical model of a

manoeuvring ship (which is used in simulation studies), NSMB carries out the following tests:

• static tests or oblique-towing tests, in order to determine the effect of s p e e d , drift angle, rudder angle and propeller revolutions;

• dynamic tests or planar motion m e c h a n i s m tests, in order to determine the influence of accelerations and angular motion.

Both static and dynamic force measurements are carried out in a correctly scaled waterdepth in order to include the effect of shallow water.

Force measurements are also carried out for the determination of disturbances due to:

• waves and current; • banks;

• passing ships;

• soft mud on the bottom of the fairway.

Real-time simulation ©f

man-steered ships

The behaviour of man-steered ships can be investigated using real-time manoeuvring simulators in Wageningen.

These simulators enable an evaluation to be made of the hydrodynamic properties of the ship and steering devices; also of navigational aids which affect the total manoeuvring behaviour of man-steered ships.

By using the two simulators in a 'coupled' fashion, ship encounters can be simulated in a realistic manner.

Determination of hydrodynamic effects occurring in an overtal<ing manoeuvre

Navigation bridge with outside view of the manoeuvring simuiator

Wavigaïioiial aspects of

•:i.nrEj)OHi'ü, Ht:5tj)rs.sas-:[i KSociyiHuici

!.md eanals

Using tine NSIVIB manoeuvring simulator, the navigational aspects of existing or projected harbour entrances, a p p r o a c h channels and canals can be evaluated. Also, It Is possible to establish the l<ind of weather conditions which are unsafe for a given ship in a particular fairway.

Simulated radar image, as presented in ttie wtieeitiouse ol the manoeuvring simulator

Training

In Wageningen, real-time simulation is used for:

8 training of mariners and pilots who are unfamiliar with certain ships, channels or navigational aids;

o practising of emergency p r o c e d u r e s ;

9 training of tow masters in the

manoeuvring of a fleet of tugs (in combination) as is the case when positioning offshore structures during installation operations.

Tow-out ot a large concrete offshore structure as studied and trained on the manoeuvring simulator

Additional Services

Computing services for the

shipbuilding and shipping

öndusÈraas

The c o m p u t e r p r o g r a m m e s of the Computer Service Department of NSIVIB can be divided into two categories:

• c o m p u t e r p r o g r a m m e s for design calculations concerning the ship, e.g. hydrostatic curves, transverse stability, tank capacity t a b l e s , etc.

• c o m p u t e r p r o g r a m m e s in which resuits are used for constructing the ship, e.g. fairing shiplines, developing shellplates, part p r o g r a m m i n g .

The calculations in the first g r o u p are mostly p e r f o r m e d with the Swedish S I K O B c o m p u t e r p r o g r a m m e . The calculations in the second g r o u p are p e r f o r m e d with c o m p u t e r p r o g r a m m e s developed at N S M B .

The results of these calculations are used in widely varying w o r k i n g methods in the s h i p b u i l d i n g industry, including handwork m e t h o d s and optical

implementation by numerically-controlled machines.

In executing these calculations, NSMB uses a c o m p u t e r of the type CYBER 175 of CDC which can be connected to a n u m b e r of terminals. Two numerically-controlled draughting machines are available for checking the input data and for delivering the results in the f o r m of drawings at any desired scale.

Strength and vibration

N S M B can assist in solving specific strength and vibration p r o b l e m s on board ships and floating structures.

s t r e n g t h analyses for vessels operating under severe conditions are dealt wilh, using NASTRAN with special developed pre- and post-processing p r o g r a m m e s . The static and dynamic loads are determined by means of the wave-diffraction theory or strip theory and, if r e q u i r e d , model tests, in

Large numerically-controlled drawing table at NSMB

addition, strengtii calculations for specific parts of structures are p e r f o r m e d . An example is tniglily-s i « w e d propellertniglily-s f o r w h i o t i , by means of the lifting surface theory, the unsteady load distribution over the blade is determined as well as the reaction effects due to blade vibrations, such as added mass and d a m p i n g . In this way a realistic picture of the stress distribution over the blade is obtained, in which the vibrational response has properly been accounted for. Other vibration problems which can be dealt with are:

® the vibrational response of the ship structure to propeller-generated dynamic excitation forces, so that the acceptability of a certain excitation system can be assessed on the basis of habitability criteria;

• the natural frequencies of local structures, such as the propeller shaft system, the deckhouse, etc., so that a proper detuning can be achieved.

Full-scale investigations

NSMB devotes close attention to the correlation between model results and the actual trial or service results obtained with the prototype.

Members of the staff of NSMB are therefore regularly assigned to attend sea trials on board the actual ships or offshore structures in order to conduct speed-power measurements, bollard pull tests, sea-keeping tests, manoeuvring and handling tests, etc., and to

check the validity of the

corresponding model predictions. The feedback thus obtained is a basic condition for assuring the reliability of future projects. The results of the full-scale measurements carried out by NSMB are very often used to establish an independent j u d g m e n t of the fulfilment of contractual obligations between builders and owners, relating to speed, horsepower, c o n s u m p t i o n , etc. Such measurements are

Result of stress calculations for propeller blade using lifting surface theory for calculation of load and a finite element procedure for the resulting stresses

therefore regularly offered by NSMB as a routine industrial service. In many cases the assistance of N S M B personnel is agreed upon by the builder and the owner at the contract stage of a new project.

To obtain m o r e detailed information on the correlation of the dynamic aspects of propeller p e r f o r m a n c e , i.e. vibration and noise characteristics, several steps beyond the scope of ordinary trials have been i m p l e m e n t e d in recent years. The staff of N S M B is now also p r e p a r e d to carry out full-scale observations of the behaviour of cavitation phenomena with synchronous recordings of p r o p e l l e r - i n d u c e d hull pressure and shaft force vibrations, particularly for research purposes.

Cavitation on propeller observed on full scale

Installation of cavitation observation eguipment on full scale

Fadiitïes

The Netherlands Ship Model Basin has continuously

e x p a n d e d its facilities. A number of special-purpose

laboratories have been built to deal with specific

types of problem. N S M B ' s staff now has at its

disposal a range of facilities which can meet the

highest requirements of today's scientific and

technical research. A description of these facilities is

given on the following pages.

Layout of laboratories situated in Wageningen

The deep water basin is used for experiments with models of seagoing ships under idealized conditions.

Wind, waves and current are not simulated. For all practical purposes, the tanl< has an unlimited water depth and w i d t h . A large part of the testing is carried out for the determination of the o p t i m u m hull form from the resistance and propulsion points of view.

This basin has a length of 252 m, a width of 10.5 m and a depth of 5.5. m. In it. models of 6 to 9 m length are towed or run under self-propelled conditions.

The towing carriage has a

m a x i m u m speed of about 9 m/sec. During the self-propulsion tests, the speed of the carriage is adjusted to compensate for any difference between model and carriage speeds.

Deep Water Towing Tani<

Resistance test in Deep Water Towing Tanlf

The towing carriage is e q u i p p e d with an electric servo mechanism to provide a constant s p e e d , if desired.

The measuring e q u i p m e n t on the carriage includes a resistance dynamometer and a guiding apparatus to keep the model on Its right course while allowing it to trim freely.

Specialized e q u i p m e n t has been developed for various types of test. Underwater television and film cameras, fixed to the towing carriage, are used for observation of the flow over the hull and appendages of models. The carriage is e q u i p p e d with electronic e q u i p m e n t for data collection a n d reduction.

Ship models are generally m a d e of paraffin wax or w o o d . Glass-reinforced polyester models are also used. A p p e n d a g e s such as rudders, bossings, shaft brackets and bilge keels are usually made of wood or metal or of a transparant material such as perspex. Propeller models are m a d e of either bronze or a l u m i n i u m , depending o n the type of tests to which they are to be s u b j e c t e d . A numerically-controlled milling machine is used for finishing the propeller castings and also for milling the wax propeller models used in the casting process. The propeller blade edges are c h e c k e d by means of a specially designed microscope.

The deep water basin came into operation in 1932. It was lengthened to its present-day measurements in 1951.

i l 4 l U

Flow-visuaiization test in Deep Water Towing Tani< witti running propeiier

Facilities

Cavitation Tunnels

Large cavitation tunnel

The large cavitation tunnel is mainly used for studying the cavitation properties of propulsion devices. A m o n g the n o n

-conventional p r o p u l s i o n devices which have been tested are ducted propellers, vertical axis propellers, overlapping propellers and supercavitating propellers. The flow at the location of the propeller behind the ship can be simulated in a simplified way by testing in oblique flow (realized by inclining the propeller shaft) or by building into the test section an a p p r o p r i a t e d u m m y model of the ship's afterbody. Tests with hydrofoils, stabilizer fins and t w o - d i m e n s i o n a l propeller blade sections have also been p e r f o r m e d .

The tunnel has a test section of 0.9 X 0.9 m and is suitable for propeller models with a m a x i m u m diameter of 0.45 m. The m a x i m u m water speed in the test section is about 11 m/sec, the flow being uniform. The m a x i m u m power a b s o r b e d by the impeller is 300 h.p., and by the propeller model 250 h.p. The m a x i m u m rotative speed of the propeller model is 3200 r.p.m.

The thrust and t o r q u e of the propeller model are measured by means of strain gauge

d y n a m o m e t e r s . The m i n i m u m obtainable cavitation n u m b e r is about 0.2. Cavitation p h e n o m e n a are observed by means of stroboscopic ligthning.

Equipment for measuring the lift, drag and pressure distributions on such profiles, in cavitating and non-cavitating condition, is available.

Equipment is also available to measure the hydrodynamic blade spindle t o r q u e of controllable pitch propeller models, with or without ventilation.

The large cavitation tunnel came into operation in 1941 and was completely modernized in 1963.

Large Cavitation Tunnei

Test section of Large Cavitation Tunnei

Cavitation tunnel with flow

ïfegiulaïor

The cavitation tunnei with flow regulator is suitable for propeller models with a m a x i m u m diameter of 0.25 m (the same model size as is used for self-propulsion tests in the deep water basin). This tunnei is provided with a flow regulator suitable for reproducing any arbitrary velocity field, as far as the axial c o m p o n e n t is concerned. Besides the normal cavitation observation tests, endurance tests to reproduce cavitation-erosion p h e n o m e n a on propellers and rudders are also performed in this tunnel.

The m a x i m u m r.p.m. of the propeller model is 3500, the m a x i m u m t o r q u e 4 l<gm, the m a x i m u m thrust 100 kg and the average speed in the test section 4.5 m/sec with the fiow regulator in operation. The m i n i m u m cavitation number in this condition is about 1.2, which is sufficiently low for research on propellers of merchant ships. The m a x i m u m power absorbed by the propeller model is 13.5 h.p.

This type of cavitation tunnel was added to the test facilities in 1956.

IVlodei of starboard part of ship aft body in test section of Large Cavitation Tunnel for simulation of wake field

Migli-apeed c f w i t a t i o n tyiimel

In the high-speed cavitation tunnel fundamental studies can be made of incipient and desinient cavitation on simple bodies, such as

hemispherical nosed bodies and two-dimensional foils. These studies provide information for a better understanding of the phenomenon of cavitation.

Cavitation erosion test using soft aiuminium test pieces imbedded in modei propeiier

m

Holographic reconstruction showing separated boundary layer around foil section in High-Speed Cavitation Tunnei (top

photograph). In decreasing pressure, cavitation occurred as shown in bottom photograph, also a holographic reconstruction.

The m a x i m u m tunnel pressure and the m a x i m u m speed in the test section are 35 bars and 65 m/sec respectively. Due to the small volume of the tunnel loop, the tunnel is suitable for tests with liquids other than water. Tests have been m a d e to study the influence on cavitation of high molecular weight polymer solutions in water. Degradation of the polymer solutions d u e to shear stresses are measured with a turbulent-flow rheometer.

The tunnel is also e q u i p p e d with a substitute rectangular test section suitable for carrying out tests with profiles.

The high-speed cavitation tunnel came into operation in 1965.

Facilities

Sea-Keeping Basin

This basin is suitable for sea-l<eeping tests on self-propelled ship models, for measurements of a d d e d resistance, motions in waves, wave loads and s l a m m i n g , and for tests on offshore

structures, e.g. s e m i - s u b m e r s i b l e platforms, drillships, pipelaying barges and m o o r i n g systems in deep water. These tests are usually carried out in waves and w i n d , while current can be simulated by towing the c o m p l e t e test set-up at a low s p e e d .

This basin has a length of 100 m and a width of 24 m. The

waterdepth a m o u n t s to 2.5 m. For sea-keeping tests, models of about 3.5 m are used and for tests on offshore structures a scale of 1 : 60 is usual.

In this basin, oblique waves of regular or irregular type can be created by means of a snake-type wavemaker consisting of 158 wave making units (flaps), placed side by side along two adjacent sides of the basin. By setting the a m p l i t u d e of each oscillating unit, the wave height can be varied. The frequency controls the wave lengths, while the phase difference between the motion of the flaps determines the angle of the waves (between 0 and 90 degrees). Irregular waves are generated by continuously varying the frequency of the wavemaker. The m a x i m u m height of regular waves is 0.30 m, the m a x i m u m significant height of irregular waves 0.25 m.

Tests witli semi-submersible crane barge in the Seakeeping Basin (by courtesy of Heerema Engineering Services N. V.)

Wave d a m p i n g beaches, installed along the basin walls opposite the wave generators, prevent reflection of the waves.

Wind can be generated by means of portable fans.

The towing carriage can attain speeds up to 3 m/sec and is equipped with a c o m p u t e r for data collection.

Ali measured signals are recorded on digital tape.

A preliminary analysis can be carried out on the towing carriage, while the final evaluation is carried out on the large CDC Cyber c o m p u t e r in the N S M B computer department.

The sea-keeping basin came into operation in 1956.

IVlodei of a small bulk carrier in waves

Tests on the towing of a single anchor leg mooring system

Basin

Preparing a iVIississippi barge fleet for testing in the Shallow Water Basin

Free-running manoeuvring test in following waives

In the past, many tests on the resistance and propulsion of vessels for inland w/aterways, e.g. for push boats and barge fleets for the Misissippi, Congo and Rhine river systems, have been carried out in the shallow water basin. The basin is also used mainly to study the manoeuvring of large ships in restricted waters, ship motions due to waves in shallow water, and the behaviour of offshore structures and mooring facilities.

This basin has a length of 210 m and is 15.75 m wide. The waterdepth is adjustable between zero and 1.2 m.

Regular and irregular waves can be generated longitudinally in the basin by means of a flap-type wavemal<er of a design, similar to that In the sea-keeping basin. The large towing carriage, which can attain speeds up to 3 m/sec, accommodates the measuring equipment.

In the field of manoeuvring, the laboratory is suitable for tests with free-sailing ship models (e.g. zigzag manoeuvring trials) as well as for experiments to determine the coefficients of mathematical models for manoeuvring ships. These measurements comprise static force measurements (oblique towing tests), dynamic force measurements by means of a planar motion mechanism and the measurement of disturbances due to banks, passing ships, etc. The mathematical models resulting from these

measurements can be used to predict standard manoeuvres on a computer or to describe the ship's behaviour on a real-time

manoeuvring simulator.

The shallow water basin came into operation in 1958.

Tests on the towing ola large deck structure on a barge in the Shallow Water Basin

Facilities

High-Speed Towing

Tank

This basin was built primarily for testing high-speed craft and propulsion devices. Because of the wave-mal<ing capabilities, however, the high-speed towing tani< is also used for testing offshore structures and m o o r i n g systems. In particular, many test p r o g r a m m e s have been carried out on the t o w i n g , launching and up-ending of steel template structures (jacl<ets). Such p r o g r a m m e s often c o m p r i s e the training of divers, who in reality have to control the ballasting during the installation p r o c e d u r e of platforms.

The high-speed basin is 220 m long, 4 m w i d e and has a

waterdepth of 3.60 m. At the end of the basin, a d o u b l e - f l a p type hydraulic wavemal<er is installed for the generation of regular and irregular waves. The m a x i m u m significant wave height is 0.40 m.

The basin is e q u i p p e d with two towing carriages. No. 1 carriage is of the conventional type and has an operational speed of 15 m/sec. The carriage is e q u i p p e d with electronic e q u i p m e n t for data collection and recording. No. 2 carriage is of a special type. It has the shape and construction of an airfoil, oriented so as to produce a lift force vertically d o w n w a r d s . This carriage is u n m a n n e d and is launched by a booster which projects a pneumatically-driven high-speed water jet against a vane on the carriage. During the measuring phase, the speed is l^ept constant by a pneumatically-driven water rocket on the carriage. A special braking system affords a very rapid deceleration of the carriage, allowing sufficient time for measuring. The carriage has a m a x i m u m speed of 40 m/sec and is especially designed for testing models of torpedoes, hydrofoils and high-speed propulsion systems.

The high-speed towing tank came into operation in 1965.

High Speed Towing Tanl< with airfoil carriage

Testing of a planing hull in the High Speed Towing Tank

B a s i n

Mooring tests occupy an important position among the worl< carried out in the wave and current basin. These are carried out with ship models up to 6 m length, m o o r e d by means of non-linear bow hawsers to single point mooring systems such as towers or buoys of special design.

These tests are normally conducted in irregular waves and with current. Forces in buoy anchor chains, underwater hoses, bow hawsers and structural members of the buoy system are measured. Motions of the ship and buoy models are measured by means of a photoelectric tracking system. Other types of m o o r i n g systems (e.g. jetties) and also drillijig rigs, pipelaying barges, dredgers, etc. are also tested. This laboratory consists of a rectangular basin with a length of 60 m and a width of 40 m. The waterdepth can be varied between Oand 1.20 m. In the centre of the basin, a waterdepth of over 3.5 m is available locally. One of the short sides of the basin is separated from a 10 X 14 m 'preparation' basin by means of a watertight gate. In the main basin, current can be generated parallel to the short sides, in opposite directions, by 3 p u m p s , each driven by a 75 h.p. D.C. motor. The total p u m p capacity is of the order of 15 m ^ / s e c , which means that, at a model scale of 50, current velocities of 3.5 knots for a

waterdepth of 50 m and 7 knots for a depth of 25 m can be simulated. Waves can be generated from one short side and one longer side of the basin by means of snake-type wave generators, enabling the generation of waves with an arbitrary direction of propagation with respect to the current direction. Regular waves of every realistic height with respect to the waterdepth can be simulated for periods between 0.8 sec and 3 sec. By changing the speed of the wave generator at a constant stroke, irregular wave trains having a prescribed energy spectrum can be generated.

At the sides of the basin opposite the wave generators, the waves are d a m p e d out by beaches, which are adjustable in height and slope in order to attain m i n i m u m wave reflection at a given waterdepth. Wind is generated by means of a battery of portable fans. With respect to the simulation of waves, wind and current, nearly every condition at a particular

offshore location can be simulated in the wave and current basin at scales of between 1 : 40 and 1 : 80. Experiments are also conducted to determine the mean and slowly varying force and m o m e n t on a vessel that has to be moored or dynamically-positioned in waves, current and w i n d . Spiral and turning circle tests to j u d g e the course and turning ability of a ship can also be p e r f o r m e d . The influence of various rudder arrangements on these

Wave and Current Basin witii experimentai arrangement for tests on a modei of a tanlier moored to a jetty

characteristics can be studied. During these tests, the model is accelerated by a carriage running over a 60 m long monorail. When the model has reached its point of self-propulsion, the carriage releases the model and the rudder turns to the desired angle. During the manoeuvre, the course angle, rate of change of heading and path of the model are m e a s u r e d , the first two by means of gyros and the latter by means of an automatic laser tracking device coupled to an X-Y plotter. The results of these tests are also used as input for the manoeuvring simulator.

The wave and current basin came into operation in 1965.

Test arrangement in the Wave and Current Basin

Facilities

yanoeuvïing

Simulators

The manoeuvring simulators are used to investigate the behaviour of manually controlled ships; for a c o m p a r i s o n of ship types, navigational aids, different displays of information, etc.; to evaluate nautical aspects of harbours and a p p r o a c h channels; and for training of ship's masters, pilots and tow masters.

The main simulator consists of a wheelhouse, an acclimatization r o o m , a ship's corridor, a visual display and a c o m p u t e r . The wheelhouse has a width of 6 m, a depth of 4 m and a height of 2.15 m.

All r o u n d , except for a part of the after b u l k h e a d , are slanted windows. The wheelhouse is built and e q u i p p e d like that of a large ship.

In the front part of the wheelhouse are m o u n t e d an instrument console, a steering wheel, an e n g i n e r o o m telegraph (which can be adapted to single and twin engine arrangements), remote engine control, bridge control, an automatic course control system, repeater c o m p a s s , rudder angle indicator, two r.p.m. indicators, log, wind velocity and wind direction meters, echo s o u n d e r and an i n t e r c o m . A Redifon radar simulator, having all the

advantages of s h i p b o r n e radar (true m o t i o n , anticollision etc.) is also installed.

In the centre of the wheelhouse are situated a chart table and a Decca Navigator.

The position of the various instruments can be c h a n g e d if desired.

The acclimatization r o o m is used to make a gradual change over f r o m full daylight to the 'daylight' of the simulator, and for discussions during test p r o g r a m m e s . A cylindrical screen with a diameter of 20 m and a height of 9 m is situated a r o u n d the wheelhquse. On this the environment is displayed.

The horizon, sea, sky, harbour entrance, buoys, and other ships are projected on the screen by means of the visual display. This device consists of a point-light-source projector, a compact arc lamp with a high light intensity and a very small filament, and an object which represents the harbour entrance, coastline, ship or buoy. The object appears as a shadow on the screen. A p p r o a c h i n g the coast, one perceives a growing shadow on the coast. This is realized by moving the object, representing the coast, towards the lamp.

A displacement of the ship along the coast is perceived e.g. by variation in the distance between two towers of a leading line. This is accomplished by rotating the object around a vertical axis. A change in course is achieved by moving the object around the lamp.

Every instruction f r o m the wheelhouse is converted into a voltage analogue, which is fed to the computer. This c o m p u t e r is e q u i p p e d with a mathematical model of the ship, together with the mathematical model of wind forces, current forces, tug forces, etc. The influence of shallow water and fairway boundaries are also included. The c o m p u t e r calculates the motion of the ship and the readings of the bridge instruments in a realistic way in accordance with the instructions received.

Drawing of the f\Aanoeuvring Simuiator with two wheeihouses, of which the upper one has an outside visuai display system

The second simulator consists of a wheelhouse with equipment similar to that of the main simulator, but without projection system for outside view. The simulators can be operated simultaneously, independently or coupled. In the latter case, interaction processes between two ships can be studied.

The experiments can be directed and followed in the control r o o m , where repeaters of all bridge indicators and recording facilities are installed.

The manoeuvring simulator came into operation in 1971.

Control room

Facilities

Depressurized

Towing Tank

The depressurized towing tanl< is used for e x p e r i m e n t s with m o d e l s of seagoing ships under idealized conditions. This means that w i n d , waves and current are not simulated in the basin. The u n i q u e feature is that the a t m o s p h e r i c pressure can be scaled d o w n . The dimensions of the model a n d the tank are such that the results of the tests may be c o n s i d e r e d to be applicable for ships sailing in water with unlimited depth and w i d t h . Model tests for the prediction of the p e r f o r m a n c e of full-sized ships are carried out. An i m p r o v e m e n t in the reliability of the prediction is obtained due to the fact that m u c h larger models (up to 12 metres In length) can be used, and that then the effect of cavitation on the propeller thrust and t o r q u e a n d on the interaction effects between screw and ship are taken into account.

Intermediate stage in the

manufacture of a 12-metre model of a tanker for testing in the Depressurized Towing Tank

Ship model entering airlock of Depressurized Towing Tank

Model tests are also p e r f o r m e d to determine the effect of different aft body shapes and

appendages, and of different propulsion devices and configurations of propulsion devices (controllable pitch propellers, ducted propellers, overlapping propellers, etc.) on the propulsion characteristics. The results of such tests can be greatly influenced by propeller cavitation. Observations of propeller cavitation are made in order to predict the anticipated degree of safety against cavitation damage.

Flow visualization tests are carried out to determine whether undesirable separation p h e n o m e n a occur at the bow or stern o t t h e m o d e l .

Wake surveys are m a d e to design w a k e - a d a p t e d propellers and to determine, in a more advanced way, the different c o m p o n e n t s of the ship's resistance.

Model tests are performed to determine the propeller-induced vibratory forces, including the effect of propeller cavitation. The vibratory forces acting on the propeller shaft are measured with a s i x - c o m p o n e n t strain gauge balance in the propeller shaft. The vibratory forces acting on the afterbody of the ship are measured by means of pressure pick-ups installed on the hull.

Tests are also carried out to determine the stresses in the blades of screw propellers. Besides these different types of investigations, this facility offers a means for acoustic research. The speed of the model at which propeller cavitation first occurs and the subsequent increase in the noise radiated by the propellers can be d e t e r m i n e d . The noise spectrum of the propellers can be measured.

Observation of bow wave during model test in the Depressurized Towing Tank

The depressurized towing tanl<, located in Ede, has a length of 240 m, a width of 18 m and a waterdepth of 8 m. The basin is constructed of special reinforced concrete. When the tank is evacuated, the upper portion (the roof) must resist a pressure difference of about 1 bar. The pressure in the tank can be lowered to 0.03 bar in about 8 hours. At this pressure, the actual conditions for cavitation on a model at a scale of 1 : 33 can be obtained.

Models of 12 m length, 2.40 m in width and 18 tons in weight can be tested.

During the tests, the ship model Is fitted to a towing carriage which can travel over the basin at speeds up to 4.6 m/sec.

The carriage is c o m p o s e d of cylindrical tubes of steel with a diameter of 2.5 m and is operated by a cable driving system. The towing carriage weighs about 80 tons. It is e q u i p p e d with a general-purpose model support bridge.

The carriage speed is remotely controlled by a CDC System 17 computer housed in an

airconditioned control room in the office building at the front of the tank. The general purpose instrumentation of the carriage is also housed in the control r o o m . The measuring equipment consists of signal conditioning e q u i p m e n t compatible with all types of transducers, and integral voltmeters, the signals from which are directly converted to the above-mentioned c o m p u t e r by means of a curtain cable. The observation of cavitation phenomena on the propeller model and of flow phenomena around the hull model can be performed through transparent parts of the hull of the model or through telescopes m o u n t e d underwater outside the model. These observations can be reproduced in the control r o o m by means of closed circuit television.

The construction of the carriage, the measuring e q u i p m e n t and the apparatus for transporting the model through a special lock in the basin and for fitting the model to the carriage are such that most of the tests can be p e r f o r m e d while maintaining the reduced pressure in the basin. Although the speed of the carriage and the model testing is completely remotely controlled, two or three men may be on board the carriage, in which normal atmospheric pressure is maintained. The carriage can be connected to a lock located at the front of the tank which makes It possible for personnel to enter or leave the carriage while the low pressure in the basin is maintained. Many precautions have been made to ensure the safety of personnel. The tank is fitted with a safety valve which enables it to be pressurized in a matter of minutes.

Model test in Depressurized Towing Tank

Cavitation on a propeller model litted betiind a ship model in the Depressurized Towing Tank

A new model shop has been built next to the basin. This is well e q u i p p e d for the construction of glass-reinforced p l a s t i c s h i p models up to 12 m in length. This material ensures operation under low pressure and has satisfactory strength. The propeller models are made at the w o r k s h o p in

Wageningen. Various appendages such as r u d d e r s , bossings, shaft brackets and propeller nozzles are also made at the w o r k s h o p in Wageningen.

The depressurized towing tank came into operation in 1972.

Facilities

List of Computer Programmes

Computer Centre

In 1961 N S M B installed its first c o m p u t e r s y s t e m , an Electrologica X - 1 . Design and p r o d u c t i o n p r o g r a m m e s for ttie s h i p b u i l d i n g industry were the first application area. As the results of these p r o g r a m m e s in many cases have to be represented graphically, N S M B quite soon started to use automated d r a w i n g e q u i p m e n t . In 1965 an A r i s t o m a t drawing table was installed.

Gradually a need developed for data processing in other areas. Statistical interpretation of laboratory r e c o r d i n g s and theoretical calculations by research w o r k e r s i m p o s e d new d e m a n d s on hardware and software alike. In 1976, a Control Data 3300 system, a m e d i u m s i z e d g e n e r a l -p u r -p o s e c o m -p u t e r , was -put into service.

Drawing capacity was e n h a n c e d by the installation of a Kongsberg MK 11-1215 drawing system in 1970, and the replacement of the Aristomat table by a K o n g s b e r g DC 300-1890 system in 1972. The 1970s s h o w e d a sharp increase in c o m p u t e r usage. The 3300 system was e n h a n c e d and had to be o p e r a t e d in two, eventually three, shifts. The application areas already mentioned d e m a n d e d m o r e resources, including c o m p u t i n g power, data storage facilities and various items of software. N S M B was able to secure most of these facilities in 1976 by entering into an arrangement with the Netherlands Energy Research Foundation (ECN) for the joint operation of a very large c o m p u t e r system. Because of a further increase in the w o r k l o a d , the processor of this system, a CDC 6600, was replaced by a CDC Cyber 175 in early 1978, making it the most powerful c o m p u t e r for technical calculations in the Netherlands.

A s u m m a r y of the computer programmes available

for calculation and design purposes is given below.

These are grouped in accordance with the principal

areas of application.

The jointly operated computer centre is physically located on the ECN site at Petten, 150 km f r o m Wageningen. At NSMB a powerful terminal concentrator, in the shape of a PDP 11/45 c o m p u t e r system, is connected to a dedicated 48,000 bits/sec data c o m m u n i c a t i o n link to Petten, providing the same i n p u t / o u t p u t facilities in

Wageningen as are available at the central site.

The configuration of the central c o m p u t e r system is characterized by a Control Data Cyber 175-216 processor {1.5 million floating point operations/sec); 20 peripheral processors; a 256 K words (60 bits) main memory; a 125 K words extended-core storage; and a variety of peripheral equipment.

Between Wageningen and Petten two c o m m u n i c a t i o n links are in use: a 48,000 bits/sec full duplex line for the normal batch operation; and a 2,400 bps half duplex line for backup purposes and for

interactive work.

Ship Powering

PRETEST P r o g r a m m e for the prediction of the resistance and propulsion properties of ships on model scale, including the calculation of scale effects on propeller characteristics, wake and resistance.

DESP P r o g r a m m e for the prediction of the resistance and propulsion properties of ships under trial conditions. (Can also be used for design purposes.) PRINTS P r o g r a m m e for the calculation of propeiier characteristics according to the Wageningen B-screw series. WAKE P r o g r a m m e for the prediction of the w a k e field on full

scale, using the model wake field as input.

HESM P r o g r a m m e for the calculation of the potential flow around a ship or other three-dimensional body. (Does not take into account free surface effects; adopts a m a x i m u m of 950 elements.)

PFLOW P r o g r a m m e for the calculation of the potential flow around a ship or other three-dimensional body. (Does not take into account free surface effects; use is made of a simplified theory.) BOLAPROG P r o g r a m m e for the calculation of t w o - and three-dimensional boundary layers. (Adopts a first order theory and an algebraic eddy-viscosity model.)

Configuration of WS/MB PDP 11/45 computer system with peripheral equipment