ARCHIEF
^' ^ ^ ' ^ ^ ^ P ^ ' * ® " ^ ' ^ " " * ' *T . . . 1 T t M Technische Hogeschool
International Jubilee Meeting
on the Occasion of the
40th Anniversary of the
Netherlands Ship Model Basin
August 30 - September 1, 1972
The NSMB - 40 years of scientific industrial service in marine
technoiogy
and
synopsis of papers
1972
Netherlands Ship Model Basin
Wageningen the Netherlands
Contents
Preface
D r R. J. H . Kruisinga, Secretary of State
The NSMB-40 years of scientific industrial service i n marine technology
Prof. Dr Ir J. D. van Manen
Contributions on some current problems of ship resistance
Prof. Dr L. Landweber
On wind resistance
Prof Dr Ing. K. Wieghardt
Recent developments i n marine propeller hydrodynamics
Dr Ir M. W. C. Oosterveld and Ir P. van Oossanen
35
36
Some developments i n the area of strength and
vibrations of ships 40
Dr E. Abrahamsen
Propeller vibratory shaft forces affected by design
and environmental conditions. 41
Prof. Dr Ir R. Wereldsma
Computer aided ship production, management and
control 41
Prof. E. G. Frankel
Design and operations 42
Ir J. Holtrop and Ir A. Koops
Cavitation and its detrimental effects
Ir J. H. J. van der Meulen
Applied mathematics in ship hydrodynamics
Prof. Dr R. Timman
36
37
Fish propulsion
Prof Th. Y. Wu
Maneuverability, State of the art
Prof. Dr S. Motora
38
Some recent advances in the prediction of ship motions
and ship resistance i n waves 38
Prof. Ir J. Gerritsma
Retrospection on 15 years NSMB seakeeping activities 39
M. F. van Sluijs and Ir S. G. Tan
Ocean Technology
Dr Ir J. P. Hooft
Preface
Though 40 years of existence do not classify the
N S M Bamong the oldest ship model basins,
the growth ofthe Wageningen laboratories and its capabihties for scientific industrial service
has been such that this anniversary may be celebrated with a feeling of pride and satisfaction.
The Netherlands Ship Model Basin has been a striking example of an independent, selfsupporting
research institute and, as such, has been of great importance to the national shipbuilding,
shipping and offshore activities.
Scope and size have grown beyond the national needs and represent a sound Dutch
contribution to international cooperation.
I consider it therefore a good idea to celebrate this anniversary together with many colleagues
from abroad and to issue this book with reviews of all speciahsms involved in the activities
of the N S M B .
The secretary of State,
Dr R. J. H . Kruisinga
The NSMB - 40 years of scientific industrial service in marine
technology
Prof. D r I r J. D . van Manen / President of the Netherlands Ship Model Basin, Wageningen
Introduction
This review aims to touch the atmosphere of scientific industrial research in marine technology as grown at the Netherlands Ship Model Basin under the management of Prof, ir L . Troost (1932-1952) and Prof, dr ir W. P. A . van Lammeren (1952-1972).
Froude's and Tideman's ship model basins i n the 19th century may be considered the first scientific industrial service centres in marine technology. Their activities were primarily restricted to the resistance and propulsion of ships, the oldest domain of marine research.
This lasted till around 1930, when 'towing tanks' ex-tended their investigations into tests i n waves to deter-mine hydrodynamic loads and ship hull excitation. Examples of the excellent level of marine technology research carried out i n the period 1930-1940 are presented in the German reviews 'Hydromechanische Probleme des Schiffsantriebs' [1], [2] and i n the pro-ceedings of the International Towing Tank Conference [3].
The post 'World War Il'-developments i n marine tech-nology have been i n some periods explosive. I n this paper the author would like to deal with the growth of the Netherlands Ship Model Basin as a representative ex-ample of the development i n scientific industrial service in marine technology.
The Netherlands Ship Model Basin is an independent foundation on a non-profit base. Its product is a scientific technical report for the shipbuilding and shipping in-dustry.
The style of management and the environmental condi-tion of zero to minimum subsidy has promoted a high scientific level and an industrial atmosphere, the combi-nation of which has been favourable for the development
of the NSMB.
New fields of industrial service have been found in specialized activities, gladly delegated by industry. Of the total activities of the model basin, about 25 % has been devoted to research to develop new fields for industrial service and to improve existing laboratory
techniques. This research was financed by the govern-ment, the industry and the foundation itself.
The complex of laboratories of the NSMB represents a value of 24 miUion Dutch guilders^ of which 17% has been granted by government and industry, 50 % has been paid f r o m the revenues obtained for industrial service and 33 % still remains as a bank loan.
The vacutank under construction required an additional investment of 32 million Dutch guilders, which capital was financed by banks under a government guarantee. The laboratory staff consists of 330 persons i n total, of which 65 have a higher professional education.
I n Table 1 a review is given of the existing facilities with their dimensions and capabilities.
I n the beginning the development of the NSMB originated in the large and increasing number of industrial orders i n the deep water towing tank. This burden of work led the management to consider it wise to design and construct special purpose laboratories to unload the daily pressure on the capacity of the deep water tank. This led to the building of the foUowing laboratories: the seakeeping laboratory (1956), the shallow water basin (1958) and the high speed basin (1965).
In order to meet the demand for advanced industrial service, additional facihties were built: the cavitation tunnel with non-uniform flow simulation (1956), the wave and current laboratory f o r offshore problems (1965), a computer centre for shipbuilding and shipping industry (1961), the manoeuvring simulator (1970) and finally the depressurized towing tank (vacutank) (1972).
The activities in these NSMB laboratories will be reviewed and illustrated i n the following sections.
Resistance and propulsion tests in the deep water basin Over 4000 ship models and propeflers have been tested in this facility.
^ not corrected for inflation. The value of the insured capi-tal is 33 million Dutch guilders.
Table 1 List of the various NSMB testing facilities
Name of facility Dimensions in metres Type of tests
1 Deep water basin 2a Large cavitation tunnel
252 X 10.5 X 5.5 0.9 X 0.9 (test section) 2b Cavitation tunnel with flow regulator 0.4 circular test section 2c High speed cavitation tunnel 0.04 circular test section 3 Computer centre (coc 3300 computer,
2 paper tape drawing machines) 4 Seakeeping laboratory
5 Shallow water basin
6 Wave and current laboratory
7 High speed towing tank 8 Manoeuvring simulator (hybrid computer)
9 Depressurized towing tank
100 X 24.5 X 2.5 216 X 15.75 X 1.25 (waterdepth is variable) 60 X 40 X 1.20 (waterdepth is variable) 220 X 4 X 4 240 X 18 X 8
Resistance, propulsion, vibratory forces, etc.
Cavitation tests with propellers, profiles etc., in various types of flows; fluctuating pressures on hull.
Cavitation tests with propellers in simulated axial wake. For fundamental cavitation study.
Hydrostatic, stability, trim, etc. calculations. Scale drawings for optical-following flame cutters. Design of ships, including economic calculations.
Ship motion measurements; necessary power increase to maintain speed; bottom and deck pressures; water shipment and screw racing; wave-induced shear forces, bending and torsional moments; measurements on semi-submersibles etc. All in regular and irregular waves. Resistance and propulsion in shallow water; squat and trim measurements; transverse forces, yawing moment and rudder torque on captive model; resistance and performance in waves; ship motions in regular and irregular waves; motions, mooring and anchorline forces of semi-submersibles or moored structures; oscillating tests; manoeuvring tests, etc.
Determination of feasibility of vessel configurations, with respect to waves, current and wind; motion and force measurements; spiral and turning circle tests; tests in harbour models, etc.
Testing planing hulls; high speed propulsion devices; ice breaking studies in simulated ice fields.
Training in ship handling; development of navigational aids; design of harbour entrances; development of criteria for manoeuvring, etc.
Resistance, propulsion and propeUer cavitation tests; flow visualization tests; wave breaking phenomena at the bow; wake surveys; propeller-induced vibratory forces in shaft and on hull; acoustical measurements; etc.
Troost initiated a 'first results three weeks after receipt of the drawings'-service. Koning and Muntjewerf reahzed and maintained this approach of industrial service, which has been and still is an important base f o r the good rela-tion between laboratory and industry.
During the 40 years of existence of the deep water towing tank, important initiatives for research and development were taken. W i t h i n the scope of this review i t may be permitted to memorize the foUowing topics.
Van Lammeren derived f r o m Baker's results the Wage-ningen systematic screw series and plotted the results of the test series i n suitable diagrams [4] for industrial appli-cations. I n the course o f t h e years, these Wageningen
screw series have been continuously extended. I n Table 2 the available series are given. Oosterveld developed a 'cross-fairing' program for the computer and recently all available Wageningen screw data were computer-faired with respect to the advance coefficient, pitch ratio, blade area ratio and blade number. A n improved Lerbs equiva-lent radius method was used to include the effect of Reynolds number [5], [6]. The 'four quadrant' character-istics of the B4-70 screw series and the corresponding Fourier series approximation is given i n Fig. 1. A contribution to the research into the scale effect i n the propulsion components was given by Van Lammeren i n studies of the Simon Bolivar and Victory
geosim-Table 2 B L A D E NUMBER Z B L A D E A R E A R A T I O A^JAq 2 j, 0 3 O.C.5 O.uu 4 0 . 4 0 0 5 5 0 . 7 0 Q 0 5 1.00 5 0 . < 1 5 Q 6 0 0 7 5 1 . 0 5 6 0 . 5 0 0.6 5 o.ao 7 0 5 5 0 . 7 0 O 0 5 T H R U S T C O E F F I C I E N T Kj K j - f ( Z , A E / A Q , P / D , a , R n o, 7 5 R ' l< T= l I I I "^iiHI 2 ' < A E / A O > ' ( P/ D j ^ o ' 1=0 k=o J=o 1 = 0 W H E R E C i j n i = l ( R n o, 5 R ) T O R Q U E C O E F F I C I E N T K Q K Q = f ( Z , A E / A Q , P / D , J , R n o 7 5 R ) K Q - I I i z C i j u i z i ( A E : / A o) ' ( P / D) ' * 3 l 1 = 0 k=o j=o 1 = 0 W H E R E C ' i j | , | = f ( R n o 7 5 f , ) E F F I C I E N C Y I p 2TtKQ Z = N U M B E R O F B L A D E S A E : / A O = B L A D E A R E A R A T I O p/ D = P I T C H / D I A M E T E R R A T I O J = C O E F F I C I E N T O F A D V A N C E Rn|-,y5f,= R E Y N O L D S N U M B E R B A S E D O N B L A D E S E C T I O N C H O R D L E N G T H A T 0 . 7 5 R
series [7], [8], [9]. The 22 meter modelboat ' D . C. Endert' (Victory ship, scale 1:6) dehvered basic and sometimes controversial data f o r 'extrapolator'-specialists. Basic, regarding the scale effect i n the wake factor, see Fig. 2, controversial, regarding the scale effect i n the thrust deduction factor.
Lap analyzed both geosim series and proved empirically the vahdity of his log A-method for all practical purposes. By introducing a f o r m factor A log A a 'ship f o r m frictional drag' curve could be derived f r o m a 'flat plate' curve [10], see Fig. 3.
Another contribution of Lap was his analysis of avail-able NSMB resistance test data. His dimension analysis of ship f o r m parameters led to instructive diagrams for the determination of ship resistance [11]. The introduction of the computer in the field of data reduction led Van Oortmerssen to evaluate polynomials for available re-sistance data [12], see Fig. 4.
In the field of wave resistance theory Timman, Vossers and Joossen complemented the 'thin ship' theory (Have-lock, Weinblum, Wigley) with the slender body theory. Van Manen introduced the screw-nozzle system as one undividable propulsion unit and produced design dia-grams for this unconventional propeller type [13], [14]. These test data solved many design problems and formed a start f o r the application of ducted propellers to larger
ships. Besides, an impulse was given to the development of ducted-screw theories.
Recently Oosterveld [15] introduced the non-axisym-metrical wake adapted nozzle. Reductions in required shaft horse power of 5 to 12% have been obtained i n the application of the ducted screw to tanker models. I n the case of a restriction of the screw diameter or the screw weight, even higher reductions have been reached for large tankers.
The development of bulbous and cylindrical bows f o r ships with very high block coefficients has been favour-ably affected by systematic bow studies. Muntjewerf reported on the results of systematic investigations per-formed at the NSMB [16], [17], some of which are given in Figs. 5, 6 and 7.
Cavitation
The large cavitation tunnel of the NSMB, designed by Lerbs, was followed by a smaller cavitation tunnel with a flow regulator for wake-simulation. With this cavitation tunnel, the NSMB has gained a vast experience and ob-tained a large knowledge of propeUer cavitation pheno-mena in ship wakes. Developments in lifting line and lifting surface theory were in this way evaluated to obtain practical design knowledge. I t became possible to define criteria for the optimum selection of pitch angles and profile-camber f r o m the view-point of a required
RPM — relation and a miiumum risk of cavitation
damage.
A n example of the obtained knowledge and experience of cavitation phenomena i n a non-uniform wake is Van Manen's explanation of the bent trailing edges of screw blades and the indications as to how to prevent this cavitation damage [18]. The theoretical justification of this explanation was given by Van Wijngaarden [19]. Contributions to the fundamental aspects have been presented by Van der WaUe on the growth of nuclei and the related scaling factors i n cavitation inception [20] and by Van der Meulen on the significance of surface and stream nuclei [21] see Fig. 8 and on the characterization and determination of erosion resistance [22] Fig. 9. Van Oossanen reanalyzed Balhan's measurements on two-dimensional profiles i n cavitating and non-cavitating conditions [23]. This analysis can f o r m the basis f o r designing profiles and propellers, promising f r o m the view-point of vibrations and noise reduction [24]. A substantial support i n the understanding of the com-plex problem of the cavitating propeller i n a non-uni-f o r m non-uni-flow has been delivered by the theoretical studies based on lifting surface theory. Though a rigorous lifting
surface theory for ship screws i n a nonuniform flow i n -cluding cavitation phenomena has not yet been obtained, important progress is being achieved.
Sparenberg developed a sound lifting surface theory f o r ship screws i n a u n i f o r m flow [25]. Van Manen and Bakker gave numerical results based on that theory. Some of these results were controversial with results obtained by other theories and received scepticism. Sparenberg and Verbrugh extended the theory f o r non-u n i f o r m flows [26]. Knon-uiper reported on nnon-umerical resnon-ults of calculations comparable with other theories [27]. How-ever, as said before, the introduction of cavitation pheno-mena i n this theory is essential f o r a f r u i t f u l symbiosis between experimental investigations and theoretical computations.
Recently Van Manen presented the results of an investi-gation into the effect of cavitation on the pressure fluc-tuations at the stern excited by the propeUer. The increase of these pressure fluctuations on the ship's afterbody by propeller cavitation was f o u n d to be considerable [28], see Figs. 10 and 11. The discovery of these phenomena may be explanatory for the vibration casualties at the stern and wiU lead to new design criteria for the blade tips [29].
Vibratory forces induced by the propeller
Important progress i n our knowledge of the dynamic components of a propeUer i n a non-uniform wake was booked by Wereldsma [30], [31]. Wereldsma designed and realized a six component dynamometer f o r ship propellers. His greatest difificulty, the bad signal-noise ratio, was overcome by developing a samphng technique, based on the assumption that the frequencies of the force fluctuations are equal to the number of revolutions times the number of blades (blade frequency) or a multi-ple thereof.
Wereldsma also developed a propeUer exciter to evaluate the hydrodynamic mass, damping and the hydrodynamic couphng between thrust and torque vibrations. I n this way he was able to solve the coupled differential equa-tions of the screw-shaft-thrustblock system and to reach a good correlation between his predictions of the torque and thrust fluctuations based on model test data and the results of measurements on the f u l l size ship [32]. After this successful penetration into the dynamics of axial shaft behaviour Wereldsma and Hylarides started investigations into the field of transverse excitation of the afterbody and hydrodynamic induced pressure fluc-tuations at the stern. This research was carried out f o r conventional screw propellers, ducted propellers,
over-lapping propellers and contra-rotating propellers. Some results are given i n Figs. 12 and 13.
Hylarides introduced a finite element method, including the eff'ect of shear stresses and advanced the interpreta-tions of hydrodynamic mass, damping and coupling in hull vibration analysis [33]. A n example of the break down into finite elements is shown i n Fig. 14.
The stress analysis of propeller blades rotating i n a non-uniform flow based on the results of model and f u l l scale experiments is being complemented by a structural propeUer blade analysis by finite element technique. Perfection of this theoretical approach is still necessary as is also a reliable input, derived f r o m a rigorous lifting surface theory f o r non-uniform flow including cavitation phenomena.
Software preparation for computer-aided studies of ship-owner operations and shipyard production
When the NSMB introduced the computer into their hydro-mechanic research and for data reduction of model test results, a possibility for a new type of industrial service was b o r n : the software preparation for computer-aided studies of shipowner operations and for shipyard pro-duction.
After the realization of programs f o r the usual set of hydrostatic calculations more advanced mathematical studies were initiated.
Via the fairing of ship lines and hull plate development Bakker and Le Grand developed a Numerical Adapted Language f o r Shipbuilding (NALS) an integrated system of computer programs for ship calculations and shipyard production. A result is shown i n Figs. 15 and 16. Paper tape preparation was realized for a numerically con-trolled propeller model milling machine and for numeric-ally controlled drawing systems. The drawings and paper tapes are used f o r optical or numerically controlled flame cutters respectively.
Programs f o r the preliminary design of cargo sliips, bulkcarriers and coasters have also been developed. W i t h these design programs parametric studies and ship opera-tion simulaopera-tion can now be performed, see Figs. 17, 18 and 19. This has also been done f o r high speed boats with emphasis on the selection of the propulsion devices. Finally, sophisticated design studies such as the study of a restricted draft tanker and of special ship-type appli-cations as alternative links of various transport chains were carried out.
inte-grated ship design, inchiding an optimized liarbour depth [34].
The seakeeping laboratory
I n 1955 the NSMB decided to build a seakeeping labora-tory in which both oblique and irregular seas could be simulated.
Sogreah's wavemaker of the snake-type was the essence, around which this special purpose laboratory has been designed. A compromise between avoiding large scale effects i n the flow around the huh and to avoid high loads on the model hull was obtained by selecting model lengths between 3 and 4 m for the self propelled models. The first research in this laboratory was an extensive systematic investigation of the 60-series [35]. The effect of the main hull f o r m parameters on the behaviour i n a seaway could be determined.
Based on experience of dilferent types of tests i n the seakeeping laboratory and a large bibliographical know-ledge, Vossers wrote his reviewing book on the behaviour of ships in a seaway [36].
Swaan reported on the systematic test results of horizontal and vertical ship bending moments and torsional
moments in order to obtain design data [37].
Experimental slamming studies were endorsed by the theoretical studies of Verhagen [38].
The predictions made by Van Sluijs for deck wetness, derived f r o m model tests, showed a striking correlation with ftfll scale observations [39].
Broaching, speed loss and roll stabilization tests are other examples of research i n this seakeeping laboratory which improve the scope and Value of industrial service performed by the NSMB. Figs. 20, 21 and 22 indicate schematic constructions and realistic test results of various types of offshore projects.
Recently the type of investigations ordered by industry has been changing. Feasibility studies of non-convention-al design concepts i n irregular and oblique seas increase in number, e.g.:
- seagoing tugs with non-conventional tows as drilling rigs,
- air cushion boats, - tug and barge systems, - single point mooring systems,
- drihing rigs aird drilling ships for relati vely deep water.
High speed towing basüi
For the sake of completeness, the existence of a high speed basin with a cross section of 4 X 4 m^ and a length of 220 m, may be mentioned.
This facility is equipped with two carriages, one con-ventional up to 15 m/sec. and one unmanned, waterjet driven, up to 30 m/sec.
The unmanned carriage has been applied f o r tests with high speed propulsion devices such as water-air ramjets [40], struts and hydrofoils. The conventional carriage is used for planing hulls.
Moreover, this facility has been used for time consuming test programs so that other facihties such as the deep water towing tank and the seakeeping laboratory can be used more efficiently.
Complicated test arrangements requiring long assembly and calibration time can be examined i n this facility, which is not permanently applied for high speed work. Ice breaker studies i n simulated ice fields and the analysis of various types of swim strokes are other examples of miscellaneous experimental research carried out here. Shallow water basin
After the test program of the Rhine tanker 'Arabia' i t became clear that model tests carried out i n shallow water, simulated by an adjustable false bottom, lead to meaningless data. The NSMB therefore decided to build a shallow water basin with a width of 16 m, especially after obtaining the favourable results of a market analysis i n the Mississippi area. There turned out to be a large need for a special purpose laboratory for the investigation of push-towing. Fleets of barges of up to 32 units have been tested in integrated and semi-integrated tows. Optimiza-tion of the bow and stern f o r m of barge units and of afterbody configurations with 2, or even 3, ducted pro-pellers and flanking rudders have beeir shown to lead to high-quahty push-towing systems.
Lap analyzed the results of the Arabia geosims and o f the many industrially ordered test programs. His f o r m factor interpretation, a log A-shift of the flat plate curve i n the log Re-direction showed the best correlation between model test results and f u l l scale measurements i n shallow waters [41].
H o o f t contributed to our insight of critical wave pheno-mena i n shallow water [42].
W i t h growing activities i n the field of the offshore i n -dustry and with increase i n tanker size, the scope of work i n the shaflow water basin changed.
Single point mooring systems i n shallow water, drilling rigs i n shallow water, fundamental studies of forces on cylinders, underwater oil storages etc., introduced new possibilities i n test work.
A wavemaker had to be installed to meet the customers' requirements.
T r i m and squat measurements f o r tankers approaching restricted water had to be carried out with and without waves. Captive model tests had to be carried out to define the coefficients of the equation of motion i n a horizontal plane.
The high demand f o r the present-day type of industrial service i n marine technology, especially i n all problems around coasts and harbours, led to the design and con-struction of a wave and current laboratory.
The wave and current laboratory
This laboratory, see Fig. 23, described by Van Lammeren and Lap [43] has been designed especially for industrial projects. A basin of 40 x 60 m^ i n which irregular waves in all directions, currents and winds could be simulated was considered the ideal basin to investigate the feasi-bility of designs f o r drilhng, mooring, dikes, launching, improving harbours, transfer of cargo i n open sea f r o m a large tanker into a smaller one, mooring of container-ships at their terminals, etc.
After a period of very intensive industrial research in this wave and current laboratory, the companies active i n the field of offshore-technology hesitated. Many 'ad hoc', though promising designs had been carefully investigated, but did not lead to the expected results. Another ap-proach was obviously necessary.
H o o f t [44] provided for such an approach by dividing the complicated construction of drilling rigs, into ele-mentary units, of which he was able to determine the hydrodynamic properties. He neglected interaction effects and superimposed these units again to the complicated construction. The correlation between the prediction based on his 'superimposed unit system' and the f u l l scale results was very striking, see Fig. 24. The computer program evaluated f r o m this idea of the superposition of elementary units, is an adequate tool for selecting and qualifying preliminary designs of complicated drilling rig constructions. I n this way only the best of some design configurations can be tested and disappointments can be avoided.
W i t h respect to the manoeuvring of ships, different types of tests can be carried out as listed below.
- Determination of the effect of an increase i n RPM
combined with a rudder angle at low speed.
- Determination of the desirable width of a waterway (tests to include traffic simulation).
- Determination of the capacity of a bow thruster required f o r a special manoeuvre.
- Derivation of data f o r programming ship manoeuvres under various environmental conditions for application on a manoeuvring simulator.
I n all these types of manoeuvring tests i n the wave and current laboratory the ship's path is determined by a laser system [45].
The ship manoeuvring simulator
The NSMB ship manoeuvring simulator, see Fig. 25, con-sists of three essential parts [46], as hsted below.
- A wheelhouse and chartroom w i t h complete nautical instrumentation, see Fig. 26.
- A projection system consisting of a point light source, circular slides and silhouettes, and a circular projection screen.
- A hybrid computer which can be programmed for any ship type with the aid of model test results (the necessary tests are carried out i n the shallow water basin and wave and current laboratory), and f u l l scale ob-servations. This system offers the possibility to simulate ship manoeuvring on a f u l l scale time base. I n this way the human aspect i n manoeuvring can be taken into account. A n example of a ship manoeuvre is given i n Fig. 27.
After a one year experience on this manoeuvring simulator, the NSMB recognizes the following items f o r i n -dustrial service.
- Qualification of harbour designs w i t h known ships and experienced pilots.
- Qualification of advanced ship designs f r o m a view-point of ship handling and manoeuvring.
- Determination o f t h e ship handling possibilities of non-existing large ships (500.000-1.000.000 t.dw. tankers). - Design of traffic rules for waterways.
- Design of criteria to assist harbour authorities i n their decision to give permission to ships to enter the harbour under known circumstances.
- The introduction of new nautical instruments. - Training of pilots under non-experienced circum-stances.
These types of industrial services may be delivered to new circles of future customers. I t is clear that instruc-tion and guidance by NSMB specialists is very important
during the first acquaintances of new organizations inte-rested in the possibilities of this three-dimensional ship manoeuvring simulator. The staff consists of hydro-dynamic specialists, applied mathematicians and nautical experts.
The depressurized towing basin (vacutank)
External views of the vacutank of the NSMB i n Ede are given i n Figs. 28 and 29. The inside dimensions of the basin are as follows:
length 240 m width 18 m depth 8 m
When the tank is evacuated, the upper section or the roof must resist a pressure difference of about 1 atmos-phere. Therefore, the upper section has been engineered as a cylindrical shell constructed of reinforced concrete with a thickness of 60 cm. The pressure i n the tank can be lowered to 0.04 of an atmosphere in about 8 hours. Models of 12 metres in length, 2.40 metres in width and 18 tons i n weight can be tested.
During the tests, the ship model is fitted to a towing carriage which can operate oVer the basin at speeds up to 4 m/sec. A t a model scale of 33, this means that ships with speeds up to about 45 knots can be investigated. The carriage is composed of cylindrical tubes of steel with a diameter of 2.5 metres and is operated by a cable driving system. The towing carriage weighs about 80 tons. The interior of the basin with the carriage and the cable driving system is shown i n Fig. 30. The carriage is equipped with a general purpose model support bridge. The carriage speed is controlled by a C . D . C . 1700 com-puter housed i n an air-conditioned control room located i n the office building at the front of the tank. Two or three men may be on board of the carriage in which normal atmospheric pressure will be maintained. The carriage can be connected to a lock located at the front of the tank which makes i t possible f o r the personnel to enter or leave the carriage while the low pressure in the basin is maintained.
The general purpose instrumentation f o r the carriage is also housed i n the control room. The construction of the carriage, the measuring equipment and the apparatus f o r transporting the models through a special lock in the basin and f o r fitting the model to the carriage are made such that most of the tests can be performed while main-taining the reduced pressure in the basin. The measuring
equipment consists of a series of signal conditioning equipment compatible with all types of transducers and integral voltmeters of which the signals are directly con-verted to the C . D . C . 1700 computer in the control room by means of a curtain cable.
The observations of cavitation phenomena at the screw and of flow phenomena around the model is performed through transparent parts of the hull of the model and through telescopes mounted under water outside the model. These observations can be reproduced in the control room by ineans of closed circuit television. Although personnel may be on board of the carriage, the speed of the carriage and the model testing will be completely remotely controlled. To ensure the safety of the personnel on board of the carriage, many precautions have been made. The tank is fitted with a safety valve which makes i t possible to pressurize the tank in a few minutes.
A new model-shop has been built next to the basin. This shop is well-equipped f o r the construction of glass re-inforced plastic ship models up to a length of 12 m. This material ensures operations under reduced pressure and has satisfactory strength. The propeller models are made at the work-shop i n Wageningen. Most of the castings of the propeller models are finished by means of a numeric-aUy controlled milhng machine. Appendages such as rudders, bossings, shaft brackets and propeller nozzles are also made at the work-shops in Wageningen. The vacutank has been designed by Sogreah-Grenoble according to specifications i n close co-operation with the NSMB. The building was finished in July 1971 and the experimental phase was started in June 1972. A photo of the interior of the vacutank on nearing completion (September 1971) is given i n Fig. 31.
The vacutank is used f o r experiments with models of seagoing ships under idealized conditions. This means that in the basin no wind, no waves and no current are simulated. The dimensions of the model and the tank are such that the results of the tests may be considered to be applicable for ships in water of unlimited depth and width. The following types of investigations can be carried out:
- Model tests f o r the prediction of the performance of f u l l size ships. A n improvement in the reliability of the prediction is obtained due to the fact that now the effect of screw cavitation on propeller thrust and torque and on the interaction effects between screw and ship are taken into account.
after-body shapes and appendages and of different propulsion devices and configurations of propulsion devices (screws, ducted propellers, overlapping screw propellers etc.) on the propulsion characteristics. The results of such tests may be strongly influenced by propeller cavitation. - Model tests f o r the observation of propeller cavitation i n order to predict the expected degree of safety against cavitation damage.
- Flow visualization tests to determine whether un-desired separation phenomena occur at the bow or stern of the model. Standard towing tank test techniques, i n which the components of the frictional resistance and the wavemaking resistance are calculated separately, are not vahd f o r models that suffer f r o m extensive flow separa-tion. They are only suitable f o r predicting the drag of ships which experience httle separation drag. Here, tests can be performed to determine whether these unwanted phenomena take place.
- Tests to study the wave breaking phenomena at the bow o f t h e model. Recently another type of ship resist-ance, the so-called 'wave breaking resistance' has been reported to occur at very f u l l ships. This resistance can be significantly reduced or ehminated by a properly designed bow.
- Wake surveys f o r wake adapted propeUer design and to determine i n a more advanced way the different com-ponents o f t h e ship's resistance.
- Model tests to determine the propeUer induced vi-bratory forces including the effect of propeUer cavitation. The vibratory forces acting on the propeUer shaft are measured with a six component strain-gauge balance i n 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. Moreover, tests are also carried out to determine the stresses i n the blades of screw propellers.
Besides these different types of investigations, this fa-cihty offers a means f o r acoustical research. The speed of the model at which propeller cavitation first occurs and the subsequent increase i n the noise radiated by the screw propellers can be determined. Also, the noise spectrum of the screw propeUers can be measured. Such investi-gations are of the utmost importance i n order to qualify alternative designs of naval ships. The provisions which have to be made i n order to perform these acoustical measurements are i n study.
Final consideration
This is more or less i n a 'nutshell' the history and
devel-opment of a present-day industrial service institute for marine technology, the Netherlands Ship Model Basin. I n its strivings after a high scientific level of industrial service combined with relatively short delivery times and reasonable prices, an industrial service centre, which has to operate on an independent base, has to look con-tinuously f o r new fields of specialized service to the shipbuilding, shipping and offshore industry. Those specialized services must be of a nature making i t un-attractive or even impossible to perform them within the industry itself
Apart f r o m unique special purpose laboratories a very competent enthusiastic staff, continuously complemented with young talent is at least necessary f o r being success-f u l i n this success-fast growing technological world.
References
1 G. Kempf and E. Foerster. Hydromechanische Probleme des Schiffsantriebs; Tefl I . Selbstverlag der Gesellschaft der Freunde und Förderer der Hamburgische Schiff bau-Ver-suchsanstalt, e.V., Hamburg, 1932.
2 G. Kempf. Hydromechanische Probleme des Schiffs-antriebs; Teil I I . Verlag R. Oldenbourg, 1940.
3 Proceedings of the summer meetings of the 75th session and International Conference on Experimental Tank Work. Institution of Naval Aichitects, London, July 10 to 13, 1934; Trans. Inst. of Naval Arch., 1934.
4 W. P. A. van Lammeren. Resultaten van voortgezette systematische proeven met vrijvarende 4-bladige schroeven, type B4-40 en B4-55. Het Schip 19, no. 8 and no. 9, 1937; N S M B publication no. 38.
5 W. P. A. van Lammeren, J. D. van Manen and M . W. C. Oosterveld. The Wageningen B-Screw Series. Society of Naval
Architects and Marine Engineers; Vol. 77, 1969; N S M B
publication no. 330.
6 M . W. C. Oosterveld and P. van Oossanen. Further Computer Analyzed Data of the Wageningen B-Screw Series. To be published.
7 W. P. A. van Lammeren, J. D. van Manen and A. J. W. Lap. Scale Effect Experiments on Victory Ships and Models. Part I , Analysis of the resistance and thrust measurements on a model family and on the model boat D . C . E N D E R T J R .
iSP Vol. 3, no. 18, 1956; N S M B publication no. 121a. 8 J. D. van Manen and A. J. W. Lap. Scale Effect Experi-ments on Victory Ships and Models. Part I I , Analysis of the wake measurements on a model family and the model boat D . c. E N D E R T J R . I S P Vol. 5, U O . 47, 1958; N S M B publication no. 147.
9 A. J. W. Lap and J. D. van Manen. Scale Effect Experi-ments on Victory Ships and Models. Parts I I I and IV, I S P Vol. 8, no. 81, 1961; N S M B publication no. 197.
10 A. J. W. Lap and L. Troost. Frictional Drag of Sliip Forms. Bulletin of the Soc. of Naval Architects and Marine Engineers, Vol. VIIL no. 2, 1953.
11 A . J . W. Lap. Diagrams for Determining the Resistance of Single-Screw Ships, I S P 1954.
12 G. van Oortmerssen. A Power Prediction Method and its Application to Small Ships, isp Vol. 18, no. 207, 1971; N S M B publication no. 391.
13 J. D. van Manen. Open-Water Test Series with Propellers in Nozzles, I S P Vol. 1, no. 2, 1954; N S M B publication no. 115a. 14 J. D. van Manen. Recent Research on Propellers in Nozzles. I S P Vol. 4, no. 36, 1957; N S M B publication no. 136. 15 M . W. C. Oosterveld. Wake Adapted Ducted Propellers. Doctor's Thesis, 1970, N S M B publication no. 345.
16 J. J. Muntjewerf. Methodical Series Experiments on Cylindrical Bows. Trans. Inst. of Naval Architects, Vol. 112, no. 2, 1970.
17 J. J. Muntjewerf. Cylindrical Bows. Jubilee Memorial W. P. A. van Lammeren 1930-1970, 1970.
18 J. D. van Manen. Bent Trailing Edges of Propeller Blades of High Powered Single Screw Ships, isp 1963. N S M B publication no. 215.
19 L. van Wijngaarden. On the Collective Collapse of a Large Number of Gas Bubbles in Water. 11th International Congress of Applied Mechanics, Munich, Germany, 1964, Proceedings, 1966.
20 F. van der Walle. On the Growth of Nuclei and the Related Scaling Factors in Cavitation Inception. 4th Sym-posium on Naval Hydrodynamics, Washington D . C , 1962. 21 J. H . J. van der Meulen. Cavitation on Hemispherical Nosed Teflon Bodies, I U T A M Symposium on Non-Steady Flow of Water at High Speeds, Leningrad, 1971.
22 J. H . J. van der Meulen. Cavitation Erosion of a Ship Model Propeller. Characterization and Determination of Erosion Resistance, A S T M S T P 474, American Society for Test-ing Materials, 1970.
23 P. van Oossanen. Profile Characteristics in Cavitating and Non-Cavitating Flows, I S P 1971, N S M B publication no. 369. 24 P. van Oossanen. A Method to Minimize the Occurrence of Cavitation on Propellers in a Wake, isp 1971, N S M B publica-tion no. 388.
25 J. A. Sparenberg. Application of Lifting Surface Theory to Ship Screws. Proceedings of 'Kon. Ned. Akademie van Wetenschappen', Amsterdam, Series B, 62, 1959.
26 J. A. Sparenberg. Note on the Ship Screw in an Inhomo-geneous Field of Flow, N S M B Memo, 1962.
27 G. Kuiper. Some Preliminary Results of an Exact Treat-ment of the Linearized Lifting Surface Integral Equation. Workshop on Lifting Surface Theory in Ship Hydrodynamics, Cambridge, Mass., 1969.
28 J. D. van Manen. The Effect of Cavitation on the Inter-action between Propeller and Ship's Hull, I U T A M Symposium on Non-Steady Flow of Water at High Speeds, Leningrad, 1971.
29 P. van Oossanen and J. van der Kooy. Vibratory Hull
Forces Induced by Cavitating Propellers. Paper presented at the Spring Meetings, Royal Institution of Naval Architects, 1972.
30 R. Wereldsma. Experimental Determination of Thrust Eccentricity and Transverse Forces, Generated by a Screw Propeller, isp Vol. 9, 1962.
31 R. Wereldsma. Some Aspects of the Research into Propeller Induced Vibrations, I S P Vol. 14, no. 154, 1967; N S M B pubhcation no. 278.
32 R. Wereldsma. Dynamic Behaviour of Ship Propellers. Doctor's Thesis, N S M B publication no. 255, 1965.
33 S. Hylarides. Ship Vibration Analysis by Finite Element Technique. Parts I and I I ; Reports no. 107S and 153S of the Netherlands Ship Research Centre T N O , 1967 and 1971 respectively.
34 M . W. C. Oosterveld. Symposium on a Restricted
Draught Tanker, N S M B , 1971, Wageningen. To be published.
35 G. Vossers, W. A. Swaan and H . Rijken. Experiments with Series 60 Models in Waves, N S M B publication no. 184; iSP Vol. 8, 1961; Trans. Society of Naval Architects and Marine Engineers, Vol. 68, 1960.
36 G. Vossers. Resistance, Propulsion and Steering of Ships. Part C, Behaviour of Ships in Waves. Technical Publishing Co. H . Stam, Culemborg, Holland, 1962.
37 W. A. Swaan. Amidship Bending Moments for Ships in Waves. ISP Vol. 6, 1959.
38 J. H . G. Verhagen. The Impact of a Flat Plate on a Water Surface. Journal of Ship Research, Vol. 11, 1967. 39 M . F. van Sluijs. Vertical Ship Motions and Deck Wetness. Spring Meeting, Society of Naval Architects and Marine Engineers, May 1969.
40 J. H . Witte. Predicted Performance of Large Water Ramjets, A I A A paper no. 69-406, 1969.
41 W. P. A. van Lammeren and A. J. W. Lap. The Shallow Water Laboratory of the Netherlands Ship Model Basin at Wageningen. I S P Vol. 6, 1959; N S M B publication no. 156a. 42 J. P. Hooft. On the Critical Speed Range of Ships in Restricted Waterways, isp Vol. 16, 1969; N S M B publication no. 324.
43 W. P. A. van Lammeren and A. J. W. Lap. The Com-bined Wave and Current Laboratory of the Netherlands Ship Model Basin, is? Vol. 11, 1964.
44 J. P. Hooft. A Mathematical Method of Determining Hydrodynamically Induced Forces on a Semi-Submersible. Annual Meeting of the Society of Naval Architects and Marine Engineers, 1971.
45 P. P. Loesberg. Model Navigator Based on Laser, I S P
P / D = I . O
4 s
"0° 40° 320 360 V2P\y^ +( 0.711 n D )^] K /4 k=0 A ( k ) c o s p k + B ( k ) s i n p k yap + ( 0.7 K n D Tl 4 D^D "^=0 A ( k ) c o s p k + B ( k ) s i n p k ' K 0 1 2 * 3 * 4 5 -6 * 7 + 8 9 -1 0 * 1 1 + 1 2 -1 3 * 1 4 * 1 5 + 1 6 + 1 7 + 1 8 + 1 9 + 2 0 -' 0 • 1 « 2 + 3 + 4 5 -6 * 7 + 8 9 -1 0 + 1 1 + 1 2 -1 3 • 1 4 * 1 5 1 6 -1 7 * 1 8 * 1 9 2 0 -A ( K ) . 2 5 3 5 0 ^ . 1 7 8 2 0 ?! . 1 4 6 7 4 f . 2 8 0 5 4 ? ! . 1 6 3 2 8 7 ' . 5 3 0 4 1 f . 6 0 6 0 5 ? < . 3 6 3 2 8 ? ! . 2 5 4 2 9 . 1 7 6 8 0 ? * . 2 7 3 3 1 ?* 2 1 4 3 6 ^ . 2 4 7 8 2 X . 1 2 3 1 7 ? ! . 5 0 9 8 0 ? ! 7 8 0 7 6 ? f . 3 7 8 1 6 ? ' . 3 5 3 5 3 ^ . 5 3 0 1 4 ?s 2 1 9 4 0 ^ . 2 8 3 0 6 ?! - 1 0 - 1 - 1 - 1 - 1 - 3 - 1 - 2 - 1 - 2 - 1 - 2 - 2 - 2 - 2 - 2 - 2 - 2 - 2 - 2 . 2 4 6 4 5 ; ' - 1 . 2 6 7 1 8 ? ! - 0 . 1 6 0 5 6 ^ - 1 . 6 5 8 2 2 » * - 1 . 2 2 4 9 7 ^ - 1 . 7 8 0 6 2 ? < - 1 . 2 4 1 2 6 ? ! - 2 . 6 1 4 7 5 ^ - 1 . 1 6 0 6 5 ^ - 1 . 3 3 2 9 1 . 1 2 3 1 1 ? ï - 1 . 3 1 1 2 3 ? ! - 1 . 1 2 5 5 9 f l - : . 1 3 9 4 8 ? ! - 1 . 8 8 3 9 7 f - 2 . 5 0 3 5 8 ^ - 3 . 7 9 9 9 0 ^ - 2 . 1 3 3 4 5 ^ - 1 . 1 1 9 2 8 ? ; - 1 . 1 3 5 5 6 ^ - 2 • 7 0 8 2 5 » ' - 2 * + 0 . 2 5 3 5 0 x 1 0 B ( K ) + . 0 0 0 0 0 ^ *0 - . 7 4 7 7 7 ?! O - 1 3 8 2 2 J* - 1 + . 1 0 0 7 7 ?s 0 - . 1 1 3 1 8 ? ' - 1 + . 4 7 1 6 6 F' - 1 + . 1 0 6 6 6 J ' - 1 - . 9 0 2 3 8 ? » - 2 - . 7 8 4 5 2 ^ - 2 * . 2 3 9 4 1 ^ - 1 + - 8 0 7 8 7 f - 2 - . 1 4 9 4 2 ? ! - 3 - . 3 1 9 2 5 5 ' - 2 * . 9 2 6 2 0 ^ - 2 + . 1 5 5 2 7 ^ - 2 - . 6 5 6 8 3 ? ! - 2 - . 6 1 6 5 5 i ' - 3 * . 5 1 0 3 3 , ' - 2 . . 6 0 2 6 3 ? i _ 3 - . 8 2 2 4 4 ? £ - 2 - . 6 3 7 8 9 ^ - 3 + O O O O O ? < + 0 - .1 1 0 8 1 f^* 1 + . 1 5 9 0 9 ^ - 2 * . 1 6 4 5 5 » ' 0 - . 2 0 6 0 1 ^ - 1 * . 8 5 3 4 3 ? ! - 1 + . 8 7 8 5 6 ? ! - 2 - . 3 1 3 2 7 ^ - 1 - . 9 6 6 5 0 ^ - 2 * . 4 3 1 9 0 ^ - 1 * 1 2 4 5 3 ? ' - 1 * . 9 5 9 8 6 3 - . 7 9 9 8 6 ^ - 2 * . 1 5 0 7 3 ? : - 1 + . 2 4 5 9 5 2 - . 1 6 9 1 8 s ' - l + . 5 1 6 0 3 ^ - 2 * . 1 1 5 0 4F! - 1 - . 4 7 9 7 6 ^ - 2 - 1 4 5 6 6 f i - 1 + . 2 3 2 8 0 ^ - 2 -1Fig. 1 Open-water test results of B4-70 screw series in four quadrants and the corresponding Fourier series approximation.
Vtot fir t W I T H O U T R UDDER V j s l S k n a c > I T H R U D D E " R O U G H " S H I P a a a c ( 0 O "StJ O O T H " S H I P | ö l A l f ^ O F VIC : T O R Y S H I P M O D E L S O F / \ P L A N E SUf F A C E ( D / L = 0 . C "^p— 7.0 7.5 log Re
0A=1,54x10'
A= 4 3 6 x 1 0 ^ 6.10x10'
SYMBOL LENGTH TEMP. A F E E T DEG. FAHR A D 23.00 72.0 6.10x10 O 18.42 72.0 4.36 A 12.28 71.8 2.37 O 9.21 70.0 1,54
•
INTERPOLATED FOR PARTICULAR VALUES O F 1 F R O U D E NO. , 1 - 1 W I T H C Y L I N D R I C A L B O W R E Y N O L D S NO. R X^IO ' 7 8 9 10 11 12 14 16 - 4 0 C f X l O - ^Fig. 3 Linearized resistance diagram for amily of models of the supertanker T I N A O N A S S I S .
O N L O A D D R A U G H T A T F n = 0 . 1 9
Fig. 5 The effect of block coefficient CB on the improvements
in specific total resistance as a function of the cyhndrical bow area coefficient A20/AM.
P R E D I C T E D T R I A L R E S U L T S 2 0 0 0 R E S I S T A N C E -+ C p e - ' " ' ' n -+ C 3 e - ' ^ ' - n -+ S i n F n - ' = -+ l / 2 p V ^ S [ 0 . 4 3 4 2 9 In ( R n ) - 2 ] ' + d | _ g ( L p / B ) ^ + d i y C ^ ^ l + d i g C ^ I ^ + d j ^ g B / T + + d i i o ( B / T ) 2 + d i „ C ^ P R O P U L S I V E E F F I C I E N C I E S -T H R U S -T D E D U C -T I O N F A C -T O R ; t = e Q + e i C p + e g C p ^ t e j C p F n + e 4 C p F n 2 + e ^ C p I c b + + e g L d / e + e y L d / D S P E E D IN k n o t s
0 7 . 0 . 5 8 < I f < 0 . 6 6 V E C O N . = ( 1 S 5 - 1 - 6 ' ! ' ) - ^ 1-1 V E C O N . I N 1 \ 1 1 5 ' ' ' ^ ^ 7 8 9 1 0 1 1 \ 1 2 1 3 1 4 f I N 7 .
\
\ ° - 9 5 V E C O N .Fig. 6 Resistance test results for fast cargo ships fitted with a hemispherical type bulbous bow.
Fig. 7 Resistance test results for tankers and bulk carriers fitted with a hemispherical type bulbous bow.
1.8| 1.6 1.4 cc LU m 1.2 3 O 1.0 < 3 0.8 Q as, 0.4 0.2 h T I r "1 1 — I — r J I I I L 0 INCREASING P • A • DECREASING P I I I I I 3 4 5 6 8 105 2 3 4 5 6 8 1 0 ° Rn.REYNOLDS NUMBER
Fig. 8 Desinent cavitation number versus Reynolds number for Teflon models and stainless steel (STT) models.
Fig. 9 Effect of time on weight loss and rate of weight loss of propeller model due to cavitation erosion.
K T = 0 . 1 2 K T = 0 . 1 5 K T = 0 . 1 8
Fig. 10 Example of results obtained of fluctuating pressure measurements on built-in afterbody in cavitation tunnel: note the influence of cavitation.
z
T R A N S V E R S E P R O P E L L E R C O E F F I C I E N T S 5z = + ^ y 6y kgf x s e c / m - 7 0 9 x 1 0 3 6z = + ^ y h kgf x s e c 2 / m - 3 . 9 9 x 1 0 2 M z 5z = + M y 5y k g f X s e c - 2 . 6 9 x l O ^ M z 5z M y 5y k g f X s e c 2 - 1 . 3 1 x 1 0 - ^ F z ^^z = + k g f X s e c - 2 . 6 3 x 1 0 ^ * F z ^ ' z = + f^y i P y k g f X s e c ^ - 1 3 3 x 10-^ M z 9 z = + M y iPy kgf x s e c x m - 1 . 2 6 x 1 0 ^ M z * z = + M y "Py kgf X s e c ^ x m - 5 . 7 8 x 1 0 ^ 5z = -F z 5y k g f x s e c / m + 1.32 x 1 0 2 F y 5z F z 6y kgf x s e c ^ / m - 1 . 6 9 X 1 0 ^ M y 6z = - M z 5y k g f X s e c - 4 . 0 6 x 1 0 ^ M y 5z = -M z 5y k g f X s e c ^ - 2 . 8 5 x 1 0 ' ' M y ^ Z = - M z Cpy k g f X s e c + 6 . 2 7 x 1 0 ^ 9z = -F z ^'y p k g f X s e c - 6 . 2 8 x 1 0 ^ M y <9z =-M z ijpy k g f x s e c x m - 1 . 8 0 x 1 0 ^ M y 9z = -M z 9y kgf X s e c x m - 2 . 3 6 x 1 0 2Fig. 12 Values of the coefficients of the dynamic excitation differential equations as calculated by lifting surface theory.
O P P J 5 . 2 8 1 L » 6 . 1 4 6
Fig. 15 Computer developed shell plate drawn on N/C drawing system.
Fig. 16 Nested parts calculated by N A L S program ready for
N/C flame cutting.
100000 12 14 16 18 200000 22 24 26 28 3 0 0 0 0 0 32 34 PRODUCTIVITY ( t o n / y e a r )
S P E E D ( k n o t s ) 0 . 7 9
/
\
D R A U S H T ( m ) 13.0 4 . 0 \ \ 15C 1 4 . 5 \ \ \ % \ \ V\
2 4 0 2 0 0 T R A N S P O R T C A P A C I T Y R E Q U I R E D F R E I G H T R A T EFig. 19 Results of a parametric study of a 70.000 ton dead-weight bulkcarrier.
WAVE FREQUENCY WAVE FREQUENCY CALCULATIONS; -SHIP MOTION -RELATIVE MOTION -ACCELERATION -SHEAR FORCES -BENDING MOMENT WAVE FREQUENCY
Fig. 20a and 20b Computer aided prediction of ship behaviour in waves. B 1 W A V E D I R E C T I O N 1 7 0 M E A S U R E D W A V E D I R E C T I O N 1 7 0 ° T H E O R E T I C A L F n = 0 . 1 5 l r \ \ f l
//
1 / / / / \\ \? i \ \ \ \ \ / / 1 / / 1 1 1 / / 1 11/7
I 1 / / / /V /
y - icG.
0 0.5 1.0 1.5
O 0.5 1P O 0.5 10 O Q5 1,0 0 0.5 tO
O) IN r a d sec ' lü IN r a d sec '
Fig. 24 Measured and calculated values of the vertical wave exciting force and the phase between wave and vertical wave exciting force on a semisubmersible.
.58/1.5 Kn .56/2.3 Kn .54/2.9 Kn c : : i ^ ^ . 5 2 / 4 . 3 K n ^ ^ ^ ^ ^ .50/4.8 Kn . 4 8 / 5 . 7 K n ' ^ 4 6 / 5 . 8 Kn E N G I N E O R D E R .44/6.1 Kn S T O P E N G I N E P U L L A H E A D S T O P E N G I N E F U L L A H E A D S T O P E N G I N E F U L L A S T E R N S T O P E N G I N E F U L L A H E A D S T O P E N G I N E F U L L A S T E R N S T O P E N G I N E F U L L A S T E R N S T O P E N G I N E R U N No. C R E W No. C U R R E N T No. C U R R E N T D I R E C T I O N ^ W S P E E D : 6 Kn START A T H E A D I N G : 0 0 0 T I M E : 1 0 . 2 8 - 1 0 5 9 I I O N E D E C C A L A N E \ O N E N A U T I C A L M I L E
Fig. 27 Registration of a manoeuvre performed witli tfie simulator.
Fig. 28 Aerial view of depressurized (vacuum) towing tank.
T O W I N G C A R R I A G E P E R S O N N A L L O C K S H I P M O D E L P N E U M A T I C T I R E S P E R I S C O P E C A B L E D R I V I N G S Y S T E M L O C K F O R M O D E L S ,
Contributions on some current problems of ship resistance On wind resistance
Prof. D r L . Landweber
Tlie University of Iowa, Institute of Hydraulic Research, Iowa City
Synopsis
The complete ship resistance problem, including the effects of the boundary layer and wake, is examined on the basis of the Reynolds equations and the exact boundary conditions on the ship hull and the free sur-face. Results obtained for the variation of head and vorticity in the wake are applied in the formulation of boundary conditions on the free surface and to refine formulas for determining viscous drag f r o m wave mea-surements and wave resistance f r o m surface profile measurements.
Systems of singularities which generate the fiow about a ship f o r m are studied for both the inviscid and the complete problem. The former requires source distribu-tions on the hull and free surface. I t was shown that a line integral of singularities around the contour of inter-section of the hull with the free surface, which has been emphasized in recent literature, can be eliminated. I n addition, for the complete problem, it is shown that the vorticity can be replaced by an equivalent volume distribution of doublets (Betz singularities) which, out-side the region of rotationality, yields the same eff'ects as the vorticity.
Integral equations for determining hull source distribu-tions are presented and discussed. I t is suggested that the force on the hull source distribution, as modified by the presence of the wake, could be interpreted as the wave resistance.
Prof. D r Ing. K . Wieghardt
Institut f i i r Schiffbau der Universitat Hamburg, Hamburg
Synopsis
After new meteorological tests the wind speed versus height over sea can be approximated by a one tenth power profile for steady wind strong enough to interest naval architects. Unfortunately, no data on duration and spatial extent of squalls are available.
For the direct wind forces on ships two examples are cited. The cross force due to side wind on the above water hull must be compensated by the under water hull. The drifting ship usually has a higher water resis-tance in addition to the direct wind drag. Two new examples have been given by B. Wagner.
W i t h sufiffcient fetch and duration of the wind a certain seastate arises. Pitching and heaving motions of the ship result in another resistance increase as shown in an example.
Recent developments in marine propeller hydrodynamics Cavitation and its detrimental effects
D r I r M . W . C. Oosterveld and I r P. van Oossanen Netherlands Ship Model Basin, Wageningen
Synopsis
This paper describes some new developments i n theoret-ical and experimental propeller hydrodynamics. I n particular, recent work performed at the Netherlands Ship Model Basin (NSMB) i n this field is considered. A review is first given of the development of screw propeller theory up to the present time. Particular atten-tion is given to recent work on non-optimum propeller design i n connection with obtaining the best possible cavitation properties of propellers operating in a wake. Due to the importance of preliminary propeller designs by means of screw series charts, an account of the now completed cross-fairing of the Wageningen B-series is presented. Attention is given to both the apphed fairing technique and the results obtained, including the final polynomials f o r propeller thrust and torque and the corresponding optimum relationships f o r propeller diameter and propeller rpm.
Recent theoretical and experimental work on non-conventional propulsion devices is next reviewed and discussed. Particular attention is given to the favourable properties of the various non-conventional propulsion devices, such as high efiiciency, acceptable cavitation performance, minimum propeller excited vibratory forces, etc.
Finally, an exposition is given of a new cavitation test-ing facility for ship models at the NSMB: the depressuriz-ed towing tank. A n account is given by the many pro-blems associated with ship model testing, i n particular in regard to the study of cavitation on marine propel-lers, which has led to the development of such a facility.
I r J. H . J. van der Meulen
Netherlands Ship Model Basin, Wageningen
Synopsis
I n this paper some aspects of the fundamentals of cavi-tation and the detrimental effects i n the field of ship propulsion are given. First, the phenomenon of cavita-tion is analyzed and several hypotheses on the origin of cavitation are discussed. A distinction is made between stream nuclei and surface nuclei. Results of tests on incipient and desinent cavitation measured i n a high speed water tunnel are given. Tunnel tests are subject to scale effects caused by differences i n air content, pressure history, Reynolds number, surface roughness and wetta-bility of the sohd. A short introduction is given into the phenomenon of cavitation suppression by polymers. Detrimental effects produced by cavitation are: thrust deduction and loss i n efiiciency, noise, vibrations and erosion. Recent investigations have estabhshed that cavitation on a propeller considerably increases the pressure fluctuations on the afterbody of a ship's huU and thus increases the vibration level. Erosion is a mechanical destruction of the material, most probably caused by water jets originating f r o m coUapsing bubbles. The rate of erosion depends on the erosion resistance of the material, the value for which is usually measured in a magnetostriction oscillator or a rotating disk appa-ratus. Results are given of a comparison between the erosion behaviour of a model propeller tested i n a cavi-tation tunnel with adjustable wake field and the erosion behaviour of specimens of the same material tested i n standard devices.
Applied mathematics in ship hydrodynamics Fish propulsion
Prof. D r R. Timman
University of Teclmology, Delft
Synopsis
I n a review of the röle of mathematics in ship hydrody-namics a certain restriction is made. Not every paper, where a formula is used, e.g. an interpolation formula for the representation of measurements, is considered as an application of mathematics. Only work, where a coherent mathematical theory is used will be accepted. The field then roughly divides into two large sub-fields:
1. Theory of boundary value problems.
1.1. Boundary value problems with free surfaces for the Laplace equation.
1.1.1. General theory with non-hnearized free surface conditions (not many results).
1.1.2. Theory of gravity waves round a ship with linearized conditions.
1.2.1. Boundary value problems in three dimensions. 1.2.2. Asymptotic approximations: thin ship theory, slender body theory; high and low Froude number approximations.
1.2. The boundary value problem of propulsion. 1.2.1. Lifting line theory (mainly propellers). 1.2.2. Lifting surface theory.
1.2.3. Special problems hke motion of fish etc.
2. Apphcations of system (control) tlieory.
2.1. Motions of ships i n waves.
2.1.1. Non-hnearized theory. Suppose the boundary value problem of the flrst part are somehow solved, we can, i n linearized approximation consider the whole system. Input quantities are the hydrodynamic forces, output quantities are the kinematic variables of the ship motions.
2.1.2.1. Deterministic theory (harmonic motion or pulse motion).
2.1.2.2. Stochastic theory:
Here a more realistic picture is developed, the whole theory of wave spectra is included here.
2.2. Manoeuvring. Here the control aspect is stressed: calculating the influence of control variables (steering angle and power) on the system in order to obtain a given course or some other criterium).
Prof. Th. Y . W u
California Institute of Technology, Pasadena, California
Synopsis
This paper attempts to discuss the fundamental princi-ples and some hydromechanical problems that are closely related to fish propulsion and may have some unsealed potential i n practical applications. For large Reynolds numbers the geometric configurations at two extremes, namely the large and small aspect ratios of lifting surfaces, have afforded some notable recent de-velopments. Of particular interest is the general case of unsteady fiow past a slender-body appended with fins and lifting surfaces of arbitrary shape, wherein the vorticity shed f r o m slant trailing edges may interact with the downstream body sections and with subsequent lifting surfaces. I t has been noted that such a generahzed slender-body theory has a wide appeal; f o r instance, its value in the application to problems of directional con-trol and stability of conventional ships, yachts and immersed bodies are beginning to be appreciated. Another class of problems of great interest arise f r o m the study of optimum shapes and control of body mo-tions in flapping propulsion of fish and birds. Even for the most general case of flexible surfaces having infinite degrees of freedom, the variational consideration shows that the optimum solutions generally involve only a finite dimensions of variables. This type of optimum control theory thus seems to be non-classical. The re-latively new concepts of proportional loading and feathering of lifting surfaces, however, have provided some simple explanation for efficient modes of motion, and have opened some interesting possibility of ex-tracting energy f r o m surrounding flow medium by an osciUatory wing.
Maneuverability State of the art
Prof. D r S. M o t o r a
University of Tokyo, Department of Naval Architecture, Tokyo
Synopsis
I n this paper, the author attempts to review the progress made i n the field of the maneuverability of ships i n recent years as summarized below.
I n a clear contrast to previous studies up to early 1940s, remarkable developments have been made i n clarifying the transient response of ships to the rudder. Several attempts to define the maneuverability of ships including transient response ability by least number of indices have been made with f r u i t f u l results which enabled us to compare the maneuverability of diff'erent ships by ra-tional measures. Remarkable developments have also been made i n f u l l scale and model test techniques to obtain transient response quality of ships and to obtain derivatives of hydrodynamic force and moment to be used i n equations of motions. Problems of ship-model correlation have always been associated with ship model tests.
I n accordance w i t h the rapid development of computers, the application o f computers to the simulation of ship motions has been developed i n recent years i n two ways. First, simulation f o r training purposes, mainly based on analogue computers, and second, the calculation and prediction of maneuvering motions, mainly based on digital computers.
Maneuverability i n restricted waters has been developed in connection w i t h navigation of ships i n inland ways and navigation of supertankers i n coastal water-ways.
Some recent advances in the prediction of ship motions and ship resistance in waves
Prof. I r J. Gerritsma
University of Technology, Shipbuilding Department, Delft
Synopsis
Since the publication of the strip theory method, as formulated by Korvin-Kroukovsky and Jacobs and modified by others, the calculation of heaving and pitching motions i n a given seaway could be carried out with sufficient accuracy for many practical purposes. Substantial experimental evidence to confirm the theory is available and the numerical methods based on the strip theory method are now used for design purposes and strength calculations. The use of ship motion theory in ship design to obtain optimum seakeeping qualities under given wave conditions is slowly expanding. Time reduction of the calculations used for this purpose is essential and some interesting developments i n this direction have been reported.
There is an increasing demand f o r the analysis of six degrees of freedom motions and loading. For this more general case, the situation is somewhat diff'erent f r o m the ship motion problem i n head waves: there is no com-parable verification of the theory available. Despite this fact considerable progress has been reported i n the analysis of lateral motions during the last few years. I t should be mentioned that implicitly the strip theory methods are restricted to certain shipforms because parts of the three-dimensional effects are ignored.
A systematic series of seakeeping experiments is planned at Delft Shipbuilding Laboratory to investigate the limits of the applicability of the strip theory methods. The tests include a very wide variation of the length/ beam ratio to include a very thin and a very fat model. Added resistance i n waves is another subject which draws the attention. A recent treatment of this problem employs the outgoing energy of the damping waves, caused by the oscillating ship. The results are confirmed by experiments which, i n addition, show that the resistance increase component varies as the wave height squared.
Retrospection on 15 years NSMB seakeeping activities Ocean Technology
M . F. van Sluijs and I r S. G. Tan
Netherlands Ship Model Basin, Wageningen
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When surface ships are operated in unprotected waters, their seaworthiness is of prime importance with respect to service performance and strength.
The hull f o r m and the propeller mechanism are, amongst others, major factors governing ship performance i n waves.
I n rough seas, large motions are experienced by the ship which can make captains decide to reduce the speed voluntarily or to change course to ease the motions. Consequently a part of the available power will not be consumed so that the sustained sea speed becomes decisive for the operation of the ship.
I n order to be informed of the behaviour, performance and wave-induced loads of the ship i n an early stage of design, model experiments are i n most cases an attrac-tive solution. The paper reviews the many investigations performed i n the Seakeeping Laboratory of the Nether-lands Ship Model Basin over the past 15 years, investi-gations ranging f r o m experiments to evaluate the merits of individual vessels to extensive systeiuatic series of tests.
Though the research discussed is mainly focussed on improving the behaviour and performance of conven-tional ship hulls, a growing interest in the field of the offshore industry initiated investigations into special purpose craft and floating or semi- submerged structures, the behaviour of which is also dealt with. Parallel to the experimental work, analytical methods to predict the motion response of ships or floating objects and to determine the loads that are acting on the structures, are reviewed.
Dr I r J. P. Hooft
Netherlands Ship Model Basin, Wageningen
Synopsis
A review is given of the hydrodynamic problems i n -volved in the design of offshore structures. Three kinds of problems are distinguished:
- problems involved i n structures fixed on the seabottom - problems involved in the behaviour of fioating or submerged constructions,
- problems involved i n the station keeping of floating or submerged constructions.
The problems do not depend on the structure only but also on the environment i n which the structure is placed. Therefore the general considerations described i n this paper will be supplemented with practical examples i n which extensive know-how has been gained.
Besides problems of the structures i n steady environ-mental conditions also problems in non-steady condi-tions will be discussed.
Steady phenomena can be investigated by model tests, analyzed and complemented by digital computations. For studies of non-steady phenomena the NSMB has the possibility to combine model tests with calculations on a hybrid computer.
Station keeping systems can be subdivided i n passive and active systems. Passive mooring systems are defined to consist of anchor chains and mooring wires at fixed locations on the construction. Station keeping by means of active systems is realized by thrusters and/or active mooring line connections; the change of mooring line length and thruster power is controlled by the excursion of the construction f r o m a prescribed position.
