DESCRIPTION OF THE NEW LABORATORIES OF THE
DEPARTMENT OF NAVAL ARCHITECTURE, UNIVERSITY
OF TECHNOLOGY, DELFT, HOLLAND
Part I. The Laboratory for Ship StrUcture Research
by
Prof. Ir. H. E. JAEGER and Ir. 3. Ch. DE DOES
Part II. The Shipbuilding Laboratory by
Ir. J. GERRITSMA
Reprinted from
INTERNATIONAL SHIPBUILDING PROGRESS ROTTERDAM
Vol. 4, No. 30 February 1957
-ON SHIPS' STRUCTURES
1. Introduction
Shipbuilding is for the Netherlands a very vital
industry. When after World-war II the necessity
for research in naval construction was felt every-where it was evident that the Netherlands wanted
to take up their share in the development of modern shipbuilding. It was clear that further development,
or even the maintenance of the level of modern Dutch shipbuilding was oniy possible as long as
fundamental as well as practical research was
undertaken on a scale unknown till 1940.
The Netherlands Shipbuilding Research
Associ-ation came into being, which correlated as far as
possible this research in shipbuilding in the Nether-lands. But this association did not own laboratories
and the yards also had very little equipment for undertaking fundamental research. Apart from hydrodynamic research in the Netherlands Ship
Model Basin, no. research in shipbuilding was carried
out in this country.
Therefore when an extension of the facilities for shipbuilding was made at the University of
Tech-nology in Delft, the idea was conceived of installing
a laboratory for testing ships' structures, a branch of research undeveloped until then.
This branch is very necessary. Immediately after
the war it became known that many difficulties had been experienced during the war with
all-welded ships. The technical reports from the U.S.A.
and Great Britain made it clear that the results of
investigations on brittle fracture of the material,
were largely influenced by the size of the structure and the way in which it was made, and that these
circumstances were of great importance with regard
to the behaviour of this structure as a part of the
ship.
Moreover new problems came into being and with a little foresight, special facilities could be
designed to ensure adequate laboratory technique in the near future. Problems such as the behaviour
*) Professor of Naval Construction at the University of
Tech-nology of Delft, Director of Research of the Netherlands'
Ship-building Research Association and of the Laboratory for Ship'
Structure Research at the University.
**) Principal scientific officer of the laboratory for Ship Structure
Research at the University of Technology in Deift.
Reprinted from ISP. Vol. 4, No. 30
-by
Prof. Ir. H. E. JAEGER*) and Ir. J. C. DE DOES**) Sunnna ry
A description of the Laboratory for Ship Structure Research at the University of Technology in Deift,
Netherlands, is given. The aim and the need for ships' structure research is discussed Special attention is drawn to the great facilities for research available in this laboratory.
of corrugated bulkheads, the behaviour of large
welded constructions as employed in supertankers, the transmission of forces by means of brackets, the
distribution of forces in large superstructures etc. etc. were asking for a solution.
Many problems as for instance research on brittle
fracture and the behaviour of structures in the
plastic range all need full scale experiments.
Theoretical considerations alone are not sufficient and they become more valuable when combined with measurements in laboratories as well as on ships.
It is clear, that under existing circumstances the best way to carry out tests on the strength of ships
is to have theoretically trained men working on this
job so that they may learn at the same time as
much as possible from it. Therefore it was evident
that this laboratory had to have combined withit the
training of our young naval architects and hence this proposition was submitted by the first author
to the Dutch Government, as the University of
Technology in Delft is a state institution. His point
of view was shared by the Minister of Education
and the laboratory resulting from the above
mentioned considerations is described hereafter.
2. Some fundamental considerations on
strength- research
Strength research on ships may be divided into two parts:
The investigation into the loads acting on the
ship due to sea waves and to the distribution of weight.
The determination of the most suitable con-structions to resist loads defined beforehand.
The first named investigations require
collabo-ration with
the Delft Ship Model Basin. The
behaviour of ships in a seaway has to be investigated first and the towing basin has already the necessaryelectronic apparatus to measure the movements of ship models in an artificial seaway. A description
of the Delft Shipbuilding Laboratory is given in
Part. II.
In Delft there is the possibility of investigating the loads due to a seaway on a plastic scale model
--I
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Fig I. General arrangement of the Laboratory first floor.
all:
'llullal-lllil.lullllaIltlllllIll TANIS roR THE TESflG
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bALUSTRA1E
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Fig. 3. Cross see/ion of Ihe Labora/ory
of a ship, where the forces, moments and stresses will be measured in a specially designed way.
The investigations mentioned in the second place
embrace a very extensive field of research.
Longi-tudinal and transverse strength of
ships, localstrength, properties of materials, connection of
structural parts as already indicated in 1 give a
great many possibilities of investigation, which for
a great part will have to be done on the full scale
to avoid the influence of scale effect. It is for
I
Reprinted from ISP. - Vol. 4, No. 50 - 1957
I
instance impossible to determine the influence of internal stresses due to welding on scale models.
This means that the complicated welded structures
of modern shipbuilding have to be tested on the actual size and built of the actual material, even
if such a structure is only a small part of the ship. Only where drawbacks due to scale effect do not
exist, will it be advantageous to resort to scale
models and therefore an extensive arrangement for strength-model-testing is available in the laboratory
and all kinds of electrical and electronical
measuring equipments can be used.
3. General description of the laboratory
Fig. 1, 2 and 3 give an indication of the general
lay-out of the new laboratory in the department
of Naval Architecture at the University of
Tech-nology in Delft. It is a part of the big building
shown in Fig. 4 where it is indicated by "A".
The principal part Consists of a hall with an area of 28,6 m X 13,2 m (95'-O" X 43'-4") and
a height of 8,O m (28'-O"). To the left of this hail
two tiers of rooms for investigators and other
personal of the laboratory are built. At B (Fig. 1)
a pit is built, in which a structure consisting of
four different bulkheads, forming a tank, may be
Fig. 4. The new Building for Mechanical Engineering and Naval ConsIrucion
a Laboratory4or Ship_StruclureReeardr b. TnuzinjJ,uh
Photo K.L.M.
a-6
I
-jerected. By means of this tank, bulkhead-investi-gations will be made, which will be described at a future date.
This pit together with the 500 tons
tensile-compression testing machine (A) fills the greater part of the floor space of the hail. Facing the large
testing machine are a 6-ton (C) and a 100 tons
fatigue testing machine (E) whereas beneath these
machines sufficient floor-space is available for
scale-model-tests. On the ground floor are installed
a store room for instruments and a measuring
room. On the gallery along the hail are the room's for the staff and the technical personel and a dark
room. The.necessary work shops are situated in the
part of the building, which contains the
towing-basin.
4. Description of the more important testing
machines
a. The 500 ton tensile-compression testing machine
This machine is of the horizontal type and is
made as large as possible in view of the large
test-pieces to be tested. The design was by Alfred J.
Amsier of Switzerland from a specification of the
University. This firm also manufactured the
hy--draulic equipment. The frame was constructed at the. Rotterdam Drydock Company. The end con-nections of the test pieces can be absolutely rigid or completely free. With 5.00 tons load an eccen-tricity of 25 cm (10") in the horizontal direction
Fig. 5. Genera! arrangesne,,! 500 ft machj,ge
and 10 cm (4") in the vertical direction is possible.
This means, that in addition to a tensile or a
compressive force the application of a limited bending moment is possible.
Fig. 5, 6 and 7 give a general idea of the machine..
It rests on a very heavy concrete foundation and consists of a steel frame, formed by two
longi-tudinal beams 21,65 m long (71'-O"), coupled to-gether at their ends. Each beam consists of a DIN 40 I beam with two heavy flanges 530 X 60 mm (1'9" X 2%") welded together. The sectional area
0 2n,.
Fig. 6. Cross sec/jo,,
0 0 0 ® .0
ii"
0 0 ® 0 0 0 0 0 0 Q© Th0331IA0 FilTh 03C*A Mu I---4;IUi
{ 0 0 0 © 0 (E1aj 0 0 ® 0 0 0 0 0 0 O® ff1501 MN COMuOMu 5Q15Fig. 8. Carriage for 1h1' guiding of the fixed crossbead before
Reprinted from ISP. - Vol. 4, No. 20 - 1957
is so large that with 500 tons load the maximum stress is only 260 KG/cm2 (3720 lbs/sq.inch), the elongation being oniy 0,23 cm (0.1").
The heavy flanges form the rails for the two crossheads, of which one is fixed and the other
movable along the beams. The fixed crosshead can
be placed at any desired place, dependent on the length of the testpiece. So for every testpiece the full stroke of the rams is available.
The ram crosshead is manipulated by 8 hydraulic rams, each giving a force of 125 tons. Four of these
rams work in the tensile direction and four in the
compression-direction.
Each crossliead is resting on a kind of carriage
Fig. 7. tOO ft testing machine
in each beam. These carriages have roller-bearings.
Fig. 8
gives a view of such a carriage before
mounting on the crosshead. In the middle is the
bearing in which the rounded pinhead of the cross-head is resting.
The crossheads are heavily welded box-shaped structures, which give the lightest weight for the greatest strength. The weight of each crosshead is
23 tons; the construction is given in Fig. 9. The
crossheads have machined pressure-faces, which, however, are not strong enough to support a
con-centrated load of 500 tons. If this
is desired aspecial set of pressure platens is inserted between the faces to distribute the force over a larger area.
0 N N N N N U LOI01L W4 P
A1
iii Ip
§ I ACYA NL
rI
LA'-) dh dhFig. 9. Construction of the fixed crossbead
Fig. 10. Arrangement of ihe rams
dh [II]
Fig. II. Fu,,damenl PjJJ 0
p
-1
a-'As
ccI.r,Ls4 1N/
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- ii1?0[]Fig. 12. Regulating values for the steering of the tam croesbead
For the connection of these platens, the crossheads
have welded through tubes connecting the fore
and aft faces.
The horizontal shearing forces are transmitted to the beams at the positions of the ram-crosshead and the fixed crosshead. The fixed crosshead will
transmit these horizontal forces directly to the foundation by means of vertical stowing beams,
which are indicated in Fig. 5 and 6. The big longi-tudinal beams are strongly fixed to the foundation
in the axial direction only at the end where the
pumproom is situated. In the axial direction, these
beams are absolutely free to elongate. The shearing
forces at that end are to be carried directly by the foundation to prevent buckling of the longitudinal beams.
In the vertical direction the beams are connected
to the foundation by means of traction-bars and
plates. The beams are absolutely horizontal and the maximum deviation from the horizontal position is
less than 0,1 mm (7250th of an inch).
The fixed crosshead is kept in place by means of
a support, which is fixed to the beams by large
steel pins. Holes are made in the beams at a pitch of 75 cm (30"), but nevertheless the fixed
cross-head can be placed at any desired distance from the
movable one by means of four rods. In this way
any object may be tested between these two
cross-heads with the full stroke of 50 cm (20"). These
supports are identical to the fixed ones, which
sup-port the 8 hydraulic rams as can be seen in Fig.
5. The construction of the rams and the supports
is given in Fig. 10.
The concrete foundation is shown in Fig. 11.
It is absolutely free from the building itself. When the test-pieces are tested to failure e.g.,
enormous quantities of energy will be released at
the moment of collapse. Therefore the
reaction-forces are taken over by the very heavily reinforced concrete foundation, which has the form of a basin. It may be desirable to support very long test pieces
and in this case the basin can be filled with water.
This makes it possible to make use of an elastic
foundation by means of pontoons.
The basin has dimensions of 2 1,65 m X 6,90 m X
X 3,13 m (71'-O" X 22'-8" X 10'-4") and the
bottom thickness is 1,00 m (3'-3"). The free width between the sides of the basin is 5,20 m (17'-l")
H4ITh
-Flhr
I4iIsI
iir
10
and the basin is constructed below groundlevel, so
that the tops of the vertical walls are only 45 cm (1'-6") high. The test space is therefore very large
and the maximum dimensions of the test pieces are
12,50 m X 5,00 m (41'-O" X 16'-S").
The right-end of the basin is separated from the
pump-room by a concrete wall. The supports of
the crossheads are placed against the concrete side
walls of the basin by means of shock-absorbers, as shown in Fig, 10.
Apart from the horizontal compression or
traction a vertical system of lateral forces up to
100 tons may be applied.
The main part of the machine is the hydraulic
installation. As already stated a special feature of the machine is the possibility of altering the end conditions of the test piece. In other words it will
be possible to test a construction with rigid or
totally free end conditions. If the end connection is to be considered as absolutely free it is essential to
give the ram crosshead the required freedom of movement. Therefore the test load is applied by four rams, that are hydraulically connected. If
fixed end conditions are desired and the crosshead
gets a movement which is not absolutely parallel
to its original position, the movable crosshead will
rectify. its direction automatically, by means of
four little axiometer-valves (see Fig. 12). Every
ram has its own oil supply via these valves.
The diagram of the hydraulic system is given in Fig. 13. There are five different systems viz.:
The low-pressure servo system. The high-pressure system.
The low pressure setting and return system.
The measuring system.
The equilibrium-system for the ram
cross-head.
This equilibrium system neutralises a possible
moment, due to the weight of the ram crosshead
or the test piece. Two small hydraulic cylinders just balance the weight moment of these parts.
In the diagram are shown the 8 high-pressure
rams (A), the pilot cylinder with axiometer-device
(C), the equilibrium cylinders (D) the control
panel (E) the pendulum-manometer (F) and the
regulating-device (G). The greater part of the
hydraulic system is placed in the pumproom (see
Fig. 11). The general arrangement of that room is given in Fig. 14. Six pumps are arranged for.
The possibility of applying an alternating load with
a period of about 7 seconds is provided.
Provision-allyonly two pumps are installed giving a period of about 1 minute for alternating loads. Thus load cycles can be applied with the same period as. in reality.
The testing machine, when used statically, has
four ranges viz. 500, 250, 100 and 50 tons. The error in the machine is smaller than
1 % for a
range from.10 % full-load to full-load. When used dynamically the pendulum-manometer is shut off and 4 Bourdon manometers with maximum- and
minimum valves indicate then the top values of the loading cycles.
The buffer in the high-pressure oil system is
provided by two nitrogen-accumulators placed in
the pumproom. All sorts of safety devices are
Fig. 14. I'umproom
PI1( VILYL
3T11V VITt PUMP
/
Reprinted from ISP. - Vol. 4. No. 30 - 1957
Fig. 15. 100 Ions Amsier Fatigue Testing Machine
installed indicating pressures, end of stroke,
maximum pressure etc. Signal lamps give all
information wanted on the control panel, which is built just above the machine as indicated in Fig. 2.
b. The 100 tons fatigue testing machine, which is
also a tensile and compression testing machine
This machine indicated in Fig. 1 as E is shown
in Fig. 15. It was manufactured by Amsier & Co.,
Schaffhausen and is equipped for tension,
compres-sion and bending tests. It is placed on a vibration-free 'foundation. The principal data of this testing
machine are:
Load capacity from + 100 tons to - 100 tons;
range of alternating load, 100 tons; maximum
stroke, 6,3 mm (¼"); load cycles per minute, 250
and 500;
max. length of test
piece 1000 mm(3'-3"); range of statical measurements 100, 50,
20 and 10 tons.
The statical measurements are made with a
pendulum-manometer. Dynamic measurements aremade with Bourdon manometers.
Fig. I 6. 6 tons Losenhansen fatigue testing machine
c. The 6 tons fatigue testing machine
This machine, indicated in Fig. 1 as C is shown
in Fig. 16. It is made by Losenhausen, Germany
and will be used for making fatigue-tests on small structures in steel and light-alloys.
The principal data are:
Load capacity from + 6 tons to - 6 tons; range of alternating load, 6 tons; number of load cycles
per minute, 1000, 1500, 2000 and 3000; maximum
length of test-piece, 400 mm (1'-4").
5. Conclusion
The description of this modern laboratory for
research on ships' structures as
set up at
theUniversity of Technology in Delft, is thought to
be of general interest. It is hoped that much
in-formation will be obtained from this laboratory,
which will be of use to
all concerned inship-building.
12
THE SHIPBUILDING LABORATORY OF THE DELFT
UNIVERSITY OF TECHNOLOGY
Swiu',,z ary
In the present article the general arrangement,
the apparatus and the method of working of the modern Shipbuilding Laboratory of
the Dclft
University of Technology arc discussed.1. Jut roduc/iou
From 1937 onward until recently the
Shiping Sub-department had, in the then existShiping
build-ing for Mechanical Engineerbuild-ing and Naval
Archi-tecture, a laboratory at its disposal in which
re-searches could be made into matters concerning
hydrodynamics with regard to ships.
The unpretentious equipment of this laboratory consisted principally of a model-experiment tank,
having a length of 37 m and a breadth of 2.7 m.
This tank was of semi-circular section and con-h
structed of steel plate.
Towing was done by an unmanned small carriage
carried by a rail over the tank.
This towing-carriage carried the resistance
dynamometer, with the aid of which the resistance
of models up to approximately 1.5 m in length
could be measured.
The equipment of the laboratory did not permit model self-propulsion tests to be carried out-; as a matter of fact, the restricted model length would
imply such a small size of model propeller that
serious difficulties could be expected in the inter-pretation of the results of the measurements.
The research work and the practical work done
by the students of naval architecture was therefore mainly confined to measurements of resistances in smooth water.
Soon however the analysis of log-books of
sea-going ships, in connection with allowances required
to be made on power and the loss of speed in a
seaway, created a need for model-experiment tests in artificially generated waves.
For obtaining some idea at least of the possibili-ties and difficulpossibili-ties met with during such a research,
a wave generator of the flap type was installed in 1953, by means of which regular waves having a
maximum length of 3 m and a maximum height of
0.09 m could be generated.
-A number of investigations were carried out with this apparatus, such as those concerning the degree
) Principal Scientific Officcr of thc Shipbuilding Laboratory at the University of Technology in Delft.
by Ir. J. GERRITSMA *)
of pitching, heaving and rolling in waves of differ
ent dimensions, the disturbance of the wave profile
by a vertical cylinder (in connection with the con-struction of the seakeeping laboratory of the Ne-therlands Ship Model Basin (N,S.M.B.) at
Wage-ningen) etc.
For carrying out statical-stability tests a so-called
moment indicator was procured in 1951.
With the aid of this apparatus the statical
sta-bility of a model of the ship to be examined can be
measured; in a few hours the curves of righting
arms of statical stability can be determined up to
angles of approximately 900. A more detailed'
des-cription of this moment indicator is given in the
present article.
One of the opportunities given to the Shipbuild-ing Sub-department by the construction of a new
building for Mechanical Engineering and Naval Architecture with the attendant laboratories was
to extend the facilities for experimental research in
a way so far unknown.
To this end, two new laboratories were built, yiz. the Shipbuilding Laboratory, whose aim, general
arrangement and method of working will be
discussed in the present article; and
the Laboratory for Ship Structure Research
(see Part. I).
2. Purpose of the Laboratory
The operations conducted in the Shipbuilding
Laboratory can be summarized in .three groups; this
classification will also give an idea of the aim
pur-sued by the laboratory.
The laboratory primarily provides mechanical aid
to teaching matters concerning the resistance and
propulsion of ships. The students of naval
architect-ure are, in the third or fourth year of their course,
expected to carry out a simple test in the laboratory and to work out the results obtained.
Besides, there is a possibility of research work
being done by student assistants under the direction
of the staff.
For those who have chosen the theoretical course
in their study of Naval Architecture, there is an
opportunity of completing their studies of a hydro-dynamical subject with regard to ships, which in-volves independent reearchwdrk
---SECTION A_B
Fig. I. Ge,:eral-arranje,,,e,,t
Secondly, a considerable portion of the operations
consists of research work carried out under the
direction of the staff of the laboratory.
In this connection the cooperation with the
Ne-therlands Ship Model Basin at Wageningen must be mentioned.
The contact between the two institutions is
evi-dent, for instance, from the monthly meetings
between the scientific workers of both laboratories, where views are exchanged upon work that is being
or going to be done.
In addition, the Shipbuilding Laboratory is re-presented in the group of workers making
invest-igations into the behaviour of ships in a seaway
(,,Zeegangsonderzoek"), which was established by
the N.S.M.B. for considering the problems arising
from a ship's behaviour in a seaway.
Thirdly, the laboratory may accept commissions
from industry.
In order to avoid undesirable competition between
the Delft Laboratory and the N.S.M.B., a specified
research which falls within the sphere of both,
institutions is to entail equal charges.
3. The construction and general arrangement of
the laboratory
Fig. I represents the general-arrangement plan of the laboratory.
The length of the building is
117 rn and itsbreadth 13.5 m, the direction of the longitudinal
axis being from east to west.
The foundation consists of 88 Franki piles having
lengths of from 16 to 17 metres below ground level.
Of these 88 piles, 30 are placed under the model
experiment tank.
The passage connecting the four front blocks of
the building. for Mechanical Engineering and Naval.
Architecture leads to the ship-model workshop (1)
with the adjoining carpenter's workshop (.5).
On the south side of the building there are in
succession: the instrument-making establishment
Eeprinted from I.S.P. - Vol. 4. No. 30 - 1957
pla,, of the Shipbui11i,,g Laboratory
(6), the store room (7)., the entrance of the south
front (8), the cloakroom and lavatories (9), the
drawing-office (1.0), the scientific officer's room (11), the rooms for the assistants (10), the
com-partment for carrying out the
statical-stabilitytests (12), the electronics workshop . which is also
used as the switch room (13). Behind these spaces
is the flow canal (19). On the. north side of the
building the large model experiment tank (16) is
situated with the cavitation tunnel (22) at its end.
Daylight enters the laboratory through small
windows in the north front.
The second storey is pirtly used as the mould
loft (23)., where on a floor having an area of 1000 sq. m lessons are given in development technique,
and partly as a drawing office (412 sq. m) for
students of naval architecture.
This second storey, therefore, does not belong to the laboratory proper, but ensures an excellent, in-sulation. against changes in temperature, as also do the series of rooms on the south side of the building. The heating elements provided have ample
capa-city for ensuring a temperature of 15° Cin the hail
during the winter months. Fig. 2 is a photograph
showing this hall together with the model-experi-ment tank and the' flow canal.
4. Apparatus and method of working
A. The ship-model workshop
In this space the ship models to' be tested are
ma-nufactured from paraffin wax (in special cases from wood). To the paraffin wax 3 per cent, of
bees wax 'is added so as to obtain a somewhat less brittle material; the melting point of the mixture is
approximately 65° C
Melting is done in an electrically heated furnace
(No. 3 of fig. 1) of 9 kW, having a capacity of
300 litres, a thermostat keeping the temperature
constant at 75° C.
14
(No. 4 of Fig. 1), during which an allowance of
about 1 cm is required.
A core of lathwork, covered with canvas leaves a thickness for the sides of the model of from 2 to
4 cm, depending on the size of the model.
The casting-mould, which is provided with the required risers, can next be filled with liquid
pa-raffin wax from the furnace, so that after the
coagulation of the material the model is ready for
further treatment. This is done in the 'milling
machine (No. 2 of Fig. 1); the milling machine
cuts waterlines into the casting, and for this purpose
a waterline drawing of the model is used. This
machine, therefore, is essentially a copying machine
transferring a waterline from the drawing to the model by means of two mills (one on the port
and one on the starboard side).
The waterlines are so many in number that they practically determine the shape of the model.
The material that is left between the waterlines
cut into the model can next be touched tip by hand until a smooth surface is obtained.
During this treatment transverse templates are used in some places to indicate the correct shape. The maximum length of the model is about 3.1 m.
For stimulating turbulent flow past the model a
so-called trip wire 1 mm diameter is provided at S
per cent, of the length of the model from the stem. After the model has been ballasted to the required displacement with the aid of a weigh bridge (having
a limit of 250 kg), the model is ready for carrying
out resistance and self-propulsion tests in still water.
'With tests carried out in longitudinal waves,
when the model is subjected to pitching, heaving
Fig. 2. Hall wi/h inoiel-cxpethnent lank a,,d flow chancl
and surging motions, care has to be taken that the
longitudinal moment of inertia of the model has the correct ratio with respect to the prototype.
With a scale a for linear dimensions, the scale for
the moments of inertia will be aa.
In the laboratory an apparatus has been con-structed, the so-called inertia table (Fig. 3), with
which the moment of inertia of a model about its
centre of gravity can be determined quickly. By
shifting ballast weights longitudinally with respect
to the centre of gravity, a certain moment of inertia can, therefore, be established.
Fig. 4 shows the principle of the inertia table
diagrammatically. In the first place the hinge shaft
(1) is, with respect to the table (2), adjusted to a
height a, which is equal to the height of the centre
of gravity of the model above the keel.
The table, on which the model is placed in such a
way that its centre of gravity is situated in the
hinge shaft, is at one of its ends connected to the
foundation (4) by means of springs ('3) capable
of being disconnected. When the table is made to oscillate about the hinge shaft, the period T of this
oscillation will be a measure of the moment of
inertia of the model.
The relation between period and moment of in-ertia can be established experimentally by placing known weights on the extremities of the table; the moment of inertia of these weights nd the period
of the oscillation can be easily determined. This
calibration has been carried out for different values of a.
It will be clear that during the shifting of the
weights the centre of gravity of the model' should
remain in the same place with regard to both length
and height. This can be verified by uncoupling the
springs (3): the inertia table will' then have become
a balance, and a tiny spirit level on the table
in-dicates the horizontal position if the centre of
gra-vity is in its correct position in the length of the
model.
If this is the case, a light weight at one of the ends of the table will result in an angular rotation which
is independent of whether the model is present or not, if the centre of gravity of the model lies in the
hinge shaft.
From the above, it will be evident that, with the aid of the inertia table:
the required moment of inertia;
the correct trim, and
the' height of the centre of gravity of the model can be fixed.
Adjacent to the model workshop is the
carpent-ers' workshop, in which some wood-working
machines are installed for the construction of
mo-dels (e.g. for wooden momo-dels, cores etc.).
B. The instrument-making establishment
This establishment is for the purpose 'of manu-facturing measuring instruments and model
pro-pellers,
for which a number of metal-working
machines are installed. Here the greatcr part of the
measuring apparatus is manufactured.
Reprinted from I.S.P. - Vol. 4, No. 30 - 1957
The model propellers to be used in the cavitation
tunnel and for carrying out self-propulsion tests
are first cast in a plaster mould, due allowance being made during casting. The material' used is a mixture
of antimony, tin and bismuth. On the propeller
workbench a large number of 'little holes are drilled
in the high- and low-pressure sides of each blade,
the greatest depth of these holes extending as far as
the required surface of the propeller. The
super-fluous material is removed by hndfi1ing, so that all holes will just have disappeared. Next, the dimens-ions of the propeller, when finished, can be checked on the measuring bench.
The instrument-making establishment also serves
as a service workshop for the Laboratory for
Shipstructure Research. For manufacturing larger
jobs the facilities of the Central Workshop of
the Delft University of Technology are available,
where a comprehensive collection of machine tools is found.
C. The' model experiment tank and the towing
carriage
The model experiment tank has the following dimensions:
the ordinary depth of water is 2.50 m. The tank, which 'is of rectangular section, was
built in 5 sections, which were afterwards inter--connected.
The first section of the tank consists of a little harbour shut off by a removable wooden partition
to protect 'the models against the waves, when they are not being used.
In front of this partition is a beach for the
pur-pose of damping the waves being generated on the
opposite side of the tank. The beach consists of an angle-bar structure covered at the top by wood on
which gravel has been provided. By means of four
screw spindles the, whole beach can be raised or
lowered and be adjusted longitudinally at the angle
desired (usually at an angle 10°)-.
Fig. 4. Principle of the j,,eriia table shown (liaRra,nmaticahl'y
length 96.80 m;
breadth. 4.28 m;
16
I. ''--'
-.
- rnttllhIHmtHIIIii
Fig. . Princi,!e of Ibr pneumatic wave genera/or shown diagramniatually
Its section is parabolic longitudinally with a
cir-cular portion at the top, which touches the surface
of the water.
-At about half the length of the tank there is a
pump room, where the water can be pumped out of the tank into the sewer or into the flow canal.
The tank is filled with ordinary company's water. No chemical substances for preventing, the growth
of algae are added. Hitherto it has appeared that
the growth of algae does not occur, which is
pro-bably due to the small amount of daylight entering
the tank from the north.
At the end of the tank a wave generator of the
pneumatic type is installed.
Some time ago, dr. Todd of the Taylor Model Basin at Washington placed the design of such a
wave generator, to be used for a tank of smaller
dimensions, at our disposal.. With the aid of the
data obtained the installation represented
diagram-matically in Fig. was constructed.
Via a valve casing a fan engine alternately
in-duces an increased and a reduced pressure in a dome which is placed above the water. The changes caused
by this in the level of the water are propagated in
the tank as waves:
At its bottom the dome can be partly shut off by a steel plate: the small opening left is used for
pro-ducing waves of very short lengths.
Behind the wave generator a filter is provided,
which causes slight disturbances in the wave profile to disappear.
The period of the valve determines the period,
hence the length of the waves since it can be stated
with fair approximation that with a depth of water
of at least half the wave -length:
T=V2;
where:
T = the period,
= the wave length, and
g = the acceleration due to gravity.
The drive of the valve is provided by an
elec-tronically controlled electric motor of 1.2 kW, with
which periods of from 0.7 to 2 seconds can be
ob-tained with corresponding wave lengths of
approx-imately 0.80 and 6.25 m. respectiiely.
-The wave height is regulated by adjusting the supply offrby thefan engine to a specified value
II
SUCTION PSINNUNI
I_,
trAI.r4urJTi
by means of a sliding bottom in the fan-engine
casing. The size of the fan engine is thus, as it were, either increased or reduced at a constant number of
revolutions, so that in- this way the supply of air
can be varied. Waves as high as about 30 cm can be obtained.
The principal data of the fan engine are:
Maximum amount of air supplied 9,000 cu. rn/h; maximum difference of pressure on high- and
low-pressure sides 60 cm of water; number of revo-lutions i3O0 rev/mm; and maximum power
re-quired 25 hp.
Fig. 6. Towing carriage
Reprinted from flIP. - Vol. 4, No. SO - 1957
18
The advantages of a pneumatic wave generator
are:
rapid control and little power for regulating
period and amplitude;
the possibility of first adjusting the period and switching in the fan engine afterwards, so that
waves of the correct length can be produced directly;
the absence of moving parts under water.
The installation discussed above is suited for
generating regular waves.
If the period of the valve is varied when the wave
generator is being used, the latter will emit waves
having different lengths and different velocities.
By superposing the single components an
irre-gular wave pattern is obtained; in this way specified wave spectra can be generated corresponding with
wave systems at sea.
To enable such a spectrum to be produced in a tank the valve is provided with an electronic
pro-gramme regulator, capable of switching in 100
periods successively, whose values may, in a special
sequence, be chosen from the progression 08, 0.9,
2.0 sec. This sequence can be adjusted at will,
but is subsequently constantly repeated after every
100 periods. The length of time between two suc-cessive periods can be regulated from I to 10 sec.
It will be evident that the use of this wave
gener-ator is restricted to the production of long-crested
waves, the direction of their propagation being
parallel to the longitudinal axis of the model-expe-riment tank.
The towing carriage') (see Fig. 6) runs with
four wheels (of 60 cm diameter) on rails having a perfectly smooth planed surface. Two sets of four horizontal roller guides prevent the carriage from
leaving the rails.
The principal data of the towing carriage are:
'Weight, inclusive of that of the measuring:
apparatus S tons;
Speed range I 0.4 -7.5 m/sec;
II 0.035-0.75 m/sec;
Drive: speed range I: on each of the wheels
a direct current shunt
motor àf 5 kW 110 V;
speed range II: a 1 kW motor on one
of the wheels;
Supply of current: a Ward-Leonard set of 25
kW,-installed in the tank hail.
Current is supplied to the carriage via sliding
contacts.
The field of the four carriage motors is excited
by a generator installed on the towing carriage.
1) The towing carriages, shaping machine, propeller
dynamo-meters and the propeller workbench were supplied by 'Messrs. 'Keuspf und Remmers of Hamburg.
For the speed range No. II the carriage speed can be regulated as follows:
1. hand control: the excitation of the field of the
Ward-Leonard generator is done by a small
Ward-Leonard set on the carriage;
'2. electronic control: an electronic arrangement
providing the excitation. This electronic
ar-rangement is controlled by a compensating
step, whose output voltage is proportional to the deviations from the speed adjusted, which
results in stabilization of the carriage speed.
For purposes of measurement there are 220 V
direct and alternating current and 12 V direct
cur-rent available on the towing carriage.
Besides the electro-magnetic braking system,
which operates automatically at the ends of the
tank, there is, on the side of the wave generator, an intercepting device, consisting of a steel wire rope
stretched across the tank. When the carriage is intercepted by the wire rope the latter raises, by
means of guide pulleys, a heavy weight suspended
from it in a pit at the end of the tank.
To the front of the carriage a plank is attached,
4.2 by 0.7 m and capable of being raised. At the end of the measuring run the plank is lowered on to
the water, and when the carriage returns smooths down, as it were, the surface of the water. Owing
to this, the waiting-time between two successive
runs is considerably reduced. If this were, not done
the transverse waves caused by the model might,
particularly in carrying out tests in waves, keep the
water in a disturbed condition for a very long time.
D. Measuring arrangement of the model (see Fig.
7) and' measuring apparatus
A set of light horizontal rollers (1) are provided
on the model forward and aft of the midship section,
and a set of vertical rollers (2), fitting between
them, are attached to the carriage. By the adoption of ball bearings the friction is reduced to a minim-um, while the model is free to pitch, to heave and
to surge. It is impossible for the model to swerve to
the right or left.
In order to enable the carriage to give the model
its required speed, a clamping arrangemcnt is fitted
on the model, consisting of two horizontal rollers
capable of being pressed against either side of a wooden box which is fastened to the model (3).
When the carriage has' gathered speed the driver can, from his position, move the two rollers apart
with the aid of a hand wheel, so that the model will be capable of moving independently of the carriage.
For carrying out resistance tests in smooth water and in waves, a gravity dynamometer (4) has been constructed, exerting a constant pull on the model
through a transmission gear of ratio 1 : 5. The
Reprinted from TSP. Vol. 4, No.30 - J957
weight which are caused by the surging movements of the model, to a negligible amount.
The towing force is transmitted to the model via
a cross (5) and a vertical rod which is, by means of
a cardan joint, secured at the centre of gravity of
the modeL The vertical rod, guided by ball; bearings in the cross, is free to follow the heaving motions of the model.
The cross itself can move freely over the hori-zontal rod by means of ball bearings.
If the motion of the model in waves is split, up
into a motion of the centre of gravity (heaving
ver-tical, and surging horizontal) and an angular
ro-tation around the centre of gravity (pitching), it
will be clear that this arrangement also enables these motions to be measured.
To this end, precision potentiometers with little friction are used which convert the displacements and the angular rotations into voltage variations; by means of a three-channel amplifier these
varia-tions can be simultaneously registered on a pen
recorder.
The pitrhing niorionjsincreased fif-teen4old by
Fig. 7. Measuring arrangenzenf of ihe model
means of toothed gearing; the heaving motion is, with the aid of rack and pinion, converted into a
rotary motion, while for the surging motion the
potentiometer is connected to one of the wheels of the resistance dynamometer.
If self-propulsion tests have to be carried out, the resistance dynamometer is replaced by an
independ-erit means of propulsion of the model. There are
two propeller dynamometers (Kcmpf und Rem-mers' system) available, with which torque and thrust can be measured. The propeller
dynamo-meters are direct-current shunt motors of 50 W .at 2,000 rev/mm.; they are of the suspension motor
design, so that the torque exerted can be measured in a simple manner.
Preparations are being made to construct an
elec-tronic dynamometer for momentarily measuring
torque and thrust during self-propulsion tests in
waves and to design the motor in such a way that
either the torque or the power can be kept
con-stant. It is possible to measure the linear acceleration
at the ship's bow and stern (6).
20
Fig. 8. Wavc-heigbl ineler
(Vibrometer) can be used for different purposes
(measurement of forces, displacements etc.), its
operation being based on the conversion of the
quantities to be measured into changes of
induct-ance which can be recorded. Together with the
Laboratory for Shipstructure Research four
mea-surement amplifiers are at the disposal of the Ship-building Laboratory.
For measuring the height of waves, a ivave-beighi
meter is attached to the front of the towing
car-riage (Fig. 8). With this apparatus the changes in
resistance due to the changes in the level of the
water between two conducting wires (of 0.4 mm
diameter) are measured. These wires are secured to a stçeamlined brace. The changes in resistance vary
linearly with the height of the waves. The wave profile and the motions of the model can be
re-corded simultaneously. Besides the two conducting
wires there is a polythene wire going round, on
which two silver contact points are provided.
Whenever the water level passes one of these contact
points a "pip" is caused in the recording of the
waves. With a known vertical distance between the points of contact, this results in a continuous cali-bration of the measurement.
The speed of the to-wing carriage can be measured in either Of two ways:
1. Via a transmission of 10 : 1 a measuring wheel
of exactly I m circumference, which runs on
one of the rails, drives a generator requiring a
very low torque. During one revolution of the
measuring wheel this generator produces 1000 impulses, which are counted by an electronic counter every 0.001, 0.01, 0.1, 1 or 10 seconds
as desired.. The counting is ica11y
re-peating.
The speed of the model is found by increasing
the speed of the carriage algebraically by the
displacement, in unit of time, of the model with
respect to the carriage. This displacement can
be measured with the "surge" potentiometer
and by recording time. It has been found,
how-ever, that with a correct adjustment of the
speed of the carriage the speed with respect to
the towing carriage may be neglected. The
counting of the electronic counter can also be
recorded..
2. A simpler method of measuring the speed of
the carriage is obtained when a measuring
wheel is made to yield an electric impulse for every 0.1, 0.5 or 1.5 rn travelled, resulting in a marking of distance on the recorder. Together
with a time base the speed over a specified
distance will then be obtained.
E. The flow channel
For carrying out model tests in restricted depth
of water, during which the water may be either
stationary or running, the laboratory has a so-called
flow channel at its disposal (fig. 9).
The principal dimensions of this tank are:
length 44.75 m, breadth 2.80 m, and depth 0.60 m, the depth of water being from 0 to 50 cm.
The flow channel has a horizontal bottom with a toleration of 1 mm.
Via a channel provided under the bottom, the
water flows back to the end of the tank where the
flowed started. The pump consists of
afour-bladed propeller having a diameter of 0.8 rn and driven by a controllable three-phase current
com-mutator motor of 30 hp. The number of
revolu-tions of the motor can be continuously varied with the aid of an induction regulator; the
correspond-ing number of revolutions of the pump varies
from 13 to 400 rev/mm. The output of the pump
is 1.4 cu. m/sec, so that a mean water velocity of
I rn/s can be obtained.
At the end of the tank, where the flow starts, a
rectifier has been built in, which eliminates the
large vortices of the arriving water.
At either end of the tank resistance elements have
been built in, consisting of gauze at the starting end of the flow, while at the other end a number
of vertical stiffeners are provided.
These resistances are for the purpose of damping
longitudinal oscillations caused in the water, for
instance when the pump is being started.
The toving carriage of the flow canal is capable of .developing a speed of 2.5 rn/s in either
direc-tion. It is
driven by means of a 2-kW
direct-current motor, again provided with an electronic
arrangement for stabilizing the speed of the
LrrtP
SECTION A_B
Reprinted from ISP. - Vol. 4, No. 1957
S n..
Owing to the limited dimensions of this tank the
tests will, in general, be restricted to measuring
resistance, investigating phenomena which occur when two ships are passing each other or the case of narrows in a fairway etc.
The resistance dynamometer works on the grav-itation principle, a spring resisting the remainder of the towing force. The, elongation of the spring
is recorded on a recording drum, together with
the marks from contacts which are secured to one
of the rails at intervals of 1 m, and a time base,
so that resistance and speed can be determined. There are two methods which may be used for measuring the velocity of flow, viz.,
the use of a pitot tube with a liquid
mano-meter. The disadvantages of this method are
the high inertia, and the low degree of accuracy at low velocities.
the use of a small propeller whose number of
revolutions, which can be measured electro-nically without any contact, is dependant on
the velocity of the water. This method of
measurement implies a very high reactionvlbc-ity (the propeller being made of plastic and
having a diameter of 1.5 cm.) while the result can be recorded.
The pitot tube as well as the propeller can be
calibrated in the model-experiment tank.
Fig. 9. Flow channel
F. The cavitation tunnel
There is a small cavitation tunnel, in which
cavitation phenomena can be investigated (fig.
10)..
The principal data of this tunnel are:
length between the vertical legs 5.03
distance between the horizontal
legs . 1.70m
sie of the measuring section . . . 0.3 X 0.3 rn
power of the screw pump 20 hp
maximum water velocity in way
of the measuring section .. 9 rn/sec
maximum torque of the propeller
dynameter 31 kgm
maximum thrust of the propeller
dynamometer 40 kg
-maximum number of revOlutions
of the model propeller 3,000 rev/mm
maximum output of the propeller
motor 4.3 hp
The screw pump can be continiuously adjusted
from 0 to 700 rev/mm by means of a hydraulic
variator. .
The cavitation tunnel enables the following in-TstigatiOns to be carried out:
1. the analysis of a propeller in a homogeneous
velocity field. In this case the elbow (1) is used, which is of ordinary construction.
22
2. with the elbow (2) a specified velocity
distribu-tion over the screw disc can be obtained ana-logous to that occurring behind a ship.
The nonhomogeneous field is produced by a
velocity regulator, containing 146 elements. By means of some type of check valve each of the
elements can be more or less shut off, which affects
the velocity of the water flowing through the
elements.
The velocity field in the vicinity of the propeller
can be measured with a so-called pilot comb. To
enable this to be done 13 pitot tubes have been fitted on a rotating arm, with which the velocity
field can be explored radially and peripherally. A detailed description of this cavitation tunnel with flow regulator has been given by Prof. dr ir
W. P. A. van Lammeren in International
Ship-building Progress, No. 16, 1955.
To enable the cavitation phenomena in a two-dimensional flow to be studied, a new measuring section has been constructed, in which the profile, having a chord of approximately 15 cm, can also
make a transverse movement, on the analogy of that of a blade profile rotating in a peripherally
unequal velocity field; the propeller blade will
then, as it.were, be oscillating with respect to the direction of the intake velocity.
G. The moment indicator
With the aid of this instrument, already referred to above, the statical stability of a ship model can
Fig. 10. Cavialion lunnel
be measured at angles of inclination of from 0 to 900 (see fig. 11).
The moment indicator is, in principle, a balance
for moments (see fig. 12).
The torque required for balancing a model at
a certain angle of inclination, is:
n.g sin y = p (ing + inn) sin (/7,
where:
the displacement;
the true metacentre; and
the false metacentre.
Fig. 12. Principle of ihe inomeni intlicalor
The moment indicator is unloaded in neutral
equilibrium with respect to the axis A. By means
of the weights Q and q the apparatus exerts on
the model a torque which is equal and opposite to the stability torque of the model. By balancing the
moments for increasing angles, the statical stability
of the model can be determined readily.
The metacentric height ing of the model can be determined in two ways:
The more accurate method is by carrying out
a stability test, during which the angle of in-clination is measured with a high degree of
accuracy by means of an optical method. If the values (ing + inn) measured are plotted
against p as base,
fairing of this curve to
= 0 will yield the value of mg, since, if
= 0,
inand n will coincide.With ing, known inn can now be found.
Reprinted from ISP. - Vol. 4, No. 50 - 1957
The righting arms of statical stability for the
ship will follow from:
(MG +MN) sin p = (MG ± a mn) sin rp,
where:
a = the model scale, and
MG = the metacentric height of the ship. The advantages of this method of measurement over a calculation are the following:
The model is free to trim, so that alterations in trim during heeling can be automatically taken
into account.
The influence of forecastle, bridge, poop and any other parts of the superstructure that may have to be included in the measurement can be taken into account in a simple manner. When a model is once available, different
con-ditions can be examined, in a short time.
Measurement is done with a high degree of accuracy; a calibration of the apparatus with
a rectangular model, whose stability-is easy to calculate, showed that the maximum error of the stability torque measured is kss than 1 per
cent.
V. Conclusion
From the above it will be evident that the
Sub-department of Naval Architecture of the Deift
University of Technology has been enriched with a
laboratory which is in every respect excellently
equipped for researches to be made into matters
concerning hydrodynamics in connection with
ships.
The author is convinced that this laboratory will render satisfactory service in teaching and research
work. In both cases the results of the work
con-ducted in this laboratory will eventually benefit
