Comparative bending moment tests with T2-SE-A1 tanker models

COMPARATIVE BNDING MOMENT TESTS WiTH

--T2-SE-A1 TANKER MODELS'

Ir. J0Ch. de -Does0

i961

ARCHIEF

Lab. vi.

$cheepsbouwk

Technische

HogeschOöl

Deth

-n.,

COMPARATIVE BENDING MOMENT TESTS WITH

T2-SEA1 TANKER MODELq

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Since Lewis paper "Ship Model Tests to Determine Bending

Moments in.Waves't presénted at the 1951j. meeting of the "Society ofNaval Architects and Marine Engineers" a great number of tests has been carried out by several towing tanks. With some exceptions all have adopted thè method described in this paper by which the model is divided by a number of

outs. Bending moment and. shear force can be measured at these

cuts for instance by connecting the several parts by a flexurE beam provided wiìh strain ganges. Another method, first

applied by Sato, makes use of undivided models and in this

case stresses can be measured, and converted into bending

moments. Part C of the list of references gives a review of

recent publications in which' tests of the above mentioned

kind are described.

For his tests Lewis used the model of a P2-SE-Al tanker.

As some other investigators have also chosen this' ship. for

the measurement of bending moments, it was recommended at the September 1960 meeting of the "Committee on Wave Loads" to

use the T2-hu].l form for comparative bending moment tests.

For completeness the lines of this ship are given in

fig. I. .

At this moment the results of tests with T2-tanker models in 6 towing tanks, are available and this gives the opportunity to compare the measurements of pitch, heave,

shear force and bending moment as obtained in different tanks and by using different dynamometers and recording

instruments.

Table I gives a

review of the

main particulars of the tests from which results are available.

Christensen (i) used a wooden model with 3 cuts. The

methods of

measuring were those developed at the Davidson

Laboratory. For 'the meaèurement of bending moment and shear forces the tour parts were connected by meafls of a flexure beam provided with inductive ' pick..ups. The freeboard of the

'I

From the motion measurements only the recorded pitching is given. Heave and phase angles will appear in a later

report.

The mod1tesdby Daizell

_(d

2) wa cut at the midship section. The free-board corresponded with the real ship.

Motions,

although measured, _{were not published. Only}

for wave length _{ship length pitch and heave are given in}

a paper by Jacobs(B

₃₅₎

A plastic model without cuts was tested by _{De Dopa.} The bending moment was obtained from strain gauges, fitted at the shear atrake after a dynamic calibration _{of the model,}

Fukuda(Q ¿1)teeted a wooden modeiwith one cutat the

midship section. Unlike the other tests mentionéd in _this report the modél was not free to surge. Fukuda studied two weight conditions *ith the same displacement but diffèrent

radii of gyration.

Pitching and heaving motions, bending moments _and.phase angles are all published in his report.

Taxiiguchi.'a niodel (C 13) had five cuts and _{theneo.eBaary}

Strength was obtained by providing the ship with _{a light} al-by longitudinal girder. to which the six parts of the ship

were fastened. Complete results of motion,, _{phase angle and}

bending moment measrementa_were_puba&._The_testprogra

included 2 variations of the weight.diatribution

_{in whioh}

the displacement and the radii of gyration were kept at the

original value.

Akitaalao tested a model with ₅ cuts and a central girder to

connect the

_{blocks, in which the ship was divided.} His dynamometers were designed in such a way that also

verti-cal hydrodynaniica]. forces acting on each block could be measured, AJcjta studied two weight distributions with the

same displacement but different radii _{of gyration. AU the} results of bending moment, motions and phase lag _measurement were published.

Com?arison of results.

Fig. 2 t ₇ shòw the results of the motion measurements as given in the above mentiöned reports. It is a pity that

the differences are

rathér large, even if the difference in gyratio of the models is kept in mind, and that at lower

Froude numbers,

results may be affected by wall influence. Fig. 9 13 show the results of bending moment measure-ments. In long waves there is excellent agreement between the results of

Christensen and De Does. However, in waves

with 1,OQ, 1,25 and. 1,50 the differences, obtained by

the different authors, are remarkable and even the trend of the curves differs considerable. As the

bending

moment is

very affective to variations in weight distribution

this may

be the cause of the differences. Perhaps it will be worth-while to determine the "bydrodynamic" part of the bending

moment by isubtraoting the moment caused by the mass jertia

forces of the ship's weight from the measured value. However

this is only possible when all phase angleof motions and

moments

are published. Moreover it looks advisable to repeat some of the tests, in which

special cane should

be devoted to obtain exactly the same wejght distribution.

Furthermore

the published oscillograph records showin

some cases

diffe-rences in wave height with time which also may have affected

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AUTHORS L

"L

CHRISTENSEN 0.23

i-40

-

-DALZELL WIDE TANK 0.23

1.

51. DALZELL 0.23

- ®

®-de DOES

0.24 -FUKUDA 0.231 TANIGUCHI .OE22 TANIGUCHI 0.22 -AKITA 0.25 -Q. AKITA 0.25 -AKITA' 0.272 _- H-

+