Model tests on impulsive water pressure acting on the hull surface of an ore-carrier in two directional waves

ARCHIEF

Lab.

v Scheepsbouwkunde

Technische Hogeschool

?lodel, Tests on Impulsive Water Pressures Acting

on the Hull Surfacé of an Ore-carrier in Two

i1#e

Directional Waves*

by Kazuo Sugai,

Kunio Goda,

Hiromitsu Kitagawa, Yukio Takei,

Nakoto Kan,

Takeshi Niyamoto,

Shigeo Obmatsu,

Michio Okamoto.

Abstract

This paper describes the résults of a model test on the

impulsive water pressures acting on the hull surface of a

gigantic ore-carrier in waves,

In order to produce the

impulsive water pressures on the free running model,

especial-ly on the ship side, short crested waves from two directions

were generated as the wave environment of the experiment in

the square tank, Ship Research Institute, in which the second

wave maker of plunger type has been installed at right angle

to the first one recéntly.

As water impact is such a quick phenomenon,

a new

measur-ing system includmeasur-ing a special pressure transducer and

record-ing apparatus was prepared.

The system worked well to catch

the impulsive water pressures even in detail o± the peak

precisely.

What parameters affect occurrence of impulsive water

pressures was discussed first.

From analysis of the test

results, it was made clear that effect of the ship speed and

the wave steepness is predominent on the phenomenon, while

that of the wave direction and the ship motions is

comparative-ly dull.

Next, on what part of the hull surface the impulsive

water pressures will appear was investigated.

From the

experimental results, it was concluded that the frequency

of the occurrence and the peak value of the preésure increase

abruptly as the measuriag position moves from the parallel

body to the bow of the ship.

Further experiments in irregular waves from two directions

are going on in the square tank for analyzing the frequency

distribution of the impulsive water pressures statistically.

* Summarized from the

paper (in Japanese) published in

Journal of the Society of Naval Architects of Japan,

Vol. 135, 1974.

1-15

2

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by Kazuo Sugai, Member Hiromitsu Kitagawa, Member Makoto Kan, Member Shigeo Ohmatsu, Member

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Model Tests on Impulsive Water Pressures Acting on the Hull Surface of an Ore-carrier in Two Directional Waves

Kunio Goda, Member Yukio Takel, Member

Takeshi Miyàmoto, Member Michio Okamoto, Member

153

Summary

This paper describes the results of a model test on the impulsive water pressures acting on the hull surface of a gigantic ore-carrier in waves. In order to generate impulsive water pressures on the free running model, especially on the ship side, the regular waves from two directions

were adopted as the wave environment of the experiment.

From analysis of the test results, it is discussed what parameters affect occurrence of impulsive

water pressures and on what part of the null surface impulsive water pressures will appear. A new measuring system including a special pressure transthicer and recording apparatus was

prepared. The system worked well to catch impulsive water pressures even in detail of the peak precisely. 1 W < b71 .

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Fig. 1 Measuring System for Impact Pressure

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Table 1 Principal Particulars

Items Ship Model

Length betw. P.P (L,,) 247.000m 4. 5000m

Breadth Mid. (B) 40.600m 0. 7397m

Depth Mid. (D) 23.000m 0. 4190m

Draft Mid.

(d)

16.000m 0. 2915m

Displacement (W) 135.950 ton 0. 8013 ton

Block Coefficient (C5) 0.8243 0.8243

C.G. from Midship

(G)

fore 7.301m fore 0. 1330m

C. G. from Keel (KG) 12.280m 0.239m

Metacentric Radius (GM) 4.130m 0.069m

Longi. Gyradius (JCL) 0.2362 L,, 0. 238L,,

Trans. Gyradius (Ks) 0. 2300B 0. 360B

Rolling Period (TR) 11.04 sec 2.01 sec

PRESSURE TRAtSICER

CINTOLA

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Item Sensitivity Linearity Natural Frequency Zero Shift Thermal Shock

Fig. 2 Details of Impact Pressure Gauge

155

135-Table 2 Characteristics of Pressure Gauge Type: TOYODA THP-3 Range : 0-0. 3 kg/cm2

Resistance : 2k (Standard) Primary driving voltage : 5.0V DC

Catalogue Test 45 mV/F. S. (Standrad) 0.5%/F. S. 40kHz no description no description 42 mV/F. S. 50 mV/F. S. max. 0.8%/F. S. not tested

initial stage 10. 3g/cm2/10 min

run stage no shift initial stage ; 4 gfc&/6°C

run stage no shock

No. Zan lOcaUo4Co.s3

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Fig. 3 Locations of Impact Pressure Gauges

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Table 3 Experimental Conditions Cross

Ang.

Swell (No. i

Wave Maker)Wave MakerSea (No.2 Heading Angle of Ship to MovingDirection of Swell

Remarks

AIL

¡ii,

AIL Hw 90' 112.5' 120' X, 157.5' 165' 180' 202.50

1.50

L/40 1.50

L/40 135' Q ®Vo=1O.44 1.50

L/40 1.25

L/40 137.40 K,1 V0=14.80 1.50

L/40 1.00

L/40 140.8 Q Q Q Q Q V0=20.77 1.50 L/40 0.75 L/40 144.7' _Q

0

0

0

in still_water 1.50

L/40 0.50

L/40 150°

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_Q

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_{Q ®V0=14.80}

1.25 L/40 0.50 L/40 147. _{Q Q @}

°

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Fig. 4 Definitions and Notations

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3 Notations

Asw wc.e Ienth of Swell

wcve ler?th cl Secs

Cx phcse velocity of swell

Cy phor.e velocity of secs

Hw %Cve height

pot tern ongle te cvcr.c.rç direction Of Swell

Op cvcncing direction of t

cr

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Xp l.eng crleof Ship to slt wfn

the thipis in bow CCrditi to the cornosed waves

Vt svp speed in Stil; wctei

Vw _{ship speeØ (rl wOres}

Ni _{total number Of impact peesur.} n _{number of freç'ercy in histogram}

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Illustrative Diagrams Showing Occurrence of Impact for Various \'ave Conditions

Fig.

T

Illustrative D agrams Sho'ing Occurrence of Impact for Various Ship Speeds

b. 4)111 flIp?

Fig. 8 lllustratiye Diagrams Showing Occurrence of Impact

for Various Wave heights

ShIoS,r,d.IL.eIu. n'il noIr

Fig. 9

Illustrative Diagrams Showing Occurrence of Impact for Various Heading Angles (n w

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Fig.12 Typical Impact Pressure Recorded by Digital Memory

0.05s.C.

Stem 142.3°

Pp-p °24.9I}tm2

0.ô05s.c.

WAVE Swell A/L!25 HwOL/40

Seo 0.30 L/40

Pp-p 22.5 gitm2

WAVE Swell XI

Sea

Fig. 13 Typical Impact Presstre Recorded by Digital Memory and Osdilograph

X 153.9° _{V 14.8 Kn in still water}

Vw IOÁ.kfl in wave

(a)

(b)

Fig. 11 Typical Impact Pressure Recorded by Digital Memory

-SCALE 0icIn OJO51C. LOCATION S.S.9l/2 UP. X 180.00

(a)

Pppo8.5 g/cm2 WAVE Swell X/L° 1.25 H L/40 Sea Ct30 L140 vo 14.8 Kn in still water Vw 10.9 Kn In wave

(b)

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1 ms fJ Table 4

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Table 4 Rise Time Rates and Peak Values of Impact Pressures under Various _Conditions Vorri4.8K,

_HwL/40

Conditions

AIL _{X Location}

Swell Sea (deg.)

1.02 2.25 4.05

I 11.80

Rise 'iiRate to

Peak Value (Max.)

0.76 1. 75 3.02 8.75 9.0 19.2 22. 5 24.9 Peak Value 4.9 10.5 12.1 13.7 0.75 0.75 135 _Stem 0.50 0.30 _{142.3 SS9'/2Up.} 0.50 _{0.30 142.3} Stem 1.25 0.30 153.9 _Stem

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Fig. 14 Histograms oi Peak Values of Ship Motions and of Impact Pressures on Various Locations

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Fig. 17 Histograms of Peak Values of Pressures Fig. 18 histograms of Peak Values of Pressures on Three Locations at S.S. 91/, on Three Locations at S.S.91/,

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