Further experiments of pitching effect on ahead resistance of ships

Further Experiments of Pitching Effect on

Ahead Resistance of Ships

By Keizo UENO

i . Introduction

1)

In the preceding paper the authors

in-vestigated the effect of pitching on ahead

resistance of ships, carrying out the

re-sistance measurement experiments in still

water on the two cargo ship models (Model No.3 and 4; block coefficients 0.041

and 0.702 respectively) artificially

forced pitching, and introduced the

em-pirical formula calculating quantitatively the amount of rate of increase of ahead resistance of ships due to pitching. In

order to obtain the effect of ships' form on the amount of

rate of increase of

ahead resistance of ships due to pitching, 2)3)

we carried out the resistance experiments

on seven ship models with various kinds of forms, artificially forced pitching by just the same method as the preceding

experiments at the Ship Model Experimen-tal Tank of Kyushu University within the

range of time between May 1908 and February 1970. In the prsent paper the above experimental results are stated.

2.Syinbos and Formulae of Calculation

Symbol s

Llength between perpendiculars in m. B=breadth in m.

H=draught in m.

CB=block coefficient

LCB=distance of longitudinal centre of buoyancy forward of midship

ex-pressed in % of L

A=weight of displacement in kg. S =area of wetted surface in rn.

Bull. C. N. A. N., 13(2) (1972) 1 (87)

g=gravitational acceleration in m.sec.2 V=velocity in m.sec.

V5=velocityin knot F=Froude number=V(gL)

T=period of pitching in sec.

Tn=corresponding period of pitching

= T (g/L)

=amplitude of pitching angle in degree CFM =frictional coefficient of model CFS=frictional coefficient of ship

CSM=total resistance coefficient of model without pitching

C = rate of increase of ahead resistance

of ship due to pitching in %

F = parameter

'y=factor of synchronism = j Tn/rFn

= i gT/rV

C1,C2,C and n

= constants to be determined by the

resistance tests with pitching

K = coefficient of scale effect Formulae of Calculation

As the expressions of the results of the

present experiments,we use the following equations, the deduction of which was mi-nutely explained in the preceding paper.i)

C1F+C2F2

C-1 +C3(±7)n<OO6

+sign for y>O,

sign for 7<0,

whe re

CFMCis}-1

40L

F

_{Tn. Fn -}

*prof., the Department of Naval Architecture, the College of Naval Architecture of

Nagasaki.

Fishing boat modol was tested at the draught with 37.7% of H trim by the stern.

As shown in Tabe 1 , ve took a cargo ship model with Maier form, an aeroplane

carrier model with a large bulbous bow,

an ex-destroyer Yudachi model, a fishing

boat model and also three supertanker

models with various kinds of block coef-ficients, among which one model has a small bulbous bow form and other two

normal forms. The model ships having the

same types as those used in the yawing 4).5)

effect experiments have the same Model

4 .5) No. as those of the previous experiments,

except the Model No. N which is the model ship of the 130,000 DWT tanker 'NlSSHO MARU" built in the shipyard of SASEBO Heavy Industries Ltd., Japan,

J963. The body plans and fore and aft

forms of all model ships are omitted in

this paper because they (except the Model No. N) are indicated in the previous paper.5 All models were made of wood with their surfaces varnished, and they

were provided with no rudder and no bilge

keel. As the turbulence stimulation

de-vices, piano wires of i m. m. diameter were

fitted on model surfaces at the stations of 1/23.L abaft the leading edges of the models.

4. Test Results and Applicaton to

Actual Ships

The explanations of the method of tests

and also the method of analysis of test results are omitted in the present paper because they are the same as the case of

the preceding experiment and minutely

explained in the preceding paper. The values of the constants C1, C2, C3 and n,

obtained by the analysis of test results for various ship types are represented in Table 2 . together with the data of two

models, Model No. 3 and 4 , used in the

i) preceding experiments. odel No. I L Type of Ships m B m I H iii. LCB 94 CB

k.

5 Cargo Ship_{(Maier Form)} 2.000 0.255 0.1170 +1.67 0.700 42.80 0.7530

Aeroplane Carrier

(Large Bulbous Bow) 2.000 0.329 0.0965 -1.45. 0.591 37.50 0.7180

8 _{(Yudachi Model)}Destroyer 2.545 0.237 0.0673 -4.20 0.434 18.61 0.5880

Fishing Boat*

(Normal Form) 1.680 0.325 0.1516 _-3.30 0.603 54.44 0.8271

10 Supertanker_{(Normal Form)} 1.800 0.277 0.1108 +2.44 0.785 43.35 0.7391

N Supertanker_{(Small Bulbous Bow)} 1800 0.281 0.1078 +2.00 0.809 44.09 0.7591

11 Supertanker_{(Normal Form)} 1.800 0.277 0.1108 42.44 0.833 46.00 0.7727

2 (88) Keizo UENO

3.Ship Models Tested

Particulars of seven models tested are

indicated in Table 1.

Further Experiments of Pitching Effect on Ahead Resistance of Ships 3 (89)

If length L, service speed V (or Vs) and type of any actual ship are given, the values of coefficient of scale effect K for the ship can be calculated by the

equation (2),using any appropriate friction

line, for instance, Keizo Ueno's friction 6)

line, model dimensions corresponding te the type of the ship represented in Table

j , and the resistancespeed curves of

The value ol C, the rate of increase of ahead resistance of a ship who advances

at any speed Vs, pitching with an arbitrary

amplitude çí and also an arbitrary period T, can be evaluated by the equation (1), using the value of K obtained above and also the values of constants C1, C2, C3 and n, corresponding to the type of the ship represented in Table 3

References

j) Keizo Ueno and others: "Some

Expe-riments of Pitching Effect on Ahead

Table 2 . Contants Obtained From Test Results

the model advaneing without pitchtng

which are omitted in the present paper. The values of K of the various types of

ships calculated by the method mentioned

above, assuming the length of actual ships L and the range of service speeds Vs be as in Table 2 , are indicated in

base the speeds Vs in FIG. i to FIG. 4

Resistance of Ships", Memoirs of the

Faculty of Engineering, Kyushu Univer-sity, Vol. XXIX, No.1, October 1969 and

Journal of the Society of Naval Archi-tects of West Japan, No.37, February

1969.

2) Takaharu Cho : "Experimental Inves-tigations of Added Resistance due to Forced Pitching in Still Water on Su-pertanker Models", Graduate Thesis, Master Course of Naval Architecture,

Engineering Division, Kyushu University

Model No. Model Length m. CB C1 C2 C3 n Length Lship m. ship Speed Vs knot 3 1.800 0.641 0.090 +0.0050 15.21 1.50 140 11-'20 4 1.800 0.702 0.078 +0.0058 11.07 1.50 140 11-18 5 2.000 0.700 0.369 -0.0208 90.00 3.27 140 11-18 7 2.000 0.591 0.253 -0.0100 40.00 4.25 280 25-35 8 2.545 0.434 0.227 -0.0090 1.42 0.75 70 10-35 9 1.680 0.603 0.182 -0.0050 4.00 1.43 40 5-12 10 1.800 0.785 0.076 -0.00233 2.70 1.42 300 13-20 N 1.800 0.809 0.080 -0.00134 3.70 1.20 300 13--20 ii 1.800 0.833 0.092 -0.00109 2.00 1.11 300 13-20

4 (90) Keizo UENO

(1969)

Takayuki Oo-oka, Yoshio Sekiguchi and Ken-ichi Mori: "Experimental

In-vestigations of Pitching Effect on Ahead Resistance of Ships", Graduate Thesis,

Department of Naval Architecture,

Faculty of Engineering, Kyush.0

University (1970)

Keizo Ueno and others: "Some

Expe-riments of Yawing Effect on Ahead Re-sistance of Ships", Memoirs of the Fa-culty of Engineering, Kyushu

University, Vol. XXII, No. 1 , July 1962.

Keizo Ueno and others: "Further

Ex-5 FIG3 4 9 3 2 o 4 6 6 10 12 14 SPEED IN KNOT 12 14 16 16 SPEED IN KNOT 20 22 24

periments of Yawing Effeet on Ahead

Resistance of Ships", Memoirs of the

Faculty of Fngineering, Kyushu Univer-sity, Vol. XXIII, No. 3 , March 1984 and

Journal of the Society of Naval

Archi-tects of West Japan,No.27, March 1964.

) Keizo Ueno and others: "On the Flat Plate Experiments of Kyushu

Univer-sity", !vlemoirs of the Faculty of

En-gineering, Kyushu University, Vol. XXIII,

No..3 , March 1964 and Journal of the Society of Naval Architects of West

Japan, No.27, March 1964.

2 3 o 10 12 2 13 14 15 16 17 18 19 20 FIG 2 15 20 25 30 35 SPEED IN KNOT 7 SPEED IN KNOT