AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U)...

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856AD-AO85 965 DAVID W TAYLOR NAVAL SHIP RESEARCH ANDDEVELOPMENT CE-ETC F/6 13/10 EVALUATION OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) JUN 80 S C FISHER UNCLASSIFIED DT NSRDC/S-P D C/013 EhhhIIIIIIEEEE Slflflflflflfllfll IIIIIIIIIhIII

Transcript of AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U)...

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856AD-AO85 965 DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CE-ETC F/6 13/10EVALUATION OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U)JUN 80 S C FISHER

UNCLASSIFIED DT NSRDC/S-P D C/013

EhhhIIIIIIEEEESlflflflflflfllfllIIIIIIIIIhIII

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-- 2 II22

A 0 11[ C.0

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MICROCOPY RESOLUTION TEST CHART

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DAVID W. TAYLOR NAVAL SHIPSRESEARCH AND DEVELOPMENT CENTER

Bethesda. Md. 20084

EVLAINO 4BU OSDRVDFO 4V

?PECTRAO4NALYSIS ON THE 1~.41 (MODEL 5367)o

by

APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITEDf

I DTlCELECTE 0

JUN 2 61980

SHIP PERFORMANCE DEPARTMENT REPORT

IC -

8f DTNSRDC/SPD-p 349-13)

7(X8O0 6 23 0 70

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MAJOR OTNSRDC ORGANIZATIONAL COMPONENTS

DTNSRDC

COMMANDER 00

TECHNICAL DIRECTOR01

OFFICER-IN-CHARGE OFFICER-IN-CHARGECARDEROCK ANNAPOLIS 04

SYSTEMSDEVELOPMENTDEPARTMENT 11

S P MAVIATION ANDSHIP PERFORMANCE SURFACE EFFECTS

DEPARTMENT I DEPARTMENT15 16

STRUCTURES COMPUTATION,

- MATHEMATICS ANDLOGISTICS DEPARTMENT

17 18

SHIP ACOUSTICS PROPULSION ANDSHIPACOUSTCS AUXILIARY SYSTEMSDEPARTMENT DEPARTMENT

19 27

SHIP MATERIALS CENTRALENGINEERING INSTRUMENTATIONDEPARTMENT DEPARTMENT

28 29

i i iL

I • I

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UNCLASSIFIED'ECUITY CLASSIFICATION OF T6IS PAGE ("onu Date Uie

REPORT D MENTATiOM PAGE READ INSTRUCTIONSREPOR DOCMENTTIONBEFORE COMPLETING FORM

I. REPORT NUMUER ,1 GOVT ACCESSION NO. S. RECIPIENT'S CATALOG NUMBER

DTNSRDC/ SPD-0049-13 'A ~ _____________

4. TITLE (ad Subtitle) S. TYPE OF REPORT b PERIOD COVEREDEvaluation of Bulbous Bows Derived From WaveSpectra Analysis on the LSD 41 (Model 5367) Final

6. PERFORMING ORG. REPORT NUMBER

7 AUTHOR(a) 8. CONTRACT OR GRANT NUMIER(s)

Steven C. Fisher

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASKAREA & WORK UNIT NUMBERSDavid W. Taylor Naval Ship R&D Center RAW U ME

Ship Performance DepartmentBethesda, MD 20084 Work Unit 1524-652

II. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

Naval Sea Systems Command (NAVSEA) JUNE 1980Code 3213 IS. NUMBER OF PAGES ii+38Washington, DC 20362.

14 MONITORING AGENCY NAME A ADDRESS(If different from Controlling Office) IS. SECURITY CLASS. (of this report)

Unclassified

lIe. OECL ASSI FICATION/ DOWNGRADINGSCHEDULE

IS. OISTRIBUTION STATEMENT (of thle Report)

APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

17. DISTRIBUTION STATEMENT (of the obotract entreed in Block 20. if dlferult (no Report)

IS. SUPPLEMENTARY NOTES

IS. KEY WORDS (Continue on revee side It necessap l aAn ti by Wock nmbe)

Bulbous Bows LSD-4iWavemaking ResistanceWave SpectraLongitudinal Wavecuts

20. ABSTRACT (Cnime.. n .vw e , aide fincos m Ide.ntit by loek " __) bulbous bows were designed

for LSD 41 Model 5367 using a theoretical approach developed by Sharma whichuses data from longitudinal wavecut experiments. The performances of the bulbsare compared to that of the original design bulb. The results indicate thatthe wavecut bulbs have the same or lower resistance at higher speeds than the

*' original bulb for the model.

DD 'JAR1,3 1473 EoITiON OF I Nov SS iS OBSoLETe UnclassifiedS'N 010-LF.0ld-601 i SECURITY CLASSIFICATION OF THIS PAGE nfa.. Doe 1m0~)

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SECURITY CLASSIFICATION OF THIS PAGE (Uimu DIO EAIWOQ

SitCRIT CLSSIICATON F TIS A~g(hORDON R~~rG

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TABLE OF CONTENTSPage

LIST OF FIGURES IV

LIST OF TABLES vI

NOTATION

ABSTRACT 1

ADMINISTRATIVE INFORMATION 1

INTRODUCTION 1

EXPERIMENTAL ARRANGEMENT 2

DISCUSSION 3

PREDICTIONS 3

REPEATABILITY 6

CONCLUSIONS 9

REFERENCES 10

Ace a icNTIS GtjWDCTABIta2oufOnedJustification

-Distributlon/

ja ilC. ~.YQo deasAvail and/or

ist special

U

a' ii

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LIST OF FIGURESPage

1 - Model 5367 (LSD 41) With No Bulb and the Elliptical Bulb 11

2 - Model 5367 (LSD 41) With the Long Circular Bulb and the 12Short Circular Bulb

3 - Wave Spectra of LSD 41 (Model 5367) Without a Bulb at 13V - 8.32 m/a (16.16 knots) from the December 1978Wivecut Experiments

4 - Wave Spectra of LSD 41 (Model 5367) Without a Bulb at 14V - 10.45 m/s (20.31 knots) from the December 1978Wivecut Experiments

5 - Wave Spectra of LSD 41 (Model 5367) Without a Bulb at 15Vs - 11.40 m/s (22.14 knots) from the December 1978Wavecut Experiments

6 - Wave Spectra of LSD 41 (Model 5367) With the Elliptical 16Bulb at V s - 8.32 m/s (16.16 knots) from the December1978 Wavecut Experiments

7 - Wave Spectra of LSD 41 (model 5367) With the Elliptical 17Bulb at V - 11.40 m/s (22.14 knots) from the December1978 Wavecut Experiments

8 - Wave Spectra of LSD 41 (Model 5367) With the Elliptical 18Bulb at V = 8.32 m/s (16.16 knots) from the March1979 Wavecut Experiments

9 - Wave Spectra of LSD 41 (Model 5367) With the Elliptical 19Bulb at Vs - 10.45 m/s (20.31 knots) from the March1979 Wavecut Experiments

10 - Wave Spectra of LSD 41 (Model 5367) With the Elliptical 20Bulb at Vs - 11.40 m/a (22.14 knots) from the March1979 Wavecut Experiments

11 - Wave Spectra of LSD 41 (Model 5367) With the Short Circular 21Bulb at V - 8.32 m/s (16.16 knots) from the March 1979Wavecut Experiments

12 - Wave Spectra of LSD 41 (Model 5367) With the Short Circular 22Bulb at V - 10.45 m/s (20.31 knots) from the March 1979Wavecut Experiments

13 - Wave Spectra of LSD 41 (Model 5367) With the Short Circular 23Bulb at V5 - 11.40 m/s (22.14 knots) from the March 1979

4i Wavecut Experiments

fiv

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LIST OF FIGURES (Continued) Page

14 - Wave Spectra of LSD 41 (Model 5367) With the Long Circular 24Bulb at V_ - 8.32 mis (16.16 knots) from the March 1979Wavecut Eiperiments

15 - Wave Spectra of LSD 41 (Model 5367) With the Long Circular 25Bulb at V5 - 10.45 m/s (20.31 knots) from the March 1979Wavecut Experiments

16 - Wave Spectra of LSD 41 (Model 5367) With the Long Circular 26Bulb at V8 - 11.40 m/s (22.14 knots) from the March 1979Wavecut Experiments

17 - Predicted Contours of n for LSD 41 (Model 5367) With the 27Elliptical Bulb at Vs = 8.32 m/s (16.16 knots) from theDecember 1978 Wavecut Experiments

18 - Predicted Contours of n for LSD 41 (Model 5367) With the 28Elliptical Bulb at Vs - 11.40 m/s (22.14 knots) from theDecember 1978 Wavecut Experiments

19 - Predicted Contours of n for LSD 41 (Model 5367) With the 29Elliptical Bulb at V - 8.32 m/s (16.16 knots) from theMarch 1979 Wavecut Experiments

20 - Predicted Contours of n for LSD 41 (Model 5367) With the 30Elliptical Bulb at Vs - 10.45 m/s (20.31 knots) from theMarch 1979 Wavecut Experiments

21 - Predicted Contours of n for LSD 41 (Model 5367) With the 31Elliptical Bulb at V8 - 11.40 m/s (22.14 knots) from theMarch 1979 Wavecut Experiments

22 - Predicted Contours of n for LSD 41 (Model 5367) With the 32Short Circular Bulb at V - 8.32 m/s (16.16 knots) from theMarch 1979 Wavecut Expertments

23 - Predicted Contours of n for LSD 41 (Model 5367) With the 33Short Circular Bulb at V - 10.45 m/s (20.31 knots) from theMarch 1979 Wavecut Expertments

24 - Predicted Contours of n for LSD 41 (Model 5367) With the 34Short Circular Bulb at V - 11.40 m/s (22.14 knots) from the

March 1979 Wavecut Expertments

25 - Predicted Contours of rj for LSD 41 (Model 5367) With the 35Long Circular Bulb at V6 - 8.32 m/s (16.16 knots) from theMarch 1979 Wavecut Experiments

V€V

t

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LIST OF FIGURES (Continued) Page

26 - Predicted Contours of '7 for LSD 41 (Model 5367) With the 36Long Circular Bulb at V - 10.45 m/s (20.31 knots) fromthe March 1979 Wavecut fxperiments

27 - Predicted Contours of 17 for LSD 41 (Model 5367) With the 37Long Circular Bulb at V - 11.40 m/s (22.14 knots) fromthe March 1979 Wavecut 1xperiments

28 - Effective Power Ratios for LSD 41 with Various Bulbs 38

LIST OF TABLES

1 - Principal Dimensions of LSD 41 and Model 5367 39

2 - Measured and Predicted Values of Ti for Model 5367 (LSD 41) 40Based on Data from Wavecut Experiments

3 - Values of the Residuary and Wavemaking Resistance 41Coefficients for LSD 41 (Model 5367)

v

I III II IIIII I [[ l ~iD' - . . . ... ... .. '- I =:i1 ... .

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NOTATION

A Cross sectional area of a bulb at the forward perpendicular0C Residuary resistance coefficient, R

CR Modified residuary resistance coefficient nondimensionalizedusing the wetted surface of the ship without a bulbWave resistance coefficient calculated from the wave

pattern, RW/h pSV2

E Wave spectra amplitude

F, G Sine and cosine components of the wave spectra, where Fand G are defined as

G(u) + i F(u) C (secetane) + i F (secetano) -

4 cos sin6 ikoyseckanO f dx f (x) e ikoxsece

k (1 + sin'e)

g Acceleration due to gravity

k°0 Wave number, g/V 2

L Ship length

p Relative bulb size (A new/A old)

P E Effective power

Q Relative bulb position (bulb length change/L)

RE RResiduary resistance

R Wave resistancew

s sece

S Wetted surface

u secetanO

V Speed, u/s

Z Longitudinal distance from the forward perpendicularof the model to the wave probe

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NOTATION (CONTINUED

y Transverse distance from the model centerline to thewave probe

Bulb influence factor, CWbulb /CWnbulb nobulb

e Angle in the x-y plane between the x-axis and thedirection of wave propagation

Nondimensional waveheight (waveheight * k )

P Density

ENGLISH/SI EQUIVALENTS

ENGLISH SI

1 inch 25.400 millimetres (0.0254 m (metres]

1 foot 0.3048 m (metres)

I foot per second 0.3048 m/sec (metres per second)

1 knot 0.5144 m/sec (metres per second)

1 pound (force) 4.4480 N (Newtons)

1 degree (angle) 0.01745 rad (radians)

1 horsepower 0.7457 kW (kilowatts)

1 long ton 1.016 tonnes, 1.016 metric tons, or 1016 kilograms

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ABSTRACT

Bulbous bows were designed for LSD 41

(Model 5367)using a theoretical approach developedby Sharma which uses data from longitudinal wave-cut experiments. The performances of the bulbs arecompared to that of the original design bulb. Theresults indicate that the wavecut bulbs have the

same or lower resistance at higher speeds than theoriginal bulb for the model.

ADMINISTRATIVE INFORMATION

This work was performed at the David W. Taylor Naval Ship R&D Center

(DTNSRDC), Bethesda, Maryland 20084. The project was funded under Naval

Sea Systems Command (NAVSEA 3213), Work Request Number 81538 and performed

under Ship Performance Department Work Unit Number 1524-652.

INTRODUCTION

As one phase of the design development of the LSD 41, a study was

undertaken to design suitable bulbs using a combined experimental and

theoretical approach. The bulbs were to be built and compared with the

conventionally-designed bulb.

The method used In designing the bulbs was developed by Sharma . It

assumes that the wave spectra of the hull and of the bulb itself

can be linearly superimposed. The wave spectra are derived from waveheight data obtained from longitudinal wavecut experiments. A

2more detailed explanation of the method is given by Reed

The longitudinal wavecut experiments were performed on Model 5367

representing the design configuration of the LSD 41. The first series of

wavecuts, performed in December 1978, was used to design the wavecut bulbs

for the model. The model was run at three speeds, with and without the

bulb initially designed by NAVSEA 3213 for the model. A later series of

resistance and longitudinal wavecut experiments was performed in March 1979,

using various bulbs, including the bulbs designed using Sharma'a method.The results of the analysis of the longitudinal wavecuts are given in

terms of the bulb influence factor and the relative bulb size and

location. The bulb influence factor, 17, is the ratio of the wave-

References are listed on page 10

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making resistance of the model with a bulb to the wavemaking resistance

of the bulbless hull. The relative bulb size, P, is the ratio of the

new bulb cross sectional area to the old bulb cross sectional area at the

forward perpendicular. The relative bulb location, Q, is the forward

or aft shift in position of the new bulb relative to the old bulb, non-

dimensionalized by the ship length. Bulb size refers to the cross sectional

area of the bulb at the forward perpendicular.

Within this report, a number of comparisons are made, and the reliab-

ility of the bulb design method is examined. The results of the towed

resistance experiments are compared to the wave resistance calculated from

the wave pattern. The data from the December 1978 wavecut experiments are

compared with the data from the March 1979 wavecut experiments to examine

repeatability.

EXPERIMENTAL ARRANGEMENT

The ship model used in this experiment was Model 5367, representing

the LSD 41. The model was constructed of wood to a scale ratio of 21.251.

The principal dimensions of Model 5367 and the LSD 41 are given in Table 1.

The model had a large cutout at the bow, extending from station 2 forward.

The cutouts simplified changes from one bulb (or bow) to another.

Three bulbs, shown in Figures 1 and 2, were used during the resistance

and wavecut experiments. The elliptical bulb was the bulb originally

designed for the model. The long and short circular bulbs were designed

using data from the wavecut experiments with the model fitted with the

elliptical bulb • The long circular bulb was the optimum

bulb at VS = 8.32 m/s (16.16 knots), while the short circular bulb was the

optimum bulb at VS . 11.40 m/s (22.14 knots) for the same bulb size. The

long circular bulb was a 1.84 m (6.05 ft) extension, at the ship scale,

of the short circular bulb, lengthened by adding a parallel section to the

bulb at the forward perpendicular. Model 5367 represented the LSD 41

without a bulb; Models 5367-1, 5367-2, and 5367-3 represented the LSD 41

fitted with the elliptical, short and long circular bulbs, respectively.

The model was towed during the wave cut experiments and was

fully appended, with shafts, struts, rudders, and fairings; and without

propellers. All of the experiments were performed at a model displacement

of 1630 kilograms (3600 pounds) which corresponded to a ship displacement

of 16,121 t (15,867 tons), and at an even keel. The model drafts did not

depend appreciably upon which bulb was used because the differences inbulb

volume were relatively small.

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Longitudinal wavecuts were taken during both series of experiments

using a resistance wire wave probe to measure wave height. The signals

from the wire wave probe were digitized and stored on magnetic tape2

for later analysis, using a package of computer programs which were

written at the University of Michigan under the direction of S. D. Sharma.

DISCUSSION

PREDICTIONS

The method that was used to design the improved bulbs for Model 5367

(LSD 41) assumes that the bulb wave spectra are linear, and can be

superimposed over a bulbless hull wave spectra. By altering the phase

and amplitud . of the bulb spectra a different bulb size and length can

be simulated. The wavemaking resistance calculated from the altered

wave spectra is used to compare different bulb sizes and lengths.

The icrngitudinal wavecut experiments were conducted at three speeds,

corresponding to 8.32 m/s (16.16 knots), 10.45 m/s (20.31 knots), and

11.40 m/s (22.14 knots), full scale. The wave spectra calculated

from the data taken during the longitudinal wavecut experiments are shown

in Figures 3 to 16. The plots include the sine and cosine components of

the wave spectra, F and G, and the wave spectra amplitude, E. The wave

spectra of the model with and without the original bulb, and with the

bulbs designed using Sharma's method are included. The contour plots of the bulb

size, P, versus the relative bulb location Q, as a function of the bulb

influence factor n , are shown in Figures 17 to 27. The contour plots

can be used to demonstrate the effects of changing bulb size or length

on the wavemaking resistance. It should be noted that all of the wavecut

data for the model without a bulb are from the December 1978 wavecut

experiments.The contour plots for Model 5367 with the elliptical bulb from the

December 1978 wavecut experiments were used to define the size and position

of the wavecut bulbs for the model. The size and position of the long

circular bulb were based on the optimum bulb at VS - 8.32 m/s (16.16 knots),

while the position of the short circular bulb was based on the best bulb

at Vs = 11.40 m/s (22.14 knots) with the same bulb size as the long circular

bulb. The long circular bulb was 0.7%L longer than the elliptical bulb,

and had a 40% larger cross section. The short circular bulb was 0.3%L

3

~c7

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shorter than the elliptical bulb, and also had a 40% larger cross section.

A circular cross section was chosen because the top of an elliptical bulb

with the required cross sectional area would have been too close to the

free surface.

The results of, and predictions from, the wave spectra analysis of the

wavecuts of Model 5367 fitted with the three bulbs are shown in Table 2.

The predictions based on the results from the December 1978 wavecut experi-

ments at VS - 8.32 m/s (16.16 knots) indicate that n will decrease from 0.47

with the elliptical bulb to 0.38 with the long circular bulb, and increase

to 0.49 with the short circular bulb. The predictions based on the results

from the March 1979 wavecut experiments indicate that '1 will decrease from

0.45 with the elliptical bulb to 0.40 with the long circular bulb, and

increase to 0.80 with the short circular bulb. The values of I calculated

from the wave spectra for the long and short circular bulbs are 0.76 and

0.78, respectively, larger than most of the predicted values.

Since there were no experiments with the elliptical bulb at VS = 10.45

m/s (20.31 knots) in December 1978, there are no corresponding predictions.

The predictions based on the results from the wavecut experiments in March 1979

at VS = 10.45 m/s (20.31 knots) indicate n will decrease from 0.54 with

the elliptical bulb to 0.34 with the long circular bulb, and increase to

0.58 with the short circular bulb. The values of 1) calculated from the

wave spectra for the long and short circular bulbs are 0.44 and 0.54,

respectively, which are close to the predicted values.

At VS - 11.40 m/s (22.14 knots), the predictions from the December

1978 wavecut experiments indicate that 7 will decrease from 0.69 with the

elliptical bulb to 0.68 and 0.62 with the long and short circular bulbs,

respectively. The predictions from the March 1979 wavecut experiments

indicate that ' will decrease from 0.63 with the elliptical bulb to 0.44

with the long circular bulb, and increase to 0.64 with the short circular

bulb. The values of q calculated from the wave spectra for the long and

short circular bulbF are 0.53 and 0.57, relatively close to the average of

the predicted values.

The values of 7 measured for the wavecut bulbs are usually within

+ 0.10 of the predicted values. An examination of the contour plots for

bulbs F and G indicate that the new bulbs are much closer to the optimum

size and length than the original bulb.

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Since the resistance experiments were conducted both with

and without the original and wave cut bulbs, a comparison can be made with

the trends of a modified residuary resistance coefficient, CRt, and 17.

CR differs from CR in that the wetted surface of the ship without a bulb,instead of the wetted surface of a given bow configuration, is used in the non-

dimensionalization of the residuary resistance. This means that differences

in C' will only reflect the changes in the residuary resistance, and notRinclude the effects due to chang',s in wetted surface.

The results of the resistance experiments for Model 5367 are presented

in Table 3. Note that by definition, n is equal to 1.0 for a model with-out a bulb, and that the CR' values are multiplied by 103. At VS = 8.23m/s (16.16 knots), the results show an increase in CR' from 0.936 with

the elliptical bulb to 0.956 with the long and 1.055 with the short

circular bulbs. These values agree with the trends in n . The CR I

value for the model without a bulb is 0.997, lower than the correspondingC R ' value for the short circular bulb. However, the short circular bulb

had a value of 7 less than 1.0, which implies the circular bulb has a

lower wavemaking resistance than the hull without a bulb. At 10.45 m/s(20.31 knots), the results show a decrease in CR' from 1.160 with the

elliptical bulb to 1.108 with the long circular bulb, and little difference

with the short circular bulb, 1.162. The CR' value of the model withouta bulb was 1.284. All of these values of CR' follow the trends in 7 .At VS W 11.40 m/s (22.14 knots), there is a decrease in CR' from 1.345 withthe elliptical bulb to 1.241 and 1.329 with the long and short circular

bulbs, respectively. The value of CR' for the model without a bulb is1.485. Again, these values of CR' follow the trends in q1

Generally, the C; values agree with the trends indicated by the values

of 77 . However, the amount of change in CR'may be much smaller than that

in 77 One reason for this is that the wavemaking resistance calculated

from the wave spectra gives only the resistance due to generating the wave

system measured at the wave probe, while CR' includes other resistance

components such as those due to form drag, local waves, and wavebreaking.

5

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A change in bulb size or length can have a positive effect on the wave

system at a distance from the model; but may have a negative effect on the

other components of residuary resistance.

The ratio of the effective power from the towed resistance ex'periments

for the LSD 41 with a given bulb to the effective power without a bulb,

(PE /PE ) plotted against speed, is shown in Figure 28. It shouldSbulb no blbbe noted that for towed resistance experiments, the experimental accuracy

is + 1 percent. The accuracy of wavecut resistance experiments has not

been thoroughly determined; however, it is probably no better than the

accuracy of the towed resistance experiments.

Above 7.7 m/s (15 knots), the long circular bulb is either the best

performing bulb, or differs from the best performing bow configuration

by an amount within the experimental accuracy. The short circular bulb is

the poorest performing bow configuration at the lower speeds. However,

above 9.6 m/s (18.6 knots) the differences between the resistance per-

formances of the model fitted with the short circular bulb and with the

elliptical bulb are within the experimental accuracy. The resistance

performance of the model with the short circular bulb improved relative

to that with the elliptical bulb and without a bulb as the speed increased.

This is not surprising since the short circular bulb was optimized for

the higher speeds.

REPEATABILITY

The results from the two sets of longitudinal wavecut experiments can

be used to examine the repeatability of this theoretical experimental bulb

design method. The optimum bulb location and size, determined from the

contour plots, are the basis of the comparison between the original and

the repeated experiments.

A comparison of the contour plots for Model 5367 with the elliptical

bulb showed that at VS = 8.32 m/s (16.16 knots), the optimum bulb from the

March 1979 experiments (Figure 19) was 0.6%L (AQ = 0.006) forward of and

16% smaller than the optimum bulb from the December 1978 experiments

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(Figure 17). At V S 11.40 m/s (22.14 knots), the optimum bulb from the

March 1979 experiments (Figure 21) was 1.6%L (AQ - 0.016) forward of and

the same size as the optimum bulb predicted from the December 1978 wavecut

experiments (Figure 18).

The comparison of the contour plots for Model 5367 with the elliptical

bulb from the December 1978 and March 1979 wavecut experiments indicates

that there are noticeable differences in the optimum bulb size and/or

position between the repeated experiments. An examination of the plots

of the wave spectra reveals that the spectra amplitude showed good

repeatability, but the phase did not. The phase differences can explain

the differences in the longitudinal position of the optimum bulb, and the

differences in optimum bulb size, since the amplitude spectra showed good

repeatability.

One possible cause of the differences in the phase of the wave spectra

is insufficient accuracy in the measurements of the distances between the

model and the wave probe. Ar. error of a few centimeters in one of the

measurements can noticeably alter the phase of the wave spectra. Since

the amplitude of the wave spectra is not affected by changes in the

phasing, the wave resistance calculated from the spectra does not change.

lf the errors in the measurements are consistent for the model with and

without a bulb, the bulb spectra amplitude will be correct, but the phase

will be wrong. It should be noted that the contour plots will not be

effected by errors in the measurements, since the error in the phase of the

bulb spectra will be compensated by the error in the phase of the hull

spectra. However, if the errors in the measurements are not consistent

between the model with and without a bulb, both the phase and the amplitude

of the bulb spectra will change, and the contour plots will be completely

altered.

7

Page 20: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

Another explanation for the differences seen in the contour plots

between the December 1978 and March 1979 experiments is insufficient

accuracy in the calibration constant for the wave probe. The wave probe

was calibrated only once, at the beginning of the experiments, and the

calibration was not repeated. If the calibration changed

during the experiments, the amplitude of the wave spectra of the bulb

itself will be incorrect and the contour plots will be inaccurate.

A further comparison can be made with the long and short circular

bulbs, since the long circular bulb is a lengthened version of the short

circular bulb. Ideally, the contour plots of the short and long circular

bulbs should have the same shape and size (at the same speed), but the

abscissa values for the long circular bulb should be shifted to the

right byv O = 0.01, the amount of the bulb length change.

The corresponding contour plots for the two circular bulbs had the

same shape and size at VS - 8.32 m/s (16.16 knots) and 10.45 r/s (20.31

knots). However, the change in Q between the bulbs was different from

that which was expected. At 8.32 m/s (16.16 knots), there was a change in

Q of 0.001 in the expected direction to give an effective AQ of 0.009. At

10.45 m/s (20.31 knots), there was a change in Q of 0.004 in the expected

direction to give an effective AQ of 0.006.

The contour plots of the two circular bulbs at 11.40 m/s (22.14 knots)

did not have the same size and showed large differences in the optimum

bulb position. Since the optimum bulb predicted from the contour plots

from the long circular bulb and the elliptical bulb had similar values of

n and A0 , the differences between the contour plots of the circular bulbs

is most likely due to inaccuracies in the short circular bulb data.

Except at 11.40 m/s (22.14 knots), the contour plots of the

long and short circular bulbs agree in shape and size, but show

changes in bulb positions which are different from that which is expected. This

indicates that this method can give good information on bulb size, but

not as good information on the fore and aft bulb location. This is

supported by previous experience with Sharma's method on other models.

8

Page 21: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

CONCLUSIONS

Linear superposition of the bulb and hull wave spectra can become a

useful tool in estimating the change in bulb size and position that may

improve the resistance performance of a ship. Further evaluation is

needed to determine if the inconsistent results are due to experimental

measurement errors or a fault of the method used. The method is not

qualitative since only the vavemaking resistance is optimized, while the

effects of the changes on the other components of the residuary resistance

are not accounted for. It should be noted that the predictions of changes

in bulb size seem to be better than the predictions of the change in the

bulb longitudinal position. This is supported by previous experience

with this method.

The model fitted with the long circular bulb has the same or lower

resistance than the model fitted with the elliptical bulb, the short

circular bulb, and without a bulb above 7.7 m/s (15 knots). The model

fitted with the long circular bulb has the same or lower resistance than

the model with the elliptical bulb and without a bulb above 9.6 m/s

(18.6 knots).

For future longitudinal wavecut experiments, more care should be

taken in measuring the distances between the model and the wave probe,

and in calibrating the wave probe. The wave probe calibration should be

repeated, and calibrations should be taken during the experiments and

after the wave cut experiments are completed.

L9

. . . .. _ _ _ _ __.. .. _ _.. . . .. ... _ _ __-_....... . . .

Page 22: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

REFERENCES

1. Sharma, S. D., "An Attempted Application of Wave Analysis

Technique to Achieve Bow-Wave Reduction," Sixth ONR Symposium on Naval

Hydrodynamics, pp. 731-73 (1966).

2. Reed, A. H., "Documentation for a Series of Computer Programs for

Analyzing Longitudinal Wave Cuts and Designing Bow Bulbs," DTNSRDC/SPD-

0820-01 (Jun 1979).

10

_~~~~~~~~ .. . ..."" .~ ..I

.I ..|rl . I . II

Page 23: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

Model 5367 With No Bulb (PSD 3968-1-80)

MIodel 5367 With the Elliptical Bulb (PSD 3970-1-80)

Figure 1 - odel 5367 (LSD 41) With No Bulb and the Elliptical Bulb

I~J PJ ItI ~ ~'u~sLi

Page 24: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

.iodel 5367 With the Long Circular Bulb (PSD 3971-1-80)

* .odel 5367 With the Short Circular Bulb (PSD 3972-1-80)

Figure 2 - odel 5367 (LSD 41) With the Long CircularBulb and the Short Circular Bulb

T14TS PAGE TS P.E3T QUJALM PRACTIC.A.lt

12 t C

Page 25: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

0

.00 1.0 .0 .0 4'.00 5'.00 6.0 7.0 1.0-0 9.00,10.00U

.4

40

0

0

0~.0 1 .00 2'.00 3.0 40 .0 60 .0 80 90 1.00U

Figure 3 -Wave Spectra of LSD 41 Ofode1 5367) Without a Bulb at Va 8.32 rn/s(16.16 imots) from the December 1978 Wavecut Experiments

13

Page 26: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

0 1.00 2.00 3.00 4.00 5.00 6'.00 7'.00 8. .00 1 0.00

~30 1.00 2 .00 3. 00 .00 6.00 6'.00 7'.00 8'.00 9.0 .00a .

0

LLU

-- 0 1'.00 2'.00 .0 4'.00 5'.00 6.-00 7'.00 8'.00 9. 00 20.00U

Figure 4 -Wave Spectra of LSD 41 (Model 5367) Without a Bulb at V8 10.45 Tn/s(20.31 knots) from the December 1978 Wavecut Experiments

14

Page 27: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

CN

0.

LL.C,.

0

.;-

U -

.00 1.00 2. 3.00 .00 5.0 . 7'.00 8.00 9.00 10.00

Cu

0

.00 2o .00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00U

Figure 5 -Wave Spectra of LSD 41 (Model 5367) Without a Bulb at Vs -11.40 m/s

: (22.14 knots) from the December 1978 Wavecut Experi~ments

01

Page 28: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

.0 .0 .00 00 4'.00 5'.00 6'.00 .0 8'.00 9.00 10.00

0U

.00 10 2'. 061 3'.00 4'.00 5'.00 ' 6.0 .00 8.0 9'.00 10.00U

0

LUU

Figure 6 - Wave Spectra of LSD 41 (Model 5367) With the Elliptical Bulb at V.8.32 mls (16.16 knots) from the December 1978 Wavecut Experiments

16

Page 29: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

a 0 .0 a,' 3'.00 5. 6.00 7.00 8'.00 9'.00 10.00

C

0.00o 1'.00 2.0 3'.0 4'.00 . 6.00 7. 00 8'.00 9'.00 1 0.00U

Fiue7 WvNpcr fLD4 Mdl56)Wt h litclBl tV

114 / 2.4kos rmteDeebr17 aeu xeiet

N1

Page 30: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

VOO 00 '-00 -ko 6' 0 7'.0 8-ow - '.00 0.0

0b 00 2.0 .00 .00 .0 6'.0 7'.00 8.0 9,g.00 10.00

UiU

0

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Fiue8WvNpcr fLD4 Mdl 37 ihteElpia uba

8.2aa(61 nt)fo h Mrh17 aeu xeiet

I18

Page 31: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

0.

L&.

0

00 1 0 2.0 .00 4.00 5.00 6'.0 7.00 6.00 9.00 '10.00U

Fiue9 Wv pcr fLD4 Mdl56)Wt h litclBl tV1040l 2.1kos rmteMrh17 aeu xeiet

01

Page 32: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

N)0 .00 2.00 9 00 4'.00 5.00 6'. 0t-0 .00 boaU

0.

OD

0

00-o

a00 .09.0 1

o_

9oo 10 2.00 3.00 4.00 5.00 6'.00 7'.00 0'.00 9.00 10.00U

Figure 10 -Wave Spectra of LSD 41 (Model 5367) With the Elliptical Bulb at V.11.40 u/s (22,14 knots) from the March 1979 Wavecut Experiments

20

Page 33: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

ca.

.00- 1.0 20 40 .0 6. 7. 00 8.0 9.00 10.00oU

OD

00 1 2.0 3'.00 4.00 5.-00 6'.0 7'.00 0'.00 9'.00 10.00

NU

Fiue10aeSetao S 1(oe 37 ihteSotCrua uba

0a 83 / 1.6kos rmteMrh17 aeu xeiet

Li21

Page 34: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

(0

.050 '.00 2.0 3'.00 4.00 -5. - G.00 7.00 8 1.00 9.00 '10.00U

Fiue10aeSetao S 1(oe 37 ihteSotCrua uba

v 04 / 2.1kos rmteMrh17 aeu xeiet

(22

Page 35: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

I.-

CDJ

tk.

a

0 1.00 23 4.00 . 6.00 7.00 6.00 9.00 b.00

NU

au

0

0

.00 '.0'.. 2'.00 . ,.oD 5.00 6.00 7'.00 8.00 9.00 10.00

Nu

0

Co

.00 1.00 2.00 3.0 0 4.00 5.00 6.00 7'.00 8.00 9'.00 10.00U

Figure 13 - Wave Spectra of LSD 41 (Model 5367) With the Short Circular Bulb atVs - 11.40 m/s (22.14 knots) from the March 1979 Wavecut Experiments

23___

Page 36: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

O"

C.0 2 4'.00 5.00 6.00 7.00 8.00 9.00 10.00

vo U

0

C

v

8-

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0 10 2.00 3.00 4.00 5.00 6.00 7.0000 0 .0 0.00

NU

Figure 14 Wave Spectra of LSD 41 (Model 5367) With the Long Circular Bulb atVs -8.32 m/s (16.16 knots) from the March 1979 Wavecut ExperimentsI

24

2 .i00

Page 37: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

10

U-U

G.00 00 20 3.00 .0 5'0 '.00 7'.00 a.0 9.00 10.00

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Page 38: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

'o

40

I:oo I 2.' / '.00 -'3 00.o 5.o006o 0:-0 - -'° ..oo 9'.00 ,b oo

ob

01

0 1.00 2 .00 3'.00 '--.M 5.00 6.00 . .00 lb.oou

C,

a

,?

0

C3

,~b00 1.0, 0 20. 0 3'.00 4'.00 5'.00 6.0 0 7/.0O0 8 00 9.0 0 10.0

U

Figure 16 - Wave Spectra of LSD 41 (Model 5367) With the Long Circular Bulb atV5 - 11.40 m/s (22.14 knots) from the March 1979 Wavecut Experiments

i• i 26

Page 39: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 40: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 41: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 42: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 43: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 44: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 45: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 46: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 47: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 48: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 49: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 51: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 52: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

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Page 53: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

ThBLE 3

VALUES OF THE RESIDUARY AND WAVEKAKING RESISTANCE COEFFICIENTSFOR LSD 41 CMODEL 5367)

V - 8.32 m/s (16.16 knots)

BULB USED C~ Cw .E!il...xl0- 3 10-3 Rno bulb

None 0.179 0.997 1.000 1.00

Elliptical Bulb 0.081 0.936 0.939 0.47

Elliptical Bulb 0.082 0.936 0.939 0.45

Short Circular Bulb 0.137 1.055 1.058 0.78

Long Circular Bulb 0.133 0.956 0.959 0.76

V - 10.45 m/s (20.31 knots)

BULB USED C CR tw CR .h1x10-3 X0 -3 C bulb

None 0.324 1.284 1.000 1.00

Elliptical Bulb 0.180 1.160 0.903 0.54

Short Circular Bulb 0.170 1.162 0.905 0.54

Long Circular Bulb 0.138 1.108 0.863 0.44

V- 11.40 m/s (22.14 knots)

BULB USED C tIXClO- 3 C'no bulb

None 0.438 1.485 1.000 1.00

Elliptical Bulb 0.300 1.345 0.906 0.69

Elliptical Bulb 0.269 1.345 0.906 0.63

Short Circular Bulb 0.246 1.329 0.895 0.57

Long Circular Bulb 0.224 1.241 0.836 0.53

Datar taken during the December 1978 experiments

41

Page 54: AND DEVELOPMENT CE-ETC EVALUATION OF … OF BULBOUS BOWS DERIVED FROM WAVE SPECTRA ANALYSIS 0-ETC(U) ... Evaluation of Bulbous Bows Derived From Wave ...

DTNSRDC ISSUES THREE TYPES OF REPORTS

1. DTNSRDC REPORTS, A FORMAL SERIES, CONTAIN INFORMATION OF PERMANENT TECH-NICAL VALUE. THEY CARRY A CONSECUTIVE NUMERICAL IDENTIFICATION REGARDLESS OFTHEIR CLASSIFICATION OR THE ORIGINATING DEPARTMENT.

2. DEPARTMENTAL REPORTS, A SEMIFORMAL SERIES. CONTAIN INFORMATION OF A PRELIM-INARY, TEMPORARY. OR PROPRIETARY NATURE OR OF LIMITED INTEREST OR SIGNIFICANCE.THEY CARRY A DEPARTMENTAL ALPHANUMERICAL IDENTIFICATION.

3. TECHNICAL MEMORANDA, AN INFORMAL SERIES, CONTAIN TECHNICAL DOCUMENTATIONOF LIMITED USE AND INTEREST. THEY ARE PRIMARILY WORKING PAPERS INTENDED FOR IN-TERNAL USE. THEY CARRY AN IDENTIFYING NUMBER WHICH INDICATES THEIR TYPE AND THENUMERICAL CODE OF THE ORIGINATING DEPARTMENT. ANY DISTRIBUTION OUTSIDE DTNSRDCMUST BE APPROVED BY THE HEAD OF THE ORIGINATING DEPARTMENT ON A CASE-BY-CASEBASIS.

r

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i~ii