Wave and wind measurements during HNLMS Tydeman full scale trials

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TECHNISCHE HOGESCHOOL DELFT

AFDELING DER SCHEEPSBOUW- EN SCHEEPVAARTKUNDE LABORATORI UM VOOR SCHEEPSHYDROMECHANICA

Rapport No. 464.

WAVE AND WIND MEASURENENTS DURING HNLMS. 'TYDEMANt

FULL SCALE TRIALS

Prof. ir. J.Gerritsma, M.Buitenhek and C.W.Jorens

Deift University of Technology

Ship Hydromechanics Laboratory

Mekelweg-2---DeIft 2208

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CONTENTS

Introduction I

Description of the wave buoy and analysis

of the wave and wind records. 2

Results of wave and wind measurements. 3

Acknowledgement.

Reference. 4

Table I. Measured wave height,wind speed,

wind direction. 5

Table 2 Wave spectra Tydeman trial. 6

Table 3 Wave and wind forecasts DTNSRDC

for 58°I8" N ,:12°s' W 7

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9

3 1. Introduction.

4 5

6 In the period of 13 22 March 1978 full scale seakeeping trials have'bêen

carried out with the ocenaographic research vessel HNLMS - Tydeman. The purpose

9 of the trials was to determine: 10 2 3 4 5 6 7 8 9

20

i The trials included the measurement of the prevailing sea conditions by means

of wave buoys, developed at the Delft Shipbuilding Laboratory [i] . Withrregard

4 to the choice of suitable wave conditions for the intended seakeeping trials, the David Taylor Naval Ship Research and Development Centre (DTNSRDC) offered

7 valuable assistance through the Royal Netherlands Navy by providing wave and wind forecastsT for the considered areá in the North Atlantic. The forecasts

30 were given for the following three locations:

i 2 3 6 7 8 9

40 i

2 3 4 5 6 7 8 9 50

i

2 3 4 5 6 7 8 9

bU

blanco

cijfer

2

-oi.-ect.os i. o;ierige aïtnkcninei ir d

onderbokn Jn)

the amplitude response functions for heave, pitch, roll and vertical acce-leration forward in longitudinal waves, as well as in oblique wave conditions the added resistance in waves in the same wave conditions

the influence on the rolling motion of the free surface anti-rolling tank of the ship in beam seas.

The wave and wind forecastst have been carried out by the Fleet Numerical Weather Control, Monterey, CA and have been transmitted dayly to the ship for conditions at 00 and 1200 GMT.

On the basis of the wave forecasts location 127 had been chosen for the main part of the seakeeping trials.

In the available time thirteen wave spectra have been measured with a recording time of forty minutes each., as well as the corresponding average wind speed and average wind direction. The main direction form which the waves were approaching has been estimated by visual observation.

The data is reported in this preliminary report and compared with the DTNSRDC forecasts as far as possible.

-1-Location 127 :

58.3N

12.3 W

Location 105 : 59.9 N 2.3 W

Location 106 : 60.6 N 8.4 W

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Correcties eu overige aantokcìiingoï t- pJoen

in dc

ach';'marge (huttu ocda boicco li'n)

i

2

3 2. Description of the wave buoy and analysis of the wave and wind records.

4 5 6 7 8 9 10

i

2 3 4 5 6 7 8 9. 20 1 2 3 4 5 6 7 8 9 30

i

2 3 4 5 6 7 8 9 40 2 3 4 5 6 7 8 9 50

VA, the apparent wind angel

A and the ships headig , using the following

4 expression: (see Figure 2).

5 6 7 8 9 bl D bi an co cijfer - 2

The wave height measuring' buoy has been developed by the Delft Shipbuilding Laboratory.The spherical buoy has a diameter of 0.43' m and is half immersed when

floating. The buoy is stabilized by means of a light tubular construction of about 1 meter length, a thin 'steel wire connected to this extension and a

stabiliziñg weight of approximately 100 N, see Figure 1 . The length of the

wire depends on the expected wave lengths which have to be measured.

In the case of the Tydeman trials a wire length of 40 meters has been used. During the launching procedure the steel wire is wound upon a small cardboard

cylinder, which allows the wire to be rolled off in a more or less controlled way, to avoid damage to the connection between buoy and wire and breaking of

the wire itself.

In a seaway the buoy follows the wave surface with sufficient accuracy and the simple stabilizing system keeps the buoy within a few degrees in a vertical position.

The buoy is equiped with an antenna and transmits a frequency modülated signal of the vertical acceleration to the ship. The vertical displacement is found by numerical integration of the digitized acceleration recording. The effective

range of the transmitter is limited to about 9 - 20 miles dpending on wave condition's. Digital data reduction methods have been used to compute the power density spectra of the wave recordings. A full description of the technical

de-tails of the buoy is given in [i]

For the determination of the power density spectra a sampling time of 1.4 seconds has' been used in the considered case, the length of each of te wave records

'being 2100 seconds.

The number of lays, to compute the autocorrelation functions has been taken as 45. A filter function according to Hann (0.25, 0.50, 0.25) has been used to

smooth the raw spectrum density estimates.

During each run of 2100 seconds the average windspeed VT and the average wind direction have been determinde from the average values of the apparent wind'speed

S A 2 VSVA cos

wA)'2

VT =

(V2

+ V2

--

i

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2 3 5 G 7 G 9

lo

1 2 3 4 5 6 7 G 9

20 i

3 4 5 G 7 8 9 30

i

2 3 4 b 6 7 8 9

40

1 2 3 4 5 G 7 8 9 50

i

2 3 4 5 6 8 9

bL

o

blanco

cii fer

Eleven wave spectra have been measured very near to location 127 and another tw

o o

spectra have been determined at 58 29 N, 02 35 W.

In Table I the significant wave heights as derived from the spectral analysis

of the-:wave recordings as well as the corresponding wind speeds and wind direc-tions are suimnarized. The run identification is defined in Figure 2, the number following the two capitals being the nominal ship speed in knots of the con-sidered run.

The spectal densities S (w) as a function of the circular frequency w are given in Tabel 2, whereas the form of the thirteen spectra is shown in the Figures 4 - 16.

All of the spectra at location 127 were unimodal, whereas for the runs BC 6 en CB 6, carried out near 58°29'N 02°35'W, a bimodal spectrum has been found.

The direction from which the waves approach cannot be measured with the buoy and a main wave direction had to be determined by visual observation. This has been done by two independent observers. The difference between the two estimates was

small (approximately 10 degrees). The seakeeping trials followed the scheme as

shown in Figure 3 with relative wave directions (with regard to the ship) of 180, 120, 90, 60, 0 degrees, 180 degrees being the head wave condition.

For the trials on 16 March the observed main direction of the primary wave system was 060 degrees. The secundary wave system approached from almost the same direction (040 - 060). This is in close agreement with the forecast, as can be seen from Tabel 3, in which the wave and wind forecasts of DTNSRDC are summarized. On 17 March the main wave direction was 040. However on this day a windsea (visual estimate: 2 - 3 meter) with main direction 320 - 290 - 280

250 - 260 degrees has been observed for the sequence of the _{runs BC 12 through}

CB 12.

WT = arc sin VA sin WA' VT

= i4

+ 11WT

Wind speed and direction have been measured by a cup anemometer and a wind vane situated in the fore mast of the ship, a location where a minimum of airf low interference from the ships uperstructure is expected.

3. Results of wave and wind measúrements.

Juig)

_{(enkelzijdig)}

iies

n o\r'i.gc

:tan

bfoo.

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-3-3 4 5 6 7 8 9 :10

i

2 3 4 5 6 7 o 9 20

i

2 3 4

.5

G 7 8 9 30.

i

2 3 4 5 G 7 8 9 40

i

2 3 4 5

L

7 8 9 50

i

2 3 4 5 G 7 8 9

bi

o blanco cijfer

On 19 March a wave direction of 170 degrees has been estimated in accordance with an observed wind sea (estimate 2 - 3 meter) from that direction.

In the Figures 17 and 18 the wind-speed and wave-height forecasts of DTNSRDC are compared with the corresponding results of the measurements.

Windspeed is very wéll predicted and also the prediction of the significant wave height on 16 Irch corresponds very good with the wave buoy data. The waveson

17 March have been slightly underestimated.

The main wave direction on both days has been predicted very well and also the forecast of the secundary wave directions on 16 and 17 March were in line with the visual observations. Apparently the waves at location 127 were guide üui. directional, on 16 March, giving satisfactory conditions for the seakeeping trials, whereas on 17 March two wave systems with different directions have been observed, the difference in direction being approximately 200 - 230 degrees.

Acknowledgement.

The cooperation of DTNSRDC in the HNUfS.Tydeman trials has been much appreciated Officers and crew ofHNu4sTydeman have given expert assistance during the trial and showed great skill in recovering the wave buoys after completion of the tiials on successive days.

Reference.

IJM. Buitenhek and J. Ooms;

An updated design of a disposable wave buoy;

Report 463 Laboratorium voor Scheepshydromechanica, Technische Hogeschool Delft May 1978.

(

orecies en orerie aar.Jï1Lr.;: .fl. ,'.' . .. c.d:.-i u:

-

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-5-Table 1: Measured wave height, wind speed, ind direction.

D at e GMT Run sign. wave Position height

w1/3

m wave direc-tion degrees True wind speed rn/s True wind direction degrees

16-3-78

0815

BC 9

58°32'N

5.7

10.2

034

11°3Ô'W

16-3-78

0900

DE 9

58°35'N

5.5

060

13.4

041

11°19'W

16-3-78

0945

FG 9

58°28'N

5.1

060

13.8

059 11°20'W

16-3-78

1100

HI 9

58°38'N

5.0.

060

13.2

038 I 1°30'W

16-3-78

1200

CB9

58°34'N

4.9

060

11.3

050 1I°20'W

.16-3-78

1330

KJ 9

5'8°26'N

4.7

060

13.2

053 11928'W

17-3-78

0830

BCl2

58°35'N

3.9.

040

4.2

321'

12'°36'W

17-3-78

0930

DEI2

58°42"N

4.2

'

040

3.4

297 12°24'W

17-3-78

1030

FCl2

58°34'N

4.. 1

040

3.8

270 12°20'W

17-3-78

1130

H112

5'8°43'N

040

4.7

248 12°42'W

17-3-78

1.215 CBI2

58°41'N

3.6

040 .5.Ó

249 12°25'W

19-3-78

1505

BC 6

'58°29'N

3.9

170

15.6

192

02°3.7'W

19-3-78

1.550

CB 6

58°25'N

36

. 170

12.0 1-82

02°35'W

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/

Tabel 2 ¡ave s2ectra TXdeman Trials.

Spectraldensity UI2. s

raps

BC 9 0E 9 .FG.9,

HI9.

CB 9.. .KJ.9 BC.12 .DE.12. FG.12 HI 12 CB 12 BC 6 CB 6

+.002f

:Óoo

-.004 -.004 +.001 +.000 +.00i -.001 -.000 -. 000 -.001 -.002 .05p.... +.008 +..003 -.001 -.000 -..Óoi -.003 i-.001 -.001 -.003 +.000 -.001 - .003 -.002 .1op -.001 -.001 -.007 -.007 +.001 +.000 +.001 -.001 -.000 +.001 -.000 -.003 -.004 .150 +.071 +.031 i-.063 +.042 +.0Ï8

.005

+.003 +.025 +.006 +.000 +.049 +.037 .199 +.578 +.252 +.461 +.592 +.232 +.160 +.047 +.217 +.136 -'-.037 +.057 +.746 +.663 .249 +1.426 +.768 +1.170 +j.437 +.790 .

+633

+.189 +.593 +.425 +.152

+.225

+1. 995 +1.802 .299 +1.668 -1.160 +1.575 +1.641 +1.378 +1.149 +.322 +.813 -i-.712 +.268

+361

+2.298 +2.064 .34 +2.249 +2.720

2.040

+1.888 +1.753 +1.625 +.649 +.955 +1.121 +.493 +.497

+1.603

+1.344 .39 +4.325 +5.287 4-3.392 +2.884 +3.182 +2.400 +1.781 +1.735 +2.166

1:436

+1.076 +1. 069 +.760 .449

5.204

+5.039 +4.037 +3.683

4.814

+3.377

2.952

+3.082 +3.358 +2.643 +2.127 -i-.735 + .545 .49 +4.188 +3.352 +3.428 +3.746 +3.967 +3.631 +2.980 . +3.707 +3.227 +2.923 +2.654 +.384

.444

.549 +3.974 +3.112 i-3.035 . +2.880 +2.584 +3.577 +2.512 +3.055. +2.526 +2.385 +2. 197 +.269 +.367 .598 +4.352

3.425

2.839

+2.315 +2.2}Ö +3.429 +2.031 +2.236 +2..163 +1.594 +1.607 4.337 +.329 .648 .698

3.505

+2.156 +3.408 +2.608 .

2.442

+1.847 +2.426 +1.814 +1.92Ó +1.683 +2.203

+1.061

+1.423 +1.038 +1.773 +1.170 +1.519 +1.038 +1.108 +1.021 +1.315 +1. 058 +.40-7 +.670 +.465 +--849 .748 +1.452 +1.733 +1.316 +1.2Ò2 +1.218 +.762 +.810 +.679 +.854 4.890 +.779 i-1 .269 +1. 083 .798 +1.025 +1.180 i-.964 +1.082 4.801 +.712

.603

+.543 +.605

.738

+.568 +1 .696- +1.039 .848 +.721 +.786 +.724 +.954 +...650 +.653 +.493 +.412 -1-.405 +.568 +.412 +1.443 +.934 .898 +.617 . +.583 -'-.663 +.769

574

+.466 +.350 +.255 +.305

.348

+ .296

+953

.749

+.516 +.368 +.224 +.212 +.232 +.205 4.197 4-.723 +.565 .997 +.467 +.347 +.343 +.384 +.411 4.410 +.175 +.205 -i-..152 4.142

+.

142

.615

+.437 1.047 +.366 +.308 +.294 +.288

.316

+.352 i-.iii +.153 +.107 +.121

+144

+.471

+345

1.097 4.295 +.286 -1-.284 +.221 4.244 .2Q:7 +.068 +.108 +.083 +.102 +.120 +.342 +.260 1.147 +.202 +.268 i-.187 4.215

.212

+.147

. +.057 +.104 +.056 +.083 4.073 +.234

i-.

1 83 1.197 +.139 +.186 +.129 4.175

.185

+.146 +.055 +.O8i +.040 +.072 +.054 +.169 4.141 1.247 +.110 +.109 +.112 4.113 +.131 4.110 +.055 +.040 -p.034 +.058

.044

4.131 +.102 1.297

+086

+087

. +.098 4.086 +.Q90 +.069 +.042 +.029 4.031 +.038 +.030 +.087 +.075 1.346 +.059 +.073 i-.081 4.075 +.060 +.063 +.029 +.030 +.028 +.028

+023

-'-.065

.069

1.396 +.045

+060

i-.054 +.064 +.038 4.052 +.020 +.024 +.021 +.019 +.019 +.057 4.061 1.446 -'-.038 --+.049 +.042 +.044 +.031 +.030 +.016

+019

+.013 +.014 +.014 +.039 +.047 1.496 +.032 . +.035 +.038 4.029 +.028 +.020 +.013 +.015 +.009 +.011 +.0:10 +.023 4.031 1.546 +.023 +.024 +.023 +.021 +.025 +.021 +.008 4.010

+.07

+.008 +.007

+021

+.020 1.596 +.017 +.016 -.Q12 +.012 +.019 +.021 +.005 +.006 +.006

.005

+.006 +.017 4.015 1.646 4.012 +.009 i-.009 +.009 +.014 +.014 +.004 +.004 4.003 +.004 +.005 +.011 +.009 1.695 +.Ó08 +.005

.006

+.007 -.008 +.006 +.002 +.003 4.002. +.003 +.003 +.007 +.006 1.745 +.004 +.002 +.002 +.002 +.003 +.002 +.001 +.00 +.001 4.001 +.001 +.003

+.003

1.795 4.000 +.fJ0 4.000 +..Q00 4.0.00 +.000

+000

4.000 4.000 4.001 +.000 +.001 1.845 -.000 -.000 -.000 .000 -.000 -.000 -.000 -.000 -.000 -.000 +.00i- -.000 -. 000 1.895 -.000 -.000 -.000 -.000 -.000 -.000 -.000 -.000 -.000 -.000 4.001 - .000 - .000 1.945 -.000 -.000 --.00Ó -.000 -.000 -.000 -.000 -.000 :.000 .000 +.001 - .000 -.000 1.995 -.000 -.000 -.000 -.000 -.000 -.000 -.000

-.000

-.000 -.000 +.001 -.000 -.000

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Table 3: Wave and wind forecasts DTNSRDC for 58°18'N, 12°l8tW.

7) 8)

Wind Wind sign. direction period direction period

Date 1T speed direction wave 1 1 2 2

height

w1 /3

rn/s degrees m degrees sec degrees sec

peak at 6 sec

broad 11 - 15 sec, very small height principally swell, very small wind sea very broad

peak at 12 sec; waves at location 127 will decrease to 4.3 meters by

1200CMTon17-3-78

small

1 = primary wave system

2 = secundary wave system.

14-3-78 0000 10.3 116 5.3 186 4 - 7 none -14-3-78 1200 8.7 065 3.7 246 16 036 6 15-3-78 0000 7.7 033 3.0 246 18 036 11 2) 15-3-78 1200 5.5 042 3.2 036 11 - 12 246 12 15-3--78 0000 1.5 294 3.3 246 18 036 15-3-78 1200 4.0 107 3.2 216 - 246 15 036 8 - 9 16-3-78 0000 11.3 064 5.1 036 11 - 15 216 15 16-3-78 1200 16.2 028 5.7 036 10 - 16 246 12 16-3-78 0000 6.6 057 3.3 246 15 036 9 16-3-78 1200 12.3 033 3.6 036 9 246 18 17-3--78 0000 12.6 007 3.8 036 9 276 14 17-3-78 0000 8.7 006 3.7 036 9 276 16 17-3-78 1200 4.6 292 3.0 246 - 276 12 006 6 18-3-78 0000 9.8 218 3.3 246 - 276 12 036e 11 18-3-78 1200 14.9 195 4.5 186 - 216 11 186-216 6