A seakeeping experiment research on Flokstra container ship model

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A Seakeeping Experiment Research

On Flokstra Container Ship Model

by Z H E N G - Q U A N Z H O U D E - C A I Z H O U NAN X I E ( July 20 , 1996 )

A B S T R A C T

An experiment is carried out to investigate the effect of wave direction and rolling motion on deck wetness and on the relative motion for a large fast container ship. The experiment results of regular waves and irregular waves are presented. From this experiment, it is evident that the wave direction and rolling motion have a considerable influence on relative motion at midship.

1. INTRODUCTION

Technicat developments in the ship building and shipping industry, demand reexamination o f the " Intemational Convention on Load Lines 1966 " ( I C L L 1966 ) with the aim o f developing a tool for the assignment o f freeboard which needs to be flexible enough to deal with conventional as well as unconventional ships.

• The goal o f this research project is to develop freeboard tables conditioned on deck wetness and setting up respective requirements for load line calculations, which w i l l support

" Intemational Maritime Organization " ( I M O ) activities to revise the 1966 convention for a year 2000 release.

According to the requirement o f the " SLF Load Lines Working Group ", The Register of Shipping o f t h e People's Republic o f China arrange an experiment to investigate the effect o f wave direction and rolling motion on deck wetaess and on the relative motion for a large fast container ship . China Ship Scientific Research Center undertake this ship model experiment .

This paper is reporting the experiment results and analyzing the phenomena revealed by this experiment.

2. D E S C R I P T I O N O F T H E M O D E L T E S T

2.1 Selection of Wave Directions

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largely concemed on head seas. This approach is rational since it has been confirmed that the bow relative motion is largest in head seas when determine the freeboard height at bow . Due to the combined effect of the vertical and lateral motion, however, higher relative motion at midship may occur in oblique waves.

For container ships having a large nahiral roll period can lead to large motion due to near-synchronous conditions in oblique waves. Therefore, in the present study, measurements o f relative motion and deck wetness were carried out at midship and at oblique wave directions.

Summarizing it may be concluded that for a larger container ship the highest relative motion due to vertical > lateral motion may be expected in 30 to 60 degree wave directions, either approaching from the bow or from the stem. Within this range no priority can be given to a certain heading. For the present research the model tests were conducted initially in bow and stem quartering waves e.g. approaching 45 degrees o f f the bow and the stem. Preference was given to 45 degrees heading since in stem quartering waves largest roll angles due to near-synchronous conditions w i l l occur in the wave length and ship speed range tested. It follows that the relative motion was considerably influenced by the roll motion.

2.2 Seakeeping Basin

This ship model experiment is carried out in the seakeeping basin o f China Ship Scientific Research Center from June 10 to July 6, 1996.

'China Ship Scientific Research Center (CSSRC) is a research and development organization in ship engineering. It offers service in R & D > model experimentation and consultation in concept design for various marine stmctures.

CSSRC's headquarters is located at W u X i , JiangSu province, with a branch office at Shanghai. CSSRC has more than 40 years of history, and has tested and given consultations to most o f t h e large marine stmctures in China.

Seakeeping basin is one of main facilities in CSSRC. The dimensions o f the seakeeping basin are 69mx 46mx 4m (water depth), wave makers on two adjacent sides, capable o f generating regular and irregular waves. A bridge spans the diagonal o f t h e basin and is rotatable 45°. Model mnning or towed by a carriage under the bridge (max. speed'4m/s) may be tested at any required angle with respect to the waves. Wind and current effect also may be simulated.

2.3 Ship Model

The tested ship is a container ship provided by " SLF Load Lines Working Group " referred to as the " Flokstra-Ship " . The main particulars o f the ship are listed in Table 1 and a body plan is reproduced in Figure 1 as well as the stem and stem outlines in Fig.2, two ship model photo in Fig. 3 and Fig. 4.

The ship model has an integral hull form including the hull form above waterline, an integral deck form, as well as a set o f appendages: bilge keels, propeller shafts, shell bossing, two propellers, a mdder.

The ship model constmcted to a scale of 1 to 80 of glass reinforced polyester .

The scale was mainly determined by the capacity o f t h e irregular wave generator installed in the Seakeeping Laboratory ofthe CSSRC .

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The model was fitted with bilge keels .

Table 1 Principal Ship Dimensions

No.

Denomination

_Symbol

_{Full Scale}

_Ship

Model

1 Total length

_284.0m

_3.55m

2 Lpngth between perpendiculars

Lpp

270.0m

3.375m

3 Breadth

_Bwr

_32.2m

_402.5mm

4 Total height

_H

_18.662m

233.3mm

5 Displacement volume

_V

_56097m^

0.1096m^

6 Displacement weight

_A

_57499t.

_109.6kg

7 Draught even keel

_T

_I0.85m

135.6mm

8 Block coefficient

_{c „}

_0.598

9 Center of gravity above base

_Zg

_13.49m

_168.6mm

. 10 L . C . G . aft of station 10

_{X g}

_-10.12m

_-125.6mm

' 1 1

Transverse gyradius in roll direction

_0:3753^,

0.375Bwr

12 Longitudinal gyradius in pitch direction

_0.248L«„

Wl.

0.248Lw,

13 Metacentric height

_{G M}

_1.15m

_14.4mm^

w l

14 Natural roll period

_24.9s

_2.78s

15 Natural pitch period

_To

_8.6s

_0.96s

16 Length of bilge keel

₁

_47.0m

587.5mm

17 Breadth of bilge keel

_b

_0.48m

6.0mm

18 Diameter of propeller

_d

_5.56m

_S2.0mm

2.4 Model Preparation And Calibration

The weight distribution in the model was adjusted on a low — mass trimming table , by means o f which the exact position of the center o f gravity in the vertical and horizontal" directions was obtained .

The longimdinal radius o f gyration in pitch direction was adjusted on the trimming table, whereas the transverse radius o f the gyration in roll direction was adjusted and verified by a roll' heeling experiment in still water.

2.5 Test Content

•I

The primary aim o f t h e present experiment is tó investigate the effect of wave •direction , wave height . period and ship speed, as well as rolling motion on relative motion and deck wetness at midship.

The main test contents are rolling decay test, regular wave test and irregular wave test. The main measurements in this ship model experiment are :

a) Determining the roll damping in still water ;

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waves ;

c) Measuring the relative motion in several stations ;

d) Measuring the frequencies o f deck wetness in several stations ; e) Measuring the vertical acceleration at bow part o f t h e ship .

2.6 Test Procedures

During the tests the model was self — propelled by two stock propellers . The model was completely free in its motions . It was kept on course by an auto — pilot , controlling the rudder in such a way that a straight course through the middle o f the basin was maintained by small rudder angles . The model was connected by a light — weight vertical rod in the center o f gravity o f t h e model to a low — mass and low — friction subcarriage , So that no appreciable forces or moments were transmitted on the model .

Each test run contained simultaneous recordings o f the following quantities by data recording computers .

— Heave . pitch and roll angles , recorded by a six — degree.freedom motion measuring system connected to the l i g h t w e i g h t rod . ••• • •

Relative motion (with respect to the wave surface ) at the bow and the stern as well as at amidship , obtained by resistance wire wave probes attached vertically on the model at the station o f 17 , 14 , 10 and Son the weather-side .

— Vertical acceleration at the station 17 , measured by a 2g accelerometer .

— Model speed , measured by a slotted disc with photo cell pick-up '. Wave height. determined by two wave probes , one fixed to the moving carriage in front

o f the ship model, another fixed on the center at basin . The wave probes were calibrated before the tests.

In irregular wave case , the frequency and probability o f deck wetness at station 17 . 14 , 10 and 5 , recorded by a computer .

The requirement o f velocity simulated in model test is listed in Table 2 .

Table 2 Velocity Simulated of Ship Model

No.

_{Full scale (knot)}

_{Ship model (m/s)}

Fn

1 ₀

₀

0

2 ₁₀

_0.575

0.10 .

22 _i.265

_{0 2 2}

4 ₂₇

_1.553

0.27 3. ANALYSIS OF T E S T R E S U L T S IN R O L L DAMPING T E S T

Roll damping tests were first performed in calm water at a speed o f 0.0, 10.0, 22.0 and 27.0 knots to determine the roll damping coefficients. During test, a transient moment acting on the ship model, then, recording the curve of decHning roll angle history. Analysis the declining curve, measuring the period o f roll motion and the roll damping coefficients.

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The test content is listed in Table 3.

Table 3 The Content of Roll Damping Test

No. Ship model velocity (m/s)

Full scale speed (knot) Test content

A—01 0 0 The history of rolling

angle

A—02 0.575 10

The history of rolling angle

A — 0 3 1.265 22

A—04 1.553 27

3.1 N a t u r a l Period of Roll

According to the measured declining curve, the period o f roll for every time can be found. Averaging several periods,, fmding the curve o f rolling period to Froude number as Fig.5. I n Fig.5, there is'.r; a little variation of rolling period as the increase o f velocity. The exact results o f rolling period list in Table 4.

Table 4 Results of Natural Period of Rolling Motion

Fn 0 _0.10 0.22 0.27

24.6 24.8 23.7 23.8

3.2 R o l l Damping Coefficient

A curve o f relative declining roll angle can be obtained according to the roll damping test. Fig. 6 is the relative declining angle curve at the zero forward speed condition. In Fig.6, A(j) is the declining value of rolling angle in every half period, (j) is the average roll angle. The rolling damping moment can formulated as following relation in linear condition.

Mi^) = B,^ ( 2 )

in which

n n

( 3 )

Where " a " is average value of relative declining angle in Fig.6, D the displacement volume, h metacentric height. In the free rolling case, = CO , , the non-dimensional roll damping coefficient represents as

T 2 A(j) 2 a

2 h * = - - ^ = — ( 4 )

TC (j) 7t ^ ^

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Linearizing, finding the value a and the non-dimensional roll damping coefficients as Table 5. Roll damping coefficients 2 varies according to the average roll angle shown in fig.7.

T a b l e 5 Non-dimensional Roll Damping Coefficients

F n 0 0.1 0.22

a 0.1519 0.2461 0.6261

2f^* 0.0968 0.1566 0.3985

The variation o f 2 according to the ship velocity, shown in Fig.8. For F L O K S T R A container ship, roll damping coefficient has little change as the increasing o f roll angle ; however, there is large change as the increasing o f velocity.

4. DISCUSSION O F R E G U L A R W A V E T E S T R E S U L T S

4,1 Content of Regular W a v e Test

The regular wave tests were conducted with different wave directions , since the roll motion has an importance influence on determining the freeboard height at midship. The wave angles are head sea . beam sea and oblique wave(135'').

The speeds are 10 and 22 knots .

A t each headings , tests were conducted in 15 regular waves with lengths varying between a ratio o f _{-0.4 ~ 3.5 ; the wave height was kept constant at 70.0 mm .}

The results o f the regular wave tests w i l l ultimately be used to check the theoretical computer program, therefore the accuracy o f the test result must be required. On the another hand, the results o f t h e regular wave test w i l l be used to predict the response in irregular seas by the linear superposition principle, therefore the selected wave frequency range in regular wave tests covers the main part o f wave energy in irregular seas and is sufficiently large to minimize the inaccuracy in the prediction due to the extrapolation o f t h e ship responses.

A l l measuring signals were recorded on hard disk o f a computer after magnified by a signal magnifier.

The content o f experiment is listed in Table 6.

T a b l e 6 Test Content and Headings in Regular Wave

Test No. _{wave direction Ship model velocity (m/s)} _{Test content}

B—01 180° 0.575 Wave , roll > pitch , heave ,

the relative motion at station \ 7 \ \ 4 \ \ 0 \ 5' and vertical acceleration at station 17*

B—02 180° 1.265

Wave , roll > pitch , heave , the relative motion at station \ 7 \ \ 4 \ \ 0 \ 5' and vertical acceleration at station 17*

B—03 135° 0.575

B — 0 4 135° 1.265

B — 0 5 90° 0.575

B—06 90° 1.265

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Harmonic analysis, was applied to determine the first harmonic o f the measured signals having the encounter frequency o f the waves. This analysis is necessary in view o f the higher frequency oscillations which were superimposed upon the recording traces. Then time analysis is applied to determine the amplitude , mean value by averaging the recordings over a number of cycles.

The measured motion responses are presented as amplitude transfer functions versus wave length/ship length ratio. The figures of results are listed as Table 7. In those figures, all parameters are dimensionless, the meanings o f parameters see symbols set, " A i s the results o f tests, lines represented as the theoretical results by the strip theory. Other condition also listed in those figures.

Table 7 The Frequency Response Function Curves in Regular Wave Test

Test No. _{B—01 B—02 B—03 B—04 B—05 B—06}

Wave direction (deg.) _180- ₁₈₀ ₁₃₅ ₁₃₅

90 90

Full scale speed (knot) 10 22 10 22 10 22

Pitch Fig.9 _{Fig. 10 Fig. 11 Fig.12}

_/

Roll

_/

_{Fig. 13 Fig. 14 Fig. 15 Fie. 16}

Heave. _{Fig. 17 Fig. 18 Fig.19 Fig.20 'Fig.21 Fie 22} Relative motion at station 17

Fig.23 Fig.24 Fig.25 Fig.26 Fig. 27 Fie 28' Relative motion at station 14 _{Fig.29 Fig.30; Fig.31 Fig.32 Fig.33, Fic.34} Relative motion at station 10 _{Fig.35 Fig.36 Fig.37 Fig.38 Fig.39 FiH.40}

Relative motion at station 5 _{Fig.41 Fig.42 Fig.43 Fig.44} P

Fig.45 Fie,46 Vertical acceleration at station 17 Fig.47 Fig.48 Fig.49 Fig.50 _{Fig.51 Fig.52}O 4.2.1 Pitch Response

Fig..9 Fig. 12 are the pitch responses. Iri those figures, The pitch response in head seas were much larger than in bow waves (ISS") the pitch response is increasing as the

increasing of velocity.

4.2.2 Roll Response

Fig. 13 ~ Fig. 16 are the roll responses. In those figures, The roll response in beam waves were much larger than in bow waves (135°) ; as t.he increasing of velocity, the roll

response is decreasing because ofthe roll damping sharply increasing. 4,2.3 Heave Response

Fig. 17 ~ Fig. 22 are the heave responses. In the case o f beam waves, the heave response r a f o tends to 1.0 since the heave motion response is essentially synchronous with waves •

The heave response in bow oblique waves(135*) is larger than in head waves ; the heave response is decreasing as the increasing of velocity.

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4.2,4 Relative Motion At Station 17

The transfer function of relative motion at station 17 are shown in Fig.23~28. From those figures, one can see that the response in bow quarter(135°) wave are larger than in head wave and beam waves; the relative motion in head waves are large than that o f in beam waves, the larger the speed, the higher the relative motion amplitude.

4.2.5 Relative Motion At Station 14

Fig 29-34 show the transfer functions o f relative motion at station 14, the tendency is similar to that of station 17.

Fig.35~40 show the transfer functions o f relative motion at station 10 (midship). The relative motion i.i'amplitude in beam waves are little larger than that in bow obliquejwave and head waves. The relative

motion in bow oblique waves are larger than that o f in head waves.

Fig.41~46 show the transfer function of relative motion at station 5. The relative motion amplitude in beam waves , bow oblique wave and head waves are almos.t the same. The relative motion in bow oblique waves are little larger that those in head waves and in beam waves.

4.2.8 Vertical Acceleration At Station 17

Fig.47~52 show the transfer fimctions o f vertical acceleration at bow. The acceleration in bow oblique waves and head waves are larger than that in beam waves . The larger the ship speed, the larger the vertical acceleration.

In general, the larger the ship speed, the larger the response of pitch, heave, relative motion and vertical acceleration, the smaller the roll response. The relative motion transfer functions in bow oblique wave are larger than that in head waves. The test results are in good agreement with the theoretical predictions.

5 T E S T S IN I R R E G U L A R WAVES

5.1 Test Contents

The tests are carried out by using self-propelled model in irregular waves, and the test mns are listed in Table 8. For each test mn, roll . heave , pitch . vertical acceleration at bow , relative motion at stations 17. 14, 10 and 5 are measured, and the number of deck wetaess in each mn are obtained. Wave headings are head sea, bow quarter and beam seas.

According to the specification of seakeeping model tests, the test period are corresponding to one

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hour at full scale time. During the test, both the wave at a fixed point in the basin and the encounter at the front o f t h e ship model are measured by wave probes.

Table. 8 Test Content and Headings in Irregular Wave

Test

No.

Wave

direction

'(deg.)

Full scale

speed

(knot)

Significant

wave height

(m) .

Average wave

period To, (s)

_{Test Content}

C-01

180

22

8.37 _14.10

_{Wave ^ roll , pitch}

heave ^ the relative

motion at station 1 7 \

U\ 1 0 \ 5\ deck

wetness and vertical

acceleration at station

**17* • .-.-^**

C-02

180

10

7.15

12.88 Wave ^ roll , pitch

heave ^ the relative

motion at station 1 7 \

U\ 1 0 \ 5\ deck

wetness and vertical

acceleration at station

**17* • .-.-^**

C-03

135

10

8.25

12.25 Wave ^ roll , pitch

heave ^ the relative

motion at station 1 7 \

U\ 1 0 \ 5\ deck

wetness and vertical

acceleration at station

**17* • .-.-^**

C-04

135

10

7.19

11.99 Wave ^ roll , pitch

heave ^ the relative

motion at station 1 7 \

U\ 1 0 \ 5\ deck

wetness and vertical

acceleration at station

**17* • .-.-^**

C-07

135

22 1.11'

12.25 Wave ^ roll , pitch

heave ^ the relative

motion at station 1 7 \

U\ 1 0 \ 5\ deck

wetness and vertical

acceleration at station

**17* • .-.-^**

C-05

45

10

1.61

11.00 Wave ^ roll , pitch

heave ^ the relative

motion at station 1 7 \

U\ 1 0 \ 5\ deck

wetness and vertical

acceleration at station

**17* • .-.-^**

C-06

45

22

8.68 • 11.20

Wave ^ roll , pitch

heave ^ the relative

motion at station 1 7 \

U\ 1 0 \ 5\ deck

wetness and vertical

acceleration at station

**17* • .-.-^**

5.2 Results of Irregular Wave Test

Basing on the curves o f calibration, the voltages are changed into physical signals after A / D . These signals are analyzed by using spectral technical, and yielding significant values o f each responses.[3]

The statistical values in irregular tests are listed in Tables 9 and 10, these values are corresponding to the full scale ship, and the responses are significant single amplimdes, roll and pitch are in degree.

Table 9 The Statistical Values in Irregular Wave Tests

No.

Test No.

_C-01

_C-02"

_C-05

_C-06

No.

_{Wave direction (deg.)}

180

45

45 No.

Full scale speed (knot)

₂₂

₁₀

_10'

22

1 _Wave

S,/3(m)

8.37

7.15

7.67

8.68

1 _Wave

Toic(s)

9.30

10.02

15.38

22.36

2 _{Relative motion at station 17}

_S,/3(na)

_6.99

_{1 5.16}

3.34

7.80

3 _{Relative motion at station 14}

_S,/3(m)

_3.36

_1.55

3.10

3.55

4 _{Relative motion at station 10}

_S|/3(m)

_2.15

_2.36

5.23

6.39

5 Relative motion at station 5

_S,/3(m)

2.48

2.16

2.99

7.33

6 Roll

_{f / 3 (deg.)}

_/

_5.34

17.61

7 Pitch

_(deg.)

_2.60

_2.19

_1.61

1.76

8 Heave

_{Zi/3 (m)}

_3.06

_1.70

1.80

1.98

9 _{Vertical acceleration at station 17}

_Ay,

_{(g) 0.301}

_0.146

0.065

0.069

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Table 10 The Statistical Values in Irregular Wave Tests

Test No. _C-03 _C-04 _{' C-07}

No. Wave direction (deg.) 135 135 135

Full scale speed (knot) _{' 10} ₁₀ ₂₂

S,/3(m) 8.25 7.19 7.72

1 Wave _To,c(s) 10.11 9.84 8.32

2 _{Relative motion at station 17} _S>o(m) _6.25 _5.62 _{.7 J O}

3 _{Relative motion at station 14} _{2.92 "} _2.64 _4.13

4

1

Relative motion at station 10 S,/3(m) 3.04 2.71 2.45

5 _{Relative motion at station 5} _Si/3(m) _{3.82 '} _{3.44 ; 3.12}

6 Roll _{<}>,/3 (deg.)} _8.62 _6.34 _{3.69 ;}

7 Pitch _{e./3 (deg.):} 2.56 2.11 2.57 •

8 Hpave _{Z,/3 (m)} 2.28 2.24 3.10

9 _{Vertical acceleration at station 17} _Ai/i_(g) _{0.236 1 0.200} _0.384

For the test conditions, numerical predictions are given by a sfrip theory program and compared with the model test. These are shown in Tabic l l - A - T a b l e 11-D.

Table 11-A Calculated And Measured Tests Statistical Values in Irregular Wave

Full scale speed (knot) ₂₂ _{1 10}

Wave direction (deg.) 180 180

Sea state H|/3=8.37m To,-14.10s H„3=7.15m To,=12.88s Test No. _C-01 _C-02 Calculatie n Experimen t Calculatie n Experimen t

Relative motion at station 17 (m) 6.35 6.99 4.43 5.16

Relative motion at station 14 (m) 3.50 3.36 1.92 1.55

Relative motion at station 10 (m) ; 1.74 .. 2.15 : 2.18 2.36

Relative motion at station 5 (m)' 2.26 : 2.48 2.32 2.16

Roll (deg.) _/ _/ _{/ ' /}

' Pitch (deg.) _2.77 _2.60 _2.17 _2.19

Heave (m) 3.04 3.06 1.94 1.70

Vertical acceleration at station 17 (g) 0.268 0.301 0.137 0.146

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Calculated A n d Measured T h e Statistical Values

in Irregular Wave

Full scale speed (knot)

₁₀

10 Wave direction (deg.)

₁₃₅

135 Sea state

To,=

=8.25m

12.25s

_T„,=

7.19m

11.99s

Test No.

_c-03

C-04

Calculatio

n

Experimen

t

Calculatio

n

Experimen

t

Relative motion at station 17 (m)

5.24

6.25 _4.72

_5.62

Relative motion at station 14 (m) i 2.95

_2.92

_2.67

2.64 Relative motion at station 10 (m)

2.17

3.04 _1.94

_2.71

Relative motion at station 5 (m)

2.90 _3.82

_2.62

3.44 Roll (deg.)

—

8.62 /

6.34 •.

Pitch (deg.)

_{" 2.55}

2.56

2.23

2.11 Heave (m)

_2.65

_2.28

2.23 _2.24

Vertical acceleration at station 17 (g)

0.200 _{0.236 I 0.179}

0.200 ' ;

11-C Calculated A n d Measured The Statistical V a l

in Irregular Wave

Full scale speed (knot)

_{22 1}

j Wave direction (deg.)

₁₃₅

• Sea state

To,=

7.72m

12.25s

Test No.

_C-07

Relative motion at station 17 (m)

Calculatio

n

6.35 Experimen

t

7.50 Calculatio

n

Experimen

t

Relative motion at station 14 (m)

Relative motion at station 10 (m)

Relative motion at station 5 fm)

S 4.14

2.27

2

6-1

4.13 1 2.45 J

Roll (deg.)

₁

3.69

•

Pitch (deg.)

Heave (m) ,

2.58

2.97

2.57 i n

Vertical acceleration at station \ 7

_{0.299 J}

_0.384

J . 1 O

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Table l l - D Calculated And Measured T h e Statistical Values

in Irregular Wave

Full scale speed (knot)

10

22 Wave direction (deg.)

45

45 H,/3=7.67m

H,;3=8.68m

• Sea state

To,=l 1.00s

To,=I 1.20s

Test No.

C-05

C-06

Calculatio Experimen Calculatio Experimen

n

t

n

t

Relative motion at station 17 (m)

3.35

3.34

4.24

7.80 Relative motion at station 14 (m)

2.27

3.10 . 2.97

3.55 Relative motion at station 10 (m)

2.70

5.23

3.64

6.39 Relative motion at station 5 (m)

2.56

2.99

2.37

7.33 Roll (deg.)

/

. 5.34-!

/

17.61 Pitch (deg.)

1.68 T.61 , 1.74

1.76 Heave (m)

1.80

2.00

1.98 Vertical acceleration at station 17 (g)

0.057 ' 0.065

0.033

0.069 5.2.1 Effect of Wave Heading

Relative motion at each station varying with heading angles is listed in Table 12. For the statistical values of relative motion at stations 14,10 and 5, significant values in bow quarter and quarter following waves are larger than those o f in head waves. In quarter following waves largest roll angles may occur due to roll resonance, relative motions are even larger than in head waves.

Table 12A T h e Significant Value of Relative Motion /Significant Wave Height

^ ' ^ " - ^ Speed Fj=10knot

Angle

Station

45°

135°

180°

17"

0.436 • 0.782

0.722 14*

0.404

0.367

0.217 10*

0.682

0.377

0.330 5*

0.390 • 0.478

0.302

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Table 12B T h e Significant Value of Relative Motion /Significant Wave Height

Speed r,=22knot

^ \ ^ ^ ^ A n g l e

Station

45°

_135°

_180°

17"

0.897 _0.972

_0.835

14*

_{0.409 i 0.535}

0.401 10*

0.736 _0.313

_0.257

5*

0.845 _0.404

_0.296

5.2.2 Effect of Ship Rolling

In order to demonstrate the effect o f rolHng to relative motion, the test resuhs o f relative motion at station 10 are listed in Table 13.

Form Table 13, it is seen that, in test mn No. C-06, the encounter wave period are approximate to the roll namral period, the ship is in roll resonance condition, large roll motion i& excited, therefore, relative motion is also large . Thus, when determining the freeboard at midship, the effect o f rolling on relative motion can not be neglected.

Table 13 Effect of Ship Rolling

Test No.

C-01

C-02

C-03

C-04

C-07

C-05

C-06

Wave direction (deg.)

₁₈₀

₁₃₅

45 Full scale speed (knot)

22"

10

22

10

22 Encounter wave period To„(s)

_9.30

_10.02

_10.11

_9.84

8.32

15.38

22.36 Natural roll period (s)

•/

/

_{24.80 24.80 23.70 24.80 23.70}

Roll (deg.)

/

8.62

6.34 _{3.69" 5.34}

_17.61

The relative motion at station

iO/significant wave height

0.257 _{0.330 0.368: 0.377 0.317 0.682 0.736}

5.2.3 Coefficient of Dynamic Swell up

The dynamic swell up coefficient is defined as:

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suc= —

where S is the real relative vertical motion, by absolute motion minus incident wave surface coefficients are listed in Table 14. the dynamic 1.1-1.2.

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is the notional relative motion which defined elevation. The measured dynamic swell-up swell up coefficients at bow are between

Table 14. Coefficient of Dynamic Swell up

Test No.

_C-02

_C-03

_C-04

_C-05

_C-01

_{' c-07}

Coefficient of dynamic swell up

1.16

1.19 " 1.19

1.00

1.10

1.18 Average

_1.

₁₄

6. CONCLUSION

From present seakeeping model experiment, test results o f motions and relative motions for the Floksh-a ship in regular and irregular waves, at head sea . bow quarter , beam sea , quarter following directions are obtained, which w i l l be used to check on the computer program. It can be concluded that the wave direction and rolling motion have a considerable influence on relative motion at midship. Thus, when determining the freeboard at midship based on the deck wetness, only the effect o f head wave taken into account is not sufficient, the effect o f oblique waves should also be taken into account.

R E F E R E N C E S

[1] Zhou.Z.Q, Xie. N and Gu M et al.: « Seakeeping Model Test Program for the Flokstra Ship " , CSSRC Technical Report, March,1996.

[2] Peng.Y.S: "Seakeeping", China Defense Press,1989.

[3] Xie. N , Zhou. Y . N et al.: " Data Processing o f Seakeeping and Ocean Engineering Model Tests " , CSSRC Technical Report,Dec,1991.

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2 0

15 o . b

Fig.5

0.30

0.25 -A

0.20 -0.15

0.10 -4

0.05 H

0 . 0 0

0.1 0.2

N a t u r a l p e r i o d of roll

0.3 Fn

A A A A A Experiment

Best fit m e t h o d

Fn = 0.0

A A —rr-A

Fig.6 Relative d e c o y a m p l i t u d e

10 11 •.i'2

4 >(deg.)

19

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1.00 - ,

CM

0.80 -4

0.60 -A

0.40

0.20 & ^ ^ ^ Fn = 0 . 0 0

P a a n a F n

= 0 . 1 0

^•i"^-^-^ F n

= 0 . 2 2

0.00 r

r

Fig.7

é ) é Ó l b l'l 1'2 l'3

A

l'5..

4>(cleg.)

Roll d a m p i n g c o e f f i c i e n t

1.00 - ,

•o0.80

0.60

0.40 -0.20

-A

0.00

0.00 Fig.8 Roll d a m p i n g c o e f f i c i e n t

o . i o 0 . ^ 5

Fn

20

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1.5 1.0 H O O O O O Experiment — - — Calculotion F „ = 0 . 1 0 / u = 1 3 5 ° 4.0

Fig. 11 C a l c u l a t e d and m e a s u r e d pitch t r a n s f e r function

1.5 1.0 0.5 H 0.0 2.'O X / L O O O O O Experiment Calculotion F „ = 0 . 2 2 3.'0 4.0

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6.0 4,0 0.0 O O O O O Experiment Calculation

r„=o.io

Fig.15 Calculated and m e a s u r e d roll transfer function

6.0 4.0 H 2.0 H O O O O O Experiment Calculation F „ = 0 . 2 2

Fig. 14 Calculated ond m e a s u r e d roll transfer function

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6.0 4.0 H 2.0 H 0.0 0.0 O O O O O Experiment Calculotion Fn = 0 . 1 0

Fig. 15 C a l c u l a t e d and m e a s u r e d roll tronsfer function

6.0 4.0 2.0 H O O O O O Experiment Calculotion F n = 0 . 2 2

F i g . 1 6 Colculated ond m e o s u r e d roll tronsfer function

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1.0 0.5 0.0

-O O O O O O E x p e r i m e n t Calculotion F n = 0 . 1 p / . i = 1 8 0 0 / O 0 / ƒ \ 0 O /

0. b i.'o 2.'0 3.'o 4!'o

Fig. 17 Calculoted a n d m e a s u r e d heave t r o n s f e r function

1.5 n

t.0 H

X / L

F i g .1 8 Colculated and m e a s u r e d heave t r o n s f e r function

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1.5 -n

O O O O O Experiment

Calculation F „ = O . 1 0

4.0

Fig.19 Calculated and m e a s u r e d heave t r a n s f e r function

1.5 1.0 -A O M 0.0 O O O O O Experiment Colculation F „ = 0 . 2 2 4.'O

Fig.20 Calculoted ond m e a s u r e d heave t r a n s f e r function

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1,5 1.0 H I x l 0.5 0.0 1.0

V L

O O O O O Experiment Calculation F„ = 0 . 1 0 ^ = 9 0 ° 3.0 4.0

Fig.21 C a l c u l a t e d and m e a s u r e d heave t r o n s f e r function

1.5 1.0 H INI 0.5 0.0 O.Ö O O l.'O 2.'o

X / L

O O O O O E x p e r i m e n t Calculation F n = 0 . 2 2 / / = 9 0 ° 3.Ö 4.0

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5.0 4.0 H ^ 3.0 H 2.0 H 1.0 0.0 O.Ö 1.0 ^ 0 O O O O O Experiment Calculation F„ = 0 . 1 0 , u = 1 8 0 ° 3.0 4.0

F i g . 2 3 Calculated and m e a s u r e d the relative motion transfer function at station 17

5.0 4.0 H ^ 3.0 \ o 00 2.0 H 1.0 H 0.0 o.b O O " 1.0 2.0

V L

O O O O O Experiment C a l c u l a t i o n F „ = 0 . 2 2 ^.0

Fig.24 Calculated and m e a s u r e d the relative motion transfer function ot station 17

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5,0 -1 4.0 H 2.0 1.0 0.0 O.b A / L O O O O O Experiment Calculotion Fn = 0 . 1 0

TF

4.0

Fig.25 C a l c u l a t e d a n d m e a s u r e d the relative motion t r a n s f e r function ot station 17 00 5.0 4.0 H 3.0 H 2.0 1.0 0.0 0.0 -S O o O O O O O E x p e r i m e n t Calculation F, = 0 . 2 2 1.0 2.Ö X / L 3.Ö 4.0

Fig.26 Calculoted and m e a s u r e d the relative motion t r a n s f e r function ot station 17

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5.0 4.0 H ^ 3.0 H \ O 2.0 H O O O O O E x p e r i m e n t C a l c u l a t i o n F„ = 0 . 1 0

Fig.27 Calculated and m e o s u r e d the relative motion transfer function ot station 17

5.0 4.0 H ^ 3.0 H 00 2.0 H 1.0 H 0.0 O O O O O Experiment Calculation F „ = 0 . 2 2

Fig.28 C a l c u l a t e d and m e a s u r e d the relotive motion t r a n s f e r function ot station 17

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5.0 4.0. H ^ 3.0 H (/) 2.0 O O O O O E x p e r i m e n t C a l c u l a t i o n F n= 0 . 1 0 M = 1 8 0 ° 4.0

Fig.29 C a l c u l a t e d a n d m e a s u r e d the relotive motion t r a n s f e r function ot station 14 5,0 4.0 ^ 3.0 -2.0 1.0 0.0 0.0 1.0 2.0 T X / L O O O O O E x p e r i m e n t C a l c u l o t i o n F , = 0 . 2 2 M = 1 8 0 ° 3.0 7 1 )

F i g . 3 0 C a l c u l a t e d a n d m e a s u r e d the relative motion t r a n s f e r function at station 14

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5.0 -n 4.0 H ^ 3.0 H \ O 00 2.0 H 1.0 H 0.0 0.0 i.b 2.0 O O O O O E x p e r i m e n t C a l c u l a t i o n F „ = 0 . i p 3.0

T'o

Fig.31 Calculoted ond m e a s u r e d the relative motion t r o n s f e r function ot station 14 5.0 4.0 H o o o o o E x p e r i m e n t C a l c u l a t i o n F „ = 0 . 2 2 M = 1 3 5 ° 4.0

Fig.32 C a l c u l a t e d a n d m e a s u r e d the relotive motion t r a n s f e r function ot stotion 14

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5.0 4.0 ^ 3.0 -2.0 1.0 H 0.0 0.0 O O O O O Experiment Calculation F „ = 0 . 1 0 M = 9 0 ° O ö " _~0_O_{u o~} 3.b o o

4.0-F i g . 3 3 C a l c u l o t e d ond m e a s u r e d ttie relotive motion t r a n s f e r function at stotion 14 5.0 4.0 H ^ 3.0 O 2.0 H 1.0 0.0 0. 1.0

V L

o o o o o E x p e r i m e n t Calculation F , = 0 . 2 2 / / = 9 0 ° O O 3.Ö

T^O

Fig.34 C a l c u l a t e d ond m e a s u r e d the relative motion t r a n s f e r function ot station 14

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5.0 n 4.0 H ^ 3.0 \

lfl

2.0 O O O O O E x p e r i m e n t •= Calculation Fn = 0 . 1 0 4.Q X / L

Fig.35 C a l c u l a t e d a n d m e a s u r e d the relotive motioin t r a n s f e r function at station 10 5.0 4.0 H ^ 3.0 H O 00 2.0 H T.0 H 0.0 O O O O O Experiment Calculation F „ = 0 . 2 2 /.i=180'' l.'O 2.0 X / L 3."0 ^0

Fig.36 C a l c u l a t e d and m e a s u r e d the relative motion tronsfer function ot station 10

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5.0 4.0 ^ 3.0 H O 00 2.0 H 1.0 H 0.0 O.Ö O O i.b

T T

X / L O O O O O E x p e n m e n t C a l c u l a t i o n F „ = 0 . 1 0 3.0 4.Ö

Fig.37 C a l c u l a t e d and m e a s u r e d the relative motion transfer function at station 10

5.0 n 4.0 ^ 3.0 H o 00 2.0 1.0 H 0.0 0.Ö O O O O O E x p e r i m e n t C a l c u l a t i o n F„ = 0 . 2 2 / ^ = 1 3 5 ° O O Q) 1.Ö

T F

X / L 3.0 4.0

Fig.38 Calculated and m e a s u r e d the relotive motion transfer function at station 10

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5.0 4.0 H ^ 3.0 -O 2.0 1.0 0.0 0.0 i . b -e e O-2.b A / L OOOOO Experiment Calculation F „ = 0 . 1 0 3,b 4.b

F j g . 3 9 C a l c u l a t e d ond m e a s u r e d the relative motion t r a n s f e r function ot station 10 5.0 -1 0 0 4.0 3.0 2.0 OOOOO Experiment Calculation F „ - 0 . 2 2

F i g . 4 0 C a l c u l a t e d and m e a s u r e d the relative motion t r a n s f e r function at station 10

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5.0 ^

OOOOO Experinnent Calculation F , = 0 . 1 0

2.0 H

Fig.41 Calculoted ond m e a s u r e d the relative motion transfer function ot station 5

4.0 1 n _J 5.0 - I 4.0 H ^ 3.0 d cn OOOOO E x p e r i m e n t Calculation Fn= 0 . 2 2 /u=180°

Fig.42 C a l c u l a t e d and m e o s u r e d the relative motion transfer function at station 5

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5.0 00 4.0 3,0 2.0 1.0 H 0.0 O.Ö O O

TF

X/ L OOOOO Experiment Calculation F „ = 0 . 1 0

FF

4.Ö

F i g . 4 3 C a l c u l a t e d and m e o s u r e d the relative motion t r a n s f e r function ot station 5 5.0 n OOOOO E x p e r i m e n t ~ — ^ — Colculotion F „ = 0 . 2 2 ^ 3.0 -2.0 H O O.Ö 1.Ö 2.Ö 3.Ö 4.b X/ L .

Fig.44 C a l c u l a t e d and m e a s u r e d the relative motion tronsfer function ot station 5

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5 . 0 - 1 4 . 0 ^ 3 . 0 -( / l 2 . 0 1.0 0 . 0

o.b

O O O O O E x p e r i m e n t C a l c u l a t i o n Fn = 0 . 1 0 o O O zr _ 2 o _ _ ^ O 1 . 0

F F

X / L

3.b

4.b

F i g . 4 5 C a l c u l a t e d ond m e a s u r e d the relative motion t r a n s f e r f u n c t i o n ot station 5 5.0 n 4 . 0 H v5 3 . 0 H Ul 2 . 0 1.0 0 . 0 0 . 0

TF

F F

X / L O O O O O E x p e r i m e n t Calculotion F „ = 0 . 2 2

11=90°

3.b

4 . 0

Fig.46 Colcutated a n d m e o s u r e d the relative motion tronsfer function ot station 5

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30.0 - 1 25.0 _{O O O O O}_{E x p e r i m e n t} C a l c u l a t i o n F „ = 0 . 1 0 / z = 1 8 0 ° 4.0

Fig.47 Calculoted ond m e a s u r e d the vertical a c c e l e r a t i o n transfer function at stotion 17

40.0 -i

35.0

-Fig.48 C a l c u l a t e d and m e a s u r e d the verticol a c c e l e r a t i o n transfer function ot station 17

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30.0 25,0 ^ 20.0 <^ 1 _5.0_H 10.0 5.0

-A

0.0 O O O O O E x p e n m e n t Calculation

Fn = 0.10

M=90°

F F

X / L 3.'0

Fo

Fig.51 C a l c u l a t e d and m e a s u r e d the vertical a c c e l e r a t i o n transfer function at station 17

30.0 - I 25.0 ^ 20.0 - { cn 15.0 H 10.0 H 5.0 0.0 O.Ö O O O O O Experiment — C a l c u l a t i o n

F„=0.22

fi=90° 1.Ö

F F

X / L 3.Ö 4.Ö

Fig.52 C a l c u l a t e d a n d m e a s u r e d the vertical a c c e l e r a t i o n tronsfer function at station 17

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