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Master thesis: Development of a practical tool to determine the hull damping of modern ship hull forms

Bilel SAAD

La Spezia 17.02.2014

Motivation

2 EMSHIP UNIVERSITÄT ROSTOCK

Roll damping prediction:

Why ?

Response in rough weather

Design of Stabilisation equipments

Aim ?

Modern hull forms

New methodology for

roll damping prediction

Alternative to Experimental model tesing

17.02.2014

Obstacles and Challenges

EMSHIP UNIVERSITÄT ROSTOCK 3

High Non linearity Equivalent linear roll

damping coefficient

Obstacles Remedy

Energy dissipation

Spring mass system Equation

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Scenario of the Numerical simulations

4 Simulation tools

CFD:

Potential flow theory: PDstrip

Component Analysis Method: IKEDA Original Method

Component Analysis Method: IKEDA Simple

formulation Method

Empirical method:

Miller method

3 Test

case ships

16000-18000 TEU Ultra large container ship

(Container ship N°1)

8000-9000 TEU Large container ship

(Container ship N°2)

DTMB 5415: ARLEIGH BURKE-class

destroyer

(US Navy Ship )

4 EMSHIP UNIVERSITÄT ROSTOCK 17.02.2014

Potential flow theory simulation: Pdstrip solver

• Potential flow solver : Strip theory+ Panel method

• Wave damping accurately predicted

• Forces on fins and appendages

• Output => Transfer function(RAO)

PDstrip => RAO 2DRoll=> Regression analysis

Roll damping coefficient

B44

5

PDstrip Numerical Simulations For the US Navy ship

Estimation of roll damping from the transfer function (RAO)

Beam seas ,0 forward speed & T=6.15 m

6

0

2

4

6

8

10

12

14

0 0,5 1 1,5 2 2,5 3 3,5 4

Ro

ll R

AO

(η

44

/kA

)

λ/L

PDSTRIP DTMB 5415 Stationary test (0 Fw speed) Beam seas

Experimental RAO DTMB 5415 Stationary test (0 FW Speed, Beam seas)

Round bottom assumption => Lower eddy making damping

EMSHIP UNIVERSITÄT ROSTOCK 17.02.2014

Shape of the bottom of the US Navy ship model DTMB 5415

7

Sharp corners

and high rake

zones


Sensitivity analysis for PDstrip RAO regarding the GM value for the container ship N°1

8

Roll transfer function(RAO) in (°/m) versus wave frequency in (rad/s)

stern quartering (45° from the stern) , 21 kts, GM=9m

0

0,5

1

1,5

2

2,5

3

0 0,2 0,4 0,6 0,8 1

Ro

ll R

AO

in (

de

g/m

)

Wave frequency in (Rad/s)

Experimental PDstrip RAO, 45°, GM=9m , 21 Kts PDStrip, 45°, GM=9.1m,21 kts

Difference due to 10 cm change in GM


Component analysis method: IKEDA original and IKEDA simple methods

9

Component analysis method

Discretisation of the damping coefficient

Be = Bw + BF + BBK + BE + BL

IKEDA Original method

- Input:

Hull Form( Offsets), Bw (wave)

- Output:

BL (Lift), BE (Eddy), BF (Friction), BBK (Bilge Keel)

IKEDA simple method

- Input:

Hull Form (B,T, Lpp…), BL (speed)

- Output:

Bw (wave), BE (Eddy), BF (Friction), BBK (Bilge Keel)


Component analysis method for Ultra large Container ship N° 1 :IKEDA Original and Simple Methods

10

90° heading (Beam seas), 21 Kts forward speed, GM=2.9 m

0

0,001

0,002

0,003

0,004

0,005

0,006

0,007

0,008

0,009

0,01

0 2 4 6 8 10 12

No

nd

imen

sio

nal

Dam

pin

g

Roll amplitude in (°)

Ikeda original method Roll decay IKEDA Simple method

Slope of damping= f(Roll amplitude) => Non linearity

Difference : BK drag ( HIGH period)


Component analysis method for the US Navy ship: IKEDA original method

Comparison of Ikeda original method results for DTMB 5415 with roll decay test results for two

different initial inclination angles( 20 ° and 15 °) at Fn=0.28.

11

0,0065

0,007

0,0075

0,008

0,0085

0,009

0,0095

0,01

0,0105

0 5 10 15 20

No

nd

ime

nsi

on

al d

amp

ing

coef

fici

en

t

Roll amplitude (°)

Roll decay fi0=15°, Fr=0,28 Roll decay fi0=20°, Fr=0,28 Ikeda original method Fn=0.28

Initial Inclination =20 °

Initial Inclination =15 °


Miller method

• Regression analysis => US Navy ships

• Early design stage

12

Miller method

Step1: Damping at zero forward speed

Non linear formula

Step 2 : Forward speed effect

Input of Froude number


Miller Method Simulations For (ultra large) Container Ship N°1

Forward speed 21Kts & Draft T=10.5m

13

0,000

0,001

0,002

0,003

0,004

0,005

0,006

0,007

0,008

0,009

0 2 4 6 8 10 12 14

No

nd

ime

nsi

on

al d

amp

ing

Roll amplitude in deg

Ikeda method,21kts,90° Roll decay Miller Method at 21Kts & T=10.5m

Good agreement for smaller angles


Miller method simulation for the US Navy ship

Forward speed 20 Kts & Draft T= 9.97m

14

0

0,002

0,004

0,006

0,008

0,01

0,012

0 2 4 6 8 10 12 14 16 18 20

No

nd

imen

sio

nal

dam

pin

g co

effi

cien

t

Roll amplitude (°)

Roll decay fi0=15°, Fr=0,28 Roll decay fi0=20°, Fr=0,28 Miller Method 20Kts & T=9.97


Conclusion

EMSHIP UNIVERSITÄT ROSTOCK 15 17.02.2014

Established methodology for roll damping prediction

16

Step 1: Selecting the prediction method according to ship type:

•Potential theory: Pdstrip => - Ships with high Bw

•Component analysis-=>Low VCG (No car carrier , No large passenger vessel)

•Miller method : => Slender ships: Navy ships (Low CB )

Step 2: Approximating the damping coefficient with the fast Miller method

•Order of magnitude

• Fast method

Step 3: Running the selected method

•Benefit from the complementarity of certain methods

No tool available for all kinds for ships


Complementarity and different possible combinations

Combination 1

Pdstrip

Wave component Bw

IKEDA original method

BF(Friction) + BL(Lift) + BBK(Bilge keel)

Combination 2

Pdstrip

Roll response

2Droll:

Damping component from regression

analysis

Combination 3


Lift component BL

IKEDA simple method

BF(Friction)+BBK(Bilge keel) + BW(wave)

Combination 4

IKEDA simple method

Wave component Bw


BF(Friction)+BL(Lift)+ BBK(Bilge keel)

17 EMSHIP UNIVERSITÄT ROSTOCK 17.02.2014

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