UNIVERSITY OF NAPLES EDERICO POLYTECHNIC AND BASIC …

HYDRODYNAMICS OF PLANING HULL BY CFD

UNIVERSITY OF NAPLES FEDERICO II POLYTECHNIC AND BASIC SCIENCES SCHOOL DEPARTMENT OF INDUSTRIAL ENGINEERING

THESIS MASTER’S DEGREE IN NAVAL ENGINEERING

SUPERVISOR CANDIDATE

PROF. ERMINA BEGOVIC, PH.D. MARCELLO IACONO

CORRELATOR

SIMONE MANCINI, PH.D. STUDENT

Academic year 2014/2015

FROUDE NUMBER

planing vessels

The Alpha-Z stepped planing hull designed by Michael Peters

TOTAL RESISTANCE

Methods for bare hull resistance: •Experimental method (e.g.: Froude method) •Empirical method (e.g.: Savitsky [1964], Savitsky [2010], Morabito [2010])

•Systematic series (e.g.: Series 62, Series 65, Series 62 Dutch, BK series, MBK series, Kowalyshyn D. and Metcalf B. Series (2006), Taunton D. J. et al. Series (2011), Begovic E. and Bertorello C. Series (2012), De Luca F. and Pensa C. Series (2014) •Statistical methods (e.g.: Radojcic’s method [1985], Holtrop) •CFD (Computational Fluid Dynamics)

PRESSURE AND SPRAY ROOT AREAS

Flat plate surface Deadrise surface

EQUILIBRIUM CONDITION FLAT PLATE

SOTTORF

EQUILIBRIUM CONDITION MONOHEDRALL HULL

SAVITSKY SHORT FORM

SAVITSKY SHORT FORM PROCEDURE

PRESSURE DISTRIBUTION

MORABITO METHOD On the spray and bottom pressures of planing surfaces, Ph.D. Thesis

Stevens Institute of Technology, 2010

Symmetry line

Effect of the transom stern

Other sections

Begovic E. and Bertorello C., 2012 Resistance assessment of warped hull forms

EXPERIMENTAL REFERENCE WORK

COMPUTATIONAL FLUID DYNAMICS

NUMERICAL SETUP

STAR-CCM+ CD-adapco Turbulence model k-epsilon Time step 0.005-0.002 Iterations 3

At four different velocities:

3.4 m/s Frb=1.667 FrV=1.921 4.6 m/s Frb=2.256 FrV=2.599 5.75 m/s Frb=2.819 FrV=3.248 6.32 m/s Frb=3.098 FrV=3.569

SCoPE Operating System For multidisciplinary

scientific Processing

RESISTANCE COMPARISON MONOHEDRAL HULL

35

40

45

50

55

60

3,4 4,6 5,75 6,32

Res

ista

nce

[N

]

v [m/s]

Exp

Coarse grid

Medium grid

Fine grid

Savitsky short form

2.6% 5.3%

WARPED HULL

40

45

50

55

60

3,4 4,6 5,75 6,32

Res

ista

nce

[N

]

v [m/s]

Exp Coarse Grid Medium grid Fine grid Savitsky short form

1.9%

1.8%

5.8% 8.1%

4.8%

TRIM COMPARISON MONOHEDRAL HULL

WARPED HULL

3,2

3,4

3,6

3,8

4,0

4,2

4,4

4,6

4,8

5,0

3,4 4,6 5,75 6,32

Trim

[d

eg]

v [m/s]

Exp Coarse grid Medium grid Fine grid Savitsky short form

2,0

2,5

3,0

3,5

4,0

4,5

5,0

3,4 4,6 5,75 6,32

Trim

[d

eg]

v [m/s]

Exp Coarse grid Medium grid Fine grid Savitsky short form

18.6%

10.3% 14.9%

5.2%

14.8%

6.4% 14.4%

4.5%

SINKAGE COMPARISON MONOHEDRAL HULL

WARPED HULL

-10

-5

0

5

10

15

20

25

30

35

40

3,4 4,6 5,75 6,32

Sin

kage

[m

m]

v [m/s]

Exp

Coarse grid

Medium grid

Fine grid

0

5

10

15

20

25

30

35

40

45

3,4 4,6 5,75 6,32

Sin

kage

[m

m]

v [m/s]

Exp

Coarse grid

Medium grid

Fine grid

WETTED SURFACE COMPARISON MONOHEDRAL HULL

WARPED HULL

0,50

0,55

0,60

0,65

0,70

0,75

0,80

0,85

3,4 4,6 5,75 6,32

Wet

ted

Su

rfac

e [m

2 ]

v [m/s]

Exp Coarse grid Medium grid Fine grid Savitsky short form

0,50

0,55

0,60

0,65

0,70

0,75

0,80

3,4 4,6 5,75 6,32

Wet

ted

Su

rfac

e [m

2 ]

v [m/s]

Exp Coarse grid Medium grid Fine grid Savitsky short form

14.3%

6.1% 1.6%

8.1%

11.7%

4.2% 7.0%

Coarse grid at v=6.32 m/s

Medium grid at v=6.32 m/s

Fine grid at v=6.32 m/s

Coarse grid at v=6.32 m/s

Medium grid at v=6.32 m/s

Fine grid at v=6.32 m/s

MONOHEDRAL HULL WARPED HULL

MONOHEDRAL HULL WARPED HULL

Experimental and numerical wetted surfaces, v=5.75 m/s Experimental and numerical wetted surfaces, v=5.75 m/s

MONOHEDRAL HULL WARPED HULL

Longitudinal pressure distribution at v=5.75 m/s Longitudinal pressure distribution at v=5.75 m/s

MONOHEDRAL HULL TRANSVERSAL PRESSURE LINES AT V=6.32 M/S

WARPED HULL TRANSVERSAL PRESSURE LINES AT V=6.32 M/S

-500

0

500

1000

1500

2000

0,00 0,05 0,10 0,15 0,20 0,25 Hyd

rod

ynam

ic P

ress

ure

(P

a)

Half beam (m)

x=-0,256 (0,25 L)

x=0,141 (0,4 L)

x=0,494 (0,55 L)

x=0,891

0

500

1000

1500

2000

2500

0,00 0,05 0,10 0,15 0,20 0,25

Hyd

rod

ynam

ic P

ress

ure

(P

a)

Half beam (m)

x=-0,344 (0,25 L) x=0,053 (0,4 L) x=0,406 (0,55 L)

TRANSVERSAL DISTRIBUTION AT 0,25 L

-50

0

50

100

150

200

0,00 0,05 0,10 0,15 0,20 0,25

Hyd

rod

ynam

ic P

ress

ure

(P

a)

Half beam (m)

v=3.4 m/s

MONO x=-0,344 (0,25 L)

W2 x=-0,256 (0,25 L)

-50

0

50

100

150

200

250

300

0,00 0,05 0,10 0,15 0,20 0,25 Hyd

rod

ynam

ic P

ress

ure

(P

a)

Half beam (m)

v=4.6 m/s MONO x=-0,344 (0,25 L)

W2 x=-0,256 (0,25 L)

-100

0

100

200

300

400

500

0,00 0,05 0,10 0,15 0,20 0,25 Hyd

rod

ynam

ic P

ress

ure

(P

a)

Half beam (m)

v=5.75 m/s

MONO x=-0,344 (0,25 L) W2 x=-0,256 (0,25 L)

0

100

200

300

400

500

600

0,00 0,05 0,10 0,15 0,20 0,25

Hyd

rod

ynam

ic P

ress

ure

(P

a)

Half beam (m)

v=6.32 m/s MONO x=-0,344 (0,25 L)

W2 x=-0,256 (0,25 L)

MONOHEDRAL HULL LONGITUDINAL PRESSURE DISTRIBUTION AT V=6.32 M/S

WARPED HULL LONGITUDINAL PRESSURE DISTRIBUTION AT V=6.32 M/S

-1000

-500

0

500

1000

1500

2000

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 Pre

ssu

re (P

a)

Length (m)

at keel

Empirical Evaluation

Numerical Evaluation by CFD - Fine grid

-2000

-1000

0

1000

2000

3000

4000

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

ssu

re (P

a)

Length (m)

at keel Empirical Evaluation

Numerical Evaluation by CFD - Fine grid

CONCLUSIONS

1. Accuracy of numerical results

2. Savitsky method gives the best results for resistance and wetted surface (difference from

experimental in the order of 2%), while CFD calculations are more accurate than Savitsky method

for trim angle

3. Stagnation and spray root lines, Pressure profiles, Longitudinal pressure distributions evaluated

from CFD calculations are very close to results of Morabito method, Peaks and transversal

pressure distributions

4. Even though experimentation remains the tool most commonly used by designers to obtain

accurate values of the hydrodynamic forces acting on the boat, empirical methods are very

inexpensive and fast to use. Advantages of numerical simulations: the flow streamlines, the wave

profiles or the pressure distribution

ACKNOWLEDGEMENTS

Thanks to availability of 32 processors at HPC Centre SCoPE of University of Naples “Federico II” and thanks to SCoPE academic staff for the given support.