Andrews RESISTANCE CHARACTERISTICS FOR HIGH SPEED HULL FORMS WITH VANES 1

Resistance Characteristics For

High-Speed Hull Forms with Vanes

Iruthayaraju Andrews2 (SM); Venkata Karthik Avala2 (SM); Prasanta K Sahoo1 (M); Sudarshanaram

Ramakrishnan2 (SM) 1 Associate Professor in Department of Marine and Environmental Systems, Florida Institute of Technology, Melbourne, Florida 2 Graduate students, Department of Marine and Environmental Systems, Florida Institute of Technology, Melbourne, Florida

ABSTRACT

In this paper an attempt has been made to investigate the resistance characteristics of high-speed round bilge hull

forms fitted with a vane in the stern region of the vessel. The Hull Vane ® is a fixed foil located below the waterline,

aft of the stern of the vessel. The Hull Vane® reduces the generation of waves and the vessel’s motions in waves. The

focus of this paper is to compare the total resistance of a single model from the AMECRC series of round bilge hull

forms with and without Hull Vane® attached to the hull.

KEYWORDS

Hull Vane®; Resistance; Computational Fluid Dynamics

(CFD); Round bilge Hull;

NOMENCLATURE

CB Block co-efficient

Fn Froude number

Fn▽ Volumetric Froude number

RT/ Resistance/weight

INTRODUCTION

As international shipping started to sail into a world of greener

ships with lower carbon emission and better fuel efficiency,

steps are taken in the form of new technologies and new

designs to improve the hydrodynamic efficiency of ships. In

order to make the existing ships more fuel efficient, research is

being carried all around the world to improve the hull form by

modifying the forward and aft regions of the hull.

BACKGROUND

Considerable amount of research has been conducted in the

past on stern appendages such as trim tabs, stern wedges, stern

flaps, interceptors and transom wedges. All of these have

proved to be able to reduce the overall resistance of a vessel by

reducing its running trim. In a study conducted on stern

wedges by Karafiath and Fisher (1987), it was shown that a

reduction of running trim of up to 2.0 degrees could result in a

2% of saving in fuel consumption. Cusanelli and Cave (1993)

investigated the application of stern flaps as a retrofit on US

Navy vessels and found a reduction in power which resulted in

reduced fuel consumption and increased top speed. In a later

study by Karafiath and Cusanelli (1997) on integrated

wedge-flap design, a reduction in power of 11.6% was

observed, while a wedge-only configuration lead to a power

reduction of 6.2%. Tsai and Hwang (2004) studied interceptors

and found that these can be used to reduce the resistance of

planning hulls.

In line with the above research, van Oossanen (1992) invented

the Hull Vane®, a fixed, resistance-reducing foil situated below

the water line, aft of the stern of the ship. Uithof, et. al (2014)

Andrews RESISTANCE CHARACTERISTICS FOR HIGH SPEED HULL FORMS WITH VANES 2

indicates that extensive research using CFD computations,

model tests and sea trials were conducted and found that the

reduction in resistance can be up to 26.5% on ships running at

Froude number between 0.2 and 0.7. The current paper

attempts to compare the total resistance of a single model from

the Australian Maritime Engineering Co-operative Research

Centre (AMECRC) series of round bilge hull forms with and

without Hull Vane®. Analysis of the resistance characteristics

has been carried out in CFD and compared against the

experimental tank test data of the AMECRC series.

AMECRC SERIES

The AMECRC systematic series, Sahoo, Doctors and Renilson

(1999), of hull forms were developed based on the high speed

displacement hull forms (HSDHF) systematic series.

AMECRC systematic series consists of 14 models. The length

of all models was 1.6 m. The main parameters of the parent

model of AMECRC series are: L/B = 8.0, B/T = 4.0 and CB

= 0.396. For the purpose of this paper, model 13 of the

AMECRC series was chosen and parameters of the model 13 is

shown in Table 1 below.

Table 1: Parameters of AMECRC model 13

Model No 13

L/B 6

B/T 3.25

CB 0.45

Model Disp.(kg) 15.784

L/∇1/3 6.379

HULL VANE® - THEORY

A Hull Vane® is a wing structure horizontally placed below the

stern of the vessel. The flow around the vane develops a lift

force as well as a forward thrust force. This reduces the

resistance which results in fuel savings. The various forces

acting on the vane are illustrated in Figure 1. It has four

different effects on the vessel which are thrust force, trim

correction, reduction of stern waves and reduction of motions.

The Hull Vane® was found to be most effective in the non-

planning regime, at Froude numbers between 0.2 and 0.7.

Since the frictional resistance is more dominant below the

Froude number 0.2, addition of a Hull Vane® to a vessel which

increases the wetted surface area also increases the frictional

resistance compared to the vessel without Hull Vane®. Beyond

Froude number of 0.2, the pressure resistance becomes a

dominant component. Since the Hull Vane® decreases pressure

resistance, likely gains are obtained in the Froude number

range of 0.2 to 0.7. At higher Froude numbers, the lift force of

the Hull Vane® creates a bow-down trim which is not

desirable.

The Hull Vane® is generally designed and optimized for the

cruising speed or maximum speed depending on the vessel’s

operating profile. Also, the shape of the stern of vessels which

have flat buttocks are ideal for fitting the Hull Vane® ensuring

a uniform flow to it.

Table 2: Particulars of Hull Vane®

Figure 1: Schematic representation of various forces on the

Hull Vane®

FINETM/MARINE MODEL SETUP

FineTM/Marine is an integrated computational fluid dynamics

software environment for the simulation of mono-fluid and

multi-fluid flows around ships, boats or yachts, including

various types of appendages. It is a commercially available

package and is used for generating the unstructured hexahedral

mesh and solving the steady flow. The model setup is used for

analyzing the bare hull model 13 of the AMECRC series with

and without Hull Vane® for Froude numbers 0.5, 0.6, 0.7. The

hull is free to trim and sink, using the 6 degrees of freedom

solver, allowing the hull to surge, sway, heave, pitch, yaw and

roll.

The simulation is started at zero speed after which the speed is

gradually accelerated to the final velocity. The "volume of

fluid" method is used to account for the free surface (i.e. both

water and air flows are solved), for which the parameters are

given in the Table 3 below. The free stream turbulence

quantities were initialized using the reference length and

velocity. Wall functions were used to simulate the flow in

regions very close to solid walls, reducing the mesh density

requirements in the boundary layer. The physical parameters

used for the solver is given in Table 3 below:

Profile NACA 4412

Span 0.224 m

Chord length 0.032m

Wetted surface area 0.01489 m2

Position

LE- X -0.032m

LE- Z -0.048m

Andrews RESISTANCE CHARACTERISTICS FOR HIGH SPEED HULL FORMS WITH VANES 3

Table 3: Parameters used in the computation

Main particular of the model

Length of water Line (LWL) 1.6 m

Wetted Surface Area 0.4431 m2

Displacement 16.218 kg

Displacement volume 0.01582 m3

Type of mesh Unstructured

(Trimmed )

Domain Physics

Homogeneous

water/Air multiphase,

SST k-ω Turbulent

Model

Initial Physics

Pressure Hydrostatic pressure

Volume Fraction Air - Volume

Fraction of lighter

Fluid

Water - Volume

Fraction of Heaver

Fluid.

Gravity In Z direction -

9.81m/s

Boundary Physics

Inlet velocity at that

Froude Number with

defined volume

fraction

Outlet Pressure outlet

Hull and Hull Vane® ® Wall with No slip

condition

Symmetry plane along the center line

of hull

Fluid Properties

Density of water 1025 kg/m3

Dynamic viscosity 1.21734*10-3 N-s/m2

DOMAIN AND BOUNDARY CONDITIONS

The domain around the hull is constructed such that the

boundaries do not influence the results. Only half of the ship

was modelled in order to reduce computational time. The

dimensions of the computational domain around the hull are

given in Table 4.

In the symmetry plane a mirror boundary condition was

applied and on the top and the bottom of the domain the

pressure was prescribed. All other domain faces have

external/free-flow boundary conditions with a prescribed flow

speed of 0 m/s.

Table 4: Limits of Domain

MESH GENERATION

The domain volume is divided into small cells to generate the

mesh. The largest cells on the hull are approximately ∆(X, Y,

Z) ≈ 0.0016 m in size. In areas with large curvature and small

features, cells as small as ∆(X,Y,Z) ≈ 0.000098 m were used to

ensure that flow features have a good resolution. Extra cells

were added perpendicular to the hull surfaces to ensure a good

resolution in the boundary layer. The first cell near the wall

was set to have a size of about 0.00064 m, such that its non-

dimensional distance (y+) to the wall was approximately 30.5.

Cells near the air-water interface were refined to have a size of

0.0016 m in z-direction. The following figure shows the mesh

on the surface of the hull.

Figure 2: Meshed model - side view

Figure 3: Meshed model showing Hull Vane®

Figure 4: Meshed model - stern view

X (longitudinal) -4.800 m 3.200 m

Y (beam) 0.000 m 3.200 m

Z (height) -3.200 m 0.800 m

Andrews RESISTANCE CHARACTERISTICS FOR HIGH SPEED HULL FORMS WITH VANES 4

Figure 5: Meshed model - bow view

PREDICTION AND EVALUATION

The RT/ value of the model obtained through CFD

simulations is compared with the actual experimental value of

bare hull. The results obtained are for the case of three

different velocities corresponding to Froude numbers 0.5, 0.6

and 0.7. The physics model used was an implicit unsteady,

Eulerian multiphase, standard k-ε turbulence model with wall

functions. Table 3 shows the % difference between the

experimental and CFD results. The error comparison between

the CFD (FineTM/Marine) and the experimental data shows an

average difference of 5% in RT/ value for the corresponding

Froude numbers 0.5, 0.6, 0.7.

Table 5: Resistance data for different Froude number

The difference is much less when only the resistance values of

CFD and experimental data are compared. But, since there is

difference in testing parameters like displacement of models

and density of fluids, RT/ values were considered to be

appropriate for comparison.

Figure 6: CFD and Experimental data for bare hull

RESULT

The 1.6 m model of the AMECRC series was run for Froude

numbers of 0.5, 0.6 and 0.7 with the Hull Vane® attached to it.

These results are compared with the bare hull resistance of the

model from CFD and the difference is calculated as a

percentage.

The comparison between the resistance of the bare hull with

and without Hull Vane® indicates a reduction in resistance for

the model with Hull Vane®. The resistance values are

compared here as RT/ values similar to the previous

comparison. The testing parameters and conditions are same

for the CFD runs.

Table 6: Resistance data of model with and without hull

vane using CFD

0.06

0.07

0.08

0.09

0.1

0.11

0.4 0.5 0.6 0.7 0.8

Res

ista

nce

/wei

ght

Froude Number

CFD vs Exp

CFD Exp Value

Froude

number

Volumetric

Froude number

FineTM

/Marine

CFD Results

Exp.

Results

%

difference

Fn Fn▽ RT/ RT/

0.5 1.263 0.06247 0.06531 -4.54% 0.6 1.515 0.08297 0.08789 -5.92%

0.7 1.768 0.09775 0.10263 -5.21%

Froude

number

Vol.

Froude

number

without

Hull

Vane®

With

Hull

Vane®

%

reduction

Fn Fn▽ RT/ RT/

0.5 1.263 0.06247 0.05465 -14.32%

0.6 1.515 0.08297 0.07507 -10.53%

0.7 1.768 0.09775 0.09028 -8.05%

Andrews RESISTANCE CHARACTERISTICS FOR HIGH SPEED HULL FORMS WITH VANES 5

Figure 7 Resistance data for the model with and without

Hull Vane® using CFD

DISCUSSION OF THE RESULTS

The results obtained are discussed in the following part.

With respect to the comparison of bare hull resistance between

experiments and CFD it was observed that RT/ values was

lower by around 5% for all Froude numbers tested. It can thus

be assumed that CFD predicts reasonably well against

experimental data for bare hull.

The next step was to analyze RT/ against CFD results when

the vessel is fitted with a vane. It can be seen from Table 6 that

the hull fitted with a vane shows substantial reduction when

compared with that of a bare hull. The percentage reduction

varying from 8 to 14% appears remarkable and would certainly

project considerable reduction in fuel consumption over the

life of the vessel.

CONCLUSION

In this paper the results of an investigation into the effect of

adding a Hull Vane® on the resistance of high-speed round

bilge hull form from AMECRC series is presented. The

difference in resistance results obtained from experimental data

and CFD (Fine/Marine) for 1.6m model is also presented.

The addition of Hull Vane® shows a significant reduction in

the total resistance of the model. A Hull Vane® is optimized

for required speed and it is to be noted that a limited number of

simulations were carried out to get these results. Further work

on Hull Vane® optimization may improve the resistance

reduction. Likewise, further work for the full-scale vessel is

likely to result in an improvement of the performance of the

Hull Vane® due to the lesser effect of frictional drag on it.

Future work shall be carried out to see the effects of the Hull

Vane® on viscous and wave resistance of the model separately.

ACKNOWLEDGEMENTS

The authors would like to thank Van Oossanen Naval

Architects and Florida Institute of Technology for their support

and encouragement through the course of this research work

without which this paper would not have seen the light of day.

REFERENCE

1. Wang, C.T., “Wedge Effect on planning hulls,” J.

Hydronautics 14, no. 4 (1980).

2. Karafiath, G., and Fisher S.C., “The effect of stern

wedges on ship powering performance,” Naval

engineers Journal, May 1987.

3. Cusanelli, D.S., and Cave W.L., “Effect of Stern flaps

on powering performance of the FFG-7 Class,”

Marine Technology 30, no.1, January 1993.

4. Cusanelli, D.S., and Karafiath G., ‘Integrated Wedge

Flap for Enhanced Powering Performance’, FAST’97,

Sidney, Australia, July 1997.

5. Cusanelli, D.S., and Karafiath G., ‘Advances in Stern

Flap Design and application’, FAST 2001,

Southampton, UK, September 2001.

6. Seo Kwang-Cheol, Gopakumar N., and Atlar M.,

‘Experimental Investigation of Dynamic Trim Control

devices in fast speed vessel’, J. Navig. Port Res., 37,

no.2 (April 2013): 137-142.

7. Tsai, J.F., Hwang, J.L., and Chou, S.K., ’Study on the

Compound Effects of Interceptor with Stern Flap for

two mono-hulls with Transom Stern’, Oceans ’04,

MTTS/IEEE Techno-Ocean 2 (2004): 1023-1028.

8. Uithof, K., P. van Oossanen, N. Moerke, van

Oossanen P.G., and Zaaijer K.S., ‘An update on the

Development of the Hull Vane® ,” HIPER 2014,

High Performance Marine Vehicles, Athens,

December 2014.

9. Sahoo, P.K., Doctors L.J., and Renilson M.R.,

"Theoretical and experimental investigation of

resistance of high-speed round-bilge hull forms,"

FAST99 Fifth Int. Conf. on Fast Sea Transportation,

Seattle, (1999): 803-814.

0.04000

0.06000

0.08000

0.10000

0.12000

0.40 0.50 0.60 0.70 0.80

Res

ista

nce

/wei

ght

Froude Number

Resistance data comparison

with Hull vane

without Hull vane