Evaluacion Metodo Van Oortmerssen

Libro de Ponencias y Conferencias del XXIII Congreso Panamericano de Ingeniera Naval, Costa Afuera e Ingeniera Portuaria COPINAVAL 2013

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Evaluation of methods for estimating power to the most

common form of hulls in the Amazon

Hito Braga de Moraes Federal University of Par - Brazil

Philip Alan Wilson University of Southampton - United Kingdom

ABSTRACT

The Amazon region has had only a few studies in the field of naval architecture. This

paper will explore the design of specific craft suitable for this environmentally

sensitive region. The design will require verification and validation of the

computational methods used to assess the hydrodynamics of the typical vessels

commonly used in the Amazon region.

This research presents estimation methods for power boats, where one seeks to

compare several statistical methods, based on systematic series and methods which

use finite element theory with the results obtained from experiments performed in the

towing tank. For the validation of the power estimate it is necessary to compare the

results generated by these methodologies with the results obtained in tests with

scaled models in a towing tank.

An identification process was used to determine three typical types of regional

powered vessels on the Amazon. The effective power was then analysed for these

vessels. After selecting the type of hull, ship models were constructed for testing in

the towing tank. Comparisons are then made between theory and scaled models.

Nomenclature

B Ship beam (m.)

CB Block coefficient

Cf Coefficient of frictional resistance

CM Mid ship area coefficient


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Cp Prismatic coefficient

Fn Froude number

Fn Froude number based on volume

L Ship length (m.)

LD Displacement length (m.)

LBP Length of ship between perpendiculars (m)

Lwl Length on waterline (m)

LCB Longitudinal centre of buoyancy (m.)

PE Effective power (kW)

RR Residual resistance coefficient

S Wetted surface area (m2)

T Ship draft (m.)

V Ship velocity (m. s-1)

Vk Ship speed in knots

D Ship displacement (tonnes)

a Angle of entrance (degs.)

1 INTRODUCTION

Passenger transport in the Amazon region has used, mostly, wooden craft built by

virtue of being the most abundant material in the region and easy maintenance and

replacement. The traditional construction technique that is used is without much

technical guidance to produce the most suitable hull shape and the power required

for the propulsion of such vessels. This practice leads to inappropriate projects and

very high operating costs due to lack of technical information about the power

required for the desired speed.

2 TYPES AND FORMS OF HULLS USED IN THE AMAZON

From a study of the actual craft used in the area three models of typical boats that

are used within the Amazon region, were used for testing in towing tank experiments.

After searching for the typical forms of hull in the Amazon region, the identification of

lines plan of the three most common forms of boats in the Amazon region (small,


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medium and large) were produced, with the goal of finding the estimates of

resistance. The range of these three boats is 11m to 28.8m. This was performed by

measuring resistance in the towing tank and also the equivalent propulsive

parameters by testing self-propelled models small-scale models were constructed of

the three types of boats for tests in towing tank.

The tests consisted of towing the model along the tank, using the dynamometer on

the support carriage, to measure the resistance force for each forward speed.

During each run, measurements were made of the forward speed and towing force,

the angle of trim and the sinkage of each model. The towing tests were

conducted over a range of scale speeds centred on the design speed giving a

range, corresponding to a full range of 4 to 15 knots. The details of the test tank used

are found in Table 1.

Table 1: Main dimensions of the towing tank

main characteristics

Length m 280.00

Width m 6.60

Water depth m 4.50

Maximum carriage

velocity

m/s 3.50

a) SMALL VESSEL

Table 2: Small Vessel

Base data Coefficients

Length 11 m. Cp 0.70

Beam 2.43 m. Cb 0.52

Draught 0.65 m.

Displacement 9 tonnes - -

Wetted Area 28.6 m2 - -


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To make the model of the hull SMALL it was necessary to use the lines plan of model

illustrated in Figure 1. The actual scale of the model is 15.0.

Figure 1: Lines plan SMALL VESSEL

Figure 2 shows the scale model produced and in Figure 3 the software

rendering of the finite elements is shown.

Figure 2: Small-scale model of the SMALL VESSEL


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Figure 3: SMALL VESSEL modelled in software

b) MEDIUM VESSEL:

Table 3: Medium Vessel

Base data Coefficients

Length 20.3 m. Cp 0.71

Beam 4.8 m. Cb 0.71

Draught 1.2 m.

Displacement 82.80 tonnes - -

Wetted Area 127.4 m2

- -

To produce the model of the ship hull MEDIUM was necessary to use the lines plan

of small-scale model illustrated in Figure 4. As with the other ship model Figure 5

illustrates the actual scale model with a scale of 15.0. Figure 6 is the software

rendered model of the finite elements.

Figure 4: Lines plan MEDIUM VESSEL


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Figure 5: Small-scale model of the MEDIUM VESSEL

Figure 6: MEDIUM VESSEL modelled in software

c) LARGE VESSEL:

Table 4: Large vessel

Base data Coefficient

s

Length 28.8 m. Cp 0,71

Beam 7.5 m. Cb 0,57

Draught 1.9 m. - -

Displacement 234.69 tonnes - -

Wetted Area 250.12 m2 - -


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To produce the model of the ship hull LARGE was necessary to use the lines plan

illustrated in the following Figure 7. The scale used is 15.0.The scale model used in

the towing tank tests is shown in Figure 8 and the equivalent rendered model used in

FEA software is shown in Figure 9.

Figure 7: Lines plan LARGE VESSEL

Figure 8: Small-scale model of the LARGE VESSEL

Figure 9: LARGE VESSEL modelled in software


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3 METHODS FOR ESTIMATING POWER

There are several methods adopted to estimate the effective power of each ship that

is presented below.

3.1 Van Oortmerssen: Small Ships

Van Oortmerssen [10] developed regression equations for estimating the resistance

of small ships such as tugs, fishing boats, stern trawlers and pilot boats, broadly in

the full scale length range 15 m to 75 m. The objective was to provide equations that

would be accurate enough for design purposes. The analysis was based on 970 data

points from 93 ship models that had been tested at The Netherlands Ship Model

Basin (NSMB) (now Maritime Research Institute of the Netherlands [MARIN]) in the

1960s.

Approximate limits of the data (extracted from the diagrams) are as follows:

Froude number, Fn = 0.2 0.5

L/ B = 3.4 6.2

LCB: - 4.4%L to + 1.6%L

: 15- 35.

Where is the half-angle of entrance of the waterline at the bow. If is not known,

an approximation is =12.0 CB - 50 (0.5


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The residuary resistance was derived using the ITTC1957 1ine for Cp. The

components of the equation for residuary resistance ratio RR / are as follows:

2 2 2

2

/9 21 2 3

24

sin

cos

n n n

n

n

n

m F mF mFR

mF

RC e C e C e F

C e F

- - -

-

- - - -

- -

= + +D

+

(2)

Where, m = 0.1434 CP -2.1976 (3)

c = {di,0 + di,1 . LCB + di,2 . LCB2 + di,3 . Cp + di,4 CP + di,5 . (LD/ B) + di,6 . (LD/ B)

2 + di,7

. CWL + di,8 . CWL2 + di,9 . (B/T) + di,l0 . (B/T)

2 + di,11 . CM} x 10 -3, (4)

where, LCB forward of 0.5 L as a percentage of L and the coefficients di are given

in Table 5.

Table 5: Van Oortmerssen [10]: Small ship resistance regression coefficients

i = 1 2 3 4

di,0 79, 32134 6714,88397 -

908,44371

3012,14549

di,1 -0,09287 19,83 2,52704 2,71437

di,2 -0,00209 2,66997 -0,35794 0,25521

di,3 -

246,45896

-19662,024 755,1866 -9198,8084

di,4 187,13664 14099,904 -48,93952 6886,60416

di,5 -1,42893 137,33613 9,86873 -159,92694

di,6 0,11898 -13,36938 -0,77652 16,23621

di,7 0,15727 -4,49852 3,7902 -0,82014

di,8 -0,00064 0,021 -0,01879 0,00225

di,9 -2,52862 216,44923 -9,24399 236,3797

di,10 0,50619 -35,07602 1,28571 -44,1782

di,11 1,62851 -128,72535 250,6491 207,2558


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Table 6: Trial allowances for CF

Allowances for CF

Roughness, all-

welded bulls

0.00035

Steering resistance 0.00004

Bilge keel resistance 0.00004

Air resistance 0.00008

The residuary resistance is calculated as:

(5)

Cf is derived using the ITTC formula.

Cf= 0.075/(log10 Re 2 )2 (6)

Cf allowances for trial conditions are again given in Table 5

Friction resistance is then derived as:

(7)

S can be calculated from:

S = 3.223V2/3 + 0.5402LD V1/3 (8)

3.2 WUMTIA: Small Craft: Round Bilge Series

A regression analysis was carried out on chine and round-bilge hull forms which had

been tested by WUMTIA at the University of Southampton. Over 600 hull forms had

been tested by WUMTIA since 1968, including both hard chined and round-bilge hull

forms representing vessels ranging typically from 10 m to 70 m.

Thirty test models of round-bilge generic form were used in the regression analysis.

Tests at different displacements were also included leading to a total of 47 sets of

round-bilge resistance data. The data were all taken from hull forms that had been


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optimised for their running trim characteristics at realistic operating speeds and

include, the effects of change in wetted are a with speed.

The analyses covered the speed range, as follows: The volume Froude number Fn

in the range 0.50 - 2.75, or approximate length Froude number range Fn = 0.25 - 1.2,

where

1/3n

VF

g=

, nV

FgL

= , and nF = 0.5

1/3( )nL

F

It is noted that for the round-bilge hulls there are few data between L/B > 5.5 - 6.5.

Above Fn=1.5, the upper limit of L/B is 5.5, and it is recommended that the data for

L/B > 5.5 be restricted to speeds < Fn = 1.5.

The data are presented in terms of a C-Factor (CFAC) which was developed by small

craft designers for the prediction of power at an early design stage

E

FACPL

VC

21266.30

D= (9)

Where the constant 30.1266 was introduced to conserve the value of CFAC, which

was originally based on imperial units. Above a Fn of about 1.0, CFAC lies typically

between about 50 and 70. Thus by rearranging equation 9 we get the effective

power,

FAC

KE

CL

VP

2

18.453 D= (10)

Where PE is in kW, is in tonnes, VK is in knots and L is in metres. The predictions

for CFAC (round-bilge hulls) are presented as regression equations.


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CFAC = ao + al (L/1/3) + a2 L/B + a3 (S/L

2)1/2 + a4 (L/1/3)2 + a5 (L/B)

2 + a6 (S/L2) + a7 (L/

1/3)3

+ a8 (L/B)3 + a9 (S/L

2)3/2 (11)

The wetted area S for the round-bilge can be estimated using Equation (12).

S = 0.355636() + 5.75893(L) - 3.17064(B) (12)

The regression coefficients ao to a9 in Equations (11) are given in Tables 6.

It should be noted that these regression equations (CFAC) tend to give slightly

pessimistic predictions of power. As a result of advances in scaling techniques and

the inclusion of extra model data in an updated analysis, it is recommended that the

original predictions for the round bilge hulls be reduced on average by 4%.

Table 7. WUMTIA Resistance regression coefficients for C-factor, round bilge

PARAMETER Frv 0,5 0,75 1 1,25 1,5

a0 1136,829 -4276,159 -921,0902 -449,8701 -605,9794

L/Vol1/3 a1 -54,50337 859,2251 460,6681 243,5577 3,073361

L/B a2 -261,8232 98,15745 2,604913 59,9026 -32,77933

(S/L2)0,5 a3 -2695,885 16369,41 737,8893 -223,2636 4097,999

(L/Vol1/3)2 a4 5,365086 -153,5496 -75,42524 -40,36861 -1,682758

(L/B)2 a5 59,31649 -24,77183 -0,706952 -12,58654 6,486023

(S/L2) a6 5300,271 -32787,07 -2325,398 7,616481 -7823,835

(L/Vol1/3)3 a7 -0,136343 9,031855 4,114508 2,222081 0,200794

(L/B)3 a8 -4,207338 1,970939 0,112712 0,901679 -0,341222

(S/L2)3/2 a9 -3592,034 21484,47 2095,625 274,9351 4961,028

Table 7 . Continuation


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PARAMETER Frv 1,75 2 2,25 2,5 2,75

a0 -437,3817 351,1909 813,1732 -622,9426 -1219,095

L/Vol1/3 a1 40,51505 -183,7483 -194,1047 200,5628 346,1326

L/B a2 -87,85154 -101,2289 -63,92188 -138,7268 -139,0729

(S/L2)0,5 a3 3101,983 956,9388 -1884,341 2745,177 4659,579

(L/Vol1/3)2 a4 -4,308722 35,62357 36,56844 -31,93601 -56,785

(L/B)2 a5 20,96359 25,14769 17,01779 36,50832 36,71361

(S/L2) a6 -6339,599 -2061,44 3417,534 -5770,126 -9650,592

(L/Vol1/3)3 a7 0,104035 -2,254183 -2,264704 1,682685 3,096224

(L/B)3 a8 -1,586765 -2,004468 -1,429349 -3,082187 -3,124286

(S/L2)3/2 a9 4302,659 1473,702 -2022,774 4046,07 6655,716

3.3 NPL Series

This systematic series of round-bilge semi-displacement hull forms was tested at NPL,

Teddington, UK, in the 1970s, Bailey. An example of the body plan for the series is

shown in figure 10 and the series covered the following range of speeds and hull

parameters.

Figure 10 - NPL series body plan

Speed. )2.36.0:,1.130.0:(,1.48.0: --- FrFrL

VR


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1/3:1.7 6.7; 0.4( ); : 4.5 8.3b

B LC fixed

T- = -

LCB was fixed at 6.4% aft of amidship. Model length Lwl = 2.54m

Data for RR/ and Cr for a 30.5 m ship are presented in graphical form for a range of

L/B, L/1/3 and Fr . RR was derived by subtracting RF, using the ITTC line, from the total

resistance RT

In order to provide a more compatible presentation of the NPL data, CR values have

been calculated for the data where,

2...5.0 VS

RC RR

l= (13)

Table 8 Coefficients in the equation nR

LaC )(

3/1D

= for series 64 monohulls, Cb =0.45

Fn a n R2

0.4 36,726 -4,41 0.979

0.5 55,159 -4,61 0.989

0.6 42,184 -4,56 0.991

0.7 29,257 -4,47 0.995

0.8 27,130 -4,51 0.997

0.9 20,657 -4,46 0.996

1.0 11,644 -4,24 0.995

Table 9 Coefficients in the equation A value for nR

LaC )(

3/1D

= for series 64,

monohulls, CB = 0.55

Fn a n R2

0.4 926 -2.74 0.930

0.5 1775 -3.05 0.971

0.6 1642 -3.08 0.983

0.7 1106 -2.98 0.972

0.8 783 -2.90 0.956

0.9 458 -2.73 0.941

1.0 199 -2.38 0.922


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The resulting values for CR are given in annex 1. Wetted surface area can be

estimated using an appropriate formula, as the following equations.

LCsS .. D= (14)

2)/.(01307.0)/.(0494.0538.2 TBTBCs ++= (15)

4 RESULTS

To verify the results of the programs that estimate effective horse power (EHP),

vessels with hull shapes of the type round-rilge, which is the most common among

the hull shapes of vessels carrying passengers on Amazon. A comparison of the

results of four different methods to estimate the EHP vessels aiming to identify which

method they best approximates the EHP regional vessels when compared to the

results found in the towing tank. The results obtained in the models were compared

with the results obtained in towing tank for three different hull shapes, which are the

most usual in the Amazon region, as the range of size and capacity.

For the most usual type of hull for small vessels, there was obtained the results

shown in graph where one can observe that the Shipflow [11] program, which uses

the finite element method, showed very good results at speeds between 5 and 9

knots, with small differences for speeds above 10 knots. The model NPL showed the

best results from among the proposed EHP estimated by regression and statistical

analyzes with very small errors when compared with the results of towing tank for the

range of 5 to 9 knots. The methods of Oortmerssen showed good applicability to the

speed of 8 knots. The Wolfson Unit method already presented satisfactory results at

speeds up to 6 knots.


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Small Vessel (length up to 11m)

For the hull vessels of medium size, all models showed very good results at speeds up

to 10 knots. From 10 knots, only the model proposed by Oortmerssen stayed with

results with a significant difference in the results presented by the towing tank, the

other models showed very good results compared to the results obtained in the towing

tank. From 11 knots, the methods Wolfson Unit began to show higher values than

those obtained in the Towing Tank, around 20%. Since the NPL method only begins to

exhibit higher values for speeds above 12 knots the NPL method that provides the best

result among the methods using regression analysed for speeds up to 12 knots.

Medium Vessel (length between 12 and 25m)


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For the results to the hull of a large vessel typical of the Amazon, it is found that the

finite element method of Shipflow is the closest to the results of the towing tank at all

speeds. All methods show good accuracy up to speed of 11 knots, and, among the

estimation methods using regression, the NPL method also gives good results

throughout the speed range studied.

Large Vessel (length between 26m up to 36m)

5 FINAL CONCLUSIONS

All estimation methods of EHP showed good results for speeds below 11 knots.

However for speeds between 11 to 15 knots, only the results of Shipflow, and NPL

present results close to those obtained from towing tank. The other prediction

methods EHP results show significant differences with those found in the towing

tank.

A more comprehensive investigation and greater universe of hull shapes must be

done to confirm the findings obtained in this work. It should also be emphasized that

the research was limited in the speed range of 5 to 15 knots, which is the speed

range higher incidence of regional vessels that operate in the Amazon.

Among the statistical methods have the following conclusions:


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The method of Van Oortmerssen [10]is very good for EHP estimates of typical craft

of the Amazon to the speed range up to 10 knots and lengths up to 25m.

The WUMTIA (WOLFSON) method is more suitable for the range between 12m and

36m, but with always higher than estimates found in the towing tank.

The NPL method showed good accuracy for all speed ranges studied, which qualifies

it for use in predictive power (EHP) of vessels that are the carriage of passengers

and cargo in the Amazon region. However its accuracy is better for vessels greater

than 11m in length.

The Shipflow program that uses the finite element method gives good results also for

all speed ranges studied, and this program great applicability to estimate power

(EHP) of vessels typical of the Amazon.

There is also that the systematic series of NPL presents results very close to those

found by Shipflow for the length range between 12 and 36 m to all speeds, with the

advantage of much less computational effort and more practical method.

6 References

[1] Molland, A.F., Turnock, S.R. and Hudson, D.A. Ship Resistance and Propulsion

Practical Estimation of Ship Propulsive Power, Cambridge, 2011.

[2] Zhang Z, Liu H, Zhu S, Zhao F. Application of CFD in ship engineering design

practice and ship hydrodynamics. Conference of Global Chinese Scholars on

Hydrodynamics. 2006

[3] Gotman, A. Navigating the wake of past efforts. The Journal of Ocean

Technology.

Volume 2. Number 1. pp 74-96. 2007

[4] The Resistance Committee. Proceedings of the 24th IIT. Volume I. ITTC, 2005

U.K.

[5] Versteeg H.K, Malalasekera W. . An introduction to Computational Fluid

Dynamics. The finite Volume Method. Essex: Longman Scientific & Technical. 1995.


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[6] Thompson J.F., Soni B.K., Weatherill N.P. . Handbook of Grid Generation. CRC

Press. 1999.

[7] Montgomery, D. Design and Analysis of Experiments. John Wiley & Sons, Inc.

2005.

[8] Molland, A.F., Wilson, P. A., Taunton, D.J., Chandraprabha, S. and Ghani, P.A.,

Resistance and wash measurements on a series of high speed displacement

monohull and catamaran forms in shallow water. International Journal of Maritime

Engineering, Transactions of RINA, 146(A2), 2004

[9] Tran, T., Harris, C. J., and Wilson, P. A., A vessel management expert system.

Journal of Engineering for the Maritime Environment, Proceedings of I. Mech. E,

216(M), , 161-177. 2002.

[10] Van Oortmerssem, G., A power prediction method and its application to small

ships, publication no 391 of NSMB, 1971.

[11] Shipflow, users manual, FLOWTECH, Gothenburg Sweden,2001.

Annex 1


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Documents

Evaluacion Metodo Van Oortmerssen