Analysis of Total Ships Resistance with Variation of Hull Bow Types,

Ulstein X-Bow, Spherical and Tapering Bulbous Bow using CFD

Method

Kiryanto, Deddy Chrismianto and Ahmad Firdhaus

Department of Naval Architecture, Faculty of Engineering, Diponegoro University, Semarang, Indonesia

Keywords: The Total Resistance, Model X-Bow, Spherical Bulbous Bow, Tapered Bulbous Bow.

Abstract: Ships must have good performance and economic value. To achieve it, optimum speed is needed with minimal

engine power usage so it can increase the efficiency of fuel use. The use of engine power is closely related

to the total resistance on a ship. One alternative way to reduce ship resistance is to install bulbous bow. This

research aims to obtain the resistance of ships with variations in the type of bow shape of the ship. The analysis

on this research uses numerical method using CFD. Variations in the modelling of bow design are; X-Bow,

spherical and tapering bulbous bow. Based on the results of CFD calculations, each model is obtained, namely;

the lowest value of the total resistances coefficient and total resistances model X-Bow 0,006565 and 242,76

KN, while for the spherical bulbous bow model is 0,007211 and 267,22 KN and for the lowest form of tapering

bulbous bow the total drag coefficient and total resistance is 0,007368 and 273,40 KN. Referring to the results

of the analysis, resistances of the ship model using the X-Bow design is the best model that can be used as an

alternative if compared to spherical and tapering bulbous bow.

1 INTRODUCTION

Nowadays, various researches have been conducted

in the field of ship which aims to improve optimum

results both in terms of economy and performance.

Ships are expected to have good performance when

sailing, so the ship can sail in bad weather or extreme

sea conditions. Besides, the target of the design

optimizing efficiency is about the speed of the ship,

which is how to get the ship design that has optimum

speed but the minimum use of engine power so that it

can increase the efficiency of fuel use. The use of

engine power is closely related to the resistance

experienced by a ship. One alternative way to reduce

ship resistance is to install bulbous on the bow of the

ship. Ships with a good bow will provide the

efficiency of the resulting barriers so that ship

operations and ship movements become better

(Chrismianto, et.al, 2014) The hydrodynamic effect

of bulb bow placement is based on changes in the

distribution of flow around the bow, interfering with

the waves that occur due to the hull so as to reduce

the overall wave system (Francisco, et.al, 2007).

Currently the concept in shipbuilding design

especially in the bow of the ship to reduce fuel

consumption is the Ulstein X-Bow Bulbous bow

concept, which is a rounded structure in the bow of a

ship that is below the surface of the water which

functions to produce waves before the ship pushes

water. The waves produced by the bulbous bow are

opposite to the waves produced by the ship's body, so

that both waves will offset each other and make the

resulting waves smaller. The effect of using a bulbous

bow can reduce the total resistance of the ship by

30%. (Watson, 1998) Therefore, through this research

is expected to analyze the value of the total resistance

experienced by ships with the Ulstein X-Bow design

and the ship uses bulbous bow spherical and tapering.

The purpose of this research was to obtain the total

resistance of ships using Ulstein X-Bow and bulbous

bow (tapering bulb and spherical bulb) with the

calculation of CFD method.

2 LITERATURE REVIEW

2.1 Ulstein X-Bow Definition

Overall the shape of the Ulstein X-Bow is different

from conventional bow. The Ulstein X-Bow is

dominated by a high, rounded and expands slightly at

the top of bow (Lewis, 1998). Ships with Ulstein

Kiryanto, ., Chrismianto, D. and Firdhaus, A.

Analysis of Total Ships Resistance with Variation of Hull Bow Types, Ulstein X-Bow, Spherical and Tapering Bulbous Bow using CFD Method.

DOI: 10.5220/0008374400600064

In Proceedings of the 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management (ISOCEEN 2018), pages 60-64

ISBN: 978-989-758-455-8

X-Bow have great buoyancy because of increasing

volume of the bow shape. Ulstein X-Bow was first

introduced in 2005. Known as inverted bow because

of the bow shape with the top flipped towards the rear.

Ulstein X-Bow was originally designed for offshore

vessel. A vessel with a bow like this has better

seakeeping than a conventional bow. In addition to

seakeeping, this bow is also able to increase fuel

efficiency and makes waves more subtly.

Figure 1: Ulstein X-Bow model.

2.2 Tapering and Spherical Bulbous

Bow

Bulbous bow is a part of the ship located in the bow

section. This part is a part that is integrated with the

hull. The main function of this section is to reduce

ship resistance when the ship is operating. The

bulbous bow shape plays an important role in

determining the magnitude of the benefits. The

optimum shape depends on the size of the Froude

number (Harvald, 1983). Most resistances on the

ships are caused by the part of the ship that has direct

contact with the fluid. The fluid, which the ships

through, forms a wave pattern due to the movement

of the ship's body that eventually causes friction with

the hull, the working principle of the bulbous bow is

to generate waves or interfere the waves of the ship

coming from the bow, so that the incoming wave will

lose power due to wave interference from bulbous

bow and in the end the wave energy around the hull

will decrease, thus the resistance of the ship will be

decrease too.

Figure 2: Bulbous bow model.

2.3 Ship Resistance

Ship resistance is the most important factor that

determines the power of the ship needed (Rawson and

Tupper, 2001). Ship resistance is the study of fluid

reactions due to the movement of the ship through the

fluid. In order for a ship to move at a desired speed,

the ship's resistance must be overcome by other forces

that push the ship (Wartono, 1982) In terms of

hydrodynamics the ship is the amount of fluid force

acting on the ship in such a way that it opposes the

movement of the ship. The main and most significant

factor is the hull geometry and the wet surface of the

vessel (Bhattacharrya, 1978). The resistance is the

same as the force component that works parallel to

the axis of the ship's velocity. the total resistance of

the ship is calculated based on the mathematical

approach of the Holtrop Method in the Principles of

Naval Architecture Vol II, Second Revision (Lewis,

1988)

𝑅



0.5𝐶



𝜌𝑉





𝑆

(1)

Where:

=total resistance coefficient,

S =wet surface area on hull (m2),

ρ = density of sea water (kg/m3)

= service velocity (m/s)

2.4 Computational Fluid Dynamic

(CFD)

Computational Fluid Dynamics (CFD) is an analysis

system that includes fluid flow, heat transfer, and

related phenomena. As a chemical reaction by using

computer based simulation (numeric). This technique

is very useful and can be applied in industrial and

non-industrial fields. CFD codes are structured on

numerical logarithms, so they can be used to solve

problems in a fluid flow. Computational fluid

dynamics code here consists of three main elements,

namely:

a. Pre Processor.

b. Solver Manager.

c. Post Processor (Visualize).

One reason why CFDs are so successful and

popular is their ability to simulate currents that are

close to the original conditions, 3 dimensions,

irregular current geometry, and phenomena that have

complex physical. This is possible because it uses

numerical solutions from equations that regulate fluid

flow rather than using analytical solutions (Jayanti,

2004).

Analysis of Total Ships Resistance with Variation of Hull Bow Types, Ulstein X-Bow, Spherical and Tapering Bulbous Bow using CFD

Method

3 RESULTS AND DISCUSSION

On the table 1 is used ship principal dimension in the

research.

Table 1: Principal Dimension.

Principal Dimension

Length of Perpendicular (LPP)

Breadth (B)

99,20 m

18,94 m

Draft (T)

Height (H)

Displacement

Wetted Surface Area

4,00 m

6,00 m

4595,00 ton

1900,50 m²

Table 2: Dimension of model.

Model Dimension

Length of Perpendicular (LPP)

Breadth (B)

2,02 m

0,39 m

Draft (T)

Height (H)

Displacement

Wetted Surface Area

0,082 m

0,12 m

0,0384 ton

0,794 m²

Furthermore, the ship's resistance analyses with

the variation of the X-Bow form and bulbous bow

model.

3.1 Modelling with CAD Software

From the main dimension data of the ship model, the

ship body modelling was made with the help of CAD

Modeller.

Figure 3: Modelling with CAD Modeller.

3.2 Modelling with CAD Software

Ship model making also uses CAD 3D software so

that it can be opened in CFD software.

Figure 4: Modelling spherical bulbous bow with CAD 3D

software.

Figure 5: Modelling tapered bulbous bow with CAD 3D

software.

Figure 6: Modelling X bow with CAD 3D software.

3.3 Computational Fluid Dynamic

(CFD) Simulation

The process of numerical simulation on

Computational Fluid Dynamic starts from making a

hull model. Modelling using the CAD software, then

the file is exported in the form of a file igs. The model

used must be solid. After the model is finished, the

work continues using numerical simulations. The

numerical simulation software used is software based

on computational fluid dynamic. This simulation

steps are divided into several stages including:

geometry, mesh, setup, solution and result.

ISOCEEN 2018 - 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management

Figure 7: Geometry solid modelling.

After the running or simulation process is

complete, the results can be seen in the result stage.

The results obtained are the resistance value of the

ship, the model and visualization of the flow on the

free surface and station behind the hull.

Figure 8: Visualization of fluid flow.

3.4 Validation

In this research to validate the results of the test model

is using the results of towing tank test that has been

done in previous research. Validation is used to

determine the right boundary condition to be used in

the boundary condition when analyzing 3 ship models

using CFD software. The maximum error for

validation between numerical method and towing

tank test results is 10%.

Table 3: Validation Data.

Ship Model

Ct x 10

-3

Experiment

Ct x 10

-3

CFD

Difference

Model of spherical

bulbous bow

model)

6.362 5.999

0.363

(5.71%)

Model of tapered

bulbous bow

model)

6.658 6.122

0.536

(8.05%)

The Ct results or the total drag coefficient

obtained on the CFD Software for the spherical

bulbous bow model is 0.005999, with the results still

in the error criteria below 10% of the towing tank test

results of 0.006362, so that there is a difference of

0.000363 or 5.71%. For the bow model of the bulbous

bow tapering model is 0.006122, the results are still

included in the error criteria below 10% from the

towing tank test result of 0.006658, so that there is a

difference of 0.000536 or 8.05%. And for the Ulstein

X-Bow bow model is 0.005699, the results are

included in the error criteria below 10% from the

towing tank test results of 0.006214, and the

difference of 0.000515 or 8.29%.

4 CALCULATION AND

DISCUSSION

The result of Ship resistance analysis using CFD

gathered, and then process it to get the final data. Ship

resistance value from each models with various speed

can be seen on the table below:

Table 4: Ct, Cf and Cr from each ship models.

Name

model

Fn Value Ct

x 10

Cf x 10

Cr x 10

1st

model

0.129

6.604

5.092

1.511

0.145

5.998

4.962

1.036

0.161

6.413

4.848

1.563

0.178

6.786

4.727

2.059

0.194

7.211

4.632

2.578

2nd

model

0.129

6.728

5.161

1.566

0.145

6.122

4.986

1.135

0.161

6.537

4.882

1.654

0.178

6.905

4.758

2.147

0.194

7.378

4.662

2.705

3rd

model

0.129

6.195

5.054

1.141

0.145

5.709

4.900

1.038

0.161

6.135

4.807

1.317

0.178

6.381

4.716

1.665

0.194

6.575

4.613

1.951

Analysis of Total Ships Resistance with Variation of Hull Bow Types, Ulstein X-Bow, Spherical and Tapering Bulbous Bow using CFD

Method

Table 5: Calculation of Rt value (Total Resistances) for

each 1: 1 scale model.

Name

model

Fn Value

Velocity

(m/s)

x 10

Rt (kN)

1st

model

0.129

4.112

6.604

108.77

0.145

4.626

5.998

125.04

0.161

5.140

6.413

165.03

0.178

6.564

6.786

211.31

0.194

6.168

7.211

267.22

2nd

model

0.129

4.112

6.728

110.96

0.145

4.626

6.122

127.79

0.161

5.140

6.537

168.45

0.178

6.564

6.905

215.32

0.194

6.168

7.378

273.40

3rd

model

0.129

4.112

6.195

101.82

0.145

4.626

5.709

118.54

0.161

5.140

6.135

157.28

0.178

6.564

6.381

198.26

0.194

6.168

6.575

242.76

Figure 9: Graphic of total ship resistance.

From the table presentation, the calculation results

and the graph image above show the difference in the

total coefficient value and the total resistance value of

each ship model according to the Froude number and

the speed of each ship model.

1. The lowest total coefficient value produced by the

three models when Froude number is 0.145 with a

ship speed of 9 knots. The Ct value of model 1

was 0.005999 with Rt of 125.04 kN. Ct value of

model 2 is 0.006122 with Rt of 127.79 kN. And

model 3 has a Ct value of 0.005699 with an Rt

value of 118.54 kN.

2. The highest total coefficient value is produced by

the three models when Froude number is 0.194

with a ship speed of 12 knots. Ct model 1 was

obtained at 0.007211 with Rt of 267.22 kN. Ct

value of model 2 is 0.007368 with Rt of 273.40

kN. And model 3 has a Ct value of 0.006565 with

an Rt value of 242.76 kN.

5 CONCLUSIONS

Based on the experiments and simulations that have

been done, it can be concluded that of the three

variations of the model, the lowest resistance value

occurs in model 3 with the design of the X-Bow

direction, namely the total coefficient of 0.006565

and the total resistance value of 242.76 kN. Whereas

for model 1 and model 2 produce a total coefficient

value of 0.007211 and 0.007368 respectively. With

the total resistance value of model 1 is 267.22 kN and

the total resistance value of model 2 is 273.40 kN.

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ISOCEEN 2018 - 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management