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CELEBRATE VIETNAMESE TEACHER’S DAY 20/11/2018

Journal of Marine Science and Technology No. 56 – November 2018

JOURNAL OF MARINE

SCIENCE and

TECHNOLOGY

No. 56

11/2018

CONTENTS

SCIENCE - TECHNOLOGY

1 ANALYSIS CURRENT CHARACTERISTICS FLOWING THROUGH MOSFETS USED IN DYNAMIC CIRCUIT OF CONTROLLER

VUONG DUC PHUC Faculty of Electrical and Electronics Engineering, Vietnam

Maritime University

3

2 RESEARCH ON AN ELECTRICAL ENERGY MANAGEMENT MODEL FOR VIETNAM MARITIME UNIVERSITY

DANG HONG HAI, PHAM THI HONG ANH Department of Industrial Automation Engineering, Vietnam

Maritime University

7

3 THE ADOPTION OF COLLISION RISK ASSESSMENT EMPLOYING FUZZY EVALUATION METHOD

DINH GIA HUY, NGUYEN MANH CUONG, NGUYEN THAI DUONG, DAO QUANG DAN

Faculty of Navigation, Vietnam Maritime University

12

4 A NOVEL APPROACH TO DETERMINE THE SHIP POSITION BY USING THE AZIMUTH OF CELESTIAL BODY

NGUYEN VAN SUONG Faculty of Navigation, Vietnam Maritime University

17

5 CALCULATION OF THE LOW FREE HORIZONTAL OSCILLATION FREQUENCY OF THE SHIP HULL, APPLYING TO A 440KW TUGBOAT

NGUYEN VAN HAN Faculty of Shipbuilding, Vietnam Maritime University

21

6 REASEARCH AND CALCULATION OF STACKING-FAULT ENERGY FOR AUSTENITIC HIGH MANGANESE STEEL WHEN CHANGING VANADIUM CONTENT

NGUYEN DUONG NAM1, LE VAN TRUNG1, HAM MAI KHANH2 1Institute of Mechanical Engineering - Maritime University Vietnam;

2School of Materials Science and Engineering - Hanoi University of Science and Technology

28

7 TOWARDS AN INTEGRATED OCEANOGRAPHIC INFORMATION INFRASTRUCTURE

TRAN DANG HOAN Faculty of Information Technology, Vietnam Maritime University

33

8 IMPROVED RESULTS FOR THE ASYMPTOTIC STABILITY PROBLEM OF NEURAL NETWORKS WITH INTERVAL TIME-VARYING DELAY

LE DAO HAI AN Departement of Basic and Fundamental Science, Vietnam

Maritime University

37

ISSN 1859 - 316X

EDITOR-IN-CHIEF:

Assoc.Prof. Dr. Pham Xuan Duong

DEPUTy EDITOR-IN-CHIEF:

Assoc.Prof. Dr. Le Quoc Tien

Dr. Nguyen Khac Khiem

EDITORIAL BOARD:

Prof.Dr. Luong Cong Nho

Assoc.Prof. DSc. Dang Van Uy

Assoc.Prof. Dr. Nguyen Viet Thanh

Assoc.Prof. Dr. Dinh Xuan Manh

Assoc.Prof. Dr. Do Quang Khai

Assoc.Prof. Dr. Le Van Diem

Assoc.Prof. Dr. Dao Van Tuan

Dr. Nguyen Tri Minh

Assoc.Prof. Dr. Tran Anh Dung

Dr. Nguyen Huu Tuan

Assoc.Prof. Dr. Dang Cong Xuong

Assoc.Prof. Dr. Vu Tru Phi

Dr. Pham Van Minh

M.A. Hoang Ngoc Diep

Assoc.Prof. Dr. Le Van Hoc

Assoc.Prof .DSc. Do Duc Luu

Assoc.Prof. Dr. Tran Van Luong

SECRETARIAT:

Assoc.Prof. Dr. Nguyen Hong Van

OFFICE

Room 206B - A1 Building Vietnam Maritime University Add. No 484 Lach Tray St.,

Le Chan Dist, Haiphong City, Vietnam

Email: [email protected]

[email protected]

Publication Permit No.1350/Ministry of Culture and

Information issued on July 30th 2012

mailto:[email protected]

CELEBRATE VIETNAMESE TEACHER’S DAY 201/11/2018

Journal of Marine Science and Technology No. 56 – November 2018

ECONOMICS - SOCIAL SCIENCE

9 THE ROLE OF THE UNITED NATIONS CONVENTION ON CONTRACTS FOR THE INTERNATIONAL SALE OF GOODS (CISG 1980) IN INTERNATIONAL BUSINESS LAW AND VIETNAM

NGUYEN THANH LE, NGUYEN DINH THUY HUONG Faculty of Navigation, Vietnam Maritime University

43

10 BASIC ELEMENTS OF COMPENSATION FOR OIL POLLUTION DAMAGE CAUSED BY SHIPS

PHAM VAN TAN1, BUI DANG KHOA1, NGUYEN THANH LE1, NGUYEN VAN TRUONG2

1Faculty of Navigation, Vietnam Maritime University 2PhD student, School of Law, Dalian Maritime University

47

11

APPLICATION OF RESIDUAL INCOME MODEL AND DIVIDEND DISCOUNT MODEL IN VALUING STOCK PRICE OF AN PHU IRRADIATION JOINT-STOCK COMPANY

TRAN THI HUYEN

The Faculty Financial Management, Vietnam Maritime University

51

12 APPLICATION OF SYNTHESIS INDEXES (SI) TO THE PORT SUSTAINABLE DEVELOPMENT MEASUREMENT: A CRITICAL REVIEW

VU THANH TRUNG Faculty of Maritime Business, Vietnam Maritime University

58

13 ANALYSING SERVICE QUALITY OF PUBLIC BUS ON THE FIXED ROUTE OF HANOI - HAI PHONG, USING THE SERVQUAL MODEL

NGUYEN THI HOA1,3, NGUYEN HONG VAN2, HOANG THI PHUONG LAN1 1Faculty of Financial Management, Vietnam Maritime University

2Department of Science and Technology, Vietnam Maritime University 3Business Administration Department, Vietnam Japan University

63

14 DEVELOPING A DECISION-MAKING FRAMEWORK TO SUPPORT SHIPPING COMPANIES IN COMPLIANCE WITH LOW CARBON SHIPPING REGULATIONS

SON NGUYEN Faculty of Maritime Business, Vietnam Maritime University

68

15 THE IMPACTS OF DIGITIZATION TO SUPPLY CHAIN MANAGEMENT IN THE 4.0 INDUSTRIAL REVOLUTION

NGUYEN THI MAI ANH

Faculty of Maritime Business, Vietnam Maritime University

72

16 DEFINING DRY PORT CHARACTERISTICS: INSIGHTS FROM A GLOBAL SAMPLE

NGUYEN CANH LAM International School of Education, Vietnam Maritime University

77

17 THE FOURTH INDUSTRIAL REVOLUTION - CHALLENGES TO EMPLOYMENT ISSUE IN VIETNAM

PHAM THI THU TRANG Faculty of Political Theory, Vietnam Maritime University

83

18 THE FUNCTION OF PORT AUTHORITIES. APPROACHING FROM TRADITIONL TO MODERN VIEWS

TRAN HOANG HAI Faculty of Political Theory, Vietnam Maritime University

87

CELEBRATE VIET NAM TEACHERS’ DAY 20/11/2018

Journal of Marine Science and Technology No. 56 – November 2018 3

Figure 1. Experiment block diagram

Figure 2. Electrical equivalent circuit of DC motor

SCIENCE - TECHNOLOGY

ANALYSIS CURRENT CHARACTERISTICS FLOWING THROUGH MOSFETS USED IN DYNAMIC CIRCUIT OF CONTROLLER

VUONG DUC PHUC Faculty of Electrical and Electronics Engineering, Vietnam Maritime University

Abstract DC motors play an important part in many applications such as robotics, machine tools, fishing-boats, winding/unwinding machines and dragline excavators, etc. It is very important to understand about how to make a quality control for them to expand projects. This paper will analyse current characteristics flowing through MOSFETs used in dynamic circuit of controller (half bridge or H-bridge driver). Analysis of these characteristics will calculate and define the maximum current in all working modes. From these results, factors affect to the quality and the hardest mode of controller are found so that solutions and parameters for selecting devices will be given in order to increase the quality of controllers.

Keywords: PWM, half bridge, H bridge, DC motor controller. Tóm tắt

Động cơ một chiều đóng vai trò quan trọng trong nhiều ứng dụng thực tế như: Rô bốt, thiết bị cơ khí, trên tàu cá, máy quấn dây, cơ cấu cần cẩu, v.v.. Chế tạo ra các bộ điều khiển có chất lượng sẽ tăng được khả năng áp dụng là vô cùng quan trọng. Bài báo này sẽ phân tích đặc tính dòng điện chạy qua các MOSFET mạch động lực của mạch điều khiển động cơ một chiều (mạch bán cầu hoặc mạch cầu H). Phân tích những đặc tính này để tính toán và tìm ra dòng cực đại trong các chế độ làm việc. Từ kết quả đó các yếu tố ảnh hưởng đến chất lượng và chế độ làm việc nặng nề nhất của bộ điều khiển sẽ được tìm ra từ đó các giải pháp và lựa chọn thiết bị được chỉ ra nhằm mục đích nâng cao chất lượng của bộ điều khiển.

Từ khóa: Điều chế độ rộng xung, Mạch bán cầu, Mạch cầu “H”, Bộ điều khiển động cơ một chiều.

1. Introduction

There are many different functional types of DC motor are available in the market because of its wide range of application for specific requirements. And the most popular type named Shunt Wound DC Motor (SWDM) is concerned in this research. To control speed of a SWDM, PWM control method [1] which changes voltage supplied to armature of motor improves speed and reduces the power losses in the system and it is very fine speed control over whole range in both directions. The controllers for SWDM use MOSFETs, fast power diodes and driver IC; however, how to choose exactly parameters of them poses many challenges which can be solved in the following parts. In a paper with about 4 pages, author analyse half bridge circuit using one MOSFET and flywheel DIODE and analysis of H-bridge that is long will be writen in the next paper.

Figure 1 shows the experiment study. The PWM signal to control MOSFETs, waveform of voltage supplied to the armature, current flows from source to motor, current flows through motor and


4 Journal of Marine Science and Technology No. 56 – November 2018

Figure 3. Half bridge circuit using one MOSFET and flywheel DIODE

0

10

i3

0

0

0

i2

i1

vD

vG

0

5

5

5

10

Figure 4. Waveform of VG, VD, i1, i2, i3 when duty cycle is 25%

reverse current are measured and analyzed. The test is implemented with a DC motor which its model is DD95-F024300 and has parameters: 24VDC, 300W, 3000rpm, shunt wound DC motor. This motor drive a DC generator (DD95-F024300) which output voltage is supplied to external

load resistance (type: 4, 100W, quantity 6). For current measurement, it is converted from A to mV (1A is equivalent to 100 mV). The controller was tested in many cases:

1. Change duty cycle of PWM

2. Change the frequency of PWM

3. Start and stop condition

4. Change load of DC motor to constant moment type.

2. Analysis of half bridge circuit using one MOSFET and flywheel DIODE

This circuit is shown in figure 3. When the drive MOSFET Q1 conducts, current flows from source positive, through the motor and MOSFET and back to source negative. At this time, electrical equivalent circuit of DC motor is shown in Figure 2 and the following equations are written [2]:

reb

b1

aaas

ωΦke

edt

diLiRV (1)

Where:

Vs: The voltages applied to the field and armature sides of the motor.

Ra, La: The resistance and inductance of armature sides of the motor.

eb: The back electromotive force.

: The flux.

r: Speed of rotor.

When the MOSFET switches off the motor current keeps flowing because of the motor's inductance. So, whenever MOSFET changes state with the motor current being non-zero, the new state has to make sure that the current can continue to flow in some way. There is a power diode connected across the motor so there is reverse current through the diode and so:

0di

i b1

aaa edt

LR (2)

As can be seen in Figure 4 and Table 1 when duty cycle of PWM is about 25% (frequency of PWM is 5 kHz), the peak of current i1 is 1.2A and I1rms is 0.8A. It is clear that i1 is much smaller than i2, i3 which their values are 3.9A and 3.6A at peak and are I2rms, I3rms 2.8A and 2.2A

VD

VG



0

10

0

10

0

10

0

10

10

i3

i2

i1

vD

vG

0

Figure 5. Waveform of VG, VD, i1, i2, i3 when duty cycle is 50%

There was a little change about values of I1rms, I2rms, I3rms if frequency was changed and the PWM value was kept (25%). However, the waveform was the same and we still received the result I1rms < I3rms < I2rms. PWM is increased to about 50% of duty cycle, the peak of current are obtained as follow: i1= 4.1A, i2= 9.6A, i3= 8.8A (Figure 5) and I1rms, I2rms, I3rms are 3.4A, 6.9A, and 4.8A so the result is still I1rms < I3rms < I2rms.

By changing the PWM values and frequency Table 1 and Table 2 were obtained. From these table, it is easy to see that: The current flowing flywheel DIODE in half bridge circuit has a peak at hight duty cycle. Nevertheless I3rms has greater value at low duty cycle. And the lower the frequency, the higher the I2rms, I3rms. When frequency is over 5 kHz the gap is small.

One important note is that i3 is regenerating current, so speed of motor does not response quickly when it is required changing fast. For example, when the motor is working at full speed and has "stop" command, at that time speed of motor will decrease slowly according inertial moment. When DC motor drives load which its value is constant then the current i3 has maximum value at low duty cycle. The duty cycle is 30% when the motor works with rate load (30% is threshold value which makes the motor's rotor start rotating) and i3 decreases when duty cycle increases.

Table 1. The relation between duty cycle of PWM and currents when f >= 5 kHz

PWM values

Peak of current (A) Root mean square of current (A)

i1 i2 i3 I1 I2 I3

10% 0.4 0.2 1.8 0.2 0.8 0.8

25% 1.1 3.9 3.6 0.8 2.8 2.2

50% 4.1 9.6 8.8 3.4 6.9 4.8

70% 9 13.4 11.8 8.3 10.8 5.7

95% 14.4 16.2 15 13.6 13.2 3.1

Table 2. The relation between duty cycle of PWM and currents when f =2 kHz

PWM values

Peak of current (A) Root mean square of current (A)

i1 i2 i3 I1 I2 I3

10% 0.5 2.5 2 0.4 0.9 0.9

25% 1.2 5.7 5 0.6 2.8 2.2

50% 5 13.7 11.6 3.8 8.2 5.4

70% 9.6 16 14.4 8 11.8 5.8

95% 14.4 17.2 16 13.6 14.8 3.6

3. Analysis of important features

3.1. Switching losses

When an output transitions from high to low or low to high, the output devices traverse a linear region where they are dissipating significantly more power than when fully turned on. This power dissipation is referred to as switching loss. Switching loss is a function of the following:

• How quickly the output swings from one extreme to the other;

• Supply voltage;



• Output current;

• Frequency that the output is switching.

In some cases, such as a DC motor driver that is only turned on or off (not subjected to PWM speed control or current control), this rate may be so small as to be negligible.

3.2. Frequency

Output voltage supplied to motor causes the motor to heat more than pure DC. If the frequency is too low, the current is discontinuous and heating will be an integral of the current squared so the lower the frequency, the higher the ripple current and the greater the heating. Range of optimum frequency would seem to be around 5-30 kHz [1], [6]

3.3. Selecting MOSFETs

‘N’ channel MOSFETs have a much lower Rds (on) so it would appear, that N-channel devices are desirable for their lower losses. They are also faster to turn on and off. For high-current applications N-channel devices are a better compromise as P-FETs.

3.4. Safety features

They can be listed as following: Low battery voltage protection, Over-temperature detection to protect for MOSFETs, Wrong input source connection, overcurrent protection for motor, short circuit and so on.

4. Conclusion

This study was conducted with a real DC motor used MOSFETs controller. From above results these following conclusion are given:

(1) The current flowing flywheel DIODE in half bridge circuit has maximum value at low duty cycle. The duty cycle is 30% when the motor works with rate load which has constant value with time.

(2) If motor is suddenly stopped at highest duty cycle (Voltage supplied to motor is maximum), the current flowing flywheel MOSFET in Half bridge circuit has maximum value.

(3) The authors showed some ideas for choosing parameters, safety features as well as devices used in circuit. These are the basis for designing a quality DC controller in many applications.

REFERENCES

[1] Jinping Wang, Jianping Xu, "A Novel PWM Control Method for Switching DC-DC Converters with Improved Dynamic Response Performance", Power Electronics for Distributed Generation Systems (PEDG), 2010 2nd IEEE International Symposium on, pp 85-88, 2010.

[2] Ali Bekir Yildiz, "Electrical equivalent circuit based modeling and analysis of direct current motors", ELSEVIER International Journal of Electrical Power & Energy Systems, Volume 43, Issue 1, pp1043-1047, December 2012.

[3] Wai Phyo Aung, "Analysis on Modeling and Simulink of DC Motor and its Driving System Used for Wheeled Mobile Robot", International Journal of Electrical, Robotics, Electronics and Communications Engineering, Vol.1, pp1153-1160, 2007.

[4] Anis Kebir, Faouzi Ben Ammar, "Cascaded H-bridges asymmetrical 11-levels optimization", Proceedings of the 14th International Middle East Power Systems Conference (MEPCON’10), Cairo University, Paper ID 206. pp465-470, 2010.

[5] Thomas Truax and Robert Stoddard, "a new, low-cost dual H-bridge motor-driver IC", Technical paper STP98-9, PowerSystems World, Santa Clara, CA on November 11, 1998.

[6] Samuel Muehleck, "Design and Simulation of Interconnected H-Bridge Inverter", Senior Project, California Polytechnic State University, 2012.

Received: 12 July 2017

Revised: 27 February 2018

Accepted: 13 March 2018



RESEARCH ON AN ELECTRICAL ENERGY MANAGEMENT MODEL FOR VIETNAM MARITIME UNIVERSITY

DANG HONG HAI, PHAM THI HONG ANH

Department of Industrial Automation Engineering, Vietnam Maritime University

Abstract

This paper presents the general issues of energy management, particularly the management of electrical energy. On that basis, a model of the electrical power management system for Vietnam Maritime University has been studied. The result of this paper is a proposed model of electrical power management system for the purpose of managing and using electricity efficiently and economically, reducing energy costs.

Keywords: Energy management, electrical power management system.

Tóm tắt

Bài báo này trình bày về các vấn đề chung về quản lý năng lượng, đặc biệt là quản lý năng lượng điện. Trên cơ sở đó nghiên cứu xây dựng hệ thống quản lý điện năng cho Trường Đại học Hàng hải Việt Nam. Kết quả thu được của bài báo là mô hình đề xuất hệ thống quản lý điện năng nhằm mục đích quản lý và sử dụng điện năng một cách tiết kiệm và hiệu quả, giảm chi phí điện năng.

Từ khóa: Quản lý năng lượng, hệ thống quản lý điện năng

INTRODUCTION

In Vietnam, efficient use of energy especially electricity is an urgent issue in the scenario of increasing imbalance between power supply and demand. The increasing population coming with high energy comsumption combining, with the wrong views in the management and use of energy in the production and business establishments, administrative offices,... is the major cause of energy waste in use. In order to make energy use more effective, economical and sustainable, we need to implement a sufficient energy management.

1. General issues of energy management

1.1. Energy management Energy management is the process of using energy economically and efficiently in order to

achieve the highest profit (lowest cost) and improving the competitiveness of enterprises. Energy management controls energy consuming devices to minimize the energy demand and consumption.

The common myth of energy saving is to cut the energy usage although that usage is necessary. In fact, the energy savings will include the following aspects:

+ Optimize the energy comsumptionfor production and life;

+ Conduct system inspection to reduce the energy waste;

+ Save energy, improve energy efficiency

The use of energy saving and efficiency is the application of management and technical measures to reduce losses and the energy consumption of vehicles and equipment while it still ensures the needs and targets [1], [2].

1.2. Electrical energy management

Efficient use of electrical energy enables commercial, industrial and institutional facilities to minimize operating cost, and increase profit and competitiveness.

Several solutions are being used to improve the efficiency of an electric system such as: Maintain voltage levels, minimize phase imbalance, maintain power factor, maintain good power quality, select efficient transformer,…

1.3. Energy manager

One very important part of an energy management program is to have top management support. More important, however, is the selection of the energy manager, who can among other things secure this support [4].

The energy manager assists the head of that facilitiy in efficient energy usage with the following works:

+ Making an annual and 5-year plan for efficient energy usage;

+ Implementing measures to use energy economically and efficiently in complicance with the approved objectives and plans;



+ Testing and evaluating the implementation of measures to use energy economically and efficiently;

+ Tracking energy consumption of the equipments and entire production line; the fluctuation of energy consumption related to the new installation, renovation and repair of equipment using energy;

+ Organizing propaganda, training activitiesin efficient energy usage.

2. Study on the model of electrical energy management for VN Maritime University (VMU)

2.1. Current infrastructure of electrical energy management in VMU

Through the survey on the actual state of electrical energy management of VMU, we can assess through the aspects: energy policy; human resources and organizational structure; relationship and exchange of information between functional departments, faculties and units within VMU; measurement information and storage of energy data.

On energy policy, the school has not issued an energy policy. There is no commitment of the Rector on the implementation of electric energy savings.Thus, in the action plan on the implementation of electrical energy savings, there is no specific instruction to step by step implement that energy policy.

On structure of organization, management and human resources:

VMU does not have an organizational structure of the electrical energy management and its own electrical energy management board, even a part-time job is not available. No assignment of rights and responsibilities for members is presented in the electrical energy management board. However, VMU has seriously considered and implemented the proposals on electrical energy saving.

About the contact and exchange of information between the relevant departments in VMU: All exchanges are usually made through the Equipment Administration Department and led by a representative of the department. It regularly sends information to lecturers, students and staff who directly use the equipment consuming electricity.

About measurement information and storage of electrical energy data:

At each building, there is a system for measuring and monitoring electricity consumption via the electricity meters, voltmeters and ammeters. The contents of the electricity consumption norms are available at meetings of functional departments. Electrical energy costs are calculated on the basis of electricity bills paid for the purchase of energy.

2.2. Model of electrical energy management system

It is based on four general principles (P-D-C-A): Plan; Do; Check; Act and detailing in the proposed model about electric energy management system for the Vietnam Maritime University presented in Figure 1 [3].

Power Supplier

Commitment of the Rector on implementing

electrical energy

Awareness of electrical energy saving

Building electricity

policy

Setting up the electrical energy board

Preliminary electrical

energy auditDetailed electrical

energy audit

Proposing cost-effective power saving

solutions or low cost ones

Monitoring

and

evaluation

Set new levels of

electrical energy

usage

Supplier of electrical

equipment

Studing feasible investment projects

Proposiny solutions for saving

electricity

PropagandaEducation

Electric power system

Procurement

of

equipment

Implementing

solution

Testing and

acceptance

Figure 1. Proposed model for electrical energy management in VN Maritime University (VMU)



The model shown in Figure 1 can be explained in detail with 6-step implementation as follows:

Step 1: Commitment of the School-board on the use of electrical energy management system

a. Appointing a senior manager to lead the management of electrical energy at the University

With organizational structure diagram of the university, the Vice Rector who is in charge of the facilities in VMU should be in charge of the management of electrical energy. With this position, he has an insight view of infrastructure and electrical energy consumption in VMU. That Vice Rector has the following responsibilities:

- Approving the electrical energy policy of the University;

- Supervising and urging the implementation of electrical energy management system;

- Offering incentive or disciplinary policies to departments or individuals for electric energy saving implementation;

- Submitting policies for the implementation of electrical energy saving measures to Rector.

b. Establishment of the Electrical Energy Management Board

According to the organizational structure of VMU, there should be members of the Equipment Administration Department in the Electrical Energy Management Board.

Tasks of the Electrical Energy Management Board:

- Direct assistance on electrical energy management for the Vice Rector who is in charge of both facilities inand Electrical Energy Management;

- Identifing objective, implement plan, recommending the electric consumption to the Vice Rector in charge;

- Making the annual electrical energy policy, getting approval from Vice Rector;

- Supervising and evaluating the electrical energy management system at the VMU. On this basis, measures should be taken to improve the efficiency of electrical equipments in VMU;

- Widely disseminating the energy policy of the University to all officials, lecturers, staff and students in VMU. At the same time, offering the energy consumption norms for buildings in the University.

The Vice Rector (Head)

Department of Planning and

Finance

Head of the Equipment

Administration Department

(Deputy Head)

Departments,

Faculties, Companies,

Units

Standing member

Financial Officer

Figure 2. Proposed electrical energy management model at VMU

c. Appointment of an electric energy manager

Electrical energy manager in VMU will be responsible for all electrical energy management activities. He conducts all activities related to the use of electricity in the university.

Electrical energy manager must have in-depth technical knowledge and project management skills in order to set up an investment project in energy saving at VMU.

Duties of electrical energy manager are:

Developing annual and long-term plans for economical and efficient use of electricity at the University;

Organizing and managing the activities of using electricity, applying electrical management system at VMU;

Implementing measures to use electricity economically and effectively complying to the objectives and plans approved by the Vice Rector;

Verifying and evaluating the implementation of measures to use electricity economically and effectively;



Monitoring the electrical energy consumption, renovation, repairing, installation of new equipment using electricity and make regular reports;

Organizing propaganda activities for efficient energy usage.

d. Set up electrical energy policy

The electrical energy policy is developed by the Electrical Energy Management Board.

After being approved by the School-board, this policy must be propagated and disseminated widely in theUniversity.

The policy must consist of five major components: motivation, applicability, implementation guidelines to achieve goals, commitment from a senior manager.

Step 2: Identify opportunities for energy and cost savings

Analyzing factors affect the electric energy consumption such as:

- List price policies will directly affect the consumption of electricity at VMU;

- Performing electrical energy audit.

As the electric demand increased over time, the power system of VMU becomes inefficient. Energy audits help find the reasons and energy lossy equipment. Based on these audits, the reasonable solutions are given to improve electrical energy efficiency in VMU. The Electrical Energy Management Boardneeds to build an energy audit program. Besides the internal audit process, the VMU may employ the external auditors to better identify energy and cost savings opportunities:

- Identifying opportunities for power saving;

- Offering solutions to save electrical energy.

Technical solutions

+ Organizing, checking to capture the situation of using electricity throughout the University;

+ Through the inspection and assessment of the electric usage of the buildings, technical solutions are proposed to save electrical energy. For the electric grid in VMU, replacing the overload cables, with the bigger size ones; old cables with new ones with the same cross section. Before taking measures to save electrical energy, additional meters should be placed in the functional departments to record, monitor and compare the power consumption of each department before and after applying the electrical energy saving measures. On that basis, allocate monthly electric consumption to those departments.

Administrative and management solutions

+ Regulations on the mode and time of electric equipment usage in the University;

+ Inspection and monitoring plan;

+ Incentives and disciplinary policies;

+ Making investment projects on electricity saving.

From the report of the energy audit, the Rector will approve projects that satisfy the criteria of energy savings such as proposed implementation measures, deadlines of the project and effects on the administration, teaching, learning and other activities in VMU.

Step 3: Planning for electrical energy management

Based on the published energy policy, the Electrical Energy Management Board sets energy goals and develops action plans to achieve them. There must be a user guide in the plan. Energy managers should write instructional procedures. The plan must be supported in terms of resources, budget to ensure implementation of the plan and approved by the Board.

Step 4: Implementing electrical energy management

In order to carry out power management effectively, the human factor plays a crucial role. To achieve success, there must first be the commitment of the school-board. Then, stepping up the activities, programs to raise awareness for staff, lecturers, employees and students in VMU about energy issues, power management and reasonable and efficient power.

On the basis of implemented electrical energy audit, members of the Electrical Energy Management Board have to establish a plan to implement solutions for electrical energy management,



in order to improve efficiency. VMU selects the suitable solutions and equipment provider to upgrade the electric system.

Step 5: Supervising the electrical energy management activities

The Electrical Energy Information Management System includes:

- Recording the power consumption and influencing factors;

- Analyzing the trends of power demand and comparing relevant data;

- Target: Set a goal for reducing power consumption;

- Supervising and reporting results to the Head of Electrical Energy Management Board;

- Taking measures of electric consumption.

Step 6: Reviewing and re-evaluating the electrical energy management activities

Ending annually, VMU must organize evaluation, review of energy management activities such as: Reviewing, checking energy policy; goals, objectives and plans; resources, roles and responsibilities of the Electrical Energy Management Board; survey and evaluation; the level of awareness of power saving; review of monitoring and measure implementation. On that basis, a new policy is offered more suitably and reasonably with the situation of using electricity of VMU.

3. Conclusion

If energy audit like doctors' exams, energy management system are essential to maintain a healthy body. The establishment and operation of an electrical energy management system will control the use of electricity in each unit in VMU. Thus, it minimizes the waste of electricity, helps energy saving plan to achieve the highest results.

REFERENCES

[1] Vietnam’s National Energy Development Strategy up to 2020, with 2050 vision - Decision No. 1855/QĐ-TTg of December 27, 2007.

[2] Law on economical and efficient use of energy, 12th National Assembly of the Socialist Republic of

Vietnam, 2011.

[3] Training materials for energy managers, General Department of Energy, Ministry of Industry and Trade.

[4] Wayne C. Turner, Energy management handbook, Marcel Dekker, 2004.

Received: 09 January 2018

Revised: 14 March 2018




THE ADOPTION OF COLLISION RISK ASSESSMENT EMPLOYING FUZZY EVALUATION METHOD

DINH GIA HUY, NGUYEN MANH CUONG, NGUYEN THAI DUONG, DAO QUANG DAN Faculty of Navigation, Vietnam Maritime University

Abstract

Close range collision avoidance for ship has never been an easy task in view of many problems faced by mariners. Therefore, this article introduces the collision risk evaluation system for early defining hazardous moving targets at sea based on fuzzy mathematics theory. The collision risk is reasoned by the fuzzy assessment system (FAS) constructed by expert’s experiences. Depending on the TCPA and DCPA values as the input source, fuzzy system desired the collision risk results with the corresponding each target ship (TS). The proposed assessment system simplifies the evaluation performance of collision risks, helping mariner reduce appreciation activities when maneuvering in a crowded area. Simulation scenarios are carried out to justify the effectiveness of such system.

Keywords: Fuzzy logic, MMG model, collision risk, expert system. Tóm tắt

Tránh va tàu biển chưa bao giờ là một nhiệm vụ dễ dàng khi người đi biển luôn phải đối mặt với rất nhiều các nguy cơ có thể xảy ra. Do đó, bài báo này sẽ giới thiệu một hệ thống đánh giá rủi ro va chạm để xác định sớm các mục tiêu nguy hiểm di chuyển trên biển dựa trên lý thuyết toán mờ. Nguy cơ va chạm được sẽ được tính toán bởi hệ thống đánh giá mờ (FAS) xây dựng bởi thống kê kinh nghiệm từ các chuyên gia. Tùy thuộc vào các giá trị TCPA và DCPA làm nguồn đầu vào, hệ thống mờ sẽ đưa ra các kết quả nguy cơ va chạm với mỗi tàu mục tiêu (TS) tương ứng. Hệ thống được đề xuất sẽ làm đơn giản hóa quá trình đánh giá nguy cơ đâm va, giúp người đi biển giảm thiểu được các công việc khi tàu hành hải tại các khu vực đông đúc. Chương trình mô phỏng sẽ được sử dụng để kiểm định tính hiệu quả của hệ thống.

Từ khóa: Fuzzy logic, mô hình MMG, nguy cơ đam va, hệ thống chuyên gia.

1. Introduction

Numerous disasters were traced to human error and negligence without available navigation support equipment on the bridge. A sensible solution for maritime navigation which is the development of decision assistance systems seemed to be the effectively forwarded step in the future to decrease the collisions at sea. A system is estimated to have optimum application only if it has certain criteria, such as determining the shortest route, the safest route, minimum figure for actions, observing the regulations etc. Recent years, the combination of a risk assessment module and an automatic collision avoidance algorithm becomes the trend for developing an automatic collision avoidance system for ship. The major of automating ship is categorized by three fields depending on the area of study, including collision risk assessment, collision avoidance for ships and optimal route planning.

Study of collision risk assessment is witnessed as the early field of the major. The first several concepts depended on the closest point of approach (CPA), time of closest point of approach (TCPA) or distance to the closest point of approach (DCPA). This method is deemed to be adequate by many studies published because of practical effectiveness. The research of Hasegawa [1] and Su Chen et al. [2] used investigation parameters, including TCPA and DCPA as the input source to obtain the value of collision risk (CR) implemented by a Fuzzy system. The evaluation of CR employing two parameters (TCPA, DCPA) is not a new method, nevertheless it is effective in both short and long ranges. In modern studies, the new trend appears, of which the phrase “ship domain” gradually becomes popular for risk assessment mission. Fujii & Tanaka (1971) [3] are the first researchers to suggest the concept of the ship domain, which represents one of the key in marine traffic modeling that has since become the basis for novel approaches to assess collision risk to this day. The suggested ship domain is an ellipsoidal shape with OS at the center, formulated from the results of a study on marine traffic in Japanese channels. Goodwin’s ship domain is introduced in 1975 [4] and discretely divided into three zones. The suggested domains have presented numerous shapes and size computing from different factors, that is proved by the number of domains published in next three decades: Coldwell (1983) [5], Z. Pietrzykowski (2009) [6], Gia Huy Dinh (2016) [7], etc.

While the application of domain method can be customized for different purposes to evaluate CR, the methods using TCPA and DCPA have the advantage of being simple in calculating and



operating at the larger distances. In this article, a collision risk assessment system based on TCPA and DCPA is introduced to arrange obstacles according to their level of threat. Target ship’s heading, velocity and position are collected for computing TCPA and DCPA. After that, two values will be used as input variables in a Fuzzy system in order to calculate the final result of CR.

2. Composition risk-based collision avoidance

2.1. The determination of TCPA and DCPA

In this section, the calculations of TCPA and DCPA are performed by a module at a current time. The way for determining DCPA and TCPA can be described by Figure1, where Vo is OS’s velocity, Vt is TS speed, D is the distance from OS to TS, α is the relative bearing of TS from OS and β is the relative bearing of OS from TS.

Vt

TS

β

DC

PA

* TCPA

OS

Vo

α

D

Vrelat

iveVre

lative

3

Figure 1. DCPA and TCPA in an approaching situation

The Eq. (1) and Eq. (2) are employed for calculating DCPA and TCPA:

2 2

( sin sin )

2 cos( )

o t

o t o t

D V VDCPA

V V V V

(1)

2 2

( cos cos )

2 cos( )

o t

o t o t

D V VTCPA

V V V V

(2)

TCPA and DCPA will be used as input variables in a proposed Fuzzy system in order to determine CR.

2.2. Fuzzy components

In modern science, the mathematics method cannot model objects in all of the situations, some reflections of object are so difficult for modeling by equations. A great number of attempts for creating mathematical models of objects was stopped. The restriction leads scientists to an alteration proposed as “intelligent control”. Fuzzy control is a well-known example of such alteration which has been applied in the wide area of real life and research department. Fuzzy theory is a rule-based representation of human knowledge and deductive performance

In the dissertation, one popular fuzzy model has been employed as a main course for finding highest variable of CR, Mamdani 1977 (Linguistic fuzzy model) known as qualitative knowledge by if-then rules:

: is and is then is , 1,2,...,i i i iIf TCPA A DCPA B CR C i K

Where TCPA and DCPA is the input linguistic variable and Ai and Bi are the antecedent linguistic labels, CR is the output linguistic variable and Ci are the consequent linguistic terms.

The Fuzzy set introduced in this paper is developed depending on Hasegawa [1], the membership functions are changed by simulation scenarios and a survey performed to 20 experienced master. The Figure 2 shows the view of the Linguistic variable and rules of FAS proposed.



Figure 2. DCPA and TCPA in an approaching situation

Where SAN: Safe Negative, MEN: Medium Negative, DAN: Dangerous Negative, VDP: Very Dangerous Positive, DAP: Dangerous Positive, DAP: Dangerous Positive, MEP: Medium Positive, SAP Safe Positive, VSP: Very Safe Positive.

In rule-based fuzzy systems, the relationships between variables are represented by fuzzy if-then rules in the form mentioned:

If DCPA is SAN and TCPA is SAN then CR is SAN

If DCPA is SAN and TCPA is MEN then CR is SAN

….

If DCPA is SAP and TCPA is VSP then CR is VSP

( , ) I( ( ), ( )) min( ( ), ( ))A B A Bx y x y x y (3)

Eq. 3 expresses Fuzzy conjunction operator applied Mandani’s implication.

1

1

( )

( )

( )

F

C j j

j

F

C j

j

cr cr

CR cog C

cr

(4)

The Center of Gravity (COG) method is applied to calculate CR in de-fuzzification step (Eq.(4)).

3. Simulation and performance analysis

In order to validate the proposed system, a real-time simulator is constructed which can get the real-time status information of ship. The simulator is programmed by using C# given in Figure 3.

Figure 3. Simulation screen



The example of the head-on situation is illustrated in Figure 4.

u

v

Delta

CR

Figure 4. Head-on simulation scenario

The environmental disturbance factors affecting on ships such as the wind, flow and wave are eliminated. That absolutely does not affect the results of avoiding a collision in the same conditions in practice (good weather), in as much as a safe turning point is always calculated for tracking module toward. The model ship is the training ship of Mokpo National Maritime University, Sae Nuri. MMG model is employed for OS’s motion description.

The results of CR were recorded in real-time for determining the most dangerous target ship. In simulation scenario, the FAS determined hazard target at CR=0.2. The avoiding action was implemented at t=389(s), thereby improving the results of CR in the next period. Additionally, the CR plays as the key component to cancel loop of automatic collision avoidance performance. Especially, CR was witnessed a suddenly decreased result at t=1224(s) from positive (CR=0.58) to negative (CR=-0.12) when OS pasted astern of TS. The negative result deemed one of the important criteria for completion of avoidance process.

4. Conclusion

The article introduced a method for automatic calculation of collision risk to be used in an automatic navigation system. The approach described is the theories of fuzzy logic which was constructed by mariner’s experience. The collision risk assessment system has two missions, combining the calculation for finding the most dangerous target ship and the main criterion for canceling automatic collision avoidance process. Besides, the simulation scenario is implemented for validating the effectiveness of the system suggested. In the next step, the Fuzzy system of weather assessment will be developed for combining with FAS proposed in this article, giving rise to a fuzzy comprehensive evaluation method. The surveys also will be expanded in both quality and quantity.

REFERENCES

[1] K. Hasegawa and A. Kouzuki, “Automatic collision avoidance system for ship using fuzzy control,” Journal of the Kansai Society of Naval Architects, no. 205, pp. 1-10, 1987.

[2] Shu Chen, Rashid AhmadByung - Gil, Lee Do Hyeun and Kim, “Composition ship collision risk based on fuzzy theory”, Journal of central south of university, vol. 21, issue 11, 11. pp4296-4302.

[3] Y. Fujii and K. Tanaka, “Traffic capacity,” The Journal of Navigation, vol. 24, pp. 543-552, 1971

[4] E. M. Goodwin, “A statistical study of ship domains,” The Journal of Navigation, vol. 28, no. 3, pp. 328-344, 1975.

[5] T.G. Coldwell, “Marine traffic behavior in restricted waters,” The Journal of Navigation, vol. 36, no.3, pp. 431-444, 1983.



[6] Z. Pietrzykowski and J. Uriasz, “The Ship Domain - A Criterion of Navigational Safety Assessment in an Open Sea Area,” The Journal of Navigation, vol. 62, no.1, pp. 93-108, 2009.

[7] G. H. Dinh and N. K. Im, “The combination of analytical and statistical method to define polygonal ship domain and reflect human experiences in estimating dangerous area,” International Journal of e-Navigation and Maritime Economy, vol.4, pp. 97-108, 2016.

[8] G. H. Dinh and N. K. Im, “A Study on the Construction of Stage Discrimination Model and Consecutive Waypoints Generation Method for Ship’s Automatic Avoiding Action,” International Journal of Fuzzy Logic and Intelligent System, vol.17, pp. 294-306, 2017.


Revised: 08 February 2018

Accepted: 26 February 2018



A NOVEL APPROACH TO DETERMINE THE SHIP POSITION BY USING THE AZIMUTH OF CELESTIAL BODY

NGUYEN VAN SUONG

Faculty of Navigation, Vietnam Maritime University

Abstract

In this paper, a novel approach is proposed to determine the ship position by combining the azimuth of a celestial body and the planning route of ship. Firstly, the equation relating the azimuth of observed body to the ship position in spherical coordinate system is described. Secondly, Mercator sailing method in the marine navigation is employed to to initialize the result of ship position. Finally, simple iterative method is applied to obtain the ship position. The advantage of this approach as comparison with other method is the ability to find the ship position when the number of observation is less than three.

Keywords: Celestial navigation, ship position, azimuth, spherical coordinate system, spherical trigonometry.

Tóm tắt Trong bài báo này, một tiếp cận mới được đề xuất để xác định vị trí tàu bằng cách kết hợp phương vị của thiên thể và tuyến đường đã định. Trước tiên, phương trình liên hệ phương vị thiên thể quan sát với vị trí tàu được biểu diễn trên hệ tọa độ cầu. Sau đó phương pháp hàng hải Mercator được sử dụng để khởi tạo ra các vị trí tàu ban đầu. Cuối cùng, phương pháp lặp đơn được ứng dụng để thu được vị trí tàu. Ưu điểm của cách tiếp cận này so với phương pháp trước đây là có thể sử dụng để giải bài toán xác định vị trí tàu khi số lượng thiên thể quan sát ít hơn ba thiên thể

Từ khóa: Hàng hải thiên văn, vị trí tàu, phương vị thiên thể, hệ tọa độ cầu, lượng giác cầu.

1. Introduction

The 2010 amendment of the STCW code on celestial navigation-related education and training encouraged that the usage of an electronic nautical almanac and celestial navigation calculation software. In response, many researchers have resorted to computer programs to deal with celestial navigation positioning. With these efforts, great advancements have been made in celestial navigation technology.

The actual ship position obtained by celestial navigation method is an intersection of two or more circles of an equal altitude (COP). Because of the complexity of computing COP equations, the line of position (LOP) equation is established to be instead of (COP) equation for finding the ship position. Recently, many researchers have suggested the new mathematical algorithms to solve the COP equations. The trigonometric technique was developed to solve the simultaneous COP equations using a spherical coordinate system [2]. Later on, the author in [1] analysed the COP equation on the Cartesian coordinate system instead of the spherical coordinate system in order to apply the vector calculus for forming two equations of COP with three unknowns, and then the technique of vector expansion was proposed to obtain the ship position.

By other approach, the genetic algorithm was employed by [5] to search the optimal ship position in COP equations. On the other hand, [3] proposed the other solution to obtain the COP equation using the Cartesian coordinate system, after that the SVD math technique was applied using the least square method to find the ship position with more stability than the normal least square method. By establishing the great-circle equation relating the observed body to the ship position on Cartesian coordinate system, [4] proposed a novel idea known as the azimuth method to fix the ship position during the night when the horizon is invisible. This method does not require horizon and sextant equipment as using.

Although the azimuth method can be used at night when the horizon is invisible, this method is very difficult to apply for the case of a single celestial body. For example, the number of observation is less than three when sighting the sun or a single star. Consequently, there are still problem regarding to the using of the single celestial body for fixing by the azimuth method. In this paper, a novel approach is proposed to determine the ship position by combining the azimuth of a simple celestial body and the planning route of ship. Firstly, the equation relating the azimuth of observed body to the ship position in spherical coordinate system is described. Secondly, Mercator sailing method in the marine navigation is employed to to initialize the result of ship position. Finally, simple iterative method is applied to obtain the ship position. The advantage of this approach as comparison with other method is the ability to find the ship position when the number of observation is less than three.



2. The celestial sphere on spherical coordinate system and the equations for ship position

The basic concept of celestial navigation includes elements of the celestial sphere such as the latitude (φ) and the longitude (λ) of the ship’s position and the Declination (δ) and Greenwich Hour Angle of the celestial body (GHA) are viewed using spherical trigonometry as shown in Figure 1.

In this study, the authors propose a novel mathematical equation to find the ship position using the azimuth of single celestial body. This equation is investigated by expanding the trigonometrical factors on spherical coordinate system, the detail of spherical triangle is shown as Figure 2.

By using the rules of expression in spherical tringle, the equation for ship position is established which combines four factors in spherical tringle (PNPC), such as ship position (φ, λ), the coordinate of celestial body (δ, LHA) and observed azimuth (A). The detail is expressed as follows:

cotanAsinLHA sin cosLHA tan cos (1)

For the ship position, Eq. (1) is expanded by multiplying two sides of this equation with

following element: 2 2

1

cotan A sin, and we have:

2 2 2 2

2 2

cotanA sinsinLHA cos LHA

cotan A sin cotan A sin

tan cos

cotan A sin

(2)

Placing the new variables as follows:

2 2

2 2

cotanAcos

cotan A sin

sinsin

cotan A sin

(3)

Moreover, the local hour angle (LHA) at ship position has the relationship to Greenwich hour angle (GHA) as following equation:

LHA = GHA ± λ (4)

Substituting Eq. (4) and Eq. (3) into Eq. (2), the equation to find the ship position by the azimuth of single celestial body has the following form:

2 2

1

2 2

tan cossin( G HA )

cotan A sin

cotanAcos ( )

cotan A sin

(5)

Figure 1. The celestial sphere on spherical coordinate system

Figure 2. The spherical triangle and its factors



Assumption that the ship positions at twice of observation are respectively P1 ( 1, λ1) and

P2( 2, λ2). Because the ship always keeps her course during observation of celestial bodies, it can

use the information of the planning route to find the ship position.

2 1

2 1 2 1

( ) ( ) ( )cos

(MP( ) MP( )) tan

DLP LP TC

a

TC

(6)

Where: a is the equatorial radius of the Earth, LP( ) is the meridional arc length according

to the unit of a from the equator to the latitute , and MP( ) is the meridional part.

The meridional arc length and the meridional part are calculated as following equations:

2 2 2 3/2

0

2

( ) (1 ) (1 sin )

1 sin( ) ln( .tan( ))

1 sin 2 4

e

LP e e d

eMP

e

(7)

3. The approach to determine ship position with the combination of azimuth of celestial body and planned route

Assuming that at the first time, the azimuth is observed on the ship position P1 which lies anywhere on Locus of position (LP1). Similarly, the ship position at the second time for observation is P2, and the Locus of position (LP2). The objective of the proposed problem is to find the ship position at the second time P2 based on some conditions as follows:

+ The ship position at first time P1 lies anywhere on LP1;

+ The ship position at first time P2 lies anywhere on LP2;

+ The distance is D between P1 and P2.

The algorithm of the proposed approach is shown as following steps:

Step 1: Initialization P1 at first time of iterative loop by using the equations (5);

Step 2: Calculating P2 at first time of iterative loop based on the equations (6) and (7);

Step 3: Iterative procedure is performed until P2 lies on LP2. During on the iterative process, the arrow moves down or up to the end of this lies on LP2 (Figure 3). On iterative process, the ship position P1 is moved and changed continually. The positions P2 are also calculated based on the positions P1. Iterative process is stopped when the function f approximates to zero value as (8).

The ship position P2 lyingon LP2 satisfies condition as follows:

2 2 2 2 2 2f cotanA sinLHA sin cosLHA tan cos 0 (8)

To verify the effectiveness of the proposed approach, some examples and simulations will be shown in the next volume of this journal.

Figure 3. The description of proposed approach for ship position by azimuth of celestial body

D

P

1

P

2

P

1

P

1

LP1 LP2



4. Conclusions

In this paper, a novel approach to find the ship position with celestial body is proposed. Conclusions of this research can be drawn as follows.

+ Firstly, the equation relating the azimuth of observed body to the ship position in spherical coordinate system is described.

+ Secondly, Mercator sailing method in the marine navigation is employed to to initialize the result of ship position.

+ Finally, simple iterative method is applied to obtain the ship position.

The advantage of this approach as comparison with other method is the ability to find the ship position when the number of observation is less than three. Due to time limitation, the examples for validation have not yet shown by the authors. In the next volumes of this journal, this will be considered.

REFERENCES

[1] Andres, R. G, Vector Solution for the intersection of two circles of equal altitude, The journal of navigation, Vol 61, No 2, pp. 355-365, 2008.

[2] Chen, C. L., Hsu, T. P., Chang, J. R, A Novel Approach to Determine the Astronomical Vessel Position. Journal of Marine Science and Technology, Vol. 11, No. 4, pp. 221-235, 2003.

[3] Nguyen, V. S., Im, N. K, Development of Computer Program for Solving Astronomical Ship Position Based on Circle of Equal Altitude Equation and SVD-Least Square Algorithm, Journal of Navigation and Port Research, Vol 38, No 2. pp. 89-96, 2014.

[4] Nguyen, V.S, Im, N.K., Dao, Q.D, Azimuth method for ship position in celestial navigation, International journal of e-Navigation and Maritime Economy, Vol 7, June, pp. 55-62, 2017.

[5] Tsou, M. C, Genetic algorithm for solving celestial navigation fix problem, Polish Maritime Research 3(75) Vol 19, pp. 53-59, 2012.






CALCULATION OF THE LOW FREE HORIZONTAL OSCILLATION FREQUENCY OF THE SHIP HULL, APPLYING TO A 440KW TUGBOAT

NGUYEN VAN HAN Faculty of Shipbuilding, Vietnam Maritime University

Abstract The theory of determining the free horizontal oscillation frequency of the ship hull was written in the article by Nguyen Van Han in "Proceedings of the Maritime Technology Science Conference 2011". As a result of that theory, in this paper, the author goes into the analysis of determining the quantities, giving the block diagram, programming and applying calculation of the free oscillation frequency level 1, 2 to a particular tugboat of 440kW.

Keywords: Free horizontal oscillation, free oscillation frequency, ship hull. Tóm tắt

Về lý thuyết xác định tần số dao động ngang tự do của thân tàu thủy đã được viết trong bài báo của tác giả Nguyễn Văn Hân thuộc “Tuyển tập báo cáo Hội nghị Khoa học Công nghệ Hàng hải năm 2011”. Từ kết quả của lý thuyết đó, trong bài báo này tác giả đi sâu phân tích xác định các đại lượng, đưa ra sơ đồ khối, lập chương trình tính toán và áp dụng tính tần số dao động tự do cấp 1, cấp 2 cho một con tàu cụ thể - Tàu kéo 440kW.

Từ khóa: Dao động ngang tự do, tần số dao động tự do, tàu thủy.

1. Introduction

Noise and vibration are the issues that often appear onboard ship, they affect to the strength, longevity, and watertightness of the ship’s hull, to the working reliability of electronic, mechanical equipment, navigational instrument, and most of all to the working productivity and the healthy of the crew, passengers (for passenger ships) onboard ship [1]. Thus, there are requirements to calculate the oscillation of the ship hull in Rules of classification for ships [3; 4; 5]. The calculation of oscillation of ship hull consists of:

- Calculation of free oscillation frequency and compare it to the frequencies of exciting force due to main engine, auxiliary engine, propeller to check the possibility of resonance.

- Find out a solution to reduce the oscillation amplitude in the case of that oscillation amplitude exceeds the limitation value given in the Rule of classification for ships.

Calculation of free oscillation frequency (1/min) of ship hull can be done by the theory method, or by using approximate equations if there are reliable data from similar real ships. In the case of no available data from similar real ships, the theory method has to be used and it has to be approved by the classification society, and it is the method written in this paper.

So far, this calculation is an option in the Basic Design Document as well as the Technical Design Document of Vietnam Register (though this kind of calculation is mandatory in the Technical Design Documents of other well known classification societies in the world). In reality, there are cases of strong oscillation of the ship hull (due to the resonance of free oscillation frequency of the ship structure and the frequencies of other exciting forces from the propeller shaft, the main engine, auxiliary engine, etc.…) when the ship is on sea trials or she is operating, and that will have a bad affect on the longevity, and strength of the ship structure, ship engine system, ship equipment, and people onboard ship. Since it will take a lot of effort and money to solve this problem, thus it will be better to calculate in advance the free oscillation frequency of the ship hull to prevent the resonance issue, and this is the reason for this paper. However, in order to get the reliable results, it needs to compare the calculated results to the real data obtained from reality measurement and make amendment if it is required.

2. Theory to calculate free horizontal oscillation frequency level 1, 2 in vertical surface (XOZ surface) of the ship hull

From article [2] we have:

2.1. Vertical oscillation level 1

Form of oscillation level 1:

L

x

L

xxf

sin

2

1)( 111

(1)

Square of free oscillation frequency level 1:



)(.

sin

..

.

2

1

2

4

42

1

xfq

q

L

x

I

I

g

Lq

EI

o

o

o

o

; (2)

Correction due to sectional rotation and shear:

2 21 1

1 2

1.1 k k

(3)

Where: k1, k2 are coefficients due to sectional rotation and shear, that can be calculated as following:

2

sin.

.. 2

2

1

2

210

4

1

L

x

I

I

L

L

LGF

EIk o

TB

o ;

)(

2.

2

1

22

1

2

21

2

xfq

q

L

LL

g

q

g

q

k

o

o

TBTB

(4)

with: 12

22 HTB is the square of the average initial radian of weights

H: Depth of ship

1, β1: coefficients determined from the dynamic equilibrium condition, corresponding to the vibration level 1;

L: Ship length, m;

E, G: Young’s modulus, Shear modulus of material;

I: inertial moment of ship hull sections;

I0: any value that has the dimension of initial moment;

L: theoretical frame span;

F10TB: Web’s area of equivalent beam - calculated shear area (approximation of sectional area of longitudinal bulkhead and ship’s side) at midship;

q1TB: ship weight intensity (without added mass);

q: load intensity that includes distributed ship weight on a length unit and added mass;

q0: any value that has the dimension of weight;

g: accelerate of gravity;

: integral sum. 2.2. Vertical oscillation level 2

a. Oscillation level 2 in the 1st approximation

Square of free oscillation frequency level 2 in the 1st approximation:

)(.

sin

..

.16

2

21

2

4

4

2

2

xfq

q

L

x

I

I

g

Lq

EI

o

o

o

o

(5)



Where: L

x

L

xxf

2sin

2

1)( 2221

is the free oscillation form level 2 in the 1st

approximation

2, β2: coefficients determined from the dynamic equilibrium condition, corresponding to the vibration level 2;

Correction due to sectional rotation and shear, we have:

21

2

2

2

2

1

1.

kk

Here:

222

2

210

4

12

2sin.

..

16

L

x

I

I

L

L

LGF

EIk o

TB

o ;

)(

2.

2

21

22

2

2

21

2

xfq

q

L

LL

g

q

g

q

k

o

o

TBTB

(6)

Correction due to the orthographical condition of the oscillation form level 1 and 2: (f(x) refinement using orthographical condition)

)(.

sin.2

sin.4

..

.

2

2

2

2

1

4

4

2

2

xfq

q

L

x

L

x

I

I

g

Lq

EI

o

o

o

o

(7)

b. Oscillation level 2 in the 2nd approximation

Oscillation frequency in the 2nd approximation:

)(

)(.

.2

22

42''

22

4

2

22

xfq

q

LxfI

I

Lq

gEI

o

o

o

o

(8)

Where:2

22 2

1f ( ) . . ( )

2

o

o

IL L L q xx f x C D

L L L I q L

is the free

oscillation form level 2 in the 2nd approximation;

C, D are coefficients determined from the dynamic equilibrium condition;

Correction due to sectional rotation and shear:

21

2

22

2*

221

1.

kk (9)

Where: 22'

22

42''

22

2101

).(

).(.

.. Lxf

LxfI

I

LGF

EIk o

TB

o

;

)(.

).(..

2

22

22'

22

2

2

12

xfq

q

Lxf

Lq

qk

o

TB

o

TB

(10)



3. Block diagram



i is the indication number (i=1÷2) accounted for 1st or 2nd frequency level

Figure 1. Calcilation diagram (continue)



4. Applying to a tugboat of 440kW

a. Input data

- Ship type: Tugboat;

- Main engine power: 440 kW;

- Length of ship: L = 37.2 m;

- Breadth of ship: B = 7.4 m;

- Depth of ship: H = 3.0 m;

- Fore Draught: TH = 1.64 m;

- Aft Draught: TK = 1.96 m;

- Displacement: D=3.14MN (=320tons);

- Midship section moment of initial : I10=0.236 m4 (calculated as shown in [6], [7]);

- Midship section area: F10=0.13m2;

- Distributional added mass;

- And the following values: 2 20 10 /

qkNs m

g ;

I0 = 0.01 m4;

- Young’s modulus E, Shear modulus G;

- Data of ship route to calculate the added mass q;

- Offset table, bonjean data;

- Ship Weigh distribution on 20 theoretical frame spacing; (calculated as shown in [6], [7])

- Data of inertial moment of ship hull sections at each theoretical section (calculated as shown in [6], [7])

b. Calculated results

Oscillation frequency level 1:

- Without sectional shear and rotation: 1134,5

s

- With sectional shear and rotation: 1133,5

s

Oscillation frequency level 2:

- Without sectional shear and rotation: 1191,6

s

- With sectional shear and rotation: 1190, 4

s

Figure 2. Tug boat 440kW



5. Conclusion

- The free oscillation frequency level 1 (1), level 2 (2) of the ship hull can be calculated using the above method.

- The calculated free oscillation frequency will help ship designers to check the oscillation of the ship according to the requirement of Rules for classification of ship in the initial design phase.

- The requirement of differences between free oscillation frequency of ship hull and other oscillation frequencies due to exciting forces must be satisfy in all operational conditions of the main engine or auxiliary engine.

- If the calculated results show that there is a possibility of resonance between free oscillation frequency of ship hull and other oscillation frequencies due to exciting forces, there must be changes in the ship structure or oscillation frequencies of exciting forces.

- The calculation of free oscillation frequency of the ship hull will help ship designers to identify in advance the possibility of resonance situation that will have bad effect to ship longevity, strength; working condition of electrical navigational equipment, and the health of ship crew.

REFERENCES

[1] Ministry of Transport, “National Technical Regulation on Control of Noise Levels onboard Ships

- QCVN 80: 2014/BGTVT”, Hanoi, 2014.

[2] Nguyen Van Han, “Research on calculation of free horizontal oscillation level 1, 2 of ship hull”,

Proceedings of the Maritime Technology Science Conference 2011, pp.22-26, 2011.

[3] TCVN 5801: 2005, “National Technical Regulation on Rule of Inland - waterway Ships

Classification and Construction”, Ha Noi, 2005.

[4] QCVN 21: 2010/Ministry of Transport, “National Technical Regulation on the Classification and

Construction of Sea-going Steel Ships”, Hanoi, 2010.

[5] Lloyd’s Register, Ship vibration and noise, Guidance notes, 7/2006.

[6] TRINA, Longitudinal bending moments on models in head seas, 1977.

[7] B. B. Дaвыдoв, Пpoчнocть cyдoв Bнyтpeннeгo Плaвaния, Tpaнcпopт, 1978.



Accepted: 18 April 2018



REASEARCH AND CALCULATION OF STACKING-FAULT ENERGY FOR AUSTENITIC HIGH MANGANESE STEEL WHEN CHANGING VANADIUM

CONTENT NGUYEN DUONG NAM1, LE VAN TRUNG1, PHAM MAI KHANH2

1Institute of Mechanical Engineering - Vietnam Maritime University 2School of Materials Science and Engineering - Hanoi University of Science and Technology

Abstract

This paper presents the results of the research on stacking-fault energy (SFE) calculation for austenitic high manganese steel (HMnS) when changing the Vanadium content. Results show that: With austenitic high manganese steel, even at temperature down to 2200K, SFE value is still greater than 20 mJ/m2 so there can not be ε - martensitic transformation. By calculation, the twinning or sliding strips can be found on this steel. In addition, when vanadium occurs there is a greater SFE value than that of non-Vanadium samples. Moreover, with the value of SFE, the mechanical of HMnS can not increased durability by the martensitic phase transformation.

Keywords: Stacking-fault energy, ε - martensitic transformation, twinning, sliding strip, high manganese steel.

Tóm tắt

Bài báo này trình bày các kết quả nghiên cứu về tính toán năng lượng khuyết tật xếp (SFE) cho thép austenit mangan cao (HMnS) khi thay đổi hàm lượng Vanadi. Kết quả nghiên cứu cho thấy: Với thép austenite mangan cao khi xử lý ở 2200K, giá trị SFE là trên 20mJ/m2 do vậy không thể có chuyển biến mactenxit dạng ε. Bằng tính toán, với thép này có thể tìm thấy song tinh hoặc dải trượt. Ngoài ra, khi đưa thêm Vanadi vào trong thép, giá trị SFE lớn hơn với mẫu không có Vanadi. Hơn nữa, với giá trị của SFE, cơ tính của thép HMnS không tăng bởi chuyển pha mactenxit.

Từ khóa: Khuyết tật xếp; chuyển pha mactenxit – ε; song tinh; dải trượt; thép mangan cao

1. Introduction

The stacking-fault energy (SFE) is a characteristic of the material to determine the phase transformation. SFE helps us determine the phase transformation; thereby enhancing the character of the material, especially the resistance to abrasion.

A stacking fault is an interruption of the normal stacking sequence of atomic planes in a crystal structure. When the SFE is high the dissociation of a full dislocation into two partials is energetically unfavorable, and the material deforms only by dislocation glide. Lower SFE materials display wider stacking faults and have more difficulties for cross-slip and climb. The SFE modifies the ability of a dislocation in a crystal to glide onto an intersecting slip plane. When the SFE is low, the mobility of dislocations in a material decreases [1,2,3,4].

So far, we have mainly four methods to calculate the SFE: transmission electron microscopy (TEM), calculation by ab-initio, embedded-atom method (EAM), and thermodynamics [5,6,7].

The stacking-fault energy is calculated according to the expression of OLSON and COHEN in [5,13] as follows:

(1)

Where ΔGγ-ε is the difference in Gibbs free energy change between the austenitic phase γ and the martensitic phase ε; ρ is the surface atomic density (111) and σγ/ε is the surface energy between γ and ε. With transition metal, the value of σγ/ε is usually taken as 9 mJ/m2. Based on the difference in Gibbs free energy, ΔGγ-ε, can be calculated by the formula:

(2)

where ΔGγ-εche, ΔGγ-εmg and ΔGγ-εseg are the molar thermochemical free energy, magnetic free energy change and the free energy change due to Suzuki effect between γ and ε, respectively. ΔGγ-εseg is very low.

Martensite ε can only be formed when the defect energy is less than 18 mJ/m2, whereby the transfer from the face of center cubic to the hexagon is smoothly arranged, while the twinning is generated when the energy defects are valued at 18-35mJ/m2 while slippage is generated when



energy defect is 35 mJ/m2 [8,9,10]. Thus, theelements of SFE reduce the austenite stability and increase the transition condition from γ (feedback) to ε (positive).

The ISF energy (ISFE) plays a central role in forming ε-martensite and deformation twins, and observation of either transformation induced plasticity (TRIP) or twinning induced plasticity (TWIP) depends on ISFE.

This paper presents the results of research and calculation of SFE values arranged to phase transformation of high austenite manganese steel.

2. Experiment Procedure

After casting, here four main elements is consideration which are Iron, Manganese, Carbon and Vanadium. Other elements have very small content, were ignored. Vanadium content in sample (1, 2) is respective 0.03%, 1.02%. Chromium and Carbon content nearly unchanged at 1.4%C and 2.0%Cr.

Table 1. Composition of specimens

Sample Fe C Si Mn P S Cr V

1 82.00 1.13 0.76 15.31 0.07 0.05 1.91 0.03

2 80.30 1.36 0.81 14.70 0.08 0.02 1.82 1.02

3. Results and Discussion

According to Equation (1) the SFE is

(3)

To determine the SFE, we have to base on the chemical composition to calculate the molar fraction of each elements Xi of samples, as follows:

and (4)

Where wt%i is the weight percent, Mi is the molar mass and ni is the amount of each elements in mole. The calculation results is shown on the Table 2.

Table 2. The calculation results of Xi

Sample Fe C Si Mn P S Cr V

1

wt% 82 1.13 0.76 15.31 0.07 0.05 1.91 0.03

ni 1.4643 0.0942 0.0271 0.2784 0.0023 0.0016 0.0367 0.0006

Xi 0.7686 0.0494 0.0142 0.1461 0.0012 0.0008 0.0193 0.0003

2

wt% 80.3 1.36 0.81 14.7 0.08 0.02 1.82 1.02

ni 1.4339 0.1133 0.0289 0.2673 0.0026 0.0006 0.0350 0.0200

Xi 0.7540 0.0596 0.0152 0.1405 0.0014 0.0003 0.0184 0.0105

The calculation of the molar surface density ρ. The the surface atomic density ρ is calculated as follows:

(5)

where a is the lattice size of the alloy and N is Avogadro’s number.

The lattice size of austenite is calculated:

(6)

where Xi is the fraction of the elements i in the system

aFCC is the lattice size of the alloy in A.

Effect of the temperature of the lattice size is given by equation as

(7)

where is equal to from Eq. (5); is linear thermal expansion coefficient of austenite is

equal to 2.065x10-9 K-1 and T is the temperature in Kelvin.



Table 3. The calculation results of ρ

Sample 1 2

T (oK) 300 220 300 220

aFCC = aγ0 3.57978 3.57978 3.58013 3.58013

aγ 3.57978 3.57978 3.58013 3.58013

ρ 0.00003 0.00003 0.00003 0.00003

The calculation of the free energy for the γ-ε transformation .

Based on the regular solution model, , can be calculated using the following formula:

(8)

where , and are the molar thermochemical free energy difference,

magnetic free energy difference and the free energy difference due to Suzuki effect between γ and

ε, respectively. is neglected here since its value is very low.

According to Yang and Wan [11], the free energy for the γ-ε phase transformation, , is

calculated by the regular solution model, as follows:

(9)

where Xi and show the molar fraction and free energy change, respectively, due to

HCP martensite formation from FCC austenite in pure metals. The is the interaction energy

between the components i and j.

The values of the thermodynamic parameters of Eq. (9) are given as follow:

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

where T is temperature in Kelvin, and is in J/mol.

Table 4. The calculation results of

Sample 1 2

-730.7061 -716.8478

-96.8889 -93.1963

-1095.6380 -1321.0221

-42.1725 -45.0281

272.5297 257.8560

1614.6452 1909.8723

60.2883 62.5222

194.3518 225.4012

176.4094 279.5572



Figure 1. The flow chart of the calculation of [12]

The in Eq. (8) is the variation in the magnetic contribution of the austenitic and martensitic

phases due to the paramagnetic to antiferromagnetic transition, as seen in the table 5.


Sample 1 2

T (oK) 300 220 300 220

βγ/μB -0.1071 -0.1071 -0.1512 -0.1512

βε/μB 0.3590 0.3590 0.3088 0.3088

Tγ 223.5805 223.5805 194.2612 194.2612

Tε 84.7468 84.7468 81.5169 81.5169

τγ 1.3418 0.9840 1.5443 1.1325

τε 3.5400 2.5960 3.6802 2.6988

fγ -0.0098 0.7571 -0.0049 -0.0231

fε -0.0001 -0.0004 -0.0001 -0.0003

0.0274 -1.5476 0.0196 0.0685

-0.0006 -0.0020 -0.0004 -0.0014

-0.0280 1.5456 -0.0200 -0.0699

Based on the calculation results of and from table 4 and 5, the can be

calculated by the Eq. (7). The calculation results are shown in Table 6.


Sample 1 2

T (oK) 300 220 300 220

176.3814 177.9550 279.5372 279.4873

As for transformation metal, the value of σγ/ε is usually taken as 9 mJ/m2. So, from the

calculation results ρ (Table 3), (Table 6), we can calculate the SFE of samples by Eq. (3).

Table 7. Stacking Fault Energy calculation results of samples

Sample SFE (mJ/m2)

300oK 220oK

1 28.55495 28.64912

2 34.7247 34.72173

Table 7 shows the calculation results of SFE for both S1 and S2 after heat treatment process and after sub-zero treatment process. We can see that the values of both samples at two different temperatures are almost equal. The value of sample 1 is about 28 mJ/m2 and the sample 2 is 34 mJ/m2. However, with this stacking fault energy, these samples can not occur γ→ε transformation.



With the results of this calculation, both samples can only happen twinning movement or sliding strip. When carbon steel is greater than 1% of energy in the region disabilities 20-30 mJ/m2 or greater, the hardening of steel will be twinning mechanism or sliding strip. The carbon steel less than 1% of defects are smaller energy 18 mJ/m2 and able to transform to martensite ε. With sub-zero temperature at -80oC, the SFE’s results is almost unchanged. This is evidenced for the results of microstructure and hardness.

4. Conclusion

The article calculated the stacking-fault energy value for two samples of vanadium non-alloyed and alloyed steels. The results showed that, even when treated at negative temperature, both samples had large SFE values and no ε- martensitic transformation. The value of stacking-fault energy is 28.64912 mJ/m2 and 34.72173 mJ/m2 with vanadium non-alloyed and alloyed samples, respectively.

REFERENCES

[1] H.S. Avery, Austenitic Manganese Steel, Metals Handbook, Vol 1, 8th ed., American Society for Metals, 1961.

[2] H.S. Avery, Austenitic Manganese Steel, American Brakeshoe Company, 1949, condensed version in Metals Handbook, American Society for Metals, pp. 526-534, 1948.

[3] "The Physical Properties of a Series of Steels, Part II," Special Report 23, Alloy Steels Research Committee, British Iron and Steel Institute, Sept 1946.

[4] Saeed-Akbari, J. Imlau, U. Prahl, and W. Bleck: Derivation and Variation in Composition-Dependent Stacking Fault Energy Maps Based on Subregular Solution Model in High-Manganese Steels.

[5] G.B. Olson, M. Cohen, Met. Mat. Trans. 7A, pp.1897-1904, 1976.

[6] A.S. Hamada: Doctoral Thesis, U

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