Summary of mechanical engineering and engineering mechanics doctoral thesis: Research on the mechanical model and calculating design of an electrical generator for sea wave energy

Objective of the thesis For the purpose of building a model of electrical generator for sea wave energy, the device operates efficient and in suitable to Vietnam''s sea condition; determining the optimal damping coefficient of the generating motor, model parameters to received the maximum output power; design, fabrication of the electrical generator with the output voltages are 12 VDC, 220 VAC frequency 50 Hz and pure sine wave.

AND TRAINING OF SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY

-

Nguyen Van Hai

RESEARCH ON THE MECHANICAL MODEL AND CALCULATING DESIGN OF AN ELECTRICAL GENERATOR FOR SEA WAVE ENERGY

Major: Engineering Mechanics

Code: 9 52 01 01

SUMMARY OF MECHANICAL ENGINEERING AND ENGINEERING MECHANICS DOCTORAL THESIS

HANOI – 2019

Supervisor: Prof DrSc Nguyen Dong Anh

Hardcopy of the thesis be found at:

- Library of Graduate University of Science and Technology

- Vietnam National Library

1 Reasons for choosing the topic

According to calculations by scientists, the received energy from fossil fuels will become gradually exhausted, and now therefore looking for new energy sources is requisite For Vietnam, the 2020 target is to become a country in which marine economics will constitute over 50% of GDP Therefore, the energy demand supplying for general economics and particular marine economics is very important The research and fabrication of electrical generators for sea wave energy are necessary Moreover, the electrical energy received from sea wave energy conversion is friendly to environment, almost endless and is a clean energy source The sea wave energy is an important energy source of the world as well as Vietnam in the future

In addition, Vietnam has the advantage of being a country with a coastline stretching over 3260 km, with more than 3000 islands and

source from the sea is huge In order to exploit the vast energy resources of the sea, the author proposes a research of thesis of building a device model to convert from sea wave energy to electricity

2 Objective of the thesis

For the purpose of building a model of electrical generator for sea wave energy, the device operates efficient and in suitable to Vietnam's sea condition; Determining the optimal damping coefficient of the generating motor, model parameters to received the

maximum output power; Design, fabrication of the electrical generator with the output voltages are 12 VDC, 220 VAC frequency

50 Hz and pure sine wave

3 Research method

The thesis uses analytical method, combining of the numerical simulation and experiment for calculation, being specifically described as follows:

- Determining the optimal damping coefficient of the generating motor and model parameters by the analytical method

- Using fourth-order Runge-Kutta and Simpson methods in numerical simulation calculations, to determine the output power of the device received from the sea wave energy and survey the device's operation according to the sea wave conditions

- Calculation, design, fabrication and experiment of the electrical generator operates in sea

4 Scientific and practical significance

- The thesis brings the electrical generator model for sea wave energy, with the process of making the electrical generator device from research to fabrication, the device operates effectively and suitable to the actual conditions of Vietnam sea

- The electrical generator can be used for signal buoys of seaway and can supply the electrical power for lighthouses

5 Structure of the thesis

The contents of the thesis include the introduction, 4 chapters, the conclusion and proposition

CHAPTER 1 OVERVIEW OF RESEARCHES ON THE ELECTRICAL GENERATOR FOR SEA WAVE ENERGY

AND APPLICABILITY IN VIETNAM

1.1 Overview of researches on the electrical generator in the world

In the world, the research and fabrication of the electrical generator devices for sea wave energy source have been considered for a long time The received electrical energy source for wave energy conversion has met some demands of society Up to now, the electrical generators from sea wave energy have been investigated and fabricated in many countries, for example, Britain, Canada, Denmark, France, Ireland, Japan, Norway, Spain, Sweden, South Korea, the United States,… The models are researched in various forms such as the on-shore device, the device fixed on the bottom of the sea, and the floating device on the sea surface [1-19]

The analyses of models show that the electrical generator devices have been researched and fabricated in many ways In device models, the generating motor is designed to operate in a rotational motion or in a vertical up-down motion Each device has different advantages and disadvantages, depending on the fabrication capabilities of each unit so that the research and fabrication devices operate effectively and suitable to the actual use

1.2 Overview of researches on the electrical generator in Vietnam

In Vietnam, several research institutions have fabricated electrical generators for sea wave energy At National Research

Institute of Mechanical Engineering, the researchers have calculated device model with Pelamis type, the device has been experimented in Hon Dau - Haiphong sea and supplied the electrical power to the border guards on the island to use [24]; At Vietnam National

generators that operate and float on the sea surface in vertical direction The device has been tested in sea with the received output power still limited [26,27]; At Institute of Energy Science - VAST has fabricated an electrical generator device from sea wave energy, the device is fixed on the sea surface The fabricated device used the vertical axis hydropower generator with 60 W power, the device has been tested in sea with the output power received 50.92 W [28];

At Institute of Mechanics - VAST has carried out researches on surveying the energy characteristics of floating wave energy converters, to propose the design, calculation and fabrication of energy conversion devices [30] Moreover, since 2013, in the professional work, the author has calculated a numerical simulation

of the electrical generator model from sea wave energy The device model is calculated with the linear electrical generator, directly generating electricity and fixed on the seabed [31]

And more, the author has leaded the project "Study, design and fabrication of the electrical power system from the renewable energy sources, project’s code: VAST 02.04/11-12" [32] The project has designed and fabricated a power generation system with input energy sources from solar panel, wind energy and sea wave energy In which, the input source from sea wave energy has been calculated

and designed to be integrated with the electrical generator for sea wave energy will be studied and fabricated in the thesis

1.3 Research on the ability to apply the electrical generator in Vietnam and research orientation of the thesis

Vietnam is a country with a coastline stretching over 3260 km, a

of the East Sea, with nearly 3000 large and small islands, it indicates that the energy source from the sea is huge From the monitoring and survey data show that the average sea wave height at the near coast

is about 0.5÷1.2 m with the wave period from 2÷8 seconds, offshore wave height is about 1.2÷2 m with a wave period from 6÷8 seconds Especially, when the rough sea, the coastal wave height reaches about 3.5÷5 m, offshore reaches about 6÷9 m [34-37] This is an abundant energy source, which is very suitable for the electrical generator devices from sea wave energy to be with small and medium power

Moreover, the demand for electricity to provide for the marine economics, electricity for national security in the protection of sea and island sovereignty is an urgent task, while Vietnam’s National electricity Network can not reach Therefore, the research and fabrication of the electrical generator devices for sea wave energy to meet the actual needs is necessary

Research orientation of the thesis:

The purpose of the thesis is research, calculate and design a device to generate electricity from sea wave energy The device is

efficient operation, and suitable for processing ability in Vietnam The power source of device generates at two voltage levels are 12 VDC and 220 VAC frequency 50 Hz, with voltage quality is pure sine wave and according to Vietnam’s National grid Standard Especially, the electrical generator can be used for signal buoys of seaway and can supply the electrical power for lighthouses

Conclusions of chapter 1

Chapter 1 presents an overview of the electrical generators in the

direction operation Having pointed out that domestic units have been realizing research and fabrication of the electrical generator with detailed analysises for each type of device model The characteristics of sea wave energy have been collected and analyzed, with data on wave energy flux, wave height and wave period to along the Vietnam coast stretching over 3260 km In which, the average sea wave height at the near coast is about 0.5÷1.2 m with the wave period from 2÷8 seconds, offshore wave height is about 1.2÷2

m with a wave period from 6 ÷ 8 seconds Especially, when the rough sea, the coastal wave height reaches about 3.5÷5 m, offshore reaches about 6÷9 m

Having indicated that the necessity and application capability of device model in Vietnam Having shown out the structure of the electrical generator model for sea wave energy, and orient the research contents of the thesis, the device operates effectively and suitable to the actual conditions of Vietnam sea

CHAPTER 2 RESEARCH ON THE MECHANICAL MODEL AND OPTIMIZATION OF THE ELECTRICAL GENERATOR

FOR SEA WAVE ENERGY 2.1 Building a model of the electrical generator for sea wave energy

The electrical generator device is fabricated for converting sea wave energy into electrical energy This requires a system that can convert the vertical slow motion of buoy to a high speed rotating motion at the input of generating motor The main structures of device include a circular cylinder-shaped buoy, a rope, a piston-rack,

a gearbox, a generating motor, a block of 12 VDC voltage stabilizer,

a DC-AC inverter and a protection system with the generating voltage being 220 VAC frequency 50 Hz and pure sine wave, as shown in Fig 2.1

Figure 2.1 The schematic illustration of an electrical generator

for sea wave energy

z(t)

z S (t)

γ k

m

b Mechanical model

The governing equation of buoy associated with piston-rack, as shown in Fig 2.1, can be written as follows:

,)()()

2

2

zzkzzkdt

dzmg

zz

where m is total mass of the buoy and the piston-rack, z= z(t) is the vertical coordinate describing the position of the buoy at time t; ρ is

small in comparison with the damping coefficient of generating

position

converter taken over the time interval [0,τ] is given by [15,20,38-41]:

.)(1

2.2 Oscillating survey in nonlinear case

From the motion equation (2.7), performing the variable

.)

2

2

xkxkdt

dxmg

xzzgSdt

2 2

2

txxfxdt

xd

0

xt

a

From the characteristics of the model, the thesis considers the case of weak nonlinear system Applying the average method of

receives the relative formula between the amplitude and frequency as follows:

.

2 2 2 0

2 2 0

2 0 2



Figure 2.2 shows the relationship between the amplitude function

of system is stable in the frequency range from point (1) to (2) and point (5 ) to (6) In the frequency range is increasing from point (2)

to (3) and decreasing from point (5) to (4), the oscillation of system

is unstable On the other hand, if there is enough data of the actual sea wave conditions in sea areas with large wave amplitude, we can exploit the operating device in the the nonlinear region, and the received oscillating amplitude of device is the largest

Figure 2.2 Graph of amplitude resonance curves versus frequency

2.3 Optimization of the electrical generator for sea wave energy With researching orientation for fabrication of the electrical generator to operate the near coast From the assumption in sea wave height is below 1 m, the effect of nonlinear component in the model

is negligible The model parameters are determined according to a linear calculation, the equation (2.7) is considered with kN = 0 and

model is considered by linear wave, and motion in the vertical direction z has the form:

.)sin( t z0A

AgSgxm

kgSdt

dxmdt

mgx

b L

(2.53) with χ is the oscillating amplitude of the system received as follows:

b

gSk

m

AgS

L

b em gm

mgSk

AgSP







The device model is researched and fabricated with the selection

of Hon Dau - Hai Phong sea to test and exploit in the actual operation At Hon Dau sea, the sea wave conditions have a period to change in the range of 3.5÷4.5 seconds and the wave height of 0.5÷1.4 m [36], so the moving velocity in the vertical direction reaches from 0.29÷0.62 m/s In the thesis, the model is determined with the smallest mechanical power level of device to reach 270 W, the oscillating range of the model is 0.45 m From the expressions (2.57), (2.58) combining the wave data in Hon Dau sea, the model

cylinder-shaped with a height of 0.42 m and radius of 0.4 m Figure 2.4 shows the graph of the mechanical power levels of the device

3.5 seconds, 4.0 seconds, 4.26 seconds, 4.5 seconds in a wave

damping coefficient of 3400 Ns/m, corresponding to the mechanical power of the device is obtained maximum

Survey of the mechanical power according to the buoy size:

In survey calculation, the buoy radius varies from 0.35÷0.55 m Calculation results given a comprehensive picture of the mechanical power levels of device received from sea wave energy In figure 2.8

is a graph of the mechanical power of the device received from sea wave energy according to the buoy radii at sea wave periods

2.4 Building a numerical simulation program and survey the operation of device to converte from sea wave energy to mechanical energy

Building a numerical simulation program:

The motion equation (2.7) is solved by the fourth-order Runge - Kutta method, applying the Simpson method to calculate the numerical integral and determine the mechanical power level of the device The numerical simulation program is programmed on Matlab software, to investigate the operation of the device with the effect of the nonlinear spring when the device operates at 1 m wave height or higher

Figure 2.8 The power versus radius of buoy Figure 2.4 The power versus

damping coefficient