NGHIÊN cứu xây DỰNG mô HÌNH cơ học và TÍNH TOÁN THIẾT kế THIẾT bị PHÁT điện từ NĂNG LƯỢNG SÓNG BIỂN tt tiếng anh

MINISTRY OF EDUCATION

VIETNAM ACADEMY

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


The thesis has been completed at: Graduate University of Science
and Technology - Vietnam Academy of Science and Technology

Supervisor: Prof. DrSc. Nguyen Dong Anh

Reviewer 1:
Reviewer 2:

Reviewer 3:

Thesis is defended at Graduate University of Science and
Technology
- Vietnam Academy of Science and Technology at…, on
date…month…2019.

Hardcopy of the thesis be found at:
- Library of Graduate University of Science and Technology
- Vietnam National Library


1

INTRODUCTION
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

over one million km2 of sea surface, it indicates that the energy
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


2

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.


3

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


4

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
University, the researchers have fabricated linear electrical
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


5

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
marine space of over 1 million km2, accounting for 29% of the area
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


6

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
world, especially, the models mounted on the seabed and vertical
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.


7

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.

zS(t)
m
z(t)

k

a. Illustration of device model [33]

γ

b. Mechanical model

Figure 2.1. The schematic illustration of an electrical generator
for sea wave energy


8

The governing equation of buoy associated with piston-rack, as
shown in Fig. 2.1, can be written as follows:
2

m

d z
dt

2

 gSb ( z s  z )  mg  

dz
em

dt

3

 k L( z  z0 )  k N ( z  z0 ) ,

(2.7)

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
the water density, g is the acceleration of gravity, Sb is the bottom
area of the buoy, zs is the vertical coordinate describing the height of
sea wave from the seabed; the damping constant γ = γf +γem , in
which the damping coefficient of fluid, γf, is assumed to be very
small in comparison with the damping coefficient of generating
motor γem [44,45], and can be neglected; kL is the linear spring
coefficient, kN is the nonlinear spring coefficient, z0 is the rest
position.
The average of the power Pgm extracted from the wave by the
converter taken over the time interval [0,τ] is given by [15,20,38-41]:
Pgm 

1
2
  em z (t ) dt .



0

(2.8)

2.2. Oscillating survey in nonlinear case
From the motion equation (2.7), performing the variable
transformation z – z0 = x, the equation (2.7) is rewritten as:

d 2x

dx

k L x  k N x 3 . (2.22)
dt
dt
The wave equation used here is z s  A cos(t )  z 0 .
m

2

 gS b ( z s  z 0  x)  mg  

em

Use symbols  2 ,  , c and B. In case of near resonance
 2   2   , performing the calculation, the author gets equation:


9

d 2x

dt
with:

2

f ( x, x , t )  c

 2 x  f ( x, x , t ),
dx
dt

(2.25)

 x  x3  B cos(t )  g.

Use transformation: x  a cos(t   )  x .

(2.26)

0

From the characteristics of the model, the thesis considers the
case of weak nonlinear system. Applying the average method of
nonlinear mechanics, to calculate at a  0 and   0, the author
receives the relative formula between the amplitude and frequency as
follows:
2   2 

3
4

2

a0  3x 2 
0

B

2

a

2

2

2

c  .

(2.39)

0

Figure 2.2 shows the relationship between the amplitude function
a0 versus frequency Ω2 with the coefficients taken as follows: m = 25
kg; a = 0.35 m; g = 9.81 m/s2; x0 = 0.4 m; kL = 1900 N/m and kN =
700 N/m3. The results showed that, in the case of the amplitudefrequency curve with the damping coefficient γem = 40, the oscillation
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.


10

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
changed the variable z  z 0  x. Sea wave function acting on the
model is considered by linear wave, and motion in the vertical
direction z has the form:
zs  A sin(t )  z0 .

(2.41)

The motion equation of model received as follows:
gS A
d 2 x  em dx gS b  k L
b


x



g

sin(t ).
2
dt

m dt

m

m

(2.42)

Root of the equation (2.42) is found as follows:
x

 mg
k L  gSb

  sin(t   ),

(2.53)

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


11



 m

gSb A
2

 k L  gSb



2

2

  em 

2

.

The mechanical power of the device received from the sea wave
energy in a period is determined:
Pgm 

1



 em (gSb A) 2

2 k  gS  m 2
L
b

2   em2 2

.

(2.56)

The maximum spring force is determined: FL_max = kLHmax.

(2.57)

The maximum Acsimet force of buoy: FAcs_max = ρgπa2h.

(2.58)

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
parameters are determined kL = 2100 N/m, the buoy is circular

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
according to the damping coefficient γem at the wave wave periods
3.5 seconds, 4.0 seconds, 4.26 seconds, 4.5 seconds in a wave
amplitude of 0.5 m. In the thesis, the selected generating motor has a
damping coefficient of 3400 Ns/m, corresponding to the mechanical
power of the device is obtained maximum.


12

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.

Figure 2.4. The power versus
damping coefficient

Figure 2.8. The power versus
radius of buoy

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.


13

Algorithm flowchart of numerical simulation program:
Bigin
Inputs
t0, Z0, Δt, tmax, ps
Calculation:

k1 = f(ti, Zi, ps)
k2 = f(ti+

ti:= ti+1

t
2
t

k3 = f(ti+

2

, Z(i) +
, Z(i) +

t
2
t
2

k1, ps)
k2, ps)

k4 = f(ti+Δt, Z(i) + Δtk3, ps)
Z

(i 1)

No

Z

(i )

ti+1:= ti + Δt
 ( k1  2k 2  2k3  k 4 ) t / 6
Integral (2.8) by Simpson method:

ti+1≥ tmax

n 1

Yes
Output results
( j)

( j)
Z1  Z1 ; Z 2  Z 2

kq1  4  Q ( Z 2( j ) , p s )
j 1, 3,...

n2

kq 2  2 

j  2 , 4 ,...

( j)

Q ( Z 2 , ps )

 Q ( Z (0) , ps )  Q ( Z (n) , ps )  t
2
2

P

gm 
3
 kq1  kq 2




End

Figure 2.9. Flowchart of the numerical simulation program
In the survey calculation, the author has performed in two cases
that is the first-order wave (linear wave) in the expression (2.41) and
Stockes's second-order wave is given by [38,51,52]:
2

zs  A sin(t ) 

A k cosh(kz0 )
3

4 sinh ( kz0 )

[ 2  cosh(2 kz0 )] sin( 2t )  z0 .

(2.59)


14

Numerical simulation calculation of the device's operation:
From the calculating results are shown that the operation of the
device depends on both the amplitude and frequency of the sea
waves. In the case, with the first-order wave, the oscillating buoy is
delayed in phase compared with the sea wave about 33.60 (Fig. 2.11).
The Figure 2.16 illustrates the relationship between velocity and
displacement of the buoy motion in the case of the second-order
wave. It shows that the phase orbit of buoy motion is stable and
varies in the frequency and amplitude components of the secondorder sea wave.

0.5

6.2

Buoy displacement
Sea wave displacement

0.4
0.3

5.8

Velocity (m/s)

Amplitude (m)

6

5.6
5.4

0.2
0.1
0
-0.1
-0.2

5.2

-0.3

5
0

2

4

6
8
Time (s)

10

12

Figure 2.11. The displacement
of buoy and the sea wave
elevation level versus time

5.2

5.3

5.4
5.5
5.6
Displacement (m)

5.7

Figure 2.16. The phase orbit of
buoy motion

Figure 2.20 shows the characteristic curves of mechanical power
according to the sea wave amplitudes, at the wave frequency appears
continuous when testing the device in sea that received 1.47 rad/s.
Figure 2.21 is the motion of the buoy according to the sea wave
amplitude with Stockes's second-order wave function. The results are
calculated at wave amplitude A = 0.5 m, the difference of power
between the two cases when considering linear system (kN = 0) and
nonlinear (with kN = 1680 N/m3) is 4.4%. For wave amplitude A =
1.5 m, the difference is 17.1%, respectively.


15

Figure 2.20. The characteristic curves
of power versus sea wave amplitude

Figure 2.21. The displacement of
buoy versus sea wave amplitude

Conclusions of chapter 2
In chapter two, the author has built the detailed schema of the
electrical generator for sea wave energy, and set up the nonlinear
motion equation of the model. The average method of nonlinear
mechanics has been applied in the resonance phenomenon survey to
obtained the graph of amplitude-frequency resonance curves, and
indicated the device's stable and unstable operation area. Providing

the ability to fabricate operattion device at nonlinear region used in
sea with large wave amplitude.
With the damping coefficient of the generating motor, the
stiffness of the spring, and the buoy size of the device have been
determined optimization from actual sea wave data. The author has
selected the generating motor of Windbluepower Power Company
with stable generating power can grow to 1500W. Writing a program
to calculate the numerical simulation. Surveying the nonlinearity and
the vibration amplitude of model according to the sea wave
amplitudes, determining the phase orbit of the buoy motion and
device's mechanical power level receives from the wave energy.
Results of chapter 2 are published in [3], [4] and [5].


16

CHAPTER 3. CALCULATING DESIGN AND FABRICATING
DEVICE
3.1. Structure of the electrical generator for sea wave energy
In the model, the device is added the solar panel to install on the
buoy. The aim is to create an efficient generation system, the solar
panel is also an extra energy source to assure that the signal lamp at
the top of buoy always operates for the time at which the sea is calm.

Figure 3.1. Structural schema of the electrical generator for sea wave
energy
3.2. Calculating design of the mechanical part
The drawings are calculated and designed on Solidworks and
AutoCad software packages. The detailed drawings, function blocks
and inner mechanical structures are calculated and installed

appropriately in the device.


17

In the device model, the buoy is designed a circular cylindershaped with height of 420 mm and a diameter of 800 mm, the casing
of device is diameter of 500 mm and 750 mm in height.

Figure 3.3. Inner of the
electrical generator

Figure 3.5. The casing of
electrical generator

Table 1. Main structural components of the electrical generator
Parameters

Value

Piston casing length (mm)

400

Piston rod length (mm)

450

With parameters:

Rack length (mm)

450

h1 = 250 mm

Pinion diameter (mm)

60

Gearbox ratio

1:30

h2 = 750 mm
h3 = 750 mm
l = 1634 mm

3.3. Calculating design of the electrical part
The electrical part in the device is calculated using a generating
motor that it is the AC three-phase type permanent magnet motor,
and the 12 VDC voltage stabilizer with the input voltage received
from AC three-phase voltage of the generating motor. These


18

equipments were imported from WindBlue Power Company. The
output voltage from the 12 VDC voltage stabilizer is connected to
the input of DC-AC inverter. In the thesis, the DC-AC converter is
designed with a 2000 W power, and according to Vietnam’s National

grid Standard. The protection circuit block is built to control the
operating device according to conditions of overload, high heat level
and weak voltage to protect the operating system [39,61].
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12VDC

3

4.7u

C25
33

5VDC

9
10

2.1.1.1. (Chữ thường, nghiêng, 11, Times New Roman)
C28

Y2

A1013

12VDC AQ
Sensor7

+

U21A
LM339
1

-

RB7
RB6
RB5

RB4
RB3
RB2
RB1
RB0
VDD
VSS
RD7
RD6
RD5
RD4
RC7
RC6
RC5
RC4
RD3
RD2

12

6
Ap chuan

RE3
RA0
RA1
RA2
RA3
RA4
RA5

RE0
RE1
PIC16LC74/FP
RE2
VDD
VSS
RA7OSC1
RA6OSC2
RC0
RC1
RC2
RC3
RD0
RD1

R57 10K

R58

U20

1
2
16
15

4

R59 1.8K

11

10u

4

C29

220V AC

225

C14

D29

R12
R
1

R15

D28

10uF
104

9

6

7

3

2
3

Q6
IRF140

R

2.2R
C15

7

HO

VCC

3 30VDC

R11

COM

13 VSS

Q5

IRF140

R

2

6

VB

11 IR2110
SHDN

4

R9

330uF

5

C23

Q15
40N60
2

C2

( Chữ thường, Times New Roman, 11)

T10

3

D15

5

3

2

10
+

D7
D20

1

C24
104

R41

U8

2

R8

R

1

C3

330uF

2

1

1

150K

1

Q4
IRF140

R

R19

2

L 220uH

3.3K

D27

VDD

R7

R52

VCC

150K

R6
R

R

2

D8
DIODE

2

330uF

2

10K

+

3.3K
R44

+

R22

R20

1
S

R31
3.3K

4148
2

2

0.15R

1.1.1.1. (Chữ thường, nghiêng, 11, Times New Roman)
R23

8

1

5

DD

Q14
40N60

1

R30

D5

5

D13

L2
294SN

4

T9

2
3

C10

104

470uF

D6

Q3
IRF140

C11

+

C7
104

8

R5

C6

470uF

2

D25

4

+

1

330uF
C5
10K

D24

R4
R

R

8

VCC

8

1

GND

VCC
4

Q2
IRF140

7

DSCHG
C4

6
7

3

R3

2
3

+

6

THR

IR4427
TRG

R2
R

3 30VDC

1

OUT

Q1
IRF140

R

5

CV

3

2

RST

Q12
40N60

1
R27
3.3K
C21 105

4148
R26

1

3

U1

1
S

R1

4

R25
3.3K

4148
R24

DIODE

3

OUT

7805

Q11
40N60

1

C12

2

5

-

4

D3

VB

IR2110

3

D23

VS

LIN

1

1

T8

2

R40

HIN

2

8

Q8
IRF140

11

GND
IN

4

330 VDC

VCC

R14
R

D21

2

D22
1

6
7

3

3

U4
10
12

2
3

R13
R

2

GND

7815
V 12

VDD

IN

D2

+

Q7
IRF140

5

D1

9

1

C8
104

OUT

U6
1

C9
2200uF +
T7

G 3. ……….

U11
5VDC

Figure 3.8. Schematic illustration of DC-AC inverter and protection system


19

3.4. Device fabrication
The electrical generator is fabricated and assembled including
the core of device, mechanical structures and the protective frame of
device when the actual experiment in sea as follows:

Figure 3.17. The core of device
Conclusions of chapter 3

Figure 3.18. The electrical
generator device

Results obtained in this chapter are as follows:
Having built the total structure of the electrical generator for sea
wave energy and showing the function blocks in the device. The
mechanical structures have been detailed calculated and designed for
device. Having calculated the electrical part with DC-AC converter
to convert from 12 VDC voltage to 220 VAC voltage frequency 50
Hz and pure sine acording to Vietnam's National grid Standard, and
the protection system for the operating device.

All parts of the device have been fabricated and complete
assembly of device, checking the operation of device in the
laboratory.
Results of chapter 3 are published in [2] and [6].


20

CHAPTER 4. EXPERIMENT AND ASSESSING THE
PERFORMANCE OF THE OPERATING DEVICE IN SEA
4.1. Experiment of the electrical generator in sea
Figure 4.1 demonstrates several pictures of field experiments of
the electrical generator for sea wave energy in the Hon Dau sea,
Haiphong province, Vietnam [33,40].

Figure 4.1. The transport of device on the HQ1788 Ship and
experiment in sea
Sea wave period: The received results are shown that the period
of wave appears more and continuously at period of 4.26 seconds,
corresponding to the frequency 1.47 rad/s. The data are obtained
from DASIM measurement equipment with Futek pressure sensor of
America. The received average pressure value is about 0.31 psi (i.e.
0.021 atm in SI unit) and maximum value is 0.74 psi (i.e. 0.05 atm).
The obtained pressure values will be used for the purpose of
fabricating buoy and device casing.
Output voltage of device: Table 4.2 shows the average values of
the received voltage and current from the generating motor of device
at the tested load levels (excluding the power from solar pannel) and
DC-AC converter performance.

21

Table 4.2. Output average power according to the tested loads
Performance
Load Voltage Current Voltage Current
power
UDC
IDC (A)
UAC
IAC (A)
ηdc-ac (%)
Pe (W) (VDC)
(VAC)
100
12
9,92
224
0,45
84,67
140
12
13,47
223
0,61
84,15
200
12
20,33
223

0,92
84,09
300
12
29,5
221
1,35
84,27
4.2. Analyzing the voltage quality of the device
The output voltage waveform of the device is measured and
analyzed by the Picoscope USB Oscilloscope 2204A of England, and
the voltage spectrum analysis software is written by the author in
Matlab. It is showed that the output voltage wave on the load in time
and in frequency is received at 220 VAC ± 1.25% frequency 50 Hz ±
0.06% and is a pure sine wave. Therefore, the author found that the
output voltage quality of the electrical generator has met according to
Vietnam's National grid Standard [71].
4.3. Analyzing the performance of the device operating in sea
From data in table 4.2, the received average performance of the
DC-AC inverter is determined as follows:


dc  ac



84,67  84,15  84,09  84, 27
4

 84,3%.

(4.2)

With the output electrical power Pe of the device has emitted and
operated stably at 200 W during the experiment, the numerical
simulation power value of device has received in chapter 2 is 295.8
W. The energy conversion performance η of the electrical generator
is determined by the expression:


22



P
200
e
100% 
100%  67%
Pgm
295,8

(4.3)

In which the performance of the mechanical energy transmission
from the received buoy to the generating motor is 88%, the
performance of the electrical part is 75.8%. The obtained results have
showed the reasonableness between theoretical and experimental
research.
Conclusions of chapter 4

In present chapter, the author has experimented the operating
device in Hon Dau sea, Haiphong province, Vietnam. The device
works in the vertical direction and fixed on the bottom of the sea, the
buoy of device floats on the sea surface. The output voltage sources
of device are 12 VDC, 220 VAC frequency 50 Hz and pure sine
according to Vietnam's National grid Standard. The conversion
performance from the mechanical energy of the received buoy to the
electrical energy is 67%. The power of device has generated up to
300 W and operated stably at 200 W during the experiment in sea.
Results of chapter 4 are published in [1], [2], [3] and [4].
CONCLUSION AND PROPOSITION
1. Conclusion of thesis
General conclusions
This thesis presents the author's research results on building
mechanical model and calculating design of the electrical generator
for sea wave energy. In the dissertation, the research approach has
been started from surveying the actual conditions of sea wave, and
then building the mechanical model, calculating the design,


23

fabricating and experimenting the device in sea. The new
contributions of the thesis are as follows:
- Having collected and analyzed the sea wave characteristics of
period and wave height in Vietnam sea.
- Having built the mechanical model and set up the nonlinear
motion equation of the model. The average method of nonlinear
mechanics has been applied in the resonance phenomenon survey,
and indicated the device's stable and unstable operation region.

Showing the ability to fabricate the operating device at nonlinear
region used in sea with large wave amplitude. The analytic method
has used for the linear model calculation, the fourth-order RungeKutta and Simpson methods used for nonlinear model calculation
and numerical integration. The damping coefficient of the generating
motor has been determined optimization for selecting the generating
motor of device, and the power level of device received from the sea
wave energy according to the model parameters and suitable to the
actual conditions of Vietnam sea.
- The electrical generator for sea wave energy has been
fabricated and experimented in Hon Dau sea, Haiphong province,
Vietnam. The output power has operated stable at 200 W load during
the experiment in sea, the conversion performance from the
mechanical energy of the received buoy to the electrical energy is
67%.
New contributions of the thesis
- The author has proposed and built a model of high-efficient
electrical generator, suitable to the actual sea wave conditions and
fabricating capability in Vietnam.
- The author has established the nonlinear motion equation of the
device, calculated the optimal damping coefficient of the generating