As a green and sustainable source of ocean energy, wave energy has huge reserves. It is estimated that the total power of global wave energy is 2.2 × 109 ~ 2.7 × 109 kW 1. How to carry out efficient large-scale development of wave energy in the low-wave high school of daily sea conditions is of great significance to the development of the world. There are many difficulties in the commercialization of wave energy harvesting devices. The effective operation of a wave energy converter (WEC) depends on the resonance between the wave field and the energy conversion device2. Among the existing technical solutions, collection efficiency is the key issue for the commercialization of wave energy collection. Our purpose is to further promote the commercialization of wave energy by improving the efficiency of wave energy collection in a certain area of the ocean and reducing the cost of power generation per kilowatt hour.
The impact of energy consumption structures on the world economy and human life is becoming more and more important. For example, affected by the economic cycle and the conflict in Russia and Ukraine, world energy prices have risen. According to data from the New York Futures Exchange, crude oil prices have risen from US $70 in December 2021 to US $130 in May 2022, an increase of 85.7 percent. Natural gas prices have risen from US $3.4 in January 2022 to US $10 in August 2022, an increase of 135 percent. People are affected by rising energy prices, and the quality of life is generally declining.
Under the influence of many factors, it is challenging to convert wave energy into usable energy efficiently. These challenges stem from the harsh marine environment, the prevailing low-wave development environment, and the implementation of efficient energy conversion technologies. Researchers in the past have developed many different wave energy conversion techniques based on various concepts. For example, combined technologies of wind3 and wave energy or nanofabrication technology concepts4 have shown promising results. Among them, the design principle of the PTO (power take-off) device for wave energy technology is to use the wave changes on the sea surface as the source of energy collection.
In the observation, the motion of the wave is a mixture of longitudinal and transverse waves. A longitudinal wave is also called a progressive wave. The particle motion and propagation direction are the same, and the horizontal motion energy is the largest, which is commonly suitable for propulsion. A shear wave is also called a shear wave. The particle motion and propagation direction are perpendicular and reset, and the vertical motion energy is the largest. It is similar to the characteristics of mechanical repetitive motion and reset and is suitable for energy transfer.
For example, in the common automobile piston movement, the torque force of the engine rotor comes from the work of the particle in the up and down movement of the shear wave.
However, for the understanding of the above information, researchers have done a lot of technical solutions in the past, and many ideas and differences have emerged in this step. In order to optimize the structure of the components and facilitate understanding, we first combine the surface floating body directly with the piston moving parts to analyze the idealized steps. The vertical movement of the surface floating body under wave conditions drives the rotor to generate torque.
Anchoring the underwater suspension to support the surface floating body model: Based on the implementation of the above steps, a stable fulcrum must be provided to support the rotor with interaction forces. We have developed an underwater suspension flexibly linked by a seafloor anchor, with a downward force anchored to the seafloor and an upward buoyancy provided by the underwater suspension to support the rotor motion. Compared with the traditional wave energy design, this scheme has the stable fulcrum condition of a coastal type and the development potential of huge offshore wave energy reserves.
In the following illustration, green is a flexible rope link, red is a rigid connection, and the blue cuboid is a floating body.
Numerical solution method:
The buoyancy of the floating body on the water surface is constantly changing under the influence of the water level change caused by the transverse wave. But the buoyancy of the floating body in the water can still be measured by the law of buoyancy. Including F static buoyancy, G itself quality, G real-time drainage quality, and F real-time force.
When the water surface is stationary, F stationary buoyancy = G real-time drainage mass, and the floating body is in a stationary floating state.
In the time-domain transformation of the sea transverse wave, when the actual water level is higher than the equilibrium water level, the buoyancy forces lift the floating body upward. When the actual water level is lower than the equilibrium water level, the floating body moves downward under the influence of gravity.
G real-time drainage quality-G floating body mass = F real-time force (when F is greater than 0, the force is upward; when F is less than 0, the force is downward).
Numerical calculation of the rotor driven by the floating body on the water surface (simulate the force data table under the same wave condition and confirm the force stability of the rotor)
In the scheme of anchoring the underwater suspension to support the floating body on the water surface, the torque force of the rotor of the energy collection component comes from the piston rod driven by the movement of the floating body on the water surface, which is determined by the difference between the real-time state buoyancy and the equilibrium state buoyancy. The capture efficiency of the floating body on the water surface and the stability of the working state are also crucial. Based on the design requirements and real data acquisition, in the simulation experiment, according to the volume scale of 1:180, a length of 0.5 meters, a width of 0.5 meters, a height of 0.4 meters, and a mass of 50kg of floating water were produced. When the floating body floats on the water's surface, the waterline height is 20cm. A fixed rotor and a tensile tester are provided at the bottom of the pool and above the float. Add and reduce water in the pool, simulate the stroke of the floating body on the water surface rising and falling by the waves, and obtain the floating force and sinking force. By adjusting the size of the puller, the center line of the floating body on the water surface is kept at the original static floating height of 60cm in the pool. Observe and record the force. The following is the data table:
Increase or decrease the amount of water
/cm
|
Pool depth/cm
|
Waterline height of floating body/cm
|
Water discharge/cubic centimeter
|
Water discharge difference with static balance 60cm height/cubic centimeter
|
Force direction of tension device
|
Force size of tension device/n
|
After releasing the puller, the water surface floating body still draught line is at the pool height/cm
|
Increase water level+10
|
70
|
30
|
75000
|
25000
|
Upper
|
245
|
70
|
Reduce water levels-10
|
50
|
10
|
25000
|
-25000
|
Down
|
245
|
50
|
Increase water level+15
|
75
|
35
|
87500
|
37500
|
Upper
|
367.5
|
75
|
Reduce water levels-15
|
45
|
5
|
12500
|
-37500
|
Down
|
367.5
|
45
|
Increase water level+20
|
80
|
40
|
100000
|
50000
|
Upper
|
490
|
80
|
Reduce water levels-20
|
40
|
0
|
0
|
-50000
|
Down
|
490
|
40
|
The data show that when the floating body on the water surface breaks away from the static state and enters the motion state, the maximum force is determined by the difference between the real-time water discharge and the static floating water discharge. Through the water discharge transformation of the floating body moving up and down in the wave, the force data of the floating body in the water is obtained. At the same time, the maximum pulling force of the piston rod connected by the floating body on the water surface and the torque force obtained by the stable rotor supported by the underwater suspension are obtained, based on the power formula:
Power = Torque Force * Frequency/9549
= (Torque * Work radius (rotor radius)) * Proton moves up and down twice in a transverse wave * Wave frequency/9549
= (force on the up and down stroke of the floating body on the water surface * 1/2 of the up and down stroke of the floating body on the water surface) * 2 * wave frequency/9549
There are many difficulties in the commercialization of wave energy harvesting devices, and the effective operation of wave energy converters (WECs) depends on the resonance realization between the wave field and the energy conversion device.5 In order to achieve the resonance effect, so that the water surface floating body capture efficiency is higher and more stable, we carried out the same volume of different densities of the water surface floating body test, using the wave to bring the same water potential energy environment motion height measurement data. The following data table shows that under the same volume, when the density of the floating body on the water surface is greater than 50% of the liquid density, the upward buoyancy of the floating body due to waves will be reduced, and when the density of the floating body on the water surface is less than 50% of the liquid density, the downward working mass of the floating body on the water surface due to gravity will be reduced. When the density value of the floating body on the water surface reaches 50% of the liquid density, the motion of the floating body on the water surface and the wave field realize the resonance fit.
(The following is the same volume length 0.5 meters * width 0.5 meters * height 0.4 meters, different density of water floating body water level measurement)
A floating body with a liquid density of 30% weighs 30kg, has a waterline of 12cm and a water discharge of 30000cm ^ 3.
Add or subtract water
/cm
|
Pool depth/cm
|
Waterline height of floating body/cm
|
Water discharge/cubic centimeter
|
Water discharge difference with static balance 60cm height/cubic centimeter
|
Force direction of tension device
|
Force size of tension device/n
|
After releasing the puller, the water surface floating body still draught line is at the pool height/cm
|
Add water +10
|
70
|
22
|
55000
|
25000
|
Upper
|
245
|
70
|
Pumping -10
|
50
|
2
|
5000
|
-25000
|
Down
|
245
|
50
|
Add water +15
|
75
|
27
|
67500
|
37500
|
Upper
|
367.5
|
75
|
Pumping -15
|
45
|
0
|
0
|
-30000
|
Down
|
294
|
45
|
Add water +20
|
80
|
32
|
80000
|
50000
|
Upper
|
490
|
80
|
Pumping -20
|
40
|
0
|
0
|
-30000
|
Down
|
294
|
40
|
Floating body with 40% liquid density, weighing 40kg, waterline 16cm, water discharge 40000cm ^ 3.
Add or subtract water
/cm
|
Pool depth/cm
|
Waterline height of floating body/cm
|
Water discharge/cubic centimeter
|
Water discharge difference with static balance 60cm height/cubic centimeter
|
Force direction of tension device
|
Force size of tension device/n
|
After releasing the puller, the water surface floating body still draught line is at the pool height/cm
|
Add water +10
|
70
|
26
|
65000
|
25000
|
Upper
|
245
|
70
|
Pumping -10
|
50
|
6
|
15000
|
-25000
|
Down
|
245
|
50
|
Add water +15
|
75
|
31
|
77500
|
37500
|
Upper
|
367.5
|
75
|
Pumping -15
|
45
|
1
|
2500
|
-37500
|
Down
|
367.5
|
45
|
Add water +20
|
80
|
36
|
90000
|
50000
|
Upper
|
490
|
80
|
Pumping -20
|
40
|
0
|
0
|
-40000
|
Down
|
392
|
40
|
Floating body with 60% liquid density, weighing 60kg, waterline 24cm, water discharge 60000cm ^ 3.
Add or subtract water
/cm
|
Pool depth/cm
|
Waterline height of floating body/cm
|
Water discharge/cubic centimeter
|
Water discharge difference with static balance 60cm height/cubic centimeter
|
Force direction of tension device
|
Force size of tension device/n
|
After releasing the puller, the water surface floating body still draught line is at the pool height/cm
|
Add water +10
|
70
|
34
|
85000
|
25000
|
Upper
|
245
|
70
|
Pumping -10
|
50
|
14
|
35000
|
-25000
|
Down
|
245
|
50
|
Add water +15
|
75
|
39
|
97500
|
37500
|
Upper
|
367.5
|
75
|
Pumping -15
|
45
|
9
|
22500
|
-37500
|
Down
|
367.5
|
45
|
Add water +20
|
80
|
40
|
100000
|
40000
|
Upper
|
392
|
80
|
Pumping -20
|
40
|
4
|
10000
|
-50000
|
Down
|
490
|
40
|
Floating body with 70% liquid density, weighing 70kg, waterline 28cm, water discharge 70000cm ^ 3.
Add or subtract water
/cm
|
Pool depth/cm
|
Waterline height of floating body/cm
|
Water discharge/cubic centimeter
|
Water discharge difference with static balance 60cm height/cubic centimeter
|
Force direction of tension device
|
Force size of tension device/n
|
After releasing the puller, the water surface floating body still draught line is at the pool height/cm
|
Add water +10
|
70
|
38
|
95000
|
25000
|
Upper
|
245
|
70
|
Pumping -10
|
50
|
18
|
45000
|
-25000
|
Down
|
245
|
50
|
Add water +15
|
75
|
40
|
100000
|
30000
|
Upper
|
294
|
75
|
Pumping -15
|
45
|
13
|
32500
|
-37500
|
Down
|
367.5
|
45
|
Add water +20
|
80
|
40
|
100000
|
40000
|
Upper
|
392
|
80
|
Pumping -20
|
40
|
8
|
20000
|
-50000
|
Down
|
490
|
40
|
After increasing the suspended body effect, power generation data
Initially, the study of the influence of the density data of the floating body on its motion stroke is completed, and then the wave energy capture situation needs to be confirmed according to the actual power generation data. In a 1-meter-wide wave culvert, when the density of the floating body on the water surface is fixed at 50% of the liquid density, the wave energy capture data of the floating body on the water surface are obtained for 20cm, 30cm, and 40cm of the up and down travel of the floating body on the water surface.
Time: X second of operating time
Voltage: V volt
Current: A ampere
Power: W Watts
Floating body movement up and down stroke 20cm(100w):
Time
|
0
|
3
|
6
|
9
|
12
|
15
|
18
|
21
|
24
|
27
|
30
|
33
|
36
|
39
|
42
|
Voltage
|
0
|
11.66
|
18.7
|
14
|
13.9
|
14
|
14.07
|
14
|
14
|
13.9
|
14.07
|
14
|
14
|
14
|
13.9
|
Current
|
0
|
5.83
|
9.38
|
7
|
6.96
|
7
|
7.03
|
7
|
7
|
6.96
|
7.03
|
7
|
7
|
7
|
6.96
|
Power
|
0
|
68
|
176
|
98
|
97
|
98
|
99
|
98
|
98
|
97
|
99
|
98
|
98
|
98
|
97
|
Floating body movement up and down stroke 30cm(230w):
Time
|
0
|
3
|
6
|
9
|
12
|
15
|
18
|
21
|
24
|
27
|
30
|
33
|
36
|
39
|
42
|
Voltage
|
0
|
17.32
|
28.6
|
21.26
|
21.3
|
21.16
|
21.3
|
21.26
|
21.26
|
21.26
|
21.3
|
21.16
|
21.16
|
21.26
|
21.26
|
Current
|
0
|
8.66
|
14.3
|
10.63
|
10.65
|
10.58
|
10.65
|
10.63
|
10.63
|
10.63
|
10.65
|
10.58
|
10.58
|
10.63
|
10.63
|
Power
|
0
|
150
|
409
|
226
|
227
|
224
|
227
|
226
|
226
|
226
|
227
|
224
|
224
|
226
|
226
|
Floating body movement up and down stroke 40cm(410w):
Time
|
0
|
3
|
6
|
9
|
12
|
15
|
18
|
21
|
24
|
27
|
30
|
33
|
36
|
39
|
42
|
Voltage
|
0
|
27.42
|
39.62
|
28.1
|
28.14
|
28
|
28.14
|
28.07
|
28.14
|
27.96
|
28.1
|
28.1
|
28
|
28.07
|
28.07
|
Current
|
0
|
13.71
|
19.81
|
14.05
|
14.07
|
14
|
14.07
|
14.03
|
14.07
|
13.98
|
14.05
|
14.05
|
14
|
14.03
|
14.03
|
Power
|
0
|
376
|
785
|
395
|
396
|
392
|
396
|
394
|
396
|
391
|
395
|
395
|
392
|
394
|
394
|
The data show that at the first wave frequency, the power generation value is lower than the later average value. After analysis, considering that the up and down travel of the floating body from the static state to the first wave frequency is lower than the average value of the following data, a low value is normal.