Download HydroKinetic_ME438_Final v2.4

ME 438 – Design of Mechanical Engineering Systems
Fall 2014
Hydrokinetic Barge
Under the Guidance of
Dr. Jeffrey Hoffman
Submitted By:
Artem Kozyrenko
John Fisher
Lowell Perry
Erichson Pascual
Introduction
Hydrokinetic technology has been around for many decades better known as hydroelectric
dams. Hydrokinetic turbines produce electricity directly from the flowing water in a river or
stream without the need of artificial head. Some more recent inventions include wave
generators and river, ocean, and tidal current turbines. Due to large environmental effects of
dams, and strong location dependency for tidal and ocean energy, river mounted turbines are
gaining more attention on the market. Such systems can be conveniently installed on virtually
any water stream without significantly disrupting wildlife [2]. High installation costs is the main
disadvantage of such systems [1], yet in certain cases such as off the grid remote locations,
construction sites, and emergency energy supplies a demand of such systems could meet the
cost. In addition a mass production and improved designs could significantly lower costs
potentially making it a viable energy source for anyone [3].
Two main types of hydrokinetic barges are both currently available on the market. Both are
similar in the barge design, but have different turbine designs. Suspended axial flow turbine has
its rotational axis parallel to the flowing direction of water. It is for deep water and is not
designed to handle debris well [4]. Cross flow paddle design has its rotational axis horizontally
perpendicular to the flow and may be used in small and shallow rivers and creeks.
Project statement
The purpose of this project is to design and build a prototype of a hydrokinetic power barge, test
it for the power efficiency, and determine efficiency difference between the two paddle designs.
Scope of project
The full system is designed for free-flowing, shallow Alaskan streams with no water-head. It is
sized to fit on a trailer for convenient transportation. The full model is to be mounted on the
shore, but the prototype model will not include the shore mount. The prototype is scaled to fit in
a flume and is to be tested with two different paddles designs to determine system’s power
output efficiency and compare power output efficiencies of paddle designs. The design will not
take into account floating and underwater debris and will not address freezing conditions.
Methods
Barge Design
The prototype was modeled in SolidWorks and was manufactured out of hand carved
polystyrene and purchased components. The SolidWorks model of the design is shown in
Figure 5. The prototype is a simplified version of a full scale model using cheaper materials,
while performing similarly to a full scale model.
The barge consists of two layers of floating foam all glued together. Balsa wood was glued to
the top of the barge allowing components to attach to the surface more securely. Figure 1
shows the foam floating. A simple weight test was done and concluded that the barge is capable
of handling over five pounds of weight before left and right pontoons are fully submerged in
water.
Figure 1 - Barge Design
Paddles
Paddles are mounted on the back side of the barge in a cutout space as seen in Figure 5. Two
different paddle designs were created using 3D printers, sized to fit in a cube of 8 inches. Due to
printer’s printing size limitations, each paddle was printed in two halves and later glued together.
Each paddle was keyed and attached to a 3/8 inch diameter keyed shaft and secured by 3/8
inch bearings. Each paddle blade will have its own shaft and 3/32 inch key. The shaft hole of the
paddles are 3D printed at a smaller radius and machined precisely to 3/8 inch with a 3/32 inch
key at the ULB machine shop. The process of getting the shaft into the hole of the paddle was
difficult, so leaving the shaft in the paddle saves time when changing them out for testing
purposes.
The first paddle design (Figure 3) has six blades with no curvature. Oval cutouts were designed
into the paddle blades. The oval holes in the paddle blades do not affect the structural integrity
overall and allow for faster printing time because less material is being used. The thickness of
the blades in paddle design 1 were optimized by using Equation 1 and running SolidWorks FEA.
𝐹 = 𝜌𝐴𝑣 2
(1)
Equation 1 was used to give a rough estimate of the water force acting upon the submerged
paddle design 1 blade, where  is density of water (999.75 kg/m3 at 10C), A is perpendicular
area of paddle impacted by water, v is the maximum velocity of water from the flume. The
maximum von Mises stress from the FEA model was then compared to the yield stress of the
ABS plastic material.
In the paddle design 1 the force is estimated to be around 4.45 N using Equation 1. This force
was then applied to paddle design 1 in SolidWorks using FEA as shown in Figure 2. The von
Mises stress results from FEA where shown to be 14.1 MPa and the yield stress of ABS plastic
is 45 MPa. Using this technique and running multiple designs of paddle thickness, the optimum
design of 2.5 mm thick was selected. Smaller sizes probably could have been used, however
due to concerns of the accuracy of 3D printer, this was chosen to be the ultimate design.
Figure 2 - Paddle Design 1 in SolidWorks FEA
The second design is based on the first design, only with curved blades is shown in Figure 4.
The curved paddle profile increased torque and the rpm obtained from the water flow by
increasing the drag coefficient. FEA was not performed on the second design since additional
curvature will not significantly affect the paddles’ strength, especially since chosen thickness is
based on printer accuracy and not thickness at the failure.
Figure 3 - Paddle Design 1
Figure 4 - Paddle Design 2
Figure 5 - Current Overall Design
Generator
The optimal geared generator for this project needs to be self starting and accommodate
various speeds induced on the paddles by water current. Since static friction in the generator
requires the highest torque, torque by water current on the paddles needs to be higher than the
torque needed to start the shaft turning. Due to its relatively low torque, cost, and matching
gearing box, a DC electric motor attached to a gear train was chosen as the generator for this
project. The motor had no relevant specifications provided, so the motor with its gearing was
tested for static torque required to turn it. Figure 6 shows geared motor tested for static torque
required to spin the shaft by wrapping a floss around the shaft and hanging weights to the point
of shaft turning. Static torque of a motor was calculated to be 3.27×10-4 Nm. This value was
important to know in the design phase because the paddles needed to provide enough torque
from the available water current velocity to overcome it.
Figure 6 - Motor Torque Measurement
Gearing available for the motor included two options. A gearing ratio of 47.1 to 1 was chosen so
that the torque needed was slightly lower than the minimum torque available from the paddles
given the water current velocity. A large difference in the torques reduces the amount of voltage
and power that can be harvested, but reduces the chance of the paddles stopping at momentary
lower water currents due to static friction in the gearing components, and additional system
uncertainties. A second gear ratio of 1.8 to 1 was provided by the timing belt attached to the
paddle shaft bringing the total system’s gear ratio to 84.78 to 1.
Using Equations 2 and 3, torque T induced by the water current on the paddles’ shaft was
calculated to be 0.20 Nm and division by the gear ratio of 84.78 to 1 yields a torque of 5.17×10-4
Nm on the motor’s shaft, where 𝐹𝑑 is drag force on the paddle, 𝜌 is water density of 999.75
kg/m3 at 10C, 𝑣𝑚 is minimal water current velocity of 0.35 m/s, vp is mid depth tangential
paddle turning speed of 0 m/s, A is paddle’s perpendicular area to the current of 0.00774 m2, 𝑐𝑑
is approximate rectangular plate drag coefficient of 1.12 [5], and 𝑑 is the radial distance of .0826
m from the center of the submerged area of the paddle to the center of the shaft. Torque
obtained from the water current applied to the motor of 5.17×10-4 Nm is higher than torque
required for geared motor of 3.27×10-4 Nm, meaning the motor is small enough to allow paddles
to turn freely for current speeds over 0.35 m/s.
1
2
𝐹𝑑 = 𝑐𝑑 𝜌(𝑣𝑚 − 𝑣𝑝 )2 𝐴
𝑇 = 𝑑𝐹𝑑
𝑃𝑒 =
𝑉2
𝑅
(2)
(3)
(4)
The motor was mounted on the front of the barge for balance and a 995 ohm resistor was
connected across the terminals to measure power. The motor was securely mounted on the
wood of the barge and protected from water with a plastic splash shield. Power was calculated
from voltage measured across the resistor using Equation 4.
Experiment and Data Analysis
Prototype Testing
The experiment was performed in a flume. The flume was set to circulate water at a certain
speed, which was calculated by placing a ping pong ball in the current and measuring the
distance it travels per time. Then the barge was placed in the flume either in the laminar or
transitioning portion of the stream, depending on the desired current speed, and output voltage
was recorded. The experiment was repeated for several different current speeds and two
different paddle designs. Further experimentation was performed with paddle design 1 by using
different sizes of resistors at equal water current speeds to observe the changes in power
efficiency under different loads.
Data Analysis
Data obtained for different water current velocities is summarized in Table 1 and Table 2.
Electrical power output ( 𝑃𝑒 ), power produced by water current velocity (𝑃) and power efficiency
(𝑛) are calculated using Equations 4, 5 and 6 respectively, where  is density of water (999.75
kg/m3), A is perpendicular area of paddle impacted by water, v is velocity of water, V is output
voltage, and R is resistance of 995 ohm.
Table 1 – Paddle Design 1 Power Efficiency Calculations
Trial 1
Current
Velocity (𝑣𝑐 ),
m/s
0.95
Current Power
(𝑃), W
6.64
Voltage
Output (V), V
1.40
Power Output
(𝑃𝑒 ), W
1.97×10-3
Power
Efficiency (𝑛)
2.97×10-4
Trial 2
0.77
3.53
0.92
8.51×10-4
2.41×10-4
Trial 3
0.65
2.13
0.88
7.78×10-4
3.66×10-4
Trial 4
0.53
1.15
0.60
3.62×10-4
3.14×10-4
Trial 5
0.51
1.03
0.81
6.59×10-4
6.42×10-4
Trial 6
0.29
0.19
0.31
9.66×10-5
5.12×10-4
Table 2 – Paddle Design 2 Power Efficiency Calculations
Current
Velocity (vc),
m/s
Current Power
(P), W
Voltage
Output (V), V
Power Output
(Pe), W
Power
Efficiency (n)
Trial 1
0.95
6.71
1.41
2.00×10-3
2.98×10-4
Trial 2
0.72
2.89
0.99
9.85×10-4
3.41×10-4
Trial 3
0.65
2.13
0.95
9.07×10-4
4.27×10-4
Trial 4
0.60
1.67
0.88
7.78×10-4
4.66×10-4
Trial 5
0.46
0.75
0.71
5.07×10-4
6.72×10-4
𝑃 = 𝜌𝐴𝑣 3
𝑛=
𝑃𝑒
𝑃
(5)
(6)
Figure 6 shows power output vs. current velocity for paddle design 1 and 2. Using velocity that
forms most laminar flow of 0.5 m/s in each equation yields power outputs 4.12×10-4 W and
5.50×10-4 W. Using Equations 4, 5 and 6 power efficiencies are 4.29×10-4 and 5.67×10-4
respectively. Using Equation 7 yields 24% higher power efficiency of paddle design 2 over
paddle design 1.
% 𝑑𝑖𝑓𝑓 =
𝑛1 −𝑛2
𝑛2
(7)
Furthermore Figure 7 shows the test results with different resistor loads. Higher power output at
lower resistance and equal water current speed suggests that the power output efficiency of the
system could be improved by applying lower resistances to the circuit.
2.10E-03
y = 0.003x - 0.001
Power Output, W
1.60E-03
y = 0.0026x - 0.0008
Paddle design 1
1.10E-03
Paddle design 2
Linear (Paddle design 1)
6.00E-04
Linear (Paddle design 2)
1.00E-04
0.20
-4.00E-04
0.40
0.60
0.80
1.00
Current Velocty, m/s
Figure 6 - Power Output, W vs. Current Velocity, m/s
0.16
0.14
Power, W
0.12
0.1
Current speed .95 m/s
0.08
Current speed .77 m/s
0.06
Current speed .65 m/s
0.04
Current speed .51 m/s
0.02
0
1
100
10000
1000000
Resistance, ohm
Figure 7 – Power Output, W vs. Resistance, ohm for paddle design 1
Uncertainties
One of the biggest uncertainties is in the current velocity measurements where the ball current
speed test was used. The ball did not travel in a perfectly linear pattern down the stream, which
increased its travel time. Also, there is a significant amount of water slipping under the ball,
causing the ball to go slower in certain turbulent spots of the stream.
Another major uncertainty occurs in transitional and turbulent streams, where the torque and
rpm are affected by the stream on the paddles being varied due to the waves, varying direction
and varying density of water.
Furthermore, a shallow stream causes a higher drag coefficient, which increases the torque on
the barge paddles and potentially contributes to a higher voltage output.
Another source of uncertainty is in the measurement of the output voltage because the DC
motor possesses an internal commutator, producing a rectified sine wave shaped output
voltage, which is difficult to measure accurately with the standard multi-meter used.
Conclusion
With a 995 ohm load and 0.5 m/s current velocity, the flat plate paddle design yielded a power
efficiency of 4.29×10-4 and the curved plate paddle design yielded an average power efficiency
of 5.67×10-4. The curved paddle design is 24% more efficient than the flat plate design.
In addition, higher circuit load on a system results in higher power output suggesting that
system efficiency could be improved by applying a higher circuit load.
Results accuracy could be improved by using a better method of calculating current velocity in
the flume, testing the system in purely laminar region, deeper water streams and using a dc
motor without a commutator.
Further research topics may include determining the optimal resistor size for the highest power
efficiency and using the constructed barge to test additional paddle designs.
Project Schedule
Figure 8 - Gantt Chart
Figure 8 shows the project schedule. Work progressed within schedule until the end. Most of the
buffer time was used for testing and to order additional parts.
Project Budget
A budget of $1000 has been allocated to this project by UAA for parts and manufacturing. The
actual materials cost of the project has amounted to $212.61.
Resources
Resources for the project include a computer lab for SolidWorks modeling, machine shop, 3d
printers, and our project advisor professor Jeffrey Hoffman.
References
1. http://oblinark.com/Pages/OblinArk%20impact%20on%20fish%20review_FINAL.pdf
2. http://en.wikipedia.org/wiki/Low_head_hydro_power
3. http://www.zero.no/publikasjoner/small-scale-water-current-turbines-for-river-applications.pdf
4. http://www.academia.edu/6494988/A_Review_of_Hydrokinetic_Technology
5. http://www.lmnoeng.com/Force/DragForce.php