ME 438 Design of Mechanical Engineering Systems

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.

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 is drag force on the paddle, is water density of 999.75 kg/m3 at 10C, is minimal water current velocity of 0.35 m/s, is mid depth tangential paddle turning speed of 0 m/s, is paddle’s perpendicular area to the current of 0.00774 m2, is approximate rectangular plate drag coefficient of 1.12 [5], and 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.

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 (), power produced by water current velocity () and power efficiency () 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

Current Current Power Voltage Power Output Power Velocity (), m/s (), W Output (V), V (), W Efficiency () Trial 1 0.95 6.64 1.40 1.97×10-3 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), Current Power Voltage Power Output Power m/s (P), W Output (V), V (Pe), W 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

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.

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.

Figure 6 - Power Output, W vs. Current Velocity, m/s

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