Drawings: Vertical Wind Turbine

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Problem Statement: Renewable energy such as wind can be inefficient and unpleasant to look at, our purpose will be to engineer more efficient, smaller scale wind energy production that will not impede local landscape views.

Specifications and Requirements:

The design must be of competitive cost and superior production capacity to comparable generation methods, be easily serviceable, have a 10+ year lifespan, withstand 100mph sustained wind, and have a more desirable appearance.  The system will need to generate on average 28.9 kWh per day and will require a base operating wind load of 5mph.

Assumptions:

The user wants an aesthetically pleasing, autonomous, on-site renewable energy production system.

Link to Matrix: https://docs.google.com/spreadsheets/d/16hIEm97Phrn8rfARYAu2CtonduKWEC1Z0tdeSWlPvzE/edit?usp=sharingLinks to an external site.

Relating the information to the Matrix:

Ease of Use and Installation: A vertical windmill is mounted at ground level, so a small cement block or anchors can be used to mount to the ground, in some cases a guy wire is needed to secure the tower. Some smaller premade units can be installed with limited special tools giving the Vertical a (5). The Shrouded horizontal wind turbine was given a (2) because of the height requirements. The Tower, at least 100ft high, requires on average 8 cu. Yards of cement to secure the turbine, creating a permanent fixture. This also requires the use of a large crane for installation.

Generation efficiency: A vertical wind turbine is not as refined as a horizontal at this current stage and leads to lower operating efficiencies, however the turbines work better at lower ground level and are omnidirectional. This means no matter which way the wind is blowing it will be generating power. Typically, the cut in windspeed is 2.5m/s. With all of this factored it gives the vertical a rating of (3). The Shrouded Horizontal turbine is the ideal candidate for efficiency. The shroud is bell mouthed directing more air into the inlet of the turbine, thus giving a score of (5)

Life span: The vertical wind turbine lives on the ground so this means that maintenance is much more accessible and can be repaired much easier giving a score of (4). The horizontal unit while in the air at over 100ft, does not have as much rotating mass due to smaller rotors, meaning less maintenance, however it is still suspended leaving a score of (4).

Aesthetics: One of the main factors in design is that surrounding skyline views would not be impeded, this leaves the horizontal wind turbine is a difficult spot, because in order to have reliable performance the turbine needs to be suspended at least 100ft in the air, this leads to a (3). A vertical however can be mounted under 50ft and while the real-estate is somewhat substantial it carries a smaller foot print than a horizontal unit. To power a typical house at 28.9Kw/Hr a day (the avg for American households) it would take a unit 4.4m in diameter and 15m high where as a horizontal unit would require a large amount of cement and a large tower carrying the turbine. The fact the vertical will not block neighboring homes and views is why it has earned (5) in the rankings.

Design and Production Cost: Vertical wind turbines are less expensive to build because they do not require the same level of exotic materials needed in a horizontal unit carrying the load 100ft above the ground. The shear forces contained in a vertical unit are much less due to not having a side loaded support tower, which means less expensive manufacturing, this earns the vertical a (5). Whereas a horizontal unit requires lightweight and strong materials that are guaranteed to last years and years which drives the overall cost up, this leads to a (3).

Considerations During Design Process: When designing the parameters for the vertical turbine the safety factor for some items was incredibly high for some components, but was necessary for clearance for other working components. For example, the outer shaft that carries the weight and rotational energy of the rotors has a safety factor of 400 during average operation, but the inner stationary support shaft has a safety factor of 80 during normal operation. This was designed in case of hurricane force winds in excess of 100mph, at 100mph the system has a safety factor of 1.5 at the weakest link.

 Module 2: Gear Driven Generator

This module turns the generator by a set of gears coupled directly to the turbine shaft, this is the preferred choice of modules because it is the sturdiest and has the least number of consumable parts, it will however require annual servicing of the gear fluid to which the gears are incased. This system has 1 degree of freedom. The gear ratio will be a 390:1 ratio and will be split using a 100:4-62.4:4 gearset. This option is the middle of the road in terms of cost as a pulley system is initially cheaper, but will have more service costs. The gearset was designed with A36 steel with a shear stress of 14,400 psi. The max load under 150MPH or 65m/s wind conditions would be 50,750 N-m or 37431ft-lbs on the shaft of the turbine, this translates to 8320 psi on the 2^nd pulley where torque will be greatest on the system. The teeth mesh was calculated to be 1.5” of positive engagement with a 3” tall gearset. This leaves a S.F of 1.73:1 at 150mph.

FRDPARRC link: Module 2:

https://docs.google.com/spreadsheets/d/12vOkNHR1OOZ5j5z8wXnyj8_GjoZaxIlxVwDAif2oCXU/edit?usp=sharingLinks to an external site.Links to an external site.

Bill of Materials Link:

https://docs.google.com/spreadsheets/d/1N2wtCTBkQeh9-5pBPS4Lco6-627q4xxgE1K4MvttwhY/edit?usp=sharing

Gantt Chart Link:

https://docs.google.com/spreadsheets/d/1tdleGEZJMNMmZWM7t1cc2XEORuoWbsCeOXpMVAx7ZMQ/edit?usp=sharing

• Components of Module 2: Given that the Forces were found in the module section above for the shaft torque translated to the gear system we now have to find the internal stresses on the components themselves. Starting with bolted gear to the shaft we will need to use the maximum value this will see with a safety factor of 1.5, the reason I am using a safety factor of 1.5 instead of the recommended 3 for rotating turbine components is because at the “maximum” calculated value the turbine will be in category 4 hurricane force winds. At the average working load the safety factor is over 400, this is calculated based of the difference in wind pressure from a 6mph average speed to 150mph theoretical maximum value. For the Gear assembly the main holding shaft for the turbine was specified to 10” in diameter .5” wall, however the inner shaft that holds the inner support shaft is 6” in diameter with a wall of .5” Finding the bearing stress on the shaft was calculated using Bearing stress σ_b= F/A_b so our bearing contact area would be (3.5²”*Pi)-(3²” Pi)=10.2in². Therefore, our bearing stress under maximum load would be  37431ft-lbs/10.2in² = 3669.7psi of bearing stress at max load. Choosing an appropriate material for this stress we will be using an Ashby Chart, there is one listed below. In selecting the proper material to use a few considerations were made regarding the family and material: Strength to weight, rigidity to weight, and relative cost to strength. In the Charts below I have drawn parallel lines representing the properties needed for this application and these lines will help determine the material choice.  The equations used for this includes P=(E^.5/Rho), converting this to y=mx+b form log E= 2log rho + 2log P. We will be plotting this on the Young’s Modulus vs Density Graph. As we move this line up we can determine the best material for the strength vs density application, this will be applicable In the first graph we can see the lines have a favorable leaning towards metals vs other materials. Steel is one of the better choices as well as titanium, Magnesium and Aluminum and CFRP or Carbon Fiber Reinforced Polymers. While CFRP’s are exceptional in Rigidity and Strength Vs weight, every other category it is underperforming certain metals. This is shown on the 3^rd Ashby plot for Cost vs. Strength. Looking at the Decision Matrix it becomes clear as to why Steel was chosen as the metal of choice, the price per strength and rigidity to density is a large factor, given that the Turbine is over 35 feet tall and has a large rotating mass, this is in reference to the support shaft in an ideal world the blades would be made from CFRP, but this module is focusing on the gear set and support shaft bearing load. The machinability of aluminum and steel is much greater than any other material and can be easily processed and welded. Steel is the obvious winner. Now that the material has been decided, we need to make the calculations for the 2^nd gear set support shaft. The maximum torque being applied will be 37431ft-lbs/100”*4”= 1497.24 ft-lb on the shaft. Given that the Shaft is 2” in Diameter the overall stress will 1500ft-lbs on the teeth of the shaft and 2037psi on the shaft itself. The shaft was calculated to need a 1/8^th wall thickness if made from A-36 steel.  

Lessons Learned:

• READ THE INSTRUCTIONS CAREFULLY
• Understand what you are making does not have to be complicated
• If something is misunderstood go back to the basics
• Over engineering is a necessity for some components that will see mother natures abuse.
• Inner components constrain outer components regarding size requirements in loaded situations
• Cold Coffee hits harder at 3am so do the tears
• Crying gives a reset to the mind
• Scaling Drawings need to be done in 2 steps

• The first for the initial drawing
• The second for feature view

Partner:

Walker Bond ( https://uncc.instructure.com/eportfolios/2270 )

Activities Date and Time: 

9/17/2021 14:00-16:00 Create group/brainstorm ideas

9/20/2021 13:30-16:00 Create solidified purpose

9/29/2021 16:00-23:30 Add Info to E-profile, Create Gantt Chart, Sketch Ideas, Research Topics More In depth

10/04/2021 16:00-20:00 Create a defined decision matrix

10/06/2021 07:00-10:00 research different turbines

10/13/2021 12:15-13:00 Talk to Dr. Fagan regarding forces on wind turbines

10/13-14/2021 18:00-01:30- Complete research, sketches and canvas update

10/18/2021- 18:00-21:00-Start load calculations for projected height and width

10/25/2021-06:00-07:30 Sketch a semi-complete assembly

10/27/2021- 12:15-14:00 Dr. Fagan information session

11/03-04/2021- 18:00-04:00 Finalize load calculations for material, Create Cad model, update webpage

11/07-08/21-19:00-05:30 RE-design modules properly and update project

11/17/2021- 10:00-14:00 Begin Drawings on NX

12/03/2021-20:00-22:00 Drawings continue on NX

12/04/2021- 16:00-23:00 Make Bill of Materials, upload info to Canvas

Resources: Generator model used in Cad thanks to Mei Rezki Rosi Pratama, https://grabcad.com/library/matari-15-kw-1Links to an external site.

Bearing assembly: https://www.mcmaster.com/7111N31/Links to an external site.

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