ea-2 design problem

8/7/2019 EA-2 Design problem

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Winter 2011 Engineering Analysis II

Design Review for the Centennial Solar Panel System

Contents

Project Description Part A: Analysis of NSU Design Part B: Design Proposal Expectations and Grading Criteria Collaboration and Plagiarism Guidelines, Submission Requirements Page CSPS Information NSU Proposal (Separate Document) Writing a Bid (Separate Document)

Project Description:

Engineers for a Sustainable World (ESW) is a Northwestern student group that engages in sustainable

engineering projects on campus and internationally. ESW is working with the NorthwesternSustainability Fund, a rotating fund for sustainable projects at Northwestern, to install the CentennialSolar Panel System (CSPS), a 17kW solar photovoltaic array on top of the Ford Design Center.

Figure 1 3D Solid model of a row of 4 Solar Panels mounted on a Truss Support

After raising the funds for the project, ESW and NU Facilities Management issued a request forproposals for the design of CSPS. The cheapest proposal from several solar design companies wasNorthshore Solar Union (NSU). Figure 1 shows a set of 4 panels, and NSUs proposed truss supports.The request for proposals and the NSU bid are in the document NSU Proposal found on Blackboard.

After receiving the proposal, CSPS project manager, Josh brought the design to the next ESW execmeeting, because the design was over $5,000 cheaper than anticipated. ESW Finance Chair Ankurdecided that this CSPS proposal should be reviewed for safety before the check is written. Sasha andWill, ESW co-presidents, then added, The EA-2 students are learning about truss structures and thisanalysis would be perfect to get them involved with ESW!


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After glancing over the design Dave, ESWs project managerfor the Portobelo, Panama WastewaterTreatment Project, asked, I dont remember 3-D trusses from EA-2, can they solve them? One ofDaves team members, Hugh, responded, Remember from fluid mechanics, the highest aerodynamicforce (and highest force on the truss), will be a straight headwind. So, since the design is based on 3 2Dtrusses and a set of cross members, if we analyze based on that worst case (a straight headwind) then wecan ignore the cross members (members with a component in the z direction.) We can always reviewthose later if necessary.

Next, ESW Publicity Chair, Sloane, chipped in, remembering from her civil and environmentalengineering classes, that all structures have a built in safety factor.Sam, the project manager for ESWGRIN (Green It Now), the building audits project, suggested a safety factor of 1.5, which is standard forthis type of structure. Sam also added that Aluminum 6063-T52 (used for this truss) was being used onthe Nicaragua Wind Turbine Project, and Scott, the project manager and material science andengineering major, just used his course work to check the turbines safety factor before heading toNicaragua to install it. Scott supplied Josh with the information inTable 1and the associated equationson page 3.

Josh called over his co-project manager for ESWs NU Clean Energy Plan (see page 8), Brooke, whoseESW summer fellowship focused on wind turbines for NU. On a hunch, Josh asked Brooke if NSUspredication of 10 mph max winds was a too low, to which she responded, OH MY GOSH! That is waytoo low! On the top of a 60ft Evanston building, you need to design for at least 100 mph gusts!

At that point, Andrea, the program coordinator for ESW University, ESWs educational curriculumspoke up. You realize that the EAII students probably could have designed a better system then NSU.Maybe you should see what they can come up with. It will probably be better a nd cheaper anyway. Tothat, Anthony an Econ major and the other project manager for CSPS added, But we will need to seesome financial documentation to see if their designs are better. To that Andrea responded, You are

underestimating our engineers, they can do it.


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Part A: Analysis of NSU Design [This part is to be turned in as a homework assignment]

1.TRUSS GEOMETRY AND SUPPORTSReview the proposal from Northshore Solar Union (the document NSU Proposal found on

Blackboard). Each row of solar panels consists of 4 solar panel units mounted on a frame (Figure 1).The frame consists of 3 identical 2D trusses mounted in the x-y plane (ADGH, BEIJ and CFKL),and a set of cross members which are angled to these. Figure 2 shows one end truss (ADGH).

The lowest point on the panel is 1ft above the roof.

The panels make a 42 angle with the horizontal.

There are three individual 2-D trusses in the x-y plane,

The weight of the panels is 0.5 lb/ft2

of panel area.

Each panel is 4ft x 6.5 ft, and the set of 4 attached to the support shown in Figure 1 is therefore16ft x 6.5 ft.

Points A, B, C, D, E, and F are 0.5 from the top and bottom edge of the panel.

Points A, C, D, and F are 1.0 from the side edges of the side panels.

The truss is supported by rollers at G,J and K and pins at H,I and L (see Figure 2).

The panel is supported by pins at D,E and F, and sliders parallel to the panel (42 to the x axis) atA,B and C.

2.LOAD CASEAssume that wind causes a drag force acting parallel to the wind direction. The drag force, F D isdefined as:

And a downforce acting normal to the wind direction:

Where is air density (at Fords 60ft roof, = 0.076 lb/ft

3), v is wind speed in ft/s, A is the objects

cross sectional area normal to the wind, and CD is the coefficient of drag (1.28 for rectangles). CL isthe coefficient of lift (For these wind speed assume CL=1.2 for rectangles).

3.AXIAL STRESS IN THE MEMBERSTruss member failure results from a variety of mechanisms including excessive elastic deformation,plastic deformation, buckling, and fracture. In order to account for uncertainties in design, such as

uncertainty in service loads, material properties, and environmental factors, a factor of safety has tobe accounted for. The factor of safety is defined as,


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The failure stress in this case is either the yield strength or buckling load, and the allowable stress is

the working stress. Stress is related to the axial force F on the truss member, and its cross-sectionalarea by,

For the design problem, consider a factor of safety of 1.5.The buckling stress is critical for the truss members in compression. The critical buckling force Fmax,is given by,

Where E is Youngs Modulus,

is the moment of inertia, and D is the diameter of the truss

member, assuming the trusses have circular cross-sections.The trusses are made from Aluminum 6063 T52 (properties inTable 1).Table 1: Mechanical Properties of Aluminum 6063 T52

Material Density (lb/in) Youngs Modulus (psi) Tensile Yield Strength (psi)Aluminum 6063 T52 0.097 10106 21,000

4.WIND LOADING EFFECT ON THE TRUSS MEMBERSa)Calculate the wind loading on the panel for a wind speed of 10mph. Use this to calculate the support

reactions for the panel at the attachment points A,B,C,D,E and F (See assumptions below).Use the loads calculated to find the member tensions in all the truss members for each of the 3trusses.Assumptions:

The total drag force, downforce, and panel weight act through the center of the panels, and areapplied to the trusses at the contact points A,B,C,D,E and F. The middle truss supports 6/14 th ofthe total load, and each end truss supports 4/14 th of the total load. The relationship between theloading points in each truss can be found by treating the panel loading as a 2D equilibriumproblem.

Weight of the truss system is negligible

Any member not in the winds direction (any member having a non-zero z component) is onlyused to deal with cross wind (i.e. ignore them in all force calculations).

The panels do not deform or break.b)Determine if any truss members in the NSU system exceed the safety factor, if so which ones?c)Make a plot of the force in each member verses wind speed, iterating the wind speed from 10 mph to

100 mph, using the same directional heading and assumptions as above. Use one plot, and if multiple

members display the exact same relationship (same exact line), only display one line (and documentthe similarity below). Do any of these members ever exceed safety factor? If so mark the highestwind speed the system can take before failing the safety factor. What is the failure wind speed? Isthe failure due to tension or compression? Which member fails first?Write the results in the form of a short report.


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Part B: Design Proposal [This part is to be handed in as a Design Proposal]Develop a proposal to answer Facilities Managements request for proposals (found on Blackboard asthe first page of the document NSU Proposal) by redesigning the rows of solar panels in the arraybased off of the template in Figure 2. In your redesign you may alter the radius of the members, thelengths of the members AP, DP, GP, and HP (and their corresponding members in trusses BEIJ andCFKL), and the type of joints (pin or slider) at G, H, I, J, K, and L (as long as the trusses are staticallydeterminate).Important note: The panel area, angle, and directional orientation must remain the same. Do not changethe number (4) of panels in a row or the total number of rows (20).You are expected to do the following:

Redesign the system in Figure 1 and 2 bymoving point P, changing the member diametersand/or redistributing pin and slider joints.

Follow the procedure used for part A to evaluatethe safety of your truss design for wind speedsof up to 100 mph. Continue using the materialproperties inTable 1.

Evaluate the cost of your design according tothe criteria laid out in the budgeting sectionbelow. Keep in mind that the maximum budgetfor the project is TBD. Exceeding this value willresult in point loss.

Use your design analysis to create a bidproposal to get a contract from FacilitiesManagement to build the Centennial Solar Panel

System.Redesigning

Redesign the system in Figure 1 and 2 by moving point P, changing the member diameters and/orredistributing pin and slider joints. Decide any combination of the following to use:

Moving point P in truss ADGH (Figure 2: 2D truss support ADGH) (and point Q in BEIJ, and R inCFKL). This may require splitting members AG and DH in the current system into two members(ex: AP and GP). Keep A, D, G, and H in their current location and move P, adjusting the anglebetween those members and the axes. Repeat this for the center truss (BEIJ) and the end trusses(CFKL) and (ADGH).

Changing the member diameters of themembers (only use the diameters in Table 2)

Switching the pin and slider joints,providing that the system is staticallydeterminate.

Create a drawing using the computer or by

hand (and scanned in) of your redesign

Table 2: Price Per Foot for Aluminum 6063 T52

Diameter (in) Cost per Foot ($/ft)

0.89

1.51

3.09

1 5.08Cost of buying 8-ft members of from McMaster-Carr

Figure 2: 2D truss support ADGH

xy

P

D

G

4.09ft

5.01ft

1.33ft


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Engineering AnalysisEvaluate your system for wind speeds between 10 mph and 100 mph. Create a plot containing the axialloads in the truss members as a function of wind speed.

Budgeting

Evaluate the cost of the array assuming you use the same row design for all 20 rows and using theparameters listed below. Each of these costs is associated with one line in the proposal budget:

a)Purchasing the Support Structure: Using Table 2: Price Per Foot for Aluminum 6063 T52,find the cost per foot for buying the materials needed.oSum the total length of members in a single row for each diameter, and fill it into the Bill

of Materials. Complete the Bill of Materials for your total cost of materials.oAdd $150 per row of for bolts, screws, and ballast (pin and slider connections).oUsing different diameters: since using different diameters or materials make design

reviewing and construction more difficult, there is an additional labor fee (see c: Laborbelow) associated with using additional materials or diameters.

oDo not forget about the members in the x direction (ignored in the force calculations).

The size of these members may be changed, but their diameter cannot go below70% of the smallest diameter used in the 2-D truss sections.

oThe overall weight of your array (structure and panels) cannot exceed 15,000 lb.b)Purchasing the Solar Equipment: This cost is $64,644 covering panels, inverters, and all

other non support structure materials.c)Labor: Calculate a labor cost multiplier, based on your system to determine your labor costs

oLabor costs are associated with how much material you are using. The base of thelabor cost multiplier is 1.5.

oAdd 0.05 to the labor cost multiplier for each member diameter used beyond the first.oMultiply your total materials costs from a) by your labor cost multiplier to get your

labor subtotal.oAdd an additional $5000 of labor for the whole array for other labor (i.e. electrical,

safety checks, logistics.) to get your labor total cost.d)Freight: $0.25 per pound of material purchased for your designed structure (whole array)

oAlso add $1500 for other freight (solar panels, inverters, other equipment).e)Permits: $1500 to the City of Evanstonf)Crane Rental: $1500g)Sum all your costs in parts a-f. This is your subtotal.h)Add a 2% contractor overhead to the subtotal costi)Add a 15% contingency fund on the total from h. This is your total cost.

Note: none of these costs per units are variable except for in part a. You should calculate most of your

costs by plugging in variables determined in your design.More details on writing a proposal can be found in the document Writing a Bid on Blackboard.


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Expectations and Grading Criteria

Your design project grade will depend not only on whether your analysis is correct and complete, butalso on the clarity of your write-up and on the neatness and professional appearance of your report.Tips:

All figures should be numbered and have a caption that describes exactly what is shown. Thecaption should be placed below the figure. If the figure is a graph, it should have axis labels(with units) and a legend when more than one curve is plotted on the same graph. All charts anddiagrams should be created so that they can be interpreted from a grayscale copy. You cannotassume that all copies of your report will always be in color.

MATLAB code must be provided in an appendix at the end of the report, and should besufficiently commented.

For basic analysis methods you should describe the procedure that was followed in the text,perhaps including sample calculations, equations, or diagrams. However, you should not include

every detail: all detailed cost calculations should not be shown, for example.

Data such as truss forces should be reported neatly in tables. These should be numbered and havecaptions like figures. Table titles should be placed above the table

Whether applying for a bid for construction or writing a research grant proposal, following theproscribed formatting requirements is crucial. Reviewers will not think twice about throwing outmillion dollar grant requests because the abstract had one too many words or the margins were0.01inches too narrow. That being said, the most efficient way to write the proposal for thisproject is to follow the example in the NSU proposal (they might be questionable engineers, buttheir proposal was correctly formatted (only exception is that italicizedvalues are one which maychange based on your design, and need not be italicized in your proposal).

Your electronic and paper versions must be identical.

Points will be assigned as follows:Technical: 25 pts (Correctness of your analysis method, MATLAB code, values, and plots.)Incentives are available for proposal costs of safe systems below 2% of target budget.

Description: 7 pts.(How well you describe in words what you did, how you did it, and what you found.)

Presentation: 8 pts.(Neatness, clarity of the figures and tables, organization of the report, conciseness, etc.)

TOTAL: 40 pt


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Design Project Collaboration and Plagiarism Guidelines

Design projects are to be completed individually. It is acceptable for you to discuss ideas on setting upand solving the design problem with other students, as well as with the course instructors and TAs, but

you must complete your own analysis, MATLAB programming, and report. Copying or sharing ofcalculations, code, results, or text is not allowed and will not be tolerated. All design projects will beanalyzed electronically for violations of the University's academic integrity policy and may also beincluded in a database for the purpose of testing for plagiarized content.

Design Project Submission Guidelines

All design projects must be submitted both in paper form and electronically via the Blackboard website

for your section. The electronic and paper versions must be identical. The electronic version must besubmitted as two separate files. The main body of your design project must be submitted as a single file,and this file must not contain your MATLAB code. The MATLAB code (which should be placed in anAppendix to the report) must be submitted in a second file. These files must be in either Microsoft Wordformat (.doc) or Adobe Acrobat format (.pdf). Equations and figures should be embedded in theelectronic submission of the project. Failure to comply with these instructions will result in a penalty.

CSPS Info

Named for McCormicks centennial last year, the Centennial Solar Panel System is the pilot project ofESWs NU Clean Energy Plan, a project which works on reducing the campus use of non-renewable

energy sources and replacing them with renewable generation technologies. The Clean Energy Planteam works on renewable energy installation projects for campus and developing the plan.The CSPS budget is around $120,000, which was raised from donations and grants, the largest of whichcame from the Illinois Clean Energy Community Foundation. Other sponsors include the Initiative forSustainability and Energy at Northwestern (ISEN), the McCormick School of Engineering and AppliedSciences and its departments, and other departments around Northwestern. This project is a partnershipbetween the students of ESW/NSF and NU Facilities Management.Tip from ESW and NSF: Simple designs are often the best and most cost efficient!

ESW and NSF wish you luck on the problem, and if you are interested in getting involved with any ofthe ESW or NSF projects, [email protected]! Look for CSPS on the roof of Ford this spring!
mailto:[email protected]:[email protected]:[email protected]:[email protected]

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