EGR 106 Project Intro While Loop

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EGR 106 Project Intro / While Loop

• Project description
• Project schedule
• Background information / terminology
• A simple example
• Examples of similar programs
• While loop

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Project Description

• Working in teams of approx. four students, each
  team is to develop a Matlab program that can be
  used to design a lightweight truss structure
• The code shall allow the designer to evaluate
  alternative designs quickly and easily
• The actual truss analysis will be performed by
  the Matlab function truss_analysis.m to be
  provided by the instructor.

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Project Description (cont.)

• The program developed by each team shall provide
  a user-friendly interface for both data input and
  interpretation of results
• Each teams code will be used in a design
  competition in which each team will be given 1
  hour to develop a truss design for a particular
  load scenario
• The team will then construct their design from
  balsa wood (required construction materials will
  be provided)

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Project Schedule (tentative)
3/27 (T) Project Introduction 3/29 (R) Quiz
2 make up / Team assignment 1 4/3 (T) Lecture
Analysis of Trusses / Graphical Interface 4/5
(R) Project work / Team assignment 2 4/10
(T) Lecture Analysis of Trusses / Graphical
Interface 4/12 (R) Quiz 3 / Project work 4/17
(T) Project work 4/19 (R) In-class design
competition 4/24 (T) Quiz 4 / Model
testing 4/26 (R) Project Presentations /
Demonstrations 5/1 (T) Written reports due
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Background Truss Structures

• Definition A planar truss is a structure
  composed of slender members joined together at
  their end points (called joints).

Photo Engineering Mechanics Statics, by R. C.
Hibbeler
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Terminology Truss Structures
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Terminology (cont.)

• Trusses are supported at certain joints at which
  motion is constrained either in the x- direction,
  y-direction or both the x- and y-directions.
  These supports are also called boundary
  conditions.

X Y displacement0 X - displacement0
Y -displacement0 (bctype1)
(bctype2)
(bctype3)
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Truss Analysis A simple example
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A simple example input data(details to be
discussed next class)
joint_def0, 0, 1, 0, 0 50,
50, 0, 0, 0 150, 150, 0, 100,
-50 250, 50, 0, 0, 0
300, 0, 3, 0, 0 200, 0, 0,
0, 0 100, 0, 0, 0, 0
member_def1, 2, 10, 10 2, 3, 10,
10 3, 4, 10, 10 4, 5,
10, 10 5, 6, 10, 10 6,
7, 10, 10 7, 1, 10, 10
2, 7, 10, 10 7, 3, 10, 10
3, 6, 10, 10 6, 4, 10, 10
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A simple example - results
Matlab command (call to function
analyze_truss) disp,stressanalyze_truss(join
t_def,member_def)

• Joint Displacments
• disp
• 0.0000
• 0.0000
• 0.2457
• -0.1750
• 0.6493
• -0.4371
• 0.2043
• -0.4578
• 0.4500
• -0.0000
• 0.3000
• -0.5536
• 0.1500
• -0.2707

Member Stresses stress 0.3536 0.3536
-1.0607 -1.0607 0.7500 0.7500
0.7500 -0.0000 0.0000 0.0000 -0.0000
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Examples of truss design programs

• Johns Hopkins University
• http//www.jhu.edu/virtlab/bridge/truss.htm
• West Point Bridge Design Contest
• http//bridgecontest.usma.edu/

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Notes on academic integrity
Truss design and analysis programs are
common. Students are welcome to look at other
programs for features to incorporate. Direct
copying of code, however, is not permitted. Do
not share code with other teams. Be sure not to
leave your codes on public computers.
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Longer Running Loops

• for loops repeat a fixed number of times
• for variable array of length n
• commands
• end
• and break can be used to stop earlier.
• Question How about repeating until done? Run
  as long as is needed.

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Answer MATLABs while loop

• while expression
• commands to be repeated as long
• as expression is true
• end

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Prior example compounded interest until the
amount doubles
for loop

• value 1000
• for year 11000
• value value 1.08
• disp(num2str(year),' years ',num2str(value)
  )
• if value gt 2000
• break
• end
• end

terminated with break
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Expected output
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while version

• format bank
• value 1000
• while value lt 2000
• value value 1.08
• disp(value)
• end

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Example Collecting and storing data until a
zero is entered
empty array

• x
• new 1
• while new 0
• new input('enter value ')
• x x, new
• end
• x x(1end1)

initialize
to drop the zero
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Example Getting valid keyboard input

• E.g. forcing the users input to be between 0
  and 10
• x 3
• while ( x lt 0 ) ( x gt 10 )
• x input( 'type a value ' )
• end

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• or
• x input('enter value ')
• while (xlt0)(xgt10)
• disp('invalid choice')
• x input('enter value ')
• end
• disp('finally!')

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Example computing pi
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Example infinite Hi-Lo

• numb round (10rand(1))
• done 0
• while done
• guess input('guess')
• if guess numb
• disp( 'You got it !!!' ) done 1
• elseif guess gt numb
• disp('too high')
• else
• disp('too low')
• end
• end

initialization
single guess
loop control
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Nesting of while loops

• while expression1
• outer loop commands
• while expression2
• inner loop commands
• end
• more outer loop commands
• end

these can also be more than 2 levels deep