PROGRAM mpg ! accounting for cross-sectional area and air density, this program ! calculates the change in gas efficiency of a car compared to a baseline as well as plots ! the efficiency as a function of cross sectional area ! Written 3-7-2007 ! by Michael Risch-Janson ! PGPLOT section is an Example from PGPLOT documentation ! comments added by Jim Crumley 1/30/2007 ! jc The line above seems odd in this context ... IMPLICIT NONE !jc It would nice nice to define the variables and their units REAL(KIND=8) :: F_r, mass, area_ft, area_m, v, k, wCw, density_air,k_base, area_base, mph, wCwA !initialize variables REAL(KIND=8) :: W, x, F_base, dist, gas2 ,miles, W_base, miles2, effic, k_car, F_car, W_car REAL(KIND=8) :: mileage(20), area_feet(20), area_meters(20), k_1(20), drag_area, drag_coeff(50) REAL(KIND=8) :: effic_car, mileage_car, mpg_car, efficiency_car REAL(KIND=8) :: Force_r(20), Work(20), mileage_base(20), efficiency(20) INTEGER :: i, PGBEG, IER, j, car_year(50) CHARACTER(len=100) :: car_name(50), enter PRINT *, 'What is the cross-sectional area in square feet?' ! promt for input of cross sectional area READ *, area_ft ! square feet PRINT *,'' area_m = area_ft * .0929 ! square feet to square meters conversion v= 30. ! calulations done at this velocity in meters per second = 67 mph x = 1600. ! distance of one mile in meters !jc a mile is not 1600 m to 4 digits. wCw = .3125 ! drag coefficient to be used for car - unitless density_air = 1.2 ! air density in kg /m^3 k= 1./2. * wCw* density_air* area_m ! kg/m - k value to be used in calculating resistance force F_r = k * v**2. ! resistive force by air on car wCwA = 5.0 * .0929 ! drag coefficient * cross sectional area for base car - m^2 ! equivilent to 16 ft^2 area * .3125 drag coefficient k_base = 1./2. * density_air * wCwA ! kg/m - k value for base car F_base = v**2.*k_base ! resistive force on base car W_base = F_base * x ! work over a mile done on base car by resistive force - Joules W = F_r * x ! work over a mile done on user's car by resistive force - Joules ! approx 136000000. joules in a gallon of gas ! since all end calulations are percentages or comparisons to base car ! the actual amount of joules doesn't matter ! the actual number will vary based on efficiency of engine but the efficiency of the engine ! is taken to be constant between the two vehicles like other factors miles = 136000000. / W !miles the car will travel on one gallon of gas based on accepted amount of joules in ! gallon of gas and work doneby air resistance force - user's car miles2 = 136000000. / W_base ! base car- miles effic = miles / miles2 * 100. ! comparison of user's car to base car- % of gas mileage efficiency !Print efficiency to screen and read statement to pause program until enter is pressed WRITE(*,'(A,F6.2,A)'), 'The gas mileage efficiency of your car based on the cross sectional area is: ', effic, '%' PRINT *, 'of that of a baseline car with cross sectional area of 16 square feet.' PRINT *,'' PRINT *, 'Please press enter to continue.' PRINT *, 'A list of drag coeffecient - cross sectional area constansts for various vehicles will be displayed.' READ *, !opens file which contains specific car models and drag coeff-cross sectional area constants corrsponding !to those cars OPEN (10, file ='cda',STATUS='OLD', ACTION='READ') !open data file which already exists and will only be read ! read and write in the data formatted DO i=1,41 ! reading in the data from the file READ (10,*) drag_coeff(i), car_year(i), car_name(i) ! x PRINT (*,'(F5.2," ", I5," ", A)'), drag_coeff(i), car_year(i), car_name(i) END DO ! input of constant by user PRINT *,'' PRINT *, "Please type in the drag coefficient-area constant assosiated with your vehicle ", & "or the vehicle which most closely resembles yours:" READ *, drag_area ! since drag - area constant is the only difference between base car and user's vehicle ! the following calculation gives the efficiency as a % of the base car ! based on that a efficiency and a value of 40 mpg for the base car it gives the !mpg of the user's car ! this is added to give the user an idea of what a certain % means in actual numbers ! the 40 mpg is not an accurate number efficiency_car = 5.0 / drag_area * 100. mpg_car = 40. * efficiency_car / 100. !print the data and pause again until enter is pressed PRINT *,'' WRITE(*,*) 'The gas mileage efficiency of your vehicle based on the drag coefficient-area constant',& ' you selected and compared to the base vehicle constant of 5.0 is:' WRITE (*,'(F6.2,A)'), efficiency_car, '%' PRINT *, '' WRITE (*,'(A,A,F6.2,A)') 'This means that if the base vehicle gets 40 mpg that your vehicle',& ' would achieve about:',mpg_car, ' mpg' PRINT *,'' PRINT *, "Please press enter to continue." PRINT *, "A graph of gas mileage efficiency vs cross sectional area will be displayed with 16 square feet as the base." READ*, ! calculate graph points for various cross sectional areas ! Here would be the calculations except as before the only ! variable between the base vehicle and the varying one is ! the cross sectional area- !area_meters(i) = area_feet(i) * .0929 !k_1(i) = 1./2. * wCw* density_air* area_meters(i) !Force_r(i) = k_1(i) * v**2. !Work(i) = Force_r(i) * x !mileage(i) = (136000000. / Work(i)) !efficiency(i) = mileage(i) / miles2 * 100. !These can be simplified to this Do loop DO i= 1, 15 area_feet(i) = 14. + 2.*i efficiency(i) = 16. / area_feet(i) * 100. END DO !graphin of the data IER = PGBEG (0, '/XSERV',1,1) IF (IER.NE.1) STOP !sets up scale on plots(xmin, xmax, ymin, ymax,scales_equal?,grid_features) CALL PGENV(16.,44., 0., 100. ,0,1) !set x and y axis labels and title in that order CALL PGLAB('Area (square feet)', 'Gas mileage efficiency (% of baseline)', 'Change in gas mileage efficiency due to area') ! Draw the line for the theoretical (num_points, x_data, y_data) CALL PGLINE(15,REAL(area_feet(1:15)),REAL(efficiency(1:15))) !close the plot CALL PGEND END PROGRAM mpg !jc Fairly well commented, though more comments about the variable !jc definitions at the debinnging would nice. Program seems reasonable, !jc though a bit boring mathematically - we probably should have found !jc a way to make the calculations more interesting.