CalcPipeTransBeam Function

private function CalcPipeTransBeam(R, A, Theta)

Arguments

Type	Intent		Name
real(kind=r64),	intent(in)	::	R
real(kind=r64),	intent(in)	::	A
real(kind=r64),	intent(in)	::	Theta
Return Value real(kind=r64)

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Source Code

CalcPipeTransBeam
Source Code

REAL(r64) FUNCTION CalcPipeTransBeam(R, A, Theta)

          ! SUBROUTINE INFORMATION:
          !       AUTHOR         Peter Graham Ellis
          !       DATE WRITTEN   May 2003
          !       MODIFIED       na
          !       RE-ENGINEERED  na

          ! PURPOSE OF THIS SUBROUTINE:
          ! Calculates the numerical integral for the transmittance of a reflective cylinder with
          ! incident collimated beam radiation as described in Swift and Smith.

          ! METHODOLOGY EMPLOYED:
          ! Since this integral can be slow, a table of values is calculated and stored during
          ! initialization of the TDD.  Intermediate values are calculated by interpolation.
          ! Transmittance of sky and ground diffuse radiation is done by other functions.

          ! REFERENCES:
          ! Swift, P. D., and Smith, G. B.  "Cylindrical Mirror Light Pipes",
          !   Solar Energy Materials and Solar Cells 36 (1995), pp. 159-168.

          ! OTHER NOTES:
          ! The execution time of this function can be reduced by adjusting parameters N and xTol below.
          ! However, there is some penalty in accuracy for N < 100,000 and xTol > 150.

          ! USE STATEMENTS: na

  IMPLICIT NONE ! Enforce explicit typing of all variables in this routine

          ! FUNCTION ARGUMENT DEFINITIONS:
  REAL(r64), INTENT(IN)            :: R            ! Reflectance of surface, constant (can be made R = f(theta) later)
  REAL(r64), INTENT(IN)            :: A            ! Aspect ratio, L / d
  REAL(r64), INTENT(IN)            :: Theta        ! Angle of entry in radians

          ! FUNCTION PARAMETER DEFINITIONS:
  REAL(r64), PARAMETER :: N = 100000.0d0 ! Number of integration points
  REAL(r64), PARAMETER :: xTol = 150.0d0 ! Tolerance factor to skip iterations where dT is approximately 0
                                              ! Must be >= 1.0, increase this number to decrease the execution time
  REAL(r64), PARAMETER :: myLocalTiny =  TINY(1.0D0)

          ! FUNCTION LOCAL VARIABLE DECLARATIONS:
  REAL(r64)       :: i            ! Integration interval between points
  REAL(r64)       :: s            ! Entry point
  REAL(r64)       :: dT
  REAL(r64)       :: T            ! Beam transmittance for collimated solar real
  REAL(r64)       :: x, c1, c2    ! Intermediate variables for speed optimization
  REAL(r64)       :: xLimit       ! Limiting x value to prevent floating point underflow

          ! FLOW:
  CalcPipeTransBeam = 0.0d0

  T = 0.0d0
  i = 1.0d0 / N

  xLimit = (LOG(N**2.0d0*myLocalTiny)/LOG(R))/xTol

  c1 = A * TAN(Theta)
  c2 = 4.0d0 / Pi

  s = i
  DO WHILE (s < (1.0d0 - i))
    x = c1 / s

    IF (x < xLimit) THEN
      dT = c2 * (R**INT(x)) * (1.0d0 - (1.0d0 - R) * (x - INT(x))) * (s**2) / SQRT(1.0d0 - s**2)
      T = T + dT
    END IF

    s = s + i
  END DO

  T = T / (N - 1.0d0) ! - 1.0, because started on i, not 0

  CalcPipeTransBeam = T

  RETURN

END FUNCTION CalcPipeTransBeam
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