Function Do_FDBR_9_4_5_4(Zeta_soll As Double, D_1_mm As Double, D_2_mm As Double, R_kante_mm As Double)
Dim Pi As Double, A1 As Double, Ao As Double, A2 As Double, m1 As Double, m2 As Double, D_h As Double, Zeta_Strich As Double, D_o_mm As Double, Zeta_cal As Double, X As Double
For D_o_mm = 0.01 * D_2_mm To D_2_mm Step 0.1
Pi = 3.14
A1 = (Pi / 4) * (D_1_mm / 1000) ^ 2
Ao = (Pi / 4) * (D_o_mm / 1000) ^ 2
A2 = (Pi / 4) * (D_2_mm / 1000) ^ 2
m1 = Ao / A1
m2 = Ao / A2
D_h = 4 * Ao / (Pi * D_o_mm / 1000)
Zeta_Strich = 0.5 - 0.47 * WorksheetFunction.Tanh(13.9 * R_kante_mm * 0.001 / D_h)
Zeta_cal = ((Zeta_Strich * (1 - m1)) ^ 0.5 + (1 - m2)) ^ 2 * (1 / m2) ^ 2
X = Abs(Zeta_soll - Zeta_cal) / Zeta_soll
Debug.Print X
If X < 0.001 Then
Do_FDBR_9_4_5_4 = D_o_mm
Exit For
End If
Next
End Function