Abstract: In this paper, a universal method for calculation of the inlet length and correction coefficient for the pressure losses and the flow in the case of laminar and turbulent flow in a smooth round pipe is put forward.With the aid of concrete examples, theoretical formulas are presented for calculation of the correction coefficient for pressure losses and flow in the case of laminar and turbulent flow. And a method for calculation of the flow is also presented here in consideration of the inlet effect of turbulent flow.By comparing the theoretical results with the experimental data, formulas presented in this paper are very simple and reliable.

Key words: H_∞ control, Rayleigh quotient, variational principle, precise integration