Civil Engineering PE Hydraulics and Open-Channel Flow 2

Question 1

A rectangular channel 4 m wide carries water at a depth of 1.2 m with a velocity of 2.5 m/s. What is the Froude number?

Accepted Answer

0.73

Answer

Fr = V/√(g·y) = 2.5/√(9.81×1.2) = 2.5/3.431 ≈ 0.73, indicating subcritical flow.

Question 2

The hydraulic radius of a trapezoidal channel with bottom width 3 m, side slopes 1.5H:1V, and depth 1.5 m is most nearly:

Accepted Answer

0.92 m

Answer

A = (3 + 1.5×1.5)×1.5 = 7.875 m², P = 3 + 2×1.5×√(1+1.5²) = 8.41 m, R = 7.875/8.41 ≈ 0.94 m, nearest answer 0.92 m.

Question 3

Which condition defines critical flow in an open channel?

Accepted Answer

The specific energy is at its minimum for a given discharge

Answer

Critical flow occurs when specific energy is minimized for a given discharge, which corresponds to Fr = 1.

Question 4

A 600 mm diameter circular pipe flowing half-full has a hydraulic radius of:

Accepted Answer

150 mm

Answer

For a half-full circular pipe, R = D/4 = 600/4 = 150 mm.

Question 5

A hydraulic jump occurs in a rectangular channel with upstream depth y₁ = 0.4 m and upstream velocity V₁ = 6 m/s. The sequent depth y₂ is most nearly:

Accepted Answer

2.0 m

Answer

Fr₁ = 6/√(9.81×0.4) = 3.03; y₂ = y₁(√(1+8Fr₁²)−1)/2 = 0.4×(√73.4−1)/2 ≈ 2.0 m.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Hydraulics and Open-Channel Flow 2