Hydraulics and Open-Channel Flow Flashcards
7 cards from real Civil Engineering PE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Hydraulics and Open-Channel Flow flashcards as text
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?
Answer: 0.73
Fr = V/√(g·y) = 2.5/√(9.81×1.2) = 2.5/3.431 ≈ 0.73, indicating subcritical flow.
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:
Answer: 0.92 m
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.
Which condition defines critical flow in an open channel?
Answer: The specific energy is at its minimum for a given discharge
Critical flow occurs when specific energy is minimized for a given discharge, which corresponds to Fr = 1.
A 600 mm diameter circular pipe flowing half-full has a hydraulic radius of:
Answer: 150 mm
For a half-full circular pipe, R = D/4 = 600/4 = 150 mm.
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:
Answer: 2.0 m
Fr₁ = 6/√(9.81×0.4) = 3.03; y₂ = y₁(√(1+8Fr₁²)−1)/2 = 0.4×(√73.4−1)/2 ≈ 2.0 m.
Manning's equation for open channel flow requires which parameter to account for channel roughness?
Answer: Manning's roughness coefficient n
Manning's equation Q = (1/n)A·R^(2/3)·S^(1/2) uses n as the dimensionless roughness coefficient.
The critical depth in a rectangular channel 5 m wide carrying a discharge of 20 m³/s is most nearly:
Answer: 1.37 m
yc = (q²/g)^(1/3) where q = 20/5 = 4 m²/s; yc = (16/9.81)^(1/3) = (1.631)^(1/3) ≈ 1.37 m.