NCEES 2011 Problem 510 (WR/E)

[matt267 PE]

Question 510 states:

The figure shows a sluice gate in a 35-ft rectangular channel. At Section 1, Y1 is 3.8 ft and the velocity is 50 ft/sec. The Froude number at Section 2 is most nearly:

To solve, I used this equation to find Y2:

(edit: d1=y1)

and this equation to find the Froude number:



I got Fr=6.83 which is wrong.

The solution used this formula to solve for Fr1:



This formula to solve for Y2:



This to solve for V2:



and this to solve for Fr2:



They got Fr2=0.31

Can anyone provide some insight on why my method was wrong?

 

[WR/ENV_Instructor]

@matt267,

For a rectangular channel with Fr2, the equation is d1/d2 (not d2/d1 as you typed.)

You were using the wrong equation.

Harry

 

[matt267 PE]

Harry,thanks for the reply. You are absolutely correct.

FYI to others: I used equation 19.92 and 19.93b from the 13th edition of the CERM to get the correct answer.

Thanks again Harry!

 

[WR/ENV_Instructor]

Matt267,

You are very welcome!

Harry