# Homework Help: More Fluid Mech

1. Aug 16, 2006

hi guys.

got another question for ya.
........................................

seems to of uploaded small but i explain.

a reservoir is designed to retain water to a max depth of 10metres. if the water level exceeds 10 metres, then a hinged semi circle gate will open to release any excess water. the gate has a radius of 1m. the gate is hinged 9 metres below the free surface.

what would be the force required to open gate?

what is the depth from the free surface to the the centre of pressure.

........................................

i know the second moment of area of a semi circular surface is 0.1102R4

but not sure how to complete the question. help with working out the answer would be much appraicated so i can work back on the answer and see how to get it.

thanks

2. Aug 16, 2006

### FredGarvin

In a general sense, you need to calculate the pressure distribution on the gate. From there, using the hinge location, you can use the area to calculate a force on the gate.

3. Aug 17, 2006

i cant calcluate the area as i do not know all the measurements

or how would i do this?

thanks

4. Aug 17, 2006

### FredGarvin

You know the radius of the gate. That's all you need.

5. Aug 18, 2006

hi

i have worked out the area and it is 1.571

once i have got the area of the gate, then how to i calculate the force required to open it?

thanks

6. Aug 18, 2006

the 2nd moment of area Ig about axis through centroid is 0.1102Rto the power of 4

so that would be 0.1102 x 1.571 to the power of 4 which is 0.272?

still confused where to go next

7. Aug 18, 2006