Principles of Hydraulics Flashcards
State the density of fresh water, sea water, light oil, glycerine and mercury.
w: 1000kgm^-3, sw: 1027kgm^-3, o:800kgm^-3, g: 1260khm^-3, m: 13,600kgm^-3
What is specific weight?
w=fluid weight/ volume= mg/v= ρg (N/m^3)
What is specific gravity?
s= (mass of fluid for specific volume) / (mass of water for same volume)
What are the different units for pressure?
p= force/area. 1 pascal= 1 N/m^2. 1 bar = 1 atmosphere =100,000 N/m^2
How do you calculate the bulk modulus (K)?
K=-VΔp/Δv. for water k=2.210^9
How do you calculate the surface tension of a fluid (σ)?
σ=(ρgDh)/(4cos(θ)
θ-angle between wall and fluid, D-diameter of thin tube, h-height of fluid in thin tube
How do you calculate the force on the base of a container due to a fluid?
F=ρgHA, as h increases pressure increases linearly at a rate of ρg
Define Gauge (engineering) and Absolute pressure.
absolute pressure= atmospheric pressure (1*10^5) + ρgh
gauge pressure= ρgh -this is used for engineering calculations
List 4 pressure measurement devices.
Barometer, Piezometer, Pressure Transducer, Manometer
Why is an inclined monometer more accurate than a vertical one?
measuring over a larger distance so is more accurate.
How do you calculate the force on a vertical wall due to a liquid?
F=ρgw[(H^2)/2] ,w-width of wall.
to calculate the force over a specific strip F=ρgw[(h^2)/2]^H0
How do you locate the point of action of a resultant force?
Taking moments about a corner at the free surface: FL=ρgwH^3/3, L=2H/3
For a sloping wall: L=2H/3sin(x)
How do you calculate the resultant force on a curved wall?
Obtain F(h) =(ρgwH^2)/2 and F(v) =weight above the curve (ρgv) F(resultant)^2 = F(h)^2 + F(v)^2 tan(θ)=F(v)/F(h)
How do you locate the resultant on a curved surface?
F(h) acts 2H/3 , F(v) acts through the centroid of the area above the curve (x=4r/3π)
Large gates are normally circular in shape as the only applied moment needed to raise it is to counter the self weight.
How do you calculate the buoyancy force on a fully submerged object?
B = ρgAD
A-plan area, D-height of the object, if the system is in equilibrium then B=W
What is the concept of a metacentre?
the point of intersection between an imaginary line drawn vertically through the centre of buoyancy of a floating vessel and a corresponding line through the new centre of buoyancy when the vessel is tilted.
How can you say whether a floating system is stable or not?
If the metacentre, m, is above the centre of mass, g, then the system is stable. (Bm>Bg)
How do you calculate Bm and Bg?
Bm=I/V , I-second moment of area (bd^3/12) , v-displaced volume.
Bg= distance from centre of mass to new centre of buoyancy
Define a streamline and a streamtube.
A streamline is a path that a small element of fluid has followed. If a surface is created of streamlines, it is possible to create a streamtube. In a small time period mass flowrate in = mass flowrate out. (ρvA) v-velocity
What is the principle of mass continuity?
V(in)A(in) = V(out)A(out)
How do you calculate the total amount of energy per unit weight of a fluid in a system?
H = p/ρg + v^2/2g + Z
no energy losses
Describe the concept of a control volume
A control volume in an engineering system is a volume that does not change shape, no fluid crosses its boundaries except at its entry and exit surfaces.
What two things do you need to know in order for a venturi meter to work?
(1) pipe and throat cross-sectional area.
(2) difference in pressure and elevation between the original pipe and the throat of the venturi meter.
How do you calculate the flowrate of a fluid?
Q(actual) = CdVA
Cd- coefficient of discharge
V- velocity = ((2g(h(a)-h(b)))/[1-(A(b)^2/A(a)^2)]) -horizontal
What is an orifice plate?
Orifice plates are normally circular and have a small sharp edged hole. The orifice plate is then inserted in a pipe and the fluid accelerates through the hole and pressure drops. Q=CvCca*V(2) -small orifices
Cv- coefficient of velocity accounts for energy loss
How do you calculate the flowrate through a large orifice?
Can no longer assume constant velocity over the orifice.
Q = (2*(2g)^1/2)/3 * W[h(2)^3/2 - h(1)^3/2]
How do you calculate discharge through a small orifice with a reducing free surface level?
Time to empty a tank T = (2AH^1/2)/(Cda(2g)^1/2)
How do you calculate the forces involved in a control volume of a pipe?
Balance momentum forces against pressure forces + reaction forces, F(m) = F(p) + F(r). Do this for (x,y).
F(m)=ρQ(V(2)-V(1)) V(2/1)-velocity out/in
