Chapter 2:Fluid Statics

Example 2.1 Page No22

In [2]:
from __future__ import division

#variable initialisation

h1=10          #column water in cm

h2=5           #column of oil in cm

rd=0.75        #relative density of oil

h3=2           #column of mercury in cm

#solution

ga=9790          #density in N/m^3

a=h1/100

p=ga*a           #pressure

print "(i)For water Column,p=",int(p),"N/m^2"

ga_o=rd*ga     

p_o=(ga_o*h2)/100 #pressure

print "(ii)For Oil Column, p=",round(p_o,2),"N/m^2"

ga_m=13.6*ga

p_m=ga_m*h3/100   #pressure

print "(iii)for Mercury Column,p=",round(p_m,1),"N/m^2"
(i)For water Column,p= 979 N/m^2
(ii)For Oil Column, p= 367.13 N/m^2
(iii)for Mercury Column,p= 2662.9 N/m^2

Example 2.2 Page No22

In [3]:
from __future__ import division

import math

#variable initialisation

d=5         #depth in m

rd=0.85     #relative density of liquid

br=0.750    #barometer reading of mercury in m

#solution

ga=rd*9790            #calculating gamma

p=int(br*13.6*9790)   #Atmospheric Pressure

print "atmospheric pressure=",p ,"N/m^2"

ap=round(((d*ga)+p),0)

print "absolute pressure in the liquid at 5.0 m depth=",ap/1000,"kPa"
atmospheric pressure= 99858 N/m^2
absolute pressure in the liquid at 5.0 m depth= 141.466 kPa

Example 2.3 Page No22

In [3]:
import math

#variable initialisation

p1=0                             #pressure

rho=0.88                         #density

ga_w=9790                        #relative density in N/m^3

h=4                              #height of water in m

h1=2                             #height of water in m

#Calculation

ga_0=rho*9790

p2=p1+(ga_0*h1)                  #pressure at the oil-water interface

p3=round(p2+(ga_w*h),1)          #pressure due to 4m of water

print "P3=",round(p3/1000,4),"kPa"
P3= 56.3904 kPa

Example 2.5 Page No23

In [4]:
#variable initialisation

k=1.4                          #assumed value

g=9.81                         #gravity

rho=1.1120                     #relative density in kg/m^3

h1=3500                        #elevation above sea level in m

h2=1000                        #elevation sea level in m

p1=89890                       #pressue in Pa

#Calculation

#For an adiabatic process,

a=k/(k-1)

p2=int(((1-(((k-1)/k)*(((g*rho)*(h1-h2))/p1)))**a)*p1)

rho2=((p2/p1)**(1/k))*rho

print "Answer given in  the book is wrong in decimal.It should be,"

print "rho2=",round(rho2,5),"kg/m^3"
Answer given in  the book is wrong in decimal.It should be,
rho2= 0.88645 kg/m^3

Example 2.6 Page No23

In [5]:
#variable initialisation

RD_oil=0.70                       #relative density of oil in kg/m^3

RD_mercury=13.6                   #relative density of mercury in kg/m^3

RD_oil2=0.8                       #relative density of oil 2 in kg/m^3

W=9790                            #unit weight of water in N/m^3

D1=10                             #diameter 1 in cm

D2=13                             #diameter 2 in cm

D3=8                              #diameter 3 in cm

#Calculation

D1=D1/100                         #converting into m

D2=D2/100

D3=D3/100
#Equating the pressures on both the limbs at the horizontal plane.

#P_A+(D1+D2+D3)*ga_A=P_B+(D2*ga_B)+(D3*ga_m)

ga_A=RD_oil*W

ga_B=RD_oil2*W

ga_m=RD_mercury*W

#P_A-P_B is taken as PD

PD=((D2*ga_B)+(D3*ga_m)-(D1+D2+D3)*ga_A)/1000

print "P_A-P_B=",round(PD,3),"kPa"
P_A-P_B= 9.545 kPa

Example 2.7 Page No23

In [6]:
#variable initialisation

ga_w=9790                          #unit weight of water in N/m^3

ga_oil=0.83                        #unit weight of oil in N/m^3

D1=3.5                             #diameter 1 in cm

D2=6                               #diameter 1 in cm

D3=12                              #diameter 1 in cm

#Calculation

D1=D1/100                          #converting into m

D2=D2/100

D3=D3/100

ga_oil=ga_oil*9790                 #unit weight

#P_A+(D1+D2+D3)*ga_A=P_B+(D2*ga_B)+(D3*ga_m)

PD=((ga_w*(D1+D2))-(ga_w*(D2+D3))-(ga_oil*D1))/1000

print "Pressure at N is larger thean at M by",-round(PD,3),"kPa"
Pressure at N is larger thean at M by 1.117 kPa

Example 2.8 Page No24

In [7]:
#variable initialisation

p1=20                         #pressure in inner tank in kPa

p2=35                         #pressure in outer tank in kPa

N=750                         #barometer reading in mm

#Calculation

#Bourdon guage records guage pressure relative to the pressure of medium

#local pressure is measured by aneroid barometer

pN_abs=N+((p2*1000)/(13.6*9.79))

print "pN_abs=",round(pN_abs,1),"mm of mercury (abs)"

pM_abs=pN_abs+((p1*1000)/(13.6*9.79))

print "pN_abs=",round(pM_abs,1),"mm of mercury (abs)"
pN_abs= 1012.9 mm of mercury (abs)
pN_abs= 1163.1 mm of mercury (abs)

Example 2.9 Page No24

In [8]:
#variable initialisation

RD_oil=0.75                         #relative density of oil in kg/m^3

RD_mercury=13.6                     #relative density of oil in kg/m^3

D1=10                               #Diameter 1 in cm

D2=150                              #Diameter 2 in cm

D3=200                              #Diameter 3 in cm

#calculation

D1=D1/100                           #Converting into m

D2=D2/100

D3=D3/100

#Considering the pressure at the horizontal plane,

ga_o=RD_oil*9790                    #specific weight of oil in N/m^3

ga_w=9790                           #specific weight of water in N/m^3

ga_m=RD_mercury*9790                #specific weight of mercury in N/m^3

P_A=(D1*ga_m)-(D3-D2)*ga_w-D2*ga_o-D1*ga_w

print "P_A=",round(P_A/1000,3),"kPa"
P_A= -3.573 kPa

Example 2.10 Page No24

In [9]:
#variable initialisation

RD_oil=0.8                                 #relative density of oil in kg/m^3

RD_mercury=13.6                            #relative density of mercury in kg/m^3

D1=20                                      #Diameter in cm

D2=16                                      #Diameter in cm

D3=12                                      #Diameter in cm

D4=15                                      #Diameter in cm

#Calculation

D1=D1/100                                  #Converting into m

D2=D2/100

D3=D3/100

D4=D4/100

ga_o=RD_oil*9790                           #specific weight of oil in N/m^3

ga_m=RD_mercury*9790                       #specific weight of water in N/m^3

e=-(ga_o*(D1+D2))+((ga_o*(D4)))+(-((ga_o)*D3))+(ga_m*(D4+D3+(D1-D2)))

print "(P_M-P_N)=",round(e/1000,4),"kPa"
(P_M-P_N)= 38.6901 kPa

Example 2.17 Page No28

In [10]:
#variable initialisation

ga_o=0.9*9790                       #relative density of oil in kg/m^3

P0=0                                #pressure at top

d=0.6                               #depth in m

s=1.5                               #sides of tank in m

#Calculation

Pi=0.9*ga_o                        #pressure at the interface in N/m^2

Pb=Pi+9790*d                       #pressure on the bottom in N/m^2

F1=(1/2)*Pi*(0.9*s)                #Force on the top of 0.l9 m of a side

F2=Pi*s*d                          #Force on the bottom of 0.6 m of a side

F3=(1/2)*(Pb-Pi)*d*s               #remaining part of force on the bottom 0.6m of a side

F=F1+F2+F3                         #Total force

print "Total force F=",round(F/1000,3),"kN"

Y_p=((F1*d)+(F2*(0.9+(d/2)))+(F3*(0.9+(2/3)*d)))/F #centre of pressure

print "Y_p=",round(Y_p,3),"m"
Total force F= 15.133 kN
Y_p= 1.005 m

Example 2.19 Page No29

In [13]:
#variable initialisation

h=4.5                   #height of board in m

#Calculation

#For critical stability,the centre of pressure must be at C

#h=height of C above B

Max=h/3

print "The maximum height=",Max,"m"
The maximum height= 1.5 m

Example 2.37 Page No38

In [17]:
#variable initialisation

D=2.5       #diameter in m

rd=0.25     #relative density 

p=1000      #pressure in kPA

f_a=120     #allowable stress in MPa

#solution

#Hoop stress in cylinder,sigma=(p*D)/(2*t)

#sigma=f_a=allowable stress

t=(p*D)/(2*f_a*1000)

print "A Thickness of",round(t*1000,2),"mm can therefore be used"
A Thickness of 10.42 mm can therefore be used

Example 2.40 Page No39

In [19]:
#variable initialisation

W_s1=10     #weight

W_s2=20     #weight 

S1=0.8      #relative density

S2=1.2      #relative density 

ga=9.79E+3  #gamma

#solution

V=(W_s2-W_s1)/(ga*(S2-S1)) 

print "volume=",round((V*1000),4),"L"

W_s1=20     

W_s=W_s1+(ga*S1*V)

print "Weight in air=",int(W_s),"N"
volume= 2.5536 L
Weight in air= 40 N

Example 2.42 Page No40

In [20]:
import math

#variable initialisation

W=0.2   #weight in N

D=5     #diameter in mm

#solution

#(i)distance between marking of RD of 1.0 and 0.95

h1=(W/(9790*((math.pi/4)*(D*D)/(1000*1000))))*((1/0.95)-1)

print "h1=",round(h1*1000,2),"mm"

#(ii)distance between marking of RD of 1.0 and 1.05

h2=(W/(9790*((math.pi/4)*(D*D)/(1000*1000))))*((1/1.05)-1)

print "h2=",round(h2*1000,2),"mm"
        
print "h2 will be below the marking corresponding to relative density of 1.0"
h1= 54.76 mm
h2= -49.54 mm
h2 will be below the marking corresponding to relative density of 1.0

Example 2.58 Page No48

In [14]:
#variable initialisation


az=2.5                     #acceleration  in m/s^2

g=9.81                     #gravity

ga=9.79                    #density 

d=1.5                      #depth in m

#calculation

#(a)When the acceleration is upwards

h=d*(d/2)

F_H=ga*h*(1+az/g)          #Pressure force on a side wall per metre width

print "F_H=",round(F_H,2),"kN"

#(b)When the acceleration is downwards

az=-2.5                    #acceleration in m/s^2

h=d*(d/2)

F_H=ga*h*(1+az/g)          #Pressure force on a side wall per metre width

print "F_H=",round(F_H,3),"kN"
F_H= 13.82 kN
F_H= 8.207 kN