L 4
Inlet length of front chamber (m);
L 5
Exhaust length of rear chamber (m);
A 1
Forced area of piston front chamber (m
2 );
A 2
Forced area of piston rear chamber (m
2 );
m
Piston mass (kg);
p b
External environmental pressure (Pa);
p s
Air compressor supply pressure (Pa);
p 1 ; p 2 Front and rear chamber pressure (Pa);
T b
External ambient temperature (K);
T f
Air compressor supply temperature (K);
T 1 ; T 2 Front and rear chamber temperature (K);
x
Piston displacement (m);
v
Piston speed (m/s);
a
Piston acceleration (m=s
2 );
V 1i ; V 2i Initial volume of front and rear chambers (m
3 );
V 1 ; V 2 Front and rear chamber volume (m
3 );
F 1
Front chamber intake orifice flow area (m
2 );
F 2
Front chamber exhaust orifice flow area (m
2 );
F 3
Rear chamber intake orifice flow area (m
2 );
F 4
Rear chamber exhaust orifice flow area (m
2 );
t
Time step (s).
11.4.3.1 Analysis of the Results of the Whole Working Process
Set the return direction to be positive and the stroke direction to be negative. The
simulation results are as follows. Figure 11.18 shows the velocity–displacement
curve of the piston. The piston moves back from rest to upward with a maximum
velocity of 5:67 m=s and a maximum displacement of 164:1 mm. After that, the
piston starts to make stroke motion, and the velocity is negative (downward). When
the displacement is zero (i.e., when the piston hits the bit), the velocity is 7:07 m=s,
and the whole process takes 0:915 s. According to the above calculation results,
important parameters such as drilling frequency and drilling power of DTH hammer
can be obtained. Figure 11.19 is the pressure–time curve of the front and rear
chambers. The front chambers undergo intake, closure, exhaust, and then closed
and intake in a single cycle. Pressure p 1 decreases from intake pressure 1:4 MPa to
atmospheric pressure and then rises to intake pressure. Rear chamber pressure p 2
undergoes the opposite process.
11.4 Dynamic Process and Theoretical Model of Large Diameter …
233
Inlet length of front chamber (m);
L 5
Exhaust length of rear chamber (m);
A 1
Forced area of piston front chamber (m
2 );
A 2
Forced area of piston rear chamber (m
2 );
m
Piston mass (kg);
p b
External environmental pressure (Pa);
p s
Air compressor supply pressure (Pa);
p 1 ; p 2 Front and rear chamber pressure (Pa);
T b
External ambient temperature (K);
T f
Air compressor supply temperature (K);
T 1 ; T 2 Front and rear chamber temperature (K);
x
Piston displacement (m);
v
Piston speed (m/s);
a
Piston acceleration (m=s
2 );
V 1i ; V 2i Initial volume of front and rear chambers (m
3 );
V 1 ; V 2 Front and rear chamber volume (m
3 );
F 1
Front chamber intake orifice flow area (m
2 );
F 2
Front chamber exhaust orifice flow area (m
2 );
F 3
Rear chamber intake orifice flow area (m
2 );
F 4
Rear chamber exhaust orifice flow area (m
2 );
t
Time step (s).
11.4.3.1 Analysis of the Results of the Whole Working Process
Set the return direction to be positive and the stroke direction to be negative. The
simulation results are as follows. Figure 11.18 shows the velocity–displacement
curve of the piston. The piston moves back from rest to upward with a maximum
velocity of 5:67 m=s and a maximum displacement of 164:1 mm. After that, the
piston starts to make stroke motion, and the velocity is negative (downward). When
the displacement is zero (i.e., when the piston hits the bit), the velocity is 7:07 m=s,
and the whole process takes 0:915 s. According to the above calculation results,
important parameters such as drilling frequency and drilling power of DTH hammer
can be obtained. Figure 11.19 is the pressure–time curve of the front and rear
chambers. The front chambers undergo intake, closure, exhaust, and then closed
and intake in a single cycle. Pressure p 1 decreases from intake pressure 1:4 MPa to
atmospheric pressure and then rises to intake pressure. Rear chamber pressure p 2
undergoes the opposite process.
11.4 Dynamic Process and Theoretical Model of Large Diameter …
233