(6) Gas energy equilibrium equation
Calculating equation of gas pressure variation in gas chamber is
dp
dt
¼
RT 0
dM
dt À p dV
dt
V
ð11:39Þ
where
dp Variation of chamber pressure;
V
Front and rear chamber volume;
T 0 Absolute temperature of gas source;
dM Gas mass variation in the chamber;
dV Volume variation of chamber.
dT
dt
¼
TR
pKV
K À 1
ð
ÞT 0
dM
dt
!
À
K À 1
KV
T
dV
dt
ð11:40Þ
where
dT Variation of temperature; other symbols have the same meaning as the
previous.
11.4.3 Numerical Calculation of Large Diameter
Pneumatic DTH Hammer
Based on the above mathematical model and the principle of finite difference, the
program is designed on the platform of MATLAB. The parameters used in the
numerical calculation include valve distribution travel parameters, piston mass, area
at both ends of piston, initial pressure and temperature of the front and rear
chambers, initial displacement, velocity, and acceleration of the piston. For the
pneumatic DTH hammer designed for 600 mm borehole diameter, the piston is
usually made of alloy steel. The diameter of the big end is 285 mm, the diameter of
the small end is 235 mm, and the mass is 230 kg. In the process of large diameter
drilling, high wind pressure is needed to overcome high-pressure resistance. An air
compressor with 1:6 MPa outlet pressure is matched for this design DTH hammer.
When the check valve is opened with a loss of 0:2 MPa and the resistance loss along
the way is neglected, the inlet pressure of the impactor is 1:4 MPa. The simulation
step is set to 0:0001 s. Figure 11.17 shows the flow chart of the numerical simulation program for valveless pneumatic DTH hammer.
11.4 Dynamic Process and Theoretical Model of Large Diameter …
231
Calculating equation of gas pressure variation in gas chamber is
dp
dt
¼
RT 0
dM
dt À p dV
dt
V
ð11:39Þ
where
dp Variation of chamber pressure;
V
Front and rear chamber volume;
T 0 Absolute temperature of gas source;
dM Gas mass variation in the chamber;
dV Volume variation of chamber.
dT
dt
¼
TR
pKV
K À 1
ð
ÞT 0
dM
dt
!
À
K À 1
KV
T
dV
dt
ð11:40Þ
where
dT Variation of temperature; other symbols have the same meaning as the
previous.
11.4.3 Numerical Calculation of Large Diameter
Pneumatic DTH Hammer
Based on the above mathematical model and the principle of finite difference, the
program is designed on the platform of MATLAB. The parameters used in the
numerical calculation include valve distribution travel parameters, piston mass, area
at both ends of piston, initial pressure and temperature of the front and rear
chambers, initial displacement, velocity, and acceleration of the piston. For the
pneumatic DTH hammer designed for 600 mm borehole diameter, the piston is
usually made of alloy steel. The diameter of the big end is 285 mm, the diameter of
the small end is 235 mm, and the mass is 230 kg. In the process of large diameter
drilling, high wind pressure is needed to overcome high-pressure resistance. An air
compressor with 1:6 MPa outlet pressure is matched for this design DTH hammer.
When the check valve is opened with a loss of 0:2 MPa and the resistance loss along
the way is neglected, the inlet pressure of the impactor is 1:4 MPa. The simulation
step is set to 0:0001 s. Figure 11.17 shows the flow chart of the numerical simulation program for valveless pneumatic DTH hammer.
11.4 Dynamic Process and Theoretical Model of Large Diameter …
231