# Numerical Simulation on Dynamic Response of Drilling Parameters in Loaded Rock Mass
## 3 Establishment of Numerical Model
### Analysis of Drilling Parameters Under Different Confining Pressure Conditions  
According to the experimental scheme of Table 4, the numerical simulation experiment is carried out, and the variation curve of coal parameters while drilling under different confining pressure conditions and the stress cloud diagram of drilling for 1 s under different confining pressures are obtained as shown in Figures 19 and 20. From the analysis of Figure 19a-c, it can be seen that at the beginning of the drilling operation, the drilling rate and torque immediately show a sharp rise. However, with the continuous advancement of the drill bit, the torque will show a reciprocating fluctuation in a certain range. Regarding the motion mode, the drilling rate of the drill bit has the characteristics of dynamic change with displacement, and its value and direction at any given time are not the same. The instantaneous drilling rate of the drill bit rises rapidly to a certain value at the beginning of drilling, then decreases rapidly, and then shows a non-uniform fluctuation in a large range. Under the condition of 3000 N of thrust and a revolution speed of 60 r/min, different confining pressures are applied to the specimen. The variation curves for the torque and drilling rate with confining pressure are shown in Figure 19d. The analysis shows that the average drilling rate of the drill bit is 71.42 mm/s when the confining pressure is 0 MPa. The average drilling rate of the drill bit is 62.37 mm/s when the confining pressure is 5 MPa. The average drilling rate of the bit is 52.91 mm/s when the confining pressure is 10 MPa. The average drilling rate of the drill bit is 42.85 mm/s when the confining pressure is 15 MPa. When the confining pressure increases from 0 MPa to 15 MPa, the drilling rate decreases from 71.42 mm/s to about 42.85 mm/s. It can be seen from Figure 20 that the drilling depth will gradually decrease with the increase in confining pressure within 1 s of drilling, which is also in line with the trend of a decreasing drilling rate with the increase in the confining pressure in the above analysis. In the absence of confining pressure, the rock stress is concentrated in the contact area of the bit, which is characterized by brittle fracturing, and the rock is easy to disintegrate locally, so the corresponding drilling rate is the fastest. As the confining pressure increases from 0 MPa to 15 MPa, the stress is gradually evenly distributed, the density and strength of the rock are improved, and the drill bit will be subjected to greater resistance during drilling, which ultimately leads to a decrease in the drilling rate. When the confining pressure is 0 MPa, the average torque of the drill bit is 36.16 N\(\cdot\)m. The average torque of the drill bit is 44.82 N\(\cdot\)m when the confining pressure is 5 MPa. The average torque of the drill bit is 58.21 N\(\cdot\)m when the confining pressure is 10 MPa. The average torque of the drill bit is 67.86 N\(\cdot\)m when the confining pressure is 15 MPa. When the confining pressure is increased from 0 MPa to 15 MPa, the torque is increased from 36.16 N\(\cdot\)m to 67.86 N\(\cdot\)m, indicating that with the increase in the confining pressure, the constraint of rock on the drill bit is enhanced, resulting in an increase in the resistance that the drill bit needs to overcome during rotation, which in turn increases the torque. In the range of 0\(\cdot\)5 MPa with lower confining pressure, the increase in torque is relatively gentle, which may be due to the fact that the compaction effect of confining pressure on rock is not significant at this time. In the range of 0\(\cdot\)10 MPa, the torque growth rate is accelerated, indicating that the compaction effect of confining pressure on rock is gradually obvious, the rock strength is increased, and the resistance to the drill bit is increased rapidly.