# Influence of Nonstationary Processes in Drill Rigs on the Durability of Structural Elements
## 5 Calculation Results of Nonstationary Processes in the Electromechanical System of the Drill Rig  
Calculation results of nonstationary processes occurring in the lifting system of a UKB-4P drill rig, which is equipped with an SKB-4 drill machine and an AO2-71-4 asynchronous motor of 22 kW power, are considered. The height of the drill rig mast is 13 m, which provides drill pipe stands of 9-9.5 m long. The diameter of drill pipes can be 42 mm, 50 mm, or 54 mm. The well is assumed to be drilled with one tool, which eliminates the need to replace the bit during the drilling process and, accordingly, while lowering the string into the well, followed by heavy braking conditions. In this case, technological operations for the lifting drill string are the heaviest operation modes in the drill rig.  
For studying start-up processes, the following values of parameters of mechanical systems were taken: \(u=13.07\); \(j_{1}=0.99\) kg\(\cdot\)m\({}^{2}\); \(j_{2}=1.55\) kg\(\cdot\)m\({}^{2}\); \(m_{1}=206.5\) kg; \(m_{2}=39.6\) kg; \(m_{3}=23.9\) kg; \(c_{d}=1200.0\) MN/m; \(c_{r}=1.9\) MN/m; \(\forall_{d}=482.0\) N\(\cdot\)s/m; \(\forall_{r}=2.0\) N\(\cdot\)s/m; \(\alpha=0\); \(r_{p}=0.13\) m; \(k=2\); \(n=1\); \(A_{1}=590\) mm\({}^{2}\) (pipe diameter is 42 mm); \(E=2.1\cdot 10^{5}\) MPa; \(\rho_{1}=9066.0\) kg/m\({}^{3}\); \(\rho=1200\) kg/m\({}^{3}\); \(b_{1}=0.4\) s\({}^{-1}\); \(\rho_{0}=500\) m; \(\alpha_{0}=0.1\) rad;\(f=0.1\).  
Figures 2-4 represent calculation results of the lifting process of drill pipe string with a diameter of 42 mm and a length of 455.0 m. The excess torque of the friction device, through which the lifting system is accelerated, was 60 N\(\cdot\)m.  
Graphs of angular velocities and moments (Figures 2 and 3) demonstrate acceleration of the driven part in the lifting mechanism, as well as the occurrence of repeated slippage in the friction device due to the excitation of intensive oscillations in a mechanical system. Graphic dependencies shown in Figure 4 indicate that the total forces in the string, wireline, and mast construction carry significant dynamic components, which can have an essential effect on the strength and durability of structural elements. As the curves shown in Figure 5 testify, the maximum force in the wireline, and, correspondently, maximum forces in the mast and drill string, significantly depend on the length of transported string \(l_{max}\), transmitting ratio of the drive mechanism, and the excess torque of the friction device.  
Figure 3: Time dependences of the moment for asynchronous motor (blue curve) and friction moment in friction device reduced to motor shaft (red curve).  
Figure 2: Time dependences of angular velocities for motor rotor shaft (blue curve) and a drawworks drum reduced to motor shaft (red curve).  
Dynamic phenomena must be considered both in the design process of drilling complexes and during their operation in order to justify the selection of strength reserves and increase the reliability of lifting system elements.  
Figure 4: Time dependences of lifting wireline tension force (blue curve), force in the upper extreme section of the drill string (green curve), and force acting by the wireline system on the drilling mast (red curve).  
Figure 5: Dependences of the maximal tension force of the wireline on the length of the drill pipe string for different values of excess torque of the friction device.