Sensitivity Analysis and Optimization of Double Action Hydraulic Hammer

Geothermal energy is a renewable and clean energy that coming from deep earth, With the background of energy crisis and environmental pollution, it is important reasonable to develop geothermal energy resources. In many enhanced geothermal system (EGS) projects, very deep and hard rock needs to be drilled, however the poor drillability causes conventional drilling methods very low efficiency and rising cost. Therefore, it is of great significance to develop efficient drilling tools to hot dry rock. In this paper a double acting hydraulic hammer is designed based on percussion and rotation mechanism targeting rocks with high hardness and high strength, However it is hard to optimize various parameters based on experience and experiments, for the matching relationships of inner pressure is complex and the impact performance is influenced by many factors. In this paper, the operating principle of double action hydraulic hammer was explained, the force applied to the critical moving components including piston and valve was analyzed and the double action hydraulic hammer model of piston and valve in each operating stage was established. With the system pressure being set at 6MPa, the percussion frequency was 25Hz predicted by the hydraulic simulation compared to 23Hz in experiments with a difference of 8.7%, which is acceptable in engineering applications and validates the hydraulic model. The sensitivity of parameters to performance was analyzed by DOE test design method. Key parameters affecting impact performance were determined by Pareto diagram. The influence trend on performance of key parameters was analyzed by main effect. The coupling effect among parameters is analyzed through interaction effect. And the following research results were obtained. First, the displacement of pump,the diameter of piston and valve,the mass of piston have great influence on impact energy, the order of contribution is the displacement of pump, the diameter of piston and valve, and the mass of piston . Second, the impact energy increases with the displacement of pump. Third, the impact energy has a quadratic relationship with the diameter of piston and valve. Fourth, the impact energy increases with the mass of piston and valve.Based on sensitivity analysis and combined with actual drilling needs, it is of great significance to design a double action hydraulic hammer with optimized impact performance to meet drilling requirements, which is great significance to carry out EGS project with high efficiency and low cost.