| With the increase of the depth and difficulty of the exploitation of coal resources,how to intensify gas drainage and improve the permeability of coal seams has become an important aspect that restricts the green mining of coal science.At present,hydraulic cutting technology has become one of the main technical means for controlling coal mine gas disasters and realizing pressure relief and relieving of coal seams.The high pressure gas-liquid two-phase jet,as a new and efficient multi medium strong jet,is superior to the traditional single medium jet in erosion rock breaking performance.At present,the research on the two-phase medium jets mainly focuses on the rock breaking test under the influence of the single-factor jet parameters.There is a lack of in-depth research on the multi-parameter and the coupling between the two phases.In view of the existing problems,based on the existing gas-liquid two-phase jet technology,this paper uses theoretical research,physical similarity tests and numerical simulations to characterize the kinetics of gas-phase high pressure bubble collapse and the interaction of two-phase jet parameters.The role and the comprehensive research of fracture mechanism of rock breaking are studied.The main research results obtained are as follows:Through the establishment of different gas content bubble motion equations and numerical simulation,the space-time evolution rule of the collapse of the micro-cavity was obtained by the impact test,and the shock characteristics of the high-pressure gas collapse were revealed.The results show that the collapse of cavitation is a pulsating evolution process,and its evolution process is divided into three stages: differential pressure driven growth,deformation shrinkage,and collapsed jet production.The collapse jet will produce a strong impact dynamic pressure.The closer to the target surface,the greater the differential pressure,the higher the dynamic pressure peak collapse,and the shorter the breakdown duration.The jet pulsation frequency increases due to the collapse of the collapse of the vacuole.The closer to the target distance,the higher the jet pressure,the higher the impact frequency of the two-phase jet.Using interaction experiments,it was verified that the combination of jet parameters existed interactions,and the factor combinations affecting the response characteristics such as depth of punching were determined.Through similar experiments,it is found that the depth of punching is positively correlated with the change of jet pressure,while the gas content is characterized by “lagging”.Under high pressure conditions,the main effect of jet pressure is more significant than the target distance;under low pressure conditions,the impact volume is affected by the target distance greater than the jet pressure.The erosion surface area increases first and then decreases with the increase of the nozzle diameter.The greater the jet pressure,the smaller the erosion surface area is affected by the nozzle diameter.The strain response characteristics of coal samples with different parameters under different confining pressure and static load conditions were studied and analyzed.It is found that the surface damage of coal samples with low pressure parameters is greater than that of high pressure,and there is a reasonable optimal combination of the interaction between jet pressure and gas content.The impact pressure affects the time of crushing,and the effect of crushing is limited by the diameter.Under low confining pressure,the surface strain changes significantly,lateral cracks appear and the depth of crack propagation becomes smaller.Under the condition of high confining pressure,the coal-rock fractures show longitudinal penetration characteristics.Studying the pore structure and crack propagation model of coal through microscopic and macroscopic scales,the results show that: after the impact of jet impact,the microscopic pores of coal are fractured and intersect with the original fractures.The higher the gas content,the greater the jet pressure.Near the edges of the fracture,the impact pits are densely distributed.Compared with the original coal rock,the fractal dimension increases slightly,and the fractal feature is more obvious.High-pressure gas-liquid two-phase jet rock breaking is caused by high-pressure liquid-phase pulsation shock and stress wave,high-pressure bubble collapse multi-stage collapse of micro-jets,and original fractures of coal and rock,under the action of gasliquid-solid three-phase coupling.result.The multi-pulse action of high-pressure gas phase and high-speed liquid phase is the main cause of rock fracture.The high-pressure liquid phase acts on the surface of the coal body in the form of impact loads and stress waves,and rock mass damage occurs and accumulates.The primary cracks in the continuous collapse of high-pressure gas bubbles under the impact of micro-jets extend in the circumferential direction to form bifurcation secondary cracks,and the secondary cracks continue to be formed by new cracks caused by the action of the “expansionintrusion-damage-breakthrough” of the voids.Through and make the rock broken.The research results of this dissertation have important guiding significance for understanding the comprehensive rock breaking law and fracturing mechanism of gasliquid two-phase jets,improving the existing hydraulic kerf technology,and improving the effect of slicing rock fragmentation.During the research period,one related Chinese EI paper was published and 7 related invention patents were authorized. |
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