Research On Rock Breaking Characteristics Of Self-excited Oscillating Pulsed Water Jet And Its Nozzle Structure Design

The self-excited oscillation pulsed water jet,as a new type of pulsed jet,has the characteristics of high efficiency,simple preparation and low cost,and has a wide range of application prospects in the field of underground engineering.However,due to the opacity and instantaneous fragmentation of the rock,it is difficult to capture the internal damage evolution characteristics of the rock under the impact of the water jet,which to a certain extent restricts the pace of exploring the rock-breaking mechanism of the water jet.The characteristics of damage evolution under the impact of oscillating pulsed water jets are particularly important for the research and application of the mechanism of pushing water jets to break rocks.In this thesis,a water jet rock breaking model is established by numerical simulation technology,and the rock breaking damage evolution process of abrasive jet,self-excited oscillation pulsed abrasive jet and self-excited oscillation pulsed water jet is explored through comparative experiments,and the main factors of self-excited oscillation pulsed jet are studied.The parameters have significant effects on the volume and depth of rock fragmentation,and on this basis,the structural parameters of the self-oscillation pulsed water jet nozzle are optimized.The main research results are as follows.Based on the SPH-FEM coupling algorithm,the numerical model of rock impacting by self-excited oscillation pulsed water jet is established in this thesis.And the numerical models of self-oscillation pulsed abrasive jet and abrasive jet breaking rock are established on the basis of the above models.However,the uniform distribution of abrasives in the abrasive jet affects the stability of the rock breaking results.To reduce the impact of the problem on the results,genetic algorithm is applied to optimize the uniform distribution of abrasive particles in the jet,and the resulting stability is increased by 18.43 times.This thesis compares and analyzes the stress wave cloud diagrams of coal under the impact of abrasive jet,pulsed abrasive jet and pulsed water jet.It can be seen the coal are only impacted by a stress wave under the impact of abrasive jet,while the part of the coal was subjected to the secondary impact of the stress wave under the impact of the pulsed abrasive jet and pulsed water jet.By comparing the axial and radial velocity distribution diagrams during the impact of the three jets,it can be seen that the pulsed abrasive jet and the pulsed water jet have radial velocity during the impact process.This radial velocity is the cause of the impact of the secondary stress wave on the coal.This thesis explores the significant and interactive relationship between the key parameters of jet uniform velocity A,jet amplitude B,and jet frequency C on the response characteristics of punching depth and punching volume through a three-level two-factor experimental design.The analysis shows that the order of the significant influence of key parameters on the punching volume is:A>B>C>AC>AB>BC.When the average jet velocity changes from low to high,the effect of jet frequency on the punching volume increases.Large;the order of the significant influence of key parameters on the punching depth is:A>C>B>BC>AC>AB,and the significance of BC,AC and AB is relatively close.In addition,this thesis combines the multi-objective particle swarm algorithm and gray theory to optimize the self-oscillating pulsed water jet nozzle.The outlet diameter d₂,the oscillation cavity diameter l_c and the oscillation cavity length D_c of the optimized nozzle are respectively are 2.24mm,33.36mm and 7.98mm,respectively.The natural frequency and The maximum amplitude is 631.45rad/s and 1.1769,respectively.Compared with the nozzle optimization before,the natural frequency and maximum amplitude are increased by 8.1%and 18.89%,respectively.