| Water jet is a stream of dynamic hi-speed fluid with high energy, which has been widely applied in the engineering fields of materials’ cleaning, cutting, crushing, etc. Water jet has the characteristics of highly efficient, non-dust, low-thermal, low-vibration and low energy-consumption. Water jet breaking rock technology is one of the main branches of the water jet technology’s application and it has played a crucial role in the engineering fields of coal mining roadway tunneling, coal-seam fracturing hole’s drill-ing, coal-seam hydraulic gaps and oil & gas drilling.The waterjet-target impat will induce huge water hammer pressure in a short time. This phenomenon is called the effect of water hammer pressure. The previous research focuses on a single spherical droplets or the normal-shaped ideal water jet impacting pressure. Thereafter, it comes to the water hammer pressure’s calculating formula. In the actual engineering practice, water jet’s shape will variously change and almost are di-vergent. The jet’s impacting loading are quite far from the theoretical calculating num-erals. Thus, for the engineering’s actual needs, and to deepen the understanding of water jet impacting water hammer pressure, the studies on hi-speed continuous jet’s impacting transient dynamic characteristics will make huge engineering and scientific differences. This thesis includes the following five main research focuses. a) The calculating formu-la for the radius of the area where water hammer pressure produced has been deduced when the water jet impacting the targets in different shapes by adopting the shock wave theory, fluid mechanics, plane geometry, trigonometric function transform and other fundamental knowledge. b) According to the principle whether waterjet shape is condu-cive to the fluid spreading, the shape of the nozzles has been successively designed as two kinds: ① shape with symmetrical center: round, square and cross; ② shape with symmetrical axis: ellipse and triangle. The research aims to analyze the water pressure’s change rules while waterjet with nozzles in different shapes impacting targets, and also aims to reveal the water pressure’s production mechanism. c) Considering the fact that shape of the target surface will affect the fluid spreading after the impacting, this thesis simplify and design four types of target surface: concave, convex, plane and slope. The former three types form central symmetry and the fourth type is axis symmetry. d) The waterjet speed has direct effects on its impacting pressure. Meanwhile, change of the waterjet speed will result in different shock wave speed and will further influence the area where waterjet being disturbed, as well as its duration. Without changing the other conditions, this thesis just studies the effects waterjet speed on water hammer pressure. e) Based on the revised water hammer calculating model, this thesis conducted the ex-periment of waterjet impacting and breaking rocks. Besides, the correctness of the mod-el has been verified with the inversion method. The main achievements are gained as follow:①Through the application of stress wave theory, fluid mechanics, plane geometry, the calculating formula of water hammer pressure forming area Rwh=F1(v/c,R,θ)for hi-speed jet impacting flat, concave, convex, and cant has been conducted, as well as the time lasting calculating formula ηwh=F2(v,c,R,θ). Theoretically, the affecting law for water hammer pressure from the jet speed v, stress wave speed c, jet radius and tilt angle θ is revealed, and the correctness of all models established has been testified through engineering practice.②Adopting the method of hi-speed video, the process of water jet impacting target with round nozzle, square nozzle, triangular nozzle, cross-shaped nozzles and elliptical nozzle is analyzed. Thus, the shapes of the front parts of the different shaped water jets, speed of the jet center um and the jet’s equivalent diameter De have been obtained. Be-sides, the distributing function of jet speed uy along the radial uy/um=y0-a·exp((y/R)/t).③Applying the hi-speed camera and image processing technology, comprehen-sively consider the jet’s internal law when water jets in different shapes impacting flat, concave, convex, and cant. To track the different fluid particle trajectories, the method of numerical simulation is adopted. Thus, the producing mechanism of water hammer pressure is: water jet’s impacting and disturbing causes the fluid’s unable to freely spread to form an highly-compressed area in the center of water jet.④According to the experiment data, adopting the methods of statistical average and data fitting, the revised mathematical model Pwh=A·v2+B·v for the water hammer pressure of hi-speed jet impacting target, together with the revised mathematical model η=M·exp(-v/s)+N for tine lasting. It is shown that the intensity of water hammer pressure will increase as quadratic function by with the water jet’s speed, lasting time will decrease as index form with the jet’s speed.⑤Based on the experiment of water jet impacting rocks, it concluded three kinds of macro cracks: radial cracks, circumferential cracks and cone cracks. It is also re-vealed that water jet impacting stress wave is the dominant factor in resulting in rock’s breaking. The wave equation of stress wave spreading in rocks(Φ(r, t)) is established and the interaction mechanism between stress wave and rock damage is studied theoret-ically.The results of this thesis makes certain contribution to water jet impacting theory, which will help to promote the development of the water jet technology in all walks of life. |
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