Method of testing for dynamic output forces from jet elements is studied, the handwidth is large in testing with this method. By establishing a model of the test system and simulating it, principles of how inherent fe...Method of testing for dynamic output forces from jet elements is studied, the handwidth is large in testing with this method. By establishing a model of the test system and simulating it, principles of how inherent features of the test system affect the dynamic force test are found out. Thus a theoretical foundation is given for the design and error modification to the actual test system.展开更多
To analyze the errors of processing data, the testing principle for jet elements is introduced and the property of testing system is theoretically and experimentally studied. On the basis of the above, the method of p...To analyze the errors of processing data, the testing principle for jet elements is introduced and the property of testing system is theoretically and experimentally studied. On the basis of the above, the method of processing data is presented and the error formulae, which are the functions of the testing system property, are derived. Finally, the methods of reducing the errors are provided. The measured results are in correspondence with the theoretical conclusion.展开更多
The basic principle and numerical technique for simulating two three-dimensional bubbles near a free surface are studied in detail by using boundary element method. The singularities of influence coefficient matrix ar...The basic principle and numerical technique for simulating two three-dimensional bubbles near a free surface are studied in detail by using boundary element method. The singularities of influence coefficient matrix are eliminated using coordinate transformation and so-called 4π rule. The solid angle for the open surface is treated in direct method based on its definition. Several kinds of configurations for the bubbles and free surface have been investigated. The pressure contours during the evolution of bubbles are obtained in our model and can better illuminate the mechanism underlying the motions of bubbles and free surface. The bubble dynamics and their interactions have close relation with the standoff distances, buoyancy parameters and initial sizes of bubbles. Completely different bubble shapes, free surface motions, jetting patterns and pressure distributions under different parameters can be observed in our model, as demon- strated in our calculation results.展开更多
Based on an analysis of the factors affecting rock breaking and the coupling between rock and fluid during water jet drilling, the rock damage model and the damage-coupling model suitable for the whole rock breaking p...Based on an analysis of the factors affecting rock breaking and the coupling between rock and fluid during water jet drilling, the rock damage model and the damage-coupling model suitable for the whole rock breaking process under the water jet is established with continuous damage mechanics and micro-damage mechanics. The evolvement of rock damage during swirling water jet drilling is simulated on a nonlinear FEM and dynamic rock damage model, and a decoupled method is used to analyze the rock damage. The numerical results agree with the test results to a high degree, which shows the rock breaking ability of the swirling water jet is strong. This is because the jet particle velocity of the swirling water jet is three-dimensional, and its rock-breaking manner mainly has a slopping impact. Thus, the interference from returning fluid is less. All these aspects make it easy to draw and shear the rock surface. The rock breaking process is to break out an annular on the rock surface first, and then the annular develops quickly in both the radial and axial directions, the last part of the rock broken hole bottom is a protruding awl. The advantage of the swirling water jet breaking rock is the heavy breaking efficiency,large breaking area and less energy used to break rock per unite volume, so the swirling water jet can drill in a hole of a large diameter.展开更多
This paper focuses on the underpinning-induced ground movement due to jet-grouting. Jet-grouting technique can cause distortions as a result of an inaccurate processing sequence and/or errors made at different stages ...This paper focuses on the underpinning-induced ground movement due to jet-grouting. Jet-grouting technique can cause distortions as a result of an inaccurate processing sequence and/or errors made at different stages of work execution. The aim of this paper is to determine the minimum value of such movement on the basis of the findings obtained at two similar construction sites located in the Historical Center of Moscow, considering that the maximum value is usually unpredictable. Numerical simulation of the process of soil eroding agrees well with the observational data at the current stage. It was found that the minimum value of deformations （only settlement was considered in this study） due to jetgrouting is no less than 2-3 mm. By contrast, the negative scenario of deformation due to foundation underpinning is clearly demonstrated. Also, this paper provides some general solutions for excavation supporting system as well as for underpinning design.展开更多
In the last two decades synthetic jet actuators have gained much interest among flow control techniques due to their short response time, high jet velocity and absence of traditional piping, that matches the requireme...In the last two decades synthetic jet actuators have gained much interest among flow control techniques due to their short response time, high jet velocity and absence of traditional piping, that matches the requirements of reduced size and low weight. A synthetic jet is generated by the diaphragm oscillation (generally driven by a piezo- electric element) in a relatively small cavity, producing periodic cavity pressure variations associated to cavity volume changes. The high pressure air exhausts through an orifice, converting membrane elastic energy in jet kinetic energy. This review paper faces the development of various lumped-element models (LEM) as practical tools to design and manufacturing actuators. LEM can predict quickly device performances such as frequency response in terms of membrane displacement, cavity pressure and jet velocity, as well as efficiency of energy conversion of input Joule power into useful kinetic power of air jet. Actuator performance is analyzed also by varying typical geometric parameters such as cavity height and orifice diameter and length, through a proper dimensionless form of the governing equations.展开更多
In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity ve...In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity vectors and stream function curves are obtained. Using the Prandtl theory, this paper derives the free jet velocity and the jet bunch width in a half-space, the latter of which is amended by experiment. The results obtained in this paper are applied to micro-type high pressure water jet cleaner and the ejector of rocket engine.展开更多
The numerical simulation method to study rock breaking process and mechanism under high pressure water jet was developed with the continuous mechanics and the FEM theory. The rock damage model and the damage-coupling ...The numerical simulation method to study rock breaking process and mechanism under high pressure water jet was developed with the continuous mechanics and the FEM theory. The rock damage model and the damage-coupling model suited to analyze the whole process of water jet breaking rock were established with continuum damage mechanics and micro damage mechanics. The numerical results show the dynamic response of rock under water jet and the evolvement of hydrodynamic characteristic of jet during rock breaking is close to reality, and indicates that the body of rock damage and breakage under the general continual jet occurs within several milliseconds, the main damage form is tensile damage caused by rock unload and jet impact, and the evolvement of rock damage shows a step-change trend. On the whole, the numerical results can agree with experimental conclusions, which manifest that the analytical method is feasible and can be applied to guide the research and application of jet breaking rock theory.展开更多
文摘Method of testing for dynamic output forces from jet elements is studied, the handwidth is large in testing with this method. By establishing a model of the test system and simulating it, principles of how inherent features of the test system affect the dynamic force test are found out. Thus a theoretical foundation is given for the design and error modification to the actual test system.
文摘To analyze the errors of processing data, the testing principle for jet elements is introduced and the property of testing system is theoretically and experimentally studied. On the basis of the above, the method of processing data is presented and the error formulae, which are the functions of the testing system property, are derived. Finally, the methods of reducing the errors are provided. The measured results are in correspondence with the theoretical conclusion.
基金supported by the Funds for Creative Research Groups of China (50921001)the State Key Development Program for Basic Research of China (2010CB832704)
文摘The basic principle and numerical technique for simulating two three-dimensional bubbles near a free surface are studied in detail by using boundary element method. The singularities of influence coefficient matrix are eliminated using coordinate transformation and so-called 4π rule. The solid angle for the open surface is treated in direct method based on its definition. Several kinds of configurations for the bubbles and free surface have been investigated. The pressure contours during the evolution of bubbles are obtained in our model and can better illuminate the mechanism underlying the motions of bubbles and free surface. The bubble dynamics and their interactions have close relation with the standoff distances, buoyancy parameters and initial sizes of bubbles. Completely different bubble shapes, free surface motions, jetting patterns and pressure distributions under different parameters can be observed in our model, as demon- strated in our calculation results.
文摘Based on an analysis of the factors affecting rock breaking and the coupling between rock and fluid during water jet drilling, the rock damage model and the damage-coupling model suitable for the whole rock breaking process under the water jet is established with continuous damage mechanics and micro-damage mechanics. The evolvement of rock damage during swirling water jet drilling is simulated on a nonlinear FEM and dynamic rock damage model, and a decoupled method is used to analyze the rock damage. The numerical results agree with the test results to a high degree, which shows the rock breaking ability of the swirling water jet is strong. This is because the jet particle velocity of the swirling water jet is three-dimensional, and its rock-breaking manner mainly has a slopping impact. Thus, the interference from returning fluid is less. All these aspects make it easy to draw and shear the rock surface. The rock breaking process is to break out an annular on the rock surface first, and then the annular develops quickly in both the radial and axial directions, the last part of the rock broken hole bottom is a protruding awl. The advantage of the swirling water jet breaking rock is the heavy breaking efficiency,large breaking area and less energy used to break rock per unite volume, so the swirling water jet can drill in a hole of a large diameter.
文摘This paper focuses on the underpinning-induced ground movement due to jet-grouting. Jet-grouting technique can cause distortions as a result of an inaccurate processing sequence and/or errors made at different stages of work execution. The aim of this paper is to determine the minimum value of such movement on the basis of the findings obtained at two similar construction sites located in the Historical Center of Moscow, considering that the maximum value is usually unpredictable. Numerical simulation of the process of soil eroding agrees well with the observational data at the current stage. It was found that the minimum value of deformations （only settlement was considered in this study） due to jetgrouting is no less than 2-3 mm. By contrast, the negative scenario of deformation due to foundation underpinning is clearly demonstrated. Also, this paper provides some general solutions for excavation supporting system as well as for underpinning design.
文摘In the last two decades synthetic jet actuators have gained much interest among flow control techniques due to their short response time, high jet velocity and absence of traditional piping, that matches the requirements of reduced size and low weight. A synthetic jet is generated by the diaphragm oscillation (generally driven by a piezo- electric element) in a relatively small cavity, producing periodic cavity pressure variations associated to cavity volume changes. The high pressure air exhausts through an orifice, converting membrane elastic energy in jet kinetic energy. This review paper faces the development of various lumped-element models (LEM) as practical tools to design and manufacturing actuators. LEM can predict quickly device performances such as frequency response in terms of membrane displacement, cavity pressure and jet velocity, as well as efficiency of energy conversion of input Joule power into useful kinetic power of air jet. Actuator performance is analyzed also by varying typical geometric parameters such as cavity height and orifice diameter and length, through a proper dimensionless form of the governing equations.
文摘In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity vectors and stream function curves are obtained. Using the Prandtl theory, this paper derives the free jet velocity and the jet bunch width in a half-space, the latter of which is amended by experiment. The results obtained in this paper are applied to micro-type high pressure water jet cleaner and the ejector of rocket engine.
基金Project supported by the National Natural Science Foundation of China (Nos.50574062 and 50234030) the Post-Doctoral Science Foundation of China (No.2004035692)
文摘The numerical simulation method to study rock breaking process and mechanism under high pressure water jet was developed with the continuous mechanics and the FEM theory. The rock damage model and the damage-coupling model suited to analyze the whole process of water jet breaking rock were established with continuum damage mechanics and micro damage mechanics. The numerical results show the dynamic response of rock under water jet and the evolvement of hydrodynamic characteristic of jet during rock breaking is close to reality, and indicates that the body of rock damage and breakage under the general continual jet occurs within several milliseconds, the main damage form is tensile damage caused by rock unload and jet impact, and the evolvement of rock damage shows a step-change trend. On the whole, the numerical results can agree with experimental conclusions, which manifest that the analytical method is feasible and can be applied to guide the research and application of jet breaking rock theory.
