Effects of the initiation position on the damage and fracture characteristics of linear-charge blasting in rock

To study the effects of the initiation position on the damage and fracture characteristics of linear-charge blasting, blasting model experiments were conducted in this study using computed tomography scanning and three-dimensional reconstruction methods. The fractal damage theory was used to quantify the crack distribution and damage degree of sandstone specimens after blasting. The results showed that regardless of an inverse or top initiation, due to compression deformation and sliding frictional resistance, the plugging medium of the borehole is effective. The energy of the explosive gas near the top of the borehole is consumed. This affects the effective crushing of rocks near the top of the borehole, where the extent of damage to Sections Ⅰ and Ⅱ is less than that of Sections Ⅲ and Ⅳ. In addition, the analysis revealed that under conditions of top initiation, the reflected tensile damage of the rock at the free face of the top of the borehole and the compression deformation of the plug and friction consume more blasting energy, resulting in lower blasting energy efficiency for top initiation. As a result, the overall damage degree of the specimens in the top-initiation group was significantly smaller than that in the inverse-initiation group. Under conditions of inverse initiation, the blasting energy efficiency is greater, causing the specimen to experience greater damage. Therefore, in the engineering practice of rock tunnel cut blasting, to utilize blasting energy effectively and enhance the effects of rock fragmentation, using the inverse-initiation method is recommended. In addition, in three-dimensional(3D) rock blasting, the bottom of the borehole has obvious end effects under the conditions of inverse initiation, and the crack distribution at the bottom of the borehole is trumpet-shaped. The occurrence of an end effect in the 3D linear-charge blasting model experiment is related to the initiation position and the blocking condition.

An improved initial rotor position estimation method using high-frequency pulsating voltage injection for PMSM

High frequency pulsating voltage injection method is a good candidate for detecting the initial rotor position of permanent magnet synchronous motor.However,traditional methods require a large number of filters,which leads to the deterioration of system stability and dynamic performance.In order to solve these problems,a new signal demodulation method is proposed in this paper.The proposed new method can directly obtain the amplitude of high-frequency current,thus eliminating the use of filters,improving system stability and dynamic performance and saving the work of adjusting filter parameters.In addition,a new magnetic polarity detection method is proposed,which is robust to current measurement noise.Finally,experiments verify the effectiveness of the method.

A method of initial welding position guiding for arc welding robot based on visual servo control

In order to solve the visual guiding task of initial welding position for arc welding robot, this paper presents a practice prone image based visual servo control strategy without calibration, and we perform validating experiments on a nine DOF arc welding robot system. Experimental results illustrate presented method has the function to fulfill the task of welding robot initial positioning with certain anti jamming ability. This method provides a basis for guiding welding gun to initial welding pose with real typical seam’s image properties to replace flag block properties, and is a significant exploit to realize visual guiding of initial welding position and seam tracing in robot welding system.

Experimental Study on the Initial Position Distribution of Taylor Bubbles in Cryogenic Upward Inclined Tubes

An experimental study was carried out to understand the phenomena of the boiling flow of liquid nitrogen in inclined tubes with closed bottom by using the high speed digital camera.The tubes in the experiment are 0.018 m and 0.014 m in inner diameter and 1.0 m in length.The range of the inclination angles is 0-45° from the vertical.The statistical method is employed to analyze the experimental data.The experiment was focused on the effect of the inclination angle on the initial position distribution of Taylor bubbles.The formation criterion of Taylor bubbles was confirmed by analyzing the images of Taylor bubbles.The experimental results show that the initial position of Taylor bubble increased first,and then decreased with the increasing inclination angle,with the maximum at 30°.The standard deviation of the initial position of Taylor bubble in tubes was different with different inner diameters.The lognormal shape was fitted to the measured the initial position distributions of Taylor bubbles in the cryogenic tubes.

Numerical model for homogeneous cohesive dam breaching due to overtopping failure

Based on the large-scale model tests, a simplified dam breach model for homogeneous cohesive dam due to overtopping failure is put forward. The model considers headcut erosion as one of the key homogeneous cohesive dam breaching mechanisms and we calculate the time-averaged headcut migration rate using an energy-based empirical formula. A numerical method is adopted to determine the initial scour position at the downstream slope in terms of the water head and dam height, and the broad-crested weir equation is utilized to simulate the breach flow. The limit equilibrium method is used to analyze the stability of breach slope during the breach process. An iterative method is developed to simulate the coupling process of soil and water at each time step. The calculated results of three dam breach cases testify the reasonability of the model, and the sensitivity studies of soil erodibility show that sensitivity is dependent on each test case's soil conditions. In addition, three typical dam breach models, NWS BREACH, WinDAM B, and HR BREACH, are also chosen to compare with the proposed model. It is found that NWS BREACH may have large errors for cohesive dams, since it uses a noncohesive sediment transport model and does notconsider headcut erosion, WinDAM B and HR BREACH consider headcut erosion as the breaching mechanism and handle well homogeneous cohesive dam overtopping failure, but overall, the proposed model has the best performance.

BLOW-UP OF THE SOLUTION FOR A CLASS OF POROUS MEDIUM EQUATION WITH POSITIVE INITIAL ENERGY

This paper deals with a class of porous medium equation ut=△u^m＋f（u）with homogeneous Dirichlet boundary conditions. The blow-up criteria is established by using the method of energy under the suitable condition on the function f（u）.

Exponential Growth of Solutions for Nonlinear Coupled Viscoelastic Wave Equations with Degenerate Nonlocal Damping and Source Terms

This paper is concerned with a system of nonlinear viscoelastic wave equations with degenerate nonlocal damping and memory terms.We will prove that the energy associated to the system is unbounded.In fact,it will be proved that the energy will grow up as an exponential function as time goes to infinity,provided that the initial data are positive initial energy.

A computational study of a capsule lateral migration in microchannel flow

A numerical method is used to model a capsule migration in a microchannel with small Reynolds number Re = 0.01. The capsule is modeled as a liquid drop sur- rounded by a neo-Hookean elastic membrane. The numer- ical model combines immersed boundary with lattice Boltz- mann method （IB-LBM）. The LBM is used to simulate fixed Cartesian grid while the IBM is utilized to implement the fluid-structure interaction by a set of Lagrangian moving grids for the membrane. The effect of shear elasticity and bending stiffness are both considered. The results show the significance of elastic modulus and initial lateral position on deformation and morphological properties of a circular cap- sule. The wall effect becomes stronger as the capsule ini- tial position gets closer to the channel wall. As the elastic modulus of membrane increases, the capsule undergoes less pronounced deformation and velocity in direction x is de- creased, thus, the capsule motion is slower than the back- ground flow. The best agreement between the present model and experiments for migration velocity takes place for the capsule with normal to moderate membrane elastic modulus. The results are in good agreement with experiment study of Coupier et al. and previous numerical studies. Therefore, the IB-LBM can be employed to make prediction in vitro and in vivo studies of capsule deformation.

Initial position estimation strategy for a surface permanent magnet synchronous motor used in hybrid electric vehicles

A novel nonlinear model for surface permanent magnet synchronous motors（SPMSMs） is adopted to estimate the initial rotor position for hybrid electric vehicles（HEVs）. Usually, the accuracy of initial rotor position estimation for SPMSMs relies on magnetic saturation. To verify the saturation effect, the transient finite element analysis（FEA） model is presented first. Hybrid injection of a static voltage vector（SVV） superimposed with a high-frequency rotating voltage is proposed. The magnetic polarity is roughly identified with the aid of the saturation evaluation function, based on which an estimation of the position is performed. During this procedure, a special demodulation is suggested to extract signals of iron core saturation and rotor position. A Simulink/MATLAB platform for SPMSMs at standstill is constituted, and the effectiveness of the proposed strategy is verified. The proposed method is also validated by experimental results of an SPMSM drive.

Application of Image Morphology in Detecting and Extracting the Initial Welding Position

A method of image morphology in detecting and extracting the initial welding position during the autonomous welding process is described.During the process,firstly visual sensing technology is used to capture the straight seam image,and secondly the image edges are detected by morphological corrosion edge detection algorithm,with which can retain the critical information while filter other interferences effectively at the same time.Then morphological processing algorithm is used to conduct the direction of filter by selecting the multidirectional linear structuring elements and finally get the initial weld position point coordinates with the Hough transform.The algorithm is simple,rapid,self-adaptability with high accuracy for interferences except long lines so as to accomplish the entire process of detecting the initial welding position.It can meet the practical demands of automatic guidance for robotic welding.

Ozonation of aromatic monomer compounds in water: factors determining reaction outcomes

For aromatic monomer compounds (AMCs), ozonation outcomes were usually predicted by the substituents of the benzene ring based on the electron inductive effect. However, the predicted results were occasionally unreliable for complex substituents, and other factors caused concern. In this study, p-chloronitrobenzene (p-CNB) and ibuprofen (IBP) were selected for ozonation. According to the electron inductive theory, p-CNB should be less oxidizable, but the opposite was true. The higher rates of p-CNB were due to various sources of assistance. First, the hydroxyl radical (•OH) contributed 90 % to p-CNB removal at pH 7.0, while its contribution to IBP removal was 50 %. Other contributions came from molecular O3 oxidation. Second, p-CNB achieved 40 % of the total organic carbon (TOC) removal and fewer by-product types and quantities, when compared to the results for IBP. Third, the oxidation of p-CNB started with hydroxyl substitution reactions on the benzene ring;then, the ring opened. However, IBP was initially oxidized mainly on the butane branched chain, with a chain-shortening process occurring before the ring opened. Finally, the degradation pathway of p-CNB was single and consumed fewer oxidants. However, both branches of IBP were attacked simultaneously, and three degradation pathways that relied on more oxidants were proposed. All of these factors were determinants of the rapid removal of p-CNB.

Remarks on Blow-Up Phenomena in p-Laplacian Heat Equation with Inhomogeneous Nonlinearity

We investigate the p-Laplace heat equation ut-△_(p)u=ζ(t)f(u)in a bounded smooth domain.Using differential-inequality arguments,we prove blow-up results under suitable conditions onζ,f,and the initial datum u_(0).We also give an upper bound for the blow-up time in each case.

Existence and Uniqueness of Positive Solutions to Sublinear-Linear Initial Value Problems

Existence and uniqueness conditions for nonnegative solutions to initial value prob- lems of general sublinear-linear differential equations are obtained.They extend the uniqueness theorem due to H.Murakami~[6] and the main results of H.G.Kaper and M.K.Kwong~[4].