Hole Spacing Research Articles

Study on Mechanism of Static Blasting-Induced Hard Rock Fracture Expansion

How to deal with hard rock cheaply and safely is a pressing issue in today’s coal mining. Weakening fractures of hard rock have always been a significant concern in China’s coal mine engineering. In this study, mechanical derivation, laboratory experiments, and numerical simulation research methodologies are used to evaluate the fracturing process of the static crushing agent (SCA). From a mechanical standpoint, the mechanism of fracturing hard rock by a crushing agent is investigated. It is assumed that single-hole fracturing is separated into three stages: the microfracture stage, the fissure development stage, and the breaking stage. The swelling and fracturing properties of SCA were quantitatively analyzed. It was found that the swelling pressure of SCA increased with the increase in pore diameter, and the range of the swelling pressure was 43.5 MPa to 75.1 MPa. SCA exhibited a delayed fracture initiation, but the rate of breakage was relatively high. The cracking effect of a single-hole specimen under no peripheral pressure was simulated using PFC2D, and the results were consistent with experimental observations. The internal dynamic effect, crack extension, distribution characteristics, and the development law of double-hole expansion pressure were analyzed for double-hole specimens with different hole diameters, hole spacings, and circumferential pressures. It was observed that the cracking effect was positively correlated with the pore diameter, while the pore spacing and surrounding pressure were negatively correlated. The size of the expansion pressure was negatively correlated with the pore diameter, while the pore spacing and surrounding pressure were positively correlated.

High quality stealth dicing of sapphire with a picosecond Bessel beam by controlling the polarization direction.

Sapphire is an important substrate material in optoelectronic devices, and it is also widely used as a touch screen panel. In order to achieve high quality cutting of sapphire, the stealth dicing of 500µm thick sapphire by a picosecond Bessel beam is studied in this paper. The influences of laser polarization direction and process parameters on cutting section roughness were studied. By controlling the laser polarization direction, different crack propagation morphologies were obtained. When the polarization direction was vertical to the cutting path, the crack propagation path was straighter, and the sapphire had better cutting quality. The laser processing parameters, including burst mode, hole spacing, and pulse energy, had a significant impact on the cutting section roughness. When the polarization direction was vertical to the cutting path under the optimal process parameters, the cutting section was uniform and flat, with no recondensable particles, no ripples, and no chamfer, and an 89.7nm average roughness of the cutting section could be obtained.

Boosting nitrogen adsorption for photocatalytic ammonia production via tuning electron distribution using zero valent iron as medium

Photocatalytic nitrogen reduction to ammonia plays an important role in agricultural production and now-generation hydrogen storage technology. However, the practicality is limited by low efficiency owing to the poor charge-transfer rate and slow ammonification reactions. Herein, a ternary Fe2O3-Fe-HCNS composite is reported with all-solid-state Z-scheme heterojunction, which zero valent iron (ZVI) with abundant electrons is employed as conductor between hollow g-C3N4 sphere (HCNS) and Fe2O3. ZVI facilitates photogenerated electrons transfer and changes charge distribution on the Fe2O3-Fe-HCNS surface, thus an electron-rich region is formed around HCNS, which improves N2 adsorption and ammonification reaction on the HCNS surface. Moreover, the dual interfacial electric fields are established in the heterojunction, which can promote efficient separation and migration of photo-induced electrons and holes in space, leading to the good photocatalytic performances with the higher ammonia yield (296.30 μmol g−1h−1) and apparent quantum yield (1.38%, 400 nm) in neutral electrolytes. In addition, compared with the catalyst powder, vertical carbon paper supporting Fe2O3-Fe-HCNS catalyst can reduce secondary pollution and facilitate recycling.

Design recommendation of cold-formed steel built-up sections under concentric and eccentric compression

A parametric investigation and design proposal for the back-to-back built-up cold-formed steel (CFS) channel sections with V-stiffeners and Σ-stiffeners under concentric and eccentric loading are presented in this paper. A nonlinear finite element model considering the initial geometric imperfection was developed and validated against experimental results. A total of 594 simulations were conducted involving a variety of slenderness ratios, eccentric axis directions, eccentricity, screw spacing and number of longitudinal holes. Simulation results including the load-carrying capacity, failure modes, ultimate bearing capacity versus eccentricity relationships, and load versus lateral displacement relationships were discussed. The influence of several member parameters on the load-carrying capacity and buckling modes was analyzed. Additionally, the applicability of the design strengths calculated from Chinese standard GB50018–2002 and North American specifications AISI S100–16 was evaluated based on the preliminary experimental results and simulation results. It was shown that both methods are conservative. Finally, a proposed DSM-based interaction equation considering the relationship between P/Pnd and M/Mnd was proposed and evaluated.

Hole control methods in feature-driven topology optimization

Hole control is an important issue in topology optimization. In this work, a comprehensive study is made to address four aspects related to the hole number, shape, size and spacing control. Hole features described by level-set functions (LSFs) are introduced as design primitives and constrained for the hole control requirements in topology optimization. To be specific, the hole number is controlled by means of the initial setting of internal hole features in the design domain. The hole shape is controlled by introducing specific hole features. The hole size is controlled directly by means of design variables describing hole features, and the hole spacing is controlled by limiting the relative positions of hole features. It is shown that different hole control can be simultaneously imposed globally over the whole design domain or in the local regions of the structure. Numerical 2D and 3D examples are used to demonstrate the effectiveness of the proposed methods.

Self-dual black holes in celestial holography

We construct two-dimensional quantum states associated to four-dimensional linearized rotating self-dual black holes in (2, 2) signature Klein space. The states are comprised of global conformal primaries circulating on the celestial torus, the Kleinian analog of the celestial sphere. By introducing a generalized tower of Goldstone operators we identify the states as coherent exponentiations carrying an infinite tower of w1+∞ charges or soft hair. We relate our results to recent approaches to black hole scattering, including a connection to Wilson lines, S\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{S} $$\\end{document}-matrix results, and celestial holography in curved backgrounds.

Blast-Fragmentation Prediction Derived From the Fragment Size-Energy Fan Concept

The size-energy fan concept formulation is developed into a prediction model of the fragment size distribution from blast design and rock mass variables. The fragment size is scaled with a characteristic size of the blast and the rock mass discontinuity spacing and orientation. The energy is scaled with the rock strength and the cooperation degree between adjacent holes. A cooperation function is introduced that modifies the energy with the in-row delay, non-dimensionalized with the P-wave velocity and the holes spacing. The cooperation increases as the delay increases up to a certain value, beyond which the cooperation decreases and the fragmentation is coarser. Several prediction models are presented, using the Swebrec-based fan slopes function of the percent passing as starting point, with subsequent improvements involving alternative formulations of that function, that encompass a non-Swebrec underlying distribution of the fragment size. The models include 12 to 14 parameters, controlling the effect on fragmentation of the variables describing the rock mass, the explosive and initiation sequence, and the blast geometry. The parameters are determined from fits to the data base that was used for the xP-frag model, expanded with seventeen additional blasts. All fragmentation data used are mass size distributions determined by sieving and weighing of blasted muckpiles. The different models are introduced sequentially and discussed. The models presented improve the performance of xP-frag, while including a much smaller number of parameters and, unlike xP-frag, keeping the physically sound size-energy fan pattern, effectively extending its nature from a descriptive frame of the fragmentation-energy relations, to a predictive tool.

Analytical method for distortional buckling load of cold-formed steel members with perforated web under bending moment

In order to reduce weight or meet specific functional requirements, cold-formed steel (CFS) members with perforated webs are widely used in practical engineering. However, these web holes, especially the un-stiffened ones, can result in stress concentrations and section deficiencies, leading to a reduction of the distortional buckling load. Existing specifications, such as the American Iron and Steel Institute (AISI 2016) and Australia New Zealand Standards (AS/NZS 4600:2018), do not fully consider this impact. By simplifying the perforated web into an equivalent beam model and modifying the calculation method of the web rotational stiffness, this paper proposes an analytical method for the distortional buckling load of perforated CFS members with arbitrary hole parameters, including the hole spacing, location, and geometric shape. The proposed method is verified by finite element analysis (FEA) and experiment results in the literature. The FEA result indicates that holes near the compressed flange or with smaller spacing can lead to more reduction in the distortional buckling load. Compared to existing methods, the calculation accuracy of the proposed method has been improved by 2% to 4%.

The Blasting Vibration Characteristics of Layered Rock Mass under High-Pressure Gas Impact

Firstly, the experimental test of blasting vibration was carried out to study the propagation characteristics of the peak particle velocity (PPV) and dominant frequency (DF) of the blasting vibration of layered rock mass under high-pressure gas impact. The test results show that the PPV and DF of blasting vibration of layered rock mass decrease gradually with the increase in distance from the explosion source. The PPV and DF of layered rock mass under the same impact pressure of high-pressure gas are lower than those of single rock mass at the same measuring points. With the increase in hole spacing, the PPV and DF of blasting vibration become smaller, and the blasting effect first becomes better and then worse. Next, the relationship models between the PPV and DF and their influencing factors were deduced by the dimensional analysis method, which can be simplified as exponential forms that decay with the scaled distance. In addition, through a numerical simulation test, it was found that the optimal hole spacing recommended in an excavation example of an underground pipe gallery is 100 cm. Finally, the blasting vibration effects under the two excavation methods of high-pressure gas impact and explosive blasting were numerically simulated and compared. The results indicate that high-pressure gas impact can significantly reduce the blasting vibration effect of layered rock mass compared with explosive blasting. This study has important theoretical guiding significance and practical value for revealing the propagation law, forecasting and controlling the harm of blasting vibration effect of layered rock mass caused by high-pressure gas impact.

Numerical simulation on jet impingement heat transfer with microcapsule phase change material suspension: Single jet and array jet

The heat transfers on the single and array jet impingement with microcapsule phase change material (MEPCM) suspension are numerically investigated. The equivalent heat capacity method and DPM model are employed to treat the latent heat absorption and motion of the MEPCM particles in suspension, respectively, as well as the VOF method for tracking the free surface from suspension to air. The results show that the latent heat absorption and disturbance effect of the MEPCM particles can significantly improve the heat transfer of the suspension compared to the water. There exists an optimal jet distance at ΔL/D = 4.2 and an optimal suspension concentration at ηp = 5% to achieve the optimal heat transfer. The jet inlet temperature has a favourable range for the heat transfer enhancement, −0.83 <θj < 0.39, which is lower than the phase change temperature range of MEPCM particles. Compared to single jet, the array jet may provide a better heat transfer although the cross-flow between neighboring jets weakens the heat transfer of central jet column. Both of hole number and hole spacing for array nozzle have a non-monotonic effect on the heat transfer, with the optimums at N = 19 and S/D = 7, respectively.

Modelling fracture of rock masses around tunnels and slopes by field-enriched finite element method

The dynamic response and mechanical behaviors of rock masses are mainly governed by discontinuities. The field-enriched finite element method is proposed to study the mechanism of crack propagation in rock mass, and the multiaxial perfectly matched layer (M-PML) is introduced to absorb the reflected wave due to the existence of artificial boundary. The fundamental theory and numerical implementation of the proposed numerical method are described in detail. By comparing two numerical models, namely one with the absorbing boundary and the other without the absorbing boundary, the necessity of considering an absorbing boundary and the ability to verify the absorption effect of the absorbing boundary on the reflected waves are demonstrated. In addition, a numerical example of underground tunnel is established to investigate the influence of dynamic waves from the hole in underground space on the crack propagation in adjacent surrounding rocks of the tunnel. Finally, a numerical model of rock slope with cracks is considered, and the influence of the combination forms of rock bridge inclination angle and fissure spacing on the crack evolution patterns of rock slope with fissures under dynamic load is studied. The research in this paper demonstrates that the dynamic field-enriched finite element method with M-PML absorbing boundary can effectively simulate the dynamic behaviors of fractured rock masses under dynamic load.

A quantitative investigation on the fragmentation performance of SCDA in cracking steel fiber reinforced concrete

A better application of Soundless Chemical Demolition Agents (SCDAs) in fragmentation is based on our knowledge on their expansive characteristics. In this study, an integration of experimental and modeling approaches was developed to investigate SCDA expansion and corresponding cracking processes of Steel Fiber Reinforced Concrete (SFRC). The expansive properties of the selected SCDA were first estimated by free volume expansion (FVE) tests and expansion pressure (EP) tests. Then, cracking experiments were performed on 150 mm cubic SFRC blocks with a predrilled hole, and the cracking process was monitored by using Acoustic Emission (AE) and Digital Image Correlation (DIC) techniques. Generally, the cracking process can be divided into three phases, termed micro-cracking phase, macro-cracking phase, and failure phase. It was observed the hole diameter and fiber content exert significant influences on the cracking process. The crack initiation time was shortened as the hole diameter increases, while it was prolonged with increasing fiber content. The cracked area ratio was further proposed and measured to assess the cracking performance of SCDA. The ratio increases from 2.73% to 8.293% as the hole diameter increases from 16 mm to 26 mm, while it decays from 9.75% to 1.823% as the fiber content increases from 0 to 2.4%. After verified with the experimental data, a modified Concrete Damaged Plasticity (CDP) model was adopted to extend the fragmentation of SFRC from the centimeter scale to the meter scale. The simulations were conducted on SFRC models with various hole diameters, spacings, and fiber contents. The simulated results show the fragmentation performance is related to both hole parameters (e.g., hole diameter, spacing, etc.) and SFRC properties (including elastic modulus, fiber content, etc.). In particular, the cracked area (DamageT > 0.9) varies directly with hole spacing, diameter, and fiber content. Built on the simulated results, an empirical equation was formulated to quantitatively evaluate the fragmentation ability of individual holes. In addition, extra simulations were conducted to assess the efficiency of SCDA in cracking PC/SFRC beams of various sizes. The obtained cracked area tends to decrease first and then approach a constant value with increasing beam sizes, indicating the existence of a size effect, which is primarily due to variations in concrete restraints provided by beams of different sizes. This work quantitatively evaluates expansive properties of SCDA and SCDA-induced cracks, and thus provides a reference for optimizing the field application parameters.

Thermodynamics of Kerr-Sen-AdS black holes in the restricted phase space

Thermodynamics of Kerr-Sen-AdS black holes in the restricted phase space

Thermodynamics under the extended uncertainty principle background: [formula omitted] criticality analysis

The study of thermodynamics in the background of the “extended uncertainty principle (EUP)” comes into interest in recent eras. In this article, we consider a charged black hole (BH) in higher dimensional space–time and present the thermodynamic parameters, based on a semiclassical framework, initially. Then we extend the same within the EUP background. We also analyze the Q−ϕ criticality and find the critical points (ϕc,Qc and Tc) when Q−ϕ criticality appears. We study the effects of EUP on phase transition for higher dimensions (d=5) by plotting the Q−ϕ diagrams. Further, we investigate the stability (thermal and global) of the BHs by employing the specific heat and the Gibbs free energy without and within EUP correction and compare the results with the Schwarzschild BHs in higher dimensions.

Real-Space Observation of Ligand Hole State in Cubic Perovskite SrFeO3.

An anomalously high valence state sometimes shows up in transition-metal oxide compounds. In such systems, holes tend to occupy mainly the ligand p orbitals, giving rise to interesting physical properties such as superconductivity in cuprates and rich magnetic phases in ferrates. However, no one has ever observed the distribution of ligand holes in real space. Here, a successful observation of the spatial distribution of valence electrons in cubic perovskite SrFeO3 by high-energy X-ray diffraction experiments and precise electron density analysis using a core differential Fourier synthesis method is reported. A real-space picture of ligand holes formed by the orbital hybridization of Fe 3d and O 2p is revealed. The anomalous valence state in Fe is attributed to the considerable contribution of the ligand hole, which is related to the metallic nature and the absence of Jahn-Teller distortions in this system.

单行小籽粒精少量播种机设计与试验

In order to meet the precision seeding of small seeds including millet and broomcorn millet in hilly and mountainous areas, a single-row small grain precision seeder was developed. Static seeding test and seeding test were carried out on the seeder. In this paper, the key parts such as socket wheel-ring groove seed metering device, transmission system and tensioning wheel are designed. The working parts such as arrow shovel furrow opener, plastic seed tube and hollow cast iron press wheel were selected to achieve seed metering. The seed metering wheel has double-row of holes. The results of static seeding test showed that rotational speed had a significant effect on the sowing quantity of millet and broomcorn millet (P &lt; 0.001). The higher the rotational speed, the greater the sowing quantity. With the increase of rotational speed of seed metering wheel, the damage rate of millet and broomcorn millet increased. At the same rotational speed, the breakage rate of broomcorn millet is smaller than that of millet. The field sowing test showed that when the seeder is at a marching speed of about 0.5 m/s, the qualified rate of the hole spacing of millet and broomcorn millet is greater than or equal to 90%, and the qualified rate of the number of grains per hole is greater than or equal to 82%. All indicators meet the requirements of the technical conditions of single-grain (precision) seeder. The design can provide reference for the design and optimization of small grain precision seeder.

Experimental Investigation of Effusion Film Cooling on a Cylindrical Leading Edge Model

Abstract Effusion film cooling is effective for cooling high-temperature turbine blades because it requires less coolant and produces a more uniform temperature distribution than conventional film cooling. Effusion cooling for a cylindrical model representing the leading edge of a gas turbine blade was investigated. The experiment was performed in a low-speed wind tunnel at a Reynolds number of 100,000. Pressure-sensitive paint was used to measure the adiabatic film cooling effectiveness. Additive manufacturing was used to fabricate a porous structure on the test cylinder for effusion cooling. Both simple and compound angles were used for cooling injection. The effects of streamwise and spanwise hole spacings, turbulence intensities (1% and 8.7%), and blowing ratios (0.075, 0.15, 0.3, and 0.6) were studied at a fixed density ratio of 1. The effusion hole diameter was 0.1 cm, and the spanwise hole pitch-to-diameter ratio was either 2 or 4. Compared with conventional film cooing, effusion cooling achieved a higher cooling effectiveness and produced a better coolant coverage. Increasing the streamwise spacing noticeably reduced the cooling effectiveness for the simple-angle design due to film lift-off; the compound-angle designs thus achieved higher effectiveness. The simple-angle holes were more sensitive to changes in the mainstream turbulence intensity; increases in the turbulence intensity promoted the mixing of the coolant with the mainstream. Moreover, effusion cooling was more resistant to coolant lift-off at high blowing ratios.

Experimental study on crushing of concrete slabs by high-voltage pulse discharge

To investigate the effectiveness of high voltage pulse discharge (HVPD) in crushing concrete slabs, HVPD in-liquid tests were conducted in pre-drilled holes in three double-layer bi-directionally reinforced and twelve single-layer bi-directionally reinforced concrete slabs. The parameters that were varied in the tests included the concrete strength, discharge hole diameter and spacing, discharge voltage and number of copper wires discharged. The results showed that the explosion caused by HVPD using copper wires increased the crack width by more than 34.8% compared to that caused by the electrohydraulic effect. After 10 explosions caused by HVPD using copper wires, the single-layer reinforced concrete slab was split into several slabs by cracks to achieve the crushing effect. The single discharge energy, i.e., discharge voltage, had a significant effect on the crushing of concrete slabs, and the width of concrete cracks produced by a 100 kV discharge was more than twice that of a 40 kV discharge. The increase in concrete strength acted as a crack arrestor for the slabs, and the crack width of C20 concrete slabs increased by approximately 10% to 25% compared to C40 concrete slabs. The increase in crack width with increasing number of discharged copper wires decreased with increasing discharge voltage. The width of concrete cracks produced by the explosion of 60 copper wires compared to 30 copper wires increased by approximately 10% at 100 kV and by approximately 20% from 60 to 80 kV. The crack width of concrete slabs with discharge holes of diameter 40 mm increased by approximately 5% to 15% compared to concrete slabs with holes of 50 mm. Expressions for the relationships between the damage degree of the concrete slab (i.e., the width of the concrete cracks around the holes on the outside of the slab) and the key parameters such as the output voltage, the number of discharged copper wires, and the strength grade of the concrete were established based on the experimental results.

Effect of Geometrical Parameters on the Exit Pattern Factors Of An Annular Combustor: An Experimental Study

Combustor is an important component of a gas turbine engine and its performance governs the overall performance of the engine. Combustor exit pattern factors are very critical from the consideration of turbine blade and vane life. To achieve the desired goal of pattern factors, the air-management through different zones of combustor is to be carried out very carefully with proper fuel-air mixing followed by complete combustion in the primary zone. During the development stage, extensive studies have been carried out to establish the effect of different geometrical parameters of the combustor on the exit pattern factors. This paper describes the details of the experimental investigations carried out on a full- scale combustor with different geometrical parameters such as diffuser geometry, swiller configuration, atomizer flow passage and dilution zone configurations to study their effect on the exit pattern factors. Dilution zone geometrical parameters and swirler configuration are found to have strong influence in controlling the combustor exit pattern factors and there is an optimum size and spacing of the dilution holes to achieve desired pattern factors at combustor exit.

Enhancing the Performance of LSSVM Model in Predicting Rock Fragmentation Size Via Optimization Algorithms

The prediction of rock fragmentation is critical to improve the efficiency and economy of blasting excavation. In this study, an attempt is made to predict the entire fragmentation size distribution using a least square support vector machine (LSSVM) model. In addition, three optimization algorithms—the bacterial foraging algorithm (BFO), artificial fish swarm algorithm (AFSA), and adaptive particle swarm optimization (APSO)–were used to determine the appropriate parameters of the LSSVM model. In the constructed LSSVM-BFO, LSSVM-AFSA and LSSVM-APSO models, the hole spacing, row spacing, change per delay and stemming were used as the input parameters, while the statistical rock fragmentation size was assigned as the output. The LSSVM model was also employed as a control group for comparing with the optimized models. The above-mentioned models were trained and tested based on a database comprising of 10 datasets collected from in-site testing of Altashi Water Control Project in China. The performance of the proposed models was compared by several statistical criteria. The viability and efficiency of the LSSVM-BFO model were confirmed with an R2 of 0.9960 and an RMSE of 1.8044, which were better than those of the LSSVM-AFSA, LSSVM-APSO and LSSVM. Last but not least, sensitivity analysis was also executed. The result of sensitivity analysis demonstrated when the size of rock fragmentation of prediction is less 80mm, the most effective parameter will be stemming; otherwise the most effective parameter will be hole spacing.