Secondary Breaking Research Articles

Dependency of crossover point on absorption changes in bilayer diffusion reflection measurements.

A better understanding of diffusion reflection (DR) behavior may allow it to be used for more noninvasive applications, including the development of in vivo non-damaging techniques, especially for medical topical diagnosis and treatments. For a bilayer opaque substance where the attenuation of the upper layer is larger than the attenuation of the lower layer, the DR crossover point ( ) is location where the photons coming from the bottom layer start affecting the DR. We aim to study the dependency of the on absorption changes in different layers for constant scattering and top layer thickness. Monolayer and bilayer optical tissue-like phantoms were prepared and measured using a DR system. The results were compared with Monte Carlo simulations. There is an agreement between the experiments and the simulations. correlates with the square root of the absorption coefficient ratio of the lower layer to the top layer. The experimental findings support and validate the theoretical prediction describing the dependency of the on the square root of the ratio of the layers' absorption coefficients. In addition, a secondary breaking point is suggested to be observed experimentally at the entrance to the noise area.

3D-imaging of boulders using a solid-state 2D profilometer: case study for autonomous robotic rock breaker

Measurements of a boulder's fundamental physical properties like volume and shape can offer valuable insights for secondary breaking of boulders by a robotic rock breaker. This study analysed boulder shapes using a pulsed time-of-flight (TOF) solid-state laser profilometer. The 3D surface of boulders was reconstructed creating triangular meshes from point clouds provided by the profilometer. The main advantages of the 2D profilometer are the good measurement precision and accuracy, high speed, small size, real-time measurement capability, low weight, eye-safety, and lack of moving parts. The results indicate that a 3D map facilitates boulder diagnostics, aids in decision making, and represents a step towards a fully integrated autonomous robotic rock breaker in the mining industry. The present procedure is not only restricted to boulders, but it has also potential for other targets in industries that require precise determination of shapes for decision making.

Autonomous robotic rock breaking using a real‐time 3D visual perception system

AbstractCrushing of blasted ore is an essential phase in extraction of valuable minerals in mining industry. It is typically performed in multiple stages with each stage producing finer fragmentation. Performance and throughput of the first stage of crushing is highly dependent on the size distribution of the blasted ore. In the crushing plant, a metal grate prevents oversized boulders from getting into the crusher jaws, and a human‐controlled hydraulic manipulator equipped with a rock hammer is required to break oversized boulders and ensure continuous material flow. This secondary breaking task is event‐based in the sense that ore trucks deliver boulders at irregular intervals, thus requiring constant human supervision to ensure continuous material flow and prevent blockages. To automatize such breaking tasks, an intelligent robotic control system along with a visual perception system (VPS) is essential. In this manuscript, we propose an autonomous breaker system that includes a VPS capable of detecting multiple irregularly shaped rocks, a robotic control system featuring a decision‐making mechanism for determining the breaking order when dealing with multiple rocks, and a comprehensive manipulator control system. We present a proof of concept for an autonomous robotic boulder breaking system, which consists of a stereo‐camera‐based VPS and an industrial rock‐breaking manipulator robotized with our retrofitted system design. The experiments in this study were conducted in a real‐world setup, and the results were evaluated based on the success rates of breaking. The experiments yielded an average success rate of 34% and a break pace of 3.3 attempts per minute.

Мобильный локализатор для разрушения негабаритов

Research objective: Development and implementation of a mobile safety screen for secondary breaking. Research methodology: Analysis of secondary breaking of oversize boulders. Research results: blasting creates oversize chunks of rock (boulders) in the pit walls and floor, which affects the productivity of the pit and the mining operation as a whole. Open pit mines with large volumes of rock formations have to handle hundreds of cubic metres of boulders every day bearing significant labour and material costs of these activities. Various methods of boulder breaking are used in open pit mining, including electrical treatment, mechanical impact, blasting, etc. A common disadvantage of these techniques is their relatively low capacity. Out of all the applied methods, drilling and blasting of boulders is the most effective, but the use of this method is limited due to the use of various equipment, increased hazards and the presence of certain other disadvantages. The autonomous mobile safety screen has been developed to solve this bottleneck. The use of this safety screen enables breaking boulders using blasting techniques, reduces the size of the hazardous area, increases the efficiency of the air shock waves, prepares safety trenches in open pits and for road construction, prepares the rock mass for long-distance transport by road or railways. Conclusions: The use of this safety screen enables breaking boulders using blasting techniques, reduces the size of the hazardous area, increases the efficiency of the air shock waves, prepares safety trenches in open pits and, during road construction, prepares the rock mass for long-distance transport by motor and railroads.

Assessment of the effect of blasthole design parameters on total cost in quarries

Crushed stone is the most important raw material for concrete and asphalt production. As a high-volume low-unit-value industry, the crushed stone production sector is highly competitive which implies the necessity to optimise the costs of all of its production operations, i.e. drilling and blasting, secondary breaking, loading, hauling and crushing. In this context, this paper investigates the effect of bench blasting design parameters on the unit-costs and total production cost of aggregate production. For this purpose, 40 blasts were conducted and investigated. The studied parameters included different blasthole length (12 m, 15 m, 18 m, 21.5 m and 25 m) and diameter (89 mm and 102 mm), in addition to different spacing, burden and stemming length. As a result, it was found that an increase in blasthole length led to an increase in the unit cost of drilling operation. In addition, it was found that a blasthole length of 15 m ensured optimum fragmentation, diminishing the costs of subsequent operations. Incrementing the blasthole diameter from 89 to 102 mm reduced the total unit cost by 0.091 $/m3. Incrementing the burden and spacing by 0.25 m also decreased the total unit cost by 0.097 $/m3. However, accreting the stemming length by 0.5 m induced a slight decrease in the total unit cost by 0.026 $/m3.

Experimental study and numerical simulation of mean longshore current for mild slope

In this paper, experimental and numerical studies were performed to investigate the characteristics of longshore current under two mild slopes, the results of which may complement the existing studies, which have mainly focused on steep slopes. The experimental results revealed that the average velocity distribution of the longshore current was significantly different under the two different mild slopes. Under the slope of 1:100, the distribution of the averaged longshore current velocity had a downward concave trend at the nearshore side, while under the slope of 1:40 the trend became convex. In addition, the analysis of the numerical results showed that the distribution of the averaged longshore current velocity was affected by the distribution of the wave height within the surf zone and the bottom friction equations, with the influence of the latter being more significant. For the slope of 1:100, the cross-shore variability of alongshore variability can be calculated using the flow-type bottom friction equation, while for the slope of 1:40, the wave-type bottom friction equation can be used instead. Finally, the secondary breaking wave heights for mild slopes and the distribution of wave set-up are also shown in the study.

Predicting the average size of blasted rocks in aggregate quarries using artificial neural networks

The prediction of the average size of fragments in blasted rock piles produced after blasting in aggregate quarries is essential for decresing the cost of crushing and secondary breaking. There are several conventional and advanced processes to estimate the size of blasted rocks. Among these, the empirical prediction of the expected fragmentation in most cases is carried out by Kuznetsov’s equation (Sov Min Sci 9:144–148, 1973), modified by Lilly (1986) and Cunningham (1987). The present research focuses on the effect of the engineering geological factors and blasting process on the blasted fragments using a more powerful, advanced computational tool, an artificial neural network. In particular, the blast database consists of the blastability index of limestone on the pit face, the quantities of the explosives and of the blasted rock pile, assessing the interaction of these parameters on the blasted rocks. The data were collected from two aggregate quarries, Drymos and Tagarades, near Thessaloniki, in the Central Macedonia region of Greece. This approach indicates significant performance stability, providing the fragmentation size with high accuracy.

The Impact of an Extreme Storm Event on the Barrier Beach of the Lefkada Lagoon, NE Ionian Sea (Greece)

The present investigation examines the characteristics of a high energy storm event, that took place on November 9-11, 2007 in the NE Ionian Sea (eastern Mediterranean), and its impact upon the barrier beach that separates the Lefkada lagoon from the open Ionian Sea. The storm event was caused by NW winds with speeds exceeding 20 m/s (40 knots), which have an annual frequency of occurrence less than 0.015%. This high energy event produced waves with >5 m significant offshore height and 9.5 s period; these waves developed on 10th November during the rapid rise of barometric pressure (~1.4 hPa/hr), which followed the barometric pressure drop from 1020.5 hPa at 06:00 (UTC) of 9th November to 1001.7 hPa at 06:00 h (UTC) of 10th November. Secondary breaking at the shoreline produced wave heights >1.5 m, associated with a surge of >0.4 m and a run-up capability of >2.4 m. The waves managed to overtop the barrier beach (elevations ~2.5 m), lowering the seaward side of the barrier beach by 10-30 cm and causing a coastline retreat of 0.9 to 2.2 m; these morphological changes correspond volumetrically to a sediment loss of approximately 8 m3/m of coastline length from the sub-aerial part of the beach. During the last three decades a significant change in the frequency of occurrence and direction (from S-SW-W to N-NW-NE) of severe storms with wind speeds exceeding 40 knots has been recorded, affecting the sediment transport pattern and contributing to the erosion of the north beaches of Lefkada.

TECHNOGENESIS ON THE SANDY SHORELANDS OF THE INLAND SEAS (PAPER 2. THE IMPACT OF THE HARBOUR PROTECTIVE CONSTRUCTIONS ON THE MORPHOLITHODYNAMICS OF THE SOUTH-EASTERN BALTIC SHORELANDS)

The protective harbour constructions have an essential impact on morpholithodynamics of the adjacent area of coastal zone. Being artificial capes, port piers make for secondary breaking up of coastal line and, as a consequence, reduce the longitudinal proportion of deposit transport in coastal zone and increase the transverse one.

Research on the Hard-Rock Breaking Mechanism of Hydraulic Drilling Impact Tunneling

In order to realize the rapid hard-rock tunneling in a safe, highly effective, and economic manner, the hydraulic drilling impact hard-rock tunneling (HDIHT) technology and method were introduced based on the theories of rock mechanics and hydraulic impact. The key parameters, including drilling radius and impact distance, were researched to reveal the stress behavior during HDIHT process. The Von Mises equivalent stress and its principal stress components were analyzed, and the breaking mechanism of HDIHT was also discussed. The simulation results show that, to ensure the effectiveness of “secondary breaking” caused by drilling hole free surfaces, the impact distance should not exceed 200 mm, and the optimal drilling radius was about 35 mm.

전자뇌관을 이용한 수평방향 데크차지 발파공법의 효율성검토 연구

도심지 근접시공 발파에는 진동 소음에 따른 민원의 문제가 주요시된다. 발파 진동 소음을 줄이기 위해 최근에 국내에 도입된 전자뇌관을 사용하여 데크차지 공법에 적용하면 cut off 등과 같은 현상이 없어져서 안전한 시공이 가능하고, 또한 수평방향으로 발파가 가능해져서 대규모 발파가 가능해진다. 본 연구에서는 전자뇌관을 사용한 수평방향데크차지 공법의 효율을 기존 공법의 것과 비교해보고, 현장적용 가능성을 평가해보았다. 그 결과 발파 진동 소음과 2차 파쇄량의 감소를 확인하였고, 뿐만 아니라 전반적으로 발파 효율이 증가하여 진동 규제 기준치 내에서 대규모 발파가 가능함을 확인하였다. In close to downtown construction, the main problem is complaints caused by blasting vibration and noise. To reduce blasting vibration and noise, deck-charge blasting method using electronic detonator can be more secure because there is no cut-off problem. And in this method it is possible to blast in horizontal direction. In this study, the efficiency of horizontal direction deck-charge blasting method using electronic detonator is compared to that of the existing blasting method. And the possibility of applying the construction site is evaluated. As a result, the reduction of blasting vibration, noise and secondary breaking has been determined, as well as large-scale blasting in the vibration criterion can be regulated by the overall increase in blasting efficiency.

Direct numerical simulation of a breaking inertia–gravity wave

AbstractWe have performed fully resolved three-dimensional numerical simulations of a statically unstable monochromatic inertia–gravity wave using the Boussinesq equations on an $f$-plane with constant stratification. The chosen parameters represent a gravity wave with almost vertical direction of propagation and a wavelength of 3 km breaking in the middle atmosphere. We initialized the simulation with a statically unstable gravity wave perturbed by its leading transverse normal mode and the leading instability modes of the time-dependent wave breaking in a two-dimensional space. The wave was simulated for approximately 16 h, which is twice the wave period. After the first breaking triggered by the imposed perturbation, two secondary breaking events are observed. Similarities and differences between the three-dimensional and previous two-dimensional solutions of the problem and effects of domain size and initial perturbations are discussed.

Application of Intensification Approaches on Recycled Aggregate

The wasted cement mortar and internal cracks induced by the secondary breaking process existing on/in recycled aggregates lead to significant reductions in the apparent density, strength and durability of recycled aggregate concrete compared to those of natural aggregate concrete. In this study, recycled aggregate intensification approaches was proposed by removing the old cement mortar from recycled aggregate surface through mechanical agitation, and immersing the recycled aggregate in chemical solutions. A series of laboratory experiments were carried out to validate that the proposed approach could improve various performances of the recycled aggregate, as well as the concrete made of it. The testing results showed that through the combination treatment or modification of mechanical and chemical intensification, both of the compressive and flexural strength of the recycled aggregate concrete could be increased to some extent.

Gravity wave breaking in easterly flow over Greenland and associated low level barrier- and reverse tip-jets

A first evidence of severe turbulence in the lower stratosphere during easterly tropospheric flow over Greenland is presented. A numerical simulation shows the turbulence to be associated with gravity wave breaking and that simulating with a horizontal resolution of 3 km gives substantially greater and more realistic turbulence than at a 9 km horizontal resolution. It is concluded that real-time simulations at high resolutions would improve aviation forecasts. As the atmospheric flow impinges on South-Greenland a barrier jet, a reverse tip jet and amplified mountain waves with secondary wave breaking are generated at the same time.

Dimensional effects in dynamic fragmentation of brittle materials

It has been shown previously that dynamic fragmentation of brittle D -dimensional objects in a D -dimensional space gives rise to a power-law contribution to the fragment-size distribution with a universal scaling exponent 2-1/D . We demonstrate that in fragmentation of two-dimensional brittle objects in three-dimensional space, an additional fragmentation mechanism appears, which causes scale-invariant secondary breaking of existing fragments. Due to this mechanism, the power law in the fragment-size distribution has now a scaling exponent of approximately 1.17 .

LOW FREQUENCY WAVES ON A BEACH FACING OPEN SEA

Field measurements were conducted using specially developed wave measuring devices at Hazaki coast in Ibaraki Prefecture. Based on the data, characteristics of infra-gravity waves have been studied. Infra-gravity oscillation becomes dominant in offshore side of secondary breaking point. The low frequency wave components around f=0.02-0.05Hz are found to be in good correlation with the envelop of incident group waves. The lower frequency wave component of f≤0.01Hz, however, does not show clear relation with the incident group waves. The existence of standing edge waves is suggested by the analyzed coherence and phase results on horizontal velocity components. Most of these results show typical characteristics as the dissipative beach which Wright-Short have classified.

Dynamics of biochemical oscillators in a large number of interacting cells

6. Summary We investigated here minimal models for coupled metabolic oscillators in cell suspensions. They are based on a feedback-activation mechanism, proposed for the explanation of the glycolytic oscillations. Despite the simplicity of the models we found a wide variety of complex dynamical phenomena. Depending on the kinetic parameters interacting cells may oscillate synchronous or asynchronous. It was shown, that there are different possibilities for asynchronous oscillations. (a) Depending on the type of coupling regular asynchronous behaviour may occur near to the boundary of stability. This type of behaviour was only possible, if the coupling metabolite belongs to the pool of products of the autocatalytic reaction. (b) Leaving the near neighbourhood of the points of Hopf-bifurcations in both models nonregular asynchronous behaviour may arise by secondary symmetry breaking bifurcations, either from the branch of synchronous oscillations or from the branch of regular asynchronous oscillations. In model II the coupling opens the possibility of multiple steady states. The whole population may be within different stable steady states or different oscillatory modes. The results of our study may be helpful for the interpretation of experimental data in this field. The mechanism of interaction, which was investigated here, has been proposed for many biological systems. Especially for yeast cell suspensions the question of the coupling intermediates is studied intensively. In recent time acetaldehyde was reported to be the synchronizer of the oscillations [5], but this substance was shown to desynchronize the oscillations too [4]. Without discussing the problem, whether or not this substance mediates the coupling, we want to emphasize that any metabolite may play the role of a synchronizer as well as that of a desynchronizer. Moreover we have demonstrated that the regular asynchronous oscillations may lead to the phenomenon of hidden oscillations, where it may be difficult to observe cellular oscillations.

Developments in rock-breaking techniques

A problem with secondary breaking at an Australian mine led to a study of new rock-breaking technologies. Many of the techniques being developed had emerged from the thrust in the U.S.A. for continuous drill-break excavation. Such approaches to rock breaking highlighted the applicability of what normally would be classified as tunnelling techniques, to the secondary breaking sector—and possibly the reverse. The investigations for suitable technologies led directly to the development of two improved rock-breaking methods specifically targeting secondary breaking, one of which could be applied to continuous excavation. Le problème d'une attaque secondaire dans une mine australienne a conduit étudier de nouvelles technologies de concassage des roches. Un grand nombre des techniques mises au point actuellement ont l'origine la poussée opérée aux Etats-Unis en faveur d'un creusement continu par foration-concassage. Ces approches sur le concassage de la roche mettent en évidence l'applicabilité de ce qui pourrait normalementêtre classé comme des techniques de creusement de tunnels au domaine des attaques secondaires, et inversement, le cas échéant. Les études portant sur des technologies adéquates ont conduit directement au développement secondaires, dont l'une peut être appliquée à un creusement en continu.

Axisymmetrization and vorticity-gradient intensification of an isolated two-dimensional vortex through filamentation

We consider the evolution of an isolated elliptical vortex in a weakly dissipative fluid. It is shown computationally that a spatially smooth vortex relaxes inviscidly towards axisymmetry on a circulation timescale as the result of filament generation. Heuristically, we derive a simple geometrical formula relating the rate of change of the aspect ratio of a particular vorticity contour to its orientation relative to the streamlines (where the orientation is defined through second-order moments). Computational evidence obtained with diagnostic algorithms validates the formula. By considering streamlines in a corotating frame and applying the new formula, we obtain a detailed kinematic understanding of the vortex's decay to its final state through a primary and a secondary breaking. The circulation transported into the filaments although a small fraction of the total, breaks the symmetry and is the chief cause of axisymmetrization.