Breaking Conditions Research Articles

Mathematical modelling of thermal stresses within the borehole walls in terms of plasma action

Purpose is the development of a mathematical model to study and describe thermal processes within the borehole wall in terms of plasma-based rock breaking. Methods. The following has been applied: theoretical analysis in the framework of a theory of brittle thermoelasticity breaking, methods of mathematical modeling, and computational experiment. Findings. Brief information on the results of the development of advanced plasma-based technology for borehole reaming for hard mineral mining has been represented. The results of industrial tests of plasma plant of 150-200 kW·s power with plasma-generating gas in the air for hard rock breaking have been represented. The plant and plasma-based technology of borehole reaming were tested in underground conditions of Kryvbas mines while reaming a perimeter hole to drive a ventilation rise in silicate-magnetite quartzites. A mathematical model has been proposed to analyze heat and mechanical fields in the rock during the plasma-based action on the borehole walls. Numerical studies of the temperature dynamics and thermal stresses within the borehole-surrounding rock layer have been carried out. It has been demonstrated that if low-temperature plasma is used (Т = 3500-4000°С), thermal compressing stresses are induced within the thin rock layer; the stresses may exceed the boundary admissible ones. It has been identified that plasma-based effect on the borehole wall makes it possible to create the conditions for intense rock fracturing and breaking. Originality. Solution of a new problem of thermoelastic state of a borehole wall in terms of plasma action has been obtained. The proposed mathematical model has been formulated in a cylindrical coordinate system and considers convective and radiation heat exchange between a plasma jet and a borehole wall. Practical implications. The obtained results make it possible to assess the rock state depending on the plasma jet parameters. The proposed methods of calculations will help carry out research to evaluate breaking parameters (the required heating time, thickness of the heated layer, and approximate spall dimensions) and develop different methods for the breaking process control.

Movement Laws of Overlying Strata above a Fully Mechanized Coal Mining Face Backfilled with Gangue: A Case Study in Jiulishan Coal Mine in Henan Province, China

The aim of this study is to obtain movement laws of overlying strata above a fully mechanized coal mining face backfilled with gangue and solve the problem of surface subsidence during coal mining. This study was carried out based on gangue backfilling mining of Jiulishan Coal Mine (Jiaozuo City, Henan Province, China) from the perspectives of deformation of backfilled gangue under compaction, surrounding rock of a stope, and activities of key strata. The method combining with rock mechanics, viscoelastic mechanics, control theory of rock mass under mining, and numerical simulation was used based on physical and mechanical characteristics of backfilled gangue. On this basis, the research analyzed the temporal‐spatial relationships of activities of surrounding rock of the stope, compressive deformation of backfilling body, failure depth of the floor, deformation characteristics of the main roof with laws of surface subsidence. The movement characteristics of overlying strata above the fully mechanized coal mining face backfilled with gangue and the traditional fully mechanized mining face were compared. It is found that, under the same conditions of overlying strata, movement laws of overlying strata are mainly determined by the mining height of coal seams and the heights of a caving zone and a fracture zone are nearly linearly correlated with the mining height. Through analysis based on thin‐plate theory and key stratum theory, the location of the main roof of the fully mechanized coal mining face backfilled with gangue in coal seams first bending and sinking due to load of overlying strata was ascertained. Then, it was determined that there are two key strata and the main roof belongs to the inferior key stratum. By using the established mechanical model for the main roof of the fully mechanized coal mining face backfilled with gangue and the calculation formula for the maximum deflection of the main roof, this research presented the conditions for breaking of the main roof. In addition, based on the theoretical analysis, it is concluded that the main roof of the fully mechanized coal mining face backfilled with gangue does not break, but bends. The numerical simulation results demonstrate that, with the continuous increase of strength of backfilled gangue, the stress concentration degree of surrounding rock reduces constantly, so does its decrease amplitude. Moreover, the compressive deformation of backfilling, failure depth of the floor, and bending and subsidence of the main roof continuously decrease and tend to be stable. The mechanical properties of backfilling materials determine effects of gangue backfilling in controlling surface subsidence. Gangue backfilling can effectively control movement of overlying strata and surface subsidence tends to be stable with the increase of elastic modulus of gangue.

MODELLING OF WAVE OVERTOPPING AT DIKES USING OPENFOAM

The average overtopping discharge is an important parameter for the design of flood defences. Several empirical formulas are available for predicting the overtopping discharge at dikes. However, these empirical formulas often have their specific applicable conditions. To complement with the empirical methods, a numerical model has been developed using the open source CFD package OpenFOAM to model the wave overtopping at dikes. Systematic calibration and validation of the numerical model are performed. The influences of the mesh, solver, turbulence model and roughness height on the modelled results of the average overtopping discharge have been investigated during the model calibration. The simulations show that the turbulence model increases the accuracy of the numerical model for predicting the average overtopping discharge under wave breaking conditions. The calibrated model is then validated by comparing the modelled average overtopping discharges with the measured ones from the physical model tests. Results show that the OpenFOAM model is capable of predicting the average overtopping discharge accurately at dikes that have a smooth straight waterside slope.

MACHINE LEARNING CLASSIFICATION OF BEACH STATE FROM ARGUS IMAGERY

Nearshore beach morphology is of interest to coastal managers due to the strong influence it exerts on subaerial beach erosion, pollutant dispersal, and recreational safety. In particular, wave breaking conditions and nearshore hydrodynamics are highly dependent on sandbar configuration. The term 'beach state' describes specific planform configurations of nearshore morphology that are in dynamic equilibrium with the time-varying forcing conditions. Beach state categories were first introduced by Wright and Short (1984), who observed sandbar systems in Narrabeen-Collaroy, Australia and extended by Lippman and Holman (1990), based on observations of time-exposure Argus imagery of sandbar systems in at Duck, NC, USA. In this study, we use machine learning algorithms to identify beach states from Argus imagery at two distinct sites: Narrabeen-Collaroy (hereafter Narrabeen), SE Australia, and Duck, NC. We assess the ability of the algorithm to classify beach states at each site and its transferability from one beach to another. Additionally, we investigate the extent to which the spatial and temporal evolution of beach states influences the ability of the algorithm to classify images into discrete beach states.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/38OM8CseIww

Widely Wavelength-Tunable Parity-Time Symmetric Single-Longitudinal-Mode Fiber Ring Laser With a Single Physical Loop

A wavelength-tunable single-longitudinal-mode fiber ring laser based on parity-time (PT) symmetry for mode selection is proposed and experimentally demonstrated. The PT symmetry is implemented using a single physical fiber-optic loop, which functions equivalently to two mutually coupled optical loops with an identical geometry but balanced gain and loss. In the proposed system, a linearly polarized light wave is split into two, which are traveling in a Sagnac loop incorporating a polarization beam splitter (PBS) and two polarization controllers (PCs). By controlling the polarization states of the light waves injected into the PBS via tuning the PCs, the gain and loss of the two equivalent loops corresponding to the light waves traveling in the clockwise (CW) and counter-clockwise (CCW) directions are controlled. When the gain and loss are balanced and exceed the coupling coefficient, PT-symmetry breaking condition is met, and single-longitudinal-mode lasing is achieved. The proposed PT-symmetric fiber ring laser is experimentally demonstrated. Single-longitudinal-mode lasing with a tunable wavelength from 1530 to 1565 nm and a narrow linewidth as small as 390 Hz is achieved. The sidemode suppression ratio is 41.9 dB confirming the effectiveness of using PT symmetry for mode selection.

Interaction of a solitary wave with an array of macro-roughness elements in the presence of steady currents

The present study focuses on the effects of following and opposing steady currents on the interactions of a solitary wave with an array of macro-roughness elements, placed on a berm beach. A series of laboratory experiments and high-fidelity numerical simulations are conducted. The large eddy simulations are carried out using the open source computational fluid dynamics package, OpenFOAM. Wave breaking conditions on the berm are found to be controlled by the intensity of the currents. The opposing currents influence the layer of water rushing up the macro-roughness elements, leading to asymmetric runup patterns. Furthermore, the vortices forming around the elements' sharp edges, resulting from the interactions of the wave with the elements, are modified to a large extent due to the combined wave and current effect. The elliptical vortex tubes become up to ~20% wider under the effect of the following current flow, whereas their size is reduced by up to ~90% when the opposing currents are present. The following currents enhance the bed shear velocity, leading to intensified bed shear stress zones throughout the macro-roughness environment. On the other hand, the intensification of the bed shear velocity and corresponding stress occurs on the seaside in the presence of opposing currents. Overall, the results indicate that the currents entirely change the hydrodynamics of the interactions between the solitary wave and macro-roughness environment.

The effect of fire on seed germination of campo rupestre species in the South American Cerrado

Fire is an important disturbance in terrestrial ecosystems and plays a key role in the germination process and seedling establishment of many species. In grassland ecosystems, seeds normally tolerate heat-shocks associated with low intensity fires but are negatively affected by higher heat doses. Additionally, smoke-stimulated germination is not commonly recognized as important in neotropical grasslands. This may result from a negative relationship between the ability to resprout after fire and fire-stimulated germination ability, as many species in these grasslands regenerate well after fire by resprouting. To ascertain the role of heat and smoke in the post-fire germination response of campo rupestre vegetation, we exposed seeds of nine species (that regenerate after fire by resprouting) to various treatments related to fire (heat, smoke, and heat plus smoke) and analysed their germination behaviour. Our results suggest that these species have high seed germination in the absence of specific dormancy breaking conditions and/or that stimulated germination triggered by fire-related cues is not common. Additionally, while seeds from some species can withstand temperatures of 80 °C for 5 min without affecting germination, most species are negatively affected by higher heat doses. However, our results suggest an important role of smoke enhancing germination rate (speed) of campo rupestre species. In view of the characteristics of campo rupestre environmental conditions and vegetation, we provide a novel outlook of enhanced germination rate by smoke as an important mechanism for seed regeneration after fire of campo rupestre’s species that resprout, particularly for seeds resulting from post-fire seed dispersion.

Chiral symmetry restoration in reduced QED at finite temperature in the supercritical coupling regime

We explore the conditions for chiral symmetry breaking in reduced (or pseudo) quantum electrodynamics at finite temperature in connection with graphene and other 2D-materials with an underlying Dirac behavior of the charge carriers. By solving the corresponding Schwinger-Dyson equation in rainbow approximation, in a Landau-like gauge and neglecting wavefunction renormalization effects, we find the need of the coupling to exceed a critical value $\alpha_c$ in order for chiral symmetry to be broken, in agreement with known results from other groups. In this supercritical regime, we add the effects of a thermal bath at temperature $T$ and find the critical values of this parameter that leads to chiral symmetry restoration.

Magnetic deformation of super-Maxwell theory in supergravity

A necessary condition for partial breaking of mathcal{N} = 2 global supersymmetry is the presence of nonlinear deformations of the field transformations which cannot be generated by background values of auxiliary fields. This work studies the simplest of these deformations which already occurs in mathcal{N} = 1 global supersymmetry, and its coupling to supergravity. It can be viewed as an imaginary constant shift of the D-auxiliary real field of an abelian gauge multiplet. We show how this deformation describes the magnetic dual of a Fayet-Iliopoulos term, a result that remains valid in supergravity, using its new-minimal formulation. Local supersymmetry and the deformation induce a positive cosmological constant. Moreover, the deformed U(1) Maxwell theory coupled to supergravity describes upon elimination of the auxiliary fields the gauging of R-symmetry, realised by the Freedman model of 1976. To this end, we construct the chiral spinor multiplet in superconformal tensor calculus by working out explicitly its transformation rules and use it for an alternative description of the new-minimal supergravity coupled to a U(1) multiplet. We also discuss the deformed Maxwell theory in curved superspace.

On the problem of steady bifurcation of a falling sphere in a Navier–Stokes liquid

We study steady bifurcation for the coupled system body-liquid consisting of a sphere freely falling in a Navier–Stokes liquid under the action of gravity. In particular, we show that, under the assumption that for the bifurcating solution, the translational velocity of the sphere is parallel to the gravity, bifurcation takes place, provided that 1 is a simple eigenvalue of a suitable linear operator and the transversality property holds. Moreover, we also give sufficient conditions for symmetry breaking.

The influence of boreal summer intra-seasonal oscillations on Indo-western Pacific Ocean surface waves

The present study examines the influence of Boreal Summer Intra-Seasonal Oscillation (BSISO) on Tropical Indian Ocean surface waves using the latest version of ECMWF reanalysis (ERA5) during summer monsoon months June through August (JJA). BSISO is a distinct mode of ISO during JJA having a northward and eastward movement from the equatorial Indian Ocean to the western Pacific Ocean. Composite analysis of anomalies of significant wave heights (SWH), wind sea, swell, and mean wave period for 8 phases of BSISO has been carried out to understand its influence. SWH anomalies in response to BSISO’s are phase-dependent. Negative SWH anomalies are noticed with strong northward and weak eastward propagation during the phases 1–3 in response to the easterly wind anomalies over the north Indian Ocean (NIO). During phases 5–7, high positive SWH anomalies (~ 0.5 m) in response to the westerly wind anomalies with northward and weak eastward propagation over NIO. Phases 4 and 8 behave like transition phases. In addition, enhanced (suppressed) SWH anomalies (~ 0.5 m) are seen during the active (break) spells of BSISO over NIO. Over the southern tip of India, negative (positive) SWH anomalies prevail during the active (break) conditions. This study clearly suggests that the wave forecast advisories during intra-seasonal time scales would be more useful for offshore and coastal activities during the summer monsoon.

Preventive maintenance of taper bearing using Arduino in the application of industry 4.0

The maintenance of industrial tools is very important to support production. Therefore, many companies apply preventive maintenance. A national industrialization agenda discussed that it is crucial especially in the manufacturing industry. The battery-powered IoT sensing device is capable of thorough monitoring of industrial machinery enabling the development of sophisticated predictive maintenance applications under set scenarios. In this paper, we applied the concept of the Internet of Thing (IoT) system using LabVIEW via Arduino. The research method used in this study was similar to Susanto et al. (2019) namely Frequency Response Function (FRF) test to investigate the dynamic characteristics of a mechanic structure to identifying damages on X, Y, and Z axes of tapered bearing using harmonic vibration from handphones. Results of FRF and Labview via Ardunio were then compared to identify the results of measurement using LabView via Arduino. It was found much noise in the measurement occupying Labview Via Ardunio because its system does not use a filter like the one in FFT Analyser. However, in general, LabVIEW via Ardunia can predict damages in taper bearing. It is because, under broken condition, there was a two-time movement of natural frequencies from good condition.

Investigating skimming flow conditions over stepped spillways using particle image velocimetry

Turbulent flow over stepped spillways can be considered the most significant flow that can cause severe problems at the downstream side, near the toe of the structure, such as sediment erosion which normally occurs due to the high amount of water energy. The presence of turbulent flow over the steps can cause cavitation damages due to pressure differences over the steps. The turbulent flow, which is induced at certain times of the year, especially during the flooding seasons, is examined experimentally and numerically in this study. Flow measurements were conducted using Particle Image Velocimetry (PIV) system in a hydraulic flume where the dam break condition is applied in order to achieve the skimming turbulent flow. Two cases of stepped spillways were tested, normal stepped spillways and gabion stepped spillways. For each case, measurements of the instantaneous turbulent velocity field were taken at different locations of the physical models of a slope of (1V:2H). A comparison has been conducted between the gabion and normal steps to assess the required time to attach skimming flow. The results indicated that the presence of the porous media could increase the required time to attach skimming flow.

Nearshore coastal flow processes using weighted-averaged equations

This work uses the weighted residual method to simulate non-hydrostatic flows in ocean and coastal areas in a vertically-averaged framework. A Vertically-Averaged and Moment equations set is developed. The system is solved through a hybrid finite volume-finite difference numerical scheme to tackle the hyperbolic and elliptic parts of the equations. Data of seven challenging tests are used to evaluate the model ability to reproduce non-linearity, dispersion, wave breaking, bore propagation, sheet flow and wave reflection. The tests comprise propagation of sinusoidal waves over a submerged bar; convergence of the numerical scheme; solitary wave transformation over a dry reef flat, a wet reef flat and an exposed reef crest; collision of two solitary waves; and solitary wave reflection on a vertical wall under non-breaking and breaking conditions. The results highlight the accuracy of the model without prescribing any treatment for wave breaking. The conjunction of long and short waves with wave shoaling, run-up and receding flows is accurately reproduced. The model is considered an alternative tool to Boussinesq-type models to solve non-linear flows in the nearshore region, with the advantage of having an automatic mimic of wave breaking due to the field variables used to produce the weighted residual depth-averaged equations.

Chip Breaking During Automated Processing by Cutting Hard-to-Work Steels by Integrated Use of Chip Breaking Tools and High-Temperature Embrittlement

Purpose of research is to increase productivity when cutting hard-to-work steels by integrated use of chip breaking tool geometry and cutting modes, which reduce the viscous properties of the chips and the processed material. The article discusses the problems of mechanical processing of parts of oil production equipment at enterprises in Western Siberia. It is presented the main condition for ensuring chip crushing and revealed the problem of low efficiency of existing methods in modern industry, to one degree or another guiding, curling and chip-cutting method.Methods. Simulation modeling, calculation of chip direction and crushing were performed; effective methods for solving the problem of chip crushing during the machining of parts made of materials with corrosion-resistant, heat-resistant properties were identified; laboratory, persistent tests of the complex method were carried out.Results of studying the mechanism of chip formation during processing by cutting heat-resistant and corrosionresistant alloys are given here. To solve the problem, we have formulated two tasks that were solved using information taken from the theory of material resistance, tensile diagrams when testing samples of corrosionresistant, heat-resistant materials with high operational properties. A chip breaking exchangeable insert with a variable rake angle is designed and presented. The results and analysis of laboratory test data, in which a plate with chip breaking geometry of the front surface is used, are presented, the operating conditions of effective chip breaking are shown. The conclusions on the solution of the first problem are formulated, it is shown that the determining factor in chip breaking is the physical and mechanical characteristics of the processed material, which vary with different cutting conditions.Conclusion. The work shows that chip removal from the cutting zone prevents it from entering the cutting edge area, reducing impact loads on it and improving the quality of machining. It is possible to form stress concentrators in the chips, leading to chip self-destruction even when processing viscous heat-resistant alloys. The hypothesis is used that the temperature conditions for the maximum workability of heat-resistant and corrosion-resistant steels and alloys correspond to the conditions of high-temperature embrittlement, with the help of which it is possible to create conditions for effective chip crushing and conditions for maximum workability when cutting heat-resistant steels and alloys.

The Nelson-Seiberg Theorem Generalized with Nonpolynomial Superpotentials

The Nelson-Seiberg theorem relates R-symmetries to F-term supersymmetry breaking and provides a guiding rule for new physics model building beyond the Standard Model. A revision of the theorem gives a necessary and sufficient condition to supersymmetry breaking in models with polynomial superpotentials. This work revisits the theorem to include models with nonpolynomial superpotentials. With a generic R-symmetric superpotential, a singularity at the origin of the field space implies both R-symmetry breaking and supersymmetry breaking. We give a generalized necessary and sufficient condition for supersymmetry breaking which applies to both perturbative and nonperturbative models.

Study on chip morphology and surface roughness in ultrasonically assisted drilling of 304 stainless steel

Difficulties in chip breaking and poor machined surface quality are usually considered as the main negative outcomes in conventional drilling (CD). Although researchers have attempted to solve these problems for many years by employing ultrasonic vibrations in the drilling process, studies containing both experimental and theoretical analyses are seldom reported. Based on an in-depth analysis of the kinematic characteristics of ultrasonically assisted drilling (UAD), the conditions for complete geometric chip breaking are derived. The results of the theoretical analysis are verified through a series of experiments, wherein good agreement is found between the experimental and theoretical results. The analyses reveal that UAD has obvious advantages over CD in breaking chips and improving the final surface quality. Additionally, the results show that a low feed rate and an appropriate rotational speed are favorable for chip breaking. The influences of the vibration amplitude, spindle speed, feed rate, and drill bit diameter on the surface roughness are analyzed, and the optimal processing parameters are investigated. The influences of the four factors on the surface roughness in descending order as obtained is amplitude, spindle speed, drill bit diameter, and feed rate. The optimum machining parameters are obtained as 15 μm of amplitude, 450 r/min of spindle speed, 4 mm of drill diameter and 0.08 mm/r of feed rate. Furthermore, a reliable prediction model of surface roughness is established through regression analysis. With this prediction model, the surface roughness under different processing parameters can be approximately predicted.

Parity-time-symmetric frequency-tunable optoelectronic oscillator with a single dual-polarization optical loop.

We propose and experimentally demonstrate a parity-time (PT)-symmetric frequency-tunable optoelectronic oscillator (OEO) in which the PT symmetry is implemented based on a single dual-polarization optical loop. By employing the inherent birefringence of a z-cut lithium niobate (LiNbO3) phase modulator (PM), two mutually coupled optoelectronic loops supporting orthogonally polarized light waves with one experiencing a gain and the other a loss are implemented. By controlling the gain, loss, and the coupling coefficients between the two loops, the PT symmetry breaking condition is met, which enables the OEO to operate in single mode without using an ultranarrow passband optical or microwave filter. The frequency tunability is realized using a microwave photonic filter (MPF) implemented using the PM and a phase-shifted fiber Bragg grating (PS-FBG). The proposed PT-symmetric OEO is experimentally evaluated. A stable and frequency-tunable microwave signal from 2 to 12 GHz is generated. The phase noise of the generated signal at 11.8 GHz is measured, which is -124dBc/Hz at a frequency offset of 10 kHz.

Core makeup tank behavior investigation during ACME integral effect tests

Passive safety systems are widely used in the advance reactors, such as AP1000 and CAP1400. As an important component in the passive safety system, the core makeup tank (CMT) plays a key role for the safety injection and the core decay heat removal. Since the CMT not only provides the full-pressure injection but also triggers the auto depressurization system by its level signal during small-break loss of coolant accident (SBLOCA), the CMT thermal hydraulic behaviors affect the SBLOCA transient process. The thermal hydraulic behaviors of the CMT were investigated by conducting different SBLOCA tests on the ACME integral effect test facility, which includes the 2.5 cm, 5 cm and 20 cm breaks, and double ended direct vessel injection (DVI) line break. Based on the test observations, the CMT injection response to SBLOCA was divided into four phases: the circulation, the drain transition, the injection inhabitation and the final drain. The CMT injection characteristics and the dominate factors were scrutinized based on the phase division. It was found that the break condition has significant impacts on the CMT operating characteristics in each phase. The CMT circulation flow rate can be predicted, and the break size determines the circulation phase length. The CMT drain transition process is controlled by the PBL voiding process that has a close relation to the liquid level change in the cold leg. The ACC-CMT interaction was modeled, and the prediction result agreed with the test result. The comparison tests showed that the ACC nitrogen gas injection still affected the CMT drain behavior. A similar thermal stratification pattern formed during the different SBLCOA tests, and the thermal stratification remained not only in the CMT internal fluid but also in the CMT wall. The estimation of the flashing amount showed it did not play a significant role for the CMT liquid level decline, but it could induce the increases in the pressure difference between the CMT and the system and thus accelerate the CMT drain rate. The CMT internal fluid temperature determined the wall temperature, and a reverse heat transfer process occurred due to the flashing induced wall cooling during the ADS depressurization.

Experimental study for the breaking properties of internal solitary waves flowing over a bottom step

The breaking properties of internal solitary waves (ISWs) flowing over a bottom step were investigated experimentally. The experiments were performed in a two-layer immiscible system to avoid the influence of diffusion and mixing. The flat bottom condition and the bottom step condition had been conducted respectively. The characteristics of incident ISWs, the process of breaking and the subsequent developments were taken into discussion. A modified internal Iribarren number was introduced, and the critical condition of breaking was considered to be related to its trend change point. The initial stage of the breaking process was found can be divided into spatially discrete characteristic structures other than messy flowing of the full interface. And the characteristic structures have close horizontal lengths for different amplitudes. The horizontal velocity gradient was identified as the key parameter of shear instability. By analyzing the subsequent developments, the completely broken ISWs were found can reform a quasi ISWs propagating upon the bottom step which has a smooth front-face and an ever-breaking back-face. Due to the breaking of the back-face, the amplitude of reformed ISWs continues to decrease. Meanwhile, the attenuation rate was noticed to be related to the incident amplitude, but not be related to whether it is broken or the degree of breaking.