Burst Control Research Articles

Coal burst mechanism in large-scale panel under extra-thick key strata

Extra-thick key strata (ETKS) are a key factor causing coal bursts. In this study, field monitoring, physical and numerical modelling, and theoretical analysis were comprehensively adopted to investigate the effect of ETKS on the static and dynamic stress and its impact on coal bursts. Firstly, the coal bursts and the stability of ETKS were investigated. The roof strata structure and the mining-induced stress in a large scale panel under ETKS were analyzed. Then, the coal burst mechanism under ETKS is discussed. The results show that when the panel reaches the 4th and 5th longwall faces, the inferior ETKS and the main ETKS break, respectively, and large-scale cantilever-articulated structures involving the ETKS are formed. This moment, the overburden load is transferred downwards massively, and the coal seam becomes overstressed and accumulates massive elastic energy. Meanwhile, the collaborative collapse of multiple strata in the large cantilever-articulated structures causes the sudden release of elastic energy and high-energy seismicity, which exerts strong dynamic disturbances on the overstressed coal mass and leads to coal burst. Finally, strategies for coal burst control under ETKS including deep-hole pre-splitting blasting and panel size optimization are proposed and validated.

On‐board charger applications: A new hybrid control strategy for bidirectional CLLC resonant converter

AbstractThis paper proposes a new hybrid control strategy to solve the problem of bidirectional wide voltage range regulation in CLLC converters. On the (LLC) side (G2V direction), the SSSA control method is employed for voltage boost, combined with bus voltage and burst control to achieve wide voltage regulation. On the (C) side (V2G direction), the SSSA and full/half‐bridge mode switching control are used to achieve V2G direction wide voltage regulation. This hybrid control strategy also enables high conversion efficiency in both directions without the need for additional components to reduce the converter power density. This is particularly suitable for OBC applications with strict requirements for converter volume and weight. A detailed analysis with mathematical derivation, hybrid control strategy, and converter operation principles is introduced in this paper. The following subchapters supplement the converter voltage gain, soft switching implementation conditions, and design considerations. Finally, the feasibility of the proposed control strategy was verified through an experimental prototype with an input voltage ranging from 340 to 430 V to an output voltage ranging from 225 to 450 V and bidirectional rated power of 6.6/3.3 kW. This prototype achieved a maximum conversion efficiency of 97.7% in the G2V direction and 97.1% in the V2G direction.

An integrated fuse information fusion method for infrared imaging detector and range finder based on improved particle filter

AbstractAiming at the traditional integrated fuse information fusion method that cannot simultaneously obtain high‐precision burst control parameters such as burst delay time, azimuth angle, and detection angle, the infrared imaging detector and range finder information fusion method based on particle filtering with BAS algorithm is proposed. Under the centralized information fusion structure that can obtain higher accuracy, first, use a faster linear interpolation method to realize the time alignment of the two asynchronous sensors. Second, for the strong non‐linear observation model in the missile target rendezvous model, use a particle filter framework that is not affected by the nonlinearity of the system function and non‐gaussian noise. Finally, Utilizing the single search BAS algorithm with low computational complexity to solve the problem of particle degradation in particle filtering and improve the accuracy of burst control. The experiment shows that in a typical simulation environment, the optimized information fusion method improves the burst delay time accuracy by 61.82%, azimuth accuracy by 66.28%, detection angle accuracy by 36.15%, and simulation time is shorter compared to traditional methods.

Adaptive MPC for Burst Incident Management in Water Distribution Networks

This paper investigates an adaptive control strategy which takes advantage of remotely actuated pumps and valves to improve the performance of water distribution networks (WDN) during burst incidents. The proposed strategy relies on model predictive control (MPC) to switch between problem formulations corresponding to normal operating conditions and burst conditions. The optimal control problems are formulated as non-convex non-linear programs (NLP), where the action of fixed-speed pumps and control valves (non-return and bi-directional) is modeled exactly and burst remedial interventions are represented using time-dependent connectivity matrices. We propose an efficient solution method based on reformulations and approximations of the non-convex objectives and constraints and apply the proposed strategy to the adaptive control of an operational WDN during a burst incident. The numerical experiments show that the computed burst control settings allow to partially or completely restore customer supply following the detection of a burst while maintaining minimum water levels in the network tanks and without increasing the cost of pumping operations. The results suggest that the proposed adaptive control strategy can be implemented alone, to mitigate the impact of bursts incidents in WDNs at minimum cost, or to complement traditional remedial interventions.

Research on the initiation pressure criterion of directional hydraulic fracturing in coal mine

Directional hydraulic fracturing (DHF) is more and more widely used in coal mines in China for hard roof and coal burst control. The key to this technology is to determine the crack initiation pressure that affected by the shape of the artificial notch and the stress state around the fracturing hole. Reasonable and simple formula for fracturing pressure calculation is essential since the fracturing pump used in coal mines is usually limited by the harsh conditions and hardly replaced once selected. Based on the superposition principle, the simplified 2D model of DHF was established as the elliptical hole with the internal pressure and solved by using the complex functions method. The analytical solution of tangential stress on the inner surface was obtained meanwhile the corresponding criterion of fracturing pressure can be set up. Considering the characteristics of DHF in coal mines, we further got a simplified formula that controlled by the ratio of major to minor axis of the ellipse-like notch, the ratio of the minimum to the maximum principal stress, as well as the tensile strength of the rock. The formula also gave a guide to the design of the notch that major diameter should be at least twice the minor diameter, and the optimal solution for the ratio is to 2～4 and recommended 4, which can resist the initiation pressure to a large extent affected by the in-situ stress. Once the pressure of the fracturing fluid is high enough to satisfy the equation cracks would arise at the tips of the notch along the major axis which belongs to mode Ⅰ crack and would grow unsteadily and rapidly. A PFC simulation model was used to verify the analysis, the results of which are very consistent with the theoretical solutions.

Circularly symmetric nanopores in 3D femtosecond laser nanolithography with burst control and the role of energy dose

Abstract The fabrication of three-dimensional (3D) nanostructures within optical materials is currently a highly sought-after capability. Achieving nanoscale structuring of media within its inner volume in 3D and with free design flexibility, high accuracy and precision is a development yet to be demonstrated. In this work, a 3D laser nanolithography technique is developed which allows producing mm-long hollow nanopores inside solid-state laser crystals and with a high degree of control of pore cross-sectional aspect ratio and size. We report an in-depth study on the formation of pores both within the non-thermal regime at which temperature is fast dissipated after each laser pulse, and for a thermally controlled regime using pulse-bursts which facilitate the formation of pores with highly circular shapes down to 1.1. We demonstrate this process for a wide range of speeds, pulse repetition rates and pulse energies, thus opening the door to a much more useful nanofabrication technique for nanophotonics. Finally, we also report the change in index of refraction that is produced at the nanoscale obtaining a positive index contrast of ∼3%. The work therefore provides a promising path towards reliable 3D nanostructuring of solid-state laser media for the flexible fabrication of large and complex structures with features sizes from the nanoscale up to the mm-scale. Moreover, due to the embedded, seamless, and monolithic nature of this technology, and since YAG crystals can sustain temperatures of up to 1900 °C and are highly chemically inert and erosion resistant, we anticipate its direct application in harsh environments.

Control Strategy of Half-Bridge Three-Level LLC Resonant Converters With Wide Output Voltage Range

A half-bridge three-level LLC (HBTL-LLC) resonant converter has low voltage stress, high power density, and a large range of soft switching, so it is widely considered and applied, but there are problems such as a small adjustable range of output voltage and difficulty in implementing soft switching. In this article, based on the detailed analysis of the working principle of an HBTL-LLC resonant converter, a three-stage hybrid control strategy is proposed: frequency modulation (FM) control is used when the gain is high, and phase shift control is used when the gain is low. If the phase shift angle achieves the critical value of the soft switch and the gain is still high, variable-frequency burst control is used to expand the adjustment range of the output voltage and improve the power efficiency at low voltage output. Finally, a 500-V, 15-A prototype was designed and analyzed and experimented. The results verified the feasibility and effectiveness of the proposed three-stage hybrid control strategy.

Numerical analysis on stall suppression of a NACA 0012 airfoil by use of burst control plates

Stall suppression is vital during takeoff, maneuver, and landing. Burst Control Plates (BCPs) suppress stall by creating vortices at the leading edge. To suppress stall on NACA 0012 (National Advisory Committee for Aeronautics) airfoil, rectangular cross-section BCPs of a constant height 0.005c and of five different widths (0.008c, 0.016c, 0.024c, 0.032c and 0.040c) are numerically analyzed at four different positions ( 0.045c, 0.05c, 0.07c and 0.1c) on airfoil using ANSYS FLUENT software with transition SST model. For this study airfoil of 200mm chord length(c) at Reynolds number (Re) 1.3 x105 is used. Coefficient of lift (CL), coefficient of drag (CD), and coefficient of pressure (CP) are studied at different angles of attack (α ) for various configurations. BCPs of thickness 0.032c and 0.040c located at 0.045c and 0.05c, suppressed stall by 4°. Other configurations suppressed stall by 2°. Stall suppression by BCP at 0.045c of a thickness 0.032c is found to be the most effective among various configurations.
 

Simulation of airfoil dynamic stall suppression with a burst control blade in a transitional flow regime

Simulation of airfoil dynamic stall suppression with a burst control blade in a transitional flow regime

A Hybrid Control Strategy for Half-bridge Three-level LLC Resonant Converter

The half-bridge three-level LLC resonant converter uses the resonant process of the inductance and the capacitance to transfer energy. It has the advantages of low voltage stress on the switch and high efficiency, but there are problems such as narrow voltage gain range. To widen the voltage gain range of the converter, a hybrid control strategy for a half-bridge three-level LLC resonant converter is proposed in this paper. The voltage gain of the converter is divided into three gain intervals: low, medium and high. Burst control is used in the low gain interval, phase shift control is adopted in the middle gain interval, and frequency modulation control is adopted in the high gain interval. The experiment results show that the proposed control strategy can realize a wide range of output voltage gain of the converter.

Distribution Law of In Situ Stress and Its Engineering Application in Rock Burst Control in Juye Mining Area

This paper presents an integrated approach for mathematical statistics, theoretical analysis, and a field test to investigate the distribution law of in-situ stress and its engineering practice of rock burst control. The test site is located in the Juye mining area, Shandong Province, China. The main conclusions included: (1) There are two types of in-situ stress states in the Juye mining area, σH > σV > σh (42.42%) and σH > σh > σV (57.57%), which are mainly caused by the tectonic stress of the Heze and Fushan faults (The σH, σV, and σh is the maximum principal stress, vertical principal stress or intermediate principal stress and minimum principal stress respectively). (2) The lateral pressure coefficients KH, Kh, and Kav show a non-linear distribution with increased depth, approaching 1.32, 0.96, and 1.41, respectively. The variation range of the horizontal difference stress μd is 0.09–0.58. (3) The average value of the stress gradient is 3.05 MPa/100 m, and the main directions of the maximum horizontal principal stress are northeast–southwest, and northwest–southeast. (4) A new combined supporting strategy, incorporating optimization of roadway layout, anti-impact support system design, and local reasonable pressure relief, was proposed for the rock burst control, and its validity was verified via field monitoring. All these design principles and support strategies for the rock burst control presented in this study can potentially be applied to other similar projects.

Electrospun Fibers Loaded with Natural Bioactive Compounds as a Biomedical System for Skin Burn Treatment. A Review.

Burns are a major threat to public health and the economy due to their costly and laborious treatment and high susceptibility to infection. Efforts have been made recently to investigate natural bioactive compounds with potential use in wound healing. The importance lies in the capacities that these compounds could possess both in infection control by common and resistant microorganisms, as well as in the regeneration of the affected tissues, having in both cases low adverse effects. However, some bioactive molecules are chemically unstable, poorly soluble, and susceptible to oxidative degradation or have low bioavailability. Therefore, developing new technologies for an efficient treatment of wound healing poses a real challenge. In this context, electrospun nanofibers have gained increasing research interest because bioactive molecules can be easily loaded within the nanofiber, resulting in optimal burst control and enhanced drug stability. Additionally, the nanofibers can mimic the extracellular collagen matrix, providing a suitable highly porous structural support for growing cells that facilitate and accelerate skin burns healing. This review gives an overview of the current state of electrospun fibers loaded with natural bioactive compounds as a biomedical system for skin burn treatment.

Mechanism of Hard-Roof Rock Burst Control by the Deep-Hole Blasting: Numerical Study Based on Particle Flow

In underground coal mines, the deep-hole blasting (DHB) technology is generally adopted for thick hard-roof control. This technology uses the energy released by explosives to weaken the energy storage capacity of hard roof so as to prevent hard-roof rock burst disasters. In this paper, a numerical simulation model of roof DHB was established based on particle flow and the damage range of single-hole blasting with concentrated cylindrical charge was studied. The temporal and spatial evolutions of overlying strata, the distribution of the force chain structure, and the working resistance of hydraulic pressure in the mining process before and after the application of DHB were contrastively analyzed. The following beneficial conclusions were drawn. The blasting-induced single-hole damage range is generally characterized by annular zoning. After the application of DHB, overall the collapse morphology of the key strata in the mining process changes from long-distance instantaneous slipping instability to stratified short-arm stepped synergistic subsidence. The density and strength of force chains in the overburden are notably reduced; the peak value of compressive force chain strength in the key strata in the mining process falls by 17.85% as a result of DHB. The monitoring results of the working resistance of hydraulic support reveal that the DHB technology can effectively shorten the step distance of periodic weighting and reduce the variation amplitude of overburden load during weighting. In summary, the mechanism of hard-roof rock burst control by DHB is reflected by both static load reduction and dynamic load reaction.

An Extendable Half-Bridge Dimmable Multi-Channel LED Driver for DC/DC Grid lighting Applications

In this paper, a light emitting diode (LED) driver with multiple outputs, suitable to use with DC grid supply, is proposed. The proposed LED driver provides the ability to individually control the brightness of each output channel. In order to control the output power of each channel, a burst control mode is employed resulting in reduction of conduction losses. Moreover, the half bridge switches are turned on and off at zero voltage (ZV) with a fixed switching frequency; therefore, the switching losses is reduced and efficiency is further increased. Design and implementation have been simplified by choosing the same structure of the resonant series for outputs. A two-channel DC/DC converter is simulated and tested to verify the theoretical analyses.The presented converter operates above resonant frequency to decrease total harmonic distortion and reduce the size and weight of the components. Therefore, it is suitable for high power application of multi-channel drivers.

Numerical Simulation Studies on Stall Suppression of a NACA0015 Airfoil

This study aims to achieve an improved airfoil performance at low Reynolds number, and to determine the optimum position and size of rectangular cross-section burst control plate (BCP) to suppress stall in airfoil. The type of airfoil used in the present study is NACA0015 (National Advisory Committee for Aeronautics) airfoil with 200 mm of chord (c) length. Here, rectangular cross-section burst control plates with different sizes and at different locations are investigated numerically at the low Reynolds number of 1.6×105. Total of three positions (0.05c, 0.1c and 0.2c from the leading edge of airfoil), and four sizes (with heights 0.3 mm, 0.7mm, 1mm and 1.5 mm, and constant width 4 mm) of rectangular BCPs are simulated in ANSYS Fluent software using Transition SST model. The results indicate that the rectangular cross-section burst control plate is an effective device in the suppression of airfoil stall. For 0.7 mm and 1 mm height BCPs, the stall angle is postponed by 2° for all positions, while for 0.3 mm and 1.5 mm height BCPs, the reduction in sudden fall of lift can be observed but at the cost of reduction in maximum lift coefficient. Among various configurations, the 1mm height BCP located at 0.2c position is found to be most effective in the suppression of stall.

Onboard Energy Storage System Based on Interleaved High-Conversion-Ratio Quasi-Resonant Converter With Small Characteristic Impedance

An onboard energy storage system (OESS) withfast-energy-exchange capability is needed to enable future grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operations. To facilitate the fast energy exchange, the OESS normally interfaces between a high voltage (HV) bus on the grid side and a low voltage (LV) bus on the vehicle side. The HV bus can be up to 1200 V, while the LV bus is as low as 48 V, which means a high conversion ratio is needed. Resonant converters are commonly used for OESS and designed with large characteristic impedance for wide-range output power and zero-voltage-switching operation. However, such a design leads to large volume and complex customization of the magnetic components. In this paper, a high-conversion-ratio OESS is proposed, which is based on interleaved quasi-resonant converters with small characteristic impedance. The resonant converters are of modular design with a small characteristic impedance to achieve small volume, low cost, and simple customization. Interleaved in LV-side-parallel and HV-side-series configuration, a high conversion ratio can be achieved. Moreover, modulated in quasi-resonant operations, all the switches can realize soft switching even at light load conditions for high efficiency. Burst control for output regulation is implemented in each modular quasi-resonant converter, while interleaved control is implemented between them to minimize the current ripple. The proposed design and control are validated by a compact 5 kW prototype with a charging/discharging current of 100 A, high power efficiency of 98.91%, a high power density of 3.86 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and high-conversion-ratio (up to 20: 1) power flow between a 1000 VDC HV bus and a 48 VDC LV bus.

Rock Burst Control and Prevention in Mufulira Mine

Rock Burst Control and Prevention in Mufulira Mine

Pillar design and coal burst experience in Utah Book Cliffs longwall operations

Longwall mining has existed in Utah for more than half a century. Much of this mining occurred at depths of cover that significantly exceed those encountered by most other US longwall operations. Deep cover causes high ground stress, which can combine with geology to create a coal burst hazard. Nearly every longwall mine operating within the Utah’s Book Cliffs coalfield has been affected by coal bursts. Pillar design has been a key component in the burst control strategies employed by mines in the Book Cliffs. Historically, most longwall mines employed double-use two-entry yield pillar gates. Double-use signifies that the gate system serves first as the headgate, and then later serves as the tailgate for the adjacent panel. After the 1996 burst fatality at the Aberdeen Mine, the inter-panel barrier design was introduced. In this layout, a wide barrier pillar protects each longwall panel from the previously mined panel, and each gate system is used just once. This paper documents the deep cover longwall mining conducted with each type of pillar design, together with the associated coal burst experience. Each of the six longwall mining complexes in the Book Cliffs having a coal burst history is described on a panel-by-panel basis. The analysis shows that where the mining depth exceeded 450 m, each design has been employed for about 38000 total m of longwall panel extraction. The double-use yield pillar design has been used primarily at depths less than 600 m, however, while the inter-panel barrier design has been used mainly at depths exceeding 600 m. Despite its greater depth of use, the inter-panel barrier gate design has been associated with about one-third as much face region burst activity as the double-use yield pillar design.

A Proposal of Rock Burst Control Measures at the Coalface No. 1 4064 at the Mining Plant 1, in OKD, A. S. Czech Republic

The paper describes a proposal of rock burst control measures for excavation and mining of the area the Coalface No. 1 4064, which is located in the 1st mining block of the Mining Plant 1, locality Karviná. It is an area that has been left in place as a protective area for safety reasons due to the high risk of rock bursts, and it is bordered on both sides by old workings.The aim of the proposal is to extract the retained area by using rock burst control measures to reduce this risk. As a measure, extensive disintegration of the rock massif in the overlying rocks of the seam by blasting works was chosen, both in driving mine workings and in mining of the coalface.The article describes the methods and scope of implementation of active and passive rock burst control measures in standard situations and in the case of detection of an unfavourable stress level.

Detection of stress redistribution in a complex isolated coal pillar with active SVT technology

The detection of stress redistribution in a mining area is essential for forecasting and preventing coal burst disasters in underground mining practices. Active seismic velocity tomography (SVT) is an effective way of investigating large-scale regional stress distribution. Active SVT technology was applied to a complex isolated coal pillar twice to assess coal burst hazard level and to guide the design of de-stress measures as well as to verify their de-stress effect. Test results show that high stress concentration existed in scattered zones along the boundary of the coal pillar rather than in the whole coal pillar. Qualitative comparison of the two SVT tests conducted before and after implementing de-stress measures indicates (1) if high-density wave sources and receivers are appropriately arranged, the spatio-temporal detection precision of active SVT technology could be sufficiently high to identify the de-stress effect of a single deep-hole roof blasting or a group of coal seam blasting upon their completion; (2) The implementation of de-stress measures in the isolated coal pillar area helped drive the stress concentration away from the de-stressed area to the adjacent area instead of fully eliminating the stress concentration. This stress-driving effect indicates that a possibly advisable strategy of coal burst control in the isolated coal pillar area could be driving stress concentration to the area further away from the area of high production activities rather than attempting to eliminate stress concentration.