Effect Of Energy Accumulation Research Articles

Detonation onset due to the energy accumulation effect of shock wave focusing

Shock wave focusing is a highly efficient and reliable method for detonation initiation, which is crucial for the successful operation of detonation engines. To refine the reflector design, a fair comparison of the energy accumulation abilities of different reflectors is necessary. In this study, seven different reflectors, namely, a 30° wedge reflector (WR30°), a 60° wedge reflector (WR60°), a 90° wedge reflector (WR90°), a 120° wedge reflector (WR120°), a reflector designed according to the Chester-Chisnell-Whitham relation (CCW), a parabolic reflector (PARA), and a semicylindrical reflector (SEMI), are investigated numerically. This study also includes a comparison between numerical and experimental results to confirm the accuracy of the simulations. The internal energy density near the apex zones of the reflectors is used as the metric to evaluate the energy accumulation abilities of different reflectors. The results show that the reflectors can be ranked in order of energy accumulation ability as follows: CCW > WR30° > WR60° > PARA > WR90° > WR120° > SEMI. This ranking is also supported by the corresponding numerical soot foils from each of the reflectors. The aforementioned reflectors have at least 2.5 times greater energy accumulation ability than the plane reflector, demonstrating the significant effect of shock wave focusing. Moreover, reflectors with longer converging depths appear to have a better energy accumulation effect. This study provides guidance for selecting different reflectors, which may contribute to higher detonation initiation reliability in detonation-based engines.

Analysis of energy dissipation characteristics and numerical simulation of surrounding rock control for backfill combinations with different ash/sand ratios

To reduce the economic cost of backfilling a mine, layers of cemented materials with different ash sand ratios are often used to backfill the void. In this study, we explored the damage evolution mechanism from the energy consumption point of view for backfill and rock combination with different ash sand ratios, and introduced the strength dissipation rate, damage value parameter and elastic strain energy rate to achieve the definition of damage in the specimens, as well as the characterization of the energy accumulation effect. In addition, the layered backfilling of the assemblage was simulated using FLAC 3D software. The results show that: (1) the elastic strain energy rate can reflect the accumulation ability of the strain energy of the specimen; the larger the strain energy rate, the stronger the accumulation ability; (2) the damage evolution of the backfill–backfill combination is divided into stages: initial damage repair stage, damage stable development stage, damage accelerated development stage and residual damage stage; and (3) the top layer with an ash/sand ratio of 1:4, the middle layer with an ash/sand ratio of 1:8 and the bottom layer with an ash/sand ratio of 1:10 is the optimal backfilling scheme. This study can provide a theoretical reference for the backfilling of a hollow area.

Vibration energy accumulation and absorption characteristics of pseudo acoustic black hole wedge

The Acoustic Black Hole (ABH) is an effective structure for harvesting and dissipating energy from flexural waves. It works by reducing the thickness of the ABH wedge in a power law relationship with m ≥ 2, which rapidly decreases the local phase velocity of flexural waves and leads to an energy convergence effect. However, the vibration performance may differ if the tapered wedge does not meet the requirements of a typical ABH. This article introduces and discusses two types of “pseudo-ABH” wedges: linear-degenerate ABH and step-degenerate ABH. These wedges do not follow the power-law and continuity conditions of typical ABH, respectively. To establish the dynamic models of pseudo-ABH wedges, the lumped-mass transfer matrix method (LTMM) and traveling wave analysis are introduced and validated using analytic solutions of the non-uniform one-dimensional Euler-Bernoulli beam and finite element method. Meanwhile, a good match between the results of the Timoshenko and Euler-Bernoulli beam theory also indicates the correctness of our model. The energy ratio and reflection coefficient are defined to characterize the energy accumulation effect and vibration absorption performance of the pseudo-ABH wedges. The vibration performance of the linear-degenerate ABH is closer to the typical ABH than the step-degenerate ABH. The step-degenerate ABH has more effective energy accumulation and reduction performance for individual frequencies. However, as the number of segments in the step-degenerate ABH increases, its dynamic performance becomes closer to that of the typical ABH. The novelty of this article is to study vibration energy accumulation and absorption characteristics of pseudo acoustic black hole wedges using LTMM model, disclose the differences of linear and step degenerate ABH for their performance, and recommend the step degenerate ABH in place of the typical ABH of a power law thickness relationship.

Offshore Ground Motion Models for Arias Intensity and Cumulative Absolute Velocity in the Japan Trench Area

ABSTRACT This study proposes offshore ground motion models (GMMs) for Arias intensity and cumulative absolute velocity by using the seafloor ground motion database in the Japan Trench area. Whether the station is buried or not will have a great influence on the Arias intensity and cumulative absolute velocity. Compared with existing GMMs, as the magnitude increases, the energy accumulation effect of offshore GMMs is greater than that of onshore GMMs with similar magnitude and distance, and the attenuation rate is slower than other models. The proposed GMMs can be used for seismic hazard and risk analysis in the Japan Trench area.

Piezoelectric Energy Harvesting Technology: From Materials, Structures, to Applications

The piezoelectric energy harvesting is a promising, interesting and complex technology. Herein, the aim is to review the key groups of parameters that contribute to the performance of energy harvesting and to offer a guideline for the future development. For this purpose, a universal theoretical model is developed. According to the model, the parameters are divided into six groups. Each group is then discussed. First, a discussion on the piezoelectric materials status, advantages and disadvantages of ceramics, polymers, single crystals, composites, nanomaterials, and lead‐free materials are summarized. The orientation of materials is also discussed. Second, the structure designs, including off‐resonance, on‐resonance, and impact design were introduced. Third, typical sources of excitations and vibrations are given, including direct contact force, low vibration force, hydraulic, pneumatic power, and acoustic power. The fourth consideration is on the effect of frequency and speed is discussed, focusing on the high‐frequency and high‐speed conditions. This is followed by the effect of electrical load on the output power of an energy harvester was discussed. Last, the parameters of energy accumulation effect and methods are also introduced. Following the above discussion, some examples are provided to show the potential applications, including the areas of structural health monitoring, vibration engines, pavement road energy harvesting, wireless sensor nodes, and human gait power. Finally, at the end of the review, the future challenges are addressed.

Numerical Investigation on the Formation and Penetration Behavior of Explosively Formed Projectile (EFP) with Variable Thickness Liner

Explosively formed projectiles (EFPs) are widely used in civil applications and the military field for their excellent impact performance. How to give full play to the energy accumulation effect of explosives and improve the penetration performance has become the main problem of EFP design. The aim of the present study was to investigate the effect of liner structure on EFP formation and its penetration behavior. In order to achieve this, a finite element (FE) model was first established on the basis of the Lagrange and ALE method. Then, formation and penetration performance tests of EFP were performed to verify the validity and feasibility of the proposed FE model, where the configuration, velocity of EFP, and penetration diameter left on the target plate were compared. Finally, by using the proposed FE model, the entire process of the formation and penetration behavior of EFP with axial symmetrical variable thickness liners were analyzed, where spherical-segment liners with uniform and non-uniform thickness were developed. The results were drawn as follows: the numerical simulation error of EFP velocity was less than 5%, and the simulated penetration diameter was compared to the 8.6% error obtained from the experimental method. It demonstrated that the proposed FE model had higher prediction precision. After the explosive was detonated, a forward-folding EFP was formed by the liner with a thin edge thickness, while the EFP formed by the liner with uniform thickness had a backward-folded configuration. It was also found that the liner with a thin edge thickness gave the largest steady velocity of EFP, and it was the lowest by using the liner with uniform thickness. There were two types of loads generated after the formation of an EFP, those were shock wave loading and an EFP, both causing damage in the target plate during the process of an EFP’s penetration into it. The shock wave induced by liners with non-uniform thickness caused higher damage in the target plate, the maximum value of stress was reached at about 4.0 GPa. The forward-folding EFP formed by the liner with the thinnest edge thickness had the largest penetration ability. The backward-folded EFP, owing to the hollow structure, had the worst penetration ability, which failed to penetrate the target plate.

Damage Analysis of Concrete Structure under Multidirectional Shaped Charge Blasting Using Model Experiment and Ultrasonic Testing

Quantitatively analyzing multidirectional shaped charge blasting energy distribution and improving the rock-fracturing efficiency have been a challenging problem in blasting and civil engineering. In this work, we carry out four groups of concrete model experiments using ultrasonic testing, comparing conventional blasting, and multidirectional shaped charge blasting. Then, the probability and statistics method is used to quantitatively analyze the blasting damage and the energy distribution. The test results show that ultrasonic testing and statistics model can quantitatively evaluate the damage law and energy distribution of blasting. By comparing with conventional blasting method, the multidirectional shaped charge blasting with V-shaped multidirectional shaped energy groove has achieved the effect of energy accumulation. It increases the distribution of energy in the rock crack district, increases the blasting damage range, and improves the rock-fracturing efficiency of blasting. The V-shaped multidirectional shaped energy groove can be used as a new approach for rock fracturing in similar projects.

Analysis of Drum Crystallizer Performance with Refrigerant Heat Accumulation

The device, the operation principle, and the results of tests of a drum crystallizer with refrigerant heat accumulation are presented. The energy accumulation effect is achieved by a special polymetallic insert in a rotating drum. The metals and alloys for the polymetallic insert are chosen. A special gland seal of the drum shaft that reduces refrigerant loss is developed and approved.

Energy-Accumulation-Based Power-Beacon-Assisted WPCN: Time Allocation and Scheduling Schemes

This letter aims to maximize the sum ergodic throughput of a power-beacon (PB)-assisted wireless powered communication network, where the PB located between several sensors and a base station (BS) first performs wireless energy transfer to the sensors and then assists forwarding the information of each sensor to the BS based on TDMA protocol. We consider the energy accumulation effect, i.e., each sensor can harvest additional energy from the PB when the PB forward the information of previous scheduled sensors, and then exhausts the accumulated energy when it starts transmission process. First, we derive the exact and approximate solutions of the ergodic throughput. Second, we prove that the optimization problem is convex and provide numerous new expressions for the optimal time allocation. Moreover, the scheduling sequence for the sensors is also optimized with two proposed methods. Simulations show the considerable gain achieved by the joint optimization scheme.

Effect of Arc Pressure on the Digging Process in Variable Polarity Plasma Arc Welding of A5052P Aluminum Alloy.

The keyhole digging process associated with variable polarity plasma arc (VPPA) welding remains unclear, resulting in poor control of welding stability. The VPPA pressure directly determines the dynamics of the keyhole and weld pool in the digging process. Here, through a high speed camera, high frequency pulsed diode laser light source and X-ray transmission imaging system, we reveal the potential physical phenomenon of a keyhole weld pool. The keyhole depth changes periodically corresponding to the polarity conversion period if the current is same in the electrode negative (EN) phase and electrode positive (EP) phase. There exist three distinct regimes of keyhole and weld pool behavior in the whole digging process, due to the arc pressure attenuation and energy accumulation effect. The pressure in the EP phase is smaller than that of the EN phase, causing the fluctuation of the weld pool free surface. Based on the influence mechanism of energy and momentum transaction, the arc pressure output is balanced by separately adjusting the current in each polarity. Finally, the keyhole fluctuation during the digging process is successfully reduced and welding stability is well controlled.

Heat storage materials based on nanomodified paraffin, controlled by a magnetic field

The article presents studies of nano-modified heat-accumulating materials controlled by a magnetic field. Paraffin is used as a material with the effect of energy accumulation in the phase transition. Carbon nanotubes are used to modify paraffin. For the synthesis of carbon nanotubes used catalyst Co-Mo/Al2O3-MgO. The synthesis process is based on the CVD method. The method of obtaining nanomodified paraffin with ferromagnetic properties is described. To impart paraffin ferromagnetic properties, a ferromagnetic powder previously ground with carbon nanotubes was introduced into it. Mechanical activation was used for the ferromagnetic powder, which provided particles with an average size of 5 ?m. The analysis of charge control regimes of a paraffin-based heat-accumulating material was carried out using a non-contact method for measuring the temperature field. For this purpose, the FLUKE Ti9 thermal imager with a 160 x 120 radiation detector and a matrix in the focal plane and a measurement range from -20 to +250? was used. The morphology and structure of the synthesized carbon nanotubes were studied by scanning electron microscopy (a Hitachi H-800 transmission electron microscope). The behavior of the modified paraffin in the conditions of mineral motor oil under the influence of electromagnetic fields was studied. The design of a heat accumulator for working with a magnetically controlled heat-accumulating material is proposed. It is established that the heat transfer in the system is provided by two simultaneously occurring processes of natural and thermomagnetic convection. In turn, convection can be realized by changing the magnetic susceptibility with a change in temperature and with a geometric change in the position of a magnet or a group of magnets.

Experimental study on the variance of mechanical properties of polyamide 6 during multi-layer sintering process in selective laser sintering

During the selective laser sintering layer-by-layer manufacturing process, many factors such as the ambient temperature and the densification effect will influence the mechanical properties of sintered specimens. In the experimental study, the porosity ratio, crystallinity, and tensile strength of sintered specimens with different ambient temperatures and layers were analyzed. The results indicated that when the ambient temperature rose from 25 to 180 °C, the average porosity ratio decreased from 60% at 25 °C to 39.7–38.7% at 140–180 °C; the relative crystallinity and tensile strength reached a maximum value of 34% and 10 MPa at 140 °C with the same number of sintered layers. According to the measurement of sintered specimens with different layers, the porosity ratio rapidly reduced by 21% from 3 to 10 layers, and the tensile strength improved by 22.5 MPa. When the number of sintered layers reached 10, the change of the porosity ratio and tensile strength were relatively slow, and it would almost disappear as the number of layers exceeded 14. The results showed that the densification process and energy accumulation effect were beneficial to reduce the porosity ratio of specimens, thereby improving its tensile strength in the early period of laser sintering.

The closed form solutions for axisymmetric modeling of thermal stress due to repetitive pulse laser heating

• Novel closed form solutions for axisymmetric modeling of thermal stress induced by repetitive pulse laser heating are obtained. • Thermal stress distributions for different radial and axial locations of material are modeled and analyzed. • Mechanisms of energy gain and stress generation for different laser irradiation regions are analyzed. • Effects of duty cycles on thermal stress distributions are investigated. Repetitive pulse laser heating is increasingly being used in the laser processing industry such as laser welding, laser cutting and laser drilling due to its energy accumulation effect. Modeling of thermo-mechanical coupling effect of repetitive pulse laser heating can enhance the understanding of its thermo physical process. In this paper, an axisymmetric modeling of thermal stress for repetitive pulse laser heating solid materials is introduced, and its closed form solutions are obtained based on a semi-analytical method. The accuracy and efficiency of the closed form solutions are verified by comparison with the existing numerical modeling software based on the finite element method. Distributions of thermal stress for different radial locations, axial locations and duty cycles are calculated, and effects of these parameters on temporal profile of the thermal stress distributions are analyzed. In the region of laser irradiation, three components of thermal stress are all shown as compressive stress. And outside the region of laser irradiation, the hoop component is shown as tensile stress. On the material surface, the change of thermal stresses is very sharp as a result of direct absorption of incident laser energy. With the increasing of the depth, the rises and decreases of thermal stresses become smooth gradually. The duty cycle has a significant effect on the profiles of thermal stresses. In the same conditions, the maximum value of thermal stresses gets higher as the duty cycle decreases. Results of this study can provide some theoretical basis for parameter inversion and optimization of repetitive pulse laser heating, as well as some corresponding experimental research.

The effect of energy accumulation and boundary slip on laminar flow between rotating plates

The poor operating conditions of fluid lubrication equipment during the start-up process are due to the resistance of the high-viscosity lubricating liquid. Moreover, the excessive reduction in fluid viscosity due to the elevated temperature resulting from power consumption during prolonged operation is not conducive to the generation of dynamic pressure. In this study, we examine the effect of energy accumulation and boundary slip on the laminar flow of a liquid between a pair of rotating plates. The experiments are conducted using a rotary rheometer, with polymethyl methacrylate (PMMA) as the thermal insulation material and polytetrafluoroethylene (PTFE) as the slip drag reduction material, and a three-dimensional simulation model is established. This model is derived by combining the energy equation including the slip length and the heat conduction equation. Thus, the temperature changes over time are predicted by this model, and the model accuracy is verified by experiments. The results reveal the following points: 1) boundary slips function as a drag reduction mechanism for short-time continuous operation; 2) under prolonged operation, the slip reduces the extent of the oil viscosity decrease and clear control of the elevated temperature by the boundary slip is observed.

Two first principles of earth surface thermodynamics. mesoscopy, energy accumulation, and the branch point in boson–fermion transition

The author constructs his thermodynamics on the following two “first principles”: the partition theory of integers and the notion of Earth gravity. On the basis of number theory, equivalence classes in mesoscopy and soft condensates in the partition theory of integers are considered. The self-consistent equation obtained by the author on the basis of Gentile statistics is used to describe the effect of energy accumulation at themoment of transition of the boson branch of the partition of a number to the fermion branch. The branch point in the transition from bosons to fermions is interpreted as an analog of a jump of the spin.

Energy Accumulation in a Functionally Graded Spatial-Temporal Checkerboard

This letter extends the analysis of wave propagation in transmission lines with LC -parameters varying in space and time and the related effect of energy accumulation emerging from the concept of dynamic materials. We consider a practically important scenario of functionally graded checkerboard in space and time, i.e., the assembly combined of two dielectrics with material property transition zones applied instead of sharp interfaces. It is shown that the energy accumulation in traveling waves is preserved for certain ranges of material and geometric parameters.

Theoretical and experimental study of energy transportation and accumulation in femtosecond laser ablation on metals

The energy transportation and accumulation effect for femtosecond (fs) laser ablation on metal targets were studied using both theoretical and experimental methods. Using finite difference method, numerical simulation of energy transportation characteristics on copper target ablated by femtosecond laser was performed. Energy accumulation effects on metals of silver and copper ablated by an amplified Ti: sapphire femtosecond laser system were then studied experimentally. The simulated results show that the electrons and lattices have different temperature evolvement characteristics in the ablation stage. The electron temperature increases sharply and reaches the maximum in several femtoseconds while it needs thousands of femtoseconds for lattice to reach the maximum temperature. The experimental results show that uniform laser-induced periodic surface structures (PSS) can be formed with the appropriate pulsed numbers and laser energy density. Electron-phonon coupling coefficient plays an important role in PSS formation in different metals. Surface ripples of Cu are more pronounced than those of Au under the same laser energy density.

Energy accumulation effect and parameter optimization for fabricating of high-uniform and large-area period surface structures induced by femtosecond pulsed laser

In this paper, theoretical and experimental investigations are performed to understand the effect of laser energy accumulation on morphologies of femtosecond laser-induced periodic surface structures (LIPSSs). Based on energy accumulation effect we put forward, scanning velocity, distance of two adjacent scan lines and pulsed laser energy density are optimized to fabricate high-uniform and large-area period surface structures for the first time. Our theoretical results can offer clues to choose experiment parameters in order to obtain high-quality LIPSSs which have extensively emerging and potential applications in optoelectronics, phononics and so on.

Measurements of neutron emission from a Z-pinch constriction

Results are presented from measurements of neutron emission generated during discharges with current amplitudes of up to 3 MA and a current rise time of ∼100 ns through profiled loads 10 mm in height and 4–5 mm in diameter. The experiments were performed with the S-300 eight-module high-power generator. To enhance the effect of energy accumulation, a≤1-mm-diameter neck was made in the central region of the load. An agar-agar foam of mass density 0.1 g/cm3 with an additive of deuterated polyethylene was used as a plasma-forming material. The formation of a hot plasma in the Z-pinch constriction was accompanied by the emission of soft X-ray (E = 1–10 keV), hard X-ray (E ≥ 30 keV), and neutron pulses with a minimum pulse duration of ≤10 ns. The neutron energy measured by the time-of-flight technique in three directions relative to the load axis (0°, 90°, and 180°) was found to be 2.5 ± 0.3 MeV, which corresponds to the dd reaction. The total neutral yield during the development of one constriction with a characteristic size of 100 μm attained 108 neutrons per pulse.

Picosecond high-repetition-rate pulsed laser ablation of dielectrics: the effect of energy accumulation between pulses

We report experiments on the ablation of arsenic trisulphide and silicon using high-repetition-rate (megahertz) trains of picosecond pulses. In the case of arsenic trisulphide, the average single pulse fluence at ablation threshold is found to be >100 times lower when pulses are delivered as a 76-MHz train compared with the case of a solitary pulse. For silicon, however, the threshold for a 4.1-MHz train equals the value for a solitary pulse. A model of irradiation by high-repetition-rate pulse trains demonstrates that for arsenic trisulphide energy accumulates in the target surface from several hundred successive pulses, lowering the ablation threshold and causing a change from the laser-solid to laser-plasma mode as the surface temperature increases.