Performances of a Stinger PDC cutter breaking granite: Cutting force and mechanical specific energy in single cutter tests

The Stinger PDC cutter has high rock-breaking efficiency and excellent impact and wear resistance, which can significantly increase the rate of penetration (ROP) and extend PDC bit life for drilling hard and abrasive formation. The knowledge of force response and mechanical specific energy (MSE) for the Stinger PDC cutter is of great importance for improving the cutter's performance and optimizing the hybrid PDC bit design. In this paper, 87 single cutter tests were conducted on the granite. A new method for precisely obtaining the rock broken volume was proposed. The influences of cutting depth, cutting angle, and cutting speed on cutting force and MSE were analyzed. Besides, a phenomenological cutting force model of the Stinger PDC cutter was established by regression of experimental data. Moreover, the surface topography and fracture morphology of the cutting groove and large size cuttings were measured by a 3D profilometer and a scanning electron microscope (SEM). Finally, the rock-breaking mechanism of the Stinger PDC cutter was illustrated. The results indicated that the cutting depth has the greatest influence on the cutting force and MSE, while the cutting speed has no obvious effects, especially at low cutting speeds. As the increase of cutting depth, the cutting force increases linearly, and MSE reduces with a quadratic polynomial relationship. When the cutting angle raises from 10° to 30°, the cutting force increases linearly, and the MSE firstly decreases and then increases. The optimal cutting angle for breaking rock is approximately 20°. The Stinger PDC cutter breaks granite mainly by high concentrated point loading and tensile failure, which can observably improve the rock breaking efficiency. The key findings of this work will help to reveal the rock-breaking mechanisms and optimize the cutter arrangement for the Stinger PDC cutter.

Preface for Special Issue on“Key Mechanical Problems of Marine Energy Development Equipment”

There are abundant energy reserves such as oil,natural gas,hydrate,and wind energy in the ocean.Countries around the globe are competing to advance their marine energy development technologies.The exploitation of marine resources relies on cutting-edge industrial equipment.After decades of R&D endeavors,China has obtained most of the key technologies for the design,production,testing,and field application of marine energy development equipment(Xie and Zeng,2021).

A novel improvement strategy and a comprehensive mechanism insight for α-MnO_(2) energy storage in rechargeable aqueous zinc-ion batteries

Aqueous zinc-ion batteries have been regarded as the most potential candidate to substitute lithium-ion batteries.However,many serious challenges such as suppressing zinc dendrite growth and undesirable reactions,and achieving fully accepted mechanism also have not been solved.Herein,the commensal composite microspheres withα-MnO_(2) nano-wires and carbon nanotubes were achieved and could effectively suppress ZnSO_(4)·3Zn(OH)_(2)·nH_(2)O rampant crystallization.The electrode assembled with the microspheres delivered a high initial capacity at a current density of 0.05 A g^(-1) and maintained a significantly prominent capacity retention of 88%over 2500 cycles.Furthermore,a novel energy-storage mechanism,in which multivalent manganese oxides play a synergistic effect,was comprehen-sively investigated by the quantitative and qualitative analysis for ZnSO_(4)·3Zn(OH)_(2)·nH_(2)O.The capacity contribution of multivalent manganese oxides and the crystal structure dissection in the transformed processes were completely identified.Therefore,our research could provide a novel strategy for designing improved electrode structure and a comprehensive understanding of the energy storage mechanism of α-MnO_(2) cathodes.

Energy evolution mechanism and failure criteria of jointed surrounding rock under uniaxial compression

The object of this article is to investigate the energy evolution mechanism and failure criteria of cross-jointed samples containing an opening during deformation and failure based on the uniaxial compression test and rock energy principle.The results show that the energy evolution characteristics of the samples correspond to a typical progressive damage mode.The peak total energy,peak elastic energy,and total input energy of the samples all first decrease and then increase with an increase of half of the included angle,reaching their minimum values when this angle is 45°,while the dissipated energy generally increases with this angle.The existence of the opening and cross joints can obviously weaken the energy storage capacity of the rock,and the change in the included angle of the cross joint has a great influence on the elastic energy ratio of the sample before the peak stress,which leads to some differences in the distribution laws of the input energy.The continuous change and the subsequent sharp change in the rate of change in the energy consumption ratio can be used as the criteria of the crack initiation and propagation and the unstable failure of the sample,respectively.

Recent advances in energy storage mechanism of aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion batteries(ZIBs)have recently attracted increasing research interest due to their unparalleled safety,fantastic cost competitiveness and promising capacity advantages compared with the commercial lithium ion batteries.However,the disputed energy storage mechanism has been a confusing issue restraining the development of ZIBs.Although a lot of efforts have been dedicated to the exploration in battery chemistry,a comprehensive review that focuses on summarizing the energy storage mechanisms of ZIBs is needed.Herein,the energy storage mechanisms of aqueous rechargeable ZIBs are systematically reviewed in detail and summarized as four types,which are traditional Zn^(2+)insertion chemistry,dual ions co-insertion,chemical conversion reaction and coordination reaction of Zn^(2+)with organic cathodes.Furthermore,the promising exploration directions and rational prospects are also proposed in this review.

Experimental investigation on the energy evolution of dry and water-saturated red sandstones

In order to investigate the effect of water content on the energy evolution of red sandstone, the axial loading–unloading experiments on dry and water-saturated sandstone samples were conducted, and the distribution and evolution of elastic energy and dissipated energy within the rock were measured.The results show that the saturation process from dry to fully-saturated states reduces the strength, rigidity and brittleness of the rock by 30.2%, 25.5% and 16.7%, respectively. The water-saturated sample has larger irreversible deformation in the pre-peak stage and smaller stress drop in the post-peak stage.The saturation process decreases the accumulation energy limit by 38.9%, but increases the dissipated energy and residual elastic energy density, thus greatly reducing the magnitude and rate of energy release. The water-saturated sample has lower conversion efficiency to elastic energy by 3% in the prepeak region; moreover, the elastic energy ratio falls with a smaller range in the post-peak stage.Therefore, saturation process can greatly reduce the risk of dynamic disaster, and heterogeneous water content can lead to dynamic disaster possibly on the other hand.

Instability energy mechanism of super-large section crossing chambers in deep coal mines

The stress concentration and failure at chamber intersections in coal mine are intense,especially in deepburied,super-large section conditions.In this paper,the plastic radius of super-large section chamber under unequal pressure was corrected on the basis of the size effect.Then,stress and failure evolution of intersections under different crossing angles and equivalent angular bisectors were revealed.Furthermore,2 trajectory curves of failure and stress were analytically expressed,which divided the intersection into 5 influencing zones in the light of stress superposition degree.After determining instability trigger point and instability path,instability energy criterion of intersection can be obtained as K>1,which means that the external energy is greater than the sum of energy consumed by surrounding rock instability and supporting structure failure.Taking coal-gangue separation system of Longgu Coal Mine as example,it was found that there was instability risk under original parameters.For long-term stability,an optimization design method was proposed by considering safety factor,and optimal support scheme was obtained.Field monitoring showed intersections deformations were relatively small with the maximum of 125 mm,which verified the rationality of theoretical analysis.This study provides guidance for the stability control of the intersections under the same or similar conditions.

CFD Simulation and Experimental Study of a New Elastic Blade Wave Energy Converter

Small moving vehicles represent an important category of marine engineering tools and devices(equipment)typically used for ocean resource detection and maintenance of marine rights and interests.The lack of efficient power supply modes is one of the technical bottlenecks restricting the effective utilisation of this type of equipment.In this work,the performance characteristics of a new type of elastic-blade/wave-energy converter(EBWEC)and its core energy conversion component(named wave energy absorber)are comprehensively studied.In particular,computational fluid dynamics(CFD)simulations and experiments have been used to analyze the hydrodynamics and performance characteristics of the EBWEC.The pressure cloud diagrams relating to the surface of the elastic blade were obtained through two-way fluid-solid coupling simulations.The influence of blade thickness and relative speed on the performance characteristics of EBWEC was analyzed accordingly.A prototype of the EBWEC and its bucket test platform were also developed.The power characteristics of the EBWEC were analyzed and studied by using the blade thickness and motion cycle as control variables.The present research shows that the EBWEC can effectively overcome the performance disadvantages related to the transmission shaft torque load and power curve fluctuations of rigid blade wave energy converters(RBWEC).

A comprehensive review of miniatured wind energy harvesters

Following the current rapid development of the Internet of Things(IoT)and wireless condition monitoring systems,energy harvesters which use ambient energy have become a key part of achieving an energy-autonomous system.Miniature wind energy harvesters have attracted widespread attention because of their great potential of power density as well as the rich availability of wind energy in many possible areas of application.This article provides readers with a glimpse into the state-of-the-art of miniature wind energy harvesters.The crucial factors for them to achieve high working efficiency under lower operational wind speed excitation are analyzed.Various potential energy coupling mechanisms are discussed in detail.Design approaches for broadening operational wind-speed-range given a variety of energy coupling mechanisms are also presented,as observed in the literature.Performance enhancement mechanisms including hydrodynamic configuration optimization,and non-linear vibration pick-up structure are reviewed.Conclusions are drawn and the outlook for each coupling mechanisms is presented.

Study on Nano-structured WC-Co Composite Powders Made by Mechanical Milling

Nano structured WC Co composite powders were prepared by high energy mechanical milling. The microstructure of as milled WC Co composite powders (including grain size, lattice strain, Co distribution and lattice defects) was investigated by X ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive X ray spectroscopy (EDS). Nano structured WC co vered and separated by cobalt thin layers with average grain size less than 10 nm was obtained by high energy mechanical milling. The morphology of WC grains is almost spherical. High energy mechanical milling could also bring about a large number of lattice defects in WC grains.

Energy Storage Mechanism of Vanadium Nitride via Intercalating Different Atomic Radius for Expanding Interplanar Spacing

As a promising anode material in supercapacitors,vanadium nitride has been widely concerned due to its ultra-high theoretical specific capacitance.However,its routine test capacitance value is still far from the theoretical value and its energy storage mechanism is controversial.In order to solve these two key problems,here we prepare interplanar spacing expanded vanadium nitride materials with different impurity atoms intercalation from two anionic precursors of vanadium-based metal organic frameworks with different functional groups.The obtained vanadium nitride reaches a higher specific capacitance;and further,through ex situ X-Ray diffraction and in situ Raman,the charge storage of vanadium nitride is contributed by two processes:the first benefit is from the K^(+) de/intercalation in the interplanar spacing,and the other one is derived from the redox reaction with OH−by adsorption on surface.Furthermore,both of the first principle calculation and extended experiments support this idea.We believe that such detailed research on the energy storage mechanism can provide a clear idea for the application of metal nitrides in supercapacitors and other energy storage devices.

Energy transfer mechanism of Sr_4Al_(14)O_(25):Eu^(2+) phosphor

Long lasting blue-green-emitting Sr4Al14O25:Eu2+ phosphors were synthesized by solid-state reactions.The phosphors were investigated by X-ray diffraction(XRD) and fluorescence spectrophotometer.A pure phase of Sr4Al14O25:Eu2+ phosphor was obtained at 1250 °C.There are two different types of Eu emission centers in Sr4Al14O25:Eu2+ phosphor.The effects of the Eu2+ concentration and the reducing temperature on the distribution of Eu2+ among different sites were investigated.The energy transfer mechanism between...

An Investigation on Hydrogen Storage Kinetics of the Nanocrystalline and Amorphous LaMg12-type Alloys Synthesized by Mechanical Milling

Nanocrystalline and amorphous LaMg_（12）-type LaMg_（11）Ni ＋ x wt% Ni（x = 100, 200） alloys were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous and electrochemical hydrogen storage kinetics of as-milled alloys were investigated systematically. The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system. And the gaseous hydrogen storage properties were investigated by Sievert apparatus and a differential scanning calorimeter（DSC） connected with a H_2 detector. Hydrogen desorption activation energy of alloy hydrides was estimated by using Arrhenius and Kissinger methods. It is found that the increase of Ni content significantly improves the gaseous and electrochemical hydrogen storage kinetic performances of as-milled alloys. Furthermore, as ball milling time changes, the maximum of both high rate discharge ability（HRD） and the gaseous hydriding rate of as-milled alloys can be obtained. But the hydrogen desorption kinetics of alloys always increases with the extending of milling time. Moreover, the improved gaseous hydrogen storage kinetics of alloys are ascribed to a decrease in the hydrogen desorption activation energy caused by increasing Ni content and milling time.

Research on Coupling Transfer Characteristics of Vibration Energy of Free Piston Linear Generator

In order to clarify the mechanism and main influencing factors of the vibration energy coupling transmission with a dual-piston structure,a thermodynamic and dynamic coupling model of the free piston linear generator(FPLG)was established.The system energy conversion,vibration energy coupling transmission,and influencing factors were studied in detail.The coupling transmission paths and the secondary influence mechanism from in-cylinder combustion on vibration energy transmission were obtained.In addition,the influence of the movement characteristics of the dual-piston on the vibration energy transmission was studied,and the typical parameter variation law was obtained,which provides theoretical guidance for the subsequent vibration reduction design of the FPLG.

Diffusion Mechanism of Energy Flow in Multi-heat-source Synthesis of SiC

Through the experiments and the numerical simulation of temperature field in multi-heatsource synthesis Si C furnace, in order to research the feature point in multi-heat-source synthesis furnace, the variation law of heat fl ux was studied and the multi-directional energy fl ow diffusion mechanism was revealed. The results show that, due to the shielding action between the heat-source and the superposition effect of thermal fields, the insulating effect is best in multi-heat-source synthesis furnace. The heat emission effect is good outside the common area between heat-sources, but the heat storage is poor. Compared with the synthesis furnace that heat source is parallelly arranged, the furnace of stereoscopic arrangement has a more obvious heat stacking effect and better heat preservation effect, but the air permeability of heat source connecting regions is worse. In the case with the same ingredients, the resistance to thermal diffusion and mass diffusion is higher in heat source connecting regions.

Study of Reactions Induced by Mechanical Milling in ZnO-α-Fe_2O_3 System

Spinel ferrite ZnFe 2O 4 powders were synthesized directly from ZnO and α Fe 2O 3 mixtures by high energy mechanical milling. X ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) were used to investigate the chemical reaction processing at different milling time. It has been found that the solid reactions between metal oxides are characterized by stages. Once the solid chemical synthesized reaction is initialized, it proceeds quickly and can be completed in very short time. Grain sizes of ZnFe 2O 4 are less than 10 nm.

Study on the energy evolution mechanism of low-temperature concrete under uniaxial compression

In order to study the mechanical properties and energy evolution of low-temperature concrete during uniaxial compres‐sion, a uniaxial compression test was performed on concrete. In addition, the evolution laws of compressive strength, deformation modulus and total energy, elastic potential energy, dissipated energy and peak energy of concrete in the process of deformation and failure are analyzed. The effects of age and temperature on low-temperature concrete is analyzed from the perspective of energy. Test results show that temperature improves the strength and deformation of concrete to varying degrees. When cured for 28 days, the compressive strength and deformation modulus of concrete at −20 ℃ is increased by 17.98% and 21.45% respectively, compared with the compressive strength and deformation modulus at room temperature of 20 ℃. At the point of failure of the concrete under uniaxial compression, the total damage energy and the dissipation energy both increase, while the developed elastic strain energy increases and then decreases. Increase in curing duration tends to increase the total destruction energy of concrete, peak point elastic strain energy, peak point dissipation energy, and peak point total energy. Whereas increase in curing durations, has shown to decrease the total destruction energy of concrete, the peak point elastic strain energy, peak point dissipation energy, and peak point total energy. The peak point strain energy reflects the ability of low-temperature concrete to reasonably resist damage. By using the principle of energy analysis to study the deformation process of concrete, it provides research methods and ideas for the deformation analysis of this type of material under load.

Methylene blue intercalated vanadium oxide with synergistic energy storage mechanism for highly efficient aqueous zinc ion batteries

With the rise of aqueous multivalent rechargeable batteries,inorganic-organic hybrid cathodes have attracted more and more attention due to the complement of each other’s advantages.Herein,a strategy of designing hybrid cathode is adopted for high efficient aqueous zinc-ion batteries(AZIBs).Methylene blue(MB)intercalated vanadium oxide(HVO-MB)was synthesized through sol-gel and ion exchange method.Compared with other organic-inorganic intercalation cathode,not only can the MB intercalation enlarge the HVO interlayer spacing to improve ion mobility,but also provide coordination reactions with the Zn^(2+)to enhance the intrinsic electrochemical reaction kinetics of the hybrid electrode.As a key component for the cathode of AZIBs,HVO-MB contributes a specific capacity of 418 mA h g^(-1) at 0.1 A g^(-1),high rate capability(243 mA h g^(-1) at 5 A g^(-1))and extraordinary stability(88%of capacity retention after 2000cycles at a high current density of 5 A g^(-1))in 3 M Zn(CF_(3)SO_(3))_(2) aqueous electrolyte.The electrochemical kinetics reveals HVO-MB characterized with large pseudocapacitance charge storage behavior due to the fast ion migration provided by the coordination reaction and expanded interlayer distance.Furthermore,a mixed energy storage mechanism involving Zn^(2+)insertion and coordination reaction is confirmed by various ex-situ characterization.Thus,this work opens up a new path for constructing the high performance cathode of AZIBs through organic-inorganic hybridization.

Energy Consumption and Erosion Mechanism of Polyester Fiber Reinforced Cement Composite in Wind-blown Sand Environments

Considering the economic and environmental benefits associated with the recycling of polyester(PET)fibres,it is vital to study the application of fibre-reinforced cement composites.According to the characteristics of the wind-blown sand environment in Inner Mongolia,the erosion resistance of the polyester fibre-reinforced cement composites(PETFRCC)with different PET fibre contents to various erosion angles,velocities and sand particle flows was investigated by the gas-blast method.Based on the actual conditions of sandstorms in Inner Mongolia,the sand erosion parameters required for testing were calculated by the similarity theory.The elastic-plastic model and rigid plastic model of PETFRCC and cement mortar were established,and the energy consumption mechanism of the model under particle impact was analyzed.The experimental results indicate that the microstructure of PETFRCC rafter hydration causes a spring-like buffering effect,and the deformation of PETFRCC under the same impact load is slightly smaller than that of cement mortar,and the damage mechanism of PETFRCC is mainly characterized by fiber deformation and slight brittle spalling of matrix.And under the most unfavorable conditions of the erosion,the erosion rate of 0.5PETFRCC is about 57.69%lower than that of cement mortar,showing better erosion resistance.

Electrothermal energy conversion mechanism of micro-scale semiconductor bridge

The response characteristics of resistance is observed by the analysis of experimental data of micro scale semiconductor bridge （MSCB） under different voltage inputs. Two critical voltages are found. One is called exploding voltage, above which the MSCB can be melted and vaporized without generating a plasma, and the other is called producing a plasma voltage, above which the MSCB is entirely vaporized, and then the current flows through the vapor producing the plasma. Based on the non Fourier heat conduction theory, the electrothermal energy conversion model is es tablished for the stage from heating to exploding, and then the correlation of MSCB and time is ob tained by graphic calculation. Importantly, the critical exploding voltage and exploding time are also derivate. With the comparison between the analytical result from the theoretical model and that from experimental data, it has been demonstrated that the theoretical model is reasonable and feasible for designing the exploding voltage and exploding time.