Study on in situ stress testing method based on Kaiser effect of acoustic emission and COMSOL simulation

In situ stress testing can improve the safety and efficiency of coal mining.Identifying the Kaiser effect point is vital for in situ stress calculations;however,the in situ stress calculation is limited by the rock sampling angle.Here,the Kaiser effect point identification theory is established and applied to the Xuyong Coal Mine.Uniaxial compression and acoustic emission experiments were carried out on sandstone with 6 sampling directions.Furthermore,COMSOL simulation is applied to study the in situ stress distribution in the coal mine to verify the calculation accuracy.The results are as follows.1)The failure mode of non-bedded and vertical-bedded rocks is primarily tensile shear failure with obvious brittleness in mechanical and acoustic emission characteristics.Shear slip along the bedding plane is the primary failure mode of inclined-bedded rock.Additional take-off points exist in the AE count curve.2)The Kaiser point identification method based on the variation of AE count curve parametersΔti andτi can effectively calculate the in situ stress.According to the numerical value of Kaiser point and sampling direction,the in situ stress of the conveyor roadway in the Xuyong Coal Mine was calculated asσ1=22.81 MPa,σ2=10.87 MPa andσ3=6.14 MPa.3)By the COMSOL simulation study,it was found that a stress concentration zone of 16.13 MPa exists near the two sides roadway.Compared with the Kaiser effect method,the deviation rates of the three-direction principal stress calculated by COMSOL were all less than 5%.This verifies that the in situ stress calculation by Kaiser effect in this study can be applied to the Xuyong Coal Mine.

Integrated Experimental and Simulation Investigation of Breakdown Voltage Characteristics Across Electrode Configurations in SF_(6) Circuit Breakers

This study investigates the breakdown voltage characteristics in sulfur hexafluoride(SF6)circuit breakers,employing a novel approach that integrates both experimental investigations and finite element simulations.Utilizing a sphere-sphere electrode configuration,we meticulously measured the relationship between breakdown voltage and electrode gap distances ranging from 1 cm to 4.5 cm.Subsequent simulations,conducted using COMSOL Multiphysics,mirrored the experimental setup to validate the model’s accuracy through a comparison of the breakdown voltage-electrode gap distance curves.The simulation results not only aligned closely with the experimental data but also allowed the extraction of detailed electric field strength,electric potential contours,and electric current flow curves at the breakdown voltage for gap distances extending from 1 to 4.5 cm.Extending the analysis,the study explored the electric field and potential distribution at a constant voltage of 72.5 kV for gap distances between 1 to 10 cm,identifying the maximum electric field strength.A comprehensive comparison of five different electrode configurations(sphere-sphere,sphere-rod,sphere-plane,rod-plane,rod-rod)at 72.5 kV and a gap distance of 1.84 cm underscored the significant influence of electrode geometry on the breakdown process.Moreover,the research contrasts the breakdown voltage in SF6 with that in air,emphasizing SF6’s superior insulating properties.This investigation not only elucidates the intricate dynamics of electrical breakdown in SF6 circuit breakers but also contributes valuable insights into the optimal electrode configurations and the potential for alternative insulating gases,steering future advancements in high-voltage circuit breaker technology.

From Simulation to Reality: A Comprehensive Study on the Efficacy of a Rotating Monopolar and Bipolar Radiofrequency System through In-Silico Modeling and Pre-Clinical and Clinical Validation

Background: Skin aging is an unavoidable process aggravated by environmental agents. Among other energy devices, non-invasive radiofrequency (RF) technology is widely used for skin tightening and body contouring as it is simpler and more affordable than other technologies that also minimize pain and side-effects. However, most of the current RF devices do not provide automatic skin temperature control and it is difficult to achieve controlled, deep, and harmless thermal increase, so treatment performance and safety is dependent on the operator’s movements and expertise. Objective: To show the potential of numerical simulations for optimizing the design of monopolar and bipolar RF electrodes that are capable of providing homogeneous, deep and controlled heating. Materials and methods: In-silico models were developed and analyzed using Comsol Multiphysics software to simulate the RF effect produced in tissue by rotating monopolar and bipolar electrodes with different geometries from the Sculpt & Shape RF device (Sinclair, Spain), operating at frequencies of 0.5 and 1 MHz. Ex-vivo and in-vivo proof-of-concept tests were carried out to validate the simulations. Finally, treatments were performed on 16 subjects and a total of 78 body areas to assess the clinical results generated by the RF electrodes for skin tightening and body contouring. Results: In-silico studies emulated the superficial and deep dispersion of heat due to the release of RF energy into human skin tissue. The rotating electrodes (monopolar and bipolar) and the selected RF frequency (0.5 and 1 MHz) determined the homogeneity of the thermal distribution, the penetration depth (between 4.37 mm and 25.0 mm) and the heating dynamics (between 30 and 100 seconds to reach the target skin temperature), which were confirmed by ex-vivo and in-vivo tests. In addition, real treatments on facial and body areas using skin temperatures of between 43˚C and 44˚C showed consistent results with good clinical efficacy for skin tightening, circumference reduction and cellulite reduction, with no adverse effects and high subject satisfaction. Conclusions: New monopolar and bipolar RF electrodes with rotating technology have been designed and optimized using numerical simulations. The use of in-silico studies and accurate models that reproduce the thermal behavior of human biological tissues can be used to better understand RF devices and to develop superior, efficient, and safer products more quickly.

Heat transfer and temperature evolution in underground mininginduced overburden fracture and ground fissures: Optimal time window of UAV infrared monitoring

Heat transfer and temperature evolution in overburden fracture and ground fissures are one of the essential topics for the identification of ground fissures via unmanned aerial vehicle(UAV) infrared imager. In this study, discrete element software UDEC was employed to investigate the overburden fracture field under different mining conditions. Multiphysics software COMSOL were employed to investigate heat transfer and temperature evolution of overburden fracture and ground fissures under the influence of mining condition, fissure depth, fissure width, and month alternation. The UAV infrared field measurements also provided a calibration for numerical simulation. The results showed that for ground fissures connected to underground goaf(Fissure Ⅰ), the temperature difference increased with larger mining height and shallow buried depth. In addition, Fissure Ⅰ located in the boundary of the goaf have a greater temperature difference and is easier to be identified than fissures located above the mining goaf. For ground fissures having no connection to underground goaf(Fissure Ⅱ), the heat transfer is affected by the internal resistance of the overlying strata fracture when the depth of Fissure Ⅱ is greater than10 m, the temperature of Fissure Ⅱ gradually equals to the ground temperature as the fissures’ depth increases, and the fissures are difficult to be identified. The identification effect is most obvious for fissures larger than 16 cm under the same depth. In spring and summer, UAV infrared identification of mining fissures should be carried out during nighttime. This study provides the basis for the optimal time and season for the UAV infrared identification of different types of mining ground fissures.

Diagnostic of capacitively coupled radio frequency plasma from electrical discharge characteristics：comparison with optical emission spectroscopy and fluid model simulation

The capacitively coupled radio frequency（CCRF）plasma has been widely used in various fields.In some cases,it requires us to estimate the range of key plasma parameters simpler and quicker in order to understand the behavior in plasma.In this paper,a glass vacuum chamber and a pair of plate electrodes were designed and fabricated,using 13.56 MHz radio frequency（RF）discharge technology to ionize the working gas of Ar.This discharge was mathematically described with equivalent circuit model.The discharge voltage and current of the plasma were measured atdifferent pressures and different powers.Based on the capacitively coupled homogeneous discharge model,the equivalent circuit and the analytical formula were established.The plasma density and temperature were calculated by using the equivalent impedance principle and energy balance equation.The experimental results show that when RF discharge power is 50–300 W and pressure is 25–250 Pa,the average electron temperature is about 1.7–2.1 e V and the average electron density is about 0.5？×10^17–3.6？×10^17m^-3.Agreement was found when the results were compared to those given by optical emission spectroscopy and COMSOL simulation.

Corrosion Behavior of Pipeline Steel in Oilfield Produced Water under Dynamic Corrosion System

In order to predict the corrosion trendency of X100 pipeline steel in flowing oilfield produced water,the effect of flow rate on the corrosion behavior of X100 pipeline steel was studied under general dynamic condition and simulated real working condition at the flow rate of 0.2,0.4,and 0.6 m·s^(-1).Potentiodynamic polarization curves and electrochemical impedance spectroscopy were used to study the corrosion behavior of X100 steel.Energy dispersive spectroscopy,X-ray diffraction and scanning electron microscopy were used to analyze corrosion product composition and micromorphology.The experimental results show that the corrosion is more serious under simulated real working conditions than that under the general dynamic conditions.In any case the corrosion current density increases with the increase of the flow rate,and the total impedance value decreases.The corrosion products include Fe_(3)O_(4),Fe_(2)O_(3),and FeOOH.The mass transfer and electrochemistry were simulated by flow coupled in COMSOL software.The multiphysical field coupling simulation results are closer to the engineering practice than the single flow field simulation,and similar results from the experiments were obtained.Both experimental and simulation results reveal that the higher flow rate is,the more serious corrosion appear and the more corrosion products accumulate.By combining experimental and COMSOL simulation data,the corrosion process model of X100 steel was proposed.

An investigation on improving the homogeneity of plasma generated by linear microwave plasma source with a length of 1550 mm

To develop a larger in-line plasma enhanced chemical vapor deposition(PECVD)device,the length of the linear microwave plasma source needs to be increased to 1550 mm.This paper proposes a solution to the problem of plasma inhomogeneity caused by increasing device length.Based on the COMSOL Multiphysics,a multi-physics field coupling model for in-line PECVD device is developed and validated.The effects of microwave power,chamber pressure,and magnetic flux density on the plasma distribution are investigated,respectively,and their corresponding optimized values are obtained.This paper also presents a new strategy to optimize the wafer position to achieve the balance between deposition rate and film quality.Numerical results have indicated that increasing microwave power and magnetic flux density or decreasing chamber pressure all play positive roles in improving plasma homogeneity,and among them,the microwave power is the most decisive influencing factor.It is found that the plasma homogeneity is optimal under the condition of microwave power at 2000 W,chamber pressure at 15 Pa,and magnetic field strength at 45 mT.The relative deviation is within−3.7%to 3.9%,which fully satisfies the process requirements of the equipment.The best position for the wafer is 88 mm from the copper antenna.The results are very valuable for improving the quality of the in-line PECVD device.

A new approach for accurate determination of particle sizes in microfluidic impedance cytometry

In microfluidic impedance cytometry,the change in impedance is recorded as an individual cell passes through a channel between electrodes deposited on its walls,and the particle size is inferred from the amplitude of the impedance signal using calibration.However,because the current density is nonuniform between electrodes of finite width,there could be an error in the particle size measurement because of uncertainty about the location of the particle in the channel cross section.Here,a correlation is developed relating the particle size to the signal amplitude and the velocity of the particle through the channel.The latter is inferred from the time interval between the two extrema in the impedance curve as the particle passes through a channel with cross-sectional dimensions of 50μm(width)×30μm(height)with two pairs of parallel facing electrodes.The change in impedance is predicted using 3D COMSOL finite-element simulations,and a theoretical correlation that is independent of particle size is formulated to correct the particle diameter for variations in the cross-sectional location.With this correlation,the standard deviation in the experimental data is reduced by a factor of two to close to the standard deviation reported in the manufacturer specifications.

Triple Wavelength and 810 nm Diode Lasers for Hair Removal: A Clinical and in Silico Comparative Study on Indian Skin

In laser hair removal treatments on dark skin, the high concentration of melanin in the skin competes with the melanin in the hair. During standard laser procedures, with wavelengths of 755 nm or 810 nm, a high level of laser light absorption by melanin in the skin is observed. Therefore, to avoid side effects, lower fluence values are used, which further reduces hair-removal efficacy. To improve results, 810 nm diode lasers operating in dynamic mode, with high frequency and multiple passes, are typically used. The aim of this study is to compare the efficacy and safety of triple-wavelength diode lasers (810 nm, 940 nm, 1060 nm) with that of 810 nm diode lasers on Indian patients. A side-by-side comparison was performed using a triple-wavelength diode laser in stamping mode on one side, and an 810 nm diode laser in dynamic mode on the other. Three subjects with skin type IV on the Fitzpatrick scale participated in the study. Efficacy was assessed through hair counting using clinical photographs, taken before and after the treatments, and the Global Aesthetic Improvement Scale (GAIS). Additionally, comparisons related to epidermal heating and thermal damage to the hair follicle were conducted through mathematical 3D simulations using COMSOL Multiphysics® software. Side effects were also evaluated. A superior end point was observed with triple wavelength compared to the 810 nm diode laser. Hair counting showed a 27% greater hair reduction with triple wavelength. No adverse effects were observed. Thermal simulations revealed 29% higher thermal damage with the triple-wavelength laser compared to the 810 nm diode laser. To conclude, on darker skin types, the triple-wavelength diode laser has been shown to be more effective at removing hair, compared to the 810 nm diode laser, while also being a safe procedure.

Combined experimental and simulation study on corrosion behavior of B10 copper-nickel alloy welded joint under local turbulence

The corrosion behavior of B10 copper-nickel alloy welded joints in seawater pipeline system was analyzed under local turbulence induced by weld residual height.The corrosion behavior was evaluated by array electrode technology,mor-phology and elemental characterization,and COMSOL Multiphysics simulation.The results provide a theoretical basis for the corrosion and leakage of B10 alloy in seawater pipeline under the action of turbulence.The results show that residual height-induced turbulence exhibits a significant effect on the corrosion behavior in different areas of welded joints in B10 alloy.Turbulence can damage some surfaces,causing polarity deflection followed by acceleration of corrosion,or it is easier to form a protective film to slow down corrosion.COMSOL Multiphysics results show that the shear rate and turbulent kinetic energy increase linearly with the increase in residual height and velocity.The corrosion behavior of alloy surface is influenced by controlling the mass transfer rate and surface state.

Theory, simulation and experiment of optical properties of cobalt ferrite(CoFe2O4) nanoparticles

Optical properties of cobalt ferrite(CoFe2O4) nanoparticles are modeled and simulated employing finite element analysis(FEA) and density functional theory(DFT) for different particle sizes. The simulated absorption maxima of electronic excitations is red-shifted from 330 nm to 410 nm using finite element analysis and from 331.27 nm to 409.07 nm using quantum mechanical method, with increasing particle sizes from 40 nm to 50 nm. The measured absorption maxima matched the simulated results reasonably well and red-shifted to longer wavelengths from 315.59 nm to 426.73 nm with the increase in particle sizes from 30 nm to 50 nm. The DFT simulated, FEA simulated and experimentally derived optical band gap energies, Eg, were also acquired and compared. The simulated Egvalues decreased from 3.228 to 2.478 e V and from 3.266 to 2.456 e V, while the experimental Egvalue decreased from 3.473 to 2.697 e V, with increasing the particle sizes. The research demonstrated that the optical absorption of CoFe2O4 nanoparticles can be described with high accuracy using the quantum mechanical interpretation based on DFT. FEA based simulations have shown limitations for smaller(< 40 nm) nanoparticles likely due to the increased surface scattering that prevented a stable solution for simulations beyond the quasistatic limit. The DFT computational tool developed by this study can enable both the low cost computation and highly reliable prediction of optical absorption properties and optical band edges, and thus contribute to understanding and design of CoFe2O4 nanoparticle properties prior to fabrication and functionalization of them, for a wide range of applications especially for sensing and photonic wave modulations.

Kinetics process for structure-engineered integrated gradient porous paper-based supercapacitors with boosted electrochemical performance

Due to their rich and adjustable porous network structure,paper-based functional materials have become a research hotspot in the field of energy storage.However,reasonably designing and making full use of the rich pore structure of paper-based materials to improve the electrochemical performance of paper-based energy storage devices still faces many challenges.Herein,we propose a structure engineering technique to develop a conductive integrated gradient porous paper-based(CIGPP)supercapacitor,and the kinetics process for the influence of gradient holes on the electrochemical performance of the CIGPP is investigated through experimental tests and COMSOL simulations.All results indicate that the gradient holes endow the CIGPP with an enhanced electrochemical performance.Specifically,the CIGPP shows a significant improvement in the specific capacitance,displays rich frequency response characteristics for electrolyte ions,and exhibits a good rate performance.Also,the CIGPP supercapacitor exhibits a low self-discharge and maintains a stable electrochemical performance in different electrolyte environments because of gradient holes.More importantly,when the CIGPP is used as a substrate to fabricate a CIGPP-PANI hybrid,it still maintains good electrochemical properties.In addition,the CIGPP supercapacitor also shows excellent stability and sensitivity for monitoring human motion and deaf-mute voicing,showing potential application prospects.This study provides a reference and feasible way for the design of structure-engineered integrated paper-based energy storage devices with outstanding comprehensive electrochemical performance.

Finite element analysis on factors influencing the clamping force in an electrostatic chuck

As one of the core components of IC manufacturing equipment, the electrostatic chuck （ESC） has been widely applied in semiconductor processing such as etching, PVD and CVD. The clamping force of the ESC is one of the most important technical indicators. A multi-physics simulation software COMSOL is used to analyze the factors influencing the clamping force. The curves between the clamping force and the main parameters such as DC voltage, electrode thickness, electrode radius, dielectric thickness and helium gap are obtained. Moreover, the effects of these factors on the clamping force are investigated by means oforthogonal experiments. The results show that the factors can be ranked in order of voltage, electrode radius, helium gap and dielectric thickness according to their importance, which may offer certain reference for the design of ESCs.

The synergistic role of Ti microparticles and CeO_(2) nanoparticles in tailoring microstructures and properties of high-quality Ni matrix nanocomposite coating

In current work,Ni-Ti-CeO_(2) nanocomposite coatings were achieved by co-adding Ti microparticles and CeO_(2) nanoparticles.Designed experiments and COMSOL computer simulation were applied to reveal the synergistic role of Ti microparticles and CeO_(2) nanoparticles in tailoring the spatial microstructures and properties of Ni-Ti-CeO_(2) nanocomposite coating.Unilaterally,the conductive Ti microparticles conducted the growth behavior of Ni grains by current density concentration,distorting electronic feld lines and heterogeneous nucleation.Individual domains consisting of inner nanograins and outer radial columnar grains surrounded Ti microparticles,where Ti microparticles acted as seeds.Ti microparticles tended to be aggregated,leading to spatial heterogeneity of microstructures.Ni deposits buried the Ti microparticles in forms of“covering model”,contributing to the formation of inside voids and rough surface and aggregation of Ti microparticles;on the other hand,the non-conductive CeO_(2)microparticles hardly changed the distribution of current density and electronic feld lines on the cathode surface.Ni deposits buried the CeO_(2)microparticle in forms of“stacking model”,avoiding the inside voids and aggregation of particles.The incorporation of CeO_(2)microparticle brought in microstructure evolutions only on its top side without disturbing the growth behavior of Ni grains on its lateral side or bottom,suggesting the limited effects.This was correlated with the presence of current concentration above the CeO_(2) microparticle at the last stage of burying CeO_(2) microparticle.The co-addition of Ti microparticles and CeO_(2) nanoparticles into Ni deposits exploited the complementary action of the two particles,which gave birth to satisfed spatial microstructures and improved hardness.Ti microparticles took major responsibility for microstructure evolutions,while the CeO_(2) nanoparticles were mainly in charge of the microstructure homogeneity.