Distribution Of Physical Fields Research Articles

Thermal Protection System Damage Diagnosis Method Using Machine Learning Algorithm

The thermal protection system (TPS) for spacecraft is easily damaged by various thermal and mechanical loads, which adversely affects the thermal protection performance of the system. TPS damages diagnosis is one of the most complex and challenging problems for spacecraft structural reliability. The embedded distributed optical fiber sensor can directly reflect the physical field distribution of the structure and then evaluate its health status. One of the challenges of this technique is to accurately extract signal characteristics and reconstruct damage state information. A quantile random forest and self-organizing map (SOM) neural-network-based two-step damage diagnosis framework for thermal protection systems is investigated in this Paper. In this Paper, the combination of physical interpretation and data driving is used to analyze the strain anomaly of the TPS specimen and obtain the damage diagnosis results, including the location, influence area, and categories of damage. First, the abnormal distribution of strain values caused by different types of damage is studied by numerical simulation. Then, the outliers of the experimental strain distribution data are detected by using quantile random forest. A signal features vector is extracted from each signal segment, and the SOM neural network is trained to classify damage. Using the trained model to classify the test set, the accuracy of damage classification is 100%. The experiment result shows great potential for the proposed approach is not only possible to detect the presence of damage, but it is also able to locate and estimate the extent of the damage, which helps one make an appropriate decision on the diagnosis.

Three-dimensional numerical simulation of physical field distribution of radio frequency thermal plasma

Radio frequency (RF) thermal plasma involves abundant and complex physics. The understanding of the physical field distributions of the RF thermal plasma is helpful to its applications in industrial field. In this paper, an electro-thermal-magnetic-flow strong coupling mathematical and physical model of three-dimensional RF thermal plasma is established, the actual solenoid structure of the induction coil is considered, and a C++ code is developed for calculating the complex electromagnetic field in a customized version of the computational fluid dynamics commercial code FLUENT. The physical fields of RF thermal plasma, such as temperature field, flow field and electromagnetic field are studied. The electrical conductivity, thermal conductivity and viscosity distribution of the plasma are investigated. The results show that the physical field distribution of RF thermal plasma has an important non-axisymmetric three-dimensional effect due to the actual shape of the non-axisymmetric induction coil structure. The plasma discharge presents an annular distribution with a certain deflection angle. The distribution of plasma flow field shows a non-axisymmetric electromagnetic pump effect which is different from that of the two-dimensional model. The results have great guiding significance for optimizing and controlling the RF thermal plasma in various application areas.

Thomson effect in thermo-electro-magneto semiconductor medium during photothermal excitation process

ABSTRACT The effect of Thomson heating on semiconductor medium is studied. Analytical discussions in the presence of thermoelectricity and magnetic field, in the context of photothermal transport process, are made. The interactions between plasma, thermoelectric, magnetic and elastic waves are taken into consideration. The governing equations are investigated in two-dimensional deformations of a homogenous, isotropic medium. The density of charge is taken only as a function of time of the induced electric current. The normal mode technique is used to obtain the physical quantities field under investigation. Some electro-mechanical loads and thermal effect through recombination process are applied at the free surface of semiconductor elastic medium. The distributions of physical fields in this phenomenon are discussed and represented graphically. The results have been discussed under the effects of thermoelectric parameter and Thomson parameter.

Influence of feed architecture on heat and mass transfer in calcium carbide electric furnace

It is of particular important to optimize the feed of calcium carbide (CaC2) production by improving the productivity and reducing the energy consumption. In this present paper, a transient mathematical model was established to analyze the effects of feed on heat and mass transfer characteristics of CaC2 electric furnace. The model was adopted to study the effects of powder and compressed feed on heat and mass transfer characteristics. In addition, the influence of the size of compressed feed particles on physical field distribution in the equipment was also investigated. The results displayed that the application of compressed feed is better than traditional powder feed in reducing serious local overheating and increasing the CaC2 production. When the three-phase alternating current (I) level increases from 10,000 A to 14,000 A, the average maximum temperature of the compressed feed furnace is about 8.8% lower than that of the traditional powder feed furnace. However, when furnace feed switches from powder feed to compressed feed, the average CaC2 production increases by about 18.6%. Small sizes of compressed feed is qualified with significant advantages in increasing the output. When I = 12,000 A and the size of compressed feed particle decreases from 5.0 mm to 0.4 mm, CaC2 production increases by about 26.5%, while when compressed feed particle size≤ 1.0 mm, with further size reduction, the differences in CaC2 output is not obvious. The study on the feed of CaC2 electric furnace on heat and mass transfer characteristics contributes to the optimization of performance in CaC2 electric furnace smelting.

Alleviating the performance degradation of fuel cells caused by the uneven distribution of internal physical fields

The performance degradation of proton exchange membrane (PEM) fuel cells is inevitable in real-time application. In particular, water management issues are related to the optimization design and the stable operation of the fuel cell system. The investigation of the mass transportation of an open-cathode PEM fuel cell based on a three-dimensional numerical model is emulated using computational fluid mechanics (CFD). The unified finite element analysis for the coupled phenomena of the charge transport, mass transport, and electrochemical reactions is discussed in this work. The simulation results are observed and compared with other experimental observations and various physical fields have shown uneven distributed inside of the fuel cell due to the single-direction gases transfer strategy. Therefore, in this study, a strategy based on interchangeable anode inlet and outlet is proposed to alleviate the uneven distribution of internal physical fields. Moreover, the optimized periods of inlet and outlet exchange are studied by comparing the experimental results.

Analysis and optimization about electromagnetics-temperature-component distribution in calcium carbide electric furnace

It is of particular value to optimize the electromagnetics-temperature-component multi-physical field in electric furnace in improving productivity and reducing energy consumption. In this paper, the effects of three-phase alternating current and electrode immersion ratio on multi-physical field in calcium carbide electric furnace were studied. Meanwhile, a new criterion called benefit evaluation factor was proposed. Benefit evaluation factor is used to comprehensively evaluate the consumption of electric energy and calcium carbide production in electric furnace. Additionally, to improve the physical field distribution in the equipment, an innovative multi-layer electrode furnace was proposed. The results show that the energy consumption and calcium carbide production decrease with the increase of electrode immersion ratio or the decrease of current. Considering benefit evaluation factor and operate temperature, the recommended electrode immersion ratio range is 0.25–0.48. More importantly, the application of multi-layer electrode has a beneficial effect on smelting performance of electric furnace. The average benefit evaluation factor of two-layer-electrode furnace is 7.5% higher than that of traditional calcium carbide electric furnace when electrode immersion ratio equals to 0.25. In this paper, the newly proposed index contributes to the calcium carbide electric furnace smelting performance evaluation, and the multi-layer electrode furnace proposal opens up novel ideas in new furnace design.

Numerical Simulation of GAEM for Asymmetric Double-Lumen Plastic Micro-Catheter

In the study, the numerical simulations of gas-assisted extrusion molding (GAEM) of double-lumen micro-catheter (DLMC) with asymmetric structure were performed via the finite element software package Polyflow. At the same time, the numerical results of traditional extrusion were also obtained. The numerical extrusion profile, deformation, and the die swell ratios of DLMC based on the traditional and GAEM were all gotten, and compared with each other. In addition, to analyze the effect of gas-assisted on the elimination of the extrusion problems, the physical field distributions of melt for both extrusions were also compared and analyzed. Numerical results show that the obvious die swell and large extrusion deformation of DLMC generated by the traditional method were all eliminated by using the GAEM.

Thomson and rotation effects during photothermal excitation process in magnetic semiconductor medium using variable thermal conductivity

This study investigates a strong magnetic field acting over an elastic rotator semiconductor medium. The Thomson effect due to the magnetic field during the photothermal transport process is studied, and the thermoelectricity theory is used to explain the behavior of waves in the homogenous and isotropic medium under the effect of variable thermal conductivity. The variable thermal conductivity is considered as a linear function of the temperature. The two-dimensional deformation equations are used to describe the overlaps among plasma, electrical, thermal, and magneto-elastic waves. The charge density of inertia-particles is considered as a function of time for studying the induced electric current. The normal mode analysis is used to obtain the exact solutions of the physical field distributions as part of this phenomenon. To obtain the complete solutions of the physical field quantities, the certain mechanical loads, electromagnetic effects, thermal effects, and plasma recombination process are applied herein. The results of the physical distributions are graphically depicted and discussed in consideration of the internal heat source, rotation, and Peltier coefficient.

Effect of permeability anisotropy on depressurization‐induced gas production from hydrate reservoirs in the South China Sea

AbstractThe permeability anisotropy (ie, horizontal, kr, to vertical, kz, permeability ratio) of gas hydrate reservoirs may be a significant factor that affects hydrate dissociation and gas production. Here, site SH2, a candidate for field testing comprising a clayey silt gas hydrate reservoir in the Shenhu area in the South China Sea, was chosen to investigate the effect of permeability anisotropy on gas production behavior through numerical simulations. The spatial distribution of physical fields (ie, pressure, temperature, and saturation) and the evolution of gas and water recovery are comparatively analyzed. The simulation results show that permeability anisotropy has a significant impact on gas extraction, especially when the horizontal permeability is higher than the vertical one. The sensitivity analyses indicate that permeability anisotropy in both medium‐permeability (10‐100 mD) and low‐permeability (1‐10 mD) sediments are conducive to hydrate dissociation and that a higher horizontal permeability is more favorable for gas production. Comparatively, permeability anisotropy in low‐permeability sediments is not beneficial for improving production efficiency. In addition, our work also suggests that heterogeneous hydrate saturation in a reservoir‐scale model should be employed in future predictions because the gas production potential will be overestimated in a homogeneous reservoir under the same conditions. These findings contribute to a clear understanding of the influence of reservoir properties on gas hydrate dissociation processes and provide a reference for future field trials and commercial production.

Response of Thermo- Electro-Magneto Semiconductor Elastic Medium to Photothermal Excitation Process with Thomson Influence

The effect of Thomson heating of semiconductor medium is studied. Analytical discussions are made in the presence of thermoelectricity theory and magnetic field in context of Photothermal transport process. The interactions between plasma, thermoelectric, electromagnetic and elastic waves are taken into consideration. The governing equations are investigated in two dimensional deformations of homogenous, isotropic medium. The density of charge is taken as a function of time only of the induced electric current. The normal mode technique is used to obtain the physical quantities field under investigation. Some electro-mechanical loads and thermal effect through recombination process are applied on the free surface of semiconductor elastic medium. The distributions of physical fields in this phenomenon are discussed and represented graphically. The results have been discussed under the effect of thermoelectric parameter and Thomson parameter.

Response of electromagnetic and Thomson effect of semiconductor medium due to laser pulses and thermal memories during photothermal excitation

In this article, the novel mathematical model under the effect of Thomson heating of a semi-infinite semiconductor elastic medium is expressed. The thermoelasticity theory is applied in the presence of magnetic field when the medium illuminated by a laser pulse in context of photothermal excitation. The discussions are focused on studying the overlapping between plasma, thermal, electro-magnetic and elastic waves when they propagated in the medium. The two dimensional (2D) deformations is used in the governing equations when the medium is homogenous and isotropic. The charge density of induced electric current is expressed for a time functionally only. The physical fields are obtained when use the normal mode technique with some thermal, mechanical and plasma loads occur at the free surface of elastic semi-infinite semiconductor medium. The numerical calculations of physical field's distributions are discussed and shown graphically under the effect of Thomson parameter.

CFD investigation on thermodynamic characteristics in liquid hydrogen tank during successive varied-gravity conditions

In the present paper, a computational fluid dynamics (CFD) model is developed to simulate the successive varied-gravity operations for a liquid hydrogen (LH2) tank, and pressure evolution, physical field distributions and phase change amounts are obtained and analyzed. The results show that owing to the existence of helium accumulation in ullage, excessive pressure decline could be restrained, and instead a relatively stable pressure is maintained during the most time of the mission. The diffusion process of helium towards liquid surface is probably beneficial to the occurrence of mass transfer from liquid to vapor. However, the H2-He diffusion is nearly terminated within a relatively short time, so that a uniform H2-He mixture could be assumed in the researches on propellant performance in space. Moreover, acceleration level plays the dominant role in liquid-gas distribution. When an acceleration change from 3g0 to 10−3g0 occurs, no apparent interface deformation is observed. The liquid-gas interface maintains approximately horizontal distribution and only a slight liquid bending upwards is observed in near-wall region. When a zero-gravity environment is encountered, however, a complete coverage of ullage by liquid phase could be reached. Specially, it should be noted that a superheated ullage could exist in the tank center region for a long time even after its coverage by liquid phase. To meet secondary ignition requirement, orbit control thrust engines, producing axial acceleration of 10−3g0 and lasting over 100 s, could realize reliable liquid-gas separation. In addition, along with pressure reduction in the beginning stage of launching, a remarkable vapor condensation occurs. Coverage of ullage by liquid phase also yields a significant vapor condensation, while under space thrust effect, liquid evaporation mostly happens. Generally, the present study gives clear exhibitions on the pressure evolution and thermodynamic behaviors of cryogenic propellant tank, which is beneficial for the design and optimization of fuel tank system.

Numerical simulation of longitudinal and transversal electron dynamics in classical microtron

Numerical simulation of 3D electron dynamics in classical Lebedev institute microtron with energy 6-10 MeV is carried out. Special attention is paid to particles transversal motion investigation. A comparison of physical electric field distribution along cavity axis with that obtained by means numerical calculation is done. The obtained results are discussed.

Seismic Exploration of the River Sand Mining Area

Engineering geophysical exploration plays an important role in the geotechnical field. It is based on the difference in physical properties of rock, ore (or stratum) and surrounding rock, magnetization, conductivity, and radioactivity, and thus the distribution of various physical fields on the earth. Observations of changes and their changes are currently used in shallow seismic exploration and transient electromagnetic surveys. Based on the exploration demand of a river sand mining area, this paper studies the shallow seismic exploration method and transient electromagnetic method which can carry out geophysical exploration in the sand mining area, and analyse its conditions of using, mechanism principle, results analysis and reliable detection. The difference between the two is that the two have their own advantages and disadvantages. However, for the exploration requirements of the river sand mining area, the shallow seismic exploration has the advantages of lower cost, simpler operation and stronger anti-interference ability. Through actual operation, shallow seismic exploration not only detects the specific collapse area of the sand mining area, but also detects the influence range and depth of sand mining, and provides a data basis for site stability evaluation.

Mathematical model for coal conversion in supercritical water: reacting multiphase flow with conjugate heat transfer

Providing heat for supercritical water gasification (SCWG) of coal by coupling subsequent products oxidation in integrated supercritical water reactor (ISWR) provides an effective method for directional control of temperature field and avoids excessive hot spots caused by uniform heating. An exploratory numerical model incorporating particle-fluid flow dynamics, multispecies transport and thermal coupling between endothermic coal gasification and exothermic product oxidation was established to simulate the reacting multiphase flow process of coal conversion in a novel lab-scale ISWR. An eleven-lump kinetic model was proposed for the prediction of chemical reactions. And the thermal coupling relationship was described by conjugate heat transfer boundary conditions (BC). Detailed physical and chemical field distribution in ISWR were analyzed and influence factors were discussed. The results showed that oxidation of gas products as inner heat source could promote the gasification reaction with only slight or even little maximum temperature increase of the pressure-bearing wall. Coal feeding rate and oxygen supply method significantly affected the field distribution. The multi-injection compressed-air supply method provided a more uniform temperature field but would reduce heat transfer temperature difference. The carbon gasification efficiency (CGE) in the gasification zone could easily reach up to 97% under mild conditions (less than 650 °C).

Effects of Control Valve's Structure Parameters on the Circulation Characteristics for an Electronic Unit Pump

The control valve is an essential component of electronic unit pump (EUP) fuel injection systems; it controls the flow rate with high-precision electrical signals. Thus, high precision and flexibility are required in the working process of a fuel injection system. The flow capacity (indicated by mass flow rate) of a control valve is an important technical indicator in the discharge of EUP fuel injection systems. In this study, the transient flow characteristics within control valve during the discharge of an EUP were evaluated using a computational fluid dynamics (CFD) approach. Three essential structural parameters of EUP control valve were investigated, and their effects on circulation characteristics were evaluated. The variation trends were observed, and the changes in significant physical parameters and crucial physical field distributions were analyzed. During the investigation, the visualization of internal flow of control valve provided more detailed information of flow fields. This study shows the effect of each parameter on flow characteristics and indicates that cavitation is the lowest for the case of 0.20 mm valve core lift; the length of slit is the shortest for the case of 7 mm seal diameter, therefore, the mass flow rate of export is the highest; at 139 deg seal cone angles, fuel velocity is the highest, therefore, 139 deg is the best seal cone angle.

Numerical Studies for the Effects of Viscoelastic Constitutive Parameters on the Extrudate Swell of Plastic Micro-Tubes

The effects of four difference viscoelastic constitutive parameters, i.e., viscosity, relaxation time, ε and ξ on the extrudate swell of plastic micro-tubes were studied by using the numerical method. Numerical results show that the extrudate swell of plastic micro-tube increases with the increase of the relaxation time, but decreases with the increase of ε and ξ. In addition, the extrudate swell ratio of plastic micro-tube is not changed with the increase of the viscosity of melt. To ascertain the effect of four different viscoelastic constitutive parameters on the extrudate swell of plastic micro-tube, the physical field distributions, i.e., flow velocity, shear rate, shear stress, and first normal stress difference distributions of melt were obtained, respectively. Results show that the extrudate swell phenomenon of plastic micro-tube is closely dependent on the elastic energy storage of melt induced by the above mentioned physical field distributions, especially at the outlet of die.

Physical mechanisms and factors influencing inductive pulsed plasma thruster performance: a numerical study using an extended magnetohydrodynamic model

The inductive pulsed plasma thruster (IPPT) is a sort of spacecraft propulsion device. To promote the development of IPPTs, the working process and performance influencing factors are investigated in this study, using a novel magnetohydrodynamic model, with an exterior circuit coupled and extended magnetic field involved in the computation.By exploring the spatial distributions of different physical fields and the global properties of the thruster, a comprehensive physical picture of the operation process is illustrated, which is comprised of the structure evolution of the plasma current sheet, the relationship between thrust force and circuit current, the coupling effect that derives from plasma back to the circuit, and the energy deposition and conversion process of the system. Besides, the positive contribution of the secondary current sheet to the ultimate thrust performance is also confirmed.Further investigations discuss the impacts of varied factors including the operating parameters, initial gas distributions, and metal structures nearby. The results indicate that by adjusting propellant mass to achieve identical specific energy, the specific impulse and efficiency of the thruster can remain almost constant under varied discharge energy. Both compressing the initial gas against the face of coil, and ameliorating its radial uniformity, can help enhance the coupling between the plasma and drive-coil. Conductive structures nearby, especially the grounded metal plate that mounts the capacitors, can impair the acceleration of the plasma, unless it is located out of the electromagnetic coupling distance of the drive-coil.This study may help to reveal the underlying physical mechanisms and improve the designs of IPPTs.

Noncontinuous Super-Diffusive Dynamics of a Light-Activated Nanobottle Motor.

We report a carbonaceous nanobottle (CNB) motor for near infrared (NIR) light-driven jet propulsion. The bottle structure of the CNB motor is fabricated by soft-template-based polymerization. Upon illumination with NIR light, the photothermal effect of the CNB motor carbon shell causes a rapid increase in the temperature of the water inside the nanobottle and thus the ejection of the heated fluid from the open neck, which propels the CNB motor. The occurrence of an explosion, the on/off motion, and the swing behavior of the CNB motor can be modulated by adjusting the NIR light source. Moreover, we simulated the physical field distribution (temperature, fluid velocity, and pressure) of the CNB motor to demonstrate the mechanism of NIR light-driven jet propulsion. This NIR light-powered CNB motor exhibits fuel-free propulsion and control of the swimming velocity by external light and has great potential for future biomedical applications.

Noncontinuous Super‐Diffusive Dynamics of a Light‐Activated Nanobottle Motor

AbstractWe report a carbonaceous nanobottle (CNB) motor for near infrared (NIR) light‐driven jet propulsion. The bottle structure of the CNB motor is fabricated by soft‐template‐based polymerization. Upon illumination with NIR light, the photothermal effect of the CNB motor carbon shell causes a rapid increase in the temperature of the water inside the nanobottle and thus the ejection of the heated fluid from the open neck, which propels the CNB motor. The occurrence of an explosion, the on/off motion, and the swing behavior of the CNB motor can be modulated by adjusting the NIR light source. Moreover, we simulated the physical field distribution (temperature, fluid velocity, and pressure) of the CNB motor to demonstrate the mechanism of NIR light‐driven jet propulsion. This NIR light‐powered CNB motor exhibits fuel‐free propulsion and control of the swimming velocity by external light and has great potential for future biomedical applications.