Transient Field Research Articles

A fast methodology for identifying thermal parameters based on improved POD and particle swarm optimization and its applications

The identification method based on the traditional Proper Orthogonal Decomposition (POD) reduced-order model has the problem of low efficiency, due to the large amount of both data and computation, when dealing with complicated problems with a large number of spatially distributed nodes. To deal with this issue, an improved POD reduced-order model is proposed in this work. The improved POD reduced-order model only requires the establishment of a three-dimensional (3D) database of training samples varied with both time and measurement locations. Therefore, the amount of data and computation is independent of the total number of spatially distributed nodes, which enables the amount of data and computation to be greatly reduced. To identify thermal parameters in heat conduction problems, a database of transient temperature field is constructed with different training parameters and space nodes by using polygonal boundary element method, and a set of POD basis vectors is obtained by the POD reduced-order model. Then, a surrogate model combined with the improved particle swarm optimization (PSO) is employed for the identification of thermal parameters. Three different inverse heat conduction problems are designed and analyzed to verify the performance of the improved methodology. The results show that the efficiency of the modified method is superior to the traditional POD method with comparable accuracy. The more of the number of spatially distributed nodes, the more obvious advantages of the efficiency. Furthermore, this method has been tested on noisy data, proving its reliability in dealing with problems arising from measurement errors.

Research on the Carrier Characteristics of Power Cables Considering the Aging Status of Insulation and Semiconducting Layers

The 10 kV XPLE cable is widely used in highly cabled transmission and distribution networks. It is necessary to closely monitor the transient current, harmonic content, and electric field distribution of each layer of the insulation and semiconductive layers of the cable when they age and deteriorate, so as to promptly carry out circuit breaking treatment and prevent safety accidents. Considering the frequency sensitivity and dielectric sensitivity of the distributed Runit, Lunit, Gunit, and Cunit parameters of long cables, this paper quantitatively analyzes the frequency variation of 10 kV cable parameters under different aging states. Reconstructing the frequency variation process of typical electrical quantities through MATLAB PSCAD joint simulation, constructing fault circuits for cable insulation and semiconducting layers, obtaining transient currents in each layer of the cable under aging conditions, and conducting total harmonic distortion (THD) analysis to provide theoretical guidance for the subsequent monitoring and fault diagnosis of distribution cable status.

Simulation Analysis of the Annular Liquid Disturbance Induced by Gas Leakage from String Seals During Annular Pressure Relief

Due to the failure of string seals, gas can leak and result in the abnormal annulus pressure in gas wells, so it is necessary to relieve the pressure in gas wells. In the process of pressure relief, the leaked gas enters the annulus, causes a the great disturbance to the annulus flow field, and thus reduces the protection performance of the annular protection fluid in the string. In order to investigate the influence of gas leakage on the annular flow field, a VOF finite element model of the gas-liquid two-phase flow disturbed by gas leakage in a casing was established to simulate the transient flow field in the annular flow disturbed by gas leakage, and the influences of leakage pressure differences, leakage direction, and leakage time on annular flow field disturbance and wall shear force were analyzed. The analysis results showed that the larger leakage pressure difference corresponded to the faster diffusion rate of the leaked gas in the annulus, the faster the flushing rate of the leaked gas against the casing wall, and a larger shear force on the tubing wall was detrimental to the formation of the corrosion inhibitor film on the tubing wall and casing wall. Under the same conditions, the shear action on the outer wall of tubing in the leakage direction of 90° was stronger than that in the leakage directions of 135° and 45° and the diffusion range was also larger. With the increase in leakage time, leaked gas further moved upward in the annulus and the shear effect on the outer wall of tubing was gradually strengthened. The leaked acid gas flushed the outer wall of casing, thus increasing the peeling-off risk of the corrosion inhibitor film. The study results show that the disturbance law of gas leakage to annular protection fluid is clear, and it was suggested to reduce unnecessary pressure relief time in the annulus to ensure the safety and integrity of gas wells.

Characterization of Crack Geometry Parameters Based on Three-dimensional Transient Magnetic Field of Rectangular Pulsed Eddy Current

Eddy current testing plays an important role in assessing the surface quality of metal structures. Based on pulsed eddy current (PEC) testing, a new magnetic field characterization technique for surface cracks is proposed in this paper. The three-dimensional transient magnetic field is studied, revealing its distribution characteristics and transient response in the presence of cracks. The results show that the transient magnetic field contains valuable information. Specifically, the distributions of the magnetic field components Bx and Bz at the initial time are effective in evaluating crack length and depth. The time response of Bx provides characteristic information about defect length, emphasizing the importance of selecting the appropriate detection location. Additionally, the peak position and response amplitude of Bz can characterize crack depth. The effects of the pulse rising time and coil liftoff on the transient magnetic field are also studied. The study shows that the pulse rising time should be as short as possible, and the characteristics of rectangular PEC help mitigate the effects of liftoff. The rich features extracted from the transient magnetic field provide a new means to evaluate crack geometry, improving testing capabilities and detection accuracy.

Experimental study on the time-dependent spatial distribution of the three-dimensional magnetic field in an inductive pulsed plasma thruster

Inductive pulsed plasma thrust generates thrust by ionizing and accelerating plasma through pulsed inductive electromagnetic field. The spatial distribution of the magnetic field within the discharge region influences both the Lorentz force exerted on plasma and the electromagnetic coupling between plasma and circuit. An experimental prototype of inductive pulsed plasma thruster with high repeatability and a three-dimensional transient magnetic field measurement system with low integration error are established. Time-dependent spatial distribution of the magnetic field in the plasma is obtained by scanning measurement employing repeated pulse discharges. Combined with the results of high-speed photographing and electrical parameter measurements, the relationship between the evolution of plasma structure and the magnetic field penetration is discussed.

Analysis of transient temperature field of five-phase induction motor with composite winding under different operating conditions

Analysis of transient temperature field of five-phase induction motor with composite winding under different operating conditions

Dynamic Ruptures on Bending Fault: Insights from Numerical Simulations of Transient Stress Field

ABSTRACT We delve into the spontaneous rupture propagation on bending faults by numerical simulations based on the boundary integral equation method with unstructured meshes. To study the effect of fault geometry on dynamic rupture propagation, special attention is paid to the role of the dynamic stress field. The numerical results demonstrate that the bending angle is a key geometrical factor influencing the rupture propagation because it affects both the initial stress distribution and the dynamic stress field on the bending branch. The rupture propagation on the bending branch can be separated into two distinct stages: first, the propagation from the main branch to the bending branch, which largely depends on the dynamic stress field near the bend; and second, a subsequent propagation stage primarily influenced by the initial stress state on the bending branch, with the influence of the dynamic stress field decreasing rapidly with distance from the bend. Geometrical smoothing of the bend can be regarded as a modification of the bending angle, which may significantly alter the behavior of rupture propagation near the bend. In theory, if the bending angle ranges between −120° and 60°, there is a potential for rupture to propagate onto the bending branch through the bend.

The Impact of a Non-Uniform and Transient Magnetic Field on Natural Convective Jeffrey Fluid Flowing over a Heated Porous Plate: A Comparitive Study

Examining the effects of varying transient magnetic fields and their orientations on boundary layers aids in understanding the flow in complex surface geometries, turbulence control, drag reduction, aircraft and ship design, groundwater management, and the study of construction and coastal engineering. The study introduces a novel dynamics of the boundary layer of a natural convective Jeffrey fluid flowing over an erect porous moving plate under the influence a non-uniform and transient magnetic field M ˜ that grows exponentially over time with α as an accelerating parameter. The governing partial differential equations (PDEs) were non-dimensionalized using similarity variables and then solved analytically using the perturbation technique. The impact of various thermosphysical properties including chemical reactions, thermal source, Jeffrey fluid parameter and plate permeability on the fluid flow were presented graphically utilizing finite difference approximation(FDA) technique in MATLAB ODE15s solver. The study highlighted a notable decrease in shear stress (skin friction) by introducing M ˜ to the vertical plate results in the reduction of momentum boundary layer, accompanied by an increment in thermal boundary layer. Also, the results shows that increasing the magnitude of α leads to decrease the velocity and increase the temperature distribution curve. Additionally, the concentration profile was also found to decrease with stronger chemical reactions. Furthermore, key parameters like heat and mass flux were estimated and discussed through comparison tables. Understanding the effects of unsteady and externally applied increasing magnetic field M ˜ on viscous fluid flow have potential applications in biomedical engineering, such as the design of magnetic drug delivery systems and the analysis of blood flow in human body.

Development and Validation of Asphalt Pavement Rutting Prediction Model with Transient Temperature Field Considered

This study developed a transient rutting analysis program based on the principles of heat transfer and the viscoelastic–viscoplastic theory of asphalt mixtures. Using the finite element model (FEM) model corresponding to the multi-layer pavement structure and the subprogram interface of ABAQUS software, along with Python programming, the program was designed to estimate rutting under transient temperature field conditions with climate conditions, traffic flow, and structure layer constitutive parameters of pavement considered. Subsequently, the program was used to validate the efficiency of the solution and analyze the influencing factors of internal temperature field and rutting depth within the asphalt pavement structure. Results showed that, based on meteorological data and recommended values of material thermal properties, the FEM of transient temperature field can accurately simulate the temperature field distribution of pavement structure. Based on loading information and dynamic modulus test, the transient temperature variable rutting with FEM proposed in this paper can simulate and calculate the rutting of pavement structure layer with some errors for different pavement conditions from 5% to 40%. Through parametric analysis of the influence factors of temperature field and rutting, the modified transient temperature field rutting prediction program can effectively simulate rutting of pavement structure, and the minor errors were less than 20%.

Stacking BSRG-PLS: A physical and data-driven real-time stability safety analysis of arch dams during operation

Anti-sliding stability is the foundation for the normal operation of arch dams. In recent years, extreme weather has occurred frequently. It is important to grasp the anti-slide stability of arch dam (ASSAD) under complex load conditions in time. Currently, the ASSAD safety factor is primarily analyzed through the finite element method (FEM), which are time-consuming, labor-intensive, and lack timeliness. To address this, this paper proposes a real-time ASSAD analysis method during operation based on the Stacking BSRG-PLS model, which integrates a Bidirectional long short-term memory network, Residual neural network, Support vector machine, Gaussian process regression model and Partial Least Squares regression method. Firstly, based on the Stacking BSRG-PLS model and measured temperature combing with FEM, the transient temperature field of arch dam is established. Subsequently, a sample dataset containing the load data and the corresponding ASSAD safety factors calculated by FEM is constructed. Whereafter, using the Stacking BSRG-PLS model again, the real-time ASSAD safety factor is obtained based on the sample dataset. Case studies indicate that this method is effective and feasible, and has high analysis precision. It provides an effective way to quickly evaluate the ASSAD safety based on the measured data.

Study on the Stress Distribution Characteristics of Rock in the Bottomhole and the Influence Laws of Various Parameters Under the Impact of a Liquid Nitrogen Jet

This study presents research on the stress distribution characteristics of rock in the bottomhole and the influence laws of various parameters under the impact of liquid nitrogen jet. A multi-field coupled numerical model considering transient flow field, conjugate heat transfer, and nonlinear solid deformation was established to investigate the damage-induced fracturing mechanism of rock under liquid nitrogen jet. The study compares the impact effects of liquid nitrogen jet and water jet on rock and analyzes the variations in the stress field under different parameters. Due to its extremely low temperature, the liquid nitrogen jet creates a strong thermal stress gradient in a short time, significantly increasing the maximum principal stress and Mises stress in the rock compared to a water jet. Solid parameters, particularly the confining pressure and elastic modulus of the rock, have a more significant impact on stress distribution, while fluid parameters such as outlet pressure and fluid temperature have a smaller and more volatile effect. An increase in confining pressure inhibits tensile failure in the rock, while a higher elastic modulus enhances both tensile and shear failure. The initial rock temperature significantly affects the stress distribution, with optimal tensile failure observed at intermediate temperatures. The liquid nitrogen jet achieves a higher maximum velocity and overflow velocity than the water jet, contributing to more effective rock fracturing. The results provide a theoretical basis for the optimization of liquid nitrogen jet drilling parameters, which can help improve drilling efficiency.

A wall-modeled large-eddy simulation of the unsteady flow in a water-jet pump based on the turbulent length scales

Non-zonal hybrid Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulation (LES) are commonly used for predicting unsteady flows in pumps. However, these hybrid methods often face challenges in the transition between the RANS and LES regions, known as the “grey area” problem. In this study, a pure LES approach, coupled with wall modeling to eliminate this issue, was employed to simulate unsteady flow in a water-jet pump (WJP). A grid generation method, based on turbulent length scales derived from a precursor RANS calculation, was developed to address the complexities of grid design in wall-modeled large-eddy simulations (WMLESs) for complex geometries. Initially, the accuracy of the wall model was validated in the fully developed channel flow. The grid generation method and the accuracy of WMLES in predicting unsteady fluctuations were validated using the flow over a flat strut with an asymmetrically beveled trailing edge. The predicted fluctuation spectra at monitored points showed strong agreement with experimental data. The grid generation method was then applied to WMLES of flow in a WJP, where experimental measurements of the pump head rise and torque were accurately calculated by the numerical simulations. The results from three different grid resolutions were compared with experimental data, revealing significant changes in the predicted mean and transient fields as the grid was refined. The grid based on the turbulent length scales reproduced both the hydrodynamics and transient vortices with high accuracy and detailed resolution. These comparisons demonstrated that pure LES with wall modeling effectively predicts the mean and fluctuating characteristics of high Reynolds number flows with reasonable computational cost. The turbulent length scale-based WMLES enhance the fidelity of computational tools for simulating pump flows.

Experimental and Numerical Evaluation of Calcium-Silicate-Based Mineral Foam for Blast Mitigation

Cellular materials such as aluminum and polyurethane foams are recognized for their effectiveness in energy absorption. They commonly serve as crushable cores in sacrificial cladding for blast mitigation purposes. This study delves into the effectiveness of autoclaved aerated concrete (AAC), a lightweight, porous material known for its energy-absorbing properties as a crushable core in sacrificial cladding. The experimental set-up features a rigid frame made of steel measuring 1000 × 1000 × 15 mm3 with a central square opening (300 × 300 mm2) holding a 2 mm thick aluminum plate representing the structure. The dynamic response of the aluminum plate is captured using two high-speed cameras arranged in a stereoscopic configuration. Three-dimensional digital image correlation is used to compute the transient deformation fields. Blast loading is achieved by detonating 20 g of C4 explosive set at 250 mm from the plate’s center. The study assesses the mineral foam’s absorption capacity by comparing out-of-plane displacement and mean permanent deformation of the aluminum plate with and without the protective solution. Six foam configurations (A to F) are tested experimentally and numerically, varying in the foam’s free space for expansion relative to its total volume. Results show positive protective effects, with configuration F reducing maximum deflection by at least 30% and configuration C by up to 70%. Foam configuration influences energy dissipation, with an optimal lateral surface-to-volume ratio (ζ) enhancing protective effects, although excessive ζ leads to non-uniform foam crushing. To address the influence of front skin deformability, a non-deformable front skin has been adopted. The latter demonstrates an increased effectiveness of the sacrificial cladding, particularly for ζ values above the optimal value obtained when using a deformable front skin. Notably, using a non-deformable front skin increases maximum deflection reduction and foam energy absorption by up to approximately 30%.

Near-petahertz fieldoscopy of liquid

AbstractMeasuring transient optical fields is pivotal not only for understanding ultrafast phenomena but also for the quantitative detection of various molecular species in a sample. Here we demonstrate near-petahertz electric field detection of a few femtosecond pulses with 200 attosecond temporal resolution and subfemtojoule detection sensitivity. By field-resolved detection of the impulsively excited molecules in the liquid phase, termed femtosecond fieldoscopy, we demonstrate temporal isolation of the response of the target molecules from those of the environment and the excitation pulse. In a proof-of-concept analysis of aqueous and liquid samples, we demonstrate field-sensitive detection of combination bands of 4.13 μmol ethanol for the first time. This method expands the scope of aqueous sample analysis to higher detection sensitivity and dynamic range, while the simultaneous direct measurements of phase and intensity information pave the path towards high-resolution biological spectro-microscopy.

Nucleic Acid-Rich Stress Granules Are Not Merely Crowded Condensates: A Quantitative Raman Imaging Study.

Liquid droplets, formed by intracellular liquid-liquid phase separation (LLPS), are called membraneless organelles. They provide transient enzymatic reaction fields for maintaining cellular homeostasis, although they might transform into aggregates, leading to neurodegenerative diseases. To understand the nature of intracellular droplets, it is crucial to quantify the liquid droplets inside a living cell as well as to elucidate the underlying biological mechanism. In this study, we performed near-infrared fluorescence and Raman imaging to quantify chemical components inside stress granules (SGs) formed by LLPS in living cells. The Raman images reveal that the nucleic acid concentration inside the SGs was more than 20% higher than the surrounding cytoplasm, whereas the lipid concentration was lower. Quantitative Raman intensity analysis using a water Raman band as an internal standard enables in situ concentration determination of nucleic acids in the SGs and other organelles. The intensity of the biomolecular C-H bands relative to the water band indicates that the crowding environment inside the SGs depends on the stress type; under oxidative stress, the inside of the SGs was nearly identical to the outside, whereas it was sparser in hyperosmotic stressed cells, suggesting that the high concentrations of nucleic acids play a pivotal role in maintaining the environments inside the SGs. These results demonstrate that intracellular droplets are not always highly condensed.

The dynamics of shock wave propagation far downstream of an abrupt area expansion

Predicting the transient flow fields that develop when a shock wave passes through an area expansion is a fundamental problem in compressible fluid mechanics and significant in many engineering applications. Experiments, large eddy simulations and geometrical shock dynamics are used to study the mechanism by which a normal shock wave that expands across an area expansion evolves into a uniform normal shock far downstream of it. This study analyses shock waves with moderate Mach numbers of 1.1–1.8 that expand at area ratios of up to 5. As the shock wave propagates into the expanded region, it experiences rapid deceleration, forming a non-uniform shock front. Impinging on the walls of the larger cross-section region, the shock wave reflects and generates a complex and highly transient shock pattern near the expansion region. We have found that as the shock front propagates further downstream, a laterally moving shock wave that intersects the shock front at a triple point reverberates laterally between the walls. This process effectively evens out the flow behind the incident shock front, thus reducing the variation of properties behind it. The extended duration of this process leads to significant pressure fluctuation behind the shock front. The results show that the evolution of the shock front can be scaled using the expanded region height and the velocity of the shock wave far downstream of the expansion. The results enabled the formulation of a simple empirical relation, allowing us to predict the shock velocity far downstream of gradual and abrupt area expansions.

Numerical simulation and experimental study on guidance performance of hypersonic seeker under aerodynamic optical transmission effects

When a hypersonic seeker flies at high speed within the atmosphere, intense interaction with the incoming flow gradually develops into a complex turbulent flow field. This interaction results in complex thermal responses at the seeker window, causing aerodynamic optical effects such as image shift, jitter, and blur of the target image, thereby restricting the seeker's detection capability and accuracy. This paper uses a numerical simulation model for the guidance performance of a hypersonic seeker under aerodynamic optical transmission effects. The study focuses on an ellipsoidal seeker, with its supersonic flight simulation on the basis of the Reynolds-Averaged Navier-Stokes (RANS) equations to get a non-uniform gradient flow field. The correctness of the flow filed results can be verified by wind tunnel experiments. The transient temperature field of the seeker is solved using an unsteady thermal conduction-radiation coupled fluid-solid heat transfer method. Finally, the guidance performance of the hypersonic seeker under aerodynamic optical effects is predicted using the ray tracing method, which employs wavefront aberration, point spread function, degraded images, and image shift.

Unsteady numerical simulations of aircraft icing based on the dynamic grid method

In this study, an unsteady numerical simulation method based on dynamic grids was established to solve unsteady aircraft icing processes. The dual-time step method was used to achieve the time advancement of the transient airflow and droplets fields. The droplets trajectory was calculated using the Euler method, which incorporates a supercooled large droplets model. The transient evolution of the water film and ice layer on the substrate surface was considered in the icing thermodynamic model. The accuracy of the unsteady method for ice-shape prediction was verified via comparison and analysis of numerical examples. Additionally, the rime and glaze ice formation processes were explored, and the coupling effects of ice horn growth and the air convective heat transfer coefficient, water collection coefficient, and water film flow on the substrate surface were studied. The ice shapes calculated by unsteady and quasi-steady methods were compared. The results indicated that the latter predicts a larger icing range than the former. Moreover, there may be more obvious distinctions between these two methods in predicting glaze ice.

An Exact Solution of the Fractional Transient Electromagnetic Field Inside an Atmospheric Duct

The objective of this paper is to find the exact solution of the fractional electromagnetic (EM) equation within an atmospheric duct (dielectric medium) of the transient EM field caused by a vertical magnetic dipole and discuss the results in both fractional D-dimensional space and integer space. The novelty of this work is the exact solution of the fractional EM equation in terms of Bessel and Mittage-Leffler functions based on Caputo fractional derivative order α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} and the Laplacian operator in D -dimensional fractional space. Using the separation of variables method, the resulting magnetic field can be controlled by D=α1+α2+α3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D=\\alpha _1+\\alpha _2+\\alpha _3$$\\end{document} and alpha as spatial and time fractional parameters, respectively. The transient magnetic field behaviour inside the duct is plotted through some of figures depending on fractional parameters D and α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document}. The classical integer results in usual space are recovered from fractional solution at D=α=1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D=\\alpha =1$$\\end{document}. The main results highlighted are that spatial frequencies grow at a faster rate during EM wave propagation; thus, the amplitude of the propagated wave in integer space is greater than that in fractional space. Increasing the fractional parameters D and α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} simultaneously increases the amplitude of the EM wave and can be used to control the power and energy of the EM wave.

Thermo-flexible coupled dynamics of composite laminated plates based on absolute nodal coordinate formulation

In this paper, a thermo-flexible coupled dynamic model of composite laminates is established by Absolute Nodal Coordinate Formulation (ANCF). In order to solve the problem of mesh mismatch and precision inconsistency between the displacement and temperature fields in the traditional thermo-flexible coupled modeling method, the ANCF hybrid element with integrated temperature description is constructed to achieve a unified description of the displacement and temperature fields. A new ANCF thin shell element with thermal effects is proposed. Based on the first law of thermodynamics, the heat capacity matrix, thermal conduction matrix, blackbody radiation matrix, internal heat source vector, and heat flux density vector caused by solar radiation for the ANCF thin shell element considering thermal effects are derived. The dynamic equation of ANCF composite laminates under a unified description is derived, and its dynamic model is established. The thermo-flexible dynamic response of ANCF composite laminates under thermal conduction, space thermal radiation, and solar radiation is analyzed by numerical simulation. The simulation results reveal the evolution process of the transient temperature field and the phenomenon of thermal-induced vibration, thus confirming that the thermal effects have an important influence on the dynamic behavior of ANCF composite laminates. The research provides a theoretical basis for the ground test of solar panels.