Transient Method Research Articles

Automatic Algorithm Applied for Calculating Thermal Conductivity by Transient Plane Source Method

As a thermal conductivity measurement method, Transient Plane Source (TPS) method has gained much popularity because of its broad applicability, short measurement times, high precision and simple sample preparation. However, the accuracy of thermal conductivity calculations based on temperature rise data is often hindered by factors such as probe thickness, contact thermal resistance, and input power. Currently, there is no standardized criteria for selecting effective temperature rise data for thermal conductivity calculation. Consequently, the accuracy of results are limited by the operator's understanding of the TPS methods, and repeatability of the results is often poor. To address this issue, an automatic algorithm based on the international standard (ISO22007-2:2008) is proposed in this paper. By applying this algorithm to the measurement of different materials, it has been demonstrated that the proposed algorithm can produce more precise and consistent results than the conventional method. Additionally, the integration of the time window function , typically utilized solely for result validation in conventional methods, further enhances the objectivity and reproducibility of the results obtained by the automatic algorithm.

Modeling the interaction between powder particles and laser heat sources

This study investigates the spheroidization of titanium Ti-6Al-4V powder particles using numerical models developed in Abaqus and OpenFOAM. Spherical particles are crucial in powder-based additive manufacturing due to their superior flowability, packing density, and mechanical properties, enhancing printing precision and the quality of final products. While conventional techniques such as gas atomization and plasma spheroidization have been extensively researched, the potential of laser spheroidization remains underexplored. To address this gap, detailed numerical analyses of laser spheroidization were conducted, modeling heat transfer from the laser to powder particles using a transient uncoupled heat transfer method with latent heat considerations, while particle deformation was simulated with a phase-fraction-based interface-capturing approach integrated with Navier-Stokes equations. The results, validated against analytical models, indicate that particles within the 20–80 μm range experience optimal spheroidization within a 0.005-second residence time under laser heating, with particles smaller than 30 μm reaching evaporation temperatures of 5,000°C, while larger particles reshape without evaporating under a typical heat flux of 94 MW/m2 (1.8 kW laser power). This study demonstrates that laser spheroidization of Ti-6Al-4V powder can potentially increase powder yield by 10%, offering higher power density and shorter melting times compared to plasma spheroidization, thus presenting a more efficient alternative for achieving spherical particles of specific sizes.

Numerical Simulation and Experimental Verification of Rotor Airflow Field Based on Finite Volume Method and Lattice Boltzmann Method

The primary focus of research in agricultural unmanned aerial vehicle (UAV) pesticide application technology is the investigation of droplet drift and deposition. The influence of the rotor airflow on droplets is particularly significant, making numerical simulations a crucial tool for airflow field analysis. Among existing numerical simulation methods, the Finite Volume Method (FVM) and the Lattice Boltzmann Method (LBM) are commonly used, but there is limited research that compares the two approaches. Therefore, this paper conducts numerical simulations of the rotor airflow of an agricultural UAV using Fluent, representing the FVM, and XFlow, representing the LBM. This research aims to reveal the distribution patterns of airflow field numerical simulations under different theoretical methods, validate them through practical experiments, and select the optimal method for simulating rotor airflow. The ultimate goal is to establish an effective airflow field model to enhance the precision of pesticide application by an agricultural UAV. The results indicate that the lift error calculated by XFlow in this paper is 2.57% smaller than that by Fluent. The wind field of Fluent entered the “stable state” earlier than XFlow, and the speed value of Fluent was smaller than that of XFlow. The difference between the two speed values became larger and larger as the distance from the rotor was longer. Compared with XFlow, Fluent changes more obviously in the core region, and the center region gradually disappears with the distance from the rotor. However, in the velocity field calculated by XFlow, there are still more turbulent flows outside the core region, indicating that the transient calculation method based on the LBM can better show the details of fluid flow than the steady-state calculation method based on the FVM. Through comparison with the actual test data, it is found that the relative error of the velocity value of XFlow at 0.2 m and 0.4 m is small, while that of Fluent at 0 and 0.2 m is small. It shows that XFlow simulation has higher accuracy for external turbulent flow, while Fluent simulation has higher accuracy for steady laminar flow. The research results provide data comparison and a basis for further analysis of the wind field model of the rotor wing of the plant protection UAV, and they lay a foundation for further research on precision application technology.

Identification of Deactivation Mechanisms by the Periodic Transient Kinetic Method

AbstractThe understanding of deactivation processes in heterogeneous catalysis is key for the development of new materials and exploration of new operation windows. In this contribution, the periodic transient kinetic method (PTK) is used to identify and separate catalyst deactivation processes for the first time. The PTK method is applied for a standard Ni/Al2O3 catalyst in CO and CO2 methanation for 24 h and compared to steady‐state experiments. For the example reactions, the study exhibits different deactivation behavior for CO and CO2 methanation. The results demonstrate that the PTK method delivers an insight into the deactivation process and furthermore gives evidence for the underlying mechanism.

Operation Analysis of Power Systems with HVDC Interconnections Using a Transient Stability Aware OPF Method

High-voltage direct current (HVDC) transmission systems are widely used today due to their several advantages over high-voltage alternative current (HVAC) systems. They are primarily utilized in connecting different large grids or smaller independent networks, especially in submarine interconnections. Many studies have been conducted globally on the optimal planning, operation, and control of these power systems. Understanding the transient stability of these systems during significant disturbances is also of great importance. This paper specifically focuses on power systems with HVDC connections and high penetration of renewable energy sources. Analytical models were developed for power system components like HVDC converters, DC lines, and full converter wind generators. A simulation of a test-case power system was conducted, including various significant disturbances such as HVDC line trips, short circuits, power unit failures, and major changes in load. The voltage and frequency stability of the system under specific operational scenarios was also examined. The results obtained indicate technical limitations and operating guidelines to avoid undesirable conditions and system failure. In conclusion, adopting short-term stability tests the optimal operation point of the system, and the limitations in the penetration by RES units can be decided.

A new validated TRNSYS module for phase change material-filled multi-glazed windows

Incorporating phase change materials (PCM) into multi-glazed windows (MW) has been recognized as an effective way to regulate the indoor thermal environment and reduce the energy consumption of buildings. However, the design and calculation of PCM-filled multi-glazed windows (MW + PCM) remain challenging due to the lack of general transient simulation methods and integrated tools. To address this issue, the present study developed a dynamic coupled thermal and optical model for MW + PCM based on the enthalpy-temperature and interface energy balance methods. Then, the model was implemented in C++ and integrated into the TRNSYS software as a new module (Type 2602). In parallel, a test platform comprising two test chambers was established to evaluate the effect of PCM on the thermal and optical properties of the window and to validate the newly proposed module. It was found that compared to the traditional triple-glazed window (TW), the PCM-filled triple-glazed window (TW + PCM) effectively reduces the irradiance through the window by 34.17 % and the maximum temperature of the inner surface by approximately 5.56 °C. While the increase in external surface radiation flux density from 600 to 1200 W/m2 has a diminishing effect on the heat flux variation rate during the heat dissipation process for TW + PCM, it effectively shortens the latent heat absorption time by 0.50 h and increases the temperature difference between the inner and outer surfaces by 3.02 °C. The new module demonstrates satisfactory accuracy through experimental validation and simulation comparisons, with the maximum heat flux coefficient of variance of the root mean square error (CV(RMSE)) less than 6.35 % and 11.25 % under TW and TW + PCM configurations.

Tracking Minority Species in Redox Reactions: A Quantitative Combined XAS and Modulation Excitation Study.

Understanding the nature of intermediates/active species in reactions is a major challenge in chemistry. This is because spectator species typically dominate the experimentally derived data and consequently active phase contributions are masked. Transient methods offer a means to bypass this difficulty. In particular, modulation excitation with phase-sensitive detection (ME-PSD) provides a mechanism to distinguish between spectator and reacting species. Herein, modulation excitation (ME) time-resolved (energy dispersive) X-ray absorption spectroscopy, assisted by phase sensitive detection (PSD) analysis, has been applied to the study of a liquid phase process; in this case the classic ferrocyanide/ferricyanide redox couple. Periodic switches of the electrical potential (anodic/cathodic) enabled the use of the ME approach. Structural changes at fractions as low as 2 % of the total number of electroactive species were detected within the X-ray beam probe volume containing ~30 pmol of Fe(II)/Fe(III).

Tracking Minority Species in Redox Reactions: A Quantitative Combined XAS and Modulation Excitation Study

AbstractUnderstanding the nature of intermediates/active species in reactions is a major challenge in chemistry. This is because spectator species typically dominate the experimentally derived data and consequently active phase contributions are masked. Transient methods offer a means to bypass this difficulty. In particular, modulation excitation with phase‐sensitive detection (ME‐PSD) provides a mechanism to distinguish between spectator and reacting species. Herein, modulation excitation (ME) time‐resolved (energy dispersive) X‐ray absorption spectroscopy, assisted by phase sensitive detection (PSD) analysis, has been applied to the study of a liquid phase process; in this case the classic ferrocyanide/ferricyanide redox couple. Periodic switches of the electrical potential (anodic/cathodic) enabled the use of the ME approach. Structural changes at fractions as low as 2 % of the total number of electroactive species were detected within the X‐ray beam probe volume containing ~30 pmol of Fe(II)/Fe(III).

A new combined transient electromagnetic noise reduction method of VMD-SVD-WTD based on improved dung beetle optimization algorithm with multi-strategy fusion

Abstract The transient electromagnetic method (TEM) is now commonly used in the detection of coal mined-out areas, but it is susceptible to various sources of noise during field site probing, significantly impacting the accuracy of detection. Variational mode decomposition (VMD) has gained widespread adoption for eliminating noise in TEM signals. However, a single VMD may not effectively address both full-band noise and residual Gaussian white noise. To address this limitation, the singular value decomposition (SVD) and wavelet threshold denoising (WTD) are introduced correspondingly. Furthermore, this paper tackles challenges related to parameters selection in VMD and traditional optimization algorithms by proposing the integration of dung beetle optimization (DBO) enhanced with circle chaotic mapping, random walk strategy, and crisscross optimization algorithm (CRCDBO). Consequently, a new combined TEM noise reduction method, VMD-SVD-WTD based on CRCDBO is presented. Through comprehensive simulation tests and comparative analyses, the signal-to-noise ratio of this method is improved by 12.79% compared with VMD and the RMSE is 0.0011, which demonstrate the superiority and effectiveness of VMD-SVD-WTD based on CRCDBO in noise reduction. Meanwhile, this method is applied to an iron ore mine in Shanxi, which can accurately monitor the location of the mined-out area and has good application value.

Experimental study evaluating the performance of thermal conductivity prediction models for air–water saturated weathered sandstone heritage

As a critical parameter, thermal conductivity directly determines the heat transfer and temperature variation within rocks, which can lead to mechanical damage and chemical corrosion. Consequently, understanding the thermal conductivity of stone heritage is vital for assessing their deterioration mechanisms and developing effective conservation strategies. This study obtained sandstone samples from the Yungang Grottoes and subjected them to freeze–thaw cycle experiments to generate weathered sandstone samples. Subsequently, the thermal conductivity of these samples was measured under both dry and water-saturated state using the transient plane source method. To analyze the relationship between air–water saturation, porosity, and thermal conductivity, a saturation influence coefficient was introduced. Thereafter, the effectiveness and applicability of 13 commonly used thermal conductivity mixing law prediction models were evaluated based on experimental data. The results suggested that the influence of water saturation on the thermal conductivity of rocks varies with porosity, and water saturation significantly enhances the thermal conductivity of weathered sandstone. Among the 13 common models, the Geometric mean model was found to be more accurate than other models, with superior performance in both dry (MAE, RMSE, MAPE are 0.148, 0.214, 5.59% respectively) and water-saturated (MAE, RMSE, MAPE are 0.244, 0.170, 8.4% respectively) state. The Albert model demonstrates a good fit in the dry state, whereas the Walsh model (with maximum effect), Ribaud model, and Huang model also exhibit good fitting efficacy in the water-saturated state. This study provides a solid foundation for better predicting the thermal conductivity of weathered stone heritage and developing effective preventive conservation strategies.

Application of the opposing-coils transient electromagnetic method combined with ground-penetrating radar for the identification of shallow geohazards: a case study in Xiacun Town, Xinyu City, China

Application of the opposing-coils transient electromagnetic method combined with ground-penetrating radar for the identification of shallow geohazards: a case study in Xiacun Town, Xinyu City, China

Deep Learning Transient Electromagnetic Inversion for Seawater Intrusion

Abstract To enhance the capability of transient electromagnetic method(TEM) in detecting seawater intrusion and delineating the boundaries in coastal areas, we developed a deep learning inversion method for TEM data based on the Swin Transformer model in this study. First many standardized resistivity models were designed and generated to describe t the subsurface resistivity structures associated with seawater intrusion in coastal areas .Then, TEM forward modelling was performed to compute the corresponding TEM responses, thereby constructing a seawater intrusion-oriented training dataset. Then, the robust Swin Transformer model was employed as the backbone network to build a deep learning inversion model, named SITEMNet, to derive a direct nonlinear transformation that maps TEM responses to subsurface resistivity models. The proposed SITEMNet inversion technique was validated using simulated data scenarios and actual field TEM measurements, showing great promise in accurately identifying seawater intrusion interface and geological formations.

Analysis of friction vibration characteristics of the end face of a T-slot sealing ring under thermal deformation

Aiming at the friction vibration problem caused by dry friction contact during the start-stop process of a dry gas sealing device, this paper takes the end face of a T-slot dry gas sealing ring as the research object and establishes a numerical calculation model of the end face of the T-slot sealing ring. The thermal coupling method is used to obtain the thermal deformation law of the seal ring end face. The transient dynamics analysis method was applied to study the frequency and vibration mode of the friction vibration instability of the seal ring end face under thermal deformation. A vibration test bench was set up for the friction ring, and the friction vibration signals of the test pieces were collected, and the characteristic frequencies were extracted. The results show that: After thermal deformation, the end face of the sealing ring changes from a parallel surface to an inward converging surface, and the friction system of the sealing ring will become unstable. When considering the influence of thermal deformation, there are more unstable frequencies and lower frequency values that are most prone to frictional vibration. As the thermal deformation of the sealing ring increases, the frictional vibration becomes greater. In areas where the characteristic frequency values of frictional vibration are concentrated during thermal deformation, the occurrence rate of frictional vibration noise is higher.

Research progress in three-dimensional forward modeling for transient electromagnetic method

Research progress in three-dimensional forward modeling for transient electromagnetic method

Screening and Functional Evaluation of Four Larix kaempferi Promoters.

Promoters are powerful tools for breeding new varieties using transgenic technology. However, the low and unstable expression of target genes is still a limiting factor in Larix kaempferi (Lamb.) Carr (Japanese larch) genetic transformation. In this study, we analyzed L. kaempferi transcriptome data, screened out highly expressed genes, cloned their promoters, and constructed plant expression vectors containing the β-glucuronidase (GUS) reporter gene driven by these promoters. Recombinant vectors were introduced into the L. kaempferi embryogenic callus by means of the Agrobacterium-mediated transient or stable genetic transformation method, and the promoter activity was then determined by measuring GUS expression and its enzyme activity in the transformed materials. Four highly expressed genes were identified: L. kaempferi Zhang Chen Yi-1 (LaZCY-1), Zhang Chen Yi-2 (LaZCY-2), Translationally Controlled Tumor Protein (LaTCTP), and ubiquitin (LaUBQ). The 2000 bp fragments upstream of ATG in these sequences were cloned as promoters and named pLaZCY-1, pLaZCY-2, pLaTCTP, and pLaUBQ. Semi-quantitative and quantitative RT-PCR analyses of transient genetic transformation materials showed that all four promoters could drive GUS expression, indicating that they have promoter activities. Semi-quantitative and quantitative RT-PCR analyses and the histochemical staining of stable genetic transformation materials showed that the pLaUBQ promoter had higher activity than the other three L. kaempferi promoters and the CaMV35S promoter. Thus, the pLaUBQ promoter was suggested to be used in larch genetic transformation.

Harnessing nano-synergy: A comprehensive study of thermophysical characteristics of silver, beryllium oxide, and silicon carbide in hybrid nanofluid formulations

Nanofluids, promising to improve heat transfer efficiency, encounter stability and durability challenges, hindering their industrial applications. The emerging concept of hybrid nanofluids, alongside surfactant-driven stability research, presents a promising solution to tackle challenges in heat transfer, potentially revolutionizing thermal management systems and advancing nanomaterial science. This comprehensive study investigates the thermophysical properties of simple and hybrid nanofluid formulations composed of silver (Ag), beryllium oxide (BeO), and silicon carbide (SiC) nanoparticles dispersed in water. Hybrid nanofluids were prepared with varying volumetric ratios of 20:80, 40:60, 60:40, and 80:20 and examined across temperatures ranging from 15 to 45 °C. The influence of surfactants on stability was explored to augment thermal characteristics. Results revealed that the surfactants have a significant effect on stability and the specific mixing ratios can lead to more favourable thermal characteristics. Thermal conductivity enhancements, evaluated via the transient hot-wire method, demonstrated improvements of 7.43 %, 7.17 %, and 5.31 % for Ag/SiC (60:40), Ag/BeO (60:40), and SiC/BeO (80:20) hybrid nanofluids, respectively, compared to water. Viscosity measurements revealed Newtonian behaviour for the Ag, SiC, and BeO nanofluids, with a minimum viscosity enhancement of 3.01 % observed for the BeO nanofluid. Hybrid Ag/SiC nanofluid demonstrated a maximum viscosity enhancement of 4.90 % for 20:80 formulation. Density analysis showed maximum augmentation of 0.25 %, 0.097 %, and 0.0775 % for the Ag, SiC, and BeO nanofluids respectively at 0.025 vol% while hybrid Ag/SiC nanofluid exhibited a maximum of 0.23 % density increase for the 80:20 composition. The statistical models were also developed to predict properties against temperature. Furthermore, the cost analysis identified Ag nanofluid as the most expensive option, while the SiC/BeO hybrid was the most economical. However, the Ag-SiC (60:40) hybrid nanofluid offered a balanced trade-off between properties and cost.

Transient voltage stability assessment and margin calculation based on disturbance signal energy feature learning

With the increasing variation of the network topology and the high complexity of the processing measurement data, the transient voltage stability assessment of the new power system is facing significant challenges in low accuracy and high time costs. To address the shortcomings of the existing method and apply it to online assessment, this paper proposes an assessment method based on feature learning for disturbance signal energy (DSE) from bus voltages. Firstly, the relationship between DSE and system transient voltage stability is established, and the calculation of DSE from bus voltage time series is detailed. Subsequently, a transient voltage stability assessment method based on the ID3 Decision Tree algorithm and DSE is proposed. Finally, by employing the Support Vector Machine (SVM) to construct the optimal boundary in the feature space formed by the key buses, the transient voltage stability margin (TVSM) for specific scenarios is proposed. Simulation results on the IEEE 39-bus system demonstrate that the proposed method can rapidly and accurately assess the transient voltage stability of the system and calculate the stability margin, providing intuitive and interpretable results with high engineering application value.

Deep learning-based inversion of soil and rock compaction density utilizing Falling Weight Deflectometer (FWD) and Surface Waves

Methods relying on a single dynamic parameter to estimate the material density for the compaction quality testing of earth-rock dams and roadbed projects, present certain limitations in terms of applicability, testing accuracy, and work efficiency. The theory of elastic wave propagation reveals that the compaction density of the medium results from the combined interaction of multiple material properties. This study proposes a method that utilizes the transient surface wave method and a vehicle-mounted Falling Weight Deflectometer (FWD) to jointly enhance the accuracy of soil and rock material compaction detection. The transient surface wave method is employed to extract surface wave velocity and compressional wave velocity. The analysis of the FWD signal involves extracting dynamic parameters closely related to material density, including stiffness coefficients, central frequencies, and stiffness impedances, from time-domain, frequency-domain, and mechanical impedance analyses. A fully connected deep neural network is introduced to intelligently estimate the compaction density. The deep learning model is optimized by selecting the optimal activation function and optimization algorithm, as well as additional tuning. Extensive testing shows that deep learning model produce results closely approximating the true compaction density values. The average relative errors for the wet density and the dry density are 2.9% and 2.85%, respectively, meeting the quality control requirements for density testing. The proposed approach enables rapid detection and control of the compaction quality of soil and rock materials, providing a new method for the in-situ rapid detection of compaction quality.

Analysis of vortex induced vibration on the hundred-meter wind turbine blade based on CFD and FEM

Abstract Along the development of wind turbine blade toward large size and light weight, the length of blade running-now has come to the level of hundred-meter, while the structure of blade trends to be flexible. During the shutdown conditions, blades are affected by wake vortex from different inflow speed and angle, which often induce blade vibration. It seriously affects the safety and service life of wind turbines, even may cause blade breakage accident. This paper focused on the vortex induced vibration on the hundred-meter wind turbine blade. Based on the Computational Fluid Dynamics (CFD) transient method, the wake flow field of three relative thickness aerofoils has been simulated under different inflow speed and angle. The distribution of vorticity has been compared. Based on the Fast Fourier Transform (FFT) method, the frequency of wake vortex has been analysed from the pressure pulsation, compared with the natural frequency of this hundred-meter blade calculated by the Finite Element Method (FEM). This result may be regarded as a simulation support to avoid vortex induced vibration of hundred-meter wind turbine blade.

Effect of salinity-clay variation on the transient magnetic field in the Quaternary aquifer, theoretically and practically

This study focuses on understanding the physical foundations of the transient electromagnetic method, such as the transition from a simple basic principle to a more complex principle, starting from the Biot-Savart law until the current concept. It calculates the steady and transient magnetic fields around any electrical wire system. Accordingly, this law will be used to determine the magnetic field around the square loop configuration, which matches the magnetic field arising from the circular loop configuration. The square loop equation was derived and extended to include changes in the half-space, which allows us to understand how the electromagnetic waves travel in the subsurface and the farthest point, that can record the TEM response from the TEM loop, according to the loop size and loop current. Accordingly, the deduced equations were applied to predict the transient magnetic field curves of the Quaternary aquifer in three different water zones along the Nile delta, depending on the values of resistivity and chargeability caused by the variations in salinity and clay contents. The calculated transient magnetic curves were then compared with other measured field curves to confirm the validity of the derived equations. Therefore, these curves are expected to be used as guide curves for the transient magnetic field response in this aquifer. Also, these curves are important in estimating the hydro-geophysical characteristics of the main groundwater aquifer in the selected area and in other areas with the same geologic and hydrogeologic settings. Also, a common model is presented for any delta environment in the world in measured and calculated data.