最新刊期
卷 57 ， 期 12 ， 2023
- 摘要：To further improve the performance of lossless compression of dynamic point clouds, a method of geometry information entropy coding under an octree structure was proposed. By this method, for intra-frame spatial correlation, the contexts of intra-frame neighbor nodes and the contexts of intra-frame neighbor parent nodes are established based on the coded neighborhood information of the current octree node; for inter-frame temporal correlation, the previously coded point cloud frame is employed as the reference frame, and the octree node inside the reference frame at the same position as the current octree node is used as the reference node. The inter-frame context is modeled using the reference node and its parent node. To fully utilize the modeled contexts and accurately estimate the conditional probability that the current node is non-empty under different contexts, a second-level probability estimation method based on the exponential moving average was proposed. By this method, the probability is first estimated under the context of intra-frame neighbor nodes and the context of intra-frame neighbor parent nodes, respectively. Then, a set of second-level contexts are modeled using the inter-frame contexts and the results of the probability estimation, and the probability is estimated again under the second-level contexts. In the end, the lossless compression is realized by the binary arithmetic encoder. To evaluate the compression performance of the proposed method, the commonly used Microsoft voxelized upper bodies(MVUB)and 8i voxelized full bodies(8iVFB)datasets were selected for performance testing. The experimental results show that the proposed method has a higher lossless compression performance than the methods developed recently, with average coding gains of 2.2% to 28.7%.关键词：point cloud compression;octree;entropy coding;arithmetic coding;probability estimation102|12|0更新时间：2025-07-09
- 摘要：The JCTVC-X0038 quantization parameter cascading(QPC)method recommended by the latest versatile video coding(VVC)standard test model VTM has low coding efficiency because the surveillance video content characteristics are not considered. For this problem, a VVC QPC method considering the spatio-temporal content characteristics of the surveillance videos, referred to as SCA-QPC, was proposed. First, based on the VVC hybrid coding framework principle, it was found that the temporal layer and spatio-temporal content characteristics of the surveillance videos were the key factors affecting the selection of quantization parameters(QP)by theoretical analysis. And the coding experiments were further carried out to verify the results of the theoretical analysis. Then the gradient and background frame difference were used to measure the spatio-temporal characteristics of the surveillance videos respectively and further used as the inputs to the back propagation neural network to construct a model predicting the optimal QPs corresponding to temporal layers in low delay structure. Finally, the SCA-QPC suitable for VVC standard was proposed to effectively improve the surveillance video coding efficiency. Compared with the state-of-the-art JCTVC-X0038 QPC method, the average BD-rate of SCA-QPC is -4.26% for all test sequences. This study can guide the optimization of QPC and rate control modules in the VVC coding framework.关键词：video coding;versatile video coding;quantization parameter cascading;surveillance video;video content characteristics68|9|0更新时间：2025-07-09
- 摘要：Water electrolysis is a green hydrogen production technology, but its energy efficiency is limited by the kinetics of anodic oxygen evolution reaction(OER). For this problem, this paper systematically summarizes and discusses a system coupling water electrolysis with pollution control to reduce energy consumption, which has an advantage that the OER reaction is replaced by anodic pollutant oxidation, which not only reduces the energy consumed during the water electrolysis hydrogen production but also treats the pollutants, so as to integrate hydrogen production and pollution control. The important role of electrolytic cell design played in the coupling system was discussed, as a well-designed electrolytic cell is beneficial to the efficiency of hydrogen production and pollution control. The development of electrode materials with stable performance is also important for an efficient coupling system. Nickel-, cobalt-, or copper-based materials and their composites are all used as electrode materials in the coupling system to improve the stability and the efficiency of hydrogen production and organic pollutant degradation. Organic compounds such as alcohols, phenols, aldehydes, urea, hydrazine, and amines, as well as liquid ammonia and sulfur-containing compounds, are also used in the coupling system. The addition of these substances can improve the electronic utilization rate of the system and prevent O2/H2 mixing, achieving green hydrogen production and degrading pollutants or even generating higher value-added chemicals during the hydrogen production. This paper also analyzes the influencing factors, reaction mechanism and existing problems of the coupling system, in order to provide a theoretical basis for the research and application of the coupling system. In addition, this paper proposes corresponding solutions and prospects for the difficulties in the mechanism, economy, and other aspects of the application of the coupling system.关键词：water electrolysis;hydrogen production;anodic oxidation;pollutant degradation;coupling of hydrogen production and pollution control134|8|0更新时间：2025-07-09
- 摘要：To improve the accuracy of the classical Peng-Robinson cubic equation of state(PR equation)to predict the high-pressure liquid density of fatty acid methyl esters, and to provide a reliable density prediction method for the further application of the biodiesel in engineering, the experimental density data of 19 saturated fatty acid methyl esters and 6 unsaturated fatty acid methyl esters at atmospheric pressure issued in the literatures were collected and the PR equation was modified using the volume translation method. According to the investigation, there were regular trends between the values of the volume translation and the temperature, carbon atom numbers and double bond numbers of the fatty acid methyl esters, and the quantitative relationship was obtained. Based on this, a new PR equation based on volume translation(VTPR equation)used to predict the density of the homologous fatty acid methyl esters was obtained. The investigation results show that the overall average relative deviation between the density of the fatty acid methyl esters at atmospheric pressure calculated with the proposed VTPR equation and the experimental density data is 0.30% and that between such density under high pressure predicted with the equation and the experimental data is 0.50%. It indicates that the VTPR equation can meet the requirement of the practical engineering.关键词：fatty acid methyl ester;density;volume translation;Peng-Robinson equation of state79|6|0更新时间：2025-07-09
- 摘要：To study the effect of oil injection parameters on the performance of the twin-screw air compressors and to provide a reference for optimizing and improving the overall performance of such air compressor, a mathematical model of the oil-injected twin-screw air compressor was developed to study the effect of oil injection volume and oil injection temperature on the performance of the air compressor and the accuracy of the model was verified by comparing the simulation results with the experimental results. The results show that, there is an optimal oil injection volume for a twin-screw air compressor to achieve the best adiabatic efficiency and specific power, and such volume decreases as the speed increases(from 3 000 r·min-1 to 4 400 r·min-1)and increases with the back pressure(from 0.7 MPa to 1.0 MPa). In addition, the increase of oil injection temperature makes the adiabatic efficiency of the compressor decrease and the specific power increase, which leads to the deterioration of the compressor performance. Thus, the oil injection temperature should be as low as possible while ensuring the exhaust temperature. At the same time, there is a significant effect of injection parameters on leakage and power consumption. In particular, with the increase of the injection temperature(from 303.15K to 323.15K), the leakage of each leakage channel shows a increasing trend, and the friction loss shows a decreasing trend, while with the increase of injection volume(from 0.5 m3·h-1 to 1.5 m3·h-1), the leakage shows a decreasing trend, and the friction loss shows a rising trend. This research provides a useful reference for optimizing the performance of the oil-injected twin-screw compressors.关键词：twin-screw air compressor;oil injection parameters;mathematical modeling;performance research and optimization103|5|0更新时间：2025-07-09
- 摘要：To establish a droplet evaporation model for the numerical simulation of brine spray evaporation, the evaporation and crystallization processes of brine droplets were investigated. Firstly, a single droplet evaporation visualization experimental platform was built to simultaneously measure the variations in droplet mass, temperature, particle size and morphology during the evaporation. Based on the flow-induced vibration characteristics of the droplet suspension device, the low-pass filtering method was proposed to eliminate the influence of vibration signals on mass measurement. Secondly, the evaporation experiment using 10% NaCl droplet was carried out to investigate the influence of the salt crystallization process on the droplet temperature, particle size and evaporation rate. Finally, based on the experimental data, the droplet's relative activation energy and dimensionless particle size as a function of the dry basis water content were calculated to establish the reaction engineering approach model. A maximum deviation of less than 8% was observed in the numerical validation. The experimental platform can provide an important reference for mass variation measurement during the drying of droplets with precipitate. The proposed reaction engineering approach model can be applied in the high-efficiency numerical simulation of the spray drying of NaCl solution.关键词：brine droplet;evaporation and crystallization;spray drying;reaction engineering approach57|23|0更新时间：2025-07-09
- 摘要：For the challenges arising from the compatibility between the high-temperature pressure-bearing parts in the supercritical CO2 power cycle system and the working medium, the corrosion kinetics and the corresponding thermodynamic products of T92 steel in supercritical CO2 environments at 600 and 700 ℃ were studied. Firstly, the adsorption process of CO2 on the surface of T92 steel was calculated by molecular dynamics and the migration and distribution of atoms in T92 steel during the initial oxidation stage were simulated. Then, the distribution of oxide layers and carbides was analyzed based on the principle of corrosion thermodynamics. Finally, the high-temperature corrosion tests were carried out to verify the simulation results. The results showed that the thickness of the oxide layer on T92 steel at 700 ℃ was about 13.5 times higher than that at 600 ℃. The oxide layer consisted of an outer layer of Fe3O4 and an inner layer of FeCr2O4. Under the oxide layer, there are C23C6 carbides. CO2 was preferentially adsorbed on the surface of Cr(111). Then Cr reacted with CO2 to form some free C deposited on the surface of the oxide layer, which diffused inwards in the state of ions. The corrosion process was dominated by ion diffusion, and the diffusion rate increased with the temperature. The study provides a composite analysis method to evaluate the corrosion resistance of materials in the supercritical CO2 and data support for materials selection and corrosion lifetime prediction of key high-temperature pressure-bearing parts.关键词：supercritical CO2;molecular dynamics;corrosion thermodynamics;high-temperature corrosion66|9|0更新时间：2025-07-09
- 摘要：This paper improves the containment spray removal models in order to address the low accuracy of the original models of the ISAA code. Based on single droplet collection particle mechanism, new inertial impaction and interception models were used to accurately calculate the collection efficiency of large particles. Additionally, a new correlation was used to explain the Brownian diffusion collection mechanism of small particles. Moreover, thermophoresis and diffusiophoresis models were introduced to consider the contribution of steam condensation in the containment to the collection efficiency. In addition, THAI, TOSQAN and CSE experiments were selected to evaluate and improve the model precision, while the calculated results were compared with the results of COCOSYS, ASTEC, and MELCOR codes. For the THAI experiment, the maximum errors of the improved ISAA and COCOSYS in calculating the spray removal constants are -28.6% and 59.1%, respectively. For the TOSQAN experiment, the maximum errors of the improved ISAA and ASTEC in calculating the spray removal constants are -12.3% and 50.9%, respectively. For the CSE experiment, the maximum errors of the improved ISAA and MELCOR in calculating the spray removal constants were -12.3% and 90.3%, respectively. The calculation results show that the improved model can simulate the attenuation trend of suspended aerosols with higher accuracies and significantly improve the calculation accuracy of the spray removal constants. This work helps to understand the scavenging mechanism of aerosol particle by containment spray droplets, and provides analysis method with higher simulation accuracy. At the same time, it discovers shortcomings in the simulation of aerosol behavior in the current ISAA code and point out the future improvement directions of the code.关键词：aerosol removal;droplet collection;nuclear safety;containment spray48|25|0更新时间：2025-07-09
- 摘要：Aiming at accurately predicting the remaining useful life of the rotating machinery with a small size of samples, a digital twin driven method for health index construction and remaining useful life prediction for rotating machinery was proposed. The degradation behavior model was constructed by combining convolutional autoencoder and Weibull distribution theory. Firstly, the convolutional autoencoder was trained with the early degradation signal of the rotating machinery to learn the early degradation signal pattern. Then, the convolutional autoencoder was used to reconstruct the test signal and calculate the reconstruction error, which was mapped into the [0,1] interval as the health index. Finally, the Weibull reliability function was fitted according to the health index to predict the remaining useful life of the rotating machinery. The above steps were repeated during the continuous operation of the rotating machinery based on real-time data. The validation results of PHM2012 public data set show that the proposed method can predict the remaining useful life of bearings without the failure degradation signal, and the predicted results are significantly superior to those predicted by existing methods, with the root mean square error of 938.8 and the mean absolute percentage error of 42.62%. The application of this method in an automated test system digital twin predictive maintenance platform of BASF Advanced Chemicals Co., Ltd. demonstrated the feasibility of the proposed method for few-shot life prediction of rotating machinery in practical industrial scenarios.关键词：digital twin;convolutional autoencoder;Weibull distribution;rotating machinery;remaining useful life prediction222|23|0更新时间：2025-07-09
- 摘要：Aiming at the problem that the lateral contact and the source of contact angle distribution between asperities are ignored in the existing fractal models, a lateral fractal model of contact stiffness of joint considering the contact angle distribution between asperities was proposed. The profile of the contact surfaces was obtained by the profile microscope, and the surface profiles were modeled by the three-point peak method to obtain the data of the horizontal distance and height difference between adjacent asperities. The analysis results based on power spectral density method show that the horizontal distances and height differences between adjacent asperities have fractal laws. According to the discovered fractal law, the distribution function law of contact angle is derived when two asperities contact with each other, then the contact stiffness model of joint is established by the fractal theory. Based on this model, the effects of fractal parameters, plastic index, normal load coefficient, and contact mode on the normal and tangential contact stiffness were studied through the numerical simulation. The results indicate that the dimensionless tangential contact stiffness increases with the fractal dimension, plastic index, and normal load coefficient, while decreases as the fractal scale parameter increases. Comparing the results of finite element analysis and modal experiment, it is found that the absolute value of the maximum relative error is 4.32%, and the accuracy is 46.80% higher than that of the LZT model, which illustrates that this model can accurately predict the contact stiffness of joint.关键词：lateral contact;contact angle distribution;fractal model;contact stiffness47|23|0更新时间：2025-07-09
- 摘要：For the problems such as fixed value of equivalent factor and poor adaptability to working conditions in the traditional equivalent consumption minimization strategy(ECMS), a predictive adaptive equivalent consumption minimization strategy(PA-ECMS)integrating tractor working condition prediction was proposed. In the study, the ECMS was applied to the power distribution of a high-horsepower tractor equipped with a hybrid hydro-mechanical continuously variable transmission powertrain. Firstly, based on the radial basis function(RBF)neural network, a tractor working condition prediction model was established to predict the working condition for a period of time in the future based on the historical working condition. Then, the equivalent factor was adjusted adaptively based on the battery state of charge(SOC)feedback and the predicted working condition. Finally, the power distribution of the hybrid tractor was optimized under the PA-ECMS framework. The results show that, compared with the ECMS with fixed equivalent factor and the adaptive equivalent consumption minimization strategy(A-ECMS)based on SOC feedback only, the fuel consumption of the tractor under ploughing condition is reduced by 6.30% and 2.55%, respectively, and that the tractor performed better in power maintenance.关键词：hybrid tractor;equivalent consumption minimization strategy;equivalent factor;neural network;condition prediction78|23|0更新时间：2025-07-09
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