Table of Content

28 March 2024, Volume 29 Issue 2 Previous Issue   
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Energy and Power Engineering
Wireless Communication
Materials Science and Engineering


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Energy and Power Engineering

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Review on Anti-Frost Technology Based on Microchannel Heat Exchanger YE Zhenhong(叶振鸿), WANG Wei(王炜), LI Xinhua(李新华), CHEN Jiangping(陈江平) 2024, 29 (2):  161-178.  doi: 10.1007/s12204-022-2539-x Abstract ( 207 )   PDF (4397KB) ( 97 )   Frosting is an inevitable adverse phenomenon in many fields such as industrial refrigeration, cryogenics, and heat pump air conditioning, which may influence the efficiency of the equipment and increase the energy consumption of the system. The complicated louvered-fin structure and fluid-channels arrangements of the microchannel heat exchanger (HEX) will affect the heat transfer performance and frosting characteristics. First, this article analyzes different factors such as refrigerant distribution, refrigerant flow pattern, and HEX surface temperature distribution. Further, combined with the features of the microchannel HEX, the existing anti-frosting technologies and various methods of surface treatment for anti-frosting are summarized. The review focuses on the preparation of superhydrophobic surfaces and their superior properties. Furthermore, the internal mechanism is analyzed in conjunction with the relevant research of our group. Superhydrophobic character has excellent anti-frosting performance and heat transfer performance, which is of great significance for improving energy-saving and system performance. Finally, the future development of superhydrophobic surface technology is analyzed and prospected. References | Related Articles | Metrics

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Performance and Optimization of Air Source Heat Pump Water Heater with Cyclic Heating LI Fan(李凡), LU Gaofeng(陆高锋), DING Yunxiao(丁云霄), ZHENG Chunyuan(郑春元), LI Bin(李斌), ZHAI Xiaoqiang(翟晓强) 2024, 29 (2):  179-187.  doi: 10.1007/s12204-022-2500-z Abstract ( 133 )   PDF (1349KB) ( 58 )   A new type of microchannel condenser applied in the air source heat pump water heater (ASHPWH) with cyclic heating was proposed in this study. The operating performance of the ASHPWH was first tested. Then,the structure of the microchannel condenser was optimized with the implement of vortex generators. Finally, a numerical model of the ASHPWH was established and the optimized microchannel condenser was studied. The experimental results showed that the average coefficient of performance (COP) of the 1 HP (735 W) ASHPWH reached 3.48. In addition, the optimized microchannel condenser could be matched with a 3 HP (2 430 W) ASHPWH with an average heating capacity of 10.30 kW, and achieving an average COP of 4.24, 14.6% higher than the limit value in the national standard. References | Related Articles | Metrics

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Working Fluid Distribution and Charge Regulation Control in Organic Rankine Cycle YE Zhenhong(叶振鸿), WANG Wei(王炜), LI Xinhua(李新华), CHEN Jiangping(陈江平) 2024, 29 (2):  188-201.  doi: 10.1007/s12204-022-2538-y Abstract ( 129 )   PDF (1116KB) ( 35 )   Charge-based studies, in particular investigations of mass distribution, are still almost absent, although the efficiency of the organic Rankine cycle (ORC) has attracted a great deal of scholarly attention. This paper aims to provide a new perspective on the intrinsic relationship among the mass distribution, phase-zone distribution in the heat exchanger (HEX), charge of working fluid (WF), rotation speed of the pump (RSP), and system performance. A comprehensive ORC simulation model is presented by linking each component’s sub-models, including the independent models for HEX, pump, and expander in an object-oriented fashion. The visualization study of mass distribution of the WF in the system is investigated under different working conditions. Furthermore, the volume and mass of the gas phase, two-phase and liquid phase of WF in the HEX and their variation rules are analyzed in-depth. Finally, the strategies of charge reduction considering HEX areas and pipe sizes are investigated. The results show that the model based on the interior-point method provides high levels of accuracy and robustness. The mass ratio of the WF is concentrated in the liquid receiver, especially in the regenerator, which is 32.9% and 21.9% of the total mass, respectively. Furthermore, 2.4 kg (6.9%) WF in the system gradually migrates to the hightemperature side as the RSP increases while 6.1 kg (17.4%) WF migrates to the low-temperature side, especially to the condenser, as the charge in the system increases. Output power and efficiency both decrease gradually after the peak due to changes in RSP and charge. Last, reducing heat transfer areas of the condenser and regenerator is the most effective way to reduce WF charge. References | Related Articles | Metrics

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Numerical Study on Comparison of Negative and Positive Surface Discharge in c-C4F8/CF3I/CO2 Gas Mixture FAN Binhai(范彬海), ZHOU Xiaoli(周小丽), QIAN Yong(钱勇), ZANG Yiming(臧奕茗) 2024, 29 (2):  202-215.  doi: 10.1007/s12204-022-2562-y Abstract ( 65 )   PDF (2362KB) ( 34 )   The dynamics of negative surface discharges in c-C4F8/CF3I/CO2 gas mixture is investigated here with a 2D fluid model. The distributions of ion concentration, electric field strength and photon flux during the propagation of the streamer are obtained by solving the drift-diffusion equations of particles and Poisson’s equation, and the photon flux variation function during the propagation is also fitted. It is found that the streamer branches occur when the streamer transitions from the upper surface of the insulator to the side surface, and then when the streamer approaches the plane electrode, the photon flux will increase significantly. On this basis, the positive and negative surface discharge models are compared in terms of streamer characteristics, particle characteristics and streamer branches. It is found that the streamer has a higher electron concentration and electric field in the positive model. The streamer develops “floating” in the positive surface discharge, while it is close to the surface of the insulator in the negative model. In addition, the negative streamer branch has a wider width and develops further. References | Related Articles | Metrics

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Transient and Steady Spray Characteristics of Soybean Oil/2,5-Dimethylfuran Blended Fuel in an Underwater Stirling Engine WANG Jigang(王继刚), QIAO Xinqi(乔信起), ZHOU Feng(周枫), WANG Lintao（王林涛） 2024, 29 (2):  216-229.  doi: 10.1007/s12204-023-2630-y Abstract ( 66 )   PDF (3635KB) ( 24 )   The reduction of oxygen consumption is a key factor to improve the energy density of underwater Stirling engine. A series of fundamental experiments are carried out to elucidate the spray characteristics of soybean oil/2,5-dimethylfuran (DMF) blended fuel in an underwater Stirling engine. Spray characteristics such as spray penetration, spray angle, spray area, and light intensity level under low injection and ambient pressures are obtained using image post-processing method. The results show that the effects of injection pressure, ambient pressure, and nozzle diameter on the transient spray characteristics of underwater Stirling engine are similar to those of diesel engine. However, in the steady spray process, the injection pressure has little effect on spray near angle, and the spray far angle increases with the increase of the injection pressure. Compared with the spray far angle at injection pressure of 3 MPa, the spray far angle at 5 MPa and 7 MPa increased by 11.38% and 18.14% respectively. The addition of DMF can obviously improve the atomization of soybean oil/DMF blended fuel. The spray angle of blended fuel in transient process increases with the increase of the DMF concentration. The spray near angle has exceeded that of diesel (46.21◦) when the DMF volume fraction exceeds 25%. The spray far angle is equivalent to that of diesel when the DMF volume fraction reaches 75%. Moreover, the spray with gas ejection no longer keeps conical, the droplet diameter distribution is more dispersed, and the droplet diameter is smaller. References | Related Articles | Metrics

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Characteristics of High-Pressure Spray of a Gasoline Direct Injection Injector Under Non-Flash Boiling and Flash Boiling Conditions WANG Sen (王森), XU Hongchang (徐宏昌), LI Xuesong (李雪松), YUAN Zhiyuan（袁志远） 2024, 29 (2):  230-236.  doi: 10.1007/s12204-022-2480-z Abstract ( 50 )   PDF (1293KB) ( 18 )   The increasingly stringent emission regulations and fuel consumption requirements have elevated the demands of internal combustion engines with higher fuel efficiency and lower emissions. It has been widely demonstrated that flash boiling spray can generate shorter and wider spray with improved atomization and evaporation to promote a better air-fuel mixing process. In this study, macroscopic (far-field) spray morphologies and primary breakup (near-field) characteristics of a two-hole gasoline direct injection injector are investigated under non-flash boiling and flash boiling conditions. High speed macroscopic and microscopic imaging was used to capture the overall spray structure and near-field characteristics, respectively. N-Hexane is used as the test fuel with the injection pressure ranging from 10 MPa up to 40 MPa. For sub-cooled liquid fuel sprays, increasing fuel pressure contributes to enhanced fuel atomization and evaporation. Evident collapses occurred under flare flash boiling conditions, and higher injection pressure weakened this phenomenon since the spray cone angle decreased due to a higher injection velocity. References | Related Articles | Metrics

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Numerical Investigation on Dynamic Response Characteristics of Fluid-Structure Interaction of Gas-Liquid Two-Phase Flow in Horizontal Pipe WANG Zhiwei(王志伟), HE Yanping(何炎平), LI Mingzhi（李铭志）, QIU Ming(仇明), HUANG Chao(黄超), LIU Yadong（亚东），WANG Zi(王梓) 2024, 29 (2):  237-244.  doi: 10.1007/s12204-022-2469-7 Abstract ( 86 )   PDF (1576KB) ( 35 )   Fluid-structure interaction (FSI) of gas-liquid two-phase flow in the horizontal pipe is investigated numerically in the present study. The volume of fluid model and standard k-ε turbulence model are integrated to simulate the typical gas-liquid two-phase flow patterns. First, validation of the numerical model is conducted and the typical flow patterns are consistent with the Baker chart. Then, the FSI framework is established to investigate the dynamic responses of the interaction between the horizontal pipe and gas-liquid two-phase flow. The results show that the dynamic response under stratified flow condition is relatively flat and the maximum pipe deformation and equivalent stress are 1.8 mm and 7.5 MPa respectively. Meanwhile, the dynamic responses induced by slug flow, wave flow and annular flow show obvious periodic fluctuations. Furthermore, the dynamic response characteristics under slug flow condition are maximum; the maximum pipe deformation and equivalent stress can reach 4 mm and 17.5 MPa, respectively. The principal direction of total deformation is different under various flow patterns. Therefore, the periodic equivalent stress will form the cyclic impact on the pipe wall and affect the fatigue life of the horizontal pipe. The present study may serve as a reference for FSI simulation under gas-liquid two-phase transport conditions. References | Related Articles | Metrics

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Numerical Study on Effect of Suction Slot Geometric Parameters on Airflow Field in Compact Spinning LIN Huiting1,2 (杨娜), WANG Jun1∗ (张淑霞), ZHANG Yongfa3 (白牡丹) 2024, 29 (2):  245-251.  doi: 10.1007/s12204-022-2521-7 Abstract ( 76 )   PDF (1054KB) ( 22 )   The airflow field in the condensing zone is crucial as it affects the fiber condensing, additional twists, and consequently yarn properties. Parameters of spinning and suction slot geometric were found to be key factors influencing the airflow characteristics. To develop a better understanding of the complex airflow field within the pneumatic compact spinning system with lattice apron, a 3D numerical simulation model was built and the influence of negative pressure and geometric of suction slot was investigated. The results reveal that the accelerating air from the top of the suction slot generates transverse condensing force and downward pressure on the fiber strand. The inclination angle has a small effect on airflow velocity. The absolute z-velocity and x-velocity in the positive x-axis were both increased with increasing the slot width from 1.0 mm to 1.5 mm. An arc suction slot increased the absolute z-velocity and x-velocity compared with a linear one, thus benefiting fiber condensing. By decreasing the outlet negative pressure to −3 kPa, the airflow velocity increased significantly. References | Related Articles | Metrics

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Explosion Hazard Analysis of Liquefied Petroleum Gas Transportation GAO Sida1 (高思达),HAO Lin 1* (郝琳), ZHU Zhenxing2* (朱振兴), WEI Hongyuan1 (卫宏远) 2024, 29 (2):  252-260.  doi: 10.1007/s12204-022-2536-0 Abstract ( 112 )   PDF (1310KB) ( 41 )   This paper presents a quantitative risk analysis of liquefied petroleum gas (LPG) transportation. An accident that happened on June 13, 2020, on the highway near Wenling, China is studied as a case. In this accident, LPG carried by a tank truck on the highway leaked and caused a large explosion, which led to 20 deaths. Different methods are combined to calculate the consequence of the accident. Multi-energy model and rupture of vessel model are employed to calculate the overpressure; the simulation result of the multi-energy model is closer to the damage caused by the accident. The safety distances in accidents of LPG transport storage tanks of different capacities are calculated in this study; the results show that the damage of explosion will increase with the filling degree of the tank. Even though the filling degree is 90% (value required by law), the 99% fatality rate range will reach 42 m, which is higher than regulated distance between road and building. The social risk of the tank truck has also been calculated and the results show that the risk is not acceptable. The calculating method used in this study could evaluate the risk of LPG tanker more accurately, which may contribute to the establishment of transportation regulation so that losses from similar accidents in the future could be reduced. References | Related Articles | Metrics

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Identification of Steady State and Transient State YU Sheng (于生), LI Xiangshun∗ (李向舜) 2024, 29 (2):  261-270.  doi: 10.1007/s12204-022-2516-4 Abstract ( 97 )   PDF (1612KB) ( 20 )   Identification of steady state and transient state plays an important role in modeling, control, optimization, and fault detection of industrial processes. Many existing methods for state identification are not satisfactory in practical applications due to problems of ideal hypothesis, too many parameters, and poor robustness. In this paper, a novel state identification approach is proposed. The problem of state identification is transformed into finding the noise band of differential signal. For practical application, automatic selection of noise band amplitude is proposed to make the method convenient to be used. Problems of gross errors, low signal-to-noise ratio and online identification are considered. And comparison with other two methods shows that the proposed method has better identification performance. Simulations and experiments also prove the effectiveness and practicability of the proposed method. References | Related Articles | Metrics

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Pressure Pulse Response of High Temperature Molten Salt Check Valve Hit by Crystal Particles LI Shuxun (李树勋), SHEN Hengyun* (沈珩云), LIU Bincai (刘斌才),HU Yinggang (胡迎港), MA Tingqian (马廷前) 2024, 29 (2):  271-279.  doi: 10.1007/s12204-023-2601-3 Abstract ( 80 )   PDF (2060KB) ( 33 )   In view of the problem that crystalline particles cause wall vibration at a low temperature, based on two-phase flow model, computational fluid dynamics is used to conduct the numerical simulation of internal flows when the valve openings are 20%, 60% and 100% respectively. The molten salt flow may be changed under strict conditions and produce forced vibration of the inner parts of molten salt particle shock valve body. Euler two-phase flow model is used for different molten salt sizes to extract temporal pressure pulse information and conduct statistical data processing analysis. The influence of the molten salt crystallization of molten salt particles on the flow and pressure pulse strength is analyzed. The results show that the crystallization of molten salt has a serious impact on the vibration of the valve body, especially in the throttle rate. The valve oscillation caused by the pressure pulsation mostly occurs from the small opening rate. As the opening increases, the pressure pulse threshold and its change trend decrease. References | Related Articles | Metrics

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Active Magnetic Compensation Based on Parametric Resonance Magnetometer GUO Yang1 (郭阳), LI Shaoliang2 (李绍良), HUANG Yiming1 (黄艺明), LUO Manruo1 (骆曼箬), LIU Hua1* (刘华) 2024, 29 (2):  280-289.  doi: 10.1007/s12204-022-2524-4 Abstract ( 91 )   PDF (1976KB) ( 20 )   Based on the parametric resonance magnetometer (PRM) theory, this paper establishes an experimental system of PRM. The experimental results are consistent with the theoretical predictions. A PRM has been developed with sensitivity of 0.5 pT/Hz1/2, which can detect the magnitude of residual magnetic field; furthermore, a proportion-integration-differentiation (PID) closed-loop magnetic compensation system of the residual magnetic field also has been realized. Compared with open-loop compensation, the PID closed-loop compensation reduces the average value of the residual magnetic field in the z-axis direction from 0.024 4 nT to −0.002 3 nT, and the mean-square error from 0.208 3 nT to 0.069 1 nT. In the same way, the average value of the residual magnetic field in the y-axis direction is reduced from 0.081 6 nT to −0.004 2 nT, and the mean-square error from 0.131 6 nT to 0.046 1 nT. The magnitude of residual magnetic fields in both directions is decreased to the order of picotesla (pT). In addition, based on the signal waveforms of the magnetometer, a method of verifying the effect of magnetic compensation is proposed. References | Related Articles | Metrics

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Distributed Photovoltaic Real-Time Output Estimation Based on Graph Convolutional Networks CHEN Liyue1 (陈利跃), HONG Daojian2 (洪道鉴), HE Xing3* (何星), LU Dongqi2 (卢东祁), ZHANG Qian2 (张乾), XIE Nina2 (谢妮娜), XU Yizhou2 (徐一洲), YING Huanghao2 (应煌浩) 2024, 29 (2):  290-296.  doi: 10.1007/s12204-022-2522-6 Abstract ( 84 )   PDF (1160KB) ( 26 )   The rapid growth of distributed photovoltaic (PV) has remarkable influence for the safe and economicoperation of power systems. In view of the wide geographical distribution and a large number of distributed PV power stations, the current situation is that it is difficult to access the current dispatch data network. According to the temporal and spatial characteristics of distributed PV, a graph convolution algorithm based on adaptive learning of adjacency matrix is proposed to estimate the real-time output of distributed PV in regional power grid. The actual case study shows that the adaptive graph convolution model gives different adjacency matrixes for different PV stations, which makes the corresponding output estimation algorithm have higher accuracy. References | Related Articles | Metrics

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Wind Speed Short-Term Prediction Based on Empirical Wavelet Transform, Recurrent Neural Network and Error Correction ZHU Changsheng(朱昶胜), ZHU Lina∗ (朱丽娜) 2024, 29 (2):  297-308.  doi: 10.1007/s12204-022-2477-7 Abstract ( 84 )   PDF (1282KB) ( 31 )   Predicting wind speed accurately is essential to ensure the stability of the wind power system and improve the utilization rate of wind energy. However, owing to the stochastic and intermittent of wind speed, predicting wind speed accurately is difficult. A new hybrid deep learning model based on empirical wavelet transform, recurrent neural network and error correction for short-term wind speed prediction is proposed in this paper. The empirical wavelet transformation is applied to decompose the original wind speed series. The long short term memory network and the Elman neural network are adopted to predict low-frequency and highfrequency wind speed sub-layers respectively to balance the calculation efficiency and prediction accuracy. The error correction strategy based on deep long short term memory network is developed to modify the prediction errors. Four actual wind speed series are utilized to verify the effectiveness of the proposed model. The empirical results indicate that the method proposed in this paper has satisfactory performance in wind speed prediction. References | Related Articles | Metrics

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Real-Time Safety Behavior Detection Technology of Indoors Power Personnel Based on Human Key Points YANG Jian1 (杨坚), LI Congmin2 (李聪敏), HONG Daojian1 (洪道鉴), LU Dongqi1 (卢东祁), LIN Qiujia3 (林秋佳), FANG Xingqi2∗ (方兴其), YU Qian1 (喻谦), ZHANG Qian1 (张乾) 2024, 29 (2):  309-315.  doi: 10.1007/s12204-022-2526-2 Abstract ( 61 )   PDF (1242KB) ( 16 )   Safety production is of great significance to the development of enterprises and society. Accidents often cause great losses because of the particularity environment of electric power. Therefore, it is important to improve the safety supervision and protection in the electric power environment. In this paper, we simulate the actual electric power operation scenario by monitoring equipment and propose a real-time detection method of illegal actions based on human body key points to ensure safety behavior in real time. In this method, the human body key points in video frames were first extracted by the high-resolution network, and then classified in real time by spatial-temporal graph convolutional network. Experimental results show that this method can effectivel detect illegal actions in the simulated scene. References | Related Articles | Metrics

Wireless Communication

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Performance Improvement of Multiband Triangular Microstrip Patch Antenna Using Frequency Selective Surface MAHENDRAN Krishnakumar∗, GAYATHRI Rajaraman 2024, 29 (2):  316-321.  doi: 10.1007/s12204-022-2492-8 Abstract ( 117 )   PDF (798KB) ( 20 )   Today’s antennas have to operate in multiple resonant frequencies to satisfy the need of recent advances in communication technologies. This paper presents split ring resonator based triangular multiband antenna whose antenna performance is enhanced with the help of frequency selective surfaces (FSSs). The antenna has multiple resonances at S, C, and X bands. An array of 4 × 3 crisscross-shaped unit cells are arranged to form the FSS layer. The antenna is fed with a microstrip line feeding technique. The proposed antenna operates at 3.5 GHz, 4.1 GHz, 5.5 GHz, 9.4 GHz, and 9.8 GHz with a better return loss and gain. Simulated and measured results yield a good match. References | Related Articles | Metrics

Materials Science and Engineering

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Novel Blasting-Like Lubricating Process for Cold Extrusion CHEN Haitang1,2 (陈海棠), HU Chengliang1,2* (胡成亮), GONG Aijun3 (龚爱军), SHI Weibing3 (施卫兵), ZHAO Zhen1,2 (赵震) 2024, 29 (2):  322-329.  doi: 10.1007/s12204-023-2599-6 Abstract ( 66 )   PDF (2044KB) ( 20 )   A blasting-like lubricating process (combination of shot blasting and lubricating processes) is proposed. In this process, the specimens to be treated, alloy shots, and solid lubricating powder are rotated together in a roller. The surface pockets formed due to the impact by the shots can store lubricants, and the lubricant can also adhere to the specimen surface by hitting. The effects of process parameters, including rolling time, rotational speed, mass of alloy shots, and the diameter of shots, on the surface topography of the steel specimen are investigated using 13 experimental schemes. The distribution ratio and average depth of surface pockets on the defined areas of the specimen are quantitatively analyzed. Four selected schemes with the MoS2 solid lubricating powder are further carried out to lubricate the cylindrical billets, and the lubricating effect is evaluated using the steady combined forward and backward extrusion test. The indicated friction factor of the novel blasting-like process is smaller than that of the conventional phosphate-soap coating process. References | Related Articles | Metrics

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Numerical Simulation of Radial Ultrasonic Assisted MIG Welding Arc HONG Lei1 (洪蕾), XIAO Hao1 (肖皓), YE Jia2 (叶佳), MA Guohong1* (马国红) 2024, 29 (2):  330-338.  doi: 10.1007/s12204-021-2380-7 Abstract ( 90 )   PDF (1906KB) ( 23 )   The numerical simulation of arc was carried out for both conventional melt inert gas (MIG) welding and ultrasonic assisted melt inert gas (U-MIG) welding. Based on the model established by Fluent, the arc shape, temperature field, and potential distribution were simulated. The study found that the shape of the arc changed when ultrasonic was added radially; the high-temperature area of the arc stretched, and the temperature peak increased. But as the current increased, the increase in temperature decreased. In addition, under the same conditions, the potential of U-MIG decreased and the pressure on the workpiece increased. To verify the accuracy of the simulation results, welding experiments under identical conditions were carried out, and a high-speed camera was used to collect dynamic pictures of the arc. The simulation results were in a favorable agreement with the experimental results, which provided a certain reference value for ultrasonic assisted arc welding. References | Related Articles | Metrics

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On-Line Detection of Porosity in Gas Tungsten Arc Welding of Aluminum Alloy Based on Spectrum Features JIANG Haoqiang (蒋浩强), CHEN Shanben* (陈善本), XU Jingyuan (许靖远) 2024, 29 (2):  339-348.  doi: 10.1007/s12204-022-2495-5 Abstract ( 54 )   PDF (2017KB) ( 21 )   The real-time detection of porosity in welding process is an important problem to be solved in intelligent welding manufacturing. A new on-line detection method for porosity of aluminum alloy in robotic arc welding based on arc spectrum is proposed in this paper. First, k-shape and the improved k-means were used for the initial feature selection of the preprocessed arc spectrum to reduce the data dimension. Second, the secondary feature selection was carried out based on the importance of features to further reduce feature redundancy. Then, the optimal sample label library was established by combining the final characteristic parameters and the X-ray pictures of welds. Finally, an on-line detection method of porosity in gas tungsten arc welding of aluminum alloy based on light gradient boosting machine (LightGBM) was proposed. Compared with extreme gradient boosting(XGBoost) and categorical boosting (CatBoost), this method can achieve better detection performance. The new method proposed in this paper can be used to detect other welding defects, which is helpful to the development of intelligent welding technology. References | Related Articles | Metrics

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Toughening Mechanism of Large Heat Input Weld Metal for Marine Engineering Extra-Thick Plate LENG Junjie1 (冷俊杰), DI Xinjie,2*1 (邸新杰), LI Chengning1,2 (利成宁), CHENG Shanghua3 (程尚华) 2024, 29 (2):  349-360.  doi: 10.1007/s12204-023-2638-3 Abstract ( 69 )   PDF (4684KB) ( 30 )   In order to study the latest designed large heat input welding material of marine engineering extrathick plate, EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85, 100 and 115 kJ/cm separately. Meanwhile, the microstructure and mechanical properties were evaluated to explore the toughening mechanism of weld metal. Results show that a lot of active inclusions are obtained in the weld metal due to the design idea of low carbon and oxide metallurgy, which contributes to the generation of numerous fine and interlocking acicular ferrite. The acicular ferrite volume ratio of weld metal exceeds 60%. Moreover, the impact energy at −40 ◦C surpasses 115 J and the crack tip opening displacement value at −10 ◦C is more than 0.2 mm under three heat inputs owing to the role of acicular ferrite, of which 85 kJ/cm is the best. The martensiteaustenite constituents are minor in size and the microstructure of the weld metal in reheated zone is dominated by small massive equiaxed ferrite, without impairing the toughness. As the heat input increases, the content of acicular ferrite drops and then rises; the impact toughness and fracture toughness first worsen consequently and then stabilize on account of the dramatic expansion of the proeutectoid ferrite size. References | Related Articles | Metrics

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Arc and Droplet Behaviors in Horizontal Short-Arc Pulsed Gas Metal Arc Welding of 9%Ni Steel with ERNiCrMo-3 Welding Wire LIU Yiwei1 (刘轶玮), HUA Xueming1* (华学明), WU Dongsheng1 (吴东升), LI Fang1 (李芳), CAI Yan1 (蔡艳), WANG Huan2 (王欢), YANG Xiurong3 (杨修荣) 2024, 29 (2):  361-376.  doi: 10.1007/s12204-022-2548-9 Abstract ( 61 )   PDF (5299KB) ( 112 )   Short-arc pulsed gas metal arc welding (P-GMAW) was used to solve the difficulties of molten pool spreading and droplet transfer of Ni-based welding wire. Suppression of short-circuit current was used to reduce spatter. Arc length stabilizer was used to acquire a proper and stable arc length maintained at the critical position where short circuit starts to occur. Short-arc P-GMAW with or without arc length stabilizer was compared. The droplet transfer, arc behaviors and weld bead profiles were investigated and compared based on the high-speed photography and observation of weld cross-section. When the arc length stabilizer was deactivated, the arc length was unstable and too short. The droplet transfer mode was mainly short circuit partial transfer, with only a small part of the droplet transferred into the molten pool, with the characteristics of no obvious necking, a few spatters, small droplet impact, long short circuit duration and high short-circuit current. There was also a small proportion of short circuit complete transfer with obvious necking, larger droplet impact, shorter short-circuit duration and lower short-circuit current. With arc length stabilizer, droplet transfer modes were short circuit complete transfer and spray transfer. The spray transfer had the largest droplet impact, no short circuit and no spatter. With the arc length stabilizer activated, a deep penetration, a high penetration ratio, a small reinforcement and a large reinforcement factor were acquired. This provides an innovative method to solve the difficulties of droplet transfer and molten pool spreading and eliminate the incomplete fusion in the GMAW of 9%Ni steel with nickel-based alloy welding wire. References | Related Articles | Metrics