查看更多>>摘要：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.
查看更多>>摘要：Based on the parametric resonance magnetometer(PRM)theory,this paper establishes an experimen-tal 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 0.0691 nT.In the same way,the average value of the residual magnetic field in the y-axis direction is reduced from 0.081 6nT to-0.004 2 nT,and the mean-square error from 0.131 6nT 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.
查看更多>>摘要：The rapid growth of distributed photovoltaic(PV)has remarkable influence for the safe and economic operation 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.
查看更多>>摘要：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 high-frequency 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.
查看更多>>摘要：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 effectively detect illegal actions in the simulated scene.
查看更多>>摘要：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 x 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.
查看更多>>摘要：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.
查看更多>>摘要：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.
查看更多>>摘要：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.
查看更多>>摘要：In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115kJ/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 ℃ surpasses 115 J and the crack tip opening displacement value at-10 ℃ 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 martensite-austenite 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.
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