Numerical Simulation of the Parallel Gap Resistance Welding Process of a Solar Cell and Mo/Pt/Ag Interconnector

Energy for space vehicles in low Earth orbit(LEO) is mainly generated by solar arrays, and the service time of the vehicles is controlled by the lifetime of these arrays, which depends mainly on the lifetime of the interconnects. To increase the service life of LEO satellites, molybdenum/platinum/silver(Mo/Pt/Ag) laminated metal matrix composite(LMMC) interconnectors are widely used in place of Mo/Ag LMMC and Ag interconnectors in solar arrays. A 2D thermal-electrical-mechanical coupled axisymmetric model was established to simulate the behavior of the parallel gap resistance welding(PGRW) process for solar cells and Mo/Pt/Ag composite interconnectors using the commercial software ANSYS. The direct multicoupled PLANE223 element and the contact pair elements TARGE169 and CONTA172 were employed. A transitional meshing method was applied to solve the meshing problem due to the ultrathin(1 μm) intermediate Pt layer. A comparison of the analysis results with the experimental results revealed that the best parameters were 60 W, 60 ms, and 0.0138 MPa. The voltage and current predicted by the finite element method agreed well with the experimental results. This study contributes to a further understanding of the mechanism of PGRW and provides guidance for finite element simulation of the process of welding with an ultrathin interlayer.

Analysis of sliding electric contact characteristics in augmented railgun based on the combination of contact resistance and sliding friction coefficient

The contact resistance between the armature and rails is an important indicator of the contact characteristics in electromagnetic launches.As the contact resistance depends not only on the contact state but also on the contact stress and temperature,there are some limitations in analyzing the contact characteristics using only the contact resistance.In this paper,the contact characteristics of the augmented railgun are analyzed by the combination of contact resistance and sliding friction coefficient.Firstly,the theoretical calculation model of the contact resistance and friction coefficient of the augmented electromagnetic railgun is established.Then the contact resistance and friction coefficient are calculated by the measured values of the muzzle voltage,rail current and armature displacement.Finally,the contact characteristics are analyzed according to the features of the waveforms of the contact resistance and the friction coefficient,and the analysis conclusions are verified by experimental rail images.The results showed that:the aluminum melt film gradually formed on the contact surface reduces the contact resistance and the friction coefficient;the wear and erosion of the armature cause deterioration of the contact state;after the transition,the reliability of the sliding contact between the armature and rails decreases,resulting in an increase in contact resistance.

Corrected Formula of Bed Resistance Coefficient for Plane Numerical Simulation of Tidal Current

By means of a logarithm law for the velocity profile, a corrected formula of bed resistance coefficient, which involves many factors such as gradient of still water depth, variation of surface elevation, flow direction, and so on, is derived from the 3D governing equations of tidal current by averaging over the whole water depth. Theoretical analysis and application have shown that the 2D plane tidal current numerical model would be more reasonable and could be applied to steep bottom topography when the corrected bed resistance coefficient is used, therefore the results of reproduction simulation and engineering calculation would be more scientific and reasonable.

Thin Film Chip Resistors with High Resistance and Low Temperature Coefficient of Resistance

High resistance thin film chip resistors(0603 type) were studied,and the specifications are as follows:1 k? with tolerance about ±0.1% after laser trimming and temperature coefficient of resistance(TCR) less than ±15×10-6/℃.Cr-Si-Ta-Al films were prepared with Ar flow rate and sputtering power fixed at 20 standard-state cubic centimeter per minute(sccm) and 100 W,respectively.The experiment shows that the electrical properties of Cr-SiTa-Al deposition films can meet the specification requirements of 0603 ty...

Key issues in rock mechanics of the Three Gorges Project in China

The Three Gorges Project is one of the essential key projects for flood controlling and water resources regulation in the Yangtze River. The project includes a river-crossing dam, underground powerhouses, and navigation structures. Because of the huge size and complicated construction technologies, the project faced a series of challenging engineering issues. In terms of rock mechanics, there are many key technical issues, including the sliding resistance and stability of the dam section along the foundations of powerhouses No.l-5, the ,,;lope stability of the double-line five-stage shiplock, excavation of large-scale underground powerhouses, and curtain grouting under the dam. With decades of scientific research and 16 years of practical construction experiences and reservoir operations, these key technical issues in construction of the Three Gorges Project are successfully resolved, which will attribute to the development of hydropower technology. On the basis of the monitoring data during construction and normal operation periods of the Three Gorges Project, this paper presents a systematic analysis of these key rock mechanical issues in terms of behaviors, solutions, dynamic controlling, monitoring arrangement and integrated assessment.

Anisotropy of Expansion Coefficient and Slag Resistance of Spinel Carbon Bricks

Effects of the pressure direction on the thermal expansion and slag corrosion resistance were investigated and anisotropic microstructures of flaky graphite in spinel carbon bricks were examined. The experimental results show that slag corrosion velocities in the direction parallel to the pressure direction display a decrease of 34% compared to those in the vertical direction. Meantime, the linear expansion coefficient in the direction parallel to the pressure direction is 2.45 times as large as that in the vertical pressure direction. Slag corrosion velocities of spinel carbon bricks soaked in the AOD melting slag display a 46%-47% decrease compared to those of magnesia carbon bricks. The microstructure observation shows that spinel carbon bricks have a high degree of preferred orientation.

Probabilistic limit state design methodof the axial resistance of post grouting pile

The reliability of post grouting pile axial resistance was studied by proposing a design method for its probabilistic limit state,which is represented by the partial coefficients of load,end,and side resistance.The hyperbolic,modified hyperbolic,and polynomial models were employed to predict the ultimate bearing capacity of test piles that were not loaded to damage in field tests.The results were used for the calculation and calibration of the reliability index.The reliability of the probabilistic limit state design method was verified by an engineering case.The results show that the prediction results obtained from the modified hyperbolic model are closest to those obtained through the static load test.The proposed corresponding values of total,side,and end resistance partial coefficients are 1.84,1.66,and 2.73 when the dead and live load partial coefficients are taken as 1.1 and 1.4,respectively.Meanwhile,the corresponding partial coefficients of total,side,and end resistance are 1.70,1.56,and 2.34 when the dead and live load partial coefficients are taken as 1.2 and 1.4,respectively.

Uphillshift decision strategy of an AMT off-road vehicle based on generalized road resistance coefficient

In order to improve the shift decision strategy for an off-road vehicle with automated manual transmission（AMT）,the generalized road resistance coefficient is defined based on the longitudinal dynamics analysis.Vehicle mass and generalized road resistance coefficient are estimated using the recursive least square（RLS）method with multiple forgetting factors.The improved shift schedule is designed based on the generalized road resistance coefficient under uphill road condition.The simulation and real vehicle test verify the effectiveness of improved shift strategy and the improvement of vehicle dynamic performance.

Analyses on schedule-cost coefficient correlation of spaceflight project based on historical statistics and its application

When analyze the uncertainty of the cost and the schedule of the spaceflight project, it is needed to know the value of the schedule-cost correlation coefficient. This paper deduces the schedule distribution, considering the effect of the cost, and proposes the estimation formula of the correlation coefficient between the in（schedule） and the cost. On the basis of the fact and Taylor expansion, the relation expression between the schedule-cost correlation coefficient and the in-schedule-cost correlation coefficient is put forward. By analyzing the value features of the estimation formula of the in-schedule-cost correlation coefficient, the general rules are proposed to ascertain the value of the schedule-cost correlation coefficient. An example is given to demonstrate how to approximately amend the schedule-cost correlation coefficient based on the historical statistics, which reveals the traditional assigned value is inaccurate. The universality of this estimation method is analyzed.

Experimental Study on Rotation Resistance Coefficient of Motor Bogie for Type A Vehicle

Rotation resistance coefficient is an important operating parameter for vehicle bogies, which influences the dynamic behavior of vehicles directly. A research on the rotation resistance coefficient of type A vehicle motor bogies was conducted by means of theoretical calculation, dynamic simulation, test certification, and so on. Result of the simulation analysis shows that the rotation resistance coefficient relates to air springs stiffness and negotiated curve radii, and it varies proportionally with the change of air springs horizontal stiffness. The greater the rotation angle is, the greater the factor becomes. The certifications made under the operating conditions(e.g., different air spring status, different rotation speeds) indicate that the rotation resistance coefficient increases with the increase of the rotation speed. The anti-yaw dampers can contribute to the rotation resistance torque acted on bogie, and the greater the rotation speeds are, the greater the torque generated by the anti-yaw dampers is. The results suggest that the theoretical analysis and dynamics simulation are in accordance with the results from the bogie bench tests, which meet the requirements in EN14363 and the indicators in vehicles safe operation.

Experimental Study on Influencing Factors of Resistance Coefficient and Residual Resistance Coefficient in Oilfield Z

In order to clarify the major influence factors of resistance coefficient and residual resistance coefficient, so as to provide the basis for optimizing the polymer flooding schemes in oilfield Z of Bohai Sea, artificial cores were made by simulated the characteristic parameters of real reservoir and the spacing of production-injection wells. The main parameters considered include reservoir permeability, polymer solution concentration and polymer injection rate. Core experiment of polymer flooding was taken by considering all the main parameters. The result showed that resistance coefficient and residual resistance coefficient decrease with the increase of core permeability. Resistance coefficient and residual resistance coefficient increase with the increase of concentration of polymer solution. The increment of displacement pressure in low permeability core is higher than in medium and high permeability core. The resistance coefficient increase with higher displacing velocity, and the increment in high permeability core is higher than in low permeability?core. The displacement velocity has little effect on the residual resistance coefficient. The experimental results can effectively guide the formulation of polymer flooding scheme in offshore oilfields, and optimize the appropriate injection rate and concentration of polymer solution for different properties of reservoirs, thus ensuring the effectiveness of polymer flooding in offshore oilfields.

Experimental Determination of Local Resistance Coefficient of Sudden Expansion Tube

Theoretical derivation of local resistance coefficient of sudden expansion tube is presented. Several assumptions are analyzed in the theoretical derivation. That the head loss shall be neglected is affirmed. Experimental data proves that the pressure before and after sudden expansion section is basically the same. That the friction force on the side face of control body is neglected is denied and it is pointed out that such neglect is the main cause for error between theoretical calculation and actual measurement. Experimental device for measuring local resistance coefficient is designed in combination with theoretical derivation process. Optimal gradually varied flow section is selected after sudden expansion pipe in Bernoulli equation based on variation of piezometer tube head. It is pointed out in accordance with experimental data analysis that the value of local resistance coefficient of sudden expansion tube determined through experimental data is closer to the actual situation during pipeline design.

Fabrication and characterization of NiCr-based films with high resistivity and low temperature coefficient of resistance

As a metal alloy,NiCr films have a relatively high resistivity and low temperature coefficient of resistance (TCR) and are widely used in electronic components and sensors.However,the resistivity of pure NiCr is insufficient for high-resistance and highly stable film resistors.In this study,a quaternary NiCrAlSi target (47:33:10:10,wt.%) was successfully used to prepare resistor films with resistivities ranging from 1000 to 10 000μΩcm and TCR within±100 ppm/K.An oxygen flow was introduced during the sputtering process.The films exhibit hightemperature stability at 450℃.The films were analyzed using Auger electron spectroscopy,x-ray diffraction,time-of-flight secondary-ion mass spectrometry,and x-ray photoelectron spectroscopy.The results show that the difference in the oxide proportion of the films caused the differences in resistivity.The near-zero TCR values were considered to be due to the competition between silicon and other metals.This study provides new insights into the electrical properties of NiCr-based films containing Si,which will drive the manufacturing of resistors with high resistivity and zero TCR.

Effect of Working Temperature on the Resistance Characteristic of a Pleated Stainless Steel Woven Filter

Effect of working temperature on the resistance characteristic including the permeability coefficient and the pressure drop evolution of a pleated stainless steel woven filter with a nominal pore size of 0.5 μm has been studied. The permeability coefficient was obtained based on the pressure drop data and the Darcy＇s law. In three filtration experiments, pure carbon dioxide at 283 K, nitrogen at 85 K and liquid helium at 18 K are adopted, respectively. It is found that the permeability coefficient decreases at the working temperature due to the cold shrink of the filter element at cryogenic temperature. Then, two kinds of feed slurries, mixture of liquid nitrogen and solid carbon dioxide at 85 K, and mixture of liquid helium and solid nitrogen at 18 K, flow into the filter cell. The solid particles are deposited on the filter surface to form a filter cake and the purified liquid flows through the filter. It is found that the pressure drop evolution shows the same trend on these two temperatures, which can be divided into three stages with high filtration efficiency, indicating the feasibility of the filter for cryogenic application. However, variant cake resistances are obtained, which is resulted from the different interactions between solid particles in the feed slurry at lower working temperature.

THE EFFECT OF COLD DEFORMATION AND HEAT TREATMENT ON COEFFCIENT OF STRAIN RESISTANCE

The coefficient of strain resistance for metals,solid solutions and ordering alloys in annealing state decreases,while K increases in cold working state.The value K of pure metals and solid solutions invaraibly decreases with temperature increass.The main factors influencing the coefHcient of strain resistance are crystal defect,dispersion and degree of atomic arrangement.

Estimation Method of Schedule-cost Correlation Coefficient of Spaceflight Project

To evaluate the cost risk and the schedule risk of the spaceflight project,the schedule-cost(S-C) correlation coefficient is directly appointed according to the experts' experience usually.This paper deduces SDMCU(the schedule distribution model considering the effect of the cost uncertainty),and then proposes the approximate formula to estimate the ln(S)-C correlation coefficient based on the models of SDMCU and CDMSU(the cost distribution model considering the effect of the schedule uncertainty).Furthermore,an approximate relationship expression of the S-C and the ln(S)-C correlation coefficients is put forward according to general facts and the Taylor expansion,and advanced by means of mass numerical validation is the general rule of obtaining the estimation value of the schedule-cost correlation coefficient based on the historical data.

The Dynamic Study on Transpiration Consumption of Black Locust Forest

To know the annual water consumption of forest, it is necessary to acquire the annual transpiration value of stands. This paper is based on the data measured in the typical weather of the growth season, from 1998 to 2000, with the LI 1600 Steady Porometer and the general weather information. The daily variation of transpiration in black locust forest ( Robinia pesudoacacia L.) is modeled by Penman Monteith equation. As a result of the model, a continuous daily transpiration in the growth season was calculated. The net radiation, intercepted by black locust forest canopy, was acquired from a semi empirical equation of measuring net radiation R n with the extinction coefficient k and leaf area index LAI . The canopy integral stomatic resistance is a mimesis with an empirical equation of measuring data. Compared with measuring data, the relative error of the modeled ones is less than 12% averagely. At last, the total transpiration of black locust forest during the period of 1998 and 2000 in the growth season of May to October, as an average transpiration of the different density stands, were 192 46, 187 07 and 195 59?mm respectively.

The effect of blending polypropylene on the electrical properties of polymeric insulation material Hifax

Extensive physical testing has suggested that polymeric material Hifax (Flexible Polypropylene)could be a promising candidate for the next generation of DC insulation. In the work presented in this paper,the DC conductivity and AC breakdown of this polymeric insulation material have been measured as a function of temperature. The results show that Hifax cable insulation has a higher AC breakdown strength than EPR and XLPE (crosslinked polyethylene), and the DC resistivity of Hifax is larger than that of XLPE and oil-impregnated paper insulations. The electrical stress coefficient of resistivity of Hifax wire insulation increases with temperature, which needs to be taken into account in calculating the electrical field distribution across DC cable insulation. It has been observed that there is an anomalous change in resistivity at high electrical field, suggesting charge trapping and detrapping processes are present in Hifax cable insulation. It is concluded that blending Hifax with 62% polypropylene decreases the breakdown strength significantly.

DEVELOPMENT OF INCONEL~ ALLOY 783，A LOW THERMAL EXPANSION，CRACK GROWTH RESISTANT SUPERALLOY

Low thermal expansion superalloys have been used for a number of years in a variety of applications, including gas turbine engines. The low thermal expansion characteristics of the most widely used class of materials are derived from the ferromagnetic characteristics of Ni, Fe, and Co-based austenitic matrices containing little or no Cr.Alloy developments have been aimed at improving the oxidation resistance and stress accelerated grain boundary oxygen (SAGBO) attack.INCONEL alloy 783 is an oxidation resistant, low coefficient of thermal expansion superalloy developed for gas turbine applications. Alloy 783 represents a culmination in the development, of an alloy system with very high alumtnum content that, in addition to forming γ′,causes βaluminide phase precipitation in the austenitic matrix.This type of structure can be processed to resist both SAGBO and general oxidation,while providing low thermal expansion and useful mechanical properties up to 700℃.Key aspects of the alloy's development are presented.

基于PROMETHEE-Ⅱ的电网科技项目后评估评价方法研究

为满足双碳背景下电网精准投资的迫切需求,面对目前电网科技项目数量的急剧增加,迫切需要构建一个后评价指标体系,以低碳绿色发展、运营效率和经济效益为特点,以便评估电网发展规模和速度、结构和安全性以及效率和效益,进而带动科技项目成果转化率的提高,加快科研项目向市场的推广进程。从组织管理、技术水平、成果应用以及影响力4个方面构建电网科技项目后评估的评价指标体系,应用三角模糊数和变异系数法结合的组合赋权法确定各评价指标的权重,基于PROMETHEE-Ⅱ方法对电网科技项目进行后评估,确定最终的评价结果。以实际案例分析,验证该模型具有可行性。