2015年3期 (共 篇) 引用文章 全选
本平台内已出版文章查询 , GUO Dan * 已出版文章查询
本平台内已出版文章查询 , REDDYHOFF Tom 已出版文章查询
本平台内已出版文章查询 , SPIKES Hugh 已出版文章查询
本平台内已出版文章查询 , LUO JianBin 已出版文章查询
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This paper describes a study of point contact elastohydrodynamic (EHD) lubrication behavior at high speeds (up to 20 m s-1). Central film thicknesses were measured by optical interferometry device. The influence of slide-roll ratio and operating temperature on the central film thickness was determined. The influence of thermal effects on the reduction of film thickness was discussed via the analysis of numerical simulation method considering thermal effects. Subsequently, the experimental data was used to amend a set of unified parameters for the thermal corrections for different types of oil at high speeds.
本平台内已出版文章查询 , WU GenSheng 已出版文章查询
本平台内已出版文章查询 , MA Jian 已出版文章查询
本平台内已出版文章查询 , YUAN ZhiShan 已出版文章查询
本平台内已出版文章查询 , SI Wei 已出版文章查询
本平台内已出版文章查询 , LIU Lei 已出版文章查询
本平台内已出版文章查询 , SHA JingJie 已出版文章查询
本平台内已出版文章查询 , CHEN YunFei * 已出版文章查询
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We study the effects of electrolyte temperature on DNA molecule translocation experimentally without and with a temperature gradient across nanopore membranes. The same temperatures on both electrolyte chambers are first considered. The DNA molecule translocation time is measured to be 2.44 ms at 2 ℃ in both chambers, which is 1.57 times longer than at 20 ℃. Then the temperature difference effect is characterized in both chambers. The results show that the DNA translocation speed can be slowed down as long as one side temperature is lowered, irrespective of the temperature gradient direction. This indicates that the thermophoretic driving force generated by a temperature gradient has no obvious effect on the threading speed of DNA molecules, while the main reason for the slowed DNA translocation speed is the increased viscosity. Interestingly, the capture rate of DNA molecules is enhanced under a temperature gradient condition, and the capture rate during DNA translocation from hot side at 21 ℃ to cold one at 2 ℃ is 1.7 times larger than that under the condition of both chambers at 20 ℃. Finally, an optimized configuration is proposed to acquire higher capture rates and lower DNA translocation speeds.
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This paper presents an overview of the AMS thermal control system and its thermal environment on the ISS. We give examples of analysis and correlation of space environmental impacting on the thermal control system of AMS. The most critical factors that affect the thermal environment to AMS are beta angle, attitude of ISS, ISS solar array and ISS radiator positions. The design of a special sandwich structure with embedded heat pipes provides the radiator with higher heat transfer ability for electronics and power crates, and it provides a large heat retaining capacity to balance the frequent changes of the space environment temperatures as well. In cold cases, the thermostatically controlled heaters are working actively to protect AMS. However, sometimes, because of ISS special operations plus extreme beta angle condition, AMS needs to request NASA to adjust the ISS configuration for thermal control. The AMS thermal control system is reliable and stable, which has been verified by its operation on the ISS for more than three years. All the detectors operate normally, the electronics and crates work within their specific temperature limits.
Simulation and experiment of vortex transport properties in a Type II superconductor with grain boundary
本平台内已出版文章查询 , XU WeiWei 已出版文章查询
本平台内已出版文章查询 , HUA Tao 已出版文章查询
本平台内已出版文章查询 , YU Mei 已出版文章查询
本平台内已出版文章查询 , AN DeYue 已出版文章查询
本平台内已出版文章查询 , CHEN Jian 已出版文章查询
本平台内已出版文章查询 , JIN BiaoBing 已出版文章查询
本平台内已出版文章查询 , KANG Lin 已出版文章查询
本平台内已出版文章查询 , WU PeiHeng 已出版文章查询
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We firstly described a simulation model to investigate the influence of grain boundary (GB) on the vortex transport properties in YBCO film. It is found that the size of inhomogeneous area caused by GB as well as the average velocity in transverse and longitudinal directions shows an angular dependence when the angle θ between the GB and the sample edge varies. We have also studied the impact of magnetic field intensity on dynamic behavior of vortex lattice and found that a lower vortex density makes it difficult for the vortex lattice to transfer from pinning state to flow state. As the magnetic field is decreased beyond a critical value, sharp jumps and strong fluctuations were observed in the I-V curve. Finally, we conducted measurements on a thin film YBa2Cu3O7-δ with an individual artificial grain boundary to support the simulation process.
Circuit model based design and analysis for a four-structure-switchable wireless power transfer system
本平台内已出版文章查询 , LIU Hao * 已出版文章查询
本平台内已出版文章查询 , LI GuiYang 已出版文章查询
本平台内已出版文章查询 , SHAO Qi 已出版文章查询
本平台内已出版文章查询 , LI HongYi 已出版文章查询
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The four-coil wireless power transfer (WPT) technology can effectively improve the transfer efficiency. The high efficiency, however, cannot be obtained along the whole transfer distance due to the phenomenon of frequency splitting in the over coupled region. Aiming at this limitation, this paper presents a switchable WPT system to improve the overall efficiency by changing the number of working coils. The switching conditions for the designed system are determined based on the analysis of the transfer efficiencies of four structures, which is deduced through modeling the equivalent circuits. The simulation results well comply with the experimental results and both of them indicate that the switchable system can greatly improve the overall transfer efficiency along the whole transfer distance. The overall efficiency of the experimental system can reach above 70% at 9.97 MHz without additional complexity, which is higher than any single structure system.
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X-ray computer tomography (CT) has been intensively applied to the research of cement-based materials, while most of the CT applications are qualitative. To have more quantitative applications, the arbitrary grayscale values and the specially defined CT numbers of the main cement constituents, including the cement clinkers, the hydrated products, and some durability products are calibrated on an industrial CT system in this study. The calibration results can deepen our understandings of the X-ray CT image of the cement-based materials. The universalities of the calibrated results and the calibration procedures are clarified. The potential applications are anticipated, such as segmentation of the individual phases, quantitative durability research, porosity determinations, and quantitative composition characterizations.
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According to the three-dimensional geometry of the engagement, the explicit algebraic expression of differential geometric guidance command (DGGC) is proposed. Compared with the existing solutions, the algebraic solution is much simpler and better for the further research of the characteristics of DGGC. Time delay control (TDC) is a useful method to tackle the uncertainty problem of a control system. Based on TDC, taking the target maneuvering acceleration as a disturbance, the estimation algorithm of the target maneuvering acceleration is presented, which can be introduced in DGGC to improve its performance. Then, the augmented DGGC (ADGGC) is obtained. The numerical simulation of intercepting a high maneuvering target is conducted to demonstrate the effectiveness of ADGGC.
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We present a new calorimetric method for measuring alternative current (AC) losses of high-temperature superconducting (HTS) tapes by optical fiber Bragg grating (FBG), which is particularly well suited for the AC loss measurement of ReBCO wires, so-called the second generation (2G) HTS wires. Compared with conventional calorimetric methods, the suggested method is both free of electromagnetic disturbance, magnetic field, and fast as well as simple. Self-field AC losses are measured by the optical FBG method and the conventional lock-in-amplifier (LIA) technique, respectively. The results show that the measured AC loss is in good agreement with those measured by the electric method, thus the presented calorimetric method would be available for measuring the AC loss of 2G wire and is expected to be generalized for the measurement of AC loss or thermal performances of HTS bulk.
本平台内已出版文章查询 , LIU HaoRan 已出版文章查询
本平台内已出版文章查询 , LIANG JunCheng 已出版文章查询
本平台内已出版文章查询 , LIU JiaCheng 已出版文章查询
本平台内已出版文章查询 , XIONG WenJun 已出版文章查询
本平台内已出版文章查询 , YUE HuiGuo 已出版文章查询
本平台内已出版文章查询 , LIU SenLin 已出版文章查询
本平台内已出版文章查询 , YANG YuanDi 已出版文章查询
本平台内已出版文章查询 , YUAN DaQing * 已出版文章查询
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The activity of tritiated water has been standardized by two liquid scintillation counting methods: The CIEMAT/NIST method with the 54Mn-standard efficiency tracing and the triple-to-double coincidence ratio (TDCR) method. The samples were prepared with Ultima GoldTM AB liquid scintillation cocktail in low-potassium glass vials. In the application of the CIEMAT/NIST method, the computer program EMILIA was used to calculate the efficiency of 3H and 54Mn according to the KL1L2L3M atomic rearrangement model. And the detection efficiency of the TDCR counter was calculated using TDCR07 code, which makes it possible to allow for the potential asymmetry between the three photomultiplier tubes. The influence of stopping power and kB factor is discussed in the paper. When a power approach is adopted for the stopping power for electrons below 1 keV and kB is chosen to be 0.0075 cm/MeV, the relative deviation will be only 0.3% between the two methods.
On-line diagnosis method of crack behavior abnormality in concrete dams based on fluctuation of sequential parameter estimates
本平台内已出版文章查询 , GU ChongShi 已出版文章查询
本平台内已出版文章查询 , WANG ZhengZhong 已出版文章查询
本平台内已出版文章查询 , WU ZhongRu * 已出版文章查询
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Research on on-line diagnosis method of crack behavior abnormality in concrete dams can provide support for timely grasping abnormality state of the crack itself and achieving real-time monitoring of the dam safety. Considering that samples of crack effects in concrete dams increase actually over monitoring time, a superiority criterion for the on-line diagnosis is determined so as to detect the abnormality moments timely and reliably. By integrating the safety monitoring statistical model of crack effect variable with change point theory, a fluctuation method of regression coefficients is established for the on-line diagnosis. In addition, each abnormality moment is detected by the cumulative sum of regression model residuals. Results indicate that abnormality of crack behavior in concrete dams can be characterized by structural instability of crack monitoring model. And causes of crack behavior abnormality can be analyzed by the established method, which will play an important role in dam safety monitoring. Further, taking the crack in a concrete gravity-arch dam as an example, the scientific rationality and validity of the established on-line diagnosis method are confirmed.
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Various microstructure-level finite element models were generated according to the real microstructure of DP590 steel to capture the mechanical behavior and fracture mode. The failure mode of the dual-phase (DP) steels, mainly resulting from microstructure-level inhomogeneity and initial geometrical imperfection, was predicted using the plastic strain localization theory. In addition, dog-bone-type tensile test specimens with different edge qualities were prepared and the deformation processes were recorded using a digital image correlation system. When the steel exhibited no initial geometrical imperfection, void initiation was triggered by decohesion between martensite and ferrite which was predicted based on the severe strain concentration, or tensile stress in areas where stress triaxiality and strain values were high. Final failure was caused by shear localization in the vicinity. Moreover, the initial geometrical imperfections severely affected the overall ductility and failure mode of the DP590 steel. When initial geometrical imperfections were deeply ingrained, an incipient crack began at the site of initial geometrical imperfection, and then caused progressive damage throughout the microstructure, from the area of shear localization to the final fracture. Overall, the depth of the geometrical imperfection was the critical factor in determining whether internal decohesion or a local crack plays a dominant role.
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A framework of continuum breakage mechanics was used to investigate the dependence of compressibility on grain size distribution (GSD) as well as relative density of sand. Compressibility dependence on GSD was considered by employing a GSD index and relative density dependence was reflected by varying the plastic-breakage coupling angle. Simulations of the experimental results including isotropic compression and one-dimensional compression of sands with different relative densities and GSDs revealed that sand compressibility increased with the increasing GSD index and plastic-breakage coupling angle. The coupling angle decreased with increasing relative density, indicating that grains would break more in sand with comparatively high relative density.
CFD investigation and PIV validation of flow field in a compact return diffuser under strong part-load conditions
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The internal flow fields in a compact return diffuser under strong part-load conditions are investigated both numerically and experimentally. For numerical simulation, three-dimensional unsteady Reynolds-Averaged Navier-Stokes equations are solved on high-quality structured grids in conjunction with the shear stress transport k-w turbulence model by employing the computational fluid dynamics (CFD) software ANSYS-Fluent 14.5. For flow field measurements, a special test rig is designed and the two-dimensional particle image velocimetry (PIV) measurements are conducted in the diffuser midplane to capture the complex flow field and for validation of the CFD results. The analysis of the results has been focused on the flow structure in the diffuser, especially under part-load conditions. The detailed comparison between CFD and PIV results is performed. Vortical flow and recirculation flow patterns in the diffuser are captured and analyzed. Large flow separation and backflow appear under the part-load flow conditions. This paper provides a good data set for developing as well as evaluating the accuracy of various CFD models for capturing the complex flow field in a compact return diffuser used with multistage pumps.
Numerical analysis on the heat transfer of three types of nozzles for the hypersonic long-run wind tunnel
本平台内已出版文章查询 , ZHONG FengQuan * 已出版文章查询
本平台内已出版文章查询 , LI DongXia 已出版文章查询
本平台内已出版文章查询 , ZHANG XinYu 已出版文章查询
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The hypersonic long-run scramjet test tunnel is one of the key ground facilities for the studies of ramjet/scramjet and hypersonic thermal management. Due to the significantly large heat loading, the nozzle of the tunnel facility demands effective cooling protection. In this work, the two-dimensional, three-dimensional and axisymmetric Mach 6.5 nozzles at an inlet total temperature of 1840 K and a total pressure of 6.4 MPa were studied with main focuses on the properties of aerodynamic heating of nozzles. The present work aims to provide insights into the design of an effective cooling system for the nozzle and other components of the hypersonic long-run wind tunnel.
Investigation of model development for deterministic correlations associated with impeller-diffuser interactions in centrifugal compressors
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The average-passage equation system (APES) provides a rigorous framework to account for the deterministic unsteady effects by the so-called deterministic correlations (DC), which include both deterministic stress correlations (DCS) and deterministic total enthalpy correlations (DCH). These correlations should be modeled to close the system of equations. In this paper, the distribution of DC in a transonic centrifugal compressor is presented, and its relative importance is revealed. The assumption made by Adamczyk that the pure unsteady fluctuation is significantly smaller than the spatial fluctuation is verified at the impeller-diffuser interface. The decomposition of DCH is also discussed to determine its two different physical mechanisms. Finally, the transport equations in terms of DCS in cylindrical coordinates are derived, and the terms are evaluated to determine the ones that are necessary to model. All these analyses significantly contribute to our model development for DC in centrifugal compressors.
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The passenger side airbags (PAB) are usually larger than the driver airbags. Therefore, the inflator of PAB is more powerful with high mass rate. In this paper, an Arbitrary Lagrangian-Eulerian (ALE) method based computational method is developed to simulate the deployment of a PAB. The tank test is used to test the property of the inflator. Through comparison of numerical and experimental results, the ALE method is validated. Based on a failed airbag test, a smaller sub-airbag is placed inside PAB to disperse the gas flow to directions which are less damaging. By applying dynamic relaxation, the initial mesh corresponding to the experimental terms is obtained. The results indicate that the interior pressure and impact force coincide with the test data, and the method in this paper is capable of capturing airbag deploying process of the PAB module accurately.
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With the rapid development of the computational fluid dynamics (CFD), a parameter-free upwind scheme capable of simulating all speeds accurately and efficiently is in high demand. To achieve this goal, we present a new upwind scheme called AUSMPWM in this paper. This scheme computes the numerical mass flux as the AUSMPW+ and computes the interfacial sound speed in a different way. Also, it computes the pressure flux by limiting the dissipation if the Mach number is less than 1. Series of numerical experiments show that AUSMPWM can satisfy the following attractive properties independent of any tuning coefficient: (1) Robustness against the shock anomaly and high discontinuity's resolution; (2) high accuracy on hypersonic heating prediction and capability to give smooth reproductions of heating profiles; (3) low dissipation at low speeds; and (4) strong grid, reconstruction scheme, and Mach number independence in low speeds' simulations. These properties suggest that AUSMPWM is promising to be widely used to accurately and efficiently simulate flows of all speeds.
本平台内已出版文章查询 , ZHOU ZhiMing * 已出版文章查询
本平台内已出版文章查询 , XIAO ZhiPei 已出版文章查询
本平台内已出版文章查询 , TU Jian 已出版文章查询
本平台内已出版文章查询 , WANG YaPing 已出版文章查询
本平台内已出版文章查询 , HUANG WeiJiu 已出版文章查询
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A Cu-50Cr alloy was treated by the high current pulsed electron beam (HCPEB) at 20 and 30 keV with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of specimens before and after the treatments were investigated by employing scanning electron microscopy and X-ray diffraction. Results show that the HCPEB technique is able to induce remarkable surface modifications for the Cu-50Cr alloy. Cracks in Cr phases appear even after one-pulse treatment and their density always increases with the pulse number. Formation reason for these cracks is attributed to quasi-static thermal stresses accumulated along the specimen surface. Craters with typical morphologies are formed due to the dynamic thermal field induced by the HCPEB and they are found to prefer the sites near cracks or boundaries between neighboring Cr phases. Another microstructural characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-50Cr alloy. Finally, a general microstructural evolution profile that incorporates various HCPEB-induced surface features is tentatively outlined.
Steady-state coupled analysis of flowfields and thermochemical erosion of C/C nozzles in hybrid rocket motors
本平台内已出版文章查询 , TIAN Hui * 已出版文章查询
本平台内已出版文章查询 , WANG PengFei 已出版文章查询
本平台内已出版文章查询 , YU NanJia 已出版文章查询
本平台内已出版文章查询 , CAI GuoBiao 已出版文章查询
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A hybrid rocket can be used in various applications and is an attractive propulsion system. However, serious erosion of nozzles is common in motor firing operations, which could restrict the application of hybrid rocket motors. Usually, the serious erosion is attributed to the high concentration of oxidizing species in hybrid motors, while the details of flowfields in the motors are not paid special attention to. In this paper, first the thermochemical erosion of C/C nozzle is simulated coupled with the flowfields in a 98% H2O2/hydroxyl-terminated polybutadiene (HTPB) hybrid rocket motor. The simulation is made on a typical axisymmetric motor, including a pre-combustion chamber, an aft-combustion chamber and nozzle structures. Thermochemical reactions of H2O, CO2, OH, O and O2 with C are taken into account. Second, the change of flowfields due to fuel regression during motor firing operations is considered. Nozzle erosion in different flowfields is evaluated. Third, the results of nozzle erosion in the coupled simulation are compared with those under uniform and chemical equilibrium flow and motor firing test results. The results of simulation and firing tests indicate that the thermochemical erosion of nozzles in hybrid motors should be calculated coupled with flowfields in the motor. In uniform and chemical equilibrium flowfields, the erosion rate is overestimated. The diffusion flame in hybrid motors protects the nozzle surface from the injected oxidizer and high temperature products in flowfields, leading to a relatively fuel-rich environment above the nozzle. The influence of OH and the geometry of motor should also be considered in the evaluation of nozzle erosion in hybrid motors.
本平台内已出版文章查询 , LIU HeShan 已出版文章查询
本平台内已出版文章查询 , LUO ZiRen 已出版文章查询
本平台内已出版文章查询 , LI YuQiong 已出版文章查询
本平台内已出版文章查询 , JIN Gang * 已出版文章查询
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Due to high data rates and reliability, inter-satellite laser communication has developed rapidly in these days. However, the stability of the laser beam pointing is still a key technique which needs to be solved; otherwise, the beam pointing jitter noise would reduce the communication quality or, even worse, would make the inter-satellite laser communication impossible. For this purpose, a bench-top of the fine beam pointing control system has been built and tested for inter-satellite laser communication. The pointing offset of more than 100 mrad is produced by the steering mirror. With beam pointing control system turned on, the offset could be rapidly suppressed to lower than 100 nrad in less than 0.5 s. Moreover, the pointing stability can be kept at 40 nrad for yaw motion and 62 nrad for pitch motion, when the received beam jitter is set at 20 mrad.
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The recently introduced multivariate multiscale sample entropy (MMSE) well evaluates the long correlations in multiple channels, so that it can reveal the complexity of multivariate biological signals. The existing MMSE algorithm deals with short time series statically whereas long time series are common for real-time computation in practical use. As a solution, we novelly proposed our dynamic MMSE (DMMSE) as an extension of MMSE. This helps us gain greater insight into the complexity of each section of time series, producing multifaceted and more robust estimates than the standard MMSE. The simulation results illustrated the feasibility and well performance in the brain death diagnosis.
Identification of flexible buildings with bending deformation and the unmeasured earthquake ground motion
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It is important to explore efficient algorithms for the identification of both structural parameters and unmeasured earthquake ground motion. Recently, the authors proposed an algorithm for the identification of shear-type buildings and unknown earthquake excitation. In this paper, it is extended to the investigation of the identification of flexible buildings with bending deformation and the unmeasured earthquake ground motion. In the absolute co-ordinate system, the unmeasured ground motion can be treated as an unknown translational force and a bending moment at the 1st floor level of a flexible building. Structural unknown parameters above the 1st story of the building can be identified by the extended Kalman estimator and the 1st story stiffness and the unmeasured ground motion are subsequently estimated based on the least-squares estimation. The proposed algorithm is further extended to the identification of tall bending-type buildings based on substructure approach. Inter-connection effect between sub-buildings is treated as ‘additional unknown inputs' to sub-buildings, which are estimated by the extended Kalman estimator without the measurements of rotational responses. Numerical examples demonstrate the identification of a multi-story, tall bending-type building and its unmeasured earthquake ground motions using only partial measurements of structural absolute responses.
Analyses of surrogate models for calculating thermophysical properties of aviation kerosene RP-3 at supercritical pressures
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Aviation kerosene is commonly used in combustion and regenerative engine cooling processes in propulsion and power-generation systems, including rocket, scramjet, and advanced gas turbine engines. In this paper, many surrogate models proposed in the open literature are examined for their applicability and accuracy in calculating thermodynamic and transport properties of the China aviation kerosene RP-3 at supercritical pressures, based on the extended corresponding-states methods. The enthalpy change from endothermic decomposition and low heating value from combustion of the jet fuel are also evaluated. Results from a number of simple and representative surrogate models, which contain species components ranging from 1 to 10, are analyzed in detail. Data analyses indicate that a surrogate model with four species is the best choice for thermophysical property calculations under the tested conditions, with fluid temperature up to 650 K at various supercritical pressures. The surrogate model is particularly accurate in predicting the pseudo-critical temperature of aviation kerosene RP-3 at a supercritical pressure. A simple surrogate model containing the n-decane species and a surrogate model containing 10 species are the other two acceptable options. The work conducted herein is of practical importance for theoretical analyses and numerical simulations of various physicochemical processes at engine operating conditions.