超临界CO_2部分冷却布雷顿循环分析

为了确定部分冷却布雷顿循环各设备节能潜力,得出应用于聚光太阳能技术(Concentrating Solar Power,CSP)的最优可能工作参数,为以后建设超临界CO_2(Supercritical Carbon Dioxide:S-CO_2)布雷顿循环太阳能热电站提供参考依据,使用EES(Engineering Equation Solver)对应用于CSP的具有一级再热的100 MW S-CO_2部分冷却布雷顿循环进行效率和损系数分析,主要分析在不同透平入口温度,再热压力以及循环压比比对循环效率的影响,同时分析各设备损系数的大小。得出冷凝器损最大,因此后续可通过增加底循环来利用冷凝器的。最大效率的最优工作参数为透平入口温度700℃,再热压力为9.5MPa,循环压比比为0.4,此时循环效率为33.73%,循环热效率为50.90%。

Evaluation of the Economic Loss Caused by Zhouqu Debris Flow

[Objective] The aim of this study was to evaluate the economic loss caused by Zhouqu debris flow. [Method] After the large debris flows happened on August 7, 2010 in Zhouqu, Gansu Province, we collected data at the first time after the disaster, and then built an assessment model to estimate the potential economic losses. [Result] The total loss reached 16.57×10^2 million Yuan, in which indirect economic loss was up to 2.42×10^2 million yaun while the actual direct economic loss was around 14.15×10^2 million Yuan. [Conclusion] The proportional coefficient method is a rapid and efficient method for evaluating the indirect loss caused by disasters.

Experimental Study on Damage Properties of Rocks Under Dynamic Loading

The damage properties of two types of rocks under dynamic loading are studied. The shock induced experiments are done using planar impact technique on the one? stage light gas gun, and the ultrasonic tests on the damaged rocks have been made by use of the ultrasonic pulse? transmission method. The shock induced damage of rock is related to the shock speed and the attenuation coefficient of sonic wave, and the latter reflects the damage degree in rock fairly well. The attenuation coefficient α can be used as main damage parameter for constructing damage model of rock under dynamic loading.

Novel Ka-band low-noise down-converter assembly

An efficient way to design a down-converter assembly for the Ka-band millimeter system is presented, in which dielectric resonators （DR＇s） are adopted in the Schottky barrier diode image recovery mixer and the local oscillator （LO）. DR structures guarantee high frequency stability with an acceptable volume. The configurations of low noise amplifier, mixer and oscillator in the assembly are described and fabricated to estimate the chain performance. According to the verification results, the assembly exhibits the noise figure of less than 5 dB over 1 GHz frequency range, and the single-sideband phase noise （200 kHz offset from carrier frequency） of - 70 dBc/Hz. Utilizing the DR structure, the frequency stability of the local oscillator is less than 60 × 10^-6/℃.

Sliding wear behavior of copper-based composites reinforced with graphene nanosheets and graphite

The mechanical and tribological properties of hot-pressed copper-based composites containing different amounts of graphene nanosheets（GNSs） are compared with those of copper-graphite（Gr） composites fabricated by the same method.The results show that the Cu-GNSs composites exhibit higher relative density,microhardness and bending strength compared with Cu-Gr composites with the same volume fraction of GNSs and Gr.Moreover,the friction coefficients and wear rates reduce significantly by the addition of GNSs,whereas the limited impact on reducing friction and wear is found on graphite.The abrasive and delamination wear are the dominant wear mechanisms of the composites.It is believed that the superior mechanical and tribological performances of Cu-GNSs composites are attributed to the unique strengthening effect as well as the higher lubricating efficiency of graphene nanosheets compared with those of graphite,which demonstrates that GNS is an ideal filler for copper matrix composites,acting as not only an impactful lubricant but also a favorable reinforcement.

Lossless Mapping from Semi-Structured Data to Structured Data

Most semi-structured data are of certain structure regularity. Having beenstored as structured data in relational database (RDB), they can be effectively managed by databasemanagement system (DBMS). Some semi-structured data are difficult to transform due to theirirregular structures. We design an efficient algorithm and data structure for ensuring losslesstransformation. We bring forward an approach of schema extraction through data mining, in whichdifferent kinds of elements are transformed respectively and lossless mapping from semi-structureddata to structured data can be achieved.

Freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures

As a frequently-used roadbed filler,soil-rock mixture is often in the environment of freeze-thaw cycles and different confining pressures.In order to study the freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures,the concept of meso-interfacial freeze-thaw damage coefficient is put forward and the meso-interfacial damage phenomenon of soil-rock mixtures caused by the freeze-thaw cycle environment is concerned;a double-inclusion embedded model for elastic modulus of soil-rock mixtures in freezing-thawing cycle is proposed.A large triaxial test was performed and the influences of confining pressure and experimental factors on elastic modulus of soil-rock mixtures were obtained,and then the accuracy of the double-inclusion embedded model to predict the elastic modulus of soil-rock mixtures in freezing-thawing cycle is verified.Experiment results showed that as to soil-rock mixtures,with the increase of confining pressure,the elastic modulus increases approximately linearly.The most crucial factors to affect the elastic modulus are rock content and compaction degree at the same confining pressure;the elastic modulus increases with the increase of rock content and compactness;as the number of freeze-thaw cycles increases,the freeze-thaw damage coefficient of meso-structural interface and the elastic modulus decrease.

Liquid Circulation in a Multi-tube Air-lift Loop Reactor

A multi-tube air-lift loop reactor (MT-ALR) is presented in this paper. Based on the energy conservation, a mathematical model describing the liquid circulation flow rate was developed, which was determined by gas velocity, the cross areas of riser and downcomer, gas hold-up and the local frictional loss coefficient. The experimental data indicate that either increase of gas flow rate or reduction of the downcomer diameter contributes to higher liquid circulation rate. The correlation between total and the local frictional loss coefficients was also established.Effects of gas flowrate in two risers and diameter of downcomer on the liquid circulation rate were examined. The value of total frictional loss coefficient was measured as a function of the cross area of downcomer and independent of the gas flow rate. The calculated results of liquid circulation rates agreed well with the experimental data with an average relative error of 9.6%.

Influence of bluff body shape on wall pressure distribution in vortex flowmeter

To investigate the influence of bluff body shape on wall pressure distribution in a vortex flowmeter,experiments were conducted on a specially designed test section in a closed water rig at Reynolds numbers of 6.2×10 4-9.3×10 4.The cross sections of the bluff bodies were semicircular,square,and triangular shaped,and there were totally 21 pressure tappings along the conduit to acquire the wall pressures.It is found that the variation trends of wall pressures are basically identical regardless of the bluff body shapes.The wall pressures begin to diverge from 0.3D(D is the inner diameter of the vortex flowmeter) in front of the bluff body due to the diversity in shape,and all reach the minimum values at 0.3D behind the bluff body.A discrepancy between the triangular or square cylinder and the semicircular cylinder in wall pressure change is observed at 0-0.1D behind the bluff body.It is also found that the wall pressures and irrecoverable pressure loss coefficients increase with flow rates,and the triangular cylinder causes the smallest irrecoverable pressure loss at a fixed flow rate.

Calculation and analysis of losses of magnetic-valve controllable reactor

Magnetic-valve controllable reactor(MCR)has characteristics of DC bias and different types of magnetic flux density in the magnetic circuit and winding current distortion.These characteristics not only lead to loss calculation method of MCR different from that of power transformer,but also make it more difficult to calculate the core loss and wingding loss of MCR accurately.Our study combines core partition method with dynamic inverse J-A model to calculate the core loss of MCR.The winding loss coefficient of MCR is proposed,which takes into account the influence of harmonics and magnetic flux leakage on the winding loss of MCR.The result shows that the proposed core loss calculation method and winding loss coefficient are effective and correct for the loss calculation of MCR.

Experimental study of a simple pressure loss coefficient model for multi-hole orifice

A throttling experiment for the multi-hole orifice （MO） using water was conducted based on the conclusion of key parameters affecting the MO throttling performance. Testing MOs and standard orifice plates （ SO ） were designed for the throttling experiment to compare the throttling effect using the equivalent diameter ratio （RED） and diameter ratio （RD ） as key parameters, respectively. Meanwhile, effective metrical conditions were provided for experimental accuracy. The throttling model form was determined according to the theoretical throttling model of SO. Then the unknown parameters involved were identified by experimental data. A good concordance between the modeling computation and experimental results shows a validation of the MO throtting model.

Enhancement of wear resistance of Ti–6Al–4V alloy by picosecond laser surface micro texturing process

A pulsed,picosecond Nd:YAG laser with a wavelength of 532 nm is used to texture the surface of grade 5 titanium alloy(Ti–6Al–4V)for minimizing its wear rate.The wear properties of the base samples and laser surface textured samples are analyzed by conducting wear tests under a sliding condition using pin-on-disk equipment.The wear tests are conducted based on the Box–Benhken design,and the interaction of the process parameters is analyzed using response surface methodology.The wear analysis is conducted by varying the load,rotating speed of the disc,and track diameter at room temperature with a sliding distance of 1500 m.The results demonstrate that the laser textured surfaces exhibited a lower coefficient of friction and good anti-wear properties as compared with the non-textured surfaces.A regression model is developed for the wear analysis of titanium alloy using the analysis of variance technique.It is also observed from the analysis that the applied load and sliding distance are the parameters that have the greatest effect on the wear behavior followed by the wear track diameter.The optimum operating conditions have been suggested based on the results obtained from the numerical optimization approach.

Casualties' States During Destructive Earthquakes

The index of casualties is introduced for the trapped that is still alive after a destructive earthquake to indicate his (her) injury degree. In order to describe the injury-developing process controlled by three factors: the initial injury degree, the trap surroundings and the physique of the cornered, a function SFC (State-Function of Casualties) can be naturally constructed. Through parameter analysis from eight pieces of figures, it can be found that the trapped with weaker physique and worse initial injury degree and in more adverse trap surroundings deserves sooner rescue.

Effect of fretting amplitudes on fretting wear behavior of steel wires in coal mines

Given that fretting wear causes failure in steel wires, we carried out tangential fretting wear tests of steel wires on a self-made fretting wear test rig under contact loads of 9 and 29 N and fretting amplitudes ranging from 5 to 180 μm. We observed morphologies of fretted steel wire surfaces on an S-3000N scanning electron microscope in order to analyze fretting wear mecha-nisms. The results show that the fretting regime of steel wires transforms from partial slip regime into mixed fretting regime and gross slip regime with an increase in fretting amplitudes under a given contact load. In partial slip regime, the friction coefficient has a relatively low value. Four stages can be defined in mixed fretting and gross slip regimes. The fretting wear of steel wires in-creases obviously with increases in fretting amplitudes. Fretting scars present a typical morphology of annularity, showing slight damage in partial slip regime. However, wear clearly increases in mixed fretting regime where wear mechanism is a combination of plastic deformation, abrasive wear and oxidative wear. In gross slip regime, more severe degradation is present than in the other regimes. The main fretting wear mechanisms of steel wires are abrasive wear, surface fatigue and friction oxidation.

Influence of heat loss through probe electrical leads on thermal conductivity measurement with TPS method

The transient plane source(TPS)method is developed recently to measure the thermal conductivity of materials.In the measurement,the heating power is influenced by the heat which is transferred via the probe electrical leads.This fact further influences the measurement accuracy of thermal conductivity.To solve this problem,the influence of heat loss through the electrical leads on the heating power is studied theoretically.The mathematical formula of heat loss is deduced,and the corresponding correction model is presented.A series of measurement experiments on different materials have been conducted by using the hot disk thermal constant analyzer.The results show that the influence of the heat loss on the measurement is sensitive to different test materials and probes with different sizes.When the thermal conductivity of the material is greater than 0.2 W/(m·K),the influence of the heat loss is less than 0.16%,which can be ignored.As to the lower thermal conductivity materials,it is necessary to compensate the heat loss through the electrical leads,and the accuracy of thermal conductivity measurement can be effectively improved.

Compensation for diffusion loss of sound wave in sonar system

Sound pressure amplitude will be attenuated with propagation distance in a certain rule when sound wave is propagated in shallow sea.When processing the attenuated signal,time-variant gain circuit is usually used to compensate its diffusion loss.In this paper,spherical diffusion loss is compensated by digital potentiometer and operational circuit and further investigation is also made on compensation of cylindrical diffusion loss and transition from spherical diffusion loss to cylindrical diffusion loss.Finally,a new compensation model is proposed for unknown propagation loss for the purpose of adjusting the dynamic range of signal to meet the requirement of A/D conversion.

Off-Design Performance Analysis of Axial Flow Fan in Helicopter

A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter,including calculation of aerodynamic parameters and performance parameters.When calculating inlet shock loss,the shock loss coefficient is obtained by comparing results of theoretical calculation,experimental and numerical calculation.The theoretical results and numerical results show that all air velocity components increase from hub to shroud in main flow area at rated condition.Tip leakage vortex moves downstream as flow rate increases.When flow rate decreases,Re decreases,and boundary layer thickness from hub to shroud area all increases gradually.Tip leakage vortex moves upstream,and secondary loss increases.Low speed area in the passage is widened along with high speed area moving to hub area,influenced by boundary layer separation.Consequently wake area and jet area at fan outlet are both larger than rated condition.Therefore optimization design for off-design performance of the fan is required on aerodynamic parameters influencing fan loss.A reliable method is supplied for estimating altitude performance of lubricating system in helicopter.

State Representation Methodology （SRM） for Bridge Condition Assessment in SHM

This paper introduces a new concept of ＂State Representation Methodology （SRM）＂ which is a kind of bridge condition assessment method for structural health monitoring system （SHM）. There are many methods for system identification from the simplicity comparison of damage index to the complicated statistical pattern recognition algorithms in SHM. In these methods, modal analysis and parameters identification or many defined indices are common-used for extracting the dynamic or static characteristics of a system. However, there is a common problem： due to the complexity of a large size system with high-order nonlinear characteristics and severe environment interference, it is impossible to extract and quantify exactly these modal parameters or system parameters or indices as the feature vectors of a system in damage detection in an easy way. The SRM considered a more general theory for the non-parametric description of system state.

Friction properties of groove texture on Cr12MoV surface

To analyze the influence of surface texture on friction properties of Crl2MoV＇, ordinary grinder and spinning technology were adopted to obtain the grooved surface morphology of samples, and then the impact of spindle speed and feed in z-direction on surface morphology in the process of spinning was studied. In addition, the corresponding friction coefficient of sample was obtained through friction and wear tests. The results show that the peak clipping and the valley filling were conducted on the grinding surface, which could improve the surface roughness effectively and make the grinding trench-type wear scar more uniform. Both the area ratio of groove and groove spacing increased initially and then decreased with the increase of the spindle speed or the feed in z-direction. As a kind of micro-process, the groove could influence the friction coefficient of sample surface, whose distribution was beneficial to the reduction of friction coefficient. Compared with the surface obtained through ordinary grinding, grooved surface morphology through spinning technology was more conductive to reduce the friction coefficient, which could be reduced by 25%. When the friction coefficient of sample was reduced to the minimum, the texture of groove corresponded had an optimal area ratio and an optimal groove spacing, 37.5% and 27.5 μm, respectively.

Determation method for water content of diesel contaminated soil

With the increasing researches on geotechnical properties of the diesel contaminated soil( DCS),the water content measured is indispensable part during the early period. In this study,the relative error of water content measurement using the traditional method is as high as 20. 78%,which is no longer suitable for contaminated soil. Through a series of tests to measure the loss coefficient of diesel in the drying time,the authors finally proposed a modified calculation formula for test samples. The results show that the maximum relative error calculated by using the modified formula is 0. 96%,far lower than that of traditional formula,which can provide accurate data for further study of diesel contaminated soil.