基于压阻数的城轨交通地面储能系统选址方法

传统选址方法存在工作量大、步骤繁琐、易用性差的不足。基于城轨交通地面储能系统功能定位提出压阻数的概念,即全运营周期内所有列车运行至某站点时,该站点出现低电压的次数与制动电阻开启且持续一定时间的次数之和;提出基于压阻数的城轨交通地面储能系统选址方法。首先通过检测站点附近的低电压发生次数及制动电阻开启一定时间的次数计算压阻数;然后采用将平峰时段发车间隔作为选址仿真时的输入,在压阻数大于2 MP (M为全线列车数、P为每列车运行周期)的站点安装地面储能系统的选址策略;最后给出选址流程。算例研究表明:压阻数具有表征站点再生制动能量利用率和电能质量的能力;提出基于压阻数的选址方法是有效的,且受工况及运营图的影响小,具有普适性。

What can the changes in shield resistance tell us during the period of shearer's cutting and neighboring shields' advance?

In order to determine the influence of shearer's cutting and neighboring shields' advance on the support resistance variation, leg pressure data of all 235 shields in the panel LW61 of Cumberland coal mine were analyzed. The results show that the relationship between the leg pressure increment and the distance from shield to front drum of shearer is a quadratic function and that the higher leg pressure increment before shield advance tends to be related to adverse roof conditions. In addition, the three proposed leg pressure increment-related parameters and the three traditional parameters(time-weighted average pressure, setting pressure, and final pressure) of approximately 32000 shield supporting cycles were calculated by a self-developed software package to analyze the correlation between them. The results show that there is a powerful connection between them, and that the three proposed leg pressure increment-related parameters could be used as the indexes to evaluate the interaction between shields and the roof, and to identify the periodic weighting.

Development of OPTO-LDR coupled timer based voltage to frequency converter

This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency of timer output waveform which is measured using a digital storage oscillator(DSO)is almost linearly proportional to the applied input voltage.Hence we obtain a linear relationship between the frequency of timer output waveform and the input voltage.Because of its quasi-digital output,the main advantages of this developed converter are linear input-output relationship,small size,easy portabilityand high cost performance.In addition,the timer output waveform can be directly interfaced with personal computer or microprocessor/microcontroller for further processing of the input voltage signal without intervening any analog-to-digital converter(ADC).

Study on the resistance spot welding technology of 22MnMoB hot stamping quenched steel

In this paper, the spot welding technology of a new kind of 22MnMoB hot stamping quenched steel sheet was systematically studied by power frequency spot welder. Through a series of technology and test experiments, we have obtained the optimal spot welding technological parameter condition. According to the results, the relations among spot welding technological parameter, welding nugget, mechanical property and fracture mode were discussed. The effects of all the welding parameters such as welding current, welding time and electrode force on the quality of joint can be boiled down to one thing--the diameter of welding nugget. The experimental results showed that welding nugget diameter determines the mechanical property of spot welding joint and the relation between welding nugget diameter and the mechanical property of joint presents a kind of linear mathematic representation. There are two typical fracture models of 22MnMoB hot stamping quenched steel sheet, i.e., interracial fracture and nugget pullout. Other than mild steel or normal high strength steel, in the shearing tensile test, hot stamping quenched steel has a great tendency to fail in interfacial mode due to the effects of high strength matrix structure, welding soft zone and the porosity level of fusion zone.

Theoretical research on aggregative dynamic pressure damper

To broaden the frequency width and increase the damping coefficient of a dynamic pressure damper, we designed an aggregative dynamic pressure damper (ADPD). Combined with the advantages of traditional dynamic pressure dampers (TDPD), ADPD can not only increase the damping coefficient in wide frequency range for valve control system, but also absorb partial pressure pulsations and impacts in the low and high frequency fields. Based on the theoretical research and the analysis compared with TDPD, we concluded that the ADPD was superior to the TDPD in the middle high frequency field, and the main parameters influencing the performance of the damper were the damping stiffness, orifice flow coefficient, pre-charge pressure, and the volume of the damper accumulator.

Analysis of the Medium Resistance for Constant Pressure Filtration

A mathematical model for constant pressure filtration is established. The distribution of hydraulic pressure within the cake and the medium resistance are measured. The medium resistance Rm is calculated from the suppositional filtration time θm. It is demonstrated that Rm is nearly a constant for a given filter cloth.

Numerical simulation on boiling heat transfer of evaporation cooling in a billet reheating furnace

The boiling heat transfer of evaporation cooling in a billet reheating furnace was simulated.The results indicate that the bubbles easily aggregate inside of the elbow and upper side of the horizontal regions in theπshaped support tubes.The circulation velocity increasing helps to improve the uniformity of vapor distribution and decrease the difference of vapor volume fraction between upper and down at end of the horizontal sections.With the increase of circulation velocity,the resistance loss and the circulation ratio both increase,but the former will decrease with the increase of work pressure.

Research on the Mechanism of Impedance Matching for Underwater Acoustic Transmitter based on Mathematical Modelling and Corresponding Balance Transformer

With the progress of power transmission technology, it is necessary for researchers to conduct related research on impedance matching. In this paper, we conduct research on the mechanism of impedance matching for underwater acoustic transmitter based on mathematical modelling and corresponding balance transformer. To realize underwater acoustic signal of wide band and high power emission, in addition to need the bandwidth performance good transducer array yuan, to a large extent also depends on a good matching between the transducer and amplifier. The result shows the feasibility and robustness of our designed system.

A prediction of drag reduction by entrapped gases in hydrophobic transverse grooves

The drag reduction effect of super-hydrophobic surface induced by the entrapped gas is unstable due to the gradual disappearance of the trapped gas.In this paper,a hydrophobic transverse grooved surface was designed to sustain gas in valleys.A detail numerical simulation was presented to investigate the flow field near the proposed surface.When water flowed over this surface,the entrapped gas was blocked by the ridges and the solid-liquid interface was replaced by the liquid-gas interface due to the entrapped gas,furthermore the micro-vortex formed in the groove.Because there was an effective slippage between water and solid induced by the entrapped gas,the velocity gradient of boundary layer decreased,which contributed to a remarkable drag reduction effect.Additionally,considering the extra undesired pressure drag reduction which negatively impacted the drag reduction effect of this method,the total drag coefficient including the viscous drag coefficient and the pressure coefficient was analyzed.An effective drag reduction rate of about 15%was achieved and the effect of this method was confirmed by experiments conducted in a high-speed water tunnel when grooves were optimized.

Studies on a low Reynolds number airfoil for small wind turbine applications

In contrast to large horizontal axis wind turbines (HAWTs) that are located in areas dictated by optimum wind conditions, small wind turbines are required for producing power without necessarily the best wind conditions. A low Reynolds number airfoil was designed after testing a number of low Reynolds number airfoils and then making one of our own; it was tested for use in small HAWTs. Studies using XFOIL and wind tunnel experiments were performed on the new airfoil at various Reynolds numbers. The pressure distribution, C p , the lift and drag coefficients, C L and C D , were studied for varying angles of attack, α. It is found that the airfoil can achieve very good aerodynamic characteristics at different Reynolds numbers and can be used as an efficient airfoil in small HAWTs.

Heat transfer and flow characteristics in a channel with one corrugated wall

The present study numerically investigates the characteristics of three-dimensional turbulent flow and heat transfer in the channel with one corrugated wall heated with constant temperature by means of large eddy simulation.The corrugated wall is sinusoidal in the streamwise and spanwise directions.The Reynolds number in terms of bulk velocity and channel half-height is fixed at 2800 and the wave amplitude to wavelength ratio is varied in the rangeα/λ=0.01,0.02,0.04 in the streamwise direction andα/λ=0.01,0.02,0.04 in the spanwise direction.The results show that flow separation bubbles appear and near-wall streamwise vortices are generated with larger population in the upslope region of the bottom wall as wave amplitude increases.Compared with flat wall,the corrugated geometry increases the pressure coefficient and decreases the friction coefficient on the corrugated wall,and consequently increases the total drag coefficient owing to the increase of pressure coefficient,as expected,the heat transfer is higher.The waves in the spanwise direction converge the vortices into the trough along the streamwise direction and push them away from the bottom wall.Finally,thermal performance factor is defined and the effects of wave amplitude on the thermal performance are scrutinized.

Effects of a Kind of Surface Groove on Flow Loss in Both Rectangular and Circular Ducts at Different Reynolds Numbers

Pipes are widely used to transport gas,oil and water in industries.Drag reduction in pipes is an increasingly concerned problem to save energy.Some researches have indicated that the non-smooth surface with special structures can reduce flow loss.In this paper,an experimental investigation has been performed on the effects of a kind of surface groove on the drag in both rectangular and circular duct at different Reynolds numbers.In the experiment of the rectangular duct,total pressure at both inlet and outlet were measured.Static pressure on the wall was measured on the surface with smooth and grooved film respectively.In the circular duct,a boundary layer pressure probe was used to measure the total pressure distribution at both inlet and outlet.Four taps at inlet and outlet were used to measure static pressure.The loss coefficient is used to evaluate the effects of the surface groove on drag reduction.The experiment was conducted with the Reynolds number range from 1.28×10~4 to 2.57×10~4.The result shows a maximum drag loss reduction of approximately 2.4% in rectangular duct at Reynolds number of 2.4×10~4.A 10%reduction of pipe pressure loss by grooved surface is measured in circular duct at a Reynolds number of 3.0×10~5.

Cotunneling transport in ultra-narrow gold nanowire bundles

We investigate the charge transport in close-packed ultra-narrow （1.5 nm diameter） gold nanowires stabilized by oleylamine ligands. We give evidence of charging effects in the weakly coupled one-dimensional （1D） nanowires, monitored by the temperature and the bias voltage. At low temperature, in the Coulomb blockade regime, the current flow reveals an original cooperative multi-hopping process between 1D-segments of Au-NWs, minimising the charging energy cost. Above the Coulomb blockade threshold voltage and at high temperature, the charge transport evolves into a sequential tunneling regime between the nearest- nanowires. Our analysis shows that the effective length of the Au-NWs inside the bundle is similar to the 1D localisation length of the electronic wave function （of the order of 120 nm _＋ 20 nm）, but almost two orders of magnitude larger than the diameter of the nanowire. This result confirms the high structural quality of the Au-NW segments.

Effects of stenoses on non-Newtonian flow of blood in blood vessels

In this paper, a mathematical model for steady blood flow through blood vessels with uniform cross-section in stenoses arteries has been proposed. Blood is assumed to be non- Newtonian, incompressible and homogeneous fluid. Blood in human artery is represented as Bingham plastic fluid. Expressions for flow rate, wall shear stress, and resistance to flow against stenoses size have been obtained. Obtained results indicate that stenoses size decreases the flow rate and increases the wall shear stress as well as resistance to flow.

Effect of the head cavity on pressure oscillation suppression characteristics in large solid rocket motors

In order to discover the effect of head cavity on resonance damping characteristics in solid rocket motors, large-eddy simulations with wall-adapting-local-eddy-viscosity subgrid scale turbulent model are implemented to study the oscillation flow field induced by vortex shedding based on the VKI （yon Karman Institute） experimental motor. Firstly, mesh sensitivity analysis and grid-independent analysis are carried out for the computer code validation. Then, the numerical method is further validated by comparing the calculated results and experimental data. Thirdly, the effects of head-end cavity on the pressure oscillation am-plitudes are studied in this paper. The results indicate that cavity volume, location and configuration have a cooperative ef- fect on the oscillation amplitude. It is proved that Rayleigh criterion can be used as a guiding principle for the design of reso- nance damping cavity. The change of the head-end cavity breaks the balance between the mass flux and acoustic energy. Therefore, the pressure oscillation characteristics change accordingly. It is concluded that a large mass flux added at the pres- sure antinode could attribute to significant amplitude. Meanwhile, the damping effect of the cavity is stronger when the dis- tance between cavity and pressure antinode becomes shorter. Finally, this method is applied to the modification of an engi- neering solid rocket motor. The static test of solid rocket motor reflects that the oscillations can be effectively suppressed by a head-end cavity.