Development of a simulation model for dynamic derailment analysis of high-speed trains

The running safety of high-speed trains has become a major concern of the current railway research with the rapid development of high-speed railways around the world.The basic safety requirement is to prevent the derailment.The root causes of the dynamic derailment of highspeed trains operating in severe environments are not easy to identify using the field tests or laboratory experiments.Numerical simulation using an advanced train–track interaction model is a highly efficient and low-cost approach to investigate the dynamic derailment behavior and mechanism of high-speed trains.This paper presents a three-dimensional dynamic model of a high-speed train coupled with a ballast track for dynamic derailment analysis.The model considers a train composed of multiple vehicles and the nonlinear inter-vehicle connections.The ballast track model consists of rails,fastenings,sleepers,ballasts,and roadbed,which are modeled by Euler beams,nonlinear spring-damper elements,equivalent ballast bodies,and continuous viscoelastic elements,in which the modal superposition method was used to reduce the order of the partial differential equations of Euler beams.The commonly used derailment safety assessment criteria around the world are embedded in the simulation model.The train–track model was then used to investigate the dynamic derailment responses of a high-speed train passing over a buckled track,in which the derailmentmechanism and train running posture during the dynamic derailment process were analyzed in detail.The effects of train and track modelling on dynamic derailment analysis were also discussed.The numerical results indicate that the train and track modelling options have a significant effect on the dynamic derailment analysis.The inter-vehicle impacts and the track flexibility and nonlinearity should be considered in the dynamic derailment simulations.     

Dynamical analysis and performance evaluation of a biped robot under multi-source random disturbances

During bipedal walking,it is critical to detect and adjust the robot postures by feedback control to maintain its normal state amidst multi-source random disturbances arising from some unavoidable uncertain factors.The radical basis function（RBF）neural network model of a five-link biped robot is established,and two certain disturbances and a randomly uncertain disturbance are then mixed with the optimal torques in the network model to study the performance of the biped robot by several evaluation indices and a specific Poincar′e map.In contrast with the simulations,the response varies as desired under optimal inputting while the output is fluctuating in the situation of disturbance driving.Simulation results from noise inputting also show that the dynamics of the robot is less sensitive to the disturbance of knee joint input of the swing leg than those of the other three joints,the response errors of the biped will be increasing with higher disturbance levels,and especially there are larger output fluctuations in the knee and hip joints of the swing leg.     

Formation of uniform reduced graphene oxide films on modified PET substrates using drop-casting method

In this work,uniform reduced graphene oxide(RGO) films were formed on poly-(ethylene terephthalate)(PET) substrates using a simple drop-casting method.We investigated four types of substrates:unmodified PET,polydopamine-coated PET.carboxyl-group-modified PET,and alkyl-group-modified PET.Upon water evaporation,the surface of the polydopamine-modified PET substrates can interact with the reduced graphene oxide sheets to form flattened and continuous RGO films,which exhibit a sheet resistance of 21.75 kΩ/sq at 82%transmittance.The result indicates that the properties of the surface groups determined whether uniform and flattened RGO films could be formed on the substrates.Hence,we proposed a simple and effective way to produce transparent and conductive films in which the catechol unit exhibits a great effect on the deposition of uniform RGO films on PET substrates.     

Stability analyses of the mass abrasive projectile high-speed penetrating into concrete target. Part Ⅰ： Engineering model for the mass loss and nose-blunting of ogive-nosed projectiles

The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the penetration efficiency of penetrator.Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface,an engineering model is established for the mass loss and nose-blunting of the ogive-nosed projectile.A dimensionless formula for the relative mass loss of projectile is obtained by introducing the dimensionless impact function I and geometry function N of the projectile.The critical value V c0of the initial striking velocity is formulated,and the mass loss of projectile tends to increase weakly nonlinearly with I/N when V0〉V c0,whilst the mass loss is proportional to the initial kinetic energy of projectile when V0     

Tribological and tribochemical properties of magnetite nanoflakes as additives in oil lubricants

This detailed the tribological and tribochemical properties of magnetite(Fe_3O_4) nanoflakes used as additives in #40 base oil in a four-ball tribo-tester.The average friction coefficient of the friction pair for lubricant containing the Fe_3O_4 nanoflakes of 1.5 wt%as a lubricant additive in the base oil is decreased by18.06%compared to that of solely base oil.The chemical composition of base oil with the Fe_3O_4 nanoflake additives did not change during the 48-h friction assessment.The decreased saturation magnetization and increased coercivity of magnetite nanoflakes occurred due to the distortion of the basal planes and the presence of hematite(α-Fe_3O_4) generated by the tribochemical reactions during the friction process.The multi-layer low-shear-stress tribochemical lubrication films on the surface of the friction pair could form because the nanoflake particles arrange and adhere onto the surface of the friction pair in an orderly manner,and the tribochemical reactions of the friction pair in the presence of the nanoflakes occur as Fe→FeO→Fe_3O_4→γ-FeOOH →γ-Fe_2O_3→α-Fe_2O_3.The formation of the films can improve the tribological properties.     

Theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains

One of the major problems in structural fatigue life analysis is establishing structural load spectra under actual operating conditions.This study conducts theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains.The quasistatic load series that corresponds to quasi-static deformation modes are identified according to the structural form and bearing conditions of high-speed train bogie frames.Moreover,a force-measuring frame is designed and manufactured based on the quasi-static load series.The load decoupling model of the quasi-static load series is then established via calibration tests.Quasi-static load–time histories,together with online tests and decoupling analysis,are obtained for the intermediate range of the Beijing—Shanghai dedicated passenger line.The damage consistency calibration of the quasi-static discrete load spectra is performed according to a damage consistency criterion and a genetic algorithm.The calibrated damage that corresponds with the quasi-static discrete load spectra satisfies the safety requirements of bogie frames.     

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H2SO4-NaCl-H2O system

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization(FGD) gypsum.When purified FGD gypsum was used as raw material,the morphology and phase structure of the hydrothermal products grown in pure water,H_2SO_4-H_2O,NaCl-H_2O,and H_2SO_4-NaCl-H_2O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated.The results indicate that calcium sulfate whiskers grow favorably in the H_2SO_4-NaCl-H_2O system.When prepared using 10-70 g NaCl/kg gypsum-0.01 M H_2SO_4-H_2O at 130 ℃ for 60 min,the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 |xm and lengths from 200 to 600 |xm,and their phase structure was calcium sulfate hemihydrate(HH).Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed.With the co-presence of sulfuric acid and sodium chloride in the reaction solution,the concentrations of Ca~(2+) and SO_4~(2-) can be kept relatively stable,which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.     

Effects of wing deformation on aerodynamic performance of a revolving insect wing

Flexible wings of insects and bio-inspired micro air vehicles generally deform remarkably during flapping flight owing to aerodynamic and inertial forces,which is of highly nonlinear fluid-structure interaction（FSI）problems.To elucidate the novel mechanisms associated with flexible wing aerodynamics in the low Reynolds number regime,we have built up a FSI model of a hawkmoth wing undergoing revolving and made an investigation on the effects of flexible wing deformation on aerodynamic performance of the revolving wing model.To take into account the characteristics of flapping wing kinematics we designed a kinematic model for the revolving wing in two-fold：acceleration and steady rotation,which are based on hovering wing kinematics of hawkmoth,Manduca sexta.Our results show that both aerodynamic and inertial forces demonstrate a pronounced increase during acceleration phase,which results in a significant wing deformation.While the aerodynamic force turns to reduce after the wing acceleration terminates due to the burst and detachment of leading-edge vortices（LEVs）,the dynamic wing deformation seem to delay the burst of LEVs and hence to augment the aerodynamic force during and even after the acceleration.During the phase of steady rotation,the flexible wing model generates more ver-tical force at higher angles of attack（40°–60°）but less horizontal force than those of a rigid wing model.This is because the wing twist in spanwise owing to aerodynamic forces results in a reduction in the effective angle of attack at wing tip,which leads to enhancing the aerodynamics performance by increasing the vertical force while reducing the horizontal force.Moreover,our results point out the importance of the fluid-structure interaction in evaluating flexible wing aerodynamics：the wing deformation does play a significant role in enhancing the aerodynamic performances but works differently during acceleration and steady rotation,which is mainly induced by inertial force in acceleration but by aerodynamic forces     

Influence of disodium hydrogen phosphate dodecahydrate on hydrothermal formation of hemihydrate calcium sulfate whiskers

The influence of Na_2HPO_4·12H_2O on the hydrothermal formation of hemihydrate calcium sulfate(CaSO_4·0.5H_2O) whiskers from dihydrate calcium sulfate(CaSO_4·2H_2O)at 135 ℃ was investigated.Experimental results indicate that the addition of phosphorus accelerates the hydrothermal conversion of CaSO_4·2H_2O to CaSO_4·0.5H_2O via the formation of Ca_3(PO_4)_2 and produces CaSO_4-0.5H_2O whiskers with thinner diameters and shorter lengths.Compared with the blank experiment without Na_2HPO_4·12H_2O,the existence of minor amounts(8.65 ×10~(-4)-4.36 × 10~(-3) mol/L) of Na_2HPO_4·12H_2O led to a decrease in the diameter of CaSO_4·0.5H_2O whiskers from 1.0-10.0 to 0.5-2.0 μm and lengths from 70-300 to50-200 μm.     

Graphite dust resuspension in an HTR-10 steam generator

Graphite dust has an important effect on the safety of high-temperature gas-cooled reactors(HTR).The flow field in the steam generator was studied by the computational fluid dynamics(CFD) method,with the results indicating that the friction velocity in the windward and the leeward of the heat transfer tubes is relatively low and is higher at the sides.Further analysis of the resuspension of graphite dust indicates that the resuspension fraction reaches nearly zero for particles with a diameter less than 1 μm,whereas it will increases as the helium velocity in the steam generator increases for particle size larger than 1 μm.Moreover,the resuspension fraction increases as the particle size increases.The results also indicate that resuspension of the particles with sizes larger than 1 μm exhibited obvious differences in different parts of the steam generator.     

Power regulation of kinematic control inputs for forward flying Drosophila

The choices of insect wing kinematic programs is not well understood,particularly the mechanism by which an insect selects a distortion to achieve flight control.A methodology to evaluate prospective kinematic control inputs is presented based on the reachable states when control actuation was constrained to a unit of power.The method implements a computationally-derived reduced order model of the insect’s flight dynamics combined with calculation of power requirement.Four kinematic inputs are evaluated based on this criterion for a Drosophila size insect in forward flight.Stroke bias is shown to be the dominant control input using this power normalized evaluation measure.     

Effects of aspect ratio on flapping wing aerodynamics in animal flight

Morphology as well as kinematics is a critical determinant of performance in flapping flight.To understand the effects of the structural traits on aerodynamics of bioflyers,three rectangular wings with aspect ratios（AR）of1,2,and 4 performing hovering-like sinusoidal kinematics at wingtip based Reynolds number of 5 300 are experimentally investigated.Flow structures on sectional cuts along the wing span are compared.Stronger K-H instability is found on the leading edge vortex of wings with higher aspect ratios.Vortex bursting only appears on the outer spanwise locations of high-aspect-ratio wings.The vortex bursting on high-aspect-ratio wings is perhaps one of the reasons why bio-flyers normally have low-aspect-ratio wings.Quantitative analysis exhibits larger dimensionless circulation of the leading edge vortex（LEV）over higher aspect ratio wings except when vortex bursting happens.The average dimensionless circulation of AR1 and AR2 along the span almost equals the dimensionless circulation at the 50%span.The flow structure and the circulation analysis show that the sinusoidal kinematics suppresses breakdown of the LEV compared with simplified flapping kinematics used in similar studies.The Reynolds number effect results on AR4 show that in the current Re range,the overall flow structure is not sensitive to Reynolds number.     

Fabrication and electrochemical performance of nanofibrous micro-frameworks of α-MnO_2

A facile solid-phase conversion route is proposed to fabricate a micro-framework of α-MnO_2 with a nanofibrous structure and high porosity.The fabrication is achieved by a three-step process using a preformed manganese tartrate with a rectangular framework as the precursor followed by thermal annealing and hydrothermal oxidation to form the final nanofibrous structure.Evolution of the phase and the morphology are characterized by FESEM,XRD,TG-DTA,and TEM measurements.The electrochemically active material α-MnO_2 exhibits both attractive stability of the Coulombic efficiency after long-term cyclic charging/discharging and acceptable specific capacitance.     

Attritor-milling of poly（amide imide） suspensions

The milling behavior of poly(amide imide),which serves as a prototypical hydrophilic high-performance polymer with a high glass transition temperature,was investigated.Various milling conditions(milling times up to 7h,stirrer tip speeds of 3.4-4.9 m/s,and mass concentrations of 5-20%) were tested,and particle sizes as low as d_(50,3) ~3μm were obtained.The milling was performed at 11℃ in an attritor.Differential scanning calorimetry and thermogravimetric analysis were performed before and after milling to investigate the effect of milling on the glass transition temperature and on the decomposition behavior of the polymer.The suspension obtained after milling was observed to be stable without the addition of stabilizers or the adjustment of the pH value,and no negative effect of milling on the polymer properties was observed.The attritor technique proved to be an adequate and efficient milling tool for the production of micrometer-sized high-performance polymer suspensions.     

A multi-functional polymer coating that is heat-resistant,hydrophobic and transparent

A multi-functional polymer film with high hydrophobicity and transparency was formed by simple casting of a polycarbonate solution onto a substrate having micro-scale roughness.The high hydrophobicity was heat-resistant,which can be retained up to 390 ℃.The polymer film may have potentially wide-ranging applications in industry and high technology.     

Dynamics of a prey-predator system under Poisson white noise excitation

The classical Lotka-Volterra （LV） model is a well-known mathematical model for prey-predator ecosystems. In the present paper, the pulse-type version of stochastic LV model, in which the effect of a random natural environment has been modeled as Poisson white noise, is in- vestigated by using the stochastic averaging method. The averaged generalized It6 stochastic differential equation and Fokkerlanck-Kolmogorov （FPK） equation are derived for prey-predator ecosystem driven by Poisson white noise. Approximate stationary solution for the averaged generalized FPK equation is obtained by using the perturbation method. The effect of prey self-competition parameter e2s on ecosystem behavior is evaluated. The analytical result is confirmed by corresponding Monte Carlo （MC） simulation.     

Investigation of scale effect for the computation of turbulent flow around a circular cylinder

In order to investigate the scale effect of turbulent flow around a circular cylinder, two similarity numbers （criteria） based on turbulent kinetic and dissipation rates associ- ated with the fluctuation characteristics of turbulence wake are deduced by analyzing the Reynolds averaged NavierStokes equations （RANS）. The RNG k-s models and finite volume method are used to solve the governing equations and the second-order implicit time and upwind space discretization algorithms are used to discrete the governing equations. A numerical computation of flow parameters around a two-dimensional circular cylinder with Reynolds numbers ranging from 102 to l07 is accomplished and the result indicates that the fluctuation of turbulence flow along the center line in the wake of circular cylinder can never be changed with increasing Reynolds numbers when Re ≥ 3 × 10^6. This conclusion is useful for controlling the scale of numerical calculations and for applying model test data to engineering practice.     

Influences of ions and temperature on performance of carbon nano-particulates in supercapacitors with neutral aqueous electrolytes

A commercial product of carbon nano-particles,Cabot MONACH 1300 pigment black(CMPB),was studied for basic structural information and electrochemical performance in neutral aqueous electrolytes,aiming at applications in supercapacitors.As confirmed by SEM and HRTEM,the CMPB had a hierarchical structure,containing basic 10 nm nano-spheres which combined into ca.50 nm agglomerates which further aggregated into larger particles ofmicrometres.The capacitance of this commercial material was found to increase with decreasing the size of hydrous cation(Li~+→ Na~*→K~+),instead of the cation crystal radius(K~+→Na~+→Li~+) when coupled with the same anion(Cl~-).In electrolytes with the same cation concentration(K~+),changing the anion from the larger dianion(SO_4~(2-)) to the smaller monoanion(Cl~-) also increased the capacitance at high potential scan rates(50mV/s).Increasing electrolyte concentration produced expected effect,including raising the electrode capacitance,but lowering the equivalent series resistance(ESR).charge transfer resistance(CTR),and the diffusion resistance.At higher temperatures,the CMPB exhibited slightly higher capacitance,which does not agree with the Gouy-Chapman theory on electric double layer(EDL).A hypothesis is proposed to account for the capacitance increase with temperature as a result of the CMPB opening up some micro-pores for more ions to access in response to the temperature increase.     

Effect of thermal treatment on structural change of anode electrocatalysts for direct methanol fuel cells

Commercially available carbon-supported Pt,PtCo and PtRu catalysts from E-TEK are heat-treated in turn at 600 ℃ and 800 ℃ each for an hour.The as-received and as-heated catalysts are used as anode catalysts for direct methanol fuel cells.Structural and surface composition changes induced by heating are analyzed by X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS),respectively.For the Pt catalyst,heating the catalysts caused only the mass activity decrease due to particle sintering,whereas the specific activity and CO tolerance remained unchanged.The performance of the PtCo and PtRu catalysts is affected differently by heating.Heating the PtRu catalyst adversely affects its catalytic activity and its CO tolerance due to Pt depletion at the surface.In contrast,although Pt depletion also takes place for the heated PtCo catalysts,these catalysts show an even higher specific activity and approximately the same CO tolerance.The observed difference is likely due to the optimum atomic ratio difference for Ru/Pt and Co/Pt;an increased atomic ratio on the surface for Co/Pt results in an activity enhancement,which is contrary to the effect of the increase of Ru/Pt atomic ratio.     

Development of an integrating sphere calibration method for Cimel sunphotometers in China aerosol remote sensing network

Based on the integrating sphere traced from the National Institute of Standards and Technology(NIST,USA), a sphere calibration method and protocol for the China aerosol remote sensing network(CARSNET)Cimel sun photometer was established. Four CE318 sun photometers were verified using the proposed calibration method and operational protocol. The calibration results showed that the instrument coefficients differed by less than 3% for visible(~5% for infrared) wavelengths from the original ones stated by Cimel Electronique. In situ validation experiment data showed that radiances at ±6° measured by sun collimator(aureole) were consistent with those measured by sky collimator(sky), under both almucantar(ALMUC)^nd principal plane(PPLAN) scenarios. Differences at all wavelengths were less than 1%, indicating that the method and protocol are suitable for CARSNET field sun photometer calibration, and would benefit improvement of data quality and accuracy of network observations.