A Review of Ultrasonic Nano Manipulation Technology 免费阅读 下载全文 Nano manipulation technology has great potential applications in the assembly,measurement and fabrication of nano materials,actuating and high-sensitivity sensing of biological samples,manufacture of nano sensors,decontamination of air and water,etc. As an actuating technology which is far from being mature,the nano manipulation still faces lots of challenges in the device principles,design,scaling up,sample safety,etc.The ultrasonic nano manipulation, in which nanoscale objects are handled and actuated by controlled ultrasound,is an emerging technology to meet some of challenges in nano manipulations. The author’s research team and other groups have proposed and realized a series of nano manipulation functions such as trapping,transfer, rotation and concentration since 2012, by controlled ultrasound. Compared with other nano manipulating techniques,the ultrasonic method has the merits such as very low temperature rise at the manipulation area,little selectivity to the material properties of manipulated samples,capability of being implemented on the substrates without MENS or NEMS structure,etc. This paper reviews the progresses in principles,functions,structures and characteristics of the ultrasonic devices for nano manipulations.
Determination of Pressure Profile During Closed-Vessel Test Through CFD Simulation 免费阅读 下载全文 Two-phase flow modeling of solid propellants has great potential for simulating and predicting the ballistic parameters in closed vessel tests as well as in guns. This paper presents a numerical model describing the combustion of a solid propellant in a closed chamber and takes into account what happens in such twophase,unsteady,reactive-flow systems. The governing equations are derived in the form of coupled,non-linear axisymmetric partial differential equations. The governing equations with customized parameters are implemented into Ansys Fluent 14. 5. The presented solutions predict the pressure profile inside the closed chamber. The results show that the present code adequately predicts the pressure-time history. The numerical results are in agreement with the experimental results. Some discussions are given regarding the effect of the grain shape and the sensitivity of these predictions to the initial pressure of the solid propellant bed. The study demonstrates the capability of using the present model implemented into Fluent,to simulate the combustion of solid propellants in a closed vessel and,eventually,the interior ballistic process in guns.
Trajectory Simulation for Underwater Vehicle with Power-Lunched 免费阅读 下载全文 The motion of combustion gas bubble produced by underwater ignition was developed based on Rayleigh-Plesset equation. Combining the bubble motion equation with the underwater launched vehicle motion equation in the longitudinal plane,a trajectory simulation model with power-launched was established. The hydrodynamic characteristics of underwater ignition at different depths and the trajectory analysis of the underwater vehicle with power-launched were given by simulation. The simulation results have a good agreement with experimental results,and show that the thrust peak caused by underwater ignition and the stable thrust both decrease slightly with the increase of the water depth,and the thrust peak will decline obviously by enlarging the initial radius of gas bubble; the thrust peak generated at the instant of ignition and the low-frequency oscillation of the stable thrust have no significant influence on the trajectory of underwater vehicle.
Reference Model of Desired Yaw Angle for Automated Lane Changing Behavior of Vehicle 免费阅读 下载全文 In this paper,it studies the problem of trajectory planning and tracking for lane changing behavior of vehicle in automatic highway systems. Based on the model of yaw angle acceleration with positive and negative trapezoid constraint,by analyzing the variation laws of yaw motion of vehicle during a lane changing maneuver,the reference model of desired yaw angle and yaw rate for lane changing is generated. According to the yaw angle model,the vertical and horizontal coordinates of trajectory for vehicle lane change are calculated. Assuming that the road curvature is a constant,the difference and associations between two scenarios are analyzed,the lane changing maneuvers occurred on curve road and straight road,respectively. On this basis,it deduces the calculation method of desired yaw angle for lane changing on circular road. Simulation result shows that,it is different from traditional lateral acceleration planning method with the trapezoid constraint,by applying the trapezoidal yaw acceleration reference model proposed in this paper, the resulting expected yaw angular acceleration is continuous,and the step tracking for steering angle is not needed to implement. Due to the desired yaw model is direct designed based on the variation laws of raw movement of vehicle during a lane changing maneuver, rather than indirectly calculated from the trajectory model for lane changing, the calculation steps are simplified.
Experimental Study and Numerical Simulation on Spray Characteristics of New-Type Air-Assist Nozzle 免费阅读 下载全文 To investigate the spray characteristics of a new-type air-assist nozzle,three-dimensional laser phase Dopper analyzer( PDA) was used to measure the spray parameters. The external flow fields of the nozzle were simulated by means of computational fluid dynamics( CFD). The distributions of the diameter and the axial velocity for the droplets were analyzed respectively. The results indicate that,the mean diameter of the droplets fluctuates along the center axis. The distance between the measurement point and the nozzle increases,the axial velocity of the droplets decreases. The further the measurement point from the center axis is,the smaller the axial velocity of the droplets is. With the increase of the nozzle pressure drop,the axial velocity of the droplets improves while the mean diameter of the droplets is reduced,and the distribution uniformity of the droplets is better for the diameter. The simulation result agrees well with the experimental data. The average deviation ranges from 3.9% to 7.7%.
A New 3D Wireless Directional Sensing Model and Coverage Enhancement Algorithm 免费阅读 下载全文 Coverage control for each sensor is based on a 2D directional sensing model in directional sensor networks conventionally. But the 2D model cannot accurately characterize the real environment. In order to solve this problem,a new 3D directional sensor model and coverage enhancement algorithm is proposed. We can adjust the pitch angle and deviation angle to enhance the coverage rate. And the coverage enhancement algorithm is based on an improved gravitational search algorithm. In this paper the two improved strategies of GSA are directional mutation strategy and individual evolution strategy. A set of simulations show that our coverage enhancement algorithm has a good performance to improve the coverage rate of the wireless directional sensor network on different number of nodes,different virtual angles and different sensing radius.
A Recursive Algorithm for Nonlinear Dynamical System Analysis Based on ADM 免费阅读 下载全文 To improve the limitation of Adomian finite term series solution reducing the convergence for nonlinear dynamical systems, a recursive algorithm for nonlinear systems analysis based on Adomian Decomposition Method( ADM) with suitable truncation order is proposed. The recursive algorithm makes use of Differential Transformation( DT) theory to convert the analytic solution from series into matrix,and then the solution matrix is used in each discrete interval to compute numerical solution iteratively. The maximum stable step-size criterion using recursion percent error( RPE) is developed for good convergence in each iteration. As classic nonlinear dynamical equations,the second-order equation with one RPE and the coupling Duffing equations with two RPEs are illustrated. Comparison results demonstrate that the presented algorithm is valid and applicable to nonlinear dynamical systems analysis.
Optimization of Process Parameters for in High-Energy Ball Milling of CNTs/Al2024 Composites Through Response Surface Methodology 免费阅读 下载全文 The mathematical models are developed to evaluate the ultimate tensile strength( UTS) and hardness of CNTs / Al2024 composites fabricated by high-energy ball milling. The effects of the preparation variables which are milling time,rotational speed,mass fraction of CNTs and ball to powder ratio on UST and hardness of CNTs / Al2024 composites are investigated. Based on the central composite design( CCD),a quadratic model is developed to correlate the fabrication variables to the UST and hardness. From the analysis of variance( ANOVA),the most influential factor on each experimental design response is identified. The optimum conditions for preparing CNTs / Al2024 composites are found as follows: 1. 53 h milling time,900 r / min rotational speed,mass fraction of CNTs 2. 87% and Ball to powder ratio 25 ∶ 1. The predicted maximum UST and hardness are 273.30 MPa and 261.36 HV,respectively. And the experimental values are 283.25 MPa and256.8 HV,respectively. It is indicated that the predicted UST and hardness after process optimization are found to agree satisfactory with the experimental values.
Structural Reliability Analysis for Implicit Performance with Legendre Orthogonal Neural Network Method 免费阅读 下载全文 In order to evaluate the failure probability of a complicated structure,the structural responses usually need to be estimated by some numerical analysis methods such as finite element method( FEM). The response surface method( RSM) can be used to reduce the computational effort required for reliability analysis when the performance functions are implicit. However,the conventional RSM is time-consuming or cumbersome if the number of random variables is large. This paper proposes a Legendre orthogonal neural network( LONN)-based RSM to estimate the structural reliability. In this method,the relationship between the random variables and structural responses is established by a LONN model. Then the LONN model is connected to a reliability analysis method,i.e. first-order reliability methods( FORM) to calculate the failure probability of the structure.Numerical examples show that the proposed approach is applicable to structural reliability analysis,as well as the structure with implicit performance functions.
Simulation of Fatigue Stiffness Degradation in Prestressed Concrete Beams under Cyclic Loading 免费阅读 下载全文 In order to investigate and research the fatigue cracking of prestressed concrete fatigue properties and loading and stiffness degeneration process,cyclic loading tests were carried out on six prestressed concrete beams and the stiffness degradation under fatigue was investigated. A simulation model of stiffness degradation is proposed based on the stiffness analysis of the fatigue-damaged section. The elastic modulus of damaged concrete and the effective residual area of steel were introduced as well as an adjusted three-stage concrete fatigue damage evolution model. The strip method was used to analyze concrete damage due to changing stress along the depth of the beam section. The simulation and test results were compared and a method of predicting fatigue deflection was presented based on the simulation model. The predicted results were compared with that of the neural network method. It is in good agreement for the simulation results with the test results. It is only less than5% error for the simulation model which can reveal the two-stage degradation of prestressed concrete beams under cyclic loading. It is more precise for the simulation prediction method under proper conditions.
Parameter Optimization on Experimental Study to Reduce Ammonia Escape in CO2 Absorption by Ammonia Scrubbing 免费阅读 下载全文 In order to research ammonia escape in CO2 absorption by ammonia scrubbing,ammonia escape was studied in CO2 absorption process using the bubbling reactor in different conditions as gas flow rate,CO2 ratio,absorbent temperature and ammonia concentration and quantity of escaped ammonia was measured by chemical titration. The results indicated that,the amount of ammonia escape can be around 20% of original amount in90 min and the escaped amount will increase with the rise of gas flow rate, absorbent temperature,concentration of ammonia while decrease as CO2 ratio goes up. Through the analysis of the law of ammonia escape,at the same time,combined with ammonia escape and the influence of the relationship between the CO2 absorption efficiency,reducing ammonia escape working condition parameter optimization is given.
A Model for Capacity Considering the Interference by Pedestrian Traffic at Signal Intersections 免费阅读 下载全文 The capacity is impacted badly by pedestrians’ violation behavior at signal intersections. In order to quantify the impact,the time-headway and the vehicular speed from start-up to reach the stable saturation flow with and without pedestrian traffic are used as the direct measurements. Using the statistical analysis,the timeheadway of saturation flow is mainly affected by the position of pedestrians and the degree of pedestrians ’influence is classified into four levels. Then the speed-time profile for the vehicular acceleration at each level is fitted by Curve Fitting Software. Based on the effect to the time-headway and acceleration time,the model of capacity influenced by pedestrians is established and the influence is quantified, which enriches the fundamental theory of traffic engineering. The result shows that the vehicular capacity can be decreased by 14%at the worst case( level I). The conclusions obtained in this paper are valuable for better management of the signal intersection.
Effect of C/N Ratio,Temperature,pH on Autotrophic Denitrification Rate with Hydrogen Gas,Iron（Ⅱ） and Sodium Sulfide as Electron Donors 免费阅读 下载全文 Nitrate is considered to be one of the most widely present pollutants leading to eutrophication of environment. The purpose of this work was to isolate and identify new anaerobic denitrifying bacteria from reservoir sediments and utilize different electron donors for isolates to improve nitrate removal efficiency. Using traditional enrichment approach,one purified anaerobic bacterium( Y12) capable of NO-3-N removal from sediments was obtained. The species identity of Y12 was determined via 16 S rRNA gene sequence analysis to be Acinetobacter. In this work,the fastest denitrification rates were observed with ferrous iron as electron donor.And,slightly slower rates were observed with hydrogen and sodium sulfide as electron donors. However,when used hydrogen gas, ferrous iron and sodium sulfide as electron donors, C / N ratios had little effect on autotrophic denitrification rate at the initial C / N ratio from 1.5 to 9.0. Meanwhile,when made use of hydrogen gas,ferrous iron and sodium sulfide as electron donors,a maximum nitrate removal ratio of 100.00%,91.43%and 87.99% at the temperature of 30 ℃,respectively. Moreover,maximum denitrification activity was observed at p H 6.0-7.0.
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