循环冲程数可变发动机研究现状概述

围绕循环冲程数可变发动机,详细阐述了近几年的研究现状。在现有技术下,冲程数可在二冲程、四冲程、六冲程以及多冲程之间进行可变,根据发动机负荷来进行不同冲程数工作模式的切换。使发动机经济性、排放性和动力性得到统一。

基于层次分析法的高压隔膜泵安全的指标体系

高压隔膜泵作为矿物管道输送过程中的核心动力设备,如何评估高压隔膜泵的安全状况已成为一个亟待解决的课题.提出了一种基于层次分析法(AHP)的基本原理评价高压隔膜泵安全状况的AHP模型,确定了评价高压隔膜泵安全状况的指标体系,采用成对比较判断矩阵的特征向量作为高压隔膜泵安全状况评价指标的权重值.结果表明:该评价指标体系能够反映高压隔膜泵安全评价中主要影响因素的权重值,其中影响高压隔膜泵安全的最主要的参数是压力和冲程数,同时,该体系为管理人员监测高压隔膜泵的安全状况提供了理论依据.

Local Scour and the Laws of Scour Pit's Shape Downstream of Debris Flow Sabo Dam

The erosion shape and the law of development of debris flow sabo dam downstream is a weak part in the study on debris flow erosion. The shape and development of scour pit have an important effect on the stability and safety of debris flow sabo dam, which determines the foundational depth of the dam and the design of protective measures downstream. Study on the scouring law of sabo dam downstream can evaluate the erosion range and reasonably arrange auxiliary protective engineering. Therefore, a series of flume experiments are carried out including different debris flow characteristics （density is varying from 1.5 t/m3 to 2.1 t/m~） and different gully longitudinal slopes. The result shows that the scour pit appears as an oval shape in a plane and deep in the middle while superficial at the ends in the longitudinal section, the position of the maximum depth point moves towards downstream with an increase of flume slope angle. The maximum depth of scour pit is mainly affected by the longitudinal slope of gully, density of debris flow, and the characteristics of gully composition （particle size and the viscosity of soil）. The result also indicates that the viscosity of soil will weaken the erosion extent. The interior slopes of scour pit are different between the upstream and the downstream, and the downstream slope is smaller than the upper one. For the viscous and non-viscous sands with the same distribution of gradation, the interior slope of non- viscous sand is smaller than the viscous sand.According to tbe regression analysis on the experimental data, the quantitative relationship between the interior slope of scour pit, slope of repose under water and the longitudinal slope of gully is established and it can be used to calculate the interior slope of scour pit. The results can provide the basis for the parameter design of the debris flow control engineering foundation.

Focusing of Spherical Nonlinear Pulses for Nonlinear Wave Equations Ⅲ. Subcritical Case

This paper studied spherical pulses of solutions of the system of semilinear wav e equations with the pulses focusing at a point in three space variables. It is shown that there is no nonlinear effect at leading terms of pulses, when the ini tial data is subcritical.

Some Notes of p-Moment Boundedness of Nonlinear Differential Equation with Pandom Impulses

A model of nonlinear differential systems with impulsive effect on random moments is considered. The extensions of qualitative analysis of the model is mainly focused on and three modified sufficient conditions are presented about p-moment boundedness in the process by Liapunov method with nonlinear item dependent on the impulsive effects, which may gain wider use in industrial engineering, physics, etc. At last, an example is given to show an theoretical application of the obtained results.

Heat Exchanging Process of Metal Target under Millisecond Pulsed Laser Shocking

Laser plays an important role in synthesizing nanometer material. A three-dimensional mathematical model is established in this paper when single pulsed millisecond laser shocks the surface of the metal target at a liquid-solid interface. By changing laser power density and target size, the temperature field variation of the metal target is investigated. Results show that the generation process of nanoparticles includes heating, melting and boiloff.

Influence of preload discreteness on air-operated separation process of low-shock separation device

To investigate the influence of design parameters on the performance of separation device,the structure and air-operated test of a low-shock separation device are introduced and analyzed in this paper.According to the law of energy conservation and aerodynamics,a mathematical model is built.Because the preload used to ensure the connection reliability has the discreteness,which will influence the separation process,the influence of preload discreteness on the air-operated separation process is simulated and tested.Simulation results are consistent with the experimental results.It is shown that the change of preload has an obvious influence on the separation process.The study is useful for the design and optimization of separation device.

Positive Solutions for Second Order Impulsive Differential Equations with Dependence on First Order Derivative

We study positive solutions for second order three-point boundary value problem：{″（t）＋f（t,x（t）,x＇（t））=0,t≠ti△x（ti）=Ii（x（ti）,x＇（ti））,i=1,2,3,…,k△x＇（ti）=Ji（x（ti）,x＇（t））,x（0）=0=x（1）-αx（η）,where 0〈η〈1,0〈α〈1,and f：[0,1]×（0,∞）×R→[0,∞）,Ii：[0,∞）×R→R,Ji：[0,∞）×R→R,（i=1,2,…,k）are continuous. Based on a new extension of Krasnoselskii fixed-point theorem （which was established by Guo Yan-ping and GE Wei-gao, the existence of positive solutions for the boundary value problems is obtained. In particular, we obtain the Green function of the problem, which makes the problem simpler.

Difference Scheme for Hyperbolic Heat Conduction Equation with Pulsed Heating Boundary

In this paper, the authors have analyzed the second-order hyperbolic differential equation with pulsed heating boundary, and tried to solve this kind of equation with numerical method. After analyzing the error of the difference scheme and comparing the numerical results with the theoretical results, the authors present some examples to show how the thermal wave propagates in materials. By analyzing the calculation results, the conditions to observe the thermal wave phenomena in the laboratory are conferred. Finally the heat transfer in a complex combined structure is calculated with this method. The result is quite different from the calculated result from the parabolic heat conduction equation.

Energy Distribution Index for robot manipulators and its application to buffering capability evaluation

This paper proposes an approach to evaluate the performance of robot manipulator from the view of energy analysis. Based on the dynamics analysis of the manipulator, the Energy Distribution Index （EDI） is defined to depict the energy increment contribution of its subsystem to the whole manipulator. EDI is applied to the evaluation of the buffeting capability of the manipulator working under unpredictable and heavy external loads. A series of buffering indices, the Static Buffering Index （SBI）, Kineto-Static Buffering Index （KBI）, Dynamic Buffering Index （DBI）, and Global Buffering Index （GBI） are proposed to evaluate the buffering capability under different conditions. In order to acquire higher calculation accuracy, the general stiffness mapping of manipulators considering the actuator stiffness, inertia of the manipulator, damping, as well as elasticity of linkages is developed. Three different robot manipulators are studied as evaluation cases, in which the buffering structures are mechanism with variable topology, linear springs, and the elasticity of linkages respectively. The case studies show that the indices based on energy analysis have the advantage of coordinate free and are effective for buffering capability evaluation.

Numerical simulation of pollution process due to resuspension of bed materials adsorbing pollutants in alluvial rivers

Resuspension of bed materials absorbing pollutants potentially poses unpredictable challenges to water management in alluvial rivers and its mechanism of transport has not been widely recognized.In this study,a transport equation that defines the movement of pollutants adsorbed on the bed materials in the active bed layer is established,on the basis of mass conservation law and continuum theory.The transport equation is coupled into the 1-D mathematical model to numerically investigate water pollution process due to the scour of the bed sediment adsorbing pollutants.Comparisons with the situation in which the dynamics of the active bed layer is not considered indicate that the periodical evolution of the bed layer plays an innegligible role in the pollution process due to sediment re-suspension.Furthermore,comparisons of the results with available experimental observations are presented,and fairly good agreement is obtained.

Diffractive Interaction for Short Pulses in 2×2 System

This paper studies the asymptotic behavior of the diffractive interaction of pulses with two linear phases of length ε ≤ 1 in 2 × 2 semilinear strictly hyperbolic system with constant coefficiients. By a formal analysis, it derives problems of profiles in the expansion of the pulse like solution with respect to the length s, and obtains that the leading profile satisfies a nonlinear Schrodinger type system. The problems of profiles are solved, and the formal expansion is justified. It is observed that there is interaction between two phases starting at the third order profiles.