最晚截止期优先带宽转让算法

基于最早截止期优先调度的实时系统，针对有新任务插入(与/或)现行任务加速但系统带宽不足的问题，提出一种最晚截止期优先(LDF)算法，用于系统在运行时选择现行任务转让带宽。采用从最晚作业截止期任务开始判断的方法，经过尽可能少的比较次数，找到合适的受压任务，平滑地完成带宽转让。算法需要的最多比较次数为2n。仿真结果表明，该算法在大多情况下只需要比较1~2次即可完成压缩任务。     

大锻件内部疏松缺陷锻造压实过程FEM分析

通过分析大型铸钢锭内部疏松缺陷的物理性质和变形特征,将疏松缺陷视为多孔可压缩材料,利用多孔可压缩材料的刚塑性有限元方法,建立了Cr5型支承辊钢锻件内部疏松缺陷锻造压实过程的非线性有限元模型。通过数值模拟,研究了上下V型砧锻造工艺下,疏松体缺陷的初始孔隙率、砧宽比、接触摩擦系数和压下量等因素对其致密压实效果的影响。在Gl...     

Finite element modelling of saturated porous media at finite strains under dynamic conditions with compressible constituents

Two finite element formulations are proposed to analyse the dynamic conditions of saturated porous media at large strains with compressible solid and fluid constituents. Unlike similar works published in the literature, the proposed formulations are based on a recently proposed hyperelastic framework in which the compressibility of the solid and fluid constituents is fully taken into account when geometrical non‐linear effects are relevant on both micro‐ and macroscales. The first formulation leads to a three‐field finite element method (FEM), which is suitable for analysing high‐frequency dynamic problems, whereas the second is a simplification of the first, leading to a two‐field FEM, in which some inertial effects of the pore fluid are disregarded, hence the second formulation is suitable for studying low‐frequency problems. A fully Lagrangian approach is considered, hence all terms are expressed with reference to the material setting; the balance equations for the pore fluid are also expressed in terms of the chemical potential and the mass flux of the pore fluid in order to take the compressibility of the fluid into account. To improve the numerical response in the case of wave propagation, a discontinuous Galerkin FEM in the time domain is applied to the three‐field formulation. The results are compared with analytical and semi‐analytical solutions, highlighting the different effects of the discontinuous Galerkin method on the longitudinal waves of the first and second kind. Copyright © 2010 John Wiley & Sons, Ltd.     

A new modeling approach of pressure waves at the inlet of internal combustion engines

This paper presents a new model used to describe the propagation of pressure waves at the inlet systems of internal combustion engine. In the first part, an analogy is made between the compressible air in a pipe and a mechanical ideal mass damper spring system. A new model is then presented and the parameters of this model are determined by the use of an experimental setup (shock tube test bench). With this model, a transfer function is defined in order to link directly the pressure and the air mass flow rate. In the second part, the model is included into an internal combustion engine simulation code. The results obtained with this code are compared to experimental ones which are measured on a one-cylinder engine test bench. This last one is driven by an electric motor in order to study only the effect of the pressure waves on the engine behavior. A good agreement is obtained between the experimental results and the numerical ones and the new approach is an alternative method for modeling the pressure wave phenomena in an internal combustion engine manifold.     

新型纸容器结构参数对其主体可压缩性能的影响

新型可变容积纸容器主体部分由可伸缩结构及直壁结构共同组成。以正方形截面主体结构为例,研究了各结构参数对其主体可压缩性能影响的主次关系及单因素影响情况,并利用双因素试验分析了各参数间的交互作用。     

弱可压缩流体边界处理算法

针对流体与固体边界的交互模拟问题,提出一种基于弱可压缩光滑粒子流体动力学(SPH)的边界处理算法.首先,引入一种新的体积权重函数,解决固体边界非均匀采样区域流体密度的计算误差问题;然后,提出一种新的边界力计算模型,避免校正流体粒子位置信息,保证固体边界不可穿透;最后,提出一种改进的流体压力计算模型,保证流体的弱可压缩性.实验结果表明,所提算法可以有效地解决基于位置校正的边界处理方法在模拟弱可压缩流体与非均匀采样固体边界交互时存在的稳定性问题,且仅需边界粒子的位置信息,在节约内存的同时避免了位置校正所带来的额外计算开销.     

基于顺序拣选策略的压缩动态虚拟视窗算法

为缩短虚拟容器长度、减少订单拣选总时间,改进了拣选设备,提出了压缩动态虚拟视窗算法。该方法为每台拣选机设置一个重力缓存区及挡板,拣选时先将货物弹射至到重力缓存区,在缓存区内压缩货物间距;再把货物从重力缓存区合并至皮带输送机,实现货物的密集排列和虚拟容器长度的缩短。基于货物的顺序拣选策略,建立了压缩动态虚拟视窗算法的数学模型。以某地市卷烟配送中心的3批订单数据为例进行了仿真,结果表明该方法将拣选时间缩短了87.45％～87.77％,并且拣选时间随着拣选机弹射速度和重力缓存区货物合并速度的增加而减少。     

基于ALE有限元法的储液罐耦合竖动响应研究

推导了一种基于ALE描述弱可压缩液体与结构非线性耦合求解的分步有限元数值计算法,速度与压力使用同阶线性插值,并对耦合系统的竖动响应进行了分析.通过二维黏性流体大晃动问题实例计算,验证了该法简便、可行有效.     

同忻矿5311回风平巷沿空掘巷让压支护技术研究及应用

小煤柱沿空掘巷受邻近采空区顶板间歇性垮落的影响,其支护系统在承受不同程度的动载作用下将发生严重的变形和破坏。针对同忻矿5311回风巷原支护方案下巷道两帮支护刚度大,让压性能差等问题,通过分析两帮支护系统存在的问题,进行了让压支护结构设计,提出了新的支护方案,增加了沿空掘巷的让压性能。经现场工业性试验表明:新的让压支护系统,在降低支护成本的基础上,支护效果得到显著提升,顶板采用让压支护后与之前巷道顶板变形量相比减少30%,帮部采用让压技术后于之前巷道两帮变形量相比减少25%.巷道围岩得到有效控制。     

Thermoacoustics and related oscillatory heat and fluid flows in micro heat exchangers

Classical linear thermoacoustic theory is applied to compact micro heat exchangers and the validity of such calculus applied to micro scale is discussed. Expressions for the radial profiles and average values of the fluid axial velocity and temperature are demonstrated, formulations for first order friction and heat transfer coefficients of oscillating flows are deduced. It is shown how aerodynamic and thermal performances of a micro heat exchanger in pulsed flow regime can be characterized with three factors: a thermal characteristic time, an aerodynamic matrix of transfer and a thermal efficiency. The model proposed is devoted to design the micro heat exchangers of micro refrigerators dedicated to the cooling of electronic components.