Numerical simulation of a fluid-saturated soil under a dynamically loaded pile

The behaviour of the soil under a dynamically loaded pile toe is studied. The soil is modelled as a fluid saturated porous continuum. The constitutive behaviour of the solid skeleton is described by the elasto-plastic model of Drücker-Prager. The wave propagation is simulated with a dynamical finite-element program.A two-phase model of soil gives useful information about effective stress and pore pressure in the soil. In saturated soil the main wave under the pile toe propagates more downards than in dry soil, due to the higher compressional stiffness in saturated soil. The plastic zone under the pile toe propagates with the velocity of the fast compressional wave. The pore fluid influences the plasticity strongly and can be expected to affect pile driving too.The distribution of effective stress and pore pressure under the pile toe depends on the permeability of the soil and cannot be calculated uniquely from a single-phase calculation. Therefore, a nonlinear soil cannot be modelled correctly as a conventional single-phase material.     

A consideration of curved interfaces in stress-assisted martensite formation

A purely mechanical, sharp interface model is developed to consider curved interfaces that have been observed between martensite phase variants. The approach is based on a theory of small strains as distinct from small displacement gradients. It admits a realistic characterization of each phase with standard elasticity tensors and allows for inhomogeneous states of strain within each phase including inhomogeneous, finite rotations. The model indicates that any signficant interface curvature must be due to material rotation because interfaces cannot be finitely curved with respect to the material lattice. It is also found that the interface driving traction is not influenced by local lattice rotations unless inertia affects the reaction.     

波长校准用低压石英汞灯驱动电源的研制

研制波长校准用低压石英汞灯电源,用于驱动汞灯起辉并维持稳态发光。电路由EMI滤波电路、桥式整流电路、LCC半桥谐振逆变电路、控制电路和保护电路5部分组成。采用系统建模与仿真验证电路的可行性并计算电路参数理论值,利用示波器和功率表验证电源输出参数,功率输出稳定性不大于0.03 W。根据紫外可见近红外分光光度计国防最高计量标准对研制的电源驱动汞灯的工作效果进行评价。结果表明,汞灯能够输出系列特征谱线,谱线相对强度稳定性不大于5.16%;汞灯工作3 h后,灯管外壳表面温度为43℃。该驱动电源的性能参数满足JJG112–2015《低压石英汞灯波长标准器检定规程》的要求。     

沉桩问题的光弹性模拟研究

实现了桩身直接贯入的沉桩光弹性模拟方法。应用这一方法研究了沉桩过程中桩周土体中的弹性应力场及其影响区域，指出Ｖｅｓｉｃ土体扩孔理论的适用范围     

MB2镁等四种金属材料的本构关系和动态断裂研究

采用炸药爆轰－分离飞片加载装置与电容传感技术相结合，由高速示波器连续记录靶板自由面速度剖面，通过波剖面的时间分辨测量，研究了ＭＢ＿２镁、ＬＹ－１２铝、钨合金、２１６９钢四种金属材料的动力学响应特性，给出了这几种材料在弹性－理想塑性模型假设下的本构关系，还给出了它们的动态断裂强度，并对标准化层裂强度与破坏比功、屈服强度之间的相关性进行了分析和讨论。     

Non-isothermal kinetics of a moving phase boundary

In this paper we derive an explicit formula for a kinetic relation governing the motion of a phase boundary in a bilinear thermoelastic material capable of undergoing solid-solid phase transitions. To obtain the relation, we study traveling wave solutions of a regularized problem that includes viscosity, heat conduction and convective heat exchange with an ambient medium. Both inertia and latent heat of transformation are taken into account. We investigate the effect of material parameters on the kinetic relation and show that in a certain range of parameters the driving force becomes a non-monotone function of the interface velocity. The model also predicts a nonzero resistance to phase boundary motion, part of which is caused by the thermal trapping. Received: November 15, 2001 / Published online September 4, 2002 RID="*" ID="*" e-mail: annav@math.pitt.edu Communicated by Lev Truskinovsky, Minneapolis     

微型化大电流脉冲激光器驱动电路研究

设计了一种用于与激光二极管芯片进行集成的基于MOSFE场效应管的大电流脉冲驱动电路方案,计算了限流电阻对驱动电路中储能电容性能的影响,分析了MOSFET场效应管峰值驱动电流与开通时间的估算公式,通过仿真软件研究了激光器的寄生电感对驱动电路波形的影响;理论和仿真结果表明,通过驱动电路与激光器芯片的一体化集成,提高了脉冲激光器性能,设计并制作了尺寸为14mm的微型化驱动电路;经测试,27V直流电压源驱动下,驱动信号上升时间小于15ns,脉宽25~150ns,最大占空比0.5%,输出幅值大于22V。     

Adaptive Multimodal In‐Vehicle Information System for Safe Driving

This paper proposes an adaptive multimodal in‐vehicle information system for safe driving. The proposed system filters input information based on both the priority assigned to the information and the given driving situation, to effectively manage input information and intelligently provide information to the driver. It then interacts with the driver using an adaptive multimodal interface by considering both the driving workload and the driver's cognitive reaction to the information it provides. It is shown experimentally that the proposed system can promote driver safety and enhance a driver's understanding of the information it provides by filtering the input information. In addition, the system can reduce a driver's workload by selecting an appropriate modality and corresponding level with which to communicate. An analysis of subjective questionnaires regarding the proposed system reveals that more than 85% of the respondents are satisfied with it. The proposed system is expected to provide prioritized information through an easily understood modality.     

我国手机阅读业务发展驱动力浅析

近年来,我国手机阅读业务蓬勃发展,成为移动互联网业务使用频率最高的业务之一。本文首先从用户、技术、产业链以及内容四个层面分析我国手机阅读业务发展的驱动力,并在此基础上得出手机阅读业务发展建议。     

基于视觉的可靠性疲劳驾驶检测技术研究

基于视觉的疲劳驾驶检测技术是疲劳检测领域的前沿技术,但由于该检测方法易受到光照强度、驾驶环境、驾驶员个体差异等诸多因素的影响,使得多数基于视觉的疲劳驾驶检测的算法不能拥有较好的稳健性。针对这一现状,提出了一套改进的疲劳驾驶检测算法。旨在提高疲劳驾驶检测的可靠性和准确度,以适应实际应用需求。