EXPERIMENTAL AND NUMERICAL RESEARCH ON BULLDOZER WORKING PROCESS

A simulative analysis coupled with experiment on behaviors of a soil bed cut by a model bulldozer blade is carried out using the finite element/distinct element method(FE/DEM) facility built in the ELFEN package. Before simulation,the soil specimens are examined through uniaxial tensile/compression,triaxial compression and direct shear tests to obtain model characteristics and relevant parameters,then soil cutting experiments are carried out via a mini-soil bin system with a soil bed of 60/120 mm in width and 10 mm in depth cut by a 1/9 scale model bulldozer blade moving with the velocity of 10 mm/s. The soil constitutive model includes the tensile elastic model for tensile breakage and the compressive elastoplastic relationship with Mohr-Coulomb criterion. The cutting length in simulation is set as 1/4 of that in the experiment divided into 1 869 triangular elements. The comparison between the simulated results and experimental ones shows that the used model is capable of analyzing soil dynamic behaviors qualitatively,and the predicted fracturing profiles in general conform to the experiment. Hence the feasibility for analyzing soil fracturing behaviors in tillage or other similar processes is validated.     

Effect of the third-body particles on the tool–chip contact and tool-wear behaviour during dry cutting of aeronautical titanium alloys

In machining process, a major limitation of the tool life is due to wear phenomena that occur at the tool–chip interface. Wear influences the surface quality and dimensional accuracy of the finished product by degrading the shape and efficiency of the tool cutting edge. The basic mechanisms of wear are controlled by the mechanical and physico-chemical properties of the tool and workpiece materials. The cutting conditions such as the cutting speed, the feed rate, and the tool geometry also have an important effect on the tool-wear behaviour. Several basic causes of tool wear have been previously investigated; some of the most important are: abrasion and adhesion wear. During the chip formation, particles are removed from the tool and/or the chip surface and are carried away by the flow of the work material along the contact. It is very hard to understand physical phenomena at the tool–chip interface using only experimental means since the contact between the tool and the machined material occurs under extreme mechanical and thermal loading. The situation is more complicated by the presence of the third body, which generates different wear mechanisms.In the present work, the discrete element method (DEM) based on molecular dynamics is used as a helpful tool to understand the behaviour of the third-body particles and their interactions with the tool and workpiece materials in the contact. Both tool and chip materials are defined as discrete particles connected by solid joints. The tool material (first body) is assumed to be degradable granular material and flows along the second material under a combination of pressure and sliding velocity. A parametric study on the transient phenomenon of the tool degradation has been carried out according to the contact conditions, which strongly depend on the machining parameters. The results show that the tribological parameters can be qualitatively evaluated by conducting both calibration–cutting experiments and DEM simulations.     

A 15-MHz bandwidth double sampling MASH25b-15b sigma-delta modulator with DEM for multibit DACs

A high SNDR discrete-time (DT) 2-1 MASH sigma-delta modulator (SDM) for 15-MHz bandwidth was presented. Cascade of integrators with feedforward (CIFF) scheme, combined with the optimized gain coefficients, was adopted to avoid of the integrators. Double sampling technique was employed to relax the OPA settling requirements by halving the clock frequency and therefore reduce the power consumption. Five-bit flash quantizer was adopted in both stages to improve the overall signal-to-noise and distortion ratio (SNDR) performance, and third-order dynamic element matching (DEM) was analyzed and applied for the multibit DACs to suppress the element mismatch noise. Fabricated in a mature 0.18-μm CMOS technology, the occupied area of the modulator was 0.24 mm² and dissipation power 25.4 mW from a 1.8-V voltage supply. As a sampling rate of 240 MHz for the input sampling and DAC and 480 MHz for the flash ADC, a SNDR of 90.2 dB over 15-MHz signal bandwidth and the corresponding effective number of bits (ENOB) of 14.69 bit were achieved. The spurious-free dynamic range (SFDR) was 98 dB with DEM turned on for a 3.75 MHz at −2.5-dBFS input signal, and the figure of merit (FOM) was 30.7 fJ/conv. for 15-MHz bandwidth. A 15-MHz bandwidth multibit MASH2-1 discrete-time sigma-delta modulator was proposed. Double sampling technique was employed to relax the OPA settling requirements by halving the clock frequency and therefore reduce the power consumption. High-order DEM was analyzed and applied for the multibit DACs to suppress the element mismatch noise. Fabricated by a 0.18-μm CMOS process, the modulator achieved a SNDR of 90.2 dB and the corresponding ENOB 14.69 bit over 15-MHz signal bandwidth. The proposed modulator was very suitable for wideband applications including wireless communication systems, high-frequency biomedical imaging or sensing systems, and so on.     

大比例尺DEM构建框架及关键技术研究

该文以河南省开封市开封县老君堂、大辛庄、徐庄北三个乡级地区的DEM(比例尺1:10000)制作为例,介绍了利用ArcGIS Desktop9.2软件构建大比例尺DEM的框架步骤,包括纸质地形图的扫描、扫描地形图的配准、数字化地形图的生成、构建TIN及Grid DEM;并探讨了大比例尺DEM制作过程中的一些关键技术,包括研究区分幅图层数据的拼接;大比例尺DEM精度控制、粗差控制及参数选择。     

数字近景摄影测量技术在矿山地表沉陷监测中的应用研究

为了解决传统的矿山地表沉陷监测方法存在的劳动强度大、不能实时观测、难以获得瞬时3维移动变形信息等缺陷,提出了一种利用基于非量测数相机的数字近景摄影测量技术进行塌陷区沉陷监测的方法。该方法首先利用标定过的高分辨率数字相机获取塌陷区的数字立体影像像对;然后采用相对定向、影像匹配等摄影测量解析处理技术提取塌陷区地表的数字高程模型;最后通过与该区域开采前数字高程模型对比分析来完成塌陷区沉陷范围、深度、体积等沉陷参数计算。应用研究结果表明,数字近景摄影测量的测定精度基本可以满足这次应用条件下沉陷监测的精度要求。该方法为矿山地表塌陷区的沉陷监测提供了一条可行的途径。     

基于嵌入式系统的三维地形生成技术研究

本文结合DEM模型、LOD技术和OpenGL ES标准等方面内容对嵌入式三雏地形生成技术进行了研究,并给出了地形的仿真结果,为嵌入式三维GIS系统的进一步研究提供了理论基础。     

基于DEM分析的引汉济渭工程受水区调蓄节点选址研究

就引汉济渭工程而言,由于关中受水区地势平坦,很难找到单一的大容量洼地修建调蓄工程,因此,需要采用分散式调蓄工程布置方案。本文在数字高程地形(DEM)数据分析的基础上,结合土地利用情况、下垫面条件以及调蓄节点与用水单元的空间关系,在受水区范围内优选了调蓄条件较好的地点25处,总共调蓄容量为1.37亿m3,可满足一般平水年份引汉济渭工程受水区的年调蓄容量要求。     

利用ERS-1/2串接雷达干涉建立高山地区数字高程模型的实验研究

以昆仑山局部地区为例,利用ERS-1/2串接雷达干涉有效建立了高山地区数字高程模型,并以美国宇航局SRTM高程数据为标准,选取高相干系数点,采用多项式拟合法对实验生成的数字高程模型进行校正,得到实验区较高精度的数字高程模型。最后以SRTM高程数据和美国地质调查局GTOPO30高程数据作为基准,对实验生成的数字高程模型的精度进行统计分析和评价,并分析了影响ERS-1/2干涉测量精度的主要因素。实验结果表明：采用ERS串接雷达干涉和基于多控制点的多项式拟合校正,可有效建立高山地区高精度的数字高程模型;在我国西部地区,建议采用ERS-1/2串接雷达干涉建立或更新数字高程模型。     

基于DEM的细沟形态分维估算方法探讨

为了促进分形理论在细沟形态量化中的应用,在回顾以往研究的基础上,探讨了一种以DEM为数据源,基于ArcGIS软件的坡面侵蚀地形数据处理、水文信息提取的方法,通过具体实例,运用网格覆盖法实现了细沟形态分形维数的计算,达到了精确、高效的应用效果。     

基于离散元的不同截面抗滑桩土拱效应分析

选取典型抗滑桩截面(方形、矩形和圆形),采用离散元(DEM)手段,从细观角度对这三种横截面桩土拱效应的形成发育过程及相关影响因素进行分析研究。结果表明:三种抗滑桩桩后均有土拱效应产生,方形桩跟矩形桩所形成的土拱效应均大致呈半圆弧状,圆形桩的土拱效应则近似马鞍形;矩形桩所能承载的极限荷载最大,方形桩次之,圆形桩最弱;不同的影响因素对同类型的抗滑桩影响规律及程度均存在差异,同一影响因素对不同截面抗滑桩影响规律相同但影响程度不同。