三阶切触法加工自由曲面无干涉刀位规划

基于三阶切触法刀具包络曲面的局部重建原理,提出了刀具可行空间约束下平底刀加工自由曲面的无干涉刀位规划方法. 通过工件表面到刀具轴线的距离来分析刀具与工件的局部和整体干涉,并解析求解二阶切触刀具姿态,进而建立二阶切触无干涉刀具可行空间. 在此基础上,通过计算设计曲面与包络曲面沿进给垂直方向的诱导法曲率导数,在可行空间内优化搜索最接近三阶切触的刀位. 拉伸曲面和螺旋曲面的刀位规划和切削带宽的计算结果表明,该方法可以有效地避免刀具干涉,并显著提高加工效率.     

自由曲面加工全局干涉检验与刀位修正

针对自由曲面加工过程中的全局干涉问题,提出了一种基于自适应模拟退火遗传算法(SAGA)的快速全局干涉检验方法,将全局干涉检验转化为自由曲面上点到刀具轴线段的最短距离的寻优问题,获得了曲面上点到刀轴最短距离的直接求解方法,并基于矢量方法对干涉刀位进行了修正。设计了一种新的非线性自适应度函数,避免算法过早收敛于局部最优值。算法融合了自适应的交叉、变异算子以及模拟退火思想,经Schaffer函数测试其收敛概率约为99%。应用算例分析表明:自适应SAGA在全局干涉检验时计算量约为离散法的1/4,且避免了极值方法求解不收敛的问题,能直接计算出干涉点位置及干涉量,为全局干涉检验和刀位修正提供了科学依据。     

复杂曲面五坐标数控加工干涉检查及刀位修正

复杂曲面五坐标ＮＣ加工编程的干涉检查和刀位修正是一个十分困难而又必须解决的问题。研究了一种行之有效的干涉检查方法。该方法首先对被加工的复杂曲面及运动到任意位置的刀身离散分割,用两组三角平面片集合代替被加工曲面和刀具;然后通过判断两组三角片是否相交以及对相交三角片的几何求交计算,来检验加工曲面是否和刀具发生干涉;并针对不同的干涉情况,给出相应的刀位修正方法。实际应用表明该方法是行之有效的。     

基于改进的粒子群算法求NURBS曲面间的最小距离

运用粒子群算法求解距离的方法,给出了任意两个NURBS曲面间的最短距离计算算法.为检验方法的可行性,先用特殊的NURBS曲面给出了验证,然后用该方法对一般的非特殊的两NURBS曲面间的距离进行求解.     

非球头刀数控加工无干涉刀位的计算方法

针对非球头刀五轴数控加工复杂曲面的干涉问题。提出了一种无干涉刀位自动生成算法，主要涉及干涉检测和干涉避免两个方面．该方法基于曲线到曲面最短距离算法进行干涉检测，计算刀轴和邻近曲面的最短距离，求取最大干涉量；根据最大干涉量进行刀位调整得到无干涉刀位．该方法的有效性已通过叶轮的加工得以证实．     

一种快速完备的自由曲线和曲面间最短距离求取算法

提出的柱刀干涉检测是基于最短距离的求取算法,获得刀轴与加工面间的最短距离,进而与刀具半径比较得到最大干涉量.曲线与曲面间最短距离算法从极值点的几何条件出发,利用赋范空间投影法迭代求取极值距离,同时充分考虑了曲线和曲面间的边界距离.保证了求取的正确性和快速收敛性.该算法为数控加工中快速、准确、完备地进行干涉检测提供了理论依据,具有实用价值.     

面齿轮传动整个啮合过程相对法曲率干涉检验的方法

两齿面在接触点处无曲率干涉才能正确啮合,由此提出一种面齿轮传动整个啮合过程的相对法曲率极值曲线曲率干涉检验的方法.建立两实体曲面干涉检验的物理模型,通过欧拉(Eurler)公式和Bertrand公式,导出曲面相对法曲率的数学解析式,对相对法曲率极值进行求解,分析两曲面在接触点无曲率干涉时相对法曲率极值的范围;建立面齿轮副的齿面方程,根据啮合原理,由插齿刀齿面的主曲率、主方向导出被展成面齿轮齿面的主曲率、主方向.通过计算机仿真得到面齿轮齿面的啮合印痕及各啮合位置相对法曲率的极值曲线,并对面齿轮传动在啮合点的曲率干涉情况进行分析.     

一种开阔自由凹曲面五坐标加工多点刀位算法

为了采用圆环面刀具加工开阔自由凹曲面,提出了一种简单快速的五坐标多点刀位算法.通过构造等距面,圆环面刀具的圆环面与理想曲面的相对关系可以等效为刀具环心圆曲线与等距面的相对关系.在等距面上构造偏置距离等于最大允许残余高度的新等距面,建立在新等距面一点处由法矢量和最小、最大主曲率方向矢量确定的局部坐标系,通过坐标变换得到空间坐标系下刀具环心圆曲线的参数方程.利用改进的求曲线曲面最小距离算法,得到不同刀位下刀具与新等距面的干涉量,当干涉量满足精度要求时停止调整刀轴,可以得到最优刀位.算例显示,新多点刀位算法不仅可以产生大的有效切削宽度,而且比以往的多点刀位算法具有更高的计算效率.     

Loop细分曲面数控加工刀具轨迹的生成

细分曲面可以方便地表示任意拓扑结构的光滑曲面 ,正逐渐成为自由曲面造型的有力工具 ;细分曲面的加工是其工业应用的基础。给出一个用于 L oop细分曲面数控加工的无干涉刀具轨迹生成的实用算法 :首先在不考虑干涉的情况下 ,由 L oop细分曲面的初始控制网格直接计算生成刀触数据 ;然后通过对刀具干涉条件的分析 ,确定干涉区域 ,去除产生干涉的刀触点 ;最后将刀触数据转换为无干涉的刀位数据。该算法提供了对基于细分曲面表示的实际零件进行曲面加工的理论基础     

Catmull-Clark细分曲面的误差界估计

Catmull-Clark细分曲面是定义在任意拓扑网格上的一种细分曲面的框架,它是双三次B样条曲面的一种推广.该文主要研究Catmull-Clark细分曲面的误差界估计.利用控制顶点的一阶差分来定义Catmull-Clark曲面的连续三层细分网格间的距离,推导出一个计算控制网格到Catmull-Clark曲面的误差界的公式.同时也说明Catmull-Clark曲面的控制网格是以指数速率收敛的.     

Particle size and energetics of gouge from earthquake rupture zones

Grain size reduction and gouge formation are found to be ubiquitous in brittle faults at all scales, and most slip along mature faults is observed to have been localized within gouge zones. This fine-grain gouge is thought to control earthquake instability, and thus understanding its properties is central to an understanding of the earthquake process. Here we show that gouge from the San Andreas fault, California, with approximately 160 km slip, and the rupture zone of a recent earthquake in a South African mine with only approximately 0.4 m slip, display similar characteristics, in that ultrafine grains approach the nanometre scale, gouge surface areas approach 80 m2 g(-1), and grain size distribution is non-fractal. These observations challenge the common perception that gouge texture is fractal and that gouge surface energy is a negligible contributor to the earthquake energy budget. We propose that the observed fine-grain gouge is not related to quasi-static cumulative slip, but is instead formed by dynamic rock pulverization during the propagation of a single earthquake.     

Slip zone and energetics of a large earthquake from the Taiwan Chelungpu-fault Drilling Project

Determining the seismic fracture energy during an earthquake and understanding the associated creation and development of a fault zone requires a combination of both seismological and geological field data. The actual thickness of the zone that slips during the rupture of a large earthquake is not known and is a key seismological parameter in understanding energy dissipation, rupture processes and seismic efficiency. The 1999 magnitude-7.7 earthquake in Chi-Chi, Taiwan, produced large slip (8 to 10 metres) at or near the surface, which is accessible to borehole drilling and provides a rare opportunity to sample a fault that had large slip in a recent earthquake. Here we present the retrieved cores from the Taiwan Chelungpu-fault Drilling Project and identify the main slip zone associated with the Chi-Chi earthquake. The surface fracture energy estimated from grain sizes in the gouge zone of the fault sample was directly compared to the seismic fracture energy determined from near-field seismic data. From the comparison, the contribution of gouge surface energy to the earthquake breakdown work is quantified to be 6 per cent.     

含有粘土矿物断层泥地震与非地震标志

实验变形的含有粘土矿物断层泥的显微结构观察提供了判别自然界断层滑动习性的标志. 含有粘土矿物断层泥的摩擦实验显示了2种模式, 一种是稳态滑动,另一种是粘滑,即有可能发生大地震. 此两种实验产物的显微结构记录了断层的滑动性质,均匀变形的断层泥是断层非地震( 稳滑) 的结果, 局部强烈变形是断层地震( 粘滑) 的产物. 均匀变形使粘土矿物产生优选方位( S 叶理) , 在一定程度上它反映了剪应变的大小, 局部变形形成吕德剪切和 Y 剪切,云南小湾 F7 断层中具有类似的结构特征,计算结果表明 F7 的稳滑量约 43%~ 52%.     

新集F10断层组断层泥分维及其水文地质特征

为研究断层水文地质特征,以新集F10断层泥数据为对象,依据分形原理,采用筛选法和悬浮相结合的方法对采自新集F10断层及其伴生断层的断层泥进行分形研究,对颗粒粒度进行分布分维。研究发现：分维值与断层的活动方式、地震几率、黏粒质量分数、渗透性、黏聚力、内摩擦角等参数有紧密的相关性,能够从多方面体现断层带的水文地质性质。     

组合曲面NC加工中刀具干涉的检查方法

分析了组合曲面ＮＣ加工中刀具干涉的类型、特性及其产生的充要条件，阐述了刀具干涉的主要检查处理方法     

Nonlinear dynamics, granular media and dynamic earthquake triggering

The 1992 magnitude 7.3 Landers earthquake triggered an exceptional number of additional earthquakes within California and as far north as Yellowstone and Montana. Since this observation, other large earthquakes have been shown to induce dynamic triggering at remote distances--for example, after the 1999 magnitude 7.1 Hector Mine and the 2002 magnitude 7.9 Denali earthquakes--and in the near-field as aftershocks. The physical origin of dynamic triggering, however, remains one of the least understood aspects of earthquake nucleation. The dynamic strain amplitudes from a large earthquake are exceedingly small once the waves have propagated more than several fault radii. For example, a strain wave amplitude of 10(-6) and wavelength 1 m corresponds to a displacement amplitude of about 10(-7) m. Here we show that the dynamic, elastic-nonlinear behaviour of fault gouge perturbed by a seismic wave may trigger earthquakes, even with such small strains. We base our hypothesis on recent laboratory dynamic experiments conducted in granular media, a fault gouge surrogate. From these we infer that, if the fault is weak, seismic waves cause the fault core modulus to decrease abruptly and weaken further. If the fault is already near failure, this process could therefore induce fault slip.     

新甘交界北山地区大泉断裂走滑特征及ESR测年证据

卫星图片显示穿过大泉断裂的水系有被左行扭曲的特征,结合野外断层面上擦痕、断裂带中劈理观测统计和室内对断层岩显微构造的分析,确定了大泉断裂是以左行为主的走滑断裂带。对断层泥的ESR年代学测定,确定了大泉断裂开始活动时间为早更新世1.2～1.5Ma,其分支断层的活动时间在晚更新世300ka左右。大泉断裂活动时间与青藏高原在上新世末-早更新世初开始强烈隆升时间一致,表明大泉断裂的形成与青藏高原的隆升过程密切相关,是晚新生代印度和欧亚两大板块持续碰撞挤压和青藏高原隆升的远程效应。     

新甘交界北山地区大泉断裂走滑特征及ESR测年证据

卫星图片显示穿过大泉断裂的水系有被左行扭曲的特征,结合野外断层面上擦痕、断裂带中劈理观测统计和室内对断层岩显微构造的分析,确定了大泉断裂是以左行为主的走滑断裂带。对断层泥的ESR年代学测定,确定了大泉断裂开始活动时间为早更新世1.2~1.5Ma,其分支断层的活动时间在晚更新世300ka左右。大泉断裂活动时间与青藏高原在上新世末-早更新世初开始强烈隆升时间一致,表明大泉断裂的形成与青藏高原的隆升过程密切相关,是晚新生代印度和欧亚两大板块持续碰撞挤压和青藏高原隆升的远程效应。     

半干旱区农牧交错带风水交互侵蚀特点研究——以内蒙古四子王旗南部为例

以内蒙古四于王旗南部为例，研究了半干旱区农牧交错带风水交互侵蚀的特点．结果表明，该地区低山丘陵与宽谷相间分布，坡地上有大量疏松的沉积物；夏季降水以暴雨为主，春秋季多大风，形成风水复合侵蚀发育．每年夏秋季节的水蚀为风蚀提供了大量的沙物质，第2年春季的大风将沙物质进一步吹扬扩散，为水蚀的搬运提供了物质基础，如此反复．使水系的上游形成沟谷，中下游沙化迅速．     

The dating of shallow faults in the Earth's crust.

Direct dating of ductile shear zones and calculation of uplift/exhumation rates can be done using various radiometric dating techniques. But radiometric dating of shallow crustal faulting, which occurs in the crust's brittle regime, has remained difficult because the low temperatures typical of shallow crusted faults prevent the complete syntectonic mineral recrystallization that occurs in deeper faults. Both old (detrital) and newly grown (authigenic) fine-grained phyllosilicates are thus preserved in shallow fault zones and therefore their radiometric ages reflect a mixture of both mineral populations. Also, the loss of 39Ar during neutron irradiation in dating of clay minerals can produce erroneously old ages. Here we present a method of characterizing the clay populations in fault gouge, using X-ray modelling, combined with sample encapsulation, and show how it can be used to date near-surface fault activity reliably. We examine fault gouge from the Lewis thrust of the southern Canadian Rockies, which we determine to be approximately 52 Myr old. This result requires the western North America stress regime to have changed from contraction to extension in only a few million years during the Eocene. We also estimate the uplift/exhumation age and sedimentary source of these rocks to be approximately 172 Myr.