Improvement to method of equivalent thicknesses (MET) for calculation of critical strains for flexible pavements

This paper presents the results of a sensitivity analysis carried out to compare the values of asphalt and subgrade strains (as well as associated fatigue and deformation lives) obtained with the method of equivalent thicknesses (MET) with those calculated with the BISAR software. The strains were calculated for a large number of 3-layer flexible pavement structures. A linear regression analysis has been performed to predict the values of strain (as well as life) calculated with BISAR from those obtained with the MET methodology and with a desired level of confidence. The analysis showed that, while subgrade strains were predicted acceptably well, differences greater than ±10% exist between the two methods in the case of the asphalt strains. An alternative model is therefore proposed to improve the MET methodology results for 3-layer pavement structures. The alternative model provides a simple and efficient method for practical purposes, for example in Pavement Management Systems or in simulation of pavement deterioration, where stresses and strains must be calculated large numbers of times.     

沥青路面结构参数对弯沉盆影响分析

利用多层弹性体程序BISAR,分析沥青路面结构层模量对弯沉盆影响。结果表明:面层模量的变化对中心点的弯沉影响最大;基层模量的变化对d0、d20、d30的影响最大;底基层模量主要的影响测点范围为0～120cm;d210与土基模量关系密切,而上层路面结构层模量和厚度对d210影响微小。同理,分析厚度对弯沉盆影响。结果表明:面层和基层厚度变化对d30影响最大。最后根据嘉浏高速公路FWD检测数据,验证了影响规律。     

沥青面层层间剪应力的影响因素分析

通过运用BISAR程序对影响路面面层的层间剪应力的因素进行分析,重点对比分析了荷载和面层厚度因素在不同层间接触条件下对层间剪应力的影响,分析结果表明：层间剪应力随着荷载的增大而逐渐增大,随着面层厚度的增加而逐渐减小。     

基层铺筑时施工车辆对石灰土底基层的力学影响分析

石灰土底基层的结构承载能力与养护时间密切相关.为探求基层施工期间,石灰土底基层在汽车轮作用下内部的力学行为、路面的损坏机理和类型,本文首先通过室内试验研究,获得了石灰土不同龄期的各种路用性能.然后利用Bisar3.0程序计算出龄期、施工车辆轴载、水平荷载等各种因素作用下,弯沉、层间剪应力和层底拉应力等力学指标变化规律,这对改善半刚性基层沥青路面早期破坏现象具有一定的借鉴作用.     

面层层间接触对沥青路面设计参数的影响

针对沥青面层层间污染导致面层层间粘结不良的问题,采用壳牌路面设计软件BISAR3.0,选择市政道路典型的两层式半刚性基层沥青路面结构,根据弹簧柔量接触模型,对比分析基、面层层间接触条件和面层层间接触条件对沥青路表弯沉和层底拉应力的影响,进而确定面层层间接触条件对半刚性基层沥青路面设计的重要性。结果表明,面层层间接触条件对路表弯沉和沥青层层底拉应力影响较小,对半刚性基层层底拉应力影响较大,在路面结构设计时有必要验算层间不连续状态下的半刚性基层层底拉应力,并采取有效措施保证面层层间粘结。     

An effective focusing approach for azimuth invariant bistatic SAR processing

This paper proposes a processing method to extend monostatic imaging algorithms for the azimuth invariant bistatic SAR (BISAR) data where the transmitter and the receiver move on parallel tracks with equal velocities. The bistatic range history is approached by a polynomial of the azimuth time. Based on this model, an analytic 2-D signal spectrum derived by the method of series reversion is utilized and a simple one-to-one mapping between the transmitter and the receiver closest ranges is established. In this way, efficient monostatic imaging algorithms which operate in the 2-D frequency domain or the range-Doppler domain are easily modified to handle the BISAR data. In this paper, a chirp scaling algorithm for the BISAR is developed as an application of the new method. By implementing two key operations, range cell migration correction by a chirp scaling, and azimuth compression by a curve fitting technique, this algorithm is able to process the azimuth invariant BISAR data. Simulation results are presented to demonstrate the validity and the efficiency of the proposed algorithm.     

基于不同导航信号的BISAR系统分辨性能分析

基于GNSS信号的双基合成孔径雷达(BISAR)成像系统具有多种突出的优势,已获得越来越多的关注。文中在广义模糊函数的基础上,针对导航卫星信号的伪随机码的特点,引入平均模糊函数的概念,以消除码元序列的伪随机性对系统模糊函数的影响。构建了适用于分析不同码元序列的平均广义模糊函数,对基于不同导航信号的BISAR系统的分辨性能进行了分析比较,并通过仿真进行验证。研究结果表明,导航卫星轨道对BISAR系统的分辨性能有较大影响,BDS导航信号拥有良好的分辨能力。     

双站SAR图像几何失真校正方法研究

针对双站合成孔径雷达(SAR)中由于发射机、接收机斜视角和速度的不同导致获取图像存在几何失真的问题,提出了一种基于坐标尺度变换的双站SAR图像几何失真校正方法．首先根据双站SAR的几何关系,详细分析了目标的斜距历程．采用等效相位中心原理,将双站SAR模型等效于单站SAR模型,结合RD成像算法,建立了几何失真校正的数学模型．最后通过该数学模型,对静止二维点阵目标的成像结果进行了几何失真校正,校正结果与地面设定的场景完全一致,从而验证了该校正方法的有效性和正确性．     

不同荷载与层间接触条件下沥青路面力学分析

利用BISAR 3.0程序,分析沪宁高速公路扩建工程的实体路面结构受力情况,得出不同荷载与层间接触条件下,路面结构拉应变、最大剪应力、竖向剪应力、拉应力的分布特征与变化规律,在此基础上,又分析了对路面使用性能的影响。结果表明：超载引起半刚性基层、沥青面层、底基层两个界面层间滑动,进而使整个路面结构受到破坏。