Development of the composite bumper beam for passenger cars

The fuel efficiency and emission gas regulation of passenger cars are two important issues in these days. The best way to increase the fuel efficiency without sacrificing safety is to employ fibre reinforced composite materials in the body of cars.

In this work, a new composite bumper that has two pads at the ends of the bumper was developed. The two pads were designed to hit the front two tyres of the car when the bumper brackets collapsed during collision. The end of the bumper beam was designed to have a tapered section to absorb energy by progressive buckling when the pads hit the rims of wheels after collapsing tyres.

The composite bumper beam was made of glass fibre fabric epoxy composite material except the elbow section. The elbow section was made of carbon fibre epoxy composite material to increase bending stiffness. From the static bending test of the prototype composite bumper, it was found that the weight of the composite bumper beam was only 30% that of the steel bumper beam without sacrificing the static bending strength.     

高速铁路客车振动特性时频分析

对于高速铁路车辆的振动试验,为克服传统傅里叶分析方法不具备时域信息的不足,引入分析非平稳数据的时频分析方法。针对轴箱和车体的垂向振动信号数据,分别采用传统的快速傅里叶变换(FFT)、短时傅里叶变换(STFT)、小波变换(WT)和希尔伯特黄变换(HHT)进行数据分析处理,并对比各种分析方法的优缺点。对比发现,HHT方法是应用于车辆振动信号处理中的最佳时频分析方法。     

Design and performance of a multiwavelength airborne polarimetric lidar for vegetation remote sensing

The University of Nebraska has developed a multiwavelength airborne polarimetric lidar (MAPL) system to support its Airborne Remote Sensing Program for vegetation remote sensing. The MAPL design and instrumentation are described in detail. Characteristics of the MAPL system include lidar waveform capture and polarimetric measurement capabilities, which provide enhanced opportunities for vegetation remote sensing compared with current sensors. Field tests were conducted to calibrate the range measurement. Polarimetric calibration of the system is also discussed. Backscattered polarimetric returns, as well as the cross-polarization ratios, were obtained from a small forested area to validate the system's ability for vegetation canopy detection. The system has been packaged to fly abroad a Piper Saratoga aircraft for airborne vegetation remote sensing applications.     

Pollutant emissions from passenger cars in traffic congestion situation in the State of Kuwait: options and challenges

Rapid population growth in Kuwait, accompanied with rising standard of living, has resulted in a sweeping increase in the use of passenger vehicles for transportation. Consequently, deterioration of ambient air quality near major roadways has become an issue of public concern. The knowledge of real world road vehicle emission factors is an essential element to the development of any strategy aimed at the reduction of air pollution in urban areas. This work focuses on investigating exhaust emission pollutants from passenger cars for idle and slow acceleration (stop-and-go) traffic conditions. We found that vehicle emissions are minimal during idle mode for all vehicle categories. However, it was interesting to observe that during the slow acceleration mode HC and CO emissions increased for light vehicles with relatively high mileage (higher than 40,000?km). We can conclude from this study that with the growing vehicle ownership, and congestion it causes, the vehicular exhaust emissions is a major sources of air pollution in densely populated centers in the state of Kuwait, where idle and stop-and-go driving cycle is a common occurrence.     

Two-dimensional pulse-to-pulse canceller of ground clutter in airborne radar

It is well known that in the airborne radar, the location of the ground clutter spectrum in the angle- Doppler space is dependent mainly on the platform velocity and radar parameters. The authors propose a two-dimensional pulse-to-pulse canceller (TDPC) that can make full use of such prior information. The more detailed formulations of the ground clutter model and the signal model are given in a matrix?vector form. The least-squares-typical cost function associated with the filter coefficient matrix of the TDPC is established on the basis of the ground clutter model and the signal model. Like the classical displaced phase centre antenna (DPCA) processing, the proposed TDPC is also a spatial-temporal suppressor of ground clutter and can decrease the ground clutter signals, even though the DPCA condition is not satisfied. The proposed TDPC can also be used as an efficient pre-filtering tool before the conventional moving target indication (MTI) processing and the classical adaptive processing. Moreover, if only the TDPC plus the conventional MTI is used, it takes less computational time than the adaptive canceller. Experimental results show that the proposed TDPC has the satisfactory ground clutter suppression capability by using both simulated data and measured data.     

A population based estimation of the driver protection provided by passenger cars: France 1996–2005

The technology used in cars to protect occupants is constantly developing. Demonstrating the beneficial effects in the field is complex as the most recent vehicles are generally used by drivers who differ from other drivers and who drive in different traffic conditions. This paper presents an overall estimation of the consequences of changes in the secondary safety of cars, taking account of most of these factors.The data come from information collected about injury road traffic crashes by the police in France between 1996 and 2005. The risk of the driver being killed has been evaluated for the 144,034 drivers involved in two-car crashes and for the 63,621 drivers involved in single-car crashes.The study shows that when a recent car is in collision with an older car the driver of the former is better protected than the driver of the latter. These improvements in secondary safety are not observed in the case of single-car crashes, very probably because of higher impact speeds. Our findings also confirm the need for protection systems to be better adapted to the specific characteristics of users and for an improvement in the crash compatibility of vehicles, in particular to overcome the consequences of differences between the masses of vehicles.     

Factors associated with the likelihood of injury resulting from collisions between four-wheel drive vehicles and passenger cars

The specific effects of vehicular type on the likelihood of an injury occurring are relatively unexplored. This study sought to assess the relative risk of injury to occupants of four-wheel drive vehicles and their counterparts in passenger cars.Data for 1143 occupants from all of the 454 crashes in Oklahoma, in 1995 that involved a four-wheel drive vehicle were used. Multiple logistic regression analysis determined the association between potential predictive factors and vehicular injury. Odds ratios revealed occupancy in a passenger car to be a major predictor of the likelihood of injury. Other factors include the driver being female, driving too fast, travel on curved or level roadways, and being hit laterally or from the rear.     

用SIR-C航天飞机双频极化干涉雷达估计植被高度的方法研究

基于重复轨道航天飞机SIR—C的L和C波段极化干涉雷达数据,提出了一种将三阶段反演方法(Three—Stage Inversion)和ESPRIT(Estimation of Signal Parameters via Rotational Invariance Techniques)算法相结合的新的相位基植被高度估计方法。首先,基于L波段极化干涉数据,用三阶段反演方法获取植被覆盖地表下地形有效散射中心的相位;接着,基于c波段极化干涉数据,用ESPRIT算法估计植被冠层有效散射中心的相位;最后,对二者的相位差进行相位到高度的转换得到植被的高度。根据研究区域的实测林相数据,对该算法估计的植被高度结果进行了比较和验证,结果表明：该方法具有足够高的植被高度估计精度,如果能得到P和X波段的双频极化干涉雷达数据,该方法估计植被高度的精度将会得到进一步的提高。     

Factors contributing to the amount of vehicular damage resulting from collisions between four-wheel drive vehicles and passenger cars

This study examines the vehicular damage resulting from motor vehicle crashes involving four-wheel drive vehicles and passenger cars in the state of Oklahoma. In particular, the focus of the analysis is on differences in vehicular damage to passenger cars and four-wheel drive vehicles. Results indicate that passenger cars sustain significantly greater vehicular damage than four-wheel drive vehicles. In addition, several other factors significantly influence the level of damage resulting from collisions between four-wheel drive vehicles and passenger cars. Driver behavior or unsafe acts, represented by the rate of travel prior to the collision, failure to yield, failure to obey a stoplight or a stop sign, the consumption of alcohol and the use of drugs, also contributed to the amount of vehicular damage. In addition, results also indicate that the level of damage was influenced significantly by environmental factors, represented by a reduced intensity of light, wet or slippery roadways and the type of collision. The findings reinforce the importance of a number of policy initiatives that may reduce the vehicular damage resulting from collisions involving four-wheel drive vehicles and passenger cars. For example, the study indicates a need to initiate legislation that lowers the speed limit during dark and twilight hours, commits additional resources to road maintenance to reduce unsafe road conditions, and stimulates improvements in automotive design that provide better lateral protection to vehicles.     

机载合成孔径雷达的宽带线性调频源设计

采用“DDS 正交调制 倍频”的结构方式,设计研制出带宽500MHz,时宽15μs的线性调频信号源。该设计在DDS信号产生部分运用外部时钟倍乘方式和防止时钟泄漏等措施,获得了更好的杂散与噪声特性;正交调制部分采用误差调整与补偿电路,不仅稳定了直流偏置,而且还对信号进行了调理,从而有效控制了I,Q通道的幅相不一致性。通过实测,该宽带线性调频信号源的无杂散动态范围(SFDR)优于100dB,杂散抑制小于-60dBc,且在带宽内最大幅度起伏为±0.5dB,相位起伏为5°,很好地满足了机载合成孔径雷达系统的要求。     

Error analysis of high-precision DEM generated from airborne dual-antenna interferometric SAR data

结合机载双天线干涉合成孔径雷达(InSAR)正侧视成像模型,分析了机载双天线InSAR数据处理中存在的影响数字高程模型(DEM)高程精度和点位精度的主要因素,包括平台高度、斜距、干涉相位、基线长度、基线倾角、中心多普勒频率以及载机姿态,着重分析了平台高度、基线长度、基线倾角以及侧视角等因素的变化与DEM误差之间的关系.选用机载双天线InSAR数据进行了干涉实验,并对生成的DEM进行了误差分析,实验分析结果和误差定量分析的结果相一致.对机载双天线InSAR数据处理进行误差分析有利于提高DEM的高程和点位精度,也有利于机载双天线InSAR系统设计及飞行试验设计,因而具有重要实用意义.     

Experimental research of unsupervised Cameron/maximum-likelihood classification method for fully polarimetric synthetic aperture radar data

In this study, experimental research on classification is applied to fully polarimetric data in X-band from China. Considering the amplitude and phase error between H and V channels in the system, the authors firstly correct the error in original data. The authors also deduce the formula of Cameron?s classification method for the real data in our study. Then Cameron?s method is used to initially classify the site image. Finally, the initial classification map defines training sets for the maximum-likelihood (ML) classifier. The advantages of this method are the automated classification and interpretation of each class based on the scattering mechanism. The experiment demonstrates the feasibility of the proposed approach, which dramatically improves the X-band data classification result compared with the Cameron method and H/α/ML method.     

Degrading effects of the lower atmosphere on long-range airborne synthetic aperture radar imaging

The imaging performance of airborne synthetic aperture radar (SAR) systems has advanced to the point that the effects of clear-air refractive index perturbations cannot be ignored. Operating at long ranges, and low grazing angles, in particular, require propagation geometries through regions of the lower atmosphere that may cause noticeable and, sometimes, severe degradation of the images. The range of image anomalies that can be attributed to the atmospheric boundary layer (ABL) is illustrated, the pertinent characteristics of the ABL is discussed, a first-order SAR imaging model that incorporates the refractive index perturbations associated with the ABL is developed and the magnitude of the image anomalies resulting from measured refractive index perturbations is estimated. The model predictions correlate well with the observed image anomalies and measured properties of the ABL. On the basis of theory and measurements, it is expected that the degrading effect of clear-air atmospheric refractive index perturbations is much more common than previously thought and may be a limiting factor for long-range SAR imaging performance.     

Measurement of ultralow supermirror birefringence by use of the polarimetric differential cavity ringdown technique

We demonstrate a novel technique for measuring ultralow linear birefringence of supermirrors (high-reflectivity dielectric mirror coatings). The polarimetric cavity ringdown technique is used in conjunction with the differential detection scheme with circular polarization to enhance the measurement sensitivity. The technique could, in principle, provide the convenience and reliability of linear detection signals and a reasonable tolerance to experimental imperfections. Phase retardation and orientation of each cavity mirror can be determined separately without the influence of the other mirror. The minimum detectable phase retardation achieved experimentally with this technique is ~6 x 10(-8) rad.     

基于点目标自动提取的机载SAR图像残余运动估计方法

对前期提出的估计单幅机载合成孔径雷达(SAR)图像中的残余运动误差的点目标多斜视方法(MTPT)进行了理论分析,并针对其存在的手工选点工作量大、受噪声影响严重的缺点,对其做了以下改进:在图像中自动选择点目标以减少工作量,并对所测得的相位进行滤波和加权平均以去除噪声,同时采用循环计算的策略来提高算法的适应性.实际的机载S...     

基于遗传算法与粒子群优化法的机载合成孔径雷达天线赋形波束综合

采用了遗传算法和粒子群优化法两种现代进化算法对赋形波束天线进行了综合,得到了很好的结果,并比较了两种算法的优缺点.首先通过对宽测绘带的机载合成孔径雷达距离向回波特性的分析,给出了天线距离向赋形辐射方向图表达式.接着利用两种现代优化算法结合谢昆若夫法对天线阵分别进行综合,得到了近似相等的天线各单元激励幅度和相位.然后选择5个单元激励并利用微带贴片天线阵列实现了赋形波束方向图,实验结果和理论优化结果基本吻合,从而证明了这两种现代进化算法对赋形天线方向图综合方法的有效性.     

Measurement of the modal birefringence of single-mode K(+) ion-exchanged planar waveguides with polarimetric interferometry

The polarimetric interference pattern on the surface of single-mode planar waveguides made by potassium ion exchange in soda-lime glass substrates can be observed through a 45 degrees analyzer, which allows for the high-precision measurement of the modal birefringence of samples in a wide range of 0 to 5 x 10(-4). Using this method, believed to be new, we investigated the effects of exchange temperature and time on the modal birefringence of single-mode potassium ion-exchanged waveguides. The modal birefringence profile was achieved by measurement of the variation of the phase difference between the TE(0) and the TM(0) modes with hydrofluoric-acid-etching depth of the sample.     

机载InSAR敏感度方程定标限制条件的仿真实验

通过对机载干涉合成孔径雷达(InSAR)常用的干涉参数定标方法——基于敏感度方程的干涉定标的仿真实验,分别在逐步增多需要定标的干涉参数个数和增大干涉参数偏差量的情况下,深入研究了这种定标方法对参与定标的干涉参数数目及干涉参数偏差边界值等的限制条件,结果表明,该方法在多干涉参数和大偏差条件下可以实现有效校准。     

机载激光雷达和高光谱组合系统的亚热带森林估测遥感试验

为了提高森林的类型识别及生物物理参数反演精度,采用国产机载激光雷达和高光谱组合系统(ALHIS),选择湖北典型亚热带森林开展了航空遥感试验,获取了试验区激光雷达点云、高光谱和CCD影像数据,提取了森林高度和优势树种类别信息。对数据的分析表明,激光雷达林分平均高的估测精度达到90.67%,激光雷达估测平均高与地面实测胸径加权平均高之间显著相关(R2=0.73,RMSE=1.29m)。按照优势树种分类结果进行统计,发现马尾松、栓皮栎和其它树种的林分平均高分别为9.62m、9.30m、8.79m,不同树种之间的林分平均高相差不大。高光谱优势树种识别总体精度达到82.00%(Kappa=0.70),试验区森林和非森林面积所占比例分别为60.01%和39.99%,马尾松、栓皮栎和其它树种面积在森林中所占比例分别为59.77%、24.99%和15.23%。试验证明,ALHIS能够同时获取高分辨率的植被遥感特征数据,以用于森林制图、优势树种/树种组识别、碳储量估算及生态环境建模等研究。