Quantification of surrogate safety measure to predict severity of road crashes at median openings

Traffic safety assessment is an integral part of transportation engineering. In a developing country like India, it is observed that in every four second, one person gets injured in road crashes. Moreover, at median openings which are usually uncontrolled in India, the severity of road crashes increase many fold. This is due to the fact that neither lane discipline nor priority rule is followed at the median openings. Conventionally, road crash data reports were used to study and analyze traffic safety. However, the drawback of this traditional method is that a lot of accidents need to be recorded for analysis and to draw any conclusions and take necessary corrective measures. In developing countries like India, available accident data are based on reports submitted by the police department of respective state governments. The accuracy of these accident data details is highly questionable. Therefore, in the recent times surrogate traffic safety measures are being used to analyze traffic safety. Various surrogate traffic measures like Deceleration Time (DT), Time to Collision (TTC), Post Encroachment Time (PET), etc. are being used to examine road safety. These values are based on the temporal and spatial proximity between road-users during possible conflict situation. Among all the traffic safety measures, PET is regarded as the most reliable and most commonly used indicator. Therefore, in this study, PET across different traffic volume levels at median opening area is calculated. A critical safe ratio has been introduced to better analyze the traffic safety at median opening based on minimum stopping sight distance (SSD) as per IRC: 66–1976 and speed to PET ratio. Finally clustering technique has been used to define various severity indices for probable road crashes at median opening area. For this study, data has been collected from different median openings located on six-lane divided urban roads.     

运营盾构隧道结构安全评估方法研究

随着隧道运营时间的增加,隧道的结构安全问题日益突出,合理评价运营盾构隧道结构安全对保障隧道安全运营和科学养护具有重要意义。针对这一问题,根据隧道结构特点确定盾构隧道结构安全评价指标,通过理论分析确定评价指标的分级标准;确立运营盾构隧道结构安全评价指标体系;以模糊综合评价法、层次分析法为基础,综合考虑指标之间相关性和不可逆特性,建立修正的模糊综合评价法;利用该方法并结合现场检测数据,对实际隧道结构安全进行评价。修正后的模糊综合评价法,不仅能体现单一因素指标对评价结果影响的敏感性而且使综合评价结果更合理,能更科学地指导盾构隧道结构养护工作。     

Hydrodynamics study of a BCF mode bioinspired robotic-fish underwater vehicle using Lighthill’s slender body model

This paper investigates the hydrodynamic characteristics of the rectilinear motion of a robotic fish underwater vehicle. This 2-joint, 3-link multibody vehicle model is biologically inspired by a body caudal fin carangiform fish propulsion mechanism. Navier–Stokes equations are used to compute the unsteady flow fields generated due to the interaction between the vehicle and the surrounding incompressible and Newtonian fluid (water) environment. The NACA 0014 airfoil aerodynamic profile has been designed to boost the swimming efficiency by reducing drag as the vehicle undergoes an undulatory/oscillatory motion. Using the Lighthill slender body model, a traveling wave mathematical function is defined to undulate the robotic fish posterior (caudal) region while the motion tracking is carried out by dynamic meshing technique. The results obtained show that though the net lift force approaches to zero, the net thrust or negative drag coefficient maintains a finite value dependent on kinematic parameters like tail beat frequency (TBF) and amplitude span (AS) at a given propulsive wavelength and the forward velocity of the vehicle. The results reveal the effects of TBF and AS on the coefficient of drag friction and the thrust force. Drag coefficients obtained from the simulations are compared and validated with the experimental results. The hydrodynamic results are found to be similar to the kinematic study results and suggest that TBF and AS play the most effective roles in the bioinspired propulsion technique. Relation of these parameters with propelling thrust force and forward velocity is also in conjunction over a given range of TBF and AS values.     

冰盖下两层流体水波与可渗透起伏海床的作用(英文)

The scattering problem involving water waves by small undulation on the porous ocean-bed in a two-layer fluid,is investigated within the framework of the two-dimensional linear water wave theory where the upper layer is covered by a thin uniform sheet of ice modeled as a thin elastic plate.In such a two-layer fluid there exist waves with two different modes,one with a lower wave number propagate along the ice-cover whilst those with a higher wave number propagate along the interface.An incident wave of a particular wave number gets reflected and transmitted over the bottom undulation into waves of both modes.Perturbation analysis in conjunction with the Fourier transform technique is used to derive the first-order corrections of reflection and transmission coefficients for both the modes due to incident waves of two different modes.One special type of bottom topography is considered as an example to evaluate the related coefficients in detail.These coefficients are depicted in graphical forms to demonstrate the transformation of wave energy between the two modes and also to illustrate the effects of the ice sheet and the porosity of the undulating bed.