基于韧性理论的盾构隧道智能建造北大核心CSCD

以盾构隧道为主的城市轨道交通在"十三五"期间已取得了跨越式的进步,盾构掘进设备在智能化方面取得了飞速发展,但隧道结构设计、结构制造和现场管片拼装的智能化方面,仍需要大的创新与突破。面对建设韧性智慧城市的战略目标,盾构隧道还存在系列问题亟需解决,如对于新材料的物性认识浅、理论少;传感的布置缺乏针对性,监测感知差;隧道管片拼装大量依靠人工,误差大。解决这些问题的关键在于构建一个基于韧性理论的智能化盾构隧道建造系统,通过利用材料和结构的韧性特点,结合计算机等信息技术,采用韧性设计、智能感知、智能制造、智能拼装等一系列措施,使得隧道结构中的材料可智能感知、结构可精准监测、数据可实时孪生、信息可高效管理、制造可自动操控、过程可全域感知、模型可动态调节、管片可智能拼装,最终实现韧性城市的盾构隧道智能化建设。     

The role of parents’ mobility behavior for dynamics in car availability and commute mode use

Transportation - Recent studies have analyzed travel behavior over the life course through the lens of the mobility biography approach. Similarities in the effects of certain key events on travel...     

Analyzing the dispersion of cargo vapors around a ship’s superstructure by means of wind tunnel experiments

In a previous study, it was found that cargo tank operations like cleaning and venting, lead to higher cargo vapor concentrations around the ship’s superstructure. Can wind tunnel experiments confirm these findings? Is there an improvement when using higher outlets at high velocities compared to lower outlets with a low outlet velocity? Is there a relation between relative wind speed and measured concentration? These questions were investigated in the Peutz wind tunnel. By using a tracer gas for the wind tunnel experiments, concentration coefficients have been calculated for various settings. The study shows that using high-velocity outlets is an efficient way to keep concentrations as low as possible. The only exception is for relative wind directions from the bow. In this last case using a manhole as ventilation outlet leads to lower concentrations. With increasing wind speeds the building downwash effect resulted in higher concentration coefficients near the main deck. This study confirms our on-board measurements and suggests the lowering of the ventilation inlet of the accommodation, so that the high-velocity outlet can be used safely at all times.     

Adaptive data dissemination for time-constrained messages in dynamic vehicular networks

With the advent of emerging wireless communication technologies, tremendous efforts have been put on promoting the safety and efficiency of transportation services by developing innovative applications. In particular, there has been significant interest in accessing information stored at RSUs (Roadside Units). The unique characteristics in vehicular networks, such as dynamic traffic factors including vehicle arrival rate, dwell time and data access patterns, bring us new challenges on data dissemination. This work dedicates to the investigation of timely and adaptive data dissemination in the dynamically changing traffic environment. Firstly, we derive an analytical model to explore and examine the effects of the dynamic traffic factors. In light of the theoretical results, an on-line scheduling algorithm is proposed for adaptive data dissemination. Finally, we evaluate performance of the new algorithm in a variety of circumstances. The simulation results demonstrate satisfactory performance of the proposed algorithm.     

Reliable route guidance: A case study from Chicago

Reliable route guidance can be obtained by solving the reliable a priori shortest path problem, which finds paths that maximize the probability of arriving on time. The goal of this paper is to demonstrate the benefits and applicability of such route guidance using a case study. An adaptive discretization scheme is first proposed to improve the efficiency in computing convolution, a time-consuming step used in the reliable routing algorithm to obtain path travel time distributions. Methods to construct link travel time distributions from real data in the case study are then discussed. Particularly, the travel time distributions on arterial streets are estimated from linear regression models calibrated from expressway data. Numerical experiments demonstrate that optimal paths are substantially affected by the reliability requirement in rush hours, and that reliable route guidance could generate up to 5-15% of travel time savings. The study also verifies that existing algorithms can solve large-scale problems within a reasonable amount of time.     

Identification and quantification of link vulnerability in multi-level public transport networks: a passenger perspective

Robust public transport networks are important, since disruptions decrease the public transport accessibility of areas. Despite this importance, the full passenger impacts of public transport network vulnerability have not yet been considered in science and practice. We have developed a methodology to identify the most vulnerable links in the total, multi-level public transport network and to quantify the societal costs of link vulnerability for these identified links. Contrary to traditional single-level network approaches, we consider the integrated, total multi-level PT network in the identification and quantification of link vulnerability, including PT services on other network levels which remain available once a disturbance occurs. We also incorporate both exposure to large, non-recurrent disturbances and the impacts of these disturbances explicitly when identifying and quantifying link vulnerability. This results in complete and realistic insights into the negative accessibility impacts of disturbances. Our methodology is applied to a case study in the Netherlands, using a dataset containing 2.5 years of disturbance information. Our results show that especially crowded links of the light rail/metro network are vulnerable, due to the combination of relatively high disruption exposure and relatively high passenger flows. The proposed methodology allows quantification of robustness benefits of measures, in addition to the costs of these measures. Showing the value of robustness, our work can support and rationalize the decision-making process of public transport operators and authorities regarding the implementation of robustness measures.     

热管--一种高效实用的散热方法

任何电子器件冷却的热电路都是由3个最基本的热阻组成的:结-壳热阻Rj-c;壳-散热器热阻Rc-s和散热器至周围介质的热阻Rs-a.为降低这些热阻的临界值,许多工程师费尽心血.文章讨论采用热管有助于降低热阻Rs-a至最小值.散热器至周围介质的热阻是由传导、对流/辐射和被加热的冷却介质形成的3个热阻组成的.典型的风冷散热器中,空气温升的热阻是通风量的直接函数,对流热阻是散热表面积的函数,传导热阻是散热器材料的热导率和几何尺寸的函数.热管能把传导损耗降至最小值,它允许加大散热表面,而且使给定风速下的流量最大,从而有效降低散热器的3个主热阻.文章讨论了能降低风冷散热器热阻的热管.     

On Control Laws for Vehicle Suspensions Accounting for Input Correlations

Input correlations involving time delays are common in active vehicle suspension system problems. One approach to control law derivation fur such systems is to restrict attention to slate feedback laws in the interests of practicality and it is then of interest to determine the law which is, in some sense, the best. Under assumptions which are common in this area. relating to input, system and cost Function forms, a new derivation of the expression for the cost, accounting for time delays, is given. The use of the expression in numerical procedures for determining effective control gains is discussed and an example for a half car planar vehicle model is described. By comparing results with existing ones which are truly optimal, an estimate is made of the loss of performance which results from the restriction of the control law form in this case. Some generalisation of the results is attempted and they are placed in a contemporary context at the conclusion.     

Design analysis and comparison between standard and rotary porting systems for IC engine

Many porting systems for internal combustion engines have been tried and tested over the years, however the basic spring actuated poppet valve system has prevailed over the last century. In the goal to lower engine output parasitic losses, a simple rotary valve porting system design is proposed and analyzed. The proposed design concept takes into consideration and combines all the prominent advantages of many ealier mutlitiple design variations over the past century. The inherent primary advantage of such a rotary porting system is the elimination of reciprocating components, thus lowering vibration, and removal of highly stiff springs which contribute to considerable system power loss. Comparable sized 3-D representations of both systems are constructed in CAD (Computer Aided Design) software in order to run mechanical and fluid simulations to validate the efficiency advantage of a rotary valve porting system. Using Pro/Engineer Mechanism Dynamics module, the minimum torque required to actuate both systems at 2000 rpm and 3000 rpm is determined. Fluid simulations are performed using a commercial software CFDesign V10. Volumetric flow rates are compared during the intake stroke as well as turbulence intensity factors which characterizes a systems ability to properly mix the Air/Fuel mixture and the combustion efficiency. Some possible improvement on the rotary geometry is suggested.     

Numerical investigation on the dynamic characteristics of an automotive A/C hose

The objective of this study is to investigate the dynamic deformation characteristics of an automotive A/C hose assembly using the finite element method and experimentation. The finite element analysis consisted of two analyses, specifically, a modal and a transient analysis. The dynamic modal analysis was conducted to assess the dynamic characteristics of the A/C hose structure, and the dynamic transient analysis was performed to investigate the dynamic stresses of an automotive A/C hose by dynamic loading with particular emphasis on the reinforced braid. Furthermore, the analyses results are expected to provide useful reference data in the design optimization of the hose layout related to the constrained design space. Modal testing was undertaken to verify the FE model. The FE result was in good agreement with the experimental results. The modal analysis result showed that the bending and swing modes of the hose occurred in the first six natural frequencies. The dynamic transient result showed that the maximum stress in the hose components occurred in the reinforced braid layers, which are particularly damage-prone.