Control of a LDPE reactive extrusion process

A constrained model predictive control strategy is implemented to control the weight-average molecular weight and the high molecular weight end of the molecular weight distribution of a low-density polyethylene (LDPE) in a reactive extrusion process. To achieve simultaneous regulation of these properties, the amplitude and width of square wave-shaped pulses of a peroxide solution injected to the extruder are independently manipulated. The two polymer properties are inferred on-line from consistency and power-law index measurements obtained with an in-line wedge rheometer. Simulations and experimental results show that independent control of the polymer properties is feasible by this method, but only in a narrow range of operating conditions.     

How to make today’s repairs durable for tomorrow — corrosion protection in concrete repair

The future of the concrete repair industry appears to be promising and bright, judging from the projections based on current trends in repair, rehabilitation, restoration and strengthening of existing infrastructure. However, this optimism must be tempered in light of the need to change the image of the industry as one that is often self-serving — the industry that is repairing the repairs. Due to the increasing public concern with durability of concrete structures in general, and repaired concrete structures in particular, the subject of steel corrosion and corrosion protection in repaired concrete structures is discussed with reference to the deficiencies in our knowledge of corrosion and corrosion protection in concrete repair, methods of testing, and in the science of repair durability.     

Cooperative vehicle path generation during merging using model predictive control with real-time optimization

This paper proposed a cooperative merging path generation method for vehicles to merge smoothly on the motorway using a Model Predictive Control (MPC) scheme which optimizes the motions of the relevant vehicles simultaneously. The cooperative merging is a merging in where the most relevant vehicle in the main lane would accelerate or decelerate slightly to let the merging vehicle merge in easily. The proposed path generation algorithm can generate the merging path ensuring the merging vehicle can access the whole acceleration area, and do not exceed it. We have introduced a state variable to the optimization problem by which the merging point for the merging vehicle is optimized. The simulation results showed that the cooperative merging path can be successfully generated under some typical traffic situations without re-adjustment of the optimization parameters.     

Synthesising carbon emission for mega-cities: A static spatial microsimulation of transport CO2 from urban travel in Beijing

Developing low carbon cities is a key goal of 21st century planning, and one that can be supported by a better understanding of the factors that shape travel behaviour, and resulting carbon emissions. Understanding travel based carbon emissions in mega-cities is vital, but city size and often a lack of required data, limits the ability to apply linked land use, transport and tactical transport models to investigate the impact of policy and planning interventions on travel and emissions. Here, we adopt an alternative approach, through the development of a static spatial microsimulation of people’s daily travel behaviour. Using Beijing as a case study, we first derive complete activity-travel records for 1026 residents from an activity diary survey. Then, using the 2000 population census data at the sub-district level, we apply a simulated annealing algorithm to create a synthetic population at fine spatial scale for Beijing and spatially simulate the population’s daily travel, including trip distance and mode choice at the sub-district scale. Finally, we estimate transport CO₂ emission from daily urban travel at the disaggregate level in urban Beijing.     

A case history of shield tunnel crossing through group pile foundation of a road bridge with pile underpinning technologies in Shanghai

According to the planning of Shanghai metro line 10, the interval tunnel from Liyang Road station to Quyang Road station has to cross through the group pile foundation of Shajinggang Bridge on Siping Road. Therefore, how to guarantee the normal traffic function and the safety of bridge structure during the tunneling process becomes a challenge to engineers and technicians. To solve this problem, the pile underpinning technology was recommended for this project. This specific scheme mainly comprises following steps, i.e. ground improvement behind abutment, foundation pit excavation under bridge deck, underpinning pile with raft and cutting pile with shield machine directly, etc. In order to verify the feasibility of this scheme, a series of theoretical analysis and numerical simulation were carried out on the entire construction process to explore the load transfer mechanism of bridge structure. The calculation results show that both the bridge static loads and traffic live loads can be successfully transferred from pile foundation to raft after pile underpinning, and the removal of obstructed piles during tunneling has very limited influence on bridge structure. Furthermore, real-time field monitoring activities, including settlement of bridge deck surface, deformation of surrounding buildings and pipelines, etc. were also conducted to ensure smooth construction. The monitored results agree well with the numerical calculation ones, which prove again that the proposed scheme is reasonable and the calculation results are reliable.     

Multi-level Bayesian safety analysis with unprocessed Automatic Vehicle Identification data for an urban expressway

In traffic safety studies, crash frequency modeling of total crashes is the cornerstone before proceeding to more detailed safety evaluation. The relationship between crash occurrence and factors such as traffic flow and roadway geometric characteristics has been extensively explored for a better understanding of crash mechanisms. In this study, a multi-level Bayesian framework has been developed in an effort to identify the crash contributing factors on an urban expressway in the Central Florida area. Two types of traffic data from the Automatic Vehicle Identification system, which are the processed data capped at speed limit and the unprocessed data retaining the original speed were incorporated in the analysis along with road geometric information. The model framework was proposed to account for the hierarchical data structure and the heterogeneity among the traffic and roadway geometric data. Multi-level and random parameters models were constructed and compared with the Negative Binomial model under the Bayesian inference framework. Results showed that the unprocessed traffic data was superior. Both multi-level models and random parameters models outperformed the Negative Binomial model and the models with random parameters achieved the best model fitting. The contributing factors identified imply that on the urban expressway lower speed and higher speed variation could significantly increase the crash likelihood. Other geometric factors were significant including auxiliary lanes and horizontal curvature.     

砂性土层泥水盾构泥浆成膜性能试验

泥水盾构在高渗透性砂性土层施工中泥浆的成膜质量会影响工程的安全与进度,设计室内试验研究泥浆相对密度对滤水量的影响,采用均匀设计法对不同制浆材料在砂性土层中的填充效果进行实测与回归分析。结果表明,泥浆的相对密度反应了单位体积内所能提供的用于孔隙填充的颗粒数量,是影响滤水量以及填充致密程度的首要因素;泥膜的形成质量受到制浆材料的影响,在中粗砂地层中,孔隙可以由膨润土和黏土颗粒共同填充,而对砾砂地层中孔隙较大的区域,黏土的填充效果已不再显著,主要依靠膨润土水化后形成的胶结颗粒集合进行填充;中、粗砂与含砾中、粗砂地层中宜采用的泥浆相对密度为1.20~1.25,制浆材料宜选取膨润土、黏土共同配制的新浆与原浆混合浆液。结合南京地铁某越江隧道,实际施工过程中泥浆相对密度控制在1.20~1.25,且每制备1 m3新浆,膨润土加入量为3~5 kg,施工反馈表明对应的掘进区间出浆相对密度稳定,研究成果可为现场泥浆的配置与管理提供一定参考。     

异形基坑支撑体系刚度及受力分析

基坑工程中内支撑系统的平面布置形式众多,在通常情况下,对于长条形地铁基坑工程中,通常采用十字正交对撑的内支撑体系,其内支撑刚度的取值可以用公式K=2EA/SL计算.对于复杂的桁架杆系结构的水平支撑系统,不能简单地采用上式来确定内支撑的刚度,但较合理地确定其桁架支撑体系刚度一直以来也是基坑工程中的一个难题.本文以上海自然...     

Refined-scale panel data crash rate analysis using random-effects tobit model

Random effects tobit models are developed in predicting hourly crash rates with refined-scale panel data structure in both temporal and spatial domains. The proposed models address left-censoring effects of crash rates data while accounting for unobserved heterogeneity across groups and serial correlations within group in the meantime. The utilization of panel data in both refined temporal and spatial scales (hourly record and 1-mile roadway segments on average) exhibits strong potential on capturing the nature of time-varying and spatially varying contributing variables that is usually ignored in traditional aggregated traffic accident modeling. 1-year accident data and detailed traffic, environment, road geometry and surface condition data from a segment of I-25 in Colorado are adopted to demonstrate the proposed methodology. To better understand significantly different characteristics of crashes, two separate models, one for daytime and another for nighttime, have been developed. The results show major difference in contributing factors towards crash rate between daytime and nighttime models, implying considerable needs to investigate daytime and nighttime crashes separately using refined-scale data. After the models are developed, a comprehensive review of various contributing factors is made, followed by discussions on some interesting findings.