Zhiyi Huang

Investigations of the Montmorillonite and Aluminium Trihydrate Addition Effects on the Ignitability and Thermal Stability of Asphalt

By means of limiting oxygen index (LOI), cone calorimeter, and TG-DSC tests, this paper investigated the effect of unmodified montmorillonite (MMT), organically modified montmorillonite (OMMT), and aluminium trihydrate (ATH) additions on the flame retardancy for asphalt combustion. Experimental results showed that adding a small amount of montmorillonite did not significantly increase the oxygen index of the asphalt but reduced the heat release rate during asphalt combustion. TGA tests had indicated that the montmorillonite (MMT and OMMT) could suppress the release of flammable volatiles and form more asphaltenes, which hence postponed the burnout time of asphalt. Furthermore, the combination of montmorillonite (MMT and OMMT) and ATH had yielded a synergistic effect, which had further reduced the heat release rate and also increased the oxygen index of asphalt. In particular, after further addition of OMMT, the barrier layer showed less crack, leading to a significant decrease in the heat release rate as compared to the adding of ATH alone.

Theoretical Analysis of Longitudinal Ventilation System in a Road Tunnel for Predictive Control Based on Inertia Effect

Speed control of longitudinal ventilation systems in road tunnels is being combined with typical model predictive control (MPC) strategies which may bring huge energy saving potential to the system. Theoretical analysis of the inertia effect is presented based on the energy equation of one dimensional incompressible unsteady flow, step response model is chosen to describe the dynamic behaviors of the system. The results show that the effect of jet speed change on CO concentration is nonlinear within fan’s economical working range and the settling time of CO level has similar change trend with that of the flow field but is a little longer. The system settling time is longer when jet speed decreases than it increases and is related to the change extent of jet speed. The effect of traffic intensity on CO concentration can be regarded as linear disturbance to the system output. These results may provide useful indexes to control the tunnel ventilation system more economically and lay foundation for the application of predictive control strategy in the system.

Adaptive Critic Design Based Control of Tunnel Ventilation System with Variable Jet Speed

In this paper, an adaptive critic design (ACD) based control algorithm is proposed for road tunnel ventilation systems with jet fans. Firstly, a comprehensive dynamic model is established for control purpose, which considers both the static and dynamic nonlinearities between the pollutant concentration and the jet speed or the air flow inside the tunnel. Vehicle speed and density are also integrated into the model as system external disturbances. To cope with the time-varying model parameters and unknown system uncertainties, one artificial neural network (NN) unit is employed in controlling the jet fans to regulate the pollutant concentration to a desired level, even in the presence of varying working conditions. An additional NN is utilized to approximate the cost-to-go function required for the performance optimization. The proposed scheme is also verified and compared with traditional control design in simulation environment. The simulation results substantiate the conclusion that the adaptive controller can achieve a better regulation performance along with less energy consumption.

Application of Digital Image Processing Technique to Simulate the Macro-Mechanical Behavior of Asphalt Concrete

The digital image processing technique is implemented to build the geometrical model, and several factors such as the properties of asphalt mastic, the size and volume content of coarse aggregate, the size and ratio of air voids, and aggregate gradations are considered in the model. In the geometrical model, the aggregate are drawn as the equivalent ellipses in order to improve the efficiency of numerical calculation. The numerical method fast multipole boundary element method is employed to predict the elastic modulus of the asphalt concrete, and the test results are compared to verify the accuracy of the established geometrical model and numerical method.

Travel Behavior, Household in the Same Life Cycle Stage, and Built Environment

The study focuses on the hypothesis that lifecycle effects are suppressed by the built environment, and this can be examined using the repeated cross-sectional data collected over the last three decades. The fraction of automobile trips for each lifecycle stage in the different residence area over time is first reviewed using descriptive statistical analysis. The effects of lifecycle, residence area and year and their interaction effects are examined by using three-way ANOVA analysis. The results show that even within each lifecycle stage, change in the fraction of auto trips over time is suppressed in commercial and mixed commercial/residential areas. However, the fraction of auto trips for autonomous areas, suburbs and unurbanized areas increased over time in the range of 2 to 7 times depending on the lifecycle stage. Keywords: Lifecycle stage, Built environment, Travel behavior

Stability of Automobility across Lifecycle Stages over Time

This paper describes how automobility characteristics changed across lifecycle stages within different residential areas over time using statistical analyses. The results confirm that lifecycle is a useful classificatory variable in explaining automobility characteristics. Through analysis of four variances (including lifecycle stage, residential area, time, and age effects), the result suggests that residence area mainly determines the automobile ownership, but household members’ age is one of the main explainers for the fraction of auto trips and total auto travel time.