Browsing by Author "Fwa, Tien Fang"

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item: Conference-Full-text
Incorporating functional performance in mixture design of porous pavement
Zhang, Lei; Ong, Ghim Ping; Fwa, Tien Fang
Skid resistance and tire/road noise are critical functional elements of a modern pavement system and can affect roadway safety and environmental comfort. Although porous surface layer serves mainly as a functional course in most applications, the considerations on skid resistance and acoustic absorption in porous mixture design is inadequate in the existing specifications. Most current mixture design procedures assume that functional performances are adequate if volumetric and composition requirements are satisfied. However, the gap between design indices and in-situ performance should be bridged through thorough understanding of the mechanisms and relationships between them. This paper proposes an analytical framework to integrate skid resistance and tire/road noise performances into porous mixture design, based on numerical prediction models previously developed and validated by the authors. The framework takes account of the long-term effect, seasonal variation and temperature influence on skid number and sound pressure level. A functional performance index (FPI) is computed as the final output of the framework, denoting the quality of a porous mixture design with respect to its functional performance. A case study is then discussed to demonstrate the feasibility and capability of the proposed framework. With adequate knowledge on mixture properties and appropriate estimation on empirical parameters, this framework can help improve the quality of porous mixture design and enhance performance of the finished pavement.
item: Conference-Full-text
Modeling nonlinear suspension system for improved braking distance estimation
Yang, Jia Sheng; Fwa, Tien Fang; Ong, Ghim Ping
Braking distance of a vehicle is an important safety consideration in highway geometric design. Braking distances have been commonly estimated based on vehicle wheel loads and assumed tirepavement friction. The use of classic vehicle dynamics simulation model, which simplifies tire stiffness as linear elastic function, is a main approach to estimate tire-pavement friction and predict braking distances. The interaction of nonlinear vehicle dynamics with pavement surface roughness has not been considered in analyzing its impact on vehicle braking distance. The impact of pavement roughness induced vehicle vibration on braking distance is the topic of interest in this paper. A nonlinear vehicle dynamics simulation model is proposed where tire stiffness is considered as a nonlinear elastic function in the analysis of vehicle dynamics. The model is implemented in MATLAB 11.0. A hypothetical example is given to illustrate the possible difference between models with linear and nonlinear tire stiffness in calculating braking distance on a wet pavement. Although the model presented is rather simplified considering only nonlinear tire stiffness, and a more elaborate simulation model is required to examine in detail the actual impact of considering nonlinear vehicle dynamics, the example does show that further study is necessary to examine the need for vehicle dynamics simulation in order to reliably predict vehicle braking distances on highways, taking into account the effect of pavement roughness.
item: Conference-Full-text
Numerical analysis of horn effect reduction on porous pavement
Zhang, Lei; Ong, Ghim Ping; Fwa, Tien Fang
Porous pavement is often seen as an effective engineering solution to reduce traffic noise. It works by reducing the horn effect of tire/road noise generation using its acoustic absorbing ability. Sound energy dissipates when it propagates through the porous surface layer due to the viscous and thermal effects resulting from the compression and expansion of air within the micro-structure of pore network. This sound absorption becomes more significant when it comes to horn effect because the multireflection process makes the absorption occur multiple times in sound propagation. Despite the significance of horn effect reduction on porous pavement, research studies on this topic are still limited to date. This paper attempts to investigate the horn effect reduction in a numerical perspective. A brief description of the acoustic characteristics of porous pavement is presented. Representative phenomenological and microstructural models which are capable to derive the acoustic impedance of porous pavement from its volumetric and composition characteristics are introduced. A numerical horn effect measurement model using boundary element method is then developed and validated against experimental results. This model is next used to analyze horn effect reduction on porous pavement. The influence of source position, the directivity of horn effect reduction, as well as the influence of the thickness and porosity of porous layer are examined. The simulation results demonstrate the feasibility of BEM model in the analysis of noise propagation on porous pavement and can provide some in-depth understanding of the horn effect on porous pavement.