Travel demand management (TDM) is an important measure that will aid in the realization of efficient and sustainable transportation systems. However, in cities where the most serious traffic ...congestion occurs, implementation of a single TDM measure might not be enough to reduce congestion, because the congestion mechanism in this case is highly complex and involves different transportation modes interacting with each other. Implementation of multiple TDM measures has rarely been discussed in the literature. Therefore, in this study, we propose a simulation-based joint optimization framework composed of dedicated bus lanes and vehicular congestion pricing. The objective of the optimization process is to minimize the congestion cost based on an advanced macroscopic flow theory called the multimodal macroscopic fundamental diagram (mMFD), which can capture the macroscopic traffic dynamics of multimodal transportation systems. In the proposed framework, we develop mMFD-based congestion pricing scheme and incorporate traveler’s behavioral model (i.e. joint departure time and mode choices) with the microscopic traffic simulator. We consider the Tokyo central area as a case study. The simulation results indicate that space allocation of 4.7% for the dedicated bus lanes would be optimal for Tokyo’s network, while the optimal congestion pricing scheme indicates that charges of 900 JPY between 7:30 and 8:00 AM and 300 JPY between 8.00 and 8:30 AM should be levied.
As a state-of-the-art computational method for simulating rock fracturing and fragmentation, the combined finite-discrete element method (FDEM) has become widely accepted since Munjiza (
2004
) ...published his comprehensive book of FDEM. This study developed a general-purpose graphic-processing-unit (GPGPU)-parallelized FDEM using the compute unified device architecture C/C ++ based on the authors’ former sequential two-dimensional (2D) and three-dimensional (3D) Y-HFDEM IDE (integrated development environment) code. The theory and algorithm of the GPGPU-parallelized 3D Y-HFDEM IDE code are first introduced by focusing on the implementation of the contact detection algorithm, which is different from that in the sequential code, contact damping and contact friction. 3D modelling of the failure process of limestone under quasi-static loading conditions in uniaxial compressive strength (UCS) tests and Brazilian tensile strength (BTS) tests are then conducted using the GPGPU-parallelized 3D Y-HFDEM IDE code. The 3D FDEM modelling results show that mixed-mode I–II failures are the dominant failure mechanisms along the shear and splitting failure planes in the UCS and BTS models, respectively, with unstructured meshes. Pure mode I splitting failure planes and pure mode II shear failure planes are only possible in the UCS and BTS models, respectively, with structured meshes. Subsequently, 3D modelling of the dynamic fracturing of marble in dynamic Brazilian tests with a split Hopkinson pressure bar (SHPB) apparatus is conducted using the GPGPU-parallelized 3D HFDEM IDE code considering the entire SHPB testing system. The modelled failure process, final fracture pattern and time histories of the dynamic compressive wave, reflective tensile wave and transmitted compressive wave are compared quantitatively and qualitatively with those from experiments, and good agreements are achieved between them. The computing performance analysis shows the GPGPU-parallelized 3D HFDEM IDE code is 284 times faster than its sequential version and can achieve the computational complexity of O(
N
). The results demonstrate that the GPGPU-parallelized 3D Y-HFDEM IDE code is a valuable and powerful numerical tool for investigating rock fracturing under quasi-static and dynamic loading conditions in rock engineering applications although very fine elements with maximum element size no bigger than the length of the fracture process zone must be used in the area where fracturing process is modelled.
This paper introduces a novel three-dimensional grain-based hybrid finite-discrete element method parallelized based on general-purpose graphic processing units (GPGPUs) and applies it to investigate ...the failure process of sedimentary fine-grained sandstones. The grain-based method considers the actual microstructures of rocks with Voronoi or grain-growth tessellations to model their failures, including transgranular, intergranular and intragranular crack propagations. The novel semi-adaptive contact activation approach (semi-ACAA) proposed by the authors and the efficient tetrahedron-to-point (TtoP) contact interaction algorithm developed by HOSS are implemented to speed up grain-based modelling in addition to GPGPU parallelization. Semi-ACAA and TtoP are approximately 2–20 times and 1.5 times faster than the brute-force contact activation approach and tetrahedron-to-triangle contact interaction algorithm, respectively, which are prevalent in the FDEM community. The grain-based modelling elucidates that most intragranular cracks are observed in the medium- and high-strength grains of the sandstones, while most intergranular cracks occur at the grain boundaries between low- and high-strength grains. The transgranular cracks do not discriminate any grains on their propagating paths but propagate and coalesce with intragranular and intergranular cracks, which results in the final failure of the sandstones.
Travel survey and behavior modeling still take obviously important roles in a series of transportation planning, including problem identification, problem structuring, travel demand analysis, ...project/policy formulation, and project/policy evaluation. Classical large-scale travel surveys (e.g. paper-based questionnaire), which have been applied in many cities in the world, have faced challenging problems such as increased survey costs, decline in quality or reliability of the results, and less continuity. The scope of transportation planning at present has become more diverse and it would cover a variety of subjects including demand management, environment, health, gender, and evacuation. Moreover, there have been dramatic expansions in travel data collection with the rapid spread of information communication technology. These issues have motivated me to set up this special issue.This special issue has welcomed papers that are related to all aspects of innovation in travel survey methods and corresponding travel behavior modeling that show innovations in approach, outcomes, and state-of-practice. Five papers have been selected for this special issue.
Due to its complexities, rock fracturing process still poses many pressing challenges despite intense research efforts. With the rapid development of computational mechanics, numerical techniques ...have gradually become robust tools for the investigation of rock fracture. Nevertheless, not all of the devised methods are capable of adequately modelling the rock fracture process. For an accurate simulation of the process, a numerical method needs to be capable of modelling crack initiation, propagation, bifurcation, coalescence and separation. This paper provided a review of recent advances in computational analysis of the rock fracture process, which is built upon a number of literature on numerical modelling of mechanics of failure in rock and other brittle materials. After briefly discussing the fundamentals of rock fracture mechanisms, the basic structure of the existing and recently developed numerical techniques such as finite element method, boundary element method, distinct element method, combined methods and multi-scale coupled method are illustrated. Finally, the strengths and weaknesses of these numerical techniques are discussed and the most promising methods are highlighted.
High-strength and ultra-low-permeability concrete (HSULPC) is thought to be useful as a radioactive waste package. Thus, a high confining ability is desirable. For cementitious materials, sealing of ...cracks may occur in water due to the precipitation of calcium compounds. This can affect the confining ability. In this study, the sealing of a crack in HSULPC in water was investigated using micro-focus X-ray computed tomography (CT). The sealing by precipitation occurred only around the end of the specimen. Sealed regions of the crack were identified using three-dimensional image registration and CT image subtraction of images obtained for the specimen before and after it was immersed in water to evaluate temporal changes of the sealing deposits in the crack. The sealing deposits increased as the HSULPC specimen was kept in water longer. It was concluded that cracks in HSULPC in water are sealed by precipitation.
•A dynamic network loading model is proposed using the macroscopic traffic variables.•The reservoir model is built on the conservation of flow in reservoir and the boundary model is built on the ...supply and demand of neighboring reservoirs.•The design parameters such as length and boundary of each internal path have been studied in depth.•This model is tested by several numerical experiments.
In this paper, we present a dynamic network loading (DNL) model that captures the traffic dynamics for multiple-reservoir networks dependent on the relationship among macroscopic traffic characteristics, and develop a numerical method based on the Godunov scheme. The proposed DNL model consists of link model and node model. The traffic dynamics of the internal paths in a reservoir are specified by a system of Lighthill–Whitham–Richards-like partial differential equations, which build on the conservation law, while the flows at the boundaries between reservoirs are determined by the supply–demand balances between upstream and downstream reservoirs. A novel numerical method is developed based on the Godunov scheme to track the movement of vehicles in the network while maintaining the relevant priority rules. In comparison with previous approaches, the proposed numerical scheme is computationally efficient, considers the non-uniform cell sizes inherent in different internal paths within a reservoir, and conserves the flow through holding and balancing rules. Numerical experiments indicate that the proposed methodology can describe the dynamics of vehicles in large-scale traffic network efficiently.
Superabsorbent polymers (SAPs) are used as internal curing agents in cementitious materials, which reduce autogenous shrinkage in concrete as they have a low water-to-cement ratios and improve the ...freeze-thaw resistance. However, the compressive strength of concrete may also be reduced due to additional voids in the hydrated cement matrix. In this study, we fabricated a delayed absorption type of SAP (I-SAP) composed of cross-linked modified acrylate and studied its absorption characteristics and effect on compressive strength after 28 days. Furthermore, the effect of curing conditions on the strength of concrete and hydrated cement paste with SAP were investigated. The absorption capacity of I-SAP in the synthetic pore solution and deionised water was examined and compared with that of a conventional SAP, and the former was absorbed more by I-SAP. The results revealed that the compressive strength of concrete increased with the addition of I-SAP, particularly with the curing condition of 60% RH. Although the compressive strength of hydrated cement paste with I-SAP reduced in water or sealed curing conditions, no loss of strength in the paste cured at 60% RH was seen. The cement matrix densification due to hydration of belite around the SAP surface is the main mechanism for strength development in concrete cured at sealed and 60% RH. However, the voids formed by SAP control the compressive strength of hydrated paste.
•Rock blasting was simulated by a unique self-developed GPGPU-parallelized FDEM.•Dynamic interactions of in-situ stresses, blast loading and fracturing were modelled.•Rock fracture and fragmentation ...process was properly replicated.•Effects of in-situ stress field and lateral pressure coefficient were clarified.•Effects of blasting decay time ratio and decoupling ratio were elucidated.
One highly effective approach for tunnelling in rock at deep depth is blasting. The damage and in-situ stress redistribution in the surrounding rock mass induced by the blast loading during this process is, however, unavoidable. In this study, a powerful GPGPU-parallelized combined finite-discrete element method is implemented to study the damage evolution during controlled contour blasting in the bench of a deep-buried tunnel. The proposed method is characterized by the simulation of the blasting-induced pressure variation via the pressure-gas volume history curve and the modelling of the transition from continuum to discontinuum behaviour in the surrounding rock mass. The in-situ stress distribution, the blasting-induced stress wave propagation, and the corresponding rock fracture and fragmentation process are modelled and analysed. The numerical simulation results indicate that the in-situ stresses play a key role in the damage evolution around the tunnel, strongly influencing the stress redistribution pattern and thus the fracture initiation and propagation around the tunnel during blasting. Several different in-situ stress regimes are considered and discussed, revealing the dominating effects of the major principal stress and lateral pressure coefficient on the rock damage behaviour. Moreover, the blasting results obtained from employing the pressure–time history curve with varying decay time ratios and decoupling ratios are also studied. Longer decay time ratios and higher decoupling ratios induce additional rock fracture and fragmentation, indicating that the model can enable the selection of stemming and explosive type for effective breakage with limited damage around a tunnel.
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