The Experts below are selected from a list of 2472 Experts worldwide ranked by ideXlab platform
Marc Barthelemy - One of the best experts on this subject based on the ideXlab platform.
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optimal geometry of transportation networks
Physical Review E, 2019Co-Authors: David Aldous, Marc BarthelemyAbstract:Author(s): Aldous, David; Barthelemy, Marc | Abstract: Motivated by the shape of transportation networks such as Subways, we consider a distribution of points in the plane and ask for the network G of given length L that is optimal in a certain sense. In the general model, the optimality criterion is to minimize the average (over pairs of points chosen independently from the distribution) time to travel between the points, where a travel path consists of any line segments in the plane traversed at slow speed and any route within the subway network traversed at a faster speed. Of major interest is how the shape of the optimal network changes as L increases. We first study the simplest variant of this problem where the optimization criterion is to minimize the average distance from a point to the network, and we provide some general arguments about the optimal networks. As a second variant we consider the optimal network that minimizes the average travel time to a central destination, and we discuss both analytically and numerically some simple shapes such as the star network, the ring, or combinations of both these elements. Finally, we discuss numerically the general model where the network minimizes the average time between all pairs of points. For this case, we propose a scaling form for the average time that we verify numerically. We also show that in the medium-length regime, as L increases, resources go preferentially to radial branches and that there is a sharp transition at a value L_{c} where a loop appears.
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Optimal geometry of transportation networks.
Physical review. E, 2019Co-Authors: David Aldous, Marc BarthelemyAbstract:Motivated by the shape of transportation networks such as Subways, we consider a distribution of points in the plane and ask for the network G of given length L that is optimal in a certain sense. In the general model, the optimality criterion is to minimize the average (over pairs of points chosen independently from the distribution) time to travel between the points, where a travel path consists of any line segments in the plane traversed at slow speed and any route within the subway network traversed at a faster speed. Of major interest is how the shape of the optimal network changes as L increases. We first study the simplest variant of this problem where the optimization criterion is to minimize the average distance from a point to the network, and we provide some general arguments about the optimal networks. As a second variant we consider the optimal network that minimizes the average travel time to a central destination, and we discuss both analytically and numerically some simple shapes such as the star network, the ring, or combinations of both these elements. Finally, we discuss numerically the general model where the network minimizes the average time between all pairs of points. For this case, we propose a scaling form for the average time that we verify numerically. We also show that in the medium-length regime, as L increases, resources go preferentially to radial branches and that there is a sharp transition at a value L_{c} where a loop appears.
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scaling in transportation networks
PLOS ONE, 2014Co-Authors: Remi Louf, Camille Roth, Marc BarthelemyAbstract:Subway systems span most large cities, and railway networks most countries in the world. These networks are fundamental in the development of countries and their cities, and it is therefore crucial to understand their formation and evolution. However, if the topological properties of these networks are fairly well understood, how they relate to population and socio-economical properties remains an open question. We propose here a general coarse-grained approach, based on a cost-benefit analysis that accounts for the scaling properties of the main quantities characterizing these systems (the number of stations, the total length, and the ridership) with the substrate's population, area and wealth. More precisely, we show that the length, number of stations and ridership of Subways and rail networks can be estimated knowing the area, population and wealth of the underlying region. These predictions are in good agreement with data gathered for about 140 subway systems and more than 50 railway networks in the world. We also show that train networks and subway systems can be described within the same framework, but with a fundamental difference: while the interstation distance seems to be constant and determined by the typical walking distance for Subways, the interstation distance for railways scales with the number of stations.
Wenrong Zhang - One of the best experts on this subject based on the ideXlab platform.
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ventilation for subway stations with adjustable platform doors created by train induced unsteady airflow
Building and Environment, 2019Co-Authors: Xin Zhang, Wenrong ZhangAbstract:Abstract At present, Subways (rail transit) are undergoing rapid developments worldwide accompanied by massive energy consumption. Train-induced unsteady airflow (TIUA) generates airflow through the entrances and platform doors, which affects the ventilation and thermal environment of subway stations. Adjustable platform door systems are increasingly being installed in subway stations to reduce the energy consumption by utilising TIUA. In this study, numerical modelling was performed by IDA Tunnel software to analyse the air inflow rate (AIR) through the entrances and adjustable platform doors (APDs). Four key factors, namely, the open and closed systems, bypass ducts, train intervals, and adjustable air vents, were analysed. The results demonstrate that for subway stations with adjustable air vents open, the average AIR through entrances with a closed system was 1.99–4.17 times that of the open system. Moreover, the variations of the average AIR through entrances caused by bypass ducts were less than 9.20%, and turning off the bypass ducts increased the average AIR via the APDs from 35.58% to 65.58%, when the adjustable air vents were open. In addition, the results show that the AIR via the APDs was decreased from 32.48% to 80.45% by shutting the adjustable air vents. Therefore, an innovative energy-saving strategy of environmental control system (ECS) was proposed based on the utilisation of TIUA. A winter case to optimize the ventilation control modes of TIUA is discussed. Compared with the worst mode, the heating requirements of subway stations with optimal ventilation control modes of TIUA can be reduced by 62.85%.
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train induced unsteady airflow effect analysis on a subway station using field experiments and numerical modelling
Energy and Buildings, 2018Co-Authors: Xin Zhang, Wenrong Zhang, Changqing Yang, Baoshun DengAbstract:Abstract In recent years, subway systems (rail transit) have become an increasingly significant means of urban transportation. Platform screen doors (PSDs) can play an important role in enhancing the thermal environment in subway stations. However, train-induced unsteady airflow results in unorganised ventilation at the entrances (supplying fresh air and causing heat exchange) and air infiltration at the PSDs (causing heat exchange) in subway stations with PSDs. In the present study, field experiments (in Xi'an, China) and numerical modelling were conducted to investigate the rate of air inflow at the entrances and the PSDs of Subways. The accuracy of the model was verified using the results from field experiments. In addition, the effects of various factors such as the traffic density, the piston vent shaft at the station downstream location (PVSASDL), and the season were analysed. The simulation results showed that turning on the PVSASDL could reduce the rate of air inflow at the entrances to 29.2–93.8%, while that at the PSDs could be enhanced to 121.8–126.3% under different traffic densities. In addition, to explore appropriate control of the PVSASDL in winter, different outdoor temperatures were simulated for a traffic density of 12 pairs/hour. It was found that the temperature in the station could meet the standard requirements when outdoor temperatures were greater higher than −5 °C with either open or closed PVSASDL conditions.
Xin Zhang - One of the best experts on this subject based on the ideXlab platform.
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ventilation for subway stations with adjustable platform doors created by train induced unsteady airflow
Building and Environment, 2019Co-Authors: Xin Zhang, Wenrong ZhangAbstract:Abstract At present, Subways (rail transit) are undergoing rapid developments worldwide accompanied by massive energy consumption. Train-induced unsteady airflow (TIUA) generates airflow through the entrances and platform doors, which affects the ventilation and thermal environment of subway stations. Adjustable platform door systems are increasingly being installed in subway stations to reduce the energy consumption by utilising TIUA. In this study, numerical modelling was performed by IDA Tunnel software to analyse the air inflow rate (AIR) through the entrances and adjustable platform doors (APDs). Four key factors, namely, the open and closed systems, bypass ducts, train intervals, and adjustable air vents, were analysed. The results demonstrate that for subway stations with adjustable air vents open, the average AIR through entrances with a closed system was 1.99–4.17 times that of the open system. Moreover, the variations of the average AIR through entrances caused by bypass ducts were less than 9.20%, and turning off the bypass ducts increased the average AIR via the APDs from 35.58% to 65.58%, when the adjustable air vents were open. In addition, the results show that the AIR via the APDs was decreased from 32.48% to 80.45% by shutting the adjustable air vents. Therefore, an innovative energy-saving strategy of environmental control system (ECS) was proposed based on the utilisation of TIUA. A winter case to optimize the ventilation control modes of TIUA is discussed. Compared with the worst mode, the heating requirements of subway stations with optimal ventilation control modes of TIUA can be reduced by 62.85%.
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train induced unsteady airflow effect analysis on a subway station using field experiments and numerical modelling
Energy and Buildings, 2018Co-Authors: Xin Zhang, Wenrong Zhang, Changqing Yang, Baoshun DengAbstract:Abstract In recent years, subway systems (rail transit) have become an increasingly significant means of urban transportation. Platform screen doors (PSDs) can play an important role in enhancing the thermal environment in subway stations. However, train-induced unsteady airflow results in unorganised ventilation at the entrances (supplying fresh air and causing heat exchange) and air infiltration at the PSDs (causing heat exchange) in subway stations with PSDs. In the present study, field experiments (in Xi'an, China) and numerical modelling were conducted to investigate the rate of air inflow at the entrances and the PSDs of Subways. The accuracy of the model was verified using the results from field experiments. In addition, the effects of various factors such as the traffic density, the piston vent shaft at the station downstream location (PVSASDL), and the season were analysed. The simulation results showed that turning on the PVSASDL could reduce the rate of air inflow at the entrances to 29.2–93.8%, while that at the PSDs could be enhanced to 121.8–126.3% under different traffic densities. In addition, to explore appropriate control of the PVSASDL in winter, different outdoor temperatures were simulated for a traffic density of 12 pairs/hour. It was found that the temperature in the station could meet the standard requirements when outdoor temperatures were greater higher than −5 °C with either open or closed PVSASDL conditions.
Baoshun Deng - One of the best experts on this subject based on the ideXlab platform.
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train induced unsteady airflow effect analysis on a subway station using field experiments and numerical modelling
Energy and Buildings, 2018Co-Authors: Xin Zhang, Wenrong Zhang, Changqing Yang, Baoshun DengAbstract:Abstract In recent years, subway systems (rail transit) have become an increasingly significant means of urban transportation. Platform screen doors (PSDs) can play an important role in enhancing the thermal environment in subway stations. However, train-induced unsteady airflow results in unorganised ventilation at the entrances (supplying fresh air and causing heat exchange) and air infiltration at the PSDs (causing heat exchange) in subway stations with PSDs. In the present study, field experiments (in Xi'an, China) and numerical modelling were conducted to investigate the rate of air inflow at the entrances and the PSDs of Subways. The accuracy of the model was verified using the results from field experiments. In addition, the effects of various factors such as the traffic density, the piston vent shaft at the station downstream location (PVSASDL), and the season were analysed. The simulation results showed that turning on the PVSASDL could reduce the rate of air inflow at the entrances to 29.2–93.8%, while that at the PSDs could be enhanced to 121.8–126.3% under different traffic densities. In addition, to explore appropriate control of the PVSASDL in winter, different outdoor temperatures were simulated for a traffic density of 12 pairs/hour. It was found that the temperature in the station could meet the standard requirements when outdoor temperatures were greater higher than −5 °C with either open or closed PVSASDL conditions.
Zhengying Li - One of the best experts on this subject based on the ideXlab platform.
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identification of ground intrusion in underground structures based on distributed structural vibration detected by ultra weak fbg sensing technology
Sensors, 2019Co-Authors: Sheng Li, Zhengying LiAbstract:It is challenging for engineers to timely identify illegal ground intrusions in underground systems such as Subways. In order toprevent the catastrophic collapse of subway tunnels from intrusion events, this paper investigated the capability of detecting the ground intrusion of underground structures based on dynamic measurement of distributed fiber optic sensing. For an actual subway tunnel monitored by the ultra-weak fiber optic Bragg grating (FBG)sensing fiber with a spatial resolution of five meters, a simulated experiment of the ground intrusion along the selected path was designed and implemented, in which a hydraulic excavator was chosen to exert intrusion perturbations with different strengths and modes at five selected intrusion sites. For each intrusion place, the distributed vibration responses of sensing fibers mounted on the tunnel wall and the track bed were detected to identify the occurrence and characteristics of the intrusion event simulated by the discrete and continuous pulses of the excavator under two loading postures. By checking the on-site records of critical moments in the intrusion process, the proposed detection approach based on distributed structural vibration responses for the ground intrusion can detect the occurrence of intrusion events, locate the intrusion ground area, and distinguish intrusion strength and typical perturbation modes.
