The expansion of e-commerce and the sharing economy has paved the way for crowdshipping as an innovative approach to addressing last-mile delivery challenges.Previous studies and implementations have predominantly con...The expansion of e-commerce and the sharing economy has paved the way for crowdshipping as an innovative approach to addressing last-mile delivery challenges.Previous studies and implementations have predominantly concentrated on private vehicle-based crowdshipping,which may lead to increased traffic congestion and emissions due to additional trips made specifically for deliveries.To circumvent these possible adverse effects,this paper explores a public transport(PT)-based crowdshipping concept as a complementary solution to the traditional parcel delivery systems.In this model,PT users leverage their routine journeys to perform delivery tasks.We propose a methodology that includes a parcel locker location model and a vehicle routing model to analyze the effect of PT-based crowdshipping.Notably,the parcel locker location model aids in planning a PT-based crowdshipping network and identifying obstacles to its development.A case study conducted in the central district of Copenhagen utilizing real-world data assesses the effects of PT-based crowdshipping.The findings suggest that PT-based crowdshipping can decrease the total kilometers traveled by vehicles,the overall working hours of drivers,and the number of vans required for last-mile deliveries,thereby alleviating urban traffic congestion and environmental pollution.Nevertheless,the growth of PT-based crowdshipping may be limited by the availability of crowdshippers,indicating that initiatives to increase the number of crowdshippers are essential.展开更多
A local vortical cavitation（LVC） model for the computation of unsteady cavitation is proposed.The model is derived from the Rayleigh–Plesset equations,and takes into account the relations between the cavitation bub...A local vortical cavitation（LVC） model for the computation of unsteady cavitation is proposed.The model is derived from the Rayleigh–Plesset equations,and takes into account the relations between the cavitation bubble radius and local vortical effects.Calculations of unsteady cloud cavitating fows around a Clark-Y hydrofoil are performed to assess the predictive capability of the LVC model using well-documented experimental data.Compared with the conventional Zwart＇s model,better agreement is observed between the predictions of the LVC model and experimental data,including measurements of time-averaged fl w structures,instantaneous cavity shapes and the frequency of the cloud cavity shedding process.Based on the predictions of the LVC model,it is demonstrated that the evaporation process largely concentrates in the core region of the leading edge vorticity in accordance with the growth in the attached cavity,and the condensation process concentrates in the core region of the trailing edge vorticity,which corresponds to the spread of the rear component of the attached cavity.When the attached cavity breaks up and moves downstream,the condensation area fully transports to the wake region,which is in accordance with the dissipation of the detached cavity.Furthermore,using vorticity transport equations,we also fin that the periodic formation,breakup,and shedding of the sheet/cloud cavities,along with the associated baroclinic torque,are important mechanisms for vorticity production and modification When the attached cavity grows,the liquid–vapour interface that moves towards the trailing edge enhances the vorticity in the attached cav-ity closure region.As the re-entrant jet moves upstream,the wavy/bubbly cavity interface enhances the vorticity near the trailing edge.At the end of the cycle,the break-up of the stable attached cavity is the main reason for the vorticity enhancement near the suction surface.展开更多
Transport-based social exclusion is currently a serious social problem in Poland,and one which is apparently most severe at the level of the county(Polish powiat)in the south-eastof the country,including the Beskid Ni...Transport-based social exclusion is currently a serious social problem in Poland,and one which is apparently most severe at the level of the county(Polish powiat)in the south-eastof the country,including the Beskid Niski and Bieszczady Mountains.A deeper illustration of this problem requires both observation of changes in the suburban public-transport network and the identification of areas in which this has deteriorated significantly in quantity and quality.The chosen starting point for the research was therefore 1990,as a year in which–on the one hand–the Polish economy was already shifted to the new free-market principles;while–on the other–state PKS(Przedsiębiorstwo Komunikacji Samochodowej)non-urban bus transport enterprises still dominated public transport.The endpoint of the study is then the beginning of 2019(the author's research year).The article introduced here seeks to identify and present cartographically the changes affecting the public-transport network in the study area over the last 30 years,as well as to point to possible consequences of these processes.The background of the described changes is also discussed,as are the observed consequences of what is taking place.展开更多
基金supported by the China Scholarship Council(202107940012).
文摘The expansion of e-commerce and the sharing economy has paved the way for crowdshipping as an innovative approach to addressing last-mile delivery challenges.Previous studies and implementations have predominantly concentrated on private vehicle-based crowdshipping,which may lead to increased traffic congestion and emissions due to additional trips made specifically for deliveries.To circumvent these possible adverse effects,this paper explores a public transport(PT)-based crowdshipping concept as a complementary solution to the traditional parcel delivery systems.In this model,PT users leverage their routine journeys to perform delivery tasks.We propose a methodology that includes a parcel locker location model and a vehicle routing model to analyze the effect of PT-based crowdshipping.Notably,the parcel locker location model aids in planning a PT-based crowdshipping network and identifying obstacles to its development.A case study conducted in the central district of Copenhagen utilizing real-world data assesses the effects of PT-based crowdshipping.The findings suggest that PT-based crowdshipping can decrease the total kilometers traveled by vehicles,the overall working hours of drivers,and the number of vans required for last-mile deliveries,thereby alleviating urban traffic congestion and environmental pollution.Nevertheless,the growth of PT-based crowdshipping may be limited by the availability of crowdshippers,indicating that initiatives to increase the number of crowdshippers are essential.
基金supported by the National Natural Science Foundation of China (Grants 11172040,51239005)
文摘A local vortical cavitation（LVC） model for the computation of unsteady cavitation is proposed.The model is derived from the Rayleigh–Plesset equations,and takes into account the relations between the cavitation bubble radius and local vortical effects.Calculations of unsteady cloud cavitating fows around a Clark-Y hydrofoil are performed to assess the predictive capability of the LVC model using well-documented experimental data.Compared with the conventional Zwart＇s model,better agreement is observed between the predictions of the LVC model and experimental data,including measurements of time-averaged fl w structures,instantaneous cavity shapes and the frequency of the cloud cavity shedding process.Based on the predictions of the LVC model,it is demonstrated that the evaporation process largely concentrates in the core region of the leading edge vorticity in accordance with the growth in the attached cavity,and the condensation process concentrates in the core region of the trailing edge vorticity,which corresponds to the spread of the rear component of the attached cavity.When the attached cavity breaks up and moves downstream,the condensation area fully transports to the wake region,which is in accordance with the dissipation of the detached cavity.Furthermore,using vorticity transport equations,we also fin that the periodic formation,breakup,and shedding of the sheet/cloud cavities,along with the associated baroclinic torque,are important mechanisms for vorticity production and modification When the attached cavity grows,the liquid–vapour interface that moves towards the trailing edge enhances the vorticity in the attached cav-ity closure region.As the re-entrant jet moves upstream,the wavy/bubbly cavity interface enhances the vorticity near the trailing edge.At the end of the cycle,the break-up of the stable attached cavity is the main reason for the vorticity enhancement near the suction surface.
基金financed by the National Science Centre entitled:An empirical pilot study on transport exclusion in mountain areas based on the example of the Low Beskids and the Bieszczady counties (Miniatura 2, contract number 2018/02/X/HS4/00451)
文摘Transport-based social exclusion is currently a serious social problem in Poland,and one which is apparently most severe at the level of the county(Polish powiat)in the south-eastof the country,including the Beskid Niski and Bieszczady Mountains.A deeper illustration of this problem requires both observation of changes in the suburban public-transport network and the identification of areas in which this has deteriorated significantly in quantity and quality.The chosen starting point for the research was therefore 1990,as a year in which–on the one hand–the Polish economy was already shifted to the new free-market principles;while–on the other–state PKS(Przedsiębiorstwo Komunikacji Samochodowej)non-urban bus transport enterprises still dominated public transport.The endpoint of the study is then the beginning of 2019(the author's research year).The article introduced here seeks to identify and present cartographically the changes affecting the public-transport network in the study area over the last 30 years,as well as to point to possible consequences of these processes.The background of the described changes is also discussed,as are the observed consequences of what is taking place.
