The ability to measure the very high heat fluxes that typically occur during the hypersonic re-entry phase of space vehicles is generally considered a subject of great importance in the aerospace field.Most of the sen...The ability to measure the very high heat fluxes that typically occur during the hypersonic re-entry phase of space vehicles is generally considered a subject of great importance in the aerospace field.Most of the sensors used for these measurements need to be checked periodically and re-calibrated accordingly.Another bottleneck relates to the need to procure thermal sources that are able to generate reliable reference heat fluxes in the range between 100 and 1000 kW/m^(2)(as order of magnitude).In the present study,a method is presented by which,starting from a calibration system with a capacity of approximately 500 kW/m^(2) only,heat fluxes in the range of interest for hypersonic applications are generated.The related procedure takes advantage of established standards for the characterization of a radiative heat flux.It also builds on the hybrid radiative-convective nature of typical hypersonic heat fluxes and the yet poorly explored possibility to use convective sources of heat to produce high-intensity fluxes.The reliability of such a strategy has been tested using a high enthalpy supersonic flow facility relying on an electric arc-heater and pure Nitrogen as work gas.Stagnation-point heat fluxes have been successfully measured(with reasonable accuracy)in the range between 600 and 1500 kW/m^(2) for values of the centerline enthalpy spanning the interval from to 6 to 24 MJ/kg.展开更多
As congestion grows in metropolitan areas, agencies tend to utilize managed lanes on their freeway systems. Managed lanes have several forms and names, such as high-occupancy vehicle （HOI0 lanes, high-occupancy toll ...As congestion grows in metropolitan areas, agencies tend to utilize managed lanes on their freeway systems. Managed lanes have several forms and names, such as high-occupancy vehicle （HOI0 lanes, high-occupancy toll （HOT） lanes, express lanes, and bus-only lanes. Although managed lanes have received significant attention as they increased the overall throughput and improved mobility without adding more lanes, little has been known about their operational capabilities. In addition, calibrating managed lane facilities can be chal- lenging as they do not necessarily follow the same behavior with general purpose freeway lanes. This paper presents an operational analysis of two HOT lane segments located in South Florida. The sites are one-lane and two-lane segments separated by flexible pylons （FPs）. The paper includes a macroscopic capacity analysis, and a microscopic calibration of the two sites using VISSIM microsimulation. The research findings assist in determining the capacity and speed-flow relationship of these segments, and also provide guidance for microsimulation model calibration for practitioners. The results of the study indicate that the percent drop in capacity for the one-lane FP site is 7.6% while the flow did not substantially change after the breakdown in the two-lane FP site. The research findings also include guidelines for simulating the breakdown events and calibrating one-lane and two-lane managed lane facilities in VISSIM microsimulation software. The Wiedemann car-following parameters （CC0 = 3.9 ft, CC1 = 1.9 s, CC2 - 26.25 ft, CC4 = -0.35, and CC5 = 0.35） provided the best fit for the one-lane FP site, while the combination （CCO = 4.92 ft, CC1= 1.9 s, CC2 = 39.37 ft, CC4 = -0.7, and CC5 = 0.7） parameters is recommended for the two-lane FP site.展开更多
文摘The ability to measure the very high heat fluxes that typically occur during the hypersonic re-entry phase of space vehicles is generally considered a subject of great importance in the aerospace field.Most of the sensors used for these measurements need to be checked periodically and re-calibrated accordingly.Another bottleneck relates to the need to procure thermal sources that are able to generate reliable reference heat fluxes in the range between 100 and 1000 kW/m^(2)(as order of magnitude).In the present study,a method is presented by which,starting from a calibration system with a capacity of approximately 500 kW/m^(2) only,heat fluxes in the range of interest for hypersonic applications are generated.The related procedure takes advantage of established standards for the characterization of a radiative heat flux.It also builds on the hybrid radiative-convective nature of typical hypersonic heat fluxes and the yet poorly explored possibility to use convective sources of heat to produce high-intensity fluxes.The reliability of such a strategy has been tested using a high enthalpy supersonic flow facility relying on an electric arc-heater and pure Nitrogen as work gas.Stagnation-point heat fluxes have been successfully measured(with reasonable accuracy)in the range between 600 and 1500 kW/m^(2) for values of the centerline enthalpy spanning the interval from to 6 to 24 MJ/kg.
基金the support and encouragement of PTV Group Management during this research study
文摘As congestion grows in metropolitan areas, agencies tend to utilize managed lanes on their freeway systems. Managed lanes have several forms and names, such as high-occupancy vehicle （HOI0 lanes, high-occupancy toll （HOT） lanes, express lanes, and bus-only lanes. Although managed lanes have received significant attention as they increased the overall throughput and improved mobility without adding more lanes, little has been known about their operational capabilities. In addition, calibrating managed lane facilities can be chal- lenging as they do not necessarily follow the same behavior with general purpose freeway lanes. This paper presents an operational analysis of two HOT lane segments located in South Florida. The sites are one-lane and two-lane segments separated by flexible pylons （FPs）. The paper includes a macroscopic capacity analysis, and a microscopic calibration of the two sites using VISSIM microsimulation. The research findings assist in determining the capacity and speed-flow relationship of these segments, and also provide guidance for microsimulation model calibration for practitioners. The results of the study indicate that the percent drop in capacity for the one-lane FP site is 7.6% while the flow did not substantially change after the breakdown in the two-lane FP site. The research findings also include guidelines for simulating the breakdown events and calibrating one-lane and two-lane managed lane facilities in VISSIM microsimulation software. The Wiedemann car-following parameters （CC0 = 3.9 ft, CC1 = 1.9 s, CC2 - 26.25 ft, CC4 = -0.35, and CC5 = 0.35） provided the best fit for the one-lane FP site, while the combination （CCO = 4.92 ft, CC1= 1.9 s, CC2 = 39.37 ft, CC4 = -0.7, and CC5 = 0.7） parameters is recommended for the two-lane FP site.
