Topic
Critical speed
About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.
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TL;DR: In this paper, the authors have carried out a large scale experiment to study the car-following behavior in a 51-car platoon and found that there exists a critical speed between 30 and 40 km/h, above which the standard deviation of car velocity is almost saturated (flat) along the platoon.
Abstract: Traffic instability is an important but undesirable feature of traffic flow. This paper reports our experimental and empirical studies on traffic flow instability. We have carried out a large scale experiment to study the car-following behavior in a 51-car-platoon. The experiment has reproduced the phenomena and confirmed the findings in our previous 25-car-platoon experiment, i.e., standard deviation of vehicle speeds increases in a concave way along the platoon. Based on our experimental results, we argue that traffic speed rather than vehicle spacing (or density) might be a better indicator of traffic instability, because vehicles can have different spacing under the same speed. For these drivers, there exists a critical speed between 30 km/h and 40 km/h, above which the standard deviation of car velocity is almost saturated (flat) along the 51-car-platoon, indicating that the traffic flow is likely to be stable. In contrast, below this critical speed, traffic flow is unstable and can lead to the formation of traffic jams. Traffic data from the Nanjing Airport Highway support the experimental observation of existence of a critical speed. Based on these findings, we propose an alternative mechanism of traffic instability: the competition between stochastic factors and the so-called speed adaptation effect, which can better explain the concave growth of speed standard deviation in traffic flow.
103 citations
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TL;DR: In this paper, the authors analyzed over 1500 ground-borne vibration records, at 17 high speed rail sites, across 7 European countries and found that soil material properties are the most influential parameter that effect vibration levels while the effect of train speed is low.
102 citations
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08 Oct 2000TL;DR: In this article, the authors describe a comprehensive design methodology for switched reluctance machines (SRMs) and present a design methodology that maximizes the desired features and minimizes the unwanted effects.
Abstract: The description of a comprehensive design methodology for switched reluctance machines (SRMs) is reported here The magnetic properties of the iron, the number of phases and the number of poles per phase all have a nonlinear effect on an SRM's performance These effects, along with design ratios, the sizing of the machine envelope and internal dimensions, make the machine design an intensive effort Maximization of torque density, power output, efficiency, speed range and first critical speed and minimization of torque ripple, temperature rise, acoustic noise and overall cost are among the many design objectives and critical issues that must be addressed during the design process A design methodology that maximizes the desired features and minimizes the unwanted effects is presented here Static and dynamic system level simulations and finite element analysis (FEA) have been carried out for a 4-phase, 8/6, 10 kW SRM as a design example to support the efficacy of the proposed design procedure
101 citations
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TL;DR: In this paper, the authors proposed a new type of ultrasonic vibration cutting, i.e., high-speed ultra-vibrant cutting (HUVC), in which the vibration is always along with the feed direction.
99 citations
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TL;DR: In this paper, the dynamic behavior of flexible rotor systems subjected to base excitation (support movements) is investigated theoretically and experimentally, focusing on behavior in bending near the critical speeds of rotation.
Abstract: The dynamic behavior of flexible rotor systems subjected to base excitation (support movements) is investigated theoretically and experimentally. The study focuses on behavior in bending near the critical speeds of rotation. A mathematical model is developed to calculate the kinetic energy and the strain energy. The equations of motion are derived using Lagrange equations and the Rayleigh-Ritz method is used to study the basic phenomena on simple systems. Also, the method of multiple scales is applied to study stability when the system mounting is subjected to a sinusoidal rotation. An experimental setup is used to validate the presented results.
98 citations