This study presents the design of a 2-pole high-speed BLDC motor for kitchen blenders and its control method with the aim to reduce the speed ripple that decreases the grinding performance in the ...high-speed region. In blender machines, the high pulsating load caused by the blending materials such as ice cubes acting on the grinding blade, create significant speed ripple in the constant power region. Because current and torque are limited to protect the drive, the actual motor torque cannot overcome the pulsated load if the speed reference is maintained. Therefore, the speed fluctuates, and the grinding performance is lowered. In the proposed variable speed reference control scheme, the speed command is continuously modified to overcome the maximum pulsating torque requirement which results in lower speed ripple. To achieve this, if the load torque suddenly increases, the current value is then set based on the maximum load and speed reference value is temporarily lowered. If then the load torque becomes lower than the actual torque, the previously set speed reference value is reused. The design result and grinding performance of the proposed control method are verified by simulations and experiments. Hard white beans are used for actual performance testing.
•Bridge frequency identification from moving vehicle at a high speed.•Combine dynamic responses of multiple vehicles moving via a high speed.•Track irregularity can be effectively eliminated using ...vehicle residual response.•The proposed method is verified through the MDOF vehicle model.
The identification of bridge frequencies using dynamic responses of moving vehicles has been studied by many researchers, however, most of them assume that the vehicle moves at a relatively low speed. In the application of high-speed railway bridges, the bridge span is typically short and the train always moves at a very high speed, which implies that the duration of the vehicle traveling on the bridge is very short and the signal recorded from the vehicle is not long enough for signal processing to extract the bridge frequency. The present study proposes a new method to identify the bridge frequency from vehicles moving at a high speed by combining the responses of multiple vehicles. The theoretical analysis is conducted using the simple vehicle-bridge interaction (VBI) model. By subtracting the acceleration responses of adjacent vehicles at the same position on the bridge, the residual vehicle responses were obtained and combined, which eliminated the additional driving frequencies and avoided its interference on the bridge frequency identification. Numerical simulations are then conducted to verify the proposed method, which shows that by combining the acceleration of several vehicles to extend the overall duration of the signal, the frequency resolution can be improved and the bridge frequency can be successfully identified using vehicles travelling at a high speed. The influence of track irregularity, vehicle speed, bridge stiffness, and bridge damping on the identification results has also been studied. In addition, a multi-degree-of-freedom vehicle model is used to further verify the proposed method.
Understanding the effect of wind speed variation on wind-induced momentary discomfort is the basis to improve the train vibration comfort. This study focuses on this challenge. Firstly, the momentary ...discomfort evaluation index Pw is developed and proved by the full-scale test. Then, setting Pw as the critical value, a multi-body nonlinear numerical investigation of the effect of the wind speed change rate, peak-wind speed duration, and wind speed variation amplitude on momentary discomfort in a train is conducted. Furthermore, the unfavourable wind speed variation condition for the wind-induced momentary discomfort in the train is obtained. Results indicate that the most intense condition for the train vibration momentary discomfort appears when the change rate of wind speed is faster and the duration of the peak wind drives the car-body rolling to the limit position. Consequently, critical wind speed for the wind-induced momentary discomfort in changing wind speed conditions is proposed, which provides a reference for an efficient train operation scheme to improve vibration comfort in a train under wind speed variation conditions.
Introduction: In November 2010 and October 2013, Utah increased speed limits on sections of rural interstates from 75 to 80 mph. Effects on vehicle speeds and speed variance were examined. Methods: ...Speeds were measured in May 2010 and May 2014 within the new 80mph zones, and at a nearby spillover site and at more distant control sites where speed limits remained 75 mph. Log-linear regression models estimated percentage changes in speed variance and mean speeds for passenger vehicles and large trucks associated with the speed limit in- crease. Logistic regression models estimated effects on the probability of passenger vehicles exceeding 80, 85, or 90 mph and large trucks exceeding 80 mph. Results: Within the 80 mph zones and at the spillover location in 2014, mean passenger vehicle speeds were significantly higher (4.1% and 3.5%, respectively), as were the probabilities that passenger vehicles exceeded 80 mph (122.3% and 88.5%, respectively), than would have been expected without the speed limit increase. Probabilities that passenger vehicles exceeded 85 and 90 mph were non-significantly higher than expected within the 80 mph zones. For large trucks, the mean speed and probability of exceeding 80 mph were higher than expected within the 80 mph zones. Only the increase in mean speed was significant. Raising the speed limit was associated with non-significant increases in speed variance. Conclusions: The study adds to the wealth of evidence that increasing speed limits leads to higher travel speeds and an increased probability of exceeding the new speed limit. Results moreover contradict the claim that increasing speed limits reduces speed variance. Practical applications: Although the estimated increases in mean vehicle speeds may appear modest, prior research suggests such increases would be associated with substantial increases in fatal or injury crashes. This should be considered by lawmakers considering increasing speed limits.
The minimal time a system needs to evolve from an initial state to its one orthogonal state is defined as the quantum speed limit time, which can be used to characterize the maximal speed of ...evolution of a quantum system. This is a fundamental question of quantum physics. We investigate the generic bound on the minimal evolution time of the open dynamical quantum system. This quantum speed limit time is applicable to both mixed and pure initial states. We then apply this result to the damped Jaynes-Cummings model and the Ohimc-like dephasing model starting from a general time-evolution state. The bound of this time-dependent state at any point in time can be found. For the damped Jaynes-Cummings model, when the system starts from the excited state, the corresponding bound first decreases and then increases in the Markovian dynamics. While in the non-Markovian regime, the speed limit time shows an interesting periodic oscillatory behavior. For the case of Ohimc-like dephasing model, this bound would be gradually trapped to a fixed value. In addition, the roles of the relativistic effects on the speed limit time for the observer in non-inertial frames are discussed.
The speed regulating differential mechanism (SRDM) enables grid-connected wind turbines (WTs) to generate constant-frequency electric power without fully- or partially-rated converters. In this ...study, the authors present a self-stabilising SRDM (SS-SRDM) consisting of a planetary gear train (PGT), a differential mechanism, and a constant speed motor for WTs to dislodge the high-cost speed sensors, servo motor and the complicated control system from the electrical controlled SRDM. The kinematic principles and the four-axis dynamic characteristics of SS-SRDM are studied. An effective parameter configuration method for tuning the speed ratios of five key connection units is also proposed and used to obtain a PGT with optimal structural parameters. The detailed simulation model of a 3 MW WT with SS-SRDM is established and then validated through physical experiments. Results show the satisfactory accuracy of the built model (maximum steady-state errors in output shaft and speed regulating shaft are, respectively, 0.76 and 1.95%). Finally, case studies and verification work of the proposed methods are carried out, in which the rotational speed, power, speed error, and power ratio among wind rotor, SRM, and synchronous generator are obtained. Case studies well-illustrate the availability of parameter design and the effectiveness of speed-regulations of the proposed SS-SRDM method.
► Average speed enforcement can reduce speeds and improve speed limit compliance. ► Average speed enforcement can reduce fatal and serious injury crash rates. ► Average speed enforcement can improve ...traffic flow and reduce vehicle emissions. ► Average speed enforcement appears to be associated with high public acceptance. ► There is a need for more rigorous evaluations of average speed enforcement.
Average speed enforcement is a relatively new approach gaining popularity throughout Europe and Australia. This paper reviews the evidence regarding the impact of this approach on vehicle speeds, crash rates and a number of additional road safety and public health outcomes. The economic and practical viability of the approach as a road safety countermeasure is also explored. A literature review, with an international scope, of both published and grey literature was conducted. There is a growing body of evidence to suggest a number of road safety benefits associated with average speed enforcement, including high rates of compliance with speed limits, reductions in average and 85th percentile speeds and reduced speed variability between vehicles. Moreover, the approach has been demonstrated to be particularly effective in reducing excessive speeding behaviour. Reductions in crash rates have also been reported in association with average speed enforcement, particularly in relation to fatal and serious injury crashes. In addition, the approach has been shown to improve traffic flow, reduce vehicle emissions and has also been associated with high levels of public acceptance. Average speed enforcement offers a greater network-wide approach to managing speeds that reduces the impact of time and distance halo effects associated with other automated speed enforcement approaches. Although comparatively expensive it represents a highly reliable approach to speed enforcement that produces considerable returns on investment through reduced social and economic costs associated with crashes.
The impact of variable speed limits (VSL) on aggregate traffic flow behaviour on motorways is shown to bear similarities to the impact of ramp metering, in particular, when addressing potentially ...active bottlenecks. A quantitative model of the VSL impact is proposed that allows for VSL to be incorporated in a macroscopic second-order traffic flow model as an additional control component. The integrated motorway network traffic control problem involving ramp metering and VSL control measures is formulated as a constrained discrete-time optimal control problem and is solved efficiently even for large-scale networks by a suitable feasible direction algorithm. An illustrative example of a hypothetical motorway stretch is investigated under different control scenarios, and it is shown that traffic flow efficiency can be substantially improved when VSL control measures are used, particularly in integration with coordinated ramp metering.
High-speed laser cladding technology can significantly improve the efficiency of coating preparation and effectively widen the application range of laser cladding. In this study, the Ni45 powders ...were deposited on steel substrate by traditional low speed laser cladding and high-speed laser cladding process, respectively. The cladding efficiency, surface forming, cross-sectional microstructure, microhardness, wear and corrosion resistance properties of the traditional and high-speed laser cladded Ni45 alloy coatings were compared. It can be seen that the thickness of the high-speed laser cladding coating was much thinner than that of the traditional laser cladding coating. Compared with traditional laser cladding, high-speed laser cladding could achieve a cladding speed of 76.86 m/min and a cladding efficiency of 156.79 cm2/min. The microstructure of the two kinds of coatings shows the same growth law, but the microstructure in high-speed laser cladding was smaller and denser, and the columnar crystal interval was narrower, only about 6 μm. It is found that the cooling rate of the traditional laser cladding coating was smaller than that of the high-speed laser cladding, and as the cladding speed increased, the cooling rate became higher and higher. The cross-section microhardness of the traditional laser cladding coating was relatively uniform of 337 HV0.2, while the microhardness of high-speed laser cladding surface increased to about 543 HV0.2. In addition, the wear and corrosion resistance of high-speed laser cladded coatings were better than that of traditional laser cladded coatings. As the cladding speed increased, the wear and corrosion resistance of the cladded coatings became better.
•High-speed laser cladding coating had low roughness and thin coating.•The cooling rate increased exponentially with a decrease of secondary dendrite arm.•The wear and corrosion resistance increased with the increase of cladding speed.•The microstructure was refined continuously with the increase of cladding speed.
The severe shaking due to wind speed variation in high-speed trains has a negative impact on driving safety and riding comfort. It is difficult to solve this problem by directly applying civil ...engineering technology because of the actual conditions. Therefore, set up a reasonable train operation plan considering the wind speed variation under strong winds is very important. In this study, a multi-body simulation model of a CRH2 high-speed rail vehicle is constructed, and the overturning coefficient is set as the safety limit, we established a crosswind model on the basis of measured wind speed curves and investigated the effect of the rate of wind speed changes, the duration of maximum wind speed and the variation of wind speed in different amplitude on the dynamics of the high-speed train. Considering the most critical wind speed variation conditions, the characteristic wind curve is obtained, which can be used as a reference to set up a reasonable train operation scheme considering the wind speed variation.
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