Search

At present, the global navigation satellite system (GNSS) is the most widely used technology in the field of vehicle navigation and positioning. However, due to satellite signal blocking, it can be challenging to obtain precise and reliable vehicle positions in completely GNSS-denied environments. In this paper, a positioning strategy utilizing ultra-wide band (UWB) and a low-cost MEMS inertial navigation system (INS) is proposed, aimed at tracking vehicles in typical GNSS-denied scenarios. UWB tech has potential for high-precision ranging due to its strong penetration ability. However, non-line-of-sight (NLOS) propagation still has a high occurrence in typical traffic scenarios due to the fact that the direct path between the radio transmitter and the radio receiver is obstructed. Therefore, a two-step NLOS error mitigation method is proposed to deal with the abnormal measurements of UWB in tunnels. First, a state-of-the-art probabilistic factor graph model is proposed to estimate the vehicle’s position information based on UWB range measurements instead of excluding the NLOS reception. Then, a residual weighting algorithm is employed during UWB/INS loosely coupled integration to further mitigate the NLOS error. Finally, the performance of the proposed methodology is evaluated through experiments. Experiments conducted in the typical NLOS environment of Nanjing show that the proposed method can achieve higher positioning accuracy when compared with the conventional UWB/INS integration.

In recent years, with the continuous development of synthetic organic chemistry, a large number of new compounds are synthesized every year. Many of these compounds not only have novel structures, but also have complex structures. The traditional four spectral analysis methods are difficult to understand its spatial structure clearly and comprehensively. At the same time, with the understanding of the spatial structure of related compounds, it is possible to further explore the relationship between the structure and properties of compounds. This paper analyzes different kinds of organic compounds, including nitrogen-containing organic compounds, polycyclic aromatic hydrocarbons and volatile organic compounds. The detection methods of volatile organic compounds and derivatization chromatography were discussed. Through VOC test, the results show that the average concentration of each substance decreases with time.

To meet the demand of ever operating in extreme environments of modern high-end vehicles or machineries, it is meaningful to perform basic research on fluid mechanics of hydraulic orifices and/or gaps under high or low temperature conditions. In this study, a novel compact experimental module which integrates the oil, the oil supply mechanism, the testing damping valve with orifices and/or gaps and several sensors was proposed, the experimental module has avoided the bulky method of using a full hydraulic system for oil supply and can be wholly placed into a high/low temperature chamber to undertake experiments; Based on the integrated experimental module, a test rig employing a variable-frequency-motor-driven ball screw driver to excite the testing module was developed. By using the virtual instrument technology, the hardware and software of automatic measurement and control system was further developed, so the automatic control and data collection of the test rig was realized. Final results show that the test rig can conveniently perform fluid mechanics experiments for various hydraulic orifices and/or gaps under high or low temperature conditions with high efficiency, so the test rig can be a very good platform for pertinent basic research works.

Aiming at performing basic research on fluid mechanics of hydraulic orifices under high or low temperature conditions, in this study, a novel compact experimental module, which integrates the oil, the oil supply mechanism, the test valve with orifice and several sensors, was firstly developed, the experimental module can be wholly placed into a high/low temperature chamber to undertake experiments; Based on the integrated experimental module, an automatic measurement test rig was further developed. By using the test rig, experiments on flow characteristics of a sharp-edged hydraulic orifice, which uses the anti-wear hydraulic oil HM46 as the working fluid, were conducted in a temperature range of -10°C∼+80°C, the Flow-Pressure Characteristics and Discharge Coefficient of the hydraulic orifice were obtained by curve fitting, the effects of different temperatures on the Discharge Coefficient and damping force were finally investigated. The results show that in the temperature range up to room temperature of 20°C, the Flow-Pressure characteristics, the Discharge Coefficient and damping force of the sharp-edged orifice are not sensitive to temperature changes, but when the temperature is below room temperatures, the discharge coefficient drops linearly, and the damping force increases with the decreasing of temperatures.

A new test rig with a compact experimental module has been developed in this study to support experiments on fluid mechanics of hydraulic orifices under high or low temperature conditions, by using the test rig, experiments on flow characteristics of a sharp-edged orifice and a thick-wall orifice were conducted in a temperature range of -10°C∼+80°C. Experimental results show that in a wide temperature range, the Flow-Pressure characteristics of the sharp-edged orifice are not sensitive to temperature changes, but that of the thick-wall orifice will vary obviously at different temperatures; In the temperature range up to 20°C, the Discharge coefficients and Damping forces of both of the two orifices remain at constants, however, when the fluid temperature is below 20°C, Discharge coefficients of the two orifice will drop linearly, damping forces of the two orifice will increase, but discharge coefficient and damping force of the thick-wall orifice will respectively drop and increase more sharply than that of the sharp-edged orifice, so this indicates that at low temperature conditions the fluid resistance and energy loss when it passes through a thick-wall orifice are larger than that when it passes through a sharp-edged orifice.

Aiming at studying the low-temperature damping characteristics of hydraulic damper, experimental research in the temperature range of -50°C∼+30°C was carried out to test the dynamic damping characteristics of a Chinese CRH high-speed train hydraulic yaw damper. Research results show that damping characteristics of the hydraulic damper will vary significantly at low temperature conditions when compared with that at normal temperatures, in general cases, the Force-displacement (F-s) curves are distorted and the damping forces are in abnormal levels; at very low temperatures, when the excitation speed is increasing, more severe empty strokes will occur during the damper compressions, so the absorption works of the damper will decrease significantly in these cases; in addition, dynamic stiffness of the damper will increase with the decreasing of temperatures, but in the compression stroke with large excitation speed, the dynamic stiffness at very low temperature conditions will drop sharply due to empty strokes. The results obtained in this study are significant for reference to improve the environment adaptability of high-speed rail hydraulic dampers and dynamics of the train operating under extreme cold weather conditions.