Driving Simulation Study on Speed-change Lanes of the Multi-lane Freeway Interchange

AbstractBecause of the interactions of the multi-lane freeway mainline, upstream, downstream, the diversity of environmental conditions, as well as the complexity of geometric configuration, speed-change lanes of the multi-lane freeway interchange present greatest safety and operational challenges for drivers. Most freeway crashes occur in the vicinity of interchange diverging and merging areas, especially in speed-change lanes. In this paper, the UC-win/Road5 software was used as the technical tool, and a three-dimensional driving scene was built. Multi-lane freeway field data were used for the calibration of model parameters. The geometry configuration of the speed-change lanes as well as the driving behavior characteristics such as speed, acceleration rate, glancing in the diverging and merging areas were studied in this paper. Based on the driving simulation study in the areas, results supply a valuable technical reference for speed-change lane geometry configuration, the length design of speed-change lane, the operational safety evaluation of multi-lane freeway diverging and merging areas, also the operation and management of multi-lane freeways

Coal Rock Breaking Simulation and Cutting Performance Analysis of Disc Cutters

The coal rock breaking ability of disc cutters directly affects the construction efficiency and safety of rescue tunnels in collapsed coal rock formations. This paper establishes the plastic constitutive relationship under the Drucker-Prager (D-P) plasticity criterion, builds up a finite-element analysis (FEA) model for the coal rock breaking with a single cutter on Abaqus FEA, and explores the influence laws of different penetrations and cutting velocities on the rock breaking performance of the cutter. The results show that: as the penetration increased from 3.0 mm to 7.0 mm, the mean vertical force of the cutter grew from 16.97 kN to 23.36 kN, and the mean rolling force rose from 1.79 kN to 3.95 kN. The increase of the cutter\u27s vertical force improves the cutting efficiency, but intensifies the vertical impact, which undermines construction safety. As the cutting velocity increased from 0.6 rad/s to 1.5 rad/s, the mean vertical force grew from 15.64 kN to 22.94 kN, and the mean rolling force rose from 1.46 kN to 4.23 kN. With the increase of cutting velocity, the cutting force grew at an increasing speed. The increase of cutting velocity can improve cutting efficiency, but an excessively fast cutting velocity will weaken the stability of the cutting operation, and add to the wear of the tool. The research method provides theoretical supports to the cutterhead design of tunnel boring machine (TBM) and tunnelling control in broken coal rock formation

What experiments on pinned nanobubbles can tell about the critical nucleus for bubble nucleation.

The process of homogeneous bubble nucleation is almost impossible to probe experimentally, except near the critical point or for liquids under large negative tension. Elsewhere in the phase diagram, the bubble nucleation barrier is so high as to be effectively insurmountable. Consequently, there is a severe lack of experimental studies of homogenous bubble nucleation under conditions of practical importance (e.g., cavitation). Here we use a simple geometric relation to show that we can obtain information about the homogeneous nucleation process from Molecular Dynamics studies of bubble formation in solvophobic nanopores on a solid surface. The free energy of pinned nanobubbles has two extrema as a function of volume: one state corresponds to a free-energy maximum ("the critical nucleus"), the other corresponds to a free-energy minimum (the metastable, pinned nanobubble). Provided that the surface tension does not depend on nanobubble curvature, the radius of the curvature of the metastable surface nanobubble is independent of the radius of the pore and is equal to the radius of the critical nucleus in homogenous bubble nucleation. This observation opens the way to probe the parameters that determine homogeneous bubble nucleation under experimentally accessible conditions, e.g. with AFM studies of metastable nanobubbles. Our theoretical analysis also indicates that a surface with pores of different sizes can be used to determine the curvature corrections to the surface tension. Our conclusions are not limited to bubble nucleation but suggest that a similar approach could be used to probe the structure of critical nuclei in crystal nucleation

3D fracture propagation simulation and pressure decline analysis research for I-shaped fracture of coalbed

After hydraulic fracturing, some treatments intended for production enhancement fail to yield predetermined effects. The main reason is the insufficient research about the fracture propagation mechanism. There is compelling evidence that I-shaped fracture, two horizontal fractures at the junction of coalbed and cover/bottom layer, and one vertical fracture in the coalbed have formed in part of the coalbed after hydraulic fracturing. Therefore, this paper aims at I-shaped fracture propagation simulation. A novel propagation model is derived on the basis of a three-dimensional (3D) model, and the coupling conditions of vertical fracture and horizontal fractures are established based on the flow rate distribution and the bottom-hole pressure equality, respectively. Moreover, an associated PDA (pressure decline analysis of post-fracturing) model is established. Both models complement with each other and work together to guide fracturing treatment. Finally, a field case is studied to show that the proposed models can effectively investigate and simulate fracture initiation/propagation and pressure decline

Effect of axial spacing on rotating stall performance of FBCDZ-10-No20 contra-rotating fan

Mining contra-rotating fan are prone to rotational stall when it operates at low flow rates, which seriously affects the operational stability. The unsteady flow in the full flow passage of a FBCDZ-10-No20 contra-rotating fan at five axial spacings was numerically simulated by using the SST k-ω turbulence model. The effect of axial spacing on the stall process of contra-rotating fan was studied, and the mechanism of stall inception and development at different axial spacings was revealed. The results shown that the axial spacing had a significant influence on the initial position, type and development of stall inception. For the axial spacings of 70 mm and 100 mm, the stall inception first occurred at the tip of the front stage, and subsequently appeared at the tip of the rear stage due to the rotor-rotor interaction between the two stages. However, compared with the axial spacing of 70 mm, the rotor-rotor interaction at the axial spacing of 100 mm was relatively weak, making it take longer for a stall inception to occur in the rear stage. For all three axial spacings of 140 mm, 170 mm and 225 mm, the stall inception occurred first in the root of rear stage. The difference was that for the axial spacing of 140 mm, the leakage flow at the tip of the front stage cannot completely flow out of the channel with the main flow, and a localized tip blockage area was formed. However, for both spacings of 170 mm and 225 mm, there was almost no blockage area at the tip of the front stage, and eventually only mature stall vortices formed in the rear stage. With the increase of the axial spacing, the blockage area formed by both the leading edge overflow and the trailing edge reverse flow those originated from the leakage flow at the tip of the front stage gradually reduced. In contrast, the blockage area formed by the radial vortex on the suction surface near the root of the rear stage gradually increased. When the leakage flow at the tip of the front stage failed to form blockage area, the stall type changed from the “spike type” induced by the tip leakage flow at the front stage to the “localized surge type” induced by the radial vortex flow at the root of the rear stage

Influence of axial spacing on stall development of FBCDZ-10-No20 mode contra-rotating fan

The rotating fan is prone to instability such as stall and even surge when operating at low flow rates. In order to study the influence of axial spacings on the stall inception and its development and propagation process of a contra-rotating fan , a Shear Stress Transport(SST) k-ω turbulence model was used to numerically simulate the unsteady flow in the whole passage of a FBCDZ-10-No20 contra-rotating fan. The stall evolution of fan under two axial spacings are investigated. The results show that the axial spacing has significant influence on the inception and development of fan stall.In the stall inception stage, when the axial spacing between the two-stage impellers is 170 mm, the stall inception first occurs within the rear impeller, which locates in the trailing edge area on the suction surface of the blade root. Then stall inception develops from the blade root to the tip area along the radial direction, and accumulates towards a blade passage along the circumferential direction and falls off on the way to form a blocking area, which eventually leads to stall. When the axial spacing is 70 mm, the stall inception successively occurs the tip area of the two-stage impellers. Then stall inception keeps increasing, which eventually leads to stall. During the full stall stage, the axial spacing has a significant effect on the propagation of the stall vortex in the circumferential, axial and radial directions. When the axial spacing is 170 mm, the type of stall vortex shows the single vortex full-blade high stall. The propagation range of the stall vortex in the axial direction is limited to the region of rear impeller, and rotates at 33.3% of the rear impeller speed in the circumferential direction; When the axial spacing is 70 mm, the type of stall vortex shows the multi-vortex partial blade high stall. The stall vortex are successively generated in the tip area of the two-stage impellers, propagating upward and downstream in the axial direction, and are dispersed in the area above 70% of the blade height of each blade channel in the radial direction. Due to the change of the axial distance between the two-stage impellers, the type of stall inception of the fan is changed from “partial surge type” to “Spike-type”

Whole-genome sequencing analysis of Klebsiella aerogenes among men who have sex with men in Guangzhou, China

Klebsiella aerogenes is a common infectious bacterium that poses a threat to human health. Nevertheless, there are limited data on the population structure, genetic diversity, and pathogenicity of K. aerogenes, especially among men who have sex with men (MSM). The present study aimed to clarify the sequence types (STs), clonal complexes (CCs), resistance genes, and virulence factors of popular strains. Multilocus sequence typing was used to describe the population structure of K. aerogenes. The Virulence Factor Database and Comprehensive Antibiotic Resistance Database were used to assess the virulence and resistance profiles. In this study, next-generation sequencing was performed on nasal swabs specimens collected in an HIV Voluntary Counseling Testing outpatient department in Guangzhou, China, from April to August 2019. The identification results showed that a total of 258 K. aerogenes isolates were collected from 911 participants. We found that the isolates were most resistant to furantoin (89.53%, 231/258) and ampicillin (89.15%, 230/258), followed by imipenem (24.81%, 64/258) and cefotaxime (18.22%, 47/258). The most common STs in carbapenem-resistant K. aerogenes were ST4, ST93, and ST14. The population has at least 14 CCs, including several novel ones identified in this study (CC11-CC16). The main mechanism of drug resistance genes was antibiotic efflux. Based on the presence of the iron carrier production genes irp and ybt, we identified two clusters according to virulence profiles. In cluster A, CC3 and CC4 carry the clb operator encoding the toxin. Increased monitoring is needed for the three main ST type strains carried by MSM. The main clone group CC4 has a large number of toxin genes, and it spreads among MSM. Caution is needed to prevent further spread of this clone group in this population. In sum, our results may provide a foundation for the development of new therapeutic and surveillance strategies for treating MSM

A Local Social Network Approach for Research Management

Traditional methods to evaluate research performance focus on citation count, quality and quantity of research output by individual researchers. These measures overlook the roles an individual plays in research collaboration, which is critical in an institutional research management environment due to the inherent interdependency among research entities. In order to address the organizational research management needs, we propose a research social network approach to better analyze local collaboration networks. For this purpose, we develop a new "collaboration supportiveness" measure to quantify an individual researcher's collaboration ability. Insights derived from this research are very helpful for managers to effectively allocate resources, identify research priorities, promote collaboration, and grow research in directions aligned with the organizational strategies. © 2012 Elsevier B.V