New York State Department of Transportation

The transition between dripping and jetting regimes of capillary jets is crucial for applications such as ink-jet printing and drug release. A liquid jet emitting from a nozzle usually exhibits a non-uniform initial velocity profile, influencing the transition between regimes, with the role of velocity relaxation remaining largely unexplored. Here we investigate the dripping–jetting transition of a capillary jet with velocity relaxation through a combination of experiments and stability analysis. Experimental measurements show that velocity relaxation consistently lowers the critical transition Weber number, ${\textit{We}}_c$ , contradicting predictions from the classic local spatio-temporal stability theory. To resolve this discrepancy, we developed a global stability model accounting for the velocity relaxation to calculate ${\textit{We}}_c$ at different Reynolds numbers ( ${\textit{Re}}$ ). Our model provides accurate predictions for jets both with and without velocity relaxation and reveals that the key to the discrepancy lies primarily in the non-parallel effects of jet disturbances caused by velocity relaxation. The velocity relaxation process upstream facilitates the non-uniformity and non-parallelism of the global disturbances and leads to stronger radial–axial coupling in the disturbance field at a higher ${\textit{Re}}$ , showing a global dynamics beyond the ability of local analysis. Formulas of ${\textit{We}}_c$ for both Poiseuille- and uniform-velocity jets are proposed based on the results of global stability analysis. These findings elucidate the dynamics of the global instability for dripping–jetting transition under the influence of velocity relaxation and provide guidance for the precise control of jet behaviours in practical applications.

This paper serves as a technical review on an emerging demand-responsive, vehicle platoon-based, exclusive lane-delimited mass transit system, which is officially named Intelligent Vehicle Platooning Transit (IVPT). Different from previous studies on vehicle platooning systems for passenger and freight transportation, the focus of this paper is on systematically analyzing IVPT’s system components and technologies, operations design and management issues, and field and simulation experiment results. We also present a techno-economic comparison between IVPT and other existing urban public transportation systems. The analysis and comparison highlight several key advantages of this new transit system: 1) The cruise speed of its moving vehicles is guaranteed to be at its design value and seldom disturbed due to the use of vehicle platoons, exclusive lanes, and signal priority; 2) its direct station-to-station passenger-carrying service eliminates passengers’ transfer time and inconvenience and enhance their arrival punctuality to a maximum extent; 3) online trip booking, passenger-vehicle matching and passenger-seat assignment allow passengers to specify their boarding and alighting stations, departure times, vehicle types, and seating preference and hence greatly reduce their waiting time at stations and enhancing overall travel satisfaction; and 4) it involves much lower construction and maintenance costs than a conventional mass transportation system with the potential of faster implementation. In our conclusion, IVPT offers a sustainable, flexible, scalable, and cost-effective mass transit solution and has potential of becoming a backbone transit system for future urban areas.

ABSTRACT To address the issue that existing testing methods cannot achieve precise in situ characterization of the mechanical parameters of solid rocket motor grain materials, this work, based on the elastic contact theory, combines the generalized Maxwell model for viscoelastic materials to derive and establish the theoretical indentation model for the relaxation characteristics of propellant. Through a coordinated analysis of indentation relaxation testing and finite element simulations at different constant indentation depths, the applicability of the theoretical indentation model was studied. The results indicate that the relaxation modulus is highly consistent at different indentation depths, but there is a certain deviation between the indentation load–time simulation curve and the testing curve. This deviation increases as the constant indentation depth increases. Based on this, the causes of the theoretical indentation model error were analyzed, a correction method for the theoretical indentation model was proposed, and the modified theoretical indentation model was validated through a comparison of simulation and testing data. The theoretical indentation model provides a new method for the mechanical property testing and evaluation of solid rocket motor grain materials.

This paper presents a fifth-order weighted compact nonlinear scheme (WCNS) enhanced with machine learning for the simulation of compressible flows. The scheme is designed to achieve robust shock capturing and low dissipation while attaining unconditionally optimal high-order accuracy. This approach extends the fundamental ideas of Bezgin et al. [J. Comput. Phys. 452, 110920 (2022)] and introduces improvements to the training strategy. By incorporating an artificial neural network that can automatically identify local flow features and integrating critical-point detection into the network, the scheme is able to dynamically optimize interpolation-weight selection, ensuring the desired order of accuracy at any critical points. Several benchmark tests demonstrate that the proposed scheme outperforms traditional schemes in terms of accuracy and spectral resolution, exhibits strong generalization across various grid resolutions, and effectively captures shocks while maintaining high-resolution properties.