A two-sided lateral gap continuum model and its numerical simulation for non-lane based heterogeneous traffic environment

Heterogeneous traffic conditions prevail in developing countries. Vehicles maintain weak lane discipline which increases lateral interactions of vehicles significantly. It is necessary to study these interactions in the form of maintained lateral gaps for modeling this traffic scenario. This paper aims at determining lateral clearances maintained by different vehicle types while moving in a heterogeneous traffic stream during overtaking. These data were collected using an instrumented vehicle which runs as a part of the stream. Variation of obtained clearance with average speed of interacting vehicles is studied and modeled. Different instrumented vehicles of various types are developed using (1) ultrasonic sensors fixed on both sides of vehicle, which provide inter-vehicular lateral distance and relative speed; and (2) GPS device with cameras, which provides vehicle type and speed of interacting vehicles. They are driven on different roads in six cities of India, to measure lateral gaps maintained with different interacting vehicles at different speeds. Relationships between lateral gaps and speed are modeled as regression lines with positive slopes and beta-distributed residuals. Nature of these graphs (i.e., slopes, intercepts, residuals) are also evaluated and compared for different interacting vehicle-type pairs. It is observed that similar vehicle pairs maintain less lateral clearance than dissimilar vehicle pairs. If a vehicle interacts with two vehicles (one on each side) simultaneously, lateral clearance is reduced and safety of the vehicles is compromised. The obtained relationships can be used for simulating lateral clearance maintaining behavior of vehicles in heterogeneous traffic.

ABSTRACTThe exact solutions for the Riemann problem concerning the one‐dimensional triple‐pressure Euler equations with the Coulomb‐type frictional term are displayed in perfectly explicit forms, where both the rarefaction and shock waves are presented in parabolic shapes with equal curvature under the action of the Coulomb‐type frictional term. Specifically, the curved delta shock wave is formed by sending the limit of Riemann solution comprised of double shock waves, and the vacuum state is also grown up by taking the limit of Riemann solution comprised of double rarefaction waves when all the three perturbation parameters are dropped to zero, where the remarkable concentration and cavitation phenomena can be closely observed and explored. Besides, the numerical simulations in correspondence are also offered to validate our results.

Unlike the freeway traffic stream, the urban traffic stream is generally interrupted by signals, and the traffic data observed may differ from the true (uninterrupted) flow characteristics. This paper deals with the transformation between interrupted and uninterrupted speeds on an urban road with signalized intersections. The conventional shock wave model and two modified versions of the shock wave boundary that address unrealistic characteristics of the conventional shock wave model are developed. A method of integrating probe and detector data for speed transformation is also discussed. The proposed methods are tested with a virtual isolated signalized intersection by varying the approach demand. The numerical results suggest that all models can significantly reduce the difference between the actual and the estimated uninterrupted (or interrupted) speeds compared with the case of doing nothing. The applications of the proposed methods, including the development of a flow-speed model and link travel time...

A simple theory of traffic flow is developed by replacing individual vehicles with a continuous “fluid” density and applying an empirical relation between speed and density. Characteristic features of the resulting theory are a simple “graph-shearing” process for following the development of traffic waves in time and the frequent appearance of shock waves. The effect of a traffic signal on traffic streams is studied and found to exhibit a threshold effect wherein the disturbances are minor for light traffic but suddenly build to large values when a critical density is exceeded.

The flows and densities of traffic streams play an important role in defining the performance of roadways and corresponding improvement strategies. Traffic flows and densities are the outco...

5 - Molecular Dynamics (MD) and Coarse Grain Simulation of High Strain-Rate Elastomeric Polymers (HSREP)

Jet electrochemical machining (Jet-ECM) is a flexible method for machining complex microstructures in high-strength and hard-to-machine materials. Contrary to mechanical machining, in Jet-ECM there is no mechanical contact between tool and workpiece. This enables Jet-ECM, like other electrochemical machining processes, to realize surface layers free of mechanical residual stresses, cracks, and thermal distortions. Besides, it causes no burrs and offers long tool life. This paper presents selected features of Jet-ECM, with special focus on the analysis of the current density during the machining of single grooves in stainless steel EN 1.4301. Especially, the development of the current density resulting from machining grooves intersecting previous machining steps was monitored in order to derive systematic influences. The resulting removal geometry is analyzed by measuring the depth and the roughness of the machined grooves. The correlation between the measured product features and the monitored current density is investigated. This correlation shows that grooves with the desired depth and surface roughness can be machined by controlling current density through the adjustment of process parameters. On the other hand, current density is sensitive to the changes of working gap. As a consequence of the changes of workpiece form and size for the grooves intersecting premachined grooves as well as the grooves with a lateral gap, working gap, and current density change. By analyzing monitoring data and removal geometry results, the suitability of current density inline monitoring to enable process control is shown, especially with regards to manufacture products that should comply with tight predefined specifications.

The Riemann problem for the Umami Chaplygin Aw-Rascle model of traffic flow with Coulomb-like friction is solved by introducing the reasonable flux-function. Three kinds of non-self-similar Riemann solutions involving delta-shock are given exactly by the means of variable substitution method. The serious traffic congestion may be explained by the delta-shock, for which, the generalized Rankine–Hugoniot relation and entropy condition are clarified. Since the friction term is involved, all waves containing the rarefaction wave, contact discontinuity, shock wave, and delta-shock are bent into parabolic curves. By analyzing the limiting behavior of the solutions, it is discovered that as the Umami Chaplygin gas pressure and flux-function vanish simultaneously, the Riemann solution containing the rarefaction wave and the contact discontinuity tends to the vacuum solution of the zero-pressure Euler equations with friction, and the solution including the shock wave and the contact discontinuity tends to the delta-shock solution of the zero-pressure Euler equations with friction.

A simple 1D model of inviscid fluid–solid interaction

A numerical study of the isothermal fluid equations with a nonmonotone equation of state (like that of van der Waals) and with viscosity and capillarity terms is presented. This system is ill-posed (i.e., elliptic in x vs. t) in some regions of state space and well-posed (i.e., hyperbolic) in other regions. Thus, it may serve as a model for describing dynamic phase transitions. Numerical computations of phase jumps, shock waves, and rarefaction waves for this system are presented. Although the solution of the Riemann problem is not unique, all of these waves are found to be stable to infinitesimal initial perturbations. Criteria are found for instability after $O( 1 )$ initial perturbations. An analytic argument is made for stability of phase transitions.

Why many theories of shock waves are necessary: Kinetic functions, equivalent equations, and fourth-order models

A brief review of the results obtained in recent research of underwater electrical explosions of wires and wire arrays using microsecond-, submicrosecond-, and nanosecond-timescale high-current generators is presented. In a microsecond-timescale wire explosion, good agreement was attained between the results of experiments and the results of magnetohydrodynamic calculations coupled with equations of state (EOS) and modern conductivity models. Conversely, in a nanosecond-timescale wire explosion, the wire resistance and the EOS were modified in order to fit experimental data. In experiments with cylindrical and spherical wire arrays, generation of a converging shock wave (SW) was demonstrated allowing formation of an extreme state of water in the vicinity of either the axis or the origin of the SW's implosion. In addition, it is shown that SW convergence in superspherical geometry allows one to achieve larger values of pressure, density, and temperature of water in the vicinity of the axis of convergence than in the case of a spherical implosion. The results of experiments and numerical analysis showed that a cylindrical SW keeps its symmetry along the main path of its convergence. In addition, it is shown that underwater electrical explosion of an X-pinch wire configuration and a cone wire array allows one to generate fast jets of metal and water, respectively, without using chemical explosions.

The MPI two-sided communication model has been widely used in scientific applications for decades. The nonblocking version of the two-sided routines allows the application to potentially improve performance on many systems by overlapping communication and computation. In practice, unfortunately, the overlap is hard to achieve because of the limitations of the MPI internal progress engine and the underlying network. The traditional approach to resolving this issue is to implement an asynchronous progress engine based on either additional threads or hardware interrupts; however, such approaches may result in reduced computing power or expensive overheads. In this paper, we present a portable process-based asynchronous progress approach for two-sided communication in the PMPI-based Casper framework. It allows the user to specify an arbitrary number of cores on a multicore or many-core architecture and offload the point-to-point communication to these cores, thus ensuring asynchronous progress with low overhead. Unlike our previous work that supports asynchronous progress for the MPI one-sided model, a completely new design is needed for the message-matching-based two-sided model in order to ensure comprehensive semantics correctness as defined in the MPI standard. We present a detailed design of this two-sided model and compare it with the traditional thread-based approach on both a multicore Intel Xeon cluster and a many-core Knights Landing cluster.

Optimization of turbofan engine air intake as well as geometry of intake lip, in-let cross-sectional area and its length is a relevant task in optimizing aerodynamic configuration of an aircraft. It is necessary to ensure a smooth entry of air flow into the engine at all modes of its operation and at various aircraft evolutions while minimizing impact on the overall aerodynamic efficiency of the aircraft. Development of engine air intake was once a very long, routine process that could last for months be-fore design completion, followed by expensive tests on determination of air intake performances on the engine test bench and in flight. Today, we can evaluate performances for a large number of air intake options using design software. The use of computational methods does not exclude tests of air intakes but dramatically reduces their quantity, testing costs and allows designers to focus mainly on the best candidates for air intakes avoiding potential surprises such as shock waves or flow separation caused by a shock wave. Optimal design of the air intake includes determining the right balance between the air intake characteristics, structural load and weight. An over-designed air intake will ultimately be overweight and thus more expensive in terms of flight cost. In a well-designed air intake the Mach number should not exceed 1, in order to avoid a sudden change in static pressure, temperature and density, which can lead to potential shock waves and flow separation caused by a shock wave in all areas throughout the flight. The use of computational fluid dynamics al-lows a better understanding of the conditions under which such adverse events occur. Adjacent to this task is the provision of necessary area on the inside of air intake to ensure sufficient noise absorption generated by the engine fan. The article considers evolution of research on the example of air intake of the D-436 engine of the An-148 aircraft.

Comparative study between turbulence models in unsteady cavitating flow with special emphasis on shock wave propagation