Analysis Of Shock Waves Research Articles

APPLICATION OF TRAVEL TIME RELIABILITY FOR PERFORMANCE ORIENTED OPERATIONAL PLANNING OF EXPRESSWAYS

Evaluation of impacts of congestion improvement scheme s on travel time reliability is very significant for road authorities since travel time reliability repr esents operational performance of expressway segments. In this paper, a methodology is presented to estimate travel tim e reliability prior to implementation of congestion relief schemes based on travel time variation modeling as a function of demand, capacity, weather conditions and road accident s. For subject expressway segmen ts, traffic conditions are modeled over a whole year considering demand and capacity as random variables. Patterns of demand and capacity are generated for each five minute interval by appl ying Monte-Carlo simulation technique, and accidents are randomly generated based on a model that links acci dent rate to traffic conditions. A whole year analysis is performed by comparing de mand and available capacity for each scenario and queue length is estimated through shockwave analysis for each time in terval. Travel times are estimated from refined speed-flow relationships developed for intercity expressways and buffer time index is estimated consequently as a measure of travel time reliability. For validation, estimated reliability indices are compared with measured values from empirical data, and it is shown that the proposed method is suitable for operational evaluation and planning purposes.

Consistency of Input-Output Model and Shockwave Analysis in Queue and Delay Estimations

This paper investigates the consistency between the simple input-output model and the shockwave analysis method as applied to traffic bottleneck problems. Mathematical derivations considering changes in arriving demand and discharge rate have shown that these models are consistent in queue and delay estimations, as both methods produce identical results at anytime during the congestion propagation and dissipation processes. Earlier findings on the inconsistency of these two methods are attributed to the lack of consideration of the baseline factor, which is dependent on the level of background traffic. Numerical examples are presented to illustrate the importance of the baseline factor, to ensure consistency regardless of the use of different flow-density relationships.

Free-electron-laser-induced shock-wave control and mechanistic analysis using pulse control

The wavelength of the free electron laser (FEL) in Osaka University can be continuously varied in the range of 5.0-20.0 microm. The FEL has a double-pulse structure, consisting of a train of macropulses of pulse duration 12 micros. Each macropulse contains a train of 330 micropulses of pulse duration 5 ps. The tunability and picosecond pulses afford new medical and biological applications. However, a macropulse of long pulse duration leads to undesirable secondary effects. Precise control of the macropulse duration is essential for the high-precision applications of the FEL. An FEL pulse control system using acousto-optic modulators has been developed to investigate mechanical (shock-wave) effects of the FEL on living tissues. With this system, we have controlled photoinduced shock waves and determine the mechanism of interaction during FEL-induced tissue ablation.

Dynamic and Quasi-Static Propagation of Compaction Waves in a Low-Density Epoxy Foam

We conducted dynamic and quasi-static compression experiments with low-density (ρ = 120 kg/m3) epoxy foam specimens. The specimens had a 10.0-mm-square cross-section and a length of 19.3 mm. Dynamic experiments were conducted with a modified split Hopkinson pressure bar (SHPB), and the quasi-static experiments were conducted with a hydraulic load frame device (MTS-810). In both cases, the specimens were loaded from one end at a constant velocity. Equally spaced grid lines were marked on the specimens to monitor the deformation history. Digital images taken at equally spaced time intervals gave the positions of each grid line. These images showed that a constant end-face velocity V produced a compaction wave front that traveled at a constant velocity C in both dynamic and quasi-static experiments. We described these results with a shockwave analysis that used a locking solid material model.

Road pricing modeling for hyper-congestion

Recently there has been a resurgence in the interest of road pricing. Most studies adopt the static modeling paradigm, typically using either separable monotone or backward-bending link travel time functions for the analysis. In this study, through the shockwave analysis, we show that separable backward-bending functions are not appropriate for modeling hyper-congestion and hence road pricing. In the absence of queue spillback, link travel time is a monotone increasing function of inflow. However, in the presence of queue spillback, we show that the static paradigm even with a monotone travel time function cannot adequately portray the congestion phenomenon. In some cases, the tolls determined by the static paradigm can be even detrimental, worsening rather than alleviating the congestion problem. In the end, to model congested networks properly, perhaps one has no other choices but to adopt a modeling paradigm that faithfully captures both the temporal as well as the spatial dimensions of traffic queuing.

On-Line Measure of Shockwaves for ITS Applications

The formation of shockwaves demarking boundaries between different flow states in time-space domains has been well studied and documented in the literature. Previous research concentrated on theoretical and mathematical analyses of shockwaves, providing valuable insights into shockwave phenomena. In the past few years, the traffic signal systems community has witnessed an increasing interest in adaptive control algorithms. These algorithms strive to achieve real-time platoon accommodation by assuming platoon speed and dispersion characteristics in order to predict its time of arrival at the downstream signal. Instead of assuming platoon speed and dispersion characteristics, we propose an on-line analysis of shockwaves at the downstream intersection to achieve the same purpose. This paper introduces a new metric that can detect and quantify shockwaves formed as a result of a suboptimal offset at an intersection. The new metric, the F′ model, captures the effects of shockwaves using cycle-based tabulation of advance detector occupancy and count. A discriminant analysis is conducted to develop thresholds to which F′ values can be compared to estimate the offset performance. The metric introduced in this paper can be used for implementing adaptive offset tuning algorithms in a traditional closed loop coordinated traffic signal system.

Analyzing Freeway Traffic under Congestion: Traffic Dynamics Approach

This paper presents an analysis of freeway traffic flows under congestion based on the principle of traffic dynamics, using the example of recurring congestion. Queuing and discharging mechanisms are analyzed using the fundamental concept of conservation of vehicles. These analysis results are applied for reviewing the two conventional macroscopic analysis tools, deterministic queuing analysis and shock-wave analysis. Comparative study results have demonstrated that (1) the two methods are fundamentally different from the traffic modeling point of view; (2) deterministic queuing analysis always underestimates the overall magnitude of delays compared to shock-wave analysis; and (3) the area between the demand and the capacity curves in a queuing diagram is analytically equivalent to total vehicle-hours of travel in congestion as opposed to the widely accepted total vehicle-hours of delay. The study results imply that the guidelines of the 1994 Highway Capacity Manual may result in the underestimation of congestion-related statistics. For the purposes of illustration and verification, a numerical example problem is provided.

ANALYSIS OF HIGHWAY BOTTLENECKS.

Engineers have made use of one of two common methods in analysing highway bottleneck problems. The two methods -queueing analysis and shock-wave analysis- are compared in this paper. The reasons why there are possible discrepancies in the results from the two methods are suggested. If the problem is compatibly formulated, the two methos give similar results, provided that these results are correctly interpreted. Although shock-wave analysis can provide an understanding of the physical length of the moving queue approaching the bottleneck, queueing analysis is still more advantageous in that it is a simpler procedure to apply.

Analysis of plane elastic-plastic shock-waves from the fourth-order anharmonic theory

A finite strain elastic-plastic formalism developed in the literature and ageneralization of the Mie-Grüneisen equation for nonhydrostatic stresses are used to calculate Hugoniot states for macroscopically isotropic materials. The general form of the free energy function resulting from the fourth-order anharmonic theory can be combined with the Hugoniot law of conservation of energy to obtain temperature-stress-strain relations for the uniaxial shock loading. In the third-order approximation, the parameters entering these relations may be found from ultrasonic data by means of a suitable averaging procedure. With the work-hardening model proposed here, it is shown that the determination of the Hugoniot curve does not require a description of the shock structure. The theoretical Hugoniot stress-strain curve for copper and aluminium is calculated in the special case of ideal plasticity for stresses up to 150 kbar. 1 A comparative study of the results with those derived from the hydrodynamic approximation is also made.

The high-temperature acoustic Grüneisen parameter in the earth's interior

The value of the acoustic Grüneisen parameter, γ a, in the earth's interior has been computed using data from recent models obtained by inversion of normal data. In this paper we emphasize the data from the PEM model of the earth because there has been sufficient smoothing of the seismic data so that the derivatives d ln ν s/d ϱ and d ln ν p/d ϱ can be well defined at all depths. The results for the lower mantle show that γ a decreases exponentially from 1.3 to 1.0, and there are several consistent cross-checks of the limiting values. We find γ a is about 1.5 for the inner core and outer core. These results confirm, in broad outline, the results of others who computed γ for the core by entirely different methods. They also confirm a higher value of γ in the inner core. The value of γ a in the lower mantle follows a ρ −1.35 law, which is reminiscent of the expirical law γρ = constant, commonly used in shock-wave analyses.

Determination of traffic delays from shock-wave analysis

The traffic shock-wave theory of Lighthill and Whitham is applied to a general incident, i.e. a moving incident with filtering (overtakings). It is shown that individual and total delays and the related costs can be determined simply by graphical means. A formulation, which is independent of any particular macroscopic theory of traffic flow, is obtained for the total delay upstream of the incident. It is shown to be identical to that obtained by using deterministic queuing theory. Simple incidents such as a red traffic signal light and a slow truck in a no passing zone are shown to be special cases.

On the Compression of Stishovite

Summary Currently available shock-wave compression data for single-crystal α-quartz and pore-free quartzite have been used to determine values for the isentropic bulk modulus of stishovite and its first pressure derivative. The shock-wave data reduction scheme makes use of the observed linearity in the shock-velocity-particle-velocity field over the pressure range 0.4–2.0 Mbar and the first-order Murnaghan equation of state. In addition, an accurate form of the temperature independent Gruneisen parameter (γ), consistent with the linear Us–up relation, has been used in the reduction of the fundamental shock-wave data to the metastable Hugoniot. The temperature derivative of the isentropic bulk modulus is provided by a least-square fit of the γ relation to available Hugoniot data directly measured on porous and fused-quartz samples in the high-pressure regime. The pertinent results are: KS= 3.35±0.19 Mbar; (∂KS/∂P)T= 5.5±0.6; and (∂KS/∂T)p= (−0.35±0.08)× 10−3 Mbar/°K. These results are consistent with recent static-compression and ultrasonic measurements on stishovite and are related systematically to corresponding data for isostructural GeO2 and TiO2. Comparison of the present results with recent shock-wave analyses by other investigators suggests that the first-order Murnaghan form of the equation of state is more appropriate than the first-order Birch equation in reproducing the compression of stishovite in the zero to 2 Mbar pressure range. An evaluation of the composition of the lower mantle in terms of the fundamental oxides, FeO, MgO, and SiO2, using the present results for the elastic properties of stishovite, support marginally the conclusions of previous investigators regarding enrichment of FeO and SiO2 relative to the upper mantle; however, such an interpretation is predicated on the mixed oxide assumption and should be considered in relation to alternative models.

Electromagnetic shockwave analysis using boundaries in moving frame of reference

Electromagnetic shockwave analysis using boundaries in moving frame of reference