Effect Of Velocity Difference Research Articles

Verification of Delayed Equilibrium Model for the R134a critical flow in a slit

R134a has the advantage of conducting visible critical flow experiments because of the lower temperature and pressure at the critical point than water. Whether the water critical flow model is suitable for predicting the flow rate and the pressure profile of R134a critical flow is unknown. An experiment on the critical flow rate and the pressure profile of R134a critical flow in a slit, mimicking the shape of a crack in the pipe, has been conducted. The dimension of the slit and the subcooling degree at the entrance are changed in the experiment. The Delayed Equilibrium Model (DEM), which is accurate for the water critical flow mass flux in a slit, is verified based on the experiment results. The empirical coefficients in the original DEM are adjusted according to the approximate saturated curve of R134a. The conservative and aggressive approaches to changing empirical coefficients are verified, respectively. For R134a, the ratio of boiling pressure to saturated inlet pressure is determined to minimize the relative error of volume flow rate and pressure profile in the slit with 0.3 mm width. It proves that the aggressive approach is lower in relative errors and differences in relative errors among different slit widths and different subcooling degrees. For the aggressive approach, the abstract value of the relative error of volume flow rate is lower than 20% in most cases. The abstract value of the mean relative error of pressure is lower than 15% in most cases. Besides, the differences in relative errors among different slit widths are not significant, and the differences in relative errors tend to be zero as the subcooling degree increases. DEM is adequate for predicting the volume flow rate and pressure profile for the R134a critical flow in a slit. Nevertheless, the relative error of the volume flow rate should disperse around zero at low subcooling degree, which is not achieved in this research. Further optimization requires more rigorous analytical methods and experiment data to find the best set of empirical coefficients, and the effect of velocity difference may be introduced.

Characterizing the 2D single atom solutions to capture CO2 by the digital twin model

The digital twin model is developed to characterize the CO2 capture by the Cu and B 2D single atom solution (2DSAS). The key digital functions distributions f[], g[] and h[] characterize the physical 2DSAS system with the digital code 1 and 0. The thermoelectrical effect of the 2DSAS is analyzed. The digital code combinations of Cu atoms sorting from 1111 to 11,111 with B atoms sorting from 00 to 000 were identified as more suitable for CO2 capture. The effects of velocity difference of Cu and B atoms, temperature and CO2 loading were discussed. CO2 desorption efficiency was increased by an average 4.2 % and the energy consumption of desorption was reduced by 35.4 % at h[] of 3.5 × 10-6 m/s to 5 × 10-6 m/s. The 2DSAS of Cu and C, Cu and N and Cu and Si were suggested for CO2 capture.

Effects of Velocity Difference and Position of Shear Flow on Performance of Micro Propeller Wind Turbine

Effects of Velocity Difference and Position of Shear Flow on Performance of Micro Propeller Wind Turbine

New Feedback Control Model in the Lattice Hydrodynamic Model Considering the Historic Optimal Velocity Difference Effect**Supported by the National Natural Science Foundation of China under Grant No. 61673168

A feedback control model of lattice hydrodynamic model is proposed by taking the information of the historic optimal velocity into account for the traffic system. The modern control theory is applied for the linear stability condition with feedback control signal. The result shows that the stability of traffic flow is closely related to the information of the historic optimal velocity. Furthermore, numerical simulations conform that the new feedback control did increase the stability of traffic flow efficiently, which is in accord with theoretical analysis.

Research on three-phase traffic flow modeling based on interaction range

On the basis of the multiple velocity difference effect (MVDE) model and under short-range interaction, a new three-phase traffic flow model (S-MVDE) is proposed through careful consideration of the influence of the relationship between the speeds of the two adjacent cars on the running state of the rear car. The random slowing rule in the MVDE model is modified in order to emphasize the influence of vehicle interaction between two vehicles on the probability of vehicles’ deceleration. A single-lane model which without bottleneck structure under periodic boundary conditions is simulated, and it is proved that the traffic flow simulated by S-MVDE model will generate the synchronous flow of three-phase traffic theory. Under the open boundary, the model is expanded by adding an on-ramp, the congestion pattern caused by the bottleneck is simulated at different main road flow rates and on-ramp flow rates, which is compared with the traffic congestion pattern observed by Kerner et al. and it is found that the results are consistent with the congestion characteristics in the three-phase traffic flow theory.

Nonlinear analysis of a new car-following model accounting for the global average optimal velocity difference

In this paper, a new car-following model is proposed by considering the global average optimal velocity difference effect on the basis of the full velocity difference (FVD) model. We investigate the influence of the global average optimal velocity difference on the stability of traffic flow by making use of linear stability analysis. It indicates that the stable region will be enlarged by taking the global average optimal velocity difference effect into account. Subsequently, the mKdV equation near the critical point and its kink–antikink soliton solution, which can describe the traffic jam transition, is derived from nonlinear analysis. Furthermore, numerical simulations confirm that the effect of the global average optimal velocity difference can efficiently improve the stability of traffic flow, which show that our new consideration should be taken into account to suppress the traffic congestion for car-following theory.

Interface instability mechanism of an annular viscous liquid sheet exposed to axially moving inner and outer gas

The interface instability mechanism of an annular viscous liquid sheet exposed to axially moving inner and outer gas is investigated. Sheet instability and breakup have been investigated using a nonlinear spatial instability analysis. A perturbation expansion method is used with the initial amplitude of the disturbance as the perturbation parameter. The evolution of the two gas–liquid interfaces is tracked until the sheet breaks up and the breakup length is determined. The model is validated by comparison with available experimental data. To investigate the interface instability mechanism of an annular viscous liquid sheet, the effects of velocity difference between gas and liquid, annular curvature on the annular sheet instability have been studied. The results show that both first-order and second-order maximum disturbance growth rates increase with increase in velocity difference between gas and liquid, and annular liquid sheet curvature. Also, with increasing velocity difference between gas and liquid, large interface deformations occur and the breakup length of the annular viscous liquid sheet becomes shorter. The shear effect difference between the outer and inner sides of the annular liquid sheet is the source of instability.

An unsteady model for fluidelastic instability in an array of flexible tubes in two-phase cross-flow

The streamtube model for fluidelastic instability in single-phase flow was extended to two-phase flow by two kinds of two-phase flow model. One was the traditional HEM, and the other was the slip ratio model. The model based on slip ratio can represent the effect of velocity difference between gas and liquid phases, and was verified with the experimental data from the literature. Comparing to the conventional HEM model, the slip ratio model and the introduction of interfacial velocity could collapse the stability data from various studies, which is beneficial for predicting the fluidelastic instability of tube bundles from existing stability maps and methods.

A Control Method Considering Two Velocity Difference Effect in the Car Following Model

A modified car following model is put forward considering the headway distance of two successive vehicles in front. A control method to suppress traffic congestion is proposed for car following model. According to the control theory, the stability conditions are derived. The feedback signals, which act on our traffic system, consider two velocity difference effect. The control signals will play an effect only if the traffic state is in congestion. The corresponding numerical simulation results are agree well with our theoretical analysis.

Discontinuous transition from free flow to synchronized flow induced by short-range interaction between vehicles in a three-phase traffic flow model

In this paper, we incorporate a limitation on the interaction range between neighboring vehicles into the cellular automaton model proposed by Gao and Jiang et al. [K. Gao, R. Jiang, S. X. Hu, B. H. Wang and Q. S. Wu, Phys. Rev. E 76 (2007) 026105], which was established within the framework of Kerner’s three-phase traffic theory and has been shown to be able to reproduce the three-phase traffic flow. This modification eliminates an unrealistic phenomenon found in the previous model, where the velocity-adaptation effect between neighboring vehicles can exist even if those vehicles are infinitely far away from each other. Therefore, in the improved model, we regulate that such interactions can only occur within a finite distance. For simplicity, we suppose a constant value to describe this distance in this paper. As a result, when compared to the previous model, the improved model mainly simulates the following results which are believed to be an improvement. (1) The improved model successfully reproduces the expected discontinuous transition from free flow to synchronized flow and the related “moving synchronized flow pattern”, which are both absent in the original model but have been observed in real traffic. (2) The improved model simulates the correlation functions, time headway distributions and optimal velocity functions which are all more consistent with the empirical data than the previous model and most of the other models published before. (3) Together with the previous two models considering the velocity-difference effect, this model finally accomplishes a significative process of developing traffic flow models from the traditional “fundamental diagram approach” to the three-phase traffic theory. This process should be helpful for us to understand the traffic dynamics and mechanics further and deeper.

Cellular-automaton model with velocity adaptation in the framework of Kerner’s three-phase traffic theory

In this paper, we propose a cellular automata (CA) model for traffic flow in the framework of Kerner's three-phase traffic theory. We mainly consider the velocity-difference effect on the randomization of vehicles. The presented model is equivalent to a combination of two CA models, i.e., the Kerner-Klenov-Wolf (KKW) CA model and the Nagel-Schreckenberg (NS) CA model with slow-to-start effect. With a given probability, vehicle dynamical rules are changed over time randomly between the rules of the NS model and the rules of the KKW model. Due to the rules of the KKW model, the speed adaptation effect of three-phase traffic theory is automatically taken into account and our model can show synchronized flow. Due to the rules of the NS model, our model can show wide moving jams. The effect of "switching" from the rules of the KKW model to the rules of the NS model provides equivalent effects to the "acceleration noise" in the KKW model. Numerical simulations are performed for both periodic and open boundaries conditions. The results are consistent with the well-known results of the three-phase traffic theory published before.

Perceived internal depth in rotating and translating objects.

Previous research has indicated that observers use differences between velocities and ratios of velocities to judge the depth within a moving object, although depth cannot in general be determined from these quantities. In four experiments we examined the relative effects of velocity difference and velocity ratio on judged depth within a transparent object that was rotating about a vertical axis and translating horizontally, examined the effects of the velocity difference for pure rotations and pure translations, and examined the effect of the velocity difference for objects that varied in simulated internal depth. Both the velocity difference and the velocity ratio affected judged depth, with difference having the larger effect. The effect of velocity difference was greater for pure rotations than for pure translations. Simulated depth did not affect judged depth unless there was a corresponding change in the projected width of the object. Observers appear to use the velocity difference, the velocity ratio, and the projected width of the object heuristically to judge internal object depth, rather than using image information from which relative depth could potentially be recovered.

Group velocity difference effect on incoherent sum-frequency generation spectrum

The spectral distribution of optical sum-frequency generation (SFG) by incoherent non-linear mixing of two chaotic beams with identical spectral width η is calculated theoretically in the first approximation of the iterative method including dispersion of the non-linear medium and the difference κ between the group velocity of the input beams. It is shown that for the same group velocities (κ=0) of the input beams in non-linear medium the resultant field has a spectral width narrower than η, and if a phase mismatch is present the spectral maximum of the resultant field is shifted towards lower or higher frequencies according to the sign of the phase mismatch. If the input beams have different group velocities (κ≠0) in the non-linear medium, then the spectral distribution of SFG is strongly dependent on η. For small η the spectral distribution of SFG is the same irrespective of κ. For large η the difference in group velocities broadens the spectrum of SFG and for very large differences in group velocity the SFG has a spectral width identical to that of the input beams.