Search

Purpose: Constructing porous wind barriers is one of the most effective approaches to increase the running safety of trains on viaducts in crosswinds. This paper aims to further improve the wind-sheltering performance of the porous wind barriers. Design/methodology/approach: Improved delayed detached eddy simulations based on the k-ω turbulence model were carried out, and the results were validated with wind tunnel tests. The effects of the hole diameter on the flow characteristics and wind-sheltering performance were studied by comparing the wind barriers with the porosity of 21.6% and the hole diameters of 60 mm–360 mm. The flow characteristics above the windward and leeward tracks were analyzed, and the wind-sheltering performance of the wind barriers was assessed using the wind speed reduction coefficients. Findings: The hole diameters affected the jet behind the wind barriers and the recirculation region above the tracks. Below the top of the wind barriers, the time-averaged velocity first decreased and then increased with the increase in the hole diameter. The wind barrier with the hole diameter of 120 mm had the best wind-sheltering performance for the windward track, but such barrier might lead to overprotection on the leeward track. The wind-sheltering performance of the wind barriers with the hole diameters of 240 mm and 360 mm was significantly degraded, especially above the windward track. Originality/value: The effects of the hole diameters on the wake and wind-sheltering performance of the wind barriers were studied, by which the theoretical basis is provided for a better design of the porous wind barrier. [ABSTRACT FROM AUTHOR]

This paper details a real time Lattice Boltzmann solver for computing unsteady wakes. The formulation of the lattice Boltzmann method is first presented followed by a discussion of boundary conditions. This is followed by the details of how the basic algorithm was improved to increase single-core efficiency. A discussion of high Reynolds number implementations, and their effect on the overall computational cost follows, and examples are presented alongside performance data on a variety of CPUs. [ABSTRACT FROM AUTHOR]

The scattering characteristics of a hypersonic near space vehicle are studied in this paper. The research takes into account the effect of the surrounding flow and wake on the radar cross section (RCS) of the near space hypersonic vehicle. The results show that the maximal plasma density of the surrounding flow, near wake and part of the far wake is higher than the critical plasma density of the ionosphere and much higher than the critical plasma density of the over-the-horizon radar whose frequency ranges from 3 MHz to 30 MHz. The plasma wake may be seen as conducting observation when the radar frequency is lower than the plasma frequency. So the RCS of the plasma wake is even larger than the hypersonic vehicle. On the basis of the numerical analysis，we suggest to detect the near space hypersonic vehicle by an over-the-horizon radar, which may provide longer reaction time for a radar warning system. [ABSTRACT FROM AUTHOR]

When a near space hypersonic vehicle (NHV) reenters the atmosphere, its scattering characteristics would be significantly changed by the formation of plasma sheath and wake. In this paper, the scattering characteristics of typical hypersonic near space vehicle are studied. Main contents included the RCS simulating of hypersonic vehicle surrounded by plasma sheath, underdense turbulent wake and laminar wake. The results show that the RCS of hypersonic near space vehicle would be decreased by plasma sheath in the back scattering direction. The RCS of hypersonic near space vehicle would be increased by the underdense turbulent wake at low frequency. But with the increase of radar frequency, the effect of underdense turbulent wake would be unobvious. Finally, Low frequency radar and bistatic radar are suggested to detect hypersonic near space vehicle. [ABSTRACT FROM AUTHOR]

Highlights: [•] An actuator blade model is developed for simulation of unsteady rotating system wakes. [•] A parallel kd-tree search locates the nearest grid node for each actuator source. [•] The actuator blade model accurately predicts root and tip vortex trajectories. [•] The actuator model computational cost was 20% of a comparable overset simulation. [•] Grid adaptation is applied to efficiently improve the resolution of wake features. [ABSTRACT FROM AUTHOR]

Abstract: Wake is the hydrodynamic footprint of a vessel at sea. The Earth’s magnetic field makes these footprints visible using magnetic sensors. Magnetic wakes induced by the motion of vessels may extend several kilometers and stay up long hours under certain conditions. From remote sensing point of view, in this work physical properties of this magnetic pattern are studied. A mathematical model is derived to simulate the magnetic wakes in a finite depth sea. Estimation of vessel traveling direction using single airborne sensors is reviewed and some problems in this method are remarked. A multi-sensor arrangement of magnetic transducers is proposed to remove these limitations. Estimation of vessel traveling direction with the proposed sensor configuration is performed. Robustness of the proposed method in dealing with Gaussian white noise and various target cutting angles is shown. [Copyright &y& Elsevier]

It is shown that the propagation of a strong electromagnetic pulse in a plasma is described by the system of nonlinear equations, averaged over the fast time. The analytical solution of this system shows that the wake field amplitude reaches its maximum value when the pulse length is of the order of the plasma wave length. It decreases in a dense plasma because the ponderomotive force effect on plasma electrons is compensated by an electrostatic field arising from the charge separation in a plasma. In the presence of an external magnetic field the efficiency of excitation of electrostatic oscillations depends on the direction of wave propagation. It is found that upper and lower hybrid electrostatic modes become parametrically unstable when an external magnetic field exceeds the threshold value. [Copyright &y& Elsevier]

• LES was employed to study suppressing the cylinder wake using a passive jet flow control method. • Influence parameters of the jet holes on aerodynamic forces and vortex shedding were studied. • Airflow exhausted from backward holes can make the main vortex move to the farther downstream wake. • Movement of the main vortex to downstream markedly reduced fluctuations of aerodynamic forces. This study presents a passive jet flow control method to suppress the wake of a circular cylinder based on a computational fluid dynamics (CFD) numerical simulation at a high Reynolds number of 5.0 × 104. The investigation mainly focuses on the control effectiveness of the pattern of jet holes on the hollow pipe. First, the three-dimensional (3D) flow past a circular cylinder at a Reynolds number of 3900 is addressed based on the large-eddy simulation (LES) method to validate the feasibility of a numerical simulation. Then, the control effects of the passive jet flow on the aerodynamic forces and the wake flow of the circular cylinder are studied at different directions, angles, and heights of the jet holes. An optimal parameter scheme for suppressing the wake of a circular cylinder is then determined according to a comparison of the control effectiveness of the aerodynamic forces. The results indicate that the jet flow from the backward holes of the circular cylinder effectively separates the shear layers rolled up on both sides of the circular cylinder, which forces the vortex formation region downstream. This control measure can dramatically reduce the aerodynamic forces and suppress the wake of the circular cylinder. [ABSTRACT FROM AUTHOR]

His regained consciousness minutes before a post-mortem examination [ABSTRACT FROM PUBLISHER]

A week after he and eight others were killed at a church shooting in Charleston [ABSTRACT FROM PUBLISHER]

New single inspired by Ferguson and NYC protests [ABSTRACT FROM PUBLISHER]

The article evaluates the architectural design of Comprehensive Cancer Center at Wake Forest Baptist Medical Center in Winston-Salem, North Carolina, designed by architecture firm HKS Inc.