Catálogo de publicaciones - revistas

<jats:p>For composite electromagnetic (EM) scattering from rough surface and target above it in near-field condition, modified shooting and bouncing ray (SBR) method and integral equation method (IEM), which are analytic methods combined with two-scale model for rough surface, are proposed to solve the composite near-field scattering problems. And the modified method is verified in effectiveness and accuracy by comparing the simulation results with measured results. Finally, the composite near-fielding scattering characteristics of a slanted plane and rough water surface below are obtained by using the proposed methods, and the dynamic tendency of composite scattering characteristics <jats:italic>versus</jats:italic> near-fielding distance is analyzed, which may have practical contribution to engineering programs in need of radar targets near-field characteristics under extra-low-altitude conditions.</jats:p>

<jats:p>The asymmetric transmission (AT) and polarization conversion of terahertz (THz) wave play a vital role in future THz communication, spectrum, and information processing. Generally, it is very difficult and complicated to actively control the AT of electromagnetic (EM) wave by using traditional devices. Here, we theoretically demonstrate a stereo-metamaterial (stereo-MM) consisting of a layer of metal structure and a layer of phase transition structure with a polyimide spacer in between. The performance of the device is simulated by using the finite-integration-technology (FIT). The results show that the AT and polarization conversion of linearly polarized wave can be dynamically controlled in a range of 1.0 THz–1.6 THz when the conductivity <jats:italic>σ</jats:italic> of vanadium dioxide (VO<jats:sub>2</jats:sub>) is changed under the external stimulation. This study provides an example of actively controlling of the AT and polarization conversion of the EM wave.</jats:p>

<jats:p>We propose a compressed ghost imaging scheme based on differential speckle patterns, named CGI-DSP. In the scheme, a series of bucket detector signals are acquired when a series of random speckle patterns are employed to illuminate an unknown object. Then the differential speckle patterns (differential bucket detector signals) are obtained by taking the difference between present random speckle patterns (present bucket detector signals) and previous random speckle patterns (previous bucket detector signals). Finally, the image of object can be obtained directly by performing the compressed sensing algorithm on the differential speckle patterns and differential bucket detector signals. The experimental and simulated results reveal that CGI-DSP can improve the imaging quality and reduce the number of measurements comparing with the traditional compressed ghost imaging schemes because our scheme can remove the environmental illuminations efficiently.</jats:p>

<jats:p>We investigate the flow patterns of irregular sand particles under avalanching mode in a rotating drum by using the spatial filtering velocimetry technique. By exploring the variations of velocity distribution of granular flow, we find a type of avalanching pattern of irregular sand particles which is similar to that of spherical particles flow. Due to the fact that the initial position of avalanche in this pattern locates at the middle of the drum and the avalanche propagates toward the edge area gradually, we named it as mid-to-edge avalanching pattern. Furthermore, we find another avalanching pattern which slumps from the edge and propagates toward the opposite edge of the flow surface, named as edge-to-edge pattern. By analyzing the temporal and spatial characteristics of these two types of avalanching patterns, we discover that these two types of avalanche patterns are caused by that the avalanching particles constantly perturb the axial adjacent particles. Thus, the particles on the flow surface are involved in avalanching sequentially in order of the axial distance from the initial position.</jats:p>

<jats:p>Laminar methane/air premixed flames at different pressures in a newly developed high-pressure laminar burner are studied through Cantera simulation and filtered Rayleigh scattering (FRS). Different gas component fractions are obtained through the detailed numerical simulations. And this approach can be used to correct the FRS images of large variations in a Rayleigh cross section in different flame regimes. The temperature distribution above the flat burner is then presented without stray light interference from soot and wall reflection. Results also show that the extent of agreement with the single point measurement by the thermocouple is &lt;6%. Finally, this study concludes that the relative uncertainty of the presented filtered Rayleigh scattering diagnostics is estimated to be below 10% in single-shot imaging.</jats:p>

<jats:p>The influence rules of square micro-pillar array porosity on the liquid motion characteristics of the near-surface layer are investigated by quartz crystal microbalance (QCM). QCM is a powerful and promising technique in studying the interfacial behavior, which exhibits great advantages in investigating the effects of surface microstructure, roughness, and array. In our experiments, three different arrays with the same height of about 280 nm and center distance of 200 μm, but different diameters of about 78 μm, 139 μm, and 179 μm are investigated. The results indicate that when the surface array has a large porosity, its influence on the liquid motion of the near surface layer is slight, thus resulting in a small increase of half-bandwidth variation due to the additional friction energy dissipation. When the surface array has a small porosity, the array tends to make the liquid film trapped in the array oscillating with the substrate, then there may be a layer of liquid film behaving like rigid film, and it also will make the liquid motion near the array layer more complicated. Thus for the #3 surface with a small porosity, both the absolute values of frequency shift |Δ<jats:italic>f</jats:italic> <jats:sub>3</jats:sub>| and half-bandwidth variation Δ<jats:italic>Γ</jats:italic> <jats:sub>3</jats:sub> increase obviously. The experimental results show good consistence with the theoretical model of Daikhin and Urbakh. This study sheds light on understanding the influence mechanism of surface array porosity on the liquid motion of near-surface layer.</jats:p>

<jats:p>The key to high manoeuvre ability in bird flight lies in the combined morphing of wings and tail. The perching of a wild Haliaeetus Albicilla without running or wing flapping is recorded and investigated using a high-speed digital video. A shape reconstruction method is proposed to describe wing contours and tail contours during perching. The avian airfoil geometries of the Aquila Chrysaetos are extracted from noncontact surface measurements using a ROMBER 3D laser scanner. The wing planform, chord distribution and twist distribution are fitted in convenient analytical expressions to obtain a 3D wing geometry. A three-jointed arm model is proposed to associate with the 3D wing geometry, while a one-joint arm model is proposed to describe the kinematics of tail. Therefore, a 3D bird model is established. The perching sequences of the wild eagle are recaptured and regenerated with the proposed 3D bird model. A quasi-steady aerodynamic model is applied in the aerodynamic predictions, a four-step Adams–Bashforth method is used to calculate the ordinary differential equations, thus a BFGS based optimization method is established to predict the perching motions.</jats:p>

<jats:p>Plasma flow control is a new type of active flow control approach based on plasma pneumatic actuation. Dielectric barrier discharge (DBD) actuators have become a focus of international aerodynamic research. However, the practical applications of typical DBDs are largely restricted due to their limited discharge area and low relative-induced velocity. The further improvement of performance will be beneficial for engineering applications. In this paper, high-speed schlieren and high-speed particle image velocimetry (PIV) are employed to study the flow field induced by three kinds of plasma actuations in a static atmosphere, and the differences in induced flow field structure among typical DBD, extended DBD (EX-DBD), and tri-electrode sliding discharge (TED) are compared. The analyzing of the dynamic evolution of the maximum horizontal velocity over time, the velocity profile at a fixed horizontal position, and the momentum and body force in a control volume reveals that the induced velocity peak value and profile velocity height of EX-DBD are higher than those of the other two types of actuation, suggesting that EX-DBD actuation has the strongest temporal aerodynamic effect among the three types of actuations. The TED actuation not only can enlarge the plasma extension but also has the longest duration in the entire pulsed period and the greatest influence on the height and width of the airflow near the wall surface. Thus, the TED actuation has the ability to continuously influencing a larger three-dimensional space above the surface of the plasma actuator.</jats:p>

<jats:p>Nonlinear evolution of multiple toroidal Alfvén eigenmodes (TAEs) driven by fast ions is self-consistently investigated by kinetic simulations in toroidal plasmas. To clearly identify the effect of nonlinear coupling on the beam ion loss, simulations over single-<jats:italic>n</jats:italic> modes are also carried out and compared with those over multiple-<jats:italic>n</jats:italic> modes, and the wave-particle resonance and particle trajectory of lost ions in phase space are analyzed in detail. It is found that in the multiple-<jats:italic>n</jats:italic> case, the resonance overlap occurs so that the fast ion loss level is rather higher than the sum loss level that represents the summation of loss over all single-<jats:italic>n</jats:italic> modes in the single-<jats:italic>n</jats:italic> case. Moreover, increasing fast ion beta <jats:italic>β</jats:italic> <jats:sub>h</jats:sub> can not only significantly increase the loss level in the multiple-<jats:italic>n</jats:italic> case but also significantly increase the loss level increment between the single-<jats:italic>n</jats:italic> and multiple-<jats:italic>n</jats:italic> cases. For example, the loss level in the multiple-<jats:italic>n</jats:italic> case for <jats:italic>β</jats:italic> <jats:sub>h</jats:sub> = 6.0% can even reach 13% of the beam ions and is 44% higher than the sum loss level calculated from all individual single-<jats:italic>n</jats:italic> modes in the single-<jats:italic>n</jats:italic> case. On the other hand, when the closely spaced resonance overlap occurs in the multiple-<jats:italic>n</jats:italic> case, the release of mode energy is increased so that the widely spaced resonances can also take place. In addition, phase space characterization is obtained in both single-<jats:italic>n</jats:italic> and multiple-<jats:italic>n</jats:italic> cases.</jats:p>

<jats:p>The plasma current ramp-up is an important process for tokamak discharge, which directly affects the quality of the plasma and the system resources such as volt-second consumption and plasma current profile. The China Fusion Engineering Test Reactor (CFETR) ramp-up discharge is predicted with the tokamak simulation code (TSC). The main plasma parameters, the plasma configuration evolution and coil current evolution are given out. At the same time, the volt-second consumption during CFETR ramp-up is analyzed for different plasma shaping times and different plasma current ramp rates d<jats:italic>I</jats:italic> <jats:sub>P</jats:sub>/d<jats:italic>t</jats:italic> with/without assisted heating. The results show that the earlier shaping time and the faster plasma current ramp rate with auxiliary heating will enable the volt-second to save 5%–10%. At the same time, the system ability to provide the volt-second is probably 470 V · s. These simulations will give some reference to engineering design for CFETR to some degree.</jats:p>