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Considering the problem of passive interference caused by electromagnetic scattering effects of transmission lines to neighboring radio stations and other communication equipment, this paper refines the passive interference calculation model for UHV transmission lines. The solution calculation is carried out by the Method of Moments, and the law of passive interference effect of the tower structure, auxiliary angles, and ground roughness under different frequency incident waves, is summarized. By designing an orthogonal test, the degree of influence of the above attributing factors on passive interference results in the established joint model of three towers with two stall distances was explored by using Analysis of Variance. The results demonstrate that both auxiliary angles and rough ground show a pattern of enhanced electromagnetic scattering effect with increasing plane wave frequency in single-factor analysis. When multiple factors are combined, the rough ground has a significant effect on the results. This method effectively evaluates the passive interference influence factor while reducing the modeling and simulation engineering and provides a reference for the passive interference prediction in subsequent practical projects. [ABSTRACT FROM AUTHOR]

In this paper, an accelerated hybrid method of physical optics (PO) shooting and bouncing ray (SBR)–physical theory of diffraction (PTD) is proposed to deal with the electromagnetic scattering of a complex target on rough ground. To accelerate the ray tracing progress, the ray marching technique based on octree structure is employed. In this technique, only the nodes passed by the ray are detected successively until the first facet intersected by ray is found or the ray passes through the bounding box, which greatly decreases the intersection test. Then, based on the accelerated PO-SBR-PTD method, the spotlight synthetic aperture radar (SAR) echo data of the composite target–ground model is obtained by the vector superposition of the echo on each meshed patch. Furthermore, the spotlight SAR image of the composite model is simulated by the polar format algorithm (PFA). In numerical simulations, both the EM scattering of the target and composite model are calculated and evaluated by comparing with the multilevel fast multipole method (MLFMM) in FEKO software. Meanwhile the spotlight SAR image of the composite target–ground model is also compared with the real image in MSTAR data, and a satisfactory similarity between them is obtained. In addition, the SAR images of two targets on rough ground for different pose angles are also presented and analyzed.

The driving force of a wheel is an important factor to determine the travelling performance of vehicles on rough grounds. An excessive driving force induces a large slip, whereas insufficient driving force prevents vehicles from overcoming obstacles. Hence, an optimum driving force distribution is necessary to improve the travelling performance of off-road vehicles on rough grounds. In this study, the driving force distribution method of four independent wheel-drive vehicles based on the energy-loss ratios of the wheels is proposed. The squared sum of the energy-loss ratios is minimized in the proposed method. To validate the proposed method, travelling tests were conducted using a model vehicle on a rough and rigid ground and a soft ground. Moreover, simulation tests were performed on a rough and rigid ground. The results obtained using the proposed method were compared with those of the distributions based on the tyre workload, even force, and wheel-velocity control. The experimental and simulation results confirm that the proposed method is the most efficient for vehicles moving on a rigid ground. The movement of the vehicle on the soft ground was the most stable when the proposed method was employed. [ABSTRACT FROM AUTHOR]

In this paper, the problem of time-reversal imaging (TRI) of buried dielectric and metallic targets under Gaussian rough surfaces is studied. For the scattering problem, a parallel finite-difference time-domain technique is used. Using a multistatic scattering matrix of a TR operator at a frequency range of 0.5-2.5 GHz, ultrawideband (UWB) TR multiple signal classification images are calculated. First, to reduce the clutter influence, near-ground UWB scattered fields are used. It is shown that employing received signals near the ground instead of those at the transmitter height improves the signal-to-clutter power ratio by at least 10 dB at 1 GHz. Second, a time-gated (TG) TRI algorithm is proposed to better detect and localize buried targets in the presence of clutter. Third, once the TG TR images are obtained, best single-frequency TR images are calculated, yielding even better target localization. [ABSTRACT FROM PUBLISHER]

Atmospheric boundary layer (ABL) is generated due to frictions induced by obstacles on the Earth's surface, such as terrains, vegetation, buildings, etc ... Inspired by this physical mechanism, horizontally homogeneous ABL flow in computational fluid dynamics is achieved by proposing an enriched canopy drag (ECD) model, which is more flexible in reproducing the effects of various physical roughness ground, not limited to vegetation types. The multi-objective evolutionary algorithm is employed to determine the appropriate near-ground drag and the acting height of the proposed ECD model. Furthermore, the evolutionary algorithm is adopted to minimize the discrepancies of mean wind velocity and turbulence kinetic energy (TKE) between the inflow condition and the flow at a target downstream location. A set of simulations using logarithmic- and power-law inlet flows over rural, suburban, and urban terrains based on the shear-stress transport k-ω turbulence model are conducted to demonstrate the effectiveness of the ECD model. The results show that the proposed ECD model is capable of reproducing the Earth's roughness numerically and improving the homogeneities of mean velocity and TKE in streamwise direction and applicable to different mesh resolutions, near-wall treatment methods, standard k-ε turbulence model and simulation dimension. • Horizontal homogeneous ABL was reproduced using an enriched canopy drag model. • Pending parameters of the model can be determined through optimization procedure. • Optimized near-ground drag can ensure horizontal homogeneities of velocity and TKE. • The model has a wide range of applicability and requires minor prerequisite condition. [ABSTRACT FROM AUTHOR]