On a pseudotensor generalization of the Hugoniot-Hadamard linking boundary conditions

В представляемой работе исследуются особенности связывающих двусторонних граничных условий на поверхностях разрывов, распространяющихся в сплошных средах (в частности, в микрополярных континуумах). Теория Югонио-Адамара, существенно развитая Г.И. Быковцевым, распространения поверхностей разрывов физических полей обобщена на случай псевдотензорного полевого описания. Вводятся понятия фундаментального ориентирующего псевдоскаляра и псевдоскалярного времени. Исследуется геометрия поверхностей уровня псевдоскалярного поля, представляющих интерес для механики наращиваемых тел. Вводится понятие псевдонормали к поверхности. Обсуждаются вопросы дифференцирования по псевдоскалярному времени и его преобразования при зеркальных отражениях и инверсиях пространства. Получены геометрические и кинематические условия совместности первого порядка в терминах псевдотензоров. Выведены условия совместности для слабых разрывов перемещений и микровращений в микрополярном континууме. The present work deals with the linking boundary conditions formulated on the both sides of a propagating wave surface (in particular, in micropolar continua). The Hugoniot-Hadamard theory of physical fields wave surfaces propagation, essentially developed by G.I. Bykovtsev, is generalized to the case of a pseudotensor field description. The concepts of fundamental orienting pseudoscalar and pseudoscalar time are introduced and discussed. The geometry of level surfaces of a given pseudoscalar field is studied. The concept of a pseudovector normal to a surface is introduced. The pseudoscalar time derivative is proposed and discussed. Geometric and kinematic first order compatibility conditions are obtained in terms of pseudotensors. The compatibility conditions are derived for weak discontinuities of displacements and microrotations due to defromations of the micropolar solid.

Investigation of the Anisotropic Patterns in the Altimeter Backscatter Measurements Over Ocean Wave Surfaces

This article attempts to analyze the influence of the anisotropic effects of the ocean wave surface on SAR altimetry backscatter coefficient (Sigma-0) measurements, which has not been intensively addressed in publications. Data of Sentinel-3A, Cryosat-2, and Jason-3 altimeters allocated by the WW3 numeric wave model were analyzed, and the patterns of Sigma-0 with respect to the wave direction were acquired under ∼2 m significant wave height. The ocean waves were classified into six categories, among which the moderate swell and short win-wave cases were analyzed intensively. Swell-dominated ocean surface shows less randomness than the wind-wave-dominated ocean surface. Clear and significant sinusoid trends are found in the Sigma-0 and SSB patterns of both operational modes (SAR mode and PLRM mode) of the Sentinel-3A altimeter for the moderate swell case, indicating the sensitivity of Sigma-0 and SSB measurements to the anisotropic features of the altimeter measurements. The anisotropic pattern in the Sentinel-3A PLRM Sigma-0 is somewhat counterintuitive, but the analysis of Jason-3 altimeter data would show similar results. Additionally, by comparing the anisotropic patterns of two orthogonally polarized SAR altimeters (Sentinel-3A and Cryosat-2), we could draw the conclusion that the Sigma-0 measurements are not sensitive to the polarization mode. As for the SSHA patterns, no clear sinusoid could be identified for the moderate swell. A possible explanation is that the SSB pattern may be overwhelmed in the complicated factors that can influence the SSHA pattern.

Perceiving Excitation Characteristics from Interactions between Field Road and Vehicle via Vibration Sensing

When agricultural vehicles operate in the field, the soft road excitation makes it difficult to measure the vehicle vibration. A camera-accelerator system can solve this issue by utilizing computer vision information; however, the relationship between the field road surface and the vehicle vibration response remains an unsolved problem. This study aims to investigate the correlation of the soft road excitation of different long-wave surfaces with the vehicle vibration response. Vibration equation between the vehicle and soft road surface system was established to produce an effective roughness model of the field soft road surface. In order to simulate the vehicle vibration state under different long-wave road surfaces, the soil rectangular pits with 21 kinds of different spans and depths were applied to the road surfaces, and a tractor vibration test system was built for vibration test. The frequency spectrum analysis was performed for the vibration response and the roughness signals of the road surfaces. The results showed that coefficient (R2) of frequency correlation between the roughness excitation and the original unevenness at the excitation point at the rear end of the rectangular soil pit fell within 0.9641∼0.9969. The main frequency band of the vibration response fell within 0∼3 Hz, and the phenomenon of quadruple frequency existed. The correlation of roughness excitation with quadruple frequency fell within 0.992165∼1. The primary excitation points were located at the rear end of the rectangular soil pit. In addition, it also indicated that when the vehicle was driven without autonomous power, the vehicle vibration frequency mainly depended on the excitation frequency of the field road surface and the frequency at the maximum vehicle vibration intensity was 2 or 3 times of that at the maximum field soft road excitation. These findings may provide a reference for optimal design of vibration reduction and control for agricultural vehicles.

Acceleration of Solar Energetic Particles in CME-Driven Coronal Shocks up to 30 Rs

<p>The lower and middle solar corona up to about 30 solar radii is thought to be an important region for early acceleration and transport of solar energetic particles (SEPs) by coronal mass ejection-driven shock waves. There, these waves propagate into a highly variable dynamic medium with steep gradients and rapidly expanding coronal magnetic fields, which modulates the particle acceleration near the shock/wave surfaces, and the way SEPs spread into the heliosphere. We present a study modeling the acceleration of SEPs in over 50 separate global coronal shock events between 1 and 30 solar radii. As part of the SPREAdFAST framework project, we analyzed the interaction of off-limb coronal bright fronts (CBF) observed with the SDO/AIA EUV telescope with realistic model coronal plasma based on results from synoptic magnetohydrodynamic (MHD) and differential emission measure (DEM) models. We used realistic quiet-time proton spectra observed near Earth to form seed suprathermal populations accelerated in our diffusive shock acceleration model (Kozarev & Schwadron, 2016). We summarize our findings and present implications for nowcasting SEP acceleration and heliospheric connectivity.</p>

Observations of migrating tides in the mid-latitude MLT using an array of SuperDARN HF-radars

<p>Solar thermal (migrating) atmospheric tides play an important role in shaping the day-to-day and seasonal variability of the Mesosphere-Lower-Thermosphere (MLT) region. Due the planetary scale of the migrating tides, observations have, however, remained sparse. This study uses meteor-echo wind measurements from a longitudinal array of SuperDARN HF-radars to isolate the amplitude and phase of the migrating diurnal, semidiurnal, and terdiurnal tide. The array of SuperDARN radars, covering nearly 180 degrees longitude at 60±5 degrees North, provide hourly horizontal wind measurements at approximately 95km altitude. The migrating components of the tides are isolated by fitting wave surfaces in space and time. The results are compared with global synoptic wind analyses from the high-altitude version of the Navy Global Environmental Model (NAVGEM-HA) to validate the method. The tides are also compared against those measured at a single station by the Trondheim (66N, 10E) meteor radar. We will present the method, a comparison between (migrating) tidal components in SuperDARN, NAVGEM-HA and the Trondheim meteor radar between 2014 and 2015, and migrating tide climatologies based on 21 years of SuperDARN data.</p>

Computational Model of Unsteady Hydromechanics of Large Amplitude Gerstner Waves

The computational experiments in the ship fluid mechanics involve the nonstationary interaction of a ship hull with wave surfaces that include the formation of vortices, surfaces of jet discontinuities, and discontinuities in the fluid under the influence of negative pressure. These physical phenomena occur not only near the ship hull, but also at a distance where the waves break as a result of the interference of the sea waves with waves reflected from the hull. In the study reported here we simulate the wave breaking and reflection near the ship hull. The problem reduces to determining the wave kinematics on the moving boundary of a ship hull and the free boundary of the computational domain. We build a grid of large particles having the form of a parallelepiped and, in the wave equation instead of the velocity field we integrate streams of fluid represented by functions as smooth as the wave surface elevation field. We assume that within the boundaries of the computational domain the waves do not disperse, i.e. their length and period stay the same. Under this assumption, we simulate trochoidal Gerstner waves of a particular period. This approach allows to simulate the wave breaking and reflection near the ship hull. The goal of the research is to develop a new method of taking the wave reflection into account in the ship motion simulations as an alternative to the classic method which uses added masses.