Reflection of waves from a mobile elastic layer in a multimode waveguide

Waveguide structures are used to transmit energy and information signals in a wide range of wavelengths and, in terms of wave-guiding physical properties, usually have mutual (identical) properties in forward and backward directions. The asymmetry of the structure and external influences can often cause non-reciprocity of structures for waves, propagating in mutually opposite directions (this property, although limited, is already used in the so-called nonreciprocal devices of microwave, EHF and optical ranges such as ferrite valves, circulators, phase shifters). At the same time, the nonreciprocal properties of wave-guiding structures, independent of their physical nature, were not considered. It is found, that the motion of the medium filling the acoustic waveguide leads to nonreciprocity of its parameters in the forward and backward directions. The degree of nonreciprocity is proportional to the velocity of the medium. The velocity of the medium also affects the propagation velocity of acoustic waves and leads to a change in the critical frequencies or critical wavelengths of the waveguide modes. As the velocity of the medium increases, the number of modes for which the propagation condition is satisfied increases as well.

The Effect of Wave Propagation on Seismic Response at Transmitting Boundary of Discrete System

When analyzing the seismic response of a very long elevated structure such as a Shinkansen viaduct, it is common practice to analyze a cutout of the structure under consideration and treat its both ends as free boundaries. This is attributable to the assumption that seismic response analysis assuming free boundary conditions is more conservative than one assuming non-free boundary conditions. In this study, after finding out that response to harmonic ground motion can be greater than under free-boundary conditions if outward energy dissipation occurs from the analysis domain, a series of numerical experiments was performed to determine whether such phenomena occur in seismic response. Then, after confirming that the frequency components of ground motion that satisfy the wave propagation condition greatly affect seismic response, the study showed that the area of the wave propagation condition region of the Fourier spectrum can be used as an indicator by which to judge the likelihood of occurrence of such phenomena.

A Non-Parametric Propagation Condition Identification Method and Non-Line of Sight Mitigation Algorithm for Wireless Sensor Network

The wireless sensor network (WSN) has received increasing attention since it has many potential applications such as the internet of things and smart city. The localization technology is critical for the application of the WSN. The obstacles induce the larger non-line of sight (NLOS) error and it may decrease the localization accuracy. In this paper, we mainly investigate the non-line of sight localization problem for WSN. Firstly, the Pearson's chi-squared testing is employed to identify the propagation condition. Secondly, the particle swarm optimization based localization method is proposed to estimate the position of unknown node. Finally the simulation experiments are implemented. The simulation results show that the proposed method owns higher localization accuracy when compared with other two methods.

Latitudinal Variations of the Convective Source and Propagation Condition of Inertio-Gravity Waves in the Tropics

Latitudinal variations of the convective source and vertical propagation condition of inertio-gravity waves (IGWs) in the tropical region (30°S–30°N) are examined using high-resolution Global Cloud Imagery (GCI) and 6-hourly NCEP–NCAR reanalysis data, respectively, for 1 yr (March 1985–February 1986). The convective source is estimated by calculating the deep convective heating (DCH) rate using the brightness temperature of the GCI data. The latitudinal variation of DCH is found to be significant throughout the year. The ratio of the maximum to minimum values of DCH in the annual mean is 3.2 and it is much larger in the June–August (JJA) and December–February (DJF) means. Spectral analyses show that DCH has a dominant period of 1 day, a zonal wavelength of about 1600 km, and a Gaussian-type phase-speed spectrum with a peak at the zero phase speed. The vertical propagation condition of IGWs is determined, in the zonal wavenumber and frequency domain, by two factors: (i) latitude, which determines the Coriolis parameter, and (ii) the basic-state wind structure in the target height range of wave propagation. It was found that the basic-state wind significantly influences the wave propagation condition in the lower stratosphere between 150 and 30 hPa, and accordingly a large portion of the source spectrum is filtered out. This is prominent not only in the latitudes higher than 15° where strong negative shear exists, but also near the equator where strong positive shear associated with the westerly phase of the quasi-biennial oscillation (QBO) filters out large portions of the low-frequency components of the convective source. There is no simple relationship between the ground-based frequency and latitude; lower latitudes are not always favorable for low-frequency IGWs to be observed in the stratosphere. The basic-state wind in the Tropics, which has seasonal, annual, and interannual variations, plays a major role not only in determining the wave propagation condition in the stratosphere but also in producing convective sources in the troposphere.

Dimensioning against fatigue - stress-based approach or fracture mechanics?

The non-propagation condition of a sharp crack introduced in the root of a generic notch is investigated. Thus, pre-existing flaws near structural stress concentrations are advantageously treated in a unified manner, giving in the limit of vanishing notch radius the case of a crack in an unnotched component, and in the limit of vanishing crack length the classical engineering case of a notched, crack-free component. Particular focus is put on the limiting case of vanishing crack length. The results are compared with the classical engineering strength estimate following the nominal stress concept. It is shown that both concepts may, with minor differences, be brought into the same formal structure. The transition between notch-like and crack-like behaviour of notches is investigated in some detail, giving an accurate estimate for the transition between both regimes as well as reliable lower bounds for the fatigue strength in both regimes with special consideration of crack arrest effects in flawed components.

Clutter and rainfall discrimination by means of doppler-polarimetric measurements and vertical reflectivity profile analysis

The estimation of rainfall rate and other parameters from radar scattering volume is heavily affected by the presence of intense sea and ground clutter and echoes which appears in anomalous propagation condition. To deal with these non meteorological echoes we present a new clutter removal algorithm which combines the results of previous works. The algorithm fully exploits both the Doppler and polarimetric capabilities of the radar used and the analysis of vertical reflectivity profile in order to achieve the better identification of the meteorological and non-meteorological targets. The algorithm has been applied to the C-band radar of Monte Settepani (Savona, Italy), which runs in a high-topography environment. Preliminary results are presented.