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For the purpose of studying the interrelation between the statistical characteristics of waves on the water surface and the laws of their variability the histograms are constructed and the cumulants and spectra are calculated for mechanical and wind waves in a wind-wave channel. The diversity of the histograms for the waves of different nature and their variability with variation in the wave type, parameters, and fetch are analyzed. The regularity in the deviations from the Gaussian wave amplitude distribution presented by their cumulants in the numerical form is noted. With account for the laws of evolution of the frequency spectrum of the waves established along the channel it is asserted that the variability of the wave statistics is uniquely determined by the variability of the shape of their spectrum rather than individual characteristics of the system (wave fetch, steepness, or age). This assertion is theoretically substantiated. [ABSTRACT FROM AUTHOR]

Flow in river bends is associated with generation of secondary flows, which leads to the development of a rather complicated flow pattern around bridge piers located in the bend. The present study investigated the flow patterns around models for rectangular and oblong piers with a collar located at the 90-degree angle of a 180-degree sharp bend in an experimental plume. The 3D flow velocity data were collected using a Vectrino velocimeter. The experimental results indicated that the presence of the rectangular pier caused a more intense deviation of the streamlines towards the outer bank of the bend. Furthermore, installation of the oblong pier, rather than the rectangular pier, decreased the maximum secondary flow power and angular velocity by 35% and 45%, respectively. It was also found that the maximum turbulence kinetic energy around the two piers was not significantly different; however, by installing the rectangular pier, a region with high values of turbulence kinetic energy was formed at 90 near the inner bank. Moreover, installation of the oblong pier could reduce shear stress. [ABSTRACT FROM AUTHOR]

Tomographic particle image velocimetry (Tomo-PIV) has been successfully applied in measuring three-dimensional (3D) flow field in recent years. Such technology highly relies on the reconstruction technique which provides the spatial particle distribution by using images from multiple cameras at different viewing angles. As the most popular reconstruction method, the multiplicative algebraic reconstruction technique (MART) has advantages in high computational speed and high accuracy for low particle seeding reconstruction. However, the accuracy is not satisfactory in the case of dense particle distributions to be reconstructed. To overcome this problem, a symmetric encode–decoder fully convolutional network is proposed in this paper to improve the reconstruction quality of MART. The input of the neural network is the particle field reconstructed by the MART approach, while the output is the regenerated image with the same resolution. Numerical evaluations indicate that those blurred or irregular particles can be significantly refined by the trained neural network. Most of the ghost particles can also be removed by this filtering method. The reconstruction accuracy can be improved by more than 10% without increasing the computational cost. Experimental evaluations indicate that the trained neural network can also provide similar satisfactory reconstruction and improved velocity fields.

This study proposes a novel velocity measurement method based on a differential capacitance sensor array (DCSA) for the solid particles in gas-solid flow. Firstly, the DCSA is modelled by the finite-element software ANSOFT, and its sensitivity characteristic is acquired. Additionally, the spatial filtering effect of DCSA is theoretically investigated, which validates the feasibility of particle velocity measurement based on DCSA. By measuring the frequency bandwidth (cut-off frequency) of the DCSA's output capacitance signal, the velocity of the local particles in the pipeline can be calculated. Further through the form of differential detection, the cut-off frequency can be accurately converged. Finally, a novel solid particle velocimeter based on DCSA is developed and tested on a gravity-delivery particle experimental device. The results indicate that the method has the feasibility for the velocity measurement and its repeatability is within 11% over the velocity range of 1–3 m/s.

Many earthquakes propagate at sub-Rayleigh speeds. Earthquakes propagating at supershear speeds, though less common, are by far more destructive. Hence, it is important to quantify the motion characteristics associated with both types of earthquake ruptures. Here we report on the spatiotemporal properties of dynamic ruptures measured in our laboratory experiments using the dynamic digital image correlation technique. Earthquakes are mimicked by the frictional rupture propagating along the interface of two Homalite plates. Digital images of the propagating ruptures are captured by an ultrahigh-speed camera and processed with digital image correlation in order to produce sequences of evolving displacement and velocity maps. Our measurements reveal the full-field structure of the velocity components, bridge the gap between previous spatially sparse velocimeter measurements available only at two to three locations, and enable us to quantify the attenuation patterns away from the interface. [ABSTRACT FROM AUTHOR]

This study proposes a novel velocity measurement method based on a differential capacitance sensor array (DCSA) for the solid particles in gas-solid flow. Firstly, the DCSA is modelled by the finite-element software ANSOFT, and its sensitivity characteristic is acquired. Additionally, the spatial filtering effect of DCSA is theoretically investigated, which validates the feasibility of particle velocity measurement based on DCSA. By measuring the frequency bandwidth (cut-off frequency) of the DCSA's output capacitance signal, the velocity of the local particles in the pipeline can be calculated. Further through the form of differential detection, the cut-off frequency can be accurately converged. Finally, a novel solid particle velocimeter based on DCSA is developed and tested on a gravity-delivery particle experimental device. The results indicate that the method has the feasibility for the velocity measurement and its repeatability is within 11% over the velocity range of 1–3 m/s. [ABSTRACT FROM AUTHOR]

The paper presents the results of a controlled‐source seismic experiment performed using a vibratory source capable of producing harmonic vibrations. The survey aimed at investigating the horizontal directional amplification mechanism observed at the Pernicana Fault (Mt. Etna in Sicily, Italy) along an N150°/N330° orientation. With the vibratory source (a shaker truck) working in shear‐wave mode in the frequency range 5–40 Hz, we recorded seismic data using both three‐component velocimeters and 4.5 Hz geophones. These two types of receivers were arranged in linear configuration along two orthogonal orientations: radial and transverse to the direction of the main polarization observed within the fault zone. The two lines of seismic stations allowed us to investigate the polarization evolution as a function of the distance from the source. Results show that when the shear excitation induced by the source is parallel to the direction of observed polarization of the ground motion, the seismic signal propagates efficiently, maintaining the same horizontal polarization induced by the active source. This polarization is well recorded up to distances as large as 300 m from the source. On the contrary, when the shear excitation is orthogonal to the predominant site polarization, the ground excitation loses its initial polarization in less than 50 m away from the source position. At larger distances, the transmitted energy propagates with the natural site polarization independently from the original source polarization. The observations in terms of polarization were combined with surface‐wave analysis, aimed at investigating the dispersion characteristics of the wavefield on the geophone lines. The data suggest that the experimental Rayleigh‐wave dispersion spectra show a more coherent signal over the frequency range along the same orientation of the observed site polarization, supporting a preferential direction in the propagation of surface waves. From inversion of the Rayleigh dispersion curves, we inferred the shear‐wave velocity (Vs) to be in the range of 120–450 m/s in the first 30 m deep of Quaternary volcanic sediments. The dispersion curves are not constant along transverse and radial directions, suggesting the presence of fracture‐induced seismic anisotropy in the near surface. [ABSTRACT FROM AUTHOR]

Highlights • The hydrodynamics of unsteady compression wave flows were experimentally investigated. • An array of two profiling velocimeters was sampled simultaneously. • In the y-z plane, large scale coherent structures were detected beneath free-surface. • Turbulent length scales increased during and after the compression wave passage. • Both strain rate and vorticity showed larger values near the channel bed. Abstract A compression wave in a canal is an unsteady motion characterised by a rapid rise of water surface elevation, resulting in an unsteady turbulent flow. In the present study, the hydrodynamics of unsteady compression wave flows were experimentally investigated using an array of two profiling velocimeters, sampled simultaneously. The two-dimensional cross-correlation data in the y-z plane, formed by the two sampling profiles, showed the existence of large scale coherent structures underneath the free-surface, resembling the shape of hairpin vortex. The length scales tended to increase during and after the compression wave passage compared to those during the initially steady flows. Both strain rate and vorticity showed larger values at lower water column near the channel bed, and during the rapid deceleration phase associated with immediate wave passage. The propagation of the compression wave was a dynamically-active process, with large scale transient coherent motions, vortical structures and intensive turbulent mixing occurring underneath. [ABSTRACT FROM AUTHOR]