Shallow and deep failure mechanisms during uplift and lateral dragging of buried pipes in sand

This paper presents results of a series of experiments modelling uplift and lateral drag of a rigid pipe buried in dry sand. The main aim of these tests is to document the gradual transition from shallow to a deep sand failure mechanism as the pipe embedment depth increases, identify which parameters affect this transition, and determine experimentally the critical embedment depth, beyond which the normalized reaction acting on the pipe remains constant with increasing pipe embedment. Measurements of the reaction as a function of the relative sand–pipe movement and analysis of images captured during the tests with the particle image velocimetry method suggest that the critical embedment depth depends on sand density, but not on the direction of pipe movement. Outcomes of this study contribute to identifying the limits of applicability of simplified methods used to determine the peak reaction on pipes subjected to ground movements and the estimation of rational parameters for the analysis of deeply buried pipes with beam-on-nonlinear Winkler foundation models.

The Velocity Field Underneath a Breaking Rogue Wave: Laboratory Experiments Versus Numerical Simulations

Wave breaking is the most characteristic feature of the ocean surface. Physical investigations (in the field and at laboratory scale) and numerical simulations have studied the driving mechanisms that lead to wave breaking and its effects on hydrodynamic loads on marine structures. Despite computational advances, accurate numerical simulations of the complex breaking process remain challenging. Validation of numerical codes is routinely performed against experimental observations of the surface elevation. However, it is still uncertain whether simulations can accurately reproduce the velocity field under breaking waves due to the lack of ad-hoc measurements. In the present work, the velocity field recorded with a Particle Image Velocimetry method during experiments conducted in a unidirectional wave tank is directly compared to the results of a corresponding numerical simulation performed with a Navier–Stokes (NS) solver. It is found that simulations underpredict the velocity close to the wave crest compared to measurements. Higher resolutions seem necessary in order to capture the most relevant details of the flow.

Laboratory Study of Secondary Flow in an Open Channel Bend by Using PIV

The present paper aims to gain deeper insight into the evolution of secondary flows in open channel bend. A U-shaped open channel with long straight inflow/outflow reaches was used for experiments. Efforts were made to precisely specify flow conditions and to achieve high precision measurement of quasi-three-dimensional velocities with a multi-pass, two-dimensional PIV (Particle Image Velocimetry) method. The experimental results show that the flow begins to redistribute before entering the bend and it takes a long distance to re-establish to uniform conditions after exiting the bend. Complex secondary flow patterns were found to be present in the bend, as well as in the straight inflow and outflow reaches. A “self-breaking” (process was identified, which correlates stream-wise velocity with the intensity of flow circulation.

Изучение структуры течения в перспективном вихревом топочном устройстве

The internal aerodynamics of isothermal laboratory model of improved four-vortex furnace of pulverized coal boiler are experimentally investigated. Using the particle image velocimetry method, the distribution of components of the air flow averaged velocity and the streamlines are obtained in a number of model cross sections for different operating modes of the furnace, determined by the ratio of the flow velocities supplied through the primary and secondary nozzles. The conditions for the formation of a stable flow structure with four symmetric conjugate vortices in the entire volume of the furnace, as well as the range of operating parameters leading to a spatially irregular vortex structure are determined.

An experimental and numerical analysis of the fluid flow in a mechanically agitated vessel

The mixing process is a widespread phenomenon, which plays an essential role among a large number of industrial processes. The effectiveness of mixing depends on the state of mixed phases, temperature, viscosity and density of liquids, mutual solubility of mixed fluids, type of stirrer, a what is the most critical - the shape of the impeller. In the present research, the objective is to analyse the process of the fluid flow in the mechanically agitated vessel with new impeller type. Velocity field values were determined using computer simulation and experimental particle image velocimetry method. The basis for the assessment of the intensity degree and efficiency of mixing was the analysis of velocity vectors distribution and power number. An experimental and numerical study was carried out for various stirred process parameters to determine optimal conditions for the mixing process.

Flow field velocity measurement of liquid interaction with rigid and flexible wall

The motivation of this research was to determine the flow interactions on the pulsation and to express the influence on the flow character in the rigid and flexible tube. The character of Newtonian liquid was measured with the Particle Image Velocimetry method (PIV). Here, we used glass tube and Tygon tube for our comparison. We build the circuit equipped with membrane pump for generating pulsatile flow. The results were analysed over the pulse period sampled in 10 time steps. The fluid flow varied from Re 560 to Re 8800. The velocity profiles uncovered backward revers flows closed to the wall. These structures are prevailing close to flexible wall. The effect of interaction between pulsatile liquid flow and flexible wall was experimentally proved.