1,214 research outputs found
A particle filter to reconstruct a free-surface flow from a depth camera
We investigate the combined use of a Kinect depth sensor and of a stochastic
data assimilation method to recover free-surface flows. More specifically, we
use a Weighted ensemble Kalman filter method to reconstruct the complete state
of free-surface flows from a sequence of depth images only. This particle
filter accounts for model and observations errors. This data assimilation
scheme is enhanced with the use of two observations instead of one classically.
We evaluate the developed approach on two numerical test cases: a collapse of a
water column as a toy-example and a flow in an suddenly expanding flume as a
more realistic flow. The robustness of the method to depth data errors and also
to initial and inflow conditions is considered. We illustrate the interest of
using two observations instead of one observation into the correction step,
especially for unknown inflow boundary conditions. Then, the performance of the
Kinect sensor to capture temporal sequences of depth observations is
investigated. Finally, the efficiency of the algorithm is qualified for a wave
in a real rectangular flat bottom tank. It is shown that for basic initial
conditions, the particle filter rapidly and remarkably reconstructs velocity
and height of the free surface flow based on noisy measurements of the
elevation alone
Versatile image-based measurements of granular flows and water wave propagation in experiments of tsunamis generated by landslides
Landslides falling into water bodies can generate destructive waves, which can be classified as tsunamis. An experimental facility to study this phenomenon has been set up. It consists of a landslidegenerator releasing gravel at high-speed into a wave basin. A non-intrusive system has been designed ad-hocto be able to measure the high velocity and the geometry of the landslide as well as the generated waves characteristics. The measurement system employs the treatment of images captured by a high-speed camera which records the launched granular material illuminated by a laser sheet. A grid of laser sheets marks thebasin water surface. The water has been filled by a small amount of kaolin to properly reflect the laser lightat water surface. Thus, by filming with high definition cameras the perturbed water surface and successively processing the resulting images, it has been possible to measure the generated waves. The measurement framework employs a versatile camera calibration technique which allows accurate measurements in presence of: (1) high lens distortions; (2) pronounced non-parallelism condition between camera sensor and plane of measurement coincident with the laser sheet. The maximum resolution of the measurement tool is0.01 mm, while the maximum uncertainty due to systematic error has been estimated to be 15% for theworst-case scenario. This work improves the suitability of image-based measuring systems in granular flows and free surface hydraulics experimentsThis work was funded by GITS and the 3 yearsâ national project DEBRIS FLOW (CGL 2009-13039) ofthe Spanish Ministry of Education. Francesco Bregoli has been supported by the 4-years grant FPU2009-3766 of the SpanishMinistry of Education. Authors want to thank Dr. Cecilia Caldini (IDOM Consulting, Barcelona) for the 3D reconstruction ofthe laboratory setup.Peer ReviewedPostprint (published version
The evolution of mobile bed tests: a step towards the future of coastal engineering
Coastal Engineering still presents significant levels of uncertainty, much larger for sediment transport and morphodynamics than for the driving hydrodynamics. Because of that there is still a need for experimental research that addresses the water and sediment fluxes occurring at multiple scales in the near shore and for some of which there are still not universally accepted equations or closure sub-models. Large scale bed tests offer the possibility to obtain undistorted results under controlled
conditions that may look at sediment transport and associated bed evolution under a variety of wave and mean water level conditions. The present limitations in conventional observation equipment preclude a
clear advancement in knowledge or model calibration. However the new developments in opto-acoustic equipment should allow such an advancement to take place provided the new experimental equipment
becomes more robust in parallel with a protocol for deployment and data processing.
This paper will present the experimental approach to erosive and accretive beach dynamics, with emphasis on the accretive experiments. These accretive tests still present further uncertainties and sometimes cannot be explained with the present state of the art. Following this there is a presentation of the novel development of an acoustic bed form and suspended sediment imager, able to monitor bed forms near bed sediment transport and their corresponding dynamics. The next section deals with an
acoustic high resolution concentration and velocity profiler that is able to infer even the elusive bed level, together with the near bed concentrated sediment transport and the details of fluxes on the stoss and lee
sides of moving bed forms. This is followed by a discussion on the merits of novel optic techniques, using structured and unstructured light sources. There is also some remarks on new approaches.
Illustrated by the use of ferro-fluids to obtain directly the shear stresses acting on a wall even under the presence of âsomeâ sediment. The paper ends with some conclusions on the use of such mobile bed tests in present and future Coastal Engineering.Postprint (published version
Drag on a partially immersed sphere at the capillary scale
We study the drag on a centimetric sphere in a uniform flow in the presence
of a free surface as a function of submergence depth. Through direct force
measurements in a custom benchtop recirculating flume, we demonstrate that the
drag can significantly exceed the corresponding drag in a single-phase flow and
achieves a peak at submergence depths just prior to complete immersion. The
additional drag in the partially immersed state is rationalized by considering
hydrostatic effects associated with the asymmetric surface height profile
induced by the obstacle in the flow direction which persists for flow speeds
below the minimum capillary-gravity wave speed. At these scales, the sphere's
wettability plays a pronounced role in determining the maximum possible drag
and results in hysteretic behaviors near touchdown and complete immersion. The
influence of flow speed, sphere size, and surface tension on the drag
characteristics are additionally explored through a combination of experiments
and numerical simulations.Comment: 9 figure
A Study of Dynamic Similitude for Modeling Starting Jet Vortices
Accurate numerical simulations needed for responding to coastal oil spills require a fundamental understanding of tidal eddy-driven transport. Tidal eddies are commonly formed along barrier islands and shipping channels connecting bays/estuaries to the coast. The transport in and out of the bays/estuaries controlled by these eddies is critical for many barrier island coastlines across the United States. Understanding this major form of transport can assist response efforts to disasters, such as the Texas City Y spill. In this spill, a bulk carrier collided with an oil tanker spilling 168,000 gallons of oil in the Galveston Ship Channel and was eventually stranded along the coasts of Galveston and Matagorda island. In order to improve the understanding of these tidal eddies, a shallow water flume was designed and constructed at Texas A&M University. This flume was designed based on the non-dimensional parameter space needed to describe the dynamic similitude of the behavior of coastal tidal eddies. The flume was then used to conduct surface particle image velocimetry (PIV) experiments for a 52.7 cm wide channel at 2cm, 3cm, and 5cm water depth, where the velocity information of the eddies was recorded during 5 to 10 tidal periods at different flow rates. A method was developed for designing a shallow water flume within the critical parameter space needed for dynamic and geometric similitude. The newly designed flume was then tested and the hydrodynamic conditions present for the new design were analyzed and recorded for use in future experimentation. Experiments were conducted with similar parameters to other relevant research on shallow water starting jet vortices in larger facilities to compare the results of the design process to existing data sets.
The results confirm that the present experiments give dynamically similar result
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