Book of Extended Abstracts. Webinar on Experimental Methods and Laboratory Instrumentation in Hydraulics, 13-15 April 2021

Abstract:

The recent development of equipment and software for hydraulic measurements, data analysis, and visualization, has introduced new opportunities but also new challenges for research and technical cadre.

Abstract:

Underwater sound techniques began since Leonardo Da Vinci which listened to approaching ships by using a tube in water and placing its outer extremity to hear. The sound speed into water was firstly measured on Lake Geneva in 1826 whereas the modern acoustics is due to Lord Rayleigh which lived in the late 19^th and early 20^th century. In spite of these well consolidated bases, the using of acoustic techniques in hydraulics is pretty recent and developed in parallel for laboratory and field applications. Ultrasound techniques are particularly relevant in case of opaque fluids and for no optical access through boundaries. This talk delineates important features of hydro-acoustics and the instruments used. Some experiences show the acoustic investigation of sediment transport, which has always been a challenging task in riverine environment, and sea waves tests carried out at the hydraulic laboratory of the University of Bologna

Abstract:

Automating hydraulic engineering experiments may allow an increased number of scenarios or repetitions to be studied within a research programme and additionally increase measurement precision by reducing human errors. Several aspects of the Aberdeen Open Channel Facility (AOCF) have already been automated, including flow configuration and control and stereoscopic particle image velocimetry deployment and calibration. We expect these developments to contribute to scientific progress through enabling larger systematic data sets in future studies.

Abstract:

Laboratory experiments were performed at the Coriolis Rotating Platform to study uni and bi-directional exchange flows in a trapezoidal channel. PIV and conductivity probes were used to measure velocity fields and density profiles. The rotation rate and the freshwater flowrate were varied. The stratified flow dynamics was found to depend on the Burger number, Bu, and for Bu < 0.5 unsteady exchange flows develop. Both the ambient rotation and freshwater flowrate affect the transverse velocity distribution and leads to the partial blockage of the lower saline outflow for the largest freshwater inflows. In addition, shear-driven interfacial instabilities are analysed and for larger rotation rates the mixing layer thickness increases

Abstract:

Experimental research of pressurized hydraulic transients is conditioned to pressure (water-hammer) waves, which are usually characterized for having high celerity values and involving high pressures. Reservoir-pipe-valve systems are the usual experimental rigs to carry out such analyses. Flow rate and pressures at specific points of the pipe system are standard measurements from which water-hammer solvers are consequently verified and validated. During this webinar first a brief introduction is provided concerning the standard numerical model and the subsequent experimental validation approach. Then the talk evolves to more advanced numerical models, where not only the transients in the fluid but also their interaction with the structure are considered. Additional lab measurements are therefore required to capture the associated structure behaviour which, additionally, involve transient waves propagating even at a higher velocity. Finally, some remarks are provided pointing out the importance of a good understanding of the physical phenomena, especially in terms of time-scale, to experimentally capture fast transient phenomena in pressurized pipe flows.

Abstract:

Ferrofluids (FFs) are colloid liquids susceptible to magnetic field. Although they represent a novelty in Hydraulics, they have been widely used in engineering sciences since the eighties, with different industrial and biomedical applications. Here, a collection of experiences carried out in hydraulic laboratories is presented. Indeed, FFs have been exploited to measure key hydraulic quantities (e.g. wall friction). Moreover, their interaction with flow have been investigated with original techniques (optical methods, microfluidics) observing the rise of novel phenomena (e.g. lubrication).

Abstract:

The complex phenomenon riverbed clogging constitutes one reason for degraded riverine ecosystems. However, measuring or monitoring of clogging is challenging because of its multifaceted character. This keynote addresses clogging from different perspectives including field and laboratory aspects and shows recent developments in measuring techniques to gather relevant involved parameters and processes.

Abstract:

The development of a bore in an open channel creates a sudden change in water surface elevation propagating upstream. In this study, physical modelling was performed to investigate both horizontal and vertical components of velocity and forces to clarify the mechanism of sediment initiation beneath a tidal bore. A laser Doppler anemometer, a highly sensitive force transducer, and ultrasonic displacement meters accompanied by video recordings were used to provide some quantitative data in terms of various force and velocity terms measured simultaneously acting on a targeted sphere. According to the experimental results, upward vertical force was the main force in destabilizing the particles however, a large upstream longitudinal force was found to be the dominant cause promoting upstream particle motion during the breaking roller passage. Furthermore, the forces were not only due to velocity but also to the sudden discontinuity in free water surface.

Abstract:

The dynamic development of sediment infiltration in gravel-bed rivers is not entirely understood yet because existing methods are unable to cope with the high spatio-temporal variability of the involved processes. Therefore, high-resolution and non-intrusive measurements of governing parameters are required to unravel the interactions of the multifaceted processes involved in the clogging or colmation phenomenon. This study presents high-resolution measurements of the dynamic process of sediment infiltration and the development of sediment accumulations in an artificial riverbed under laboratory conditions using an advanced non-intrusive and undisturbed method.

Abstract:

The use of a 3D Scanner allowed the acquisition of dam breach geometry on a physical model. This technique is widely used in interactive movement entertainment and was adapted for this study’s aims. The conceived apparatus collected breach geometry from a physical model built to evaluate a channel’s cascade dam break. The 3D Scanner mapped breach surfaces and allowed the input on image processing software to generate its digital surface and elevation contours, reducing measurement errors since it is a non-contact method. An apparatus was then developed to enable accurate scanning since this feature’s original function was motion detection. The apparatus consisted of a platform assembled on rails, installed over channel walls, supporting a Kinect II (Microsoft Corporation ® 3D Scanner), connected to a notebook.

Abstract:

An experimental flume study was undertaken to compare water velocity in a bore for a given cross section using an Acoustic Doppler Velocimeter (ADV) and an Electromagnetic Current Meter (ECM). We present a comparison of two among nine elevations above the flume bed. Average and standard deviation of ECM velocities are somewhat higher than those of ADV. However, ADV vertical velocities showed an unexpected trend for the first 4 s after bore arrival when turbulent intensity (TI) from ECM varied from 8% to 2%.

Abstract:

This contribution presents the application of the videography as a low-cost, non-intrusive alternative to measure the wave-structure interaction processes. To this purpose, a full-HD camera was used to film laboratory tests of wave overtopping against a sea-dike. From the image processing, the flow depths over the dikes, the wave celerities, the wave spectra and the amount of the air entrapped in the overtopping tongue were estimated. The results of this analysis were successfully compared to the measurements from traditional techniques.

Abstract:

To investigate fluvial processes under laboratory conditions the application of similarity laws is a well-accepted experimental method. Studying natural systems in scaled physical models is usually limited by the laboratory’s infrastructure and by similarity validities, which confines the model’s realisable geometric dimension. Using similarity laws becomes barely feasible if complex geomorphic fluvial events are studied with physical laboratory models, especially due to the steep slope and broad grain size distribution. Nevertheless, computational models predicting the outcomes of these hazard events require reliable data sets for calibration and validation. In this work, we present a synoptic model approach to overcome this dilemma. Derived from other research disciplines, we will discuss, how the synoptic functionality could be applied to fluvial problems based on the example of the 2017 Piz Cengalo–Bondo landslide.

Abstract:

The high rotational speed of ship propellers generates a strongly turbulent jet which can impact the stability of channel, river and ocean beds, as well as harbour structures. For the design of protective measures against scouring, the boundary shear stresses induced by propeller jets must be estimated. However, so far there is no general method available for such estimations. This is partly related to the intrinsic difficulties to perform direct measurements of boundary shear stress. We present preliminary results of measurements of bottom shear stresses generated by a ship propeller. To this end a novel shear plate which operates with strain gauges was developed. The measurements result in the expected quadratic relation between bed shear stress and the propeller rotational speed, and also give evidence of a good reproducibility. The new shear plate shows to be an affordable and reliable tool for the measurement of submerged boundary shear stresses.

Abstract:

In this article a low-cost high-resolution photogrammetric method is presented to characterize the 3D geometry of scour cavity and bar induced by a ski jump jet. From the obtained 3D model all the main characteristics of the scour cavity and bar: the central longitudinal and transversal scour profiles, maximum scour depth and maximum bar height were determined with resolutions up to 0.0049 m. This technique allowed also to analyse the time evolution of the scour volume.

Abstract:

Tragic oil spills such as the Exxon Valdez episode in the 1989 are a reminder of such events and their consequences. It is therefore important to have tools capable of detecting and tracking the fate of such spills. This paper presents some imaging-based tools developed to track the evolution of pollutant spills and tested in laboratory environment with two types of pollutants: a liquid and a dust-type pollutant.

Abstract:

The dynamics of steady two-dimensional gravity currents interacting with slopes and overhangs are investigated by laboratory experiments. Parameters such as the initial volume of the dense fluid and the angle of the barrier positioned inside the tank are varied. An image analysis technique is adopted to evaluate the instantaneous density fields. The analysis performed showed how the nature of the barrier affects the dynamics of the dense current.

Abstract:

This paper describes the in-situ survey of an unstructured block ramp to obtain a detailed topographical digital model for a research project focusing on the fish-based identification of migration corridors. The strategy to drain the block ramp in the field for the survey is described and the obtained digital model is presented. The digital model will be used in subsequent experiments with live fish in the field and laboratory to link fish trajectories, the local flow field, and the bed topography to improve the development of new and enhanced design criteria for nature-like unstructured block ramps.

Abstract:

The dynamics of lock-release gravity currents interacting with a triangular barrier are investigated experimentally by applying non-intrusive density measurements based on image analysis, to measure the instantaneous density fields. The relevant parameter varied is the ratio between the height of the obstacle and the initial water depth. Results suggest that the image analysis based on a calibration curve is a suitable technique for the study of the gravity currents dynamics, which is strongly affected by the presence of a bottom obstacle depending on the relative obstacle height.

Abstract:

The study estimates the turbulence anisotropy for flow in a sinuous channel under the influence of downward seepage. Anisotropy provides the deviation from the isotropic turbulence. Given the complex flow processes in a sinuous channel, it is vital to investigate the turbulent flow characteristics. 

Abstract:

Flooding events in rivers are usually causing an increment in sediment transport. To investigate the relationships between bedload, bed shear stress and wave characteristics, laboratory experiments were performed in a 12-m-long flume at the University of Agriculture in Kraków, Poland. Three sets of experiments were conducted, imposing singular trapezoidal flood waves as forcing terms. The maximal wave height differed between runs, but the water volume and bed slope stayed the same. The bed was covered with mixed gravel, and the sediment was weighted using a trap at the end of the flume. The water level was measured at 5 points along the flume, while the velocity was measured in the middle of the flume by Acoustic Doppler Velocimeter at a point 7 cm above the bed. Preliminary results show that unsteadiness of flow induces the variation of bedload transport during the wave passage and that the total yield of sediment is positively correlated with the wave magnitude.

Abstract:

Laser Profilometry refers to a surface measurement by laser sheet projection on the geometry of interest. This technique is routinely used in industrial and in hydraulics laboratory applications. In this paper, we present a development of this technique for overtopping induced dike breaching experiments. The Laser Profilometry Technique (LPT) presented hereafter allows for high resolution continuous monitoring of the three‐dimensional (3D) evolving breach in laboratory models of fluvial dikes. The reconstructions of submerged parts of the dike were allowed by use of a dedicated refraction correction module. The LPT was selected for this application as it is compatible with commercial cameras and standard sheet projecting lasers while offering accurate and sufficient spatiotemporal resolution of the 3D reconstructions. The method has also advantages in terms of flexibility and compatibility with different experimental configurations and could be used on different scale models.

Abstract:

A novel and low cost tool, namely the instrumented particle, that is potentially able to directly monitor the near bed surface flow hydrodynamics and can be used by researchers and practitioners alike is presented. The particle is fitted with micro-electro-mechanical-systems, MEMS, sensors that are able to quantify its inertial dynamics and detect the particle’s incipient motion accurately. A well-controlled laboratory flume experiment for assessing the incipient entrainment of the instrumented particle which mimics the behaviour of a naturally rounded pebble resting on a riverbed for a range of flowrates near the threshold of motion is conducted. The logged acceleration readings, after appropriate post-processing, are used to assess the entrainement threshold of the instrumented particle. Appropriate theories that take into account the dynamic characteristics of particle’s entrainment are considered to interpret these readings with an ultimate goal of back-estimating hydrodynamic drag which is representative of the hydrodynamic forces acting on the bed-surface.

Abstract:

Acoustic Doppler velocimetry profilers (ADVPs) are widely used in both experimental and field studies because of their robustness in velocity measurements. The acquired measurements offer estimates of the instantaneous flow velocity at the interrogated measurement volume and can also be further processed for the estimation of the bed surface shear stresses and turbulent kinetic energy, thus finding a wide range of applications ranging from water engineering to geomorphology and eco-hydraulics. This study aims to evaluate the performance of an ADVP in obtaining hydrodynamics measurements under fixed flow conditions, with various probe configurations. Different assessment criteria are used for the evaluation including qualitative observations as well as quantitative error metrics to assess the uncertainties in the estimation of shear stresses using log Law of the Wall and turbulent kinetic energy due to the probe configuration settings. The methodology implemented herein, for a given flow, and the suggestions presented represent a generalized hierarchical framework which can find use from practitioners and researchers alike.

Abstract:

Common practices related to the use of fluorescent tracers include multiple dyes in branches of convergent streams, and multiple dyes to compare the performance and to control the quality of the results. Although the control software of spectrofluorometers presents advanced features like multiple peak identification, a spectral separation function is usually not available. It is worth to note that a typical field campaign may result hundred or even a few thousand of samples whose tracers need to be identified and have its concentration measured. To deal with this issue, a set of Python scripts for background subtraction and spectra separation was tested with a dataset of samples with a single tracer and with mixtures of Eosin and Fluorescein. The uncertainty of the results is dependent on the concentration ratio of the tracers in the sample.

Abstract:

In this study, Digital Surface Model (DSM) was created to investigate to what extent unsteady flow affects gravel bed surface in laboratory conditions. Bed elevation was measured before and after the passage of unsteady flow using a Digital Close Range Photogrammetry (DCRP) technique and the processing of photographic data was performed using PhotoScan software. From these preliminary outcomes, it can be concluded that the DCRP technique can be considered as a complementary method to track the changes of gravel beds at the laboratory scale.

Abstract:

Establishing and operating a harmonised sediment monitoring system along large rivers such as the Danube is a challenging international task. Our objective is to develop a time- and cost-effective suspended sediment measurement protocol that can be easily carried out in the Upper-Hungarian Danube. In this study, we present the results of the comprehensive testing of direct and indirect (acoustic and optical) suspended sediment analysis methods, during which, we established moderate to strong relationships between the determined suspended sediment.

Abstract:

Pumping in waterways, particularly in artificial canals, is energy-intensive, costly and may be responsible for the emission of large quantities of CO₂. Innovative pumping technologies have the potential to reduce energy consumption; but their performance needs to be thoroughly assessed. This communication presents the design, sizing and construction of an experimental test bench for evaluating the performance of large submersible and dry-action centrifugal pumps typically used in waterways. It enables testing prototype-scale pumps and was designed in close collaboration with stakeholders such as canal operators. This experimental facility is challenging on many aspects given its size, as well as requirements for power supply and for measurement of system efficiency.

Abstract:

The experimental and numerical simulation of the three dimensional flow around fully submerged vertical aligned square and circular cylinder due to steady current over plane bed is reported. The focus of the present investigation is toward assessing the flow characteristics and reattachment length around these cylinders. Streamlines around these cylinders are obtained from normalized longitudinal velocity. In addition, power spectra are determined to explain the variation of dominant vortex shedding frequency around cylinders, which is employed to determine the entrainment of the bed sediment particles around these cylinders. The dominant shedding frequency is evident for circular than square cylinder. Results show that the magnitude of the normalized streamwise velocity is 20–40% less for square than circular cylinder. Further, scour prone zone is determined from the bed shear distribution around various cylinders. Bed shear stress is higher for circular than aligned square cylinder. Reattachment length is higher for higher size of the cylinders. 

Abstract:

In this study, the comparison of measured suspended sediment concentrations, calculated light transmissivity and underwater images was done in order to assess the visibility conditions in a large river and to investigate the opportunities of a possible forecasting methodology that could support diving operations and underwater image processing methods. Further discussion will be made based on the first set of results. The measurements were carried out in the Hungarian section of river Danube.

Abstract:

The present study investigated flow characterization around tandem piers of circular shape having diameter (d = 8.8 cm) at different radial angles, θ = 0°, 45°, 90°, 135°, and 180° and compared with single pier of same diameter on rigid bed condition with identical flow conditions. The velocity fields at different depth around piers was measured using Acoustic Doppler Velocimeter (ADV). To characterize the flow, turbulence intensities, turbulence kinetic energy, and Reynolds shear stresses distributions are quantified and plotted for single and tandem piers. The Reynolds shear stresses are increased by 30% around the front pier and decreased by 30% around rear pier in tandem pier arrangement vis-à-vis single pier. In tandem case, turbulence intensity has shown 30% increase in front pier and 30% decrease in rear pier, as compared to the single pier. Further, in tandem arrangement, it has been found that there is significant decrease in the turbulence kinetic energy around the rear pier (≈ 50%) vis-à-vis single pier.

Abstract:

Image processing techniques we deployed to measure bedload transport characteristics. The bedload velocity was successfully measured and in some cases the bedload concentration and particle size were estimated. Two different approaches were used and good corelations were reported from both the laboratory and the field data. Comparing the field video results to conventional bedload sampling measurements showed promising results for further development of the image-based techniques. Moreover, the captured videos could help understanding the performance of the conventional samplers, pointing out typical sampling errors.

Abstract:

The knowledge of riparian vegetation bio-mechanical and morphometric features is one of the main topics in the analysis of the hydrodynamic interaction between riparian plants and water flow in vegetated streams. In this work, the scanning of real riparian plants was performed through a portable device composed of RGB sensors and structured-light 3D scanner, and the outcomes of the 3D image processing in terms of Plant Area Index (PAI) based on Digital Hemispherical Photography (DHP) were compared and then employed in real-scale hydraulic simulations. The results of this study furnish useful insights to ecohydraulic researchers dealing with ecohydraulic experimental analyses and numerical modeling of real vegetated flows.

Abstract:

Spatially and temporally distributed in-situ wave data is difficult or expensive to collect, however, such a dataset is important for understanding wave propagation and validating numerical models. Here we explored an alternative to array of underwater pressure gauges, consisting of cheap and easy-to-install ultrasonic wave gauges mounted on tripods above the water surface, measuring the downward distance, equipped with telecommunication modules and solar panels. In a pilot application, these wave gauges were deployed in a shallow lake, and their data was compared to those collected simultaneously with an underwater, upward looking echosounder. The presented network proved to be able to provide an accurate picture of the sea state at a fraction of the cost of a “professional” instrumentation.

Abstract:

Laboratory investigations into the breaching of rockfill dams is an ongoing research at NTNU. The current model represents a full dam profile and is a development of earlier models used for investigating stability of rockfill dams and ripraps under throughflow and overtopping situations. Instrumentation of the model includes pore pressure measurements along the dam foundation, water level recording and video recording from multiple angles. Video is used to extract images at intervals throughout the breaching process and 3D models of the breach opening created using “structure from motion” and “multi view stereo” processing techniques. The overall aim is to enhance current knowledge on the breaching of rockfill dams. Modelling of the impervious element is a major challenge for the experiments and the process of finding an appropriate solution to this is described in the present study along with preliminary results.

Abstract:

Local scour has been widely identified as one of the primary threats to bridge pier stability. To better understand how the turbulent flow field modified by bridge piers interacts with the bed surface, it is relevant to assess the flow structures that are potentially sufficient to remove the bed material. Thus, the accuracy and measurement quality in estimating the flow field is of primordial importance, mainly in a well-controlled laboratory environment. In the present study, time-averaged velocities and Reynolds shear stresses were measured by using a high-resolution acoustic velocimeter. Due to the highly turbulent nature of the flow, an assessment of the signal acquisition time’s influence on the statistics of turbulent quantities is performed, including the inherent uncertainties regarding the flow field measurement technique. The results showed that the required sampling time for mean and fluctuation velocities, and the lateral Reynolds shear stress, differ by one order of magnitude.