Surface Velocity Measurements Research Articles

Experimental investigation of flood hydrograph induced by landslide dam breach based on transient surface velocity measurement

Experimental investigation of flood hydrograph induced by landslide dam breach based on transient surface velocity measurement

FLOW-3D Model Development for the Analysis of the Flow Characteristics of Downstream Hydraulic Structures

Hydraulic structures installed in rivers inevitably create a water level difference between upstream and downstream regions. The potential energy due to this difference in water level is converted into kinetic energy, causing high-velocity flow and hydraulic jumps in the river. As a result, problems such as scouring and sloping downstream may occur around the hydraulic structures. In this study, a FLOW-3D model was constructed to perform a numerical analysis of the Changnyeong-Haman weir in the Republic of Korea. The constructed model was verified based on surface velocity measurements from a field gate operation experiment. In the simulation results, the flow discharge differed from the measured value by 9–15 m3/s, from which the accuracy was evaluated to be 82–87%. The flow velocity was evaluated with an accuracy of 92% from a difference of 0.01 to 0.16 m/s. Following this verification, a flow analysis of the hydraulic structures was performed according to boundary conditions and operation conditions for numerous scenarios. Since 2018, the Changnyeong-Haman weir gate has been fully opened due to the implementation of Korea’s eco-environmental policy; therefore, in this study, the actual gate operation history data prior to 2018 was applied and evaluated. The evaluation conditions were a 50% open gate condition and the flow discharge of two cases with a large difference in water level. As a result of the analysis, the actual operating conditions showed that the velocity and the Froude number were lower than the optimal conditions, confirming that the selected design was appropriate. It was also found that in the bed protection section, the average flow velocity was high when the water level difference was large, whereas the bottom velocity was high when the gate opening was large. Ultimately, through the reviewed status survey data in this study, the downstream flow characteristics of hydraulic structures along with adequacy verification techniques, optimal design techniques such as procedures for design, and important considerations were derived. Based on the current results, the constructed FLOW-3D-based model can be applied to creating or updating flow analysis guidelines for future repair and reinforcement measures as well as hydraulic structure design.

Free-Surface Velocity Measurement Using Direct Sensor Orientation-Based STIV.

Particle image velocimetry (PIV) is a quantitative flow visualization technique, which greatly improves the ability to characterize various complex flows in laboratory and field environments. However, the deployment of reference objects or ground control points (GCPs) for velocity calibration is still a challenge for in situ free-surface velocity measurements. By combining space-time image velocimetry (STIV) with direct sensor orientation (DSO) photogrammetry, a laser distance meter (LDM)-supported photogrammetric device is designed, to realize the GCPs-free surface velocity measurement under an oblique shooting angle. The velocity calibration with DSO is based on the collinear equation, while the lens distortion, oblique shooting angle, water level variation, and water surface slope are introduced to build an imaging measurement model with explicit physical meaning for parameters. To accurately obtain the in situ position and orientations of the camera utilizing the LDM and its embedded tilt sensor, the camera’s intrinsic parameters and relative position within the LDM are previously calibrated with a planar chessboard. A flume experiment is designed to evaluate the uncertainty of optical flow estimation and velocity calibration. Results show that the proposed DSO-STIV has good transferability and operability for in situ measurements. It is superior to propeller current meters and surface velocity radars in characterizing shallow free-surface flows; this is attributed to its non-intrusive, whole-field, and high-resolution features. In addition, the combined uncertainty of free-surface velocity measurement is analyzed, which provides an alternative solution for error assessment when comparing measurement failures.

Measuring the Water Surface Speed of the Cikidang River as a Supporting Facility for the Development of Ecotourism Areas

Pangandaran Regency is famous for its natural beauty, especially the beauty of its beaches. In this district there are many famous beaches. Besides the beach, there are also rivers that offer beautiful views. However, not many tourists have made the rivers in Pangandaran as tourist destinations, especially the Cikidang River. Cikidang River has the potential to be used as ecotourism. In building an ecotourism area on the banks of a river, it is necessary to carry out an in-depth analysis of the damage that might occur due to erosion. One of the factors that can increase erosion is the speed of water on the surface. Therefore, in this paper, measurement of river surface velocity is carried out in a simple way and analyzed using the velocity formula. From the results of this measurement, a recommendation was made to direct all parties involved in measuring the surface velocity of the Cikidang River as a means of supporting the development of ecotourism areas.

Investigations of transient sloshing induced impulsive hydrodynamics

Sloshing-induced impulsive pressures may be extremely high and of short rise time duration. A compressible Volume of Fluid (VoF) method was adopted to study these pressures in a partially filled three-dimensional tank with various oblique tank ceiling angles. Comparative available experimental model test measurements of free surface profiles and velocity and pressure time histories validated this numerical method. To obtain a sufficiently fine grid to yield converging predictions, grid sensitivity studies were performed. The influence of the oblique tank ceiling angle on sloshing-induced impulsive pressures was examined. Results demonstrated that the VoF method obtained accurate predictions of sloshing phenomena. The oblique tank ceiling angle dampened impulsive pressure and, therefore, this angle had to be accounted for in the design of the tank.

Development of drone-type float for surface-velocity measurement in rivers

Development of drone-type float for surface-velocity measurement in rivers

Adaptive large-scale particle image velocimetry method for physical model experiments of flood propagation with complex flow patterns

This work presents an Adaptive Large Scale Particle Image Velocimetry method (ALSPIV), which measures surface velocity of a physical model experiment with complex flow pattern. In the experiment, the eleven low-cost, high-resolution surveillance cameras are adopted to achieve a large-scale flow field in real time. The lenses of them are shined perpendicularly on water surface to minimize perspective distortion. A camera calibration method is also designed to enhance measurement accuracy. In addition, an adaptive cross-correlation algorithm can contribute to cross-correlation and a lower signal-to-noise ratio. Finally, an experimental method is employed to verify the ALSPIV method’s accuracy, and the surface velocity distributions under three different steady flows are measured to demonstrate its applicability. Results show that the method is demonstrated to be a low-cost and automatic flow diagnostic tool and an accurate means of measuring surface velocities in the physical model experiments of flood propagation with complex flow patterns.

Experimentally determining power flow in cylindrical shells using a scanning laser Doppler vibrometer

Power flow methods are used to identify energy sources and sinks in objects and to visualize transmission pathways. The most common method uses surface acceleration or velocity measurements and finite difference methods to compute power flow. In flat structures, a scanning laser Doppler vibrometer (SLDV) has been used to increase the measurement resolution. For more complicated surfaces, the general approach has been to use accelerometers at a few key points and measure transmission rather than seeking to get a full visualization of the power flow. This research uses a 3-D-SLDV to take surface velocity measurements for a simply supported cylinder. The 3-D velocity data is used to solve for a quintic B-spline representation of the velocity field. Similar representations for each of the force resultants are generated using an isotropic material model and the Love equations for cylindrical shells. The resultant and velocity fields are used to compute the direction and magnitude of the energy transfer. This method is validated by comparing experimental results to the outputs of an analytical solution and to a finite element model.

Challenges with Regard to Unmanned Aerial Systems (UASs) Measurement of River Surface Velocity Using Doppler Radar

Surface velocity is traditionally measured with in situ techniques such as velocity probes (in shallow rivers) or Acoustic Doppler Current Profilers (in deeper water). In the last years, researchers have developed remote sensing techniques, both optical (e.g., image-based velocimetry techniques) and microwave (e.g., Doppler radar). These techniques can be deployed from Unmanned Aerial Systems (UAS), which ensure fast and low-cost surveys also in remotely-accessible locations. We compare the results obtained with a UAS-borne Doppler radar and UAS-borne Particle Image Velocimetry (PIV) in different rivers, which presented different hydraulic–morphological conditions (width, slope, surface roughness and sediment material). The Doppler radar was a commercial 24 GHz instrument, developed for static deployment, adapted for UAS integration. PIV was applied with natural seeding (e.g., foam, debris) when possible, or with artificial seeding (woodchips) in the stream where the density of natural particles was insufficient. PIV reconstructed the velocity profile with high accuracy typically in the order of a few cm s−1 and a coefficient of determination (R2) typically larger than 0.7 (in half of the cases larger than 0.85), when compared with acoustic Doppler current profiler (ADCP) or velocity probe, in all investigated rivers. However, UAS-borne Doppler radar measurements show low reliability because of UAS vibrations, large instrument sampling footprint, large required sampling time and difficult-to-interpret quality indicators suggesting that additional research is needed to measure surface velocity from UAS-borne Doppler radar.

Alpine glacier surface velocity measurement from UAV imagery – examining the effect of image resolution on the accuracy of results

The reliability and validity of the Glacier Surface Velocity (GSV) measurement results based on remote sensing datasets depends on the quality and spatial resolution of the image used. The typical pixel size of space-borne satellite imagery is often larger than the annual and inter-annual displacement of small alpine debris-covered glaciers. In addition, the pixel size of medium resolution satellite images (10–30 m), limits the size of a feature that can be matched. This is even more of an issue for glaciers located in arid and semi-arid environments (e.g. glaciers in Iran and high mountains of Asia) where flow velocities are not exceeding a few metres per year. Consequently, high-resolution data such as Unmanned Aerial Vehicle (UAV) images are required to calculate the surface velocity of such glaciers. However, the optimal resolution of UAV images is one of the most important challenges in GSV measurement. This paper explores the influence of UAV image resolution on the quality of GSV results. Analysis was carried out at 19 different resolutions of UAV images from 10 to 100 cm with a 5 cm bin over a debris-covered glacier, in Iran. COSI-Corr algorithm was used to perform the image correlation. To evaluate the accuracy of obtained results, manual digitisation was performed and the differences between manual GSV and frequency cross-correlator were assessed for all data sets. Moreover, displacement calculated for a stagnant off-glacier area was evaluated. While the quality of the results of the images between 10 and 30 cm is substantially the same, the obtained results indicate that the best result of GSV was not obtained using the finest image resolution. Results revealed that the highest correspondence between the measured GSV and manual digitisation was obtained in a 30 cm spatial resolution image. In addition, the 30 cm image resolution shows the minimum uncertainty over the off-glacier static area. Obtained results revealed that using too fine resolution images will lead to computational redundancy, while no improvement is observed in the accuracy of GSV results.

Sensitivity of tidal hydrodynamics to varying bathymetric configurations in a multi‐inlet rapidly eroding salt marsh system: A numerical study

AbstractWe describe the development of a high‐resolution, two‐dimensional hydrodynamic model for a multi‐inlet rapidly eroding tidal wetland on the western shore of Delaware Bay, using the finite‐volume, primitive equation community ocean model (FVCOM). Topo‐bathymetric surveys, together with water surface and current velocity measurements during calm and stormy conditions, have been conducted to support model validation. The tested model is then used to quantify the tide‐induced residual transport and asymmetry at major inlet entrances to determine the governing hydrodynamics. We chose a skewness method to calculate the tidal asymmetry and serve as a proxy for sediment transport estimates. The effects of the dredging of an artificial entrance channel and progressive channel deepening in shifting wetland hydrodynamics are shown by developing a scenario analysis. Model results show that the artificially dredged channel has altered the volume exchange at other inlet entrances and increased the net seaward export. The changes in the characteristic frequency of the frictional dissipation in the channel and the system's natural frequency are investigated using a simple ocean–inlet–bay analytical model. Subsequently, we have compared the channel friction scale to the inertia scale and observed that the new connection and gradual channel deepening reduce the overall frictional dominance. Ultimately, the study has shown how the short‐ and long‐term channel bathymetry changes, mainly the artificially dredged channel and progressive channel deepening, can affect the connected system's net circulation and trigger internal marsh erosion.

Permafrost in monitored unstable rock slopes in Norway – new insights from temperature and surface velocity measurements, geophysical surveying, and ground temperature modelling

Abstract. The warming and subsequent degradation of mountain permafrost within alpine areas represent an important process influencing the stability of steep slopes and rock faces. The unstable and monitored slopes of Mannen (Møre and Romsdal county, southern Norway) and Gámanjunni-3 (Troms and Finnmark county, northern Norway) were classified as high-risk sites by the Norwegian Geological Survey (NGU). Failure initiation has been suggested to be linked to permafrost degradation, but the detailed permafrost distribution at the sites is unknown. Rock wall (RW) temperature loggers at both sites have measured the thermal regime since 2015, showing mean rock surface temperatures between 2.5 and −1.6 ∘C depending on site and topographic aspect. Between 2016 and 2019 we conducted 2D and 3D electrical resistivity tomography (ERT) surveys on the plateau and directly within the rock wall back scarp of the unstable slopes at both sites. In combination with geophysical laboratory analysis of rock wall samples from both sites, the ERT soundings indicate widespread permafrost areas, especially at Gámanjunni-3. Finally, we conducted 2D thermal modelling to evaluate the potential thermal regime, along with an analysis of available displacement rate measurements based on Global Navigation Satellite System (GNSS) and ground- and satellite-based interferometric synthetic aperture radar (InSAR) methods. Surface air and ground temperatures have increased significantly since ca. 1900 by 1 and 1.5 ∘C, and the highest temperatures have been measured and modelled since 2000 at both study sites. We observed a seasonality of displacement, with increasing velocities during late winter and early spring and the highest velocities in June, probably related to water pressure variations during snowmelt. The displacement rates of Gámanjunni-3 rockslide co-vary with subsurface resistivity and modelled ground temperature. Increased displacement rates seem to be associated with sub-zero ground temperatures and higher ground resistivity. This might be related to the presence of ground ice in fractures and pores close to the melting point, facilitating increased deformation. The study demonstrates and discusses the possible influence of permafrost, at least locally, on the dynamics of large rock slope instabilities.

Prediction of river discharges at confluences based on Entropy theory and surface-velocity measurements

Hydrodynamic features of the confluence zone of large rivers are complicated because of their three-dimensional flow structure. The confluence between the Rio Negro and the Rio Solimões, characterised by black and white waters, respectively, ranks among the largest river junctions on Earth. An Entropy-based investigation was carried out to assess the discharge and analyse the 2D structure of velocity distribution for large river flows relying on monitoring of near-surface velocity only. The estimated flow data where compared with in-situ ADCP data gathered across some transects of the Negro and Solimões rivers during both low and relatively high flow conditions. Results are illustrated through some transects at the confluence zone, upstream and downstream of the zone and in the Careiro Channel. Comparisons highlight that the Entropy-based flow velocity in terms of depth-averaged velocity, cross-sectional mean flow velocity and vertical velocity distributions, starting from the measured surface velocity, is in agreement with those determined by the ADCP measurements, with an error in mean flow velocity and discharge lower than 15%. The research highlights the potential of the Entropy method to estimate the discharge and velocity in very large rivers just relying on near-surface velocities monitoring.

Pressure amplification and modelization in laser shock peening of Ti-6Al-4V and AA7085 with adhesive-backed opaque overlays

The effects of adhesive-backed overlays, specifically vinyl tape and aluminum tape, on the peak pressures generated by laser shock peening (LSP) of 7085 aluminum alloy and Ti-6Al-4V were investigated and the results are reported. Peak pressures were determined from photon doppler velocimetry measurements of rear surface velocity. Incorporating adhesive-backed opaque overlays in LSP provided up to 50 % pressure enhancement compared to processing without the overlays. Contrary to processing without the overlays, the temporal characteristics of LSP impulses with adhesive-backed overlays are shown to be independent of the laser pulse width in the range studied. This finding is an important impulse consideration in LSP parameter selection and has not been investigated or reported in the literature. A novel physics-based analytical model to predict shockwave pressures is proposed and validated with experimental data agreeing nominally within 15 % of the predicted values across the parameter space. The results provide insight into the improved residual stresses and enhanced material properties of published opaque overlay studies. Moreover, the results provide vital information for selecting LSP parameters for optimizing component performance and potential extension into previously unreachable pressure regimes.

Flow velocities of the debris-covered Miyar Glacier, western Himalaya, India

ABSTRACT Spatiotemporal surface velocity measurements of the alpine valley type debris-covered Miyar Glacier of the Chandrabhaga (Chenab) basin, western Himalaya, were assessed based on the cross-correlation of Landsat images spanning nearly three decades (1992-2019). Long-term (1950-2015) temperature and precipitation trends were evaluated using Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation (APHRODITE) datasets. The mean velocity (1992-2019) of the Miyar Glacier is ∼29 m/yr, with spatial patterns revealing that the debris-covered tongue is nearly stagnant (∼5 m/yr) compared to the debris-free up-glacier zone (∼35 m/yr). The transition zone from clean to debris-covered ice in the mid-ablation area shows the highest long-term mean velocities of ∼60 m/yr during the observation period, likely resulting from a steep surface gradient and greater ice thickness than the other regions of this glacier. The slow-moving and nearly stagnant debris-covered area reveals the highest amount of surface lowering due to the expansion of supraglacial ponds. Miyar Glacier experiences summer speed-up of ∼67–80% in seasonal velocity compared to winter, interpreted as a result from enhanced basal sliding during summer months due to warmer temperatures inputting more meltwater into the subsurface drainage system. Inter-annual velocity variations are greatest in the upper glacier, with higher velocities observed more frequently in recent decades. Future work should aim to elucidate the causes of this pattern, considering the overall rising air temperature trend in the western Himalaya.

A photogrammetry-based variational optimization method for river surface velocity measurement

The ease of access to media resources and computational power has recently generated interest in using vision-based approaches for hydraulic monitoring. A key challenge for non-intrusive, image-based hydrology measurement methods is incorporating different hydraulic variables as prior knowledge with image information. We propose a photogrammetry-based method called L1-Diffusion derived from the convection–diffusion equation commonly used in hydrodynamics with an additional regularization term to estimate the fluid motion field in the image plane, from which the free surface velocity can be further obtained using the photogrammetric projection relationship between the image plane and world coordinates. The inverse problem is used to discuss the relationship between the widely used space–time image velocimetry (STIV) and the proposed L1-Diffusion. To validate the proposed method, unmanned aerial vehicle (UAV) images as well as in-situ acoustic Doppler current profiler (ADCP) experiments were carried out. Based on comparison results with the ADCP measurement and vision-based flow field estimation, the newly proposed L1-Diffusion algorithm can accurately and efficiently estimate the free surface velocity of a river from the image sequences in a variety of scenarios.

Early Holocene rock glacier stabilisation at col du Lautaret (French Alps): Palaeoclimatic implications

Rock glaciers, usually preserved in periglacial environments of cold-climate high-relief regions, are useful (palaeo)climate indicators. In the European Alps, numerous studies have focused on describing these geomorphological features. However, very few have attempted directly dating them. This lack of measurement is particularly evident in the French Alps. To fill this gap, we performed Cosmic Ray Exposure (CRE) dating through beryllium-10 (10Be) on 10 granitic rock samples collected from two relict rock glaciers, hereafter referred as RG1 and RG2, located at col du Lautaret in the French Alps. This first CRE dating of rock glaciers in the French Alps yielded mean ages of 11.8 ± 0.5 kyrs and 11.6 ± 0.6 kyrs for RG1 and RG2, respectively. While RG2 is clearly a talus-derived rock glacier, the origin of RG1 is less clear. It could potentially be talus-derived, glacier-derived or of mixed origin. The 10Be ages indicate that both rock glaciers became inactive during the transition between the Younger Dryas and the onset of the Holocene, consistently with other studies in the Northern Hemisphere. Considering surface velocity measurements carried out since the 1980s on neighbouring rock glaciers, we hypothesise that the rock glaciers were formed either during the Younger Dryas or slightly earlier, between the Heinrich Stadial 1 and the Younger Dryas. During this period, we estimated temperatures ~3.6 °C lower than the 1980s and precipitation up to 30% lower than at present.

Laser-driven shocks to explore the effects of aging on the adhesion of silver sintered on copper substrate

The adhesion of thin silver joints sintered on metallic substrates is a major issue for their potential use in power electronics modules. Here, we explore how laser shock-induced spallation can provide a way to study this adhesion. Due to wave interactions inside the shock-loaded assembly, dynamic tensile stresses are induced near the copper-silver interface, resulting in partial or full removal of the silver layer. In order to investigate the effects of aging on the interface strength, experiments are performed on both as-sintered and aged samples. Time-resolved measurements of the free surface velocity provide information on wave dynamics and interface failure, but finite-element simulations show that inferring a quantitative value of the bonding strength from these data is still challenging. Nevertheless, post-recovery observations provide original insight into the debonding process, including some complex effects of aging, consistent with trends reported in the literature.

Image-based river discharge estimation by merging heterogeneous data with information entropy theory

An information entropy based approach for the discharge measurements is evaluated for the gaging of the Isère river at the Grenoble university campus. Over a four month period, six discharge measurements were made using a vessel-mounted aDcp. Simultaneously, particle tracking velocimetry (PTV) from video images was used to estimate surface velocities. The surface velocities are projected along the regularly surveyed river section of the Isère-Campus gaging station. The vertical velocity profile at each stream-wise location is approximated by a 1D entropy profile. Information entropy 1D velocity vertical profile depends on two parameters which are fitted using aDcp and surface velocity measurements. The inclusion of the surface velocities reduces the dispersion of the estimated entropy parameters. The measurements show that the two parameters are linearly related with a slope that is stage dependent and thus, surface velocity dependent. From there, the information entropy theory for 1D velocity distribution offers a protocol by which surface velocities only are used to compute the discharges. The protocol is calibrated with both aDcp and surface velocity measurements. It is finally validated with several events during which only surface velocities are measured. For the high water flood event the estimated discharge falls within 2% of the one estimated with the rating curve of the gaging station.

Large Scale Infrared-Based Remote Sensing of Turbulence Metrics in Surface Waters: Going Beyond Mean Flow

In recent years field-scale applications of image-based velocimetry methods, often referred to as large scale particle image velocimetry (LSPIV), have been increasingly deployed. These velocimetry measurements have several advantages—they allow high resolution, non-contact measurement of surface velocity over a large two dimensional area, from which the bulk flow can be inferred. However, visiblelight LSPIV methods can have significant limitations. The water surface often lacks natural features that can be tracked in the visible and generally requires seeding with tracer particles, which creates concerns regarding the fidelity with which tracer particles track the flow, and introduces challenges in achieving sufficient and uniform seeding density, in particular in regions with appreciable velocity accelerations such as turbulence. In LSPIV, image collection is generally limited to daylight hours, and can suffer from non-uniformity of illumination across the camera’s field of view. Due to these issues LSPIV often requires spatio-temporal averaging, and as a result is generally able to extracting the mean, but not the instantaneous, velocity field, and hence is often not a suitable tool for calculating turbulence metrics of the flow.