Deformation Of Water Surface Research Articles

Fluid Dynamics of Interacting Rotor Wake with a Water Surface

Rotor-type cross-media vehicles always induce considerably complex mixed air–water flows when approaching the water surface, resulting in relative thrust loss and structural damage on rotor. The interactions between a water surface and rotor wake bring potential risks to the cross-media process, which is known as the near-water effect of the rotor. In this paper, experimental investigations are used to explore the fluid dynamics of the near-water effect of the rotor. Qualitative droplet observation was carried out on the 0.25 m and 0.56 m diameter commercial rotor blades and the 0.07 m diameter ducted fan near the water surface first to gain a qualitative understanding of droplet characteristics. The results show that the rotor wake caused water surface deformation, droplet tearing off, splashing, and entrainment into the rotor disk. The depression formed by the rotor downwash flow impacting the water surface is named as three modes: dimpling, splashing, and penetrating, and the correlation between the depression modes and the aerodynamic characteristics of the rotor is primary analyzed. The flow mechanisms of dimpling mode were studied using the particle image velocimetry (PIV) technique. The results showed that the cavity and liquid crown obviously alter the flow direction of water surface jets, but not all rotors near water enter the vortex ring state. Two splashing mechanisms were revealed, including the direct ejection of droplets at the rim of depression and the tearing of liquid crown by the water surface jets. The blade tip vortex in the surface jet is a potential cause of entrainment into the rotor disk and secondary breakup of the droplet.

Analyzing the Seasonal Vertical Displacement Fluctuations Using the Global Navigation Satellite System and Hydrological Load: A Case Study of the Western Yunnan Region

The non-tectonic deformation caused by hydrological loads is an important influencing factor in GNSS vertical displacement. Limited by the temporal and spatial resolution of global models and model errors, the hydrological load results calculated by traditional methods are difficult to meet the high temporal and spatial resolution requirements of small to medium-scale regions. This paper introduces the idea of the remove–restore method, assimilates regional high-resolution hydrological data, and obtains higher temporal and spatial-resolution hydrological load results. Subsequently, utilizing data from 12 CORS observed in the western Yunnan region between January 2018 and December 2020, the quantitative relationship and variation characteristics between GNSS vertical displacement and hydrological load displacement were analyzed in detail. Furthermore, the annual signals of both were extracted using the SSA method for comparative analysis. After removing the effects of atmospheric load and non-tidal ocean load, the average correlation coefficient between GNSS vertical displacement and hydrological load displacement is 0.84, with an average reduction of WRMS (%) reaching 37.17%. The average correlation coefficient of the annual signals between GNSS vertical displacement and hydrological load deformation is 0.94, with an average reduction of WRMS (%) reaching 46.5%, indicating that the contribution of hydrological load to the GNSS non-tectonic vertical displacement annual signal is close to 50%. The research results provide scientific support and important references for studying surface tectonic deformation by removing non-tectonic deformations such as hydrological loads from GNSS vertical displacement. Additionally, it helps to explore the mechanisms of interaction between water storage migration and surface deformation.

Water-exit impact of deep-sea mining vehicles: Experimental and numerical investigations

The operation of the deployment and retrieval system of a deep-sea mining vehicle (DSMV) is closely related to its water exit process; rapid water exit processes under wave conditions tend to exert negative influences on the safety and reliability of the entire system. To evaluate the specific effect of the interaction between the DSMV and the surrounding seawater, computational fluid dynamics (CFD) was used to predict the hydrodynamic characteristics and water-exit impacts of the DSMV at different retrieval speeds. First, a stokes-wave-free surface based on an overset mesh method integrating the volume of fluid (VOF) method was developed to reproduce level 4 sea conditions. Subsequently, the water surface deformation and water resistance were recorded to verify the proposed numerical method. These numerical and experimental findings indicate that when a vehicle body passes through wavy water at a relatively high speed, its lifting cable experiences a water-esistance force that is several times its weight. Finally, a vehicle body with a small retrieval speed might undergo several wave cycles, resulting in its lifting cable becoming loose.

Hydrodynamics and turbulence of free-surface flow over a backward-facing step

Three large-eddy simulations of open channel flow over a backward-facing step are performed to investigate the effect of submergence on the turbulence, hydrodynamics, and water surface deformation downstream of the step. The deformation of the water surface, the extent of the recirculation zone as well as the strength of the shear layer are a function of relative submergence. All flows downstream of the step exhibit elevated levels of turbulent shear stress and contain significant amounts of turbulent kinetic energy. The instantaneous flow features rollers immediately behind the step and horseshoe-shaped vortices shed from the shear layer, the latter being advected towards the water surface where they cause deformations. It is shown that these vortices can originate from any location along the dividing streamline; however, they contain more energy the closer to the mean attachment location they originate.

Large-eddy simulation of free-surface turbulent channel flow over square bars

The results of large-eddy simulations of free-surface turbulent channel flow over spanwise-aligned square bars are used to investigate the effects of bed roughness and water surface deformations on the root-mean-squared velocity fluctuations, dispersive shear stress, double-averaged Reynolds shear stress, wake kinetic energy and double-averaged turbulent kinetic energy. Two bar spacings, corresponding to transitional and k-type roughness, at similar Reynolds and Froude numbers are considered. The main peak of all statistical quantities occurs at the bar crest height. The effects of a standing wave at the water surface in flow over k-type roughness is marked by a local peak under the water surface for all statistical quantities considered here except wall-normal and spanwise velocity fluctuations. Quadrant analysis shows that sweeps and ejections are the strongest events contributing to both dispersive and double-averaged Reynolds shear stress but their contributions are different for the two bar spacings. Examining the budgets of dispersive and double-averaged Reynolds shear stress reveals that the dominant terms of these stresses are pressure–strain correlation and pressure transport and the contribution of wake production is similar for both of these stresses but with opposite sign. In addition to the main role of the bars in consuming or producing wake kinetic energy through production and transport and convection, the standing wave at the water surface in flow over k-type roughness induces large convection in the bulk flow too. The dominant terms in the double-averaged turbulent kinetic energy budget are similarly production, transport and convection. Large shear production renders large temporal fluctuations than spatial fluctuations of flow variables. The interaction of bars, bed and water surface is seen in the convection term in flow over k-type roughness.

Water surface response to turbulent flow over a backward-facing step

The water surface response to subcritical turbulent flow over a backward-facing step (BFS) is studied via high-resolution large-eddy simulation (LES). The LES method is validated first using data of previously reported experiments. The LES-predicted water surface is decomposed into different types of gravity waves as well as turbulence-driven forced waves. Analysis of the LES data reveals the interplay between low-frequency large-scale turbulence structures, which are the result of flow separation from the step and reattachment behind the step, and the dynamics of the water surface. The water surface deformation is mainly the result of freely propagating gravity waves and forced waves, owing to turbulence in the form of rollers and/or hairpin vortices. Gravity waves with zero group velocity define the characteristic spatial and temporal scales of the surface deformations at higher frequencies, while large eddies determine their low-frequency modulation. These deformations are mainly confined in lateral bands that propagate downstream following the advection of the near-surface streamwise vortices (rollers) that are shed from the step. Steeper surface waves are observed in regions of negative perturbation velocity gradient and down-welling, downstream of the larger rollers, and are associated with thin isolated regions of high vorticity near the surface. The investigation of such a complex flow has shown that the decomposition of the water surface fluctuations into its different physical components may be used to identify the dynamics of the underlying flow structure.

Study on the Characteristics of Strata Movement and Surface Subsidence Induced by Multiseam Mining

Multiseam mining generates enhanced characteristics of strata movement and surface subsidence (CSMSS) than single seam mining, which strongly increases the possibility of mine water disasters and surface deformation. In this study, the effect of seam separation distances and key stratum (KS) configurations on CSMSS is evaluated using the discrete-element method. The results of the analyses indicated that control function loss of the KS aggravated the failure of the overlying strata and expanded the original water-flowing fractured zone, which grew by 91.49% and 23.40% in short-distance and medium-distance multiseam mining. In addition, the subsidence was higher in the first two cases and also in the tilts and strains. The separation and penetrating tensile cracks determined the upper boundary of the caved and fractured zones in the discrete-element method simulation analysis supported by field data. Finally, this study provides a method for identifying the multiseam category according to the CSMSS resulting from multiseam mining operations, which is the first step toward effective disaster prevention and management.

Numerical Investigation on Solitary Wave Interaction with a Vertical Cylinder over a Viscous Mud Bed

This study investigated the hydrodynamics of a solitary wave passing a vertical cylinder over a viscous mud bed for the first time. A highly viscous Newtonian fluid was assumed as a simplified model for fluid mud. A three-dimensional numerical wave flume consisting of a fixed cylindrical structure and three viscous fluids—air, water, and mud—was constructed and validated. Numerical experiments were performed to investigate solitary wave interaction with a vertical cylinder over a viscous mud bed. Numerical results showed the mud surface deformation to be one order of magnitude smaller than the water surface deformation and their behaviors to be different: mud surface depressions occurred on the upstream and downstream sides of the cylinder, whereas mud surface elevations occurred on the lateral sides of the cylinder. This solitary wave induced scour pattern on a muddy seabed is different from that commonly observed on a sandy seabed. Water flow reversal near the water–mud interface was made more evident by the mud bed. Although the mud bed attenuated water waves, it nevertheless increased the total horizontal force and toppling moment exerted on the cylinder due to the wave-induced mud flow. These findings may be valuable to the design of marine structures on a muddy seabed and worthy of further investigation.

The Crustal Vertical Deformation Driven by Terrestrial Water Load from 2010 to 2014 in Shaanxi–Gansu–Ningxia Region Based on GRACE and GNSS

The terrestrial water resources in Shaanxi–Gansu–Ningxia (SGN) region are relatively scarce, and its climate change is unstable. Research on the deformation driven by terrestrial water load is of great significance to the dynamic maintenance of reference station networks. In this paper, data derived from Gravity Recovery and Climate Experiment (GRACE) and Global Navigation Satellite System (GNSS) from 2010 to 2014 were combined to monitor the spatiotemporal characteristics of surface vertical deformation caused by terrestrial water load change. The single scale factor was calculated by comparing CPC, WGHM, and GLDAS hydrological model to restore filtering leakage signal. The singular spectrum analysis (SSA) method was used to extract the principal component of temporal vertical deformation, and its spatial distribution was analyzed. At the same time, in order to study the relationship between the terrestrial water load deformation from GRACE and that from GNSS, the first-order term correction, the Atmosphere and Ocean De-aliasing Level-1B product (GAC) correction, and the first-order load LOVE number correction for GRACE were adopted in this paper. In addition, a quantitative comparative analysis of both the monitoring results was carried out. The results show that the time-variable characteristics of surface vertical deformation characterized by the filtered three hydrological models were consistent with those of GRACE. The correlation coefficient and Nash–Sutcliffe efficiency coefficient (NSE) values were the highest in the GLDAS model and the GRACE model, respectively; the former index is 0.93, while the latter is 0.85. The crustal vertical deformation from terrestrial water load showed a declining rate from 2010 to 2014. Its spatial change rate showed an obvious ladder distribution, with the surface subsidence rate gradually decreasing from south to north. In addition, weighted root mean square (WRMS) contribution rate of the crustal vertical deformation resulting from GRACE with GAC correction between the different GNSS stations ranged from 18.52% to 54.82%. The correlation coefficient between them was close to 0.70. After deducting the mass load impact of GRACE only, the WRMS contribution rate of the corresponding stations decreased from −8.42% to 21.18%. The correlation coefficient between them reduced noticeably. Adding GAC back can increase the comparability with GRACE and GNSS in terms of monitoring the crustal vertical deformation. The annual amplitude and phase of surface vertical deformation resulting from GRACE with GAC correction were close to those of GNSS. The research results can help to explore the motion mechanism between water migration and surface deformation, which is of benefit in the protection of the water ecological environment in the region.

Vortex shedding and evolution induced by the interactions between a solitary wave and a submerged horizontal plate

This paper presents results of a solitary wave propagating over a submerged horizontal plate based on a non-hydrostatic model. A high-resolution advection scheme is employed based on a second-order flux-limiter method. The model is first validated by comparing numerical results with recently obtained measured data. Then, a series of simulations are carried out to investigate the effect of the plate length on the characteristics of vortex shedding and evolution. With the increase in the length of the plate, more dominant vortical structures induced by the solitary wave with the same wave height can be identified near the lee side of the plate. There are two separate positive vortex shedding from the lower corner of the plate near the lee side, which are not presented in experiments. The secondary positive vortex leads to the water surface deformation for the case that is close to the limit when wave breaking occurs.

Free surface flow over square bars at different Reynolds numbers

Large-eddy simulations of free surface flow over bed-mounted square bars are performed for laminar, transitional and turbulent flows at constant Froude number. Two different bar spacings are selected corresponding to transitional and k-type (reattaching flow) roughness, respectively. The turbulent flow simulations are validated with experimental data and convincing agreement between simulation and measurement is obtained in terms of water surface elevations and streamwise velocity profiles. The water surface deforms in response to the underlying bed roughness ranging from mild undulation for transitional roughness to distinct standing waves for k-type roughness. The instantaneous water surface deformations increase with an increase in Reynolds number. Contours of the mean streamwise and wall-normal velocities, the total shear stress and the streamfunction reveal the presence and extension of recirculation zones in the trough between two consecutive bars. The flow is governed by strong local velocity gradients as a result of the rough bed and the deformed water surface. The local Froude number at the free surface increases for low Reynolds number in the flow over transitional roughness and decreases for low Reynolds number in the flow over k-type roughness. The transitional and turbulent flows exhibit a very similar distribution of the pressure coefficient Cp in both cases, whilst Cp is generally lower for the laminar flow. Regarding the friction coefficient, Cf, it is significantly lower in the turbulent case than in the transitional and laminar cases. The bar spacing does not affect significantly the relative contribution of friction and pressure forces to the total force, neither does the Reynolds number. The friction factor is greater for transitional roughness and decreases with increasing Reynolds number.

Application of the sampling moiré method to shallow open-channel flows with circular roughness elements

This research presents an application of the sampling moiré method, a novel technique originally developed for measuring slight deformation of a static object such as a plate, to fluctuating free water surface in rough open channel flows. The method was used to capture the two-dimensional water surface deformation at a high sampling rate by dyeing the color of water white. The target flow was a very shallow subcritical flow with a depth of 1.5 times the height of the roughness. As a result, a series of instantaneous water surface profiles with non-uniform rough planes were successfully measured at a sampling rate of 100 Hz.It has become clear that the effect of dispersive gravity waves traveling on the water surface is greater than that of non-dispersive waves driven by the turbulence, and that this feature becomes more pronounced as the Froude number increases in such shallow flow conditions. Furthermore, it was experimentally and theoretically verified that the intensity of water surface fluctuation increases with the square of the Froude number. The decomposition of surface fluctuations due to gravity waves and subsurface turbulence using the wavenumber frequency spectrum revealed that the effects of subsurface turbulence are about 20%. This is much less than the contribution from gravity waves in very shallow flows as in this experiment.

Model tests of the evolutionary process and failure mechanism of a pile-reinforced landslide under two different reservoir conditions

Anti-slide piles are widely used for stabilizing landslides and a large number of landslide-piles systems were constituted in reservoir areas. How these landslide-piles systems evolve under reservoir effects is vital for the safe operation of dams. In this study, two reservoir conditions, namely condition of static water level and water level fluctuations, were considered for detailly exploring the influence of static and dynamic water pressure on a landslide-piles system in physical model tests. The pore water pressure, surface deformation and photographs of visual observations were obtained for comparatively analyzing the deformation characteristic and failure mechanism of landslide-piles models under the two conditions. The results show that the soil deformation and failure around the piles were similar in the two tests due to the same pile arrangements. However, retrogressive deformation and two soil collapses occurred in the landslide front area under water level fluctuations instead of slight deformation and shallow erosion under the static water level. The outward hydrodynamic pressure caused by reservoir drawdowns was the primary reason for the soil collapses in the landslide front area. The progressively intensified deformation around the piles which indirectly decreased the soil stability in the landslide front area was the secondary cause for the collapses. The Majiagou landslide-piles system in the field was identified as in the early period of the uniform deformation stage at present based on the field observations, monitoring data and the test results under water level fluctuations.

Experimental and Theoretical Study of Evaporation of a Volatile Liquid Lens on an Immiscible Liquid Surface.

The evaporation of a hexane lens on a distilled water surface was experimentally and theoretically studied. The formation of the hexane lens was recorded by a high-speed camera from the side to observe the variations of the contact diameters and contact angles. The experimental results showed that the shape variation of the hexane lens experienced the spreading stage and the evaporation stage. The spreading stage lasted for about 6% of the lens lifetime. For most time of the evaporation stage, the square of the lens contact radius decreased linearly with time, while the contact angle remained almost unchanged. During the final rapid evaporation stage (about 2% of the lens lifetime), the shape of the hexane lens changed and the lens shrank rapidly until it disappeared. A theoretical model based on diffusion-controlled evaporation under the constant contact angle mode was developed to describe the evaporation of the hexane lens on the water surface. In terms of geometry, the model assumes that a lens is composed of upper and lower spherical caps, and the apparent contact angle is defined based on the intersection of the two caps. The results calculated using the model were found to be in good agreement with the experimental data. Finally, the effects of initial lens volume, water temperature, and water surface deformation on lens evaporation were discussed through calculations. The results showed that increase in the water temperature and deformation of the water surface accelerated the evaporation process.

Investigation of physical issues of the initial conditions of free water surface due to underwater disturbances on the basis of SPH numerical simulation of the phenomenon

The current paper discusses the physical impacts of the various initial boundary conditions of the free surface of a waterbody on the initiation and propagation characteristics of water waves due to the underwater perturbations. Differences between traditional point of view and applied numerical method in this paper for exertion the initial conditions of the generated waves by surface deformation were surveyed in the Lagrangian domain vs. Eulerian. In this article, the smoothed-particle hydrodynamics (SPH) technique was applied for simulating of wave generation process using initial boundary condition of water surface deformation through utilizing DualSPHysics numerical code and comparing the modeling results with recorded data. As a distinct approach, we studied the effects of discrete water particles on properties of produced surface waves by using the Lagrangian analytical capability of SPH model. Illustrative compatibility on simulation results with experimental data proves that meshless techniques such as applied in DualSPHysics software can reproduce physical properties of the event very well, and this is a suitable alternative to existing classical approaches for prediction of shock occurrences with nonlinear behavior such as generated surface water waves by underwater disturbance. Besides, the waveforms and their characteristics behave more realistic by considering the thrown upward water mass which was not directly considered in old formula and theories. The results of numerical modeling indicated rational agreement between numerical and empirical data proving that a complicated nonlinear phenomenon could be predicted by an SPH model which modified initial boundary conditions were supposed into the model with actual assumptions.

Water entry of rounded cylindrical bodies with different aspect ratios and surface conditions

In the present study, we experimentally investigate water surface deformation due to the impact of rounded cylindrical projectiles with different aspect ratios (1.0–8.0). The subsequent jet and splash formation is closely related to the dynamics of an underwater cavity. To control the cavity formation, two kinds of surface conditions (smooth and rough) are applied to the front parts of the projectiles, and two impact speeds are considered. The Froude, Reynolds and Weber numbers are in the ranges of 32–90, $5\times 10^{4}{-}8.4\times 10^{4}$ and 1700–5000, respectively. When the front is smooth, the water film rises up along the body surface immediately after impact, and the temporal variation of its height is analytically estimated. The film converges at the rear pole to create an apex jet at lower aspect ratios and simply rises up and falls with the body at higher aspect ratios. The jets could be further distinguished as thin and thick jets, whose breakdown is found to be a function of the viscous force and surface tension, i.e. the Ohnesorge number. On the other hand, when the front is rough, the water film cannot rise up along the body surface, and instead early separation occurs to make the splash above a free surface. The splash size is quantified to assess the effects of the aspect ratio and impact speed. Upon splash formation, a cavity is created under the free surface, which emanates from the nose of the projectile. As the body sinks, the cavity pinch-off occurs due to the imbalance between the hydrostatic pressure and air pressure inside the cavity. At higher aspect ratios, cavity pinch-off occurs on the side wall of the projectile and leaves a portion of the cavity bubble on it. When the surface is smooth, no underwater cavity forms. Finally, we compare the hydrodynamic force acting on the sinking bodies with and without cavity formation, based on the underwater trajectory of each projectile. It is found that the underwater cavity reduces the drag force on the sinking body when it fully encapsulates the body; however, if the air bubbles are partially attached to the body after pinch-off, they tend to detach irregularly or impose additional drag on the body.

Numerical investigation of water surface deformation due to corona discharge

A two-phase electrohydrodynamic flow in a corona discharge system of a sharp needle and a water electrode is studied considering free interface deformation. The governing equations were solved using finite volume method implemented in a developed solver using the OpenFOAM platform. Recommendations are given about selection of equivalent electrical properties of water. For a constant electrode-water gap, a 60% increase in the applied voltage results in a 90% enhancement of maximum downward air velocity. Interface deformation depth could reach 2 mm (20% of initial water layer depth), revealing that consideration of deformation in a shallow water layer is very important.

Free surface flow over square bars at intermediate relative submergence

ABSTRACTResults from large-eddy simulations and complementary flume experiments of turbulent open channel flows over bed-mounted square bars at intermediate submergence are presented. Scenarios with two bar spacings, corresponding to transitional and k-type roughness, and three flow rates, are investigated. Good agreement is observed between the simulations and the experiments in terms of mean free surface elevations and mean streamwise velocities. Contours of simulated time-averaged streamwise, streamfunction and turbulent kinetic energy are presented and these reveal the effect of the roughness geometry on the water surface response. The analysis of the vertical distribution of the streamwise velocity shows that in the lowest submergence cases no logarithmic layer is present, whereas in the higher submergence cases some evidence of such a layer is observed. For several of the flows moderate to significant water surface deformations are observed, including weak and/or undular hydraulic jumps which affect significantly to the overall streamwise momentum balance. Reynolds shear stress, form-induced stress and form drag are analysed with reference to the momentum balance to assess their contributions to the total hydraulic resistance of these flows. The results show that form-induced stresses are dominant at the water surface and can contribute significantly to the overall drag, but the total resistance in all cases is dominated by form drag due to the presence of the bars.

A Simplified Method for Analyzing Water Impact in the Initial Stages on an Elastic Rectangle Plate

For most flat-bottom marine structures, impact loads are generated by complex transient coupling effects of solid, air, and water. However, simplified forecasting methods to obtain impact loads and dynamic responses of flat-bottom structures by considering both hydroelastic and air cushion effects are rare. In this article, a new simplified analytical method of water impact on the elastic plate is proposed based on Verhagen's model for the rigid plate. The analysis is focused on the initial stage during which the highest hydrodynamic loads are generated. Interactions between the plate, the air, and the water are simulated and analyzed. Also, fluid-structure coupling results by simplified method are compared with numerical results from Arbitrary Lagrangian-Eulerian method in LS-DYNA code. Experimental results are used to validate the feasibility and accuracy of the simplified method. Water impact on plates with different drop heights, rigidities, and added mass is analyzed. The air cushion effect, elastic effect, and three-dimensional effect in the simplified model are also discussed. 1. Introduction Over half a century, there has been more and more attention given to the phenomenon known as "slamming" which exists widely in both the natural environment and engineering application. As a complex transient process, slamming can be considered as a three-phase coupling model containing solid, liquid, and gas. Water entry problem is one of the most typical phenomena of slamming. The problem of a rigid wedge entering water was studied in detail starting from the thirties of the last century. This study was motivated by the design of hydroplane landing on water. Von Karman (1929) first carried out an analytical study on water entry problem by potential theory. Considering the deformation of the water surface, Wagner (1932) extended the Von Karman model. In the following several decades, many complex models of water impact were developed by Wagner model (Hirano & Miura 1970; Armand & Cointe 1986; Cointe 1991). In addition, new models are proposed (Dobrovol' skaya 1969; Greenhow 1987; Howison et al. 1991; Muzaferija et al. 1997). More factors in the water impact problem were taken into consideration, including gravity (Greenhow 1987), liquid viscosity (Muzaferija et al. 1998), liquid compressibility (Korobkin 1996; Korobkin 1997; Campana et al. 1998), and so on.

Through-water terrestrial laser scanning in hydraulic scale models: proof of concept

ABSTRACTRiver engineering research demands increasingly high-resolution topographic data of both exposed and submerged surfaces. Detecting the topography through water is challenging in real world applications and in hydraulic laboratories. For hydraulic scale models, non-intrusive and accurate methods are needed to detect the dynamics of the river bed and its morphology without model draining. The Leica ScanStation P15 terrestrial laser scanner was tested for dry surface and through-water laser scanning. An existing procedure was adapted to reduce the distortion caused by refraction at the air/water interface. A series of tests with flow depths smaller than 0.15 m indicated an accuracy of less than 1.4 mm, resulting in a method that can be applied in hydraulic scale models with a movable bed. A sensitivity analysis revealed that the angle of incidence is the most sensitive parameter whereas the refractive index is a robust parameter. A strong decay in accuracy was observed for angles of incidence larger than 60° due to uncertainties in the flow depth. The major limitations for an application in the laboratory are high turbidity and water surface deformations that lead to an inaccurate detection of the water surface.