1,721,133 research outputs found
Experimental and Numerical Modeling of Runup Induced by Impulsive Waves
No full textLandslide Tsunamis have been extensively studied during the last years. However, recent events (e.g. last volcanic eruption Anak Krakatau in 2019) motivated the increase of the attention paid to this phenomenon and on its destructive effects. To protect human life, knowledge of maximum expected runup could be of great help for administrators and civil protection. This paper aims at investigating the performances of different numerical models (DualSPHysics, an OpenFOAM solver, and SWASH) to assess the landslide induced runup by comparing the numerical results to experimental findings. Results show good accuracy for all the models in reproducing wave generation, while the wave propagation features are correctly reproduced only for the biggest of the two water depths. The OpenFOAM solver and SPH show good performances in evaluating impulse wave runup compared to experimental results, while SWASH lacks in the accuracy
The Effects of Submerged Berms on the Seabed Pressure around Rubble Mound Breakwaters
No full textBerms deployed at the toe of conventional breakwaters may be needed to reduce bottom settlements and to limit scour in front of the structure. Due to their influence upon the wave loads acting on the armor, the submerged berms may be also effective in increasing the stability of the armor layer, as well as of the soil-foundation system, if compared to straight sloped conventional breakwaters. This research deals with the influence of submerged berms on the wave-induced dynamic pressure in front of and beneath rubble mound breakwaters, whose detection is paramount for the evaluation of momentary liquefaction phenomenon. The present paper summarizes the preliminary results, obtained from experimental tests and numerical models
Measuring (Oblique) Wave Run-Up and Overtopping with Laser Scanners
Full text linkWave overtopping is commonly measured using overtopping tanks. In this paper, an alternative system is developed by using two laser scanners. It measures wave run-up, as well as layer thicknesses and front velocities, both during normally and obliquely incident waves on a dike in the field. The paper considers the first field validation tests with the system, with normal and oblique waves generated by the wave run-up simulator on a grass dike slope. Furthermore, a range of environmental conditions are simulated, to determine the robustness of the system. From the measured distance and reflection, the run-up is determined, which corresponds well to the observed run-up. From the data, the layer thickness and front velocity are determined as well. Layer thicknesses and front velocities are determined reliably with the laser scanners. Also, the (virtual) wave overtopping discharge can be calculated, which corresponds well with the most commonly used overtoppingequations.Hydraulic Structures and Flood RiskEnvironmental Fluid Mechanic
Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry
Full text linkReconstructing the topography of shallow underwater environments using Structure-from-Motion—Multi View Stereo (SfM-MVS) techniques applied to aerial imagery from Unmanned Aerial Vehicles (UAVs) is challenging, as it involves nonlinear distortions caused by water refraction. This study presents an experiment with aerial photographs collected with a consumer-grade UAV on the shallow-water reef of Fuvahmulah, the Maldives. Under conditions of rising tide, we surveyed the same portion of the reef in ten successive flights. For each flight, we used SfM-MVS to reconstruct the Digital Elevation Model (DEM) of the reef and used the flight at low tide (where the reef is almost entirely dry) to compare the performance of DEM reconstruction under increasing water levels. Our results show that differences with the reference DEM increase with increasing depth, but are substantially larger if no underwater ground control points are taken into account in the processing. Correcting our imagery with algorithms that account for refraction did not improve the overall accuracy of reconstruction. We conclude that reconstructing shallow-water reefs (less than 1 m depth) with consumer-grade UAVs and SfM-MVS is possible, but its precision is limited and strongly correlated with water depth. In our case, the best results are achieved when ground control points were placed underwater and no refraction correction is used
Groundwater Levels in a Drained Beach in Long and Short Waves Conditions
Full text linkDrainage of beaches is thought to be a soft engineering solution to counteract erosion. The present work aims to show the response of the groundwater table level when it is influenced by a drain inside the sand, in the vicinity of the shoreline. The knowledge of the water table dynamics helps to identify the role played by the drain, and consequently it is useful to address its function on the overall BDS functioning. The water table dynamics has been mathematically investigated, in presence of both long and short waves. An analytical solution for the Boussinesq equation with long waves and a drainage boundary condition within the porous medium is presented. A VOF numerical tool has been used to study the groundwater table fluctuations driven by the short waves swash. A comparison between the analytical solution and the numerical results in terms of groundwater level has been carried out. The numerical model reproduces the drain-induced dynamics inside the beach. The analytical model, on the other hand, although it is developed under the long wave hypothesis, seems to catch, at least qualitatively, the water table evolution in case of short period regular waves. It enables to think of it as a preliminary evaluation tool for the BDS design
Effect of Venting Holes to Relieve Wave Impact Pressures on Flood Gates with Overhangs
Full text linkFlood gates in storm surge barriers or outlet sluices can be prone to violent wave impacts. When an obstruction is present at the sea side above the gate, confinement of the incoming waves can lead to impulsive wave loads, even when the waves are non-breaking. The large loads can increase the stresses in the gate and structure considerably. One of the measures that is often discussed to relieve the pressures of these impacts is to apply small openings in the gates. In this paper the potential effect of these venting holes on the wave impact loads is determined. The decrease in impact pressure impulse is determined for a range of venting hole geometries is determined by numerical 2D and 3D solutions of a schematized wave impact. In this model the pressure impulse P (integral of the local pressure over the small impact duration) is determined directly by the so-called pressure impulse theory. The potential decrease in pressure impulse due to wave impacts is presented. Moreover, some initial CFD modelling is applied, and the applicability of the pressure impulse theory is discussed.Hydraulic Structures and Flood Ris
Numerical Evaluation of Design Rules for Non-Breaking Wave Loads on Vertical Walls
Full text linkThis paper describes a numerical evaluation of design rules for the determination of wave loads of non-breaking waves on vertical structures. Design guidelines were proposed by Sainflou (1928) and Goda (1974). These guidelines use geometric parameters of the structure, an incident wave height and a wave period. In practice (cf. CERC, 1984), a Rayleigh distribution of individual wave heights is assumed to determine the design wave height in an irregular wave field. Their reliability and range of applicability are poorly known, especially when the incident wave condition consists of a mixed sea state, like a local wind sea and a low-frequency (swell) component. To validate the above described design methods, we applied the non-hydrostatic numerical wave model SWASH to simulate wave loading on a rigid vertical wall for single and mixed sea states. In addition, we compared the results with linear wave theory and the spectral response approach using transfer functions based on linear wave theory.Hydraulic Structures and Flood RiskEnvironmental Fluid Mechanic
Wave Impact Pressure-Impulse on Vertical Structures with Overhangs
No full textThe study of wave impact physics and magnitudes are key for the design of vertical coastal hydraulic structures. This research addresses the study of standing wave impacts on vertical coastal hydraulic structures with a relatively short horizontal overhang, which is especially relevant for structures such as lock gates, sluice gates, dewatering sluices, flood gates and storm surge barriers. This paper applies the pressure-impulse theory to predict the pressure-impulse caused by standing wave impacts. These theoretical estimates are compared with results from four extensive regular wave tests from laboratory experiments conducted at the Hydraulic Engineering Laboratory of the Delft University of Technology. The agreement for two test cases is good, while differences are observed in the other two cases. This study concludes that a prediction method based on the pressure-impulse theory will allow to carry out preliminary load estimations from standing wave impacts on vertical structures with overhangs. Nevertheless, further research is required considering a larger range of structure dimensions, incident wave characteristics and influencing processes such as air entrapment.Hydraulic Structures and Flood Ris
Soil temperature, volumetric water content, electrical conductivity, air temperature and atmospheric pressure measured every 10 minutes in a grass- and a herb-dominated area at a summer dike, Butjadingen, Germany (Nov 2022–Nov 2023)
No full textTo understand the role of plant species and functional diversity on the physical soil parameters of a sea dike, especially under prolonged drought conditions, continuous measurements of soil temperature, volumetric water content (soil moisture), soil electrical conductivity (EC), air temperature and atmospheric pressure were carried out from 22 November, 2022, to 22 November, 2023. The measurements were taken using six soil sensors from METER Group's TEROS 12 series, which were installed at three distinct soil depths (4 cm, 14 cm, 24 cm) and on two differently vegetated dike areas: one area with a grass-dominated plant community (referred to as 'Mix-Grass') and one area with a herb-dominated plant community (referred to as 'Mix-Herb'). The sensors were mounted on the southern (inland) side of a summer dike, which is located at the south-eastern North Sea coast of Germany (Butjadingen, Wesermarsch; 'Mix-Grass': 53.61211876 ° N, 8.330925695° E, 'Mix-Herb': 53. 61210826° N, 8.330989015° E), about 1 m below the dike crest. The dike height is approximately 3.6 m above mean high water (MHW). The measurement data was logged at 10-minute intervals using a ZL6 logger from the METER Group
Numerical Modelling of Landslide-Generated Tsunamis with OpenFOAM®: a New Approach
Full text linkIn this paper we present a new method for numerically modelling landslide-generated tsunamis in OpenFOAM® by using a new approach based on the Overset mesh technique. This technique, which is based on the use of two (or more) numerical domains, is new in the coastal engineering field and appears to be extremely powerful to model the interaction between a moving body and one or more fluids. Indeed, the accurate resolution around the moving body (i.e. body-fitted approach), guaranteed by this method, offers a great advantage to study the momentum exchange between the body and the water. Furthermore, in order to overcome a drawback of the Overset mesh implementation we modelled the solid boundaries, along which the landslide body moves, as a porous media with a very low permeability. The new approach has been preliminarily, and successfully, validated through the numerical reproduction of past experiments for landslide-generated tsunamis triggered by a solid and impermeable wedge at a sloping coast
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