1,720,969 research outputs found
Numerical characterisation and efficient prediction of landslide-tsunami propagation over a wide range of idealised bathymetries
Full text linkLandslide-tsunamis are generated by masses, such as landslides or icebergs, impacting into water bodies. Such tsunamis resulted in major catastrophes in the recent past. Generic research into landslide-tsunamis has widely been conducted in idealised water body geometries at uniform water depths. However, varying bathymetries can significantly alter landslide-tsunamis. This article investigates this effect in a 2D flume using selected idealised bathymetries to provide methods to predict the transformed wave characteristics downwave of each feature. The selected bathymetries are: (a) linear beach bathymetries, (b) submerged positive and negative Gaussian bathymetric features and (c) submerged positive and negative step bathymetries. The hydrodynamic model SWASH, based on the non-hydrostatic non-linear shallow water equations, was used to simulate 9 idealised landslide-tsunamis (1 approximate linear, 2 Stokes, 2 cnoidal and 4 solitary waves), for a total of 184 tests. The analysed parameters include the free water surface, wave height and amplitude. Shoaling in (a) is represented by either Green's law or the Boussinesq's adiabatic approximation up to wave breaking with an accuracy of −7% to +10% for cnoidal and solitary waves, respectively. The results are then analysed with an (i) Artificial Neural Network and (ii) a regression analysis. (i) shows a smaller Mean Square Error (MSE) of 0.0027 than (ii) (MSE =0.024) and good generalisation in predicting the transformed wave characteristics and, after defining the best dimensionless parameters, (ii) provides empirical equations to predict transformed waves. In addition, simulations were conducted in a 3D basin to investigate the combined effect of the bathymetry and geometry. The efficient use of the developed prediction methods is demonstrated with the 2014 Lake Askja landslide-tsunami where a good accuracy is achieved compared to available numerical simulations
Numerical modelling of landslide-tsunami propagation in a wide range of idealised water body geometries
Full text link© 2019 Elsevier B.V. Large landslide-tsunamis are caused by mass movements such as landslides or rock falls impacting into a water body. Research of these phenomena is essentially based on the two idealised water body geometries (i) wave flume (2D, laterally confined wave propagation) and (ii) wave basin (3D, unconfined wave propagation). The wave height in 2D and 3D differs by over one order of magnitude in the far field. Further, the wave characteristics in intermediate geometries are currently not well understood. This article focuses on numerical landslide-tsunami propagation in the far field to quantify the effect of the water body geometry. The hydrodynamic numerical model SWASH, based on the non-hydrostatic non-linear shallow water equations, was used to simulate approximate linear, Stokes, cnoidal and solitary waves in 6 different idealised water body geometries. This includes 2D, 3D as well as intermediate geometries consisting of “channels” with diverging side walls. The wavefront length was found to be an excellent parameter to correlate the wave decay along the slide axis in all these geometries in agreement with Green's law and with diffraction theory in 3D. Semi-theoretical equations to predict the wave magnitude of the idealised waves at any desired point of the water bodies are also presented. Further, simulations of experimental landslide-tsunami time series were performed in 2D to quantify the effect of frequency dispersion. This process may be negligible for solitary- and cnoidal-like waves for initial landslide-tsunami hazard assessment but becomes more important for Stokes-like waves in deeper water. The findings herein significantly improve the reliability of initial landslide-tsunami hazard assessment in water body geometries between 2D and 3D, as demonstrated with the 2014 landslide-tsunami event in Lake Askja
Numerical analysis and prediction of the effect of debris initial configurations on their dispersion during extreme-hydrodynamic events
Full text linkTsunamis and other extreme hydrodynamic events have the potential to transport large debris that, along
with the flow, are capable of causing severe damage to coastal structures and infrastructures. Therefore,
modelling such processes is essential when assessing the multiple hazards associated to this type of events.
In harbour areas, transport inland of shipping containers and subsequent impacts are relevant examples of
waterborne debris hazards. The present work addresses two gaps in the scientific research of this problem using
numerical methods; the understanding of the effect of containers initial layouts and that of the flow impact
angle on the transport and diffusion. To fill these gaps a numerical study was carried out using idealised flow
conditions. To this end a Smoothed Particles Hydrodynamics solver (DualSPHysics), coupled with a Discrete
Element Method model (Project CHRONO), was used and initially validated with experiments published in the
literature. Subsequently, four layouts commonly used in shipping containers yards were simulated, including
incident flow depth and impact angle variability, resulting in 76 total simulations. The results were analysed
in terms of normalised standard deviation and normalised range differences with respect to the initial values
of both parameters. These parameters were related to the flow impact angle, water depth to containers height
ratio DhR, and normalised displacement of the container clusters centroids. Standard deviation and range
are shown to reach, for almost all results, a quasi-steady state by the end of the simulations. It is shown
that the standard deviation and range are more sensitive to the impact angle for DhR ≤ 1.7. In this case,
the configurations with flow impacting orthogonally to one of the containers axes show larger values of the
two parameters than for intermediate angles. For larger values, DhR drives the standard deviation and range,
independently from the impact angle. DhR is shown to be a physical parameter that well describes the relative
importance of dispersion and advection of containers transported in extreme hydrodynamic events. Finally,
existing relationships, that assume an infinite growth of the range, are shown to overestimate numerical results
at the stage in which dispersion does not grow further. Two new regression formulae are numerically derived
to predict the dispersion parameters at this stage. They include the effects of the cluster layout, impact angle
α and DhR making them a valid alternative to existing relationship
NUMERICAL INVESTIGATION OF LANDSLIDE-TSUNAMI PROPAGATION ANDTRANSFORMATION IN A WIDE SPECTRUM OF WATER BODY GEOMETRIES
Full text linkLarge landslide-tsunamis are caused by mass movements such as landslides and rock falls impacting into a water body. Landslide-tsunami research is essentially based on the two idealised water body geometries (i) wave flume (2D, laterally confined wave propagation) and (ii) wave basin (3D, unconfined wave propagation). The wave heights in 2D and 3D vary by over one order of magnitude in the far field and the wave characteristics in intermediate geometries are currently not well understood. This article focuses on numerical landslide-tsunami propagation in the far field to quantify the effect of the water body geometry. The wave model SWASH, based on the non-hydrostatic non-linear shallow water equations, is used to simulate Stokes and solitary waves in 6 different idealised water body geometries. This includes 2D, 3D as well as intermediate geometries consisting of “channels” with diverging side walls. The wavefront length was found to be an excellent parameter to correlate the wave decay along the slide axis in all these geometries in agreement with Green’s law. Semi-theoretical equations to predict the wave magnitude of the idealised waves in any desired point of the water bodies are also presented. The findings herein significantly improve the reliability of preliminary landslide-tsunami hazard assessment in water body geometries between 2D and 3D, as demonstrated with the application on the 2014 landslide-tsunami event in Lake Askja
Analysis of the performance of different sediment transport formulations in non-hydrostatic Xbeach
Full text linkProcess-based, wave-resolving models are essential tools to resolve the complex hydro-morphodynamics in the swash zone. The open-source Non-Hydrostatic XBeach model can solve the depth-averaged wave-by-wave flow in the nearshore region up to the shoreline and the intra-wave bed changes during time-varying storms. However, validation and testing of its morphological response are still limited in the context of sandy beaches. This work aims to assess the performance of the wave-resolving sediment dynamics modelling within Non-Hydrostatic XBeach for different sediment transport formulations. The sediment transport modelling approaches considered in this study were tested and compared to laboratory experiments involving wave trains over an intermediate beach. Numerical results show a better performance in the prediction of the intra-swash sediment dynamics when the newly implemented wave-resolving transport equation is applied compared to the existing approach within the model
Numerical characterisation of landslide-tsunamis in idealised and real water bodies
Full text linkLandslide-tsunamis are caused by mass movements such as landslides and rockfalls impacting into a water body. This phenomenon has caused catastrophes in recent history that significantly affected both human lives and the economies of countries. Landslide-tsunamis also need to be assessed in high risk countries such as China with 87000 reservoirs. For this reason, reliable hazard assessment methods are required. Next to landslides generating the tsunamis, two additional water body characteristics affect their propagation before reaching the shore. These are: the water body geometry affecting the landslide-tsunami energy spread, and the bathymetry affecting phenomena such as shoaling and reflection.
Landslide-tsunamis research under idealised conditions, is essentially based on the two idealised water body geometries (i) wave flume (2D, laterally confined wave propagation) and (ii) wave basin (3D, unconfined wave propagation). The wave heights in 2D and 3D can differ by over one order of magnitude in the far field and the wave characteristics in intermediate geometries are currently not well understood. Further, under idealised conditions, the majority of the studies use a uniform water depth to better isolate other effects. However, it has been demonstrated that also the bathymetry can considerably affect tsunami propagation via shoaling and other depth and shore related effects.
This study focuses on how these two described aspects affect landslide-tsunami propagation. The numerical model SWASH, based on the non-hydrostatic non-linear shallow water equations, was used to simulate approximate linear, Stokes, cnoidal and solitary waves. The effect of the water body geometry was investigated in 6 different idealised water body geometries including 2D, 3D and intermediate geometries with water body side angles of θ=7.5°, 15°, 30° and 45° at uniform water depths. The effect of the bathymetry was mainly studied in 2D using a wide range of potential conditions representing real cases namely beach, positive and negative Gaussian and positive and negative step bathymetries. This resulted in a total of 184 numerical tests. In addition, the combined effect of the water body geometry and bathymetry was investigated in selected bathymetries with wave conditions spanning from deep to shallow water.
The wavefront length, i.e. the arc length of the circle sector formed by the wave front, e.g. a semi-circle in 3D, was found to be an excellent parameter to correlate the wave decay along the slide axis in all investigated geometries in agreement with Green's law and diffraction theory in 3D. Semi-theoretical equations to predict the wave magnitude of the idealised waves at any desired point in the water bodies are also presented. Further, simulations of experimental landslide-tsunami time series were performed in 2D to quantify the effect of frequency dispersion. This process may be negligible for solitary- and cnoidal-like waves for initial landslide-tsunami hazard assessment but results in approximations in deeper waters.
The results of landslide-tsunami propagation over different bathymetries showed that shoaling on beaches follows either Green's law or the Boussinesq's adiabatic approximation up to wave breaking with an error of -7% to +10% for cnoidal and solitary waves. The results were then analysed with an Artificial Neural Network (ANN) and a regression analysis to find the transformed wave characteristics downwave of the investigated bathymetries with the first showing better performance. In addition, the combined effects of the water body geometry and bathymetry were studied revealing that relations derived for a 2D geometry result in under-predictions of the wave characteristics for deep-water waves while they are more appropriate for shallow-water when θ>0°.
The 2014 Lake Askja case, Iceland, was used to validate and define a prediction procedure to calculate the wave characteristics for a real case with variable geometry and bathymetry. The derived semi-theoretical equations resulted in an error of 10% for the wave height and 1.5% for the amplitude when compared with the detailed numerical simulations of Gylfadóttir et al. (2017). This is under the condition that only the effect of the water body geometry is relevant. When both the effect of the water body geometry and bathymetry are relevant then additional prediction methods were employed with the ANN resulting in the best performance with errors of 23.4% and 1.0% for the wave height and amplitude, respectively. Note that the lower agreement found when combining the two effects can be attributed to non-linear superposition effects which are highly dependent on the wave type.
The findings herein are expected to significantly improve the reliability of preliminary landslide-tsunami hazard assessment in water body geometries between 2D and 3D and with variable bathymetries. However, the combined effect showed that the water body geometry and bathymetry play an important role. Therefore, future developments should investigate this combined effect for both idealised and real cases using numerical simulations and laboratory experiments. Also, the impact on defense structures and buildings should be investigated by using inundation models to improve design equations to mitigate future risks
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Numerical characterisation of landslide-tsunamis in idealised and real water bodies
Full text linkLandslide-tsunamis are caused by mass movements such as landslides and rockfalls impacting into a water body. This phenomenon has caused catastrophes in recent history that significantly affected both human lives and the economies of countries. Landslide-tsunamis also need to be assessed in high risk countries such as China with 87000 reservoirs. For this reason, reliable hazard assessment methods are required. Next to landslides generating the tsunamis, two additional water body characteristics affect their propagation before reaching the shore. These are: the water body geometry affecting the landslide-tsunami energy spread, and the bathymetry affecting phenomena such as shoaling and reflection.
Landslide-tsunamis research under idealised conditions, is essentially based on the two idealised water body geometries (i) wave flume (2D, laterally confined wave propagation) and (ii) wave basin (3D, unconfined wave propagation). The wave heights in 2D and 3D can differ by over one order of magnitude in the far field and the wave characteristics in intermediate geometries are currently not well understood. Further, under idealised conditions, the majority of the studies use a uniform water depth to better isolate other effects. However, it has been demonstrated that also the bathymetry can considerably affect tsunami propagation via shoaling and other depth and shore related effects.
This study focuses on how these two described aspects affect landslide-tsunami propagation. The numerical model SWASH, based on the non-hydrostatic non-linear shallow water equations, was used to simulate approximate linear, Stokes, cnoidal and solitary waves. The effect of the water body geometry was investigated in 6 different idealised water body geometries including 2D, 3D and intermediate geometries with water body side angles of θ=7.5°, 15°, 30° and 45° at uniform water depths. The effect of the bathymetry was mainly studied in 2D using a wide range of potential conditions representing real cases namely beach, positive and negative Gaussian and positive and negative step bathymetries. This resulted in a total of 184 numerical tests. In addition, the combined effect of the water body geometry and bathymetry was investigated in selected bathymetries with wave conditions spanning from deep to shallow water.
The wavefront length, i.e. the arc length of the circle sector formed by the wave front, e.g. a semi-circle in 3D, was found to be an excellent parameter to correlate the wave decay along the slide axis in all investigated geometries in agreement with Green's law and diffraction theory in 3D. Semi-theoretical equations to predict the wave magnitude of the idealised waves at any desired point in the water bodies are also presented. Further, simulations of experimental landslide-tsunami time series were performed in 2D to quantify the effect of frequency dispersion. This process may be negligible for solitary- and cnoidal-like waves for initial landslide-tsunami hazard assessment but results in approximations in deeper waters.
The results of landslide-tsunami propagation over different bathymetries showed that shoaling on beaches follows either Green's law or the Boussinesq's adiabatic approximation up to wave breaking with an error of -7% to +10% for cnoidal and solitary waves. The results were then analysed with an Artificial Neural Network (ANN) and a regression analysis to find the transformed wave characteristics downwave of the investigated bathymetries with the first showing better performance. In addition, the combined effects of the water body geometry and bathymetry were studied revealing that relations derived for a 2D geometry result in under-predictions of the wave characteristics for deep-water waves while they are more appropriate for shallow-water when θ>0°.
The 2014 Lake Askja case, Iceland, was used to validate and define a prediction procedure to calculate the wave characteristics for a real case with variable geometry and bathymetry. The derived semi-theoretical equations resulted in an error of 10% for the wave height and 1.5% for the amplitude when compared with the detailed numerical simulations of Gylfadóttir et al. (2017). This is under the condition that only the effect of the water body geometry is relevant. When both the effect of the water body geometry and bathymetry are relevant then additional prediction methods were employed with the ANN resulting in the best performance with errors of 23.4% and 1.0% for the wave height and amplitude, respectively. Note that the lower agreement found when combining the two effects can be attributed to non-linear superposition effects which are highly dependent on the wave type.
The findings herein are expected to significantly improve the reliability of preliminary landslide-tsunami hazard assessment in water body geometries between 2D and 3D and with variable bathymetries. However, the combined effect showed that the water body geometry and bathymetry play an important role. Therefore, future developments should investigate this combined effect for both idealised and real cases using numerical simulations and laboratory experiments. Also, the impact on defense structures and buildings should be investigated by using inundation models to improve design equations to mitigate future risks
Numerical modelling of flow‐debris interaction during extreme hydrodynamic events with DualSPHysics‐CHRONO
Full text linkFloods can transport debris of a very wide range of dimensions, from cohesive sediments to large floating debris, such as trees and cars. The latter increases the risk associated with floods by, for example, obstructing the flow or damaging structures due to impact. The transport of this type of debris and their interaction with structures are often studied experimentally in the context of tsunamis and flash floods. Numerical studies on this problem are rare, therefore the present study focuses on the numerical modelling of the flow‐debris interaction. This is achieved by simulating multiple laboratory experiments, available in the literature, of a single buoyant container transported by a dam‐break flow in order to validate the chosen numerical approach. The numerical simulations are carried using the open source DualSPHysics model based on the smoothed particle hydrodynamics method coupled with the multi‐physics engine CHRONO, which handles the container–bottom interactions. The trajectory, as well as the velocity of the centroid of the container, were tracked throughout the simulation and compared with the same quantities measured in the laboratory. The agreement between the model and the experiment results is quantitatively assessed using the normalised root mean squared error and it is shown that the model is accurate in reproducing the floating container trajectory and velocity
- …
