Impulse Wave Propagation Research Articles

River blockage and impulse wave evolution of the Baige landslide in October 2018: Insights from coupled DEM-CFD analyses

On 11 October 2018, the Baige landslide in Southwest China blocked the Jinsha River and induced waves amplifying the landslide-affected area significantly. Devastating flood damage was caused by the consequent dam breach. Such a complex sequence can lead to catastrophic consequences but has rarely been fully reproduced. This paper investigates the landslide-river interaction of the first Baige landslide based on coupled discrete element method (DEM) and computational fluid dynamics (CFD) analyses. To this end, the volume of fluid (VOF) and virtual sphere model are adopted to realise impacted river tracing and accurate terrain modelling. The damming process and impulse wave evolution of the first event are well represented. In addition, the simulated cumulative landslide spreading path, deposit geometry, maximum wave elevation and cumulative wave erosion area satisfactorily match the survey results. Our findings further indicate that the movement path and deposit morphology of the Baige landslide are mainly affected by local terrain, while the propagation of impulse waves is driven by the sliding mass and modulated by the riverbank and hydrodynamic conditions. In particular, we discussed the evolution patterns of impulse waves caused by river damming landslides, encompassing run-up on the opposite bank and quasi-3D propagation along the river direction. This research provides a valuable guide for the practical simulation of river blockage and impulse wave evolution and supports the mitigation of landslide disasters in mountainous areas.

Numerical study of hydraulic characteristics of impulse waves generated by subaerial landslides

Impulse waves generated by subaerial landslides of a block model along a frictionless surface are investigated numerically based on a combination of immersed boundary method and lattice Boltzmann method. A wave propagation model is proposed through machine learning. The observed impulse waves are classified into Stokes-like waves, solitary-like waves, cnoidal-like waves, and bore-like waves. The influence of the slope angle and the slide front angle on the generation and propagation of impulse waves is investigated from the perspectives of the quantitative analyses on primary wave amplitude and energy transformation. The energy release, dissipation, and propagation of the impulsive waves are investigated based on energy conservation principles. The wave propagation model based on the random forest model is established upon a priori classification of wave types. By comparison with the available numerical results, the accuracy of the proposed wave propagation model in predicting free water surface elevations is demonstrated.

The Effect of River Channel Characteristics on Landslide-Generated Waves and the Dynamic Water Pressure of the Dam Surface

In a reservoir area, impulsive landslide surges induced by slope failure may pose huge damage to the dam and the lives in the shoreline areas, which are greatly affected by river channel characteristics. In this study, water depth, the width of the water surface, and the bending angle of river channel were chosen as the main influencing factors. The numerical method was used to investigate the influence of river channel characteristics on wave propagation and the distribution of dynamic water pressure on the dam surface. The effect mechanism was analyzed, and a prediction model considering river channel characteristics for the propagation wave height was established. Results show that water depth and the bending angle of the river channel play a positive role in the attenuation of the energy carried by landslide surges. The width of the water level mainly influences the propagation of impulse waves in the far-field area. The river channel characteristics affect the value of the dynamic pressure on the dam surface but have a minor effect on dynamic pressure distribution. The distribution of dynamic pressure on the dam is greatly influenced by the distance between the dam site and the place where the landslide occurs.

Multi-phase flow simulation of landslide dam formation process based on extended coupled DEM-CFD method

The landslide-river interaction and the impulse waves involved in the landslide dam formation process may not be insignificant and have not been extensively investigated and simulated. This paper presents a numerical investigation on the formation process of landslide dams and resulting free surface flow dynamics in the impacted river via coupled discrete element method (DEM) and computational fluid dynamics (CFD) with the volume of fluid (VOF). The accuracy and validity of the extended coupled method are verified using a series of test cases involving three-phase interaction and free surface evolution. It is then applied to simulate the landslide dam formation processes related to landslide and river flow scenarios of different kinematic characteristics. Furthermore, quantitative analysis is performed to describe the complex evolution of the dam morphology and dynamic evolution of impulse waves. It is found that the impact between the landslide, river flow and valley drives the dam formation process. The landslide velocity considerably influences the propagation of impulse waves, while the river flow velocities control the dam morphology in opposite ways in the upstream and downstream. This research provides a practical modeling framework to understand the formation mechanism of landslide dams and support applications in hazard prediction and mitigation.

Numerical simulation of landslide generated impulse waves using a δ+-LES-SPH model

In this article, a δ+-LES-SPH model is presented to study the generation and propagation of impulse waves. In this model, a density diffusion term is added to the continuity equation to eliminate the numerical high-frequency oscillation of the pressure field. A particle shifting technique is introduced and modified in the motion equation to improve the accuracy and robustness of the smoothed particle hydrodynamics (SPH) model. The physical viscosity term and the turbulence viscosity term based on the large eddy simulation (LES) are used in the momentum equation to calculate the viscous force. To predict the rigid slide motion more effectively, we propose a rigid slide motion model that considers friction in the δ+-LES-SPH frame. The δ+-LES-SPH code was implemented in Fortran 90, and OpenMP programming technology was used to improve the calculation efficiency. Subsequently, this parallel SPH code was used to simulate subaerial and submarine rigid landslides in 2-D and more realistic 3-D applications. The SPH results were compared with the experimental data and other numerical results. The results show that the proposed model has a good convergence and less numerical dissipation. Satisfactory results were obtained for the rigid slide motion, wave generation, and long-distance propagation.

Numerical studies on the radiation of train-tunnel impulse waves

An impulse wave is always discharged from the exit of a train tunnel when a weak compression wave induced by a moving high-speed train at the tunnel entrance propagates outside of the tunnel exit. An impulse wave is a micro-pressure wave, which leads to environment problems such as noise, vibration and other structural damages in the vicinity of the tunnel exit. Currently, due to the development of the optimization and acceleration systems of the high-speed train, the train speed becomes much higher than before and environmental problems become more serious as well. Therefore, it is significantly important to find effective methods to control and reduce magnitudes of impulse waves discharged from the tunnel exit. In the present study, numerical simulations were carried out to investigate the generation and propagation of impulse waves discharged from the exit of a model tunnel. Weak compression waves with different pressure gradients were assumed at the tunnel entry for investigating the relationship between the compression wave and the impulse wave radiated from the tunnel exit. Several tunnel exit geometries with and without a flange at the exit portal of the tunnel were simulated to check their effects on the radiation of impulse waves. Coefficient of effective radiation solid angle indicating the effects of the surrounding environment near the tunnel exit was discussed in-depth. The comparison was made in terms of the magnitudes of impulse waves and coefficients of effective radiation solid angle at different boundary conditions.

Molecular separation with carbon nanotubes

The feasibility of molecular separation with carbon nanotubes is studied by investigating a separation of water molecules and lead nanoparticles with a carbon nanotube-based nanopore system from molecular dynamics simulations. The nanopore system is comprised of a single-walled carbon nanotube and two graphene sheets placed at two ends of the nanotube. The nanotube is subjected to impact loads on a local portion on the wall to generate the propagation of impulse waves in the tube for pumping the encapsulated water molecules out of the tube, while blocking lead nanoparticles by the two graphenes. Studies indicate that the separation is a result of van der Waals interactions between the nanotube and the encapsulated molecules through the propagation of impulse waves in the nanotube. The efficiency of the molecular separation is found to be dependent on the amount of impact loads and the size of the impacted portion of the tube.

Detection of gas atoms with carbon nanotubes

Owning to their unparalleled sensitivity resolution, nanomechanical resonators have excellent capabilities in design of nano-sensors for gas detection. The current challenge is to develop new designs of the resonators for differentiating distinct gas atoms with a recognizably high sensitivity. In this work, the characteristics of impulse wave propagation in carbon nanotube-based sensors are investigated using molecular dynamics simulations to provide a new method for detection of noble gases. A sensitivity index based on wave velocity shifts in a single-walled carbon nanotube, induced by surrounding gas atoms, is defined to explore the efficiency of the nano-sensor. The simulation results indicate that the nano-sensor is able to differentiate distinct noble gases at the same environmental temperature and pressure. The inertia and the strengthening effects by the gases on wave characteristics of carbon nanotubes are particularly discussed, and a continuum mechanics shell model is developed to interpret the effects.

Comparison between Computed and Experimentally Generated Impulse Waves

Large water waves caused by massive slide impacts are a potential hazard along waterways, coastal areas and Alpine regions. Experimental research has been conducted at the Swiss Laboratory of Hydraulics to assess the risk from landslide-generated impulse waves. Analogously, the Centro Elettrotecnico Sperimentale Italiano performed numerical simulations of initial landslide and consequent impulse wave propagation using two mathematical models based on the conservative shallow-water equations. This paper presents the experimental test results and numerical predictions of impulse waves in a flume for a range of stillwater depths, landslide volumes, and impact velocities at laboratory scale. The comparison between the measured and predicted wave free surface profiles generally produced corresponding wave heights, although the initial wave peak is too steep and arrives too early. Excluding spurious random effects, the relative differences between measured and numerically computed maximum wave heights ranged wi...

AN EXPERIMENTAL TECHNIQUE TO STUDY IMPULSE- WAVE PROPAGATION IN MATERIALS

Summary A reliable experimental technique designed to study impulse-wave propagation in materials is described. This technique uses a mechanical shaker to subject vertically mounted cylindrical specimens to impulsive forces. The method is applicable to the study of impulse-wave propagation in cylindrical specimens when the length of the pulse is great compared to the diameter of the specimen, and the material is not stressed beyond its proportional elastic limit. The procedure is particularly suited for biomechanical measurements in which the specimen is to be subjected to repeated impulsive loading. Shockabsorption capacity of bone joints can be studied with this setup. The apparatus can also be used for modal analysis.

Impulsive wave propagation and the cuspoid caustics

The caustics of short wavelength wave propagation may be classified according to catastrophe theory. After establishing this connection the behavior of the time‐dependent wave field due to an impulsive wave in the vicinity of the general cuspoid catastrophe is examined. Numerical results are presented for the fold, cusp, and swallowtail catastrophes which show the smooth variation of the time‐dependent acoustic field as the control parameters are varied. These results vividly demonstrate the phenomenon of ray focusing, showing the number of rays which converge at each catastrophe, the resulting phase shifts they undergo as well as their decay in shadow regions. Analytical results are given which describe the most important properties of the time‐dependent acoustic field on and at large distances away from each of the cuspoid catastrophes.

Impulsive wave propagation and the elliptic, hyperbolic, and parabolic umbilic caustics

The time‐dependent wave field due to an impulsive wave in the vicinity of the elliptic, hyperbolic, and parabolic umbilic caustics is examined. Numerical results are presented which show the smooth variation of the time‐dependent acoustic field in the vicinity of all three caustics. Analytical results are given which describe the most important properties of these wave fields. The time‐dependent structures of these wave fields are qualitatively different than those associated with the cuspoid caustics. The reason for the difference stems from the difference in phase shifts which individual ray arrivals undergo as a result of touching one of the two types of caustic (cuspoid versus umbilic).

On impulsive wave propagation in a spherically symmetric model

Slowness methods have been widely used to study impulsive wave propagation and to compute synthetic seismograms. The generalized ray method and WKBJ seismograms are examples. When applied to a spherically symmetric model, asymptotic or numerical approximations have been used for the Legendre function. In this note it is pointed out that an analytic inverse transform exists for the Legendre function. This can be used when the waveslowness integral is real but cannot be used in the generalized ray method.

Operational interpretation of some integral equations occurring in impulsive wave propagation problems in layered media

Inversion formulae for the operational interpretation of some integral equations, with the exponent of the integrand involving any number of radicals, are given. Equations of the form considered here are of common occurrence to quite a wide variety of impulsive wave propagation problems.