Mechanism of Tsunami-Induced Erosion of Bridge-Abutment Backfill and Its Countermeasures

Tsunamis can destroy bridges in coastal areas. Studies have attempted to unravel the mechanism of tsunami-induced damage and develop effective countermeasures against future tsunamis. However, the mechanisms of tsunami-induced erosion of bridge-abutment backfill and its countermeasures have not been studied adequately. This study investigates this topic using numerical analysis. The results show that the tsunami flowing down along the downstream wing of the abutment induces bedload sediment transport on the ogive section of the backfill on the downstream side of the abutment, resulting in the onset of backfill erosion. Sediment suspension and bedload sediment transportation occur when the backfill inside the abutment starts to flow out from below the downstream wing. This leads to subsidence of the backfill at the upstream side of the downstream wing. The subsequent backfill erosion is mainly caused by bedload sediment transport. Numerical experiments on countermeasures show that extending the wings downward can prevent the acceleration of backfill erosion in the presence of the abutment. A combination of multiple countermeasures, including extended wings, would be more effective in maintaining the stability of the abutment after a tsunami. This suggests the application of such countermeasures to actual bridges as an effective countermeasure against backfill erosion.

Foehn effect during easterly flow over Svalbard

This article presents a comprehensive analysis of the foehn episode which occurred over Svalbard on 30–31 May 2017. This episode is well documented by multiplatform measurements carried out during the ACLOUD/PASCAL campaigns. Both orographic wind modification and foehn warming are considered here. The latter is found to be primarily produced by the isentropic drawdown, which is evident from observations and mesoscale numerical modelling. The structure of the observed foehn warming was in many aspects very similar to that for foehns over the Antarctic Peninsula. In particular, it is found that the warming was proportional to the height of the mountain ridges and propagated far downstream. Also, a strong spatial heterogeneity of the foehn warming was observed with a clear cold footprint associated with gap flows along the mountain valleys and fjords. On the downstream side, a shallow stably-stratified boundary layer below a well-mixed layer formed over the snow-covered land and cold open water. The foehn warming downwind Svalbard strengthened the north-south horizontal temperature gradient across the ice edge near the northern tip of Svalbard. This suggests that the associated baroclinicity might have strengthened the observed northern tip jet. Positive daytime radiative budget on the surface, increased by the foehn clearance, along with the downward sensible heat flux provoked an accelerated snowmelt in the mountain valleys in Ny-Alesund and Adventdalen, which suggests a potentially large effect of the frequently observed Svalbard foehns on the snow-cover and the glacier heat and mass balance.

Dam Break Wave Propagation on a Non- Erodible Bed – Comparison of Experimental and Numerical Results

Dams are vital for production of electricity, storage of water and irrigation purposes but pose a serious risk to the community, if breached. The downstream flood wave propagation, resulting from failure of a dam can subject the population and infrastructure to considerable damage. No matter how low the chances of failure, the cost of failure makes it a higher risk. Mitigation of such risks requires better understanding of the hazard that a dam may pose in case of failure. This study focuses on the effects of flood wave propagation on a fixed bed on the downstream side resulting from sudden dam break. Two conditions are simulated: 1. when the downstream side is open, 2. when the downstream side is closed. It is observed that the flood wave diminishes in velocity and height with increase in time for both cases. For downstream open condition, the flood wave attains maximum height in 2 to 4 sec and maximum velocity within 2 to 5 sec. For downstream closed condition, the flood wave attains maximum height within 5to 10 sec and maximum velocity within 3 to 5 sec. The results obtained from the two-dimensional shallow water equation based numerical model are in close agreementwith the experimental results.

Experimental analysis of scour under circular pier

For economical design, scour around the bridge piers is required to be controlled. In the present study, an attempt has been made to minimize scour depth by placing a triangular prism on the downstream side of a circular pier (35 mm dia) with one of its noses facing the direction of flow and other facing opposite to the direction of flow. Three different bed samples collected from Ghaggar, Patialki-Rao and the Kotla super-passage have been placed in a rectangular flume. Discharge values were varied from 0.0015 to 0.0186 m3/sec. Results are compared for observed scour-depth for upstream (U/S) and downstream (D/S) piers with and without protection. Arrangement with a triangular prism of 2.5 times the diameter of the circular pier in the upstream direction of the flow is very effective in reducing scour depth. Further, it is possible to reduce the scour depth with an average efficiency of 65% for Ghaggar, 56% for Patialaki-Rao and 64% for the Kotla super-passage with respect to the circular pier. The comparison of observed values of scour-depth with computed values of Lacey's scour-depth was underestimated with a maximum of ±70%. Hence, a new site-specific relationship between scour depth, discharge intensity and silt factor has been proposed. Validation of the new proposed relationship with observed data is in a good agreement ±20%.

The Influence of a Submarine Canyon on the Circulation and Cross-Shore Exchanges around an Upwelling Front

The response of a coastal ocean numerical model, typical of eastern boundaries, is investigated under upwelling-favorable wind forcing and with/without the presence of a submarine canyon. Experiments were run over three contrasting shelf depth/slope bathymetries and forced by an upwelling-favorable alongshore wind. Random noise in the wind stress field was used to trigger the onset of frontal instabilities, which formed around the upwelling front. Their development and evolution are enhanced over deeper (and less inclined) shelves. Experiments without a submarine canyon agree well with previous studies of upwelling frontal instabilities; baroclinic instabilities grow along the front in time. The addition of a submarine canyon incising the continental shelf dramatically changes the circulation and frontal characteristics. Intensified upwelling is channeled through the downstream side of the canyon in all depth/slope configurations. Farther downstream a downwelling area is generated, being larger and stronger on a shallow shelf. The canyon affects mainly the location of the southward upwelling jet, which is deflected inshore and accelerated after passing over the canyon. This process is accompanied by a break in the alongshore scale of the instabilities on either side of the canyon. Term balances of the depth-averaged cross-shore momentum equation reaffirm the downstream acceleration of the jet and the increased wavelength of the instabilities, and clarify the dominant balance between the advection and ageostrophic terms around the canyon.

CFD–DEM Simulations of Seepage-Induced Erosion

Increases in seepage force reduce the effective stress of particles and result in the erosion of particles, producing heave failure and piping. Sheet piles/cutoff walls are often employed in dams to control the seepage. In this study, a computational fluid dynamics solver involving two fluid phases was developed and coupled with discrete element method software to simulate the piping process around a sheet pile/cutoff wall. Binary-sized particles were selected to study the impact of fine particles on the mechanisms of seepage. The seepage phenomenon mainly appeared among fine particles located in the downstream side, with the peak magnitudes of drag force and displacement occurring around the retaining wall. Based on the particle-scale observations, the impact of seepage produced a looser condition for the region concentrated around the retaining wall and resulted in an anisotropic condition in the soil skeleton. The results indicate that heave behavior occurs when the drag force located adjacent to the boundary on the downstream side is larger than the corresponding weight of the bulk soil.

Deposition of Highly Transparent and Conductive Films on Tilted Substrates by Atmospheric Pressure Plasma Jet

We study the influence of the substrate tilt angle on the microstructure and optoelectronic properties of gallium-doped zinc oxide (GZO) thin films deposited by the atmosphere pressure plasma jet (APPJ) method. The nozzle trajectories play a key role in oblique angle deposition. In the process of oblique angle deposition, if the nozzle scanned from the upstream side to the downstream side, the electrical properties such as resistivity, carrier concentration and mobility deteriorate considerably. The optical properties also worsen — specular transmittance goes down and diffuse transmittance increase to a significant amount. This degradation can be attributed to the “pre-deposition” of the GZO adsorbed particles (ad-particles) on the downstream side of the raw glass where the nozzle has not scanned. These GZO ad-particles serve as nuclei on which the incoming vapor particles deposit preferentially. Scanning electron microscopy (SEM), and grazing incidence X-ray diffraction (GIXRD confirmed that the film near the downstream is thicker, less smooth, and porous than that near the upstream. The undesirable situation can be mitigated or even completely removed via proper nozzle scanning trajectories — reversing the scanning trajectory of the nozzle. If the nozzle scans from the downstream side to the upstream side, no pre-deposition of the GZO ad-particles to deteriorate the film properties and therefore the obliquely deposited films perform as well as the films deposited without tilt, i.e. flat substrate. This work presents a solution to the challenge of depositing TCO on tilted and curved surfaces.

Study on Analytical Method for Thermal and Flow Field of a Turbocharger With the Catalyst Unit

The analytical and experimental study on thermal and flow field of a turbocharger with the catalyst unit has been conducted for the thermal management at the downstream side of turbochargers, which have crucial effects on activation of catalyst units. CHT (Conjugate Heat Transfer) calculations, working for simulating heat transfer with mutual dependence between solid structures and fluid, are applied to the turbocharger including the turbine section, the bearing housing and the catalyst unit to acquire the whole of thermal and flow field accurately. The modeling for catalyst element has also been developed. In addition, the gas stand test demonstrated turbochargers under cold start-up condition to validate CHT calculations. Analytical results are evaluated against experimental data. Eventually, the proposed analytical method has been proved to have the advantage of designing for heating catalyst units.