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Showing 11 results for Erosion

H.r. Ghafouri,
Volume 1, Issue 1 (9-2003)
Abstract

A two-dimensional mathematical model for the prediction of time-variations of river-bend displacements was developed which is particularly applicable to meandering rivers. The computational procedure consists of two stages, that is , in the first stage by utilizing depth-averaged continuity and momentum equations, velocity field as well as water surface profile in a river is determined. The well-known Finite-Element technique was applied to the governing equations. In the second stage the rate of river bank erosion is computed in terms of determined depths and velocities. The model utilizes Odgaards (1989) bank-erosion model in this stage. The procedure is then performed repeatedly over the entire time span in a staggered manner. The developed model was applied to simulate the migration of Qezel Ozan river. The fairly good match obtained indicates the applicability of the model.
Asghari K.,
Volume 1, Issue 2 (12-2003)
Abstract

The solution of shallow-water equation for a two-dimensional .simulation of overland /low for an actual watershed, is presented. The Petorv-Galerkin weighted residual method is used to overcome spurious oscillations inflow depth. For modeling overland flow over complex topography and variable surface, ct pre and postprocessor was developed to utilize the Triangulated Irregular Network (TIN) model and to generate finite element mesh. Close agreement of the model with measured data is obtained. This model can be used to better analyze the influence of varying surface roughness and topography on overland flow characteristics, including distribution of flow depth and velocity (is well as resulting hydrographs. Detailed spatial and temporal output parameters provide a basis fur further study of the patterns of soil erosion and evaluation of runoff natural slopes.
Asghari K.,
Volume 1, Issue 2 (12-2003)
Abstract

The solution of shallow-water equation for a two-dimensional .simulation of overland /low for an actual watershed, is presented. The Petorv-Galerkin weighted residual method is used to overcome spurious oscillations inflow depth. For modeling overland flow over complex topography and variable surface, ct pre and postprocessor was developed to utilize the Triangulated Irregular Network (TIN) model and to generate finite element mesh. Close agreement of the model with measured data is obtained. This model can be used to better analyze the influence of varying surface roughness and topography on overland flow characteristics, including distribution of flow depth and velocity (is well as resulting hydrographs. Detailed spatial and temporal output parameters provide a basis fur further study of the patterns of soil erosion and evaluation of runoff natural slopes.
Pakbaz M.c., Ahmadi C.,
Volume 1, Issue 2 (12-2003)
Abstract

This research include, more than 400 erosion tests performed on coarse and fine grain suspension materials. The purpose of tests was to determine erosion characteristics of mixtures of different materials. Samples of the .same constituents in different groups were cured tit two different setting time of // and 16 !tours before they were subjected to the constant hydraulic heads of 20 and 40 cm for ct time period of 30 urinates. The amount of erosion was measured as the weight loss of the samples offer the test. /n general the lower setting tune and the higher hydraulic head for a large group of samples showed higher erosion. For uniform sand samples when the cement content was 60-70 % the percentage of erosion (PE) was below 2. For the mixture of sand-cement, with the clay content below, 20% the percentage of erosion was below 2 and it increased to 15.5 for the clan, content of 58dc. Die addition of bentonite in the soil-cement mixtures in general did not affect the erosion.
Mehrdad M.a., Neshaei M.a.l.,
Volume 2, Issue 3 (9-2004)
Abstract

Seawalls are commonly constructed to prevent landward erosion of the shoreline and to maintain the configuration of the area behind them against wave action. In order to consider the effect of seawalls on surf zone hydrodynamics, experiments have been performed at laboratory model scale on partially reflective seawalls located in the surf zone. The main objectives of these experiments were to undertake a quantitative comparison of near-bed velocities in two cases (i.e. with and without the reflective structure). The presence of a reflective structure and the influence of reflected waves result in significant changes in the mean flow and the near-bed horizontal velocities in the surf zone. The latter is illustrated by comparing the probabilistic properties of velocities measured with and without a reflective structure. In this paper, a semi-empirical approach based on the measured probability density functions of near-bed horizontal velocities, is presented to predict the short-term response of a partially reflective seawall to random wave attack. The results obtained from the model and comparison with the experimental results, which have been reported previously are promising and encouraging for further developments of the preliminary model.
Y. L. Luo,
Volume 11, Issue 1 (5-2013)
Abstract

The occurrence of piping failures in earth structures demonstrates the urgency and importance of studying piping. With this

intention, a new piping model was developed in the framework of continuum mixture theory. Assuming that porous media are

comprised of solid skeleton phase, fluid phase and fluidized fine particles phase, the fluidized fine particles phase is considered

to be a special solute migrating with the fluid phase. The three phases interact while being constrained by the mass conservation

equations of the three phases, and a sink term was introduced into the mass conservation equation of the solid skeleton phase to

describe the erosion of fluidized fine particles, then a new continuum fluid-particle coupled piping model was established and

validated. The validation indicates that the proposed model can predict the piping development of complicated structures under

complex boundary and flow conditions, and reflect the dynamic changes of porosity, permeability and pore pressure in the

evolution of piping.


H. Ghiassian, M. Jalili, I. Rahmani, Seyed M. M. Madani,
Volume 11, Issue 4 (12-2013)
Abstract

The concept of Geosynthetic Cellular Systems (GCS) has recently emerged as a new method in construction of breakwaters and coastal protective structures. The method potentially has significant advantages compared to conventional systems from the standpoint of constructability, cost effectiveness, and environmental considerations. This paper presents the results of physical model testing on the hydraulic responses of GCS structures under wave action. A series of model tests were carried out in a wave flume on GCS models with different shapes and soil types, subjected to various wave characteristics. Horizontal wave forces acting on the models were measured at different elevations. The maximum horizontal force in each test was calculated and compared with conventional formula of predicting wave pressure on breakwaters. The results show that Goda’s equation overestimates the hydrodynamic water pressure on these structures. This can be attributed to the influence of seeping water through the GCS models because of relative permeability of the GCS.
N. Abedimahzoon, A. Lashteh Neshaei,
Volume 11, Issue 4 (12-2013)
Abstract

In this paper, a new approach is presented for estimating the vertical and horizontal distribution of undertow in the surf zone for reflective beaches. The present model is a modification of the original model presented by Okayasu et al., (1990) for natural, non-reflective beaches to include the effect of partially reflected waves. The nonlinearity of waves, wave-current interaction and nonlinear mass drift of the incident wave are also included in the present model. The results of experimental investigation and model development show that existence of reflective conditions on beaches results in a reduction in the magnitude of undertow and modifies its distribution across the beach profile. Comparison of the results by those obtained from the experiments clearly indicates that by taking the nonlinearity and wave-current interaction, the predictions of undertow in the surf zone are much improved. In particular, due to the effect of turbulence induced by wave breaking for nonlinear waves, the predicted results show more consistence with the measurements.
Shuai Li, Jian-Min Zhang, Wei-Lin Xu, Jian-Gang Chen, Yong Peng, Jun-Ning Li, Xiao-Long He,
Volume 14, Issue 1 (1-2016)
Abstract

The cavitation erosion induced by high flow velocities is very prominent in high head and large unit discharge tunnel. Air entrainment is an effective technology to solve this problem. In this study, numerical simulation and physical model test are applied to the comparative study of air-water flows on bottom and lateral aerator in tunnel. The flow pattern, aeration cavity, air concentration and pressure distribution were obtained and there is a close agreement between the numerical and physical model values. The hydraulic characteristic and aeration effect of anti-arc section are analyzed. The results indicated that added lateral aeration facilities on 1# and 2# aerator can weaken backwater and increase the length of the bottom cavity, but it is limited to improve the air concentration and protect sidewall downstream of the ogee section. Air concentration improved on side walls downstream of anti-arc section when added lateral aeration facility on 3# aerator. The black water triangle zone disappeared and the floor and side walls well protected.


Duc Do Minh, Mr. Hieu Nguyen Minh,
Volume 15, Issue 3 (5-2017)
Abstract

Climate change and global warming have led to severe typhoons and sea level rise (SLR) which may threat the stability of coastal structures. However, countermeasures to enhance coastal protection against SLR and severe typhoons have not appropriately considered. The Hai Hau coast with 33.3 km of sea dikes is located in the Red River delta of Vietnam. Herein, coastal dikes have collapsed twice over the last 30 years, which lead to about 1.5 km of coastline retreat. This paper aims to assess quantitative impacts of SLR on sea dike stability. Change in pore water pressure (PWP) in the dikes was monitored by piezometers. Distribution of PWP at different tide levels was then used to calculate factors of safety (Fs) of inner and outer slopes. Projected SLR until 2100 will reduce Fs of the outer slopes, but sea dikes have no problem with sliding stability. The main threats of SLR to sea dike stability are indirect impacts such as accelerated erosion, scouring, and wave overtopping-induced soil erosion on the inner slopes. Troughs of sea dikes in Hai Hau coast could fail in 6–10 years due to accelerated coastal erosion. A solution of multiple protections to adapt to SLR in Hai Hau coast was proposed which includes conventional structures (i.e. dike, revetment, groins, and mangrove) together with geotubes as submerged breakwaters and vetiver grass.


Younes Aminpour, Javad Farhoudi,
Volume 15, Issue 5 (7-2017)
Abstract

Local scour downstream of hydraulic structures is one of the critical phenomena which has absorbed a vast amount of interests by researchers. The designers of hydraulic structures, particularly, spillways try to utilize proper means to minimize the consequences of excess energies downstream of such structures which usually tend the erosion at their immediate downstream reaches. The stepped spillway is designed to create a large amount of energy dissipation by means of steps and would decrease the amount of scour evolution at its downstream. This article presents the results of 67 experiments conducted at two different scales of stepped spillways, to study the local scour downstream the structure. The experiments were planned to consider a wide range of geometrical factors, flow characteristics, and sediment properties. The time length of experiments was ranged from 6 to 24 hours which produced more than 80000 data points for analytical considerations. The results were used to render a regression equation to define the similarity among the scour hole profiles. It was observed that, a long term observation would be needed to reach the equilibrium state. However, semi-equilibrium conditions will be achieved after 24 hours. It was also noted that the depth of scour hole adjacent to channel walls was bigger than that at centerline. 



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