Sharif Digital Repository

Solar heating in aqautic systems, causes tempreture increasing.This temperature difference will promote an exchange flow between the vegetation and open water. The exchange flow generated by the differential heating and cooling associated with depth variation has also been studied through laboratory experiment and modelling. Differential solar heating can result from shading by rooted emergent aquatic plants, producing a temperature difference between vegetated and unvegetated regions of a surface water body. Horizontal density difference between shaded and open water regions drives currents that carry fluxes between biologically and chemically distinct regions of an aquatic system. Such... 

In this study, the effect of submerged vanes on the bed erosion pattern at a 90° open-channel junction has been evaluated experimentally. In this study, 41 tests have been conducted in four different steps. In each test, the bed surface level has been measured at the end of 1st, 2nd and 24th hour. In the first step, the preliminary tests have been conducted. In this step, six different formations of submerged vanes have been selected and their performance has been evaluated and the most efficient formation, in the field of maximum scour depth reduction, has been selected. In the second step, six different formations of submerged vanes have been selected and their performance has been... 

Lakes and estuaries are usually density stratified. Interaction between surface and interfacial waves causes turbulence in such systems. The interaction between a surface wave and harmonic interfacial waves has been previously studied analytically using a perturbation scheme. However, the calculations have been long and time consuming. In this study, we improve the solution process by using a variational approach to mathematical modeling. We also present the results of an experimental study of the problem. The experiments were video-taped and were analyzed using an image processing method. The conditions leading to generation of harmonic interfacial waves are determined. Limitations of the... 

Wetlands and aquatic systems are abundant on the earth. Since many biological and chemical processes take place in aquatic regions, an understanding of hydrodynamics of flow in these areas is essential. Exchange flows or gravity currents driven by horizontal density gradients constitute a significant transfer mechanism in many lentic systems. Light blockage by emergent vegetations, which are a common feature of littoral zones, leads to a horizontal density gradient and hence an exchange flow between the vegetated and the open area. Also, existence of vegetations affects the behavior of the flow by inserting the drag force to the system and damping its energy. Previous studies have modeled... 

Selective withdrawal is withdrawing water with desired quality from a reservoir and has many applications in water quality management of reservoirs. Topographic effects such as a sill alter the withdrawal layer properties. In this study, the effect of a sill on selective withdrawal of a two-layer fluid through a line sink at the bottom of a rectangular reservoir is studied using two-layer hydraulics theory, numerical model and laboratory experiments. Experiments were done for studying surge, and the results are compared with two-layer hydraulics theory and numerical model. After reservoir gate is opened, some disturbances upstream of sill lead to creation of a surge. The results show this is... 

The aquatic canopy areas such as wetlands play an important role in ecology of these area. The exchange flow between open water and vegetated area occurs due to sunlight and surface cooling. Wind also causes surface evaporation and create a cold layer at the surface of water. The creation of exchange flow and its magnitude depends on parameters like solid volume fraction and thermal gradient. In this thesis, the goal is to determine the effects of floating vegetation on the hydrodynamic characteristics of exchange flowas a result of surface cooling experimentally. In this research, the PIV method was used to measure velocity profiles. In the experiments, solid volume fraction, depth of... 

Presence of emergent vegetation can change the governing forces in flow through such systems and affects the turbulence structure and scalar transport. On the other hand, vertical variation of physical characteristics of stems, which is fairly observed in reality, leads to variation in frontal area and the called vertical density difference. In this study we experimentally investigate the effect of vertical density difference on both flow and vertical transport of mass. The results will be compared with theoretical predictions.
Using rigid emergent model of cylinders as stems with step density variation in depth I simmulate field conditions considering actual variation of frontal area.... 

Existing closed form solutions of contaminant transport problems are limited by the mathematically convenient assumption of uniform flow. These solutions cannot be applied for coastal aquifers where seawater intrusion induces a variable velocity field. The Fourier series method is adapted to obtain a semi-analytical solution for contaminant transport in confined coastal aquifer in which the saltwater wedge is in equilibrium with a freshwater discharge flow. The developed method can be applied for different scenarios of contamination. Two scenarios dealing with, respectively, contaminant leakage from a source at the aquifer top surface and aquifer contamination from the landward boundary are... 

In this study, existing prediction methods of maximum scour depth around complex piers are studies using available experimental data and a new relationship for scour prediction is presented. Complex pier consists of a column, pile cap and pile group and is frequently used for foundation of bridge piers in hydraulic and marine structures. The results of 52 clear-water scour experiments on 4 CP models are reported which can be valuable to hydraulic design of a CP. The 4 models had different values of pile cap thickness and number of piles inline with the flow and were tested at different pile cap elevations. The duration of experiments ranged from 24 to 120 hours. Then a database of laboratory... 

There is an importance issue for preservation and survival of ecological systems by vegetation. A study focusing on the hydrodynamics of these complex ecosystems could help to explain the filtering ability of vegetation in wetlands and estuaries. Wetlands assist in flood control, shoreline protection, and groundwater recharge.In addition, they play a purification role, removing sediments and contaminants from polluted waters, nutrient uptake, and oxygen production. Laboratory experiments have been designed to study the influence of marsh vegetation on lateral dispersion. The flow through vegetation is modeled by a circulating flow going through an array of plastic dowels in an experimental... 

The three dimensional resonant interaction between a surface wave and harmonic interfacial waves in a horizontally infinite two-layer fluid was investigated theoretically and experimentally. Initially, both layers assumed to be inviscid, but after obtaining the final equations of the interfacial wave's amplitude, with perturbation, the viscous damping effect, was incorporated in to the interaction equations. It is shown that, surface wave can trigger four opposite- traveling interfacial waves whose amplitudes grow with time. But because of viscosity damping effect, these amplitudes will become constant and won't change with time. The frequencies of the interfacial waves are approximately... 

Recently, a new tool in the study of two-dimensional continuous phase transition was provided by Schramm-Loewner evolution. The main part of SLE is a conformal map which relates growth process of a two-dimensional simple curve to one-dimensional motion on the real axis (so-called Loewner driving function). Time evolution of this map and Loewner driving function is connected via the Loewner differential equation. It turns out that for a certain class of stochastic and conformally invariant curves in two dimensions, the driving function shows Brownian motion in one dimension. Strength point of SLE comes from this fact that all the geometrical properties of such curves is described through a...