Sharif Digital Repository

A resonant interaction analysis is used to study the two-dimensional interaction of a surface wave with two waves on a diffuse interface in a stratified fluid. The fluid system is modeled as a combination of two homogenous finite-depth layer with a free surface, divided by a thin third layer. Two possibilities for the interaction are found: one between the surface wave and two first-mode interfacial waves and a second between the surface wave, a first-mode, and a second-mode interfacial wave. By taking the nondimensional density difference δ as a small perturbation parameter, the evolution equations of the interfacial waves are derived asymptotically. The analysis indicates that growth of... 

In this paper, implosion of a micron-sized air bubble was studied numerically using OpenFoam software package. Then a parametric investigation on the flow physics of the problem was performed. The results show that as the initial pressure of the liquid increases, the pressure and the temperature inside the bubble increases such that in some cases, the temperature is as high as the one required for luminescence. Also, increasing the density and the temperature of the liquid solely, decreases the intensity of the collapse. © 2018  

Prediction of threshold conditions and incipient motion is the essential issue for the study of sediment transport. This work compares existing empirical threshold curves proposed for Shields diagram, a method based on the concept of probability of sediment movement, and an empirical method based on movability number. These methods are used to predict the incipient motion conditions for experimental runs taken from various studies. Most of the experimental data, used in this work, have not been used before in derivation of alternative formulations for Shields diagram and other methods. The empirical threshold curves based on the Shields entrainment function was the least successful at... 

In this paper, we present a computational study on the electrical behaviour of self-switching transistors (SSTs) based on InGaAs/InP heterojunction. Our simulation is based on the solution of Poisson and Schrodinger equations self-consistently by using Finite Element Method (FEM). By using this method, electrical characteristics of device, such as (Formula presented.) ratio, subthreshold swing, and intrinsic gate-delay time are investigated. Also, the effects of geometrical variations on the electrical parameters of SSTs are simulated. We show that appropriate design of the device allows current modulation exceeding (Formula presented.) at room temperature. © 2021 Informa UK Limited, trading... 

In this work, we introduce a new ellipsoid model to describe bubble acceleration of electrons and discuss the required conditions of forming it. We have found that the electron trajectory is strongly related to background electron energy and cavity potential ratio. In the ellipsoid cavity regime, the quality of the electron beam is improved in contrast to other methods, such as that using periodic plasma wakefield, spherical cavity regime, and plasma channel guided acceleration. The trajectory of the electron motion can be described as hyperbola, parabola, or ellipsoid path. It is influenced by the position and energy of the electrons and the electrostatic potential of the cavity. In the... 

In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and diffuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was... 

Rubble-mound breakwaters are common marine structures that provide a safe area for human coastal activities. The stability of these structures against sea-waves requires their seaward slope to be protected by an armor layer consisting of natural rock or concrete units. To provide a safe breakwater, it is reasonable to establish a relation between the exerted wave loads and the stability of the armor units. However, up to now, the empirical design equations, derived from model tests, relate wave parameters to armor weight, and keeps the effect of wave loads in a black box. In this paper, a new approach, based on numerically-derived wave loads on the armor, is presented to evaluate the... 

The effect of temperature and impeller speed on the performance of induced gas flotation (IGF) systems for the removal of oil from produced water in different ranges (5-300 g/L) of total dissolved solids (TDS) was investigated in a pilot plant study. Furthermore, it was evaluated whether the IGF pilot plant effluent could reach the 15 mg/L outlet oil content as required by Article VI of the Kuwait Convention for Persian Gulf region, before being discharged to the sea. The results showed that oil removal efficiencies up to 90% could be reached at high temperature (80°C) in just one single flotation cell without adding any chemicals. Flotation unit, however, should be followed by at least one... 

A new structural connection with special unique features was developed. While under bending it showed very high rotational capacity, in shear, unlike other existing connections, it also demonstrated a large shear deformation capacity. The ductile response of this connection stems from its innovative geometry as well as the ductility of the elements embedded in it. Since the previous shear tests on the specimens of this connection were carried out under 'unrestricted' conditions, the tests reported here were all under 'restricted' conditions. These shear tests consisted of 'monotonie' as well as 'cyclic' tests on mild steel specimens. Due to the restrictions imposed on the specimens during... 

The present work is a numerical investigation into the waves generated by a pressure source moving in straight channels with a nonrectangular cross-channel depth profile. Wave fields generated by the moving pressure source are described, and the effects of channel bathymetry on the generated wave characteristics of wave height, wave-breaking location, wave-breaking type and intensity, and peel angle are presented. Four different channel cross-section shapes were investigated, and the results were analyzed. It was concluded that the maximum wave height depended primarily on pressure-source parameters and that the investigated channel shapes did not have a significant effect on the maximum... 

Due to the noise that is present in remote sensing data, a robust method to retrieve information is needed. In this study, the active learning method (ALM) is applied to spectral remote sensing reflectance data to retrieve in-water pigment. The heart of the ALM is a fuzzy interpolation method that is called the ink drop spread (IDS). Three datasets (SeaBAM, synthetic and NOMAD) are used for the evaluation of the selected ALM approach. Comparison of the ALM with the ocean colour 4 (OC4) algorithm and the artificial neural network (ANN) algorithm demonstrated the robustness of the ALM approach in retrieval of in-water constituents from remote sensing reflectance data. In addition, the ALM... 

The performance of friction dampers to mitigate the wave-induced vibrations in jacket-type offshore platforms has been investigated in this study. Due to the random nature of ocean waves, a full stochastic analysis method has been used to evaluate the response of the structures equipped with these devices. A stochastic linearization technique has also been used to take the nonlinear behavior of these hysteretic dampers into account. At last, the developed mathematical formulation has been applied to evaluate the response of realistic models, and to find out the optimal values for the adjustable parameters of the friction dampers to dissipate the wave induced vibrations of the platforms. ©... 

Performances of tuned mass dampers and friction dampers to mitigate the wave induced vibrations in jacket type offshore platforms have been compared in this study. Due to the random nature of ocean waves, a full stochastic analysis method has been used to evaluate the response of the structures equipped with these devices. A stochastic linearization technique has been used to take the nonlinear behavior of friction dampers into account. The developed mathematical formulation has been applied to evaluate the response of realistic models, and to find out the optimal values for the adjustable parameters of friction dampers. The results have been verified in comparison with time domain nonlinear... 

Adapting natural phenomena rendering for realtime applications has become a common practice in computer graphics.We propose a GPU-based multi-band method for optimized synthesis of "far from coast" ocean waves using an empirical Fourier domain model. Instead of performing two independent syntheses for low- and high-band frequencies of ocean waves, we perform only low-band synthesis and employ results to reproduce high frequency details of ocean surface by an optimized iterative up-sampling stage. Our experimental results show that this approach greatly improves the performance of original multi-band synthesis while maintaining image quality. © Springer-Verlag 2009  

As radar signals propagate above the ocean surface to determine the trajectory of a target, the signals that are reflected directly from the target arrive at the receiver along with indirect signals reflected from the ocean surface. These unwanted signals must be properly filtered; otherwise, their interference may mislead the signal receiver and significantly degrade the tracking performance of the radar. To this end, we propose a low-elevation target tracking mechanism considering the specular and diffuse reflection effects of multipath propagation over the ocean surface simultaneously. The proposed mechanism consists of a state-space model and a particle filtering algorithm and promises... 

Solar heating and cooling technologies can have a vital role to play in understanding the targets in energy security, economic development, and mitigating climate change. This study aimed to investigate the performance of the combined solar cooling/heating system using a Photovoltaic Thermal collector (PVT) for residential applications. The main advantage of using PVT is the conversion of the maximum amount of solar energy into electricity and thermal energy. In this work, water is used to cool the panel and, consequently, increase the efficiency. The cooling cycle comprises a hybrid ejector-compression refrigeration cycle with two evaporator temperatures. To reduce the effect of the global... 

In this paper, the effects of different environmental parameters on power probability density function (PDF) curve and annual energy production of a wind turbine are studied. In each step one of these parameters is changed, and in each case, Wind turbine and wind speed is simulated and produced power has been calculated in every hours of one year. At last it was concluded that altitude above sea level (that affects the air density) and the k factor of weibull distribution have more important effects on wind turbine produced power than the others. © 2008 IEEE  

The present study is concerned with the numerical simulation of free-surface waves and wave induced separation in the presence of an intrusion. The results of several simulations are reported. The first study was performed for a NACA0024 surface piercing hydrofoil over a range of several Froude numbers (0.19, 0.37, 0.55), along with wave breaking at Fr = 1.0 The NACA0024 foil was of particular interest, as it almost has no separation at large depths; thus the effect of the free-surface wave and the wave induced separation could be studied. Free- surface waves and wave induced separation results were evaluated and compared with both the available experimental data and the previous numerical... 

Remotely sensed data inherently contain noise. The development of inverse modelling methods with a low sensitivity to noise is in demand for the estimation of geophysical variables from remotely sensed data. The Active Learning Method (ALM) is well known to have a low sensitivity to noise. For the first time, ALM was utilized for the inversion of radiative transfer calculations with the aim of estimating chlorophyll a (Chl a), coloured dissolved organic matter (CDOM), and suspended particulate matter (SPM) in the Caspian Sea using MERIS (MEdium Resolution Imaging Spectrometer) data. ALM training is straightforward and fast. The ALM inversion models revealed the most relevant variables and... 

Using the ellipsoidal cavity model, the quasi-monoenergetic electron output beam in laser-plasma interaction is described. By the cavity regime the quality of electron beam is improved in comparison with those generated from other methods such as periodic plasma wave field, spheroidal cavity regime and plasma channel guided acceleration. Trajectory of electron motion is described as hyperbolic, parabolic or elliptic paths. We find that the self-generated electron bunch has a smaller energy width and more effective gain in energy spectrum. Initial condition for the ellipsoidal cavity is determined by laser-plasma parameters. The electron trajectory is influenced by its position, energy and...