Sharif Digital Repository

Sparse representation can be extended to high dimensions and can be used in many applications, including three-dimensional (3D) Inverse synthetic aperture radar (ISAR) imaging. In this study, the high-dimensional sparse representation problem and a recovery method called high-dimensional smoothed least zero-norm (HDSL0) are formulated. In this method, the theory and computation of tensors and approximating L0 norm using Gaussian functions are used for sparse recovery of high-dimensional data. To enhance the performance of HDSL0, modified regularised high-dimensional SL0 (MRe-HDSL0) algorithm, which benefits from the regularised form of SL0 and an additional hard thresholding step, is... 

The main concern in Molecular Dynamics (MD) simulations is the computational cost, and coarse-graining methods accelerate simulations by reducing the degrees of freedom in the system. Yet, the utilization of these methods should be carefully followed. In this paper, we presented an energy-based coarse-graining method for Tersoff and Stillinger-Weber potential functions. The presented coarse-graining method is based on the domain mapping and modification of potential function. The focus of this paper is on Carbon and Silicon materials; however, this method can be applied to model other materials for which Tersoff and Stillinger-Weber potentials are defined. This method has been validated by... 

Proton exchange membrane fuel cell (PEMFC) is a rich source of renewable energy. A non-destructive prediction method is needed to determine the content of water in the PEMFC. In the gas channel of a transparent PEMFC, water is detected with image processing. This method has a high computational cost and is sensitive to the initial position of the camera and ambient lighting. In this paper, the deep neural network (DNN) has been trained to learn the transparent PEMFC's labeled images as a way to determine the content of water, limit human interference and employed in a real-time process. This DNN model is a virtual sensor for measuring the water coverage ratio. To produce the label of images,... 

In this paper, a novel moving object modeling suitable for multicamera correspondence is introduced. Taking into consideration the color and motion features of foreground objects in each independent video stream, our method segments the existing moving objects and constructs a graph-based structure to maintain the relational information of each segment. Using such graph structures reduces our correspondence problem to a subgraph optimal isomorphism problem. The proposed method is robust against various resolutions and orientations of objects at each view. Our system uses the fuzzy logic to employ a human-like color perception in its decision making stage in order to handle color inconstancy... 

The contour integral (CI) method is developed to analyze H-plane waveguide circuits filled with inhomogeneous dielectric such as circuits including full height dielectric posts. In order to reduce the computational costs, the multimode CI method, which considers the effect of higher order TEnO modes, is introduced and we present a hybrid method based on multimode CI and mode matching (MM) techniques. The accuracy of method is validated by comparison of results with those reported in literatures  

The value-based seismic design framework is a new design method that efficiently balances the construction resources and the seismic consequences, through reliable evaluation of the building performance at an affordable computational cost. This paper employs the value-based design approach to optimize the cross-section proportions of the steel wide-flange members. An optimization problem is proposed within the framework of value-based design. Construction cost and seismic consequences are selected as the value components. Moreover, the minimum code requirements are formulated as the design constraints. FEMA-P58 framework is exploited for the prediction of the seismic consequences including... 

Constructing an accurate geological model of the reservoir is a preliminary to make any reliable prediction of a reservoir's performance. Afterward, one needs to simulate the flow to predict the reservoir's dynamic behaviour. This process usually is associated with high computational costs. Therefore, alternative methods such as the percolation approach for rapid estimation of reservoir efficiency are quite desirable. This study tries to address the Well Testing (WT) interpretation of heterogeneous reservoirs, constructed from two extreme permeabilities, 0 and K. In particular, we simulated a drawdown test on typical site percolation mediums, occupied to fraction "p"at a constant rate Q/h,... 

An uncertain economic order quantity (UEOQ) model with payment in advance is developed to purchase high-price raw materials. A joint policy of replenishments and pre-payments is employed to supply the materials. The rate of demand is considered LR-fuzzy variables, lead-time is taken to be constant, and it is assumed that shortage does not occur in the cycles. The cycle is divided into three parts; the first part is the time between the previous replenishment-time to the next order-time (t0), the second part is the period between t0 to a payment-time (tk), and the third part is the period between tk to the next replenishment-time. At the start of the second part (t0), α% of the purchasing... 

In this article, a multiscale modeling procedure is implemented to study the effect of interphase on the Young's modulus of CNT/polymer composites. For this purpose, a three-phase RVE is introduced which consists of three components, i.e., a carbon nanotube, an interphase layer, and an outer polymer matrix. The nanotube is modeled at the atomistic scale using molecular structural mechanics. Moreover, three-dimensional elements are employed to model the interphase layer and polymer matrix. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using this Molecular Structural Mechanics/Finite Element... 

Kinetic theory based numerical scheme such as direct simulation Monte Carlo (DSMC) and information preservation (IP) schemes properly solve micro-nano flow problems in transition and free molecular regimes. However, the high computational cost of these methods encourages the researchers toward extending the applicability of the continuumbased equations beyond the slip flow regime. In addition to correct velocity profile, the continuum-based equations should predict accurate mass flow rate magnitude. The secondorder velocity slip models derived from the kinetic theory provide accurate velocity profiles up to Kn=0.5; however, they yield erroneous mass flow rate magnitudes because the basic... 

The kinetic-theory-based numerical schemes, such as direct simulation Monte Carlo (DSMC) and information preservation (IP), can be readily used to solve transition flow regimes. However, their high computational cost still promotes the researchers to extend the Navier-Stokes (NS) equations beyond the slip flow and to the transition regime applications. Evidently, a suitable extension would accurately predict both the local velocity profiles and the mass flow rate magnitude as well as the streamwise pressure distribution. The second-order slip velocity model derived from kinetic theory can provide relatively accurate velocity profiles up to a Knudsen (Kn) number of around 0.5; however, its... 

The track fusion combines individual tracks formed by different sensors. Tracks are usually obtained by Kalman Filter (KF), since it is suitable for real-time application. The KF is an optimal linear estimator when the measurement noise has a Gaussian distribution with known covariance. However, in practice, some of the sensors do not have these properties, and the traditional KF is not an optimal estimator. In this paper, a novel adaptive Kalman filter (NAKF) is proposed. In this approach, the measurement noise covariance is adjusted by using an introduced simple mathematical function of one variable, called the degree of matching (DoM), where it is defined on the basis of covariance... 

Horizontal Ground Heat Exchangers (HGHE) as a means of exploiting geothermal energy has come to the fore for a few decades. Various analytical and Computational Fluid Dynamics (CFD) methods have been proposed to predict the performance of the HGHEs. The available analytical approaches are fast; however, they are based on various simplifications and assumptions, affecting their accuracy. On the other hand, CFD methods are more accurate, but their computational cost is a burden. Therefore there is an acute need for an accurate and fast method for predicting the long-term performance of HGHEs. To this aim, this study puts forward a novel hybrid analytical-numerical model for predicting the... 

Airflow simulation of the whole respiratory system is still unfeasible due to the geometrical complexity of the lung airways and the diversity of the length scales involved in the problem. Even the new CT imaging system is not capable of providing accurate 3D geometries for smaller tubes, and a complete 3D simulation is impeded by the limited computational resources available. The aim of this study is to develop a fully coupled 3D-1D model to make accurate prediction of airflow and particle deposition in the whole respiratory track, with reasonable computational cost and efficiency. In the new proposed method, the respiratory tree is divided into three parts to be dealt with using different... 

Overall turbine analysis requires large CPU time and computer memory, even in the present days. As a result, choosing an appropriate computational domain accompanied by a suitable boundary condition can dramatically reduce the time cost of computations. This work compares different geometries for numerical investigation of the 3D flow in the runner of a Francis turbine, and presents an optimum geometry with least computational effort and desirable numerical accuracy. The numerical results are validated with a GAMM Francis Turbine runner, which was used as a test case (GAMM workshop on 3D computation of incompressible internal flows, 1989) in which the geometry and detailed best efficiency...