Sharif Digital Repository

Empirical mode decomposition as a complete data driven method is typically employed to obtain constitutive components of all kinds of signal including non-stationary and nonlinear. Extracting modes using this method is normally associated with multiple sources of errors such as stop criteria, end effects, interpolation function and etc. In order to reduce end effects errors in this paper a modified method is proposed based on combination of auto regressive model and mirror method. In this combination method, to extract some of first intrinsic mode functions of a given signal, auto regressive model is initially implemented to forecast tails of maximum and minimum envelops for only a short... 

The main objective of this work is to propose a scheme to extract intrinsic mode functions of online data with an acceptable speed as well as accuracy. For this purpose, an individual block framework method is firstly employed to extract the intrinsic mode functions. In this method, buffers are selected such that they overlap with their neighbors to prevent the end effect errors with no need for the averaging process. And in order to avoid the mode mixing problem, a bandwidth empirical mode decomposition scheme is developed to effectively improve the results. Through this scheme, an auxiliary function made of both high- and low-frequency components corresponding to noise and dominant... 

Using a combination of the pole placement and online empirical mode decomposition (EMD) methods, a new algorithm is proposed for adaptive active control of structural vibration. The EMD method is a time-frequency domain analysis method that can be used for nonstationary and nonlinear problems. Combining the EMD method and Hilbert transform, which is called Hilbert-Huang transform, achieves a method that can be implemented to extract instantaneous properties of signals such as structural response dominant instantaneous frequencies. In the proposed algorithm, these estimated instantaneous properties are utilized to improve the pole-placement method as an adaptive active control technique. The... 

In this paper we present a new exact solution for scalar field with cosmological constant in cylindrical symmetry Associated cosmological models including a model that describes a cyclic universe are discussed  

This article presents a study on the capability of the time domain OMA method, NExT-ERA, to identify closely spaced structural dynamic modes. A survey in the literature reveals that few experimental studies have been conducted on the effectiveness of the NExT-ERA methodology in case of closely spaced modes specifically. In this paper we present the formulation for NExT-ERA. This formulation is then implemented in an algorithm and a code, developed in house to identify the modal parameters of different systems using their generated time history data. Some numerical models are firstly investigated to validate the code. Two different case studies involving a plate with closely spaced modes and... 

An analytical modified method is presented to investigate the clearance effects on the dynamic behavior of cantilever beams. In this work, apart from clearance, all other nonlinearities are avoided to be considered during the analytical solution. The beam is idealized using an equivalent single-degree-of-freedom structure. A tri-linear stiffness system is also adopted to simulate the beam together with the clearance. Subsequently the analytical solution is derived for a cantilever beam structure with and without considering structural damping. The experimental method is employed to verify the results from the presented analytical solutions. It is noted that the results obtained by the... 

In this paper a modal coupling procedure is developed to improve residual modal effects based on experimentally generated data. While showing that CraigChangs proposed approximation function for higher frequency modes does not compare well with the exact function, a new procedure is developed in order to re-express the dynamic residuals. For this purpose, all frequency dependent terms of the Maclaurin series in CraigChangs proposed method are replaced by a general compatible function, which includes the neglected higher order terms. However, this function no longer appears in final equation of motion. Results from case studies for the discrete, continuous and experimental models are... 

Control1,2 of a class of uncertain nonlinear systems which estimates unavailable state variables is considered. A new approach for robust tracking control problem of satellite for large rotational maneuvers is presented in this paper. The features of this approach include -a strong algorithm to estimate attitude, based on discrete extended kalman filter combined with a continuous extended kalman filter and attitude nonlinear model -a robust controller based on sliding-mode with perturbation estimation. The estimation result of interval kalman filtering is a sequence of interval estimates that encompasses all possible optimal attitude estimates, which the interval system may generate. The... 

Control of a class of uncertain nonlinear systems which estimates unavailable state variables is considered. A new approach for robust tracking control problem of satellite for large rotational maneuvers is presented in this paper. The features of this approach include -a strong algorithm to estimate attitude, based on discrete extended kalman filter combined with a continuous extended kalman filter and attitude nonlinear model -a robust controller based on slidingmode with perturbation estimation. The estimation result of interval kalman filtering is a sequence of interval estimates that encompasses all possible optimal attitude estimates, which the interval system may generate. The... 

In this paper a new control method is presented that keeps the attitude of satellite in desired conditions only by electromagnetic coils. Recently small satellites are used more commonly because of the low launching cost and development of microelectronics. Also lower weight, size, cost and the power consumption of magnetorquer, has made the application of them in controlling attitude of the satellites common. Intensive changes and non-ability of geomagnetic field are some of the problems, which have limited the efficiency of magnetorquers.The distinction of this method is its abilities in comparison with other methods. In this analytic method a direct relation between design parameters,... 

In recent years, there has been a rapid change in the portfolio of road vehicles. This transformation needs to be supported by reshaping fuel stations. The existing structures can be modified to supply multiple vehicle types while utilizing renewable energies. In this article, we introduce a hybrid fuel station (HFS) to supply both electric and natural gas vehicles. We incorporate an energy hub and thoroughly explain the structure and components in detail. The configuration of the proposed HFS includes renewable energy sources (RESs), a power-to-gas unit (P2G), a natural gas distributed generator (NGDG), an energy storage device, a compressor, and a gas storage device. The optimal operation... 

Economic policies for managing agricultural water use are often complicated by the challenge of using water prices as an efficient economic tool when other non-economic concerns are involved in the decision-making process. This study aims to analyse the impact of water pricing policies on preserving agricultural water resources in Iran. This study applies a system dynamics approach to simulate the system performance and behaviour of stakeholders and the economic implications. Our finding shows that water pricing policies will likely fail due to low water price elasticity and if there are lack of institutional and physical infrastructure, alternative professions, manufacturing technology,... 

In this study, the hardness inhomogeneity of billets during multi-passes of equal channel angular pressing (ECAP) at elevated temperatures is investigated and the effect of large strain deformation during ECAP on the hardness inhomogeneity characteristics due to dynamic aging of aluminum 6061 under a variety of temperatures and ram speed was studied by TEM and hardness measurements. The hardness results showed that the hardness distribution is more homogenous after four passes using the pressing route Bc. However, when the deformation temperature was considered, performing ECAP at 100 C may provide the most homogeneous microstructure after multi-pressing as long as the total number of... 

In this work a new method for analyzing nanostructured materials has been proposed to accelerate the simulations for solid crystalline materials. The proposed Structural Approximation Method (SAM) is based on Molecular Dynamics (MD) and the accuracy of the results can also be improved in a systematic manner by sacrificing the simulation speed. In this method a virtual material is used instead of the real one, which has less number of atoms and therefore fewer degrees of freedom, compared to the real material. The number of differential equations that must be integrated in order to specify the state of the system will decrease significantly, and the simulation speed increases. To generalize... 

Computer networks courses are hard to teach as there are many details in the protocols and techniques involved that are difficult to grasp. Employing programming assignments as part of the course helps students to obtain a better understanding and gain further insight into the theoretical lectures. In this paper, the Partov simulation engine and experience using this engine in a computer networks course are discussed. Since 2009, various programming assignments based on the Partov system have been set to help students in their learning process. Student feedback has been very good; this has been quantified in two surveys in which a majority of students expressed their satisfaction with this... 

Network protocol design and evaluation requires either full implementation of the considered protocol and evaluation in a real network, or a simulation based on a model. There is also a middle approach in which both simulation and emulation are used to evaluate a protocol. In this article the Partov engine, which provides both simulation and emulation capabilities simultaneously, is presented. Partov benefits from a layered and platform-independent architecture. As a pure simulator, it provides an extensible plugin-based platform that can be configured to perform both real-time and non-real-time discrete-event simulations. It also acts as an emulator, making interaction with real networks... 

In this work a new method for analyzing nanostructured materials has been proposed to accelerate the simulations for solid crystalline materials. The proposed Structural Approximation Method (SAM) is based on Molecular Dynamics (MD) and the accuracy of the results can also be improved in a systematic manner by sacrificing the simulation speed. In this method a virtual material is used instead of the real one, which has less number of atoms and therefore fewer degrees of freedom, compared to the real material. The number of differential equations that must be integrated in order to specify the state of the system will decrease significantly, and the simulation speed increases. To generalize... 

Emergence of instrumentation frameworks has vastly contributed to the software engineering practices. As the instrumentation use cases become more complex, complexity of instrumenting programs also increases, leading to a higher risk of software defects, increased development time, and decreased maintainability. In security applications such as symbolic execution and taint analysis, which need to instrument a large number of instruction types, this complexity is prominent. This paper presents an architecture based on the Pin binary instrumentation framework to abstract the low-level OS and hardware-dependent implementation details, facilitate code reuse in heavyweight instrumentation use... 

Too much effort has been done for manipulating individual atoms, using nano-manipulators and Scanning Tunneling Microscopes (STM). On the other hand, characterization and manipulation of nano-flows is of great concern. In the current work a molecular valve has been considered, which is made up of six atoms placed on the circumstance of a circle. A fuzzy controller has been designed for controlling the diameter of this molecular valve. The designed fuzzy controller used singleton fuzzifier, Mamdani inference engine, center average defuzzifier and exponential membership functions. A model based on the classical Molecular Dynamics (MD) is used for modeling the nano-system and passing the states...