Sharif Digital Repository

The structural dynamics (SD) behavior of Elastic Flapping Wings (EFWs) is investigated analytically as a novel approach in EFWs analysis. In this regard an analytical SD solution of EFW undergoing a prescribed rigid body motion is initially derived, where the governing equations are expressed in modal space. The inertial forces are also analytically computed utilizing the actuator induced acceleration effects on the wing structure, while due to importance of analytical solution the linearity assumption is also considered. The formulated initial-value problem is solved analytically to study the EFW structural responses, where the effect of structure-actuator frequency ratio,... 

In this paper, a new method is proposed to determine parameters of some types of fractional order models to represent a system dynamics using its step response. The model structure is assumed to have rational commensurateorder as α = M/N . By this assumption infinite terms of the model step response is converted into finite terms limited to N. The proposed method is practically applicable on all fractional order model structures due to the order approximation imposed by the limited precisions in available computational tools  

The interpretation of a vast number of cosmological observations in the framework of FRW models suggests that the major part of the energy density of the universe is in form of dark energy with still unknown physical nature. In some models for dark energy, which are motivated by particle physics theory, the equation of state and the contribution of dark energy to the energy density of the universe can be variable. Here we study structure formation in a parameterized dark energy model, and compare its predictions with recent observational data, from the Supernova Ia gold sample and the parameters of large scale structure determined by the 2-degree Field Galaxy Redshift Survey (2dFGRS), and... 

An age-hardening model has been developed to predict the evolution of the hardness of Al-Mg-Si alloys during non-isothermal ageing before peak age. The concurrent precipitation and dissolution have been considered in the structural model. Then the structural model has been combined with strengthening model to predict the precipitation-hardening behavior of the alloy AA6061. The results indicate that the developed model can be used as a predictive tool to model the mechanical properties evolution of Al-Mg-Si alloys during non-isothermal heat treatment. © 2008 Elsevier B.V. All rights reserved  

This paper offers a systematic framework for the design of suboptimal integer-order controllers based on fractional-order structures. The proposed approach is built upon the integer-order approximations that are traditionally used to implement fractional-order controllers after they are designed. Accordingly, the fractional-order structures are exploited to derive a suitable parameterization for a fixed-structure integer-order controller. The parameters, which describe the structure of the fixed-order integer controller, are the same as those used to describe the original fractional structure. Optimal tuning is then performed in the parameter space of the fractional structure and the... 

This paper presents a new experimental-numerical method for deriving the transfer functions of a half-automobile model, containing: chassis, body, engine, engine mount and steering wheel, with five degrees of freedom. In this method different parts of system are not required to be disassembled from the main system and the transfer functions of subsystem are obtained through testing of the whole system. This method is based on the experimental results and does not need a mathematical model of the half-automobile. In this method, transfer functions of various parts of chassis are calculated through obtaining the response of secondary elements mounted on the chassis to the displacement input... 

For a moving camera recognizing that it has seen a place before now, is one the most important issues in the 3D reconstruction problems. In these problems, the main goal is to create a three-dimensional model from a sequence of 2D captured images during different times. That part of the scene which is rendered by a camera is often modeled by a frustum. Calculating the amount of intersection of two camera view frustums at different times can help to solve this problem. However, there are two major difficulties. First, calculating the intersection of two frustums, in general, is so complicated. And second, there are some uncertainties in the moving camera parameters over time. In this paper,... 

A central machine is interested in estimating the underlying structure of a sparse Gaussian Graphical Model (GGM) from a dataset distributed across multiple local machines. The local machines can communicate with the central machine through a wireless multiple access channel. In this paper, we are interested in designing effective strategies where reliable learning is feasible under power and bandwidth limitations. Two approaches are proposed: Signs and Uncoded methods. In the Signs method, the local machines quantize their data into binary vectors and an optimal channel coding scheme is used to reliably send the vectors to the central machine where the structure is learned from the received... 

We present an analytically tractable non-linear model of structure formation in a Universe with only dust. The model is a Lematre-Tolman-Bondi solution (of general relativity) and structures are shells of different density. We show that the luminosity distance-redshift relation has significant corrections at low redshift when the density contrast becomes non-linear. A minimal effect is a correction in apparent magnitudes of order . We discuss different possibilities that could further enhance this effect and mimic dark energy. © IOP Publishing Ltd  

In order to study the interaction of sloshing and structural vibrations of baffled tanks, a reduced order model based on modal analysis of structure model and boundary element method for fluids motion is developed. For this purpose, the governing equations of elastic structure and incompressible flow are used to derive simple models to simulate both fields. Using the modal analysis technique, the structural motions are applied to the fluid model and on the other hand by using boundary element method, the fluid loads are applied to the structural model. Based on this formulation, a code is developed which is applicable to an arbitrary elastic tank with arbitrary arrangement of baffles. The... 

In this paper, a multiple model-based nonlinear identification approach is introduced for a conventional aircraft in the presence of different types of actuator faults. Occurrence of actuator faults can obviously reduce the validity of a predetermined dynamic model of nonlinear systems. In such cases, use of multi-model structures can be an effective choice. However, determining the optimal validity functions of the local models in a multi-model structure is still a challenging problem. This problem becomes even more challenging in case of unpredictable faults, which are not considered in training the local models. In this paper, two effective techniques are proposed for online determination... 

In this paper completely closed RBS (CC-RBS) is proposed as a function of a new ribbed bracing system (RBS). RBS is an innovative system which has capacity of performing variable stiffness that can be used for controlling structural deformations and frequency shifting to compensate seismic energy. The overstrength, ductility, and response modification factors of steel moment frames equipped with CC-RBS was evaluated by performing pushover analysis of model structures with various stories and compared with those which Iranian seismic code of practice, Standard No. 2800 is supposed for steel moment frame equipped with ordinary brace.The results were compared with those from nonlinear... 

This article investigates the free vibration of the rotating, tapered, thin-walled, composite box beam. The structural model incorporates a number of non-classical effects, such as transverse shear, warping inhibition, non-uniformtorsional model, and rotary inertia.The results obtained in this article seek to clarify the effect of flap-twist coupling, taper ratio, slenderness ratio, angular velocity, fibre orientation, and hub ratio on natural frequencies and mode shapes of the rotating thin-walled composite beams. The results are expected to offer better predictions of the vibrational behaviour of these kinds of structures in general, and in the design of rotor blades of turbo machinery, in... 

In this paper, firstly a four-parameter fractional order model structure is introduced to approximate processes having S-shaped step responses. Three different strategies are presented in order to determine the parameters of the proposed model. In a special case where the proposed model is not satisfactory, another fractional order model structure with five free parameters is introduced to improve the model approximation. Also in this case, a procedure is provided to estimate the parameters of the introduced five-parameter model. Then, some common classical integer order control design approaches are modified or extended to their fractional order counterparts in order to incorporate the... 

Reliability of any model-based failure detection and isolation (FDI) method depends on the amount of uncertainty in a system model. Recently, it has been shown that the use of joint torque sensing results in a simplified manipulator model that excludes hardly identifiable link dynamics and other nonlinearities such as friction, backlash, and flexibilities. In this paper, we show that the application of the simplified model in a fault detection algorithm increases reliability of fault monitoring system against modeling uncertainty. The proposed FDI filter is based on a smooth velocity observer of degree 2n where n stands for the number of manipulator joints. No velocity measurement and... 

Standpoints about atrium design have been revolutionized. Nowadays, design of atrium is not only for shine of light, but is also for natural ventilation as well. In high rise building, residents have not a same advantage of buoyancy-driven ventilation that arising from existence of atrium. One strategy to more equalize ventilation and thermal comfort in different levels, is designing building with various opening area in different heights. Present study aims to overcome the problem by changing the atrium shape. Thus, the atrium's wall angularity is changed in different case studies and these shapes are compared with each other in order to find the relations between atrium wall angularity and... 

The shape memory alloys (SMAs) and smart composites have a large use in high and low level industry, while a lot of research is being done in this field. The existence of smart composite structures is because of the advance mechanical benefits of the above materials. This work refers to dynamic and quasi static nonlinear explanation of these materials. After mathematical model consideration on the rate of strain, a model which is about martensite ratio of NiTi has been presented. This work has been done because of the high sensitivity of these materials to strain rate and use of visual and measurable engineering criteria to access other variables. As the martensite ratio is not engineering... 

Various durations of Endurance Time Acceleration Functions (ETAFs) associated with different seismic hazard levels are presented to enable Endurance Time (ET) method for use in probabilistic seismic demand assessment studies. Various Intensity Measures (IMs) were, first, considered for establishing multiple "IM-duration" relationships. A set of 30 RC moment resisting frames were, then, subjected to IDA analysis using 44 ground motion records and the median IM values corresponding to different structural response levels were extracted. These values were compared with the ET-derived IMs by computing the errors corresponding to various demand levels and summating these errors over a complete... 

The most common use of FG materials is as barrier coating against large thermal gradients. Thermal stresses in FG materials, if not released, may cause structural discontinuities in outer surfaces or even inside the material such as cracks, debonding, etc. In this research work, using Finite element method and micromechanical modeling of FG thermal barrier coatings, stresses under thermal and mechanical loadings of the same and different phases have been investigated. Also, the effect of some parameters such as refinement and offsetting of particles on stresses are studied. As for the loading, thermal cycle and in-phase and out-of-phase thermo-mechanical cyclic loadings are considered. The...