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nonlinear-structure
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Cosmological Nonlinear Structure Formation by Excursion Set Theory of
Peaks
,
M.Sc. Thesis
Sharif University of Technology
;
Baghram, Shant
(Supervisor)
Abstract
The statistics of Dark matter halos and their relation to luminous matter is one of the most important observational and theoretical tools in putting constraint on Cosmological models.There are two approaches for studying the statistics of dark matter halos in the context of non-linear structure formation: Excursion set theory (density contrast- variance space), and Peak theory (density contrast- position space). The goal of this thesis is studying the combination of these two approaches, which is known as Excursion Set of Peaks. We also address the ”cloud in cloud” problem, proposing an approximation for up-crossing problem. Then,we will address the bias parameter for matter-halo in the...
The Study of Fossil Galaxy Groups by Excursion Set Theory of Nonlinear Structure Formation
, M.Sc. Thesis Sharif University of Technology ; Baghram, Shant (Supervisor) ; Rahvar, Sohrab ($item.subfieldsMap.e)
Abstract
In the standard cold dark matter (CDM) family of cosmological models,the cosmological structures form hierarchically with the assumption of cold dark matter existence. The structure formation in the current CDM paradigm is capable of estimating the distribution function of the structures. It gives us a correct view from our observations of galaxies and structures. One of the successful methods to explain the statistics of cosmlogoical structures and their formation time is Excursion Set Theory. The excursion set theory considers the density field for each point in the universe smoothed with a spatial window function using the physics of random processes. The statistics of the structures can...
Non-linear Structure Formation in Cosmology and First Up-crossing in Non-markov Processes
, M.Sc. Thesis Sharif University of Technology ; Baghram, Shant (Supervisor) ; Moghimi Araghi, Saman (Co-Supervisor)
Abstract
Observations of the Cosmic Microwave Background (CMB) and Large- cale Structures (LSS) confirm that cosmological standard model is in good agreement with observational data. The standard model predicts the existence of Cold Dark Matter (CDM) and cosmological constant. It also assumes primordial Gaussianities, scale-invariance, adiabatic and homogeneous initial conditions. Despite the agreements with observations, the dark components and early conditions of the Universe are yet unknown. Investigations of LSS distribution can act as a probe in learning about the dark Universe. Excursion Set Theory (EST) offers a practical approach for these investigations, which take place in the non-linear...
From local similarity to global coding: An application to image classification
, Article Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition, Portland, OR ; 2013 , Pages 2794-2801 ; 10636919 (ISSN) ; Rabiee, H. R ; Farajtabar, M ; Ghazvininejad, M ; Sharif University of Technology
2013
Abstract
Bag of words models for feature extraction have demonstrated top-notch performance in image classification. These representations are usually accompanied by a coding method. Recently, methods that code a descriptor giving regard to its nearby bases have proved efficacious. These methods take into account the nonlinear structure of descriptors, since local similarities are a good approximation of global similarities. However, they confine their usage of the global similarities to nearby bases. In this paper, we propose a coding scheme that brings into focus the manifold structure of descriptors, and devise a method to compute the global similarities of descriptors to the bases. Given a local...
Development of a high-order compact finite-difference total Lagrangian method for nonlinear structural dynamic analysis
, Article Applied Mathematical Modelling ; Volume 63 , 2018 , Pages 179-202 ; 0307904X (ISSN) ; Hejranfar, K ; Sharif University of Technology
Elsevier Inc
2018
Abstract
A high-order compact finite-difference total Lagrangian method (CFDTLM) is developed and applied to nonlinear structural dynamic analysis. The two-dimensional simulation of thermo-elastodynamics is numerically performed in generalized curvilinear coordinates by taking into account the geometric and material nonlinearities. The spatial discretization is carried out by a fourth-order compact finite-difference scheme and an implicit second-order accurate dual time-stepping method is applied for the time integration. The accuracy and capability of the proposed solution methodology for the nonlinear structural analysis is investigated through simulating different static and dynamic benchmark...
Simulation and optimization of a pulsating heat pipe using artificial neural network and genetic algorithm
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 52, Issue 11 , 2016 , Pages 2437-2445 ; 09477411 (ISSN) ; Abbasi Godarzi, A ; Saber, M ; Shafii, M. B ; Sharif University of Technology
Springer Verlag
Abstract
In this paper, a novel approach has been presented to simulate and optimize the pulsating heat pipes (PHPs). The used pulsating heat pipe setup was designed and constructed for this study. Due to the lack of a general mathematical model for exact analysis of the PHPs, a method has been applied for simulation and optimization using the natural algorithms. In this way, the simulator consists of a kind of multilayer perceptron neural network, which is trained by experimental results obtained from our PHP setup. The results show that the complex behavior of PHPs can be successfully described by the non-linear structure of this simulator. The input variables of the neural network are input heat...
A modified unsteady-nonlinear aeroelastic model for flapping wings
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; 2022 ; 09544100 (ISSN) ; Zare, H ; Bighashdel, A ; Sharif University of Technology
SAGE Publications Ltd
2022
Abstract
A novel integrated aeroelastic model of flapping wings (FWs) undergoing a prescribed rigid body motion is presented. In this respect, the FW nonlinear structural dynamics is enhanced via a newly proposed modification of implicit condensation and expansion (MICE) method that better considers the structural nonlinear effects. In addition, the unsteady aerodynamic model is also an extension of the widely utilized modified strip theory (MST) in which the flexibility effects are accounted for (MST-Flex). The integrated utility of the proposed generalized MICE and MST-Flex is demonstrated to be more realistic for elastic FW flight simulation applications. The prescribed rigid body motion is...
Nonlinear unsupervised feature learning: How local similarities lead to global coding
, Article Proceedings - 12th IEEE International Conference on Data Mining Workshops, ICDMW 2012 ; 2012 , Pages 506-513 ; 9780769549255 (ISBN) ; Rabiee, H. R ; Tahaei, M. S ; Salavati, E ; Sharif University of Technology
2012
Abstract
This paper introduces a novel coding scheme based on the diffusion map framework. The idea is to run a t-step random walk on the data graph to capture the similarity of a data point to the codebook atoms. By doing this we exploit local similarities extracted from the data structure to obtain a global similarity which takes into account the nonlinear structure of the data. Unlike the locality-based and sparse coding methods, the proposed coding varies smoothly with respect to the underlying manifold. We extend the above transductive approach to an inductive variant which is of great interest for large scale datasets. We also present a method for codebook generation by coarse graining the data...
Equivalent linearization of non-linear soil-structure systems
, Article Earthquake Engineering and Structural Dynamics ; Volume 41, Issue 13 , 2012 , Pages 1775-1792 ; 00988847 (ISSN) ; Jahankhah, H ; Ghannad, M. A ; Sharif University of Technology
Wiley
2012
Abstract
The concept of equivalent linearization, in which the actual nonlinear structure is replaced by an equivalent linear single-degree-of-freedom (SDOF) system, is extended for soil-structure systems in order to consider the simultaneous effects of soil-structure interaction (SSI) and inelastic behavior of the structure on equivalent linear parameters (ELP). This is carried out by searching over a two-dimensional equivalent period-equivalent damping space for the best pair, which can predict the earthquake response of the inelastic soil-structure system with sufficient accuracy. The super-structure is modeled as an elasto-plastic SDOF system whereas the soil beneath the structure is considered...
Iterative implicit integration procedure for hybrid simulation of large nonlinear structures
, Article Earthquake Engineering and Structural Dynamics ; Volume 40, Issue 9 , October , 2011 , Pages 945-960 ; 00988847 (ISSN) ; Ahmadizadeh, M ; Sharif University of Technology
2011
Abstract
A fully implicit iterative integration procedure is presented for local and geographically distributed hybrid simulation of the seismic response of complex structural systems with distributed nonlinear behavior. The purpose of this procedure is to seamlessly incorporate experimental elements in simulations using existing fully implicit integration algorithms designed for pure numerical simulations. The difficulties of implementing implicit integrators in a hybrid simulation are addressed at the element level by introducing a safe iteration strategy and using an efficient procedure for online estimation of the experimental tangent stiffness matrix. In order to avoid physical application of...
Nonlinear analysis of 2D flexible flapping wings
, Article Nonlinear Dynamics ; Volume 81, Issue 1-2 , July , 2015 , Pages 299-310 ; 0924090X (ISSN) ; Zohoor, H ; Yoon, Yong Jin ; Sharif University of Technology
Kluwer Academic Publishers
2015
Abstract
Natural flyers have flexible wings, which deform significantly under the combined inertial and aerodynamic forces. In this study, we focus on the role of chord wise flexibility in 2D pitch and plunge motions. We derive the exact nonlinear 2D equations of motion for a flexible flapping wing with flying support. In achieving the closed-form equations, we use the exact strain field concerning considerable elastic deformations. After numerically solving the novel equations, we validate them in simulations with highly deformable wings. By coupling the derived equations of motion with fluid flow, we study the aerodynamic performance of the geometrically nonlinear flexible flapping wing. Through...
More efficient lateral load patterns for seismic design of steel moment-resisting frames
, Article Proceedings of the Institution of Civil Engineers: Structures and Buildings ; Volume 171, Issue 6 , 2018 , Pages 472-486 ; 09650911 (ISSN) ; Hajirasouliha, I ; Hosseini Gelekolai, S. M ; Sharif University of Technology
ICE Publishing
2018
Abstract
The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural...
Modified sliding mode design of passive viscous fluid control systems for nonlinear structures
, Article Engineering Structures ; Volume 162 , 1 May , 2018 , Pages 245-256 ; 01410296 (ISSN) ; Ahmadizadeh, M ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
A strategy is developed for design of passive control systems for structures experiencing inelastic deformations during earthquake loading. Besides the addition of passive energy dissipation devices, the proposed method suggests the required changes to the stiffness and strength of the structure, to reduce the absolute acceleration and relative deformation responses simultaneously. For this purpose, the locations and amounts of modifications in stiffness, strength and damping are determined by a sliding mode control algorithm to consider the nonlinear behavior of the structure. Being originally designed for active control, the sliding mode algorithm is modified to facilitate the extraction...
Time-varying structural reliability assessment method: Application to fiber reinforced composites under repeated impact loading
, Article Composite Structures ; 2020 ; Pourtakdoust, S. H ; Crawford, B. J ; Seethalerc, R ; Milani, A. S ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Reliability evaluations play a significant role in engineering applications to ensure the serviceability and safety of advanced structures such as those made of composites. Here, a dynamic reliability evaluation analysis based on the probability density evolution Method (PDEM) has been adapted to assess the reliability of composite structures under uncertainties within the material properties and the external loadings. A Back-Propagation Neural Network approach is employed to identify the system's nonlinear structural response, which is often the case under large deformations. To exemplify, a split Hopkinson pressure bar system was employed to mimic the mechanical behavior of a...
Incorporation of Soil-Structure Interaction into seismic performance evaluation of buildings
, Article 8th US National Conference on Earthquake Engineering 2006, San Francisco, CA, 18 April 2006 through 22 April 2006 ; Volume 15 , 2006 , Pages 9008-9017 ; 9781615670444 (ISBN) ; Ghannad, M. A ; Sharif University of Technology
2006
Abstract
It has been known for many years that the type of soil under structures affects the structural performance during earthquakes. In fact, the soil affects the structural response in two ways, through the change in the free-field motion (usually known as the site effect) and due to Soil- Structure Interaction (SSI). The site effect has been included in the seismic codes from the most beginning. However, the SSI effect had not attracted much attention. The most significant intervention in this regard has been the 1978 inclusion of SSI in the tentative provisions of ATC3-06 in the United States, which is based on the results of studies on elastic response of soil structure systems. The effect of...
Time-varying structural reliability assessment method: Application to fiber reinforced composites under repeated impact loading
, Article Composite Structures ; Volume 261 , 2021 ; 02638223 (ISSN) ; Pourtakdoust, S. H ; Crawford, B. J ; Seethaler, R ; Milani, A. S ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Reliability evaluations play a significant role in engineering applications to ensure the serviceability and safety of advanced structures such as those made of composites. Here, a dynamic reliability evaluation analysis based on the probability density evolution Method (PDEM) has been adapted to assess the reliability of composite structures under uncertainties within the material properties and the external loadings. A Back-Propagation Neural Network approach is employed to identify the system's nonlinear structural response, which is often the case under large deformations. To exemplify, a split Hopkinson pressure bar system was employed to mimic the mechanical behavior of a...
Time-varying structural reliability assessment method: Application to fiber reinforced composites under repeated impact loading
, Article Composite Structures ; Volume 261 , 2021 ; 02638223 (ISSN) ; Pourtakdoust, S. H ; Crawford, B. J ; Seethaler, R ; Milani, A. S ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Reliability evaluations play a significant role in engineering applications to ensure the serviceability and safety of advanced structures such as those made of composites. Here, a dynamic reliability evaluation analysis based on the probability density evolution Method (PDEM) has been adapted to assess the reliability of composite structures under uncertainties within the material properties and the external loadings. A Back-Propagation Neural Network approach is employed to identify the system's nonlinear structural response, which is often the case under large deformations. To exemplify, a split Hopkinson pressure bar system was employed to mimic the mechanical behavior of a...