Sharif Digital Repository

The aim of this research was an investigation, development, and application of low- dimensional proper orthogonal decomposition (POD) method for simulation of unsteady flow around bodies. Since analytical methods have low accuracy and limitations and also experimental methods have other problems, researchers usually use computational approaches, which mostly do not have acceptable efficiency and speeds of computations (especially in 3-D unsteady flows). On the other hand, the idea of application of reduced order modelling, which orginally comes from control theories and structural analysis, have attracted many researchers in recent years. In this research, we also used POD for reduced order... 

Reduced-order modeling (ROM) is a novel approach in all realms of computational science including reservoir simulation. Among various ROM methods, Trajectory Piecewise Linearization (TPWL) is on its evolution for reservoir applications. Previous investigations reflect promising future for incorporating TPWL into the next generations of enhanced reservoir simulators. In this work, we employ TPWL to investigate the claimed efficiency, robustness and accuracy of this method as a surrogate simulator for a developed reservoir simulator. The self construction of the used simulator gives us the opportunity to explore this method and to examine previous assertions on the subject. The efficiency of... 

In this research, the instability analysis of single-walled carbon nanotubes (SWCNTs) and graphitic shells conveying fluid is investigated based on the molecular structural mechanics. Using the reduced order models for fluid and structure, the dynamic behavior of carbon nanotubes (CNTs) conveying fluid is accurately modeled via a few number of lowest flow modes and natural frequencies and mode shapes of CNTs structure. In addition, the boundary element method (BEM) is used to model the potential flow. The molecular mechanics (MM) model is applied to modal analysis and driving the natural frequencies and mode shapes of SWCNTs. The effect of chirality on flow-induced instability is taken into... 

In recent decades, micro-electromechanical systems – MEMS – havefound extensive applications in applied science and engineering. One of the most popular MEMS actuatorsis micro Scratch Drive Actuator (SDA), which can be used in various applications, for instance: precision positioning, micro-chip displacement and rotating micromotors. Their outstanding capabilities such as: high controllability, precise step displacement, vast transportation domain and large force relative to their small size, have made them popular among researchers. Recently, a new generation of SDA is introduced, known as Bounce-back Scratch Drive Actuator or BSDA, which is fundamentally different in motion generation from... 

The aim of this research was investigation, development and application of lowdimensional proper orthogonal decomposition method for simulation of flow field and airfoil design. Sine analytical methods have low accuracy and limitations and also experimental methods have other problems, researchers usually use computational approach, which mostly do not have acceptable efficiency and speeds of computational. The idea of application of reduced order modeling which originally comes from control theories and structural analysis, have attracted many researcher in recent years. In this research, we also used POD and flow data to obtain a fast module of aerodynamic airfoil design. The goals of... 

The purpose of this study is to develop the reduced order nonlinear modeling of single cell closed section thin walled composite beams. In this way, global behavior of one dimensional beam under axial load, bending and torsional moment is produced. This model is based on the classical lamination theory, and the nonlinear model is developedby usingthe von-karman strains. In this process the effects of material anisotropy and axial warping are considered. Numerical results are obtained for thin-walledcomposites box beams, addressing the effects of fiber angle and laminate stacking sequence. The nonlinear model is compared with theoretical results of homogeneous beams and the natural... 

This study aims at investigating the vibration analysis and stability of Graphene Nano-Ribbon (GNR) under a magnetic field using continuum mechanics approach and an efficient hybrid modal-molecular dynamics method. The force distribution on the GNR due to the magnetic field is determined by Maxwell's equations, Biot-savart law, magnetic dipoles and Lorentz force law.
Using the continuum mechanics model, the vibration of the GNR in a magnetic field is investigated by some problems and the resonance frequencies, stability boundaries and critical load are studied.
Furthermore, in this present study, an efficient hybrid modal-molecular dynamics method is developed for the vibration... 

In this project, the acoustoelastic simulation of baffled cavities using boundary element method is investigated. At first step, the acoustic field for an enclosed rigid cavity with baffle is formulated and then solved by dual reciprocity boundary element method. In order to derive the governing equation, the acoustic domain is considered without mean flow and the fluid is assumed to be compressible and inviscid. Using the developed model and applying the zoning method, behavior and response of baffled cavities are investigated. In order to study the structure_acoustic interaction, modal reduced order model is used to explain the vibration of structure in combination to acoustic field. The... 

This M.Sc thesis aims at studding system of fluid and solid interaction. Based on the potential flow assumption along with using the perturbation technique, the governing kinematic and dynamic boundary conditions of the first- and second-order velocity potential are derived. Then, a boundary element model is developed for the sloshing dynamics which is formulated in terms of the velocity potential of the liquid free-surface. The boundary element model is used to determine the natural mode shapes of sloshing and their corresponding frequencies. Using the modal analysis technique, a nonlinear model is represented for calculation of the first- and second-order potential which can be used to... 

Battery thermal management system is the indispensable part of the electric vehicles working with Lithium-ion batteries. Accordingly, Lithium-ion batteries modelling, battery heat generation and thermal management is the main focus of researchers and car manufacturers. While Computational Fluid Dynamics (CFD) has been used quite successfully for battery thermal management, CFD models can be too large and too slow for assembling in battery pack level models or vehicle models. In this research a much smaller reduced order model is developed, which is in the core is based on CFD models. Thus, without losing the accuracy, this model can be implemented in the vehicle model. The developed model... 

In this Thesis hydroelastic analysis of 3D hydrofoil is investigated while partial sheet cavitation effects are considered. To this aim, first steady cavity boundary must be recognized.This region is calculated by means of conventional iterative procedure, stood upon potential flow theorem. In the second step, the reduced order fluid dynamics equations are derived based on potential flow theorem along with finite element method. This procedure is done in a way that real time system of equations are derived and iterative algorithm of conventional methods is omitted. To this aim, it is assumed that amplitude and frequency of the body oscillations are altered so that the cavity length in... 

With the advent of virtual memory machines and parallel processing, there has been a considerable shift toward computer-aided design and nonlinear analysis of structures. But increasing the size of computer memory or increasing the number of processing units are not the only ways to achieve a satisfactory solution to a large, complex problem. Another useful method is to reduce the size of the problem so that the reduced model is small enough to be solved at an appropriate processing level, and yet the important engineering behavior of the model is preserved in the reduced problem.Reduced models as an alternative, have gained considerable attention throughout the years in order to meet the... 

This thesis deals with developing and applying reduced order modeling techniques for fluid and structure interaction problems. First, the basis and formulations of reduced order modeling technique in the function space are reviewed. Then the governing equations of structural dynamics as well as incompressible flow are reviewed and some simplifications are applied. Based on the modal analysis technique along with the finite element model of the structure and the boundary element model for flow field, some reduced order models are represented. The represented models are developed for liquid sloshing in moving and elastic tanks, fluid structure interaction in flexible shells conveying flow,... 

The present thesis aims at investigating the dynamic interaction of slosh and aeroelasticity in the fuel contained aero vehicles. The main approach in this research is to develop reduced order models for description of the coupled system. In this regard, boundary element method is used to develop slosh dynamic model. Axisymmetric boundary element method with non-symmetric boundary conditions is used to develop slosh dynamic model for axisymmetric containers. Zoning method is used to develop slosh dynamic model for the multi-baffled tanks and based on it, slosh equivalent mechanical model is developed for multi-baffled tanks. Finite element method along with modal technique is used to develop...