Sharif Digital Repository

In this thesis, we consider a system containing fluid equations, structure equations, and equations of these two materials’ common interface in three dimensions and on the regular domains. We suppose that the solid which is described by the Lamé system of linear elasticity, moves inside an incompressible viscous fluid in three dimensions, and the fluid obeys the incompressible Navier-Stokes equations in a time-dependent domain. At the fluid–solid interface, natural conditions are imposed, continuity of the velocities and of the Cauchy stress forces. The fluid and the solid are coupled through these conditions. By this interaction, the fluid deforms the boundary of the solid which in turn... 

Reducing the seismic response of structures under dynamic loads has been highly considered by many researchers in the past few decades. Among them, Tuned Mass Dampers (TMD) have been studied extensively and used as a mean to control the response of structures under earthquake and wind loadings. In the majority of these studies, it is assumed that the structural models are located on rigid base and only their linear response has been considered. Soil-Structure Interaction (SSI) and nonlinear response of structures could have significant effect on the dynamic characteristics of structures that could results in detuning of TMDs. In this study, a number of 3-D nonlinear steel structural models... 

The main purpose of this study is to estimate the natural frequency and damping ratio for soil-structure systems with embedded foundation with sufficient accuracy. The results are then compared to guidelines in current seismic codes. This is done through an extensive parametric study using a set of non-dimensional parameters, which define the soil-structure systems. For this purpose a simplified soil-structure model is used. Although more rigorous models and numerical solutions are available, they are time consuming and not suitable for parametric study. Existing formula for seismic provisions for the equivalent period and damping ratio of soil-structure systems are based on studies on... 

Considering the role of fluid storage tanks within or after an earthquake and the irreparable damages from their destruction that arise from the nature of the fluids of flammable or toxic nature stored in those tanks, it is very important to ensure stability and durability of the tanks when an earthquake is occurring. One of the most important damages to storage tanks within the past earthquakes has been lack of stability of their walls taking place in the form of elephant buckling. A certain storage tank was subject to a case study in this research and the tank's body, foundation, anchorages, the tread between the fluid and tank's body and between the bottom sheet and foundation were... 

In the present project an analytical model is proposed for the instability of spinning composite cylindrical shells partially filled with fluid. For this purpose, using the linearized Navier-Stokes equation for the incompressible flow, a 2-D model is developed for fluid motion at each section of the cylinder. The resultant pressure exerted on the cylinder wall as the result of the fluid motion, are calculated in terms of elastic displacements of the cylinder. Applying the Hamilton principle, the governing equations of motion of the cylinder are derived and then combined with the equations describing the fluid pressure to obtain the coupled-field equations of the structural-fluid motion.... 

Atherosclerosis in coronary arteries is one of the most important topics due to its high prevalence and the importance of these arteries for supplying blood to the heart. The morphology of endothelial cells (ECs) is an independent index for determining the atheroprone sites. The ECs show a regular elongated and aligned configuration to the blood flow, at the atheroprotected regions; on the other hand, at the atheroprone regions, the cells have a polygonal, randomly oriented morphology. The thesis intended to propose a method for coronary artery simulation, which is able to determine the atheroprone sites regarding the ECs morphology. In addition, the attempts were made to investigate the... 

In this research the flexibility of subterranean levels on foundation input motion (FIM), especially rocking component is investigated through parameter analyses. The so-called motion is induced as a result of kinematic soil-structure interaction (SSI). The foregoing interaction reduces the translational component of foundation input motion in rigid embedded foundations when compared to the free-field motion (FFM), as well as yielding rocking component in the foundation. On the other hand, increasing the embedment depth which is equivalent to the presence of subterranean levels in a building decreases the commonly-held “rigid” assumption’s accuracy for the embedded part. Given this effect,... 

In the present study, the numerical simulation of the panel flutter in compressible inviscid flow is performed by the compact finite difference method. For this purpose, the 2D compressible Euler equations written in the arbitrary Lagrange-Eulerian form are considered and the resulting system of equations in the generalized curvilinear coordinates is solved by the fourth-order compact finite-difference method. An appropriate nonlinear filter is applied for the shock capturing and for the solution to be stable. The governing equation for the panel is also numerically solved by using the fourth-order compact finite difference method. The time integration in the flow domain is made by the... 

Up till now, various contributions of research to soil-structure-interaction context have been primarily focused on structural systems exhibiting elastic-perfectly plastic material behavior. In this paper, combined effects of material degradation, p-delta, and soil-structure-interaction considering foundation uplift have been deemed to determine seismic response of a single degree of freedom system. The system is composed of a column with a lumped mass on top that is placed on a rigid foundation. The foundation is mounted on Winkler springs and dashpots to account for soil-foundation compliance and material/radiational damping. The springs are tensionless to guarantee that uplift phenomenon... 

This paper proposes a novel probabilistic approach to account for soil-structure interaction (SSI) in the seismic design of building structures. In this approach, an SSI response modification factor, RSSI, is introduced to capture SSI effects on the seismic performance of structures. The proposed procedure quantifies RSSI such that the probability distribution of the collapse capacity of the structure designed to account for SSI concurs with that of the structure designed using the default fixed-base provisions. The proposed approach is employed for special steel moment frame buildings with surface foundation. A surrogate single degree of freedom (SDOF) system is developed in this study and... 

The issue of solid and fluid interaction in horizontal axis wind turbines with diameter of more than 120 meters is one of the most important researching subjects of this type of turbines. This issues needs quick and exact solutions because of the high computational cost of fluid and structural domains.In this research a quick method with acceptable accuracy has been suggested which is based on computational fluid dynamic to examine the aeroelastic behavior of rotor and wind turbine tower. The actuator disc method in two domains of axisymmetric and three-dimensional has been used to compute aerodynamic forces. For this purpose a code has been written in C++ to set down virtual momentum on... 

This thesis studies the effect of soil-structure interaction on the seismic performance of structures with due account of uncertainties. The motivation for this study stems from the significant uncertainty in the earthquake ground motion and in the properties of the soil and the nonlinear behavior of the structure. The soil-structure system is modeled by the sub-structure method. The uncertainty in the properties of the system is described by random variables that are input to this model. Monte Carlo sampling is employed to compute the probability distribution of responses that describe the seismic performance of the structure, such as the ductility demand. In each sample, a randomly... 

The objective of this research is to investigate the use of passive control system to reduce the seismic response of fixed-roof, above-ground, cylindrical steel tanks as well as to decrease the damage caused to these structures in the event of an earthquake. The most crucial step for a safe design in this case is determining the lateral forces due to earthquake with sufficient accuracy; These forces are eventually resisted by the storage tank walls and the supports. Determining analiytical solution to the problem is not possible due to the interaction of the liquid with the structure. Therefore, numerical approach was adopted to determine the response of the tank using ANSYS program. Two... 

The simultaneous effect of uplift phenomenon and vertical vibration of soil-structure system is investigated in this study. The super-structure is modeled as an equivalent single-degree of freedom with bilinear behavior mounted on a rigid foundation resting on distributed tensionless Winkler springs and dampers. The effect of vertical excitation on the response of soil-structure systems allowed to uplift is investigated parametrically through time history analysis for a wide range of systems subjected to sine pulse and a group of ground motions recorded on the soil type of C. The results consist of maximum displacement of the uplifting system and ductility demand of the super-structure as a... 

The prediction of deposition efficiency of submicron particles in the pulmonary alveoli has received special attention due to its importance for drug delivery systems, and for assessing air pollutants health risks. In this work, the pulmonary alveoli of a healthy human are idealized by a three dimensional honeycomb like configuration and a fluid-structure interaction analysis is performed to study the normal cyclic breathing hydrodynamics. A viscoelastic model is used for the mechanical behavior of alveolar wall tissue. In contrast to previous works in which the inlet flow rate is predefined, in this model a negative pressure is imposed on the outside surface of the alveolus which causes air... 

Vibration is one of the major problems in gas and oil pipelines. Vibrations can cause damage to the pipes, supports, valves and other equipment installed in the system. These vibrations can be caused by equipment installed on pipelines like compressors and pumps or by fluid flow in pipes and fixed equipment like connections and valves. This research investigates the dynamic behavior of fluid flow in pipelines in Karanj and Parsi oil fields located in the southern part of Iran. The pipeline is responsible for injecting gas into the field. Excessive vibrations in the system cause repeatable damage which in turn increases the operating and maintenance cost. First, the vibration of pipelines has... 

This paper proposes a novel probabilistic framework for output-only identification of a soil-structure system. The system is modeled by a vertical shear beam resting on the soil representative springs. The proposed framework estimates the unknown parameters of the system and the foundation input motion time history simultaneously, using sparsely measured responses of the structure. The unknown parameters of the system include stiffness of the sway and rocking springs, shear modulus of the beam, and the modal damping ratios of the system. These parameters are modeled as random variables whose joint probability distribution is updated in a Bayesian scheme using the observations of structural... 

Patients with a single ventricle disease who have undergone Fontan surgery have always had long-term complications. These complications include pulmonary artery stiffness and decreased ability to exercise. In fact, due to removal of the right ventricle from the circulatory system, blood pressure and pulsatility inflow to total cavopulmonary connection (TCPC) are reduced following this surgery. Creating waves (radial displacement) on the IVC (Inferior Vena Cava) wall can increase pulmonary flow pulsations. The Objective of this study is to test the effect of induced wave amplitude on the pulmonary flow pulsations at the rest condition. Computational fluid dynamic (CFD) simulations were... 

The feasibility of passive energy dissipation devices such as viscous fluid dampers in controlling the torsional response of structures against seismic loadings has been explored by different researchers in recent years. In the majority of these studies, it is assumed that the structures are located on rigid bases. On the other hand, the effect of Soil-Structure Interaction (SSI) for the structures located on soft soil, on their dynamic parameters and structural responses can be prominent. In this study, the application of viscous fluid dampers in improving the torsional behavior of asymmetric concrete moment resisting frame buildings is investigated, taking into account the soil-structure... 

Dynamic characteristics of structures—viz., natural frequencies, damping ratios, and mode shapes—are central to earthquake resistant design (model validation) and health monitoring. For civil structures like buildings and bridges, these characteristics can be highly influenced by surrounding soil in addition to the super-structure’s properties and cannot be correctly estimated using numerical modeling. For example, soil’s flexibility decreases the natural frequencies of the system; and in most cases, soil provides additional damping due to material hysteresis and radiation. On account of this fact, system identification techniques must be applied to extract such information from field data,...