Sharif Digital Repository

This paper presents a unified solution to buckling analysis of rectangular symmetrically laminated composite plates with elastically restrained edges. The plates are subjected to biaxial compression and boundary conditions are simulated by employing uniform distribution of linear and rotational springs at all edges. The buckling loads and corresponding mode shapes are obtained based on classical lamination theory and using the Ritz method with simple polynomials as deflection function without any auxiliary functions. The verifications of current study are carried out with available combinations of classic boundary conditions in the literature. Through parametric study with wide range of... 

In the present study, the energy absorption mechanism is presented that used in two-dimensional microstructures. By studying the angular geometric parameters and the narrow ratio of the tilted members, we can use the property of the geometry of the structure to be bistable. In this way, there can be two stable geometries with different energies, which enters energy into the structure, such as the phase transformation to the second geometry that has more energy. By changing the geometric parameters, the deformed state can be stable or unstable. Because of the complex geometries that exist in this mechanism, additive production methods are more effective than geometric ratios or sharp points... 

Tortuosity is an abnormality that may occur in some arteries, such as carotid. It can reduce the blood flow to distal organs, and even in severe cases, causes ischemia and stroke. Tortuosity can be congenital or occurs due to hypertension and reduced axial pre-stretch of artery, in which case called buckling. Since atherosclerotic plaques disrupt the normal pattern of blood flow, and thus make the artery more susceptible to buckling, in this study, the effect of atherosclerotic plaques on arterial stability has been investigated using computational simulation of fluid-structure interaction under pulsatile flow and large deformation. Ideal geometry of normal and atherosclerotic carotid artery... 

Since previous models can not give a complete description for electrospinning electrical instability, using polymer solutions with diifferent properties, the aim of the existing thesis is to propose a new model that covers a range of materials from non-conducting to conducting and from viscous to elastic and also the initial jet’s tension. In addition, since the previous models have used large wave length approxiamtions, using accurate calculations we showed that the new model has better results for small wavelengths of about two times the jet’s radii. To compare the model to experimental results, we designed and made a proper setup to record the electrospinning process for a PEO solution... 

In this study, the thermal buckling behavior of thin metal liner reinforced by composite shell in present of the initial imperfection is investigated. For this purpose, the Ryzener – Myndlyn shear-deformation theory & the virtual work method are used to extract equilibrium equations. In this work, the conical shell with c-c, s-s, c-f boundary conditions has been studied. The outer layer of reinforced composite is exposed to constant ambient temperature and iner layer is exposed to heat. Metal liner and reinforced composite shell are merged with together. In other words, the degrees of freedom at each node for both shells are assumed to be equal. Solution method is finite element method using... 

The thesis addresses the buckling and post-buckling analysis of an elastic conical shell under non-uniform axial loading using finite element method. Non-uniform axial load is applied to one end of the truncated cone in the form of two equal-length loaded zones, diametrically opposite to each other. Material used in this thesis is isotropic with linear elasticity. The results are presented for different boundary condition. The results show that the buckling strength obtained by nonlinear analysis may be upto 40% less than the buckling strength obtained by linear analysis. The effects of boundary conditions and geometry on the results has been investigated  

Considering the role of fluid storage tanks within or after an earthquake and the irreparable damages of such structures that arise from the flammable or toxic nature of the fluids stored in them, it is very important to ensure stability and durability of the tanks under seismic loading. One of the most important damages to storage tanks within the past earthquakes has been lack of stability of their shells taking place in the form of a local bulge of wall, known as “elephant foot buckling’. This phenomenon is a subsequent of high levels of hoop tension, which is a result of containing liquid pressure, along with axial load of surrounding walls. Recent studies reveal that there is no... 

Coronary arteries often experience tortuosity under internal blood pressure and longitude axial twisting. Arterial tortuosity can enhance the stress concentration on the artery walls. Now if the coronary arteries suffer from atherosclerosis (a common disease among adults) the stress concentration on the tortuous artery plaque will be enhanced as well. Increased stress on the plaque may result in plaque rupture and its consequent damages. This study aims to investigate the stress concentration on the plaques and blood flow patterns within the coronary arteries with plaque. Moreover, the plaque growth was predicted taking into account various geometrical parameters including fibrous cap... 

Cylindrical shells are widely used in industries. For example, they are used as type 3 pressure vessel's liner. In this work, linear buckling of bead stiffened cylindrical shells under axial load or lateral pressure has been investigated by using numerical modeling. Bead form of cylindrical shell in longitudinal and circumferential direction and combination of both direction is considered. Different parameters such as number, dimension, direction (inside or outside) and cross-section's area of beaded form are considered. The obtained results show that creation of longitudinal beads decrease and increase the critical load and pressure compared to the simple cylindrical shell respectively. The...