Sharif Digital Repository

All supersonic intakes with external compression, having a good level of performance at all the critical poin t. Exhibit a marked instability of flow in subcritical operation below some value of the flow ratio, in the form of an oscillation of the shock system, colloquially known as “buzz", which can lead to thrust loss, engine surge or even structural damages. Therefore the effort to understand the nature and cause of this phenomenon is important in order that the starting of buzz can be predicted and more effectively avoided without losing performance. This phenomenon has been the subject of many studies, mainly experimental. In this research, we design and build an axisymmetric supersonic... 

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.... 

In this thesis, chaotic behavior of a photonic micro-resonator is investigated. First, a Lagrangian formulation is introduced for the system. Then, by applying a multi-reflection method, a closed formula is obtained for the radiation pressure. Use of this equation in the coupled differential equations describing dynamics of the problem gives us a suitable model for exploring the behavior of the micro-resonator. In this stage, we compare our results with experimental data too. On the other hand, using above mentioned formulation, chaotic behavior of the micro-resonator is investigated using numerical method. Finally, a period-doubling route to chaos appears in our results as is observed in... 

One of the classic problems in the aeroelasticity field is panel Fluttr that occurs in supersonic flow. Panels as wing skins, fuselage missile, and so are prone to this phenomenon, which causes fatigue and structures, will be demolished.In many cases, the wall panels and a full tank of fuel, this in this case, the vibration of the fluid-filled panels will be affected. There is clearly fluid into a tank filled with considering the approximation of incompressible fluid dynamics and vibration modes of the panel will change. In this study, a three-dimensional rectangular tank is considered the high walls on the elastic and supersonic flow passes.Fuel density and structural dimensions of Full... 

In this thesis fluid flow stability will be studied using Chebychev collocation spectral method. In general instability occurs between layers of a single fluid or at the interface of two different fluids. In case of an unstable flow small imposed perturbations on the flow will grow with time and their amplitudes will grow larger. Instability in most cases is an unfavorable phenomenon and therefore should be avoided.Two-phase flow processes in horizontal or vertical pipes under various conditions like natural or forced convection are of considerable importance in industrial applications. Two-phase flow can be found in many devices and industries like boilers, nuclear reactors, cooling and... 

Constant drilling in the shale formation causes many problems such as shale swelling and well instability. Annually many costs are spent dealing with these problems in the drilling industry. Many factors can affect this issue. The most important factor is the type of drilling fluid and its additives. The use of oil-based mud is the best option to deal with the clays instability but, due to environmental problems resulting from OBM, their use has been banned in most parts of the world. Therefore, the water-based mud is the only option for the oil industry that can modify its property by use of additives. In this study, the muds contain Nano silica have been introduced. Silicate as shale... 

Aiming to improve the extraction performance of wind energy has led to the noticeable increase of the structural dimensions in the modern wind turbines. The larger blade with more flexibility experiences large structural deformation even under nominal operational loading, so the nonlinear modeling and analysis of these structures have become as important subject of the recent wind turbine researches. In this dissertation, the geometrical exact model of the rotating wind turbine blade under the effects of the tower tip's motion, and also the operational loading comprising the aerodynamic and gravitational loadings is presented. In this way, the geometrical exact beam formulation is developed... 

Today, oscillating heat pipes play an undeniable role in energy recovery due to their high thermal capacity. Studies show that the working fluid plays a more effective role in improving the performance of the oscillating heat pipes. In this study, a model is proposed to determine the optimal concentrations of Fe3O4-MWCNT/DI Water hybrid nanofluid based on NSGA-II multi-objective optimization algorithm. The Thermophysical properties of the fluid have been optimized to obtain the concentrations that provide the highest thermal conductivity and specific heat capacity and the lowest dynamic viscosity and density for hybrid nanofluids. Then a number of these concentrations¬ have ¬been selected... 

Magnetohydrodynamic is used to study many phenomena. In non-relativistic terms, it can be used to express dynamo theory and to study the evolution of a magnetic field in a conductive fluid medium. In the case of fluid particles having chiral imbalance, the instability associated with this property is observed in the system response to the small perturbation from the equilibrium state. In a relativistic framework, these equations can describe the quark-gluon plasma in the heavy ions collision in a decentralized manner and the nucleus of neutron stars. In many studies, chirality has been considered for such environments. Obtaining the dispersion relation and investigating the response of the... 

There is many operational problems in the drilling industry. One of these basic problems is stuck pipe. This problem occurs with different intensities in different formations due to particles falling into the well, pressure difference in the formation and drilling mud and instability of the wellbore and creates conditions in which the drilling string can neither rotate nor move, so all Drilling operations are stopped so that according to studies, pipe sticking is one of the most important reasons for stopping drilling operations. This stop imposes millions of dollars of operational damage on oil services companies annually. Therefore, identifying and prediction of stuck pipe as a major... 

This study proposes a robust technique for large displacement analysis of slack cable structures subjected to dynamic loadings using a novel method, entitled Node Relaxation. Ordinary numerical methods are usually unable to analyze cable structures due to singularities arising from large displacements and rotations following any alteration of the applied loads. When dynamic loads are considered, handling these singularities in numerical analyses becomes even more challenging. In this thesis, an effective iterative method is proposed for three-dimensional large-displacement dynamic analysis of structures consisting slack cables as the primary load-bearing system. The cable structure is... 

We study the phenomenon of parametric amplification and instability in the context of time-varying electromagnetic structures, particularly dielectric slabs with periodically modulated permittivity. These structures show particular promise inasmuch as they are capable of very large amplifications when illuminated by an electromagnetic wave of half the modulation frequency. Successive studies have corroborated this finding but none have yet been able to ascertain the nature of amplification in such devices. On top of that, the problem of instability in time-periodic slabs has either been disregarded altogether or it has been subjected to loose analysis, leading to mere speculations which are...