Sharif Digital Repository

Rotary machines including gas turbines have been widely used in many industries like gas reducing pressure stations and power plants. Blades are important components of gas turbines which are subjected to failure due to different kind of damages like crack occurrence. There are various reasons for crack occurrence and its propagation in blades. Presence of crack in the blades may lead to major failure, which in turn, result in emergency shutdown of the system. Therefore condition monitoring is employed to check the possibility of failures. In recent years, condition monitoring techniques have been developed to prevent unnecessary shutdown of the systems. The present thesis aims to... 

Material selection is one of the most important works should be done prior to the designing of any part of the mechanical and/or nonmechanical structures. Various material selection methods, such as digital logic, modified digital logic, z-transformation and fuzzy logic, have been introduced and used in recent years. All these methods have some advantages and disadvantages in selection of appropriate materials. Since, all these methods exhibit some disadvantages, the main objective of thesis is to introduce the new method to reduce or eliminate the other method’s disadvantages with less complexity. The fuzzy logic method which is mostly used in this thesis will result in some problems due to... 

The most important challenge and the most time consuming part of the gradient based optimization algorithms in the aerodynamic shape optimization problems is the evaluation of the sensitivity of the objective function with respect to the design variables. The adjoint method which has been the subject of many research in the recent three decades, is capable of computing the complete gradient information needed for optimization by solving the governing flow equations and their corresponding adjoint equations only once, regardless of the number of design parameters. In this study, the continues adjoint equations for compressible inviscid and viscous flows are derived and the formulation of... 

Vibrations in HAWT reduce their efficiency and increase maintenance costs. In this paper, the blade edgewise vibrations are reduced by using several actuators in different parts of the wind turbine blade and optimization of the number and locations of actuators. The wind turbine blade dynamic behavior is investigated by using dynamic modeling. The actuators are trusses that are located inside each blade and apply control force to different parts of the blade. Active control force is applied to reduce edgewise vibrations. The designed controller is applied and simulated on NREL 5MW wind turbine. By applying the controller, the edgewise vibrations of wind turbine blades are significantly... 

Because of the importance and value of Superalloy, In this research has been treid to remelting scrap of gas turbine blades cobalt based Superalloy X-45, In order to restore it to the cycle of consumption. For this purpose, scraps were remelted under different conditions, for example changing the atmosphere, changing slag composition, changing type of the furnace for remelting and changing time of remelting process. Then in order to investigate effect of the above factors, microstructure were studied by optical microscope and Scanning Electron Microscopy (SEM) And also in order to investigate changings of element composition, chemical analysis were examined by atomic absorption analysis and... 

Well worn gas turbine blade made of Nickel based superalloy, IN738LC was remelted due to remove inclusion and use it in casting process of new blade after microstrucrure investigation in neutral atmosphere and vacuum. The composition of slags for removing inclusions used for this practice were 70CaF2-20CaO-10Al2O3 and 55CaO-45Al2O3. The microstructural characterization involved use both optical as well as electron microscope including application of EDS technique for denoted the type of carbides and inclusion investigation. Chemical composition was determined by despersive spectroscopy method. The changing in main elements were reported too low. Number of inclusions were decreased in the... 

Aeroelasticity analysis and prediction of wind turbines sturcture deformations are fundamental parts in their design. Increasing the size of wind turbine blades and development of Mega-watt sized wind turbines have enhanced the importance of these studies. In this study, the aeroelasticity analysis of a wind turbine blade has been done based on flexible multibody dynamics method. For this purpose, the modal approach has been used for modeling blade structure which has been considered as a flexible beam with bending and torsion degrees of freedom. The unsteady vortex lattice method has been used to calculate aerodynamic loads in order to combine with wind turbine blade structure model. Using... 

This study develops an aerodynamic shape optimization code using parallel processing capability based on a gradient-based adjoint method. Calculation of the gradient of the objective function with respect to design variables is the most costly part of the gradient-based optimization algorithms. Applying adjoint methods, gradients can be calculated with solving some additional equations known as the "adjoint equations", instead of direct calculation. In this study, the blade shape optimization is performed by inverse design method and using steepest descent optimization algorithm. The objective function of inverse design problem is the desired blade surface pressure distribution. In each... 

Prediction techniques of axial flow turbine performance for different operating conditions are always developing due to high costs and lack of reliable empirical data. In axial gas turbines, fluid flow is three-dimensional, viscous, and highly turbulent. Nowadays, although flow field specifications are predicted accurately well using computational and numerical tools, the appropriate loss models are required for one-dimensional modeling and optimization in early design phases. In this research, an accurate and a complete investigation of aerodynamic losses in axial flow turbines will be discussed. Some suggested models for calculating losses in axial gas turbines, are considered and...