This paper deals with the investigation of thermo-vibrational convection induced by harmonic vibrations of the temperature boundary conditions in a square cavity heated from bellow and containing a low Prandtl number fluid. The governing equations are solved by using a finite volumes method. Effects of thermal modulation on the all regimes occurring in the cavity when convection intensity increases are analyzed. A characteristic modulation frequency allowing the reduction of the average intensity of the flow and heat transfer at the cold wall has been identified. The effect of phase difference between hot and cold temperature is also studied.
The present study deals with optimization of hydraulic efficiency and shaft fatigue life of a micro cross-flow hydraulic turbine. A micro cross-flow turbine (KTP-B60) with shaft fatigue failure was considered as a case study. Numerical flow simulations were performed using a 3D- two phase flow solver, and the results have shown a good agreement with experimental data. Using an analytical method, the shaft fatigue factor of safety (FOS) was extracted from numerical simulation. CFD results were utilized in the optimization process in order to improve hydraulic efficiency and shaft fatigue life simultaneously using a meta- model (Artificial Neural Network) and genetic algorithm (GA). The priority of hydraulic efficiency and shaft fatigue life was altered by defining different objective functions in the optimization process. In one of the cases comparison of initial and optimal turbine showed a hydraulic efficiency improvement of 10.14 % and relative shaft FOS improvement of 4.86 %. The proposed optimization method could be exploited as an efficient and low cost procedure for energy generation improvement in micro hydro turbines.
Buckling is one of the most complicated concepts in mechanical engineering. Buckling often happens by compressive loads on thin structures. Thermal gradient between two ends of a column may cause a deflection in it. This will add an extra deformation to the one provided by compressive loads on the column. This phenomenon occurs when two ends of the column are at different temperatures, which can be seen at various structures. Because of the considered temperature gradients, the critical load of the column will decrease. In the current paper, various columns are modeled and the effect of thermal gradient and compressive load and other parameters on the Bi-material columns are studied. In other words, influences of compressive load and temperature gradient on critical load of Bi-material columns with interface crack are investigated. Effect of change in each parameter on critical load of column and crack opening was investigated. First, the thermal gradient was only applied to the model and in the next step; only the effect of mechanical loading was studied. Furthermore, artificial neural network (ANN) was used to extend the results to a bigger range of temperature conditions through the columns. Based on the results, ANN and finite element results are in a good agreement and the thermal effects may have a significant role in buckling of the column.
Functionally Graded Steels (FGSs) are possible solutions to improve the properties of steels made by Martensite and Bainite brittle phases. These phases are usually present in the interface between the carbon ferritic steel and the stainless austenitic steel. FGSs materials are widely investigated in the recent literature but only few works have been devoted to investigate the impact energy in the case of crack arresters. To partially fill this gap, the effect of the distance between the notch tip and the position of the median phase on the Charpy impact energy is investigated in the present paper. The results show that when the notch apex is close to the median layer the impact energy reaches its maximum value due to the increment of the absorbed energy by plastic deformation ahead of the notch tip. On the other hand, when the notch apex is far from the median layer, the impact energy strongly decreases. Keeping into account the relationship between the Charpy impact energy and the plastic volume size, a new theoretical model has been developed to link the composite impact energy with the distance from the notch apex to the median phase. The results of the new model show a sound agreement with previous results taken from the literature.
This paper deals with exact solution for free vibration analysis of simply supported rectangular plates on elastic foundation. The solution is on the basis of three dimensional elasticity theory. The foundation is described by the Pasternak (two-parameter) model. First, the Navier equations of motion are replaced by three decoupled equations in terms of displacement components. Then, these equations are solved in a semi-inverse method. The obtained displacement field satisfies all the boundary conditions of the problem in a point wise manner. The solution is in the form of a double Fourier sine series. Then free-vibration characteristics of rectangular plates resting on elastic foundations for different thickness/span ratios and foundation parameters are studied. The numerical results are compared with the available results in the literature. Important parameters on the accuracy of plate theories and free-vibration characteristics of rectangular plates resting on elastic foundations are discussed.
A land-based gas turbine may operate at the different environment including corrosive and dusty environments. These conditions can cause early damages in the “cold” parts as well as in the “hot” parts of the gas turbine. In this research, fatigue life of a compressor blade is predicted with and without damages. Damage is considered as a notch at the blade and is classified as three types of short, medium and long notches. These are numerically simulated in the compressor blade and fatigue crack initiation life is calculated. Stress analysis is carried out using finite element analysis followed by fatigue life calculations. Furthermore, the influence of blade tip displacement on life of the undamaged and damaged blade is investigated. Moreover, the effect of damage & apos; s size and location on blade’s life is reported. This procedure can be tuned with corrosion damages observed during the minor inspection where the gas turbines are operating in the unusual environments.
This piece of work aims at the modeling and using the finite element method approach (FEM) to analyze the fatigue behavior of bolted beam to column end-plate connection in the structural steel framework subjected to static loading. A detailed three dimensional (3D) simulation model of the bolted beam to column end-plate connection is constructed in PRO-E wildfire and it is analyzed in the ANSYS workbench to obtain its behavior. The bolted end-plate connection is chosen as an important type of beam to column joint. The end-plate connection is chosen for its complexity in the analysis and behavior due to the number of connection components and their inheritable behavior. The solid elements, bonded contact and the bolt pretension are included to obtain the behavior of the structure. The FEA results of the structure with or without bolt pretension are compared with the available literature. At last the fatigue behavior of connections under over tensioning is presented in this work.
Mode I and mode II stress intensity factors (SIFs) through the thickness of edge crack in semi circular bend (SCB) and center cracked circular disc (CCCD) specimens have been analyzed using three dimensional finite element analysis. The effect of the CCCD and SCB specimen thickness on the through-thickness variations of SIFs has been studied. For all mode of mixity, the peak value of mode I SIF is found at mid plane of SCB specimen and for thin CCCD specimen, while, this location is shifted to be near the free surface plane in thick CCCD specimen. The variation of mode II SIF in CCCD and SCB specimens have a similar trend.
The novel equivalent material concept, proposed originally by the author, was utilized together with the mean stress and the point stress failure concepts to predict the load-carrying capacity of O-notched ductile steel plates under pure tension. Unlike for V and U-notches, it was found that the point stress criterion combined with the equivalent material concept could estimate successfully the limited available experimental results reported in literature regarding four O-notched plates made of very ductile steel. By using the model, one may predict well the onset of tensile crack initiation in O-notched ductile components without requiring performing experiments or elastic-plastic analysis.
Semi-submersible drilling platforms are huge bulk structures for extracting the oil products from great depth of seas. For such bulk structures, the Morrison’s equations are no longer valid for determining the loads applied to the semi-submersible drilling platforms. The diffraction theory should be used for evaluating the hydrodynamic interactions between the platform and the sea waves. In this theory, the Laplace equation is solved by considering the boundary conditions of the diffraction theory. In this paper, after a brief description of the diffraction theory, the hydrodynamic interactions between the Iran’s Amirkabir semi-submersible drilling platform and the regular linear waves of Caspian Sea is investigated numerically using boundary element method in the ANSYS/AQWA software. The induced waves exciting forces and moments with different wave heading angles are estimated for six degrees of freedom relative to the waves frequencies using the diffraction theory. The performed hydrodynamic analysis is also validated with the previous works performed for Spar platforms.