Modeling in Engineering
Year:2009 | Volume:7 | Issue:17|Papers Count:10

Voltage collapse is an inherently nonlinear phenomenon and it is suitable to use nonlinear analysis techniques such as bifurcation theory to study voltage collapse and to devise ways of avoiding it. For a power system, there are three different kinds of bifurcation points: the singularity induced bifurcation, saddle-node and hopf bifurcation. These three bifurcation sets are the boundary of the feasible region of the power system stability. When one equilibrium point passes through the boundary, the system will lose its stability. This paper focuses on bifurcation analysis for dynamic voltage stability. It also studies the eigenvalues behavior of the power system close to bifurcation points. This paper considers both unreduced Jacobian matrix eigenvalues and reduced ones, and it compares their results, too. MATLAB software has been used in this paper.

Following unexpected failures of beam to column welded moment connections in more than 100 steel moment frames during 1994 Northridge California earthquake, widespread research program started in united states to inspect the reasons of these failures and find solutions to them. The result of these investigations suggested that the main reason for these failures was the lack of plastic rotation capacity in welded connections. Following these researches, different types of moment connections and their improved details were proposed for using in special moment frames to provide minimum required plastic rotation capacity and desirable plastic behavior. To ensure plastic hinge formation in desired location in beam span and achieve proper plastic rotation capacity in suggested connections, one of the two strategies of “connection strengthening” or “local weakening of the beam section” was mainly adopted. Rib reinforced moment connections are one of the new connection types designed and suggested by “connection strengthening” strategy. This article reviews rib reinforced moment connections cyclic behavior and particular issues about these connections including strut action and inaccuracy of beam classical theory predictions in the rib area. Finally, it has been resulted that rib reinforced moment connections plastic rotation capacity in steel moment frames is quite suitable and this connections are able to achieve plastic rotation of 0.03 radian and higher.

In this study, effects of three dimensional standard finite element modeling of intake tower-reservoir interaction on the linear and nonlinear seismic behavior of intake towers are discussed and results obtained are compared with the common method “Hydrodynamic added mass”. Intake tower of Doosti dam; located at Iran-Turkmenistan border; has been modeled with water of surrounding reservoir in ANSYS software, to investigate linear seismic responses due to Naghan, Tabas and Elcentro earthquakes records. Results obtained from over than 20 seismic analyses show that the seismic response of intake tower, hydrodynamic pressure distribution pattern, shear force and bending moment distribution at height and first principal stress; strongly depend on the type of modeling, type of excitation and the time of maximum top response.

In this article a recommended method is introduced for face recognition in colored images, based on combination of template matching, conversions of color filter. In this method, firstly based on the recommended Gaussian filter, skin points of image based on a cluster including all the elements of skin are determined and by extraction of color elements, the standard of skin color separation is determined. Then the linked areas similar to skin color that are separated from different parts of image are introduced as recognized face by template matching and based on a model. The results of simulation on an induced images bank show that the above mentioned method has not only a low positive and negative mean error but also a high resistance against noise.

In this paper, the J integral method is used to calculate and analyze the crack of laminate composite materials. In this study, crack under different angles in different layer will be investigated and the critical state is determined. The analysis of crack will be done at first by finite element software and then a separate program for integral J on finite element software is calculated numerically. By using the calculated J, the stress concentration coefficient was calculated. The error is considerable when we utilize software for calculating stress concentration directly because of the existence of singularly at the tip of crack. By changing the path of integration of J. t the stress concentration obtained are more admissible.

One of the custom seismic structural systems for mid-rise and high-rise steel structures is braced steel moment frames. Each bracing systems behaves differently at earthquake. To reach useful applications of these bracing systems, seismic behavior at steel structures braced with eccentric (EBF) or concentric (CBF) bracing systems is rarely investigated. Having correct understanding of bracing behaviors and design at such structures are very important in order to assure appropriate dual performance. Hence most accuracy must be made in selecting of bracing system types and its configuration to satisfy code requirements and serviceability. Because of material nonlinearity that will be necessarily accurse in the structure due to real earthquake; in the absence of nonlinear dynamic analysis, static nonlinear pushover method can approximately describes the inelastic behavior of structure. 10, 15, 20 and 30 story 2D steel moment frames braced with CBF and EBF have been modeled in this study. Effects of change of bracing systems level from CBF to EBF with respect to nonlinear behavior of structure based on the area of load-displacement diagram are investigated. Analytical results obtained from over 100 analysis show that change of bracing system configuration at the specific level of structure changes the pattern of plastic hinges formation and cause to increase the general ductility.

Studies and researches accomplished about humanoid robots, to deem exact recognition of robot dynamics parameters necessary to execute a human-like motion. The high number of degree of freedom (DOF) of these robots makes achievement to this recognition more complex. In this paper the walking pattern of a 12 DOFs robot is generated using human motion model. Then relations between robot links are obtained by Denavit-Hartenberg method. Then necessary equations to execute the selected pattern are obtained using these relations and center of gravity (COG) Stability criteria. These equations are solved with composition of Newton-Raphson and singular value decomposition methods. The angular velocity functions of active DOFs are obtained by using linear path generation pattern with parabolic boundaries. Then the Kinematics-Kinetic parameters of robot are calculated at each step. Finally by using Simulink toolbox in Matlab software, a schematic model of robot is simulated in Visual Nastran software and the results are presented.