نشریه روش های عددی در مهندسی
سال سی‌ام شماره 2 (زمستان 1390)

Multigrid methods, such as the Algebraic MultiGrid methods (AMG), are among the most efficient methods for solving discrete linear equations resulting from elliptic PDEs. In this paper, some classic AMG techniques are used for solving a typical two dimensional diffusion equation. The present work focuses on different coarsening techniques such as the standard and aggressive coarsening based on the RS algorithm. Results indicate that the standard coarsening technique together with direct interpolation minimizes the CPU-time and the computational work. Regarding the memory requirement, using a variant of aggressive coarsening with direct interpolation minimizes the size of memory usage. In addition, the setup phase time (coarsening process) is minimum in this technique. Nevertheless, the increase in convergence factor results in higher overall time for the solution phase. Analysis of the aspect ratio of the computational cells shows that the convergence rate is affected little by this parameter. However, the coarsening process work and the total CPU-time are slightly increased when cells with high aspect ratios are used for the numerical simulations. Overall, the standard-coarsening method with direct interpolation is found to be appropriate for two-dimensional diffusion problems.

Undrained shear strength is the main parameter in most problems concerned with short-term stability or total stress analysis states (TSA). Mechanism of soil deposit formation leads to inherent variability in soil strength and stiffness parameters.Inherent variability as the primary source of uncertainty in geotechnical problems consists of deterministic and stochastic components. In this paper, a generic deterministic trend is proposed by utilizing a good amount of well-documented in-situ test data. The new concept of transformation depth was introduced as the depth where it changes from a decreasing trend to an increasing one. Random field theory and local average subdivision (LAS) technique was employed in order to produce realization of undrained shear strength. Undrained shear strength was assumed to inherit a deterministic trend in vertical direction while preserving its stochastic behavior in horizontal direction.

Owning to important role of the cardiovascular system in the human body and increase of cardiovascular diseases day by day, in this study we try to simulate a system of arteries by using one dimensional numerical modeling. For the first time in the one dimensional simulation, we use the finite volume method for discretization of Navier-Stocks equations coupled with the state equation. In order to develop the outflow boundary condition, we use a kind of lumped model called arteriole structure tree.Results of this study are verified by results of another one dimensional modeling, i.e., the characteristic method, showing that finite volume method is able to demonstrate characteristics of blood flow in arteries. Normal pressure and flow profiles in main systemic arteries are determined, and it is found that the pressure profile becomes steeper with distance from the heart, which is in agreement with physiological patterns. Furthermore, we show that when elasticity of arteries is increased in arterioscleroses disease, systolic pressure increases, yet diastolic pressure decreases. Finally, according to available results it is clear that the finite volume method is useful to simulate the cardiovascular system numerically and one dimensionally.

Light steel framing can be a good alternative to the traditional construction systems in Iran because of special benefits such as possibility of industrial manufacture, pre-fabrication and being a lightweight system. Shear wall panels composed of cold formed steel frame and sheathing materials are one of the most common lateral bracing systems in these structures. Because of lightness and low lateral forces of the earthquake, the sheathings generally are made of wooden materials.In this study, lateral strength and displacement of the shear wall panels were determined using a finite element model. The panels were modeled using ANSYS software and a nonlinear push-over analysis was carried out. By comparing the numerical results of the present study with those of different experimental works done by other researchers, the finite element model was verified.Then a parametric study was performed to determine the effect of frame, sheathing and connections characteristics on the lateral behavior of shear wall panels.

In this paper, the effect of stiffeners on static behavior of semi rigid beam to column bolted connections in steel frames was investigated. Also, finite element models of semi rigid stiffened bolted connections were made and compared with experimental results. In the analytical models, the material and end plate-column flange contact nonlinearities and geometrical discontinuities were taken into account. The results of parametric analyses by using ABAQUS were presented and the effect of various parameters on tension force distribution in bolt row, rotational stiffness and flexural durability were investigated. Due to the effects on flexural durability, rotational stiffness and connection behavior, it is necessary to consider the effects of panel zone and end plate stiffeners in design method.

Experience of the past earthquakes indicates that topographic magnification and surroundings of structure contribute to the destruction of structures after the earthquake. In this article, the dynamic interaction formulation of structures is presented. The method is based on the boundary element method in frequency domain. In order to assess the accuracy and efficiency of the proposed formulations for the dynamic interaction of structures, several problems are considered. Also, the structural analysis of morning glory spillway of Barzu dam located in Shirvan was investigated. For this purpose, every domain placed around the structure was modeled and analyzed separately, and then a model incorporating all the domains was presented.For realistic analysis, the problems were modeled and analyzed three-dimensionally. In this study, the effects of parameters such as shape irregularities, mechanical properties of materials (density, Poisson coefficient, shear modulus), stimulation frequency,incident wave type (P, SH, SV), azimuth and angle of incident wave on dynamic analysis of mentioned structure were considered.The results show that the foundation flexibility causes stiffness reduction and thus reduction of frequency vibrational modes of the system. The fluid-structure interaction brings about a high change in seismic response of the system in a way that the values of the displacements increase at frequencies lower than the 1.5 times of the first vibration mode and decrease at higher frequencies. The fluid in contact with structure increases the effective mass and reduces vibration frequencies of the system.

Joint shear deficiency in concrete beam-column connections arising form diagonal cracks is one of the main causes of connection failure. This factor, apart from connection damage, results in column deterioration and degradation of structural performance. In this paper, an experimental and analytical investigation into the behavior of exterior concrete beam-column joints is carried out. The variables include the type and location of beam longitudinal bar anchorage in joint, longitudinal and transverse reinforcement of column at the joint region, and strength of concrete. In the experimental part, 8 semi-scale exterior beam-column joints are manufactured and subjected to a constant column axial load and beam quasi-static cyclic load. In the analytical part, ABAQUS software is used for modeling and analyzing the test specimens. Based on the results, both experimental and analytical joint capacities are in good agreement. Results show that increasing the concrete strength, in addition to increasing the load capacity, can change the failure mechanism of a connection from shear failure in joint to flexural failure in beam. Also, by making appropriate changes in reinforcement at the joint region, the load capacity, energy dissipation and ductility of connection can be increased