نشریه روش های عددی در مهندسی
سال سی و یکم شماره 1 (تابستان 1391)

This article investigates influence of neighboring structures on seismic behavior of a tunnel by using Finite Element Method. Dynamic interaction between a tunnel and a neighboring building is studied by comparing seismic behavior and internal forces of the tunnel and building. In other words, effects of existence of a building on internal forces of a tunnel are examined. This study includes several variables such as the distance between building and tunnel, soil properties, height and width of building, motivation frequncy, depth of tunnel and other parameters which dominate seismic bahavior of the tunnel. By changing the main parameters, the effective distance whithin which the adjacent building may influence the internal forces of the tunnel is determined.

Recently, a three-dimensional two scale damage model has been proposed for high cycle fatigue applications. The model takes into account plasticity and damage at the microscale and the behavior is considered as elastic at the mesoscale. In this paper, a robust numerical algorithm of the two scale damage model has been implemented. The explicit stress update scheme is performed for the model. This model can be used to predict failure for any kind of loading, cycle or random, mechanical,and thermo-mechanical. The cylindrical pipe subjected to complex thermo-mechanical fatigue loading and the helicopter main rotor shaft subjected to non-proportional loading are investigated by the two scale damage model.

The past numerical studies on seismic behavior of topographic features have been actually limited to individual single shapes. However, realistic observations in nature show that ground surface variation and its complexity is much greater and topographic features appear almost in complex forms. The main objective of this paper is presenting the results of a numerical study on seismic behavior of two adjacent 2D homogenous semi-sine shaped hills subjected to vertically propagating incident SV waves. It is shown that the combination of two adjacent hills generates an amplification pattern qualitatively similar to that of a single hill. The adjacency of the hills increases the amplification potential at both crests, especially on that hill which possesses a smaller shape ratio. Although the area created amid the two adjacent hills shows a seismic behavior similar to the valley qualitatively, it is not equivalent quantitatively to the valley of the same shape ratio. The inside base of adjacent hills demonstrates a greater amplification potential compared to the edges of the single valley with the same shape ratio, particularly against short and medium incident waves. It is also shown that adjacency effect could be considered as an effective factor in justifying some large amplification potentials reported in experimental observations.

Heat transfer from a domestic gas burner heating unit is enhanced by use of vortex generators. The heating unit is first modeled as a three dimensional physical domain for flow of gases, and conservation equations of mass, momentum, energy,species and radiation are discretized over the meshing system of control volumes provided in the domain. Experimental set-up to measure and validate the numerical results is equally established. Two triangular cross section bars are employed as inserts to disturb the flow of gases running inside the combustion chamber. The effect on heat transfer enhancement is then studied both numerically and experimentally. Results show that a jet forms between the insert and the combustion chamber wall. Also, some vortices are formed at downstream to the insert causing the heat transfer augmentation by 16.24% to the surrounding air. The overall efficiency is improved by 2.7% compared to the case of similar environment but with no vortex generators..

A computational model was presented to simulate peristaltic transportation of urine isolated bolus through the ureter. In this model, muscular stimulation was implemented using fluid-structure interaction and contact analysis. Urine drainage to the bladder was analyzed using two methods of numerical simulation and sonographic imaging in the region of bladder near the ureteral orifice. Moreover, pressure distribution in the ureter and dynamic variations of urine back flow during peristalsis were investigated. The results indicated that when urine bolus reached near the bladder, the maximum magnitude of urine pressure in the ureter increased up to nearly 5 times the ureteral inlet pressure. The average magnitude of urine flow rate computed from velocity profile in ureteral outlet during urine drainage was 2.267 ml/min.

Free surface seepage flow problems in porous medias have many industrial and agricultural applications. In these problems, the geometric shape of the phreatic surface is unknown a priori and therefore the unconfined seepage problems are categorized as variable domain problems. Solving these problems using methods such as finite element method undergoes some difficulties because the domain boundary changes in each iteration and remeshing is inevitable. In the present paper, the smoothed fixed grid finite element method which is a new numerical approach based on non-boundary-fitted meshes is used to solve free surface seepage problems. The use of non-boundary-fitted meshes leads to simplification of solution of variable domain problems. In this method, gradient smoothing technique is used to formulate internal and boundary intersecting elements. To evaluate the applicability of the proposed method, some numerical examples are solved and the results are compared with those presented in the literature.

Fuzzy autoregressive integrated moving average models are improved versions of the classic autoregressive integrated moving average (ARIMA) models, proposed in order to overcome the data limitation of ARIMA models. In this paper,FARIMA models are combined with probabilistic classifiers in order to yield a more accurate model than FARIMA in financially incomplete data situations. Empirical results of using proposed hybrid model in exchange rate market forecasting indicate that the proposed model exhibits effectively improved forecasting accuracy. Thus, the proposed model can be used as an alternative to exchange rate forecasting tools, especially when the scant data is made available over a short span of time.

There are different numerical investigations performed on hydrodynamic behavior of dam break flood in straight canals based on 1-D modeling. But, little has been done based on two dimensional analyses. Hence, this study used the two dimensional SVE equations to study flood behavior in meandering rivers with consecutive bends. Also, to investigate the dam break phenomena in meandering rivers under real conditions, the Zayande-Rood dam and river data were used as the case study.Results showed that the bends and their consecution have significant effects on decreasing the maximum flood discharge and also cause a considerable time delay in flood movement toward the downstream.