فهرست مطالب سید امیرالدین صدرنژاد

In a perforated well, fluids enter the wellbore through arrays of perforation tunnels. These perforations are typically distributed in a helical pattern around the wellbore. Available numerical models to simulate production flow into cased-and-perforated vertical wells have complicated boundary conditions or suffer from high computational costs. This paper presents a simple and at the same time efficient finite element model to simulate flow around a well with helically symmetric perforations. In the proposed model, by taking advantage of the symmetry, only a thickness of perforated interval containing a single perforation tunnel needs to be meshed. Angular phasing between adjacent perforations is considered by applying periodic boundary conditions on the upper and lower boundaries of the representative reservoir thickness. These boundary conditions involve periodic-pressure and periodic-velocity parts. Unlike the periodic-pressure part, the method of imposing the periodic-velocity condition within a single-variable flow problem is rather vague. In this regard, it is proved that in the proposed model, periodic-velocity condition is automatically satisfied in a weak sense. The accuracy and the computational efficiency of the proposed model are verified through comparison with available models. The model results, in terms of skin factor, are compared with the common semi-analytical model as well, and good agreement is obtained. The proposed model can readily be used as a numerical tool to study inflow of wells with helically symmetric perforations.

In the oil industry, production of sand particles or detached sand clumps together with the formation fluids is called sand production. Sand production in oil wells is usually related to two fundamental mechanisms. The first mechanism is mechanical instability and degradation of the rock in the vicinity of the wellbore and the other is hydrodynamical instability due to flow induced drag force on the degraded material. In this paper, considering both the mechanisms, a new numerical model for predicting the onset of sanding as well as the amount of sanding is proposed. Implementation of the model in an explicitly coupled flow and deformation finite element program is described. The proposed model by removing the elements that have satisfied the sanding criteria as well as isolated rock chunks from reservoir can capture cavity evolution associated with sand production. The model is calibrated and validated against published results of a sanding experiment in a perforated reservoir rock. Results of the model in terms of initiation and amount of sanding are compares well with the experimental observations which suggests it can be used for sanding analysis of oil wells.

Considering passive defense in construction and rehabilitation of military and residential structures is a proper method for blast-induced damage mitigation. In this paper، the behavior of end plate bolted connections under blast is studied. To assure the accuracy of finite element models، verification is carried out using the results of an experimental test.. A 5-story structure is designed according to national steel structures code using ETABS and one of the first storey connections is studied under blast load using nonlinear dynamic analysis in ABAQUS considering the effects of high strain rates. The results show that the beam experiences significant torsion. Moreover، the critical area in moment connection is the area adjacent to lower bolt holes as well as the area between end plate and lower beam flange. It is also observed that the use of small bolts in higher number provides more desirable response in blast loading.

Considering the terrorist and hostile threats against Iran and the dire need of passive defense in structures to reduce casualty and financial damage caused by implosion and explosion in structures, reviewing the performance of structures against blast is of utmost importance. One of the most important structural members which severely affect the overall performance of the structure is the connection of pole to the pillar. The inappropriate performance and defect of these connections can contribute to the surface and in subsequent steps cause the increasing defect in structures and its collapse. In this article, the blast loading effect on the performance of connections of pole to twist shielding pillar has been studied. This kind of connection is used in steel structures in Iran. To do the research, the Limited Elements Method and the ABAQUS software which is one of the most robust Limited Elements Method that exists today was used. To ensure the results of Limited Elements modeling, the authenticity of the model using the results of a laboratory research was first utilized and an appropriate compliance between the predicted results by the Limited Elements Method and the measured results in the laboratory were observed. After ensuring the precision of the Limited Element in the simulation of the connection behavior, a non-linear dynamic analysis taking into account the effects of high rate strain resulting from blast, was performed. Due to the presence of symmetry, only 1/8 of the room was studied for the modeling. The weight of the explosive approximated 15 kilograms of TNT. The test results showed that the occurrence of blast inside the room causes a twisting deflection in the pole. It was also noticed that this kind of connection has a relatively formable behavior against blast loading.

In this paper, a numerical investigation on behavior of concrete in filled columns using nonlinear finite element method is done. Numerical results are verified using experimental results. Behavior of rolled steel tubes witch are filled with concrete of different strength on the axial applied loads is present. Effect of steel tubes thickness and confining stress are considered and the results are compared with concrete columns. The results showed that with increasing thickness of steel tubes, axial load capacity and confinement stress and ductility is increased and with increasing the concrete strength, confining stress and ductility is reduced. Specimens with different concrete strength of 30,60,80 MPaand different ratioare analyzed and all the specimens have the same length of 300 mm. The main objects are: 1) to investigate effect of prominence on axial load capacity. 2) to investigate the effect of different parameters like thickness of steel tubes, friction coefficient and the ratio of prominence area over total perimeter area. 3) to investigate effect of loading(i.e. loading concrete only or loading concrete and steel tubes simultaneous. 4) to investigate the ductility of columns.

Simulation and analysis of bullet (projectile) impact to structures is one of the needed subjects in retrofit of structures. To study the penetration phenomenon in structures, the affecting parameters should be indentified and this identification leads to prediction of penetration depth and then, to minimizing it. One of the main affecting parameters on the final penetration depth is the type and amount of energy dissipation during the penetration process. Generally, energy dissipation occurs in three steps of penetration process including impact, tunnel and exit steps in three different forms. In the first step, i.e. the projectile impact on concrete target, the compressive strength of concrete is the affecting parameter on energy absorption. However, the shear-frictional strength and concrete tensile strength are respectively the main affecting parameters in the second and third steps. In this paper, the affecting parameters on energy dissipation during these three steps are studied and it will examine that the energy dissipation during the tunnel (shear-frictional between projectile and concrete) is lower than that of the two other steps because of the geometrical shape of projectile head. In other words, the main portion of energy dissipation during the penetration phenomenon occurs when the projectile clashes the front surface and when it exits the back face of slab. Considering the above results, it can be said that to increase the strength and efficiency in penetration phenomenon, an applicable and inexpensive method is to implement a specific thickness of multilayer concrete with small clearance between the layers. The energy dissipation of this assembly is higher than that of a single layer concrete of the same thickness and thus, the penetration depth will be reduced.

As experiments show, there is nonlinear behavior of carbon nanotubes after exceeding a certain boundary surface while loading continues. Avoiding being involved in molecular dynamics methods and quantum mechanics approach, a continuum macro mechanics based method is employed to predict the nonlinear behavior of bonding forces in carbon nanotubes. Both analytical and numerical approaches, assuming elasto-plastic behavior of tubes are considered in this research. The presented results are well compared with the test as well as molecular dynamics results. Finally, the limitation and advantages of the proposed method are pointed out.

Abnormal loads induced by blast or impact results in local damages in structures and these local damages may propagate and affect whole structural system. Therefore, structures should be designed in a way that progressive collapse is prevented. Connections have important effect on ductility and strength of structural systems and preventing progressive collapse. Consequently, the behavior of bolted angle connection under blast load is studied in this paper using finite element method. In this study, top and seat bolted angle connection with web angles is investigated using ANSYS finite element software. The models are verified comparing the analysis results with those of experimental tests. The verified models are then exposed to blast load and their behavior is evaluated. Critical areas are determined in the connection and failure modes and applicability of mentioned connections against blast loading is investigated.

One of the main principles in passive defense is to retrofit of structures against blast loads. The first step to achieve this purpose is understanding and simulation of blast effects on structures. The most convenient method for simulation and analysis of blast effect on structures is numerical simulations. Free explosion problems or explosion with fragment problem are characterized as severe dynamic loads that are induced by blast or impact and last for some micro-seconds. Therefore, in numerical simulations, wave propagation should be accurately modeled. General continuous mechanics that is used for simulation of such phenomena is based on mass, momentum and energy equations in reactions that describe material behavior. Since the equations consist of nonlinear partial derivatives, analytical solutions cannot be used generally because inputs and initial values are too complicated. Numerical techniques are the only method for achieving available complete solutions. Some hydro-codes are now used for such simulations. Each code has features that individualize it, but none of these codes or numerical methods is better than others in all problems. In this study, to show the abilities and accuracy of numerical methods in such simulations, simulation of concrete structure behavior under blast load is conducted using LS-DYNA code. Besides, the used patterns and governing equations are accurately studied.