Sharif Digital Repository

In this study a new version of adjacency, which provides a more flexible layout design, is proposed. In the proposed version, departments which are nonadjacent yet close to each other are considered to be adjacent with a smaller adjacency rating. It is shown that the proposed adjacency is a generalized version of the traditional adjacency. A mathematical programming model is developed for the proposed facility layout problem. To show the flexibility and efficacy of the proposed model, a computational study is conducted. The solution of an illustrative example as well as the solutions of several test problems, reveal flexibility and efficacy of the proposed model  

An effective facility layout implies that departments with high flow are laid adjacent. However, in the case of a very narrow boundary length between the neighbouring departments, the adjacency would actually be useless. In traditional layout design methods, a score is generally assigned independent of the department’s boundary length. This may result in a layout design with a restricted material flow. This article proposes a new concept of adjacency in which the department pairs are laid adjacent with a wider path. To apply this concept, a shop with unequal rectangular departments is contemplated and a mathematical programming model with the objective of maximizing the sum of the adjacency... 

Many concrete structures such as bridges, offshore structures, and pavements are under cyclic loads when they are exposed to different environmental conditions during their lifespan. The durability and fatigue performance of these structures are significant issues that should be considered. Therefore, this study investigated the long-term environmental effects on Polymer Concrete (PC) and Ordinary Cement Concrete (OCC) subjected to cyclic fatigue loading under four different environmental conditions (freshwater, seawater, acidic and alkaline) for six months. Concrete specimens are tested under high cyclic loading with the frequency of 6 Hz and low cyclic loading with a frequency of 1 Hz.... 

In this study, a fully coupled dynamic finite element model was employed for numerical simulation of the response of level to gently sloping saturated sand layers subjected to cyclic loading. This model utilized a critical state two-surface-plasticity constitutive model to simulate the cyclic behavior of sandy soil. Moreover, a recently proposed variable permeability function was implemented in the numerical model to reflect the effects of soil permeability variations during the liquefaction phenomenon. The numerical model was validated by simulating a number of well-documented geotechnical centrifuge tests with different relative density of sand, base acceleration time history, and surface... 

Dynamic compaction is a widely used method for improvement of loose granular deposits. Its applicability in saturated layers generally considered to be less effective because of the fact that part of the applied energy is absorbed by pore water. Up to now the majority of numerical simulations have focused on the analysis of dynamic compaction in dry/moist soils. In this paper, a fully coupled hydro-mechanical finite element code has been developed and employed to evaluate the dynamic compaction effects on saturated granular soils. After verification of the results by comparing the numerical results with those measured in a real field case of DC treatment in a highway, some sensitivity... 

Dynamic compaction (DC) is a popular soil improvement method that is extensively used worldwide. DC treatment design is usually carried out based on past experiences and empirical relations. To establish a rational design approach, all important factors affecting the DC process should be taken into account. In this paper, a finite element code is developed for modeling the impact behavior of dry and moist granular soils. The code is verified with the results of some centrifuge tests. Several analyses were conducted in order to study the effects of energy/momentum per drop, tamper base radius, and number of drops on compaction degree, compacted depth, and extension of the improved zone in the... 

Dynamic compaction (DC) is a common soil improvement technique, used extensively worldwide. DC treatment design is usually based upon empirical relations and past experience. The common problem with all empirical relations is oversimplification of the mechanisms, and the use of parameters that are highly dependent on engineering judgement. In this paper, a developed finite-element code is used for modelling the impact behaviour of dry and moist sandy soil. The code is verified against the results of centrifuge tests. Then the validity of the popular Menard empirical relation for determination of improvement depth in DC design is investigated. The effect of initial relative density, tamper... 

The equalizing wake flow into the propeller behind the ship is important from the hydrodynamic performance viewpoint. In this study, numerical simulations of the DTMB4119 propeller with two symmetric and asymmetric duct types behind the KRISO Container Ship (KCS) are performed using Computational Fluid Dynamics (CFD). In order to improve the wake equaling flow, a combined duct and stators' configurations are installed before the propeller in the stern of the ship and its hydrodynamic performance is studied using CFD. A duct with the NACA4415 section and two types of stator configurations are selected. The STAR-CCM+ software using the finite volume discretization method was used to solve the... 

Grain geometry is an important factor affecting the stability envelop of solid rocket motors. This paper presents a series of subscale tactical motor firings, clearly showing the effect of combustion chamber internal geometry on stability. Three types of grain cartridges were used in these motors: a circular perforation (CP) and two variations of a seven-pointed star. Combination of these three basic grains produced motors that have completely different internal geometries. A polyurethane-based 81% solids composite propellant was used in all tests. This marginally stable propellant has a nominal burning rate of 7.1 mm/s for the metalized formulation that contains 7% aluminum powder and 5.7... 

Dynamic compaction is a widely used soil improvement method in dry and/or saturated soils. Despite its vast application, its design basis is still empirical and the mechanisms that are involved in the procedure are not fully understood. A fully coupled dynamic finite element code has been developed in order to clarify the ambiguities in the process and predict the strain/displacement field in the ground, determine depth and degree of improvement, and also calculate the pore pressure variation during the process. This model can be used as a rational design tool for dynamic compaction projects  

Classical continuum mechanics fails to give accurate solution near the crack tip, moreover, it implies that a solid is able to sustain an infinite stress at the Griffith-Inglis crack tips. Among other critical issues is the inability of the classical approach to sense the size effect. For these reasons, for more in-depth understandings and accurate behavioral predictions, it is essential to develop some atomistic methods which properly accounts, not only for the structure but also the long and short range atomic interactions effectively. In this work the interaction of inhomogeneity and crack under polynomial loading is simulated by using the many body Rafii-Tabar and Sutton potential... 

In this study, a coupled numerical approach based on Lattice Boltzmann Method (LBM) and Discrete Element Method (DEM) is employed for 2D simulation of fluid flow in porous media comprising of movable circular particles. The developed model is used for simulation of sand production which is one of the important problems in petroleum industry. The numerical tool has proved to have the capability of investigating the mechanisms involved in sand production problem. The results show that the rate of sand production is strongly affected by flow rate and confining pressure  

In this study, a coupled numerical approach based on Lattice Boltzmann Method (LBM) and Discrete Element Method (DEM) is employed for two-dimensional simulation of fluid flow in deformable particulate media comprising of movable circular particles. The developed LB-DE code is validated against the results of a bi-axial shear test as well as two well-known benchmark problems including settling of a circular particle under gravity force inside a viscous fluid, and motion of a neutrally buoyant particle released in a Poiseuille flow. The verified code is then utilized for simulation of "Sand Production" phenomenon which is of importance for oil producing wells in weakly cemented sandstone... 

Relative permeability curves have practical implications in petroleum reservoir simulations. Study of the effects of reservoir wettability, pore shape geometry, and viscosity ratio of flowing fluids on the relative permeabilities is of great importance in reservoir modeling. In this paper, lattice Boltzmann method (LBM) is employed for analyzing the two-fluid flow in rigid porous media. The developed LBM code proved to be a robust numerical tool for analyzing the factors that influence the relative permeabilities of two immiscible fluids flowing through porous media. The numerically derived relative permeability curves demonstrate that in neutrally wet reservoirs, the effect of viscosity... 

In this paper, Lattice Boltzmann method (LBM) has been used to study the effects of permeability and tortuosity on flow through saturated particulate media and identify the relationships between permeability and tortuosity with other parameters such as particles diameter, grain specific surface, and porosity. LBM is a simple kinematic model that can incorporate the essential physics of microscopic and mesoscopic processes involved in flow through granular soils. The obtained results indicate that the 2D LB model, due to its inherent theoretical advantages, is capable of demonstrating that the porosity and specific surface are the most influential parameters in determining the intrinsic... 

Polymer concrete is well-known for quick repairing of concrete structures and pavement. However, there are relatively few studies on the durability of epoxy polymer concrete (EPC). This study aims to investigate the long-term environmental effects on the mechanical properties of EPC. Therefore, EPC and ordinary cement concrete (OCC) specimens were prepared and exposed to four chemical solutions with pH values of 2.5, 7, 12.5 and artificial seawater in intervals of 1, 3, 6, 9 and 12 months. Epoxy resin (10 and 12% by weight) and Portland cement were used as binder phase in EPC and OCC specimens, respectively. Scanning electron microscopy (SEM) was additionally applied to investigate the... 

Regarding increasing popularity of Ad hoc networks, the routing protocols employed in these networks should be validated before deployment. Formal methods are used nowadays to find defects in protocols specification. In this paper, we explain different methods of formal modeling and verification of routing protocols of ad hoc networks. We derive the key concepts that are vital in modeling ad hoc network protocols and then modify process algebra, appropriate for verifying protocols at network layer. This process algebra implements mobility behaviors of underlying infrastructure implicitly in the semantics of broadcasting. The semantics of broadcast communication also abstracts away the...