Sharif Digital Repository

Because of errors in the geometric parameters of parallel robots, it is necessary to calibrate them to improve the positioning accuracy for accurate task performance. Traditionally, to perform system calibration, one needs to measure a number of robot poses using an external measuring device. However, this process is often time-consuming, expensive and difficult for robot on-line calibration. In this paper, a methodical way of calibration of parallel robots is introduced. This method is performable only by measuring joint variable vector and positioning differences relative to a constant position in some sets of configurations that the desired positions in each set are fixed, but the moving... 

Most of the heavy oil reservoirs contain discontinuous shale which affects fluid flow through porous media as well as recovery efficiency during enhanced oil recovery processes. However, the role of shale geometrical characteristics (including orientation, length, discontinuity, and spacing of the shale) on oil recovery remains a topic of debate in the literature, especially during miscible injection of heavy oils and five-spot systems. Here, a series of hydrocarbon solvent injection tests have been performed on various five-spot glass micromodels containing barriers which are initially saturated with heavy oil under fixed flow rate conditions. Oil recoveries as a function of pore volumes of... 

Petroleum production often involves simultaneous flow of three immiscible fluids through underground porous rock formation. In this work, we measure two- and three-phase relative permeabilities with which we examine the performance of various 3-phase relative permeability models. The rock-fluid systems used in these measurements are comprised of sandstone samples, oil (n-decane), water (Nacl, 6000. ppm) and gas (nitrogen). The measurements were carried out at 23 ± 1 °C and 5.44 MPa. Two- and three-phase relative permeability measurements were obtained using the steady-state technique. The three-phase experiments were conducted such that the flow rates of brine and gas were increased... 

During any microbial enhanced oil recovery process, both cells and the metabolic products of bacteria govern the tertiary oil recovery efficiency. However, very accurate examination is needed to find the functionality of these tiny creatures at different reservoir conditions. In this regard, the effect of cell structure on ultimate microbial recovery efficiency which is the most dominant mechanism based on the microorganism types (gram-negative or gram-positive) was systematically investigated. At the first stage, possible different active mechanisms using Bacillus stearothermophilus SUCPM#14 strain were tested using specially designed injection protocol, in situ and ex situ core flooding... 

The blade element momentum (BEM) theory is based on the actuator disc (AD) model, which is probably the oldest analytical tool for analysing rotor performance. The BEM codes have very short processing times and high reliability. The problems of the analytical codes are well known to the researchers: the impossibility of describing inside the one-dimensional code the three-dimensional (3D) radial flows along the span-wise direction. In this work, the authors show how the 3D centrifugal pumping affects the BEM calculations of a wind turbine rotor. Actually to ascertain the accuracy of the analytical codes, the results are compared with rotor performance, blade loads and particle image... 

Mixed-convection flow of nanofluids inside a vertical rectangular channel partially filled with open-cell metal foam and subject to a constant wall-heat flux was investigated experimentally and numerically. Al2O3-water nanofluids with different concentrations were prepared and their stability was examined using UV-Vis spectroscopy. Dynamic light scattering method was used to determine particle size distribution of the nanofluid feedstock. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature... 

The inflow pattern of liquid into a droplet is studied experimentally using a surface active dye and compared with results of CFD simulations. The results show visual agreement between experiments and simulations. The CFD simulations show also good agreement with the surface tension measured by drop profile analysis tensiometry (PAT). The inflow of the surfactant induces a Marangoni instability caused by the local arrival of the surfactant at the drop surface. The onset of this Marangoni instability observed experimentally has a delay of about 10. s when compared with the simulation results. Different scenarios are discussed, including a boundary layer barrier, a kinetic-controlled... 

Using gas-liquid lifting pumps is a quite different technology for pumping two or three phase flows rather than other types of pumping systems. Therefore, finding performance characteristic chart for this type of pumping system seems to be necessary. In this type of pumping system, the liquid phase is pushed upward by the compressed air which has been injected in the bottom of upriser pipe of the pump. Therefore, compressed air acts as the driving force in gas lifting pumps instead of moving parts in ordinary pumps. It can be concluded that the definition of characteristic curve used for ordinary pump is not very appropriate for this type of pumping system. In this study, it has been... 

In common catamaran vessels, demihulls are parallel to each other. In this paper, the total resistance of a catamaran vessel with non-parallel demihulls is investigated experimentally and numerically. Experiments are carried out at different Separation Ratios (S.R.), that is the ratio of fore to aft separation of the catamaran demihullsand also in two ratios of length to separation in amidships (L/Sm). The FLUENT solver, based on the Finite Volume Method (FVM), was used for numerical solution. Applying the VOF model, the free surface around the catamaran vessel and total resistance are calculated and compared with experimental results. Finally, the frictional resistance of the catamaran from... 

Identification and minimization of error sources are important issues in experimental investigations. Mainly in micro-scale problems, precise settings should be applied to high-tech test beds to reduce disturbance and induced motion. An experimental study is conducted to assess the role of induced forces and velocity fields in a particulate system used for particle identification and separation. Two main effects caused by disturbances are sampling errors and induced motion in the channel, either on fluid or dispersed phases. Different disturbance scenarios are implemented on the test bed and then the system response is reported. In order to assess induced motion as a result of applied... 

Fatigue life and crack growth retardation due to periodic tensile overloads, which are superposed on constant amplitude cycles, have been investigated in the present study. In the numerical analyses, the Walker equation with the generalized Willenborg model has been used. The analyses and experiments have been performed on C(T) specimens made of 7075 aluminium. The periodic overloads have been induced at two different periodicities and the effect of overload ratio and overload periodicity on the fatigue life has been studied. The results of the experiments and analyses reveal that the normalized fatigue life versus overload ratio curve has a maximum point, which indicates that there are... 

A damage plastic constitutive model for metals is proposed in this paper. An anisotropic damage tensor and a damage surface are adopted to describe the degradation of the mechanical properties of metals. The model is developed within the thermodynamic framework and creates an anisotropic damage plastic model with the ability to describe the plastic and damage behavior of iron based materials. According to the principle of strain energy equivalence between the undamaged and damaged materials, the linear elastic constitutive equations for the damaged material expressed a stiffness tensor in the damaged configuration. The damaged material is modeled using the constitutive laws of the undamaged... 

Background: In the recent study, optimum operational conditions of cathode compartment of microbial fuel cell were determined by using Response Surface Methodology (RSM) with a central composite design to maximize power density and COD removal. Methods: The interactive effects of parameters such as, pH, buffer concentration and ionic strength on power density and COD removal were evaluated in two-chamber microbial batch-mode fuel cell. Results: Power density and COD removal for optimal conditions (pH of 6.75, buffer concentration of 0.177 M and ionic strength of cathode chamber of 4.69 mM) improve by 17 and 5%, respectively, in comparison with normal conditions (pH of 7, buffer concentration... 

This work represents the efficiency of a solar desalination pond as a second stage of proposed zero discharge desalination processes to reach fresh water and also concentrated brine from the effluent wastewater of the desalination unit of Mobin petrochemical complex. So a solar desalination pond is constructed after a pretreatment unit to concentrate the softened wastewater to about 20wt%. The concentrated wastewater is as a suited feed for a forced circulation crystallizer. During one year, the effects of major parameters such as ambient temperature and solar insolation rate are investigated, experimentally. specific gravity in each layer of concentrated brine wastewater is evaluated. Also,... 

A rectangular labyrinth weir has a very good flood release capacity as well as strong economical and structural advantages. In this study, combined analytical and experimental investigations were undertaken for a rectangular labyrinth weir. The analytical model is based on the synthesis of general weir equations and spatially varied flow dynamic equations. A comprehensive set of experiments led to characterisation of the flow behaviour for low and high heads over the weir and indicated the influences of weir geometry on the release capacity. The results show that this type of weir represents an effective weir alternative and could be five times more efficient than a corresponding traditional... 

The overall design of cold gas propulsion systems is pretty complicated when considering the mission requirements, operating constraints and functional limitations imposed by the mechanical components. To address this complication, a precise design process is proposed, which attempts to optimize the cost of operation as well as to minimize the waste volume and weight by using multi-objective trade-off analysis. This analysis is based on a set of ordinary differential equations that are solved iteratively to describe the optimal behavior of the system. Therefore, a numerical code is being developed to give insight on the design sensitivity with respect to uncertainties on the design... 

Optical separation, which is a contactless and accurate technique, has been mostly used to manipulate single particles. This work mainly aims to present an effective technique for optical propulsion and separation of a group of microscopic particles that are suspended in liquids. An experimental study is conducted to assess the effect of radiation pressure of a high-power laser on a dilute dispersion of microparticles in water using microscopic image analysis. Results of separation experiments indicate that the manipulation mechanism is capable of sorting the microscopic particles in two size classes. Compared to common optical separators, this configuration has a benefit of separating many... 

Finesmigration is a noticeable problem in petroleum-production engineering. Plugging of throats in porous media occurs because of detachment of fine particles from sand surfaces. Thus, the study of interactions between fines and pore surfaces and the investigation of governing forces are important factors to consider when describing the mechanism of the fines-release process. The main types of these forces are electric double-layer repulsion (DLR) and London-van der Waals attraction (LVA). It may be possible to alter these forces with nanoparticles (NPs) as surface coatings. In comparison with repulsion forces, NPs increase the effect of attraction forces. In this paper, we present new... 

Reduction in ship resistance, in order to decrease fuel consumption and also achieve higher speeds, has been the topic of major research over the last three decades. One of the most attractive ideas in this field is micro bubble drag reduction, which attempts to obtain optimum injection flow rate based on ship specifications. The model test results of a 70 cm catamaran model was used to quantify the effect of air injection rate on drag reduction, and to estimate a simple formulation for calculating an efficient injection rate by considering the main parameters of the ship, such as: length, width and speed. The test results show that excessive air injection decreases the drag reduction... 

Wind tunnel experiments were conducted to evaluate surface pressure distribution over a semi span swept wing with a sweep angle of 33°. The wing section has a laminar flow airfoil similar to that of the NACA 6-series. The tests were conducted at speeds ranging from 50 to 70 m/s with and without surface roughness. Surface static pressure was measured on the wing upper surface at three different chordwise rows located at the inboard, middle, and outboard stations. The differences between pressure distributions on the three sections of the wing were studied and the experimental results showed that roughness elements do not influence the pressure distribution significantly, except at the inboard...