Sharif Digital Repository

One of the major problems in directional and extended reach wells is poor hole cleaning. Directional and horizontal drilling is more complex than vertical wells. Ineffective particles transport leads to several undesirable issues during drilling. This thesis analyzed all parameters which have directly affected directional hole cleaning. The thesis is based on an experimental set-up designed in Sharif University. In the experimental work, two types of drilling fluid, Newtonian and Non-Newtonian with numerous rheological parameters, three different flow rate, three various nozzle sizes and three individual RPMs in three distinct inclinations 30°, 60° and 90° were used to simulate. Also, to... 

During the past two decades, laminated composite structures have been used for many engineering applications, including aerospace, automotive, sport equipment and pressure vessels.
In spite of the excellent properties of strength to weight ratio, composite structures are vulnerable to failure when subjected to impact and vibration. It is well known that impact damage may severely degrade the strength and stability of laminated composite structures. For this reason the effect of impact on composites has been a subject of extensive research.
There are several ways of decreasing the vibration energy of structures, such as diminishing the source energy, designing structures... 

Vibration is one of the most important factors in design, operation and lifetime of drill string. Evaluation of vibration in the drill string like other rotating machines is very important and according to the length of drill string, whirling is one of the issues discussed. The aim of this thesis is non-linear analysis of the oblique long drill string. By considering the effects of passing drill mud around drill as well as properties of the drilling mud and stick - slip effect in creating whirling. Therefore, the equations related to kinetic and potential energy of a rotating drill string by taking longitudinal and transverse vibrations are written and by using the Lagrange method, equations... 

In this thesis its considered the characterization of an ultrasound wave in a medium with some obstacles. Derivation of speed of molecules and pressure of the wave is carried out in the Cartesian coordinates system. Simulation is carried out to prove the dependency of wave speed to set up parameters such as the target point (x,y,z) at which the speed value is obtained, the location of the obstacles, the amplitude of original wave emitting from the source, and the propagation speed in different layers of the medium. From the numerical results, it is apparent that the amplitude of the speed wave gets degraded as the wave travels through the medium which is a function of reflection and... 

To study the structure of materials, among materials containing hydrogen, an instrument called the "small-angle neutron scattering instrument" is used. Having a monochromatic neutron beam is the most basic component of this instrument. This beam is often produced using a device called the "neutron velocity selector". The neutron velocity selector is a rotating mechanical piece that allows for passage of neutrons at a certain speed, according to its rotational speed. In fact, this device produces a monochromatic neutron beam with continuous flux. Until now, it has been designed and manufactured in a variety of models, which are generally divided into two groups of multi-disc and multi-blade... 

Dispersed phase holdup has been measured in a 75 mm diameter pulsed disc and doughnut extraction column for three different liquid-liquid systems. The effects of operational variables such as pulsation intensity and dispersed and continuous phases flow rates on holdup have been investigated and found to be significant. The existence of three different operational regimes, namely mixer-settler, dispersion, and emulsion regimes, was observed when the energy input was changed. The results indicated that the characteristic velocity approach is applicable to this type of extraction column for analysis holdup in transition and emulsion regions. Empirical correlations are derived for prediction of... 

Multi-part rotating parts are used in various industries with very high revolutions. Therefore, the method of assembling each part and keeping the axis of rotation of each part close to the axis passing through two supports (bearings) is important. In this research, three main steps are followed, the development of the differential equations governing the multi-part rotating system and the calculation of the range of oscillations created at the critical points, and then the calculation of the optimal assembly angles with the aim of reducing the introduced oscillations, and finally the discussion of crossing the speeds A crisis is being investigated. The method of obtaining the system of... 

During the last 5 decades, the operation of scramjet engines has not been without limitations and technical challenges; i.e., the start-up speed of the engine. Conventional scramjet engines do not have the ability to start from a standstill and even at a flight Mach lower than 5. Therefore, reducing the start-up speed of the scramjet engine is not only very attractive in terms of operation but it will also reduce many technical challenges. The purpose of this research is to identify and analyze the flight speed to start the scramjet engine and the requirements to achieve it. In this regard, first by examining the quasi-one-dimensional equations of gas dynamics, the effect of the static... 

The velocity of the hot outflow gas in laminar premixed flame is one of the important properties of combustion, along with other properties such as temperature and flame components. In fact, laminar flame velocity has been employed in a multitude number of concepts ranging from engine design to achieving flame properties under turbulent conditions. In this research, a cylindrical Bunsen burner and appropriate TIO2 particles were used. Particles with diameters between 10-23 microns were used and the exit diameter of burner considered 14 mm. In this study, the equivalence ratio with a value between 0.9-1.2 are fed with LPG fuel to create a laminar premixed flame. As a result of the present... 

The purpose of this study is to establish a lateral-torsional-axial dynamic model for spur and helical geared rotor systems subject to shaft bow manufacturing error. Timoshinko shaft element, elastic bearings and rigid disks used to simulate different element in the model. Tooth contacts is modeled with linear spring and damper along the pressure line.Results show that the vibration pattern of the unbalanced load and shaft bow effect is different. These obtained patterns might help with the fault diagnostics of rotating machinery. The vibration will be lowest if the unbalanced load and the shaft bow amplitude locates out of phase. The previous researches show that different pattern of the... 

Various public transportation types, e.g., Trains, Buses, and Airplanes, are susceptible to damages made by the impacts of the external objects, which are typically classified as low to medium velocity impacts. This problem reveals the significance of investigating the effects of impact on thin-walled structures, which are the main components of these vehicles' bodies. Owing to the controllable rheological properties of the Magnetorheological fluid with respect to the magnetic field, it can be utilized to control the structure exposed to impact adaptively and minimize the damages. Due to this purpose, sandwich structures such as sandwich beams and plates, thanks to their extended response... 

In this thesis an analytical model is applied to the dynamic response of fiber-metal laminate beams subjected to low-velocity impact. By using quasi-static consider-tions, a static model is developed using first order shear deformation beam theory and minimum total potential energy. In the next step, this static model is applied to the one degree of freedom non-linear spring-mass system for developing a model to predict dynamic response of low-velocity impact with the inclusion of material plasticity. By new explicit and simple expression, load-deflection curve, velocity-deflection curve, force-time history and deflection-time history can be derived. By using this analytical approach... 

Bubble cluster has attracted the interests of many researches since the early twentieth century. Despite its easy generation and numerous occurrences, its study is extremely complex. Describing the dynamical behavior of bubble clusters is possible when quite a few simplifying assumptions are utilized. In other words, one can observe that with current approaches, the relevant theoretical researches are not very valuable. In this research, however, lattice Boltzmann method, a rather recent mesoscopic approach, was used to study the behavior of bubbles in a bubble cluster. Of course, this is only the beginning and there is a long way before getting close to experimental results. However, there... 

The main purpose of this study is the analysis of low velocity impact on the light weight sandwich beams. Some parameters such as weight, failure mode, and impact energy absorption capability are very essential in the design of sandwich beams. The failure mode map is a technique to design sandwich structures, in which no single component is over-designed with respect to other components. In this study, the failure mode map of foam core sandwich beams composed of E-glass/Epoxy and PVC foam is drawn and investigated by an analytical method. For this purpose, displacement relations for bending of a sandwich beam are written using higher order theory. In addition, the sandwich beam is modeled... 

In this thesis, fuzzy logic is used to suggest a simple algorithm in guidance and control suitable for upper stage decoupler transfer with finite and continuous thrust. It is attempted to improve injection accuracy utilizing classic guidance and control methods and fuzzy logic, while unpredictable errors exist. Orbital perturbations, uncertainties in thrust vector, and initial injection errors in parking orbit, are considered in order to actualize results. In this research, Lambert guidance, velocity to be gained, and fuzzy logics are used for upper stage guidance. Fuzzy-PD control is designed and applied into the upper stage. Final results show acceptable position errors and suitable fuel... 

In this thesis, vibration analysis of multi-walled carbon nanoconesstudied by molecular mechanics approach. In this simulation, atoms of carbon and bondings of them modeled by concentrated mass and structural elements, respectively and then mode shapes and natural frequencies of these structures calculated and effects of height, apex angle, boundary conditions and number of layers on natural frequencies of carbon nanocones studied. Also, critical buckling load of multi-walled carbon nanocones due to axial and in-plane loads obtained and effects of height, apex angle and number of layers on critical buckling loads of carbon nanocones studied. These results validated by molecular dynamics and... 

In this thesis, maneuverability enhancement of a given twin engine fighter aircraft with integrated thrust-vector and conventional aerodynamic control surfaces havebeen studied. For this purpose a nonlinear 6DOF simulation program base on a near exact mathematical model has been prepared for the aircraft, and then a thrust vectoring system for producing moments about three body axes, like that used in F/A-18, has been added to the simulation. The control method that is employed to control the aircraft in simulation environment is based on Nonlinear Dynamic Inversion (NDI). Finally the Velocity Vector Roll (VVR) maneuver has been considered as an example tostudymaneuverability enhacement. It... 

In the present study, the numerical simulation of the compressible inviscid flow around helicopter rotor is performed using the solution of the preconditioned Euler equations. Three preconditioners proposed by Eriksson, Choi and Merkel, and Turkel are implemented in two- and three-dimensional upwind Euler flow solvers on unstructured meshes. The mathematical formulations of these preconditioning schemes for different sets of primitive variables are drawn and their eigenvalues and eigenvectors are compared with each others. For this aim, these preconditioning schemes are expressed in a unified formulation. A cell-centered finite volume Roe's upwind method is used for the discretization of the... 

The environmental friendliness and sustainable development of rammed earth structures has attracted the attention of numerous researchers in recent years. Obviously, a better understanding of the structural and mechanical performance of rammed earth is the way to use rammed earth as a sustainable building material. Structural fire safety is one of the primary considerations in the design of structures. Several experiments and investigations had been conducted to investigate the behavior of materials at high temperatures. Base on author knowledge at present, few studies are available on thermomechanical properties of earthen construction materials at temperatures higher than 100°C and even... 

In recent decades, particle composite materials have a wide range of applications in engineering. Particle composites are a group of heterogeneous materials with different length scales and are characterized by particles that are randomly distributed in a matrix phase. Geopolymer concrete is a special type of concrete that its binder is made by reacting alumina and silicate carriers with an activating agent and in recent years with the expansion of its use has reduced the amount of cement consumption. In addition to the many advantages of geopolymer concrete, it has disadvantages in terms of setting time. That is why the use of cement has been proposed as a solution to the problem. This...