Sharif Digital Repository

Ultrasonic assisted machining (UAM) is an efficient nontraditional machining operation for brittle, hard-to-cut and poor-machinability materials. In UAM, high frequency oscillation in ultrasonic range at low amplitude is imposed on the workpiece or cutting tool. In most cases, the equipments that generates and transfers the vibration, have a complicated structure, and requires significant effort to achieve their optimum function. In this work, a mathematical model is developed and an optimization method is employed for design process. This makes it possible to achieve proper setup and reduce the amount of calculation. For this purpose, the combination of a two level full factorial design is... 

The dynamic response analysis of a delaminated composite beam with a general lay-up traversed under an arbitrary moving/non-moving force is presented. By employing the energy method and introducing a new finite element, the global mass and stiffness matrices for a Laminated Composite Beam (LCB) of Timoshenko type are derived in which the material couplings (bending-tension, bending-twist, and tension-twist couplings) with the Poisson's effect are considered. In deriving the governing equation the non-penetration condition is imposed by employing the method of Lagrange multipliers. Out of a self-developed finite element program, the natural frequencies and time response of such LCB are... 

This paper presents the results of an experimental study on the flexural behavior of ten 10 × 15 × 120 (cm) steel reinforced high strength concrete beams under deflection control loading conditions. Test variable includes volumetric percentage of steel fibers (0%, 1.5%, 3%, 4%, 5%). The plain concrete strength was 30MPa. The monotonic concentrated load was applied at the center of the beam, the relative deflection was measured, and demec points were used to determine curvature of the beam. Load-deflection and moment-curvature diagrams have been obtained and plotted for each beam individually. Test results indicate that higher fiber content considerably improves flexural behavior and provides... 

A new strategy for enhancing the efficiency and reducing the production cost of TiO 2 solar cells by design of a new formulated TiO 2 paste with tailored crystal structure and morphology is reported. The conventional three- or four-fold layer deposition process was eliminated and replaced by a single layer deposition of TiO 2 compound. Different TiO 2 pastes with various crystal structures, morphologies and crystallite sizes were prepared by an aqueous particulate sol-gel process. Based on simultaneous differential thermal (SDT) analysis the minimum annealing temperature to obtain organic-free TiO 2 paste was determined at 400°C, being one of the lowest crystallization temperatures of TiO 2... 

In this paper, application of a new dynamic procedure called Endurance Time (ET) method in seismic analysis of steel frames is explained. In this method, structures are subjected to gradually intensifying ground shaking and their performance is assessed based on their response considering relevant design criteria at each intensity level. By considerably reducing the number of time history analyses for assessment of structural response at different intensities, this procedure tends to pave a way for practical performance based design of structures. The accuracy of ET method in predicting the response of structures in linear and nonlinear analysis is investigated by considering a set of steel... 

The endurance time (ET) method is a time history based dynamic analysis in which structures are subjected to gradually intensifying excitations and their performances are judged based on their responses at various excitation levels. Using this method, the computational effort required for estimating probable seismic demand parameters can be reduced by an order of magnitude. Calculation of the maximum displacement or target displacement is a basic requirement for estimating performance based on structural design. The purpose of this paper is to compare the results of the nonlinear ET method with the nonlinear static pushover (NSP) method of FEMA 356 by evaluating performances and target... 

Stepped spillways have been widely used in Roller Compacted Concrete (RCC) dams in the recent decades. Considering complexity of hydraulics of stepped chutes, their initial design involves pre-selection of some empirical formulae for calculation of flow characteristics and design parameters. In this paper, accuracy of several empirical formulae, proposed for calculating locations of aeration inception (LI), uniform flow (Lu) and rate of energy dissipation (ΔH/Hmax), were compared in relation to results of physical model tests of four stepped spillways and the preferred formulae, providing least amounts of relative errors, were identified. Such a feedback will be helpful for improvement of... 

Pozzolanic materials, either naturally occurring or artificially made, have long been in practice since the early civilization. In recent years, the utilisation of pozzolanic materials in concrete construction has become increasingly widespread, and this trend is expected to continue in the years ahead because of technological, economical and ecological advantages of the materials. One of the latest additions to the ash family is palm oil fuel ash, a waste material obtained on burning of palm oil husk and palm kernel shell as fuel in palm oil mill boilers, which has been identified as a good pozzolanic material. This paper highlights test results on the performance behavior of palm oil fuel... 

This study is about the performance assessment of steel moment resisting frame structures under nearfield strong ground motions. A number of 3 and 9-story, 3-D structural models being designed using the strength method, are considered. A set of 7 near-field earthquake records, scaled according to ASCE- 7(05), are considered for nonlinear dynamic time history analyses using OpenSees program. Park and Ang damage index is considered for quantitative measurement of the performance of structural models. Maximum values of inter-story drifts along with the local and global damage indices are determined to be used in the performance assessment process. Considering the average results of different... 

Earned value project management is a well-known management system that integrates cost, schedule and technical performance. It allows the calculation of cost and schedule variances and performance indices and forecasts the project cost and schedule duration. The Earned Value concept was conceived by industrial engineers working in American factories over a century ago. This concept improved by the time and in July 1998, the Earned Value Management System became the American National Standards Institute (ANSI/EIA) Standard #748. By concise reports derived from using Earned Value Method (EVM) in the project, the manager is able to have exact information about the project details and also can... 

In the present work, an unsymmetric laminated plate with surface bonded piezoelectric sensors, and actuators has been considered. Piezoelectric sensor were used to monitor the load and deformation bifurcation occurs. Monitoring the shape and load of a morphing structure is essential to ascertain that the structure is properly deployed and it is not loaded excessively, thus, preventing structural to failure. A piezoceramic actuator is used to provide activation load and to force the structure to change its stability state from one to another. A non-linear finite element model based on the layerwise displacement theory considering the electro-mechanical coupling effects of piezoelectric... 

One of the main challenges in earthquake risk mitigation nowadays is the seismic performance assessment of existing buildings that were not designed according to modern building code standards and the development of effective techniques to retrofit these structures. In this paper seismic performance of an existing 5-story RC frame building which is typical building stock in central region of Tehran retrofitted by three methods (Concrete jacketing, Steel jacketing, CFRP wrapping) is investigated by developing fragility curves. Corresponding Fragility curves are constructed for three structural damage limit states, collapse prevention (CP), Life Safety (LS) and immediate occupancy (IO) and... 

This paper presents the results of an experimental study on the behavior of concrete cylinders externally wrapped with fiber-reinforced polymer (FRP) composites and internally reinforced with steel spirals. The experimental work was performed by testing 30 concrete cylinders (120 × 400mm2) subjected to pure compression to achieve the complete stress-strain curve. Test specimens were confined with various internal and external confinement ratios and different types of confining material such as steel, Carbon FRP (CFRP) and Glass FRP (GFRP). The compressive strength, corresponding strain and the complete stress-strain curve of the tested specimenswere indicated. The test results showthat the... 

The current study aims at introducing a 2D and fast-running code for the issues pertinent to design, analysis and safety in modular high temperature reactors. While the porous media approach is only applied to pebble bed type, the analysis in this paper covers both pebble bed and prismatic reactor. A time-dependent mass equation along with energy conservation equation for the cooling gas and a time-dependent energy conservation equation for the solid was solved. Appropriate series of constitutive equations (e.g. heat transfer coefficient, effective heat conductivity of solid, heat transfer coefficient, pressure drop etc.) has been recruited as well. In addition a finite-volume method is... 

Integral abutment bridges have many advantages over bridges with expansion joints in terms of economy and maintenance costs. However, in the design of abutments of integral bridges temperature loads play a crucial role. In addition, seismic loads are readily transferred to the substructure and affect the design of these components significantly. Currently, the European and American bridge design codes consider these two load cases separately in their recommended design load combinations. In this paper, the importance and necessity of combining the thermal and seismic loads is investigated for integral bridges. A 2D finite element combined pile-soil-structure interactive model is used in this... 

All the star trackers must be composed of a baffle system to removes stray lights intensity. The baffle is designed to mount in front of the optical system. The performance of a star tracker is often limited by the stray light level on the detector. According to the space conditions, the baffle may deflect due to the temperature variation during the mission. Sun heat flux imposed to the baffle from one side and heat radiates from baffle to the space in all sides. In our case, the baffle is fixed to the satellite structure by four titanium screw. A finite element model has been used to modeling the baffle and temperature distribution and deflection is obtained in worst cold and hot... 

Performance of a haptic device is evaluated based on the concept of transparency which indicates the match between the impedance transmitted to the user and the target virtual impedance. Stability of a haptic device prevalently has been evaluated based on the passivity criterion. Due to conservativeness of passivity, it appears as an obstacle to improve transparency. In this paper, passivity is suggested to be replaced by the complementary stability criterion which accounts for the robust stability of the interaction in the presence of uncertain user hand dynamics In this respect, an algorithm is proposed which guarantees transparency of the haptic device in a stable manner. Assuming that... 

Molecular dynamics simulations are used to study the assembly of metallic nanoclusters using manipulation process. These particles are assumed as potential building blocks for bottom-up manufacturing of nanoscale structures. One of the key factors in the assembly of nanoclusters is their precise positioning by a manipulation system. Prediction of the corresponding behavior under the influence of working conditions is of crucial importance for planning of controlled positioning and assembly of nanoclusters. The focus of the present research is on ultra-fine metallic nanoclusters. The effects of material type and manipulation strategy on the success of the process are investigated by molecular... 

Today's information technology capabilities enable the enterprises to increase the manufacturing collaboration and interoperability among their different departments. These departments are engaged in different product development processes from design to manufacturing. INFELT STEP is a three-layered platform. These layers have functions and structures that enable the INFELT STEP platform to manage the product development collaboration among different CAD/CAM application software with an integrated product data structure. INFELT STEP has structures and functions in its interoperability layer that enable different CAD/CAM application software and CNC post processors to use their own data... 

Flapping wings are promising lift and thrust generators, especially for very low Reynolds numbers. To investigate aeroelastic effects of flexible wings (specifically, wing's twisting stiffness) on hovering and cruising aerodynamic performance, a flapping-wing system and an experimental setup were designed and built. This system measures the unsteady aerodynamic and inertial forces, power usage, and angular speed of the flapping wing motion for different flapping frequencies and for various wings with different chordwise flexibility. Aerodynamic performance of the vehicle for both no wind (hovering) and cruise condition was investigated. Results show how elastic deformations caused by...