Sharif Digital Repository

v.1. Structural engineering and earthquake engineering.-- v.2. Geotechnical engineering.-- v.3. Transportation, civil engineering materials, construction management.-- v.4. Water resources and environmental engineering, surveying and mapping  

This paper proposes a model for a financial assessment of construction companies. This model is derived from the combination of data envelopment analysis (DEA), entropy method (EM), and TOPSIS. In the first step of the model, the financial ratios are calculated based on balance sheets and income statements. In the next step, the 15 ratios are categorized and classified utilizing a combination of TOPSIS and EM methods. Finally, they are aggregated in six indicators. Then, the BCC model of DEA with the type of output-oriented is used for these six indicators to calculate companies' relative efficiency. In the paper's conclusion, the model is examined in 20 construction companies that obtained... 

In this paper an effective numerical technique is presented to model turbulent motion of a standing surface wave in a tank. The equations of motion for turbulent boundary layers at the solid surfaces are coupled with the potential flow in the bulk of the fluid, and a mixed BEM-finite difference technique is used to obtain the wave and boundary layer characteristics. A mixing-length theory is used for turbulence modeling. The results are compared with previous experimental data. Although the technique is presented for a standing surface wave, it can be easily applied to other free surface problems. Copyright © 2008 by ASME  

Responses of human body were studied in two adult age groups. The healthy subjects with no records of falling down or occupation in a crowded and noisy environment were elected. Mean age was 24 and 71 yrs. in young and elderly groups, respectively. Four experimental tasks were presented to subjects. Two involving flat standing with open and closed eyes and two were involving imposed disturbances. Two optoelectronic camera systems were used to measure body motion. The extents of postural sway were determined by processing the recorded data from force plate. The results were compared, and also provided the basis for kinematics analysis of body segments. For dynamic analysis, we used 3-link... 

In this research, new software package for neutronic calculations, especially kinetic parameters of PWR reactors, has been developed. The program used to link the WIMS-D5, BORGES and CITVAP nuclear codes has been written in Visual C# programming language. This software was used for calculation of kinetic parameters of WER-1000 and NOK Beznau reaction The ration (βeff)i/(βeff)corewhich are an important input data for the reactivity accident analysis, were also calculated. The results were compared with final safety analysis report (FSAR) and published documents. Copyright  

The Eulerian methods are susceptible to generate the nonphysical spurious currents in the multiphase flow simulations near the interfaces. This paper presents a new Eulerian method to accurately simulate the velocity fields, especially near the multiphase flow interfaces and prevents the numerical results from generating the nonphysical currents. A Eulerian central difference finite-volume scheme equipped with the suitable numerical dissipation terms is used to simulate incompressible multiphase flows. The interface is captured by Flux Corrected Transport-Volume of Fluid method (FCT-VOF). Increasing the accuracy near the sharp gradients, such as interface, the conservative form of... 

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... 

Several investigators worked on various aspects of tensile behavior of concrete because of its wide usage in structural design. One of the observable phenomena during tensile failure of concrete is strain softening, i.e. a negative slope in the stress-deformation diagrams. There are many kinds of experiment-based softening curves for concrete. In current research, use of newly introduced concept of fractal geometry and a failure model yields to a new softening curve for concrete. This new curve is denominated "Quasi-fractal" softening curve, which is a theorybased softening model. Comparison of Quasi-fractal softening curve with a set of proposed experimental softening curves has been... 

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... 

In this paper the framework for a constitutive model which is developed for a cemented gravely sand is presented. The model is based on separation technic namely the separation of the behavior to the uncemented soil and the cemented bonds. They are combined in a manner to satisfy the deformation consistency and energy equilibrium equations. The uncemented soil behavior is modeled using a modified model originally proposed by Pastor et al. (1985) for sandy soils. Also, based on the results of the experiments, a new model for the bonds is developed. Combination of these two parts results in the modeling of the behavior of cemented gravely soils in drained and undrained states  

This paper presented a numerical study that predicts critical mass flow rate, pressure, vapor quality, and void fraction along a very long tube with small diameter or capillary tub under critical condition by the drift flux model. Capillary tubes are simple expansion devices and are necessary to design and optimization of refrigeration systems. Using dimensional analysis by Buckingham's π theory, some generalized correlations are proposed for prediction of flow parameters as functions of flow properties and tube sizes under various critical conditions. This study is performed under the inlet pressure in the range of 0.8 ≤ pin ≤ 1.5Mpa, subcooling temperature between 0 ≤ ΔTsub ≤10 °C. The... 

In this research, a functionally graded microbeam bonded with piezoelectric layers is analyzed under electric force. Static and dynamic instability due to the electric actuation is studied because of its importance in micro electro mechanical systems, especially in micro switches. In order to prevent pull-in instability, two piezoelectric layers are used as sensor and actuator. A current amplifier is used to supply input voltage of the actuator from the output of the sensor layer. Using Hamilton's principle and Euler-Bernoulli theory, equation of motion of the system is obtained. It is shown that the load type (distributed or concentrated) applied to the microbeam from the piezoelectric... 

Derailment of a passenger wagon on a rail with random irregularities is investigated in this paper. The wagon having 48 degrees of freedom is assumed to travel over a rail on a viscoelastic foundation. The wagon model is a 3-D, non-linear model of a passenger train car, considering non-linear elements for the primary and secondary suspension systems having friction and slack between their elements, the center pivot with kinematics constraints, forces between pads, and bolster. The motion of the wagon on rail with random vertical irregularities is simulated for different line grades and travel speeds. Derailment coefficient and a new derailment criterion are used to investigate probability of... 

In this paper, localization of a noise source from limited neutron detectors sparsely distributed throughout the core of a typical VVER-1000 reactor is investigated. For this purpose, developing a 2-D neutron noise simulator for hexagonal geometries based on the 2-group diffusion approximation, the reactor dynamic transfer function is calculated. The boxscheme finite difference method is first developed for hexagonal geometries, to be used for spatial discretisation of both 2-D 2-group static and noise diffusion equations. The dynamic state is assumed in the frequency domain which leads to discarding of the time disrcetisation. The developed 2-D 2- group neutron noise simulator calculates... 

Derailment of a passenger wagon on a rail with random irregularities is investigated in this paper. The wagon having 48 degrees of freedom is assumed to travel over a rail on a viscoelastic foundation. The wagon model is a 3-D, non-linear model of a passenger train car, considering non-linear elements for the primary and secondary suspension systems having friction and slack between their elements, the center pivot with kinematics constraints, forces between pads, and bolster. The motion of the wagon on rail with random vertical irregularities is simulated for different line grades and travel speeds. Derailment coefficient and a new derailment criterion are used to investigate probability of... 

The flow and spray parameters can have noticeable roles in heavy fuel oil (HFO) spray finesse. As known, the interaction between droplets and cross flow should be considered carefully in many different industrial applications such as the process burners and gas turbine combustors. So, it would be so important to investigate the effect of injecting HFO into a crossflow more subtly. In this work, the effects of various flow and spray parameters on the droplet breakup and dispersion parameters are investigated numerically using the finite-volume-element method. The numerical method consists of a number of different models to predict the droplets breakup and their dispersion into a cross flow... 

The present study tries to investigate the impact of different speed limits value in the severity of accidents. For this reason, head-on accidents on rural roads have been investigated. Speed limitations in different types of rural roads including inter-state rural arterials, major rural arterials, minor rural arterials, rural main collectors, rural minor collectors, rural local roads or streets in two cases, two-lane and four-lane roadways will be examined individually. The artificial neural network is trained based on the severity of the injuries of drivers of both vehicles involved in head-on accidents. The descriptive variables used in addition to the speed limit include age and gender... 

The diffusion phenomenon has a remarkable impact on Online Social Networks (OSNs). Gathering diffusion data over these large networks encounters many challenges which can be alleviated by adopting a suitable sampling approach. The contributions of this paper is twofold. First we study the sampling approaches over diffusion networks, and for the first time, classify these approaches into two categories, (1) Structure-based Sampling (SBS), and (2) Diffusion-based Sampling (DBS). The dependency of the former approach to topological features of the network, and unavailability of real diffusion paths in the latter, converts the problem of choosing an appropriate sampling approach to a trade-off.... 

This paper presents a new approach for fuel burn up evaluation and radioactive inventory calculation used in Tehran Research Reactor. The approach is essentially based upon the utilization of a program written by C# which integrates the cell and core calculation codes, i.e., WIMSD-4 and CITVAP, respectively. Calculation of fuel burn up and radioactive inventories has been done for 26 core configuration of Tehran Research Reactor with HEU fuel element. The present inventory and fuel enrichment of each fuel element have been calculated  

The entropy generation rate has become a useful tool for evaluating the intrinsic irreversibilities associated with a given process or device. This work presents an analytical solution for entropy generation in hydrodynamically fully developed thermally developing laminar flow in a microtube. The rarefaction effects as well as viscous heating effects are taken into consideration, but axial conduction is neglected. Using fully developed velocity profile, the energy equation is solved by means of integral transform. The solution is validated by comparing the local Nusselt numbers against existing literature data. From the results it is realized that the entropy generation decreases as Knudsen...