Sharif Digital Repository

This paper presents the results of an experimental study on the application of strapping technique for retrofit of concrete compressive specimens. In this technique, standard strapping devices, which are used in the packaging industry, are applied to post-tension high strength metal strips around the concrete columns. Experimental program included axial compressive tests on 72 cylindrical and prismatic compressive specimens, which were actively confined by pre-stressed metal strips. The effects of various parameters on strength and ductility of confined concrete were studied including compressive strength of concrete, mechanical volumetric ratio of confining strips, post-tensioning force in... 

This paper presents the results of experimental and analytical study on a new technique of seismic retrofitting of concrete columns. In this technique, standard strapping devices, which are used in the packaging industry, are used to post-tension metal strips around concrete columns. The two ends of the strip are tightened in sealed clamps to maintain the pre-stress force in the strip. Experimental program included axial compressive tests on 30 cylindrical as well as 30 prismatic small-scale columns which were actively confined by pre-stressed metal strips. Longitudinal and lateral strain of concrete and strain in the strips were monitored. Test Results showed significant increase in... 

Cooperative cloud providers in the form of cloud federations can potentially reduce their energy costs by exploiting electricity price fluctuations across different locations. In this environment, on the one hand, the electricity price has a significant influence on the federations formed, and, thus, on the profit earned by the cloud providers, and on the other hand, the cloud cooperation has an inevitable impact on the performance of the smart grid. In this regard, the interaction between independent cloud providers and the smart grid is modeled as a two-stage Stackelberg game interleaved with a coalitional game in this article. In this game, in the first stage the smart grid, as a leader... 

Crystal-size distribution (CSD) is one of the most important parameters in sugar production. The objective is to grow crystals of uniform sizes or narrow CSD. CSD appears to be determined by the growth-rate history of the crystals and the relative supersaturation (SS) of the solution from which crystals growth takes place. Three methods for preparation of nucleation seeds were described and used for industrial crystallization of raw and white sugars; these are wet milling filtered sugar (ML), agitating saturated solution (AS) and powdered sugars (PD). Rosin-Rammler (RR) and mathematical models were adopted to investigate CSD and the uniformity of the produced crystals. Higher uniformity... 

In this paper a new method of modeling shear force-displacement relationship for confined masonry walls by neural networks has been presented. Although the mathematical models have been very useful in the simulations so far, however developing more accurate models is necessary. While developing precise mathematical models for highly hysteretic materials is itself challenging and practically cumbersome, the use of learning algorithms is an attractive alternative. The issue of material modeling by neural networks has been a challenging one itself, noticing available neural networks have some limitations in the learning of non-linearity. In this paper a new type neural network, called Prandtl... 

A new model is proposed to predict the Forming Limit Diagrams (FLDs) of Tailor Welded Blanks (TWBs). This model is derived by modification of the Marciniak and Kuczynski (MK) analysis and imposing the weld constraints to deformation state of each blank at each strain increment. Based on this model, it is possible to predict the strains of both weaker and stronger blanks once necking occurs. By comparison to the experimental results of two laser welded TWBs, it is demonstrated that this model provides a close prediction of FLD of TWBs, when necking occurs far from the weld line at a region out of HAZ (Heat Affected Zone) and close to it so that it is affected by the weld line constraints  

The aim of this work is to produce two layered thin-walled Cu/Al composite tube by the spin-bonding process. The process is utilized to bond the aluminum tube into the copper one at thickness reductions of 20-60% and process temperatures of 25°C, 130°C, and 230°C. The bond strength is measured by T-peeling test, and the bond interfaces are examined by metallography and scanning electron microscopy (SEM). The results show that after a threshold thickness reduction of about 30%, the bond strength increased with the amount of deformation. SEM fractography of the peel surfaces confirms that the copper oxide film is broken in a shear manner during deformation. Severe shear strains applied during... 

A novel SPD process for manufacturing of high strength tubes and cylinders by accumulative spin-bonding (ASB) is proposed. It is demonstrated that due to incremental deformation in this process, high strain rate without considerable temperature rise is achieved. This is accompanied with a high value of Zener-Hollomon parameter as a characteristic of this SPD process. ASB was applied to a commercially pure aluminum up to four cycles and its effects on the microstructure and mechanical properties were examined by optical microscopy, TEM, EBSD, microhardness and tension tests. The results show that ultra-fine grains are developed during the process by formation of subgrains at early stages... 

Utilizing the so-called tube spinning, a cold-bonding process entitled as "spin-bonding" is developed to produce seamless thin-walled clad tubes and cylinders. By this method, two layers of AA 1050 tubes were successfully bonded together to form a clad tube at room temperature. Based on mechanical aspects of the tube spinning process, the mechanism of spin-bonding is explained in two stages: surface preparation before occurrence of a stable bond and bond strengthening thereafter. The effects of process temperature, thickness reduction, feed rate and roller attack angle as the parameters of tube spinning on the bond strength are studied. It is shown that the bond strength increases by... 

In this study, ultrafine grained aluminum sheets AA1050 and AA5052 are incrementally cryo-rolled after precooling in liquid nitrogen. Cryogenic deformation is considered as an effective approach to postpone saturation of the grain refinement by conventional severe plastic deformation. However, for a quantitative understanding of the resulted microstructure and mechanical properties, accurate values of the deformation parameters (strain, strain rate and temperature) are needed. The aim of this study is, therefore, to find values of the applied cryo-rolling parameters. As the experimental measurements of parameters such as temperature are infeasible in the thin specimens, a FEM simulation is... 

Strain rate sensitivity (m-value) of ultrafine grain (UFG) AA 1050 and AA 5052 sheets processed by accumulative roll-bonding is investigated versus strain rate by stress relaxation (SR) test at ambient temperature. The results show a weak viscous nature of deformation for AA 5052 specimens as compared to AA 1050 ones. So that much less stress relaxation and negligible strain rate sensitivity are obtained for this material due to dislocation and grain boundary mobility limitation caused by Mg solute atoms. In order to formulate strain rate sensitivity of UFG aluminum as a function of strain rate, three phenomenological and two empirical models are developed and assessed by the experimental... 

In this study the ability of artificial neural network (ANN) in forecasting the daily NASDAQ stock exchange rate was investigated. Several feed forward ANNs that were trained by the back propagation algorithm have been assessed. The methodology used in this study considered the short-term historical stock prices as well as the day of week as inputs. Daily stock exchange rates of NASDAQ from January 28, 2015 to 18 June, 2015 are used to develop a robust model. First 70 days (January 28 to March 7) are selected as training dataset and the last 29 days are used for testing the model prediction ability. Networks for NASDAQ index prediction for two type of input dataset (four prior days and nine... 

In this paper, the problem of coarse timing synchronization in orthogonal frequency-division multiplexing (OFDM) systems is investigated, and two new timing metrics with better performance are presented. The new metrics take advantage of two novel differential normalization functions that are based on the fourth-order statistics and are designed depending on the value of carrier frequency offset (CFO). The proposed timing metrics are theoretically evaluated using two different class separability criteria. It is shown that the new schemes considerably increase the difference between the correct and wrong timing points in comparison with previous methods. The computational complexity of the... 

Due to role of polymer in increasing sweep efficiency during oil recovery, much attention has been paid to the using polymer solutions in enhanced oil recovery methods. In spite of the existence of the great researches in this area, the role of nanoparticles in modification of the polymer performance in the presence of salts has not been examined before. Furthermore, there is no information about how the dispersed silica nanoparticles affect the heavy oil recovery during the polymer flooding in the presence of divalent cations. In this study, a series of polymer flooding experiments are performed in a quarter five-spot glass micromodel saturated with heavy oil. Solutions of polyacrylamide... 

By displacing oil in porous media with other fluid, different mechanisms of fluid displacing occur. The importance of understanding the trapping mechanisms like pore body filling is irrefutable. Pore body filling mechanism with a coordination number of four has different events like I0, I1, I2 and I3. Previous studies showed that the event of I0 occurs when the pore is only filled by a compressible non-wetting phase, but this study showed that this event could also occur by an incompressible non-wetting phase. Trapping mechanisms can be examined in a glass micro-model. In this research, a glass micro-model with three different patterns was used. Results showed that at two spots of the... 

Reactivity controlled compression ignition has been introduced to implement controllable, clean, and high thermal efficiency without undermining the advantages of premixed combustion. However, simultaneous auto-ignition introduced by reactivity controlled combustion challenges the combustion under higher load operations. This experimental study incorporates a dual phase heat release concept with the purpose of improving the performance of reactivity controlled compression ignition engine. Different ratios of ethanol/diethyl-ether blends (from 0% to 40% diethyl ether and 70% premixed ratio) were applied to a light duty diesel engine at various combustion timings and engine loads. The diesel... 

In this paper a new least mean square (LMS) based adaptive weighting algorithm is proposed. It is appropriate for antenna array systems with moving targets and mobile applications. The essential goal of this algorithm is to reduce the complexity of weighting process and to decrease the time needed for adjusting the antenna radiation pattern. The main lobe of antenna will be adjusted in the direction of desired signal (main signal) and nulls pointed in the direction of undesired signals (interference signals). By predicting the relative velocity of source, the next location of the source will be estimated and the array weights will be determined using LMS algorithm before arriving to the new... 

Reducing the computational complexity as well as convergence time is the main task of adaptive antenna array processing. This article proposes an improved algorithm for estimating the weights of adaptive array elements based on Constant Modulus Algorithm (CMA). In this new type of algorithm, those weights that have higher effect on the radiation pattern will be estimated and antenna pattern will be adjusted by changing these weights. In this research, 3 new algorithms are proposed. By simulating these algorithms and comparing them with conventional full weight CMA, finally new algorithm that has a reduced complexity and an acceptable performance at different signal to noise ratios (SNRs) is...