Kiani Y.,Shahrekord University
Composite Structures | Year: 2017
Present research deals with the postbuckling problem of carbon nanotube reinforced composite plates subjected to uniform temperature rise loading. Distribution of carbon nanotubes as reinforcements may be uniform or functionally graded. To account for the large deformations of the plate, von-Kármán type of geometrical nonlinearity is included into the formulation. The virtual displacements principle associated with the conventional Ritz formulation whose shape functions are selected as the Chebyshev polynomials is used to obtain the matrix representation of the nonlinear equilibrium equations. The solution method is general and may be used for arbitrary combination of boundary conditions. The postbuckling equilibrium path which is governed by a nonlinear eigenvalue problem is traced using a displacement control strategy. Results of this study are compared with the available data in the open literature for the cases of isotropic homogeneous plates and cross-ply laminated plates. Afterwards numerical results are given for FG-CNTRC plates. It is shown that, FG-X pattern results in higher buckling temperature and also decreases the postbuckling deflection of the plate. Furthermore, this type of composites are eager to exhibit the secondary instability which is designated with a snap-through phenomenon in the post-buckling equilibrium path. © 2016
Zeighampour H.,Shahrekord University |
Tadi Beni Y.,Shahrekord University
International Journal of Engineering Science | Year: 2014
In this paper, the cylindrical thin-shell model is developed based on modified strain gradient theory. For this purpose, the study develops the thin shell theory, having considered size effects through modified strain gradient theory. Besides, partial equations of shell motion with classical and non-classical corresponding boundary conditions are derived from Hamilton principle. Finally, by way of example, the free vibration of the single-walled carbon nanotube (SWCNT) is investigated. The study models the SWCNT as a simply-supported shell. Besides, the Navier procedure is used to solve the vibration problem. The results of the new model are compared with those of the couple stress model and the classical theory, leading to the conclusion that the mentioned models are special cases of the modified strain gradient theory. The findings also indicate that the rigidity of the nanoshell in the modified strain gradient theory is greater than that in couple stress model and the classical theory, which leads to the increase in natural frequencies. Furthermore, the effect of the material length scale parameter on the vibration of the nanoshell for different lengths is taken into account. © 2014 Elsevier Ltd. All rights reserved.
Amini-Harandi A.,Shahrekord University
Journal of Global Optimization | Year: 2013
In this paper, we introduce a new class of maps, called cyclic strongly quasi-contractions, which contains the cyclic contractions as a subclass. Then we give some convergence and existence results of best proximity point theorems for cyclic strongly quasi-contraction maps. An example is given to support our main results. © 2012 Springer Science+Business Media, LLC.
Fallah A.A.,Shahrekord University
Food Control | Year: 2010
In the present study, 298 dairy product samples consisting of pasteurized milk (91 samples), yoghurt (68 samples), white cheese (72 samples), butter (31 samples) and ice cream (36 samples) collected from popular markets in four large Iranian cities were examined for aflatoxin M1 (AFM1) by thin layer chromatography (TLC) technique. The toxin was detected in 66 (72.5%) pasteurized milk samples (mean: 0.052μg/l; range: 0.013-0.250μg/l), 45 (66.1%) yoghurt samples (mean: 0.032μg/kg; range: 0.015-0.119μg/kg), 59 (81.9%) white cheese samples (mean: 0.297μg/kg; range: 0.030-1.200μg/kg), 8 (25.8%) butter samples (mean: 0.005μg/kg; range: 0.013-0.026μg/kg) and 25 (69.4%) ice cream samples (mean: 0.041μg/kg; range: 0.015-0.132μg/kg). The concentration of AFM1 in 36.2%, 20.6%, 30.5%, 9.6% and 27.7% of pasteurized milk, yoghurt, white cheese, butter and ice cream samples, respectively, were higher than Iranian national standard limits. Levels of AFM1 in samples of pasteurized milk, yoghurt, butter and ice cream collected in winter were significantly higher (P<0.05) than those collected in summer. In the case of white cheese, level of AFM1 was higher in winter than in summer, but the difference was not statistically significant (P>0.05). The results indicated that the contamination of the dairy products in such a level could be a serious public health problem at the moment. © 2010 Elsevier Ltd.
Ebrahimi R.,Shahrekord University
Mathematical and Computer Modelling | Year: 2011
The performance of an air standard Atkinson cycle is analyzed using finite-time thermodynamics. In the model, the linear relation between the specific heat ratio of the working fluid and its temperature, the friction loss computed according to the mean velocity of the piston, the internal irreversibility described by using the compression and expansion efficiencies and the heat transfer loss are considered. The relations between the power output and the compression ratio and between the power output and the thermal efficiency are derived by detailed numerical examples. The results show that if the compression ratio is less than a certain value, the power output decreases with increasing mean piston speed, while if the compression ratio exceeds a certain value, the power output first increases and then starts to decrease with increasing mean piston speed. With further increase in the compression ratio, the increase of mean piston speed results in decreasing the power output. Throughout the compression ratio range, the power output increases with increasing cylinder wall temperature while it first increases and then starts to decrease with the increase of equivalence ratio. The conclusions of this investigation are of importance when considering the designs of actual Atkinson engines. © 2010 Elsevier Ltd.
Ebrahimi R.,Shahrekord University
Computers and Mathematics with Applications | Year: 2011
The performance of an air standard Miller cycle is analyzed using finite-time thermodynamics. The results show that if the compression ratio is less than certain value, the increase of the value of the specific heat ratio will make the power output bigger. In contrast, if the compression ratio exceeds certain value, the increase of the value of the specific heat ratio will make the power output less. The results also show that if the compression ratio is less than certain value, the power output decreases with increasing engine speed, while if the compression ratio exceeds certain value, the power output first increases and then starts to decrease with increasing engine speed. With a further increase in compression ratio, the increase of engine speed results in decreasing the power output. The results are of importance to provide good guidance for the performance evaluation and improvement of practical Miller engines. © 2011 Elsevier Ltd. All rights reserved.
Keyvani A.,Shahrekord University
Journal of Alloys and Compounds | Year: 2015
The spallation of ceramic coating from the bond coat is important problem for TBC systems. And the spallation is caused the oxidation and hot corrosion at the interface of ceramic layer and bond coat. In the present work oxidation and hot corrosion behavior of plasma sprayed nanostructured Al2O3/YSZ composite TBC coatings on Ni-base (IN-738LC) super alloy substrate was studied and compared to conventional YSZ. The coatings have been deposited by plasma spray method. High temperature oxidation test at 1100 °C and hot corrosion test at 1050 °C using Na2SO4 and V2O5 molten salts were performed on the coatings. The experimental results showed nanostructured Al2O3/YSZ composite coating had higher oxidation and hot corrosion resistance than those of the conventional YSZ coating. The microstructural analysis indicated that the growth of TGO was much less for this nanostructured Al2O3/YSZ composite coating while it reduced infiltration of both oxygen and aggressive molten salt. © 2014 Elsevier B.V. All rights reserved.
Ghasemi B.,Shahrekord University
Numerical Heat Transfer; Part A: Applications | Year: 2013
This article presents the results of a numerical study of laminar natural convection in a U-shaped enclosure that is filled with a water-Cu nanofluid and is under the influence of a horizontal magnetic field. A computational domain was defined and a numerical scheme based on the control volume formulation using the SIMPLE algorithm was developed. The convection-diffusion terms were discretized using a power-law scheme. The effects of the Rayleigh number, the solid volume fraction, the Hartmann number, and the enclosure aspect ratio on the heat transfer performance of the enclosure were examined. The thermal performance of the enclosure was found to be a function of the enclosure aspect ratio. The results also showed that the heat transfer rate increased with an increase of the Rayleigh number and the solid volume fraction, but it decreased with an increase of the Hartmann number. © 2013 Taylor and Francis Group, LLC.
Fallah A.A.,Shahrekord University
Food and Chemical Toxicology | Year: 2010
This study was conducted as a screening survey to determine the occurrence of aflatoxin M1 (AFM1) in 225 commercial liquid milk samples composed of pasteurized milk (116 samples) and UHT milk (109 samples) obtained from popular markets in central part of Iran. The competitive enzyme-linked immunosorbent assay method was employed to determine level of the toxin in the samples. Aflatoxin M1 was detected in 151 (67.1%) samples, consisted of 83 (71.5%) pasteurized milk samples (mean: 52.8 ng/l; range: 5.8-528.5 ng/l) and 68 (62.3%) UHT milk samples (mean: 46.4 ng/l; range: 5.6-515.9 ng/l). Considering the US FDA and Iranian national standard limits for AFM1 in milk (500 ng/l), 2 samples (1.7%) of pasteurized and 3 samples (2.7%) of UHT milk had levels above the maximum tolerance limit. However, according to European Commission limit (50 ng/l), this figure increased to 31 (26.7%) and 19 (17.4%) samples for pasteurized and UHT milk, respectively. The results indicated that the contamination of the samples with AFM1 in such a level could be a serious public health problem at the moment. This paper represents the data of the first survey on the occurrence of AFM1 in commercial liquid milk marketed in central part of Iran. © 2010 Elsevier Ltd. All rights reserved.
Raiesi F.,Shahrekord University
Plant and Soil | Year: 2012
Background and Aims: Land abandonment might be an alternative management for restoring soil conditions and C from prolonged cultivation and agricultural practices. In the present study, the influence of 18-22 years of land abandonment on soil properties, C dynamics and microbial biomass was evaluated in closely situated wheat and alfalfa farmlands, and abandoned lands on calcareous soils, Central Iran. Methods: Soil properties of the 0-15 and 15-30 cm depths from abandoned lands were compared to those from conventionally cultivated lands (i. e., continuous wheat-fallow and alfalfa-wheat rotation) common in calcareous soils of Central Zagros Mountains. Results: Soil bulk density in the 0-15 and 15-30 cm layers decreased significantly while total porosity increased significantly in abandoned lands. Generally, soil aggregate stability tended to increase within the abandoned fields owing to increased water-stable macro-aggregates. Soil organic C (OC) contents (g kg -1) and pools (Mg ha -1) in the 0-15 cm soil layer increased significantly in abandoned lands compared with cultivated lands, with no effect in the 15-30 cm soil layer after 18-22 years of land abandonment, suggesting the restoration of C is pronounced in the upper 0-15 cm soil depth. The total C accumulation in abandoned lands was 7. 0 Mg C ha -1 for the entire sampling depth (0-30 cm) over the 18-22 years of land abandonment, which was 26% greater relative to cultivated lands. Carbon mineralization (Cmin) followed a trend similar to organic C, whereas C turnover (Cmin/OC ratio) was slightly greater in wheat fields. However, soil microbial biomass C (MBC) did not vary considerably among the three land uses. Conclusions: In brief, improvements, albeit slowly, in soil properties of the top layer with the cessation of cultivation indicated that land abandonment may result in enhanced soil C sequestration, and would maintain fertility and productivity of the farmlands of semi-arid climates. © 2011 Springer Science+Business Media B.V.