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RISS 인기검색어
- 검색키워드
- 저자 : Mehrabi M. (검색결과 8 건)
- 무료
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M. Mohammadimehr,E. Shabani Nejad,M. Mehrabi 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.4
Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton’s principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.
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Mehrabi M.,Goudarzi K.,Farahani S. Davoodabadi 대한설비공학회 2023 International Journal of Air-Conditioning and Refr Vol.31 No.1
One of the most important parts of direct evaporative cooling systems is the cooling pad. Pads vary in materials and construction features. The parameters studied in the performance of the pads are air speed, pad thickness, geometrical characteristics, and its configuration and the provided water flow rate. The performance of the pads is usually determined through saturation efficiency, pressure drop, temperature drop and humidity increase in the treated air, evaporation and water consumption, cooling capacity, coefficient of performance, and heat and mass transfer coefficients. Since the geometry and how to place the pad in the evaporative cooling system is one of the most important issues related to the performance of such systems, the present work experimentally investigates the amount of cooling and evaporation of the direct evaporative cooling system under 5 different angles of placement of the cellulose pad in relation to the vertical position. It includes angles of , , , , and in 5 different air speeds, 2 different inlet water flow rates, 2 inlet air temperatures, and 2 different inlet water temperatures. Results show that the lowest output temperature, highest air relative humidity, highest coefficient of performance (about 12% more than ), highest saturation efficiency, and highest evaporation rate are obtained in the case of a of cooling pad placement angle.
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Mohammadimehr, M.,Nejad, E. Shabani,Mehrabi, M. Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.4
Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.
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K. Mehraby,H. Khademhosseini Beheshti,M. Poursina 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.7
Impact is very common source of noise in the industries. The impacts can be visible, such as forging, and can be invisible, such as impacts due to clearance of hinges. As a result of this generality, the control of impact noise needs more attention. Reduction of this tiresome noise needs enough perception about the impact. A study of this noise sources presents difficult problems both theoretically and experimentally. This is partly due to the many complex interconnected mechanical phenomena that occur and partly due to the fact that usual steady-state techniques of analysis cannot be applied. In such complex problems numerical techniques can help to acousticians. To gain some insight into this source of sound, in this paper collision of two steel spheres are studied with finite element method (FEM). Then the FEM results were compared with experiments to show authority of this numerical method to simulate impact noises. FEM results show that if the vibrational modes are excited by impact, the vibrational modes can be as effective as rigid body motion.
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S. Rezazadeh,M. Mehrabi,T. Pashaee,I. Mirzaee 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.11
In this paper, an adaptive neuro-fuzzy inference system (ANFIS) is used for modeling proton exchange membrane fuel cell (PEMFC)performance using some numerically investigated and compared with those to experimental results for training and test data. In this way,current density I (A/cm2) is modeled to the variation of pressure at the cathode side PC (atm), voltage V (V), membrane thickness (mm),Anode transfer coefficient αan, relative humidity of inlet fuel RHa and relative humidity of inlet air RHc which are defined as input (design)variables. Then, we divided these data into train and test sections to do modeling. We instructed ANFIS network by 80% of numerical-validated data. 20% of primary data which had been considered for testing the appropriateness of the models was entered ANFIS network models and results were compared by three statistical criterions. Considering the results, it is obvious that our proposed modeling by ANFIS is efficient and valid and it can be expanded for more general states.
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Mehdi Mohammadimehr,Hasan Afshari,M. Salemi,K. Torabi,Mojtaba Mehrabi 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.5
In the present study, buckling and free vibration analyses of annular thin sector plate made of functionally graded materials (FGMs) resting on visco-elastic Pasternak foundation, subjected to external radial, circumferential and shear in-plane loads is investigated. Material properties are assumed to vary along the thickness according to an power law with Poisson’s ratio held constant. First, based on the classical plate theory (CPT), the governing equation of motion is derived using Hamilton’s principle and then is solved using the generalized differential quadrature method (GDQM). Numerical results are compared to those available in the literature to validate the convergence and accuracy of the present approach. Finally, the effects of power-law exponent, ratio of radii, thickness of the plate, sector angle, and coefficients of foundation on the fundamental and higher natural frequencies of transverse vibration and critical buckling loads are considered for various boundary conditions. Also, vibration and buckling mode shapes of functionally graded (FG) sector plate have been shown in this research. One of the important obtained results from this work show that ratio of the frequency of FG annular sector plate to the corresponding values of homogeneous plate are independent from boundary conditions and frequency number.
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Bordbar, A.K.,Nasehzadeh, A.,Ajloo, D.,Omidiyan, K.,Naghibi, H.,Mehrabi, M.,Khajehpour, H.,Rezaei-Tavirani, M.,Moosavi-Movahedi, A.A. Korean Chemical Society 2002 Bulletin of the Korean Chemical Society Vol.23 No.8
Binding of dodecyl trimethylammonium bromide (DTAB) to human and bovine hemoglobin and globin samples has been investigated in 50 mM glycine buffer pH = 10, I = 0.0318 and 300 K by equilibrium dialysis and temperature scanning spectrophotometry techniques and method for calculation of average hydrophobicity. The binding data has been analyzed, in terms of binding capacity concept $({\theta})$, Hill coefficient (nH) and intrinsic Gibbs free energy of binding $({\Delta}Gbv).$ The results of binding data, melting point (Tm) and average hydrophobicity show that human hemoglobin has more structural stability than bovine hemoglobin sample. Moreover the results of binding data analysis represent the systems with two and one sets of binding sites for hemoglobin and globin, respectively. It seems that the destabilization of hemoglobin structure due to removal of heme group, is responsible of such behavior. The results indicating the removal of heme group from hemoglobin caused the depletion of first binding set as an electrostatic site upon interaction with DTAB and exposing the hydrophobic patches for protein.
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