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Response of the beams on random Pasternak foundations subjected to harmonic moving loads
Davood Younesian,Mohammad Hossein Kargarnovin 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.11
Dynamic response of infinite beams supported by random viscoelastic Pasternak foundation subjected to harmonic moving loads is studied. Vertical stiffness in the support is assumed to follow a stochastic homogeneous field consisting of a small random variation around a deterministic mean value. By employing the first order perturbation theory and calculating appropriate Green’s functions, the variance of the deflection and bending moment are obtained analytically in integral forms. To simulate the induced uncertainty, two practical cases of cosine and exponential covariance are utilized. A frequency analysis is performed and influences of the correlation length of the stiffness variation on the beam responses are investigated. It is found that in each frequency response there is a peak value of frequency, which behaves as a decreasing function of the correlation length. Among two coefficient of variation of the beam deflection and the bending moment, the former is higher in the case of exponential covariance and it is independent of the magnification of the correlation length.
Davood Khoeini,Ebrahim Shirani 한국유체기계학회 2018 International journal of fluid machinery and syste Vol.11 No.2
The influences of different configurations of impeller diffusers and splitter blades on performance of a centrifugal pump have been analyzed experimentally and numerically. Each impeller with different configurations including three different splitter blades with lengths of 0, 0.45L and 0.75L (L is the length of impeller blades) and three different cases of impeller with diffuser of α=0o (α is the divergence angle of diffuser walls) and angular diffuser of α=10o and impeller without diffuser have been investigated in this study. Data analyses revealed that there is good compatibility among experimental and numerical results and the highest head discrepancy is only 7 percent. Results showed that simultaneous use of impeller diffuser and splitter blade have profound impact on the centrifugal pump performance. Actually, among all configurations, the maximum performance is achieved for the impeller equipped with angular diffuser of α=10o and splitter blades of 0.75L concurrently. In that case, the head at high flow rate is 1.51 times of the head value of original impeller without impeller diffuser. In addition, at BEP (Best Efficiency Point), efficiency increased by 3.4 percent and its position displaced towards the high flow rate as well.
Nonlinear vibration of laminated composite plates subjected to subsonic flow and external loads
Davood Younesian,Hamed Norouzi 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.6
We study chaotic motion in a nonlinear laminated composite plate under subsonic fluid flow and a simultaneous external load in this paper. We derive equations of motion of the plate using the von-Kármán's hypothesis and the Hamilton's principle. Galerkin's approach is adopted as the solution method. We then conduct a divergence analysis to obtain critical velocities of the transient flow. Melnikov's integral approach is used to find the critical parameters in which chaos takes place. Effects of different parameters including the aspect ratio, plate material and the ply angle in laminates on the critical flow speed are investigated. In a parametric study, we show that how the linear and nonlinear stiffness of the plate and the load frequency and amplitude would influence the chaotic behavior of the plate.
Davood Poorveis,Majid Khayat,Shapour Moradi 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.2
The objective of this paper is to investigate buckling behavior of composite laminated cylinders by using semi-analytical finite strip method. The shell is subjected to deformation-dependent loads which remain normal to the shell middle surface throughout the deformation process. The load stiffness matrix, which is responsible for variation of load direction, is also throughout the deformation process. The shell is divided into several closed strips with alignment of their nodal lines in the circumferential direction. The governing equations are derived based on the first-order shear deformation theory with Sanders-type of kinematic nonlinearity. Displacements and rotations of the shell middle surface are approximated by combining polynomial functions in the meridional direction and truncated Fourier series along with an appropriate number of harmonic terms in the circumferential direction. The load stiffness matrix, which is responsible for variation of load direction, is also derived for each strip and after assembling, global load stiffness matrix of the shell is formed. The numerical illustrations concern the pressure stiffness effect on buckling pressure under various conditions. The results indicate that considering pressure stiffness causes buckling pressure reduction which in turn depends on various parameters such as geometry and lay-ups of the shell.
Prediction of Thermal Decomposition Temperature of Polymers Using QSPR Methods
Davood Ajloo,Ali Sharifian,Hossein Behniafar 대한화학회 2008 Bulletin of the Korean Chemical Society Vol.29 No.10
The relationship between thermal decomposition temperature and structure of a new data set of eighty monomers of different polymers were studied by multiple linear regression (MLR). The stepwise method was used in order to variable selection. The best descriptors were selected from over 1400 descriptors including; topological, geometrical, electronic and hybrid descriptors. The effect of number of descriptors on the correlation coefficient (R) and F-ratio were considered. Two models were suggested, one model having four descriptors (R2 = 0.894, Q2 cv = 0.900, F = 172.1) and other model involving 13 descriptors (R2 = 0.956, Q2 cv = 0.956, F = 125.4).
On buckling analysis of laminated composite plates using a nonlocal refined four-variable model
Davood Shahsavari,Behrouz Karami,Maziar Janghorban 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.2
This study is concerned with the stability of laminated composite plates modelled using Eringen’s nonlocal differential model (ENDM) and a novel refined-hyperbolic-shear-deformable plate theory. The plate is assumed to be lying on the Pasternak elastic foundation and is under the influence of an in-plane magnetic field. The governing equations and boundary conditions are obtained through Hamilton’s principle. An analytical approach considering Navier series is used to fine the critical bucking load. After verifying with existing results for the reduced cases, the present model is then used to study buckling of the laminated composite plate. Numerical results demonstrate clearly for the first time the roles of size effects, magnetic field, foundation parameters, moduli ratio, geometry, lay-up numbers and sequences, fiber orientations, and boundary conditions. These results could be useful for designing better composites and can further serve as benchmarks for future studies on the laminated composite plates.
Davood Allahverdy,Ahmad Fakharian,Mohammad Bagher Menhaj 대한전기학회 2019 Journal of Electrical Engineering & Technology Vol.14 No.6
In this study, back-stepping integral sliding mode control (BISMC) with iterative learning control (ILC) algorithm are presented for nonlinear translational and rotational dynamics of the Quadrotor UAVs. The proposed controller (BISMC) can track desired trajectories and (ILC) is responsible for inclining the accuracy and robustness of the control strategy. In order to prove the stability of the closed loop system, Lyapunov theorem is used. The simulation results indicate that the proposed control strategy has high accuracy, suitable robustness, disturbance rejection, good trajectory tracking and fast transient responses for the Quadrotor UAVs despite the uncertainties and external disturbances.
The Single-Allocation Heuristic Hub Location Problem Solving
Davood Jafari,Mahdi Hadian Pour 대한산업공학회 2018 Industrial Engineeering & Management Systems Vol.17 No.3
Hubs are special facilities that consolidate and disseminate flows in many-to-many distribution systems. The hub location problem aims to find locations of hubs and allocate non-hub nodes directly to the hubs. However, this problem is necessary to extend when nodes do not have sufficient demand to justify direct connections between the non-hub nodes to the hubs since such direct connections increase the number of vehicles required and decrease the utilization of vehicles. In this research, after analyzing the definitions of the location of the hub and a variety of location models and their solving algorithms, we solved a case study of the classic Hub Location model algorithm by adding an annual fixed cost to determine the best way to carry goods from one country to another from the top 5 most requested destinations, aimed at minimizing shipping and distribution costs.
Effect of Cationic and Anionic Porphyrins on the Structure and Activity of Adenosine Deaminase
Davood Ajloo,Samaneh Hajipour,Ali Akbar Saboury,Saeed Zakavi 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.9
Kinetic and structural studies have been carried out on the effects of meso-tetrakis(4-sulfonatophenyl)-porphyrin (H_2TPPS_4) as an anionic and meso-tetrakis(3-N-methyl-pyridyl)porphyrin (H_2TMPYP) as a cationic porphyrin with adenosine deaminase (ADA) in 25 mM citrate/phosphate buffer, pH = 4-8, at 37 ^oC using UVvis spectrophotometry, circular dichroism (CD), fluorescence spectrophotometry as well as molecular dynamics (MD) and molecular docking. Kinetic results showed that the two porphyrins are non-competitive inhibitors. Increasing pH, increases K_I and cationic porphyrin has a higher K_I and lower binding constant (K_b)at all pH ranges. Analyzing the secondary structure revealed that both ligands decrease the secondary structure and that the anionic porphyrin is more effective.