New formulation for vibration analysis of Timoshenko beam with double-sided cracks

M.R. Ayatollahi,R. Hashemi,H. Rokhi 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

It is the intention of this study to synthesize the effects of double-edge cracks on the dynamic characteristics of a beam. The stiffness matrix is first determined for a Timoshenko beam containing two same-line edge cracks. The presented model is then developed for elements with two parallel double-sided cracks, considering the interaction between the stress fields of adjacent cracks. Finally, a finite element code is implemented, to examine the influence of depth and location of double cracks, on the natural frequencies of the damaged system.

New formulation for vibration analysis of Timoshenko beam with double-sided cracks

Ayatollahi, M.R.,Hashemi, R.,Rokhi, H. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

It is the intention of this study to synthesize the effects of double-edge cracks on the dynamic characteristics of a beam. The stiffness matrix is first determined for a Timoshenko beam containing two same-line edge cracks. The presented model is then developed for elements with two parallel double-sided cracks, considering the interaction between the stress fields of adjacent cracks. Finally, a finite element code is implemented, to examine the influence of depth and location of double cracks, on the natural frequencies of the damaged system.

On thermally induced instability of FG-CNTRC cylindrical panels

Hashemi, Razieh,Mirzaei, Mostafa,Adlparvar, Mohammad R. Techno-Press 2021 Advances in nano research Vol.10 No.1

In this study, thermally induced bifurcation buckling of shallow composite cylindrical panels reinforced with aligned single-walled carbon nanotubes is investigated. Distribution of carbon nanotubes across the thickness of the cylindrical panel as reinforcements may be either uniform or functionally graded. Thermo-mechanical properties of the matrix and reinforcements are considered to be temperature dependent. Properties of the cylindrical panel are obtained using a refined micromechanical approach which introduces the auxiliary parameters into the rule of mixtures. The governing equations are obtained by using the static version of the Hamilton principle based on the first-order shear deformation theory and considering the linear strain-displacement relation. An energy-based Ritz method and an iterative process are used to obtain the critical buckling temperature of composite cylindrical panel with temperature dependent material properties. In addition, the effect of various parameters such as the boundary conditions, different geometrical conditions, distribution pattern of CNTs across the thickness and their volume fraction are studied on the critical buckling temperature and buckled pattern of cylindrical panels. It is shown that FG-X type of CNT dispersion is the most influential type in thermal stability.

An Adaptive UPFC Based Stabilizer for Damping of Low Frequency Oscillation

M. R. Banaei,A. Hashemi 대한전기학회 2010 Journal of Electrical Engineering & Technology Vol.5 No.2

Unified power flow controller (UPFC) is the most reliable device in the FACTS concept. It has the ability to adjust all three control parameters effective in power flow and voltage stability. In this paper, a linearized model of a power system installed with a UPFC has been presented. UPFC has four control loops that by adding an extra signal to one of them, increases dynamic stability and load angle oscillations are damped. In this paper, after open loop eigenvalue (electro mechanical mode) calculations, state-space equations have been used to design damping controller and it has been considered to influence active and reactive power flow durations as the input of damping controller, in addition to the common speed duration of synchronous generators as input damper signal. To increase stability, further Lead-Lag and LQR controllers, a novel on-line adaptive controller has been used analytically to identify power system parameters. Closed-loop calculations of the electro mechanical mode verify the improvement of system pole placement after controller designing. Suitable operation of adaptive controller to decrease rotor speed oscillations against input mechanical torque disturbances is confirmed by the simulation results.

Priorities for conservation of endemic trees and shrubs of Iran: Important Plant Areas (IPAs) and Alliance for Zero Extinction (AZE) in SW Asia

A.R. Mehrabian,S. Sayadi,M. Majidi Kuhbenani,V. Hashemi Yeganeh,M. Abdoljabari 국립중앙과학관 2020 Journal of Asia-Pacific Biodiversity Vol.13 No.2

Owing to narrow geographical distribution, endemic species indicates higher vulnerability than othertaxa, so they have been used as surrogate elements to identify the priorities. Little attention has beenpaid to distribution patterns, hot spots, and conservative zones of endemic trees and shrubs in scale ofIran. The main purpose of this study was to identify and introduce the Important Plant Areas (IPAs) aswell as Alliance for Zero Extinction (AZEs) of endemic trees and shrubs in Iran. The total number ofendemic trees and shrubs in the studied area included 75 species belonging to 32 genera of 22 plantfamilies. Chorological elements mainly (65:86.6%) belong to the Irano-Turanian region. The geomorphologicalbarriers have confined plant immigrations in the north-south as well as east-west slopes,appearing as a center of plant speciation in Iran. Our results indicate a significant percentage (36.2%) ofthese endemics classified in the threatened categories. Central as well as southern Zagros, Central Alborzand with more limited range N. Zagros, Kopet Dagh as well SW Iran are classified as AZE under bothCriteria of AZE.

An Adaptive UPFC Based S tabilizer forDamping of Low Frequency Oscillation

Banaei, M.R.,Hashemi, A. The Korean Institute of Electrical Engineers 2010 Journal of Electrical Engineering & Technology Vol.5 No.2

Unified power flow controller (UPFC) is the most reliable device in the FACTS concept. It has the ability to adjust all three control parameters effective in power flow and voltage stability. In this paper, a linearized model of a power system installed with a UPFC has been presented. UPFC has four control loops that by adding an extra signal to one of them, increases dynamic stability and load angle oscillations are damped. In this paper, after open loop eigenvalue (electro mechanical mode) calculations, state-space equations have been used to design damping controller and it has been considered to influence active and reactive power flow durations as the input of damping controller, in addition to the common speed duration of synchronous generators as input damper signal. To increase stability, further Lead-Lag and LQR controllers, a novel on-line adaptive controller has been used analytically to identify power system parameters. Closed-loop calculations of the electro mechanical mode verify the improvement of system pole placement after controller designing. Suitable operation of adaptive controller to decrease rotor speed oscillations against input mechanical torque disturbances is confirmed by the simulation results.

A comparison between hydrothermally prepared Co3O4 via H2O2 assisted and calcination methods

S. E. Hashemi Amiri,M. R. Vaezi,A. Esmaielzadeh Kandjani 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.3

In this paper Co3O4 nanoparticles were synthesized via two different synthesis procedures. In the first method, hydrothermally synthesized β-Co(OH)2 particles were calcined at different temperatures. In the other method, H2O2 was used to eliminate the production of cobalt hydroxide. The amount of H2O2 was the main variable investigated in this study. All samples synthesized via these methods, were investigated for their structure, morphology, specific surface area and magnetization. The results showed that an increase in the temperature of the post heat treatment substantially increased particle sizes and consequently decreased the specific surface area of nanoparticles which influences magnetization. In the H2O2 assisted route, the minimum amount of the oxidant necessary for the complete elimination of the β-Co(OH)2 phase and production of the pure Co3O4 phase was determined to be 0.25 volume fraction. In the H2O2 assisted method, due to elimination of the post heat treatment, the nanoparticles become smaller with a higher specific surface area in comparison with the calcination method. However, the magnetic properties of the nanoparticles in the H2O2 assisted method are influenced by changing the amount of H2O2.

Investigation of a flame holder geometry effect on flame structure in non-premixed combustion

S. A. Hashemi,N. Hajialigol,A. Fattahi,K. Mazaheri,R. Heydari 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.11

In this paper the effect of flame holder geometry on flame structure is studied. The obtained numerical results using realizable k-ε and β-PDF models show a good agreement with experimental data. The results show that increasing in flame holder length decreases flame length and increases flame temperature. Additionally, it is observed that flame lengths decrease by increasing in flame holder radius and increase for larger radii. Furthermore in various radii, the flame temperature is higher for smaller flame lengths. It was found that behavior of flame structure is mainly affected by the mass flow rate of hot gases that come near the reactant by the recirculation zone.

Effect of the Traffic Load Distribution on the Progressive Collapse of a Cable-Stayed Bridge Under Blast Load

S. K. Hashemi,H. R. Valipour,M. A. Bradford 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.6

The advanced coupled fi nite element models can be used to model the structures and the extreme load of air blast as well as the interaction between them. However, the structural response of long-span bridges can be signifi cantly infl uenced by the magnitude and location of blast load and pattern and magnitude of traffi c load along and across the deck. In addition, the previous studies considered the cable loss when the bridge is intact, however the damage of explosion on a bridge causes new deformation and characteristics. Accordingly, in this study, the eff ect of fi ve diff erent traffi c loading cases has been investigated on the maximum response of a cable-stayed bridge under eight diff erent blast scenarios and the possibility of progressive collapse has been evaluated. It is concluded that the traffi c load confi gurations on the bridge can vary maximum actions on diff erent components up to 30%. Cable loss or anchorage zone destruction under blast loading scenarios are observed independent of the traffi c load distribution. Meanwhile, the progressive collapse of bridge due to cable loss likely occurs in a number of the blast scenarios. Moreover, the vulnerability of more than one cable loss is clearly observed in some cases and designing bridges based on only one cable loss is not safe if the occurrence of hazards on the bridge is unavoidable. Besides, two symmetric traffi c loading scenarios (i.e. 50% of traffi c load applied on the entire bridge, and 50% of the traffi c load only applied on middle span) are identifi ed as the most critical in terms of the bridge components response.

Analysis of competing risks in the burr XII model in presence of progressive type-II censoring

A. Pourdarvish,R. Hashemi,J. Azar 장전수학회 2012 Proceedings of the Jangjeon mathematical society Vol.15 No.1

In reliability and survival analysis, it is quite common that the failure of any individual or any item may be attributable to more than one cause (competing risks). In this paper, we will study the competing risks in the Burr XII model in the presence of progressive type II censoring scheme. We study the model under the assumption of independent causes of failure. The maximum likelihood estimator was developed to estimate the unknown parameters. The asymptotic distribution of the maximum likelihood estimators is used to construct approximate confidence interval. We also present a simulation study to illustrate the results.