Nonlocal-strain gradient forced vibration analysis of metal foam nanoplates with uniform and graded porosities

Barati, Mohammad Reza Techno-Press 2017 Advances in nano research Vol.5 No.4

Forced vibration behavior of porous metal foam nanoplates on elastic medium is studied via a 4-variable plate theory. Different porosity distributions called uniform, symmetric and asymmetric are considered. Nonlocal strain gradient theory (NSGT) containing two scale parameters is employed for size-dependent modeling of porous nanoplates. The present plate theory satisfies the shear deformation effect and it has lower field variables compared with first order plate theory. Hamilton's principle is employed to derive the governing equations. Obtained results from Galerkin's method are verified with those provided in the literature. The effects of nonlocal parameter, strain gradient, foundation parameters, dynamic loading, porosity distributions and porosity coefficient on dynamic deflection and resonance frequencies of metal foam nanoscale plates are examined.

Vibration analysis of FG nanoplates with nanovoids on viscoelastic substrate under hygro-thermo-mechanical loading using nonlocal strain gradient theory

Mohammad Reza Barati 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.64 No.6

According to a generalized nonlocal strain gradient theory (NSGT), dynamic modeling and free vibrational analysis of nanoporous inhomogeneous nanoplates is presented. The present model incorporates two scale coefficients to examine vibration behavior of nanoplates much accurately. Porosity-dependent material properties of the nanoplate are defined via a modified power-law function. The nanoplate is resting on a viscoelastic substrate and is subjected to hygro-thermal environment and in-plane linearly varying mechanical loads. The governing equations and related classical and non-classical boundary conditions are derived based on Hamilton’s principle. These equations are solved for hinged nanoplates via Galerkin’s method. Obtained results show the importance of hygro-thermal loading, viscoelastic medium, in-plane bending load, gradient index, nonlocal parameter, strain gradient parameter and porosities on vibrational characteristics of size-dependent FG nanoplates.

Coupled effects of electrical polarization-strain gradient on vibration behavior of double-layered flexoelectric nanoplates

Mohammad Reza Barati 국제구조공학회 2017 Smart Structures and Systems, An International Jou Vol.20 No.5

A vibrating double-layered nanoscale piezoelectric plate is developed accounting for the flexoelectricity and surface effects. The flexoelectricity is due to the coupling between electrical polarization and strain gradient. Applying Hamilton\'s principle, the governing equations and related boundary conditions are derived. Assuming suitable approximate functions, the governing equations are numerically solved for simply-supported and clamped boundary conditions. Obtained results indicate that both the flexoelectricity and surface effects possess notable impact on the vibration frequencies of the system. Only flexoelectricity yields a considerable difference between the present model and previous investigations on conventional piezoelectric nanoplates. Generally, a parametric study has been performed to examine the effects of surface elasticity, flexoelectricity, applied electric voltage, interlayer stiffness, geometrical parameters and boundary conditions on vibration frequencies of piezoelectric nanoplates.

Role of Organizational Climate in Organizational Commitment: The Case of Teaching Hospitals

Mohammad Amin Bahrami,Omid Barati,Malake-sadat Ghoroghchian,Razieh Montazer-alfaraj,Mohammad Ranjbar Ezzatabadi 질병관리본부 2016 Osong Public Health and Research Persptectives Vol.7 No.2

Objective: The commitment of employees is affected by several factors, including factors related to the organizational climate. The aim of this study was to investigate the relationship between organizational commitment of nurses and the organizational climate in hospital settings. Methods: A cross-sectional study was conducted in 2014 at two teaching hospitals in Yazd, Iran. A total of 90 nurses in these hospitals participated. We used stratified random sampling of the nursing population. The required data were gathered using two valid questionnaires: Allen and Meyer’s organizational commitment standard questionnaire and Halpin and Croft’s Organizational Climate Description Questionnaire. Data analysis was done through SPSS 20 statistical software (IBM Corp., Armonk, NY, USA). We used descriptive statistics and Pearson’s correlation coefficient for the data analysis. Results: The findings indicated a positive and significant correlation between organizational commitment and organizational climate (r = 0.269, p = 0.01). There is also a significant positive relationship between avoidance of organizational climate and affective commitment (r = 0.208, p = 0.049) and between focus on production and normative and continuance commitment (r = 0.308, p = 0.003). Conclusion: Improving the organizational climate could be a valuable strategy for improving organizational commitment.

A four-variable plate theory for thermal vibration of embedded FG nanoplates under non-uniform temperature distributions with different boundary conditions

Mohammad Reza Barati,Hossein Shahverdi 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.4

In this paper, thermal vibration of a nonlocal functionally graded (FG) plates with arbitrary boundary conditions under linear and non-linear temperature fields is explored by developing a refined shear deformation plate theory with an inverse cotangential function in which shear deformation effect was involved without the need for shear correction factors. The material properties of FG nanoplate are considered to be temperature-dependent and graded in the thickness direction according to the Mori-Tanaka model. On the basis of non-classical higher order plate model and Eringen’s nonlocal elasticity theory, the small size influence was captured. Numerical examples show the importance of non-uniform thermal loadings, boundary conditions, gradient index, nonlocal parameter and aspect and side-to-thickness ratio on vibrational responses of size-dependent FG nanoplates.

Equivalent material properties of perforated metamaterials based on relative density concept

Mohammad Reza Barati,Hossein Shahverdi 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.44 No.5

In this paper, the equivalent material properties of cellular metamaterials with different types of perforations have been presented using finite element (FE) simulation of tensile test in Abaqus commercial software. To this end, a Representative Volume Element (RVE) has been considered for each type of cellular metamaterial with regular array of circular, square, oval and rectangular perforations. Furthermore, both straight and perpendicular patterns of oval and rectangular perforations have been studied. By applying Periodic Boundary conditions (PBC) on the RVE, the actual behavior of cellular material under uniaxial tension has been simulated. Finally, the effective Young’s modulus, Poisson’s ratio and mass density of various metamaterials have been presented as functions of relative density of the RVE.

Spatio-temporal analysis of fire incidences in urban context: the case study of Mashhad, Iran

Mohammad Mahdi Barati Jozan,Alireza Mohammadi,Aynaz Lotfata,Hamed Tabesh,Behzad Kiani 대한공간정보학회 2024 Spatial Information Research Vol.32 No.1

The study aims to identify fire patterns in Mashhad, the second-most populous city in Iran, between 2015 and 2019. Spatial scan statistics were utilized to determine the spatiotemporal patterns of 29,889 fire events in the research area. There were four primary types of fires: (1) structural fires (39%), (2) vehicle fires (11%), (3) green and open space fires (19%), and (4) others (31%). The interval from 12:00 to 23:00 h was identified as the high-risk period for all fire incidents. Fires were common in the nearby city core. Additionally, three significant hourly spatial-temporal clusters of firefighting operations were identified: the western part of the city between 12:00 and 23:00, the city center between 11:00 and 22:00, and the southeastern part between 11:00 and 22:00. Population density, illiteracy ratio, unemployment ratio, youth ratio, lowincome population, and the number of old buildings might be socio-economic criteria that contribute to the spatiotemporal pattern of urban fires. Urban planners might prioritize high-risk neighborhoods when allocating resources for fire safety. Future research could specifically investigate high-risk regions to identify relevant characteristics in these areas.

Flutter behavior of graded graphene platelet reinforced cylindrical shells with porosities under supersonic airflow

Mohammad Mashhour,Mohammad Reza Barati,Hossein Shahverdi 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.5

In the present work, the flutter characteristics of porous nanocomposite cylindrical shells, reinforced with graphene platelets (GPLs) in supersonic airflow, have been investigated. Different distributions for GPLs and porosities have been considered which are named uniform and non-uniform distributions thorough the shell’s thickness. The effective material properties have been determined via Halpin-Tsai micromechanical model. The cylindrical shell formulation considering supersonic airflow has been developed in the context of first-order shell and first-order piston theories. The governing equations have been solved using Galerkin’s method to find the frequency-pressure plots. It will be seen that the flutter points of the shell are dependent on the both amount and distribution of porosities and GPLs and also shell geometrical parameters.

In-vitro experimental analysis of magnetic fluid hyperthermia in soft tissue with artificial blood perfusion

Mohammad Mahdi Attar,Farzan Barati,Gita Rezaei,Behroz Adelinia 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.1

Magnetic fluid exposed to an alternating magnetic field generates heat that it can be used for treatment and removal of cancerous tissue. The aim of this study is to investigate the thermal behavior of kidney tissue in magnetic fluid hyperthermia. Considering the fact that doing experiments on live tissue have some limitations, a new method is provided to test on dead tissue. In this study, an artificial circulation of the current vessels of kidney is used to make closer the behavior of dead tissue to live ones. The superparamagnetic nanoparticles with an average diameter of 20 nm have been used to heat tissue and an overview of the hardware devices needed to generate a magnetic field and to record temperature has been mentioned. Finally, the heating process has been simulated by the finite element software of Ansys. The nanoparticles injected to the tissue have a relatively spherical distribution which inevitably increases with increasing the intensity of the magnetic field and temperature difference dose. On the other hand it was observed that the rate of blood flow plays a key role in the analysis of tissue behavior and it is able to decrease the rise in temperature at most 70 %. Based on the results, it is inferred that the circulation along magnetic field intensity and dose of nanoparticles, plays a key role in the process of heating the tissue.

Failure analysis of unidirectional polymeric matrix composites with two serial pin loaded-holes

Mohammad Mahdi Attar,Farzan Barati,Mahdi Ahmadpour,Ehsan Rezapour 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.6

The objective of this study is to investigate the effects of geometrical and physical parameters on failure modes and failure loads in unidirectional polymeric matrix composites with two serial pin loaded holes, analytically and experimentally. It is assumed that all of unidirectional fibers in the laminate lie in one direction while loaded by a load p 0 at infinity, parallel to the direction of the fibers. To derive equilibrium equations based on a Shear-Lag theory, a rectangular arrangement of fibers is considered and with the proper use of boundary and boundness conditions, stress and displacement fields are computed within the laminate, along with the surrounding pinholes. Finally by using the Hashin criterion failure modes and failure loads are estimated. To validate analytical results based on shear-lag theory, an experimental program is carried out. A very good agreement is observed between two procedures. Based on results, in small sizes of two pins, the dominant failure mode is bearing and with the increasing of hole sizes, failure modes are changed to tension and shear modes.