Free vibration analysis of cracked thin plates using generalized differential quadrature element method

Hossein Shahverdi,Mohammad M. Navardi 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.62 No.3

The aim of the present study is to develop an elemental approach based on the differential quadrature method for free vibration analysis of cracked thin plate structures. For this purpose, the equations of motion are established using the classical plate theory. The well-known Generalized Differential Quadrature Method (GDQM) is utilized to discretize the governing equations on each computational subdomain or element. In this method, the differential terms of a quantity field at a specific computational point should be expressed in a series form of the related quantity at all other sampling points along the domain. However, the existence of any geometric discontinuity, such as a crack, in a computational domain causes some problems in the calculation of differential terms. In order to resolve this problem, the multi-block or elemental strategy is implemented to divide such geometry into several subdomains. By constructing the appropriate continuity conditions at each interface between adjacent elements and a crack tip, the whole discretized governing equations of the structure can be established. Therefore, the free vibration analysis of a cracked thin plate will be provided via the achieved eigenvalue problem. The obtained results show a good agreement in comparison with those found by finite element method.

Aeroelastic stability analysis of a two-stage axially deploying telescopic wing with rigid-body motion effects

Sayed Hossein Moravej Barzani,Hossein Shahverdi Techno-Press 2023 Advances in aircraft and spacecraft science Vol.10 No.5

This paper presents the study of the effects of rigid-body motion simultaneously with the presence of the effects of temporal variation due to the existence of morphing speed on the aeroelastic stability of the two-stage telescopic wings, and hence this is the main novelty of this study. To this aim, Euler-Bernoulli beam theory is used to model the bending-torsional dynamics of the wing. The aerodynamic loads on the wing in an incompressible flow regime are determined by using Peters' unsteady aerodynamic model. The governing aeroelastic equations are discretized employing a finite element method based on the beam-rod model. The effects of rigid-body motion on the length-based stability of the wing are determined by checking the eigenvalues of system. The obtained results are compared with those available in the literature, and a good agreement is observed. Furthermore, the effects of different parameters of rigid-body such as the mass, radius of gyration, fuselage center of gravity distance from wing elastic axis on the aeroelastic stability are discussed. It is found that some parameters can cause unpredictable changes in the critical length and frequency. Also, paying attention to the fuselage parameters and how they affect stability is very important and will play a significant role in the design.

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.

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.

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.

Thermo-mechanical analysis of soft tissue in local hyperthermia treatment

Mohammad Mahdi Attar,Mohammad Haghpanahi,Hossein Shahverdi,Ali Imam 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.3

Magnetic fluid hyperthermia is a new subclass of hyperthermia cancer treatment that can selectively heat up a tumor without damaging the surrounding healthy tissues. Some authors studied the temperature distribution of a magnetically mediated tumor assuming a homogeneous distribution of nanoparticles inside the tumor. Viscoelastic behavior of cancerous and healthy tissues have been studied in various articles and many methods have been introduced for computation of physical-mechanical properties of the tissue considering the fact that thermo-mechanical properties of the tissue completely change when the tissue becomes cancerous. Purpose of this study is to investigate thermo-visco-elastic behavior of tumorous and healthy bovine liver tissue. Therefore, the tumor is simulated as a solid sphere having radius denoted as r along with the surrounding healthy tissue. Any discontinuity between cancerous and healthy tissues is neglected. Since the resulting constitutive equations are highly complex, the stress and displacement fields were calculated by using finite difference method. An experimental test was designed to validate numerical results. Numerical results are found to be in good agreement with experimental data and with other references on homogeneous dispersion of nanoparticles.

Effects of intraperitoneal administration of Papaver rhoeas L. extract on mouse ovaries

Afsaneh Golkar-Narenji,Hussein Eimani,Firooz Samadi,Saeid Hasani,Abdol hossein Shahverdi,Poopak Eftekhari-Yazi,Mohammad Kamalinejad 한국통합생물학회 2013 Animal cells and systems Vol.17 No.2

This research studies the effect of water-alcohol Papaver rhoeas L. (P. rhoeas) extract on mouse ovaries and in vitro development (IVD) of oocytes. Different dosages of P. rhoeas extract (25, 50, 100, 200 mg/kg body weight) were injected intraperitoneally (i.p.) during a period of 12 days. Following superovulation, the numbers of ovulated oocytes, the rates of in vitro fertilization, IVD and the cellularity of blastocysts were recorded. Additionally, effect of the best dosage on ovarian follicle population and the ability of immature oocytes to mature in vitro were evaluated. Administration of 200 mg/kg significantly increased the percentage of 48 cells, morula and blastocyst embryos compared to the control group (pB0.05). Furthermore, total cellularity of blastocysts was significantly higher with the administration of 200 mg/kg of extract in comparison to control group (pB0.05). Therefore, the most effective dosage was considered to be 200 mg/kg. With the administration of 200 mg/kg no marked changes were observed in the IVM rate of retrieved oocytes from treated group in comparison to control group. Furthermore, the percentage of ovarian follicles was not significantly different when compared to control group. Also, during visual evaluations no abnormal apoptosis was detected in follicles of ovaries treated with 200 mg/kg when compared to control group. Higher IVD and blastocyst cellularity in the group treated with defined dosage of P. rhoeas indicates that the extract affects ovaries in a dose dependent manner. The extract possibly increases the quality of ovulated oocytes and IVD competence of oocytes.