Nonlocal vibration of carbon/boron-nitride nano-hetero-structure in thermal and magnetic fields by means of nonlinear finite element method

Hamid M. Sedighi,Mohammad Malikan,Ali Valipour,Krzysztof Kamil Zur 한국CDE학회 2020 Journal of computational design and engineering Vol.7 No.5

Hybrid nanotubes composed of carbon and boron-nitride nanotubes have manifested as innovative building blocks to exploit the exceptional features of both structures simultaneously. On the other hand, by mixing with other types of materials, the fabrication of relatively large nanotubes would be feasible in the case of macroscale applications. In the current article, a nonlinear finite element formulation is employed to deal with the nonlocal vibrational behavior of carbon/boron-nitride nano-hetero-tubes in the presence of magneto-thermal environment. Euler–Bernoulli beam model in conjunction with the Eringen’s nonlocal theory of elasticity is adopted to derive the governing equation of motion. In order to conduct a nonlinear frequency analysis, the von-K´arm´an nonlinearity associated with moderate rotations is also considered. It is well known that temperature gradients can significantly change the dynamic behavior of nanotubes. On the other hand, the coefficients of thermal expansions of carbon and boron-nitride nanotubes are quite different that may affect the structural stability of hybrid nanotubes. Hence, to explore the vibration characteristic of such composite structures, the influence of magneto-thermal environment is also taken into account. Finally, the eigenvalue analysis is performed to exhibit the nonlinear mode shapes and natural frequencies of the system due to initial displacement. It is expected that the recognition of dynamic behavior of such hybrid nanotubes may open the doors to the creative design of next-generation nano-devices.

Static and dynamic pull-in instability of multi-walled carbon nanotube probes by He’s iteration perturbation method

Hamid M. Sedighi,Farhang Daneshmand 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.9

A continuum model is utilized to extract the nonlinear governing equation for Carbon nanotube (CNT) probes near graphite sheets. The van der Waals (vdW) intermolecular force and electrostatic actuation are included in the equation of motion. Static and dynamicpull-in behavior of the system is investigated in this paper. To this end, a new asymptotic procedure is presented to predict the pull-ininstability of electrically actuated CNTs by employing an analytic approach namely He's iteration perturbation method (IPM). The effectsof basic non-dimensional parameters such as initial amplitude, intermolecular force, geometrical parameter and actuation voltage on thepull-in instability as well as the fundamental frequency are studied. The obtained results from numerical simulations by employing threemode assumptions verify the strength of the analytical procedure. The qualitative analysis of the system dynamics shows that the equilibriumpoints of the autonomous system include stable center points and unstable saddle nodes. The phase portraits of the carbon nanotubeactuator exhibit periodic and homoclinic orbits.

Forward and backward whirling of a spinning nanotube nano-rotor assuming gyroscopic effects

Ouakad, Hassen M.,Sedighi, Hamid M.,Al-Qahtani, Hussain M. Techno-Press 2020 Advances in nano research Vol.8 No.3

This work examines the fundamental vibrational characteristics of a spinning CNT-based nano-rotor assuming a nonlocal elasticity Euler-Bernoulli beam theory. The rotary inertia, gyroscopic, and rotor mass unbalance effects are all taken into consideration in the beam model. Assuming a nonlocal theory, two coupled 6th-order partial differential equations governing the vibration of the rotating SWCNT are first derived. In order to acquire the natural frequencies and dynamic response of the nano-rotor system, the nonlinear equations of motion are numerically solved. The nano-rotor system frequency spectrum is shown to exhibit two distinct frequencies: one positive and one negative. The positive frequency is known as to represent the forward whirling mode, whereas the negative characterizes the backward mode. First, the results obtained within the framework of this numerical study are compared with few existing data (i.e., molecular dynamics) and showed an overall acceptable agreement. Then, a thorough and detailed parametric study is carried out to study the effect of several parameters on the nano-rotor frequencies such as: the nanotube radius, the input angular velocity and the small scale parameters. It is shown that the vibration characteristics of a spinning SWCNT are significantly influenced when these parameters are changed.

Repair of Tetralogy of Fallot in Infancy via the Atrioventricular Approach

Hamid Bigdelian, M.D.,Mohsen Sedighi, Ph.D. 대한흉부외과학회 2016 Journal of Chest Surgery (J Chest Surg) Vol.49 No.1

Background: Tetralogy of Fallot (TOF) is a well-recognized congenital heart disease. Despite improvements in the outcomes of surgical repair, the optimal timing of surgery and type of surgical management of patients with TOF remains controversial. The purpose of this study was to assess outcomes following the repair of TOF in infants depending on the surgical procedure used. Methods: This study involved the retrospective review of 120 patients who underwent TOF repair between 2010 and 2013. Patients were divided into three groups depending on the surgical procedure that they underwent. Corrective surgery was done via the transventricular approach (n=40), the transatrial approach (n=40), or a combined atrioventricular approach (n=40). Demographic data and the outcomes of the surgical procedures were compared among the groups. Results: In the atrioventricular group, the incidence of the following complications was found to be significantly lower than in the other groups: complete heart block (p=0.034), right ventricular failure (p=0.027) and mediastinal bleeding (p=0.007). Patients in the atrioventricular group had a better postoperative right ventricular ejection fraction (p=0.001). No statistically significant differences were observed among the three surgical groups in the occurrence of tachycardia, renal failure, and tricuspid incompetence. The one-year survival rates in the three groups were 95%, 90%, and 97.5%, respectively (p=0.395). Conclusion: Combined atrioventricular repair of TOF in infancy can be safely performed, with acceptable surgical risk, a low incidence of reoperation, good ventricular function outcomes, and an excellent survival rate.

Dynamic load concentration caused by a break in a Lamina with viscoelastic matrix

Arash Reza,Hamid M. Sedighi,Mahdi Soleimani 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.6

The effect of cutting off fibers on transient load in a polymeric matrix composite lamina was studied in this paper. The behavior of fibers was considered to be linear elastic and the matrix behavior was considered to be linear viscoelastic. To model the viscoelastic behavior of matrix, a three parameter solid model was employed. To conduct this research, finite difference method was used. The governing equations were obtained using Shear-lag theory and were solved using boundary and initial conditions before and after the development of break. Using finite difference method, the governing integro-differential equations were developed and normal stress in the fibers is obtained. Particular attention is paid the dynamic overshoot resulting when the fibers are suddenly broken. Results show that considering viscoelastic properties of matrix causes a decrease in dynamic load concentration factor and an increase in static load concentration factor. Also with increases the number of broken fibers, trend of increasing load concentration factor decreases gradually. Furthermore, the overshoot of load in fibers adjacent to the break in a polymeric matrix with high transient time is lower than a matrix with lower transient time, but the load concentration factor in the matrix with high transient time is lower.

Nonlinear vibration and stability of FG nanotubes conveying fluid via nonlocal strain gradient theory

Van-Hieu Dang,Hamid M. Sedighi,Do Quang Chan,Ömer Civalek,Ahmed E. Abouelregal 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.78 No.1

In this work, a model of a functionally graded (FG) nanotube conveying fluid embedded in an elastic medium is developed based on the nonlocal strain gradient theory (NSGT) in conjunction with Euler-Bernoulli beam theory (EBT). The main objective of this research is to investigate the nonlinear vibration and stability analysis of fluid-conveying nanotubes. The governing equations of motion are derived by means of Hamiltonian principle. The analytical expressions of nonlinear frequencies and critical flow velocities for two different types of boundary conditions including pinned-pinned (P-P) and clamped-clamped (C-C) conditions are obtained by employing Galerkin method as well as Hamiltonian Approach (HA). Comparison of the obtained results with the published works show the acceptable accuracy of the current solutions. The effects of the power-law index, the nonlocal and material length scale parameters and the elastic medium on the stability and nonlinear responses of FG nanotubes are thoroughly investigated and discussed.

Higher order and scale-dependent micro-inertia effect on the longitudinal dispersion based on the modified couple stress theory

Delara Soltani,Majid Akbarzadeh Khorshidi,Hamid M. Sedighi 한국CDE학회 2021 Journal of computational design and engineering Vol.8 No.1

The conventional modified couple stress theory cannot model the correct behavior of the longitudinal dispersion and acts the same as the classical theory in the face of such problems. In this paper, the micro-inertia-based couple stress theory is used to triumph over this deficiency. The developed theory is imposed to tackle the longitudinal dispersion of aluminum beams in two distinct scales. Convenient available experimental data obtained for a macro-scale aluminum rod and aluminum crystals are utilized to determine the corresponding micro-inertia length scale parameters and show the scale-dependent nature of this parameter for the first time. In addition, a higher order micro-rotation relation is employed to describe the higher order micro-inertia effects. This relation leads to a developed equation of motion containing an additional term compared with the first-order relation. The obtained results indicate that only higher order micro-inertia effect that is proposed in this study for the first time is able to capture the highly nonlinear behavior of dispersion curves (including an extremum/inflection point), which has experimentally been observed for phonons propagating in the longitudinal direction in an aluminum crystal.

Thermoelastic deformation properties of non-localized and axially moving viscoelastic Zener nanobeams

Ahmed E. Abouelregal,Badahi Ould Mohamed,Hamid M. Sedighi Techno-Press 2024 Advances in nano research Vol.16 No.2

This study aims to develop explicit models to investigate thermo-mechanical interactions in moving nanobeams. These models aim to capture the small-scale effects that arise in continuous mechanical systems. Assumptions are made based on the Euler-Bernoulli beam concept and the fractional Zener beam-matter model. The viscoelastic material law can be formulated using the fractional Caputo derivative. The non-local Eringen model and the two-phase delayed heat transfer theory are also taken into account. By comparing the numerical results to those obtained using conventional heat transfer models, it becomes evident that non-localization, fractional derivatives and dual-phase delays influence the magnitude of thermally induced physical fields. The results validate the significant role of the damping coefficient in the system's stability, which is further dependent on the values of relaxation stiffness and fractional order.