Three dimensional frequency analysis of bidirectional functionally graded thick cylindrical shells using a radial point interpolation method (RPIM)

This paper considers a functionally graded (FG) shell using a meshless radial point interpolation method (RPIM). The material is assumed to be bidirectional FG, where the variation is present in both the radial and the axial directions. Based on the three-dimensional equations of motion, the frequency equations are stated using RPIM. Numerical results are presented for a thick shell for various boundary conditions. These results illustrate the influence from the material variation concerning eigenfrequencies and eigenmodes. In addition, the study shows that the RPIM is an efficient method to solve dynamical shell problems

Oscillatory characteristics of metallic nanoparticles inside lipid nanotubes

This study is concerned with the oscillatory behavior of metallic nanoparticles, and in particular silver and gold nanoparticles, inside lipid nanotubes (LNTs) using the continuum approximation along with the 6-12 Lennard-Jones (LJ) potential function. The nanoparticle is modeled as a dense sphere and the LNT is assumed to be comprised of six layers including two head groups, two intermediate layers and two tail groups. To evaluate van der Waals (vdW) interactions, analytical expressions are first derived through undertaking surface and volume integrals which are then validated by a fully numerical scheme based on the differential quadrature (DQ) technique. Using the actual force distribution between the two interacting molecules, the equation of motion is directly solved utilizing the Runge-Kutta numerical integration scheme to arrive at the time history of displacement and velocity of the inner core. Also, a semi-analytical expression incorporating both geometrical parameters and initial conditions is introduced for the precise evaluation of oscillation frequency. A comprehensive study is conducted to gain an insight into the influences of nanoparticle radius, LNT length, head and tail group thicknesses and initial conditions on the oscillatory behavior of the metallic nanoparticles inside LNTs. It is found that the escape velocity and oscillation frequency of silver nanoparticles are higher than those of gold ones. It is further shown that the oscillation frequency is less affected by the tail group thickness when compared to the head group thickness

Exact solution for the vibrations of cylindrical nanoshells considering surface energy effect

It has been revealed that the surface stress effect plays an important role in the mechanical behavior ofstructures (such as bending, buckling and vibration) when their dimensions are on the order ofnanometer. In addition, recent advances in nanotechnology have proposed several applications fornanoscale shells in different fields. Hence, in the present article, within the framework of surfaceelasticity theory, the free vibration behavior of simply-supported cylindrical nanoshells with theconsideration of the aforementioned effect is studied using an exact solution method. To this end, first,the governing equations of motion and boundary conditions are obtained by an energy-basedapproach. The surface stress influence is incorporated into the formulation according to the Gurtin-Murdoch theory. The nanoshell is modeled according to the first-order shear deformation shell theory.After that, the free vibration problem is solved through an exact solution approach. To this end, thedimensionless form of governing equations is derived and then solved under the simply-supportedboundary conditions using a Navier-type solution method. Selected numerical results are presentedabout the effects of surface stress and surface material properties on the natural frequencies ofnanoshells with different radii and lengths. The results show that the surface energies significantlyaffect the vibrational behavior of nanoshells with small magnitudes of thickness. Also, it is indicatedthat the natural frequency of the nanoshell is dependent of the surface material properties

IMECE2010-38693 Multi-objective crashworthiness optimization of Composite Hat-shape Energy Absorber using GMDH-type Neural Networks and Genetic Algorithms

Abstract Reducing the weight of car body and increasing the crashworthiness capability of car body are two important objectives of car design. In this paper, a multi-objective optimization for optimal composite hat-shape energy absorption system is presented At the first, the behaviors of the hat shape under impact, as simplified model of side member of a vehicle body, are studied by the finite element method using commercial software ABAQUS. Two meta-models based on the evolved group method of data handling (GMDH) type neural networks are then achieved for modeling of both the absorbed energy (E) and the Tsai-Hill Failure Criterion (TS) with respect to geometrical design variables using those training and testing data obtained models. The obtained polynomial neural metamodels are finally used in a multi-objective optimum design procedure using NSGA-II with a new diversity preserving mechanism for Pareto based optimization of hat-shape. Two conflicting objectives such as maximizing the energy absorption capability (E), minimizing the Tsai-Hill Failure Criterion are considered in this work

Effects of Fluid Environment Properties on the Nonlinear Vibrations of AFM Piezoelectric Microcantilevers

Nowadays, atomic-force microscopy plays a significant role in nanoscience and nanotechnology, and is widely used for direct measurement at atomic scale and scanning the sample surfaces. In tapping mode, the microcantilever of atomic-force microscope is excited at resonance frequency. Therefore, it is important to study its resonance. Moreover, atomic-force microscopes can be operated in fluid environments such as their applications in chemical and biological sensors. Additionally, piezoelectric microcantilevers are used to enhance atomic-force microscope scanning. Motivated by these considerations, presented herein is a finite element investigation into the nonlinear vibration behavior of piezoelectric microcantilever of atomic-force microscopes in fluid environment. For this purpose, a 3D finite element model coupled with a computational fluid dynamics model is introduced based upon a fluid-solid interaction analysis. First, the reliability of present fluid-solid interaction analysis is revealed by comparison with experimental data available in the literature. Then, numerical results are presented to study the influences of fluid dynamic viscosity and density on the resonance frequency, resonance amplitude and time response of piezoelectric microcantilever. It was shown that increasing the fluid density and dynamic viscosity results in the decrease of resonance frequency. For example, for density equal to 1000 kg/m3 , increasing the viscosity of fluid environment from 0.1 to 1, 10 and 20 mPa.s leads to decrease of resonance frequency about 3%, 29% and 42%, respectively. Also, the resonance amplitude of microcantilever increases as the density increases, while increasing dynamic viscosity has a decreasing effect on the resonance amplitude