3D waviness effect of carbon nanotubes on fundamental natural frequency and modeling of resonance of nanocomposite structure

Optimum waviness of carbon nanotubes (CNTs) inside a matrix composite beam and composite bridge is endeavor to obtain its utmost natural frequencies considering a volume fraction of CNTs. 3D FE model of the beam is generated via ABAQUS along with Python programming and thereafter to calculate an optimal waviness under encastre boundary conditions and different vibration modes. The effect of waviness and the number of waves on mode shapes, natural frequency, and corresponding stiffness of a beam are examined, and the outcomes are compared to those of a pure polymer beam, straight CNT-based composite beam and nanobridge value. It was decided to conduct a convergence analysis and the optimum value of the number of elements and nodes was studied and found that 19666 nodes are reliable to give correct results. The FE analysis results reveal that the waviness effect of CNTs significantly depends on mode shapes. The fundamental natural frequency, as well as other related vibrational properties, is observed to be enhanced. By decreasing the waviness from 50 to 25, there is an increment in natural frequency in the 3rd mode by 68.68, 5th mode by 44.6 and 6th mode by 62.4, but in other modes, there is negligible difference. When single-wave CNTs were compared, the sine wave produced more frequency in the third mode by 206.03, 4th mode by 199.8 and 6th mode by 478.6[Formula: see text]Hz. After comparing the results of different waviness types, single sine waviness, multi-waved CNTs, straight CNTs and neat matrix, it is found that for the highest value of waviness of CNT fiber-based nanocomposites, the natural frequency of CNT-reinforced nanocomposite reaches the frequency of the neat matrix and further adding of CNTs does not increase the value of frequency. The result showed that the finite element model (FEM) is a good simulation of the vibratory system.

Long-term monitoring of dynamic characteristics of high-rise and super high-rise buildings using strong motion records

Seismic behavior of a structure is directly related to its dynamic characteristics, which include natural frequency, damping ratio, and mode shape. This study focuses on the long-term monitoring of dynamic characteristics of six selected target structures. The covariance-driven stochastic subspace identification (SSI) approach is used to estimate the fundamental natural frequency and damping ratio of target buildings based on long-term motion records in order to examine the temporal variation of dynamic properties. The fundamental natural frequency and damping ratio variations over time are first discussed. It is found that the fundamental natural frequency of some structures reduces dramatically after the 2011 Tohoku Earthquake, accompanied by a rise in damping ratio. Then, regression analysis is used to assess the relationship between dynamic characteristics and ground motion parameters (Peak ground acceleration (PGA), magnitude, focal depth, and epicentral distance) and structural response (root mean square acceleration, maximum response amplitude). It is discovered that the identified natural frequency has no clear correlation with the focal depth, a slight negative correlation with the epicentral distance, and a strong negative correlation with the magnitude and PGA. The root mean square acceleration and the maximum response amplitude are negatively correlated to the target buildings’ natural frequencies. Finally, the influence of environmental factors on dynamic properties is investigated.

Natural Frequency Analysis of Multilayer Truncated Conical Shells Containing Quiescent Fluid on Elastic Foundation with Different Boundary Conditions

In this paper, natural frequency of a multilayer truncated conical composite shell conveying quiescent fluid on elastic foundation with different boundary conditions is investigated and analyzed. The governing equations are presented based on the first-order shear deformation theory. Bernoulli’s equation and velocity potential have been used in the shell-fluid interface to obtain the fluid pressure. The fluid used in this study is considered non-compressible and non-viscous. The beam functions and the Galerkin weight functions method are used to describe and solve the coupled system of differential equations. Three types of boundary conditions are considered to investigate the natural frequency of the conical shells. The results show that the presence of the fluid in the conical shell reduces the fundamental natural frequency values. Also, by changing the semi-vertex conical angle from [Formula: see text] to [Formula: see text] for the simply support boundary conditions, the fundamental natural frequency value for the composite conical shell without and with fluid increases, and the presence of the elastic foundation increases the frequencies of the empty and full-fluid composite conical shells.

Free flexural vibrations of homogeneous beams with symmetrically variable depths

The subject of the paper are homogeneous beams of symmetrically variable depth and bisymmetrical cross sections. Free flexural vibrations of these beams are analytically and numerically studied. Based on Hamilton’s principle, the differential equations of motion of these beams are obtained. The equations of motion are analytically solved with consideration of the bending lines of these beams subjected to their own weight. The fundamental natural frequency for exemplary beams is derived and presented in Tables and Figures.

Application of alternative II theory to vibration and stability analysis of thick rectangular plates (Isotropic and orthotropic)

This work analysed the free vibration and stability of thick isotropic and orthotropic plates with SSSS and SSFS support conditions by applying the alternative II theory based on polynomial shape function. The total potential energy which was obtained by combining the strain energy and external work was reduced to three governing equations using Ritz method. Polynomial shape function which varies with Poisson’s ratio was substituted into the governing equation to obtain the fundamental natural frequency, linear frequency and critical buckling load. The values of frequencies of the first mode and critical loads obtained were compared with those obtained using first order shear deformation theory. For span depth ratio of 10, the fundamental linear frequency for orthotropic SSFS plate corresponding to modulus of elasticity ratios (E1/E2) of 10, 25 and 40 are 0.00156, 0.00219 and 0.00255Hz. The corresponding values using first order shear deformation theory are 0.00152, 0.00212 and 0.00245Hz. Keywords: Fundamental natural frequency, SSSS plate, SSFS plate, Ritz method, Orthotropic thick plate, Isotropic thick plate, Stability, Free vibration