This study aims to achieve effective analysis and fast modeling in free vibration and flutter analyses of low aspect ratio composite wings in subsonic flow for the preliminary design stage instead of using the computationally expensive finite element method. It uses an equivalent plate method for structural modeling. Also, it uses the Doublet point and the U-g methods for calculation of unsteady aerodynamic loads and carrying out flutter analysis, respectively. We investigate the effects of different parameters on the flutter behavior. The present results confirm that the structural tailoring can make a harmonious balance to the wing sweep angle effect upon the flutter behavior of composite wings, and a considerable improvement upon flutter performance is achieved by using composite materials.

On August 11, 2012, within several minutes, two shallow destructive earthquakes with moment magnitudes of 6.5 and 6.4 occurred in Varzagan, Azerbaijan-e-Sharghi Province, in the northwest of Iran. In this study, the Empirical Green Function (EGF) method was used for strong ground motion simulation to estimate the source parameters and rupture characteristics of the earthquakes. To simulate the first earthquake, two aftershocks with magnitudes of 5.6 and 5.2 were used as the EGFs. In the second event, an aftershock with a magnitude of 5 was used as the small event. The size of the main fault caused by the first event was about 18 km in length and 10 km in width. Also, the size of the asperity in the second earthquake was about 16 km in the strike direction and 11 km in the dip direction. The durations of the ruptures in the first and second events were more than 9 and 10s, respectively. The estimated fault plane solution showed strike-slip faulting for the first earthquake and a reverse mechanism with a strike-slip component for the second one. Strike, dip and rake of a causative fault of the first and second earthquakes were determined as 270, 81 and 175 degrees and 230, 57 and 134 degrees, respectively. In addition, the stress drop in the first and second events was calculated to be about 22 and 34 bar, respectively.

Precursors as informer pioneers of near future occurrence of earthquakes, are very diverse in their natures. We examined three short term possible precursors contain foreshocks, b-value variations, and amplitude abnormalities in the Very Low Frequency (VLF) radio signals for the November 14, 2021 Fin double-earthquakes (M > 6). By searching-zoom method in earthquakes one degree on each side of the hypocenter location in the Iranian Seismological Center (IrSC), the International Earthquake Engineering and Seismology (IIEES) and the Building and Hosing Research Center (BHRC) catalogs, those data for the reviewing foreshocks were provided, then they analyzed by use of ZMAP for the b-value changes based on the Guttenberg-Richter empirical relation methodology. Whereas, in the BHRC accelerometer portal reported 8 events before the main shock times, none of them are not in the other catalogs. The temporal b-value variations from the normal, shown non sharp fits to the rises or falls of the seismicity as an expected indicator. Some b-value in accordance with the seismic up and down rate tracks, have high spatial uncertainties. We observed some amplitude anomalies in the VLF received signals from mean standard deviation in VLF signal measurements (2σ criterion in the statistical method) in about 4 days before and up to 5 days after the main shocks. Albeit, in follow the null hypothesis, for verifying (and not refused) these relations, are needed to be qualified data. As you will see, all three catalogs used in the coverage, quality, verification and appropriate data for logical and reliable review and processing are not less error than the expected standards. The main goal has been to investigate the possible precursors before the 2021 Fin Doublet earthquakes by using available local ground base data and obtainable facilities in this field and considering their improvement. The possibility of some foreshocks associated with double earthquakes cannot be ruled out. Therefore, the reliability of the studied precursors completely dependent to the proper data, that sufficient-precise instruments for their observations and recording are vital requirement. It is possible to use that kind of reliable and high-quality data in the analysis of pre-earthquake signals or even reasonable forecasting, which, if possible, will bring a valuable achievement in the future. We came to the conclusion that with such researches, the necessity of data quality and improving the level of their acquisition/standard in the country's research centers, must be carefully defined for more scientific and practical effects.

This paper investigates the lateral vibration of single-layered graphene sheets based on a new theory called Doublet mechanics with a length scale parameter. After a brief reviewing of Doublet mechanics fundamentals, a sixth order partial differential equation that governs the lateral vibration of single-layered graphene sheets is derived. Using Doublet mechanics, the relation between natural frequency and length scale parameter is obtained in the lateral mode of vibration for single-layered graphene. It is shown that length scale parameter plays a significant role in the lateral vibration behavior of single-layered graphene sheets. Such effect decreases the natural frequency compared to the predictions of the classical continuum mechanics models. However with increasing the length of the plate, the effect of scale parameter on the natural frequency decreases. For validating the results of this method, the results obtained herein are compared with the existing nonlocal and molecular dynamics results and good agreement with the latter is observed.

In the present work, an analytical study is proposed to investigate the flutter behavior of low-aspect-ratio wings in subsonic flow. An equivalent plate model is used for structural modelling of a semi-monocoque main wing, consisting of ribs, skins, and spars. Legendre polynomials are used in the Rayleigh-Ritz method as trial functions, and the first-order shear deformation theory is utilized to formulate the structural deformation. Boundary conditions are enforced by applying proper artificial springs. A Doublet point method is used to calculate the unsteady aerodynamic loads. Chordwise pressure coefficient distribution at the tip and root of a rectangular wing oscillating in pitching motion is calculated. Flutter analysis is performed using the k method. Instead of using the computationally expensive finite element method, the proposed approach is intended to achieve purposes of quick modelling and effective analysis in free vibration and flutter analyses of low-aspectratio wings for preliminary design applications. The effects of aspect ratio on the flutter behavior of wings in subsonic flow are investigated. The obtained results are validated with the results available in the literature.

This paper investigates the coupled axial-radial (CAR) vibration of single-walled carbon nanotubes (SWCNTs) based on Doublet mechanics (DM) with a scale parameter. Two coupled forth order partial differential equations that govern the CAR vibration of SWCNTs are derived. It is the first time that DM is used to model the CAR vibration of SWCNTs. To obtain the natural frequency and dynamic response of the CAR vibration, the equations of motion are solved and the relation between natural frequencies and scale parameter is derived. It is found that there are two frequencies in the frequency spectrum and these CAR vibrational frequencies are complicated due to coupling between two vibration modes. The advantage of these analytical formulas is that they are explicitly dependent to scale parameter and chirality effect. The influence of changing some geometrical and mechanical parameters of SWCNT on its CAR frequencies has been investigated, too. It is shown that the chirality and scale parameter play significant role in the CAR vibration response of SWCNTs. The scale parameter decreases the higher band CAR frequency compared to the predictions of the classical continuum models. However, with increase in tube radius and length, the effect of the scale parameter on the natural frequencies decreases. The lower band CAR frequency is nearly independent to scale effect and tube diameter. The CAR frequencies of SWCNTs decrease as the length of the tube increases. This decreasing is higher for higher band CAR frequency. To show the accuracy and ability of this method, the results obtained herein are compared with the existing theoretical and experimental results and good agreement is observed.

Using Galerkin vector approach closed-form analytic expressions for the displacements and stresses caused by a Doublet source buried in a homogenous, isotropic, perfectly elastic half-space have been obtained. Further, the viscoelastic deformation field has been obtained by applying the correspondence principle of linear viscoelasticity, assuming the medium to be elastic in dilatation and Kelvin, Maxwell, or SLS (Standard linear solid) type viscoelastic in distortion. The effect of Poisson’ s ratio on the deformation field due to a Doublet source is examined in elastic half-space. The effect of relaxation time on displacement and stress fields is studied due to a Doublet source in viscoelastic half-space. The variation of the displacements and stresses with the epicentral distance is studied graphically using MATLAB software. Stresses for a Doublet with axis parallel to x-axis attain minimum value for Poissonian half-space. Viscoelastic displacements and stresses attain maxima for the Maxwell model and minima for the Kelvin model.

example of a fully relativistic equation with both negative and positive energy solutions. The effect of the negative energy states was mitigated by maximizing the energy with respect to a relevant parameter while at the same time minimizing it with respect to another parameter in the wave function. The Cornell potential and a power-law scalar and vector potentials were used in our calculations for the quark confinement. Cares were taken to avoid the Klein paradox by the dominance of the scalar component over the vector part.