JOURNAL OF SIMULATION AND ANALYSIS OF NOVEL TECHNOLOGIES IN MECHANICAL ENGINEERING (JOURNAL OF SOLID MECHANICS IN ENGINEERING)
Year:2016 | Volume:8 | Issue:4 |Papers Count:6

In this paper, the non-linear dynamic response of rectangular atomic force microscopy in tapping mode is considered. The effect of cantilever’s geometrical parameters (e.g., cantilever length, width, thickness, tip length and the angle between the cantilever and the sample's surface in liquid environment has been studied by taking into account the interaction forces. Results indicate that the resonant frequency, amplitude and phase are very sensitive to changes of geometrical parameters. In order to improve and optimize the system's behavior, the sensitive analysis (SA) of geometrical parameters on the first resonant frequency and amplitude of cantilever's vertical displacement has been conducted using Sobol's method. Results show that the influence of each geometrical variable on frequency response of the system can play a crucial role in designing the optimum cantilever in liquid medium for soft and sensitive biological samples. Also, one way to speed up the imaging process is to use short cantilevers. For short beams, the Timoshenko model seems to be more accurate compared to other models such as the Euler-Bernoulli. By using the Timoshenko beam model, the effects of rotational inertia and shear deformation are taken into consideration. In this paper, this model has been used to obtain more accurate results.

Based on the nonlocal Timoshenko beam theory, the dynamic stability of functionally gradded (FG) nanoeams under axial load is studied in thermal environment, with considering surface effect. It is used power law distribution for FGM and the surface stress effects are considered based on Gurtin-Murdoch continuum theory. Using Von Karman geometric nonlinearity, governing equations are derived based on Hamilton’s principle. The developed nonlocal models have the capability to interpret small scale effects. Winkler and Pasternak types elastic foundation are employed to represent the interaction of the nano FG beam and the surrounding elastic medium. A parametric study is conducted to investigate the influences of the static load factor, temperature change, nonlocal elastic parameter, slenderness ratio, surface effect and springs constant of the elastic medium on the dynamic stability characteristics of the FG beam, with simply-supported boundary conditions. It is found that the difference between instability regions predicted by local and nonlocal beam theories is significant for nanobeams with lower aspect ratios. Moreover, it is observed that in contrast to high temperature environments, at low temperatures, increasing the temperature change moves the origins of the instability regions to higher excitation frequencies and leads to further stability of the system at lower excitation frequencies, considering surface stress effect shifts the FG beam to higher frequency zone.

Due to geographic and climatic conditions in mountainous northwest area, Roads in these areas are often covered with snow, ice and mud. Hence Transportation of equipment and soldiers encounter hardship and difficulties in rural area and specially outposts. To solve these problems, it is needed to fabricate portable roadway or traction mats. These high strength mats cover surface of roads and are compatible with mentioned conditions. In this Research an Aluminum alloy profile used as a portable pad and loads was analyzed and simulated for a Toyota Hilux with 3 ton weight. In order to selection optimal geometry, relation between stress and geometric parameters such as dimension, profile channel length and forming angle of pad was investigated.Results showed that the optimal profile angel, thickness and channel length is 90o, 4 mm and 3 mm respectively.

One of the recently considered applications of fiber optic, in their usage in building lighting systems. In this research, in order to reduce energy consumption, by transmission of sun light from the roof to the desired place (i.e. an office), the required standard luminance is produced. The main aims of this research are:1. Reduction of energy consumption.2. Making the place compatible with the human favorable mental conditions and environment.3. Preparing the basics of mass production of the system and economical benefits for the universityIn this research besides concentrating the sun light to magnify its density, some investigations are made for light transmission by fiber optics, because, no mathematical model was found for this per pose, practical tests are made in addition to statistical analysis.Using different lenses and fiber optics and a position control system (which specially designed for this research), many experiences were made and iluminances were measured by a lux meter. After that by SPSS V.17 software, the results were analyzed. Finally the best Lenz and fiber were selected and a straight forward method was presented for designing a typical office in such manner.

Energy absorption capability of thin-walled structures with various cross sections has been considered by researchers up to now. These structures as energy absorbers are used widely in different industries such as automotive and aerospace and protect passengers and goods against impact. In this paper, mechanical behavior of thin-walled aluminum tubes with and without polyurethane foam filler subjected to axial impact has been investigated. The tubes are very thin so that (D/t) ≈ 550 governs for cylindrical specimen. Structure behavior was analyzed through finite element analysis by LS-DYNA. Circular, hexagonal, and square cross sections with the same length, thickness, and circumference of sections were studied. The results show that circular cross section has the highest energy absorption while experiences the lowest change in length compared to hexagonal and square cross sections. Besides, the effects of stress concentration in hexagonal and square sections can be observed on the corners of walls. Also under the dynamic loading circular structure was crushed more symmetric, while hexagonal and square structures tended to the buckling. Also an Artificial Neural Network is introduced to predict load & energy Absorption behavior. The Neural Network's data obtained from LS-DYNA. The introduced model could present acceptable results in comparison with analysis of LS-DYNA.

In this paper, a discontinuity in beams whose intensity is adjusted by the spring stiffness factor is modeled using a torsional spring. Adapting two analyses in strong and weak forms for discontinuous beams, the improved governing differential equations and the modified stiffness matrix are derived respectively. In the strong form, two different solution methods have been presented to make an analogy between the formulation of the Euler-Bernoulli and Timoshenko theories that indicates the influence of the shear deformation in discontinuous beams. The flexural stiffness of discontinuous beams is corrected by using the Dirac’s delta function. In the weak form, the reduced stiffness matrix is derived from the strain energy equation established by the continuity, kinematics and constitutive equations. The linearity assumption of the geometry and material is considered to construct the kinematics and constitutive equations respectively. The continuity conditions mathematically connect two divided parts of the Euler-Bernoulli beam for which an improved Hermitian shape function is employed to interpolate displacement field. An application shows the comparison and validation of the results of the strong and weak forms, and also the static behavior of discontinuous beams.