For the first time, the nonlinear bending behavior of porous functionally graded (FG) curved nanotubes is studied in this paper. The stiffness enhancement and stiffness reduction effects are ...described by the nonlocal strain gradient theory. The FG curved nanotubes have uniformly distributed pores in the radial direction. The material properties of the nanotubes corresponds to a modified power-law function. The asymptotic solutions of the curved nanotubes is obtained by using the two-step perturbation method. It shows that the nonlinear bending behavior of the curved nanotubes is influenced by the size effects, power law index, porosity distribution, temperature variation, boundary conditions, and physical dimension. Furthermore, the jump changes as well as snap-through buckling can take place when the FG curved nanotubes are under the influence of normal bending loads.
•Thermal buckling analysis of FGM beams by various theories are presented.•A two-step perturbation method is employed to determine the critical buckling loads and post-buckling equilibrium paths.•The ...post-buckling equilibrium path for FGM beam with two clamped ends is also of the bifurcation type for any various displacement fields.
In the present work, attention is focused on the prediction of thermal buckling and post-buckling behaviors of functionally graded materials (FGM) beams based on Euler–Bernoulli, Timoshenko and various higher-order shear deformation beam theories. Two ends of the beam are assumed to be clamped and in-plane boundary conditions are immovable. The beam is subjected to uniform temperature rise and temperature dependency of the constituents is also taken into account. The governing equations are developed relative to neutral plane and mid-plane of the beam. A two-step perturbation method is employed to determine the critical buckling loads and post-buckling equilibrium paths. New results of thermal buckling and post-buckling analysis of the beams are presented and discussed in details, the numerical analysis shows that, for the case of uniform temperature rise loading, the post-buckling equilibrium path for FGM beam with two clamped ends is also of the bifurcation type for any arbitrary value of the power law index and any various displacement fields.
On wave propagation of porous nanotubes She, Gui-Lin; Yuan, Fuh-Gwo; Ren, Yi-Ru
International journal of engineering science,
September 2018, 2018-09-00, Letnik:
130
Journal Article
Recenzirano
An analytic model of porous nanotubes for the wave propagation analysis is formulated with the help of the nonlocal strain gradient theory. The dispersion relations between phase velocity and wave ...number is determined by solving an eigenvalue problem. It is found that the asymptotic phase velocity can be increased by increasing the strain gradient parameter or decreasing the nonlocal parameter. In addition, the heterogeneity of functionally graded materials and temperature variation have a substantial influence on the dispersion relations of nanotubes. The nonlocal parameter and strain gradient parameter have significant effects on the dispersion relation at high wave numbers, in contrast, this effects can be negligible at low wave numbers. Meanwhile, it can be inferred that the phase velocity can decrease or increase as the porosity volume fraction rises, which depends on the power law index.
In this paper, the nonlinear bending and vibrational characteristics of porous tubes are analyzed for the first time. Within the framework of the nonlocal strain gradient theory, a size-dependent ...model for the tubes with radial inhomogeneity is formulated. It is assumed that the tube is made from functionally graded materials (FGM). Employed a new model for tubes which takes into account of the shear deformation effects, the motion equations are derived with the help of Hamilton variational principle and determined by the two-step perturbation technique. The validity and feasibility of the method are verified by actual examples. The effects of different parameters such as scaling parameters, porosity volume fraction, power law index and inner-to-outer radius ratio on the nonlinear bending and vibration behaviors of the porous tubes are particularly discussed.
In this paper, the snap-buckling behaviors of functionally graded (FG) porous curved nanobeams resting on three parameters elastic foundations are studied for the first time. The curved nanobeams are ...subjected to uniform transverse loads. Two ends of the nanobeam are simply-supported or clamped and immovable. Based on the nonlocal strain gradient theory in conjunction with the Reddy's higher-order shear deformation beam theory, the nonlinear governing equations are derived. By using the two-step perturbation technique, the perturbation equations and the approximate boundary value problems are obtained. It shows that the snap-buckling characteristics of porous curved nanobeams are influenced by size effects, elastic foundations, geometry, material composition, porosity, and boundary conditions. Furthermore, it can be found that the curved nanobeams subjected to the uniform distributed loads may result in the snap-through buckling.
•For the first time, the snap-buckling of porous nanobeams is investigated.•The nanobeams subjected to bending loadings will result in snap-through buckling.•The snap-buckling may occur depending on the shallowness and the size parameters.•The effects of porosity and nonlinear elastic foundations are also discussed.•The asymptotic solution are determined by using the two-step perturbation method.
Antibiotic resistance is a significant global health concern that requires novel approaches to tackle this serious crisis. In this study, we designed an intelligent supramolecular antibacterial agent ...using dequalinium chloride (DQ), cucurbit7urils (CB7), and maleic anhydride-cyclohexylamine hydrochloride (ADA-MA) based on supramolecular chemistry. The antibacterial activity of DQ was regulated by CB7 and ADA-MA, based on the pH value of the infection microenvironment. The acidic infection microenvironment triggered the release of DQ from CB7 and restored its antibacterial activity, while the neutral physiological environment maintained the stability of DQ@2CB7 and turned off its antibacterial activity. This process provides a simple and effective strategy for regulating the biological activity of DQ on demand. It could "turn on" and "turn off" its antibacterial activity according to the needs of the infection microenvironment, thus delaying the generation of resistant bacteria and reducing the toxicity of the drug under physiological conditions.
Supramolecular chemistry regulates the antibacterial activity of DQ using CB7 and ADA-MA according to the pH value of the infection microenvironment.
On vibrations of porous nanotubes She, Gui-Lin; Ren, Yi-Ru; Yuan, Fuh-Gwo ...
International journal of engineering science,
April 2018, 2018-04-00, 20180401, Letnik:
125
Journal Article
Recenzirano
In this study, the vibration behaviors of porous nanotubes are investigated for the first time. The nonlocal strain gradient theory in conjunction with a refined beam model are employed to formulate ...the size-dependent model. It is presumed that the porous nanotubes are made from functionally graded materials, and the material parameters of nanotubes relate to temperature variation and vary continuously in the radial direction. Employing a refined beam theory which includes the effects of transverse shear deformation, the equations of motion are derived based on Hamilton's variation principle and solved by the Navier solution method. Some comparisons are presented to valid the correctness of present solution method. The effects of the nonlocal parameter, strain gradient parameter, temperature variations, porosity volume fraction and material variation on the vibration characteristic of the nanotubes are discussed in detail.
On buckling and postbuckling behavior of nanotubes She, Gui-Lin; Yuan, Fuh-Gwo; Ren, Yi-Ru ...
International journal of engineering science,
December 2017, 2017-12-00, 20171201, Letnik:
121
Journal Article
Recenzirano
For the first time, the size-dependent thermal buckling and post-buckling behavior of nanotubes made of functionally graded materials (FGMs) with porosities is investigated by using a refined beam ...theory. This non-classical nanotube model is based on Eringen nonlocal elasticity model which incorporates the small scale effect. Two types of porosity distribution, including even and uneven distribution, are taken into account. The material properties of the nanotubes are temperature-dependent and vary in the radial direction. The size-dependent governing differential equations are derived by employing the generalized variation principle and solved by using a two-step perturbation method. The effects of small scale parameter, porosity volume fraction, the volume fraction index and boundary conditions on thermal buckling and post-buckling of FGM nanotubes are studied by several numerical examples. It can be concluded that the porosity volume fraction and small scale parameter change the buckling and post-buckling behavior of the nanotubes.
This study uses laboratory experiments and a Large Eddy Simulation (LES) model to investigate the sloshing phenomenon in a rectangular water tank with multiple bottom-mounted baffles. The kinematic ...motion of the water surface was solved by the Volume of Fluid (VOF) method. The simulation results were verified by the measured wave heights in a water tank installed on a shaking table. The numerical model was employed to systematically determine the effects of the spacing and height of the baffles on the sloshing phenomenon. The simulation results indicate that the natural frequency of the tank was altered by the multiple baffles and was related to the effective water depth above the baffles. The diminishing effect of multiple baffles on the hydrodynamic force is better than that of a single baffle. In addition, the sloshing force on the sidewalls of the tank can be characterized by the excitation amplitude, frequency, and water depth. While the sloshing height and hydrodynamic force decrease as the baffle number or baffle height increase, the effect of baffles on the sloshing lessens when the relative baffle height hb/hw ≥ 0.75.
•Laboratory experiments and a Large Eddy Simulation model are used to study the sloshing in a water tank with multiple vertical baffles.•The natural frequency of the tank with multiple baffles is dependent on the effective water depth, not the total water depth.•The diminishing effect of multiple baffles on the hydrodynamic force is better than that of single baffle.•The wave height and hydrodynamic force decrease as the baffle number or baffle height increase.•The sloshing force on the sidewalls of the tank can be normalized by the excitation amplitude, frequency, and water depth.
Nonlinear bending, thermal buckling and post-buckling analysis for functionally graded materials (FGMs) tubes with two clamped ends by using a refined beam theory are investigated. The theory ...satisfies the traction-free boundary conditions on the inner and outer surfaces of the tube and also takes into account the transverse shear effects without artificially introducing shear correction factors. The material properties of FGM tubes are assumed to be temperature-dependent and vary in the radial direction. The asymptotic solutions of the FGM tubes under nonlinear bending and thermal post-buckling are solved by using a two-step perturbation method. The analytical solutions of Timoshenko beam and Euler beam are also presented. Detailed parametric studies are performed to investigate effects of inner-to-outer radius ratio, volume fraction as well as shear deformation on nonlinear bending, thermal buckling and post-buckling characteristics of the FGM tubes.
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