The solution of elastostatic and dynamic problems using the boundary element method based on spherical Hankel element framework

In this paper, new spherical Hankel shape functions are used to reformulate boundary element method for 2‐dimensional elastostatic and elastodynamic problems. To this end, the dual reciprocity boundary element method is reconsidered by using new spherical Hankel shape functions to approximate the state variables (displacements and tractions) of Navier's differential equation. Using enrichment of a class of radial basis functions (RBFs), called spherical Hankel RBFs hereafter, the interpolation functions of a Hankel boundary element framework has been derived. For this purpose, polynomial terms are added to the functional expansion that only uses spherical Hankel RBF in the approximation. In addition to polynomial function fields, the participation of spherical Bessel function fields has also increased robustness and efficiency in the interpolation. It is very interesting that there is no Runge phenomenon in equispaced Hankel macroelements, unlike equispaced classic Lagrange ones. Several numerical examples are provided to demonstrate the effectiveness, robustness and accuracy of the proposed Hankel shape functions and in comparison with the classic Lagrange ones, they show much more accurate and stable results.     

Comparison of cure characteristics and mechanical properties of nano and micro silica‐filled CSM elastomers

In this study, the effect of micro and nano silica and their combination on mechanical and thermal properties of Chlorosulfonated Polyethylene compounds were investigated. Cure characteristics were studied using a Monsanto Moving Die Rheometer at 155°C. Incorporation of nano silica accelerated the vulcanization whereas the micro silica particles decelerated the curing process. Both micro and nano silica increased the crosslink density as evidenced by swelling test. However, this value has been more improved in CSM/nano silica composites. The physico‐mechanical properties of CSM/nano silica are superior compared to CSM/micro silica. Nano silica provided reinforcing efficiency which is not only because of higher specific surface area but also because of various interactions and especially physical interactions which are discussed in the text. Nano silica particles also improved the thermal properties more efficiently. Incorporation of 15 phr (part per hundred) nano and 5 phr micro silica to polymer improved the initial decomposition temperature for about 51°C and 16°C, respectively, using a TGA. The combination of micro and nano silica, showed that by coupling nano and micro fillers, the loading of fillers can be minimized. In other words, the hybrid samples with a lower filler loading behave as efficient as their separate counterpart with higher loading. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42668.     

Microstructure and properties of poly(ethylene terephthalate)/organoclay nanocomposites prepared by water‐assisted extrusion: Effect of organoclay concentration

Poly(ethylene terephthalate) (PET)/Cloisite 30B (C30B) nanocomposites containing different concentrations of the organoclay were prepared using two different twin‐screw extrusion processes: conventional melt mixing and water‐assisted melt mixing. The reduction of the molecular weight of the PET matrix, caused by hydrolysis during the water‐assisted extrusion, was compensated by subsequent solid‐state polymerization (SSP). X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses showed intercalated/exfoliated morphology in all PET/C30B nanocomposites, with a higher degree of intercalation and delamination for the water‐assisted process. Rheological, thermal, mechanical, and gas barrier properties of the PET nanocomposites were also studied. Enhanced mechanical and barrier properties were obtained in PET‐C30B nanocomposites compared to the neat PET. The nanocomposites exhibited higher tensile modulus and lower oxygen permeability after SSP. The elongation at break was significantly higher for SSP nanocomposites than for nanocomposites processed by conventional melt mixing. POLYM. ENG. SCI., 54:1879–1892, 2014. © 2013 Society of Plastics Engineers     

Experimental and theoretical investigation of molecular diffusion coefficient of propylene in NMP

In this study, the absorption of propylene in N-methyl pyrolidone (NMP) was experimentally performed at three different temperatures (276.15, 293.15, and 328.15 K) using the pressure decay method and as a result, the equilibrium data, Henry's law constants, and kinetic data were reported. It was shown that the solubility and diffusivity are two important factors affecting the kinetic behavior of the system. This absorption system was mathematically modeled using Fick's second law accompanied by a time dependent boundary condition. An analytical method followed by numerical optimization was used to estimate the diffusion coefficient of propylene in NMP at different operating temperatures. The results demonstrated that the calculated diffusion coefficient obeys an Arrhenius type model. The resulting mathematical model was applied to calculate the number of absorbed moles of the gas. It shows a deviation of about 10% in comparison with the experimental measurements. Furthermore, the time dependent concentration profile along the liquid depth was also predicted.     

Supported liquid membrane separation of propylene-propane mixtures using a metal ion carrier

Experimental results for the separation of propylene from a propylene/propane mixture using facilitated transport membrane system with silver nitrate as carrier are presented. The equilibrium constant of the reaction between propylene and silver ion (Ag⁺) at different operating conditions was determined, experimentally. For a 50:50 (vol.%) propylene-propane mixture, at feed pressure of 50-120 kPa, the separation performance of a facilitated transport membrane system was evaluated. It was observed that increasing carrier concentration and trans-membrane pressure, separation factor was increased. At feed pressure of 120 kPa and the carrier concentration of 20 wt.%, a separation factor of 270 was obtained.     

Gelation versus liquid crystal phase transitions in suspensions of plate-like particles

Gelation is a common effect in aqueous suspensions of charged colloidal clay platelets at concentrations as low as 1 wt%. However, in systems of charged gibbsite [Al(OH)3] platelets, gelation can be delayed to concentrations as high as 50 wt% depending on the ionic strength. We investigated the phase behaviour of this system approaching the state of gelation in the delicate region between attractive and repulsive states that originate from competition between Coulomb repulsion and van der Waals attraction. As a function of the ionic strength, isotropic-nematic, nematic-columnar and isotropic-columnar phase separations were observed. Moreover, compression by gravitational forces allowed us to observe phase separation that is arrested by gelation in the homogeneous suspensions.     

Analytical approximate solution of competitive facilitated transport of acid gases through liquid membranes

An analytical approximate solution for the competitive facilitation factor of components A and E across a liquid membrane is developed in the case of instantaneous reactions inside the liquid membranes. This analytical solution solves the dimensionless, nonlinear diffusion-reaction transport problem governing the competitive facilitated transport of two gaseous components through liquid membranes. Prediction of the facilitation factors has been obtained for the equilibrium chemical reaction regime, considering the unequal complexes diffusivities and cases of zero and nonzero permeate side solute concentrations. This mathematical solution leads to analytical expressions for the concentration profiles of the species across the liquid membrane. In comparison with the present numerical solution and also numerical calculations and experimental data from the open literature, the difference between the analytical predictions and those obtained from the numerical solution were found to be in well agreement.     

Terahertz graphene optics

The magnitude of the optical sheet conductance of single-layer graphene is universal, and equal to e ²/4? (where 2??? = h (the Planck constant)). As the optical frequency decreases, the conductivity decreases. However, at some frequency in the THz range, the conductivity increases again, eventually reaching the DC value, where the magnitude of the DC sheet conductance generally displays a sample- and doping-dependent value between ??e ²/h and 100 e ²/h. Thus, the THz range is predicted to be a non-trivial region of the spectrum for electron transport in graphene, and may have interesting technological applications. In this paper, we present the first frequency domain measurements of the absolute value of multilayer graphene (MLG) and single-layer graphene (SLG) sheet conductivity and transparency from DC to 1 THz, and establish a firm foundation for future THz applications of graphene.      

An Efficient Modified HPSO-TVAC-Based Dynamic Economic Dispatch of Generating Units

Abstract

This paper proposes a novel particle swarm optimization (PSO) algorithm with population reduction, which is called modified new self-organizing hierarchical PSO with jumping time-varying acceleration coefficients (MNHPSO-JTVAC). The proposed method is used for solving well-known benchmark functions, as well as non-convex and non-smooth dynamic economic dispatch (DED) problems for a 24?h time interval in two different test systems. Operational constraints including the prohibited operating zones (POZs), the transmission losses, the ramp-rate limits and the valve-point effects are considered in solving the DED problem. The obtained numerical results show that the MNHPSO-JTVAC algorithm is very suitable and competitive compared to other algorithms and have the capacity to obtain better optimal solutions in solving the non-convex and non-smooth DED problems compared to the other variants of PSO and the state of the art optimization algorithms proposed in recent literature. The source codes of the HPSO-TVAC algorithms and supplementary data for this paper are publicly available at https://github.com/ebrahimakbary/MNHPSO-JTVAC.     

Piecewise constant level set method for structural topology optimization with MBO type of projection

In this paper, we combine a Piecewise Constant Level Set (PCLS) method with a MBO scheme to solve a structural shape and topology optimization problem. The geometrical boundary of structure is represented implicitly by the discontinuities of PCLS functions. Compared with the classical level set method (LSM) for solving Hamilton–Jacobi partial differential equation (H-J PDE) we don’t need to solve H-J PDE, thus it is free of the CFL condition and the reinitialization scheme. For solving optimization problem under some constraints, Additive Operator Splitting (AOS) and Multiplicative Operator Splitting (MOS) schemes will be used. To increase the convergency speed and the efficiency of PCLS method we combine this approach with MBO scheme. Advantages and disadvantages are discussed by solving some examples of 2D structural topology optimization problems.