An online GA-based output-feedback direct adaptive fuzzy-neural controller for uncertain nonlinear systems.

In this paper, we propose a novel design of a GA-based output-feedback direct adaptive fuzzy-neural controller (GODAF controller) for uncertain nonlinear dynamical systems. The weighting factors of the direct adaptive fuzzy-neural controller can successfully be tuned online via a GA approach. Because of the capability of genetic algorithms (GAs) in directed random search for global optimization, one is used to evolutionarily obtain the optimal weighting factors for the fuzzy-neural network. Specifically, we use a reduced-form genetic algorithm (RGA) to adjust the weightings of the fuzzy-neural network. In RGA, a sequential-search -based crossover point (SSCP) method determines a suitable crossover point before a single gene crossover actually takes place so that the speed of searching for an optimal weighting vector of the fuzzy-neural network can be improved. A new fitness function for online tuning the weighting vector of the fuzzy-neural controller is established by the Lyapunov design approach. A supervisory controller is incorporated into the GODAF controller to guarantee the stability of the closed-loop nonlinear system. Examples of nonlinear systems controlled by the GODAF controller are demonstrated to illustrate the effectiveness of the proposed method.     

Growth characteristics of hierarchical ZnO structures prepared by one-step aqueous chemical growth

By varying the initial precursor concentrations of (KOH/Zn(NO₃)₂ 6H₂O) without addition of surfactants, the branched nanostructures with different growth characteristics can be obtained. In this study, the growth behavior of the three-dimensional hierarchical structure arrays varied from randomly oriented to well-defined sixfold symmetry by altering pH value of the solution and the related effect of erosion phenomenon have been illustrated. In summary, the hierarchical structures with different morphologies can be obtained on preformed Zn microtips through a simple one-step solution method.     

Null-field BIEM for solving a scattering problem from a point source to a two-layer prolate spheroid

In this paper, the acoustic scattering problem from a point source to a two-layer prolate spheroid is solved by using the null-field boundary integral equation method (BIEM) in conjunction with degenerate kernels. To fully utilize the spheroidal geometry, the fundamental solutions and the boundary densities are expanded by using the addition theorem and spheroidal harmonics in the prolate spheroidal coordinates, respectively. Based on this approach, the collocation point can be located on the real boundary, and all boundary integrals can be determined analytically. In real applications of a two-layer prolate spheroidal structure, it can be applied to simulate the kidney-stone biomechanical system. Here, we consider the confocal structure to simulate the kidney-stone system since its analytical solution can be analytically derived. The parameter study for providing some references in the clinical medical treatment is also considered. To check the validity of the null-field BIEM, a special case of the acoustic scattering problem of a point source by a rigid scatterer is also done by setting the density of the inner prolate spheroid to infinity. Results of the present method are compared with those obtained using the commercial finite element software ABAQUS.     

Exact solutions for plastic responses of orthotropic strain-hardening rotating hollow cylinders

This paper presents exact solutions for plastic responses of plastically orthotropic strain-hardening rotating hollow cylinders. Hill’s yield criterion and the Voce hardening law were adopted. The concept of sequential limit analysis was employed to deal with the strain-hardening behavior by updating the yield criterion and the deformed configuration sequentially. First, exact solutions of the plastic angular velocity were acquired by solving both static and kinematic limit analysis problems. The existence of closed-form exact solutions for some cases was also illustrated. Moreover, the global hardening behavior was analytically evaluated. The corresponding distributions of plastic stress components and equivalent plastic strain were also developed. Second, the elastic–plastic capability of the commercial finite-element code ABAQUS was employed for rigorous validations of analytical solutions. Finally, good agreement is observed between analytical solutions and numerical results.     

Thermoelastic Analysis of Functionally Graded Rotating Disks with Variable Thickness Involving Non-Uniform Heat Source

The research aims to investigate thermoelastic behavior of functionally graded rotating disks with variable thickness involving a non-uniform heat source. We assume material properties and thickness of rotating disks to vary in the radial direction. Axisymmetric thermal loads including non-uniform heat source, heat flux, and temperature boundary conditions are considered. To conduct corresponding simulations, two user subroutines are edited and incorporated into the commercial finite-element code ABAQUS. For verification, analytical formulations are derived and solved uniquely by symbolic calculations using the computing software Mathematica. The developed finite-element technique is then verified with very good agreement between results by ABAQUS and Mathematica.     

Improved additive manufacturing of silicon carbide parts via pressureless electric field-assisted sintering

High solids loading silicon carbide (SiC)-based aqueous slurries containing only .5 wt. % organic additives were utilized to create specimens of various geometries via an extrusion-based additive manufacturing (AM) technique. Pressureless electric field-assisted sintering was performed to densify each specimen without deformation. The combination of these techniques produced parts with >98% relative density despite containing only 5 wt.% oxide sintering additives. After sintering, specimens contained only the α-SiC and yttrium aluminum perovskite phases. This suggests the evolution of a nonequilibrium yttrium aluminate phase, as well as transformation from β-SiC to α-SiC. The fabrication method presented in this work has advantages over other AM techniques commonly used with SiC, because it does not require significant organic additives nor additional postprocessing steps such as chemical vapor infiltration or polymer impregnation and pyrolysis.     

Poly(ethylene terephthalate)/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate)/clay nanocomposites: Mechanical properties,optical transparency,and barrier properties

Poly(ethylene terephthalate) (PET)/clay, PET/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate) (PETG), and PET/PETG/clay nanocomposites were fabricated using the twin‐screw extrusion technique. The spherulitic morphologies, thermomechanical, mechanical, and gas‐barrier properties, as well as the effect of clay on the transparency of the resulting nanocomposites were identified. The clay induced the heterogeneous nucleation of the nanocomposites during the cold crystallization process, thereby increasing the crystallinities and melting temperatures of the resulting nanocomposites. The incorporation of clay increased the storage moduli, Young's moduli, impact strengths, and barrier properties of the PET, PETG, and PET/PETG blend. Regarding the optical transparency, the inclusion of clay can make the crystallizable PET matrix crystalline opaque. However, the amorphous PETG maintained its transparency. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39869.     

Freeze-form extrusion fabrication of functionally graded materials

Presented in this paper is a novel additive manufacturing technology for making three-dimensional parts with functionally graded materials (FGMs), called Freeze-form Extrusion Fabrication (FEF). The system development included a triple-extruder mechanism, extruder modeling and control, pastes extrusion planning for desired composition gradients, and software coding for motion and extrusion control. The effectiveness of the developed FEF system was demonstrated first by fabricating limestone (CaCO₃) parts with graded colors and then by fabricating ‘green’ parts with graded compositions between alumina (Al₂O₃) and zirconia (ZrO₂). The fabricated part went through post-processing, and the sintered part was analyzed using energy dispersive spectroscopy (EDS) to determine its material compositions.     

Novel impacts of glycol-modified poly(ethylene terephthalate)(PETG) to crystallization behavior of polyethylene naphthalate (PEN) within stretched miscible blends

For studied blends of amorphous glycol-modified poly(ethylene terephthalate) (PETG) and semicrystalline polyethylene naphthalate (PEN), melt miscibility is understood from the linear variation of a single glass transition temperature (T_g) over the entire composition range. The diluent effect of PETG component severely retarded the crystallization of PEN component within blends. Nevertheless, after being through isothermal stretching at 120 °C, crystallization was able to progress efficiently during heating in a continuous manner. Instead of being thermally relaxed back to amorphous state, parallel sliding motions of stretched PEN segments toward crystallization appear rather dominant. Within stretched blends, the PETG content emerged as a critical factor to the crystallinity increase of PEN fraction and the absence of lattice defect, instead of behaving as a diluent component. Furthermore, as being indicated by in-situ small-angle X-ray experiments, regular lamellar stacking gradually developed within stretched blends through heating, which indicates the involvement of thermally activated self-association of randomly distributed crystalline lamellae. With including a higher fraction of PETG component, these secondary ordering processes including lamellar thickening can be activated at lower temperature. Hence, the accompanied thermal relaxation of flexible PETG segment is inferred able to lubricate the sliding of stretched PEN segments in amorphous regions via lowering encountered frictional hindrance, and thus enhance both primary and secondary ordering processes within stretched blends.