An improved progressive preconditioning method for steady non‐cavitating and sheet‐cavitating flows

An improved progressive preconditioning method for analyzing steady inviscid and laminar flows around fully wetted and sheet‐cavitating hydrofoils is presented. The preconditioning matrix is adapted automatically from the pressure and/or velocity flow‐field by a power‐law relation. The cavitating calculations are based on a single fluid approach. In this approach, the liquid/vapour mixture is treated as a homogeneous fluid whose density is controlled by a barotropic state law. This physical model is integrated with a numerical resolution derived from the cell‐centered Jameson's finite volume algorithm. The stabilization is achieved via the second‐and fourth‐order artificial dissipation scheme. Explicit four‐step Runge–Kutta time integration is applied to achieve the steady‐state condition. Results presented in the paper focus on the pressure distribution on hydrofoils wall, velocity profiles, lift and drag forces, length of sheet cavitation, and effect of the power‐law preconditioning method on convergence speed. The results show satisfactory agreement with numerical and experimental works of others. The scheme has a progressive effect on the convergence speed. The results indicate that using the power‐law preconditioner improves the convergence rate, significantly. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of graded triple delta-doped sheets on the performance of GaAs based dual channel pseudomorphic high electron mobility transistors

The characteristics of InGaP/InGaAs/GaAs dual channel pseudomorphic high electron mobility transistors (DCPHEMTs) with different graded triple delta-doped sheets are investigated and experimentally demonstrated. Based on a two-dimensional simulator of ATLAS, the band diagrams, electron densities and DC characteristics of studied devices are comprehensively analyzed. Due to the use of properly graded triple delta-doped sheets, good pinch-off and saturation characteristics, improved transport properties and wide current swing are obtained. For comparison, a practical DCPHEMT with good device performances is fabricated as well. It is found that the simulated data are in good agreement with experimental results.     

MHD flow and heat transfer over permeable stretching sheet with slip conditions

The magnetohydrodynamic (MHD) flow and heat transfer characteristics for the boundary layer flow over a permeable stretching sheet are considered. Velocity and thermal slip conditions are taken into account. Problem formulation is developed in the presence of thermal radiation. Governing non‐linear problem is solved by a homotopy analysis method. Convergence of the derived solutions is studied. Numerical values of skin‐friction coefficient and local Nusselt number are tabulated. Effects of pertinent parameters on the velocity and temperature profiles are discussed. Comparison between the present and previous limiting results is shown. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical model for the transverse interference pattern of GRIN optical fiber using a laser sheet of light

A new technique (El-Ghandoor et al., Opt. Laser Technol. 31(7) (1999) 481–488) has been applied to study the shape of transverse interference fringes, instead of multiple beam Fizeau fringes (Marhic, Stein, Appl. Phys. Lett. 35 (1975) 1678–1682), from a GRIN optical fiber. In this technique, a laser light sheet is used to illuminate and pass directly through the optical fiber. Theoretical expressions are derived for the optical path differences of three groups of interference beams. The first one passes through the cladding, the core, and then the cladding once again; the second passes through the cladding only, and the third passes through the surrounding air. Theoretical expressions for the shape of transverse interference fringes formed across isotropic non-absorbing optical fibers are also calculated.     

Flange earing and its control on deepdrawing of anisotropy circular sheets

The Hill's quadric anisotropy yield function and the Barlat-Lian anisotropy yield function describing well anisotropy sheet metal with stronger texture are introduced into a quadric-flow corner constitutive theory of elastic-plastic finite deformation suitable for deformation localization analysis. And then, the elastic-plastic large deformation finite element formulation based on the virtual power principle and the discrete Kirchhoff shell element model including the yield functions and the constitutive theory are established. The focus of the present research is on the numerical simulation of the flange earing of the deep-drawing of anisotropy circular sheets, based on the investigated results, the schemes for controlling the flange earing are proposed. Supported by NSFC(No. 19832020) and National Automobile Dynamic Simulation Laboratory of China.     

Bifurcation Instability of sheet metal during spring-back

In automotive and home appliance industries, there are many complex-shaped sheet metal components which need to be fabricated in multiple stamping operations. For example, the manufacturing of an outer case of washing machine consists of stamping followed by a bending operation. After the first stage of the stamping process, a large amount of spring-back takes place, and therefore, it is difficult to proceed to the next stage of the bending process. In the stamping process of that kind of sheet component with low geometric constraint, the forming area is large compared to the forming depth. Therefore, the formed part is in an unstable state and is less geometrically constrained, which causes a large amount of spring-back. To investigate this phenomenon, finite element analyses are carried out. During a spring-back analysis after forming, bifurcation takes place and the finite element solution procedure using the Newton–Raphson scheme becomes unstable. To get a stable post-bifurcation solution, a bifurcation algorithm is introduced at the bifurcation point. The deformed shapes obtained from finite element analyses are in good agreement with the experimental data. From this study, it is shown that the bifurcation behaviour enlarges the spring-back and the degree of dimensional error. To obtain additional possible post-bifurcation solutions, non-bifurcation analyses using initial guesses obtained in a modal analysis are carried. For the initial guesses, lowed four eigenmodes are utilized. Finally, the post-bifurcation behaviour and spring-back amount are investigated for various process parameters including the forming depth, punch width and corner radius.     

Stochastic functional differential equations modelling materials with selective recall

We study a problem in stochastic functional differential equations which, in addition to a standard one-one-parameter noise term involves a random perturbation of the memory. This problem can also be regarded as a first order hyperbolic system of stochastic partial differential equations with given initial data and nonlocal boundary data. Existence and uniqueness of a solution is established and the generator of the associated Markov process is analyzed. Thereafter, for two model problems arising from first- and second-order integro-differential equations suggested by physical applications we establish asymptotic stability in probability of the associated stochastic processes.     

Effect of biaxial orientation on dielectric and breakdown properties of poly(ethylene terephthalate)/poly(vinylidene fluoride‐co‐tetrafluoroethylene) multilayer films

Polymer films with enhanced dielectric and breakdown properties are essential for the production of high energy density polymer film capacitors. By capitalizing on the synergistic effects of forced assembly nanolayer coextrusion and biaxial orientation, polymer multilayer films using poly(ethylene terephthalate) (PET) and a poly(vinylidene fluoride‐co‐tetrafluoroethylene) [P(VDF‐TFE)] copolymer were produced. These films exhibited breakdown fields, under a divergent field using needle/plane electrodes, as high as 1000 kV mm^?1. The energy densities of these same materials, under a uniform electric field measured using plane/plane electrodes, were as high as 16 J cm^?3. The confined morphologies of both PET and P(VDF‐TFE) were correlated to the observed breakdown properties and damage zones. On‐edge P(VDF‐TFE) crystals induced from solid‐state biaxial stretching enhanced the effective P(VDF‐TFE) layer dielectric constant and therefore increased the dielectric contrast between the PET and P(VDF‐TFE) layers. This resulted in additional charge buildup at the layer interface producing larger tree diameters and branches and ultimately increasing the breakdown and energy storage properties. In addition to energy storage and breakdown properties, the hysteresis behavior of these materials was also evaluated. By varying the morphology of the P(VDF‐TFE) layer, the low‐field dielectric loss (or ion migration behavior) could be manipulated, which in turn also changed the observed hysteresis behavior. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 882–896     

Study of Polymer-Cement Composite Containing Portland Cement and Aqueous Poly (methyl methacrylate) Latex Polymer by Fourier-Transform Infrared (FT-IR) Spectroscopy

The polymer-cement composite is an immiscible band having modified morphology. Polymer phase improves the toughness of brittle cement and has a reinforcing effect, and interactions between cement components and polymers provide stability. In this study, polymer latex [poly(methyl methacrylate), PMMA] – cement paste was prepared with different weight proportions of polymer content. The main scientific objective of this report has been the analysis and the prediction of high strength with the aim of understanding the interactions of PMMA polymer with Portland cement after hydration reaction of cement pastes and curing the specimens for 28 days. The samples were studied by Fourier transform infrared (FT-IR) spectroscopy. The results are critically examined. It is shown that bands support the interaction of PMMA with cement in the composite.     

Ultrasound regulated flexible protein materials: Fabrication,structure and physical-biological properties

Ultrasound can be used in the biomaterial field due to its high efficiency, easy operation, no chemical treatment, repeatability and high level of control. In this work, we demonstrated that ultrasound is able to quickly regulate protein structure at the solution assembly stage to obtain the designed properties of protein-based materials. Silk fibroin proteins dissolved in a formic acid-CaCl₂ solution system were treated in an ultrasound with varying times and powers. By altering these variables, the silks physical properties and structures can be fine-tuned and the results were investigated with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), gas permeability and water contact angle measurements. Ultrasonic treatment aids the interactions between the calcium ions and silk molecular chains which leads to increased amounts of intermolecular β-sheets and α-helix. This unique structural change caused the silk film to be highly insoluble in water while also inducing a hydrophilic swelling property. The ultrasound-regulated silk materials also showed higher thermal stability, better biocompatibility and breathability, and favorable mechanical strength and flexibility. It was also possible to tune the enzymatic degradation rate and biological response (cell growth and proliferation) of protein materials by changing ultrasound parameters. This study provides a unique physical and non-contact material processing method for the wide applications of protein-based biomaterials.