Singularity in structural optimization

Singularity conditions that arise during structural optimization can seriously degrade the performance of the optimizer. The singularities are intrinsic to the formulation of the structural optimization problem and are not associated with the method of analysis. Certain conditions that give rise to singularities in linear elastic structures have been identified in earlier papers, along with a proposition to alleviate the consequences of their presence.^1-3 These singularities were global in nature, encompassing the entire structure. Further examination revealed more complex sets of conditions in which singularities occur. Some of these singularities are local in nature, being associated with only a segment of the structure. Moreover, the likelihood that one of these local singularities may arise during an optimization procedure can be much greater than that of the global singularity identified earlier. This paper provides examples of these additional forms of singularities. It gives a framework in which these singularities can be recognized. In particular, the singularities can be identified by examination of the stress-displacement relations along with the compatibility conditions and/or the displacement-stress relations derived in the integrated force method of structural analysis. Methods for the elimination of the effects of these singularities are suggested and numerical illustrations are given.     

The low-temperature structure of poly(di-n-hexyl germane)

The structure of poly (di-n-hexyl germane) has been investigated using X-ray and conformational energy analysis. Wide-angle X-ray diffraction analysis shows that the polymer undergoes an order/disorder transition at about 15°C. The polymer is known to exhibit thermochromism associated with this phase transition. Below the transition temperature, the backbone conformation is all-trans and the molecules are arranged in an orthorhombic unit cell. Above the transition temperature, the backbone disorders and the polymer loses long-range ordering. Fixed bonding conformational energy calculations found the lowest energy structure to be a 7/3 helix, very similar to that found for poly(di-n-hexyl silane). Most probably, the observed all-trans backbone conformation is due to intermolecular interactions which force the germanium backbone to an all-trans conformation. In order to carry out the molecular mechanics calculations, non-bonded energy parameters for germanium atoms were derived.     

Systolic architecture for B-spline surfaces

B-spline surfaces are among the most commonly used types of surfaces for modeling objects in computer graphics and CAD applications. One of the time consuming operations in B-spline surface generation is that of inversion. An efficient algorithm is proposed for solving this problem. This algorithm is implemented on a systolic architecture in order to facilitate fast interactive surface design.     

Designing rectangular patch antenna using the neurospectral method

This paper presents a new method for developing computer-aided design (CAD) models, using spectral domain (SD) formulation. Using the artificial neural network (ANN) technique, a combination of continuous function and delta functions constitutes the spectral domain Green's functions. We obtain closed-form formulas for integration involving these equations. Another neural network relates different antenna parameters. Utilizing the reverse modeling for patch dimension determination, it becomes useful as a CAD model for patch antenna design. Designs, of simple rectangular patch antennas, serve as illustration of this method.     

Polyaniline/zinc oxide nanocomposite as room‐temperature sensing layer for methane

Methane detection in ambient condition has become essential as it is being increasingly used as compressed natural gas in many industrial processes and for domestic and transportation purposes. Hence, in this work, we report a room‐temperature methane sensor based on polyaniline/zinc oxide (PANI/ZnO) nanocomposite. The PANI/ZnO nanocomposite was prepared by chemical polymerization of aniline in the presence of ZnO nanoparticles. Electron microscopy results revealed the successful formation of nanocomposites with rod‐like ZnO nanoparticles embedded into the network of nanofibrillar PANI matrix. The PANI/ZnO nanocomposites exhibited a high response to methane at room temperature within a short response time of 20 s for a methane concentration (500 ppm) much lower than its flammability limit. Moreover, the humidity dependence of the sensor response was found to be very low. POLYM. ENG. SCI., 58:1438–1445, 2018. © 2017 Society of Plastics Engineers     

A skewed kernel approach for the simulation of shocks using SPH

A wide variety of jump discontinuities, such as shock fronts, are abound in high‐speed flows. An accurate approximation of these fronts may require higher order techniques either under mesh‐based methods or mesh‐free methods. In the latter class, the smoothed particle hydrodynamics (SPH) is becoming popular as a promising method. However, the standard approach in SPH (like any other discrete methods) can result in highly diffusive solutions because of the inevitable use of artificial viscosity to suppress numerical oscillations. On the other hand, the SPH formulation allows innovative ways to model complicated phenomena. In this paper, we introduce the novel idea of a skewed Gaussian kernel, to improve the shock capturing capability in high speed flows. Here, the standard Gaussian kernel function is modified, and its ‘shape’ is altered with a predesigned tunable skewness parameter, while the basic unity property of the kernel function is still preserved. The SPH with the proposed skewed Gaussian kernel is then applied on a number of benchmark problems in computational fluid dynamics, featuring shocks. The simulations have shown significantly better shock capture through the skewed kernel approach as against the standard techniques, with almost no increase in computational time. Copyright © 2016 John Wiley & Sons, Ltd.     

THE EFFECT OF MACROMIXING ON OSCILLATORY BEHAVIOR IN RECOMBINANT FERMENTATION IN A CONTINUOUS STIRRED TANK REACTOR

A general model is presented for recombinant fermentation in a chemostat in which micromixing may be imperfect. Using the production of tryptophan synthetase as an example and the dilution rate, D, as the bifurcation parameter, conditions are first derived for Hopf bifurcation in a perfectly mixed chemostat. The bifurcation surfaces in three-dimensional space are such that oscillatory solutions exist above the surfaces and washout conditions below. A similar analysis is done for imperfect mixing. The bifurcation region is a concave hyperboloid in the [D,f, n]-space, where f and n ; are model parameters. It is argued that poor macromixing reduces the range of D over which bifurcation to periodic solutions is possible.     

Neural Optimization of Fed‐batch Streptokinase Fermentation in a Non‐ideal Bioreactor

Microbial fermentations involving two or more kinds of competing cells and operating under realistic conditions are difficult to monitor, model and optimize by model‐based methods. They deviate from ideal behavior in two significant aspects: incomplete dispersion in the broth and the influx of disturbances. The approach here has been to optimize the filtered noise and dispersion on‐line through neural networks. This method has been applied to the fed‐batch production of streptokinase (SK). The culture has two kinds of cells — active (or productive) and inactive — and their growth is inhibited by the substrate and the primary metabolite (lactic acid). Using simulated data, the fermentation was optimized by a system of three neural networks, updated continually during successive time intervals. Such sequential optimization with dynamic filtering of inflow noise generated better cell growth and SK activity than static optimization and even an ideal fermentation.     

Optimization of wire electrical discharge machining (WEDM) process parameters using Taguchi method

Wire electrical discharge machining (WEDM) is extensively used in machining of conductive materials when precision is of prime importance. Rough cutting operation in WEDM is treated as a challenging one because improvement of more than one machining performance measures viz. metal removal rate (MRR), surface finish (SF) and cutting width (kerf) are sought to obtain a precision work. Using Taguchi’s parameter design, significant machining parameters affecting the performance measures are identified as discharge current, pulse duration, pulse frequency, wire speed, wire tension, and dielectric flow. It has been observed that a combination of factors for optimization of each performance measure is different. In this study, the relationship between control factors and responses like MRR, SF and kerf are established by means of nonlinear regression analysis, resulting in a valid mathematical model. Finally, genetic algorithm, a popular evolutionary approach, is employed to optimize the wire electrical discharge machining process with multiple objectives. The study demonstrates that the WEDM process parameters can be adjusted to achieve better metal removal rate, surface finish and cutting width simultaneously.     

Reaction of phenol with nitrite ion: pathways of formation of nitrophenols in environmental waters

When sodium nitrite is spiked into phenolic waters, 2-nitrophenol is produced immediately while 4-nitrophenol forms in minor yield after an induction period. The reaction occurs at ambient temperature under acidic, neutral and alkaline conditions. The reaction also occurs in the dark. The nature and yield of the products formed in the dark are analogous to that obtained under ordinary light. Results show that the formation of 2-nitrophenol is first order in nitrite, however, within a narrow range of concentrations. No such order of reaction could be determined for 4-nitrophenol, the yield of which increases in presence of excess nitrite ions and at high nitrite to phenol ratios. Results of this study indicate that NO(2)(-) is the active species in the reaction, attacking the phenol ring at the ortho position and at the same time undergoing a para-substitution in excess nitrite atmosphere. Neither any photo-induced oxidation nor any nitronium ion, NO(2)(+) formation is involved as active species in the nitration of phenol. Our study indicates that in environmental waters a simple contact of nitrite ion with phenolic wastewaters under ambient conditions may form mononitrophenols, which are toxic to aquatic species.