A Review on the Application of the Lattice Boltzmann Method for Turbulent Flow Simulation

The Lattice Boltzmann Method (LBM) is a potent numerical technique based on kinetic theory, which has been effectively employed in various complicated physical, chemical, and fluid mechanics problems. In recent years, turbulent flow simulation by using this new class of computational fluid dynamics technique has attracted more attention. In this article, a review of previous studies on turbulence in the frame of LBM is presented. Recent extensions of this method are categorized based on three main groups of turbulence simulation: DNS, LES and RANS methods.     

The Use of Thermal Lattice Boltzmann Numerical Scheme for Particle-Laden Channel Flow with a Cavity

In this article, particle-laden flow in a channel with heated cavity has been investigated. Calculations were performed using a point force scheme for particle dynamics, while the process of fluid renewal was modeled using the double-population thermal lattice Boltzmann method. Point-particle formulation accounts for the finite-size dispersed phase and the forces acting on the particles were modeled through drag force correlations. Two-way interactions of solid-fluid calculation were considered by adding an external force term for feedback that forced particles in the evolution of fluid distribution function. The method was first validated with steady state flow in a channel with cavity in the presence and absence of a heat source. It was then applied to mixed convection flow laden with particles at various Grashof numbers. The particle dispersion characteristics were examined in detail, where the particle removal rate from cavity upon cavity aspect ratio was emphasized. The effect of the Reynolds number on particle distribution was further investigated numerically by varying the speed of inlet flow into the channel.     

Structure-based substitutions for increased solubility of a designed protein

Manipulation of protein solubility is important for many aspectsof protein design and engineering. Previously, we designed aseries of consensus ankyrin repeat proteins containing one,two, three and four identical repeats (1ANK, 2ANK, 3ANK and4ANK). These proteins, particularly 4ANK, are intended for useas a universal scaffold on which specific binding sites canbe constructed. Despite being well folded and extremely stable,4ANK is soluble only under acidic conditions. Designing interactionswith naturally occurring proteins requires the designed proteinto be soluble at physiological pH. Substitution of six leucineswith arginine on exposed hydrophobic patches on the surfaceof 4ANK resulted in increased solubility over a large pH range.Study of the pH dependence of stability demonstrated that 4ANKis one of the most stable ankyrin repeat proteins known. Inaddition, analogous leucine to arginine substitutions on thesurface of 2ANK allowed the partially folded protein to assumea fully folded conformation. Our studies indicate that replacementof surface-exposed hydrophobic residues with positively chargedresidues can significantly improve protein solubility at physiologicalpH. Received June 23, 2003; revised August 22, 2003; accepted August 28, 2003.     

A new semantics for ACL based on commitments and penalties

In complex multiagent systems, the agents may be heterogeneous and possibly designed by different programmers. Thus, the importance of defining a standard framework for agent communication languages (ACL) with a clear semantics has been widely recognized. The semantics should be verifiable, clear, and practical. Most classical proposals (for instance, mentalistic semantics) fail to meet these objectives. This paper proposes a logic‐based semantics, which is social in nature. The basic idea is to associate with each speech act a clear meaning in terms of a commitment induced by that speech act, and a penalty to be paid in case that commitment is violated. A violation criterion based on the existence of arguments is then defined per speech act. We show that the proposed semantics satisfies some key properties that ensure that the approach is well founded. The logical setting makes the semantics verifiable. Moreover, it is shown that the new semantics is practical because it captures the dynamic of dialogues and shows clearly how isolated speech acts can be connected for building dialogues. © 2008 Wiley Periodicals, Inc.     

Effect of silica and rice husk ash fillers on the modulus of polysiloxane networks

The preparation of polymethylvinylsiloxane rubbers with silica (SC) and black rice husk ash (BRHA) as fillers is reported. We conducted stress–strain experiments on these vulcanized rubbers to study the reinforcement properties of the fillers. Curves showing the dependence of the stress on the reciprocal of the elongation ratio displayed, in most cases, a slow upturn starting at rather low values of the elongation ratio attributed to a rather wide distribution of chain lengths between crosslinking points. Physical crosslinks between the hydroxyl groups of SC fillers and the polymer matrix seemed to enhance the modulus. BRHA–polymer interactions were rather weak in comparison with those occurring between SC and the polymer, presumably as a consequence of the carbon coating of the surface of the former fillers. These interactions were even less important for calcined BRHA. The absence of voids in the polymer–filler interfaces was proven by the analysis of gas diffusion across the rubbers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 421–429, 2003     

Phase Evolution,Microstructure, and Mechanical Properties of Alumina–Mullite–Zirconia Composites Prepared by Iranian Andalusite

This paper investigates the effects of Iranian andalusite and short milling times on alumina–mullite–zirconia composites. Andalusite powder was added at 0, 2.5, 5, and 10 wt% to an alumina–zircon mixture and the raw materials were milled for 1 or 3 h. The sintering of samples was carried out at the temperatures of 1550°C, 1600°C, and 1650°C for 3 h. Microstructural changes, phase composition, physical properties, and mechanical strength of the sintered composites were characterized by scanning electron microscopy, X‐ray diffraction, density, and strength measurement tests. Results show that andalusite promoted the decomposition of zircon and accelerated the reaction sintering of alumina–zircon, which leads to the formation of much more mullite phase and improvements to the composites’ thermal shock resistance up to about 50%.     

Joint optimization of lot-sizing and maintenance policy for a partially observable two-unit system

In this paper, we present a new model to find the jointly optimal economic manufacturing quantity (EMQ) and preventive maintenance (PM) policy for a complex production facility. Unlike the previous joint models which dealt with EMQ and maintenance policy considering a single unit production facility and traditional maintenance approaches, we consider a production facility which consists of two modules with economic dependence. The more expensive module (unit 1) is subject to condition monitoring (CM), and only the age information of the second module (unit 2) is available, which follows a general distribution. The deterioration process of unit 1 is modeled as a continuous time hidden-Markov process. CM data is available at the end of each production run, and it provides only partial information about the hidden state of unit 1. The failure state of unit 1 is observable at any time. The objective is to develop a jointly optimal lot sizing and maintenance policy for a two-unit production facility using multivariate Bayesian control approach by minimizing the long-run expected average cost per unit time. The problem is formulated and solved in the semi-Markov decision process (SMDP) framework. Also, a formula for the mean residual life (MRL) of the production facility is derived, which is an important statistic for practical applications. A practical example of the wind turbine CM and maintenance is provided and a comparison with other policies shows an outstanding performance of the new model and the control policy proposed in this paper.     

Porous Carrageenan-<Emphasis Type="Italic">g</Emphasis>-polyacrylamide/bentonite superabsorbent composites: swelling and dye adsorption behavior

A novel superabsorbent composite based on kappa-Carrageenan (κC) was prepared by graft copolymerization of acrylamide (AAm) onto κC in the presence of bentonite powder using methylenebisacrylamide (MBA) as a crosslinking agent, ammonium persulfate (APS) as an initiator, and sodium carbonate as a pore-forming agent. The swelling behavior in distilled water and in solutions with different pH values was investigated. The results indicated that with increasing carrageenan/bentonite weight ratio, the swelling capacity is increased but the gel content is decreased. The swelling rate of the hydrogels was improved by introducing sodium carbonate as pore-forming agent. The prepared superadsorbent composites were used as adsorbent for a cationic dye, methylene blue. Isotherm of adsorption and the effect of pH, adsorption dosage, contact time and initial dye concentration on dye adsorption were also studied. The results showed that maximum adsorption capacity of methylene blue on the prepared adsorbents is 156.25 mg g^?1 and adsorption is well-described by Langmuir isotherm model.     

Morphology and viscoelastic behavior of silicone rubber/EPDM/Cloisite 15A nanocomposites based on Maxwell model

Blends of silicone rubber (SR) and ethylene propylene diene monomer (EPDM) are immiscible due to different polarity and poor interfacial surface tension between their rubber chains. In this study, compatibilizing effect of a nanoclay addition in SR/EPDM blends was investigated. Viscoelasticity and morphology of nanocomposites based on SR and EPDM, containing 10, 20 and 30 wt% of EPDM and 3, 6 and 9 phr of nanoclay (Cloisite 15A), were studied. The curing behavior of the samples showed that the vulcanization rate and cross-link density of the blends increased with increases in SR content. Morphological study was conducted by XRD, SEM and EDX analyses and they indicated that the nanoparticles tended to disperse in the EPDM phase and consequently caused hardness and the elasticity of this phase in nanocomposites increased. Tensile properties of the samples showed a good fitting between that of experiments and the Maxwell model at initial time of testing (1.5 s) for all the blends. Sample parameters including modulus (E), viscosity (η) and relaxation time (τ) calculated by the Maxwell model revealed that those samples with higher content of nanoparticles exhibit higher modulus and lower relaxation time. The good match in tensile properties based on Maxwell model and those of the experimental data was attributed to good dispersion of nanoclay in the blends.