Deterministic Excitation Forces for Simulation and Identification of Nonlinear Hysteretic SDOF Systems

This paper investigates how to design deterministic excitation forces in studying nonlinear single-degree-of-freedom systems, especially those with rate and path dependency and strength and stiffness degradation. One frequency-modulated periodic excitation and its amplitude-modulated counterpart are proposed as a solution, and a series of numerical exercises are carried out to show that these forces can be designed for sufficient forcing functions to study the complex nonlinear hysteresis. To rapidly reveal the underlying characteristics of the system and also to further lead to an effective system identification, four evaluation tools are proposed to be utilized together with the proposed excitation forces. These tools include the response curves, force-state map, intercycle drift, and intercycle pattern change, based on which some distinctive “patterns” are obtained to reveal the existence of nonlinearities, types of nonlinearities, existence of memory, and degradation. By using both Bouc-Wen and Bouc-Wen-Baber-Noori models for the system in all the simulations, the writers compare the commonly used forces with the proposed excitation forces to further demonstrate the advantages of the proposed excitation forces and evaluation tools. The writers also explore challenges in terms of implementing the proposed excitation forces. The results of this study are expected to benefit both physical testing and numerical simulation of complex nonlinear hysteretic systems in a time- and cost-effective manner, as well as leading to efficient schemes for system identification.     

Impact of Si and Zr addition on the surface defect and photocatalytic activity of the nanocrystalline TiO2 synthesized by the solvothermal method

In the present work, the effects of Si and Zr addition on the surface defect and photocatalytic activity of the solvothermal-derived TiO₂ were investigated. The metal-doped TiO₂ samples were prepared with the molar ratio Si/Ti and Zr/Ti ranging from 0.002 to 0.1 and were subjected to two different cooling temperatures (room temperature and 77 K) after calcination as a post-synthesis treatment. The presence of a small amount of metal dopant caused a slight change in the TiO₂ crystallite and BET surface area (ranging from 7.8 to 10.6 nm and corresponding surface area 95 to 159 m²/g). The photocatalytic activity of TiO₂ did not depend solely on the surface area but rather affected by the concentration of Ti³⁺ on the catalyst surface as shown by a linear ascending trend of the ethylene conversion and the amount of Ti³⁺/surface area of the catalysts. It is noted that addition of Zr had more positive effect than Si and the effect of post-treatment on the photocatalytic activity of TiO₂ catalysts was more pronounced than the addition of metal dopants.     

Methane partial oxidation over NiO-MgO/Ce0.75Zr0.25O2 catalysts

Methane partial oxidation (MPO) is considered as an alternative method to produce hydrogen because it is an exothermic reaction to afford a suitable H₂/CO ratio of 2. However, carbon deposition on a catalyst is observed as a major cause of catalyst deactivation in MPO. In order to find suitable catalysts that prevent the carbon deposition, NiO-MgO/Ce_0.75Zr_0.25O₂ (CZO) supported catalysts were prepared via the co-impregnation (C) and sequential incipient wetness impregnation (S) methods. The amount of Ni loading was fixed at 15 wt-% whereas the amount of MgO loading was varied from 5 to 15 wt-%. The results revealed that the addition of MgO shifted the light-off temperatures to higher temperatures. This is because the Ni surface was partially covered with MgO, and the strong interaction between NiO and NiMgO₂ over CZO support led to the difficulty in reducing NiO to active Ni⁰ and thus less catalytic activity. However, among the catalysts tested, the 15Ni5Mg/CZO (S) catalyst exhibited the best catalytic stability for MPO after 18 h on stream at 750°C. Moreover, this catalyst had a better resistance to carbon deposition due to its high metallic Ni dispersion at high temperature.     

Light cured fluoride filled denture‐coating materials

Light cured denture‐coating materials were prepared by formulating an acrylate monomer with a photoinitiator system (camphorquinone and dimethylaminoethyl methacrylate) using one of three base monomers [bisphenol A glycerolate diacrylate (Bis‐GDA), glycerol 1,3‐diglycerolate diacrylate (GDA), and diurethane dimethacrylate (DU‐DMA)] each with four diluents [triethylene glycol dimethacrylate (TEGDMA), di(ethylene glycol) methyl ether methacrylate, 2‐hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA)] at a fixed 1 : 1 molar ratio of base monomer to diluent. The twelve formulations were then evaluated for their surface hardness and water sorption as coating materials. The DU‐DMA/MAA, DU‐DMA/HEMA, Bis‐GDA/HEMA, and GDA/MAA based coatings provided a high level of both surface hardness and water sorption properties. When sodium fluoride (NaF) or calcium fluoride (CaF₂) was incorporated into those formulations, the fluoride ion release rate from all four NaF containing coating materials was extremely high in the first week, decreasing sharply in the second week and then decreasing in the later 2 weeks. In contrast, the CaF₂ containing coating materials showed a slower sustained rate of fluoride ion release over the 4‐week test period, with the DU‐DMA/HEMA based coating having a fluoride ion release pattern that meets the requirements for dental use. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Linking Nonlinear System Identification with Nonlinear Dynamic Simulation under OpenSees: Some Justifications and Implementations

This study seeks to bridge the gap between nonlinear system identification and nonlinear dynamic finite-element analysis. Motivated by the needs in earthquake simulation, it is first investigated under which conditions and to what degree the prediction of maximum lateral drift and base shear requires accurate nonlinear hysteretic moment-rotation joint models. A series of simulations is carried out using a simple but typical steel frame under two different earthquake ground motion time histories scaled up to various levels. As one of the two major classes of models in nonlinear system identification, nonparametric models are proposed to be implemented into OpenSees. A methodology with details is provided to effectively implement feedforward neural networks with one hidden layer as a new one-dimensional nonlinear smooth material model directly from a MATLAB environment to OpenSees. The same methodology can be applied to benefit the implementation of other parametric and nonparametric models with linear parameterization. Numerical examples are provided. Challenges are discussed and future work is identified.     

Correlating the Speed of Sound with the Gibbs Energy and Estimating the Speed of Sound in Fatty Acid Methyl Ester and Biodiesel

The relationship between the speed of sound (u) in biodiesel and the change in Gibbs energy (ΔG) has not been described in the literature. With the Gibbs energy additivity method, the relationship between u and ΔG can be expressed as ln(u²) = ΔG/RT + A, where R is the universal gas constant, T is the absolute temperature, and A is a constant. The molecule of fatty acid methyl ester (FAME) was arbitrarily sub-divided into groups of atoms and a ΔG was assigned to each group of atoms. A new model correlating the speed of sound to the structure of fatty acid was derived. The proposed model was good for estimation of the speed of sound in both FAME and biodiesel at various temperatures with good accuracy. The absolute average deviations for the speed of sound in FAME (65 data points) and in biodiesel (175 data points) were 0.23% and 0.36%, respectively. Only the number of double bonds and carbon atoms of the fatty acid are required for the calculation.     

Total and inorganic arsenic in rice and rice bran purchased in Thailand

Concentrations of total and inorganic arsenic were determined in 180 samples of polished and brown rice of three rice types, namely white, jasmine, and sticky, and 44 samples of rice bran from these three rice types purchased in Thailand. Concentrations (expressed in nanograms per gram) of inorganic arsenic in polished white, jasmine, and sticky rice were 68.3 ± 17.6 (with a range of 45.0 to 106), 68.4 ± 15.6 (41.7 to 101), and 75.9 ± 24.8 (43.5 to 156), respectively, while those in the three brown rice samples were 124 ± 34.4 (74.5 to 193), 120 ± 31.6 (73.1 to 174), and 131 ± 35.6 (78.0 to 188), respectively. Inorganic arsenic concentrations (expressed in nanograms per gram) in rice bran produced from the three rice types were 633 ± 182 (375 to 919), 599 ± 112 (447 to 824), and 673 ± 195 (436 to 1,071), respectively. Rice bran contained concentrations of total and inorganic arsenic approximately seven and nine times higher, respectively, than those found in the corresponding polished rice. The levels of inorganic arsenic in the three rice types of both polished and brown rice were within the only published regulatory limit of 200 ng/g.     

Energy Additivity Approaches to QSPR Modeling in Estimation of Dynamic Viscosity of Fatty Acid Methyl Ester and Biodiesel

Viscosity is an important physical property of fatty acid methyl esters (FAME) and biodiesel (mixture of FAMEs). In this work, quantitative structure–property relationship (QSPR) for estimation of dynamic viscosity of FAMEs and biodiesel is approached via the Gibbs energy additivity method. The Gibbs energy of dynamic viscous flow is simply derived from the sum of the Gibbs energy of kinematic viscous flow and Gibbs energy of volumetric expansion. The derived model can be used for estimation of dynamic viscosity of saturated and unsaturated FAMEs commonly found in nature. Also, the proposed model can be extended to a mixture of FAMEs or biodiesel as well as biodiesel blends. Thus, the dynamic viscosity of FAMEs as well as neat and blended biodiesels can be estimated by the same equation from the carbon number (z) and number of double bonds (n_d) at different temperature (T). The average absolute deviation (AAD) values for saturated, unsaturated FAMEs, biodiesels, and biodiesel blends (at 20–100 °C) are approximately the same as the original model for estimation of kinematic viscosity.     

An Empirical Equation for Estimation of Kinematic Viscosity of Fatty Acid Methyl Esters and Biodiesel

Kinematic viscosity (µ) is an important physical property of fatty acid methyl esters (FAME) and biodiesel. In this work, the Martin's rule of free energy additivity is extended to cover the kinematic viscosity of saturated and unsaturated FAME commonly found in nature. The proposed model can also be extended to estimate kinematic viscosity of biodiesel. The kinematic viscosity of a FAME or a biodiesel can be easily estimated from its carbon number (z), number of double bonds (n_d) at different temperatures (T) without a prior knowledge of the viscosity of individual FAME. Both z_ave and n_d(ave) can be derived from its fatty acid composition. Thus, kinematic viscosity of biodiesel at temperatures between 20 and 100 °C and at atmospheric pressure can be estimated. The average absolute deviation (AAD) estimated at 20–100 °C for saturated, unsaturated FAME, biodiesels and biodiesel blends are 4.15, 3.25, 6.95 and 2.79 %, respectively. The biodiesels collected in this study (191 data points) have the z_ave and n_d(ave) between 14.10 and 17.96 and 0.21–1.54, respectively. The standard deviation was 0.249. The proposed model would be good for estimation of viscosity of biodiesel containing normal fatty acids, generally found in biodiesel feed stocks.