Complex fields in heterogeneous materials under shock: modeling,simulation and analysis

In this mini-review we summarize the progress of modeling, simulation and analysis of shock responses of heterogeneous materials in our group in recent years. The basic methodology is as below. We first decompose the problem into different scales. Construct/Choose a model according to the scale and main mechanisms working at that scale. Perform numerical simulations using the relatively mature schemes. The physical information is transferred between neighboring scales in such a way: The statistical information of results in smaller scale contributes to establishing the constitutive equation in larger one. Except for the microscopic Molecular Dynamics(MD) model, both the mesoscopic and macroscopic models can be further classified into two categories,solidic and fluidic models, respectively. The basic ideas and key techniques of the MD, material point method and discrete Boltzmann method are briefly reviewed. Among various schemes used in analyzing the complex fields and structures, the morphological analysis and the home-built software, GISO, are briefly introduced. New observations are summarized for scales from the larger to the smaller.     

A method for accurate in silico modeling of ultrasound transducer arrays

This paper presents a new approach to improve the in silico modeling of ultrasound transducer arrays. While current simulation tools accurately predict the theoretical element spatio-temporal pressure response, transducers do not always behave as theorized. In practice, using the probe’s physical dimensions and published specifications in silico, often results in unsatisfactory agreement between simulation and experiment. We describe a general optimization procedure used to maximize the correlation between the observed and simulated spatio-temporal response of a pulsed single element in a commercial ultrasound probe. A linear systems approach is employed to model element angular sensitivity, lens effects, and diffraction phenomena. A numerical deconvolution method is described to characterize the intrinsic electro-mechanical impulse response of the element. Once the response of the element and optimal element characteristics are known, prediction of the pressure response for arbitrary apertures and excitation signals is performed through direct convolution using available tools. We achieve a correlation of 0.846 between the experimental emitted waveform and simulated waveform when using the probe’s physical specifications in silico. A far superior correlation of 0.988 is achieved when using the optimized in silico model. Electronic noise appears to be the main effect preventing the realization of higher correlation coefficients. More accurate in silico modeling will improve the evaluation and design of ultrasound transducers as well as aid in the development of sophisticated beamforming strategies.     

Qualitative characterization of ultrasound reactors for heterogeneous sonochemistry

Several measurement methods (thermocouple probe, perforation of aluminium foils by cavitation, chemical dosimeter) are used to characterize the sound fields of low and high intensity ultrasound reactors and to find optimal conditions for the ultrasonic irradiation of heterogeneous reaction mixtures. In this Paper it is shown that, due to the formation of standing waves, the local ultrasound intensity in a flask fixed in an ultrasonic cleaner is strongly susceptible to small changes in experimental conditions. It is also shown that high intensity ultrasound sources, such as an ultrasonic horn, tend to uncouple: that is, cavitation only occurs at the radiating surface and only marginal ultrasound intensity can be detected elsewhere in the surrounding liquid.     

A mathematical treatment of the use of ultrasound in homogeneous and heterogeneous catalysis

The possibility of increasing the effectiveness of a catalyst in the form of porous granules by artificially changing the activity profile of a catalytic reaction proceeding under non-steady-state conditions is shown. The results can also be used for the analysis of homogeneous reactions. Ultrasound can be used to generate the non-uniform concentration and temperature fields with time in the reaction mixture. Ultrasound can also be used for the activation and deactivation of the catalytic centres.     

Indium-mediated allylation and Reformatsky reaction on glyoxylic oximes under ultrasound irradiation

A novel and more convenient method for the indium-promoted allylation of glyoxylic oximes based on the use of ultrasonic waves is reported. A similar procedure was used to develop the first example reported in the literature of an indium-mediated Reformatsky reaction on oxime ethers.     

Monolithic diphasic gels of mullite by sol-gel process under ultrasound stimulation

Diphasic gel in the mullite composition was prepared from a colloidal sol of boehmite mixed with a hydrolyzed tetraethoxisilane (TEOS) solution. The boehmite sol was obtained by peptization of a poorly crystallized or very small mean crystallite size (approximately 34 A) precipitate, resulting from the reaction between solutions of aluminum sulfate and sodium hydroxide. Ultrasound was utilized in the processes of the TEOS hydrolysis and the boehmite peptization, and also for complete homogenization of the mixture to gel. The wet gel is almost clear and monolithic. The gel transparency is lost on drying, when syneresis has ended, so that the interlinked pore structure starts to empty and is recovered upon water re-absorption. Cracking closely accompanies this critical drying process. Differential thermal analysis (DTA) and X-ray diffraction (XRD) show that the solid structure of the gel is composed of an amorphous silica phase, as a matrix, and a colloidal sized crystalline phase of boehmite. Upon heat treatment, the boehmite phase within the gel closely follows the same transition sequence as in pure alumina shifted towards higher temperatures. Orthorhombic mullite formation was detected at 1300 degrees C.     

A stochastic multiscale framework for modeling flow through random heterogeneous porous media

Flow through porous media is ubiquitous, occurring from large geological scales down to the microscopic scales. Several critical engineering phenomena like contaminant spread, nuclear waste disposal and oil recovery rely on accurate analysis and prediction of these multiscale phenomena. Such analysis is complicated by inherent uncertainties as well as the limited information available to characterize the system. Any realistic modeling of these transport phenomena has to resolve two key issues: (i) the multi-length scale variations in permeability that these systems exhibit, and (ii) the inherently limited information available to quantify these property variations that necessitates posing these phenomena as stochastic processes.A stochastic variational multiscale formulation is developed to incorporate uncertain multiscale features. A stochastic analogue to a mixed multiscale finite element framework is used to formulate the physical stochastic multiscale process. Recent developments in linear and non-linear model reduction techniques are used to convert the limited information available about the permeability variation into a viable stochastic input model. An adaptive sparse grid collocation strategy is used to efficiently solve the resulting stochastic partial differential equations (SPDEs). The framework is applied to analyze flow through random heterogeneous media when only limited statistics about the permeability variation are given.     

Autoignition and combustion of hydrocarbon-hydrogen-air homogeneous and heterogeneous ternary mixtures

A numerical simulation of the ignition and combustion of hydrocarbon-hydrogen-air homogeneous and heterogeneous (gas-drop) ternary mixtures for three hydrocarbon fuels (n-heptane, n-decane, and n-dodecane) is for the first time performed. The simulation is carried out based on a fully validated detailed kinetic mechanism of the oxidation of n-dodecane, which includes the mechanisms of the oxidation of n-decane, n-heptane, and hydrogen as constituent parts. It is demonstrated that the addition of hydrogen to a homogeneous or heterogeneous hydrocarbon-air mixture increases the total ignition delay time at temperatures below 1050 K, i.e., hydrogen acts as an ignition inhibitor. At low temperatures, even ternary mixtures with a very high hydrogen concentration show multistage ignition, with the temperature dependence of the ignition delay time exhibiting a negative temperature coefficient region. Conversely, the addition of hydrogen to homogeneous and heterogeneous hydrocarbon-air mixtures at temperatures above 1050 K reduces the total ignition delay time, i.e., hydrogen acts as an autoignition promoter. These effects should be kept in mind when discussing the prospects for the practical use of hydrogen-containing fuel mixtures, as well as in solving the problems of fire and explosion safety.     

OctTES/TEOS system for hybrid coatings: real‐time monitoring of the hydrolysis and condensation by Raman spectroscopy

The hybrid organic–inorganic system Tetra‐ethyl‐ortho‐silicate functionalized with Octyl‐triethoxy‐silane, studied as protective coating for the preservation of historical glasses from the environmental weathering agents, has been characterized by Raman spectroscopy by monitoring the sol‐gel reactions over time through characteristic features in the spectrum. In particular, for the hydrolysis reaction the disappearance of the 653 cm⁻¹ (Si‐O symmetric breathing) and 810 cm⁻¹ (CH₂ rocking in Si‐alkoxides) peaks and the growth of the 710 cm⁻¹ band, because of hydrolyzed alkyl‐silane, and of the 881 cm⁻¹ peak (ethanol C–C symmetric stretching) have been checked. Moreover, the condensation reaction can be tracked by the disappearance of the two main peaks of the alcohols at 816 and 881 cm⁻¹, going along with the growth of the broad band between 250 and 500 cm⁻¹ (Si–O–Si symmetric bending) and of the feature at 840 cm⁻¹ (Si–O–Si stretching). At the end of the condensation process the Raman spectrum still displays spectral bands unique to the alkyl chain in Octyl‐triethoxy‐silane, in the 1330–1450 cm⁻¹ and 2725–3000 cm⁻¹ ranges. Copyright © 2016 John Wiley & Sons, Ltd.     

Dehydration reaction of hydroxenin monoacetate in carbon tetrachloride and an aliphatic alcohol under ultrasound irradiation

A new method for the preparation of an E/Z mixture of vitamin A acetate from hydroxenin monoacetate is described. This two-step reaction was studied by changing the reaction parameters (reaction temperature, ultrasound power, and reaction time) and the alcohol used. This approach consists of the dehydration reaction of hydroxenin monoacetate under ultrasound irradiation in CCl4 and an aliphatic alcohol under an inert atmosphere. The formation of small amounts of HCl from CCl4 and an aliphatic alcohol under ultrasound irradiation is followed by the dehydration reaction of hydroxenin monoacetate. An E/Z mixture of vitamin A acetate was obtained resulting in the desired pentaenes. Some ethers derivatives were also formed as by-products, isolated and characterized. Study of the reaction mechanism is also reported here.     

多孔介质中含溶解反应的互溶驱替过程格子Boltzmann研究

采用格子Boltzmann方法研究了孔隙尺度下多孔介质内含流固溶解反应的互溶驱替过程,重点研究了被驱替流体与驱替流体黏性差异较大的情况下,溶解反应引起的多孔介质内部结构变化对驱替过程的影响;定量分析了不同达姆科勒数及佩克莱数下多孔介质孔隙率和驱替过程驱替效率随时间的演变.研究结果表明:达姆科勒数较大时,溶解反应的发生会在多孔介质内部生成虫洞,导致一部分被驱替流体不能被波及,驱替流体沿虫洞离开多孔介质,造成驱替效率的减少.在此基础上,随着达姆科勒数的增大,孔隙率变化越大,生成的虫洞越宽,最终驱替效率变大,但仍小于无溶解反应时的驱替效率;随着佩克莱数的增大,指进增长速度越快,孔隙率变化越小,驱替效率越小.     

Comparison of two modeling approaches for highly heterogeneous porous media

The purpose of this paper is to study the acoustic behavior of highly heterogeneous, low density porous structures having a complex pore size distribution using two distinct theoretical approaches. The first approach requires the direct numerical integration of the Biot viscosity correction function. The main requirement here is a knowledge of the probability density function of the pore size, which can be achieved by an optical pore-counting technique. The fact that the observed pore size distribution in these materials could be distinctively split into two parts suggested the use of the second approach based upon the double-porosity theory by Olny and Boutin [J. Acoust. Soc. Am. 114(1), 73-89 (2003)]. The latter approach assumes a low permeability contrast between the two porous scales so that the acoustic properties could be estimated using the semi-phenomenological models of Johnson and Lafarge for the viscous and thermal dynamic permeabilities. Numerical results predicted by the two models are then compared with impedance tube experimental data showing good accuracy of the selected prediction methods.     

Use of focused ultrasound for stimulation of nerve structures

Pulsed focused ultrasound can stimulate the receptor and conductive nerve structures of humans and animals as well as the neurons of the central nervous system of invertebrates. The possibility of a wide practical use of this method in medicine and physiology is considered. For example, the stimulating ability of focused ultrasound is applied to the diagnosis of neurological diseases, to the study of skin and tissue sensitivity in man, to the diagnosis of hearing disorders, and to the introduction of auditory information to the deaf with certain forms of hearing pathology. The factors that affect focused ultrasound as a stimulus for the irritation of nerve structures are discussed.     

Palm oil hydrolysis catalyzed by lipases under ultrasound irradiation--the use of experimental design as a tool for variables evaluation

Diacylglycerol oil has been increasingly recognized by its good nutritional properties and therefore, different technologies have been developed for obtaining it. The present work focuses on the diacylglycerol production by hydrolysis reaction of the palm oil using the PS IM and TL IM commercial lipases as biocatalysts under ultrasound irradiation. An experimental design (central composite rotatable design - CCRD) adopting surface response was applied as a tool to evaluate the optimal reaction conditions beyond a restrict number of experiments. Reactions were performed in an ultrasound equipment and different variables were investigated, such as temperature (30-55 °C), enzyme content (1-2 wt.% of oil mass), mechanical stirring (300-700 rpm) and reaction time. Both, PS IM and TL IM enzymes showed the best results after 1 h and 30 min of reaction under 30 °C and, applying 300 rpm as stirring. On these conditions, the diacylglycerol yield was around 34% and 39%, respectively; considering that 1% PS IM was applied for the first one and, 2% TL IM for the second one. Therefore, it was obtained good yield of a diacylglycerol-rich oil in shorter reaction times under sonication and soft conditions. The mathematic model proposed suggested a satisfactorily representation of the process and good correlation among the experimental results and the theoretical values predicted by the model equation were achieved.     

A unified treatment of nonclassical nonlinear effects in the propagation of ultrasound in heterogeneous media

Recent experiments on rocks and other materials, such as soil, cement, concrete and damaged elastic materials, have led to the discovery of nonlinear (NL) hysteretic effects in their elastic behaviour. These observations suggest the existence of a NL mesoscopic elasticity universality class, to which all the aforementioned materials belong. The purpose of the present contribution is to search for the basic mathematical roots for nonclassical nonlinearity, in order to explain its universality, classify it and correlate it with the underlying meso- or microscopic interaction mechanisms. In our discussions we explicitly consider two quite different kinds of specimens: a two-bonded-elements structure and a thin multigrained bar. It is remarkable that, although the former includes only one interface and the latter very many interstices, the same "interaction box" formalism can be applied to both. Another important result of the proposed formalism is that the spectral contents of an arbitrary system for any input amplitude may be predicted, under certain assumptions, from the result of a single experiment at a higher amplitude.     

Moisture effects on improved hydrolysis reaction for TESPT and TESPD-silica compounds

The moisture(55 wt%)-treated silica compounds, bis(triethoxysilylpropyl)disulfide (TESPD)/silica/carbon black (CB)/SBR and bis(triethoxysilylpropyl)tetrasulfide (TESPT)/silica/CB/SBR, have been processed in a batch mixer and they are investigated with respect to the alcohol residue level in silane, the processability, the vulcanization characteristics, and the mechanical properties. The alcohol level is low at the moisture treated compounds. The TESPD compounds show lower alcohol level than the TESPT ones on moisture treated and untreated compounds. The probe temperatures of the moisture treated compounds are lower than the drop temperature, while those of the untreated compounds are higher than the drop ones, respectively. The vulcanization properties of the compounds are changed by the moisture treatment and this improves the physical properties of the compounds. The moisture treatment on silica surface increases the hydrolysis reaction of the alkoxy silane and the hydrolyzed silane improved the coupling reaction with the hydroxyl group on silica surface during reactive batch processing. It also reduces the rate of temperature rise during batch mixing due to the latent heat of the moisture and the endothermic reaction between silica and silane. At the vulcanization stage, it seems to further increase the coupling reaction between silica and silane. The steric hindrance theory of an alkoxy silane (TESPT) has to be reconsidered with a large amount of moisture treated silica/TESPD/CB/S-SBR compound system.     

Effect of ultrasound on ester hydrolysis in aqueous ethanol.

Kinetics of the acid-catalyzed hydrolysis of ethyl acetate in ethanol-water binary solutions were investigated without sonication and under ultrasound at 22 kHz. Rate enhancements by 1.03-2.4 times were found with a minimum at 18 wt.% and a maximum at 45 wt.% of ethanol. The results suggest that ultrasonic acceleration of the reaction may be interrelated to the perturbation of the molecular structure of the binary solvent.     

A multi-spectral reordering technique for the full spectrum SLMB modeling of radiative heat transfer in nonuniform gaseous mixtures

A Multi-Spectral Reordering (MSR) scheme is introduced to improve the performances of the Spectral-Line Moment-Based (SLMB) modeling for the handling of full spectrum radiative heat transfer calculations in nonuniform media. Using this simultaneous reordering of the spectrum for several thermophysical conditions together with employing approximate formulations to evaluate path-averaged transmission functions for nonisothermal and nonhomogenous gaseous paths, a novel full spectrum gas radiation modeling method in nonuniform gaseous mixtures is constituted. The method is presented in details as well as the building of associated databases for CO₂ and H₂O at atmospheric pressure and for the temperature range of 300-2700 K. The new model is validated against line-by-line reference computations for a series of existing benchmarks and for a flame configuration. The MSR-SLMB modeling is shown to perform accurately and better than the standard SLMB one, while involving reasonable additional computational costs.     

Synergistic effect and mechanisms of ultrasound and AlOOH suspension on Al hydrolysis for hydrogen production

Ultrasound can accelerate and change the reaction process and is widely used in the field of hydrogen production and storage. In this study, ultrasound (US) and AlOOH suspension (AH) are used to promote hydrogen production from Al hydrolysis. The results indicate that both US and AH greatly shorten the induction time and enhance the hydrogen production rate and yield. The promoting effect of US and AH on Al hydrolysis originates from the acoustic cavitation effect and catalytic effect, respectively. When AH is used in combination with US, Al hydrolysis has the best hydrogen production performance and the hydrogen yield can reach 96.6 % within 1.2 h, because there is a synergistic effect on Al hydrolysis between AH and US. Mechanism analyses reveal that the micro-jets and local high temperature environment arising from acoustic cavitation improve the catalytic activity of AlOOH, while the suspended AlOOH particles enhance the cavitation effect of US. This work provides a novel and feasible method to promote hydrogen production from Al hydrolysis.