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11.
An adaptive three-dimensional isogeometric formulation based on rational splines over hierarchical T-meshes (RHT-splines) for problems in elasto-statics and elasto-dynamics is presented. RHT-splines avoid some short-comings of NURBS-based formulations; in particular they allow for adaptive h-refinement with ease. In order to drive the adaptive refinement, we present a recovery-based error estimator for RHT-splines. The method is applied to several problems in elasto-statics and elasto-dynamics including three-dimensional modeling of thin structures. The results are compared to analytical solutions and results of NURBS based isogeometric formulations. 相似文献
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Luu Thai Danh Le Ngoc Han Ngo Duy Anh Triet Jian Zhao Raffaella Mammucari Neil Foster 《Food and Bioprocess Technology》2013,6(12):3481-3489
The effects of three different extraction methods, namely hydrodistillation, supercritical CO2 extraction (SCE) and hexane extraction on the yield, chemical composition and antimicrobial and antioxidant activities of lavender essential oil were investigated in this study. SCE produced a yield of 6.7 % (dry weight), which was comparable to that of solvent extraction (7.6 %), but significantly higher than that of hydrodistillation (4.6 %). The chemical composition of the oils showed considerable variations among the extraction methods, with linalool, linalyl acetate, camphor and borneol making up approximately 80 % of identified components in all extracts. Hexane extraction produced oils with the presence of waxes, colour pigments and albuminious materials with semi-solid consistency, while hydrodistillation extracts showed signs of thermal degradation. The SCE extracts had an aroma with the closest resemblance to the starting material, showing negligible thermal degradation, and exhibited significantly higher antioxidant activity than the hydrodistillation and hexane extracts. Oils produced by SCE and hydrodistillation had antimicrobial activities higher than hexane extracts. The results of this study demonstrate that SCE is a promising process for the extraction of lavender essential oil. 相似文献
15.
Syngas production from methane dry reforming over Ni/SBA-15 catalyst: Effect of operating parameters
Osaze Omoregbe Huong T. Danh Chinh Nguyen-Huy H.D. Setiabudi S.Z. Abidin Quang Duc Truong Dai-Viet N. Vo 《International Journal of Hydrogen Energy》2017,42(16):11283-11294
The influence of operating conditions including reactant partial pressure and reaction temperature on the catalytic performance of 10%Ni/SBA-15 catalyst for methane dry reforming (MDR) reaction has been investigated in this study. MDR reaction was carried out under atmospheric pressure at varying CH4/CO2 volume ratios of 3:1 to 1:3 and 923–1023 K in a tubular fixed-bed reactor. SBA-15 supported Ni catalyst exhibited high specific surface area of 444.96 m2 g?1 and NiO phase with average crystallite size of 27 nm was detected on catalyst surface by X-ray diffraction and Raman measurements. H2 temperature-programmed reaction shows that NiO particles were reduced to metallic Ni0 phase with degree of reduction of about 90.1% and the reduction temperature depended on the extent of metal-support interaction and confinement effect of mesoporous silica support. Catalytic activity appeared to be stable for 4 h on-stream at 973–1023 K whilst a slight drop in activity was observed at 923 K probably due to deposited carbon formed by thermodynamically favored CH4 decomposition reaction. Both CH4 and CO2 conversions increased with rising reaction temperature and reaching about 91% and 94%, respectively at 1023 K with CO2 and CH4 partial pressure of 20 kPa. CH4 conversion improved with increasing CO2 partial pressure, and exhibited an optimum at of 30–50 kPa depending on reaction temperature whilst a substantial decline in CO2 conversion was observed with growing . Additionally, CH4 and CO2 conversions decreased significantly with rising CH4 partial pressure because of increasing carbon formation rate via CH4 cracking in CH4-rich feed. Post-reaction characterization shows that active Ni metal phase was not re-oxidized to inactive metal oxide during MDR reaction. The heterogeneous nature of deposited carbons including carbon nanofilament and graphite was detected on catalyst surface by Raman measurement. 相似文献
16.
A TEM study of microstructural changes during retrogression and reaging in 7075 aluminum 总被引:11,自引:0,他引:11
Nguyen Cong Danh Krishna Rajan W. Wallace 《Metallurgical and Materials Transactions A》1983,14(9):1843-1850
Microstructural changes occurring during retrogression, and during retrogression plus reaging in 7075-T6 aluminum alloy have
been investigated by means of transmission electron microscopy, and related to mechanical properties. TEM results indicate
that the drop in strength during the initial stage of retrogression was due to the partial dissolution of G.P. zones while
the growth of the semi-coherentη ′ was responsible for the rapid recovery of strength. It is suggested that the retrogression and reaging treatment resulted
in the increase in volume fraction of G.P. zones and especially η′ precipitates over both the T6 and retrogressed conditions,
therefore significantly improving the strength of the alloy. 相似文献
17.
The optical absorption spectra of an irradiated zirconium-barium-lanthanum aluminum- lithium fluoride glass prepared with 1 wt% BaC12 were resolved into Gaussian bands identified as the Vk , and VH centers, Zr3+ , and two bands associated with Cl, i.e., FCl− at 4.78 eV and Cl− 2 at 3.90 eV. These latter bands are more thermally stable than the VH and V, trapped hole centers, persisting to 450 and 550 K, respectively. 相似文献
18.
Vien Minh Nguyen-Thanh Lu Trong Khiem Nguyen Timon Rabczuk Xiaoying Zhuang 《International journal for numerical methods in engineering》2020,121(21):4811-4842
We propose a surrogate model for two-scale computational homogenization of elastostatics at finite strains. The macroscopic constitutive law is made numerically available via an explicit formulation of the associated macroenergy density. This energy density is constructed by using a neural network architecture that mimics a high-dimensional model representation. The database for training this network is assembled through solving a set of microscopic boundary value problems with the prescribed macroscopic deformation gradients (input data) and subsequently retrieving the corresponding averaged energies (output data). Therefore, the two-scale computational procedure for nonlinear elasticity can be broken down into two solvers for microscopic and macroscopic equilibrium equations that work separately in two stages, called the offline and online stages. The finite element method is employed to solve the equilibrium equation at the macroscale. As for microscopic problems, an FFT-based collocation method is applied in tandem with the Newton-Raphson iteration and the conjugate-gradient method. Particularly, we solve the microscopic equilibrium equation in the Lippmann-Schwinger form without resorting to the reference medium. In this manner, the fixed-point iteration that might require quite strict numerical stability conditions in the nonlinear regime is avoided. In addition, we derive the projection operator used in the FFT-based method for homogenization of elasticity at finite strain. 相似文献
19.
Activated carbons with metal containing bentonite binders as adsorbents of hydrogen sulfide 总被引:4,自引:0,他引:4
Danh Nguyen-Thanh 《Carbon》2005,43(2):359-367
Wood-based activated carbon was ground and mixed with 10% bentonite binders containing either iron, zinc or copper cations adsorbed within the interlayer space and/or on the external surface of bentonite flakes. To better understand the role of transition metals, carbon was also impregnated with iron, zinc and copper salts. The structure of materials after modification was determined using nitrogen adsorption. The modification resulted in a decrease in porosity, especially in micropore volume, as a result of combined mass dilution effect and adsorption/re-adsorption of metals in small pores. Introduction of bentonite binders containing adsorbed metal increased the capacity of carbon for hydrogen sulfide only in the case of material containing copper. Copper also significantly increases the performance of carbon as an H2S adsorbent when impregnation is applied whereas the effects of other metals used in this study are much less pronounced. It is likely that copper present in the small pores acts as a catalyst for oxygen activation causing hydrogen sulfide oxidation. As a result of this process, elemental sulfur is formed which, when present in small pores, is oxidized to weakly adsorbed SO2. The SO2 is removed from the surface when continuous reaction with hydrogen sulfide occurs. Thus, even though binding carbon with spent bentonites after copper adsorption increases the capacity of carbon toward H2S removal, the formation of SO2, another undesirable pollutant, does detract somewhat from the procedure. 相似文献
20.
Characterization and activity of vanadia-promoted Pt/ZrO2 catalysts for the water–gas shift reaction
Pt/ZrO2 catalysts for the water–gas shift (WGS) were promoted with various amounts of vanadia. Analyses by XRD, N2 adsorption, Raman, and UV–vis DRS showed that vanadia is present below monolayer coverage as monovanadate and polyvanadate, with the former dominating at lower loadings, and that following monolayer formation, VO5 species appear, with the eventual generation of V2O5 and ZrV2O7 for a vanadia weight loading of 13%. Though in all cases vanadia induced an enhancement in WGS activity, the best catalyst, that contained 3 wt.% of vanadia, gave a rate that was nearly double that of the unpromoted Pt/ZrO2. That superior global activity probably results from the monovanadate that is the main species at low loadings. It is believed that monovanadate promotes the WGS by rendering the support's surface more oxidizing through its VOZr bonds. 相似文献