Adaptive finite element method for high-speed flow-structure interaction

An adaptive finite element method for high-speed flow-structure interaction is presented. The cell-centered finite element method is combined with an adaptive meshing technique to solve the Navier-Stokes equations for high-speed compressible flow behavior. The energy equation and the quasi-static structural equations for aerodynamically heated structures are solved by applying the Galerkin finite element method. The finite element formulation and computational procedure are described. Interactions between the high-speed flow, structural heat transfer, and deformation are studied by two applications of Mach 10 flow over an inclined plate, and Mach 4 flow in a channel. The project supported by the Thailand Research Fund (TRF)     

Degradation kinetics of trisaccharides comprised of glucose residues in subcritical water

Degradation kinetics of three trisaccharides, i.e., maltotriose, isomaltotriose, and panose, in subcritical water at 190, 200, 220, and 240°C were studied and compared. Irreversible, first-order reaction for each step of the degradation was applied to evaluate the rate constants for trisaccharide, disaccharide, and monosaccharide degradations. Estimation of reaction rate constants indicated that the overall degradation rates decreased in the following order: maltotriose > panose > isomaltotriose; therefore, it could be concluded that α-1,4-glycosidic bond is more easily cleaved than α-1,6-glycosidic bond in subcritical water. The temperature dependency for rate constants could be described by the Arrhenius equation.     

Healing of shock instability for Roe's flux‐difference splitting scheme on triangular meshes

Healing of nonphysical flow solutions and shock instability from the use of Roe's flux‐difference splitting scheme is presented. The proposed method heals nonphysical flow solutions such as the carbuncle phenomenon, the shock instability from the odd–even decoupling problem, and the expansion shock generated from the violated entropy condition. The performance and efficiency of the proposed method are evaluated by solving several benchmark and complex high‐speed compressible flow problems. Copyright © 2008 John Wiley & Sons, Ltd.     

Adaptive delaunay triangulation with multidimensional dissipation scheme for high-speed compressible flow analysis

IntroductionHigh-speed compressible flows normally involve many complex flow phenomena,suchas shock waves,flow expansions,and shock-shock interactions[1].Effects of thesephenomena are critical in the design of high-speed structures.These flows are charact…     

用于高速可压缩流体分析的带多维耗散格式的自适应Delaunay三角剖分

利用自适应Delaunay三角剖分并结合胞格中心迎风算法,分析非粘滞高速可压缩流体问题.推导了多维耗散格式,并采用非结构化三角网格的迎风算法,改善了激波的计算结果.解精度评价中引入误差估计,在网格重划分算法中,解梯度变化大的区域生成小单元格,解梯度变化小的区域使用大单元格.该格式能进一步推广到高阶时空的解精度分析中.通过稳态和不稳态的高速可压缩流体超音速激波和激波传播特性的分析,可以评估该算法的效率.     

Finite volume element method for analysis of unsteady reaction–diffusion problems

A finite volume element method is developed for analyzing unsteady scalar reaction-diffusion problems in two dimensions. The method combines the concepts that are employed in the finite volume and the finite element method together. The finite volume method is used to discretize the unsteady reaction-diffusion equation, while the finite element method is applied to estimate the gradient quantities at cell faces. Robustness and efficiency of the combined method have been evaluated on uniform rectangular grids by using available numerical solutions of the two-dimensional reaction-diffusion problems. The numerical solutions demonstrate that the combined method is stable and can provide accurate solution without spurious oscillation along the high-gradient boundary layers.     

Additional Paper Waste in Pulping Sludge for Biohydrogen Production by Heat-Shocked Sludge

Dark anaerobic fermentation is an interesting alternative method for producing biohydrogen (H₂) as a renewable fuel because of its low cost and various usable organic substrates. Pulping sludge from wastewater treatment containing plentiful cellulosic substrate could be feasibly utilized for H₂ production by dark fermentation. The objective of this study was to investigate the optimal proportion of pulping sludge to paper waste, the optimal initial pH, and the optimal ratio of carbon and nitrogen (C/N) for H₂ production by anaerobic seed sludge pretreated with heat. The pulping sludge was pretreated with NaOH solution at high temperature and further hydrolyzed with crude cellulase. Pretreatment of the pulping sludge with 3% NaOH solution under autoclave at 121 °C for 2 h, hydrolysis with 5 FPU crude cellulase at 50 °C, and pH 4.8 for 24 h provided the highest reducing sugar production yield (229.68 ± 2.09 mg/g_TVS). An initial pH of 6 and a C/N ratio of 40 were optimal conditions for H₂ production. Moreover, the supplement of paper waste in the pulping sludge enhanced the cumulative H₂ production yield. The continuous hydrogen production was further conducted in a glass reactor with nylon pieces as supporting media and the maximum hydrogen production yield was 151.70 ml/g_TVS.