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901.
A fibrous porous medium with two length scales is modeled as a bed of porous cylinders aligned perpendicular to the flow of viscous fluid. The flow behavior is described using Stokes and Darcy flow equations in the regions around (higher length scale) and within the cylinders (lower length scale) respectively. The typical ratio of higher and lower length-scale regions enable us to invoke lubrication approximation and simplify the equations to develop a closed form solution for the overall permeability of this dual-scale porous medium. A parametric analysis is performed to explore the dependence of permeability on factors such as the volumetric ratio of higher and lower length-scale regions, permeability and size of inclusions in the smaller length-scale region. The analytical model is compared with the numerical results and the trend is compared with the experiments. 相似文献
902.
Germano (Theor Comput Fluid Dyn 17:225–331, 2004) proposed a hybrid-filter approach, which additively combines an LES-like filter operator (F) and a RANS-like statistical operator (E) using a blending function k: H?=?kF?+?(1???k)E. Using turbulent channel flow as an example, we first conducted a priori tests in order to gain some insights into this hybrid-filter approach, and then performed full simulations to further assess the approach in actual simulations. For a priori tests, two separate simulations, RANS (E) and LES (F), were performed using the same grid in order to construct a hybrid-filtered field (H). It was shown that the extra terms arising out of the hybrid-filtered Navier–Stokes (HFNS) equations provided additional energy transfer from the RANS region to the LES region, thus alleviating the need for the ad hoc forcing term that has been used by some investigators. The complexity of the governing equations necessitated several modifications in order to render it suitable for a full numerical simulation. Despite some issues associated with the numerical implementation, good results were obtained for the mean velocity and skin friction coefficient. The mean velocity profile did not have an overshoot in the logarithmic region for most blending functions, confirming that proper energy transfer from the RANS to the LES region was a key to successful hybrid models. It is shown that Germano’s hybrid-filter approach is a viable and mathematically more appealing approach to simulate high Reynolds number turbulent flows. 相似文献
903.
This paper examines the modeling and solution of large-order nonlinear systems with continuous nonlinearities which are spatially
localized. This localization is exploited by a combined component mode synthesis (CMS)—dynamic substructuring approach for
efficient model reduction. A new ordering method for the Fourier coefficients used in the Harmonic Balance Method (HBM) is
proposed. This allows the calculation of the slave dynamic flexibility matrix, using simple analytical expressions thus saving
considerable computational effort by avoiding inverse calculation. This procedure is also capable of handling proportional
damping. A hypersphere-based continuation technique is used to trace the solution, and hence track bifurcations since it has
the advantage that the augmented Jacobian matrix remains square. The reduced system is also solved using a time-variational
method (TVM) which generates sparse Jacobian matrices when compared with HBM. Several systems including those with parametric
excitation and internal resonances are solved to demonstrate the capability of the proposed schemes. A comparison of these
techniques and their effectiveness in solving extremely strong nonlinear systems with continuous nonlinearities is discussed. 相似文献
904.
Suneetha P. Krishna T. S. Gowrisankar M. Reddy M. Srinivasa Ramachandran D. 《Journal of Thermal Analysis and Calorimetry》2018,134(2):1151-1167
Journal of Thermal Analysis and Calorimetry - In the present paper, we reported the accurately measured densities (ρ), speed of sound (u) and refractive index (nD) for the binary mixture of... 相似文献
905.
Krishnaprasad Madica Krishna Chaitanya Nadimpally Gangadhar J. Sanjayan 《Tetrahedron letters》2017,58(16):1568-1571
Rapastinel (GLYX-13) is a C-amidated tetrapeptide drug under clinical development for adjunctive treatment of major depressive disorder (MDD). Rapastinel features two consecutive proline residues centered at the peptide sequence (Thr-Pro-Pro-Thr-NH2), which are detrimental to its biological activity. In this communication, we report the synthesis of very close structural analogues of rapastinel comprising silaproline (Sip) as proline surrogate. By virtue of its enhanced lipophilicity and metabolic stability, Sip introduction in the native rapastinel sequence is expected to improve its pharmacokinetic profiles. 相似文献
906.
Krishna C. Bhargavi M. V. Rao Y. J. Krupadanam G. L. D. 《Russian Journal of General Chemistry》2017,87(8):1857-1863
Russian Journal of General Chemistry - An efficient and straight forward procedure for the syntheses of isoxazoline/isoxazole fused coumarin analogues 7a–7g and 8a–8g from the... 相似文献
907.
908.
Sourav Mete Krishna Gopal Goswami Priyadarsi De 《Journal of polymer science. Part A, Polymer chemistry》2020,58(5):766-778
To study the composition-dependent crystallization behavior of copolyperoxides, herein a series of copolymers were prepared by varying the ratios of methyl methacrylate (MMA) and 4-vinylbenzyl stearate (VBS) under 100 psi oxygen pressure using AIBN as an initiator at 50°C in toluene. Both 13C NMR and electron impact mass spectroscopy (EI-MS) approved an alternative placement of either of the monomer and peroxy (–O–O–) links throughout the polymer chain. Thermal stability of the resulting copolyperoxides was investigated by thermogravimetric analysis (TGA) and the degradation fragments have been recognized from EI-MS study. In addition, differential scanning calorimetry (DSC) displayed an endothermic peak as well as an exotherm associated with the melting of the side chain crystalline domains and degradation of –O–O– links in the polymer main chain, respectively. Furthermore, DSC thermograms unveiled a systematic decrease of the crystalline melting temperature (Tm) with the enhancement of MMA content in the copolymers. Small angle X-ray scattering (SAXS) revealed the existence of lamellar morphology (depends on VBS content in the copolyperoxide) in the synthesized polyperoxide materials, further supported by atomic force microscopy (AFM) analysis showing a layered fibrillar assembly with multiple heights of the lamella. The significant crystalline nature of the polyperoxides was further evidenced from the appearance of lattice fringes in the transmission electron microscope (TEM) micrographs. The crystalline morphology with birefringent texture was further evidenced from the polarized optical microscopy (POM) study. Thus, the present study reported the effective variation of crystalline behavior in copolyperoxide materials with the incorporation of MMA units in the copolyperoxide chains. 相似文献
909.
An atom economical, selective, and convenient one-pot protocol for the synthesis of the medicinally privileged novel chromeno [2,3-d] pyrimidine scaffold, viz, multicomponent reaction of barbituric acid derivatives, 1,3 cyclic diketone, and various aldehydes in the presence of tetra n-butyl ammonium iodide (TBAI) as an electrolyte in water media under room temperature, is reported. This ecologically sound novel concept offers environmentally benign synthetic route, short reaction times, and easy workup procedure with excellent yield (88% to 90%) and is also beneficial for diversity-oriented large-scale processes. The synthesized products were characterized by IR, MS, NMR, and CHN analysis. 相似文献
910.
Yelamaggad CV Mathews M Hiremath US Rao DS Prasad SK 《Chemical communications (Cambridge, England)》2005,(12):1552-1554
The first mesoionic nematic and smectic A mesogens derived from sydnones that are characterized by both covalent and ionic features have been synthesized and evidenced by optical, calorimetric and X-ray diffraction studies. 相似文献