排序方式: 共有23条查询结果,搜索用时 15 毫秒
11.
In multibody systems (MBS), where elastic bodies are represented in the frame work of the ‘floating frame of reference formulation’ (FFRF), structural deformation is usually computed by the superposition of time invariant trial vectors (commonly called ‘modes’). However, the mode bases, which are discussed in the literature, do not take joints into special account at the stage of mode generation. In the presented paper we propose a problem–oriented extension of classical mode bases in order to consider the presence of joints. In the novel extension which we call ‘Joint Interface Modes’ (JIMs), Newton's 3rd law across the joint is taken into account at the stage of mode generation, which leads to a superior convergence at the stage of mode based computation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
For reliable computational predictions of transonic flows, it is important to resolve the significant effects of physical variations on the shock wave locations. The resulting discontinuities in probability space require extremum diminishing uncertainty quantification to avoid overshoots and undershoots in the response surface approximation. In this paper, the extremum diminishing concept in probability space is extended to infinite parameter domains using inverse distance weighting interpolation of deterministic samples. Based on results for three analytical test functions, the combination of Halton sampling and power parameter limit value c → ∞ is selected. The approach is employed to model spatial-free-stream velocity fluctuations in the highly sensitive transonic AGARD 445.6 wing test case in an up to ten-dimensional probability space. The 0.5% input variations are amplified to a coefficient of variation for the wave drag of cvD?=?9.58% in combination with an increase of the mean drag by 1.75% compared to the deterministic value. 相似文献
13.
The Unsteady Adaptive Stochastic Finite Elements (UASFE) method resolves the effect of randomness in numerical simulations of single-mode aeroelastic responses with a constant accuracy in time for a constant number of samples. In this paper, the UASFE framework is extended to multi-frequency responses and continuous structures by employing a wavelet decomposition pre-processing step to decompose the sampled multi-frequency signals into single-frequency components. The effect of the randomness on the multi-frequency response is then obtained by summing the results of the UASFE interpolation at constant phase for the different frequency components. Results for multi-frequency responses and continuous structures show a three orders of magnitude reduction of computational costs compared to crude Monte Carlo simulations in a harmonically forced oscillator, a flutter panel problem, and the three-dimensional transonic AGARD 445.6 wing aeroelastic benchmark subject to random fields and random parameters with various probability distributions. 相似文献
14.
Powder-susceptibility measurements in the temperature region 2–80° K on the chain compounds MII(N2H5)2(SO4)2, with M = Mn, Fe, Co, Ni, and Cu, show that the magnetic properties of these compounds can be interpreted in terms of antiferromagnetic linear-chain systems. The experimental results provide information on the magnitude of the intrachain interactions. In addition, ESR linewidth experiments were used for a determination of the intrachain interaction in Mn(N2H5)2 (SO4)2. For the interpretation of the data on Fe(N2H5)2(SO4)2, the parallel susceptibility of Ising chains with S = 2 is calculated theoretically. An estimate for the ratio between the intra- and interchain coupling is given. Use is made of preliminary results of specific heat measurements on these compounds for the interpretation of the magnetic data. 相似文献
15.
Marco J. van der Burgt Jouke Jansen A.Herbert Huizer Cyril A.G.O. Varma 《Journal of Molecular Structure》1996,385(3):175-183
The X-ray diffraction of crystalline 1,2-dihydro-3H-benz[e]inden-3-one (DHBI) reveals that the molecular geometry is fully planar in the electronic ground state. Glassy solutions of naphthaldehyde, 2-acetonaphthone and methyl 2-naphthoate in the mixtures methylcyclohexane/iso-pentane (MIP) and methanol/ethanol (ME) are phosphorescent. DHBI in ME shows phosphorescence, but in MIP it is non-phosphorescent. The phosphorescence spectra of these compounds and of naphthalene have a strong resemblance. This is in accordance with a molecular distortion in the lowest triplet state, which decouples the π electron systems of the carbonyl group and the naphthyl group. The absence of phosphorescence of DHBI in MIP, indicates a geometry of the triplet state, having a non-planar naphthalene ring, when the molecule is in the non-hydrogen bonded form. 相似文献
16.
17.
Assessment of Uncertainties in Modeling of Laminar to Turbulent Transition for Transonic Flows 总被引:1,自引:0,他引:1
Rene Pecnik Jeroen A. S. Witteveen Gianluca Iaccarino 《Flow, Turbulence and Combustion》2013,91(1):41-61
The effect of physical variability and uncertainty in model correlations on laminar-turbulent transition in transonic flows is computed using two different Stochastic Collocation methods. Physical variability in the boundary conditions is first investigated for a flow over a flat plate with and without pressure gradient to quantify the uncertainties on the skin friction distribution along the plate surface. Since the laboratory conditions for the flat plate test cases are well defined and the applied transition model has been tuned for these cases, good agreement with experiments is achieved and the variability in the output is low. The second investigated cases exhibit boundary layer transition on the surface of a highly loaded turbine guide vane under transonic flow conditions. Comparisons between the predicted and measured wall heat transfer are used to quantify uncertainties in the free stream turbulence and the model correlations that accounts for compressibility effects on the onset and extension of the bypass transition. The computational results show that the uncertainties have a significant impact on the transition location for the turbine guide vane simulations and, consequently, on the reliability of the predictions for compressible flows. The output uncertainty accounts to a large extent for the difference between the deterministic simulation and the experiments. The results from the Simplex Stochastic Collocation method are computationally more efficient than those of the Stochastic Collocation based on Clenshaw–Curtis quadrature. 相似文献
18.
Jeroen A.S. Witteveen 《Journal of computational physics》2010,229(7):2719-2739
A second order front tracking method is developed for solving the hyperbolic system of Euler equations of inviscid fluid dynamics numerically. Meshless front tracking methods are usually limited to first order accuracy, since they are based on a piecewise constant approximation of the solution. Here second order convergence is achieved by deriving a piecewise linear reconstruction of the piecewise constant front tracking solution. The linearization is performed by decomposing the front tracking solution into its wave components and by linearizing the wave solutions separately. In order to construct a physically correct linearization, the physical phenomena of the front are taken into account in terms of the front types of the previously developed improved front interaction model. This front interaction model is also extended to include front numbers used in the wave decomposition. It is illustrated numerically for Sod’s Riemann problem, the two interacting blast waves problem, and a two-dimensional supersonic airfoil flow validation study that the proposed front tracking method achieves second order convergence also in the presence of strong discontinuities and their interactions. 相似文献
19.
O. N. Bakharev A. V. Dooglav A. V. Egorov E. V. Krjukov Yu. A. Sakhratov M. A. Teplov H. B. Brom J. Witteveen 《JETP Letters》1996,64(5):398-403
The nuclear magnetic relaxation of 169Tm in TmBa2Cu3O6+x
(x=0.1–1.0, Δ x=0.1) and TmBa2Cu4O8 is studied at temperatures below 5 K. In all the samples, the Tm spin-lattice relaxation proceeds via intrinsic paramagnetic
centers (PCs) like Cu2+ or copper-oxygen spin-polarized clusters. The experimental data for TmBa2Cu3O6+x
support the idea of the structural (chemical) micro-phase separation in oxygen-deficient 123 compounds. Apparently, the samples
with x⩾0.4 contain hole-poor nonsuperconducting regions, enriched with PCs, and hole-rich (PC-poor) superconducting regions. The
volume fraction f
n of the PC-rich phase reaches a maximum value of 0.85 at x=0.4 and decreases monotonically with increasing x (f
n=0.5, 0.3, and 0.25 at x=0.5, 0.6, and 0.7, respectively). The Tm spin-lattice relaxation in the underdoped TmBa2Cu4O8 compound indicates that this sample, in contrast to oxygen-deficient TmBa2Cu3O6+x
, has a homogeneous composition. However, the Tm spin-spin relaxation measurements reveal two sorts of the Tm nuclear spins
in Tm124, having different NMR spectra and different relaxation times T
2. The latter result is evidence of electronic phase separation in CuO2 phases.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 365–370 (10 September 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
20.
The susceptibilities of polycrystalline samples of various antiferromagnetic linear-chain compounds ANiX3 (A =Tl, NH4, Rb, Cs and X = Cl, Br) have been measured in the temperature region 2–200 °K. The results, amongst which the already known data for RbNiCl3 and CsNiCl3, are interpreted in terms of a theory, developed by Weng, for antiferromagnetic Heisenberg linear-chain systems with spin S = 1. By means of Oguchi's Green function theory and the experimentally determined transition temperatures TN the order of magnitude of the ratio between inter- and intra-chain interaction is obtained. 相似文献