Congrès International d'Architecture Moderne

About: Congrès International d'Architecture Moderne is a based out in . It is known for research contribution in the topics: Boundary value problem & Jet (fluid). The organization has 393 authors who have published 403 publications receiving 4104 citations.

Compressibility Effectsy in One-Equation Turbulence Models

Abstract: The one-equation turbulence models by Spalart and Allmaras (SA) and Sekundov et al. (Nut-92) are tested against two compressible two-dimensional flows, namely, the turbulent flat-plate boundary layer at zero pressure gradient and the mixing layer. The boundary layer (BL) approximation is applied to the system of Reynolds equations (RANS). The BL results obtained are compared with the available RANS results and the results of direct numerical simulation (DNS). The modified Nut-92m model proposed predicts the characteristics of the turbulent flat-plate boundary layer at zero pressure gradient more accurately than the Nut-92 and SA models.

Number of limit cycles for homogeneous polynomial system

Abstract: In this paper the bifurcation of limit cycles at infinity for a class of homogeneous polynomial system of degree four is examined. This requires a problem for bifurcation of limit cycles at infinity be converted from the original system to the class of complex autonomous differential system. The evaluation of the conditions from the origin to be a centre and the highest degree fine focus results from the calculation of singular point values. A quartic system is constructed for which it can bifurcate with only one limit cycle at infinity when the normal parameters are constant.

Thermal Integrity of Anisotropic Bodies

Abstract: Thermal strength for anisotropic bodies is considered in case of single-crystal nickel alloys widely used in manufacturing of high-temperature gas turbine blades. Anisotropy of mechanical properties and failure conditions, typical for single crystals, is described. Experimental data for deformation and damage of single-crystal specimens under extension are compared with results of theoretical predictions. The role of the «Schmid factor» describing the relative level of tangential stresses in different slip systems is discussed. It is shown that its maximum value corresponds to a critical stress state related to the initiation of plastic deformation or material damage only for specimen extension and cannot be considered as a failure criterion of a single-crystal body for other loading orientations. Comparison of calculated maximal tangential stresses, with their critical values, obtained by testing specimens of chosen orientation under appropriate loading gives better results. It is demonstrated that strength analysis of single-crystal machine parts under combined stresses may rely on material properties associated with uniaxial loading at a certain “equivalent” specimen orientation. Several problems of creep, low and high cyclic fatigue, and thermal fatigue of anisotropic bodies are also discussed.

Creep and Long-Term Strength at Stationary Stresses and Temperatures

Abstract: The developed computational models for creep and long-term strength of structural materials under multi-axial proportional loading associated with steady or monotonically varying mechanical and thermal disturbances are justified using numerous experimental data. Specialized and generalized models for non-isothermal creep and ranges of applicability are discussed. A complete three-stage creep diagram is also presented. The latter may be described by six material parameters depending upon stress and temperature. Creep of statically determinate and indeterminate mechanical systems is considered along with computational methods oriented to the prescribed kinematic laws of steady creep velocity distribution over a body. Several examples for various creep conditions show that the stress field resulting from external loading, and especially induced by non-uniform thermal expansion, may deviate considerably from the field corresponding to purely elastic calculation and also from that related to the average body temperature. In case of creep, temperature variation makes a major impact on stress redistribution caused by stress relaxation as well as on the magnitude of residual stresses originated from unloading and cooling. The possibility for predicting structure durability in case of long-term maintenance is addressed, including equivalent trials under heavier stress and temperature conditions.