Efficient stochastic structural analysis using Guyan reduction

This paper introduces the application of the Guyan reduction within the stochastic finite element (SFE) analysis, which employs a Galerkin-based Polynomial chaos (P-C) expansion formulation. It is shown that by reducing the size of the deterministic FE model, a substantial improvement in the overall computational efficiency can be achieved. An implementation exploiting the features of the proposed formulation is presented. In this regard, especially the interaction with the 3rd party FE solvers has been addressed. The suggested method has been tested on a simple grid structure and also on a large building model, where the accuracy and efficiency of the introduced approach have been quantified.     

End formation of a round tube into a square section having small corner radii

Expansion and reduction are the two common end forming processes for tubes. In the tube end expansion process using a square punch, it is difficult to obtain a small corner radii due to the stretching of the tube around the punch corners. The wall thickness around the corners is small when compared to the side wall. Hence, a tube having a poor square look is formed. In this study, a 2-stage end expansion of a round tube end into a square section having an improved square look i.e. small corner radii and increase in wall thickness around corners is developed. In the 1st stage, the tube end is flared into a cone shape using a 30° conical die by axial compression. In the 2nd stage, the conical end of the tube is drawn through a taper square die using a conical bottom square punch, and a near square section is formed. A 15% ironing ratio is applied during the drawing process to flatten the side wall of the square. Experimental and FEM simulation were performed to evaluate and to verify the forming process. Although the height of the square section increases when the punch stroke at the 1st stage is increased. However, this increase is limited by the buckling of the pipe at the circular section of the thick blank tube. Since the conical end is drawn into a square section having different radial lengths, the bottom of the square section is uneven. The uneven bottom end is trimmed off in the later process. A square section having a maximum height of 32 mm after trimming is successfully obtained from the experiment for the punch stroke, S = 44 mm using an API 5 L tube.     

硫酸装置膨胀节选型方案的分析

本文对硫酸装置膨胀节选型问题进行了详细的技术方案讲座和技术经济比较，对存在的一些问题提出了建议和改进措施。     

连铸钢包用铝镁尖晶石-炭砖的研制及应用

针对铝镁炭砖在使用过程中残余膨胀过大、热导率较高等问题，从基质组成、鳞片石墨的粒度及加入量和生产工艺等方面进行了研究试验，在铝镁炭砖基础上研制开发出了综合性能优良的铝镁尖晶石-炭砖。     

Determination of Thermophysical Properties of Fluid Metals by Wire-Explosion Experiments

Wire explosion experiments were used to obtain thermophysical properties of tungsten. These properties are specific heat, thermal expansion coefficient, compressibility, and electrical and thermal conductivities and their dependences on temperature. There are strong indications that the emissivity in the liquid range should be dependent on temperature. A proposal has been made for determining the emissivity from comparison of experiments with model calculations. The temperature range is extended up to 10,000 K, and first indications for the near-critical-point behavior were obtained. Other properties such as diffusivity, viscosity, and surface tension may possibly also be derived in this range.     

The impact of Ti and temperature on the stability of Nb5Si3 phases: a first-principles study

Abstract

Nb-silicide based alloys could be used at T > 1423 K in future aero-engines. Titanium is an important additive to these new alloys where it improves oxidation, fracture toughness and reduces density. The microstructures of the new alloys consist of an Nb solid solution, and silicides and other intermetallics can be present. Three Nb₅Si₃ polymorphs are known, namely αNb₅Si₃ (tI32 Cr₅B₃-type, D8_l), βNb₅Si₃ (tI32 W₅Si₃-type, D8_m) and γNb₅Si₃ (hP16 Mn₅Si₃-type, D8₈). In these 5–3 silicides Nb atoms can be substituted by Ti atoms. The type of stable Nb₅Si₃ depends on temperature and concentration of Ti addition and is important for the stability and properties of the alloys. The effect of increasing concentration of Ti on the transition temperature between the polymorphs has not been studied. In this work first-principles calculations were used to predict the stability and physical properties of the various Nb₅Si₃ silicides alloyed with Ti. Temperature-dependent enthalpies of formation were computed, and the transition temperature between the low (α) and high (β) temperature polymorphs of Nb₅Si₃ was found to decrease significantly with increasing Ti content. The γNb₅Si₃ was found to be stable only at high Ti concentrations, above approximately 50 at. % Ti. Calculation of physical properties and the Cauchy pressures, Pugh’s index of ductility and Poisson ratio showed that as the Ti content increased, the bulk moduli of all silicides decreased, while the shear and elastic moduli and the Debye temperature increased for the αNb₅Si₃ and γNb₅Si₃ and decreased for βNb₅Si₃. With the addition of Ti the αNb₅Si₃ and γNb₅Si₃ became less ductile, whereas the βNb₅Si₃ became more ductile. When Ti was added in the αNb₅Si₃ and βNb₅Si₃ the linear thermal expansion coefficients of the silicides decreased, but the anisotropy of coefficient of thermal expansion did not change significantly.     

Parameter identification of discrete systems via discrete Chebyshev transformation

Abstract

A new method is proposed for the parameter identification of linear time‐invariant discrete single‐input‐single‐output systems by the application of the discrete Chebyshev transformation. The input and output data sequences of a system represented by difference equation are first transformed into discrete Chebyshev spectra. Using spectrum matching, the parameter identification problem becomes the solution of a set of overdetermined simultaneous linear algebraic equations. Examples with and without noise contamination are given to illustrate the new method.     

调味品行业现状与发展趋势分析(一)

文章综述介绍了调味品行业的总体状况、行业特点和发展趋势;从多角度对不同规模调味品企业发展的商业机遇和不同类别产品的市场拓展途径进行了探讨;提出了开发新型调味产品的几点建议.     

高性能水听器用胶管的研制

研制了一种高性能水听器用胶管,基体材料采用氯化丁基橡胶,配合一定份数的补强橡胶,进行了配方设计及挤出工艺研究。研制出的胶管满足水密和透声使用要求并且耐老化。     

Double-perovskites YBaCo2−xFexO5+δ cathodes for intermediate-temperature solid oxide fuel cells

Double-perovskites YBaCo_2−xFe_xO_5+δ (YBCF, x = 0.0, 0.2, 0.4 and 0.6) are synthesized with a solid-state reaction and are assessed as potential cathode materials for utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs) on the La_0.9Sr_0.1Ga_0.8Mg_0.115Co_0.085O_2.85 (LSGMC) electrolyte. The YBCF materials exhibit chemical compatibility with the LSGMC electrolyte up to a temperature of 950 °C. The conductivity of the YBCF samples decreases with increasing Fe content, and the maximum conductivity of YBCF is 315 S cm⁻¹ at 325 °C for the x = 0.0 sample. A semiconductor-metal transition is observed at about 300-400 °C. The thermal expansion coefficient of the YBCF samples increases from 16.3 to 18.0 × 10⁻⁶ K⁻¹ in air at temperatures between 30 and 900 °C with increase in Fe content. The area-specific resistances of YBCF cathodes at x = 0.0, 0.2 and 0.4 on the LSGMC electrolyte are 0.11, 0.13 and 0.15 Ω cm² at a temperature of 700 °C, respectively. The maximum power densities of the single cells fabricated with the LSGMC electrolyte, Ce_0.8Sm_0.2O_1.9 (SDC) interlayer, NiO/SDC anode and YBCF cathodes at x = 0.0, 0.2 and 0.4 reach 873, 768 and 706 mW cm⁻², respectively. This study suggests that the double-perovskites YBCF (0 ≤ x ≤ 0.4) can be potential candidates for utilization as IT-SOFC cathodes.