The Optimum Allocation of Spare Components in Systems

This paper considers a system whose components may be divided into two subsystems, each containing components whose lives are exponentially distributed but with different scale parameters. Each system can be assigned a store of replacement spares for failed components. Charts are presented for allocating a fixed number of spare components between the two sub systems to provide maximum reliability over some specified interval of time. Expected life is also taken as a maximand, and a table is given of combinations of spares of each type so as to maximize system life. The effect of non-exponential component densities upon these optimum allocations of components is also discussed.     

Wet snow accretion on overhead lines with French report of experience

This article deals with the accretion mechanisms of wet snow observed both on a stranded conductor sample in wind tunnel conditions and on real power lines in natural weather conditions. It summarizes the theory and practical observations. Report of experience from France are given in order to demonstrate the efficiency of this passive preventive method based on the increase of torsional stiffness of conductors and to introduce wet snow risk map and countermeasures in France.     

Mode III fracture of a large-scale welded extruded aluminum panel

As part of the research on deformation and fracture of the large-scale welded thin-walled AA 6061 panels, this paper presents the experimental and numerical investigation on its fracture under Mode III loading. The proposed local fracture approach is applied by incorporating the calibrated damage input data into the finite element model. The investigations demonstrate that the present finite element model can successfully predict the global force–deflection response, the deformation modes, as well as the crack formation and propagation, in this quite sophisticated problem involving welded joints.     

浅海地声参数宽带匹配场反演的实验研究

根据不同浅海环境参数在不同的频段对匹配场功率具有不同贡献的特点,提出了宽带匹配场反演的多步优化策略,并与直接全参数反演进行了实测数据的性能对出。采用多步反演策略对亚洲海实验(ASIAEX2001)数据进行处理,按照不同海区水条件的差异,分别进行了水平不变和水平变化的环境参数反演,得到了东中国海3个局部海域的地声参数。     

生物工艺实验改革研究与实践

生物工程作为一门实践性很强的学科,综合性、设计性及研究性实验教学在应用型创新人才培养过程中显得尤为重要,我们通过合理设置实验项目、改革实验教学方式及考核方式,对生物工艺实验进行了改革,对培养社会需要的高级应用型创新人才起到了积极的作用。     

MICROWAVE VACUUM DRYING OF POROUS MEDIA: VERIFICATION OF A SEMI-EMPIRICAL FORMULATION OF THE TOTAL ABSORBED POWER

Vacuum drying experiments were performed on a laboratory scale dryer with two porous materials: a packing of initially saturated glass beads and of unsaturated pharmaceutical granules. Several incident powers and two vacuum pressure levels were tested in order to demonstrate different drying mechanisms. The drying kinetics, temperature of the product and the absorbed power are presented and the coupling between the drying rate and the absorbed power is shown. A semi-empirical formulation of the total absorbed power is proposed taking into account the water content, the temperature and the dielectric properties of each phase. This formulation is based on a quasi-static assumption which allows the local electric field inside the material to be expressed with an analytical equation.     

Modeling deformation of a melt-infiltrated SiC/SiC composite under fatigue loading

Results from fatigue experiments done on a SiC/SiC composite are presented. A micromechanics-based model is used to study the observed behavior under cyclic loading. The model includes consideration of progressive damage, creep and oxidation of the fiber and matrix. Comparison of model predictions with test data showed that the deformation during fatigue in this material is explained primarily by damage in the form of matrix microcracking and interface debonding, in combination with creep under the cyclic load. Stiffness of the material was observed to not change significantly during fatigue indicating that the contribution of fiber fracture to deformation is limited. Fiber fracture however was found to determine final failure of the composite. Failure under cyclic fatigue loading was found to be affected by load transfer from the matrix to the fiber due to damage and creep, and by progressive degradation of the load-carrying fibers due to the combined effect of oxidation and load cycling.     

G型π桥溢流阀试验研究

以π桥液阻网络理论为指导，研制了G型π桥溢流阀，对其稳态和动态特性进行了试验研究，研究表明，改变G型π桥溢流阀先导回路的液阻参数，可使该阀的稳态调压偏差△p为正、为零，也可以为较小的负值。在△p为正和零时，该阀具有良好的动态特性。当△p从零向负的方向增加时，其动态特性逐步变差并很快趋向不稳定。