运用现代CFD方法设计高效率的汽轮机(续前期)

论述了运用现代计算流体动力学(ComputationalFluidDynamics,CFD)技术设计高效率汽轮机的方法,典型应用的实例有全三维叶片级流场、叶片汽封和排汽蜗壳计算。计算结果和实际是相符的。进一步对结构性单元和非结构单元程序的计算结果进行了比较,已证明,非结构单元CFD程序用于复杂形状的流场计算时,结果与实际相当一致,并具有独特的功能。     

Solution of the general moment problem via a one-parameter imbedding

This paper presents a computational theory for the general scalar moment problem. The formalism is sufficiently general to encompass problems in sensor arrays with arbitrary geometry and dynamics, and in nonuniform multidimensional sampling. Given a finite set of moments, the theory provides a test for the existence of a positive measure which is consistent with such data. At the same time, the theory also provides a characterization of all such consistent positive measures. It should be noted that classical results (e.g., in the theory of the trigonometric moment problem, Hamburger, Stieljes, Nevanlinna-Pick interpolation, etc.) are not applicable to the general setting sought herein where there is no natural shift operator in the space spanned by the integration kernels. The centerpiece of the theory is a differential equation which depends on the given finite set of moments and on an arbitrary positive function /spl Psi/-which plays the role of a "free parameter." The differential equation has an exponentially attractive point of equilibrium if and only if there exists a consistent positive measure. For each /spl Psi/, the fixed point determines a corresponding measure. Suitable choice of /spl Psi/ allows recovering any measure which is consistent with the data. The fixed point of the differential equation corresponds to an extremum of an entropy-like functional, and the differential equation is constructed via an appropriate homotopy that follows changes in the Lagrange multipliers from a convenient starting value to a value for the multipliers that corresponds to the given moments.     

Influence of halide ions and alloy microstructure on the passive and localized corrosion behavior of alloy 22

Alloy 22 (N06022) is the current candidate alloy used to fabricate the external wall of the high-level nuclear waste containers for the Yucca Mountain repository. It was of interest to study and compare the general and localized corrosion susceptibility of Alloy 22 in fluoride and chloride solutions at 90 °C. Standard electrochemical tests such as cyclic potentiodynamic polarization, amperometry, and electrochemical impedance spectroscopy were used. Studied variables included the solution pH and the alloy microstructure (thermal aging). Results show that Alloy 22 is highly resistant to general corrosion in all the solutions tested. Thermal aging is not detrimental and even seems to be slightly beneficial for general corrosion at the higher solution pHs. Pitting corrosion was never observed. Crevice corrosion was found only for high chloride-containing solutions after anodic polarization. The presence of fluoride ions together with chloride ions seems to increase the susceptibility of Alloy 22 to crevice corrosion compared to pure chloride solutions. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Modelling the FEBEX THM experiment using a state surface approach

Buffer materials being considered as engineered barriers in nuclear fuel waste (NFW) disposal systems possess a pronounced nonlinear behaviour in the unsaturated state. In order to simulate such non-linear responses,the authors adopted an incrementally nonlinear poro-elastic approach where the coefficients of the governing equations are assumed to be functions of suction and the void ratio. These functions are in turn developed from a state-surface equation obtained from suction-controlled oedometric tests. In this paper we show the derivation of the governing equations of the poro-elastic model. A finite element computer code, FRACON, was developed by the authors to numerically solve the above equations. We first use the code to simulate laboratory tests to characterize the swelling properties of a typical bentonite. That same bentonite was used in the FEBEX in-situ heater experiment, conducted at the Grimsel site, Switzerland. The FRACON code was also used to perform blind predictions of the FEBEX heater experiment. It is shown that the model correctly predicts drying of the bentonite near the heaters and re-saturation near the rock interface. The evolution of temperature and the heater thermal output were also reasonably well predicted by the model. The trends in the total stresses developed in the bentonite were correctly predicted; the absolute values however were underestimated probably due to the omission of pore pressure build-up in the rock mass.     

Synthesis, characterization and devitrification behaviour of an yttrium containing boroaluminate glass

The glass forming region in the B₂O₃-Al₂O₃-Y₂O₃ composition diagram has been determined by a melting and quenching procedure at temperatures up to 1800°C. Different physical characteristics (density, coefficient of thermal expansion, glass transition and crystallization peak temperatures) have been determined for a 35B₂O₃-40Al₂O₃-25Y₂O₃ glass composition (in mol.%). By using a predictive model and some NMR structural data, different elastic moduli (Young's modulus, bulk modulus, shear modulus and Poisson's ratio) have been calculated. The devitrification behaviour has also been studied. Internal crystallization is the dominant mechanism and a new (Y, Al)BO₃ ternary phase has been characterized by X-ray powder diffraction. The temperature and time nucleation dependence have been determined from DTA experiments as well as the crystallization kinetics (i.e. the Avrami exponent and the activation energy for crystal growth).     

An Experimental Investigation into the Feed Rate Capacity of Rotary Valve and Blow Tank Feeders

Industry widely uses rotary valves and blow tanks for the pneumatic conveying of products, each having their pros and cons depending on the specific application. This article shows the differing results obtained when low-velocity conveying a product through a common pipeline using both a drop-through rotary valve and a bottom-discharge blow tank feeder. A number of issues arise in the rotary valve system, the main one being rotary valve air leakage. A blow tank system, on the other hand, does not leak, as it is an enclosed system. The experimental results show dramatic differences in product throughput. Further exploration leads to a novel modification being made to the rotary valve system in an attempt to increase its capacity. The result of this modification shows a slight increase in output tonnage, but still significantly less than that obtained from the blow tank.     

Effect of sampling density on the measurement of stream condition indicators in two lowland Australian streams

There is widespread application of indicators to the assessment of environmental condition of streams. These indicators are intended for use by managers in making various comparative and absolute assessments and often have a role in resource allocation and performance assessment. Therefore, the problem of formally defining confidence in the results is important but difficult because the sampling strategies used are commonly based on a compromise between the requirements of statistical rigour and the pragmatic issues of access and resources. It is rare to see this compromise explicitly considered and consequently there is seldom quantification of the uncertainty that could affect the confidence a manager has in an indicator. In this paper, we present a method for quantitatively assessing the tradeoffs between sampling density and uncertainty in meeting various monitoring objectives. Assessments using judgement‐based representative reaches are shown to be unreliable; instead a sampling approach is recommended based on the random selection of measuring sites. A detailed dataset was collected along two streams in Victoria, Australia, and the effect of sampling density was assessed by subsampling from this dataset with precision related to the number of sites assessed per reach length and the intensity of the sampling at each site. The sampling scheme to achieve a given precision is shown to depend on the monitoring objective. In particular, three objectives were considered: (1) making a baseline assessment of current condition; (2) change detection; and (3) detection of a critical threshold in condition. Change detection is shown to be more demanding than assessing baseline condition with additional sampling effort required to achieve the same precision. Sampling to detect a critical threshold depends on nominating acceptable values of Type I and II error and the size of the effect to be detected. Copyright © 2006 John Wiley & Sons, Ltd.     

Sampling and the discretization theorem

An algorithm was obtained for restoration of a continuous process from a finite number of its equispaced discrete samples. The necessary and sufficient sampling conditions were formulated.     

Learning with belief levels

We study learning of predicate logics formulas from “elementary facts,” i.e. from the values of the predicates in the given model. Several models of learning are considered, but most of our attention is paid to learning with belief levels. We propose an axiom system which describes what we consider to be a human scientist's natural behavior when trying to explore these elementary facts. It is proved that no such system can be complete. However we believe that our axiom system is “practically” complete. Theorems presented in the paper in some sense confirm our hypothesis.