An Improved On-line Contingency Screening for Power System Transient Stability Assessment

This paper presents a contingency screening method and a framework for its on-line implementation. The proposed method carries out contingency screening and on-line stability assessment with respect to first-swing transient stability. For that purpose, it utilizes the single machine equivalent method and aims at improving the prior developed contingency screening approaches. In order to determine vulnerability of the system with respect to a particular contingency, only one time-domain simulation needs to be performed. An early stop criteria is proposed so that in a majority of the cases the simulation can be terminated after a few hundred milliseconds of simulated system response. The method’s outcome is an assessment of the system’s stability and a classification of each considered contingency. The contingencies are categorized by exploiting parameters of an equivalent one machine infinite bus system. A novel island detection approach, appropriate for an on-line application since it utilizes efficient algorithms from graph theory and enables stability assessment of individual islands, is also introduced. The New England and New York system as well as the large-scale model of the Continental-European interconnected system are used to test the proposed method with respect to assessment accuracy and computation time.     

Microstructure-Based Estimation of Strength and Ductility Distributions for $$\alpha +\beta $$ Titanium Alloys

Titanium alloys are processed to develop a wide range of microstructure configurations and therefore material properties. While these properties are typically measured experimentally, a framework for property prediction could greatly enhance alloy design and manufacturing. Here a microstructure-sensitive framework is presented for the prediction of strength and ductility as well as estimates of the bounds in variability for these properties. The framework explicitly considers distributions of microstructure via new approaches for instantiation of structure in synthetic samples. The parametric evaluation strategy, including the finite element simulation package FEpX, is used to create and test virtual polycrystalline samples to evaluate the variability bounds of mechanical properties in Ti-6Al-4V. Critical parameters for the property evaluation framework are provided by measurements of single crystal properties and advanced characterization of microstructure and slip system strengths in 2D and 3D. Property distributions for yield strength and ductility are presented, along with the validation and verification steps undertaken. Comparisons between strain localization and slip activity in virtual samples and in experimental grain-scale strain measurements are also discussed.

     

High Temperature Oxidation Behavior of Conventional and Nb-Modified MAR-M246 Ni-Based Superalloy

The present investigations focused on the thermal oxidation of two variants of MAR-M246 alloy having the same contents of Ta and Nb in at. pct, considering the effects of total replacement of Ta by Nb. The alloys were produced by investment casting using high purity elements in induction furnace under vacuum atmosphere. The alloys were oxidized pseudo-isothermally at 800 °C, 900 °C and 1000 °C up to 1000 hours under lab air. Protective oxidation products growing on the surface of the oxidized samples were mainly Al₂O₃, Cr₂O₃. Other less protective oxide such as spinels (NiCr₂O₄ and CoCr₂O₄) and TiO₂ were also detected as oxidation products. The conventional alloy exhibited slight internal oxidation at 800 °C and an enhanced resistance at 900 °C and 1000 °C. The Nb-modified alloy presented an exacerbated internal oxidation and nitridation at 900 °C and 1000 °C and an enhanced resistance at 800 °C. At 1000 °C, Nb-modified alloy was particularly affected by excessive spalling as the main damage mechanisms. From a kinetic point of view, both alloys exhibit the same behavior at 800 °C and 900 °C, with k_p values typical of alumina forming alloys (2 × 10⁻¹⁴ to 3.6 × 10⁻¹³ g² cm⁻⁴ s⁻¹). However, Ta modified alloys exhibited superior oxidation resistance at 1000 °C when compared to the Nb modified alloy due to better adherence of the protective oxide scale.

     

Effect of Thermomechanical Fatigue on Precipitation Microstructure in Two Precipitation-Hardened Cast Aluminum Alloys

Thermal loading induces modifications of the precipitation microstructure of Al–Si–Cu–Mg alloys. This study focuses on the effect of deformation on precipitation microstructure during thermomechanical loadings. Several specimens were thermomechanically cycled while others were exposed to the same thermal cycles without any mechanical loading. The nature and morphological characteristics of the precipitation microstructure of the thermomechanically cycled specimens are compared to those of the thermally aged ones, using transmission electron microscopy (TEM), in order to assess the effect of deformation on the precipitation microstructure and especially on the kinetics of precipitate growth. The absence of any significant effect of superimposed straining during thermal cycling is discussed. Implications for the prevision of yield strength degradation during service operation are briefly presented.

     

Power Supply at Metallurgical Iron-and-Steel Works: Features and Development Prospects

Metallurgist - The article provides a brief assessment of the current state of power supply units at metallurgical plants and prospects for their future development. The principal power-supply...     

Microdistortions,Hardness, and Young’s Modulus of Multicomponent Bcc Solid Solutions

Powder Metallurgy and Metal Ceramics - The phase composition, type II microstresses, and coherent scattering domains (CSDs) of multicomponent (medium- and high-entropy) bcc solid solutions with an...     

Applications of dynamic programming in survey engineering

Recent research has shown that probabilistic and non-probabilistic dynamic programming techniques can be applied beneficially in the solution of optimal design and management problems in surveying. The survey design system is presented. A non-probabilistic dynamic programming solution of a second order, one dimensional optimal survey design problem is outlined and some applications of Bayesian dynamic programming to survey logistics and management problems are demonstrated. A useful 'technology transfer' technique is included to illustrate one method of introducing systems theory and operations research to survey engineering.     

LEARNING ABOUT COMPLEX SYSTEMS

Learning about complex systems is a fundamental engineering skill; it is often the first task of an engineer when faced with a complex problem in an unfamiliar context. The nature of learning is discussed. Contributions from cognitive psychology, artificial intelligence, management and sociology are drawn together to show that fundamentally, system learning is a matter of forming well-constructed system or conceptual models. The skills needed for this are discussed.     

Understanding traditional residential architecture in Anatolia

Traditional architecture and associated environments created by residential buildings provide an important focus of interest in contemporary Turkey.1 1. The main thesis of this article is based upon my paper ‘Traditional Residential Architecture in Anatolia’, presented to a seminar on Conservation and Rehabilitation of Half-Timber Structures, Ankara: METU, 1989 and the doctoral thesis submitted to METU, Faculty of Architecture, Program of Restoration in 1994. The concepts have, however, been revised according to more recent surveys. They are generally accepted as physical witnesses of the past to be preserved and studied. Continuity in the traditional characteristics of the social group living in these environments has been observed in many of the extant settlements in Turkey. The reciprocal relationship between the dwelling and its owners, or users, has led to a dual definition of the ‘traditional dwelling unit’: the social unit being the ‘family’, the architectural unit the ‘dwelling’. The existing, modest-scaled, traditional dwellings in Turkey, which constitute the subject of this study, were mostly constructed after the seventeenth century, but more recent buildings exhibiting similar characteristics are also covered by the term ‘traditional’.2 2. The concepts of ‘tradition’, ‘culture’, ‘vernacular’, ‘historical’, ‘regional’, ‘pre-industrial’, ‘popular’ and ‘folk’ fall outside the limits of this study. The term ‘traditional’ has been used throughout the text; the term ‘Ottoman’ has not been adopted due to its attribution to the 1923 constitution of the Turkish Republic — it cannot, consequently, be used as reference to the continuation of tradition, which is one of the main ‘givens’ of this study. A term referring to a geographical distribution of archetype under investigation has been sought. There is an important building stock incorporating similar architectural characteristics within contemporary political boundaries of other countries, such as Iran, Bulgaria, Greece, etc., which had once formed part of the Ottoman Empire. ‘Turkey’ has not been preferred for its reference to the political boundaries of the Republican era for the same reason. Instead, another geographical term ‘Anatolia’ is considered in a widened context throughout the text to refer to a more generic concept than it implies geographically. Anatolia is considered to be the land of origin on which many cultures have emerged, generated and spread to the affected lands throughout history. Furthermore, the concentration of this study focuses specifically on extant dwellings in Anatolia. Within the confines of the term ‘traditional residential architecture in Anatolia’, there are further limitations. The origin of traditional residential architecture in Anatolia, its typological evolution, its social, cultural and/or historical aspects are not the major concerns of this study, which focuses on existing examples. A limitation of the period covered by this study accords with the construction dates of extant buildings from the seventeenth century onwards. This is an open-ended period because of the continuity in ‘traditional’ aspects in many of the settlements. The concept of ‘privacy’ serves as the basis of evaluation in analysing the interrelation of any two units. The interface of two units can be defined as an hierarchy of privacy represented sociologically by the interrelations of person/family/neighbourhood relationships and architecturally through the interrelations of room/dwelling unit/street/neighbourhood.3 3. This dwelling unit was the subject of the studio course ARCH 405 in 1989—1990, Autumn semester. The project was supervised by the author and Res.Asst. Ertu?rul Morçöl; the students were Önder Kaya, Ufuk Serin, Murat Aya?, Deniz Kutay and Gül Vanl?. This approach will include a brief summary of some previous studies of traditional residential architecture (Fig. 1).     

Lead and cadmium in teeth,bone and kidneys of rats with a standard Pb‐Cd supply

Male Wistar rats received a combination of 25 ppm PbCl₂ and 5 ppm CdCl₂ in drinking water at different developmental stages. Pb and Cd levels of incisors, molars, epiphyses, diaphyses and kidney cortex were recorded by atomic absorption spectrophotometry. The results confirmed that Pb has an affinity for hard tissue and especially to teeth, but it also accumulated in soft tissues under the above conditions. In addition, the results indicated none or only a moderate placental or mammary barrier for Pb, and suggested a high absorption of lead from the intestine of sucklings. The results also confirmed that kidney cortex is a primary target for Cd, and indicated that Cd has crossed the placental and mammary barriers to some degree. The positive significant correlation between Cd levels in molars and kidney cortex suggested that rodent molars indicate a degree of Cd absorption, whereas incisors do not. It is supposed that rodent molars are comparable to human deciduous teeth. It is thus confirmed that human deciduous teeth indicate previous lead exposure. It is further inferred that they also can be used as indicators of previous Cd‐exposures.