Inteligentni multiagentski sistemi zasnovani na distribuiranom ne-aksiomatskom rezonovanju

The agent technology represents one of the most consistent approaches to distributed artificial intelligence. Agents are characterized by autonomous, reactive, proactive, and social behavior. In addition, more complex, intelligent agents are often defined in terms of human-like mental attitudes, such as beliefs, desires, and intentions. This thesis deals with software agents and multiagent systems in several ways. First, it defines a new reasoning architecture for intelligent agents called Distributed Non-Axiomatic Reasoning System (DNARS). Instead of the popular Belief-Intention-Desire model, it uses Non-Axiomatic Logic, a formalism developed for the domain of articial general intelligence. DNARS is highly-scalable, capable of answering questions and deriving new knowledge over large knowledge bases, while, at the same time, concurrently serving large numbers of external clients.  Secondly, the thesis proposes a novel agent runtime environment named Siebog. Based on the modern web and enterprise stan-dards, Siebog tries to reduce the gap between the agent technology and industrial applications. Like DNARS, Siebog is a distributed system. Its server side runs on computer clusters and provides advanced functionalities, such as automatic agent load-balancing and fault-tolerance. The client side, on the other hand, runs inside web browsers, and supports a wide variety of hardware and software platforms. Finally, Siebog depends on DNARS for deploying agents with unique reasoning capabilities.Agentska tehnologija predstavlja dosledan pristup razvoju distribuirane veštačke  inteligencije. Ono što agente izdvaja od ostalih pristupa su autonomno, reaktivino,  pro-aktivno, i socijalno ponašanje. Pored toga, kompleksniji, inteligentni agenti se često definišu koristeći ljudske mentalne konstrukcije, kao sto su verovanja, želje i namere. Disertacija se bavi softverskim agentima i multiagentskim sistemima sa nekoliko aspekata. Prvo, definisana je nova  arhitektura za rasuđivanje sa primenom u razvoju  inteligentnih agenata, nazvana Distribuirani sistem za ne-aksiomatsko rasuđivanje  (eng. Distributed Non-Axiomatic Reasoning System) (DNARS). Umesto popularnog   BDI modela za razvoj inteligentnih agenata (eng. Belief-Desire-Intention),  arhitektura  se zasniva na tzv. ne-aksiomatskoj logici, formalizmu razvijenom u domenu veštačke  opšte inteligencije. DNARS je skalabilan softverski sistem, sposoban da odgovara na   pitanja i da izvodi nove zaključke na osnovu veoma velikih  baza znanja, služeći pri   tome veliki broj klijenata. Zatim, u disertaciji je predložena nova multiagentska platforma nazvana Siebog. Siebog je zasnovan na modernim standardima za razvoj veb aplikacija, čime pokušava da smanji razliku izmedu multiagentskih sistema i sistema koji se koriste u industriji. Kao DNARS, i Siebog je distribuiran sistem. Na serverskoj strani, Siebog se izvršava na računarskim klasterima, pružajući napredne funkcionalnosti, poput automatske distribucije agenata i otpornosti na greške. Sa klijentske strane, Siebog se izvršava u veb pretrazivačima i podržava široku lepezu hardverskih i softverskih platformi. Konačno, Siebog se oslanja na DNARS za ravoj agenata sa jedinstvenim sposobnostima za rasuđivanje

A new methodology for prediction of high-cycle contact fatigue for spur gears

High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

Determination of critical size of corrosion pit on mechanical elements in hydro power plants

Researchers in the field of fracture mechanics, predominantly developing appropriate solution algorithms for problems of solid bodies with cracks. Problems in mechanics generally, related with fracture and fatigue for solid bodies with various geometries of sharp notches, are studied to a much lesser extent. This situation can be explained by analytical difficulties arising in solving problems of elasticity theory for bodies with rounded notches. To solve problems of such class, starting from data on stress concentration in the rounded notch tip with a significant radius of curvature, simplified solutions with are therefore of great importance. Recent years, due to constant rise of computing power and development of numerical methods, re-evaluation of stress concentration factors from a viewpoint of theory of elasticity is present. This is mainly as a feedback from industry, which have requirements toward mega and nanostructures. Corrosion represents an important limitation to the safe and reliable use of many alloys in various industries. Pitting corrosion is a form of serious damage on metals surface such as high-strength aluminum alloys and stainless steel, which are susceptible to pitting when exposed to a corrosive attack in aggressive environments. This is particularly valid for dynamic loaded structures. The basic idea behind this paper is finding links between different scientific and engineering disciplines, which will enable useful level of applicability of existing knowledge. The subject of this paper is application of new method of determine length scale parameter for estimating the mechanistic aspect of corrosion pit under uniaxial/multiaxial high-cycle fatigue loading…

A new methodology for prediction of high-cycle contact fatigue for spur gears

High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

A new methodology for prediction of high-cycle contact fatigue for spur gears

High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

Service life prediction of running steel wire ropes

Vrlo visoka čvrstoća omogućava žičanom užetu da prenese velike zatezne sile i da se kreće po koturima relativno malog prečnika. Žice od čelika vrlo visoke čvrstoće su postojale više od sto godina pre nego što su patentirane, kada je uveden specijalni postupak zagrevanja i usavršen postupak izvlačenja. Dalja poboljšanja posle toga su uvedena u relativno malim koracima. Žičana užad uvek imaju ograničen radni vek. Zbog toga ona moraju da se podvrgnu inspekciji i ispitaju u pravilnim intervalima da bi se zamenila znatno pre otkaza. Krajnji korisnik mašine sa čeličnim žičanim užetom u svakom slučaju želi da ima grubu ocenu radnog veka užeta već u ranoj fazi razvoja mašine. tako da bude u mogućnosti, ako zatreba, da poboljša sistem mašine. To je jedan od razloga zbog kojih su tokom niza godina izvedena obimna istraživanja kako bi se poboljšali postupci proračuna za predviđanje radnog veka žičanih užadi. Namena ovog rada je da ponudi pregled informacija o postupcima proračuna i da prikaže mogućnosti i ograničenja postupaka prognoziranja za predviđanja radnog veka čeličnih žičanih užadi u eksploataciji.Very high strength enables wire ropes to support large tensile forces and to run over sheaves with relative small diameters. Very high strength steel wires had already been in existence for more than a hundred years when patenting, a special heating process was introduced and the drawing process improved. Since then, further improvements have only occurred in relatively small steps. Wire ropes always have a limited service life. Therefore they must be inspected and examined at regular intervals so that they are replaced well before failure. End-users of machinery with steel wire ropes, however, would like to have a rough estimation of the service life of the ropes already in the early stages of conceiving their machines, so that they can, if necessary, improve the revving system. This is one of the reasons why for many years extensive research is carried out in order to improve calculations for predicting the service life of wire ropes. This paper is meant to offer an overview information on the method of calculation and to demonstrate the potential and limitations of the forecasting procedure for service-life prediction of running steel wire ropes

Combined load simulation vs component loads simulation in machine design: A case study

Na sadašnjem nivou razvoja tehnologije, u stvarnim radnim uslovima, gotovo svi mašinski elementi su opterećeni kombinovanim opterećenjima. Cilj istraživanja prikazanog u ovom radu je ukazivanje na značaj proračuna nosivosti mašinskih elemenata simuliranjem kombinovanog opterećenja. Istraživanje prikazano u radu inspirisano je jednim stvarnim otkazom turbinskog vratila hidroturbine. Vratilo sa prirubnicom i visokim odnosom prečnika vratila i prirubnice bilo je predmet obimnih proračuna u cilju pronalaženja uzroka otkaza. Klasični analitički proračun ovog vratila koristi Peterson-ov faktor koncentracije napona i proračun maksimalnih napona za pojedine naponske komponente kombinovanog opterećenja, a onda analitičku vrednost ukupnog napona proračunava na osnovu hipoteze o maksimalnom normalnom naponu. Sa druge strane, prikazani proračun naponskog stanja vratila metodom konačnih elemenata bazira se na simuliranju realnih radnih opterećenja u uslovima kombinovanog opterećenja istovremenim definisanjem svih komponenti (savijanja, uvijanja i zatezanja). Oba proračuna urađena su za nekoliko različitih radijusa na prelazu vratila ka prirubnici. Dobijeni rezultati prikazani su uporednim dijagramima dobijenih vrednosti ukupnih napona i odgovarajućih faktora koncentracije napona. Analiza ovih dijagrama vodi do zaključka da proračun ukupnog napona u slučaju kombinovanog i složenog opterećenja na bazi Peterson-ovih faktora koncentracije napona i standardnog analitičkog postupka treba da bude zamenjen naprednim tehnikama proračuna koji obezbeđuju tačnija rešenja koja se istovremeno i jednostavnije analiziraju i koriste.At a present level of technology, almost all machine parts are subjected to combined loads in real working condition. The aim of research described in this paper is to highlight the importance of combined load simulation for the calculation of machine parts load capacity. This research is inspired by one failure case study of hydro turbine shaft. The shaft with flange and high ratio of shaft/flange diameter is the subject of excessive calculation in order to find the cause of failure. The classic analytical calculation of this shaft uses the Peterson's elastic stress concentration factor and calculates stress concentration factors and maximum stresses for different stress components of combined load and then calculate analytical values of total stress by the hypothesis of maximum normal stress. On the other hand, presented Finite Element Analysis simulates shaft stress state under real conditions of complex load by simultaneously applying all load components (bending, torsion and tension). Both of the calculations are performed for few different radii in shaft-flange sections. The results are presented by comparative diagrams for obtained values of total stresses and stress concentration factors. The analysis of these diagrams leads to conclusion that the use of Peterson's stress concentration factors and standard analytical techniques for total stress calculation has to be replaced with modern calculation techniques that provide a more accurate, easier-to-handle solution

Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

Primary energy savings using heat storage for biomass heating systems

District heating is an efficient way to provide heat to residential, tertiary and industrial users. The heat storage unit is an insulated water tank that absorbs surplus heat from the boiler. The stored heat in the heat storage unit makes it possible to heat even when the boiler is not working, thus increasing the heating efficiency. In order to save primary energy (fuel), the boiler operates on nominal load every time it is in operation (for the purpose of this research). The aim of this paper is to analyze the water temperature variation in the heat storage, depending on the heat load and the heat storage volume. Heat load is calculated for three reference days, with average daily temperatures from -5 to 5°C. The primary energy savings are also calculated for those days in the case of using heat storage in district heating.[Projekat Ministarstva nauke Republike Srbije, br. TR 33051: The concept of sustainable energy supply of settlements with energy efficient buildings