PARTIAL COVERING OF A CIRCLE BY EQUAL CIRCLES. PART I: THE MECHANICAL MODELS

How must n equal circles of given radius be placed so that they cover as great a part of the area of the unit circle as possible? To analyse this mathematical problem, mechanical models are introduced. A generalized tensegrity structure is associated with a maximum area configuration of the n circles, whose equilibrium configuration is determined numerically with the method of dynamic relaxation, and the stability of equilibrium is investigated by means of the stiffness matrix of the tensegrity structure. In this Part I, the principles of the models are presented, while an application will be shown in the forthcoming Part II

Statistical analysis of data describing the relationship between driver, truck and characteristics of the road

Road vehicles equipped with appropriate measurement equipment, computing facilities, data storage and data communication capabilities can be considered valuable data sources for the description and quantitative characterisation of road traffic. The data obtained from these vehicles provide valuable direct and indirect information pertaining to traffic states and various aspects of traffic safety in respect of the analysed road network. In this study, trucks’ abrupt braking events, detected by the trucks’ on-board safety protection units, were analysed. The road locations of the detected abrupt braking events can be characterised by a number of features ranging from the specific traffic regulations (e.g., speed limits) in force to the socio-cultural environment of the location. The abrupt braking data evidence was used for identification and description of non-trivial interactions of drivers, trucks and roads. Some of the more interesting results and conclusions of the experiments are reported herein

Időkésést tartalmazó dinamikai rendszerek stabilitása és nemlineáris rezgései = Stability and non-linear vibrations of dynamical systems containing time delay

A kutatási projekt célja késleltetett dinamikai rendszerek vizsgálata volt. A kutatást három fő részre bonthatjuk. Az első az a periodikus és késleltetett dinamikai rendszerek stabilitásvizsgálatára kidolgozott numerikus módszer, az ún. szemi-diszkretizáció hatékonyságának növelése magasabb rendű közelítések bevezetésével. Ezeket az eredményeket a másik két, alkalmazás orientált kutatásnál fel is használtuk. A második terület a szerszámgéprezgések vizsgálata, mely során a fő cél olyan paramétertartományok meghatározása volt, amelyeknél a megmunkálás hatékonysága jelentősen növelhető instabil rezgések megjelenése nélkül. Itt az időkésés az úgynevezett regeneratív hatás miatt jelenik meg a forgácsoló szerszám és a munkadarab rezgéseit leíró egyenletekben. A harmadik terület a dinamikai rendszerek szabályozása, ahol az időkésés a szabályozott jel visszacsatolása miatt illetve digitális szabályozás esetén a mintavételezés miatt is keletkezik. Kidolgoztunk egy új szabályozási technikát, az ún. beavatkozom-és-várok szabályozási elvet. A szerszámgéprezgéssel és a szabályozással kapcsolatos elméleti eredményeket kísérletekkel is alátámasztottuk. A jelentősebb eredmények publikálása során 22 folyóiratcikk (Szum IF = 17.58), 12 konferencia cikk, 3 könyvfejezet, és egy sikeresen megvédett PhD értekezés született. Az OTKA támogatás a 38 publikációból 32-ször fel volt tüntetve. | The goal of the research project was the analysis of delayed dynamical systems. The project can be divided into three parts. First, the efficiency of the so-called semi-discretization method for parametrically excited delayed systems was increased by applying higher order approximations for the delayed term. These results were then used in the other two application oriented topics. The second topic was the investigation of machine tool chatter. The main goal was to determine the regions of the technological parameters where high material removal rate can be achieved without unstable vibrations of the tool and the workpiece. Here, the time delay arises in the governing equations due to the surface regeneration of the workpiece. The third topic was the analysis of the performance of control processes, where time delay occurs in the feedback loop and due to the digital effects, as well. A new control technique was developed, the so-called act-and-wait control concept. The theoretical results of the machine tool chatter and control problems were verified by experiments. The main results were published in the form of 22 journal articles (Sum IF = 17.58), 12 conference paper, 3 book chapters and one PhD dissertation. The support of OTKA was indicated in 32 publications of the 38

Különböző rendű mechanikai elméletekről

The static analysis of elastic structures uses a mechanical model of the real structure. The mathematical model describes this mechanical model, and provides the first-, second- and third-order theories, depending on the order of simplification. The goal of analysis is the equilibrium path that is derived from the geometrical, physical, and equilibrium relationships between the internal and external state variables. There is a standard method to represent these relationships in a fundamental diagram, in which the relationships are displayed with partially common axes in four quarters of a graph. The paper answers the following questions:  What is the exact meaning of the four quarters of this graph?  Does the fundamental diagram give information on the stability of the structure?  What is the reliability of the results obtained from the second-order theories?  How can we generalise our statements to models with more than one degrees of freedom

Increasing life expectancy of road pavements

Cilj je ovog rada predstaviti najvažnije faktore koji pridonose povećanju kvalitete i produljenju uporabljivosti kolnika. U radu je dan pregled američkih i europskih istraživanja koja se bave problemima kolnika iz aspekta održavanja, a vezano uz projektiranje, tehnologiju građenja, odabira građevnih materijala te poboljšanje svojstava kolnika. Predstavljeni su i neki budući trendovi vezani za tematiku produljenja uporabljivosti kolnika.The objective of this paper is to present the most important factors that contribute to the quality and good life expectancy of road pavements. An overview of American and European research dealing with pavement maintenance issues, as related to the design, construction technology, material selection, and improvement of pavement properties, is provided in the paper. Some future trends relating to the extension of life-expectancy of pavements are also presented

Egy egyszerű viszkoelasztikus modell elemzése

Ha egy viszkoelasztikus szerkezetet állandó teherrel megterhelünk, akkor általá- ban a terhelés pillanatában létrejön egy rugalmas alakváltozás, majd változatlan te- her esetén is további deformáció alakul ki. Itt, és a továbbiakban, feltételezzük, hogy a terhelés kvázistatikus, vagyis olyan lassan jut a teher a szerkezetre, hogy a létrejövő elmozdulások sebessége, gyorsulása figyelmen kívül hagyható. Ugyan- akkor azt is feltételezzük, hogy a terhelés folyamata elég gyors ahhoz (vagy a visz- kozitási anyagjellemzők olyanok), hogy az azalatt létrejövő viszkózus alakváltozások elhanyagolhatók a létrejövő rugalmas alakváltozások mellett

Theory and practice of cement concrete pavements in Hungary

U Mađarskoj kasnih 90-ih godina prošlog stoljeća različite varijante asfaltnih kolničkih konstrukcija nisu imale dovoljnu otpornost na deformacije koja bi spriječila ranu pojavu kolotraga na iznimno prometnim autocestama. To je uzrokovalo ponovno vraćanje betonskih kolnika kao tehnološkog izbora. U ovom radu prikazana je povijest mađarskih betonskih kolnika, postupci u njihovu "oživljavanju", tehnološki izazovi kod izrade pokusnih dionica te tijek istraživanja betonskih kolnika s ciljem dugoročnog zadržavanja povoljnih površinskih svojstava.In the late 1990’s, various asphalt pavement alternatives did not present the level of deformation resistance that would be sufficient to prevent early rutting on the extremely heavily trafficked motorways in Hungary. This resulted in the reinstatement of concrete pavements, which became once again a technological choice in motorway construction. This paper presents the history of Hungarian concrete pavements, steps for their "revival", technological challenges in the preparation of test sections, and an ongoing research aimed at ensuring long-term preservation of favourable surface properties