Linear Time Algorithm for Optimal Feed-link Placement

Given a polygon representing a transportation network together with a point p in its interior, we aim to extend the network by inserting a line segment, called a feed-link, which connects p to the boundary of the polygon. Once a feed link is fixed, the geometric dilation of some point q on the boundary is the ratio between the length of the shortest path from p to q through the extended network, and their Euclidean distance. The utility of a feed-link is inversely proportional to the maximal dilation over all boundary points. We give a linear time algorithm for computing the feed-link with the minimum overall dilation, thus improving upon the previously known algorithm of complexity that is roughly O(n log n)

Outline design of compact GNC module for missile flight control purposes

Da bi se obezbedilo da vođeni projektil bide u mogućnosti da prati unapred zadatu putanju leta velika količina sofisticirane opreme mora da bude uključena u to. Sa praktične tačke gledišta i ako to konstrukcija projektila dozvoljava, neophodni podsistemi koji moraju da budu korišćeni za upravljanje letom projektila trebalo bi da budu zasebna celina (jedan segment / modul projektila). Ukoliko je to prihvatljiv koncept, dva problema treba da budu rešena tokom projektovanja: postizanje zadovoljavajućeg odnosa između korisnog tereta (bojeva glava) i ukupne težine projektila (uključujući odgovarajuće podsisteme za vođenje, navigaciju i upravljanje) i minimizacija / optimizacija iskorišćenog prostora. Koncepcija kompaktnog modula za vođenje /engl.: Guidance/, navigaciju /engl.: Navigation/ i upravljanje /engl. Control/ (skraćeno: GNC modul) koji se sastoji od pomenutih podsistema je prezentovana u ovom radu.To ensure that the guided rocket missile could be in position to follow predefined flight trajectory, a lot of very sophisticated equipment has to be involved in. From a practical point of view and if the general design of the missile allows that, the necessary subsystems to be used in missile flight control purposes have to be assembled as a separate whole (one segment /module of the missile). If this concept is acceptable, two problems have to be solved during the designing: achieving of the satisfactory ratio between load capacity (warhead) and total weight of the missile (that includes the appropriate subsystems for guidance, navigation and control of the missile too) and minimization /optimization of the used space. The outline design of compact Guidance, Navigation and Control Module (short: GNC Module) which consists of the subsystems mentioned before is presented in this paper

Outline design of compact GNC module for missile flight control purposes

Da bi se obezbedilo da vođeni projektil bide u mogućnosti da prati unapred zadatu putanju leta velika količina sofisticirane opreme mora da bude uključena u to. Sa praktične tačke gledišta i ako to konstrukcija projektila dozvoljava, neophodni podsistemi koji moraju da budu korišćeni za upravljanje letom projektila trebalo bi da budu zasebna celina (jedan segment / modul projektila). Ukoliko je to prihvatljiv koncept, dva problema treba da budu rešena tokom projektovanja: postizanje zadovoljavajućeg odnosa između korisnog tereta (bojeva glava) i ukupne težine projektila (uključujući odgovarajuće podsisteme za vođenje, navigaciju i upravljanje) i minimizacija / optimizacija iskorišćenog prostora. Koncepcija kompaktnog modula za vođenje /engl.: Guidance/, navigaciju /engl.: Navigation/ i upravljanje /engl. Control/ (skraćeno: GNC modul) koji se sastoji od pomenutih podsistema je prezentovana u ovom radu.To ensure that the guided rocket missile could be in position to follow predefined flight trajectory, a lot of very sophisticated equipment has to be involved in. From a practical point of view and if the general design of the missile allows that, the necessary subsystems to be used in missile flight control purposes have to be assembled as a separate whole (one segment /module of the missile). If this concept is acceptable, two problems have to be solved during the designing: achieving of the satisfactory ratio between load capacity (warhead) and total weight of the missile (that includes the appropriate subsystems for guidance, navigation and control of the missile too) and minimization /optimization of the used space. The outline design of compact Guidance, Navigation and Control Module (short: GNC Module) which consists of the subsystems mentioned before is presented in this paper

Analysis and design of the gas generator multifunctional bulkhead considering the thermal and structural loads

The operation of gas generators brings relatively high thermo-mechanical loads on the gas generator structure. The objective of this article is to determine the operating conditions, in terms of mechanical loads at extremely high temperatures in very limited and narrow space, of a multifunctional bulkhead for application on specific kinds of gas generators with back-to-back rotor concept. The paper contains numerical analysis and experimental investigation for determining the loads and behavior of the structure. Numerical analysis indicates that there is significant influence of the Tesla turbine effect on flow parameters. Also, uneven pressure distribution and significant thermal loads are identified. With experimental investigation and subsequent exploitation tests, it was concluded that the presented methodology identifies the operating conditions, truthfully simulates the bulkhead stress state and deformations and that the presented design solution satisfied all demands. Regarding results obtained by these numerical simulations, the innovative design solution for the multifunctional bulkhead was proposed

Research of expendable turbojet tubular combustion chamber

This paper presents research related to the tubular combustion chamber of an expendable turbojet. Although annular combustors are dominant at present, tubular combustors are still attractive because they are simpler to produce and require lower amounts of air flow for testing. The objective of this research was to assess the combustor's primary zone configuration, and four configurations were tested to obtain experimental answers for use in future work. The configuration of the combustion chamber is a simple and classic design in line with its expendable purpose. The test methodology was to perform initial testing of the primary and secondary zones under atmospheric conditions using the four configurations, and then to subsequently complete the combustor using the best configuration. The complete combustor was then tested under both atmospheric conditions and working conditions. The results showed that the stability margin was wide enough to cover the combustor's entire working area. The measured efficiency and pressure drop were in very good agreement with the corresponding designed values. The design and testing methodology proposed here could be used for similar scientific and engineering research applications

EPR study of the production of OH radicals in aqueous solutions of uranium irradiated by ultraviolet light

The aim of the study was to establish whether hydroxyl radicals (•OH) were produced in UV-irradiated aqueous solutions of uranyl salts. The production of •OH was studied in uranyl acetate and nitrate solutions by an EPR spin trap method over a wide pH range, with variation of the uranium concentrations. The production of •OH in uranyl solutions irradiated with UV was unequivocally demonstrated for the first time using the EPR spin-trapping method. The production of •OH can be connected to speciation of uranium species in aqueous solutions, showing a complex dependence on the solution pH. When compared with the results of radiative de-excitation of excited uranyl (*UO22+) by the quenching of its fluorescence, the present results indicate that the generation of hydroxyl radicals plays a major role in the fluorescence decay of *UO22+. The role of the presence of carbonates and counter ions pertinent to environmental conditions in biological systems on the production of hydroxyl radicals was also assessed in an attempt to reveal the mechanism of *UO22+ de-excitation. Various mechanisms, including •OH production, are inferred but the main point is that the generation of •OH in uranium containing solutions must be considered when assessing uranium toxicity

Booking limits and bid price based revenue management policies in rail freight transportation

In this paper, the possibility and potential benefits of implementing discriminatory policies in rail freight transportation are analyzed, with the aim of revenue maximization. A regular, cyclic, single train service with fixed composition and capacity is studied. The problem is decomposed into discrete time periods. Transportation requests arise randomly over time, and the decision of either accept or reject a certain request has to be made. The problem is formulated via dynamic programming, and the deterministic approximations of the problem are used in order to formulate booking limits and bid price policies. Results obtained are compared with those of standard first come – first served policy, which is implemented by the Serbian railways. Although not acceptable in all contexts, the proposed aggressive policies demonstrated promising benefits

Dynamic stability of high speed turboshaft engine with reducer

The dynamic behavior of machines which rotate at extreme high speeds is crucial for stable and long operation. In design process some dynamics calculation must be taken into account to avoid potential operation near resonance areas. This paper considers dynamic analysis of the high speed reducer, designed together with the turbo-shaft engine. Resonances can occur when frequency of rotation and teeth mesh frequency are close to gear pair in mesh natural frequency, to the shafts natural frequencies and to the other parts natural frequencies. Problems can be avoided by translating resonant areas to higher or lower level of frequency by changing some design parameters, mass, stiffness and by variation of the stiffness of bearing supports. The paper presents the approaches to natural frequencies identification for the example of high speed reducer design. Some examples of design solutions, especially for elastic bearing supports and their experimental testing are also presented