State and Perspectives of Underwater Robotics - Role of Laboratory for Underwater Systems and Technologies

The state and perspectives of underwater robotics is presented. The role and achievements of Laboratory for underwater systems and technologies (LABUST) in this domain is described. Two LABUST projects are shortly described

Testing the Accuracy of Large-Scale GNSS-R Applications

Global Navigation Satellite System Reflectometry (GNSS-R) is a promising technology with a huge potential. Naming just few most interesting applications, remote sensing of the sea surface roughness and salinity, snow structures, and sea-ice characterization, we can realize the importance of GNSS-R. Due to a variety of possible platforms (satellites, aircrafts, helicopters, etc.) different resolutions are available for the final users, which imply, also, different scopes of the accuracy. In this paper we are testing the resolution and accuracy of a water surface level obtained by GNSS-R. We utilizied a platform set to a pedestrian bridge, with two GNSS receivers. One of them is attached to the upper side of the platform, while the other is placed upside-down, directing to the water mirror. The upper GNSS will receive only the direct signals from the satellites, while the latter one will create its position only according to the „false“ measurements, meaning the signals reflected from the water. Knowing the mutual positional relation between the two receivers, we can calculate the height of the water mirror and, after longer measuring sessions, monitor the change of the river level

Interactions of charged particles with double-layer graphene

Nowadays we are witnesses of a development of one promising branch of applied physics, called plasmonics. Especially interesting issue is plasmonics in quasi-two-dimensional (q2D) crystals deposited on various dielectric substrates. Here arise the main questions: how to increase the 2D plasmon propagation length and how to excite 2D plasmon most efficiently. We will focus on describing the interaction between electronic excitations in two graphene layers with phonons in aluminium oxide (Al2O3) slab on which the graphene layers are deposited. Special attention will be paid to explain the hybridization between 2D plasmons and surface (TO) phonons. Because of multiple intersections of 2D plasmons and TO phonons the 2D plasmon moves to lower energies which allows it to be excited by charged particles moving at subthreshold speeds, [1]. We will present the results for wake potential induced by a charged particle which moves parallel to the graphene/dielectric interface. It will be shown how various substrates modify the efficiency of particle/plasmon coupling. The electronic excitations in graphene are obtained by using plane waveab initio approach where we have addressed the problem of calculation of EELS spectra in the optical limit ( → 0) and how to avoid intersupercell Coulomb interaction [2].28th Summer School and International Symposium on the Physics of Ionized Gases - SPIG 2016, August 29 - September 2, 2016, Belgrad

3D Line Following for Unmanned Underwater Vehicles

When designing guidance controllers for unmanned underwater vehicles, an assumption is often made that the vessel operates at a constant depth. However, in many applications the desired depth often changes with the position of the vessel in the horizontal plane. This paper addresses the problem of three dimensional line following with the application to underactuated underwater vehicles. The problem is resolved by separating the desired line into two components. The main contribution of this paper is the design of 3D line following controllers for underactuated underwater vehicles. The control design is based on constant controlled surge speed and a simplifi ed decoupled model of an under water vehicle. Detailed design procedure is presented. The simulation results are obtained from a complex, coupled model, which proves that the proposed algorithm can be used on real vehicles

Analysis of grease contamination influence on the internal radial clearance of ball bearings by thermographic inspection

One of the most important factors influencing ball bearings service life is its internal radial clearance. However, this parameter is also very complex because it depends on applied radial load and ball bearings dimensions, surface finish, and manufacturing materials. Thermal condition of ball bearings also significantly affects internal radial clearance. Despite many researches performed in order to find out relevant facts about different aspects of ball bearings thermal behaviour, only few of them are dealing with the real working conditions, where high concentration of solid contaminant particles is present. That is why the main goal of research presented in this paper was to establish statistically significant correlation between ball bearings temperatures, their working time, and concentration of contaminant particles in their grease. Because of especially difficult working conditions, the typical conveyor idlers bearings were selected as representative test samples and appropriate solid particles from open pit coal mines were used as artificial contaminants. Applied experimental methodology included thermographic inspection, as well as usage of custom designed test rig for ball bearings service life testing. Finally, by obtained experimental data processing in advanced software, statistically significant mathematical correlation between mentioned bearings characteristics was determined and applied in commonly used internal radial clearance equation. That is the most important contribution of performed research the new equation and methodology for ball bearings internal clearance determination which could be used for eventual improvement of existing bearings service life equations

Overview of elements of national logistics system in the Republic of Serbia

There are various interpretations of the concept of national logistics. According to one of such interpretations, national logistics is a system which is comprised of resources, infrastructure and economy as its elements. This system functions in a general milieu set by the regulatory framework while interconnections of the system elements are established on the basis of mutual conditionality and interaction. Consideration of the elements of national logistics of a particular country renders the given term more concrete and specific features. This paper addresses the elements of the national logistics system of the Republic of Serbia. Thus, a general overview of the system concerned is being presented since an elaborate description is not possible within the given framework. Such a general overview of the elements of the national logistics system provides the basis for assessment of different systems in the country, from economic to security systems

Identifikacija bespilotnih ronilica korištenjem postupka vlastitih oscilacija

Control of underwater vehicles is a challenging task since these systems demonstrate highly coupled and nonlinear behavior in uncertain and often unknown environment. In order to successfully design higher levels of control hierarchy, sufficiently accurate parameters of a mathematical model describing the vessel is required. These parameters vary significantly depending on the payload; hence conventional, time-consuming identification methods are tedious. This paper introduces a self-oscillation based method for determining inertia and drag parameters for underwater vehicles. The procedure is easily implementable in field conditions and gives satisfactory results. Both linear and nonlinear models of yaw, heave and surge degree of freedom can be identified. Experimental results obtained from yaw identification experiments on a real underwater vehicle will be presented. In addition to this, the same methodology will be used to determine which model describes the vehicle dynamics more suitably. Modifications of the proposed algorithm for systems with delays and discrete-time systems will be described, together with an estimate of parameter error bounds due to quantization levels.Upravljanje bespilotnim ronilicama predstavlja zahtjevan zadatak budući da ronilice pokazuju snažno spregnuto i nelinearno ponašanje u nepredvidljivim i često nepoznatim okruženjima. U svrhu uspješnog projektiranja viših razina u njihovoj upravljačkoj hijerarhiji, potrebno je dovoljno dobro poznavati parametre matematičkog modela plovila. Ovi se parametri mogu znatno mijenjati ovisno o opremi i drugim uvjetima tijekom misije, stoga su uobičajeni, vremenski zahtjevni identifikacijski postupci neprikladni. Članak opisuje postupak koji koristi vlastite oscilacije za određivanje inercije i otpornosti bespilotnih ronilica. Postupak je lako primjenjiv u terenskim uvjetima i daje zadovoljavajuće rezultate. Linearan i nelinearan model zaošijanja, zaranjanja i napredovanja mogu´ce je identificirati. U radu su prikazani eksperimentalni rezultati dobiveni na identifikacijskim ekperimentima zaošijanja na stvarnoj ronilici. Uz navedeno, ista metodologija je iskorištena za odlučivanje o modelu koji prikladno opisuje stvarnu ronilicu. U radu su opisane i preinake predloženog algoritma za sustave s transportnim kašnjenjem i diskretne sustave, kao i procjene pogrešaka u određivanju parametara koje su posljedica kvantizacije

Direct laser dynamic displacement measurement of structural response during testing

The paper presents part of the conducted research on laser-displacement sensors for the measurement of structural response in civil engineering applications. Usually, the level of displacement in laboratory or on-site testing is in small to mid-range levels of 1.00 to 25.00 mm and in the frequency range of up to 100 Hz. Appropriate sensors were selected and used according to performance in the sense of resolution/accuracy. Experiments are conducted on steel model beam in the laboratory and on-site real bridge structure. In both analysed cases, data analysis was carried out in the sense of modal frequencies and damping estimation with comparison with numerically computed values. Presented are the results of two experiments, a laboratory-tested model of steel beam and an onsite tested real bridge structure. In both cases have achieved good argument of test results, estimated modal frequencies and damping of tested model/structure. Data analyses conducted used a developed MATLAB script, while the numerical computation conducted used SAP2000_v14 FEM package for structural analysis. Excellent agreement of extracted results was achieved in the case of the laboratory-tested structural model, as well as of extracted results of on-site tested real-world structure in the sense of extracted modal frequencies and modal damping. Finally, the conclusion is that laser-displacement sensors are quite appropriate for small to midrange of expected displacement and are quite appropriate for such applications according to the possibility of installation so that such sensors could be applied for structural testing, particularly for dynamic testing of such structures because of their possibility of high sampling frequency and high resolution/accuracy

Interactions of fast ions with supported graphene: Quantum hydrodynamic model

We use a quantum hydrodynamic (QHD) model to describe the high-frequency plasmon excitations of the carbon valence electrons responding to fast ions which move parallel to a single sheet of graphene supported by an insulating substrate. We calculate the stopping and the image forces on ions. Numerical results are obtained showing the effects of variation in size of the gap between graphene and the SiO2 substrate, as well as the effects of a finite frictional coefficient, on these quantities24th Summer School and International Symposium on the Physics of Ionized Gases : 23 August - 3 September 2010, Donji Milanovac, Serbi