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Zagreb, Croatia

In the pipelines of water supply systems, the water hammer phenomenon often arises during rapid unsteady developments. Pipelines are mostly protected using an air vessel, which is designed by means of equations for oscillations of water mass. In this study, an analysis is made of the impact of pressure increases caused by water hammer on pressure variations in pipelines protected by an air vessel. The analysed unsteady (transient) developments occurred in a pressure system between the Ravnik pumping station and the Veliko Brdo reservoir, and thereby the measured pressure values were compared with values calculated with a numerical model. It was observed that although the air vessel converts kinetic energy into oscillations of water mass, part of the energy is transformed into elastic deformations of pipelines and into water compression. This study assesses the relationship of the conversion of kinetic energy into significant changes in pressure (phenomenon called water hammer), depending on the extent of the velocity change in time.

This article closely defines the stratigraphic and structural relations within the eastern part of the Drava depression. These relations are explained in detail for the more important fields located in the area of exploration such as Beničanci, Klokočevci, Števkovica and others. A geological column has been synthesized for the Beničanci area together with correlation profiles to better display the lithology of the Lower and Middle Miocene. Furthermore, structural maps of key bed H and EL-markers G, Z', Rρ, α have been developed and interpreted and the stratigraphic-structural relations of the investigation area have been laid down. © The Author(s).

Ancic M.,Svetosimunska cesta 25 | Pernar R.,Svetosimunska cesta 25 | Bajic M.,Kaciceva 26 | Seletkovic A.,Svetosimunska cesta 25 | Kolic J.,Svetosimunska cesta 25
IForest | Year: 2014

Silver fir is one of the most important commercial and ecological species in Croatia, and is currently the most damaged tree species in Croatian forests. It is increasingly infested by white mistletoe, whose relevant consumption of water and nutrients contributes to physiological weakening of the tree. Early mapping of mistletoe infestation based on remote-sensed methods may overtake current limitations of standard field methods and their high costs in the assessment of tree health over large areas. The main goal of this study was to develop an efficient and reliable method for mistletoe detection based on hyperspectral images and supervised classification methods. Surveying was performed in a mountain area of Croatia characterized by beech-fir forests using a hyperspectral scanner. The Spectral Angle Mapper (SAM) classification with 5° threshold value proved to be the best classification method. The first "spectral signatures" - endmembers for fir and mistletoe, were determined and entered into a spectral library database. Using the above approach, a reliable picture of the spatial distribution of mistletoe-infected silver fir trees over the whole studied area was obtained. Results were validated by aerial surveying with a non-pilot aircraft from ~30 m above the crowns. The approach used here may allow a cost-effective mapping of the distribution and intensity of mistletoe infection in silver fir, and can be considered an helpful tool for forest management and planning, forest protection and harvesting. © SISEF.

Novakovic G.,Kaciceva 26 | Marendic A.,Kaciceva 26 | Grgac I.,Kaciceva 26 | Paar R.,Kaciceva 26 | Ilijas R.,Poljoopskrba d. O. O
Geodetski List | Year: 2015

Although the Global Navigation Satellite Systems (GNSS) have been widely used in many areas of positioning and navigation, it is well known that this technology, in a specific environment, has its limitations or can not be applied. To overcome these limitations many researches were conducted to complement GNSS with other, mainly terrestrial technologies. One of the solutions is the application of pseudolites, ground-based generators and transmitters of GPS-like signals, for use in the local area. However, the technology based on pseudolites also has its limitations. The basic problem is that the pseudolites operate independently in so-called „unsynchronised mode“. In fact, the synchronization of transmitters that are broadcasting a positioning signal is the fundamental requirement for radio-positioning systems. In 2003, Locata Corporation (Canberra, Australia), began with the development of the concept of positioning for the purpose of establishing “a local autonomous terrestrial replica of GNSS”. The result is Locata positioning technology, designed to overcome the limitations of GNSS and other positioning systems, by developing a time-synchronized transceivers called LocataLite. These transceivers form a network - LocataNet, which transmits signals that allow carrier-phase point positioning, with cm-level precision, for a mobile Locata receiver. The biggest technical achievement of Locata system is completely new, patented, wireless technology of time synchronization between LocataLites, called TimeLoc. Therefore, there is no need for base station, the connection for data transfer from the base to the mobile receiver, and no need to double differentiation measurements. Locata incorporates proprietary signal transmission structure that operates in the licence free Industry Stientific and Medical (ISM) band (2.4 GHz). This allows high power of transmitted signals so that Locata can be used for the indoor applications too. Locata is not a substitute for GNSS. It can be easily combined with GNSS, or can be used as an independent measuring system, where the GNSS is unavailable or unreliable. The article presents a brief overview of the development of Locata positioning technology, its basic components: LocataLite - transceiver and Locata - receiver, process of synchronization - TimeLoc, then the establishment of a network of LocataLites transceivers - LocataNet, the application of Locata technology in some areas of positioning and navigation, and at the end a brief description of the project “Project Wanderland” which includes the acquisition of the Locata equipment. It is an opportunity, for the first time in Croatia, to practically apply this new technology of positioning and navigation. The authors of this article will soon be able to present their own results and experience to the local professional community. © 2015, Croatian Geodetic Society. All rights reserved.

Determination of construction displacements and deformations are an important parameter in assessing the condition and safety of the construction in its exploitation. Also, we get confirmation whether a structure is consistent with project solutions. Constant development of surveying instruments enables us to deal with more complex and demanding tasks that are facing engineering geodesy. Surveying instruments can measure, not only static and very slow displacements of the constructions, but also and faster (dynamic) displacements. In order to determine the accuracy, limitation and possibilities of surveying instruments, dynamic displacements of the constructions were simulated at the testing field. Surveying instruments were measuring simulated dynamic displacements with predefined frequency (up to 7.5 Hz) and amplitude of oscillation. Achieved results from the testing field, as well as results of the measurements from the roof construction of sports hall "Arena Zagreb" are presented in the paper.

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