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Numerical and Experimental Investigation of the Flow Field in Five Blade Linear Cascade in Subsonic Flow
Šnábl, Pavel ; Chindada, Sony ; Bublík, O. ; Procházka, Pavel P. ; Prasad, Chandra Shekhar
In large steam turbines, last stage blades are very long and must be designed very thin and with no shroud to minimize the centrifugal force which leads to low eigenfrequencies and low structural damping. In this case, aero-elastic damping plays important role on last stage bladed disc’s dynamics. Three major aero-elastic issues found in turbomachinery are forced response, non-synchronous vibrations, and flutter. Flutter is an unstable, self-excited vibration resulting from coupling between the structural vibrations and unsteady aerodynamic forces. It is clear that this unstable behaviour must be avoided and predictions of flutter behaviour need to be performed during design stage of the turbine.\n
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Use of GNSS Methods in Mapping Regional Tectonic Structures
Švábenský, Otakar ; Pospíšil, Lubomil
The article is devoted to the analysis and interpretation of geoscientific data in the area around the Rodl-Kaplice-Blanice (RKB) fault system. The RKB system, which has been active since the Proterozoic, appears as a significant interface in geological and geophysical maps. According to the occurrences of earthquake foci, the southern (central) part is also a seismically active zone. DPZ, GNSS, geophysical and geomorphological data were used to assess possible recent activity, with the main output in the form of a recent-kinematic model. The results show that the blocks on opposite sides of the RKB show diametrically different, opposite horizontal movement tendencies, the intensity of which increases towards the system of the South Bohemian Cretaceous-Tertiary basins.
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The New National Realization of the EVRS Height System in Slovakia
Jančovičová, Miroslava ; Droščák, Branislav ; Bublavý, Ján
Since 1957, in Slovakia the Baltic height system after adjustment with the reference tide gauge Kronstadt has been valid. The measurements in the National leveling network (Štátna nivelačná siteť – ŠNS) are still incorporated into this height system. In 2009 the EVRS height system, realization EVRF2000 was implemented to the decree of the Office of Geodesy, Cartography and Cadaster of the Slovak Republic (ÚGKK SR). However, the adjustment of the ŠNS in the EVRF2000 has not been performed. In 2019, the ÚGKK SR expressed interest in transitioning from the Bpv to the EVRS and its latest realization EVRF2019 as a primary height system by using the latest available measurements and the modern approach to calculating the normal heights through geopotential numbers. In the same year, a new, more accurate quasi-geoid model named GMSQ2019 was procured. The Geodetic and Cartographic Institute Bratislava (GKÚ) therefore realized the adjustment of the geopotential numbers of the 1st order points of the ŠNS in the realization EVRF2019. Currently, the GKÚ works on the connection of the leveling lines of the 2nd order of the ŠNS. The new national realization was named SKVRF2023. The testing at the points of the National spatial network (Štátna priestorová sieť – ŠPS) showed that the normal heights in the EVRS realization EVRF2019 in combination with the new quasi-geoid model GMSQ2019 will enable to determine the heights using GNSS methods on the territory of Slovakia with a high accuracy of 1 to 2 cm. An advantage of the transition to the EVRS and its realization EVRF2019 will be the direct connection of the ŠNS to the EVRS (and also to the International Height Reference System) and a simple transformation between its next realizations.
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Practical Aspects of Real-Time Kinematic Measurements With Topcon Hiper+ And Trimble SPS855 Receivers in the CZEPOS And TOPNET Networks
Kostelecký, Jakub
The Real-Time Kinematic method is the most commonly used Global Navigation Satellite Systems (GNSS) method for positioning in geodetic practice. Within the framework of the article, the behavior of two GNSS devices Topcon HiPer+ and Trimble SPS855 during positioning by RTK method using corrections provided by networks of permanent stations CZEPOS and TopNet is assessed. Specifically, the use of 4 types of corrections from the CZEPOS network and 4 types of corrections from the TopNet network were evaluated. The behavior of the devices is assessed both according to the time required to perform the initial initialization and the time required to average the measurement result, and also according to the RMS (root mean square) error of the vertical component of the position. The evaluation found that the Trimble SPS855 fixed faster than the Topcon HiPer+ (3.6 minutes vs. 5.7 minutes). The averaging time is slightly shorter with the Topcon HiPer+ apparatus than with the Trimble SPS855 apparatus (30 seconds vs. 37 seconds), which is mainly related to the intuitiveness of the control software in the controller. Overall, it is stated that the Topcon HiPer+ equipment is more suitable for corrections from the TopNet network, and the Trimble SPS855 equipment works better with corrections from the CZEPOS network.
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Aplikace Galileo High Accuray Service
Kazmierski, Kamil ; Hadas, Tomasz ; Kudłacik, Iwona ; Marut, Grzegorz ; Madraszek, Szymon
Since January 2023 the Galileo High Accuracy Service (HAS) is available to registered users. Within the HAS users can retrieve clock and orbit corrections, as well as code biases for Galileo and GPS constellations. Galileo HAS covers almost the entire globe and is the next system, after the Japanese CLAS (Japanese Centimeter Level Augmentation Service) and the Chinese PPP-B2b, that provides corrections via a satellite signal. These Galileo corrections are transmitted in the Galileo E6 signal but also via the Internet stream. The official HAS Service Definition Document indicates that the positioning accuracy is better than 25 cm and better than 30 cm for horizontal and vertical components, respectively. HAS corrections can be used in difference real-time applications without Internet connection. The presented work shows the use of Galileo HAS corrections in various geoscience applications such as positioning, timing, troposphere monitoring or coseismic vibrations detection. Additionally, the quality of the transmitted HAS correction is also verified using the SISRE parameter. The computations are carried out in the in-house developed GNSS-WARP software with the Internet HAS corrections saved in the ASCII files by the BKG Ntrip Client software. The Galileo HAS corrections quality using SISRE parameter equal to 8.6 cm and 13.0 cm for GPS and Galileo respectively. The experiment with Precise Point Positioning reveal sub-decimeter and centimeters accuracy in kinematic and static approach, respectively. In terms of timing precision Galileo HAS ensure precision of single nanosecond. Zenith Tropospheric Delay estimation with the use of evaluated corrections meet the requirement of troposphere monitoring and coseismic vibrations detection was also possible.
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The Network of Trigonometric Points of First Order of JTSK and Its Connection With the Implementation of the ETRS89 System in the Czech Republic
Taraba, Pavel
The JTSK First order trigonometric points (TP) network was being built on the Czechoslovakia territory between 1921 and 1953.Its initial implementation was completed in the spring of 1927 and included 268 trigonometric points, which thus form the basic framework of the Czechoslovak positional geodetic control. In the following years, the network was supplemented with additional points, especially in the territory of Bohemia and Sub Carpathian Russ, and connected with similar networks in the surrounding states. After its completion in 1953, it contained 388 trigonometric points. After launch of GNSS technology, in 1991, 6 of its points (3 in the Czech Republic and 3 in Slovakia) were chosen for the measurement campaign EUREF-EAST-91 (EUREF-CS/H-91), which was part of building the European framework of the ETRS89 system. In order to implement the ETRS89 system in former CSFR (Czech and Slovak Federal Republic) in more detail, the CS-NULRAD-92 campaign was carried out by the CSFR national geodetic service. This included 18 TPs (10 on the territory of the Czech Republic and 8 on the territory of Slovakia) and 17 of them were TPs of the First order. After division of Czechoslovakia into the Czech and Slovak Republics, a multi-stage CS-DOPNUL measuring campaign was carried out in the Czech Republic in the years 1993-1994, which included 176 points, 28 TP of which were of the First order. In the next stages of densification TPs with coordinates and in ETRS89 on the territory of the Czech Republic, other TPs of the First order of the JTSK were only sporadically involved. The First-order TB network is currently still part of the geodetic control, is still used for measuring purposes and is administered by the Land Surveying Office in the Czech Republic and by the Geodetic and Cartographic Office in Slovakia. Even though today its main parts are located on the territory of three sovereign states, namely the Czech Republic, Slovakia and Ukraine (Zakarpattia region), it can be stated that it has been preserved as a compact unit in almost its entirety, including connecting points on the border of Hungary and Austria. As part of the citizen's initiative, 367 out of 388 First Order TPs were visited during the years 2009-2021 and their status was documented. (Unfortunately, the completion of the initiative is impossible due to the martial law in Ukraine after its invasion by Russia.) Surface stabilization of points was not found in 26 cases (i.e. 7.1 %), with only 12 cases (i.e. 3.2 %) being assumed, that point was destroyed completely.
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Characterization and elimination of thermomechanical effects in interferometric length measurement
Řeřucha, Šimon ; Holá, Miroslava ; Lazar, Josef ; Mikel, Břetislav ; Číp, Ondřej
Continuous efforts to develop dimensional measurements at both the nano- and macro-scale continue to present challenges in extending high-precision measurement procedures from the well-controlled experimental environment of a typically single measurement cycle to a constant-load production environment. In the field of laser interferometry, which is both a cornerstone of length metrology in general and an essential part of nanometrology, we have focused on long-term measurement stability (so-called zero-drift) in measurement scenarios and applications based on (mostly laser) interferometry. A well-characterized and compensated measurement zero-drift in such applications becomes more important both with applications in less controlled environments and with increasing measurement timeframes, such as long scans in microscopic nanometrology, long exposures in electron lithography, or interferometric reference calibrations with a larger number of calibration points or repetitions. The goal of the current research effort is to comprehensively investigate error effects and contributions to measurement uncertainty related to zero-drift in laser interferometry-based applications, with a particular focus on temperature effects (as these typically appear to be the dominant contribution) and approaches to suppress them. This effort involves several complementary directions.
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Optical frequency distribution with full compensation of induced phase noise
Pravdová, Lenka ; Čížek, Martin ; Hrabina, Jan
In applications demanding high optical frequency stability, two or more reference stages are usually necessary to ensure the laser source's short-term and long-term stability. The short-term stability can be obtained by locking the laser to a high-finesse optical cavity, while the long-term stability can be formed by, for example, a hydrogen maser referenced by a synchronisation signal from a GPS receiver. During the distribution of stable optical frequencies to the target applications, the transmitted signal is affected by the interfering effects of the surrounding environment. This is especially evident in optical fibre transfers, where acoustic interference, vibrations and environmental temperature changes cause induced phase noise. This work describes the distribution network of stable optical frequencies between individual frequency references within the ISI CAS laboratories. The key parts of the setup are realised by free-space optics, and all of the optical links are fully compensated to induced phase noise effects.
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The surface quality of the fused silica machined by ultrafast laser
Novotný, Jan ; Mrňa, Libor
The quality of ultrafast laser-machined surfaces depends on several process parameters. In the experiment, the parameters window that yields the lowest roughness and lowest number of defects were found. The most important parameter after laser fluence is scan line overlap, which has the biggest impact on residual heat dissipation and related stresses in the specimen. The second harmonic wavelength yielded 10 % better surface roughness, lower waviness, and a lower number of defects on the surface and edges of the processed area.
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Frequency references and dissemination
Hrabina, Jan ; Pravdová, Lenka ; Šarbort, Martin ; Čížek, Martin ; Holá, Miroslava ; Oulehla, Jindřich ; Pokorný, Pavel ; Lazar, Josef ; Číp, Ondřej
The work deals with an overview of research topics of the “Frequency references and dissemination” group, Department of Coherence Optics, Institute of Scientific Instruments, Czech Academy of Sciences. These topics include frequency locking of lasers by laser spectroscopy and high-finnese optical cavities, digital holography and optical frequency tranfers through fiber and free-space optical links.
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