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CFD-based insights into KCA propellers for high-speed vessels
No full textThis study focuses on the development and application of Computational Fluid Dynamics (CFD) methodology for analyzing hydrodynamic characteristics of KCA propellers. The research emphasizes the verification of CFD methodology using existing experimental data for three-bladed propellers of KCA series and
Potsdam propeller CFD benchmark. Following the validation of the methodology, a series of simulations
will be conducted for four-, five- and six-bladed propellers, analyzing key hydrodynamic characteristics
such as thrust, torque and efficiency coefficients. This approach aims to establish a foundational database
for segmental section propellers with more than three blades. This research is particularly significant for
high-speed vessels, which are currently exempt from certain regulatory frameworks but are expected to
contribute to global efforts to mitigate the environmental impact of maritime transport. The developed
methodology and CFD results provide a foundation for more efficient KCA propeller case-by-case designs
in the early stages of development, while the expanded database creates opportunities for further studies
and applications. The proposed approach contributes to modernizing the initial propeller design process in
line with contemporary technologies and energy efficiency improvements
Fast response aerodynamic multihole probe – mechanism for calibration and possibilities for measurements
No full textSimultaneous measurements of 3D velocity field and pressure is of great importance. Complex air flows exist in nature, as well as in numerous technical systems. These flows exhibit high levels of turbulence, requiring high sampling rates for accurate measurement. Analyzing such flows is possible using optical methods (laser Doppler velocimetry or particle image velocimetry), hot-wire anemometry or spatial probes. The advantage of multihole probes is simultaneous measurement of 3D velocity field and pressure.
The problem with optical methods is that they require laboratory conditions and they are not often used, except in special well prepared cases, on-site.Their advantage lies in non-invasiveness, high sampling rates and precision. On the other hand, standard spatial multiholeprobes are not suitable for measuring flows with high levels of turbulence. Newer generations of the multiholeprobes are capable of these measurements with fewer drawbacks. Integrating fast pressure transducers into the probe handles has enabled high sampling rates. These probes are known as FRAP (Fast Response Aerodynamic Probe).
In this paper is presented five hole FRAP, mechanism and installation for its calibration. The developed half-automatic mechanism for pitch-yaw calibration in the Laboratory of the Hydraulic Machinery and Energy Systems Department, at the University of Belgrade, Faculty of Mechanical Engineering is introduced. Calibration is performed by placing the probe in a known flow field in the nozzle of the wind tunnel with low level of turbulence (less than 2%). Specified pitch-yaw calibration angles should cover all the angles of attack that will encounter during application.no. 451-03-65/2024-03/20010
Application of Artificial Intelligence in Testing Conformity with Benford’s Law in Chaotic Dynamical Systems
No full textBenford’s Law, a logarithmic distribution of leading digits, has
proven useful in domains such as fraud detection, natural sciences,
and numerical data validation. Despite its widespread empirical
success, its application to data generated by chaotic dynamical
systems remains a relatively unexplored area. Given the sensitive
dependence on initial conditions and long-term unpredictability of
chaotic systems, the question arises whether their numerical outputs
inherently align with Benford’s distribution.No. 451-03-137/2025-03/200105, dated February 4, 202
Thermal imaging spectrometry and thermographic snapshots for three building blocks of different ages
No full textThermograms and their interpretation are a very customary routine in finding building
construction flaws. Infrared thermography has been used in building diagnostics for
approximately four decades now. These hand-held instruments dated from the 1800th
year, but their successive use started in the 1990s. In this manuscript, three differently
aged building blocks, (one from 1974th, the other from 2000th, and up-last from 2019th
year) were thermographically monitored and analyzed. For the thermographic
surveillance of these three differently aged building blocks, was used a Chinese-branded
thermal imaging camera, Guide D384A. The thermodynamic assessments of the
thermograms were done and according to the building's physics postulates, analytical
interpretations were made. Each building type had a resume of conclusions regarding the
construction drawbacks and quality of the construction. The relationship between the
architectural form of the building and the typology of thermograms was established. As
an appendix to this manuscript served the quantitative allegations of heat radiation
APPLICATION OF CFD FOR SIMULATION OF TRANSITIONAL FLOW IN SMOOTH CIRCULAR PIPES
No full textThe transitional flow regime in internal pipe flow presents unique challenges for accurate computational fluid dynamics (CFD) modelling due to its inherently unstable and intermittent nature. Transitional flows in pipes are encountered in numerous engineering applications, ranging from oil and gas pipelines to biological systems and various industrial processes. Experimental studies investigating the effects of flow transition have been conducted across a broad range of scales, from large industrial setups to microscopic systems. Intermittency, as a hallmark of transition, significantly influences flow characteristics such as velocity distribution, heat transfer, and pressure loss. Capturing the intermittent nature of transitional flows in CFD remains a significant challenge. Emphasis is placed on turbulence models enhanced with intermittency functions, such as the SST Transition (γ–Reθ) model, which is capable of capturing the gradual and spatially non-uniform onset of turbulence. Here, a set of simulations were completed for the case of a straight, circular pipe, long enough to establish fully developed conditions (L/D = 200), for different values of turbulence intensity levels at the inlet and for different Reynolds numbers. Fluid is water. This simulation study highlights the importance of turbulence transition modelling in predicting pressure drop, velocity profiles, and flow development length, providing insight into optimizing fluid transport with systems that can operate within this sensitive flow regime.contract 451-03-136/2025-03/ 20010
Estimation of Hover Endurance for an Electric Multicopter with Experimental Validation of Results
No full textOne of the key characteristics of multicopters is their ability to hover precisely, which enables their use in various missions. Furthermore, electric multicopters are already widespread today due to their simplicity and ease of operation. However, they have relatively short hover endurance, making the ability to accurately determine hover time crucial. Hover endurance is calculated based on momentum theory and the application of fundamental equations. The procedure is validated through experimental results on an electric multicopter with a takeoff weight of 48.8 kg
Aeroelastic Behavior of 3D-Printed Tapered Polylactic Acid Plates Under Subsonic Flow Conditions
No full textThis research investigates the aeroelastic stability of tapered polylactic acid (PLA) plates produced through fused deposition modeling (FDM) under low-Mach-number airflow conditions. While the static properties of 3D-printed structural components for drones, unmanned aerial vehicles (UAVs), and unmanned aircraft systems (UAS) have been thoroughly explored, their dynamic behavior, especially flutter, has been less studied. This study applies a binary flutter model to thin PLA plates, and the analytically predicted flutter speeds are compared with experimental data from wind-tunnel tests. The strong agreement between theoretical predictions and experimental results confirms the validity of the proposed dynamic aeroelastic analysis approach. This methodology provides valuable insights into designing aerodynamic lifting and stabilizing surfaces for UAS applications
A New Approach to Fire Resistance Design of Boiler Room Building Structure
No full textis the inapplicability to industrial facilities in which energy is produced or distributed. In this paper a novel approach is presented in order to determine the necessary fire resistance of the building structure of a boiler room. The method of separating the boiler room from fuel storage, as well as storage and transport of fuel from storage to the boiler room are not considered in the paper.
The aim of this paper is to determine the necessary fire resistance of the building structure of a general boiler room. The analysis will include boiler rooms with boilers that use different types of fuels (gaseous, liquid and solid fuels). The proof of the adequacy of the class of fire resistance for building structure will be given independently using the Purt methodology (according to the
Euroalarm standard) while the obtained results will be verified by using the Gretener methodology - version TRVB according to the TRVB 100:2010 recommendations and Gretener methodology - version SIA according to the SIA81 recommendations. Assumed fire prevention and protection measures include: installation of an automatic fire alarm system; constant presence of the
person on duty next to the fire control panel; sufficient number of fire extinguishers before the arrival of the fire brigade; existence of appropriate fire hydrant installation; professional fire brigade located up to 5 km from the building; access to the boiler room is provided from three sides for the purpose of fire-fighting, i.e. there is at least one opening that can be used for fire-fighting purpose
on every 20 m of the walls that border the fire sector. Considering the initial assumptions from presented results it can be concluded that for boiler rooms, in which liquid fuel is not in
use, it is sufficient to provide fire resistance of the building structure of 30 minutes.Contract 451-03-137/2025-03/ 200105 - 4.2.2025
Novel tabular method for estimation of heat Extraction factor
No full textDesign of industrial buildings significantly depends on the required fire resistance time of
the building structure. In order to determine this parameter, one of the most used procedures is
defined by German standard DIN 18230. In Serbia, calculation procedures given in this standard are mandatory for application according to the current Rulebook of technical standards for fire safety of industrial buildings. In this paper the calculation procedure for determining the heat extraction factor by applying standard DIN 18230 will be analysed. In order to simplify the calculation procedure and reading of input data, the tables will be proposed as an alternative to nomograms given in standard DIN 18230.Grant number 451-03-137/2025-03/ 200105 - 4.2.2025
INVERSE KINEMATICS SOLUTIONS OF ROBOTIC MANIPULATORS USING PADEN-KAHAN SUBPROBLEMS AND SCREW THEORY
No full textIn this paper, we used the Paden-Kahan subproblems and their extensions in the context of screw theory to solve the inverse kinematics of common robot manipulators: RR, RRR, RPR planar, and RPP spatial robot models. The inverse kinematics problem of a robot is fundamental to determining a robot’s mechanics, and among the different ways to solving it, we chose the Paden- Kahan subproblems approach for its effectiveness and simplicity. The canonical subproblems have been significantly extended and of particular interest to us are the inclusion of solutions to parallel screw axes for the second subproblem and prismatic joints instead of only revolute joints, also known as Pardos-Gotor subproblems, After solving the inverse kinematics of each robot model and representing the solutions via graphs, we then proceeded to demonstrate the correctness of our solutions against the desired configuration and found that the orientational and positional errors between the desired configuration and our solution were in the range of floating-point arithmetic errors. Taking into account the simplicity during solving the inverse kinematics and the number of operations performed, we concluded that, at least where applicable, the Paden-Kahan subproblems and their extensions provide significant advantages to other methods.No. 451-03-137/2025-03/ 200105 from 04.02.2025