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A Comparison of Methods Recovering Signals from Non-Uniform Samples
(Elsevier, 2024-08-14) Mihálik, Ondrej; Mesárošová, Michaela; Čelko, Jakub; Sýkora, Tomáš; Bradáč, Zdeněk
Band-limited signals play a vital role in signal acquisition, transmission, processing and storage for decades. However, their recovery from non-uniformly spaced samples is still subject to discussion. There are multiple authors advancing different approaches and the user has to deal with an abundance of literature. Therefore, this paper offers a brief theoretical review of the most promising reconstruction methods. We also consider the importance of regularisation if the signal samples are noisy, which, surprisingly, seems to be neglected by many authors. Subsequently, the suitability of the methods is illustrated using an example of a real-world signal. Assessment of accuracy and speed of the methods is repeated for varying noise levels in signal amplitude, and for increasing degree of non-uniformities in sampling time. Cubic spline methods and sinc function reconstruction offer the best compromise between speed and accuracy for the concrete signal tested in this paper.
Thermal stability of electron beam welded AlCoCrFeNi2.1 alloy
(IOP Publishing, 2024-09-30) Rončák, Ján; Jozefovič, Patrik; Müller, Peter; Adam, Ondřej; Judas, Jakub; Dupák, Libor; Zavdoveev, Anatoliy; Jan, Vít; Zobač, Martin
AlCoCrFeNi2.1 alloy, which belongs to the group of eutectic high-entropy alloys (EHEAs), possesses a combination of increased strength and ductility. It should retain these properties over a wide temperature range due to the high entropy effect of the system. At the same time, eutectic alloys are generally considered to have good castability, which increases the possibility of casting the alloy in larger volumes. One of the processes, that the alloy does not avoid when applied in industry, are the various joining techniques including electron beam welding. The weld area is often in a non-equilibrium state, which increases the risk of failure during operation. The paper therefore discusses the stability of the microstructure and mechanical properties of AlCoCrFeNi2.1 alloy when exposed to short-term elevated temperatures. The material heated at 900 degrees C for 1 h in a vacuum furnace was observed using light and electron microscopy, analyzed for chemical and phase composition and finally subjected to HV0.1 hardness measurement and tensile strength test. The resulting condition was compared with the welded joint before exposure to elevated temperature. The microstructure of the weld was formed by a fine lamellar eutectic over the entire observed area. EBSD analysis confirmed the presence of a combination of FCC and BCC phases. The material hardness reached an average value of 370 HV0.1. Maximum tensile strength of the weld joint was measured at 944 MPa with the corresponding displacement of the crosshead 6.1 mm. The welded joint demonstrated sufficient stability and the ability to withstand short-term severe elevated temperature conditions.
Evaluating the Effect of Fatigue on Driver’s Performance
(Elsevier, 2024-06-19) Jirgl, Miroslav; Šedivá, Soňa; Bradáč, Zdeněk
The paper presents an experimental cybernetic approach for the evaluation of drivers’ performance in connection with fatigue based on mathematical modelling and description of human behavior during a simple lane-changing task. Data are acquired via the in-house developed car driving simulator under defined conditions. Statistical evaluation of the used parameters for 50 active drivers is presented as an initial data set for the determination of the described drivers’ performance decision-making system built on fuzzy logic. The system was then used for calculating the DPI (Driver performance index) as a self-determined relative measure of drivers’ performance. Then, an example of applying the method with three volunteers influenced by fatigue is presented. All of these participants reached lower DPI in the case of fatigue induced by a 3-hour-long simulated loading drive on a highway. Although the results cannot be statistically significantly interpreted, they indicate a potential for further and deeper research.
Fuzzy Logic-based Techniques for Human Driver Behavior Modelling during a Simple Lane-changing Task
(Elsevier, 2024-06-19) Jirgl, Miroslav; Mesárošová, Michaela; Fiedler, Petr; Arm, Jakub
The paper presents an experiment with fuzzy-logic-based models for approximating data representing human driver behavior during a simple lane-changing task. Data are acquired via the self-developed car driving simulator under defined conditions. Three fuzzy-logic-based models are considered: fuzzy Hammerstein model, fuzzy PD controller with a fixed structure (analogy to the linear PD controller) and fuzzy PD controller with an optimized structure. A comparison of the effectiveness of the individual approaches was evaluated using a criterion representing the fitness of the model output and the measured data. Although only one dataset was considered in the frame of this paper, the results indicate an investigative potential of the fuzzy models for this kind of task connected with the modelling of human behavior.
A Simple State-Space Model of Human Driver Applicable to Windy Conditions
(Elsevier, 2024-08-14) Čelko, Jakub; Mihálik, Ondrej; Husák, Michal; Bradáč, Zdeněk
The paper is concerned with the design, verification and evaluation of a car-driving test scenario for human driver assessment. The scenario implemented in Unreal Engine adds four different wind characteristics which disturb the motion of a simulated vehicle. Besides, the driver is instructed to change the driving lane at defined intervals. These forcing functions enable the identification of the human-machine loop using state-space models. The parameters characterising the human dynamics are extracted from the model of the whole loop. As opposed to rather obsolete McRuer models, this approach follows the recent trends in the modelling of human-machine systems as multiloop systems or quadratically optimal controllers. Our results suggest that the model relying on a single transfer function with 4 parameters loses prediction capabilities during more realistic scenarios, in which random disturbances, such as wind gusts, affect the vehicle. In such cases, the multiloop model with the same number of parameters is able to capture human behaviour more accurately than McRuer model.

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