CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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Augmented emergency lighting as a soft early warning: measures on road users when moving over
Get PDFA novel interface to provide robust, intuitive, and timely alerts to road users to move over for emergency vehicles (EVs) was tested in a seven-minute driving-simulator experiment. The interface, Augmented Emergency Lighting (AEL), mimics emergency lighting on emergency vehicles (i.e., flashing blue light), by using the cars’ interior lighting. AEL was initiated 30 seconds before an EV caught up and increased its brightness proportionally to the distance to the EV. The AEL alert was after 16 seconds accompanied by an Emergency Vehicle Approaching (EVA) alert, presented as a voice command and a text message on the dashboard. Comparisons were made between AEL+EVA alerts, EVA-only alerts, and no alerts, between groups (N = 61). Both AEL+EVA alerts and AEL-only alerts were highly successful in getting drivers to move over by slowing down and pulling off to the side as compared to when there were no alerts, but no significant difference between AEL+EVA and EVA-only was found. Questionnaire responses showed that AEL+EVA alerts were generally appreciated and that their timing was good. Further studies on learning effects and usability are discussed
Ageing effects on the mechanical properties stability of 3D printed material under compression
Get PDFThe paper deals with the examination of the ageing effects on the mechanical properties stability of 3D printed material via stereolithography under compression when subjected to various conditions, including UV radiation, X-rays, and the effects of time, from the opening of the bottle with the material to the 3D-printing process. The sets of samples under investigation were subjected to quasi-static and dynamic compression loading using an Split Hopkinson Pressure Bar. The aim of this paper is to investigate the long-term stability of the samples in terms of their mechanical properties and material behaviour and their degradation pattern. Despite the manufacturer’s information, it was found that the mechanical behaviour of the printed samples was significantly affected by the ageing process
Impact of bolt positioning on the stiffness of angular support brackets
Get PDFBolts and screws are usually preferred over other joining techniques when assembly and disassembly operations are required. However, they add extra weight to the system, so it is essential to reduce their size and weight by optimizing bolt parameters. Additionally, the stiffness of bolted members is very crucial; those with low stiffness may affect the correct functioning of the other connected components. This study focuses on the impact produced by bolt positions, specifically their center of gravity and spacing among them, on the stiffness of angular L-shaped brackets using Finite Element Analysis. Bending and torsional loads were applied to the free end of the member and deformations were recorded under these loads. The results revealed that a triangular bolt pattern is recommended for three bolts, whereas for four or more bolts, the pattern should be uniform to avoid stress concentrations. Moreover, the center of gravity and bolt spacing have a significant impact on stiffness. By optimizing bolt spacing and the center of gravity, a combination of six bolts can be replaced with four bolts of the same size while maintaining the same stiffness
Study of non-stationary cutting processes in power skiving
Get PDFThe paper presents the results of the modelling and study of the cutting process in the cut-in phase during the machining of external gears by the power skiving. The studies were carried out on the basis of the previously developed graphical model of the cut layers and the model of the cutting force as a function of the chip cross-sectional area, the shear strength limit of the workpiece material, and the intensity of plastic deformation during cutting. The regularities of the cutting force in the cut-in phase of gear machining are shown for successive tool revolutions in four passes with a gradual increase in the depth of cut. It is shown that the peak values of the cutting force at the contact between the front face of the cutter and the face plane are two times higher than under the conditions of steady stationary cutting in a preformed gap. At the same time, the amplitude of the cutting force and its average value over the cut-in passes are 1.7–3.7 times and 1.2–1.5 times higher, respectively, than the corresponding values of these parameters for steady state cutting. It is these peak jumps in the cutting force that limit the maximum depth of the cut, number of passes, and axial feed. Based on the data obtained, recommendations were developed to modify the traditional gear cutting scheme in power skiving. It is proposed to use short tool strokes with a low cutting depth along the length of the cut-in path and, after forming a gap in this area, to cut at a full depth to the full height of the gear rim. The possibility of a significant reduction of gear machining time using the proposed scheme of technological operation is demonstrated
Optimising load transfer using temporary supports in monolithic construction
Get PDFWhen constructing a ceiling slab, it is essential that the load is effectively transferred to the lower floors. However, challenges arise when the lower ceiling slabs do not meet the specified design strengths, potentially indicating inadequate load bearing capacity. This article explores a novel approach to solving this problem by using supports that are not traditionally used for slab formwork, but rather as backpropping mechanisms. These supports serve as static reinforcements for the ceiling slabs, optimising the load distribution. This article delves into the distinctive features of these supports and evaluates their potential impact on the overall structural integrity of the implemented design
Changing the integrity of the material surface by combining laser surface texturing and PVD magnetron sputtering technologies
Get PDFThe presented research combines laser micromachining technology (LST, Laser Surface Texturing) using an ultra-short femtosecond laser beam and PVD deposition of thin layers using magnetron sputtering. This combination has multiple benefits. It provides uniform and highly adhesive coatings with improved tribological properties. By optimising the deposition parameters when applying a thin layer of TiN, an improvement in the tribological properties of the tool steel surface and the laser micromachining (LST) surface can be achieved. On the laser-modified and coated surface with Ellipses-texture, the wear reduction was almost 19 % compared to the reference texture. The TiN coating exhibited very good adhesion to the substrate with critical force values of LC3 greater than 45 N and a nano hardness value of 26.5 GPa. The adhesion of the TiN coating to the laser-affected substrate, as well as the resistance of the coating to damage, was high. Damage primarily occurred on the original polished surface around the edges of the machined textures, where stresses are likely to concentrate
THE IMPACT OF NEUROMUSCULAR WARM-UP ON MUSCLE CONTRACTILITY AND INJURY PREVENTION IN FEMALE SOCCER PLAYERS: ANALYSIS USING TENSIOMYOGRAPHY
Get PDFAs female soccer\u27s popularity and participation rise, injury rates are expected to increase due to the sport\u27s complexity, highlighting the importance of regular health and neuromuscular function screenings for injury prevention. The aim of the study was to determine how neuromuscular warm-up affects the contractility of the lower limb muscles and its significance in the prevention of injuries in female soccer players. The research sample consisted of 36 female soccer players, who were divided into an experimental (EG) and a control (CG) group with an average age 17.45 ± 2.63 years (EG) and 16.24 ± 1.09 years (CG). The contractility of the lower limb muscles was monitored using Tensiomyography (TMG). We evaluated bilaterally five muscles of the lower limbs for each soccer player: m. biceps femoris, m. gastrocnemius medialis, m. gluteus maximus, m. vastus lateralis, and m. vastus medialis. The experimental factor in the research, implemented during the warm-up phase of the training session, was neuromuscular warm-up over 12 weeks of EG. To assess the effect of the intervention program on changes in the muscle contractility of the soccer players, we employed the non-parametric Wilcoxon signed-rank test for dependent samples and the Mann-Whitney U test for independent samples. Results indicates that the speed of muscle contraction (Tc) and muscle stiffness (Dm) vary among different muscles and even between dominant and non-dominant limbs of soccer players. The impact of neuromuscular warm-up on contraction time and maximal displacement was negligible, except for a moderate effect in m. gluteus maximus of the non-dominant limb. Although the impact of neuromuscular warm-up on lower limb muscle contractility was not significant, more regular monitoring and inclusion of neuromuscular warm-up at a higher weekly frequency may have beneficial effects
ARTERIAL BLOOD PRESSURE WAVEFORM ARTIFACTS DETECTION USING SHORT-TIME FOURIER TRANSFORM
Get PDFHigh-frequency waveform recordings of biological signals enable more detailed data analysis and deeper physiological exploration. However, the waveform data—like invasive arterial blood pressure (ABP)—are particularly susceptible to frequent contamination with artifacts that can devalue the subsequent calculations like pressure reactivity index (PRx). This study aimed to verify the ability of the short-time Fourier transform (STFT) based algorithm to detect artifacts in the ABP waveform. Four types of modeled artifacts (rectangular, fast impulse, sawtooth and baseline drift) with different durations and amplitudes were inserted into undisturbed ABP waveforms. Short-time Fourier transform with a 5-second time window is computed on artifact-polluted ABP signals to detect changes in the frequency domain caused by these artifacts. An algorithm with three decision-making rules based on the dominant frequency component, standardized power spectrum, and the value of the second harmonic of the dominant frequency was used. Only segments that passed all three rules were labeled as artifact-free. Results indicated high sensitivity (93.35% and 94.83%) in detecting rectangular and sawtooth artifacts, with specificity exceeding 99% for both. Baseline drift artifact was detected with a low sensitivity of 5.02%, and fast impulse was not detected. This study proposes the application of a short-time Fourier transform-based algorithm to enhance the detection of clinically significant artifacts in arterial blood pressure signals, particularly relevant for PRx and other secondary calculations
A simplified design of a concrete sandwich structure containing a reinforcing rib
Get PDFThis article presents the use of a strut and tie analogy for modelling the behaviour of a concrete sandwich structure, which is formed by thin outer concrete layers made of high-performance concrete and reinforcing ribs. The beams transmitting shear are made of a rigid material with low thermal conductivity (Purenit) in combination with a carbon fibre reinforced polymer. The purpose of these ribs is to ensure reliable shear interaction of the outer concrete layers regardless of the thermal insulation of the sandwich structure. A simplified model using the truss analogy in the Scia Engineer software was used for the design of this structure. Furthermore, this design was verified experimentally on a section of the sandwich panel where the feasibility and functionality were tested by a four-point bending test. Finally, the theoretical values from the model were compared with the experimental results. This also includes a simple evaluation of whether this simplified modelling of the structure’s behaviour is appropriate. The paper contains a summary of the conditions that could have affected the results
Experimental Study of Prestressed Steel Wire Rope-Composite Mortar for Flexural Strengthening of RC Beams
Get PDFThis paper proposes a new method for strengthening structures using prestressed steel wire rope-composite mortar. Firstly, the flexural performance test was conducted on reinforced concrete rectangular beams using composite mortar and prestressed steel wire rope. The test included one reference beam and four reinforced beams. The different arrangements of steel wire ropes and the influence of composite mortar on the flexural performance of the beams were analyzed. ANSYS finite element analysis software was used to perform nonlinear numerical simulations of the reinforced and unreinforced beams, and the results of the finite element modeling were compared with the test results to verify the reliability of the experimental findings. By comparing and analyzing the data of deflection, strain, and other parameters before and after strengthening, it was found that the prestressed steel wire rope strengthening method can significantly improve the load-carrying capacity of the existing bridge, greatly improve the structural performance, and have a good effect on resisting cracking in the reinforced concrete beams. The composite mortar can extend the service life of the prestressed steel wire rope and has excellent durability