CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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The concept of fractured rock-mass modeling using DFN-based statistical volume elements
Get PDFThe overall mechanical response of a fractured rock mass is, to a large extent, affected by naturally occurring fractures that exhibit sizes from millimeters to kilometers. Thus, in analysis of underground structures, such as tunnels, it is required that the fractures’ influence on the stress and deformation state in the vicinity of the structure is taken into account. In the present work, we examine the applicability of the statistical volume element (SVE) approach to determining the apparent stiffness tensor of an equivalent continuum representation of the fractured rock, which is then used in the framework of the finite element method. The equivalent continuum properties are determined by volume-averaging the effect of individual fractures that intersect the SVE, while the fractures are represented using the “parallel plate model”. Stochastically generated discrete fracture networks are used to represent the fractures’ geometry. Presently, we solve the problem linearly for an incremental change of the stress state. An application of the concept is demonstrated on simulation of tunnel excavation
Wind tunnel test study on lattice high support of bridge in typhoon areaWind tunnel test study on lattice high support of bridge in typhoon area
Get PDFBridge grid support stability against typhoons is a key factor in ensuring the safety of bridge construction. This study employs wind tunnel force tests and Particle Image Velocimetry (PIV) experiments to investigate the typhoon stability of grid-type high supports. Based on wind tunnel force tests, the static force coefficients of grid-type high supports are measured under different flow conditions and wind angles. Utilizing PIV technology, a novel analysis is conducted on the flow field visualization of high-pier steel tube support models in horizontal and vertical plane flows. Quantitative analyses of the vortex core intensity and turbulence of single and double-pier supports are performed. The impact of wind direction on the aerodynamic characteristics of grid-type high supports is determined.The research indicates significant changes in drag, lift, and torque when calculating the wind resistance of grid-type high supports. Therefore, the influence of static wind loads in three directions needs to be fully considered in the calculations. Under a 45° wind deflection angle, vortex movement becomes more intense, reaching maximum vortex strength and turbulence intensity. This results in an increase in the average and fluctuating aerodynamic forces of the model. Compared to the four-legged grid-type high support model, the six-legged model exhibits relatively smaller vortex strength and turbulence intensity at the vortex core. Noticeable interference exists among the components of the grid-type high support, thus spatial three-dimensional characteristics should be considered in numerical simulations.By conducting wind tunnel experiments on grid-type high supports in typhoon-prone areas, the study ensures the safe use of these supports, enhances economic benefits, and broadens the application scope of grid-type high supports
THE PRODUCTION OF HYBRID PROSTHETIC SOCKETS THROUGH THE INTEGRATION OF 3D PRINTING AND CONVENTIONAL LAMINATION
Get PDFCurrently, due to the relatively high number of active users with amputation of the lower limbs, it is important to increase user comfort, innovate and optimize the connection between the residual limb and the prosthesis, i.e. the prosthetic socket. The purpose of this work is to combine the potential and advantages of both conventional and innovative (modern) production processes for the design and fabrication of personalized hybrid sockets to optimize production, comfort, and patient safety. The socket was designed and constructed for a highly active user (Functional Classification Level 4) to ensure comfort and safety during high-stress sports activities (skiing). Unlike traditional plastering, a 3D scanner was used to take measurement data. The 3D model of the stump was edited in a software environment instead of laborious and lengthy processing of the plaster positive. Subsequently, a matrix of the prosthetic socket was made from PETG material using FFF 3D printing, which was laminated to increase strength. 3D printed samples of PETG material were tested for tension and pressure according to the relevant standard (EN ISO 527-2: 1996). The last phase was static and dynamic testing of the hybrid socket. No deviations were recorded in the monitored parameters, both at a slow (1.0 km/h) and at a standard (2.5 km/h) walking speed. Once the socket integrity has been assessed, a greater dynamic load was initiated in the form of activities with higher dynamic levels (lateral leaning on the knee and jumps). According to the test results, there has been no change in the shape or integrity of the socket, and the subjective point of view of the volunteer rated the hybrid prosthetic socket as comfortable
The effect of a malfunctioning braking system on the behaviour of a special vehicle during an emergency braking in a curvilinear movement
Get PDFVehicle mobility is an increasingly important issue today, even in the military field. Mobility depends on the condition of the vehicle, the route and, of course, the experience of the driver. Vehicle failures and damage are very common in military operations. It is therefore important to find out how these failures and damage can affect mobility. One of the essential parts of a vehicle is the braking system. The authors therefore decided to investigate what is the effect of a malfunctioning brake system on emergency braking behaviour of a special vehicle in a curvilinear movement. Simulation tests were performed based on an experimentally validated model. The tests were performed with a wheeled vehicle on three different surfaces: concrete, wet asphalt, and ice. The experimental conditions were given as follows – the braking process was considered for a braking system with ABS on and off and for two states of braking system sufficiency (8 braked wheels or 4 rear braked wheels). These tests allowed us to analyse the effect of the extent of the damage on safety, in this case the stopping of the vehicle on a specified curved route. The results of braking and stability on different surfaces and under given conditions are evaluated and described in this paper. On the basis of the results, it is possible to prepare training programmes (scenarios) for drivers of special vehicles for the purpose of driving techniques in critical situations
Research on the evaluation model of non-motorized travel environment in historical districts considering riding speed
Get PDFEncouraging the use of non-motorized transportation is an effective strategy for alleviating traffic congestion in historic districts. This study utilizes data from a survey on 48 representative roads in Xi\u27an\u27s historic districts. By considering the cycling environment, the non-motorized roadways in these districts are classified into three categories. The recommended average cycling speed that meets the psychological needs of cyclists at each category is chosen as the evaluation indicators. Based on OLS model, Poisson regression model and negative binomial regression model, an evaluation model for the non-motorized traffic environment in historic districts is established. By comparing the fitting performance of regression models, suitable evaluation models for the non-motorized traffic environment are determined. The results indicate that the Negative Binomial model performs well in fitting the results for class I and class III roads, with fitting coefficients of 0.8070 and 0.9199, respectively. On the other hand, the OLS regression model demonstrates a better fit for class II roads, with a fitting coefficient of 0.7003. The non-motorized travel environment on class III auxiliary roads in Xi\u27an\u27s historic districts is poor, as most roads fail to meet the speed requirements of cyclists. Class I roads exhibit a favorable non-motorized travel environment, indicating the potential for further encouraging non-motorized travel. Most class II roads in the districts generally meet the requirements for non-motorized travel, but there is limited room for increased non-motorized traffic volumes in the future. The research findings provide a theoretical basis for enhancing the quality of cycling environment in historic districts
Green mobility in courier services – aspects of using electric vehicles
Get PDFCountries in the EU, as part of the Paris Agreement, committed to achieving EU climate neutrality by 2050. To meet this goal, the EU aims to reduce its net greenhouse gas emissions across the entire economy by at least 55 % by 2030 compared to 1990 levels, continuing the reduction of emissions until 2050. The transport sector, responsible for a quarter of EU greenhouse gas emissions, must transform, requiring a 90 % reduction in greenhouse gas emissions by 2050. It is crucial to enhance the efficiency of both personal and freight transport in the EU and reduce dependence on fossil fuels. Our paper presents the cost calculation results of using electric vehicles with a total weight of up to 3.5 tons in the courier services sector, compared to conventional vehicles. Based on our analysis, electric vehicle usage is effective and environmentally beneficial. However, BEVs (battery electric vehicles) have higher acquisition costs than ICEVs (internal combustion engine vehicles). This paper analyses the vehicle fleet of a significant courier company. Thanks to their data, it was possible to provide a closer look at the economic efficiency of BEV in courier services
Automatic detection of sleep spindles by neural networks algorithms
Get PDFSleep constitutes an essential aspect of human existence, with the average individual dedicating approximately one-third of their life to this physiological activity. Consequently, comprehending and accurately analyzing sleep patterns is of paramount importance. This research aims to introduce, formulate, execute, and assess diverse machine/deep learning methodologies tailored for the processing of EEG signals geared explicitly towards identifying sleep spindles. The learning algorithms underwent training using meticulously annotated data from the Montreal Archive of Sleep Studies (MASS) data center. The convolutional neural network emerged as the most effective classification model, achieving an accuracy surpassing 67 %
Fatigue analysis on flax-epoxy composites: insights and implications
Get PDFThis study investigates the performance of flax fiber and epoxy resin composites, focusing on fatigue testing, which is scarcely reported in the literature. Fatigue behavior is evaluated under full reverse bending loading conditions: R = −1. Apart of the definition of the classic S-N curve, the analysis deeply investigated the evolution of the hysteresis leaf generated during each cycle over the entire fatigue life. This approach allows evaluating interesting parameters such as the evolution of the loss factor and the apparent modulus over life, being these informations fundamental for practical application of natural-fiber composites in engineering applications
EXPERIMENTAL STUDY ON QUALITY LOSS AND MICROSTRUCTURAL CHARACTERISTICS OF REINFORCED CONCRETE IN BRIDGE DECK PANELS AFTER SALT
Get PDFThe reinforced concrete structure is the most widely used structural form today. In the western salt-alkali areas and in road and bridge projects in the northern regions where de-icing agents are applied, chloride ion intrusion into concrete leads to rebar depassivation and corrosion. With the occurrence and intensification of corrosion, the expansion of corrosion products leads to cracking or spalling of the concrete cover, resulting in durability damage to the reinforced concrete structure. Among all the components of the bridge, the bridge deck panels suffer the most severe and direct damage from salt freezing. Therefore, predicting the service life under salt freezing conditions is an urgent issue to address for the durability design, evaluation, and structural maintenance decision-making for reinforced concrete bridge deck panels
Digital reconstruction of real (near) accidents of vulnerable road users (VRU) in the Czech Republic – modern technology brings new perspectives
Get PDFProtecting vulnerable road users (VRUs) remains an issue despite significant advances in the development of integrated safety, autonomous driving and cooperative environments. As part of accident/collision processes, the urban area of municipalities continues to constitute a risk environment with a relatively high frequency of serious injuries (VRU) even at relatively low speeds. In order to understand and increase road safety, it is necessary to analyse the causes of traffic accidents in more detail using video recordings, virtual reality (VR) and automated computer vision methods. The state of the art in the Czech Republic is limited due to the absence of high-quality and extensive data sets. This article constitutes a proof-of-concept solution for the digital reconstruction of selected accident/collision events in 4 cities of the Republic, specifically in Prague, Liberec, Česká Lípa and Jaromeř. It makes it easier to identify, parameterize and virtualize the results of a traffic conflict study and can provide input data for the testing and validation of sensors, interaction models of road users’ behaviour, and preparation of scenarios for a simulated environment; ultimately it reinforces prevention efforts