CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
Not a member yet
4735 research outputs found
Sort by
The effects of potassium permanganate on the geotechnical properties of soils
Get PDFIn Nigeria, potassium permanganate (KMnO4) is used as a chemical oxidant in the removal of hydrocarbons from polluted soils and groundwater, but there is no information on the effects of KMnO4 on the geotechnical properties of the soil. In this study, KMnO4 was added separately to lateritic soil and kaolin at concentrations of 0 %, 2 %, 5% and 10 % by weight of dry soil. Each of the mixes was then subjected to grain size analysis, Atterberg limits, specific gravity, compaction, and California bearing ratio (CBR) tests. The results showed that an increase in KMnO4 from 0 % to 10 % generally decreased the values of maximum dry density (MDD), optimum moisture content (OMC) and both unsoaked and soaked CBR for both soils. In conclusion, the study shows that although KMnO4 is excellent for the remediation of contaminated sites, it reduces the geotechnical properties of soil and therefore should not be used alone (without the use of other additives) for soil stabilisation
Construction of angular-dependent potentials from trigonometric Pöschl-Teller systems within the Dunkl formalism
Get PDFWe generate solvable cases of the two angular equations resulting from variable separation in the three-dimensional Dunkl-Schrödinger equation expressed in spherical coordinates. It is shown that the Dunkl formalism interrelates these angular equations with trigonometric Pöschl-Teller systems. Based on this interrelation, we use point transformations and Darboux-Crum transformations to construct new solvable cases of the angular equations. Instead of the stationary energy, we use the constants due to the separation of variables as transformation parameters for our Darboux-Crum transformations
Shock wave configuration in a transonic flow through a mid-section of a last stage turbine blade cascade equipped with a part-span connector
Get PDFThis paper deals with the study of a flow field and namely the configuration of shock waves in a blade cascade equipped with a part-span connector called tie-boss. The cascade consists of prismatic blades formed from the mid-section of a very long last-stage blade of a steam turbine. The study is based on numerical simulations of the flow through a cascade that was previously tested in a wind tunnel. Commercial software Ansys CFX was used for the simulations and Ansys ICEM for the mesh generation. The computational domain contains non-homogenous mesh interfaces. The simulations showed that the presence of the tie-boss has a profound effect on the configuration of the shock waves. The blade exit shock waves are disturbed and new lateral shock waves are introduced into the flow
Safety analysis of the method of implementation of crash cushions
Get PDFThe topic of the article are vehicle restraint systems. Specifically, the paper focuses on the safety analysis of the way of implementation of crash cushions. Within the safety analysis carried out on the territory of the Ústí Region of the Czech Republic, the most frequently occurring deficiencies in crash cushions and their possible impacts on road safety were identified. The output is the creation of catalogue sheets of crash cushions, which contain the most frequently installed crash cushions on the road network and a summary of methodological requirements for their adequate implementation. The work is intended to serve as an effective tool and a quality source of information for road managers and road safety auditors during their subsequent inspection
Dynamic tests of the protective and security barrier system probar
Get PDFThe purpose of this paper is to present a series of dynamic tests for testing the protective and security barrier of the PROBAR system, developed by STRIX Chomutov, a.s., according to the PAS 68:2013 standard. The goal of the tests was to assess how the obstacle resist impacts and whether it can absorb the energy exerted on it. Verification of the mechanical properties of the device was performed in two types of impact configurations. Emphasis was placed on the behaviour of both the obstacle and the vehicle during the impact and in the short time interval after the collision. In terms of criteria for evaluating the impact tests, it can be stated that Test 2 exceeded the Theoretical Head Impact Velocity (THIV) criterion by 20 km h−1, while Test 1 did not exceed the limit value. However, all values for other criteria (ASI, PHD, HIC, 3ms) were within the specified limits, and the safety barrier met the required criteria which allows to be certificated
Arc Voltage as an Indicator of Nozzle Ablation Degradation in High-voltage CO2 Gas Circuit Breakers
Get PDFEnergy released by electric arc during short-circuit current interruption is mostly absorbed by the surrounding cold gas and partly transferred to the arcing contacts and nozzle. The radiation is the main mode of thermal energy transfer between the electric arc and nozzle surface. Experimental research on the nozzle ablation has been carried out at a model circuit breaker, in which CO2 is filled in the chamber and poly-tetrafluoro-ethylene (PTFE) is used as the nozzle material. It is found that the arc voltage can be as an indicator of nozzle ablation degradation by comparing the voltage at current peak and arc voltage extinction peak. Under 20kA and 35kA peak current interrupting conditions, the voltage at current peak decreases with the number of operations. There are two factors that affect the arc voltage at current peak. One is the size of the arc cross section, and the other is the content of PTFE entering the arc zone, which affects its conductivity
Plasma Properties of Electric Arc Discharge Burning Between Cu-W Composites Electrodes
Get PDFPlasma of electric arc discharge burning between different types of composite Cu-W electrodes was investigated. Electrodes manufactured of Cu-W composite materials (30/70% by mass) by shock sintering technology at temperatures of 750, 850, 950, and 1050°C were used. Optical emission spectroscopy techniques were applied to determine the main plasma parameters. Specifically, the side-on spectra of plasma emission were registered using a space-resolved spectrograph with a CMOS camera as a sensor device. The plasma thermodynamics properties were calculated based on the equilibrium plasma composition, which was determined using experimentally obtained radial distributions of temperatures and atom concentrations of the metals
Mechanical and physical properties of cement mixtures for 3D processing
Get PDFIn this paper, information about cementitious composite materials for further 3D processing is discussed and supplemented. Many of the research in this area focuses primarily on cement composites suitable for 3D printing. Nevertheless, 3D printing is not the only robotic processing technique. Another such a technology is modelling with the help of a robotic arm, which can be used to create various elements that fulfil their original but also aesthetic function. The robotic arm creates, using a variety of sculptural or hand tools, a final unique relief of a given element. Three different cement composite mixtures are discussed and their mechanical, physical and thermophysical properties are evaluated. The research aims to investigate and optimise these composites for robotic sculpturingand 3D printing
Treatment of polypropylene microfibers by atmospheric and low-pressure plasma – application to a reinforced cement composite containing recycled concrete
Get PDFThe effect of atmospheric and low-pressure plasma modification on polypropylene (PP) microfibers was examined. Mechanical changes on the microfiber surfaces were observed using scanning electron microscopy (SEM). Next, wettability was measured using the packed-cell method. The fibers were applied into a cement matrix containing micro-milled recycled concrete. Test specimens were made and then the dynamic modulus of elasticity was continuously measured. After 28 days were made in the test specimens central notches to a depth of 14 mm. Finally, bending tests were performed. From the results, the fracture energy of the composite material was calculated. It was proven that low-pressure plasma modification as well as atmospheric plasma modification increases the wettability of PP fibers with water. Furthermore, it was found that samples containing plasma-modified microfibers have a higher fracture energy compared to the same samples with fibers without plasma modification. Conversely, plasma modification had no effect on the dynamic modulus of elasticity
Benchmark VERCORS 2022: blind prediction of time-dependent behavior of concrete containment building with low and high-fidelity models
Get PDFThe VERCORS program aims to acquire an extensive experimental dataset collected to provide a solid basis for numerical modeling of concrete containment buildings (CCBs). In order to cover the entire life-span of a real containment, the measurements are done on 3× smaller mock-up which leads to 9-fold acceleration of all processes related to drying. The goal for the participants of the third VERCORS benchmark was to predict the behaviour of the CCB based on standard laboratory measurements on VERCORS concrete. The previous paper [1] presented the calibration procedure of material models for moisture transport and time-dependent behavior of concrete and summarized the results obtained with a computationally efficient low-fidelity model (LFM). The present paper compares the responses of the LFM and a high-fidelity model (HFM) with a detailed geometry of the entire containment and presents a comparison with the experimental data collected over the last 8 years on the VERCORS mockup