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Published By Czech Technical University In Prague - Central Library

1805-2363, 1210-2709

2021 ◽  
Vol 61 (6) ◽  
pp. 740-748
Author(s):  
Vadzim Parkhats ◽  
Rafał Krzywoń ◽  
Jacek Hulimka ◽  
Jan Kubica

A correct choice of a bond model for prestressing tendons is crucial for the right modelling of a structural behaviour of a pretensioned concrete structure. The aim of this paper is the determination of an optimal bond model for 7-wire strands in a prestressed concrete beam produced in a precast concrete plant of Consolis Poland. ATENA 3D is used to develop finite element models of the beam that differ only in a bond stress-slip relationship of tendons. The bond stress-slip relationships for modelling are taken from the results of bond tests carried out by different researchers in previous years. Moreover, for comparison purposes, a simplified 2D model of the beam is created in Autodesk Robot. The strain distribution at the time of the strand release is found for each of the finite element models. The determined strain distributions are compared with the strain distribution in the beam established by an experimental test using a measuring system based on a digital image correlation. On the basis of the comparison results, the most appropriate bond models for 7-wire strands used in the beam are identified.


2021 ◽  
Vol 61 (6) ◽  
pp. 672-683
Author(s):  
Anita Agárdi ◽  
László Kovács ◽  
Tamás Bányai

The Vehicle Routing Problem (VRP) is a highly researched discrete optimization task. The first article dealing with this problem was published by Dantzig and Ramster in 1959 under the name Truck Dispatching Problem. Since then, several versions of VRP have been developed. The task is NP difficult, it can be solved only in the foreseeable future, relying on different heuristic algorithms. The geometrical property of the state space influences the efficiency of the optimization method. In this paper, we present an analysis of the following state space methods: adaptive, reverse adaptive and uphill-downhill walk. In our paper, the efficiency of four operators are analysed on a complex Vehicle Routing Problem. These operators are the 2-opt, Partially Matched Crossover, Cycle Crossover and Order Crossover. Based on the test results, the 2-opt and Partially Matched Crossover are superior to the other two methods.


2021 ◽  
Vol 61 (6) ◽  
pp. 768-776
Author(s):  
Andrii Sliusenko ◽  
Vitalii Ponomarenko ◽  
Inna Forostiuk

In the paper, the hydrodynamics of the liquid-gas mixture in the mixing chamber of the ejectors at different spatial positions was analyzed and the comparative study of such ejectors was carried out. It was found that a more ordered mode of movement of the mixture in the mixing chamber is created as a result of the coincidence of the velocity vector of liquid drops and the direction of gravity in the vertical position of the ejectors. This leads to increasing the volume entrainment ratio almost twice. The analysis of the liquid-gas mixture flow in the mixing chamber, evaluation calculations and research allowed to develop and to patent a jet apparatus with a conical-cylindrical (combined) mixing chamber. It was also found that for such ejectors, the volume entrainment ratio is 15–55% higher than for a jet apparatus with a cylindrical mixing chamber due to the reduction of the resistance of the passive flow into the mixing chamber and prevention of the formation of reverse-circulating flows. A study has been conducted on liquid-gas ejectors in the range of the main geometric parameter m (ratio of the mixing chamber area to the nozzle area) 9.4–126.5, which allowed to establish its rational values at which the maximum volume entrainment ratio is achieved (m = 25–40).


2021 ◽  
Vol 61 (6) ◽  
pp. 703-721
Author(s):  
Irina Karpiuk ◽  
Denis Danilenko ◽  
Vasyl Karpiuk ◽  
Anna Danilenko ◽  
Tatiana Lyashenko

Experimental data on the bearing capacity of damaged reinforced concrete beams with the dimensions of 2000×200×100 mm, reinforced with prestressed metal casings, are presented. Damaging in the form of through normal and crossing inclined cracks, as well as excessive vertical moving of the beam were obtained during previous tests for the effect of high-level transverse alternating loads.The authors of the article have developed a method and equipment for restoring and strengthening damaged reinforced concrete beams using a casing. Beams are manufactured and tested in accordance with the three-level design of an experiment.Previously damaged and reduced to the ultimate (pre-emergency) state, the beams were strengthened with the declared method and equipment, and then retested. New data on the bearing capacity of ordinary and damaged beams, as well as reinforced concrete elements strengthened with casings and tested for the action of transverse forces and bending moments were obtained. The research results are presented in the form of experimental-statistical dependences of the bearing capacity of the support areas, deformability and crack resistance of the investigated elements on the ratio of the most significant design factors and external factors. A comparative analysis of the influence of these factors on the main parameters of the bearing capacity of ordinary as well as previously damaged and then strengthened test beams is carried out.The possibility and appropriateness of using the proposed method of strengthening reinforced concrete beams damaged by through normal and cross-inclined force cracks in the conditions of an existing production has been experimentally proved.


2021 ◽  
Vol 61 (6) ◽  
pp. 684-688
Author(s):  
Asaad K. Edaan Al-mashaal ◽  
Rebecca Cheung

Wet etching is a critical fabrication step for the mass production of micro and nanoelectronic devices. However, when an extremely corrosive acid such as hydrofluoric (HF) acid are used during etching, an undesirable damage might occur if the device includes a material that is not compatible with the acid. Polyimide thin films can serve as sacrificial/structural layers to fabricate freestanding or flexible devices. The importance of polyimide in microelectronics is due to its relatively low stress and compatibility with standard micromachining processes. In this work, a fast delamination process of a 4-μm-thin film of polyimide from a silicon substrate has been demonstrated. The films’ detachment has been performed using a wet-based etchant of HF acid. Specifically, the effect of HF concentration on the delamination time required to detach the polyimide film from the substrate has been investigated. This study is intended to provide the information on the compatibility of using polyimide films with HF, which can help in the design and fabrication of polyimide-based devices.


2021 ◽  
Vol 61 (6) ◽  
pp. 733-739
Author(s):  
Adam Orlický ◽  
Alina Mashko ◽  
Josef Mík

The paper deals with the problem of a communication interface between autonomous vehicles (AV) and pedestrians. The introduced methodology for assessing new and existing e-HMI (external HMI) contributes to traffic safety in cities. The methodology is implemented in a pilot experiment with a scenario designed in virtual reality (VR). The simulated scene represents an urban zebra crossing with an approaching autonomous vehicle. The projection is implemented with the help of a head-up display – a headset with a built-in eye tracker. The suggested methodology analyses the pedestrian’s decision making based on the visual cues – the signals displayed on the autonomous vehicle. Furthermore, the decision making is correlated to subjects’ eye behaviour, based on gaze-direction data. The method presented in this paper contributes to the safety of a vehicle-pedestrian communication of autonomous vehicles and is a part of a research that shall further contribute to the design and assessment of external communication interfaces of AV in general.


2021 ◽  
Vol 61 (6) ◽  
pp. 722-732
Author(s):  
Emeka Segun Nnochiri ◽  
Olumide Moses Ogundipe ◽  
Samuel Akinlabi Ola

This study investigated the geotechnical and microstructural properties of cement-treated laterites stabilized with rice husk ash and bamboo leaf ash. In going about the tests, the soil sample was subjected to compaction, California Bearing Ratio (CBR) and preliminary tests; such as specific gravity, particle size distribution and Atterbergs limits to determine its index properties. Thereafter, the soil sample was mixed with cement at varying proportions of 0–12% at 2% intervals and also, separately mixed with bamboo leaf ash (BLA) and rice husk ash (RHA) in proportions of 0–16% at 2% intervals. The mixes at each stage were subjected to compaction, Atterberg limits and CBR tests. The highest values were 66.7% and 54.8% for unsoaked and soaked CBR at 6% cement+8% BLA and 78.5% and 63.8% for unsoaked and soaked CBR at 8% cement+8% RHA. Samples at these optimal CBR values were subjected into Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) tests. Results showed that new compounds were formed and there were changes in the microstructural arrangements. It can therefore be concluded that pozzolanic and cement hydration reactions actually took place in the course of stabilization.


2021 ◽  
Vol 61 (6) ◽  
pp. 762-767
Author(s):  
Hanna Rostova ◽  
Victor Voyevodin ◽  
Ruslan Vasilenko ◽  
Igor Kolodiy ◽  
Vladimir Kovalenko ◽  
...  

The microstructure, hardness and cavitation wear of Eurofer 97, Cr18Ni10Ti and 42HNM have been investigated. It was revealed that the cavitation resistance of the 42HNM alloy is by an order of magnitude higher than that of the Cr18Ni10Ti steel and 16 times higher than that of the Eurofer 97 steel. Alloy 42HNM has the highest microhardness (249 kg/mm2) of all the investigated materials, which explains its high cavitation resistance. The microhardness values of the Cr18Ni10Ti steel and the Eurofer 97 were 196.2 kg/mm2 and 207.2 kg/mm2, respectively. The rate of cavitation wear of the austenitic steel Cr18Ni10Ti is 2.6 times lower than that of the martensitic Eurofer 97.


2021 ◽  
Vol 61 (6) ◽  
pp. 749-761
Author(s):  
Ubong Williams Robert ◽  
Sunday Edet Etuk ◽  
Okechukwu Ebuka Agbasi ◽  
Grace Peter Umoren ◽  
Samuel Sunday Akpan ◽  
...  

It has been observed that clay soil cannot be used for building design, unless it is modified by firing or with cement. Either method of stabilization can adversely affect the environment and public health just like indiscriminate dumping or open burning adopted in developing countries as the prevalent disposal technique for waste papers. This paper sought to examine the feasibility of using assorted waste papers to derive an alternative stabilizer to Portland Limestone Cement for modification of clay soil into composite materials suitable for building design. Specifically, clay-based composites were fabricated at 0 %, 5 %, 10 %, 15 %, and 20% replacement levels by weight with cement, and then hydrothermally-calcined waste paper ash nanomaterial (HCWPAN). Water absorption, sorptivity, bulk density, thermal conductivity, specific heat capacity, thermal diffusivity, flaking concentration, flexural strength, and compressive strength were investigated for each of the fabricated samples. Irrespective of the stabilizing agent utilized, 10% loading level was found to be the optimum for possession of maximum mechanical strength by the samples. Only samples with the HCWPAN content were found to be capable of reducing building dead loads and improving thermal insulation efficiency over un-stabilized clay material, if applied as walling elements in buildings. Generally, it was revealed that the cement and HCWPAN have comparable influences on the properties of clay soil, thus indicating that HCWPAN could be utilized as an alternative stabilizer to cement. In addition, the preparation of HCWPAN was found to be more energy-saving than that of the cement.


2021 ◽  
Vol 61 (6) ◽  
pp. 689-702
Author(s):  
Ilyas Haouam

In this paper, we address the energy eigenvalues of two-dimensional Dirac oscillator perturbed by a dynamical noncommutative space. We derived the relativistic Hamiltonian of Dirac oscillator in the dynamical noncommutative space, in which the space-space Heisenberg-like commutation relations and noncommutative parameter are position-dependent. Then, we used this Hamiltonian to calculate the first-order correction to the eigenvalues and eigenvectors, based on the language of creation and annihilation operators and using the perturbation theory. It is shown that the energy shift depends on the dynamical noncommutative parameter τ . Knowing that, with a set of two-dimensional Bopp-shift transformation, we mapped the noncommutative problem to the standard commutative one.


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