CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
Not a member yet
4735 research outputs found
Sort by
Influence of carbonation on torrent air permeability of concrete
Get PDFAir permeability testing is increasingly being used to measure the impermeability of concrete and to estimate the durability of reinforced concrete structures using this property. This paper presents the results of a preliminary study on the influence of the carbonation of concrete on its air permeability measured using the Torrent apparatus. Three batches of concrete made with CEM I cement and differing in the w/c ratio (0.45, 0.50, and 0.55) were tested. The influence of the relative humidity of concrete on the air permeability index kT was assessed using relationships available in the literature. It was shown that in carbonated concrete, these relationships need to be modified. The air permeability values obtained in tests are lower than the theoretical values calculated using the equation. The results obtained suggest that the effect of carbonation on the air permeability of concrete is significant and further research in this area is highly recommended
Prediction of temperature field distribution in a gas turbine using a higher order neural network
Get PDFThis paper presents the prediction of temperature field distribution in a single annular section using an artificial neural network (ANN). This temperature distribution is non-uniform on the outer tube due to continuous natural convection and radiation caused by the homogeneous steady-state heating of the inner tube, which represents the hot gas flow path through the turbine. The outer tube represents the case of a gas turbine. This temperature is important for the electronic components attached to the engine or the overall engine deformation. The presented approach allows for a quick estimation of the temperature distribution without the need to perform time consuming computational fluid dynamics (CFD) simulations. This can greatly accelerate the design and development of gas turbines. A machine learning approach is applied to an extensive set of CFD simulations under different operating conditions and geometry setups
Expert questionnaire on the issue of economical use of the railway traffic path capacity and buildings preparation on the railway
Get PDFThe railway traffic path capacity and the issue of railway buildings planning are topics that are widely discussed in professional groups. Experts often do not the same opinions on these topics. The issue of the allocation of railway traffic path capacity is given in general legislation and further by regulations or directives of a particular railway operator. Carriers are obliged to agree to these conditions. In the case of railway buildings planning, there are also comprehensive defined procedures and selected methods and models which are used to evaluate buildings planning (for example, a four-stage transport model or a logit model). However, it is appropriate to deal with the idea of whether all these procedures are correct and whether it is not appropriate to make changes, especially in the long-established procedures, that would better reflect the current and future reality and society needs
Neutronic analysis of a heat-pipe cooled reactor
Get PDFHeat-pipe cooled reactors belong to the group of nuclear reactors using heat pipes filled with liquid metals (such as sodium or potassium) to cool the core. Due to the passive heat removal system, there is no need to use closed loops with pumps, and the reactor can be operated with reduced operational requirements. Consequently, this system can be used in remote locations without access to an electrical grid, or it can be used for space applications.This paper deals with a neutronic study of the Special Purpose Reactor Design-B concept from the Idaho National Laboratory. Using Monte Carlo code Serpent 2 and ENDF/B VIII.0 library, a fixed-temperature model was created to calculate the safety characteristics of the system. This included reactivity coefficients, power distribution, neutron flux spectrum, and criticality safety. In a simplified depletion calculation, an effect of fuel depletion on safety systems was determined as well as a decay heat
LIQUID-SOLID COUPLING RESPONSE OF SURROUNDING ROCK MASS OF LARGE-DIAMETER RIVER-CROSSING SHIELD TUNNEL
Get PDFThe purpose is to investigate the response of seepage field, displacement field and stress field in the surrounding rock mass during dynamic tunneling in soft soil area. Relied on a large-diameter river-crossing shield tunnel project, considering driving force, shield tail grouting pressure, and the friction resistance between the shield shell and the soil, a three-dimensional fine tunnel model considering the liquid-solid coupling effect in the soil during dynamic tunneling was established by employing the finite difference method. The response characteristics of pore water pressure, displacement and stress in the surrounding rock mass were obtained. The results show that during shield tunneling and shield tail grouting, the pore water pressure in the range of 0.5 times the hole diameter around the tunnel decreases and increases respectively due to the liquid-solid coupling in the surrounding rock mass. When the shield tunneling moves away, the pore water pressure of the soil near the vault decreases, and the pore water pressure near the tunnel arch bottom increases. The impact range of shield tail grouting on the vertical settlement of the upper soil is about 0.5 times the hole diameter. The shield tail grouting can effectively reduce the vertical settlement of the top soil and slow down the vertical uplift of the bottom soil. During shield tunneling the vertical stress distribution of the soil above the vault of the working position and around the excavation surface is funnel-shaped, and the vertical stress around the excavated tunnel decreases
TESTING OF CLOSE-RANGE PHOTOGRAMMETRY AND LASER SCANNING FOR EASY DOCUMENTATION OF HISTORICAL OBJECTS AND BUILDINGS PARTS
Get PDFIn contemporary times, technology has dramatically simplified the process of documenting cultural heritage objects. This paper aims to illustrate modern methodologies for documenting historical monuments by applying advanced technologies, as these case studies show. Two technologies were used: laser scanning and digital photogrammetry. The first subject of our study was a historically significant 16th-century building located in Jachymov, situated in the North-West region of the Czech Republic. The object was documented by laser scanning (BLK360) and using a standard digital camera Canon Powershot SX230 HS. The laser scanning data were post-processed using Cyclone Register 360 Plus, while photogrammetric point clouds were generated with Agisoft Metashape. The second objects were a building and a sculpture in the historical UNESCO city of Telč; here laser scanning instruments, digital photogrammetry and a new one low-cost ViDoc documentation system were use. Our study is focused on analyzing the sets of point clouds obtained from the data processing, conducted using CloudCompare to draw insights and conclusions. It turns out that the rapid development of techniques and technology makes it possible to use low-cost devices for sufficiently accurate and fast documentation; however, the mentioned ViDOC device can only be used for very close and small objects up to about 5 meters. For the documentation of sculptures, classic close-range photogrammetry is especially appropriate; for the documentation of buildings, laser scanners are suitable; the problem here is with hidden spaces and it is often necessary to use either a platform or a combination with photogrammetry using a drone, especially for the upper parts of the object
Experimental investigation of flow characteristics and performance parameters of a podded aft engine air intake
Get PDFThis experimental study investigates the flow characteristics and performance parameters of a podded intake in aft-engine configuration at the aerodynamic interface plane (AIP), which is a typical configuration of a generic twin-engine regional jet aircraft. A scaled model aircraft with the port side hollow nacelle is equipped with total pressure rakes positioned exactly at the AIP to obtain the total pressure recovery and distortion. Multiple flight configurations (landing, take-off, and climb-out) with varying angle of attack (AoA) and side slip angle (SSA) are considered; attention has been paid to those with undesirable effects to the flow approaching the engine, by deploying flaps, slats, spoilers, and landing gear compartment. The mass flow rate and thus the mach number at the AIP is adjusted by changing the size of the exhaust nozzle. The Reynolds number dissimilarity is partially compensated by transition band application on the fuselage as well as engine inlet
Assessment of structures repeatedly exposed to thermal loading and extinguishing water: a case study of a firefighting training facility
Get PDFWhen designing a new structure or assessing an existing one, the risk of fire and its effect on the structure must be considered. Structures are usually assessed for fire resistance at the design stage – i.e. before the possible exposure to fire. If structure is exposed to fire during its service life, a post-fire assessment must be conducted in order to evaluate whether the structure is still safe and reliable for use. The post-fire assessment is conducted quite regularly; however, the assessment is usually conducted for structures exposed to fire only once. This paper presents an interesting and unique case study of a post-fire structural analysis of a firefighting training facility exposed to cyclic fire loading and the effect of extinguishing water. The main conclusion of the study is that though means of protection are recommended, the structure still has a sufficient load-bearing capacity and can continue being used as a firefighting training facility in the future. Aside from the specific conclusions for the investigated structure, this paper presents the best practices and methods for the post-fire assessment of structures exposed to repeated fire loading, and can thus be used as a guidance by other engineers and researchers interested in this topic
Determining 3D coordinates based on the track geometry description
Get PDFThis paper is focused on the data description of the railway infrastructure. Its aim is to present the possibilities of constructing of linear elements representing tracks in 2D and their subsequent transformation into 3D using the parametric description of horizontal and vertical curves. The transformation is based on determining the spatial coordinates of the newly emerging 3D linear elements. This process is supposed to be implemented in such a graphical editor environment that allows the relevant data to be transferred to the the database based on the Multipurpose Railway Infrastructure Model. With the use of this data, it is possible to perform, among other things, the visualization of the railway infrastructure
Long-term experience of the thermo-active ground source system at the metro station Taborstrasse in Vienna
Get PDFFour of the stations newly opened during the underground extension of the U2 line in Vienna in 2008 have been covering a large part of their heating and cooling needs for now almost one and a half decades by using geothermal energy, which is generated by means of energy diaphragm walls, energy piles and energy bottom slabs of the station buildings. As this was the first infrastructure building of this type and scale worldwide at the time of construction, one of the diaphragm walls of the Taborstraße station was equipped with numerous sensors to obtain data sets for the thermo-mechanical long-term behavior of these wall elements for the very first time. Continuous measurements with automatic data recording were initially carried out from April 2008 until May 2011. In October 2020, the measurements were resumed with the existing sensors, this time manually and once a month, in order to carry out a long-term comparison of the measurement data and to create a basis for assessing the effects of the geothermal operation on its structural components. This paper gives an overview of the Taborstraße station with a focus on the thermally activated geostructures and their instrumentation. A comparison of the recorded generated energy with the predicted heating and cooling demand is discussed in the context of the energy data. In addition, the temperature and the strain behavior of the observed energy diaphragm wall is discussed based on the measurement data collected over a period of around 14 years of operational experience