CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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Thermophysical Properties of Air-PA66-Copper Plasmas for Low-Voltage Direct Current Switches
Get PDFThis paper presents the thermophysical properties of an air-PA66-copper mixture in thermal plasma. Equations based on mass action law, conservation of neutrality and perfect gas law are used to calculate particle number densities. Thermodynamic properties and transport coefficients were obtained from equilibrium compositions and computed using the Chapman-Enskog method. Radiative properties are described in terms of the total absorption coefficient and the net emission coefficien
Heat transfer characteristics of double pipe heat exchanger having externally enhanced inner pipe
Get PDFAn investigation on enhancement of heat transfer is carried out for a double pipe heat exchanger in which the outer wall of the inner pipe is provided with circumferential labyrinth passages. Rectangular and triangular cavities with fixed labyrinth tooth thickness, height, and pitch are considered and the effect of added labyrinth structures on the heat transfer characteristics is discussed. A two-dimensional steady numerical simulation is carried out using ANSYS-FLUENT software. The flow Reynolds number equals to 20 000 and 43 000 for the hot and cold fluids, respectively, while other fluid properties are constant. From the numerical analysis carried out in this work, it is identified that the added labyrinth passages in the heat exchange surface improve the heat transfer rate and can reduce the length of the heat exchanger. Numerical predictions agree well with the results obtained from the experiment conducted
The measurement of the influence of the adhesion loss on the dynamic load of the drive reaction rod on the roller rig
Get PDFThe dynamic behaviour and dynamic phenomena in traction drives of railway vehicle has been studied for decades. Generally, in these days the motivation for this research is to look for answers related with service problems, which has been risen, e.g. an overloading of mechanical components as wheelsets or an intention to improve control systems of traction drives of railway vehicles. This problematic has also motivated the research at the Faculty of Mechanical Engineering at the Czech Technical University (CTU) in Prague. Nowadays it is also usual, that the main research tool has been a simulation based on a mathematical model of a railway vehicle or its specific components, as testing on real vehicles is very demanding regarding costs. However, there is an alternative – a roller rig. At the CTU in Prague there has been modernized the second roller rig for purposes of measurement regarding the torsion dynamics research, to support PhD students for their theses and possibly to extend the education for students oriented on the railway vehicle’s design. This contribution brings results of measurements just from the problematics of torsion oscillations and dynamics. Specifically, further presented measurements are on the loss of the adhesion in the contact of the wheelset and rollers, as the substitution for the railway, its impact on the reaction rod overloading and study of the axle load influence on the transition phenomena
Benefits of remote control on the railway lines
Get PDFRailway transport in the Czech Republic largely uses transit corridors, which are significantly more used than the rest of the railway network. This assumption leads to an increase in the safety of these lines and gradual double-tracking. All these aspects lead to the fact that the given lines are controlled from dispatching centres, while other lines are controlled from regional dispatch offices. The above parameters also apply to other non-corridor but still busy lines. It can therefore be concluded that this trend of remote control brings significant operational and technological advantages. The most visible benefit is the personnel saving of operational employees, but another significant benefit, which is not so obvious at first glance, is the benefit of a more efficient organization and management of railway transport. This impact brings the effect of smoother traffic, which manifests itself in a lower burden on the environment, thanks to fewer train starts and stops, or there will be no complete stop, but only a reduction in train speed. Furthermore, this influence is evident in the more frequent overtaking of trains not in railway stations, but in inter-station sections. All these advantages lead to an increase in an important operational indicator, which is the throughput of the track
The influence of the construction of tram fronts on the consequences of accidents with passenger cars
Get PDFIn recent years, there has been a large increase in passenger and public transport in cities. An increase in traffic flow results in an increasing risk of accidents. Manufacturers and operators of trams are increasingly subject to higher requirements for ensuring the safety of vehicles. Vehicle safety can be divided into two groups: active and passive safety. Systems and elements of active safety are intended to reduce the risk of accidents. Systems and elements of passive safety are intended to minimize the consequences of accidents. The requirements for the passive safety of newly designed railway vehicles are described in standard EN 15227. Standard EN 15227 was created due to the effort to protect passengers and crew inside railway vehicles in the event of an accident, so it is a so-called self-protection. The standard EN 15227 does not stipulate any requirements for so-called partner protection. Partner protection means an approach in which the vehicle protects passengers inside and outside the vehicle with its deformation elements.This article deals with the issue of how the construction of the front of tram vehicles designed according to the requirements of the standard EN 15227 will affect the consequences of tram´s accidents with passenger cars. The first part of the article describes the requirements of the standard EN 15227 for newly designed trams. Than it describes the creation and evaluation of tram accident statistics in the Czech Republic for the years 2016 to 2018 with regard to the types of collision vehicles, collision directions and consequences of accidents. From the results of the evaluation of the accident statistics, a collision scenario was determined, in which the passengers inside cars were most often injured. The last part of the article is devoted to the creation of simulation models of accidents of three trams with a car and evaluation of simulation calculations with regard to the risk of injury to car´s driver in an accident with trams using human biomechanical criteria
Geophysics for underground engineering
Get PDFThe growth of underground engineering brought a need for the use of geophysical methods for research of underground constructions rather different in approach compared to that of civil engineering. These changes relate to surface measurement on the one hand and the development of new specialised methods used for underground work on the other. The results of a complete documentation of mining work, the application of the resistivity methods used underground and also the use of 3D electrical resistivity tomography, are all presented here
AN INVESTIGATION OF DAMPING MODIFICATION FACTORS CORRESPONDING TO DIFFERENT DAMPING RATIOS FOR SDOF SYSTEMS
Get PDFThe damping ratio is an important parameter in dynamic analyses and plays a key role in the design of building structures. Elastic response spectra are widely used in this design to describe the earthquake action in specific site classes. 5% damped response spectra are generally used for most of the conventional structures. However, other types of structures may not have a damping ratio of 5% and can have much lower or much larger damping ratios. The damping ratio is recommended at about 5% for concrete structures whereas it is estimated at 2% for steel structures. Tall slender buildings may have much lower damping ratios and low-rise buildings may be designed using much larger damping ratios than 5%. For these types of buildings, elastic response spectra are modified to account for different levels of damping ratios. This study proposes the damping modification factors (DMFs) which are computed using 5% response spectra as the benchmark. A strong ground motion set has been selected for the stiff site class and the displacement, pseudo-velocity, and pseudo-acceleration response spectra have been computed for single-degree-of-freedom (SDOF) systems. DMFs have been obtained in terms of these spectra and 3%, 10%, 20%, and 30% damping ratios have been considered. Variations of DMFs with different damping ratios have been obtained graphically. It can be seen from the results that DMFs are sensitive to the vibration period of the SDOF system
CASE STUDY ON THE LARGE DIAMETER PIPE JACKING FOR UTILITY TUNNEL
Get PDFPipe jacking have been widely used in utility tunnel constructions as an environment-friendly method in China. This study is focus on the critical technologies used in the pipe jacking for the utility tunnel in Huanggang Mingzhu road. The inner and outer diameter of this utility tunnel are 4m and 4.8m respectively, which is the largest circular pipe jacking project in China at present. This utility tunnel is designed under the urban main road with a heavy traffic, so the control accuracy of pipe jacking construction is required to be high. According to the characteristics of the project and actual construction technical measures, the key construction technologies including pipe jacking equipment, launching of small spacing, slurry circulating, the drag reduction technology, and the control of surface settlement are discussed in this paper. Meanwhile, the jacking force and ground settlement during pipe jacking construction are monitored. The results show that the selected pipe jacking machine has good adaptability to the geological conditions of the project. The actual jacking force is much smaller than the theoretical value, and the two intermediate jacking stations are not activated. In addition, the road surface deformation is -8–5mm during the whole process of pipe jacking construction, which has no impact on surface traffic
CONSTRUCTION VERIFICATION OF UNDER-BEARING ARCH BRIDGE BASED ON CONSTRUCTION MONITORING AND TEST
No full textIn this paper, a bottom-bearing arch bridge is taken as an example to carry out the bridge construction monitoring and load tests. In order to ensure the safety of the arch bridge structure in construction and reach the internal force state of the bridge, in the construction monitoring, the construction process of the main girder type and stress, construction error and safety state is monitored. At the same time, in order to verify whether the bridge can meet the design requirements, static and dynamic load tests are carried out after the bridge is completed. The results of construction monitoring show that the stress state of the structure during the construction process is basically consistent with the theoretical calculation and design requirements, and both meet the design and code requirements. The final measured stress state of the structure is within the allowable range of the beam and arch composite bridge, and the stress state of the structure is normal and meets the code requirements. The results of load test show that the measured deflection values of the middle section of the main girder of the test hole are all less than the theoretical calculation values, and the deflection is between 1.54~3.40 mm, indicating that the bearing capacity of the structure meets the design requirements. In addition, under the four working conditions, the measured values of the transverse strain of the main girder are all less than the theoretical values, and the values are all positive. The stress at the measured points is in the tensile state, which meets the design requirements, indicating that the structure has a good elastic recovery ability after unloading. This study can provide important reference value for the construction and design of the same kind of under-bearing arch bridge
Electrical Erosion Resistance of Graphene Reinforced Cu-W Circuit Breaker Contact Materials under 5 kA Arc
Get PDFThis work integrates experimental and MD simulation approaches to study the role of graphene in G-Cu-W composites. Arcing tests were conducted on G-Cu-W and Cu-W contact samples under a 5kA peak current. Experimental results show that adding graphene leads to a lower surface roughness of the sample following arcing. MD simulation results indicate that the G-Cu-W model exhibits a smoother surface and fewer lost metal atoms than the Cu-W model due to the protective effect of graphene layer