Number of found documents: 386
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Methodology of Controlled Crack Introduction in Cementitious Materials
Schreiberová H.; Fládr J.; Trtík T.; Chylík R.; Kohoutková A.
2021 - English
Crack formation is a common and generally inevitable phenomenon in the field of concrete structures. On the other hand, the ever-increasing demand for sustainable construction, thus the structures durability, has led researchers to propose and investigate various crack-sealing methods. This study deals with the key aspect of these investigations – the in-vitro creation of cracks. A large number of the conducted studies have been carried out on artificially cracked specimens, and various methodologies of the controlled crack introduction were presented; however, no specific method was clearly preferred. In this paper, several approaches to the crack introduction are applied: cracking through compressive loading, tensile loading, and 3-point bending. Further, different types of specimens are presented: plain concrete, reinforced with short and long steel fibers, and reinforced with steel rod. The achievable crack characteristics, such as widths or its stability over time, are evaluated and compared. This study thus provides valuable overlook of the possible approaches to the controlled crack creation and points out their potential and limitations. Based on the comparisons presented in this paper, the long steel fiber reinforced concrete specimens subjected to 3-point bending are identified as the most appropriate method of crack induction. Keywords: concrete; controlled cracking; self-healing; non-destructive testing Available in digital repository of ČVUT.
Methodology of Controlled Crack Introduction in Cementitious Materials

Crack formation is a common and generally inevitable phenomenon in the field of concrete structures. On the other hand, the ever-increasing demand for sustainable construction, thus the structures ...

Schreiberová H.; Fládr J.; Trtík T.; Chylík R.; Kohoutková A.
České vysoké učení technické v Praze, 2021

Concentration and size distribution of solid particle emissions from oxy-fuel combustion of biomass in a fluidized bed
Červený O.; Vybíral P.; Hemerka J.; Mareš L.
2021 - English
The presented work summaries results of measurement of solid particle emissions from experimental 30 kW combustion unit, which has been used for research of oxy fuel combustion of biomass in fluidized bed. Keywords: solid particle emissions; oxy-fuel combustion of biomass in fluidized bed; impactor; particle size distribution Available in digital repository of ČVUT.
Concentration and size distribution of solid particle emissions from oxy-fuel combustion of biomass in a fluidized bed

The presented work summaries results of measurement of solid particle emissions from experimental 30 kW combustion unit, which has been used for research of oxy fuel combustion of biomass in fluidized ...

Červený O.; Vybíral P.; Hemerka J.; Mareš L.
České vysoké učení technické v Praze, 2021

Study on pervious recycled aggregate fiber-reinforced concrete for airfield pavement
Novák J.; Chylík R.; Trtík T.; Kohoutková A.
2020 - English
For the last several years, the attention has been devoted to the development of ecofriendly construction materials with the aim to reduce the environmental impact of construction. The integral part of this development is to find applications for which the recycled materials could be used efficiently. The presented study deals with the development of recycled aggregate fibre reinforced concrete which is going to be used for an innovative precast concrete pavement system. The system is being developed recently at Czech Technical University in Prague with the aim to provide a system for airfield pavement with rapid construction and recycled material utilization. The investigated material is going to be used for construction of a sub-base course which is underneath a surface course of precast concrete elements. Within the scope of the work,standard laboratory tests were conducted with the aim to observe mechanical properties of recycled aggregate fibre reinforced concrete. The obtained findings showed that the material exhibits ductile behaviour likely due to very long polypropylene fibres used for strengthening concrete matrix. On the contrary, the tested material has low modulus of elasticity in comparison with conventional concrete. Subsequently, the pilot construction of the sub-base course was carried out in order to examine both concrete mixture preparation and concrete course installation in practice. The obtained findings showed that a compaction ratio of the material is about 20%. Moreover, a flat surface of the sub-base course was hard to achieve considering the used manufacturing technology. Keywords: pervious concret; fiber reinforced concrete; airfiled pavement; recycled aggregate; flexural strength Available in digital repository of ČVUT.
Study on pervious recycled aggregate fiber-reinforced concrete for airfield pavement

For the last several years, the attention has been devoted to the development of ecofriendly construction materials with the aim to reduce the environmental impact of construction. The integral part ...

Novák J.; Chylík R.; Trtík T.; Kohoutková A.
České vysoké učení technické v Praze, 2020

A comparative study of synchronverter stability
Vetoshkin L.; Müller Z.
2020 - English
Electric grids, after a large scale installation of renewable energy sources, have dramatically changed. One of the major concerns in the operation of the modern power system is low grid inertia. Different approaches are being proposed to overcome this challenge. However, the prevalent idea is to introduce virtual inertia to the system using a sophisticated control strategy of power electronics in the electric grids. This paper investigates the synchronverter, which is a possible solution to the mentioned problem. The first chapter briefly describes the problem and the synchronverter control strategy of power converters. The second chapter provides a mathematical model of the synchronverter in d-q frame connected to an infinite bus. Furthermore, it analysis the small signal stability of the synchronverter. The third chapter gives a brief overlook of small signal stability of traditional vector control. Moreover, this chapter provides a comparison between the researched approach and the conventional one. Keywords: Mathematical model; Inverters; Virtual Inertia; Synchronverter Available in digital repository of ČVUT.
A comparative study of synchronverter stability

Electric grids, after a large scale installation of renewable energy sources, have dramatically changed. One of the major concerns in the operation of the modern power system is low grid inertia. ...

Vetoshkin L.; Müller Z.
České vysoké učení technické v Praze, 2020

Photodetectors for cylindrical illuminance sensor
Kozlok M.; Žák P.
2020 - English
The paper describes the basic principles of illuminance measurement and possibilities of multi-point measurement of light field spatial properties. Based on the research, the description contains three steps of the development of a multi-point cylindrical illuminance sensor and their hardware architectures. The development aims to create a functional prototype that would allow measurement in addition to one scalar quantity of cylindrical illuminance also the prevailing direction of light in one plane in space, symmetrical, diffuse component, and visual appearance indicator calculated from the ratio of horizontal and cylindrical illuminance. Keywords: photodiode; photodetector; illuminance; cylindrical illuminance; illuminance vector Available in digital repository of ČVUT.
Photodetectors for cylindrical illuminance sensor

The paper describes the basic principles of illuminance measurement and possibilities of multi-point measurement of light field spatial properties. Based on the research, the description contains ...

Kozlok M.; Žák P.
České vysoké učení technické v Praze, 2020

Supplementary damping control design for large scale PV power plant at transmission level interconnection
Isbeih Y.J.; Shawky El Moursi M.; Lotfi M.; Catalao J.P.S.; Abdelwahab M.
2020 - English
The deployment of large scale photovoltaic (PV) power generation has been witnessed in several countries worldwide with different installed capacities. Accordingly, codes and regulations to ensure secure and economical operation have been revised to address the challenges related with PV integration into electrical networks. This paper presents an H∞ mixed sensitivity robust control design for enhancing the overall damping of low frequency oscillations. The presented architecture will implement the output signal of the power oscillator damper (POD) at the control loop of the PV-based solar power plant. The effectiveness of the proposed approach is tested using the New-England, 10machines test system. Available in digital repository of ČVUT.
Supplementary damping control design for large scale PV power plant at transmission level interconnection

The deployment of large scale photovoltaic (PV) power generation has been witnessed in several countries worldwide with different installed capacities. Accordingly, codes and regulations to ensure ...

Isbeih Y.J.; Shawky El Moursi M.; Lotfi M.; Catalao J.P.S.; Abdelwahab M.
České vysoké učení technické v Praze, 2020

Matematický model provozu deskového otopného tělesa
Boháč J.; Bašta J.
2020 - Czech
Příspěvek shrnuje poznatky týkající se experimentálního sledování a modelování nestacionárního chování otopných těles. Je popsán komplexní model využívající aproximaci podle Strejce a také matematický diskrétní ARX black-box model v softwaru Matlab (ukázka pro deskové otopné těleso 10 – 500 x 1000), včetně jejich předpokladů a okrajových podmínek. Cílem bylo nalezení takového způsobu stanovení rozhodujících parametrů popisujících dynamiku otopných těles a vlastní vyhodnocení dynamického děje, na jehož základě by bylo možné aplikovat model pro různá otopná tělesa, a to bez nutnosti jejich měření v akreditovaných laboratořích. Uvedený model je nástroj poskytující možnost zjišťovat dynamiku velice rychle a takto získané údaje mohou být základem pro návrh a optimalizaci funkce regulátorů tepelného výkonu, ale také podkladem pro jejich optimální součinnost například s konkrétním typem otopného tělesa. Keywords: dynamics; modelling; Matlab; radiator; control Available in digital repository of ČVUT.
Matematický model provozu deskového otopného tělesa

Příspěvek shrnuje poznatky týkající se experimentálního sledování a modelování nestacionárního chování otopných těles. Je popsán komplexní model využívající aproximaci podle Strejce a také matematický ...

Boháč J.; Bašta J.
České vysoké učení technické v Praze, 2020

Light trespass in street LED lighting systems
Bálský M.; Terrich T.
2020 - English
Increasing the efficiency of lighting systems can be achieved not only by increasing the luminous efficacy of the light sources, but also by reducing the useless luminous flux, which is referred to as the light trespass. The luminous flux is in artificial lighting systems generated from electrical power and therefore the light trespass means the loss of electrical power. The paper deals with the possibilities of increasing the efficiency of street lighting by optimizing the luminous flux distribution of luminaires and its influence on the light trespass. Keywords: Street Lighting; Luminaire; Light Trespass; Luminous Flux; Luminous Intensity Distribution; Light Emitting Diode; High Pressure Sodium Lamp Available in digital repository of ČVUT.
Light trespass in street LED lighting systems

Increasing the efficiency of lighting systems can be achieved not only by increasing the luminous efficacy of the light sources, but also by reducing the useless luminous flux, which is referred to as ...

Bálský M.; Terrich T.
České vysoké učení technické v Praze, 2020

Comparison of power control method for B4 converter connected to unbalanced grid
Simek P.; Valouch V.
2020 - English
The aim of the paper is to present a power control of a three-phase inverter with only four inverter legs (connections B4) connected to an unbalanced grid. The results obtained by the predictive power control with a finite set of control values, the results obtained using a modified direct power control strategy, and the results obtained using a generalized predictive control are compared and discussed. Keywords: power control; B4 converter; unbalanced grid; modified reactive power theory; predictive control component Available in digital repository of ČVUT.
Comparison of power control method for B4 converter connected to unbalanced grid

The aim of the paper is to present a power control of a three-phase inverter with only four inverter legs (connections B4) connected to an unbalanced grid. The results obtained by the predictive power ...

Simek P.; Valouch V.
České vysoké učení technické v Praze, 2020

Human vs. Automation - Who Drives The Future?
Jirovský V.
2020 - English
The sprint in technology during the last hundred years has brought us to new questions in almost all subjects of science, including transport. This brought question outstanding the greatest challenge since switch from horses to cars andmotorcycles – autonomous road transport. The answer whether or not we shall follow this path and put driving aside to the position of enjoyment for wealthy, similarly as we did with horses, is not clear. Transport sector is highly interdisciplinary and affects the whole population, in minor cases only indirectly. This makes it sensitive to political decisions, investments, marketing and media. Therefore, it is hard to provide strictly single-subject related scientific answer, because due to the nature of transportation there is simply none. The following paper picks up aspects of several disciplines influencing design of autonomous vehicles and systems including decision making process in transport and trying to bring a focus to the path to follow in automation features in complex socio-technological system of road transport. Keywords: autonomous vehicles; holistic transport; socio-technological system; driver reliability; Mobility-as-a-Service; mobility Available in digital repository of ČVUT.
Human vs. Automation - Who Drives The Future?

The sprint in technology during the last hundred years has brought us to new questions in almost all subjects of science, including transport. This brought question outstanding the greatest challenge ...

Jirovský V.
České vysoké učení technické v Praze, 2020

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