No (6380)
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6380
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Aspects of Dosage from Short and Long Duration Emissions
Robins, A.; Hayden, P.; Gallacher, D.; Pace, S.; Chaloupecká, Hana
2022 - English
The objectives of this work were to use wind tunnel concentration measurements to describe the structure of dispersing clouds from an elevated source in a deep turbulent boundary layer and to develop scaling rules that reduce the results to a universal form. The experiments were carried out in the EnFlo meteorological wind tunnel at the University of Surrey. Ensembles of between 100 and 200\nrepeat emissions were used, emission durations between 0.067 and 1.02s and a reference flow speed of 2ms-1. The fetch studied extended to about six source heights downwind (about two boundary layer depths). The structure of the evolving clouds was analysed to determine time of flight, along-wind spread and dosage and to compare the dosage behaviour with the concentration field in a plume from the same source. This illustrated how the two were related and how cloud dosage statistics (mean and\nstandard deviation) could be derived from plume data. It also demonstrated that much larger ensembles were required to reduce the statistical uncertainty in the mean cloud properties. The next steps involve testing these conclusions in a wider range of flow and dispersion conditions, in the presence of obstacles or complex urban areas.
Keywords:
wind tunnel; dose; dosage; gas releases
Available at various institutes of the ASCR
Aspects of Dosage from Short and Long Duration Emissions
The objectives of this work were to use wind tunnel concentration measurements to describe the structure of dispersing clouds from an elevated source in a deep turbulent boundary layer and to develop ...
Nanoparticels from brake pads wear
Švábenská, Eva; Roupcová, Pavla; Friák, Martin; Schneeweiss, Oldřich
2022 - English
Exposure to particulate air pollution has been associated with a variety of health problems. One of the main\nsources of metal-rich airborne particulate pollution in roadside environments are brake-wear emissions. The \nscanning electron microscopy (SEM) and transmission electron microscopy (TEM), Mössbauer spectroscopy \n(MS), X-ray powder diffraction (XRD) was used to a make quantitative evaluation of wear particles in two \nsamples. Sizes, morphologies, oxidation state, and trace element compositions of wear particles were\ninvestigated using combination of several methods revealed high concentrations of Fe species and phases, \noften associated with carbonaceous material. SEM and TEM observations show that brake wear particles with \na size of tens to hundreds of nm mainly form particle agglomerates. However, ultrafine (<100 nm) particles are \nlikely to pose a health threat after inhalation and/or ingestion.
Keywords:
Wear particles; analysis; TEM; iron oxides; metallic particles
Available at various institutes of the ASCR
Nanoparticels from brake pads wear
Exposure to particulate air pollution has been associated with a variety of health problems. One of the main\nsources of metal-rich airborne particulate pollution in roadside environments are ...
Numerical simulations of aeroelastic instabilities in turbine blade cascade by modified Van der Pol model at running excitation
Pešek, Luděk; Šnábl, Pavel; Prasad, Chandra Shekhar; Delanney, Y.
2022 - English
Apart from rotary test rig for evaluation of structural dynamics of the bladed wheels, the control flutter experiments has been performed on the linear cascade model in the subsonic wind tunnel in the Institute of Thermomechanics, of CAS, in Prague. These experiments are aimed at stability evaluation of the cascade at running waves or at stability limit testing by flow speed changes or by force impulses of blades. The onset of flutter and its spreading in the cascade are observed, too. The linear cascade model consists of five NACA010 blades. All the blades can be separately excited with electromagnetic torque excitation mechanism and all of them are instrumented to measure the aerodynamic moments which can be used to calculate the aerodynamic work. A more details about the linear blade cascade experimental set up can be found in [1-2]. To predict a dynamic behaviour in the blade cascade, we have been dealing with simplified theoretical modelling of the aeroelastic instability in turbine blade cascade [3-5]. Due to the application of the reduced cascade model consisting of simple elements – springs, rigid bodies, linear dampers – and aeroelastic forces introduced by analytical Van der Pol model, it facilitates to study the dangerous states of vibration of such complicated turbine parts [6-9]. This study is aimed at examination of aeroelastic instabilities of 10-blade cascade at running excitation that arises due to the wakes flowing from stator the blades to the rotating blades. They cause forced excitation in the narrow frequency range.
Keywords:
rotary test; structural dynamics; bladed wheels
Available at various institutes of the ASCR
Numerical simulations of aeroelastic instabilities in turbine blade cascade by modified Van der Pol model at running excitation
Apart from rotary test rig for evaluation of structural dynamics of the bladed wheels, the control flutter experiments has been performed on the linear cascade model in the subsonic wind tunnel in ...
Estimation of damping in human vocal folds vibration: measurements in vivo and on model
Horáček, Jaromír; Radolf, Vojtěch; Bula, Vítězslav; Košina, Jan; Geneid, A.; Laukkanen, A. M.
2022 - English
This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal folds damping is important for testing and further development of mathematical modelling of phonation. The measurements of the damping ratio, based on high-speed videolaryngoscopic registrations, were realized in vivo on a male subject and in vitro using an originally developed silicon replica of the human vocal folds. In both cases the results show remarkable decrease of vibration frequency of the vocal folds and increase of damping ratio D in the phonation offset limiting to the values D=0.12 in vivo measurement and D=0.11 in vitro measurement. The results for vocal folds’ damping are in good agreement with previous measurements performed in humans using different methods.
Keywords:
phonation offset; high-speed videolaryngoscopy
Available at various institutes of the ASCR
Estimation of damping in human vocal folds vibration: measurements in vivo and on model
This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal folds damping is important for testing and further ...
Experimental investigation of the frequency-modal properties of the measuring container for LUNA mission
Zolotarev, Igor; Bula, Vítězslav; Šnábl, Pavel; Snížek, Jan; Souček, Jan
2022 - English
This paper continues investigations of the measuring equipment for space missions. The frequency-modal properties of the measuring container for LUNA mission were obtained by experimental investigation.
Keywords:
modal analysis; natural frequencies; modes of vibration
Available at various institutes of the ASCR
Experimental investigation of the frequency-modal properties of the measuring container for LUNA mission
This paper continues investigations of the measuring equipment for space missions. The frequency-modal properties of the measuring container for LUNA mission were obtained by experimental ...
Identification of material constants of rubber damping segments by modal analysis for railway rubber-resilient wheels
Šulc, Petr; Šnábl, Pavel; Pešek, Luděk; Bula, Vítězslav
2022 - English
In this paper, an experimental and numerical modal analysis is described to assess two rubber compounds for the damping segments of a railway wheel. The subject of this comparison is materiál parameters such as Young’s modulus and loss factor for both compounds in the frequency range up to 6.5 kHz. From this comparison, an idea of the damping, stiffness and durability of these rubber segment materials inside these wheels is obtained.
Keywords:
modal analysis; rubber; railway wheel; damping segment
Available at various institutes of the ASCR
Identification of material constants of rubber damping segments by modal analysis for railway rubber-resilient wheels
In this paper, an experimental and numerical modal analysis is described to assess two rubber compounds for the damping segments of a railway wheel. The subject of this comparison is materiál ...
Stone surface topography of Prague historic monuments over the centuries
Kovářová, K.; Cihla, Michal; Malát, R.; Semerád, M.; Tryml, M.
2022 - English
Stonemasons tool traces on stone surface are undoubtably a significant part of monument historic value. As any other profession, stonemasons craft develops over time and has its own specifics in every period. Each work has its own unique pattern and bears traces of individual stonemason workshops, tradition, etc. The study of building stone cutting is based on evolving methods of mechanoscopy and analytical traceology. Stone traceology deals with traces in material and the subsequent reconstruction of tools and the processes of stoneworking. The interpretation of data in terms of determining the actual trace is called a mechanoscopy. When studying a stone surface, the latest 3D modelling technology is used with subsequent analyses by means of Global Mapper software. The use of these methods enables reconstruction of the craftsman’s tools. The presented article is an extract of a study that systematically maps the stone cutting work in the territory of Prague from the oldest buildings to the present day. For example, stonework in 9th century Prague was gradually evolving from simple stone block modelling to sophisticated cutting of blocks in the 12th century. This information can be very useful in the process of monument care.
Keywords:
stone topography; Prague; craftmanship; stonemason tool; tool traces
Available at various institutes of the ASCR
Stone surface topography of Prague historic monuments over the centuries
Stonemasons tool traces on stone surface are undoubtably a significant part of monument historic value. As any other profession, stonemasons craft develops over time and has its own specifics in every ...
Creep of oak dowel: various loading and environmental conditions
Hasníková, Hana; Kunecký, Jiří; Hataj, M.
2022 - English
For research of timber joints, the crucial role in force distribution inside the joint is played by distribution and variability of stiffness of the dowels. Not only the instant stiffness, but the one that we can encounter after some longer period. Also, this value and its statistical distribution is influenced by many other factors, however, humidity and temperature are in timber (oak) dowels of utmost importance. In the work results of a creep experiment made using a special testing rig is presented. It has been found, that biggest changes in creep behavior are in case if very humid conditions are present, and, also, that cycling the temperature in high humidity conditions can produce about 104% of the original instantaneous displacement. The result is not surprising, however, new insights are made thanks to relatively high number of samples and ability to produce some statistics. Another outcome is relation of dowel stiffness in time to the level of applied stress, which is quantified in the article.
Keywords:
oak dowel; creep; humidity
Available at various institutes of the ASCR
Creep of oak dowel: various loading and environmental conditions
For research of timber joints, the crucial role in force distribution inside the joint is played by distribution and variability of stiffness of the dowels. Not only the instant stiffness, but the one ...
Comparison of mechanical properties of wood determined by local gently destructive tests and fully destructive tests on building elements
Drdácký, Miloš; Kloiber, Michal; Valluzzi, M. R.; Casarin, F.
2022 - English
Demolition or repair of historic buildings is a valuable source of test materials for testing nondestructive and gently destructive methods for estimating the mechanical properties of built-in wood. The article uses the results of one such opportunity, when it was possible to study the mechanical properties of wood obtained by local measurements on a larger sample of historic and new wooden beams and compare them with the properties calculated from destructive tests of structural elements. Thirty-one wood elements (nineteen recovered from disassembled buildings and twelve new) were subjected to considerately destructive local tests using a loading mini-jack method. In this method, a small loading jack is inserted into a precisely drilled hole and a load test of the wood in compression along the fibers is performed on a part of the hole wall while measuring the achieved deformation under load. Red and white firs, and pine species constituted the recovered elements - red fir and larch the new ones. Destructive tests (in bending and compression) were also carried out on ten recovered and six new elements, and results were correlated with those of considerately destructive tests. Comparison of the assessed mechanical properties shows reasonably good correlation and promising conclusions for practical applications.
Keywords:
considerately destructive tests; mini-jack method; destructive tests; assessment of mechanical characteristics of wood; historic timber
Available at various institutes of the ASCR
Comparison of mechanical properties of wood determined by local gently destructive tests and fully destructive tests on building elements
Demolition or repair of historic buildings is a valuable source of test materials for testing nondestructive and gently destructive methods for estimating the mechanical properties of built-in wood. ...
Effect of molecular structure on liquid crystalline behaviour for chiral lactic acid derivatives
Mironov, Sergei; Bubnov, Alexej
2022 - English
Liquid crystals are self-organizing materials that have great potential for practical applications. The relationship has not been fully established and understood despite numerous studies. We discuss a relatively broad subclass of calamitic chiral lactic acid derivatives and provide specific examples of effective tuning of their mesomorphic and electro-optical behaviour using various types of lateral substitution placed on the molecular core.
Keywords:
chiral liquid crystals; lateral substitution; ferroelectric smectic phase; spontaneous polarization; lactic acid
Available at various institutes of the ASCR
Effect of molecular structure on liquid crystalline behaviour for chiral lactic acid derivatives
Liquid crystals are self-organizing materials that have great potential for practical applications. The relationship ...
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