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Data availability: The complete experimental measurements presented in Figs. 6 and 7, along with some of the used Matlab codes and Simulink models, are located on the following link: https://drive.google.com/file/d/1OlNfo56QIgJUaKioGhenOJ28WNt88y3/view?usp=sharing. It can be downloaded with the permission of the authors.

This work is the result of a problem of premature development of rail corrugation found on a new metro line. As urgent solutions, a rail grinding was carried out and friction modifier started to be applied. Experimental corrugation measurements have been taken periodically in this line at 60 control points since 2018, and an extensive database has been collected since then. As a second stage, a computationally efficient new model has been developed to predict corrugation growth under different running conditions. The aim of this work has been to obtain feasible solutions to delay corrugation growth in metro type lines. The authors gratefully acknowledge financial support from the European Horizon 2020 Joint Technology Initiative Shift2Rail (IN2TRACK3) [101012456], from the Spanish Research Ministry MICINN/Economy and Competitiveness Ministry MINECO and MCI/AEI [PID2019-109483RB-I00], including funding by the FEDER-ERDF European Regional Development Fund, and from the Basque Government [IT1764-22, PRE_2021_2_0047, KK-2023/00029].

The COVID-19 pandemic highlighted the importance of indoor air quality (IAQ) and ventilation, which researchers have been warning about for years. During the pandemic, researchers studied several indicators using different approaches to assess IAQ and diverse ventilation systems in indoor spaces. To provide an overview of these indicators and approaches in the case of airborne transmission through aerosols, we conducted a literature review, which covered studies both from before and during the COVID-19 pandemic. We searched online databases for six concepts: aerosol dispersion, ventilation, air quality, schools or offices, indicators, and assessment approaches. The indicators found in the literature can be divided into three categories: dose-, building-, and occupant-related indicators. These indicators can be measured in real physical spaces, in a controlled laboratory, or modeled and analyzed using numerical approaches. Rather than organizing this paper according to these approaches, the assessment methods used are grouped according to the following themes they cover: aerosol dispersion, ventilation, infection risk, design parameters, and human behavior. The first finding of the review is that dose-related indicators are the predominant indicators used in the selected studies, whereas building- and occupant-related indicators are only used in specific studies. Moreover, for a better understanding of airborne transmission, there is a need for a more holistic definition of IAQ indicators. The second finding is that although different design assessment tools and setups are presented in the literature, an optimization tool for a room’s design parameters seems to be missing. Finally, to efficiently limit aerosol dispersion in indoor spaces, better coordination between different fields is needed.

U ovom diplomskome radu analiziran je utjecaj vakuuma na koeficijent prigušenja i efikasnost uređaja za žetvu vibracija. Također, konstruiran je i karakteriziran sustav koji se sastoji od primarne strukture sa integriranim uređajem za žetvu vibracija koji ujedno služi i kao dinamički prigušivač vibracija. Mehanički dijelovi uređaja konstruirani su tako da budu pogodni za izradu tehnologijom 3D ispisa i to upotrebom 3D pisača, Prusa i3 MK3S. Uređaj je tako konstruiran da se unutrašnjost uređaja za žetvu vibracija može evakuirati korištenjem standardne vakuum pumpe kakva se koristi za servisiranje klima uređaja. Također konstrukcija je osmišljena na način da se dinamički odziv može dobro aproksimirati matematičkim modelom za linearni vibracijski sustav s dva stupnja slobode gibanja. To je postignuto korištenjem računalnih CAD/CAM alata za modeliranje i konstruiranje, kao i alata za analizu slobodnih vibracija mehaničkih sustava s raspodijeljenim parametrima metodom konačnih elemenata. Nadalje, uređaj je osmišljen na način da se za pretvorbu mehaničke energije u električnu koriste dva paralelno povezana elektrodinamička pretvornika PBA Systems CVC40–HF–6.5. Konačna konstrukcija je izrađena, sklopljena a zatim karakterizirana mjerenjem prijenosne funkcije na slobodno ovješenom uređaju između napona narinutog na terminale zavojnice jednog od pretvornika i napona induciranog na terminalima zavojnice drugog pretvornika. Mjerenjima je utvrđen utjecaj vakuuma na prigušenje unutar elektrodinamičkih pretvornika. Analitički su definirani optimalni parametri sustava sa ciljem maksimiziranja razvijene korisne snage i minimiziranja vibracija primarne strukture u slučaju sa ili bez vakuuma unutar uređaja za žetvu vibracija. Usporedbom korisnih snaga za oba slučaja definiran je utjecaj vakuuma na efikasnost uređaja. In this thesis the influence of vacuum on the damping coefficient and efficiency of a vibration energy harvester is analysed. Also, this thesis deals with design and characterization of a primary structure with integrated vibration energy harvester which also acts as a dynamic vibration absorber. Mechanical parts of the device are designed in such a way that they can be manufactured using 3D printing technology, in particular, using Prusa i3 MK3S 3D printer. The structure is designed in such a way that it can be evacuated using a standard vacuum pump that is ordinarily used for air conditioning systems maintenance. Also, the dynamic response of the structure is approximated using a mathematical model assuming a two degrees of freedom linear mechanical system. This is achieved by using CAD/CAM tools for modelling of the mechanical parts of the device, and Finite Element Method (FEM) tools for the free vibration analysis of the flexible mechanical parts of the device. Furthermore, the harvester has been designed so that two electrodynamic transducers PBA Systems CVC40–HF–6.5 mounted in parallel can be used for the transduction of mechanical into electrical energy. The final design has been manufactured, assembled and characterized by measuring the frequency response function between the voltage applied to the electrical terminals of one of the two transducers and the voltage induced on the electrical terminals of the other transducer. Effect of vacuum on the damping coefficient of the two electrodynamic transducers has been defined experimentally. Optimal parameters of the system were found analytically which maximise useful power output and minimize the primary structure vibrations in cases with and without vacuum inside the energy harvester. Effect of vacuum on the energy conversion efficiency was evaluated by comparing the harvested energy in the case when the air is present in the energy harvester interior to the harvested energy in the case when its interior is evacuated.

The great expansion in offshore power plants is raising the concern regarding the cumulative effect of the electromagnetic field emissions caused by submarine power cables. In this sense, owners are required to predict these emissions during the permitting and consenting process of new power plants. This is a challenging task, especially in the case of HVAC three-core armored cables due to their complex geometry. Customarily, 2D approaches based on the finite element method (FEM) have been employed for evaluating the magnetic field emissions caused by these cables. However, inaccurate results are obtained since the phase conductors and armor twisting is omitted. This work develops, for the first time in the literature, an in-depth analysis of the magnetic field caused by this type of cable through an ultra-shortened 3D-FEM model, which is also faced to experimental measurements taken on an actual 132 kV, 800 mm2 three-core armored cable. Relevant conclusions are derived regarding the impact of the cable design on the magnetic field emissions, including material properties, as well as single and double-layer armors, presenting the proposed model not only as a valuable tool for predicting purposes, but also for optimizing cable design in terms of magnetic field emissions.

Bubbly liquids are widely present in the natural environment and industrial fields, such as seawater near the ocean bottom, the multiphase flow in petroleum reservoirs, and the blood with bubbles resulting in decompression sickness. Therefore, accurate measurement of the gas content is of great significance for hydroacoustic physics, oil and gas resources exploration, and disease prevention and diagnosis. Trace bubbles in liquids can lead to considerable changes in the acoustic properties of gas–liquid two-phase media. Acoustic measurements can therefore be applied for trace bubble detection. This study derived the reflection coefficient of acoustic waves propagating in a sandwich layering model with liquid, bubbly liquid, and liquid. The influences of gas contents on the reflection coefficient at the layer interface were analyzed based on theoretical calculations. It was revealed that the magnitude of the reflection coefficient and the frequency interval between its valleys have a quantitative correlation with the gas contents. Thus, a novel means to detect the contents of trace bubbles was proposed by evaluating the reflection coefficients. The reflection features of a thin layer with bubbly liquid were then studied through experiments. It was validated by acoustical measurements and theories that the reflection coefficient is considerably sensitive to the change of gas contents as long as the gas content is tiny. With the increasing gas content, the maximum value of the reflection coefficient increases; meanwhile, the frequency intervals between the valleys become smaller. However, when the gas content is extensive enough, e.g., greater than 1%, the effect of the change of gas content on the reflection coefficient becomes inapparent. In that case, it is not easy to measure the gas content by the acoustic reflection signals with satisfying precision. This proposed method has potential applications for the detection of trace gas bubble content in several scenarios, e.g., decompression illness prevention and diagnosis.

Monitoring transmission systems is a huge scientific focus to prevent any anomaly and malfunctioning damaging the system. Several methods were used to investigate the gears behaviour and mainly its state. And until the last century, vibrations signals were the most performing technique in this field. However, nowadays, other alternatives are considered more accurate and accessible such as controlling the motor current signals to study the behaviour of the mechanical system. Within this context, this paper aims to study the electromechanical interaction between a double stage of planetary gearboxes driven by an asynchronous machine. The model used is based on a Park transformation for modelling the asynchronous machine and a torsional model to describe the dynamic behaviour of the double-stage planetary gearbox. Through this approach, the numerical simulations illustrate the impact of the tooth gear defect on the signature of the motor current. The results obtained from the simulations will be presented in the time domain and the frequency domain using the fast Fourier transform and the Hanning window to highlight the mechanical frequencies in the phase current spectrum. This work will be distinguished by validating the numerical results using experimental measurements, which will be displayed in order to justify the sensitivity of the model developed. The authors would like to acknowledge the help provided by the project “Dynamic behaviour of gear transmissions in nonstationary conditions”, ref. DPI2017-85390-P, funded by the Spanish Ministry of Science and Technology. They would like to thank the University of Cantabria cooperation project for the doctoral training to Sfax University students.

The grinding process is commonly used as the final stage of processing. It is used to produce elements that require more tolerance and smooth surface. Considering other processing, such as turning or milling, grinding requires very high energy input per unit volume of material removal. A significant proportion of this energy in the process turns into heat in the grinding zone, which leads to increased temperature. This paper describes and compares two methods of temperature measurement in the cutting zone during surface grinding. The study aimed to determine the differences in the results of temperature measurements using an indirect method, using an analysis of thermal images, and a direct method, using a thermocouple. Two different sets of measurement apparatus were used in the experiment: a thermal imaging camera and a thermocouple with appropriately selected software. The factors affecting the errors obtained with each of the above measurement methods are discussed and the resulting differences in the results are discussed.

The thermal properties of parts obtained by 3D printing from polymeric materials may be interesting in certain practical situations. One of these thermal properties is the ability of a material to expand as the temperature rises or shrink when the temperature drops. A test experiment device was designed based on the thermal expansion or negative thermal expansion of spiral test samples, made by 3D printing of polymeric materials to investigate the behavior of some polymeric materials in terms of thermal expansion or contraction. A spiral test sample was placed on an aluminum alloy plate in a spiral groove. A finite element modeling highlighted the possibility that areas of the plate and the spiral test sample have different temperatures, which means thermal expansions or contractions have different values in the spiral areas. A global experimental evaluation of four spiral test samples was made by 3D printing four distinct polymeric materials: styrene-butadiene acrylonitrile, polyethylene terephthalate, thermoplastic polyurethane, and polylactic acid, has been proposed. The mathematical processing of the experimental results using specialized software led to establishing empirical mathematical models valid for heating the test samples from −9 °C to 13 °C and cooling the test samples in temperature ranges between 70 °C and 30 °C, respectively. It was found that the negative thermal expansion has the highest values in the case of polyethylene terephthalate and the lowest in the case of thermoplastic polyurethane.

This paper presents experimental results of the study of falling water film evaporation from water wall. The contribution is divided into several parts. The introduction is devoted to the theoretical part of the use, then the prototype of the water wall is presented and its most important parts are described. In order to verify the humidification performance of the water wall, experimental verification under laboratory conditions (climate chamber) was chosen. One task for the definition of water wall evaporation potential is to determine and develop the measuring system, which is clearly defined in article. The present document describes the methodology and boundary conditions during experiments. Plate heat exchanger ensured a water temperature in the system approximately 23 °C hot during all measurements. A total of 4 measurements were performed at different air temperatures and relative humidity. The results showed that at different temperatures and relative humidity of air, the water wall has a different humidification performance.

Combustion noise is relevant to current aviation, rocket, and ground-based gas turbine engines, as it contributes to environmental noise pollution and can trigger thermoacoustic instabilities. These consequences are particularly prevalent in lean, premixed, prevaporised combustors, which are designed to reduce nitrous oxide (NOx) emissions. As a result, there is a need to better understand the mechanisms that drive sound generation in such systems. There are two components to combustion noise: direct noise – generated by the unsteady heat release of a flame – and indirect noise – produced by the acceleration of entropic, vortical, or compositional inhomogeneities. Separation of the respective contributions has proven to be complex to achieve in real engines – for this purpose, model experiments have been developed. These are non-reacting experiments that use unsteady, synthetic perturbations to emulate the fundamental physics of combustion acoustics processes and provide clear data for comparison with theory. Indirect noise models have been theorised for compositional perturbations and experimental validation has been provided via the measurement of acoustic waves (i.e. the output), while assuming a constant compositional perturbation (i.e. the input). This thesis follows on from such experiments by simultaneously measuring both acoustic and compositional waves in a model setup, making use of numerical, analytical, and experimental studies. It first builds upon a previous model experiment through a numerical investigation on the generation, mixing, and convection of entropic and compositional waves generated by heat addition and gas injection. The computed temperature and mass fraction fields are compared with experimental results and inform the design of a new model setup – the Canonical Wave Rig (CWR). The CWR is then used to study direct and indirect noise under simplified, well-controlled conditions. Subsonic and sonic (choked) conditions are investigated for a convergent-divergent nozzle. Acoustic, entropic, and compositional perturbations are generated via the co-flow injection of air or methane into a low Mach number mean flow of air. Spontaneous Raman spectroscopy (1.5 kHz) is employed for the time-resolved measurement of the local concentration upstream of the nozzle. Single pulse experiments in the infra-sound range are used to validate the derived analytical model for direct noise due to co-flow injection. The measurement of non-reverberated indirect noise is made for the first time and is contrasted with results obtained via dereverberation (i.e. removing the effect of pressure build up due to acoustic reflections). Indirect noise transfer functions are calculated using the acoustic and compositional measurements, and issues pertaining to the methods applied are highlighted. Lastly, the pulse burst injection of methane at frequencies up to 250 Hz is presented. The goal of these experiments is to provide data at more realistic frequencies and amplitudes., Engineering and Physical Sciences Research Council (EPSRC), the School of Technology (Qualcomm Scholarship), and Rolls-Royce.

Due to recent advances, the numerical analysis of submarine three-core armored cables can nowadays be developed through the finite element method (FEM) in a small slice of the cable. This strongly reduces the computational burden and simulation time. However, the performance of this ultra-shortened 3D-FEM model is still to be fully assessed with experimental measurements. This paper focuses on this validation for an extensive variety of situations through the experimental measurements available in the specialized literature for up to 10 actual cables. In particular, it deals not only with relevant calculations at power frequency, like the series resistance and inductive reactance or the induced sheath current, but also with other aspects never analyzed before through 3D-FEM simulations, such as the zero sequence impedance, the magnetic field distribution around the power cable, as well as side effects due to the nonlinear properties of the armor wires. All this considering different armoring and sheath bonding configurations. Results show a very good agreement between measured and computed values, presenting the ultra-shortened 3D-FEM model as a suitable tool for the analysis and design of three-core armored cables, and opening the possibility to reduce the need of extensive experimental tests in the design stage of new cables. FEDER / Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (Spain) project ENE2017-89669-R Universidad de Sevilla (Spain) VI PPIT-US grant 2018/00000740

For 662, 1173, 1275, and 1333 keV gamma-ray energy, photon transmissions, linear attenuation coefficients, half value layer, tenth value layer, and mean free path values of bismuth-borophosphate glasses were measured experimentally. Then, the measured findings were compared to the FLUKA code. The FLUKA code findings agreed well with the experimental results. Furthermore, the findings show that adding Bi2O3 to the glass network improves the shielding properties. The current data reveal that when the Bi2O3 content rises, so does the absorbance. Furthermore, the optical constants of the present gasses, such as optical band gap, phonon energy, and tails of localized states, were examined. Fourier transform infrared (FTIR) spectrometer was used to analyze the Fourier transform infrared (FTIR) spectra of our samples at room temperature in the 4000–400 cm−1 wavenumber range. From a shielding standpoint, bismuth-borophosphate glasses offer excellent gamma-ray shielding properties. © 2022

In recent years, numerous policies have been issued with requirements to reduce the energy use of appliances and emission of greenhouse gases. As one of the biggest energy users, large attention has been given to reducing the energy use of residential buildings. With renovation techniques of these dwellings that lower the space heating demand, low temperature heating systems can be applied. In this regard, electrically driven air to water heat pumps are the most used low temperature heating systems. Due to their easy installation requirements and low price in comparison to other heat pumps, it is expected that these units will be the leaders in replacing gas-fired boilers that currently dominate the market. However, in severe winter conditions, these heat pumps have a decrease in thermal capacity while the dwelling has an increase in energy demand. In this case, the difference in energy supply is mostly compensated by electrical auxiliary heaters. With an increase in sales of electrically driven heat pumps, the current electricity grid could suffer from voltage instabilities and overloading. To face these challenges, fuel cell units that are capable to generate both electrical and thermal energy are nowadays a large topic of scientific interest. With the use of reformer units, natural gas can directly be broken up into hydrogen which further supplies the fuel cell stack. In this case, the existing natural gas grid could be used, and the provision of hydrogen ensured throughout the season. With aspirations towards the decarbonisation of the natural gas grid, a blend-in of 5 Vol% of hydrogen is already approved while a larger share of hydrogen in the gas grid is expected in the years to come. In the scientific literature, there is a lack of research devoted to analysing the experimental performance of the currently used fuel cells and their adaptations to natural gas-hydrogen mixtures. In this regard, this research analyses the performance of a fuel cell unit for different fuel mixtures containing up to 30 Vol% hydrogen. The results show deviations in efficiency values of less than 5% and no pattern in the total efficiency trends for the two different controlling strategies of the unit.

Sea spray droplets are aqueous phase aerosols generated from the water surface. In the open ocean, they are generated as a result of wind-forced wave breaking and surface-tearing mechanisms. To this day, knowledge of sea spray particles larger than 20 µm radius is sparse. The present thesis aims to improve knowledge of the sea spray generation flux, as well as transport and impacts on the properties of the marine atmospheric boundary layer (MABL). To this end, the effects of wind–wave interactions on the surface sea spray generation flux are investigated during the MATE2019 experiment, conducted at the large wave–wind facility in Luminy (Marseille, France). Scaling analysis shows that the sea spray generation is best correlated with the wave-slope variance for thelarger spume droplets generated by surface tearing. For the smaller jet droplets generated by bubble bursting, the highest correlation is found with a nondimensional number combining the wave-slope variance, the wave age, and a windsea Reynolds number. This resulted in the formulation of two wave-state-dependent sea spray generation functions, each valid for wind speeds 12–20 m s-1 and radii 3–35 µm. Upscaled to the field, the laboratory-derived generation functions are parameterized in the MACMod and MESO-NH numerical models, and validated using field data collected during the thesis in the Bay of Biscay for this purpose. Best model performance is found with the laboratory generation functions. Such results are encouraging for the study of sea spray impacts on the properties of the MABL.; Les embruns sont des aérosols en phase aqueuse générés à la surface de l’eau. Au large, ils sont générés par des mécanismes tel que le déferlement et l’écrêtage. Aujourd’hui, la connaissance portant sur les embruns excédant 20 µm de rayon reste limitée. Cette thèse vise à améliorer la compréhension des processus de génération, de transport, et les impacts sur les propriétés de la couche limite atmosphérique marine (CLAM). La campagne MATE2019 est ainsi menée à l’installation air-mer de Luminy (Marseille, France) afin d’étudier le rôle des interactions vague-vent sur la génération. Une analyse d’échelle révèle que la génération d’embruns corrèle le mieux avec la variance de pente de vagues pour les plus grosses gouttelettes ‘spume’ générées par écrêtage. Pour les plus petites gouttelettes ‘jet’ générées par éclatement de bulles, la meilleure corrélation est obtenue avec un nombre adimensionnel combinant la variance de pentes de vagues, l’age de vague, et un nombre de Reynolds adapté aux mers de vent. Il en résulte la formulation de deux fonctions de génération d’embruns dépendantes sur l’état de mer, valides pour des vents de 12–20 m s-1 et des rayons de 3–35 µm. Extrapolées aux conditions in situ, les fonctions de génération issues du laboratoire sont paramétrées dans les modèles numériques MACMod et MESO-NH, à leurs tours validés à l’aide de mesures terrain, dont une nouvelle campagne de mesure effectuée pendant la thèse dans le Golfe de Gascogne. Les meilleures performances de modélisation sont obtenues avec les fonctions de génération issues du laboratoire. Ces résultats permettent de mieux appréhender l’impact des embruns sur la CLAM.

Nowadays, the application of composite materials and light-weight structures is required in those industrial applications where the primary design aims are weight saving, high stiffness, corrosion resistance and vibration damping. The first goal of the study was to construct a new light-weight structure that utilizes the advantageous characteristics of Carbon Fiber Reinforced Plastic (CFRP) and Aluminum (Al) materials; furthermore, the properties of sandwich structures and cellular plates. Thus, the newly constructed structure has CFRP face sheets and Al stiffeners, which was manufactured in order to take experimental measurements. The second aim of the research was the elaboration of calculation methods for the middle deflection of the investigated sandwich-like structure and the stresses that occurred in the structural elements. The calculation methods were elaborated; furthermore, validated by experimental measurements and Finite Element analysis. The third main goal was the elaboration of a mass and cost optimization method for the investigated structure applying the Flexible Tolerance optimization method. During the optimization, seven design constraints were considered: total deflection; buckling of face sheets; web buckling in stiffeners; stress in face sheets; stress in stiffeners; eigenfrequency of the structure and constraints for the design variables. The main added values of the research are the elaboration of the calculation methods relating to the middle deflection and the occurred stresses; furthermore, elaboration of the optimization method. The primary aim of the optimization was the construction of the most light-weighted structure because the new light-weight sandwich-like structure can be utilized in many industrial applications, e.g., elements of vehicles (ship floors, airplane base-plate); transport containers; building constructions (building floors, bridge decks).

Systémy zelených stěn a fasád jsou moderním prvkem pozemních staveb. Pro zajištění správného návrhu a funkčnosti těchto systémů v průběhu jejich životního cyklu je nezbytný popis jejich vlastností. Jednou ze základních vlastností fasádních a obkladových prvků je plošná hmotnost. Ta závisí na zvoleném systému provedení vegetační stěny či fasády, zvoleném množství a druhovém zastoupení vegetace a v neposlední řadě na okolních podmínkách místa instalace. Vzhledem k tomu, že se jedná o živé prvky, je nutné konstatovat, že tato vlastnost nelze vyjádřit jednou hodnotou, ale hmotnostním rozsahem. Z důvodu velké odlišnosti těchto systémů od standardních obkladových či fasádních prvků jsou pro zjištění plošné hmotnosti standardní metody zkoušení nepoužitelné. Tento příspěvek popisuje možnou metodiku pro stanovení plošné hmotnosti systémů vegetačních fasád a jejich změn v čase. Green wall and facade systems are a modern element of building construction. To ensure the correct design and functionality of these systems during their life cycle, it is necessary to describe their properties. One of the basic properties of facade and cladding elements is the basis weight. It depends on the chosen system of vegetation wall or facade, the chosen amount, and species representation of vegetation and, last but not least on the surrounding conditions of the installation site. Given that these are living elements, it must be stated that this property cannot be expressed in a single value, but in a mass range. Due to the great difference between these systems and standard cladding or façade elements, standard testing methods are not applicable for determining the basis weight. This paper describes a possible methodology for determining the basis weight of vegetation facade systems and their changes over time.

The homogeneous density of the liquid phase is experimentally investigated for methyl diethanolamine. Data are obtained along five isotherms in a temperature range between 300 K and 360 K for pressures up to 95 MPa. Two different apparatuses are used to measure the speed of sound for the temperatures between 322 K and 450 K with a maximum pressure of 95 MPa. These measurements and literature data are used to develop a fundamental equation of state for methyl diethanolamine. The model is formulated in terms of the Helmholtz energy and allows for the calculation of all thermodynamic properties in gaseous, liquid, supercritical, and saturation states. The experimental data are represented within their uncertainties. The physical and extrapolation behavior is validated qualitatively to ensure reasonable calculations outside of the range of validity. Based on the experimental datasets, the equation of state is valid for temperatures from 250 K to 750 K and pressures up to 100 MPa.

This article deals with the investigation of wind effects on a façade of a rectangular residential building with explicit modelling of the windows for specific wind conditions. The external wind pressure coefficients were treated on the façade and at the places of the window sills, linings, and lintel for the direction of the wind from 0° to 90° with increments of 22.5°. For a detailed analysis, the CFD simulation using Ansys Fluent was used. The method selected for the CFD simulation solution and its setting (quality of meshing, horizontal homogeneity of the boundary layer, etc.) were verified by known results of similar objects. The purpose of this analysis is to show how important it is to consider wind effects to determine the suitable placement of passive ventilation devices. Research shows the potential optimal position of ventilation units in terms of favourable pressure distribution. Zones with negative pressure and corners or façades in a wake are not suitable for applying passive ventilation units. The results can serve as a basis for designers to achieve optimal comfort in residential buildings.

Solar air collectors are increasingly used nowadays due to their important potential in reducing the energy consumption of buildings. In this context, glazed transpired solar collectors (GTCs) represent an interesting solution, but this type of solar air collector is less studied. Consequently, the objective of this work is to thoroughly assess the performance of a GTC prototype under real long-term climatic conditions. First, the design of the GTC is optimized based on methodically experimental tests. The results show that the GTC configuration with a 30 mm air gap among the absorber and the glazing leads to improved heat transfer efficiency and superior global effectiveness, regardless of airflow rates through the solar air collector. This optimized GTC configuration is further studied by integration within the façade of a full-scale experimental building (container-type, light structure). Comparative experimental studies are then carried out concerning the heating energy consumption and ventilation load of the experimental building without/with GTC implemented in the ventilation system, under Bucharest real weather conditions. The data achieved indicate that the GTC prototype is capable of substantially reducing the ventilation load: up to 25% for low solar radiation (below 200 W/m2) and over 50% (achieving even 90%) for moderate solar radiation (between 250 and 380 W/m2). Finally, for high solar radiation (over 400 W/m2), the GTC outlet air temperature exceeds the interior temperature set-point (22 °C) of the experimental building.

Thermal bridges may have a significant prejudicial impact on the thermal behavior and energy efficiency of buildings. Given the high thermal conductivity of steel, in Lightweight Steel Framed (LSF) buildings, this detrimental effect could be even greater. The use of thermal break (TB) strips is one of the most broadly implemented thermal bridge mitigation technics. In a previous study, the performance of TB strips in partition LSF walls was evaluated. However, a search of the literature found no similar experimental campaigns for facade LSF walls, which are even more relevant for a building’s overall energy efficiency since they are in direct contact with the external environmental conditions. In this article the thermal performance of ten facade LSF wall configurations were measured, using the heat flow meter (HFM) method. These measurements were compared to numerical simulation predictions, exhibiting excellent similarity and, consequently, high reliability. One reference wall, three TB strip locations in the steel stud flanges and three TB strip materials were assessed. The outer and inner TB strips showed quite similar thermal performances, but with slightly higher thermal resistance for outer TB strips (around +1%). Furthermore, the TB strips were clearly less efficient in facade LSF walls when compared to their thermal performance improvement in load-bearing partition LSF walls. © 2022 by the authors.

The variation of the thermo-hydrodynamic behavior of the airflow in the ventilated cavity behind external claddings in a wall structure could potentially affect the overall thermal resistance of the entire structure. Although the impact of an enclosed air-space in the wall on the total R-value of the assembly has been thoroughly investigated in the literature, it has not been addressed for a ventilated cavity. In the present study, as a first step, plausible definitions to determine the thermal resistance of the ventilated cavity behind external claddings in transient conditions are described. As the second step, the dynamic thermal resistance of the naturally ventilated air-spaces behind passive (i.e., brick and fiber cement) claddings and active (i.e., BIPV) facades are studied using two approaches. In the first approach, a 2-D numerical model validated against measurements is employed to compute the thermal resistance of the ventilated air gap under different conditions. Accordingly, the impact of the cladding type, seasonal variation, cavity thickness, and presence of the reflective insulation in the air gap on the dynamic change of the thermal resistance of the air-space is analyzed. In the second approach, in-field measurements are performed in a test facility to experimentally examine the contribution of the thermal resistance of the cavity to the total R-value of the wall structure. The results obtained from both approaches are compared with the design values calculated based on the ISO 6946:2017 and ISO 9869–1:2014 standards. The results reveal that the dynamic change of the thermal resistance of the air gap during a day could be captured using numerical simulations. It is shown that the daily averaged thermal resistance of the cavity could reach up to 47 times higher than the design R-value of the BIPV façade. The experimental measurements confirm that the thermal resistance of the ventilated air-space could converge to a steady-state value after a certain duration of time following the requirements provided in the standards, which could be practically used for the code-compliant analysis. It is also observed that the ventilated cavity could act as an insulation layer with higher thermal resistance compared to some of the solid materials used in the wall assembly.

This paper is devoted to track-bridge interaction phenomena in railway bridges of short simply-supported (SS) spans composed by ballasted tracks. These structures may experience high vertical acceleration levels under operating conditions. In particular, the coupling effect exerted by the ballast track shared by structural parts that are theoretically independent, such as consecutive simply-supported spans or twin adjacent single-track decks, is investigated. Experimental evidence shows that in these cases there may be an important vibration transmission from the loaded to the unloaded track, and that the interlocked ballast granules couple some of the lowest modes of vibration to an important extent. To this end a detailed three-dimensional (3D) Finite Element (FE) model of an existing bridge is implemented where the ballast in weakly connected regions is simulated as transversely isotropic material, in order to represent in a simplified manner the degraded state due to the relative motion between the disconnected structural parts. First, the bridge numerical model is updated from the ambient vibration response of the structure previously measured by the authors. Second, a sensitivity analysis is performed on the properties of the degraded ballast and their effect on the first five modes of vibration of the bridge is discussed. Finally, the response of the bridge under operating conditions is computed numerically, compared with the response measured experimentally in the time and frequency domains and conclusions are extracted regarding the model adequacy. Spanish Ministry of Science and Innovation PID2019-109622RB FEDER Andalucía 2014–2020 Operational Program US-126491 Generalitat Valenciana, Spain and Universitat Jaume I, Spain AICO2019/175 Generalitat Valenciana, Spain and Universitat Jaume I, Spain UJI/A2008/06

One of the goals of modern internal combustion engines is the NOx-soot trade-off, and this would be better achieved by a better control of the fuel injection. Moreover, this feature can be also useful for high-performance hydraulic systems. Actual fuel injection technology either allows only the control of the injection time or it is based on very complex mechanical-hydraulic systems, as in the case of piezo-actuators. This work describes the basic steps that brought the authors to the realization of a concept fuel injector based on a Terfenol-D magnetostrictive actuator that could overcome the previous issues, being both simple and controllable. The study provides the design, development, and a feasibility analysis of a magnetostrictive actuator for fuel injection, by providing a basic magneto-static analysis of the actuator, the adaptation of a suitable standard fuel injector, and its experimental testing in a lab environment, with different shapes and amplitude of the reference signal to follow.

International audience; The study deals with the mechanical behaviour of a glass plain weave composite reinforcement. The experimental activities were focused mainly on uniaxial and biaxial extension tests. Besides, in-plane shear deformation was measured by bias extension test, and for the sake of completeness out-of-plane bending behaviour. In the numerical study, a hyperelastic constitutive model for the yarn material was adopted and validated for the meso scale prediction of the mechanical behaviour of the glass plain weave reinforcement. The model was validated for biaxial tensile and in-plane shear deformation.

In microwave imaging, it is often of interest to inspect electrically large spatial regions. In these cases, data must be collected over a great deal of measurement points which entails long measurement time and/or costly, and often unfeasible, measurement configurations. In order to counteract such drawbacks, we have recently introduced a microwave imaging algorithm that looks for the scattering targets in terms of equivalent surface currents supported over a given reference plane. While this method is suited to detect shallowly buried targets, it allows one to independently process all frequency data, and hence the source and the receivers do not need to be synchronized. Moreover, spatial data can be reduced to a large extent, without any aliasing artifacts, by properly combining single-frequency reconstructions. In this paper, we validate such an approach by experimental measurements. In particular, the experimental test site consists of a sand box in open air where metallic plate targets are shallowly buried a (few cm) under the air/soil interface. The investigated region is illuminated by a fixed transmitting horn antenna, whereas the scattered field is collected over a planar measurement aperture at a fixed height from the air-sand interface. The transmitter and the receiver share only the working frequency information. Experimental results confirm the feasibility of the method.

This research presents a validation methodology for computational fluid dynamics (CFD) assessments of rooftop wind regime in urban environments. A case study is carried out at the Donadeo Innovation Centre for Engineering building at the University of Alberta campus. A numerical assessment of rooftop wind regime around buildings of the University of Alberta North campus has been performed by using 3D steady Reynolds-averaged Navier–Stokes equations, on a large-scale high-resolution grid using the ANSYS CFX code. Two methods of standard deviation (SDM) and average (AM) were introduced to compare the numerical results with the corresponding measurements. The standard deviation method showed slightly better agreements between the numerical results and measurements compared to the average method, by showing the average wind speed errors of 10.8% and 17.7%, and wind direction deviation of 8.4° and 12.3°, for incident winds from East and South, respectively. However, the average error between simulated and measured wind speeds of the North and West incidents were 51.2% and 24.6%, respectively. Considering the fact that the upstream geometry was not modeled in detail for the North and West directions, the validation methodology presented in this paper is deemed as acceptable, as good agreement between the numerical and experimental results of East and South incidents were achieved.

International audience; A centralized solar domestic hot water system for a multi-family building is analyzed numerically. The solar preheated water in the solar tank is flowing into an auxiliary tank, connected to a gas boiler. At its output, a mixing device is used to ensure hot water at steady temperature before going through the recirculation loop. This reference system is sized as a typical installation under mild climate in France. The load profile is generated statistically with a one-minute time step. Small time scale phenomena have consequences on the global system behavior: recirculation flow rate variations due to pressure drop change is modeled and validated experimentally. This work's goal is to analyze these effects on two sub-parts of the plant: mixing valve and recirculation loop connection to solar storage. In each case, yearly simulations with 6 s time step provide quantitative performance indicators for different sizing and control options. Results show that mixing valve slow response, due to ageing or bad design, leads to a loss of 3.5% energy savings compared to using a fast component. Furthermore, health risks increase as the minimal temperature in the recirculation loop is often under 50 • C, which promotes legionella development due to cold water plug flows generated in the loop by the mixing valve dynamic response. The recirculation loop, linked to a solar tank, leads to performance improvement with 6-15% increase in energy savings following solar oversizing and reduced overheating risks.

Sun-tracking microwave (ST-MW) radiometry is a ground-based technique where the Sun is used as a beacon source to infer the atmospheric path attenuation in all-weather conditions. ST-MW radiometry shows an appealing potential for overcoming the difficulties to perform satellite-to-Earth radiopropagation experiments in the unexplored millimeter-wave and submillimeter-wave frequency region, especially where experimental data from beacon receivers are not available. The theoretical framework, the ad hoc procedures and data processing will be presented, together with the estimate of the overall error budget. The applications and challenges during field deployments, such as the recent WRad campaign in Italy based on ST-MW data analysis, funded by ESA and carried out together with AFRL (NY, USA), will be discussed.

Applications in energy and combustion science: heat, power and process 5, 100014 (2021). doi:10.1016/j.jaecs.2020.100014, Published by Elsevier B.V., Amsterdam

The growing applications involving unmanned aerial vehicles (UAVs) are requiring more advanced control algorithms to improve rotary-wing UAVs’ performance. To preliminarily tune such advanc...

Buildings of strategic importance should be able to resist seismic forces in accordance with potential earthquakes that may occur at the location and remain fully operational afterwards. However, many of them were constructed before the modern principles of seismic design were known (especially regarding detailing and ductility), and therefore may be considered substandard. The first step in mitigating the seismic risk of such structures is to assess their seismic performance and, in particular, to identify their structural deficiencies. This study presents a comprehensive methodology for the seismic performance assessment of individual buildings, applied to an existing reinforced concrete (RC) hospital. This building is of an irregular layout, constructed as a structural wall system, and it is located in the seismically active region of Croatia. It includes the assessment of seismic hazards on the location, ambient noise measurements, experimental determination of structural modal parameters, creation of a detailed numerical model calibrated with experimental data, and a seismic performance assessment using various analysis methods. As a result, the building collapse mechanisms were determined and critical structural elements identified, which is the basis for future actions directed to the reduction of its risk (e.g., applications of specific measures for a target retrofit, proposal of evacuation routes and safe places inside the building, etc.).

Biofuels have attracted considerable attention for current and future utilization because of their benefits as promising alternative, ecological and economical viable fuels, with particular reference to biodiesel and alcohols. In order to use biodiesel in diesel engines, the volumetric and transport properties of the fuel (i.e. density and viscosity) must be improved since they affect spray properties, atomization and combustion processes of a fuel. In addition, the derived thermodynamic magnitudes, such as isothermal coefficient and isobaric thermal expansion coefficient, greatly influence the atomization process and, consequently, the fuel consumption of diesel engines. Therefore, knowledge of these properties at different pressures and temperatures is important in order to predict and improve the performance of diesel engines. Densities, viscosities, sound velocities and refractive indices of pure components: 1-butanol, 1-propanol, ethyl laurate, ethyl linoleate, ethyl myristate, ethyl oleate, methyl laurate and n-hexadecane were measured at temperatures T= (293.15 to 343.15) K and atmospheric pressure. The measured values were compared to several available literature data, and good agreement was noticed: an overall absolute average percentage deviation (AAD) of 0.04%, 0.07%, 3 % and 0.1% for density, speed of sound, viscosity and refractive index data, respectively. Besides that, densities, viscosities, speeds of sound and refractive indices of ternary mixture ethyl oleate + n-hexadecane + 1-butanol (3), and for the corresponding binary mixtures: ethyl laurate + 1- propanol, ethyl oleate + 1-butanol, ethyl oleate + 1-propanol, ethyl oleate + n-hexadecane, nhexadecane + 1-butanol and n-hexadecane + 1-propanol were measured in the temperature range T= (293.15 to 343.15) K at atmospheric pressure. The measurements were performed on an Anton Paar DSA 5000 M density and sound velocity meter, Anton Paar SVM 3000 digital viscometer, and Anton Paar RXA 156 refractometer. From the experimental data, a number of thermodynamic parameters were also calculated, namely, excess molar volumes (VE), viscosity deviation functions (∆), deviations in refractive index (∆nD), excess molar Gibbs energy of activation of viscous flow (∆G*E) and deviation in isentropic compressibility (∆κs). The binary and ternary properties are then correlated as a function of the mole fraction by using the Redlich–Kister and Nagata and Tamura equations, respectively, and then used to analyze molecular interactions present in the mixtures... Biogoriva su privukla značajnu paţnju, kako za trenutnu, tako i za buduću upotrebu zahvaljujući svojim prednostima kao obećavajućim alternativnim, ekološkim i ekonomičnim gorivima, a posebno se ističu biodizel i bioalkoholi. Da bi se biodizel koristio u dizel motorima moraju mu se poboljšati volumetrijska i transportna svojstva (tj. gustina i viskoznost), jer utiču na raspršivanje, atomizaciju i sagorevanje goriva. Pored toga, izvedene termodinamičke veličine, kao što su izotermska stišljivost i izobarni koeficijent termičkog širenja, značajno utiču na proces atomizacije, a samim tim i na potrošnju goriva u dizel motorima. Stoga je poznavanje ovih svojstava pod različitim pritiscima i temperaturama vaţno kako bi se predvideo i poboljšao rad dizel motora. Gustine, viskoznosti, brzine zvuka i indeksi refrakcije čistih komponenti: 1-butanola, 1-propanola, n-heksadekana, etil oleaat, etil linoleata, etil laurata, etil miristata i metil laurata su mereni na temperaturama T = (293,15 do 343,15 ) K pri atmosferskom pritisku. Izmerena vrednosti su poreĎene sa nekoliko dostupnih literaturnih podataka, I primećeno je dobro slaganje, ukupno prosečno pocentualno odstupanje (AAD) je bilo oko 0,04%, 0,07%, 3% i 0,1%, redom za gustine, brzine zvuka, viskoznosti i indekse refrakcije. Pored toga, merene su i gustine, viskoznosti, brzine zvuka i indeksi refrakcije ternerne smeše etil oleat + n-heksadekan + 1-butanol , i odgovarajućih binarnih smeša etil oleat + 1-butanol, etil oleat + 1-propanol, etil oleat + n-heksadekan, etil laure + 1-propanol, n-heksadekan + 1-butanol i nheksadekan + 1-propanol u temperaturnom opsegu T = (293,15 do 343,15) K sna atmosferskom pritisku. Merenja su izvršena na Anton Paar DSA 5000 M ureĎaju za merenje gustine i brzine zvuka, Anton Paar SVM 3000 digitalnom viskozimetru i Anton Paar RKSA 156 refraktometru. Iz eksperimentalnih podataka su, takoĎe, izračunai I brojni termodinamički paramtetri, kao na pr. Dopunska molarna zapremina (VE), odstupanje viskoznosti (∆), odstupanje indeksa refrakcije (∆nD), dopunska molarna Gibsova energija aktivacije viskoznog toka (∆G*E) i višak izentropske kompresibilnosti (∆κs). Binarna i ternarna svojstva su nakon toga korelisana u zavisnosti od molekulskih sastava primenom Redlih-Kister i Nagata i Tamura jednačina, redom, a potom su korištena za analizu molekulskih interakcija unutar smeša...

Power line communications (PLC) is a known low cost technology which is easily installed and extended to the various connections especially to areas with poor wireless coverage. Unfortunately, designers and users experience technical problems that arise from the difficulty of operating on a complex time varying medium and that limits the expected high throughput. Therefore, testing and understanding network dynamics of PLC systems before usage is a necessity. This paper presents the findings obtained from the experiments carried out in order to verify the throughput performance of PLC systems. Experimental measurements are realized in different testbeds, under different times and conditions, in order to achieve an idea of the practical PLC performance. Data obtained from the measurements have been stored and the throughput is analyzed by the help of software. Following, using distribution fitting methods, it is shown that the PLC throughput may be modeled by the extreme value distribution. Furthermore, adding a basic noise to the network, simply by lamps, results with a degraded performance. The noise changes the parameters of the derived distributions; a decrease in expected value and an increase in standard deviation are observed.

Graphical abstract, The experimental study of vibrating plates having simply-supported boundary conditions can be difficult to achieve due to the complexity of preventing translation, but allowing rotation along all boundaries simultaneously. Only a few methods have been proposed, but all are either time-consuming to set up and involve customization of the test rig for each plate or do not allow the plate to be reused for other purposes. The method described in this paper offers a low-cost, simple, accurate and non-destructive way of experimentally measuring the modal properties of thin, simply supported plates and can be used for quick validations of models and designs without modification for multiple trials and varying plate properties. The key attributes of this method include: • An adjustable sliding support frame which can be made of a distinct material from the plate and which can accommodate variations in plate geometry and properties without modification. • Removable flexible sealant applied in a v-groove on the supporting frame which can be easily used to fix and support the plate according to the simply-supported boundary conditions. • A low-profile design, which can be used to accommodate most experimental testing methods for determining modal properties of vibrating plates.

At the present time in the research of particulate materials, computer methods that work independently with individual particles are coming to the forefront. One such method is the Discrete Element Method – DEM, which is already widely used. Its usage, however, is complex, mostly due to the input data – what the properties of the researched material are, plus their interaction in processes. And despite the progress, it is still always necessary to validate the experimental equipment and to verify the individual simulations by an experimental measuring or by theoretical knowledge. This study focuses on the verification of the simulation of the mixing of a particulate material with the help of the DEM method, whereby simulations are compared with an experimental measurement and theoretic calculations. The theoretical calculation was carried out by the Novosad model, while the experimental material was granulated polyethylene with strictly defined mechanical-physical properties.

A combined method using statistical and numerical models has been developed by the authors for selecting a pump running as turbine to be applied in micro-hydro plants. The data of the hydrological site chosen for the installation (head and capacity) allow the calculation of two conversion factors which identify the pump to use successfully as turbine in that place. Then, a one-dimensional model, starting from data available on the pumps manufacturers catalogues, reconstructs a virtual geometry of the pump running as turbine, and calculates the performances curves, head vs. capacity, efficiency vs. capacity, useful for identifying the operating point. Two study cases are presented to apply the proposed methodology, concerning the feasibility of the installation of a pump running as turbine in the purifier water plants of Casali and Sersale, located at 1,000 m above sea level (Calabria, South Italy).The assessment of the annual energy yield gives a confirmation of the effectiveness and convenience of using pumps running as turbines.

Effective ventilation could reduce COVID-19 infection in buildings. By using a computational fluid dynamics technique and advanced experimental measurement methods, this investigation studied the air velocity, air temperature, and particle number concentration in an office under a mixing ventilation (MV) system and a displacement ventilation (DV) system with different ventilation rates. The results show reasonably good agreement between the computed results and measured data. The air temperature and particle number concentration under the MV system were uniform, while the DV system generated a vertical stratification of the air temperature and particle number concentration. Because of the vertical stratification of the particle number concentration, the DV system provided better indoor air quality than the MV system. An increase in ventilation rate can reduce the particle concentration under the two systems. However, the improvement was not proportional to the ventilation rate. The increase in ventilation rate from 2 ACH to 4 ACH and 6 ACH for MV system reduced the particle concentration by 20% and 60%, respectively. While for the DV system, increasing the ventilation rate from 2 ACH to 4 ACH and 6 ACH reduced the particle concentration by only 10% and 40%, respectively. The ventilation effectiveness of the MV system was close to 1.0, but it was much higher for the DV system. Therefore, the DV system was better than the MV system.

The purpose of this article is the assessment of energy efficiency and indoor air quality for a single-family house located in Cluj-Napoca County, Romania. The studied house is meant to be an energy-efficient building with thermal insulation, low U-value windows, and a high efficiency boiler. Increasing the energy efficiency of the house leads to lower indoor air quality, due to lack of natural ventilation. As the experimental campaign regarding indoor air quality revealed, there is a need to find a balance between energy consumption and the quality of the indoor air. To achieve superior indoor air quality, the proposed mitigation systems (decentralized mechanical ventilation with heat recovery combined with a minimally invasive active sub-slab depressurization) have been installed to reduce the high radon level in the dwelling, achieving an energy reduction loss of up to 86%, compared to the traditional natural ventilation of the house. The sub-slab depressurization system was installed in the room with the highest radon level, while the local ventilation system with heat recovery has been installed in the exterior walls of the house. The results have shown significant improvement in the level of radon decreasing the average concentration from 425 to 70 Bq/m3, respectively the carbon dioxide average of the measurements being around 760 ppm. The thermal comfort improves significantly also, by stabilizing the indoor temperature at 21 °C, without any important fluctuations. The installation of this system has led to higher indoor air quality, with low energy costs and significant energy savings compared to conventional ventilation (by opening windows).

The main subject of this paper is application of a Computational Fluid Dynamics (CFD) model in determination of the muzzle blast overpressure and its physical manifestations, as well as its validation through measurements of primary parameters. Unsteady Reynolds-averaged Navier-Stokes equations (URANS) with a corresponding turbulence model were applied for numerical simulation of complex gas-dynamic process of propellant gases release from the barrel after firing. The unstructured adaptive mesh for spatial discretization was applied, as suitable model for numerical calculation and physical interpretation of these intensive dynamic processes. The provided experimental results were compared with the results of numerical simulations, which were thus validated, according to adopted minor simplifications.

Analysis of wind flow acting upon high-rise buildings is a very common topic. This paper deals with experiment in the Boundary Layer Wind Tunnel (BWLT) in Bratislava and comparison with the computational fluid dynamics (CFD) simulation and values given in the Eurocode. The analyzed object was the model of building with circular cross section (cylinder). External wind pressure coefficients were compared in three height levels of model.

This work introduces an extension of the semi-analytical reduced model presented in Ríos Rodriguez et al. (2016), with the aim of analyzing the thermo-fluid dynamic behavior of a power transformer radiator working in ONAF (Oil Natural Air Forced) mode, considering vertical blowing of the fans. The objective of this research paper is the development of a numerical tool to be used during the design process of power transformers in order to obtain more detailed information about the radiators performance, either they are working in ONAF or ONAN (Oil Natural Air Natural) mode. Since it is observed both in the experimental measurements and in the numerical simulations that not all the radiator panels are blown by a single fan, the reduced model here presented considers a mixed situation wherein the heat is removed by natural convection in a fraction of the radiator while in the rest the heat is removed by forced convection. As a consequence, besides adding to the set of conservation equations introduced in Ríos Rodriguez et al. (2016) those corresponding to the momentum and energy balance for considering forced heat convection transfer, there appears the need of introducing additional equations for coupling the natural and forced heat convection transfer models. The reduced model developed in this work is applied to estimate different characteristic parameters of a power transformer radiator working in ONAF mode, like the oil flow rate, dissipated power, outlet and inlet oil temperatures, among others. The computed results are compared to those obtained by CFD simulations and experimental measurements carried out on an ad-hoc workbench for validation purposes. It is found that the reduced model reproduces with acceptable accuracy the values of the most important design variables at a very low computation cost. In this manner, it can be considered as a reliable and valuable tool in the design of power transformers, allowing to carry out parametric studies. Fil: Garelli, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Rios Rodriguez, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Storti, Mario Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Granata, Daniel. Tadeo Czerweny S. A.; Argentina Fil: Amadei, Mauro. Tadeo Czerweny S. A.; Argentina Fil: Rossetti, Marcelo. Tadeo Czerweny S. A.; Argentina

This paper presents semi-analytical calculations, computational fluid dynamic simulations and experimental measurements accomplished on a typical 30 MVA power transformer. An ad hoc workbench was devised to carry out the experimental measurements. This facility allowed to estimate the values of different key variables involved in heat dissipation within the radiator, like convective heat transfer coefficients, oil-flow rate, air-flow speed between radiator fins and overall dissipated heat, among others. The main objectives of the study are to analyze the cooling capacity of the current radiator design working in ONAN mode and to validate the numerical simulation and calculation procedures for further design optimizations. The coupled thermo-hydraulic numerical simulations were performed on a computer cluster due to the high computational cost of the resulting models. The results of the simulations show good agreement with the experimentally measured values and with those obtained with the semi-analytical model, thus confirming that this model together with the CFD simulations are an accurate analysis tool. The heat transfer coefficients in the oil, the radiator panel and the air are computed. It is found that convective heat transfer from the panel to the air is approximately 10 times lower than heat transfer in the oil. Possible improvements on the current radiator design are briefly mentioned. Fil: Rios Rodriguez, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Garelli, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Storti, Mario Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Granata, Daniel. Tadeo Czerweny S.a.; Argentina Fil: Amadei, Mauro. Tadeo Czerweny S.a.; Argentina Fil: Rossetti, Marcelo. Tadeo Czerweny S.a.; Argentina

U školskoj godini 2018./2019. u Prvoj gimnaziji Varaždin provedeno je istraživanje mikroklimatskih uvjeta na rezultate vrednovanja učenika. Cilj našeg projekta je dokazati ili opovrgnuti utjecaj mikroklime na uspješnost učenika i to u konkretnim situacijama, odnosno prilikom uobičajenog načina provjera znanja: pisanih provjera. Budući da se i ispiti državne mature u ovom trenutku temelje na takvom modelu provjere znanja, smatramo da je važno identificirati korelaciju između mikroklime i uspješnosti učenika na provjeri znanja, a u slučaju potvrde značajnog utjecaja doprinijeti i razvoju standarda uređenja postojećih školskih prostora ili izgradnji novih. Ispitivani mikroklimatski uvjeti bili su temperatura, relativna vlažnost, strujanje zraka. Testiranje je provedeno u 10 različitih učionica i 5 različitih predmeta ili skupina predmeta. Rezultati ukazuju na lošije rezultate vrednovanja pri većim odstupanjima od preporučenih vrijednosti promatranih mikroklimatskih uvjeta., In the 2018/2019 school year at the Prva gimnazija Varaždin in Varaždin, a study of microclimatic conditions was conducted on the results of student evaluation. The goal of our project is to prove or disprove the impact of the microclimate on student performance in specific situations, that is, in the usual way of knowledge testing: written tests. Given that state examinations are currently based on such a model of assessment, we believe that it is important to identify a correlation between the microclimate and student performance in the knowledge test and, if confirmed, to contribute to the development of standards for the existing school premises or the construction of new ones. The microclimatic conditions tested were temperature, relative humidity and airflow. Testing was conducted in 10 different classrooms and five different subjects or groups of subjects. The results indicate poorer evaluation results at greater deviations from the recommended values of observed microclimatic conditions.

Friction and wear are recognized as one of the most puzzling problems, not only in many engineering and manufacturing applications, but also in a fundamental scientific sense. In fact, friction is a nonlinear stochastic effect with a distinct time, position and temperature variability. While frictional phenomena on the macro- and meso-scales can be considered well described, and their characteristic features can be simulated via suitable models, as well as generally efficiently compensated by using proper control typologies, the study of friction, the parameters that influence its value and the respective models in the nanometric domain are still in an early stage, due to various experimental and modelling complexities. The research performed in the framework of the doctoral thesis provides a scientific contribution to the study of dry (unlubricated) friction by characterising the parameters influencing its value at the nanometric scale, and especially the dependence of friction on material properties, loading conditions, the velocity of motion, as well as temperature. The characterisation of the dependence of friction on the listed parameters is based on experimental measurements performed by employing a Scanning Probe Microscope (SPM). Due to the number and variety of the monitored influences, the number and type of measurements is determined by a state-of-the-art Design of Experiment (DoE) methodology by employing Voronoi tessellations. To obtain predictive models linking the process variables to the value of nanometric friction, the obtained measurement results are then validated numerically via a thorough comparative analysis of state-of-the-art machine learning methods. Despite the marked complexity of the analysed phenomena and the inherent dispersion of the measurements, the developed symbolic regression models, show, depending on the type of the sample, an excellent prediction accuracy between 72 and 91%., Trenje i trošenje su jedan od najizazovnijih problema u mnogih inženjerskim i proizvodnim primjenama. Doista, trenje je nelinearna stohastička pojava s izraženom vremenskom, prostornom i temperaturnom varijabilnošću. Dok je trenje u makro- i mezodomeni dobro objašnjeno te je njegove učinke, primjerenim modelima, moguće modelirati i, primjerenim sustavima regulacije, najčešće i uspješno kompenzirati, u nanometarskom području je proučavanje trenja, parametara koji utječu na trenje, te nalaženje odgovarajućeg modela tih pojavnosti još u zametku. Karakterizacijom utjecajnih parametara u nanometarskom području, a posebice ovisnosti trenja o svojstvima materijala, opterećenju, brzini relativnog gibanja te temperaturi tribološkog para, istraživanje provedeno u sklopu doktorske disertacije daje znanstveni doprinos izučavanju trenja klizanja bez podmazivanja. Eksperimentalno su analizirani tanki filmovi pet različitih materijala: aluminijevog oksida (Al2O3), aluminija, molibden disulfida (MoS2), titanijevog dioksida (TiO2) te martenzitnog nehrđajućeg čelika (X39CrMo17-1). Doista, zbog povoljnih svojstava otpornosti na trošenje i njihove tvrdoće, prevlake od Al2O3 i TiO2 su često korišteni materijali za primjene u mikro- i nanoelektromehaničkim sustavima (M(N)EMS) kao i, općenito, u preciznim konstrukcijama. Ti su uzorci sintetizirani u obliku tankog filma metodom taloženja atomskih slojeva (Atomic Layer Deposition – ALD) na silicijev (Si) supstrat. Ostali proučavani uzorci su odabrani za istraživanje zbog njihove široke primjene u općem strojarstvu te u preciznim konstrukcijama. Zbog povoljnih kliznih svojstava sulfida, MoS2 se, tako, često koristi kao kruto mazivo. Čisti Al je jedan od najčešće korištenih materijala za lake i precizne konstrukcije, dok je martenzitni nehrđaju čelik X39CrMo17-1 odabran kao predstavnik visokokvalitetne grupe čelika za strojne elemente. Ovi uzorci su sintetizirani metodom taloženja pulsirajućim laserom (Pulsed Laser Deposition – PLD), što je omogućilo i da se prvi puta postigne sintetiziranje tankog filma visokolegiranog čelika. Eksperimentalno mjerenje pretražnim mikroskopom atomskih sila u modalitetu rada mjerenja poprečne sile (Lateral Force Microscopy – LFM) vršeno je na svim uzorcima strukturiranim načinom u eksperimentalnim točkama definiranim trima promjenjivim tehnološkim parametrima: normalnom silom FN = 10...150 nN, brzinom klizanja v = 5...500 nm/s i temperaturom  = 20...80 °C. Pedeset mjernih točaka je pritom definirano Voronoi teselacijskom Design of Experiment (DoE) metodom podjele domene mjerenja u granicama promjene navedenih utjecajnih parametara, te je mjerenje u svakoj točki ponovljeno pet puta, Marko Perčić: Characterization of Parameters Influencing Friction in the Nanometric Domain pa je tako u analizi ukupno izvršeno 1,250 mjerenja. Eksperimentalna metodologija je u tom kontekstu strukturirana na način da u kalibracijskom postupku uzima u obzir i promjenjive učinke adhezije ali i vodeći računa o potrebi kompenzacije temperaturnih rastezanja. Razvijenom metodologijom je po prvi puta uopće postignuto mjerenje trenja na nanometarskoj razini s tri promjenjive veličine. Dobiveni rezultati mjerenja omogućavaju ne samo uvid u ponašanje pojedinog analiziranog materijala u danim promjenjivim uvjetima, već i određivanje korelacijskih funkcija koje povezuju parametre procesa s vrijednošću sile trenja na nanometarskoj razini. Temeljita komparativna analiza primjene različitih naprednih metoda strojnog učenja na mjerne podatke je omogućila određivanje korelacijskih funkcija, odnosno prediktivnog modela trenja. Usprkos kompleksnosti analiziranih fizikalnih pojava te značajnom rasipanju mjernih rezultata, provedena je analiza omogućila da se, ovisno o uzorku, primjenom razvijenog matematičkog modela metodom simboličke regresije, dobije točnost predviđanja sile trenja, u odnosu na radne parametre, na razini od 72 do 91%. Takva izvanredna točnost predikcije omogućava ne samo uvid u funkcijsku ovisnost trenja na nanometarskoj razini o promatranim varijablama, nego i stvara preduvjete za proširenje postojećih modela trenja, čime bi se njihova praktična primjenjivost proširila i na nanometarsku razinu.

In the present paper, an experimental investigation on the application of high-speed sweeping jet actuators was carried out. It examines the feasibility of a super sonic exit jet to control boundary layer separation caused by an adverse pressure gradient in a compressible Mach number regime. The first part of the investigation includes a thorough assessment of the used sweeping jet actuator by three dimensional numerical simulations using OpenFoam®. A validation of the results was done by means of schlieren visualization within the actuator and dynamic pressure measurements at the actuator outlet. The outlet signal of the actuator features a characteristic switching frequency of fs [almost equal to] 1200 Hz and a peak Mach number of Ma [almost equal to] 1.4 which was evident in the experiments and the CFD simulation. The supply pressure ratio of the actuator was set to PR = 3.6 using compressed air. The second part of the paper presents the results of the wind tunnel experiments using a test section with the geometry of a half-diffusor ramp equipped with two sweeping jet actuators. Inflow conditions of Mach numbers ranging from Ma[infinity] = 0.3 to Ma[infinity] = 0.8 were investigated. The conducted wind tunnel experiments include detailed oil flow surface visualizations and mean surface pressure measurements in order to demonstrate the impact of the active flow control system. By varying the mass flow rate of the actuator system different operating points were studied. The presented results indicate the positive effect of active flow control regarding the pressure rise over the ramp in a compressible Mach number regime. The separated flow region was significantly reduced.

Buildings of strategic importance should be able to resist seismic forces in accordance with potential earthquakes that may occur at the location and remain fully operational afterwards. However, many of them were constructed before the modern principles of seismic design were known (especially regarding detailing and ductility), and therefore may be considered substandard. The first step in mitigating the seismic risk of such structures is to assess their seismic performance and, in particular, to identify their structural deficiencies. This study presents a comprehensive methodology for the seismic performance assessment of individual buildings, applied to an existing reinforced concrete (RC) hospital. This building is of an irregular layout, constructed as a structural wall system, and it is located in the seismically active region of Croatia. It includes the assessment of seismic hazards on the location, ambient noise measurements, experimental determination of structural modal parameters, creation of a detailed numerical model calibrated with experimental data, and a seismic performance assessment using various analysis methods. As a result, the building collapse mechanisms were determined and critical structural elements identified, which is the basis for future actions directed to the reduction of its risk (e.g., applications of specific measures for a target retrofit, proposal of evacuation routes and safe places inside the building, etc.).

Ponència presentada al XI International Conference on Structural Dynamics (Eurodyn 2020), del 23 al 26 de novembre de 2020 This paper is devoted to the analysis of rail-bridge interaction effects in railway bridges under the circulation of moving trains. In a first approach, a bidimensional Finite Element model is implemented. The rail and the bridge are represented as Bernouilli-Euler beams, and a three-layer discrete track model accounting for the damping and flexibility of rail pads, ballast and subgrade is considered. In the model, several elastically supported spans are included, coupled by the presence of the track. First a sensitivity analysis is performed on the track parameters. A numerical receptance test is simulated on the rails showing that the track damping parameters influence the response only in the vicinity of the track natural frequencies, which are much higher than the bridge’s. Then, the maximum acceleration of the bridge is evaluated under equidistant trains and consistent conclusions are extracted regarding the track parameters. Last, the number of spans included in the model is evaluated showing that limiting the model to one span does not necessarily lead to the highest response in terms of the bridge acceleration. Finally, the response of an existing two-span single-track bridge belonging to a conventional Spanish line is evaluated under the circulation of the Altaria Talgo train. Numerical predictions are compared to experimental results obtained in a recent campaign. The prediction of the vertical acceleration at the sensors located along the longitudinal symmetry axis is adequate. From the experimental results the coupling effect between the adjacent decks in each span is evident suggesting the need of analyzing this phenomenon with more sophisticated models.