Search

This article concentrates on the numerical analysis of hydration heat resulting in formation of cracks on the experimental block of the spillway at Orlik Reservoir and its verification with the experimental measurement. In order to eliminate the maximum of critical factors which could lead to appearance of early age cracking and faulty execution of the spillway, an experimental block was concreted. It served as a trial block for all steps of the execution process as well as a validating temperature measurement during cement hydration to confirm with the preliminary numerical analysis. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to investigate the hydrodynamic and vibrational behavior of the 2000 mm diameter Howell Bunger valve that will be installed in the Khodaafrin dam. The existence of a historical bridge downstream of this dam makes it important to investigate the vibration and hydrodynamic behavior of the valve, so that its design and operation should be in such a way that the historical bridge located downstream will not be damaged. In order to achieve this goal, the valves are considered to have submerged discharge, and this has raised the need to investigate the hydrodynamic behavior of the valve and compare it with the non-submerged state. To investigate the behavior of the valve, a 1:20 model of the valve, hood and discharge pool were designed and built. Then, the experimental rig was designed and equipped with measuring equipment, and the model valve was subjected to hydrodynamic and vibration tests with different opening percentages in non-submerged and submerged states with different downstream pool depths. These experiments have been repeated for the valve with hood and without hood and the results have been compared. Then, the finite element model of the 1:20 model valve was developed and hydrodynamically analyzed and the numerical results were compared with the experimental data. After ensuring the correctness of the numerical model, it was used to investigate the behavior of the valve in different conditions. The results show that there is not much change in the flow rate when the valve is submerged, but the range of vibrations decreases significantly. This decrease in the amplitude of vibrations becomes more dominant with increasing the depth of the pool. Also, it has been shown that the range of vibrations in the case without the hood is lower than the case with the hood. [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional (3D) numerical model based on the finite element method (FEM) is developed to determine the fluid flow and heat transfer phenomena in a real multi-tube downhole heat exchanger (DHE), designed ad hoc for the present application, considering natural convection inside a geothermal reservoir. The DHE has been effectively installed and tested on the island of Ischia, in southern Italy, and the measurements have been used to validate the model. In particular, the authors analyze experimentally and numerically the behavior of the DHE based on the outlet temperature of the working fluid, thermal power, overall heat transfer coefficient, and efficiency. Furthermore, the influence of the degree of salinity on the performance of the DHE has been studied, observing that it degrades with the increase in the degree of salinity. The results show that the DHE allows to exchange more than 40 kW with the ground, obtaining overall heat transfer coefficient values larger than 450 W/m2 K. At the degree of salinity of 180 ppt, a decrease in the efficiency of the DHE of more than 8% is observed. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) can reduce cognitive abilities at higher concentrations. CO2 can be used as a proxy for gas transport in an indoor environment and as an index to determine Indoor Air Quality (IAQ). In the present work, CO2 transport inside a real university classroom has been analysed experimentally and numerically. The main novelty is related to the experimental characterization of the airflow, boundary conditions for swirl diffusers and CO2 transport occurring in an actual university classroom equipped with a Turbulent Mixing Airflow (TMA) system. The numerical methodology, validated against the experimental measurements performed by the authors, has been used to identify the most suitable turbulence model for both thermo-fluid dynamic and CO2 transport simulations. Three different RANS k-ε turbulence models have been compared: the Standard k-ε, the RNG k-ε and the Realizable k-ε. Moreover, the evacuation time and the effects of turbulent diffusivity have been analysed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Solar chimney is nowadays an important source of renewable energy, especially in the hot region of the world. In this paper, the solar chimney is investigated based on the ambient conditions of Tunisia. An experimental setup is developed to study the solar chimney under the Tunisia weather conditions. Numerous simulations are performed to study the chimney diameter effect. The airflow characteristics are analyzed for the different chimney diameters. The depression zone in the chimney inlet increases with the increase of the chimney diameter. Consequently, the velocity value increases. The comparison between the numerical and the experimental results shows a good agreement. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Direct contact thermal energy storage (TES) for use in conventional air-conditioning systems is proposed to reduce the operational energy demand. Thermal performance of a novel kind of phase change material (PCM) prepared for use in conventional air-conditioning systems with the proposed direct contact TES tank, is evaluated. A 3-dimensional (3D) numerical model is built using ANSYS FLUENT to investigate dynamic characteristics of the discharging process of TES system. The model is validated by comparing the numerical with the experimental results. The effects of heat transfer fluid (HTF) flow rate, HTF inlet temperature, liquid PCM volume fraction, complete discharging time, discharging capacity of the tank, and temperature distribution in direct contact TES tank are investigated. The results indicate that increasing the HTF flow rate speeds up the discharging capacity and the discharging time of the direct contact TES system reduces. When the flow rate increases from 0.503 m 3 /h to 0.936 m 3 /h, the melting PCM increases from 63.33 vol.% to 70.74 vol.% within 600 s. The discharging capacity increases with HTF inlet temperature; however, the whole discharging capacity does not change obviously by changing HTF inlet temperature. [ABSTRACT FROM AUTHOR]

Many authors have focused their research on the vibrations caused by railway traffic, and have developed diverse models of railway tracks: from half-track analytical models up to complex numerical models. This paper presents numerical models, built using FEM software, for different types of railway tracks. These models describe in detail the superstructure vibratory response induced by vertical forces acting on the top of the rail head, and include aspects not reflected in the analytical models. The numerical results are compared with previously presented analytical ones, as well as with experimental measurements. [ABSTRACT FROM AUTHOR]

A reliable numerical procedure using the control volume formulation has been built up for predicting the hydrogen-generation process. The hydrogen production is due to the flow of an electrolyte between cathode and anode at different current densities. A bubbly two-phase flow process has been considered and a mathematical model based on Eulerian–Eulerian two-fluids has been adopted. The transport equations have been solved for both phases with allowance of interfacial transfer of mass and momentum. The conservation equations have been discretized using a finite volume method and solved by the SIMPLE algorithm. Measurements have been carried out along a tested cell gap at different current densities to visualize the hydrogen generation process. New insights into the model of hydrogen bubble-size variation in the computations are considered. Comparisons of numerical results based on the model with both experimental measurements and results available in the literature have been performed. The results indicate that the developed numerical model accurately predicts the hydrogen production process. The study shows also that the best production process is reached by decreasing the main flow velocity. Increasing the current density and reducing the gap distance between the cathode and the anode of the electrochemical cell helps improving the hydrogen production process. The bubble-diameter formulation of the dispersed hydrogen gas considerably influences the local and global characteristics of two-phase stream. [ABSTRACT FROM AUTHOR]

It has been proven that cyclic loading induced by the circulation of trains at very high speeds (>300 km/h) results in important track vibrations progressively amplified in a repeated process leading to the deterioration of track geometric quality and an unwanted increase in track maintenance needs and track life cycle costs. Having this as concern, the present paper focuses on a numerical model which was built to correctly predict train/track dynamic response (confidence assured by an extensive validation process with real experimental measurements in railway high speed lines) not only instantaneously but also in a long-term perspective. The innovation consists on the fact that the same tool enables both accessing track vibration levels and evaluating track settlement evolution throughout millions of cyclic train passages, maintaining low computing time. Different track design solutions are simulated, such as: softening railpads, applying under sleeper pads, placing ballast mats or using bituminous subballast as an alternative to granular subballast. Results are evaluated in the perspective of track vibrations mitigation and track maintenance needs. [ABSTRACT FROM AUTHOR]

Radiant heating panel systems provide high thermal comfort because of low noise level and few required equipments. These panels are installed on walls, floor, and roof in a scale room model. This study aims to investigate the performance of radiant panel heaters. Temperatures inside the room and on its walls were experimentally measured. A numerical model was also employed to study flow pattern inside the room and to predict temperature distribution. The turbulent flow was solved by using RNG k - ɛ turbulent model. Heat transfer by radiation was modeled by using DO radiation model. The results showed that the used numerical technique could accurately predict temperatures distribution in the room. The model was used to study the effect of panel heater locations and sizes on the air flow and air temperature distributions. The heat transfer rates were also calculated numerically as well. It was found that the minimum heat transfer rates were achieved by using the heating panel on the floor, and the scale room model was able to simulate the full-size room within a small percentage error about 20% especially in heater load and the temperature distribution was about less than 1%. [ABSTRACT FROM AUTHOR]

Highlights: [•] A real-scale vegetal façade was monitored during three years in a Mediterranean climate. [•] Results show that the vegetation layer improves interior environmental conditions. [•] A predictive numerical model was fitted and experimentally validated. [•] Results show the high accuracy of the model, being the R-squared around 85%. [•] The model is suitable for buildings located in similar climates to the one studied. [ABSTRACT FROM AUTHOR]

Abstract: Pre-stressing of masonry is one of the most widespread building/facility reconstruction methods. In the Czech Republic it is very successful, especially in the Moravian-Silesian Region, which is subject to a considerable amount of disturbances of buildings/facilities due to undermining. Pre-stressing in masonry can be achieved by means of steel wire ropes or rods. These steel elements are inserted into the pre-milled grooves, which may be in the external or internal wall face. The ends of the steel elements are clamped into steel angles or special anchors. In these reconstruction methods it is necessary to follow the pre- stressing procedures and technologies. It is important to properly select the pre-stressing anchoring system, appropriate layout and arrangement of pre-stressing wires, pre-stressing procedure and dimension of pre-stressing forces in the individual wires. This contribution deals with experimental measurements of deformations in the place exposed to local load caused by additional pre-stressing. The measurements are taken on a masonry corner built in the laboratory equipment. This laboratory equipment was designed at the Faculty of Civil Engineering VSB – TU Ostrava for measurement of the tri-axial stress-strain conditions in masonry. Two pre-stressing bars are placed in this masonry corner. These bars are at different heights and are anchored to the anchor plates, which transfer pre-stressing forces to the masonry. The specimen for laboratory testing is performed at the actual proportion of 1:1. Mathematical modeling of the brick corner is based on the finite element method using ANSYS software and then the results are compared with results of the laboratory tests. On the basis of these results it should be possible to improve the models and come closer to achieving an accurate and at the same time, simple procedure for the design of pre-stressed masonry. [Copyright &y& Elsevier]

Highlights: [•] We monitored a high insulted real-scale green roof in a Mediterranean climate. [•] It was monitored during three summers characterized by diverse vegetation density. [•] Results show that high vegetation density green roof is a passive cooling system. [•] It reduces thermal load of about 60% compared with the roof with no vegetation. [•] A roofing resistance numerical model was developed and experimentally validated. [Copyright &y& Elsevier]

Abstract: A novel design for a contraction nozzle, based on a logarithmic profile, is presented and developed to enhance aerodynamic measurements in a low-speed wind tunnel. The improvements obtained with this new proposal are validated, both, numerically and experimentally. As a starting point, four different wind tunnel contraction profiles were firstly considered and tested using the Computational Fluid Dynamics (CFD) package ANSYS FLUENT®. Both polynomial, due to its classical inclusion for wind tunnels, and logarithmic profiles, due to its expected enhancement, have been studied in terms of avoidance of separation of the boundary layer, procurement of a maximum level of exit-flow uniformity, and minimum turbulence levels at the outlet. Numerical comparison between obtained results shows the benefits of the new logarithmic profile developed by the authors, which was finally employed to construct the nozzle. To characterize its real performance, intensive experimental measurements have been conducted using pressure transducers and both single and dual hot wire anemometry. The pressure coefficient along the nozzle sidewall reveals an optimal evolution, matching perfectly with the theoretical design. In addition, low levels of turbulence and high flow uniformity is confirmed at the nozzle discharge. Turbulence intensities below 0.7% are obtained for the whole range of velocities available in the wind tunnel, and even practically constant uniform flow is obtained for all the traverses tested for validation. These indicators conclude that the contraction designed with the new profile is a good enhancing of the wind tunnel benefits. [Copyright &y& Elsevier]

The circulation of trains at very high speeds (higher than ) leads to important vibrations in the track and its environment. Concerning the track behavior, this dynamic cyclic loading conduces to the deterioration of its geometric quality, which progressively amplifies the vibration levels in a repeated process, leading to an increase in track lifecycle costs. Within this framework, this paper presents a dynamic numerical model that was built with this concern and was consistently validated with real experimental measurements at different maximum speeds, also above . The implementation in the model of long-term estimations of plastic deformations accumulations is described and highlighted. The influence of increasing train speeds in the level of vibrations reached in different types of tracks may be evaluated, as well as the track settlement evolution along the track and throughout millions of cyclic train passages. Different design alternative solutions are simulated: softening railpads, placing under-sleeper pads or ballast mats, or using bituminous subballast as an alternative to granular subballast. Critical analyses on the results obtained in the paper enable one to draw recommendations on the mitigation of track vibrations and maintenance interventions, that is, on the possible improvements to be made to ballasted high-speed track design considering its maintenance needs. [ABSTRACT FROM AUTHOR]

Abstract: The study of stress and deformation of a road pavement–subgrade system under vehicle traffic loads is one of the most important areas in the field of transportation. In this paper, a physical model with all the road structure layers was built to study the dynamic behaviour of the layered pavement–subgrade system. Experiments were performed to determine the stresses, elastic deformations and irreversible permanent deformations at different depths to better understand the dynamic behaviour of a portion of a pavement–subgrade system. According to the physical model, the transmission and reflection matrices (TRM) method was used, and the general solutions for the stresses and displacements of the layered system subjected to dynamic double-circular loads at its surface were obtained. Numerical results in the space domain were derived by performing the inverse Hankel’s transform and were used to compare its results with the experimental measurements. The agreement between the numerical and the experimental results was good, which indicates that the TRM method is useful in predicting the stresses and elastic deformations of a multi-layered road structure. Moreover, the stresses and elastic deformations were analysed for different properties of the structure using numerical computation. [Copyright &y& Elsevier]

Abstract: On the basis of the field (natural) measurements, which were carried out by the authors in cold regions such as Siberia in The Russian Federation, the temperature distributions and the phase front propagation are analyzed during thawing process in frozen soils (permafrost). The treatment of the experimental data was carried out on the basis of the likeness and dimensionality theory. In this way the temperature distribution as a function of the dimensionless values (criteria), characterizing the geometry of the calculation domain, thermo-physical properties of the soils and also level of the phase transitions — a criterion of Stefan was to be obtained in general form. The treatment of the experimental measurements in obtained general dimensionless form shows that the natural measurements for a wide range of both the soil surface temperature variation and thawing depth group near certain universal curves for the loamy and sandy soils, respectively. These curves may be approximated by the dimensionless self-similar function with a parameter which depends on the thermal and physical properties of the soil massif. By the method of linear regression the dependence of the front penetration coordinate on time is obtained and discussed in detail. It is shown that this dependence is different from the self-similar solution. The phase front propagation described by generalized approximation function obtained in this study is in good agreement with experimental data. On the basis of the nonlinear system of equations (general Boundary Value Problem) corresponding to the considered problem, the numerical solution for the temperature distribution in the soil is presented. For the temperature distribution the good agreement between experimental measurements and numerical solution is observed. [Copyright &y& Elsevier]

Abstract: A simplistic numerical methodology for calculating the magnetic fields in open air type substations around bus bars and single line conductors is suggested based on the finite element analysis of electrodynamics equations. The suggested methodology is firstly validated through direct comparison with experimental results at the 66/11kV substation of Latsia in Cyprus. Thereafter, the validated numerical methodology is used to predict the magnetic field values at nominal currents and the resulting fields are compared with the International Commission on Non Ionizing Radiation Protection (ICNIRP) field guidelines, dictating whether regulation limits are surpassed. It is found that the measured and the predicted magnetic field values are within the safety guidelines of the ICNIRP. [Copyright &y& Elsevier]

• Experimental validation of ultra-shortened 3D-FEM models in three-core armored cables. • An in-depth assessment of relevant aspects at power frequency in 10 real cables. • Good match with measurements in sequence impedances and induced sheath current. • Good accuracy in predicting the magnetic field induction in the vicinity of the cable. • Replicates nonlinear behavior seen in the laboratory due to the armor properties. 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. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we simulate heat transport in complex three-dimensional particulate microstructures using a computational procedure based on the formalism of hierarchical partition of unity field compositions (HPFC) recently developed by the authors. The computational procedure is based on constructing complex behavioral fields through Boolean compositions of primitive fields. It is demonstrated that the Boolean compositions efficiently model topological changes caused by the modification/rearrangement of the second phases in the heterogeneous material microstructure. The developed method is applied to evaluate the effective thermal conductivity of two particulate systems, namely, alumina particles in silicone oil and aluminum particles in silicone oil. Three-dimensional simulations of thirty random arrangements of the heterogeneous microstructure at a fixed 58% volume fraction were carried out so as to enable comparisons with experiments (15 measurements of each particle–matrix combination) conducted at an identical volume loading. The microstructures are systematically (and statistically) characterized using matrix-nearest surface exclusion probability functions. The agreement between the experiments and the simulations (mean values were within 10% of each other) validated the near-percolation transport mechanism in these practical material systems. The simulations also underscore the importance of capturing complex three-dimensional (random) particle arrangements and inter-particle interactions. It is demonstrated that these complex three-dimensional microstructural effects may explain experimental results that are sometimes ascribed to an imperfect interface and a non-verifiable interfacial resistance. [Copyright &y& Elsevier]