machinery
Not a member yet
8395 research outputs found
Sort by
INERTNI GASOVI I AEROSOLI KAO ALTERNATIVNA SREDSTVA HALONIMA ZA GAŠENJE POŽARA
No full textPasivni (inertni) gasovi i aerosoli igraju važnu ulogu u savremenim sistemima za zaštitu od
požara, obezbeđujući efikasno suzbijanje požara u različitim okruženjima, gde su drugi agensi za
gašenje nepraktični ili predstavljaju rizik za osetljivu opremu. Određene vrste halogenih derivata
alkana dokazani su kao veoma efikasna sredstva za gašenje požara, ali od Montrealskog sporazuma njihova proizvodnja i upotreba se zabranjuju, dok se samo u izuzetnim slučajevima tzv. kritične primene, ograničavaju. Postepeno ukidanje proizvodnje halona značajno je uticalo na sektor prevencije požara i eksplozija, i utrlo je put istraživanju i primeni alternativnih sredstava. U radu će biti prikazane ekološki prihvatljive alternative halonima za gašenje različitih klasa požara u vidu inertnih gasova i aerosola, njihova svojstva, kompatibilnost primene u različitim prostorima i proračunske procedure za izračunavanje koncentracije sredstva date različitim standardima, sa ciljem da se istakne njihov potencijal u projektovanju instalacija za gašenje požara „čistim“ sredstvima
Investigating the influence of plate geometry and detonation variations on structural responses under explosion loading: A nonlinear finite-element analysis with sensitivity analysis
No full textThis study presents the results of a numerical analysis of the response of Domex 700 and Dormex 1100 steel plates with varying geometries, combined with several different parameters such as a thickness of up to 6 mm and a trinitrotoluene (TNT) mass. Using ABAQUS software, finite-element analysis was run to examine the structural response ability of the steel plates to explosions. In terms of deformation and energy dissipation, the results showed a large differentiation. A sensitivity analysis was used to examine each simulation result in terms of the structural response performance to explosions and identify the variables that had the greatest impact on variations in the thickness, material, geometry, and TNT mass. The best numerical simulation results were found using the multi-attribute decision-making (MADM) approach. Annotations are utilized to assist in identifying the various modifications made during testing. Annotations LXXI to LVIII achieved the lowest value of 6.176 × 10−09, signifying the best results according to calculations made using the MADM approach. This is evidenced by the structural events, demonstrating that the deformation, von Mises stress, and energy dissipation in the circular plate structure were not significantly impacted by the explosion. The variables that most significantly affect variations in deformation, von Mises stress, and dissipated energy – variables that significantly impact the structural response to explosions – are identified through the sensitivity analysis approach. The results of this research can be used to optimize the structural response performance of circular plates
Assessing green hydrogen potential and utilization for sustainable energy production in Serbia
No full textThe paper provides a comprehensive examination of resources available for the deployment of green hydrogen in Serbia. The assessment encompasses various aspects, including renewable energy potentials, technological advancements, and future projections. The evaluation considers factors such as solar and wind power capacities, which are pivotal for green hydrogen production. Additionally, the study delves into the policy landscape, addressing initiatives aimed at fostering the integration of green hydrogen into Serbia's energy matrix. The analysis combines quantitative data on energy production capacities with qualitative insights into the economic and environmental implications of green hydrogen utilization. While the nation boasts abundant renewable energy resources, challenges such as high production costs and infrastructure limitations hinder widespread adoption. However, with strategic initiatives and technological advancements, Serbia can overcome these hurdles and pave the way for a sustainable hydrogen economy. Assessing Serbia's green hydrogen potential, driven by over 24 095 MWp from solar and 10 750 MWp from wind, highlights the nation's capacity to harness renewable resources, with hydrogen production set to grow from 1915 tons in 2019 to 37 ,123 tons by 2040. The findings aim to contribute to the ongoing discourse on sustainable energy transitions and the role of green hydrogen in Serbia's evolving energy landscape.Ministry of Science, Technological Development and Innovation; Faculty of Technical Sciences, University of Novi Sad through project "Scientific and Artistic Research Work of Researchers [01-3394/1]; [451-03-65/2024-03/200156
Decompositions of optimal averaged Gauss quadrature rules
No full textOptimal averaged Gauss quadrature rules provide estimates for the quadrature error in Gauss rules, as well as estimates for the error incurred when approximating
matrix functionals of the form u
T
f (A)v with a large matrix A ∈ R
N×N by lowrank approximations that are obtained by applying a few steps of the symmetric or
nonsymmetric Lanczos processes to A; here u, v ∈ R
N
are vectors. The latter process
is used when the measure associated with the Gauss quadrature rule has support in
the complex plane. The symmetric Lanczos process yields a real tridiagonal matrix,
whose entries determine the recursion coefficients of the monic orthogonal polynomials
associated with the measure, while the nonsymmetric Lanczos process determines a
nonsymmetric tridiagonal matrix, whose entries are recursion coefficients for a pair of
sets of bi-orthogonal polynomials. Recently, it has been shown, by applying the results
of Peherstorfer, that optimal averaged Gauss quadrature rules, which are associated
with a nonnegative measure with support on the real axis, can be expressed as a
weighted sum of two quadrature rules. This decomposition allows faster evaluation of
optimal averaged Gauss quadrature rules than the previously available representation.
The present paper provides a new self-contained proof of this decomposition that
is based on linear algebra techniques. Moreover, these techniques are generalized to
determine a decomposition of the optimal averaged quadrature rules that are associated
with the tridiagonal matrices determined by the nonsymmetric Lanczos process. Also,
the splitting of complex symmetric tridiagonal matrices is discussed. The new splittings
allow faster evaluation of optimal averaged Gauss quadrature rules than the previously
available representations. Computational aspects are discussed
APPLICATION OF INDUSTRIAL AIR CLEANERS IN PRODUCTION HALLS
No full textAir cleaners are devices that an increasing number of people use to improve Indoor Air Quality (IAQ) in their homes and workplaces, especially in areas where the outdoor air is often excessively polluted. However, such devices, from small to large air flow capacities, are also widely used in the industries of developed countries to control and reduce the impact of the pollutants’ emission. This study deals with the analysis of experimental data regarding IAQ in a production hall with CNC machines in conditions of high concentration of emulsion vapors, focusing on the applica tion of mobile industrial air cleaners, as independent and supplementary components of HVAC systems. Experimental data is obtained through measurements, conducted by two different methods using two different measuring instruments.
Analyzed results show that the application of mobile industrial air cleaners can lead to significant increase of the num ber of production hall working hours, during which, according to U.S. Environmental Protection Agency (EPA), indoor air quality, according to PM2.5 (µg/m3), coincides with the “Moderate” air quality category, while it may also lead to occurrence of working hours during which indoor air quality, according to PM2.5 (µg/m3), coincides with the “Good”
indoor air quality category. Furthermore, the application of mobile industrial air cleaners leads to the decrease of the indoor air concentration of particulate matter of all sizes in the range of PM0.3 to PM10. However, analysis also shows that the devices’ effectiveness in the PM concentration reduction is heavily dependent on the mobile air cleaners mutual position, as well as the time that has passed since their actuation
Investigation of occupants’ characteristics impact on thermal comfort assessment using a novel neural network PMVo calculation model
No full textThe main aim of this study is the analysis of the impact that occupants’ characteristics have on thermal comfort assessment, through establishing a novel PMVo model using an approximation method, based on the experimental data. The parameters which are chosen as model’s inputs are the air temperature, mean radiant temperature, relative humidity, basic clothing insulation, air velocity and occupants characteristics – gender, age, height, and body mass, while the output is the PMVo, a novel thermal comfort index. Since existing standards concerning thermal comfort do not consider these occupants’ characteristics, the main novelty of the introduced model is the inclusion of occupants’ characteristics in the thermal comfort assessment. To ensure enhanced precision, the model is established using both linear regression and by training neural network. These two approximation methods are compared to determine which one is more applicable in the context of data approximation. Study shows that regardless of dataset based on which models are established and regardless of testing input values, neural network (R2 in the range of 99.87% to 99.96%) is a superior mathematical approximation algorithm compared to the linear regression (R2 in the range of 95.3% to 97.5%). Novel neural network based thermal comfort assessment model is used for investigation of occupants’ characteristics impact on thermal comfort assessment. Analysis of the results showed that gender, age, height and body mass may significantly impact thermal comfort indices calculation, which implies the necessity of their inclusion in thermal comfort prediction and evaluation. Thus, the presented PMVo model may be highly beneficial to implement within existing thermal comfort standards, ensuring well-being and satisfaction with conditions of indoor environment for wider range of the occupants
NUMERICAL SIMULATION OF POOL BOILING WITH TWO-FLUID MODEL AND GRID-RESOLVED HEAT TRANSFER MECHANISMS
No full textMost nucleate boiling simulations are based on the Eulerian modelling of bulk liquid-vapour two-phase flow and subgrid presence of all mechanistically partitioned heat transfer modes in fluid control volumes in contact with the heated wall. Such mechanistic partitioning heat transfer approach predicts the total heat flux from the heated wall towards the boiling two-phase mixture as the sum of (i) the single-phase convection heat transfer from the heated wetted wall not covered with the rising bubbles, (ii) the transient conduction caused by the rewetting of the heated wall hot spot after the bubble detachment, known as quenching heat flux and (iii) the evaporation heat flux. Here presented research introduces a new approach to the numerical modelling of pool boiling based on the grid resolved mechanisms of boiling heat transfer. The spots of bubble growth and the wetted areas are distinguished and two grid resolved modes of heat transfer are considered: the conjugate heat transfer from the heated wall to the rising bubble at the bubble footprint until the bubble departure and the conjugate heat transfer from the heated wall to the wetting liquid. The constituents of the heat transfer model at the footprint of the bubble growth are the bubble residence time and the bubble departure diameter. The presented model is validated by experimental data from the literature. It was shown that the model can predict the wall temperature transient at bubble footprint location as well as the mean wall superheating. Appropriate modelling of vapour generation at the discrete locations of the bubble growth enables good prediction of two-phase mixture pattern in the boiling pool, the void fraction distribution along pool height and swell level position. Further analysis includes the application of both subgrid and grid resolved modelling approaches to the simulation of pool boiling under high heat fluxes. It is shown that the subgrid wall boiling model does not predict adequately the wall temperature transient behaviour and the void fraction distribution in the boiling pool under high heat fluxes, while the grid resolved model provides plausible results. Presented simulations are obtained with the in-house computer code based on the modified Semi-Implicit Method for Pressure Linked Equations (SIMPLE) for the solving of mass, momentum and energy balance equation for each phase and appropriate closure laws for the prediction of vapour-liquid interface transport phenomena
Structural optimization of a composite structure of a vertical take-off and landing (VTOL) unmanned air vehicle (UAV)
No full textIn order to design the optimal composite structure of a contemporary unmanned air vehicle
(UAV) with vertical take-off and landing (VTOL) capability, a finite element (FE) model was
developed and incorporated into an optimization cycle. Structure is assumed as a layered
carbon-fiber shell, whose lay-up sequence (defined by layer thicknesses and orientations) is
optimized by genetic algorithm (GA). As illustrated in Fig. 1 (left) the beam is constrained at
places corresponding to connections with the wing, and forces are introduced at one end,
simulating worst-case scenario (e.g. a sudden impact). The goal function is the minimal mass,
whereas different constraints (such as failure criterion, or maximal strain) are imposed. The
population is made up of 100 individuals, that are matched and crossed for 50 generations, until
converging to the optimal solution, as represented in Fig. 1 (right). The proposed methodology
can significantly facilitate and accelerate the design process of composite structures present in
aerospace engineering
Computing aerodynamic damping in roll and pitch of a supersonic finner model
No full textAccurate aerodynamic coefficients and their derivatives are crucial for flight dynamics analysis and appropriate control definition. Even when the investigated geometry is simple (e.g. a revolution body, with simple control or stabilizing surfaces), determination of its aerodynamic derivatives, particularly at supersonic regimes, is rather challenging, and usually includes extensive computational and experimental campaigns. This paper computationally investigates quasi-steady or unsteady supersonic flows that include rigid body motion effects around the Army-Navy Finner geometry (a basic, revolution body with L/D = 10 fineness, slender, conical nose section, and wedge-section fins in × configuration). To elucidate the flow fields, the Reynolds-averaged Navier-Stokes equations are closed by k-ω SST turbulence model. Roll and pitch damping are estimated by different approaches, and the obtained values are compared mutually, but also to the available experimental data. In addition, some representative flow visualizations are included