Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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CFD-Powered Ship Trim Optimization: Integrating ANN for User-Friendly Software Tool Development
No full textThis study presents a comprehensive approach to trim optimization as an energy efficiency improvement measure, focusing on reducing fuel consumption for one RO-RO car carrier. Utilizing Computational Fluid Dynamics (CFD) software, the methodology incorporates artificial neural networks (ANNs) to develop a mathematical model for estimating key parameters such as the brake power, daily fuel oil consumption (DFOC) and propeller speed. The complex ANN model is then integrated into a user-friendly software tool for practical engineering applications. The research outlines a seven-phase trim optimization process and discusses its potential extension to other types of ships, aiming to establish a universal methodology for CFD-based engineering analyses. Based on the trim optimization results, the biggest DFOC goes up to 10.5% at 7.5 m draft and up to 8% for higher drafts. Generally, in every considered case, it is recommended to sail with the trim towards the bow, meaning that the ship’s longitudinal center of gravity should be adjusted to tilt slightly forward
Numerical investigations of steam accumulator dynamics: Assessment of computational models
No full textSteam accumulators are crucial components of systems for thermal energy storage in various facilities utilizing
either fossil or renewable energy source. Accurate predictions of steam accumulator dynamics are of immense
importance for the proper design and the reliable operation of these storage systems. For this purpose, the numerical
modelling of transient behaviour of two-phase steam-liquid water system within the steam accumulator
is applied in the majority of reported investigations. It is observed that there are differences in these applied
modelling approaches, which raises concerns regarding their validity. In that regard, this paper deals with
assessment of contemporary computational models for numerical investigations of the steam accumulator dynamics.
The focus is placed on modelling approaches based on differential mass and energy balance equations of
the two-phase steam-liquid water system in the steam accumulator. Models based on assumption of either
thermal equilibrium or thermal non-equilibrium between phases are considered. The validity of both, the
structure of governing equations and the applied closure laws are investigated using available measured data.
The results of conducted analyses show that in some modelling approaches the energy equation is not correctly
formulated. Therefore, some terms in this equation associated with the transfer processes at the steam-liquid
water interface are either omitted or abundant, which leads to erroneous numerical results. Further, the heat
transfer to the walls of the steam accumulator vessel may not be neglected as it affects dynamics of the two-phase
system not only during, but also after the transient. Finally, the heat transfer due to the difference in temperature
between liquid water and steam needs to be accounted for. Otherwise, the steam temperature could attain
unphysically high values.
The critical issue in closure laws for the evaluation of mass transfer rate at the phase interface is the so-called
relaxation factor, which accounts for a finite time of the phase transition. Commonly, this parameter is either
adopted as empirical constant or estimated by experimental investigations of the considered steam accumulator.
The existing methodology for the theoretical determination of the relaxation factor turned out to be of limited
applicability. This paper introduces an improved relation for evaluation of the relaxation factor, which takes into
account the geometry of the steam accumulator, i.e. the dependance of the interfacial area concentration for the
phase transition on the ratio of the wetted walls area to the liquid volume. The relation is validated using
available data measured during the charging of industrial and lab-type steam accumulators
Comparative Mechanical Analysis of PLA and ABS Materials in Filament and Resin Form
No full textAdditive manufacturing (AM), also known as 3D printing, represent technologies where the production of physical models with complex shapes is performed in a layer-by-layer manner, directly from the CAD model. With these processes, there is no need for additional tools or fixtures, and there is no excess material. There are seven different AM technologies, all utilizing different materials depending on the needed final part properties. Recent years were particularly significant for the development and advancement of polymer materials in AM. Among available technologies where polymer materials are used, this research covers extrusion-based Fused Deposition Modeling (FDM) and liquid resin photopolymerization technology called Digital Light Processing (DLP). Concerning the fact that these technologies processmaterials from different forms, the filament and resin form, the goal of this research was to compare the mechanical properties
of two of the most widespread materials in AM, Acrylonitrile Butadiene Styrene (ABS) and PolyLactic Acid (PLA), in filament and resin form. Specimen geometry and test protocols followed the dedicated standards. For a comprehensive analysis tensile, compression, and (three-point) bending tests were utilized here, along with surface fracture 2D optical microscopy and Shore A hardness test
STRAIGHTNESS ANALYSIS OF MACHINE TOOL WITH NON-LINEAR KINEMATICS
No full textStraightness of the machine tool affects the accuracy of the workpiece to a great extent. Using wellestablished technics the straightness of linear axis of the machine tools can be determined with a high accuracy. Machine tools with non-linear kinematics are much different in relation to the machine tools with serial mechanisms. It is necessaryto be sure that the existing procedures are appropriate for determining the straightness of machine tools with non-linear kinematics. For that purpose the straightness accuracy of linear axis of a machine tool with socalled O-X glide parallel mechanism, which has non-linear kinematic characteristics, is determined through laser displacement measurements.Editor: Dr Boris Dumnić, full professor, dean
Technical treatment and design: Dr Đorđe Vukelić, full professor
Dr Milana Ilić Mićunović, assistant professor
MSc Aleksandar Milošević, assistan
APPLICATION OF WASTE RAW MATERIALS AS A REINFORCEMENT FOR PROTECTIVE COATINGS BASED ON PYROPHYLLITE
No full textIn this study, pyrophyllite was used for the first time in the composition of protective refractory coatings together with supplementary waste resources. The proposed refractory coatings are applicable for metallic and non-metallic structures, with the option of using them to protect machinery components in the chemical industry, metallurgy, and mining. Given that pyrophyllite has a low hardness, the goal was to improve the coating's resistance to cavitation erosion by adding 20 wt.% of hard refractory materials, i.e., crushed and micronized waste bricks based on mullite and corundum, respectively. Previous studies have demonstrated that protective coatings using a pyrophyllite filler have refractory qualities but insufficient resistance to cavitation erosion. As a result, the composition of refractory coatings, the preparation techniques, and the coating manufacturing process were altered. This study presents a simple method for combining conventional coatings made of refractory fillers (primary resource: pyrophyllite) with waste materials (mullite brick and corundum brick) used as reinforcement in protective refractory coatings for metal and non-metal structural elements that are highly resistant to cavitation erosion
Fixed point theorem for extended nonlinear quasi-contractions on b-metric spaces
No full textIn this paper, we present fixed point theorem for mappings defined on b-metric spaces, which
satisfies extended quasi-contractive inequality with nonlinear comparison function. Our result
generalizes and improves several recent results from fixed point theory
The safety climate, hierarchical levels and resilience assessment in transport and mining companies
No full textTransport and mining companies are vulnerable to a variety of hazards, and this paper offers a novel conceptual framework for organisational resilience assessment at different organisational levels. It is based on a safety climate and performances assessment in companies in the transport and mining sector. The framework contains factor and reliability analysis and continues by applying the SMART method from the perspective of resilience corners: anticipate, monitor, react and learn. The highest resilience coefficients at all organisational levels are obtained regarding safety awareness, safety training and safety communication areas, while the lowest values are observed for risk assessment and the organisational environment. The obtained results indicate that the ‘monitor’ resilience corner must be improved at all organisational levels, employees trained and procedures changed, since employees do not sufficiently use experience from previous events. The very high values at all organisational levels of the coefficients regarding the ‘anticipate’ and ‘learn’ resilience corners indicate organisational adaptation to changes through corrective activities, rather than planned preventive ones. All hierarchical levels have good resilience indicators, except for middle management, which expressed an adequate resilience index, due to the lower ratings of the safety training, organisational commitment, risk assessment and management support areas
Travel time model for multiple-deep shuttle-based storage and retrieval systems
No full textThe paper presents an analytical model for travel time evaluation in double-deep, triple-deep, quadruple-deep and fivefold-deep tier-captive shuttle-based storage and retrieval system (SBS/RS). Under the assumption of the deepest location rule for the storage process and the nearest neighbour rule for the retrieval process, the expressions for single-command and dual-command cycle times of the shuttle vehicle and elevator are developed, from which the SBS/RS performance can be estimated. The model based on the probability theory enables the evaluation of all individual times that make up the cycle times and assessment of the average number of totes relocated during a retrieval process. Special attention is devoted to the modelling of the relocation of totes which block access to the requested tote during the retrieval process. The validity of the analytical model is examined via the developed simulation model. The given case study shows that the proposed analytical travel time model results match the results of the simulation model. The presented modelling strategy could be applied to bigger system racking depths following the same modelling logic