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DIVERSITY OF FOULING ORGANISMS ON A CARGO SHIP SAILING THE SAVA RIVER, SERBIA
No full textThe study investigates the constituents of biofilm formed on a hull of a cargo ship in the
Sava River, Serbia. Thickness of biofilm play main role in energy efficiency of ship during
exploitation. A biofilm sample was collected from the ship's surface on March 2023 from
the site of the “Vahali” Shipyard in Mačvanska Mitrovica using a brushing method. For
mycological analysis a 100 μL aliquot made from the biofilm sample was inoculated onto
a standard PDA medium under aseptic conditions. The average bacterial count in the
sample was 315.33 CFU per Petri dish/100 μL of the sample, while the average fungal
count was 11 CFU per Petri dish/100 μL of the sample. Based on colony characteristics
and microscopic features of reproductive structures, filamentous fungi Cladosporium
cladosporioides, Mucor megalocarpus and Penicillium spp. were identified. Additionally,
yeast Candida sp. was observed alongside filamentous fungi. Microscopic analysis of the
ship's biofilm revealed densely interwoven, branched hyphae predominantly enveloping
threads of green algae from the Cladophora genus. Besides mycelia, the presence of
micro- and macroconidia, as well as chlamydospores of Fusarium species, was noted in
the biofilm.
Light microscope observations of algal material was made using a Zeiss AxioImagerM.1
microscope. Seven algal species from four divisions were identified through microscopic
analysis: Aphanothece sp., Audouinella chalybea, Cladophora glomerata, Cocconeis
pediculus, Gomphonema parvulum, Navicula sp., and Rhoicosphaenia abbreviata.
Quantitatively, the most dominant biofilm species was Cladophora glometara, completely
covered with diatoms Cocconeis pediculus and Rhoicosphaenia abbreviata
Numerical investigation of fatigue behavior in Ti-6Al-4V orthopedic hip implants subjected to different environments
No full textIn this paper, hip implants made of Ti-6Al-4V titanium alloy are analyzed numerically using Extended Finite Element Method XFEM. The combined effect of corrosion and fatigue was considered here since this is a common cause of failure of hip implants. Experimental testing of Ti-6Al-4V alloy was performed to determine its mechanical properties under different working environments, including normal, salty, and humid conditions. The integrity and life of the hip implant were assessed using the Linear Elastic Fracture Mechanics (LEFM) approach. For this purpose, the conditional fracture toughness Kq using CT specimens from all three groups (normal, humid, salty conditions) were determined. This provided insight into how different aggressive environments affect the behavior of Ti-6Al-4V alloy; i.e., how much its resistance to crack growth would degrade depending on conditions corresponding to the real exploitation of hip implants. Next, analytical and XFEM analyses of fatigue behavior in terms of the number of cycles were performed for all three groups, and the obtained results showed good agreement, confirming the validity of the integrity assessment approach shown in this work, which also represented a novel approach since fatigue and corrosion effects were investigated simultaneously
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
Developing thermal insulation cement based mortars with recycled aggregate in accordance with Net Zero principles
No full textThe performance of thermo insulation rendering mortars with alternations in ratios
of powdered cordierite and talc was examined. The goal was to confirm that recycled
kilnware cordierite can be reapplied in the mortar design without significant deterioration in
performance in comparison with OPC mortar. Differential thermal analysis was employed for
examining thermally induced reactions. The ca vitation erosion, in testing sequences ranging
from 30 to 120 minutes, was used to assess the compa ctness of the mortar structure. The
physico mechanical properties of experimental mortars were investigated. The morphologies
of the mortar tablets upon cavi tation were studied using a scanning electron microscope. It
was established that cordierite and talc filler in amounts up to 20% enhance microstructural
packing and mechanical strengths due to improved cementation and therefore contribute to
cavitation er osion resistance. Hig her amounts of talc cause structural degradation and mass
loss during cavitation tests. Reducing manufacturing costs, energy consumption, and
greenhouse gas emissions are the main objectives of t he production of this waste based
constr uction composite, as the reuse of waste materials can help achieve a number of
Sustainable Development Goals
Merging Eco-Art and Recycling to Advance Environmental Preservation
No full textEco-art and recycling initiatives often involve comprehensive community engagement and participation in specific conditions. This paper explores the synergy between eco-art and recycling processes, as an optimal strategy to advance environmental preservation, alongside the integration of land art with ecological concepts. As environmental concerns escalate, the integration of ecoartistic measures and practices with recycling initiatives emerges as a potential to enhance environmental consciousness and sustainability. The study delves into the interconnectedness of these two disciplines, examining how the creative expression of eco-art can amplify the impact of recycling efforts and activities, leading to heightened environmental awareness and conservation. By detailed examination of the intersections of these creative and ecological disciplines, the research aims to contribute insights into innovative approaches that simultaneously harmonize artistic expression and environmental conservation aspect, with the final important task of protecting our planet and ensuring sustainable development
Erosion wear of HCCI alloys
Get PDFFailures in industrial plants, which operate under extreme conditions, could occur after a short time of exploitation. Erosion wear of materials is caused by the relative movement of solid particles and the surfaces of components. Such erosive wear can lead to the failure of industrial components in a very short time and/or a sharp decline in the structural integrity of industrial equipment. For example, the wear of the ash disposal system in a coal-burning thermal power plant, due to impact of ash particles with a high content of mineral residues, is a very common case of failure and outages in the operation of such industrial systems.
Two high chromium cast irons (HCCI) were tested to determine the erosion wear. These alloys contain 15% Cr and 25% Cr, and it was tested in as-cast and after heat treatment (annealing). A specially designed installation was used for the gas blast sand erosion test. Type of erodent was foundry quartz sand. Erosion tests were done with high erodent particle velocity (90 m/s) and high erodent feed rate (3000 g/min). This conditions represents those similar to extreme wear conditions of some components of thermal power plants using pulverized high mineral content coals.
Microstructural characterization was done at samples before and after erosion tests, Fig. 1. The main results indicate that matrix plastic deformation and distribution of carbide phase have a significant contribution to erosion resistance of HCCI alloys in such conditions
Testing of the condition and performance of coupling links from screw couplings of train
No full textThis paper presents an analysis of train screw coupling used mainly in Europe as mechanical
connection of wagons in train. An analysis of train breaks apart incidents revealed that less than
30 % of the cases were caused by elements of the screw coupling, with coupling links accounting
for only 5 % of the failures. Therefore, the investigation focused on testing the coupling links,
which are safety elements of the screw coupling. The coupling links underwent various inspections,
including visual inspection, dimensional control, non-destructive testing, examination
of chemical composition, and mechanical tests. Dimensional control found longitudinal plastic
deformations of the links. Chemical examination revealed that the links were made of different
material than recommended, but their mechanical properties generally met the recommended
values. However, variations were observed among different links, likely due to different rates of
deformation during testing and operational conditions. Overall, the analysis and inspections
provided insights into the condition and performance of coupling links in the screw coupling
system, highlighting the importance of monitoring and maintaining these elements to ensure safe
and efficient railway operations
RELIABILITY-BASED RISK ASSESSMENT OF AUXILIARY MACHINERY IN OPEN-PIT MINES: A BACKHOE LOADER CASE STUDY
Get PDFNumerous authors have demonstrated the effectiveness of the risk-based approach in the mining sector. However, the majority of earlier research has ignored the role that auxiliary machines, in total risk management play in favor of heavy machinery. This study aims to analyze backhoe loader maintenance data in order to offer a risk assessment approach for auxiliary machinery in open-pit mines. The severity, occurrence, and detection of failures were the three component indicators that together determined the overall risk, as per the FMEA method. The purpose of the Pareto chart was to grade the detection indicator by illustrating the failure type distribution and distinction. The downtime data statistical testing results enabled analytical calculation of the system's reliability and mean downtime, which in turn allowed for the evaluation of the frequency and severity of failures. As a result, a framework for evaluation was put out, supported by data that was gathered, and included a three-dimensional risk assessment matrix. The focus of further research efforts should be on expanding the present sample data in sense of quantity and also to analysis of other machines in the whole mining system
A HYBRID RELIABILITY - FMEA METHODOLOGY IN RISK ASSESSMENT OF A BELT CONVEYOR SYSTEM
Get PDFAn appropriate maintenance strategy can maximize a machine’s capacity and economic lifetime and also produce yearly savings of several million euros. That being said, a risk assessment approach can help companies identify the systemic bottlenecks that are interfering with their development and cut a large portion of their profit each year. This paper presents a hybrid reliability-Failure Mode and Effects Analysis (FMEA) methodology to assess the risk associated with belt conveyor systems, particularly in open-pit mining environments. By integrating severity, occurrence, and detection indicators, a 3D risk assessment matrix was developed. Using data from conveyor system maintenance, including downtime and failure occurrences, chi-square tests to analyze system reliability and mean downtime were applied. The methodology allows for a nuanced understanding of the frequency and severity of failures, enabling more informed decision-making about maintenance strategies. The paper highlights the economic implications of system failures and the potential for substantial financial savings through optimized maintenance planning