Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Guest editorial: Innovative methods for structural integrity and reliability assessment and material characterisation under environmental effects
No full textAvailable data from practice and case studies can often provide significant data input needed for the analysis and assessment of structural failure and its prevention during the exploitation period, which ensures its reliability and safety. Still, with all the available knowledge nowadays, this cannot be considered a general rule. From the structural integrity point of view (in general), cracks and defects in engineering structures can be researched by applying various scientific and engineering approaches, including classical mechanics, fracture mechanics, standard probabilistic and risk analysis methods used for wider applications, etc. Standards and directives often provide conservative solutions during construction design, sometimes leading to overly conservative and ineffective results, i.e. non-optimized structures. The complexity of new engineering structures and the application of new materials and new manufacturing technologies impose the need for different approaches in structural integrity assessment, modification of existing ones or the application of multidisciplinary methods involving several scientific and engineering disciplines as one.
Taking into account the aforementioned, adequate material characterization has an important role, especially if environmental effects are involved, making the problem of structural integrity and reliability assessment more complex. Depending on environmental effects, caution is paid to damage mechanisms, including corrosion (which mostly refers to process equipment, as an example). The heterogeneity of welded joint areas in engineering structures, combined with environmental effects (or without them), adversely affects their service life. All aforementioned factors impose the need for reliable probabilistic methods of assessment of engineering structures, consisting of compromise solutions for the fulfillment of technical, reliability, safety and economic requirements.
This special issue, dedicated to The Second International Symposium on Risk Analysis and Safety of Complex Structures and Components (IRAS 2023), held in Belgrade, Serbia, from April 2–4, 2023, aims to include submissions concerning innovation and recent trends, multidisciplinary approaches, as well as case studies involving structural integrity assessment, risk analysis and the safety of engineering structures, while taking into account environmental effects, material behavior, its characterization, and the specificity of the structure itself.
The following seven papers are accepted for publishing after the peer review process:
(1) The role of the second non-vanishing terms in the material failure curve on APL 5L steel;
(2) Tensile, flexural and free vibration characteristics of sustainable recycled polypropylene filled with spherical SiC through experimental and RVE Analysis;
(3) Comparative study of corrosion-based service life prediction of reinforced concrete structures using traditional and machine learning approach;
(4) Damage assessments of designed sandwich cores against an idealized impact loading of ship accidents: experiment-based validated nonlinear finite element approach;
(5) Sustainability and environmental life cycle analysis of welding processes;
(6) Research of criteria for analyzing the load-bearing capacity of buildings in areas of technogenic impact caused by mining operations and
(7) Determination of the influence of FDM printing parameters on tensile strength and fracture occurrence of additively manufactured ABS material.
Both guest editors would like to express their sincere gratitude to the authors for their valuable contributions and also extend their thanks to the numerous reviewers for their diligent efforts in ensuring the high quality of the manuscripts
Аssessment of welded joints impact on structural integrity of a pressure vessel
No full textPrevious experience with integrity assessment of welded structures and elements had confirmed
the usefulness of numerical simulations, among other things in terms of how rigidity and geometry of such structures affect the stress distribution. This approach worked well for elastic calculations for welded structures, efficiently providing accurate results which were easy to compare with the yield stress levels of selected materials. In the case where stresses are above yield stress levels, the differences in mechanical properties of individual weld regions become a crucial factor in terms of influence on the integrity of the observed structure, unlike the elastic region, where this influence was negligible. In order to obtain proper input data (mechanical tensile properties of all welded joint
regions), previouslu developed methodology, that combines experimental and numerical method, is
used. Herein the experimental approach provided the strain fields (as obtained by digital image correlation) while specimen was subjected to tensile testing, which were used to improve numerical
computational models. In this way, it was possible to accurately determine the mechanical properties of all individual weld regions in an iterative manner. Using the previously described input data, two computational models of a pressure vessel were developed, with and without welded joints. During typical exploitation conditions under service operations, there was no difference between the two models, as the stresses were still in the elastic area. However, once the stresses reached plasticity, considerable differences between these models were observed in the welded joints area. Noticeable stress concentration was present in the zone of welded joints (in a computational model containing welded joints), increasing the stresses by around 50% (stress concentration factor of 1.5) in comparison to computational model without welded joints and without stress concentration. This had shown good agreement with previous research, which involved the application of this methodology to a pipeline, and these two cases were similar, since they involved welded structures made of shell elements loaded with internal pressure, causing membrane stresses.Project no. 451-03-137/2025-03/ 200105 from 04.02.202
Speed Control of a Rotary Servo-Base Unit: Lyapunov and MIT Rule Approaches
No full textThis paper presents a comparative study of two speed control techniques for a rotary servo-base unit using Lyapunov-based adaptive control and the MIT rule technique. The primary objective is to achieve precise and stable speed control and to analyze the influence of adaptation gain on the system performance. A mathematical model of the rotary system is analyzed, followed by the development of adaptive controllers based on the Lyapunov stability theory and the MIT rule. Choosing a suitable reference model is examined, and parameter adaptation laws are designed to optimize system performance. The impact of different adaptation gains on system response is evaluated through simulations in MATLAB/Simulink. Figures illustrating the evolution of adaptation parameters over time, as well as system response, are provided. Various performance criteria, settling time, overshoot, and different objective functions are used to compare the control approaches. The results highlight the advantages and limitations of each method. Recommendations for tuning adaptation parameters are provided to improve overall system performance.under contract 451-03-137/2025-03/200105, from date 04.02.202
Lifetime Corrosion Loss of Bulk Carriers
No full textThis paper analyzes the total steel replacement due to corrosion degradation in four Handymax-class bulk carriers, based on corrosion measurements recorded throughout their operational lifespan. Each ship was divided into 11 lightship mass subgroups, enabling detailed examination of cumulative lifetime corrosion losses for both entire ships and individual subgroups. Utilizing similar ship data obtained from the shipyard, the study also provides estimations of the total steel weights of each of lightship subgroups. The findings offer valuable insights into the overall aging effects on ship structures, crucial for maintenance planning, structural integrity assessments, and recycling, especially from the perspective of sustainable shipping. Additionally, the estimated weights of lightship subgroups can serve as reference data for preliminary ship design, aiding in the estimation of lightship weights and potential steel loss due to corrosion
DIGITAL IMAGE CORRELATION-ENABLED DIGITAL TWIN FRAMEWORK FOR STRUCTURAL INTEGRITY ASSESSMENT OF WELDED STEEL PIPELINES
No full textEnsuring the structural integrity of welded steel pipe networks that operate under fluctuating pressure and temperature remains a core challenge for mechanical engineers. Point-based sensors capture only a fraction of the complex strain fields that develop around welds, elbows, and other stress concentrators, limiting the predictive accuracy of numerical models used for fitness-for-service evaluations. From a digital image correlation (DIC) perspective, the solution lies in coupling high-resolution, full-field measurements with continuously updating computational twins. This paper presents a practitioner-oriented concept in which a compact 2D DIC module, comprising an industrial camera, LED illumination, and a graphics board, acquires displacement data directly on the pipe surface. Indicators, such as equivalent plastic strain, wall ovality, and local curvature change, serve as update inputs to a physics-informed twin that combines nonlinear finiteelement mechanics with data-driven parameter estimation. Planned verification includes laboratory cyclicloading studies and numerical sensitivity analyses to establish permissible correlation noise, optimal update frequency, and convergence criteria for critical load assessments. By integrating field-deployable DIC instrumentation with an adaptive digital twin, the proposed framework offers a realistic, low-latency pathway for condition-based maintenance of pressure pipeline and aligns with emerging industry standards for assetintegrity management
Comprehensive Method for Predicting Gas Turbine Cycle Performances Considering the Impact of Various Fuels
No full textGas turbines have advanced significantly in recent years, particularly in compressor and turbine efficiency because of aerodynamic breakthroughs based on numerical flow simulations. Additionally, modern energy demands have driven the adoption of alternative, environmentally friendly fuels such as hydrogen, ammonia, and methanol. These fuels significantly influence combustion gas composition, turbine inlet temperature, mass flow, blade cooling, and overall performance. Traditional cycle performance tools often rely on 0D maps for compressors and turbines, which have limitations in simulating these recent advancements. The proposed method replaces such maps with a 2D approach, utilizing detailed flow calculations for compressors and turbines at each operating point. It integrates combustion processes and secondary air systems and iteratively determines the turbine inlet temperature for precise predictions. This method accurately simulates air bleeds, cooling injections, and adjustments in inlet guide and stator vanes while accounting for the effects of fuel composition on performance. This paper demonstrates the methodology using an industrial gas turbine in which natural gas, hydrogen and hydrogen carriers are used as fuels. It shows the consequences of this for several components as well as the main thermodynamic operating parameters. The approach is fast and effective, enabling the optimization of diverse designs throughout development
Structural integrity assessment of oil storage tank: Non-destructive
No full textThis work presents the method for monitoring the integrity of oil methanol tanks located in Serbia and Norway. Considering the importance of safe operation of such equipment, it was necessary to use advanced non-destructive testing inspection for this purpose. The inspection, which involved state-of-the-art ultrasonic testing method, was completed in order to collect data required for evaluation of structural integrity and fitness for continued service of the tanks in question. Inspection and structural integrity analysis will include assessment of the most critical elements of these tanks, including their foundations, shell, roof and floor/bottom of the methanol tanks. This analysis included the calculation of thickness in various parts of the tanks, and it was determined that they were all within the allowed limits, implying that both tanks were safe for continued service
COMPOSITE MATERIALS IN GEAR DESIGN
No full textComposite materials, known for their high strength to weight ratio, corrosion resistance, and enhanced mechanical properties, are increasingly being employed in various high performance appli cations. This review examines the state of the art developments in composite gear design, focusing on the types of composites uti lized and their applicability for high stress and high strain loading conditions. The aim is to provide a comprehensive understanding of the material properties, manufacturing techniques, and performance outcomes associated with composite gears. Composite materials have revolutionized gear design, particularly in applications involving high strain and high stress, such as power transmission systems. The application of
composites in gear design offers significant advantages, including enhanced strength to weight ratios,
improved fatigue resistance, and superior wear properties. This pape r also focuses on the possibility of
certification analysis of advanced composite gears subjected to high loads. The primary objective is to
enhance simulation tools and numerical and experimental methods, facilitating the design of lighter, safer, and
mor e energy efficient structures. Additionally, the research aims to support and prepare the necessary
standardization steps for the certification of composite structures, including gear transmissions made of
composite materialsGrant number: 451 03 137/2025 03/ 20010
Sustainable Aviation Innovations, Advancements, and Destinations
No full text- Discusses future strategies and priorities in the field of aviation sustainability
- Addresses a broad range of aviation topics with an emphasis on environmental issues
- Provides access to the complete ISSA 2024 proceeding
CII Compliance for a Fleet of 50 Bulk Carriers and Tankers
No full textThis study evaluates the Carbon Intensity Indicator (CII) for a fleet comprising 25 bulk carriers and
25 tankers, focusing on their energy efficiency and environmental performance in compliance with
the International Maritime Organization's (IMO) regulations. The CII, measured in grams of CO2 emitted
per cargo-carrying capacity and nautical mile, serves as a critical metric for assessing the carbon footprint
of maritime operations. Initial assessments reveal that a significant proportion of both vessel types
are likely to fall into lower CII rating categories (C, D, or E) due to operational inefficiencies and the increasing
stringency of CII thresholds leading up to 2030. To meet the CII requirements, it is estimated that
a reduction in operational speed will be necessary for many vessels in the fleet. This speed reduction aims
to enhance fuel efficiency and lower carbon emissions per unit of cargo transported. The study highlights
the necessity for ship owners to implement corrective measures to improve their CII ratings. Furthermore,
the findings underscore the importance of developing tailored decarbonization strategies for each vessel
class to ensure compliance and competitiveness in a rapidly evolving regulatory landscape. This evaluation
not only contributes to understanding the current performance of bulk carriers and tankers but also provides
a roadmap for future improvements in carbon emissions reduction across the maritime industry