Publications

The finite element method (FEM) is widely recognized as a powerful numerical analysis technique for approximating solutions in structural mechanics. Addressing the configuration of plate-type structures, particularly those with discontinuities, is crucial not only in ship and aircraft construction but also in various other fields. Structural discontinuities occur when there are sudden changes in the cross-section of structural members due to material imperfections or high-stress areas. This paper focuses on the fundamental principles of FEM for solving two-dimensional plane stress problems and analyzing stresses such as normal stress, shear stress, and von-mises stress at the four integration points (gauss points) in different sections of ship structures, particularly in vulnerable regions. To address structural discontinuity problems in various ship structures, a finite element program utilizing object-oriented techniques was developed, employing four-node quadrilateral elements. The analysis results of gauss point stresses obtained from the developed program were validated against a commercial finite element analysis software to ensure accuracy and reliability. Additionally, a mesh viewing program has been developed in the Python programming language to enable the visualization and analysis of the generated mesh using the developed object-oriented finite element program. J. Nav. Arch. Mar. Engg., Vol 20(2), December, 2023; p 1-14

The finite element method (FEM) is already well-established as a strong and widely used numerical analytical methodology for determining solutions to a wide variety of structural mechanics issues. One of the most significant subjects in the design of not only ships, but also airplanes and other structures is the configuration of plate type structures, particularly with discontinuities. A structural discontinuity occurs when the cross section of a structural part changes abruptly due to material defects or high stress locations. This article primarily focuses on the fundamental concepts of FEM for finding solutions of two-dimensional plane stress and plane strain problems to evaluate stresses such as normal stress, shear stress, and von-mises stress at the four integration points (gauss points) for various sections of ship structures (especially at the most vulnerable areas), such as plate with holes, plate with bracket and holes, and plate with fillets. To study structural discontinuity problems for various ship structures, an object-oriented programming method is used to create a finite element program for four node quadrilateral elements. With the aid of commercial finite element analysis software, the analysis findings of gauss point stresses for different ship sections produced from the developed program are validated.

Two distinct binary blended concrete mixes were prepared for the study. The first mix involved a cement replacement of 50% slag, denoted as SL. The second mix incorporated a cement replacement of 20% fly ash, referred to as FA. No chlorides were added during the preparation of these concrete specimens. To accelerate chloride transport, electromigration was employed by placing specimens with varying reservoir lengths (ranging from 2.5 cm to 17.5 cm) on their top surfaces. These reservoirs were subsequently filled with a 10% NaCl solution. In this paper, corrosion propagation was monitored over a period of approximately 650 days using electrochemical measurements such as open circuit potential, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). The evolution of rebar potential, polarization resistance, solution resistance, and corrosion current were analyzed to understand the corrosion behavior. This paper focuses on how the length of the solution reservoirs influences the corrosion-related parameters such as polarization resistance, solution resistance, rebar potential, and corrosion current. During the monitored propagation period, the corrosion current values (last 7 sets of readings) exhibited higher magnitudes for the embedded rebars in specimens made with SL mix in comparison to those made with FA mix. Corrosion current measurements likewise showed an increasing trend as the reservoir lengths increased. None of the specimens had any visible cracks or corroded products that could reach the concrete surface throughout the monitored period. The experimental results provide insights into the corrosion mechanisms and the effectiveness of accelerated corrosion techniques in simulating real-life conditions.

This study investigates the long-term corrosion behavior of reinforced concrete (RC) subjected to accelerated chloride ingress over approximately 1600 days, employing electrochemical methods such as linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and galvanostatic pulse (GP) testing. Two concrete mixes (T1 and T2), incorporating distinct supplementary cementitious materials (SCMs), were evaluated to determine their performance in aggressive environments. Specimens with varying reservoir lengths were exposed to a 10% NaCl solution, with electromigration applied to accelerate chloride transport. Electrochemical assessments, including measurements of rebar potential, concrete solution resistance, corrosion current, and mass loss, were conducted to monitor the degradation of embedded steel. The findings revealed that smaller reservoirs (2.5 cm) significantly restricted chloride and moisture penetration, reducing corrosion, while larger reservoirs (10 cm) resulted in greater exposure and higher corrosion activity. Additionally, T1 mixes (cement replacement of 20% fly ash and 50% slag) showed higher corrosion currents and mass loss, whereas T2 mixes (cement replacement of 20% fly ash and 8% silica fume) demonstrated enhanced matrix densification, reduced permeability, and superior durability. These results underscore the importance of mix design and exposure conditions in mitigating corrosion, providing critical insights for improving the longevity of RC structures in aggressive environments.

The development of small‐scale wind turbines with composite materials continues to gain momentum due to their cost‐effectiveness, high energy conversion efficiency, and ease of deployment. Despite these advantages, such composite structures are susceptible to operational failures such as fiber rupture, matrix cracking, and delamination. This research introduces a comprehensive design and analysis methodology for a 30 kW‐class small wind turbine blade engineered for low noise and enhanced durability. The blade incorporates a sandwich composite structure, utilizing E‐glass, S‐glass, and carbon fiber face sheets combined with a balsa wood core to improve weight efficiency and mechanical stability. To determine the most effective structural configuration and understand potential failure modes, nine composite sandwich variants were analyzed, considering core and layer failure limits, fiber orientation, and laminate stress distribution. Finite element analysis (FEA) was applied to evaluate stress responses and deformation behavior under static loads. Among the configurations tested, the one employing epoxy S‐glass unidirectional face sheets with a multidirectional fiber layup exhibited the lowest peak stress and superior resistance to deformation. An experimental tensile test on dog‐bone specimens further supported the numerical outcomes, with the unidirectional carbon fiber sample achieving the highest tensile strength of approximately 92 MPa. The FEA results for the optimized configuration remained safely within this failure limit. This study establishes a robust, data‐driven framework for optimizing composite blade structures, ensuring both performance and structural integrity in small wind turbine applications.

At present, structural optimization is a highly demanding area of research in engineering. Engineers aim to minimize material in a body while maintaining its usability and safety at the same time. Developing a user-friendly program to optimize a structure using the finite element method (FEM) is the goal of the current study. With the advent of additive manufacturing, the production of complex-shaped designs is showing promise. A detailed optimization algorithm based on solid isotropic material with penalization (SIMP) is presented in this paper. UnTop2D: An object-oriented Python program with a graphical user interface (GUI) has been developed, which can be applied to structures with both structured and unstructured meshes. The mesh is not required to be topologically ball and can be imported from professional meshing software. Any selected element can be frozen to prevent its removal during optimization, and wall elements can also be frozen for real-world scenarios. The optimized structure can be exported as an Abaqus input file for structural analysis and STL file for 3D printing. This paper presents several examples to demonstrate the effectiveness of the proposed procedure.

This study investigates the corrosion currents in four reinforced concrete mixes—SL (cement replacement of 50% slag), FA (cement replacement of 20% fly ash), T1 (cement replacement of 50% slag and 20% fly ash), and T2 (cement replacement of 20% fly ash and 8% silica fume)—using an electromigration method to accelerate chloride transport and initiate corrosion within weeks/months. The corrosion propagation was monitored over 1600 days using electrochemical techniques such as Linear Polarization Resistance (LPR), Electrochemical Impedance Spectroscopy (EIS), and Galvanostatic Pulse (GP) measurements. The study evaluated how the composition of the concrete mixes and reservoir length influenced corrosion, by testing both binary mixes (SL and FA) and ternary mixes (T1 and T2). The results show that the LPR readings, which uses prolonged polarization, generally produces higher corrosion current values than GP readings, offering a dynamic view of corrosion but greater variability. The binary mixes with slag (SL) or fly ash (FA) exhibit higher corrosion currents, while ternary mixes, especially those containing fly ash and silica fume (T2), show reduced corrosion currents, suggesting improved resistance. The larger reservoir length contributed to higher corrosion currents, highlighting the critical influence of exposure conditions, concrete mix composition, and measurement techniques in evaluating corrosion. This underscores the importance of considering these factors collectively when assessing the durability and long-term performance of concrete in corrosive environments.

Samples with two different binary blended concrete mixes were prepared, one containing cement replacement of 50% slag (referred here as SL mix) and the other containing cement replacement of 20% fly ash (termed here as FA mix). The water to cementitious ratio used to produce concrete specimens was 0.41. On the top surface of each specimen, various reservoir lengths that ranged from 2.5 cm to 17.5 cm were fitted, and these reservoirs were filled with a 10% NaCl solution. Electromigration was used to accelerate the transport of chlorides, with an applied potential of 9V at first, and subsequently reduced to 3V after about a week. For a period of about 1100 days, the corrosion related parameters such as concrete solution resistance, rebar potential, and corrosion current were monitored via the rebar potential measurements, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements, the latter used only to obtain the solution resistance. The corrosion current values determined through experimental observations were then converted to mass loss using Faraday’s law. The readings of corrosion current values (last 10 sets of readings) as well as the calculated mass loss values were found to be larger for the rebars embedded in specimens prepared with SL mix, followed by rebars embedded in specimens prepared with FA mix. Corrosion current and calculated mass loss values in general tended to increase with increasing solution reservoir lengths. No cracks or corrosion products that reached the surface of the concrete were observed on the specimens for the duration of the reported monitored propagation period. This study offers a framework for future studies on accelerated steel corrosion in concrete.

This study investigates the long-term corrosion behavior of reinforced concrete (RC) under accelerated chloride exposure for about 1600 days, using electrochemical methods like galvanostatic pulse (GP) testing. Two concrete mixes (T1 and T2), incorporating distinct supplementary cementitious materials (SCMs), were evaluated to determine their performance in aggressive environments. Specimens with varying reservoir lengths were exposed to a 10% NaCl solution (by weight), with electromigration applied to accelerate chloride transport. Electrochemical assessments, including measurements of rebar potential, concrete solution resistance, concrete polarization resistance, corrosion current, and mass loss, were conducted to monitor the degradation of embedded steel. The findings revealed that smaller reservoirs (2.5 cm) significantly restricted chloride and moisture penetration, reducing corrosion, while larger reservoirs (10 cm) resulted in greater exposure and higher corrosion activity. Additionally, T1 mixes (partial cement replacement with 20% fly ash and 50% slag) showed higher corrosion currents and mass loss, whereas T2 mixes (partial cement replacement with 20% fly ash and 8% silica fume) demonstrated enhanced matrix densification, reduced permeability, and superior durability. These results underscore the importance of mix design and exposure conditions in mitigating corrosion, providing critical insights for improving the longevity of RC structures in aggressive environments.

Samples with two different binary blended concrete mixes were prepared, one containing cement replacement of 50% slag (referred here as SL mix) and the other containing cement replacement of 20% fly ash (termed here as FA mix). The water to cementitious ratio used to produce concrete specimens was 0.41. On the top surface of each specimen, various reservoir lengths that ranged from 2.5 cm to 17.5 cm were fitted, and these reservoirs were filled with a 10% NaCl solution. Electromigration was used to accelerate the transport of chlorides, with an applied potential of 9 V at first, and subsequently reduced to 3 V after about a week. The electromigration was applied for a short period (few weeks to a couple of months). For a period of about 1100 days, the corrosion related parameters such as concrete solution resistance, rebar potential, and corrosion current were monitored via the rebar potential measurements, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements, the latter used only to obtain the solution resistance. The corrosion current values determined through experimental observations were then converted to mass loss using Faraday’s law. The readings of corrosion current values (last 7 sets of readings) as well as the calculated mass loss values were found to be larger for the rebars embedded in specimens prepared with SL mix, followed by rebars embedded in specimens prepared with FA mix. Corrosion current and calculated mass loss values in general tended to increase with increasing solution reservoir lengths. No cracks or corrosion products that reached the surface of the concrete were observed on the specimens for the duration of the reported monitored propagation period. This study offers a framework for future studies on accelerated steel corrosion in concrete.

Specimens with binary (SL, FA) and ternary (T1, T2) concrete mixes (30.5 cm x 12.7 cm x 7.6 cm) were prepared without any chlorides, using a w/cm ratio of 0.41 or lower. Each specimen, reinforced with #3 rebar, have a 0.75 cm concrete cover. The specimens had reservoirs of varying lengths on their top surface. A 10% NaCl solution by weight was introduced into the reservoirs, and electromigration was applied for a period ranging from few weeks to several months to accelerate chloride transport. Corrosion current values were monitored for approximately 1600 days using galvanostatic pulse techniques and converted to mass loss using Faraday’s law. The SL mix specimens showed the highest average corrosion current values, followed by FA, T1, and T2 mix specimens. Despite the prolonged exposure, no visible corrosion such as cracks or surface-reaching corrosion products were observed over the monitoring period.

A growing number of Offshore Wind Turbines (OWT) are vulnerable to collision with offshore support and supply vessels. A major collision can lead to a catastrophic accident in the marine environment and resources. This paper focuses on the modeling of a 3-legged Z-braced, and 3- legged X- braced tripod jacket structures type platform using nonlinear finite element analysis. A supply vessel has also been modeled to simulate the collision with the jacket structures. The number of deformed members, indentations, and stresses in the region of impacted legs were obtained from the numerical analysis. The extent of damage was then compared between Z-braced, and X- braced platforms. This study provides a better understanding of the structural performances of different tripod jacket structures.