• Tribology and Lubricants
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• v.40 no.3
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• pp.71-77
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• 2024

Hydrogen has emerged as an eco-friendly and sustainable alternative to fossil fuels. However, the utilization of hydrogen requires high-pressure compression, storage, and transportation, which poses challenges to the durability of compressor components, particularly the diaphragm. This study aims to improve the durability of 304 stainless steel diaphragms in hydrogen compressors by optimizing their surface roughness and corrosion resistance through wet etching. The specimens were prepared by immersing 304 stainless steel in a mixture of sulfuric acid and hydrogen peroxide, followed by etching in hydrochloric acid for various durations. The surface morphology, roughness, and wettability of the etched specimens were characterized using optical microscopy, surface profilometry, and water contact angle measurements. The friction and wear characteristics were evaluated using reciprocating sliding tests. The results showed that increasing the etching time led to the development of micro/nanostructures on the surface, thereby increasing surface roughness and hydrophilicity. The friction coefficient initially decreased with increasing surface roughness owing to the reduced contact area but increased during long-term wear owing to the destruction and delamination of surface protrusions. HCl-30M exhibited the lowest average friction coefficient and a balance between the surface roughness and oxide film formation, resulting in improved wear resistance. These findings highlight the importance of controlling the surface roughness and oxide film formation through etching optimization to obtain a uniform and wear-resistant surface for the enhanced durability of 304 stainless steel diaphragms in hydrogen compressors.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4678-4684
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• 2023

Using the Monte Carlo method, the impact of the angular distribution of the electron source on the dose distribution for the 2.5 MeV ELV electron accelerator was explored. The experiment measured the 3-D dose distribution in the irradiation chamber for electron energies of 1.0 MeV and 2.5 MeV. The simulation used the MCNP6.2 code to evaluate three angular distribution models of the source: a mono-directional beam, a cone shape, and a triangular shape. Of the three models, the triangular shape with angles θ = 30°, φ = 0° best represents the angle of the scan hood through which the electron beam exits. The MCNP6.2 simulation results demonstrated that the triangular model is the most accurate representation of the angular distribution of the electron source for the 2.5 MeV ELV electron accelerator.

• Archives of Plastic Surgery
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• v.51 no.4
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• pp.367-371
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• 2024

Skin defects of the total nasal columella can significantly impact both nasal respiratory function and aesthetics. The reconstruction of total columella is a complex process and represents a significant challenge for plastic surgeons. Various factors can cause the loss of the columella. Numerous columella reconstruction procedures have been proposed, each with their own set of advantages and disadvantages. The main issues to address include the need for regional flaps from the forehead or nasofacial sulcus, a long pedicle to reach the columella, and the double angular folding that causes a risk of malnutrition or venous congestion. Additionally, using horizontal nasolabial flaps may lead to deformation of the upper lip. In this study, we present a new procedure to reconstruct the nasal columella using "Domino flaps" with two flaps (the horizontal upper lip island flap and nasocheek island flap). This new procedure ensures adequate skin for reconstruction of nasal columella and partial tip, minimizes rotation angle, reduces the angular folding of the pedicle, furthermore limits deformation of the upper lip. "Domino flaps" are a valuable option for surgeons when reconstructing the total nasal columella. However, it is important to consider whether the patient has a beard at the donor sites.

• Geomechanics and Engineering
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• v.39 no.1
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• pp.27-41
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• 2024

Accurately estimating the performance of tunnel boring machines (TBMs) is crucial for mitigating the substantial financial risks and complexities associated with tunnel construction. Machine learning (ML) techniques have emerged as powerful tools for predicting non-linear time series data. In this research, six advanced meta-heuristic optimization algorithms based on long short-term memory (LSTM) networks were developed to predict TBM penetration rate (TBM-PR). The study utilized 1125 datasets, partitioned into 20% for testing, 70% for training, and 10% for validation, incorporating six key input parameters influencing TBM-PR. The performances of these LSTM-based models were rigorously compared using a suite of statistical evaluation metrics. The results underscored the profound impact of optimization algorithms on prediction accuracy. Among the models tested, the LSTM optimized by the particle swarm optimization (PSO) algorithm emerged as the most robust predictor of TBM-PR. Sensitivity analysis further revealed that the orientation of discontinuities, specifically the alpha angle (α), exerted the greatest influence on the model's predictions. This research is significant in that it addresses critical concerns of TBM manufacturers and operators, offering a reliable predictive tool adaptable to varying geological conditions.

• Structural Engineering and Mechanics
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• v.91 no.4
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• pp.383-391
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• 2024

Conical shell is a common engineering structure, which is widely used in machinery, civil and construction fields. Most of them are usually exposed to external environments, temperature is an important factor affecting its performance. If the external temperature is too high, the deformation of the conical shell will occur, leading to a decrease in stability. Therefore, studying the thermal-post buckling behavior of conical shells is of great significance. This article takes graphene platelets reinforced metal foams (GPLRMF) conical shells as the research object, and uses high-order shear deformation theory (HSDT) to study the thermal post-buckling behaviors. Based on general variational principle, the governing equation of a GPLRMF conical shell is deduced, and discretized and solved by Galerkin method to obtain the critical buckling temperature and thermal post-buckling response of conical shells under various influencing factors. Finally, the effects of cone angles, GPLs distribution types, GPLs mass fraction, porosity distribution types and porosity coefficient on the thermal post-buckling behaviors of conical shells are analyzed in detail. The results show that the cone angle has a significant impact on the nonlinear thermal stability of the conical shells.

• Geomechanics and Engineering
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• v.38 no.4
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• pp.397-408
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• 2024

Buried box culverts are crucial elements of transportation infrastructure. However, their behavior under foundation loads is not well understood, indicating a significant gap in existing research. This study aims to bridge this gap by conducting a detailed numerical analysis using the Finite Element Method and Abaqus software. The research evaluates the behavior of buried box culverts by examining their interaction with surrounding soil and the pressures from surface foundation loads. Key variables such as embedment depth, culvert wall thickness, concrete material properties, foundation pressure, foundation width, soil elastic modulus, and friction angle are altered to understand their combined effects on structural response. The methodology employs a validated 2D numerical model under plane strain conditions. Parametric studies highlight the critical role of culvert depth (H) in influencing earth pressure and bending moments. Foundation pressure and width demonstrate complex interdependencies affecting culvert behavior. Variations in culvert materials' elastic modulus show minimal impact. It was found that the lower wall of the buried culvert experiences higher average pressure compared to the other two walls, due to the combined effects of the culvert's weight and down drag forces on the side walls. Furthermore, while the pressure distribution on the top and bottom walls is parabolic, the pressure on the side walls follows a different pattern, differing from that of the other two walls.

• Ocean Systems Engineering
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• v.14 no.3
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• pp.301-314
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• 2024

In this study, the lift coefficient and wave deformations for a two-dimensional flat-plate in non-cavitating condition were computed using a closed-form (analytic) solution. This plate moves at a constant speed beneath a free surface in water of finite depth. The model represents the flat-plate using a lumped vortex element within the constraints of potential flow theory. The kinematic and dynamic free surface conditions were combined and linearized. This linearized free surface condition was then applied to get the total velocity potential. The method of images was utilized to account for the effects of finite depth in the calculations. The lift coefficient of the flat-plate and wave elevations on the free surface were calculated using the closed-form solution. The lift coefficients derived from the present analytic solution were validated by comparing them with Plotkin's method in the case of deep water. Wave elevations were also compared with those obtained from a numerical method. A comprehensive discussion on the impact of Froude number, submergence depth of flat-plate from the calm free surface, the angle of attack and the depths of finite bottom on the results - namely, lift coefficients and free surface deformations - is provided.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.953-960
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• 2013

This study aimed to investigate the penetration characteristics of a segmented penetrator with normal and inclined angles. The length to diameter ratio (L/D) of the segmented penetrator was varied as 1.0, 0.5, and 0.25. Moreover, impact velocities of 1.5, 2.0, and 2.5 km/s and inclination angles of $15^{\circ}$, $30^{\circ}$, and $45^{\circ}$ were successively applied. The AUTODYN-3D code was used to simulate the penetration performance of the segmented penetrator. The results show that the penetration performance of the segmented penetrator with steel plates was obviously higher than that of the corresponding continuous penetrator with steel plates. The outstanding penetration performance of the segmented penetrator can be observed when the impact velocity was 2.0 km/s and L/D = 1. In this case, the penetration performance of the segmented penetrator was 7% higher than that of the corresponding continuous penetrator. This trend was attributable to the interaction between the reactive plate and the projectile. The extent of the interaction relies on the relative velocities of the plate and projectiles, inclination angle, and number of segmented penetrators. It was proven that the penetration performance of the segmented penetrator can be improved by increasing the impact velocity, number of segmented penetrators between segments, and penetrator length.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3833-3838
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• 2009

This paper introduces a measurement system for mechanical properties of sport shoes using an industrial robot. The robot system used in this paper is a commercial Puma type robot system(FARA AT2 made by SAMSUNG Electronics) with 6 joints and the end-effector is modified to produce a human walking motion. After analyzing human walking with a high speed video camera, each joint angle of the robot system is extracted to be used in the robot system. By using this system, ground impact forces were measured during stepping motion with 3 different shoe specimens made of 3 different hardness outsoles, respectively. As other mechanical properties, both bending moments to bend the toe part of the same specimen shoes and pronation quantities during walking motion were measured as well. In the impact test with the same depth of deformation under the ground level, the effect of the outsole hardness was clearly appeared such that the harder outsole produces the higher ground reaction force. The bending test and the pronation test also show proportional increments in the bending stiffness and the moment Mx according to the outsole hardness. Throughout such experiments, the robot system has produced consistent results so that the system could be used in obtaining valuable informations for a shoe designing process.

• Journal of Environmental Impact Assessment
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• v.33 no.1
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• pp.1-8
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• 2024

Amphibians are a taxonomic group that ecologically connects terrestrial ecosystems and aquatic ecosystems. They play a very important role in the food chain of the ecosystem. It is known that there are about 5,948 species distributed all over the world, but after the Industrial Revolution, due to industrialization and urbanization, there has been a decrease in species and populations. In particular, it is becoming a factor in exacerbating habitat fragmentation or fragmentation due to artificial canals. In orderto improve the survivalrate of wild animals in artificial canals, escape facilities are installed to reduce it. This study analyzed the slope, height of the escape facility, escape rate, and travel distance in the operating facility for Bombina orientalis, which mainly inhabits near forests. The slope of the escape facility showed a relatively similar escape success rate regardless of height at 50° and 60°, while at 70°, it showed a relatively high escape success rate at only 40cm in height. The success rate of escape from the waterway escape facility in operation was 14.71%, showing a very low utilization rate, and the recognition rate of the artificial canal escape facility was found to be very low as it moved along the side wall of the artificial canal. Therefore, in the case of a waterway escape facility for Bombina orientalis, it is possible to construct it at an angle of 60°, and if the side walls of the artificial canals are built within 60°, Bombina orientalis can move freely in both directions, overcoming the low utilization rate of existing waterway escape facilities. It is expected to minimize the impact of movement and death of artificial canals. In addition, if the spacing between escape facilities is narrowed from the installation standard of 30m and ramps are constructed in both directions upstream and downstream, the escape success rate of amphibians,reptiles, and small mammals otherthan lady frogs is expected to improve.