• Journal of the Institute of Convergence Signal Processing
• /
• v.24 no.4
• /
• pp.236-241
• /
• 2023

Water quality problems in rivers, lakes, and estuaries have become serious in Korea. In order to overcome eutrophication of freshwater lakes and river basins, systematic management of water quality is necessary. To manage water quality in freshwater lakes and basins, apply hydrological models suitable for the basin and water quality models such as rivers and lakes to reduce water pollution based on the prediction results of these models. Improvement measures must be presented. In order to apply appropriate water pollution improvement measures in the watershed, accurate pollution sources must be identified and pollution loads must be predicted and presented. Based on GIS, the connection between the pollutant database and the hydrological and water quality prediction model will be integrated based on spatial location, making it possible to provide systematic support to improve watershed water quality by comprehensively including the water quality modeling process. In this paper, in order to accurately predict water pollution in freshwater lakes and river basins, a water quality model system is established using GIS-based spatial information to present a comprehensive water quality management method for freshwater lake basins in the future, and to systematically manage pollution sources through water quality modeling. This study was conducted to easily and efficiently operate hydrological and water quality models using automated spatial information.

• Korean Journal of Construction Engineering and Management
• /
• v.25 no.5
• /
• pp.15-24
• /
• 2024

System support is a facility that is temporarily installed to support vertical loads at construction sites, and is assembled and installed by reused individual members. These characteristics are likely to lead to poor performance of installed system supports, and even though it is institutionalized to check structural safety at the their design phase, accidents continue to occur at the construction site. Accordingly, safety management of system support is implemented through various institutional methods, but the current system does not consider the performance degradation of temporary facilities due to the reuse of individual temporary members. Therefore, the purpose of this study is to verify the performance of assembled system support. In order to do achieve this purpose, the authors divided individual system supports into unused and used groups and performed compression performance test with defined models assembled with those two groups of system supports. The results of this study are expected to be meaningful as a research case that can quantitatively evaluate safety systems and standards for the performance of existing temporary facilities and suggest directions for improving the safety management system of temporary facilities in the future.

• Journal of the Society of Disaster Information
• /
• v.20 no.3
• /
• pp.563-572
• /
• 2024

Purpose: This study aims to assess the physical cognition according to changes in the weight of firefighting Self Contained Breathing Apparatus (SCBA), and to provide foundational data for establishing standards for firefighting SCBA based on these results. Method: The study investigated and analyzed changes in physical changes, Rating of Perceived Exertion (RPE), and cognitive factors among firefighters and non-firefighters wearing three different types of SCBA with varying weights, following appropriate exercise loads. Result: In the case of the firefighter group, wearing SCBA with varying weights during exercise did not show significant differences in respiratory rate, heart rate, and blood pressure. Similarly, in the non-firefighter group, differences in weight change were not significant. Additionally, both groups did not demonstrate differences in RPE based on SCBA weight changes, and participants did not cognize changes in SCBA weight during the experiment. Conclusion: Due to the low level of physical cognition based on changes in SCBA weight, it is inferred that even if the current firefighting SCBA weight is additionally increased to 4kg, firefighters' cognitive fatigue levels would remain similar to or not significantly higher than current levels

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.44 no.2
• /
• pp.203-214
• /
• 2024

Ports often suffer pavement damage due to soft ground and heavy equipment operations, leading to issues such as differential settlement and cracks. In this study, we developed port concrete blocks and applied them to a port in two configurations to figure out settlement characteristics. Falling weight deflectometer (FWD) tests on asphalt pavement and block pavements were conducted to figure out deflection and bearing capacity. The block pavement with the cement treated base showed improved bearing capacity with the port operation since lower settlements were detected than asphalt pavement. In the cement treated base, the relative deflection ratio to asphalt concrete pavement was less than 1, indicating enhanced bearing capacity. LiDAR measurements identified multiple settlements in the crushed-stone base due to surface loads after construction. Both relative deflection ratio and LiDAR measurements suggested that block pavement can be widely applied to various port sites with its applicability and bearing capacity of cement-treated base.

• Journal of Bio-Environment Control
• /
• v.32 no.4
• /
• pp.442-448
• /
• 2023

This study aimed to develop an optimal greenhouse model for strawberry seedling during the summer high-temperature period based on the results of field surveys. We conducted a survey on the structure types of 46 strawberry seedling farms nationwide, including width, ridge height, eaves height, ventilation method, seedling bed width, and spacing. Based on the survey results, we derived the optimal greenhouse model by considering various factors. The greenhouse width was set at 14 meters to maximize the efficiency of seedling beds and overall space. The height was determined at 2 meters, taking into account ventilation during the summer season. To reduce stress on the supporting structure due to snow loads, we established a reinforcement installation angle of 50 degrees. We analyzed two different models that use support beams with dimensions of φ48.1×2.1t and φ59.9×3.2t, respectively, to ensure structural safety against meteorological disasters, considering regional design wind speeds and snow accumulation. We utilized these developed greenhouse model to conduct strawberry seedling experiments, resulting in a high survival rate of average 93.2%. These findings confirm the usefulness of the strawberry seedling greenhouse in improving the seedling environment and enhancing overall efficiency.

• Journal of Aerospace System Engineering
• /
• v.18 no.4
• /
• pp.81-88
• /
• 2024

The payload BioCabinet of CAS500-3 is designed for 3D stem cell differentiation, culture, and analysis utilizing bio 3D printing techniques in space. The 3D printing technique was initially developed for orbital use; however, it lacks separate validation for extreme launch vibration environments, necessitating a design that mitigates the launch load on the payload. This paper proposes a passive vibration isolator with a low-stiffness elastic support structure and high damping characteristics to reduce the launch loads affecting the BioCabinet. We explore the high-damping characteristics through the superelastic effects of SMA (Shape Memory Alloys) and a multi-layered structure incorporating viscoelastic tape. The effectiveness of the proposed vibration isolation system was confirmed via launch vibration tests on a qualification model.

• Advances in concrete construction
• /
• v.17 no.2
• /
• pp.111-126
• /
• 2024

During the clinkering stages of cement production, the chemical composition of fine raw materials such as limestone and clay, which include iron oxide (Fe₂O₃), silicon dioxide (SiO₂) and aluminum oxide (Al₂O₃), significantly influences the quality of the final product. Specifically, the chemical interaction of Fe₂O₃ with CaO, SiO₂ and Al₂O₃ during clinkerisation plays a key role in determining the chemical reactivity and overall quality of the final cement, shaping the properties of the concrete produced. As an extension, this study aims to investigate the physical effects of incorporating nanosized Fe₂O₃ particles as fillers in concrete matrices, and their impact on concrete structures, namely slabs. To accurately model the reinforced concrete (RC) slabs, a refined trigonometric shear deformation theory (RTSDT) is used. Additionally, the stochastic Eshelby's homogenization approach is employed to determine the thermoelastic properties of nano-Fe₂O₃ infused concrete slabs. To ensure comprehensive coverage in the study, the RC slabs undergo various mechanical loads and are exposed to temperature fields to assess their thermo-mechanical performance. Furthermore, the slabs are assumed to rest on a three-parameter viscoelastic foundation, comprising the Winkler elastic springs, Pasternak shear layer and a damping parameter. The equilibrium governing equations of the system are derived using the principle of virtual work and subsequently solved using Navier's technique. The findings indicate that while ferric oxide nanoparticles enhance the mechanical properties of concrete against mechanical loading, they have less favorable effects on its performance against thermal exposure. However, the viscoelastic foundation contributes to mitigating these effects, improving the concrete's overall performance in both scenarios. These results highlight the trade-offs between mechanical and thermal performance when using Fe₂O₃ nanoparticles in concrete and underscore the importance of optimizing nanoparticle content and loading conditions to improve the structural performance of concrete structures.

• Journal of the Microelectronics and Packaging Society
• /
• v.31 no.3
• /
• pp.24-37
• /
• 2024

Due to the thin nature of semiconductor packages, even minor thermal loads can cause significant warpage, impacting product reliability through issues like delamination or cracking. The mold curing process, which encloses the package to protect the semiconductor chip, is particularly challenging to predict due to the complex thermal, chemical, and mechanical interactions. This study proposes a cost-effective machine learning model to predict warpage in the mold curing process. We developed methods to characterize the curing degree based on time and temperature and quantify the material's mechanical properties accordingly. A Finite Element Method (FEM) simulation model was created by integrating these properties into ABAQUS UMAT to predict warpage for various design factors. Additionally, a Warpage formula was developed to estimate local warpage based on the package's stacking structure. This formula combines bending theory with thermo-chemical-mechanical properties and was validated through FEM simulation results. The study presents a method to construct a machine learning model for warpage prediction using this formula and proposes a cost-effective approach for building a training dataset by analyzing input variables and design factors. This methodology achieves over 98% prediction accuracy and reduces simulation time by 96.5%.

• The Journal of Korean Academy of Prosthodontics
• /
• v.46 no.4
• /
• pp.396-408
• /
• 2008

Statement of problem: Within the elastic limit of the screw, the greater the preload, the tighter and more secure the screw joint. However, additional tensile forces can incur plastic deformation of the abutment screw when functional loads are superimposed on preload stresses, and they can elicit the loosening or fracture of the abutment screw. Therefore, it is necessary to find the optimum preload that will maximize fatigue life and simultaneously offer a reasonable degree of protection against loosening. Another critical factor in addition to the applied torque which can affect the amount of preload is the joint connection type between implant and abutment. Purpose: The purpose of this study was to evaluate the influence of tightening torque on the implant-abutment screw joint stability. Material and methods: Respectively, three different amount of tightening torque (20, 30, and 40 Ncm) were applied to implant systems with three different joint connections, one external butt joint and two internal cones. The initial removal torque value and the postload (cyclic loading up to 100,000 cycles) removal torque value of the abutment screw were measured with digital torque gauge. Then rate of the initial and the postload removal torque loss were calculated for the comparison of the effect of tightening torques and joint connection types between implant and abutment on the joint stability. Results and conclusion: 1. Increase in tightening torque value resulted in significant increase in initial and postload removal torque value in all implant systems (P < .05). 2. Initial removal torque loss rates in SS II system were not significantly different when three different tightening torque values were applied (P > .05), however GS II and US II systems exhibited significantly lower loss rates with 40 Ncm torque value than with 20 Ncm (P < .05). 3. In all implant systems, postload removal torque loss rates were lowest when the torque value of 30 Ncm was applied (P < .05). 4. Postload removal torque loss rates tended to increase in order of SS II, GS II and US II system. 5. There was no correlation between initial removal torque value and postload removal torque loss rate (P > .05).

• The Journal of Korean Academy of Prosthodontics
• /
• v.46 no.4
• /
• pp.359-371
• /
• 2008

Purpose: The purpose of this study was to investigate the stress distribution in mandibular implant overdentures with telescopic crowns compared to bar attachment. Material and methods: Three-dimensional finite element models consisting of the mandibular bone, 4 implants, and primary bar-splinted superstructure or secondary splinted superstructure with telescopic crowns were created. Vertical and oblique loads were directed onto the occlusal areas of the superstructures to simulate the maximal intercuspal contacts and working contacts such as group function occlusion. Maximum stress and stress distribution were analysed in mandibular bone, implant abutments, and superstructures. Results: 1. In comparison of von Mises stress on mandibular bone, telescopic overdenture had a little lower stress values in vertical load and working side load except oblique load. In the mandible, the telescopic overdenture distributed more uniform stress than the bar overdenture. 2. In comparison of von Mises stress on implant abutments, telescopic overdenture had much lower stress values in all load conditions. In implant abutments, the telescopic overdenture distributed stress similar to the bar overdenture. Stress was concentrated on the distal surfaces of the posterior implant abutments in both mandibular overdentures. 3. In comparison of von Mises stress on superstructures, the telescopic overdenture had much more stress values in all load conditions. However, the telescopic overdenture distributed more uniform stress on superstructure than the bar overdenture. In the bar overdenture, stress was concentrated on each cental area of bar structures and connected area between implant abutments and bar structures. Conclusion: In the results of this study, the telescopic overdenture had lower stress values than the bar overdenture in mandibular bone and implant abutments, but more stress values in superstructures. However, if optimal material was selected in making superstructures, the telescopic overdenture was compared to the bar overdenture in stress distribution.