• Journal of Korea Water Resources Association
• /
• v.56 no.10
• /
• pp.667-678
• /
• 2023

In this study, quasi-3D inundation flow simulations were conducted for a simplified subway station configuration. The effects of variations in rainwater inflow locations and discharge were investigated, analyzing the resulting inundation flow patterns and flood risk. The inundation simulation results calculated the incipient velocities for slipping and toppling accidents to assess pedestrian safety. The results indicated that velocities exceeding the incipient velocity for slipping accidents mainly occurred on the flooded staircase. Meanwhile, velocities surpassing the incipient toppling accidents were observed around the staircase and the corridor near the staircase leading to B2F. This observation is consistent with the results from the specific force distribution analysis. To provide detailed flood risk assessments, the Flood Hazard Degree (FD) was applied with four levels of criteria, along with the Flood Intensity Factor (FIF). The results demonstrated that FD identified a broader area at risk of flood-induced consequences compared to FIF. When comparing the different inundation risk assessment methods, the specific force method tended to overestimate the risk area, whereas FIF tended to underestimate it. Furthermore, among all assessment methods, the influence of rainwater discharge was found to have a more dominant effect on flood risk assessment compared to the number of rainwater inflow locations. Additionally, the direction of inundation flow influenced the assessed risk, with collision-induced flow patterns leading to higher flood risk than those with identical flow directions.

• Journal of the Korean Society of Industry Convergence
• /
• v.26 no.6_2
• /
• pp.1011-1017
• /
• 2023

In this study, the harmless crack size (a_hml) by double shot peening (DSP) using shot balls with different diameters was evaluated on carburized, quenched-tempered SCM822H steel. The minimum crack size (a_NDI) detectable by non-destructive inspection was also evaluated. The relationship between the crack size (a_25,50) that reduces the fatigue limit by 25% and 50% and a_hml was evaluated. The residual stress of DSP was greater in SP_(0.6+0.08) than SP_(0.8+0.08) and appeared deeper in the depth direction. In addition, the hardness below the surface appeared larger. The fatigue limit of DSP increased 2.07 times and 1.95 times compared to non-SP. All a_hml of the DSP specimen was determined at the depth (a). The compressive residual stress distribution affects a_hml, and the a_hml of SP_(0.6+0.08), which has a large compressive residual stress and a high fatigue limit, appeared large. a_hml of SP_(0.6+0.08) introduced deeper than the residual stress of SP_(0.8+0.08) is larger in the range of As=1.0-0.3. Since the residual stress in the thickness direction has a greater effect on a_hml than the residual stress at the surface, it is necessary to introduce it more deeply. The relation of a_hml, a_25,50, and a_NDI were evaluated in the point for safety and reliability.

• Tunnel and Underground Space
• /
• v.33 no.6
• /
• pp.483-494
• /
• 2023

Measurement of the physical properties of rocks or minerals is an important factor in determining the distribution of the underground medium as well as mineral resource investigations. Resistivity and induced polarization, which are widely used in Korea, are methods for measuring electrical properties, which are representative properties of obtaining subsurface information. In order to precisely analyze the exploration data obtained from various sites, it is important to accurately measure the material properties. Electrical properties of rock is measured using two-electrode or four-electrode method. Compared to the four-electrode method, the two-electrode method is generally used because it is very easy to contact the sample and the electrode, but there is a problem in that the impedance of the electrode and the sample is measured together. In this study, the time-domain the induced polarization effects were measured using the 2-electrode method and the 4-electrode method for artificial samples mixed with graphite and cement having induced polarization characteristics, and the results were compared. Although the 4-electrode method has difficulties in installing potential electrodes, it was confirmed that it is effective in measuring electrical properties because it can reduce the problem caused by the impedance of potential electrodes compared to the 2-electrode method.

• Composites Research
• /
• v.37 no.1
• /
• pp.46-52
• /
• 2024

The development of transportation methods has improved human transportation convenience and made it possible to expand the travel radius of people with disabilities who have difficulty moving. However, in the case of WAV (wheelchair Accessible Vehicle), the safety that may occur in a vehicle accident is still lower than that of regular passenger seats. In particular, in the case of a rear-end collision that may occur in a defenseless situation, it can cause fatal neck injuries to disabled passengers. Therefore, a more detailed design plan must be reflected in the headrest to be applied to WAV. In this study, a multi-cell headrest was proposed to implement local compression characteristic distribution of the headrest during rear-end collision of WAV. Afterwards, a correlation analysis was performed between the passenger's NIC (Neck Injury Criterion) and impact energy absorption using the data set construction through analysis and the clustering results using k-means clustering. As a result of clustering, it was confirmed that data clusters with similar characteristics were formed, and a correlation analysis between NIC and impact energy absorption through the characteristics of each cluster was performed. As a result of the analysis, it was confirmed that the softer the cell compression characteristics in Mid3 and Mid6, the more impact energy absorption increases, and the harder the cell compression characteristics in Front2, Mid3, and Mid6, the more effective it is in reducing NIC.

• Korean Journal of Construction Engineering and Management
• /
• v.25 no.1
• /
• pp.62-72
• /
• 2024

Due to the distribution structure of domestic temporary equipment, quality control of temporary equipment is essential because more than 80% of temporary equipment is repeated and reused. Due to this importance, the Ministry of Land, Infrastructure and Transport has proposed quality management standards for temporary equipment for 10types of temporary equipments, including steel pipe support, but the overall quality of temporary eqipment cannot be confirmed because the quality is managed through sampling quality tests. In addition, although quality control standards exist for temporary material rental company, practical utilization was investigated and analyzed to be very low as they are mainly presented based on qualitative inspection standards by visual inspection. Therefore, the purpose of this study is to develop individual temporary material/quality/delivery management standards (Guides) for temporary equipment rental company to preemptively secure the quality of temporary equipment before bringing them into the construction site. If the standards developed through this study are applied to domestic temporary equipment rental companies, it is expected that high-quality temporary equipment with secured quality will be brought into the construction site as the quality of temporary equipment quality of domestic medium and small temporary equipment rental companies is improved safety accidents related to temporary structures.

• Journal of Navigation and Port Research
• /
• v.47 no.6
• /
• pp.367-375
• /
• 2023

This study developed a new distance metric for vessel trajectories, applicable to marine traffic control services in the Korean coastal waters. The proposed metric is designed through the weighted summation of the traditional Hausdorff distance, which measures the similarity between spatiotemporal data and incorporates the differences in the average Speed Over Ground (SOG) and the variance in Course Over Ground (COG) between two trajectories. To validate the effectiveness of this new metric, a comparative analysis was conducted using the actual Automatic Identification System (AIS) trajectory data, in conjunction with an agglomerative clustering algorithm. Data visualizations were used to confirm that the results of trajectory clustering, with the new metric, reflect geographical distances and the distribution of vessel behavioral characteristics more accurately, than conventional metrics such as the Hausdorff distance and Dynamic Time Warping distance. Quantitatively, based on the Davies-Bouldin index, the clustering results were found to be superior or comparable and demonstrated exceptional efficiency in computational distance calculation.

• Journal of Navigation and Port Research
• /
• v.48 no.3
• /
• pp.221-231
• /
• 2024

The aim of this study was to enhance the safety and care of mental health for seafarer working in passenger ship workspaces. Brightness, color values, and color distribution were investigated with issues and improvement ways identified through seafarers' interviews. Firstly, previous studies, references, current policy, regulations, and accident case studies were reviewed. Color compositions of wheelhouse and engine room of M Ship were then surveyed in the field. Color values of each space were analyzed using a colorimeter. Colormeter analysis of brightness and color measurements in the wheelhouse and engine areas indicated that ceilings, walls, and floors were generally dark, with the engine area being very dark. Regarding color, green and blue were distributed in the ceiling of the wheelhouse and engine area, while red and blue were in the walls and floors of the wheelhouse and engine area. According to interviews with seafarers currently working at engine rooms, they responded about their experience of near miss incidents due to a decrepit indoor environment, a dark working environment, slippery and bright flooring, and stairs that were not suitable for domestic users. Thus, when installing lighting in the future, the brightness of the space should be improved by distinguishing between night and day. A lighting plan considering the location of lighting, level of shadow formation and contrast, reflectance of the facility, glare, color of light, floor color plan, and material selection is needed. A facility design suitable for domestic users is also needed.

• Steel and Composite Structures
• /
• v.50 no.6
• /
• pp.705-720
• /
• 2024

Analyzing the collapse behavior of thin-walled steel structures holds significant importance in ensuring their safety and longevity. Geometric imperfections present on the surface of metal materials can diminish both the durability and mechanical integrity of steel shells. These imperfections, encompassing local geometric irregularities and deformations such as holes, cavities, notches, and cracks localized in specific regions of the shell surface, play a pivotal role in the assessment. They can induce stress concentration within the structure, thereby influencing its susceptibility to buckling. The intricate relationship between the buckling behavior of these structures and such imperfections is multifaceted, contingent upon a variety of factors. The buckling analysis of thin-walled steel shell structures, similar to other steel structures, commonly involves the determination of crucial material properties, including elastic modulus, shear modulus, tensile strength, and fracture toughness. An established method involves the emulation of distributed geometric imperfections, utilizing real test specimen data as a basis. This approach allows for the accurate representation and assessment of the diversity and distribution of imperfections encountered in real-world scenarios. Utilizing defect data obtained from actual test samples enhances the model's realism and applicability. The sizes and configurations of these defects are employed as inputs in the modeling process, aiding in the prediction of structural behavior. It's worth noting that there is a dearth of experimental studies addressing the influence of geometric defects on the buckling behavior of cylindrical steel shells. In this particular study, samples featuring geometric imperfections were subjected to experimental buckling tests. These same samples were also modeled using Finite Element Analysis (FEM), with results corroborating the experimental findings. Furthermore, the initial geometrical imperfections were measured using digital image correlation (DIC) techniques. In this way, the response of the test specimens can be estimated accurately by applying the initial imperfections to FE models. After validation of the test results with FEA, a numerical parametric study was conducted to develop more generalized design recommendations for the stainless-steel shell structures with the initial geometric imperfection. While the load-carrying capacity of samples with perfect surfaces was up to 140 kN, the load-carrying capacity of samples with 4 mm defects was around 130 kN. Likewise, while the load carrying capacity of samples with 10 mm defects was around 125 kN, the load carrying capacity of samples with 14 mm defects was measured around 120 kN.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.37 no.4
• /
• pp.233-241
• /
• 2024

In this study, finite element analyses of coated steel pipes were conducted to research the development of sensing-based monitoring smart pipes. The coated steel pipes underwent a chemical coating pretreatment process that used modified polyethylene on both the inside and outside surfaces. Furthermore, the steel pipes were designed to minimize damage during the expansion process by incorporating connecting parts. To evaluate structural performance under various loads, four loading conditions were established: static structural analysis by earth pressure, fatigue life evaluation by vehicle load, and resistance to water leakage under both tensile and compressive loads. The analysis estimated a higher fatigue life for the developed steel pipe, compared with that of a steel pipe using ready-made epoxy coatings and joints. In addition, an average maximum displacement reduction of 56.1% and a maximum stress reduction of 61.2% were confirmed under identical conditions and diameters, thereby verifying the safety of the connecting parts of the developed coated steel pipe. Furthermore, the results of stress distribution contour analyses revealed superior water leakage resistance at the fastening parts, compared with the centers of the pipes.

• The Journal of Engineering Geology
• /
• v.19 no.4
• /
• pp.509-515
• /
• 2009

Three earthquakes with local magnitude ($M_L$) greater than 3.0 occurred on April 24, June 2 and September 12 in 1999 nearby the Gyeongju area. Redetermined epicenters were located within the radius of 1 km. We carried out waveform inversion analysis to estimate focal mechanism of June 2 event, and P and S wave polarity and their amplitude ratio analysis to estimate focal mechanisms of April 24 and September 12 events. June 2 and September 12 events had similar fault plane solutions each other. The fault plane solution of April 24 event included those of other 2 events, but its distribution range was relatively broad. Focal mechanisms of those events had a strike slip faulting with a small normal component. P-axes of those events were ENE-WSW which were similar to previous studies on the P-axis of the Korean Peninsula. Considering distances between epicenters, similarities of seismic waves and sameness of polarities of seismic data recorded at common seismic stations, these events might occurred at the same fault. The seismic moment of June 2 event was estimated to be $3.9\;{\times}\;10^{14}\;N{\cdot}m$ and this value corresponded to the moment magnitude ($M_W$) 3.7. The moment magnitude estimated by spectral analysis was 3.8, which was similar to that estimated by waveform inversion analysis. The average stress drop was estimated to be 7.5 MPa. Moment magnitudes of April 24 and September 12 events were estimated to be 3.2 and 3.4 by comparing the spectrum of those events recorded at common single seismic station.