• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.193-198
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• 2021

In this study, the rheological characteristics and of 3D printing composite materials and the compressive strength characteristics according to the lamination patterns were evaluated. As a result of rheology test, rapid material change was observed after 60 minutes of extrusion, yielding stress 1.4 times higher than immediately after mixing, and plastic viscosity was 14.94-25.62% lower. The compressive strength of the specimens manufactured in the mold and the laminated specimens were compared, and the lamination pattern of the laminated specimens were 0°, 45°, and 90° as variables. The compressive strength of the mold casting specimen and the laminated specimen from 1 to 28 days of age showed similar performance regardless of the lamination pattern. In particular, at the age of 28 days, the modulus of elasticity, maximum compressive strength, and strain at maximum stress of all specimens were almost the same. In order to analyze the interface of the laminated specimens, X-ray CT analysis of the specimen whose compressive strength were measured was performed. Through CT analysis, it was confirmed that cracks did not occur at the lamination interface, which can be judged that the interface in the laminated specimen behaved in an integrated manner.

• Journal of the Korean Wood Science and Technology
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• v.30 no.1
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• pp.25-33
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• 2002

Improvement of density profile and sound absorption capability of particleboard was attempted. Three types of hot pressing methods examined ; flat-platen pressing method (A-type pressing), hot pressing in forming box (B-type pressing), and hot pressing set up jagged caul in forming box (C-type pressing). The raw materials were larch(Larix leptolepis (S, et. Z.) Gorden) shavings, phenol formaldehyde resin, and the particleboard perforated with stair type. The physical and mechanical properties such as specific gravity, bending strength (MOR), internal bonding strength (IB) and sound absorption coefficients were examined. The results are summarized as follows : 1) The MOR and internal bonding strength of the board pressed in forming box were higher than those of flat-platen pressed board. 2) The minimum density to average density ratio in thickness direction which pressed in forming box showed about 923%, in the case of 35 mm commercial particleboard and 50 mm flat-platen pressed board, its values showed about 66.4% and 865% respectively. 3) Sound absorption coefficients of the particleboard perforated with stair type were higher than those of flat-plated pressed board and commercial particleboard.

• Membrane Journal
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• v.32 no.5
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• pp.314-324
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• 2022

This study is aimed to design a membrane process that systematically removes contaminants including microplastics in sun-dried salt using a separation membrane. In this study, we selected the separation membrane material, pore size, and module suitable for the sun-dried salt fields, and proceeded with the experiments under the salt fields and laboratory conditions. A pilot plant was constructed and tested in our lab and in the actual saltern with the selected 200 kDa, 4 kDa ultrafiltration membranes, and 3 kDa nanofiltration membranes. Most of the impurities in the sea salt were 0.1 ㎛ in size, and more than 7 types of various microplastics were detected in the impurities. After that, as a result of checking the filtered water through the separation membrane process, no impurities were detected. As a result of comparing the existing sea salt component and the sea salt component prepared with separation membrane filtrate, impurities were effectively removed without change in the sea salt component.

• Journal of Aerospace System Engineering
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• v.17 no.4
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• pp.133-143
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• 2023

As drones (also known as UAV) become popular with advanced information and communication technology (ICT), they have been utilized for various fields (agriculture, architecture, and so on). However, malicious attackers with advanced drones may pose a threat to critical national infrastructures. Thus, anti-drone systems have been developed to respond to drone threats. In particular, remote identification data (R-ID)-based UAV detection and identification systems that detect and identify illegal drones with R-ID broadcasted by drones have been developed, and are widely employed worldwide. However, this R-ID-based UAV detection/identification system is vulnerable to security due to wireless broadcast characteristics. In this paper, we analyze the security vulnerabilities of DJI Aeroscope, a representative example of the R-ID-based UAV detection and identification system, and propose a replay-attack-based neutralization method using the analyzed vulnerabilities. To validate the proposed method, it is implemented as a software program, and verified against four types of attacks in real test environments. The results demonstrate that the proposed neutralization method is an effective neutralization method for R-ID-based UAV detection and identification systems.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.5
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• pp.667-674
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• 2023

In the event of a disaster occurring within a building, the prompt and efficient evacuation and rescue of occupants within the building becomes the foremost priority to minimize casualties. For the purpose of such rescue operations, it is essential to ascertain the distribution of individuals within the building. Nevertheless, there is a primary dependence on accounts provided by pertinent individuals like building proprietors or security staff, alongside fundamental data encompassing floor dimensions and maximum capacity. Consequently, accurate determination of the number of occupants within the building holds paramount significance in reducing uncertainties at the site and facilitating effective rescue activities during the golden hour. This research introduces a methodology employing computer vision algorithms to count the number of occupants within distinct building locations based on images captured by installed multiple CCTV cameras. The counting methodology consists of three stages: (1) establishing virtual Lines of Interest (LOI) for each camera to construct a multi-camera network environment, (2) detecting and tracking people within the monitoring area using deep learning, and (3) aggregating counts across the multi-camera network. The proposed methodology was validated through experiments conducted in a five-story building with the average accurary of 89.9% and the average MAE of 0.178 and RMSE of 0.339, and the advantages of using multiple cameras for occupant counting were explained. This paper showed the potential of the proposed methodology for more effective and timely disaster management through common surveillance systems by providing prompt occupancy information.

• Journal of the Korean Geotechnical Society
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• v.26 no.6
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• pp.5-19
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• 2010

The purpose of this study is to figure out the effect of pressurized grouting on the pullout resistance and the group effect of the compression ground anchor by performing pilot-scale chamber tests and field tests. The laboratory tests are carried out for 3-types of soils which are abundant in the Korean peninsular. Experimental results showed that the enlargement of anchor diameters estimated from the cavity expansion theory matches reasonable well with that obtained from experiments. Moreover, the required injection time as a function of the coefficient of permeability of each soil type was proposed. A series of in-situ anchor pullout tests were also performed to experimentally figure out the effect of pressurized grouting on the pullout resistance. Experimental results also showed that the effect of the pressurized grouting is more prominent in a softer ground with smaller SPT-N value in all of the following three aspects: increase in anchor diameter; pullout resistance; and surface roughness. The pressurized grouting effect in comparison with gravitational grouting was found to be almost nil if the SPT-N value is more than 50. Based on experimental results, a new equation to estimate the pullout resistance as a function of the SPT-N value was proposed. And based on in-situ group anchor pullout tests results, a new group effect equation was proposed which might be applicable to decomposed residual soils which are abundant in the Korean peninsular.

• Journal of the Korea Organic Resources Recycling Association
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• v.30 no.1
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• pp.41-47
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• 2022

In this study, rainfall water outlet water quality monitoring was performed on the C industrial complex to evaluate the characteristics of non-point pollutant runoff from the industrial complex during rainfall and to use it as basic data for calculating the load and unit of non-point pollutant. As a result of calculating EMC according to the outflow amount by rainfall event, the 1st rainfall showed EMCs ranges of BOD, COD_Mn, SS, T-N, and T-P of 1.32~48.76, 3.32~43.75, 2.89~199.43, 2.76~8.93, 0.08~068, and the 2nd rainfall was 0.5~2.9, 2.71~7.13, 2.82~174.94, 1.33~4.03, 0.01~1.28 mg/L, respectively. As a result of calculating the ratio of cumulative outflow and cumulative pollution load, most of the pollution load was less than the rainfall outflow, but over time, the initial washing phenomenon occurred as the ratio of cumulative rainfall outflow and cumulative pollution load increased to more than 1.

• Korea Science and Art Forum
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• v.19
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• pp.243-257
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• 2015

The Cultural Heritage Administration has selected Seoul Fortress Wall as the representative heritage of Korea to be applied for being registered as UNESCO World Heritage and announced the plan to restore and organize it, which has increased the interest to the Seoul Fortress Wall, the Historical Site No. 10. The great work to make the heritage value of Walls, 4 Big Gates and 4 Small Gates composing the Seoul Fortress wall with the length of 18.627 km to be recognized worldwide has limits if it is focused only on the physical restoration. It is because the Seoul Fortress Wall represents the long historical and cultural value as the space of life which connects closely the capital city and its vicinity. We need the plan to discover and utilize historical and cultural contents of Seoul Fortress Wall and its vicinity. Especially, Gwangheemun, which is one of the four Small Gates of Seoul Fortress Wall, is a precious cultural heritage which represents the transition of fortification technology of Chosun period as the space representing ordinary people. However, now Gwangheemun and its vicinity does not stand out the charm because of passive accessibility, landscape falling behind and absence of program. This made the lack of domestic and overseas tourists and the convenient space and various contents. This reality is because the value of space has been considered simply as a cultural heritage without considering the traditional, historical and cultural specificity. Therefore, this study is aimed to find the meaning and value of Gwangheemun by discovering its own latent intangible cultural, historical and artistic resource, and to find the way to connect with Gwangheemun, the existing tangible traditional architectural space and the way of vitalizing Gwangheemun as a new space.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2C
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• pp.71-79
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• 2009

This study is to develope the resilient modulus prediction model, which is the function of mean effective principal stress and axial strain, for three types of railroad trackbed materials such as crushed stone, weathered granite soil, and crushed-rock soil mixture. The model consists of the maximum Young's modulus and nonlinear values for higher strain, analogous to dynamic shear modulus. The maximum value is modeled by model parameters, $A_E$ and the power of mean effective principal stress, $n_E$. The nonlinear portion is represented by modified hyperbolic model, with the model parameters of reference strain, ${\varepsilon}_r$ and curvature coefficient, a. To assess the performance of the prediction models proposed herein, the elastic response of a test trackbed near PyeongTaek, Korea, was evaluated using a 3-D elastic multilayer computer program (GEOTRACK). The results were compared with measured elastic vertical displacement during the passages of freight and passenger trains at two locations, whose sub-ballasts were crushed stone and weathered granite soil, respectively. The calculated vertical displacements of the sub-ballasts are within the order of 0.6mm, and agree well with measured values. The prediction models are thus concluded to work properly in the preliminary investigation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2D
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• pp.243-248
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• 2008

Moisture damage of asphalt pavements can usually occur because of the loss of adhesion and cohesion between the asphalt binder and aggregate in the asphalt mixture due to presence of water. And this is one of the causes that is effect on the main distress of asphalt pavement. The objective of this study is to find out moisture damage characteristics of asphalt pavement. Effects of this study changes of the material properties and resistance characteristics of moisture damage on the asphalt mixtures under various temperatures and repeated immersion using indirect tensile test and modify Lottman test were evaluated during this study. The asphalt mixtures were produced using straight asphalt binder, SBS modified asphalt binder and aggregates. The material properties (resilient modulus, indirect tensile strength, failure energy and $DCSE_f$) of the asphalt mixtures were generally decreased with increasing to moisture damage caused by the number of repeated immersion. The decrease ratios of material properties by repeated immersion on SBS modified asphalt mixtures were lower than those of straight asphalt mixtures at all three test temperatures. As a conclusion, current criterion for evaluation moisture damage of asphalt mixtures is difficult for using distinction standard because of the limited evaluation criterion with one time immersion and single material property. Based on this research, to evaluate long term moisture damage on asphalt mixtures, material property tests of various kinds with repeated immersion test are considered.