• Environmental Engineering Research
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• v.15 no.3
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• pp.167-172
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• 2010

The effects of low impact development (LID) techniques, such as green roofs and porous pavements, on the runoff and pollutant load from an apartment complex were simulated using the Site Evaluation Tool (SET). The study site was the Olympic Village, a preexisting apartment complex in Seoul, South Korea, which has a high percentage of impervious surfaces (approximately 72% of the total area). Using the SET, the effects of replacing parking lots, sidewalks and driveways (37.5% of the total area) having porous pavements and rooftops (14.5% of the total area) with green roofs were simulated. The simulation results indicated that LID techniques reduced the surface runoff, and peak flow and pollutant load, and increased the evapotranspiration and soil infiltration of precipitation. Per unit area, the green roofs were better than the porous pavements at reducing the surface runoff and pollutant loads, while the porous pavements were better than green roofs at enhancing the infiltration to soil. This study showed that LID methods can be useful for urban stormwater management and that the SET is a useful tool for evaluating the effects of LID on urban hydrology and pollutant loads from various land covers.

• Steel and Composite Structures
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• v.36 no.6
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• pp.703-710
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• 2020

This paper presents numerical and theoretical investigations on the strain rate in steel-concrete composite (SC) panels under low-velocity impact of a hemispherical rigid body. Finite element analyses were performed on five specimens with different loading rates. The impact energy was kept constant to eliminate its influence by simultaneously altering the velocity and mass of the projectile. Results show that the strain rate in most parts of the specimens was low and its influence on bearing capacity and energy dissipation was limited in an average sense of space and time. Therefore, the strain rate effect can be ignored for the analyses of global deformation. However, the strain rate effect should be considered in local contact problems. Equations of the local strain and strain rate were theoretically derived.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.9-10
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• 2010

In this study, the static and low velocity impact tests for two-way concrete specimens strengthening with the CFRP sheets were carried out. The specimens that had a dimension of $50{\times}350{\times}350mm$ with 40 MPa plain concrete and steel fiber reinforced concrete which had same mixture to plain concrete and 0.75% steel fibers were fabricated. The specimens reinforced with the CFRP or steel fibers showed mixed failure modes, splitting and punching, also splitting cracks and fragments were much reduced than plain concrete specimens'. Two-way concrete members reinforced with the CFRP and steel fiber simultaneously dissipated 6.8 times larger energy than not-retrofitted members' under the low-velocity impact loading.

• Ecology and Resilient Infrastructure
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• v.3 no.2
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• pp.130-133
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• 2016

The increase in impervious surfaces due to urban development has caused a groundwater drawdown through the reduction of underground infiltration, flood disaster due to increased rainfall runoff and environmental pollution in higher pollutant concentrations of first flush rainwater. As an alternative to these problems, the needs of low impact development (LID) techniques is increasing in urban areas. In this study, the restoration efficiency of water cycle was assessed at a residential site development applied with the LID rainwater management system. The results of monitoring the water cycling showed that the efficiency of water cycle of LID rainwater management system was improved 41% more than that of conventional methods.

• Journal of Korean Society on Water Environment
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• v.36 no.1
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• pp.29-35
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• 2020

To manage the non-point source pollution and restore the water circulation, many technologies including infiltration or reservoir systems were installed in the urban area. These facilities have many problems regarding maintenance as their operation period becomes lengthier. The purpose of this study was to estimate the optimal maintenance timing through a long-term load test on the infiltration trench as one of the low impact development techniques. An infiltration trench was installed in the demonstration test facility, and stormwater was manufactured by Manual on installation and operation of non-point pollution management facilities from the Ministry of Environment, Korea and entered into the infiltration trench. Particle size distribution (PSD), suspended solids (SS) removal efficiency, and infiltration rate change tests were performed on inflow and outflow water. In case of the PSD, the maximum particulate size in the outflow decreased from 64 ㎛ to 33 ㎛ as the operating duration elapsed. The SS removal efficiency improved from 97 % to 99 %. The infiltration rate changed from 0.113 L/sec to 0.015 L/sec during the operation duration. The maintenance timing was determined based on the stormwater runoff requirements with these changes in water quality and infiltration rate. The methodologies in this study could be used to estimate the timing of maintenance of other low impact development techniques.

• Advances in environmental research
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• v.2 no.4
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• pp.279-290
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• 2013

In this study, a comprehensive model developed to estimate greenhouse gas (GHG) emissions from urban area with low impact development (LID) and its integrated management practices (IMPs). The model was applied to the actual urban area in Asan Tangjeong district (ATD) as a case study. A rainwater tank (1200 ton) among various LID IMPs generated the highest amount of GHG emissions ($3.77{\times}10^5kgCO_2eq$) and led to the utmost reducing effect ($1.49{\times}10^3kgCO_2eq/year$). In the urban area with LID IMPs, annually $1.95{\times}104kgCO_2eq$ of avoided GHG emissions were generated by a reducing effect (e.g., tap water substitution and vegetation $CO_2$ absorption) for a payback period of 162 years. A sensitivity analysis was carried out to quantitatively evaluate the significance of the factors on the overall GHG emissions in ATD, and suggested to plant alternative vegetation on LID IMPs.

• Steel and Composite Structures
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• v.46 no.4
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• pp.525-538
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• 2023

This paper focuses on the energy absorption of lattice core sandwich structures of different configurations. The diamond lattice unit cell, which has been extensively investigated for energy absorption applications, is the starting point for this research. The energy absorption behaviour of sandwich structures with an expanded metal sheet as the core is investigated at low-velocity impact loading. Numerical simulations were carried out using ABAQUS/EXPLICIT and the results were thoroughly compared with the experimental results, which indicated desirable accuracy. A parametric analysis, using a Box-Behnken design (BBD), as a method for the design of experiments (DOE), was performed. The samples fabricated in three levels of parameters include 0.081, 0.145, and 0.562 mm² Cell sizes, and 0, 45, and 90-degree cell orientation, which were investigated. It was observed from experimental data that the angle of cells orientation had the highest degree of influence on the specific energy absorption. The results showed that the angle of cells orientation has been the most influential parameter to increase the peak forces. The results from using the design expert software showed the optimal specific energy absorption and peak force to be 1786 J/kg and 26314.4 N, respectively. The obtained R2 values and normal probability plots indicated a good agreement between the experimental results and those predicted by the model.

• Nuclear Engineering and Technology
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• v.56 no.2
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• pp.402-409
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• 2024

High energy neutron irradiations impact on structural and electrical properties of alumina are studied with particular emphasis on real time in-situ radiation induced conductivity measurement in low flux region. Polycrystalline Al₂O₃ samples are subjected to high energy neutrons produced from D-T neutron generator and Am-Be neutron source. 14 MeV neutrons from D-T generator are chosen to study the role of fast neutron irradiation in the structural modification of samples. Real time in-situ electrical measurement is performed to investigate the change in insulation resistance of Al₂O₃ due to radiation induced conductivity at low flux regime. During neutron irradiation, a significant transient decrease in insulation resistance is observed which recovers relative higher value just after neutron exposure is switched off. XRD results of 14 MeV neutron irradiated samples suggest annealing effect. Impact of relatively low energy neutrons on the structural properties is also studied using Am-Be neutrons. In this case, clustering is observed on the sample surface after prolonged neutron exposure. The structural characterizations of pristine and irradiated Al₂O₃ samples are performed using XRD, SEM, and EDX. The results from these characterizations are analysed and interpreted in the manuscript.

• International Journal of Highway Engineering
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• v.18 no.6
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• pp.123-130
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• 2016

OBJECTIVES : The objective of this research is to determine the moisture resistance of the freeze-thaw process occurring in low-noise porous pavement using either hydrated-lime or anti-freezing agent. Various additives were applied to low-noise porous asphalt, which is actively paved in South Korea, to overcome its disadvantages. Moreover, the optimum contents of hydrated-lime and anti-freezing agent and behavior properties of low-noise porous asphalt layer are determined using dynamic moduli via the freeze-thaw test. METHODS : The low-noise porous asphalt mixtures were made using gyratory compacters to investigate its properties with either hydrated-lime or anti-freezing agent. To determine the dynamic moduli of each mixture, impact resonance test was conducted. The applied standard for the freeze-thaw test of asphalt mixture is ASTM D 6857. The freeze-thaw and impact resonance tests were performed twice at each stage. The behavior properties were defined using finite element method, which was performed using the dynamic modulus data obtained from the freeze-thaw test and resonance frequencies obtained from non-destructive impact test. RESULTS : The results show that the coherence and strength of the low-noise porous asphalt mixture decreased continuously with the increase in the temperature of the mixture. The dynamic modulus of the normal low-noise porous asphalt mixture dramatically decreased after one cycle of freezing and thawing stages, which is more than that of other mixtures containing additives. The damage rate was higher when the freeze-thaw test was repeated. CONCLUSIONS : From the root mean squared error (RMSE) and mean percentage error (MPE) analyses, the addition rates of 1.5% hydrated-lime and 0.5% anti-freezing agent resulted in the strongest mixture having the highest moisture resistance compared to other specimens with each additive in 1 cycle freeze-thaw test. Moreover, the freeze-thaw resistance significantly improved when a hydrated-lime content of 0.5% was applied for the two cycles of the freeze-thaw test. Hence, the optimum contents of both hydrated-lime and anti-freezing agent are 0.5%.

• KSTLE International Journal
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• v.3 no.2
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• pp.84-89
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• 2002

Clearance movements of engine piston are very related to the piston impact to the engine block as well as many tribological problems. Some of the major parameters that influence these kinds of performances are piston profiles, piston offsets and clearance magnitudes. In our study, computational investigation is performed about the piston movements in the clearance between piston and cylinder liner by changing the skirt profiles and piston offsets. Our results show that curved profile and more offset magnitude to thrust side have better performance that has low side impact during the engine cycle.