• Proceedings of the KSR Conference
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• 2004.06a
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• pp.303-308
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• 2004

It is recently reported that the importance of environmental impact assessment(EIA) about groundwater outflow problems is beingy raised in the case of tunnel excavation during railroad construction. The EIA about groundwater outflow into railroad tunnel is generally performed using the results of numerical analysis embodied through groundwater flow modeling program like MODFLOW. The basic data for this modeling include (1) the geological and hydrogeological investigation data along the planned block of tunnel excavation, (2) total amount of outflowed groundwater during tunnel excavation, and (3) the status of groundwater level fluctuation in the water-supply wells distributed in the planned block of tunnel excavation. In this study, the authors analyzed the cases of the computational modeling about groundwater outflow in three planned blocks of railroad tunnel, and suggest the environmental impact factors and mitigation plan during EIA of tunnel excavation in railroad construction.

• KIEE International Transactions on Power Engineering
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• v.4A no.3
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• pp.122-128
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• 2004

With the advent of distributed generation, power systems are fundamentally impacted in regards to stability and power quality. Distributed generation has a positive impact on system restoration following a fault, higher reliability, and mitigation of effect due to voltage sag. However, distributed generation also has a negative impact on decrease of reliability such as changes of protective device setting and mal-operation. Because bulk power systems consist of various sources and loads, it becomes complicated to analyze a power system with distributed generation. The types of distributed generation are usually classified by both rotating machinery and the inverter-based system. In this paper, distributed generation is designed by rotating machinery, and the distributed system having a model of the distributed generation is simulated using EMTP. In addition, this paper presents the simulation results according to the types of distributed generation.

• Journal of Communications and Networks
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• v.17 no.6
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• pp.622-633
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• 2015

The coexistence among different systems is a major problem in communications. Mutual interference between different systems should be analyzed and mitigated before their deployment. The paper focuses on two aspects that have an impact on the system performance. First, the coexistence analysis, i.e. evaluating the mutual interference. Second aspect is the coexistence techniques, i.e. appropriate system modifications that guarantee the simultaneous use of the spectrum by different technologies. In particular, the coexistence problem is analyzed between ultra-wide bandwidth (UWB) and narrow bandwidth (NB) systems emphasizing the role of spectrum sensing to identify and classify the NB interferers that mostly affect the performance of UWB system. A direct sequence (DS)-time hopping (TH) code design technique is used to mitigate the identified NB interference. Due to the severe effect of Narrowband Interference on UWB communications, we propose an UWB transceiver that utilizes spectrum-sensing techniques together with mitigation techniques. The proposed transceiver improves both the UWB and NB systems performance by adaptively reducing the mutual interference. Detection and avoidance method is used where spectrum is sensed every time duration to detect the NB interferer's frequency location and power avoiding it's effect by using the appropriate mitigation technique. Two scenarios are presented to identify, classify, and mitigate NB interferers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.3
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• pp.916-937
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• 2023

Most of the existing Distributed Denial-of-Service mitigation schemes in Software-Defined Networking are only implemented in the network domain managed by a single controller. In fact, the zombies for attackers to launch large-scale DDoS attacks are actually not in the same network domain. Therefore, abnormal traffic of DDoS attack will affect multiple paths and network domains. A single defense method is difficult to deal with large-scale DDoS attacks. The cooperative defense of multiple domains becomes an important means to effectively solve cross-domain DDoS attacks. We propose an efficient multi-domain DDoS cooperative defense mechanism by integrating blockchain and SDN architecture. It includes attack traceability, inter-domain information sharing and attack mitigation. In order to reduce the length of the marking path and shorten the traceability time, we propose an AS-level packet traceability method called ASPM. We propose an information sharing method across multiple domains based on blockchain and smart contract. It effectively solves the impact of DDoS illegal traffic on multiple domains. According to the traceability results, we designed a DDoS attack mitigation method by replacing the ACL list with the IP address black/gray list. The experimental results show that our ASPM traceability method requires less data packets, high traceability precision and low overhead. And blockchain-based inter-domain sharing scheme has low cost, high scalability and high security. Attack mitigation measures can prevent illegal data flow in a timely and efficient manner.

• Geomechanics and Engineering
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• v.29 no.5
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• pp.567-582
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• 2022

In the present study, a series of physical experiments and numerical simulations were conducted to investigate the effects of mode I and mixed-mode I/II cracks on the fracture modes and stability of roadway tunnel models. The experiments and simulations incorporated different inclination angle flaws under both static and dynamic loads. The quasi-static and dynamic testing were conducted by using an electro-hydraulic servo control device and drop weight impact system (DWIS), and the failure process was simulated by using rock failure process analysis (RFPA) and AUTODYN software. The stress intensity factor was also calculated to evaluate the stability of the flawed roadway tunnel models by using ABAQUS software. According to comparisons between the test and numerical results, it is observed that for flawed roadways with a single radical crack and inclination angle of 45°, the static and dynamic stability are the lowest relative to other angles of fractured rock masses. For mixed-mode I/II cracks in flawed roadway tunnel models under dynamic loading, a wing crack is produced and the pre-existing cracks increase the stress concentration factor in the right part of the specimen, but this factor will not be larger than the maximum principal stress region in the roadway tunnel models. Additionally, damage to the sidewalls will be involved in the flawed roadway tunnel models under static loads.

• Journal of Environmental Impact Assessment
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• v.9 no.3
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• pp.215-228
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• 2000

This paper presents a novel method to predict a flushing rate in an embayment system, which can be utilized to assess an environmental impact caused by harbor construction. The method was successfully applied to the Ulsan-Onsan coastal area. The flushing rate was computed on the basis of water quality changes predicted by US Army Corps of Engineers' RMA-2/RMA-4 models. After calibration and verification to the measured tidal elevation and current velocity, the model was used to estimate the flushing rate in the proposed harbor. The water quality was simulated for 96 hours and the flushing rate was computed. The results indicated that the proposed harbor would significantly reduce the flushing rate in the Onsan harbor, especially at the small embayment area near the south breakwater. The flushing rate was evaluated for several alternatives, of which the tidal flow channel of 1,000 $m^2$ in the south pier appeared to be the best mitigation measure. This study proposes that the prediction of flushing rate would be a novel method to assess a water quality impact caused by harbor construction.

• Korean Journal of Remote Sensing
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• v.33 no.6_2
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• pp.1119-1137
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• 2017

This study assessed the water provisioning and climate mitigation ecosystem services of the urban forest in Seoul and Gyeonggi-do. The ecosystem service assessment is conducted based on natural function, natural function and population, and natural function and the beneficiary of the ecosystem service. Then, the impact of climate change on ecosystem services is analyzed to figure out the sensitivity of the impact on the beneficiary when the natural function of forest destroys under climate change. Gyeonggi-do has higher function-based water provisioning ecosystem service than Seoul. And population-based water provisioning ecosystem service appears to be higher in the densely populated area. On the other hand, beneficiary-based water provisioning ecosystem service by applying both natural water supply function and beneficiary distribution appears different with the result of population-based water provisioning service assessment. In other words, regions with high beneficiary population show higher ecosystem service than those with a low beneficiary population even though they have the same water storage function. In addition, climate change has a negative impact on the water provisioning ecosystem service. Under climate change, water provisioning service is expected to decrease by 26%. For climate mitigation service, regions close to the forest seem to have a low temperature, which indicates their high climate mitigation service. The center of the city with high beneficiary population shows high beneficiary-based ecosystem service. The climate change impacts the forest growth to decrease which affect the beneficiary-based climate mitigation ecosystem service to decrease by 33%. From this study, we conclude that beneficiary-based function and ecosystem service assessment is needed as well as the supply-based classification of forest function suggested by Korea Forest Service. In addition, we suggest that not only supply-based function classification and ecosystem service assessment but also beneficiary-based function classification and ecosystem service assessment is needed for managing the urban forest, which has been destroyed by climate change. This will contribute to revaluing cases where a forest with low natural function but high beneficiary-based ecosystem service, which is not considered under the current forest function-based assessment system. Moreover, this could assist in developing a suitable management plan for the urban forest.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.3085-3099
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• 2021

Investigations of large commercial aircraft impact effect on nuclear power plant (NPP) buildings have been drawing extensive attentions, particularly after the 9/11 event, and this paper aims to numerically assess the damage and vibrations of NPP buildings subjected to aircrafts crash. In Part I of present paper, two shots of reduce-scaled model test of aircraft impact on NPP were conducted based on the large rocket sled loading test platform. In the present part, the numerical simulations of both scaled and prototype aircraft impact on NPP buildings are further performed by adopting the commercial program LS-DYNA. Firstly, the refined finite element (FE) models of both scaled aircraft and NPP models in Part I are established, and the model impact test is numerically simulated. The validities of the adopted numerical algorithm, constitutive model and the corresponding parameters are verified based on the experimental NPP model damages and accelerations. Then, the refined simulations of prototype A380 aircraft impact on a hypothetical NPP building are further carried out. It indicates that the NPP building can totally withstand the impact of A380 at a velocity of 150 m/s, while the accompanied intensive vibrations may still lead to different levels of damage on the nuclear related equipment. Referring to the guideline NEI07-13, a maximum acceleration contour is plotted and the shock damage propagation distances under aircraft impact are assessed, which indicates that the nuclear equipment located within 11.5 m from the impact point may endure malfunction. Finally, by respectively considering the rigid and deformable impacts mainly induced by aircraft engine and fuselage, an improved Riera function is proposed to predict the impact force of aircraft A380.

• Journal of Environmental Impact Assessment
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• v.4 no.3
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• pp.1-8
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• 1995

In generally speaking, the purpose of Environmental Impact Assessment(EIA) is to give the environment its due place in the decision-making process by clearly ealuating the environmental consequence of a proposed activity before action is taken. The introduction of conventional EIA is to be seen as an end product of a very long evolutionary process, starting with rudimentary but evolving pollution control measures for air, water, noise, land and chemicals, each governed by separate, and separately administered pieces of legislation. In EIA process, the measures of status, scoping, proposed mitigation and communication have not been very quantitative in their significancy. Of course, the determinations have uncertainity in the implications for significant impacts. To improve the determination of significant impacts, some more comprehensive methodologies of EIA has been proposed with the concepts of risk analysis in the proposed projects. The concepts of risk analysis has been introduced to the expression of human health impairment due to environmental pollutants since the early 1980's. The risk analysis being meant by the statistical significance of impact has a process quantitatively considering uncertainities and importances of ecological systems and human health as well. The process of risk analysis shows assessment, doseresponse in toxicity, exposure assessment and risk characterization. With the risk assessment, it could be suggested for the proper measurements against their anticipated risk in the EIA. This paper deals the priciples developing process and application of the risk-based analysis in EIA.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.535-540
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• 2005

In environmental impact assessment, noise impact assessment usually consists of three stages surveying the existing noise levels by measurements, predicting noise levels induced by construction works and predicting noise levels after the completion of project. When predicting noise level in urban area, this method does not consider acoustic phenomena like multi reflection, diffraction and absorption due to complex topographic configuration of building and terrains. For the purpose, a noise mapping tool is utilized to produce a series of noise maps, which are those for the present, for the works of construction and for the future. For accurate noise mapping, acoustical and topographic information is essential. Standard sound power levels and directivities of various construction equipments are required and scheduling of construction processes and locations of the equipments should be provided. In the case of exceeding legal limit, mitigation measures are applied to satisfy the legal limits and subsequent noise map is obtained and checked.