• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.10
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• pp.4883-4901
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• 2016

Energy efficiency in Wireless Sensor Networks (WSNs) is very appealing research area due to serious constrains on resources like storage, processing, and communication power of the sensor nodes. Due to limited capabilities of sensing nodes, such networks are composed of a large number of nodes. The higher number of nodes increases the overall performance in data collection from environment and transmission of packets among nodes. In such networks the nodes sense data and ultimately forward the information to a Base Station (BS). The main issues in WSNs revolve around energy consumption and delay in relaying of data. A lot of research work has been published in this area of achieving energy efficiency in the network. Various techniques have been proposed to divide such networks; like grid division of network, group based division, clustering, making logical layers of network, variable size clusters or groups and so on. In this paper a new technique of group based WSNs is proposed by using some features from recent published protocols i.e. "Energy-Efficient Multi-level and Distance Aware Clustering (EEMDC)" and "Energy-Efficient Multi-level and Distance Aware Clustering (EEUC)". The proposed work is not only energy-efficient but also minimizes the delay in relaying of data from the sensor nodes to BS. Simulation results show, that it outperforms LEACH protocol by 38%, EEMDC by 10% and EEUC by 13%.

• Journal of KIISE:Information Networking
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• v.33 no.1
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• pp.91-102
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• 2006

We analyze the performance of MAC-layer Reed-Solomon error recovery in the cdma2000 1xEV-DO Broadcast and Multicast Services (BCMCSs) environment, with respect to the size of the ECB (Error Control Block) and the air-channel condition, and establish the relationship between ECB size, error recovery capacity and service latency. From this we propose an adaptive error recovery scheme which adjusts the size of the ECB to reflect the environment of the mobile nodes so as to meet the required service quality (target bit error-rate), while reducing the latency of real-time applications. Extensive simulation results show the effectiveness of our approach compared to the current static scheme. Proposed adaptive schemes achieves near optimal solution with respect to service latency while satisfying the required service quality.

• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.352-360
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• 2019

This paper proposes a docking assessment algorithm for an autonomous underwater vehicles (AUVs) with sensor uncertainties. The proposed algorithm consists of two assessments, state assessment and probability assessment. The state assessment verifies the reachability by comparing forward distance to the docking station with expected distance to reach same depth as the docking station and necessity for correcting its route by comparing calculated inaccessible areas based on turning radius of the AUV to position of the docking station. When the AUV and the docking station is close enough and the state assessment is satisfied, the probability assessment is conducted by computing success probability of docking based on the direction angle, relative position to the docking station, and sensor uncertainties of the AUV. The final output of the algorithm is decided by comparing the success probability to threshold whether to try docking or to correct its route. To verify the validation of the suggested algorithm, the scenario that the AUV approaches to the docking station is implemented through Matlab simulation.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.291-291
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• 2018

하천 및 수자원의 효율적인 관리와 더불어 다양한 수공구조물의 운영 및 관리를 위해서 구조물 주변에서 발생하는 불연속 흐름 및 급변류 등의 현상과 구조물 운영을 반영한 수치해석 기법을 이용한 모델 개발의 중요성이 커지고 있다. 본 연구에서는 하천의 불연속 흐름을 모의하기 위한 1차원 흐름해석 모형(K-River)을 개발하였다. 본 모형은 천이류와 급변류를 수치적으로 안정하게 처리하기 위하여 지배방정식을 보존형 Saint-Venant 방정식으로 선정하고, FVM과 Forward Euler 방법을 이용하여 이산화를 수행하였다. 수치흐름률을 계산하기 위해서 불규칙 단면과 하상의 급경사 등에 신뢰도가 높은 기법으로 판단되는 근사 Riemann해법 중 하나인 HLL flux를 이용하였다. 개발된 K-river 모형의 검증을 위해서 해석해가 존재하는 타원형의 하상융기가 있는 하도에 적용하였으며, 국내에서 하천 설계 및 관리를 위해서 광범위하게 이용되고 있는 1차원 흐름해석 모형인 FDM기반의 HEC-RAS 모의결과와 비교 검토를 수행하였다. 그 결과, FDM기법에서는 모의되지 않는 일부 급변류 패턴을 개발 모형을 통해 모의가능하였으며, 전체적으로 K-River가 기존 모형 보다 해석해에 근사한 결과를 나타내었다. 또한, 배수문을 비롯하여 합류부, 분류부, 펌프장, 암거 등이 설치되어 운영되고 있는 아라뱃길에 적용하여 K-River의 적용성을 평가하였다. K-River를 이용하여 아라뱃길의 흐름분석을 수행한 경우가 HEC-RAS를 이용한 경우보다 수위와 유량의 유동을 시간에 따라 세밀하게 모의하였으며, 이는 배수효과에 의한 파의 전달이 FDM기법 대비 정확히 모의되기 때문으로 판단된다. 추후 연구에서는 현재보다 시간간격을 상세화 하여 수집된 관측수위를 통해 추가적인 검증을 수행하고, 다양한 특성을 가진 타 하천 등에 적용하여 모형의 적용성을 확대하고자 한다.

• Journal of the Korea Society of Computer and Information
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• v.17 no.2
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• pp.119-126
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• 2012

Local monitoring is an effective technique in securing data of wireless sensor networks. Existing solutions require high communication cost for detecting false data and this results in a network lifetime being shortened. This paper proposes novel techniques of monitoring based secure data aggregation and filtering false data in wireless sensor networks. The aim is to reduce energy consumption in securing data aggregation. An aggregator and its monitoring node perform data aggregation in a 60o sextant cluster. By checking Message Authentication Codes (MAC), aggregation data will be dropped by a forward aggregator if data aggregated by the aggregator and data monitored by the monitoring node are inconsistent. The simulation shows that the proposed protocol can reduce the amount of average energy consumption about 64% when comparing with the Data Aggregation and Authentication protocol (DAA)[1]. Additionally, the network lifetime of the proposed protocol is 283% longer than that of DAA without any decline in data integrity.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.923-929
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• 2018

In this study, we analyzed the resistance performance and running attitude of a catamaran by numerical analysis with a conventional bow, which is generally applied, and a reverse, protruding bow. The shape of the reverse bow was compared through numerical analysis and model tests. The reverse bow shape showed an improved wave pattern by shifting the generation position of the forward divergent wave to the aft in comparison with a conventional bow shape. This effect was found to be effective in determining resistance and stable running attitude. The hull resistance improved by about 2.95 %. The comparative numerical analysis and model test for the reverse bow shape completed in this study should be useful for future hull design application.

• Journal of the Korea Society of Computer and Information
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• v.26 no.1
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• pp.69-76
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• 2021

Recentlly neural network approach for solving a singular perturbed integro-differential boundary value problem have been researched. Especially the model of the feed-forward neural network to be trained by the back propagation algorithm with various learning algorithms were theoretically substantiated, and neural network models such as deep learning, transfer learning, federated learning are very rapidly evolving. The purpose of this paper is to study the approaching method for developing a neural network model with high accuracy and speed for solving singular perturbed problem along with asymptotic methods. In this paper, we propose a method that the simulation for the difference between result value of singular perturbed problem and unperturbed problem by using neural network approach equation. Also, we showed the efficiency of the neural network approach. As a result, the contribution of this paper is to show the possibility of simple neural network approach for singular perturbed problem solution efficiently.

• Journal of Ocean Engineering and Technology
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• v.35 no.6
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• pp.434-445
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• 2021

This paper proposes an optimal design method for an unmanned underwater vehicle (UUV) platform to overcome strong current. First, to minimize the hydrodynamic drag components in water, the vehicle is designed to have a streamlined disc shape, which help maintaining horizontal motion (zero roll and pitch angles posture) while overcoming external current. To this end, four vertical thrusters are symmetrically mounted outside of the platform to stabilize the vehicle's horizontal motion. In the horizontal plane, four horizontal thrusters are symmetrically mounted outside of the disc, and each of them has the same forward and reverse thrust performances. With these four thrusters, a specific thrust vector control (TVC) method is proposed, and for external current in any direction, four horizontal thrusters are controlled to generate a vectored thrust force to encounter the current while minimizing the vehicle's rotation and maintaining its heading. However, for the numerical simulations, the vehicle's hydrodynamic coefficients related to the horizontal plane are derived based on both theoretical and empirically derived formulas. In addition to the simulation, experimental studies in both the water tank and circulating water channel are performed to verify the vehicle's various final performances, including its ability to overcome strong current.

• Journal of Korea Society of Industrial Information Systems
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• v.14 no.4
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• pp.16-29
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• 2009

This paper investigates the kinematic and dynamic analysis of a spherical three degree of freedom parallel joint module, which is used in the exercise equipment for balance and leg-strength improvement of aged people. The joint module has three dyads which consist of two links and three revolute joints, and their all joints intersect at the global point located at the module's center. The paper shows the explicit mathematical procedure for deriving the closed form solutions in the inverse and forward position analysis of this parallel joint module. In velocity and acceleration analysis, we derived relations for joint velocities and accelerations of dyads and rotational velocity and acceleration of the top plate. For applying this module to rehabilitation exercise, we determined the dynamic model of the Korean males in their 50s and examined the model's results by dynamic model simulation.

• Journal of Korea Society of Industrial Information Systems
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• v.15 no.2
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• pp.31-39
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• 2010

VoD(Video-on-Demand) servers have to provide timely processing guarantees for continuous media and reduce the storage and bandwidth requirements for continuous media. The compression techniques make the bit rates of compressed video data significantly variable from frame to frame. A VoD system should be able to provide the client with interactive operations such as fast forward and fast rewind in addition to normal playback of movie. However, interactive operations require additional resources such as storage space, disk bandwidth, memory and network bandwidth. In a stored video application such as VoD system, it is possible that a priori disk access patterns can be used to reserve the system resources in advance. In addition, clients of VoD server spend most of their time in playback mode and the period of time spent in interactive mode is relatively small. In this paper, I present the new buffer management scheme that provides efficient support for interactive operations in a VoD server using variable bit rate continuous media. Simulation results show that our strategy achieves 34% increase of the number of accepted clients over the LRU strategy.