• ETRI Journal
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• 제45권3호
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• pp.519-533
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• 2023

This paper implements a simultaneous solar and thermal energy harvesting system, as a hybrid energy harvesting (HEH) system, to convert ambient light into electrical energy through photovoltaic (PV) cells and heat absorbed in the body of PV cells. Indeed, a solar panel equipped with serially connected thermoelectric generators not only converts the incoming light into electricity but also takes advantage of heat emanating from the light. In a conventional HEH system, the diode block is used to provide the path for the input source with the highest value. In this scheme, at each time, only one source can be handled to generate its output, while other sources are blocked. To handle this challenge of combining resources in HEH systems, this paper proposes a method for collecting all incoming energies and conveying its summation to the load via the current mirror cells in an approach similar to the maximum power point tracking. This technique is implemented using off-the-shelf components. The measurement results show that the proposed method is a realistic approach for supplying electrical energy to wireless sensor nodes and low-power electronics.

• 공학교육연구
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• 제26권6호
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• pp.40-50
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• 2023

This study is to examine the validity of assessing basic-level proficiency in physics among incoming engineering freshmen through item analysis and standard setting. For empirical analysis, we examined the physics subject taken by the freshman class of 2021 at K University, considering its significance for engineering students. In this study, we initially performed item analysis utilizing both classical test theory and item response theory. Subsequently, leveraging the item and test information, we employed a modified Angoff method and the Bookmark method for standard setting. Consequently, the difficulty level initially set during item development was found to be higher than the actual performance level exhibited by the students. This study highlights a discernible disparity between the expected university standard and the real proficiency level of incoming freshmen in terms of basic academic ability in physics. Based on these research findings, a comprehensive discussion on the fundamental academic competence of engineering students was conducted, underscoring the necessity for formulating a tailored learning approach leveraging the outcomes from the basic ability test.

• 한국실내디자인학회논문집
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• 제25권1호
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• pp.151-162
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• 2016

Various mixed-use buildings have been developed in the process of resolving the issue of 'urban regeneration' in the modern city. In this urban regeneration process, the size of the mixed-use buildings and the level of their functional complexity have been increased. It requires a quantitative and systematic approach in order to analyze the internal circulation flow within the large-scale commercial mixed-use buildings. Circulation system and environmental factors, respectively, have been vital criteria for the effectiveness of a Wayfinding design within the mixed-use buildings. The circulation system in this paper consists of 1) the number of the incoming paths at each node, and 2) the angle of directional transition from the incoming paths at the node. The environmental factors include 1) color tone, 2) materials, 3) lighting, and 4) pattern of the interior design of the mixed-use buildings. In this paper, the author develops a method of investigating the influence of the correlation between the circulation system and the environmental factors on the design of Wayfinding on the view of the remodeled COEX MALL interior design.

• 한국수자원학회논문집
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• 제37권6호
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• pp.479-485
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• 2004

이 연구에서는 일교차를 이용하여 일평균 증발산량을 산정한다. 이를 위하여 Thornton과 Running(1999)의 일평균 태양 복사열 산정을 위한 경험식을 이용하여 태양복사열을 계산하여 이를 현장 자료와 비교한 결과 비교적 정확한 범위 내에 있다는 것을 확인하였다. 이렇게 산정된 일평균 태양 복사열을 증발산량의 계산을 위해 Priestly Taylor 공식과 Penman 공식에 적용함으로써 현장에서의 정확성과 사용가능성을 확인해 보고자 하였다. 그 결과로 태양 복사열에 중점을 둔 Priest-Taylor 공식은 과다추정하는 경향을 보이나, Penman 공식은 비교적 정확한 증발산량의 산정을 보여 줌으로써 기상 관측 자료가 풍부하지 않은 지역에서의 사용가능성을 보여주었다. 또 계산된 증발산량을 일단위 온도만을 이용하여 증발산량을 산정하는 Hargreaves 공식과 비교하여 각 공식의 장단점을 공학적 측면에서 알아보고자 하였다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.15-22
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• 2006

This paper presents a novel signal tracking algorithm for GNSS receivers using a MLE technique. In order to perform a robust signal tracking in severe signal environments, e.g., high dynamics for navigation vehicles or weak signals for indoor positioning, the MLE based signal tracking approach is adopted in the paper. With assuming white Gaussian additive noise, the cost function of MLE is expanded to the cost function of NLSE. Efficient and practical approach for Doppler frequency tracking by the MLE is derived based on the assumption of code-free signals, i.e., the cost function of the MLE for carrier Doppler tracking is used to derive a discriminator function to create error signals from incoming and reference signals. The use of the MLE method for carrier tracking makes it possible to generalize the MLE equation for arbitrary codes and modulation schemes. This is ideally suited for various GNSS signals with same structure of tracking module. This paper proposes two different types of MLE based tracking method, i.e., an iterative batch processing method and a non-iterative feed-forward processing method. The first method is derived without any limitation on time consumption, while the second method is proposed for a time limited case by using a 1st derivative of cost function, which is proportional to error signal from discriminators of conventional tracking methods. The second method can be implemented by a block diagram approach for tracking carrier phase, Doppler frequency and code phase with assuming no correlation of signal parameters. Finally, a state space form of FLL/PLL/DLL is adopted to the designed MLE based tracking algorithm for reducing noise on the estimated signal parameters.

• 대한음성학회지:말소리
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• 제48호
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• pp.155-173
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• 2003

This paper proposes a noise reduction-based speech detection method under telephone channel environments. We adopt the AURORA front-end noise reduction algorithm based on the two-stage mel-warped Wiener filter approach as a preprocessor for the frequency domain speech detector. The speech detector utilizes mel filter-bank based useful band energies as its feature parameters. The preprocessor firstly removes the adverse noise components on the incoming noisy speech signals and the speech detector at the next stage detects proper speech regions for the noise-reduced speech signals. Experimental results show that the proposed noise reduction-based speech detection method is very effective in improving not only the performance of the speech detector but also that of the subsequent speech recognizer.

• ETRI Journal
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• 제43권3호
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• pp.538-548
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• 2021

This paper proposes an approach to improve the performance of no-reference video quality assessment for sports videos with dynamic motion scenes using an efficient spatiotemporal model. In the proposed method, we divide the video sequences into video blocks and apply a 3D shearlet transform that can efficiently extract primary spatiotemporal features to capture dynamic natural motion scene statistics from the incoming video blocks. The concatenation of a deep residual bidirectional gated recurrent neural network and logistic regression is used to learn the spatiotemporal correlation more robustly and predict the perceptual quality score. In addition, conditional video block-wise constraints are incorporated into the objective function to improve quality estimation performance for the entire video. The experimental results show that the proposed method extracts spatiotemporal motion information more effectively and predicts the video quality with higher accuracy than the conventional no-reference video quality assessment methods.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권2호
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• pp.127-136
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• 2016

Springing is the resonance phenomenon of a ship hull girder with incoming waves having the same natural frequency of the ship. In this study, a simple and reliable calculation method was developed based on quadratic strip theory using the Timoshenko beam approach as an elastic hull girder. Second-order hydrodynamic forces and Froude-Krylov forces were applied as the external force. To improve the accuracy of the strip method, the variation in the added mass along the ship hull longitudinal direction, so called tip-effect, was considered. The J-factor was also employed to compensate for the effect of three-dimensional fluid motion on the two-node vibration of the ship. Using the developed method, the first- and second-order vertical bending moments of the Flokstra ship were compared. A comparative study was also carried out for a uniform barge ship and a 10,000 TEU container ship with the respective methods including the J-factor and tip-effect.

• Ocean Systems Engineering
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• 제13권2호
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• pp.147-172
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• 2023

This study investigates the influence of loading and inflow conditions on tidal turbine performance from a hydrodynamic and hydroacoustic point of view. A boundary element method is utilized for the former to investigate turbine performance at various loading conditions under zero/non-zero yaw inflow. The boundary element method is selected as it has been selected, tested, and validated to be computationally efficient and accurate for marine hydrodynamic problems. Once the hydrodynamic solutions are obtained, such as the time-dependent surface pressures and periodic motion of the turbine blade, they are taken as the known noise sources for the subsequence hydroacoustic analysis based on the Ffowcs Williams-Hawkings formulation given in a form proposed by Farassat. This formulation is coupled with the boundary element method to fully consider the three-dimensional shape of the turbine and the speed of sound in the acoustic analysis. For validations, a model turbine is taken from a reference paper, and the comparison between numerical predictions and experimental data reveals satisfactory agreement in hydrodynamic performance. Importantly, this study shows that the noise patterns and sound pressure levels at both the near- and far-field are affected by different loading conditions and sensitive to the inclination imposed in the incoming flow.

• 한국통신학회논문지
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• 제22권10호
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• pp.2357-2363
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• 1997

본 논문에서는 최소 다중 UIO를 사용했을 때보다 비 최소 다중 UIO를 사용했을 때 시험열의 길이가 줄어들 수 있음을 보여준다. 본 논문에서 제안하는 시험열 생성 방법은 Shen의 방법이 어떤 상태에서 들어오는 에지와 나가는 에지의 차가 클 때에는 최적화된 시험열을 생성하지 못한다는 데에 기초하고 있다. 이 성질을 이용하여 시험열의 길이를 줄이는 관점에서 UIO에 기초한 보다 향상된 기법을 제안하고 기존의 방법과 시험열의 길이와 적합성 검사를 위하여 걸리는 시간, 시험열을 생성하는데 걸리는 시간이 보다 효율적임을 기존의 방법과 비교하여 설명한다.