• Ocean and Polar Research
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• v.39 no.4
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• pp.293-300
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• 2017

Various approaches have been tried in an effort to improve the power performance of a flapping tidal stream turbine after it was introduced as an alternative to conventional rotary turbines. Among the different approaches, researches on mimicking the morphology and behavior of animals have been conducted. In this study, we utilized a flapper to mimic the multi-joint pectoral fin of a Manta-ray and investigated its effect on power generation. Experiments were conducted by a dual flapping apparatus with rigid and flexible flappers in a towing tank facility. First, in order to determine the conditions that can produce high power generation, the performances of the dual rigid flappers were compared when input arm angles and frequencies are changed, and the two conditions $40^{\circ}$, 0.2 Hz and $40^{\circ}$, 0.3 Hz for the input arm angle, frequency were selected. When the mimicked flexible flapper was used instead of the front rigid flapper and the rear one, the power was improved by an average of 22% and 38% in the experimental conditions, respectively. Moreover, it was recognized from the apparent camber observed during the experiment that the flexible flapper had been successfully applied. If the feasibility of the Manta-Ray mimicked flapper is improved through subsequent researches, the flapping tidal turbine can be a viable alternative to rotary turbines in the near future.

• KCID journal
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• v.17 no.2
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• pp.71-81
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• 2010

Stream Pilot Project, which began in May 2003 and finished in December 2003, was selected to develop effective methods applicable to nature-like streams. Stream restoration projects aim to maintain or increase ecosystem goods and services while protecting downstream and coastal ecosystems. Fields environmental monitoring such as flow discharge and precipitation were conducted along the Idong stream for amount of channel zone change in 2007. This study selected three monitoring positions to measure the water level and discharge of flowing water. A stage-discharge relation is obtained from direct discharge measurements for three stations by fitting an empirical relationship to the data set. Since discharge measures are made only for low flow conditions, a curve of discharge against stage can then be built by fitting these data with a power curve. And this study used data obtained from floodmark checkup as well as HEC-RAS model to analyze the hydrodynamic characteristics of monitoring sites. Reach-averaged hydraulic parameters for the supply reach were calculated from the small area's HEC-RAS model for Idong stream, and a HEC-RAS model used to analyze hydraulics for a period in 2007, after the stream was considered bank stabilization.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2670-2689
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• 2022

STREAM - a lattice transport calculation code with method of characteristics for the purpose of light water reactor analysis - has been developed by the Computational Reactor Physics and Experiment laboratory (CORE) of the Ulsan National Institute of Science and Technology (UNIST). Recently, efforts have been taken to develop a photon module in STREAM to assess photon heating and the influence of gamma photon transport on power distributions, as only neutron transport was considered in previous STREAM versions. A multi-group photon library is produced for STREAM based on the ENDF/B-VII.1 library with the use of the library-processing code NJOY. The developed photon solver for the computation of 2D and 3D distributions of photon flux and energy deposition is based on the method of characteristics like the neutron solver. The photon library and photon module produced and implemented for STREAM are verified on VERA pin and assembly problems by comparison with the Monte Carlo code MCS - also developed at UNIST. A short analysis of the impact of photon transport during depletion and thermal hydraulics feedback is presented for a 2D core also from the VERA benchmark.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.6
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• pp.415-423
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• 2018

This study uses a level selection algorithm with fixed sampling frequency for modular multilevel converter (MMC) systems. Theoretically, the proposed method increases the level infinitely while the sampling time remains the same. The proposed method called cluster stream buffer (CSB) consists of several clusters, wherein each cluster is composed of 32 submodules that depend on the level of the submodules in the MMC system. To increase the level of the MMC system, additional clusters are used, and the sampling time between clusters is determined from the sampling time between levels needed for utilizing the entire level from the MMC system. This method is crucial in the control of MMC-type HVDC systems because it improves scalability and precision.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.119-121
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• 2008

Pattern matching is increasingly being employed in various researches as health care service, RFID-based system, facility management, and surveillance. Geosensor filter correlates a data stream to match specific patterns in distribution environments. In this paper, we present a geosensor query language to represent efficiently declarative geosensor query. Geosensor operators are proposed to use for fast query processing in terms of spatial and temporal area in distribution environments. We also propose a geosensor filter to match new query predicates into incoming stream predicates. Our filter can reduce the volume of transmission data and save power consumption of sensors. It can be utilized the stream data mining system to process in real-time various data as location, time, and geosensor information in distribution environments.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.3-5
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• 2007

Many continuous queries are important to be process efficiently in a data stream environment. It is applied a query index technique that takes linear performance irrespective of the number and width of intervals for processing many continuous queries. Previous researches are not able to support the dynamic insertion and deletion to arrange intervals for constructing an index previously. It shows that the insertion and search performance is slowed by the number and width of interval inserted. Many intervals have to be inserted and searched linearly in a data stream environment. Therefore, we propose Hashed Multiple Lists in order to process continuous queries linearly. Proposed technique shows fast linear search performance. It can be utilized the systems applying a sensor network, and preprocessing technique of spatiotemporal data mining.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1519-1527
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• 2007

In order to combat the security threats that sensor networks are exposed to, a cryptography protocol is implemented at sensor nodes for point-to-point encryption between nodes. Given that nodes have limited resources, symmetric cryptography that is proven to be efficient for low power devices is implemented. Data protection is integrated into a sensor's packet by the means of symmetric encryption with the Dragon stream cipher and incorporating the newly designed Dragon-MAC Message Authentication Code. The proposed algorithm was designed to employ some of the data already computed by the underlying Dragon stream cipher for the purpose of minimizing the computational cost of the operations required by the MAC algorithm. In view that Dragon is a word based stream cipher with a fast key stream generation, it is very suitable for a constrained environment. Our protocol regarded the entity authentication and message authentication through the implementation of authenticated encryption scheme in wireless sensor nodes.

• Journal of Satellite, Information and Communications
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• v.6 no.1
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• pp.19-27
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• 2011

In this paper, we propose the data stream allocation algorithms for maximizing sum capacity of downlink multiuser MIMO (Multiple-input Multiple-output) systems with BD (Block Diagonalization). The conventional BD precoding algorithms maximize the capacity by controlling power against channel gain of each user. In multiuser MIMO systems, however, the number of data streams for each user can be used to as another control parameter, which determines the capacity. This paper proposes the data stream allocation algorithm of BD for increasing capacity in multiuser MIMO systems. The proposed algorithm allocates unequal bit stream to each user based on channel matrix of each user for maximizing sum capacity. It is proved that proposed algorithm can achieve the significantly improved sum capacity by computer simulation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.1
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• pp.79-92
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• 1984

The analysis of total load was carried out by using the theory of unit stseam power (USP). The dimensionless USP equation of $S_R$ which was the rate of suspended load and bed load was derived from the USP function by applying the Einstein's reference concentration and Stokes' fall velocity. And the R relationship between the water discharge and Reynolds number (Re) was discussed, and it was shown that USP was closely related with Re. The value of $S_R$ was determined from the experimental data of Han River downstream and Mantz. And it was tested to several observatories of Korean Rivers. A good correlation among USP, suspended load and $S_R$ was shown and USP was increased with the increment of the turbulent intensity. Judging from the above results, it is considered this study can be contributed to estimate the total load.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.166.1-166.1
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• 2011

The rotor design is fundamental to the performance and dynamic response of the Counter-rotating marine tidal current turbine. The wind industry has seen significant advancement single rotor blade technology, offering considerable knowledge and making it easy to transfer to tidal stream energy converters. In this paper, 3D flow and performance an alysis on a 100 kW counter-rotating marine current turbine blade was carried out by using the 3-D Navier-Stokes commercial solver(ANSYS CFX-11.0) to provide more efficient design techniques to design engineers. The front and rear rotor diameter is 8m and the rotating speed is 24.72rpm. Hexahedral meshing was generated by ICEM-CFD to achieve better quality of results. The rated power and its approaching stream velocity for design are 100 kW and 2 m/s respectively. The pressure distribution on the blade's suction side tells us that the pressure becomes low at the leading edge of the airfoil as it moves from the hub to the tip.