• International Journal of Fuzzy Logic and Intelligent Systems
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• 제16권1호
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• pp.59-63
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• 2016

Secondary damage to the user is a problem in biometrics. A brain-wave has no shape and a malicious user may not cause secondary damage to a user. However, if user sends brain-wave signals to an authentication system using a network, a malicious user could easily capture the brain-wave signals. Then, the malicious user could access the authentication system using the captured brain-wave signals. In addition, the dataset containing the brain-wave signals is large and the transfer time is long. However, user authentication requires a real-time processing, and an encryption scheme on brain-wave signals is necessary. In this paper, we propose an efficient encryption scheme using a chaos map and adaptive junk data on the brain-wave signals for user authentication. As a result, the encrypted brain-wave signals are produced and the processing time for authentication is reasonable in real-time.

• Ocean Systems Engineering
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• 제7권4호
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• pp.345-369
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• 2017

The ocean environment offshore West Africa is considered to be mild. However, the generated swell from distant North and South Atlantic during austral winter and summer can reach high wave amplitudes with relatively low wave periods or low wave amplitudes with long wave periods, the later can be a crucial scenario to consider when the assessment of vessel resonance is of importance. Most offshore operations, which include offshore drilling, and installation in West Africa, are carried out from floating systems. The response of these systems and performance are governed by characteristics, such as amplitude and frequency of the wave and swell seas. It is therefore important to fully understand the sea conditions offshore Nigeria. This study covers the description of the swell sea offshore Nigeria using Bonga offshore wave measurements collected from the directional wave-rider (DWR), positioned at the Bonga site off the coast of Nigeria.

• 한국산업융합학회 논문집
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• 제23권2_2호
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• pp.245-254
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• 2020

This study investigated the so far little-researched characteristics of the behaviors of rock slopes at the time of an earthquake. For the selection of the rock block, a proper model was formed by applying the similarity in consideration of the roughness and strength of the rock slope(10m) on the site, and shaking table tests were carried out according to seismic excitement acceleration, and seismic waves. In the case of the inclination angle of the joint plane of 20°, the long period wave at 0.3g or more at the time of the seismic excitement surpassed the length of 100mm, the permissible displacement (0.01H, H:slope height), which brought about the collapse of the rock; the short period wave surpassed the permissible displacement at 0.1g, which caused the collapse of the slope. The rock slope was close to a rigid block and a structure more vulnerable to the long period wave than to the short period wave. It collapsed in the short period wave even at the seismic amplitude smaller than the maximum design acceleration in Korea.

• Journal of Communications and Networks
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• 제16권5호
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• pp.512-522
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• 2014

This paper proposes fast millimeter-wave (mm-wave) beam training protocols with receive beamforming. Both IEEE standards and the academic literature have generally considered beam training protocols involving exhaustive search over all possible beam directions for both the beamforming initiator and responder. However, this operation requires a long time (and thus overhead) when the beamwidth is quite narrow such as for mm-wave beams ($1^{\circ}$ in the worst case). To alleviate this problem, we propose two types of adaptive beam training protocols for fixed and adaptive modulation, respectively, which take into account the unique propagation characteristics of millimeter waves. For fixed modulation, the proposed protocol allows for interactive beam training, stopping the search when a local maximum of the power angular spectrum is found that is sufficient to support the chosen modulation/coding scheme. We furthermore suggest approaches to prioritize certain directions determined from the propagation geometry, long-term statistics, etc. For adaptive modulation, the proposed protocol uses iterative multi-level beam training concepts for fast link configuration that provide an exhaustive search with significantly lower complexity. Our simulation results verify that the proposed protocol performs better than traditional exhaustive search in terms of the link configuration speed for mobile wireless service applications.

• 한국항해항만학회지
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• 제27권1호
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• pp.55-61
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• 2003

계류된 선박의 시뮬레이션을 위해 조종방정식을 사용하였고, 파 중의 선박에 가해지는 파강제력은 3차원 특이점 분포법에서 얻어진 주파수 전달함수로부터 시간영역해석법을 적용하였다. 운동을 유발하는 입사파의 주기와 동일한 선형 파강제력과 성분파 주파수의 차이에 기인하는 장주기 표류력을 외력항에 고려하였다. 규칙파와 불규칙 중에서의 선박의 거동을 비교하여 계류 중 선박에 발생할 수 있는 SLEW MOTION에 불규칙파 및 비선형 파강제력이 미치는 영향을 고찰하였다.

• 한국항해항만학회지
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• 제41권5호
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• pp.345-352
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• 2017

Recently, a new port reserves deep water depth for safe navigation and mooring, following the trend of larger ship building. Larger port facilities include long and huge breakwaters, and mainly adopt vertical type considering low construction cost. A vertical breakwater creates stem waves combining inclined incident waves and reflected waves, and this causes maneuvering difficulty to the passing vessels, and erosion of shoreline with additional damages to berthing facilities. Thus, in this study, the researchers have investigated the response of stem waves at the vertical breakwater near the entrance channel and applied numerical models, which are commonly used for the analysis of wave response at the harbor design. The basic equation composing models here adopted both the linear parabolic approximation adding the nonlinear dispersion relationship and nonlinear parabolic approximation adding a linear dispersion relationship. To analyze the applicability of both models, the research compared the numerical results with the existing hydraulic model results. The gap of serial breakwaters and aligned angles caused more complicated stem wave generation and secondary stem wave was found through the breakwater gap. Those analyzed results should be applied to ship handling simulation studies at the approaching channels, along with the mooring test.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.225-228
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• 2008

There are many studies about submerged structures or porous wave absorbers to decrease damage of coast and structures. Submerged structures and porous wave absorber are decreasing energy of incoming wave by reflecting or dissipation with changing depth or with porous rubble mound. This study addresses the reflection and transmission of long wave from a trapezoidal breakwater and a vertical porous wave absorber at the same time. A systematic shape transfer is derived to determine wave reflection and transmission. And periodic solutions are matched at the slope and the front face of the absorber by assuming continuity of pressure and mass. The transmission coefficient is determined as a function of parameters describing the incoming waves, transmitting waves through the trapezoidal breakwater and the absorber characteristics.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.526-544
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• 2021

Based on the potential flow theory, a fully nonlinear numerical procedure is developed with boundary element method to analyze the interaction between a fixed semi-submersible platform and incident waves in open water. The incident wave is separated from the scattered wave under fully nonlinear boundary conditions. The mixed Euler-Lagrangian method is used to capture the position of the disturbed wave surface in local coordinate systems. The wave forces exerted on an inverted conical frustum are used to ensure the accuracy of the present method and good agreements with published results are obtained. The hydrodynamic characteristics of the semi-submersible platform interacting with regular waves are analyzed. Pressure distribution with time and space, tension and compression of the platform under wave action are investigated. 3D behaviors of wave run-ups are predicted. Strong nonlinear phenomena such as wave upwelling and wave interference are observed and analyzed.

• 해양환경안전학회지
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• 제21권6호
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• pp.637-644
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• 2015

항내 정온도 평가는 이상파 및 평상파 조건에 대해 수행이 되어야 하나, 어항개발 시 이루어지는 평가는 이상파에 대해서만 수행되고 있다. 축산항, 교암항, 궁평항 및 시산항에 대한 사례를 통해 해역이용협의 시 정온도 평가에 대한 실태를 분석하였다. 대상항 모두 이상파에 대한 항내 정온도를 평가를 수행하였으나, 목표 정온도를 만족하지 못하였다. 평상파에 대한 정온도는 가동률로 평가하며, 가동률을 평가하기 위해서는 장기간의 파랑관측이 필요하나 수행되지 않고 있었다. 가동률에 대한 평가는 계획의 적정성과 관련 있는 평가항목이기 때문에 개발로 인한 해양환경에 미치는 악영향을 최소화할 수 있는 계획의 수립과 어업인들의 정주환경 개선을 평가하기 위해서는 수행이 필요하다. 정온도 평가를 위해서는, 정온도 평가에 대한 이해가 선행되어야 하고, 장기간의 파랑관측이 수행되어야 하며, 평상파 및 이상파에 대한 평가절차를 명확히 해야 한다. 그리고 실효적인 계획이 수립될 수 있도록 조석정보와 같은 파랑정보의 제공 및 정온도를 평가할 수 있는 가이드라인의 수립이 필요하다.

• 한국도로학회논문집
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• 제20권1호
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• pp.9-18
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• 2018

PURPOSES : In this research, the initiation and development of corrugation on a gravel road with certain wheel and boundary conditions were evaluated using a coupled discrete-element method (DEM) with multibody dynamics (MBD). METHODS : In this study, 665,534 particles with a 4-mm diameter were generated and compacted to build a circular roadbed track, with a depth and width of 42 mm and 50 mm, respectively. A single wheel with a 100-mm diameter, 40-mm width, and 0.157-kg mass was considered for the track. The single wheel was set to run slowly on the track with a speed of 2.5 rad/s so that the corrugation was gradually initiated and developed without losing contact between the wheel and the roadbed. Then, the shape of the track surface was monitored, and the movement of the particles in the roadbed was tracked at certain wheel-pass numbers to evaluate the overall corrugation initiation and development mechanism. RESULTS : Two types of corrugation, long wave-length and short wave-length, were observed in the circular track. It seems that the long wave-length corrugation was developed by the longitudinal movement of surface particles in the entire track, while the short wave-length corrugation was developed by shear deformation in a local section. Properties such as particle coefficients, track bulk density, and wheel mass, have significant effects on the initiation and development of long-wave corrugation. CONCLUSIONS : It was concluded that the coupled numerical method applied in this research could be effectively used to simulate the corrugation of a gravel road and to understand the mechanism that initiates and develops corrugation. To derive a comprehensive conclusion for the corrugation development under various conditions, the driver's acceleration and deceleration with various particle gradations and wheel-configuration models should be considered in the simulation.