• Title/Summary/Keyword: Directional wave

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Hydraulic Experiments of Stem Waves due to Multi-Directional Random Waves along a Vertical Caisson (다방향 불규칙파에 의한 직립벽 주위의 연파특성)

  • Yoo, Hyung-Seok;Kim, Kyu-Han;Jung, Eui-Jin
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.22 no.6
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    • pp.429-436
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    • 2010
  • Hydraulic experiments were conducted to analyze the characteristics of stem waves due to multidirectional random wave incidence with the different incident angles of main wave direction. Both multi-directional and uni-directional random waves were used to generate the stem waves and their results were compared with each other. The experiment shows multi-directional random waves developed along the vertical wall tend to increase as the incident angle increases similar to the uni-directional waves. Moreover, the stem wave widths were almost same as those in uni-directional random wave cases. However, the experiment demonstrate the stem wave heights were significantly smaller in multi-directional random wave cases than in uni-directional random wave cases.

On Generation Methods of Multi-directional Random Waves in 3-D Numerical Wave Basin with Non-Reflected Wave Generation System (무반사 조파시스템을 적용한 3차원 수치파동수조에서 다방향불규칙파의 조파방법)

  • Hur, Dong-Soo;Lee, Woo-Dong;Jeon, Ho-Sung;Yeom, Gyeong-Seon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.3B
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    • pp.305-308
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    • 2011
  • In this study, generation methods of 3-D multi-directional random wave are examined using the fully non-linear numerical model with non-reflected wave generation system (LES-WASS-3D). Directional distribution functions obtained by EMLM method are compared for multidirectional random waves generated by various generation methods. As a results, it is revealed that multi-directional wave field can be simulated using LES-WASS-3D.

Wave Exciting Forces on Multiple Floating Bodies of Semisubmersible Type in Multi-directional Irregular Waves (다방향 불규칙파중에서의 반잠수식 부체군에 작용하는 파강제력)

  • 조효제;구자삼;김경태
    • Journal of Ocean Engineering and Technology
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    • v.11 no.4
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    • pp.76-89
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    • 1997
  • The hydrodynamic interaction characteristics between multiple floating bodies of semisubmersible type are examined to present the basic data for the design of huge offshore structures supported by a large number of the floating bodies in multi-directional irregular waves. The numerical approach is based on a combination of a three-dimensional source distribution method, the wave interaction theory and the spectral analysis method. The effects of wave directionality on the wave exciting forces acting on multiple floating bodies in multi-directional irregular waves also have been pointed out.

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Validity of Ocean Wave Spectrum Using Rayleigh Probability Density Function

  • Choi, Young Myung;Yang, Young Jun;Kwon, Sun Hong
    • International Journal of Ocean System Engineering
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    • v.2 no.4
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    • pp.250-258
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    • 2012
  • The distribution of wave heights is assumed to be a Rayleigh distribution, based on the assumption of a narrow band and Gaussian distribution of wave elevation. The present study was started with doubts about the narrow band assumption. We selected the wave spectra widely used to simulate irregular random waves. The wave spectra used in this study included the Pierson-Moskowitz spectrum, Bretschneider-Mitsuyasu spectrum, and JONSWAP spectrum. The directionality of the waves was considered. The cosine 2-l type directional spreading function and mixed form of the half-cosine 2-s type with Mitsuyasu type directional spreading are considered here to investigate the effects of a directional spreading function on random waves. The simulated wave height distribution is compared with a Rayleigh distribution.

Breaking Directional Wave Spectrum in Water of Variable Depth in the Presence of Current (쇄파와 조류의 영향을 고려한 천해성에서의 Wave Spectrum에 대한 연구)

  • 조용준
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.5 no.2
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    • pp.76-83
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    • 1993
  • In this study, an approximate method for calculating the directional spectrum of waves encountering a current in shallow water is developed. The wave trains in tile directional spectrum are assumed to be linear and Gaussian; development of the spectrum requires that the waves also be short crested. The Miche's breaking criterion is imposed to determine the upper limit of wave height and to establish an expression for the breaking wave elevation in terms of the ideal wave's elevation and the second time derivative of wave elevation. Two examples are given; one for a Wallops directional spectrum encountering a shear current and another with an upwelling current.

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Mathematical Analysis for Efficiency of Eavesdropping Attack Using Directional Antenna in mmWave Band (밀리미터파 대역에서 지향성 안테나 사용에 의한 도청공격 대응 효율성의 수학적 분석)

  • Kim, Meejoung;Kim, Jeong Nyeo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38C no.11
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    • pp.1074-1077
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    • 2013
  • This paper analyzes the benefit of using directional antennas against eavesdropping attack in millimeter wave (mmWave)-based networks. All devices are equipped with a directional antenna or an omni-directional antenna in a single-hop communications. The probability of a device being detected by an eavesdropper is analyzed based on the exposure region of a device. The relative detection rate is introduced to represent the benefit of using directional antenna. Numerical results show that there exists an optimal number of devices that maximizes the detection probability and it varies according to the parameters such as antenna beamwidth. It shows that the use of directional antenna enables to protect the devices from the detection by an eavesdropper for almost the whole situation in mmWave band communication.

A Study of Statistical Properties of Waves in the Sea Area of Pohang (포항해역에서의 파랑의 통계적 특성에 대한 연구)

  • 안용호;김도영
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2001.05a
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    • pp.216-221
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    • 2001
  • In this paper, statistical properties of waves in the sea area of Pohang, Korea are examined absed on 1998-1999's wave data from directional wave buoy which is located Pohang(Janggigog). Wave data aquisition rate, monthly maximium, minimum and mean wave heights, frequency of wave direction are summarized. Wave height and period scatter diagrams and n-year return period wave heights are estimated. Wave periods of maximum wave heights are also estimated.

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Numerical Simulation of Directional Spreading Characteristics in a Snake Type Wave Generator considering Side Wall Reflection

  • Lee, Jin-Ho;Hirayama, Tsugukiyo
    • Journal of Ship and Ocean Technology
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    • v.4 no.1
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    • pp.28-36
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    • 2000
  • Numerical simulation based on the superposition of ring waves generated by the linear periodic source distributions for the plunger type wave maker was accomplished. The characteristics of directional spreading function were investigated. Mirror images are also introduced to consider reflections of side-wall together with the reflection coefficient to account for the imperfect reflection from the real side wall in the long experimental towing tank. Unexpected spurious waves, resulting from the combined effect of finite breadth of segmented wave maker, wavelength and main wave maker, wavelength and main wave propagating direction, were observed in the line source method and also in the analysis of the directivity. The influence of spurious waves to the directional spreading function was also investigated.

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Field Measurements of Wave Directionality in Water of Finite Depth

  • Memos, Constantine;Ziros, Athanassios
    • Ocean and Polar Research
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    • v.25 no.4
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    • pp.437-446
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    • 2003
  • Field measurements of directional waves were carried out during the summer of 2002 at two coastal sites in water of finite depth. A couple of general purpose instruments were used employing acoustic Doppler technology. The aim of the study was to investigate the spatial behavior of the directional movement of waves as they come ashore. In total,74 tests were carried out during which sea states of low to moderate intensity were recorded. A great number of these runs displayed bimodal characteristics of the spreading function at high frequencies. It was found that in general, the frequency-integrated directional width tends to broaden as the water shoals and when refraction effects are negligible. This is attributed to wave-wave interactions that become pronounced in shallow water. The same directional width showed, also, a tendency to increase with increasing peak frequency of the sea state spectrum. The behavior of the kurtosis of the spreading function was also examined. It was found that for higher frequencies this index tends to increase in wave spectra above a certain sea severity threshold.

Behavior of Regular Waves and Multi-Directional Random Waves Passing a Breakwater (방파제를 통과하는 규칙파와 다방향 불규칙파랑의 거동)

  • Park, Sang-Il;Park, Jin-Ho;Cho, Yong-Sik
    • 한국방재학회:학술대회논문집
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    • 2008.02a
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    • pp.439-442
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    • 2008
  • Diffraction of multi-directional random waves passing semi-infinite breakwater is investigated by using analytic solution derived by Penny and Prices(1952). An irregylarity of period and incident angle of waves and regular periods for regular waves are considered in addition by expanding from the past study which used only monochromatic wave in general. The Bretschneider-Mitsuyasu frequency spectrum and Mitsuyasu directional spectrum are used for incident waves. And diffraction of multi-directional random waves is reappeared by decomposing numerical results of several monochromatic waves which have variable period and incident angle. Analytic solution on the diffraction of regular waves and multi-directional random waves calculated in this study.

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