• Title/Summary/Keyword: High Waves

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Note on the appearance of Freak Waves from in-situ ocean wave data

  • Tomita, Hiroshi;Waseda, Takuji
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2006.11a
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    • pp.105-112
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    • 2006
  • Freak waves in the ocean are recently drawing much attention as a natural disaster to ocean structures and navigating ships as well. Several observation data, among them the Draupner New Year Wave, show the very impressive feature of Freak waves whose wave height is up to three times as high as the significant wave height of surrounding waves, In addition, Freak wave appears as an isolated very high crest in somewhat stationary random waves of same order in their wavelengths. Bearing such characteristics in mind, one notices its extraordinary steepness. This strongly suggests that Freak wave is not long lived but transient nature on the whole. A great number of studies to explain these natures were published from both theoretical and numerical point of view. However it is not sure if they are applicable to actual ocean environment. In this paper, we deal with the results concerning abnormal and/or Freak waves from in-situ ocean wave data and point out several remarks to the problems lain behind the contributions in this context. A physical experiment is described to reinforce the subject discussed from the observation data.

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Sound Absorption Characteristics of Finite-Amplitude Acoustic Waves in Poroelastic Materials (탄성다공성 재질에서 유한진폭 입사음파의 흡음 특성)

  • Lee, Soo-Il;Kim, Jin-Seop;Kang, Yeon-June
    • Proceedings of the KSME Conference
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    • 2000.04a
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    • pp.591-595
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    • 2000
  • Sound absorbing characteristics of poroelastic materials is known to be greatly affected by high intensity acoustic waves. However, this effect has not been considered yet. In this study, the extended semilinear model based on Biot's theory for the porous materials and the characteristics of nonlinear waves in poroelastic sound absorbing materials were introduced. The expressions for the finite-amplitude acoustic plane waves were presented. By combining each nonlinear wave with appropriate matching conditions, we could investigate the effects of finite-amplitude acoustic waves on absorption characteristics of poroelastic materials. In the most ideal case considered in this paper, the absorption coefficient was found to become larger than that of linear incident waves. It was shown that the absorption coefficient became greater especially as frequency goes higher and as distance from the source goes larger. These phenomena may be inferred to result from 'dissipation effects due to nonlinearity'. This finding may have important implications for high intensity noise control.

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Resolution Enhancement of Scanning Tomographic Acoustic Microscope System

  • Ko, Daesik
    • The Journal of the Acoustical Society of Korea
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    • v.15 no.1E
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    • pp.70-76
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    • 1996
  • We proposed to use shear waves instead of longitudinal waves in a STAM (scanning tomographic acoustic microscope system) in which the specimens are solid. For any specimen with a shear modulus, mode conversion will take place at the water-solid interface. Some of the energy of the insonifying longitudinal waves in the water will convert to shear wave energy within the specimen. The shear wave energy is detectable and can be used for tomographic reconstruction. The resolution limitation of STAM depends on the available angular view and the acoustic wavelength. While wave transmission in most solid specimens is limited to about 20°for longitudinal waves, we show that it is about twice that high for shear waves. Since the wavelength of the shear wave is shorter than that of the longitudinal wave, we are able to achieve the high resolution. In order to compare the operation of a shear-wave STAM with that of the conventional longitudinal-wave STAM we have simulated tomographic reconstruction for each. Our simulation results with aluminum specimen and back-and-forth propagation algorithm showed resolution of a shear-wave STAM is better than that of a longitudinal-wave STAM.

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Growth of Wind Waves with Fetch in the Sea of Japan under Winter Monsoon Investigated using Data from Satellite Altimeters and Scatterometer

  • Ebuchi, Naoto
    • Proceedings of the KSRS Conference
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    • 1998.09a
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    • pp.31-36
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    • 1998
  • By using wind vectors observed by NSCAT and significant wave heights observed by TOPEX/POSEIDON and ERS-2 altimeters, one-dimensional fetch growth of wind waves Is investigated under conditions of strong wind and high waves of the East Asian winter monsoon. The evolution of fetch-limited wind waves can be observed by the altimeters along the ground tracks. The fetch is estimated by using vector wind field observed by NSCAT. The derived growth characteristics of wind waves are compared with empirical relationships between the non-dimensional fetch and significant wave height proposed by previous studies. Good agreement with the empirical fetch graph formula normalized by the friction velocity is discemible, while the formulas normalized by the wind speed at a height of 10 m tend to underestimate the wave height under such severe conditions of high wind and very long fetch.

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Dynamic Experiment to Evaluate Response Characteristics of High-Rise Buildings on Period Characteristics of Seismic Waves (지진파 주기특성에 따른 고층건축물의 응답특성 평가를 위한 동적실험)

  • Oh, Sang-Hoon;Kim, Ju-Chan
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.35 no.10
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    • pp.127-133
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    • 2019
  • Damage to high-rise buildings caused by earthquakes is less frequency due to small distribution of high-rise buildings and low transmissibility of seismic motion to high-rise buildings. However, demand for high-rise buildings is increasing for development of construction technology and efficient land use. In addition, if high-rise buildings are constructed on soft ground such as landfill, transmissibility of seismic motion due to long-periodization of seismic waves is likely to increase. Thus, with development of technology, buildings are required to expand range of seismic design such as safety for long-period seismic waves. Therefore, in this study, dynamic experiments were performed to evaluate response characteristics of high-rise buildings according to period characteristics of seismicwaves and time history analysis was performed to verify them.

Numerical and experimental analysis of hydroelastic responses of a high-speed trimaran in oblique irregular waves

  • Chen, Zhanyang;Gui, Hongbin;Dong, Pingsha;Yu, Changli
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.11 no.1
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    • pp.409-421
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    • 2019
  • Investigation of hydroelastic responses of high-speed vessels in irregular sea state is of major interest in naval applications. A three dimensional nonlinear time-domain hydroelastic method in oblique irregular waves is developed, in which the nonlinear hydrostatic restoring force caused by instantaneous wetted surface and slamming force are considered. In order to solve the two technical problems caused by irregular sea state, the time-domain retardation function and Proportional, Integral and Derivative (PID) autopilot model are applied respectively. Besides, segmented model tests of a high-speed trimaran in oblique waves are performed. An oblique wave testing system for trimarans is designed and assembled. The measured results of main hull and cross-decks are analyzed, and the differences in distribution of load responses between trimarans and monohull ships are discussed. Finally, from the comparisons, it is confirmed that the present concept for dealing with nonlinear hydroelastic responses of ships in oblique irregular waves is reliable and accurate.

A Study on Analysis of Mental Fitness, Perspective Taking, Attitude toward the Elderly, and Quantitative Encephalogram among Caregivers (요양보호사의 마음건강, 관점수용, 노인 돌봄태도 및 정량 뇌파 분석 연구)

  • Weon, Hee Wook;Son, Hae Kyoung
    • Korean Journal of Occupational Health Nursing
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    • v.29 no.1
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    • pp.88-96
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    • 2020
  • Purpose: This study aimed to identify the mental fitness, perspective taking, attitude toward the elderly, and quantitative encephalogram among caregivers. Methods: In this mixed method research, 14 female caregivers at an elderly care facility in Y city were participated from December 1st to December 31st, 2019. Structured questionnaires were applied to measure general characteristics, mental fitness, perspective taking, and attitude toward the elderly. Brain waves were measured by quantitative encephalogram in the prefrontal lobe. High frequency and high level of care tasks were analyzed using content analysis. Results: According to analysis of brain waves, caregivers experienced high level of physical strain & stress and psychological distraction & stress. Mental fitness (p<.05) and perspective taking (p<.001) were associated with attitude toward the elderly. Moreover, physical strain & stress was associated with psychological distraction & stress (p<.05, p<.001). High frequency and high level tasks were excretion and position change & movement care related tasks, respectively. Conclusion: These findings should be consider as an evidence for supporting care tasks based on concrete and objective understanding of caregivers using self-reported index as well as neurophysiological indicators including brain waves.

Backshore Erosion due to High Swell Waves (너울성고파랑에 기인한 후빈 배후 침식)

  • Kim, Kyu Han;Shim, Kyu Tae
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.24 no.5
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    • pp.366-371
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    • 2012
  • High swell has been known for the one of the main causes of beach erosion in the east coast of Korea. In this study, coastal topography changes due to high swells are simulated to find its effect on the backshore by using movable bed experiments and numerical experiments. Sea bottom topographical changes due to various incident waves were investigated using CSHORE model in the numerical experiments. Furthermore, the mechanism and the phenomena of beach erosion due to waves and high swells on the foreshore and backshore were analyzed and compared with movable bed hydraulic experiments.

The Characteristics of Frequency Spectrum of Radiated Electromagnetic Waves with AC Discharge Progress in Liquid Nitrogen (액체 질소중 교류방전 진전에 따른 방사전자파의 주파수 스펙트럼 특성)

  • 박광서;윤대희;이상훈;이현동;김충년;최병주;김기채;이광식
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.52 no.3
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    • pp.123-129
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    • 2003
  • In this paper, a relationship between AC discharge progress and the radiated electromagnetic waves was investigated by measuring electromagnetic waves using a biconical antenna and a spectrum analyzer. The frequency spectrum of the radiated electromagnetic waves were measured at the atmospheric pressure in liquid nitrogen($LN_2$) during partial discharges progressed by AC high voltage in nonuniform electric field. Front the results of this study, a new method was introduced for measurement and analysis of the radiated electromagnetic waves with discharge progress in $LN_2$ Besides. according to the consideration of the mutual relation between frequency spectrum of the radiated electromagnetic waves and discharge progress, it was confirmed that detecting partial discharge and estimating discharge progress could be possible. It is considered that these results obtained from this investigation may be used as fundamental data for diagnosis and prediction of electric insulations about superconducting and cryogenic power equipments.

On the Stochastic Stability Criteria for the Analysis and Simulation of Ocean Waves (수치실험조건에 따른 해양피낭특성의 통계적 안정한계)

  • RYU Cheong-Ro;KIM Hyeon-Ju
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.20 no.5
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    • pp.457-462
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    • 1987
  • Stochastic stability criterias for ocean wave analysis add simulation are studied using the data simulated by the linear superposition method. To clarify the criterias, the effects of the simulation parameters on the variance of stochastic properties of ocean waves are investigated, and the stable conditions of the parameters are estimated through the comparative study on the stochastic properties of simulated waves and well-known ocean waves. The simulation parameters considered are high frequency cut-off, data length, and number and phase angle of component waves. Statistical characteristics analysed are wave height, period and steepness, and the formation of groups of higher waves, resonance periods, steeper higher waves and extreme run-length of the run.

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