• 제목/요약/키워드: High Waves

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동해에서 돌연고파의 기준 제안 (A Proposal for Criterion of Sudden High Waves in the East Sea)

  • 김인철;오지희;서경덕
    • 한국해안·해양공학회논문집
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    • 제28권3호
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    • pp.117-123
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    • 2016
  • 동해에서 주로 겨울철에 발생하며 파고가 크고 주기가 긴 너울성 고파의 주요 특성 중 하나는 잔잔한 상태에서 갑자기 파가 커지는 돌발성이다. 본 연구에서는 이러한 돌발성을 나타내기 위하여 돌연고파라는 용어를 도입하였다. 돌연고파의 기준을 제안하기 위하여 강릉과 왕돌초에서 2005년부터 8년간 관측된 파랑자료와 같은 기간동안 강원도와 경상북도 연안에서 발생했던 해상 사고 기록을 비교하였다. 그 결과 ${\Delta}(H^2L)/{\Delta}t$가 상위 20% 값인 $88.6m^3/hr$ 이상일 때 대부분의 사고 기록과 일치하는 것으로 나타나 이를 돌연고파의 기준으로 제안하였다. 사용된 변수는 한 파장당 파랑 에너지의 단위시간당 증가율을 나타내며, 고파의 파고 및 주기뿐만 아니라 돌발성도 포함한다.

Nonlinear response of stiffened triceratops under impact and non-impact waves

  • Chandrasekaran, Srinivasan;Nassery, Jamshed
    • Ocean Systems Engineering
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    • 제7권3호
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    • pp.179-193
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    • 2017
  • Dynamic response analysis of offshore triceratops with stiffened buoyant legs under impact and non-impact waves is presented. Triceratops is relatively new-generation complaint platform being explored in the recent past for its suitability in ultra-deep waters. Buoyant legs support the deck through ball joints, which partially isolate the deck by not transferring rotation from legs to the deck. Buoyant legs are interconnected using equally spaced stiffeners, inducing more integral action in dispersing the encountered wave loads. Two typical nonlinear waves under very high sea state are used to simulate impact and non-impact waves. Parameters of JONSWAP spectrum are chosen to produce waves with high vertical and horizontal asymmetries. Impact waves are simulated by steep, front asymmetric waves while non-impact waves are simulated using Stokes nonlinear irregular waves. Based on the numerical analyses presented, it is seen that the platform experiences both steady state (springing) and transient response (ringing) of high amplitudes. Response of the deck shows significant reduction in rotational degrees-of-freedom due to isolation offered by ball joints. Weak-asymmetric waves, resulting in non-impact waves cause steady state response. Beat phenomenon is noticed in almost all degrees-of-freedom but values in sway, roll and yaw are considerably low as angle of incidence is zero degrees. Impact waves cause response in higher frequencies; bursting nature of pitch response is a clear manifestation of the effect of impact waves on buoyant legs. Non-impact waves cause response similar to that of a beating phenomenon in all active degrees-of-freedom, which otherwise would not be present under normal loading. Power spectral density plots show energy content of response for a wide bandwidth of frequencies, indicating an alarming behaviour apart from being highly nonlinear. Heave, being one of the stiff degrees-of-freedom is triggered under non-impact waves, which resulted in tether tension variation under non-impact waves as well. Reduced deck response aids functional requirements of triceratops even under impact and non-impact waves. Stiffened group of buoyant legs enable a monolithic behaviour, enhancing stiffness in vertical plane.

동해안에서의 이상 고파 (Abnormally High Waves on the East Coast)

  • 정원무;오상호;이동영
    • 한국해안해양공학회지
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    • 제19권4호
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    • pp.295-302
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    • 2007
  • 2006년 10월 $23{\sim}24$일 동해안 일대에서 발생한 이상 고파(高波)를 5개 지점에서 관측하고 기상청에서 제공하는 바람 자료를 함께 이용하여 고파의 특성을 분석하였다. 이번 이상 고파는 높은 너울이 동해안에 영향을 미치기 시작하는 시점에 동해상에 발달한 온대성 저기압의 영향으로 동해선풍이 지속적으로 강하게 불어서 발생하였다. 5개 관측 지점 중 가장 북쪽에 위치한 속초에서는 최대 순간풍속 63.7 m/s의 강풍과 최대 유의파고 9.69 m, 첨두주기 12.8 s의 고파가 관측되었다. 이처럼 높은 파가 발생한 이유는 강풍이 부는 동안 높은 너울이 지속적으로 유지되었고 강풍이 너울의 진행과 같은 방향으로 불어서 너울과 풍파의 중첩에 의한 파고 상승 효과가 극대화되었기 때문이다. 동해안에서는 겨울철에 이러한 돌발성 폭풍파가 발생할 가능성이 매우 높으므로 이를 고려하여 피해를 최소화하도록 대응 방침을 수립해야 할 것이다.

겨울철에 발생한 이상 남파 관측 (Observation of Abnormal Waves from South in Winter)

  • 김태림;전기천;박광순;김상익
    • 한국해안해양공학회지
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    • 제12권1호
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    • pp.11-18
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    • 2000
  • 1997년 11월 25일 겨울철에 남해안에서 이례적으로 남쪽으로부터 전파되는 높은 파고가 관측되었다. 4m 정도의 이러한 이상 파고는 시간차를 두고 마라도, 부산 그리고 울릉도 순서로 각각에 설치한 파고계에 관측되었으며 특히 서귀포항 공사 중에 발생하여 큰 피해를 입혔다. 겨울철에 발생하는 이상 남파는 저기압의 이상 발달 및 이동으로 인한 것으로 추측되며 이를 살펴보기 위하여 일기도 및 수치모델에 의한 파랑장의 분포 등을 조사하여 그 발생 가능성에 대하여 연구하였다. 앞으로도 겨울철에 발생할 수 있는 이러한 이상 남파에 대한 주의를 요한다.

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선미 규칙파 중 고속 활주선의 연직면 운동에 대한 실험적 연구 (An Experimental Study on the Vertical Motion of a High-Speed Planing Craft in Regular Following Waves)

  • 김동진;이기표;유영준;박한솔
    • 대한조선학회논문집
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    • 제47권4호
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    • pp.496-507
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    • 2010
  • It is well known that when a high-speed planing craft travels in following seas it experiences long-periodic motions due to low encounter frequency, and it often loses its course keeping stability. Therefore, it is necessary to study the sea-keeping performance and stability of it in the following seas. In this paper, the vertical motions of a planing craft were measured in following regular waves, and the test results were compared with the theoretical results. In the case of the same encounter frequency, non-dimensionalized motion amplitudes become larger as Froude number is higher, and non-dimensionalized motion amplitudes in head waves are larger than those in following waves. The mean values of the motions in following waves are similar to the running attitudes of a craft in calm water at the same Froude number.

CFD computation of ship motions and added resistance for a high speed trimaran in regular head waves

  • Wu, Cheng-Sheng;Zhou, De-Cai;Gao, Lei;Miao, Quan-Ming
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제3권1호
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    • pp.105-110
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    • 2011
  • Some research work on CFD computation of ship motions and added resistance in waves for a high speed trimaran is carried out in this paper. The governing equations, Reynolds Averaged Navier-Stokes and continuity equations are discretized by finite volume method. Volume of fluid method is adopted to deal with the nonlinear free surface. The incident waves are generated from the inflow boundary by prescribing a velocity profile resembling flexible flap wavemaker motions, and the outgoing waves are dissipated inside an artificial damping zone located at the rear part of the wave tank. In this paper, the computed results of ship motion and added resistance for a high speed trimaran are presented. The results of seakeeping experiment for the high speed trimaran carried out in CSSRC towing tank are also presented in this paper. Rather good agreements are shown between the computational and experimental results. The work in this paper provides a numerical tool for the study of seakeeping performance of high speed trimarans.

구급차량 내 전자파 방출에 관한 조사 (Research on the emission of electromagnetic waves in ambulance)

  • 윤종근
    • 한국응급구조학회지
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    • 제23권1호
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    • pp.61-69
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    • 2019
  • Purpose: The study aims to provide basic data to enhance the health of paramedics responsible for patient transport and treatment by analyzing the exposure level of paramedics to electromagnetic waves generated by electric devices used in ambulances. Methods: The study measured electromagnetic waves in ambulances in N region from July to December 2018. ME3030B produced by German Gigahertz Solutions was used to measure these waves and the maximum value was selected by moving it slowly in various directions. Each measurement part was selected and the mean value was calculated by repeatedly measuring at 10-minute intervals three times in total: $1^{st}$, $2^{nd}$, and $3^{rd}$ phase. Results: Among the electrical devices installed in the patient room of the ambulance measured at distances of 1 cm or 30 cm, results showed a high level of electric waves at the inverter ($26.25{\pm}39V/m$) and high level of electromagnetic waves ($564.00{\pm}31.75nT$) at the ozone sterilizer. According to measurements toward the front near the driver's seat, results indicated high levels of electric waves ($3.67{\pm}1.15V/m$) and electromagnetic waves ($450.00{\pm}19.52nT$) at the black box hard drive. Conclusion: Electromagnetic waves within the ambulance were stable and not beyond the range that might impact human health. However, in the case of the black box hard drive ($3.67{\pm}1.15V/m$, $450.00{\pm}19.52nT$) located under the passenger seat, it may have a direct effect on the human body and, thus it is necessary to move it to a storage area further away from the paramedics to minimized the impact.

태풍 매미 내습시 해일$\cdot$고파랑에 의한 호안$\cdot$안벽에서의 수위증가 패턴 고찰 (Patterns of Water Level Increase by Storm Surge and High Waves on Seawall/Quay Wall during Typhoon Maemi)

  • 강윤구
    • 한국해양공학회지
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    • 제19권6호통권67호
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    • pp.22-28
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    • 2005
  • We investigated the characteristics of the overflow/wave overtopping, induced by the storm surge and high waves in Masan bay and Busan Coast during Typhoon 'Maemi', which landed at the southeast coast of the Korean peninsula on September, of 2003, causing a severe inundation disaster. Characteristics of the water level, increase by the overflow / wave overtopping, were discussed in two patterns. One is the increase of water level in the region, located inside of a bay, like Masan fishing port, and the waves are relatively small. The other is in the open sea, in which the waves act directly, as on the seawall in Suyong bay. In the former region, the water level increase was affected by the storm surge, as well as the long period oscillation and waves. In Masan fishing port, about $80\%$ of the water level increase on the quay wall was caused by the storm surge. In the latter one, it was greatly affected by the wave run-up. In Suyong bay, about $90\%$ of the water level increase on the seawall was caused by the wave run-up.

우리나라 서해에서 발생한 겨울철 고파의 관측자료 분석 (Analysis of the Observation Data for Winter-Season High Waves Occurred in the West Sea of Korea)

  • 오상호;정원무;김상익
    • 한국해안·해양공학회논문집
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    • 제27권3호
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    • pp.168-174
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    • 2015
  • 우리나라 서해안 다섯 개 관측점에서 취득된 파랑자료를 분석하여 겨울철 서해에서 발생한 고파의 특성을 분석하였다. 고파가 발생하였던 네 시기를 선별하여 그 기간 동안의 파랑 및 기상자료를 함께 분석에 이용하였다. 이들 관측 기간 중 유의파고의 최대값은 2005년 12월 4일에 관측된 6.42 m였다. 분석 결과로부터 온대성저기압이 급속하게 발달할 때 서해상에 형성되는 강한 바람장에 의해 고파가 발생함을 확인하였다. 파랑 관측점에서의 파고의 시간적 변화는 인근 기상관측점에서의 풍속의 시간적 변화와 밀접한 관련을 나타냈으며, 이는 서해상에서 생성된 고파가 풍파의 성격이 지배적임을 나타낸다.

Critical earthquake loads for SDOF inelastic structures considering evolution of seismic waves

  • Moustafa, Abbas;Ueno, Kohei;Takewaki, Izuru
    • Earthquakes and Structures
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    • 제1권2호
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    • pp.147-162
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    • 2010
  • The ground acceleration measured at a point on the earth's surface is composed of several waves that have different phase velocities, arrival times, amplitudes, and frequency contents. For instance, body waves contain primary and secondary waves that have high frequency content and reach the site first. Surface waves are composed of Rayleigh and Love waves that have lower phase velocity, lower frequency content and reach the site next. Some of these waves could be of more damage to the structure depending on their frequency content and associated amplitude. This paper models critical earthquake loads for single-degree-of-freedom (SDOF) inelastic structures considering evolution of the seismic waves in time and frequency. The ground acceleration is represented as combination of seismic waves with different characteristics. Each seismic wave represents the energy of the ground motion in certain frequency band and time interval. The amplitudes and phase angles of these waves are optimized to produce the highest damage in the structure subject to explicit constraints on the energy and the peak ground acceleration and implicit constraints on the frequency content and the arrival time of the seismic waves. The material nonlinearity is modeled using bilinear inelastic law. The study explores also the influence of the properties of the seismic waves on the energy demand and damage state of the structure. Numerical illustrations on modeling critical earthquake excitations for one-storey inelastic frame structures are provided.