• Title/Summary/Keyword: Equivalent wave pressure

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A time-domain simulation of an oscillating water column with irregular waves

  • Koo, Weoncheol;Kim, Moo-Hyun
    • Ocean Systems Engineering
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    • v.2 no.2
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    • pp.147-158
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    • 2012
  • A time-domain simulation of a land-based Oscillating Water Column (OWC) with various irregular waves as a form of PM spectrum is performed by using a two-dimensional fully nonlinear numerical wave tank (NWT) based on the potential theory, mixed Eulerian-Lagrangian (MEL) approach, and boundary element method. The nonlinear free-surface condition inside the OWC chamber was specially devised to describe both the pneumatic effect of the time-varying pressure and the viscous energy loss due to water column motions. The quadratic models for pneumatic pressure and viscous loss are applied to the air and free surface inside the chamber, and their numerical results are compared with those with equivalent linear ones. Various wave spectra are applied to the OWC system to predict the efficiency of wave-energy take-off for various wave conditions. The cases of regular and irregular waves are also compared.

Analysis of Blast Wave of Explosives by the Scaling Law (축척법에 의한 화약 폭풍과 분석)

  • Park, Jung-Su;Kim, Sung-Ho;Lee, Keun-Deuk;Lee, Jai-Min
    • Journal of the Korea Institute of Military Science and Technology
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    • v.8 no.4 s.23
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    • pp.120-129
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    • 2005
  • To analyze a blast effect of developed explosives, three different kinds of aluminized tastable explosives and melted cast explosive TNT were used. Conventional explosive TNT was used as a reference. Each tested explosive charge of 340mm diameter spherical type was initiated at the charge center with DXD-65(${\sim}750g$) booster and RP-87 EBW detonator. Thirteen piezo type pressure sensors were located at a range from 4 to 50m away from the charge. From the blast wave profiles, we calculated a peak blast pressure and impulse of the explosion. The calculated pressures and in pulses were converted to TNT Equivalent Weight(TEW) factor by the scaling ]aw method. The average TEW factors based on the blast pressure of TX-01, TX-02, TX-03, TX-04 were 1.298, 1.05, 1.266, 1.274 and the average TEW factors based on impulse were 1.504, 1.686, 1.640, 1.679. From the results, we concluded that TEW factors based on blast pressure and based on impulse of aluminized explosives were superior to TNT. This results are owing to the high contents of aluminum in formulations.

Experimental Study of Wall Pressure Fluctuations in the Regions of Flow Transition (천이 경계층 유동의 벽면 변동 압력에 관한 실험적 연구)

  • 홍진숙;전재진;김상윤;신구균
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.4
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    • pp.280-286
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    • 2002
  • It has been long suspected that the transition region may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. Experimental investigation described in this paper concerns the characteristics of pressure fluctuations at the transition. Flush-mounted microphones and hot wires are used to measure the pressure fluctuations and local flow velocities within the boundary layer in the low noise wind tunnel. From this experiment we could observe the spatial and temporal development process of T-S wave using Wigner-Ville method and find the relations between the characteristic frequency of T-S wave and free stream velocity and the boundary layer thickness based on nondimensional pressure spectra scaled on outer variables.

Experimental Study of Wall Pressure Fluctuations in the Regions of Flow Transition (천이 경계층 유동의 벽면 변동 압력에 관한 실험적 연구)

  • Shin, Ku-Kyun;Hong, Chin-Suk;Jeon, Jae-Jin;Kim, Sang-Yoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.811-816
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    • 2000
  • It has been long suspected that the transition region may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. Experimental investigation described in this paper concerns the characteristics of pressure fluctuations at the transition. Flush-mounted microphones and hot wires are used to measure the pressure fluctuations and local flow velocities within the boudary layer in the low noise wind tunnel. From this experimental we could observe the spatial and temporal development process of T-S wave using Wigner-Ville method and found the possibility of relation between the characteristic frequency of T-S wave and free stream velocity and the boundary layer thickness based on nondimensional pressure spectra scaled on outer variables.

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Experimental study of compression waves propagating porous walls (다공벽을 전파하는 압축파의 실험적 연구)

  • Kim, Hui-Dong;Setoguchi, Toshiaki
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.12
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    • pp.4036-4043
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    • 1996
  • When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study tested the effect of porous walls on the compression wave propagating into a model tunnel. Experimental results were obtained using a shock tube with an open end. The results showed that the cavity/porous wall is very effective for the compression wave with a large nonlinear effect. The porosity of 30% is most effective for attenuation and pressure gradient reduction of the compression wave front. Also the impulsive noise reduction increases with increasing the length and height of the cavity, compared with the tunnel equivalent diameter.

Analysis of Abnormal Settlement Aspect of Caisson Breakwater by Incoming Wave Action in Affected Area of Typhoon (태풍영향권 내습파랑에 의한 직립방파제 이상침하 현상분석)

  • Lee, Joong-Koo;Kim, Hyo-Seob;Park, Koo-Yong;Ahn, Ik-Seong
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.21 no.6
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    • pp.508-517
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    • 2009
  • The real time movement of the caisson was measured when it was open to the waves during breakwater construction. As a result of measurement, no more settlement after the preloading in condition of designed loading was expected but sudden abnormal settlement took place through whole area of the breakwater when waves occurred by typhoon effect. To clarify the reason of this case, wave of the site has been reproduced and the equivalent wave pressure on the caisson was calculated. The numerical analysis of the effect of wave to the ground had been done. Site measurement data is in accordance with the result of numerical analysis.

Correlation of Peak Time Shift in Blood Pressure Waveform and PPG Based on Compliance Change Analysis in RLC Windkessel Model

  • Choi, Wonsuk;Cho, Jin-Ho
    • Current Optics and Photonics
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    • v.1 no.5
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    • pp.529-537
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    • 2017
  • We explored how changes in blood vessel compliance affected the systolic rise time (SRT) of the maximum blood pressure (BP) peak wave and the diastolic fall time (DFT) of the minimal BP peak wave, compared to photoplethysmograpic (PPG) parameters, using a two-compartment, second-order, arterial Windkessel model. We employed earlier two-compartment Windkessel models and the components thereof to construct equivalent blood vessel circuits, and reproduced BP waveforms using PSpice technology. The SRT and DFT values were obtained via circuit simulation, considering variations in compliance (the dominant influence on blood vessel parameters attributable to BP changes). And then performed regression analysis to identify how compliance affected the SRT and DFT. We compared the SRTs and DFTs of BP waves to the PPG values by reference to BP changes in each subject. We confirmed that the time-shift propensities of BP waves and the PPG data were highly consistent. However, the time shifts differed significantly among subjects. These simulation and experimental results allowed us to construct an initial trend curve of individual BP peak time (measured via wrist PPG evaluations at three arm positions) that facilitated accurate individual BP estimations.

Prediction of Bow Flare Impact Pressure and Its Application to Ship Structure Design - Tanker and Bulk Carrier - (선수 플레어 충격압력 추정과 구조설계에의 응용 - 탱커와 산적화물선 -)

  • 김용직;신기석;신찬호;강점문;김만수;김성찬;오수관;임채환;김대헌
    • Journal of the Society of Naval Architects of Korea
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    • v.40 no.3
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    • pp.22-28
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    • 2003
  • In rough seas, bow-flare regions of the full ships (tanker and bulk carrier) are subiect to high impact pressures due to the on-coming breaking waves. And many ships suffer structural damages in that region, even though they were built under the bow structure strengthening rules of the ship classes. So, a new design method for bow-flare structure is highly required. In this paper, a new prediction method of the bow-flare impact pressure (in terms of equivalent static pressure) acting on the full ships' bow is presented. This method is based on the 6 full ships' damage analysis and the breaking wave impact mechanism. Calculation results of the bow-flare impact pressure and the shell plate thickness are shown and discussed. Through the example calculations, it was found that the present method is useful for the structure design of the full ships' bow.

Performance Prediction of an OWC Wave Power Plant with 3-D Characteristics in Regular Waves

  • Hong, Do-Chun;Hong, Keyyong
    • Journal of Navigation and Port Research
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    • v.36 no.9
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    • pp.729-735
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    • 2012
  • The primary wave energy conversion by a three-dimensional bottom-mounted oscillating water column (OWC) wave power device in regular waves has been studied. The linear potential boundary value problem has been solved following the boundary matching method. The optimum shape parameters such as the chamber length and the depth of the front skirt of the OWC chamber obtained through two-dimensional numerical tests in the frequency domain have been applied in the design of the present OWC chamber. Time-mean wave power converted by the OWC device and the time-mean second-order wave forces on the OWC chamber structure have been presented for different wave incidence angles in the frequency-domain. It has been shown that the peak period of $P_m$ for the optimum damping parameter coincides with the peak period of the time.mean wave drift force when ${\gamma}=0$.

Detailed Investigation on the Dynamic Excess Pore Water Pressure through Liquefaction Tests using Various Dynamic Loadings (다양한 진동하중의 액상화 시험을 통한 동적 과잉간극수압에 대한 상세분석)

  • Choi, Jae-Soon;Jang, Seo-Yong;Kim, Soo-Il
    • Journal of the Earthquake Engineering Society of Korea
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    • v.11 no.2 s.54
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    • pp.81-94
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    • 2007
  • In most experimental researches on the liquefaction phenomenon, an earthquake as a random vibration has been regraded as a sinusoidal wave or a triangular wave with an equivalent amplitude. Together with the development in the part of signal control and data acquisition, dynamic experimental equipments in the soil dynamics have also developed rapidly and further more, several real earthquakes have been simulated in the large model test such as shaking table tests and centrifuge tests. In Korea, several elementary laboratory tests to simulate the real earthquake load were performed. From these test results, it was reported that the sinusoidal wave cannot reliably reflect the soil dynamic behavior under the real earthquake motion. In this study, 4 types of dynamic motions such as the sinusoidal wave, the triangular wave, the incremental triangular wave and several real earthquake motions which were classified with shock-type and vibration-type were loaded to find something new to explain the change of the excess pore water pressure under the real earthquake load. Through the detailed investigation and comparison on all test results, it is found that the dynamic flow is generated by the soil plastic deformation and the velocity head of dynamic flow is changed the pressure head in the un-drained condition. It can be concluded that the change of the excess pore water pressure is related to the pressure head of dynamic flow. Lastly, a new hypothesis to explain such a liquefaction initiation phenomenon under the real earthquake load is also proposed and verified.