• Title/Summary/Keyword: Pressure time history

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The Effects of Stress and Time History on Pore Pressure Parameter of Overconsoldated clay (과압밀점토의 간극수압계수에 응력이력과 시간이력이 미치는 영향)

  • 김수삼;김병일;한상재;신현영
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.14 no.4
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    • pp.286-294
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    • 2002
  • This study investigated the effects of stress and time history of overconsolidated clayey soils on pore pressure parameter, A. Laboratory tests were carried out under the conditions of both varying stress and time history. The stress history is classified into (i) rotation angle of stress path, (ii) overconsolidation ratio, and (iii) magnitude of length of recent stress path. The time history is divided into (i) loading rate of recent stress path and (ii) rest time. Pore pressure parameters are different both in the magnitude and trend with the rotation angle, depending on the magnitude of overconsolidation ratio but not in a trend. In addition, the pore pressure parameters have no effects on the magnitude of length of recent stress path except the level of initially small strain, while loading rates of recent stress path have effects on it. Finally, the pore pressure parameters of overconsolidated clays increase with the existence of the rest time, until either the deviator stress exceeds 70 kPa or the strain up to 0.1%.

Consideration of residual mode response in time history analysis using residual vector (Residual Vector를 이용한 시간이력해석의 잔여모드 응답 고려 방법)

  • Chang Ho Byun;Han Geol Lee;Jung Yong Kim
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.17 no.2
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    • pp.137-144
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    • 2021
  • The mode superposition time history analysis method is commonly used in a seismic analysis. The maximum response in the time history analysis can be derived by combining the responses of individual modes. The residual mode response is the response of the modes which are not considered in the time history analysis. In this paper, the residual vector method to consider the residual mode response in the time history analysis is introduced and evaluated. Seismic analyses for a sample structure model and a reactor vessel model are performed to evaluate the residual vector method. The analysis results show that residual mode response is well calculated when the residual vector method is used. It is confirmed that the residual vector method is useful and acceptable to consider the residual mode response in a seismic analysis of the nuclear power plant equipment.

A Fundamental Study for Time History Modeling of Fluid Impact Pressure (유체 충격압력 시계열의 모델링에 관한 기초 연구)

  • Nho, In-Sik;Lee, Jae-Man;Yeom, Cheol-Woong
    • Journal of the Society of Naval Architects of Korea
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    • v.47 no.2
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    • pp.242-247
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    • 2010
  • To consider effects of essential parameters of water impact pressure on dynamic structural responses of bow bottom structures, a parametric study for a ship bottom panel is carried out. The idealized pressure time history models were assumed by triangular and rectangular shapes in time domain. The main loading parameters are duration time and peak pressure value maintaining the same impulse value. The structural models for local bottom stiffened panels of a container ship are analysed. The natural frequency analysis and transient dynamic response analysis are performed using MSC/NASTRAN. Added mass effects of contacting water are considered and the pressure distributions are assumed to be uniform in the whole water contacting surface. The effects of loading parameters on the structural responses, especially maximum displacements, are considered. Besides the peak pressure value, effects of duration time correlated with natural frequencies are thought to be the important parameters.

A Study on Physicochemical Characteristics of Hydrogen Gas Explosion (수소가스 폭발의 물리화학적 특성 연구)

  • Jo, Young-Do
    • Journal of the Korean Institute of Gas
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    • v.16 no.1
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    • pp.8-14
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    • 2012
  • Hydrogen is considered to be the most important future energy carrier in many applications reducing significantly greenhouse gas emissions, but the explosion safety issues associated with hydrogen applications need to be investigated and fully understood to be applicable as the carrier. The risk associated with a explosion depends on an understanding of the impacts of the explosion, particularly the pressure-time history during the explosion. This work provides the effects of explosion parameters, such as specific heat ratio of burned and unburned gas, equilibrium maximum explosion pressure, and burning velocity, on the pressure-time history with flame growth model. The pressure-time history is dominantly depending on the burning velocity and equilibrium maximum explosion pressure of hydrogen-air mixture. The pressure rise rate increase with the burning velocity and equilibrium maximum explosion pressure. The specific heat ratio of unburned gas has more effect on the final explosion pressure increase rate than initial explosion pressure increase rate. However, the specific heat ratio of burned gas has more influence on initial explosion pressure increase rate. The flame speeds are obtained by fitting the experimental data sets. The flame speeds for hydrogen in air based on our experimental data is very low, making a transition from deflagration to detonation in a confined space unlikely under these conditions.

A Suggestion of Simplified Load Formula for Blast Analysis (폭발해석을 위한 간략 폭발하중 제안식)

  • Jeon, Doo-Jin;Han, Sang-Eul
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.29 no.1
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    • pp.67-75
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    • 2016
  • In this paper, a pressure-time history curve of blast load and Conwep model are presented, and a simplified blast load formula is suggested. Generally, a blast load are applied as a pressure-time history curve, and it is calculated by blast load formula such as Conwep model. The Conwep model which is used in most of the blast analysis is quiet difficult to calculate because of its complex process. Therefore, a simplified formula is proposed to calculate blast load by simple rational expressions and to make a simplified pressure-time history curve. In this process, a curve fitting method was used to find the simple rational expressions. The calculation results of the simplified formula have an error of less than 1% in comparison with the Conwep model. And, blast analyses using finite elements method are accomplished with the Conwep model and simplified formula for verification.

A Study on the Noise Produced by Unsteady Exhaust Efflux of Engine (기관의 비정상 배기배출에 의해 생성되는 소음에 관한 연구)

  • 이민호;박명규
    • Journal of the Korean Society of Safety
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    • v.12 no.4
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    • pp.191-200
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    • 1997
  • This paper discusses prediction of the sound pressure level produced by simple engine exhaust systems(plain pipe, plain expansion chamber pipe, plain expansion chamber with internally extended inlet and outlet pipe, perforated pipe enclosed in a plain expansion chamber) and a computer program has been developed which predicts the sound pressure level and the frequency spectrum. The program utilizes unsteady flow gas dynamic theory and acoustic theory to predict the pressure-time history in the exhaust system and the mass flow rate-time history at the open end of the system and the sound pressure levels(1/3 Octave band levels) and the frequency spectrum in semi-anechoic room. The predictions are compared with measured levels and show a high degree of correlation.

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Rapid response calculation of LNG cargo containment system under sloshing load using wavelet transformation

  • Kim, Yooil
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.5 no.2
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    • pp.227-245
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    • 2013
  • Reliable strength assessment of the Liquefied Natural Gas (LNG) cargo containment system under the sloshing impact load is very difficult task due to the complexity of the physics involved in, both in terms of the hydrodynamics and structural mechanics. Out of all those complexities, the proper selection of the design sloshing load which is applied to the structural model of the LNG cargo containment system, is one of the most challenging one due to its inherent randomness as well as the statistical analysis which is tightly linked to the design sloshing load selection. In this study, the response based strength assessment procedure of LNG cargo containment system has been developed and proposed as an alternative design methodology. Sloshing pressure time history, measured from the model test, is decomposed into wavelet basis function targeting the minimization of the number of the basis function together with the maximization of the numerical efficiency. Then the response of the structure is obtained using the finite element method under each wavelet basis function of different scale. Finally, the response of the structure under entire sloshing impact time history is rapidly calculated by synthesizing the structural response under wavelet basis function. Through this analysis, more realistic response of the system under sloshing impact pressure can be obtained without missing the details of pressure time history such as rising pattern, oscillation due to air entrapment and decay pattern and so on. The strength assessment of the cargo containment system is then performed based on the statistical analysis of the stress peaks selected out of the obtained stress time history.

An analysis of the causes of prehospital delays in patients with suspected acute stroke (급성 뇌졸중 의심 환자의 병원 전 지연 원인 분석)

  • Lee, Nam-Jin;Moon, Jun-Dong
    • The Korean Journal of Emergency Medical Services
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    • v.24 no.2
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    • pp.27-38
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    • 2020
  • Purpose: Stroke is a time-sensitive disease that could have reduced complications and mortality with timely diagnosis and treatment. This study aimed to analyze the causes of delay in detecting the clinical signs and symptoms of stroke. Methods: This retrospective observational study analyzed the emergency medical services reports of suspected stroke patients with positive predictive values on the Cincinnati Prehospital Stroke Scale. The study was conducted in Daejeon, Republic of Korea from January 1, 2016 through December 31, 2017. Results: Prolonged prehospital time was associated with high blood pressure, history of cerebrovascular disease, and incidences during daily activities, and sleep. High blood pressure and complications from a previous stroke strongly associated with the prolonged stroke-detection phase (p<.05). Total prehospital time was shortened when patients had evident stroke symptoms, such as decreased level of consciousness, dysarthria, and hemiplegia (p<.05). There was no significant difference in gender or age as a factor that delayed the total prehospital time of the suspected stroke patients. Conclusion: Many patients did not recognize the early clinical symptoms and signs of a stroke. Furthermore, risk factors, such as high blood pressure and history of stroke, prolonged the total prehospital time. Therefore, we need targeted interventions that educate about warning symptoms of stroke, along with emphasis on the importance of emergency calls to substantially reduce the prehospital delays.

Analysis on the Dynamic Respone of the Hull Structure due to Slamming Impact - By Finite Element Method - (슬래밍 충격을 받는 선체의 동적 응답해석 -유한요소법으로-)

  • Hong, Bong-Ki;Moon, Duk-Hong;Bae, Dong-Myung
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.19 no.2
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    • pp.117-124
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    • 1983
  • In rough seas, actual behaviours of a ship may not be estimated by the linear strip theory, because of Nonlinearities due to the hull shape, bottom slamming and bottom and/or bow-flare slamming. In case of slamming, impulsive hydrodynamic pressure occurs on the fore body surface of the ship, resulting hull vibration called whipping, by which the ship may suffer from serious structural damages and the impact pressure, depends critically on the relative velocity at re-entry. In this paper, the Time history of impact froce at each station, the longitudinal distribution of impact force at critical time, the Time history of acceleration at F.P. and the Time history of Bending moment at midship are illustrated. That is, authors analyzed Dynamic response of container ship to be subjected slamming impact force.

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Acoustical Performance Analysis of the Simple Expansion Chamber by using CFD (CFD를 이용한 단순확장관의 음향특성 해석)

  • Kim, Dae-Hwan;Cheong, Cheol-Ung;Jeong, Weui-Bong;Kim, Hyung-Tae
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.11a
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    • pp.1354-1359
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    • 2007
  • This paper discusses the acoustic performance of simple expansion chamber using computational fluid dynamics(CFD). The CFD model consists of an axisymmetric grid with a single period sinusoid of acceptable amplitude and duration imposed at the inlet boundary condition. The time history of the static pressure is recorded at two points, one in the inlet pipe and one point in outlet pipe. The time history of the static pressure is converted to the frequency domain using Fourier Transform and the transmission loss (TL) of the muffler is obtained from the ratio of the static pressure at the inlet and outlet pipe. The transmission loss of CFD result is compared with that of the computational acoustic analysis using the boundary element method (BEM). There are some differences in two results due to the pressure drop according to the inlet and outlet pipe length. Therefore, the effects of the pressure drop to the transmission loss have to be considered.

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