• Title/Summary/Keyword: Sea Field

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Rock mechanics and wellbore stability in Dongfang 1-1 Gas Field in South China Sea

  • Yan, Chuanliang;Deng, Jingen;Cheng, Yuanfang;Yan, Xinjiang;Yuan, Junliang;Deng, Fucheng
    • Geomechanics and Engineering
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    • v.12 no.3
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    • pp.465-481
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    • 2017
  • Thermal effect has great influence on wellbore stability in Dongfang 1-1 (DF 1-1) gas field, a reservoir with high-temperature and high-pressure. In order to analyze the wellbore stability in DF1-1 gas field, the variation of temperature field after drilling was analyzed. In addition, the effect of temperature changing on formation strength and the thermal expansion coefficients of formation were tested. On this basis, a wellbore stability model considering thermal effect was developed and the thermal effect on fracture pressure and collapse pressure was analyzed. One of the main challenges in this gas field is the decreasing temperature of the wellbore will reduce fracture pressure substantially, resulting in the drilling fluid leakage. If the drilling fluid density was reduced, kick or blowout may happen. Therefore, the key of safe drilling in DF1-1 gas field is to predict the fracture pressure accurately.

Numerical Analysis of Deep Seawater Flow Disturbance Characteristics Near the Manganese Nodule Mining Device (망간단괴 집광기 주위 해수 유동교란 수치해석)

  • Lim, Sung-Jin;Chae, Yong-Bae;Jeong, Shin-Taek;Cho, Hong-Yeon;Lee, Sang-Ho
    • Ocean and Polar Research
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    • v.36 no.4
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    • pp.475-485
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    • 2014
  • Seawater flow characteristics around a manganese nodule mining device in deep sea were analyzed through numerical investigation. The mining device influences the seawater flow field with complicated velocity distributions, and they are largely dependent on the seawater flow speed, device moving speed, and injection velocity from the collecting part. The flow velocity and turbulent kinetic energy distributions are compared at several positions from the device rear, side, and top, and it is possible to predict the distance from which the mining device affects the seawater flow field through the variation of turbulent kinetic energy. With the operation of the collecting device the turbulent kinetic energy remarkably increases, and it gradually decreases along the seawater flow direction. Turbulent kinetic energy behind the mining system increases with the seawater flow velocity. The transient behavior of nodule particles, which are not collected, is also predicted. This study will be helpful in creating an optimal design for a manganese nodule collecting device that can operate efficiently and which is eco-friendly.

On the Joint Distribution of Wave Height, Period and Wave Direction in Random Sea Waves (다방향불규칙파랑장에서의 파고, 주기, 파향의 종합확률분포 유도과정 및 적합성)

  • 권정곤
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.2 no.2
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    • pp.75-82
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    • 1990
  • A Wave transformation including wave breaking in shallow water region is a non-linear and discontinuous Phenomenon. Therefore, a so-called individual wave analysis (or a wave by wave analysis) rather than spectral approach seems to be adequate to investigate the wave transformation in such regions. In this study, a theoretical joint distribution of wave height, period and wave direction of zero-down crossing waves, which is required in the individual wave analysis in the shallow water region, is derived based on the hypothesis that sea surface is a Gaussian stochastic process and that a band-width of energy spectra is sufficiently narrow. The derived i oint distribution is found to be an effective measure to investigate characteristics of three-dimensional random wave field in shallow water through field measurements.

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Analysis of Electromagnetic Wave Scattering From a Perfectly Conducting Pierson-Moskowitz Surface Using a Monte-Carlo FDTD Technique (몬테칼로 유한차분 시간영역 해석기법을 이용한 피어선-모스코위츠 완전도체 표면에서의 전자파 산란 해석)

  • 최동묵;김채영
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.40 no.6
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    • pp.253-259
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    • 2003
  • In this paper, the scattered field from a Pierson-Moskowitz sea surface assumed as the PEC by the Finite-Difference Time-Domain(FDTD) method was computed. A one-dimensional surface used to analysis scattering was generated by using the Pierson-Moskowitz model. Back scattering coefficients are calculated with different values of the wind speed(U) which determine configuration of the Pierson-Moskowitz sea surface. The number of surface realization for the computed field, the point number, and the width of surface realization are set to be 50, 8192, and 128k, respectively. In order to verify the computed values these results are compared with those of small perturbation methods, which show good agreement between them.

Physical Characteristics of Internal Waves and the Effect of Short Depression Internal Wave on Acoustic Transmission in the East Sea (동해 내부파의 물리적 특성과 단주기 오목형 내부파가 음파전달에 미치는 영향)

  • Han, Bong-Wan;Lim, Se-Han;Park, Kyeong-Ju;Kim, Seong-Il
    • Journal of the Korea Institute of Military Science and Technology
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    • v.12 no.1
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    • pp.37-43
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    • 2009
  • Fluctuations in the ocean are closely related with the underwater acoustic propagation. Internal waves are generated by fluctuation of isopycnal layer in the upper part of the stratified ocean, which are propagated from offshore to coastal area. Physical characteristics of the internal waves existed in the East Sea were derived from the five field experimental data and the ocean monitoring buoy nearshore the mid-east coast of Korea. The dominant periods are appeared in the near-inertial period about $17{\sim}20hours$ and the short period about a few minutes. The wavelengths of them are $10{\sim}50km$ and $300{\sim}1000m$, and the phase speeds are $20{\sim}100cm/s$ and $30{\sim}70cm/s$, respectively The maximum amplitudes are about $20{\sim}25m$. Under the environment of short depression internal wave propagation, the variations of transmission loss field were investigated using an range-dependent acoustic transmission loss model(RAM). The result shows that the large irregular variations of transmission loss caused by progressing the internal wave from offshore toward coast.

Some Thoughts on the Issues and Improvement Strategies for Coastal Zone Safety through Field Survey-Safety Standards (실태조사를 통한 연안역 안전의 문제점 및 개선방향에 관한 소고-안전기준)

  • Yi, Gyu-Sei;Sung, Ik-Hyun;Bae, Sang-Won;Lim, Nam-Hyoung
    • Journal of the Korean Society of Hazard Mitigation
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    • v.11 no.2
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    • pp.53-57
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    • 2011
  • Recently, the risk of safety accidents in the coastal zone has been increased due to revitalization of marine leisure and tourism. The effective measures, however, to prevent safety accidents in the coastal zone have not taken with increasing rate of the accidents. The nature of land and sea should be taken into account properly when the countermeasures to prevent the safety accidents in the coastal zone are devised, since the characteristics of land and sea are mixed in the environmental condition of the coastal zone. Through the field survey, this study analyzes the current problems on the safety in the coastal zone. Also, it suggests the future direction of the safety standards in the coastal zone on the basis of the safety improvement direction in the coastal zone.

Numerical Simulation of the Sea Water Circulation Characteristics according to the development phases of Busan Port (부산 북항 개발전후의 해수순환특성 수치모의)

  • Moon, Yeong-Ki;Yoo, Chang-Il;Yoon, Han-Sam
    • Proceedings of KOSOMES biannual meeting
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    • 2009.06a
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    • pp.89-94
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    • 2009
  • This study aims to examine the the characteristics if the sea water circulation in related to the change of the water exchange rate according to the the development phases of Busan Port. To clarify the characteristics, the water exchange caused by construction if new-port and river discharge conditions was examined by the numerical experiments using the Lagrangian particle tracking model based on 2-D shallow water equation. This study deals with the charge of flow field and water exchange after redevelopment using numerical simulation technique, based on the field observation and 4 rivers discharge flow. As a result if numerical simulation, Variation if current velocity in Busan North Port is almost nothing before and after construction. Water exchange of channel in area of redevelopment is a little. Futhermore, the tidal exchange had a tendency to be small both before and after redevelopment by 60%.

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Hydraulic conductivity estimation by considering the existence of piles: A case study

  • Yuan, Yao;Xu, Ye-Shuang;Shen, Jack S.;Wang, Bruce Zhi-Feng
    • Geomechanics and Engineering
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    • v.14 no.5
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    • pp.467-477
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    • 2018
  • Estimation of hydraulic parameters is a critical step during design of foundation dewatering works. When many piles are installed in an aquifer, estimation of the hydraulic conductivity should consider the blocking of groundwater seepage by the piles. Based on field observations during a dewatering project in Shanghai, hydraulic conductivities are back-calculated using a numerical model considering the actual position of each pile. However, it is difficult to apply the aforementioned model directly in field due to requirement to input each pile geometry into the model. To develop a simple numerical model and find the optimal hydraulic conductivity, three scenarios are examined, in which the soil mass containing the piles is considered to be a uniform porous media. In these three scenarios, different sub-regions with different hydraulic conductivities, based on either automatic inverted calculation, or on effective medium theory (EMT), are established. The results indicate that the error, in the case which determines the hydraulic conductivity based on EMT, is less than that determined in the automatic inversion case. With the application of EMT, only the hydraulic conductivity of the soil outside the pit should be inverted. The soil inside the pit with its piles is divided into sub-regions with different hydraulic conductivities, and the hydraulic conductivity is calculated according to the volume ratio of the piles. Thus, the use of EMT in numerical modelling makes it easier to consider the effect of piles installed in an aquifer.

Dimethylsulfide (DMS) in the Coastal Areas of the Cheju Island, Korea (제주도 연안해역을 중심으로 한 DMS 농도의 관측)

  • 김기현;이강웅;허철구;강창희
    • Journal of Korean Society for Atmospheric Environment
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    • v.13 no.2
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    • pp.161-170
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    • 1997
  • The concentrations of dimethylsulfide (DMS) were determined using samples collected from a station located at Kosan, Cheju Island during two field campaigns held in December 1996 and January 1997. The atmospheric DMS concentrations measured at 6-hr intervals during the entire campaign periods, after excluding a few extreme values, spanned in the range of 14 to 410 pptv with mean and 1 SD value of 127 $\pm$ 94 pptv (N=42). Between two month periods during which the field campaigns were conducted, a notable reduction in DMS levels was observed which was comparable to the dramatic shift in air temperature. A considerable difference was also noted in DMS levels, when data were grouped by day/night basis. The cause of unexpected, high day-to-night DMS ratios is best explained in terms of high efficiency of daytime source processes relative to low efficiency of nighttime sink processes due to the characteristics of the study location. The surface water DMS of the study site, although scarcely measured, also behaved similarly to its atmospheric counterpart with its range from 0.3 to 19 nM (N=11). When correlation analysis was conducted between the atmospheric DMS concentration and other concurrently determined parameters, significant correlations were observed from most basic meteorological parameters such as windspeed, relative humidy, and air temperature. However, the existence of "not-so-strong" correlations between air temperature and DMS concentrations relative to other ones indicated that the effect of temperature on DMS behavior must be reflected in more complicated manners at the study site. The sea-to-air flux of DMS was approximated through an application of the mass-balance flux calculation method of Wylie and de Mora (1996) under the assumption that sink mechanism within the marine boundary layer is in steady-state condition with its counterpart, source mechanism. Based on this estimation method, we reached a conclusion that oceanic DMS emitted from the southwest sea of the Korean Peninsula can amount to approximately 9 $\sim$ 36 Gg S $yr^{-1}$.$yr^{-1}$.

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Construction of Gridded Wind-stress Products over the World Ocean by Tandem Scatterometer Mission

  • Kutsuwada Kunio;Kasahara Minoru;Morimoto Naoki
    • Proceedings of the KSRS Conference
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    • 2004.10a
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    • pp.192-195
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    • 2004
  • Products of gridded surface wind and windstress vectors over the world ocean have been constructed by satellite scatterometer data with highly temporal and spatial resolutions. Even if the ADEOS-II/SeaWinds has supplied surface wind data only for short duration in Apr. to Oct. 2003 to us, it permits us to construct a product with higher resolution together with the Qscat/SeaWinds. In addition to our basic product with its resolution of $1^{\circ}\times1^{\circ}$ in space and daily in time, we try to construct products with $1/2^{\circ}\times1/2^{\circ}$ and semi- and quarter-daily resolution. These products are validated by inter-comparison with in-situ data (TAO and NDBC buoys), and also compared with numerical weather prediction(NWP) ones (NCEP reanalysis). Result reveals that our product has higher reliability in the study area than the NCEP's. For the open ocean regions in the middle and high latitudes where there are no in-situ data, we find that there are clear differences between them. Especially in the southern westerly region of 400-600S, the' wind-stress magnitudes by the NCEP are significantly larger than the others, suggesting that they are overestimated. We also calculate wind-stress curl field that is an important factor for ocean dynamics and focus its spatial character in the northwestern Pacific around Japan. Positive curl areas are found to cover from southwest to northeast in our focus region and almost correspond to the Kuroshio path. It is suggested that the vorticity field in the lower atmosphere is related to the upper oceanic one, and thus an aspect of air-sea interaction process.

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