The effects of drag reduction by ribbons attached to cylindrical pipes   总被引：1，自引：0，他引：1  

S. H. Kwon  J. W. Cho  J. S. Park  H. S. Choi 《Ocean Engineering》2002,29(15):1945-1958

This study proposes a drag reduction device that uses three ribbons attached 120 degree apart to vertical pipes. Experiments were conducted in a circulating water channel to investigate the effects of the ribbon length and the direction of the flow on various current velocities. Drag on a vertical cylinder was measured by a resistance dynamometer. Flow visualizations were conducted using laser sheet beams. Laser Doppler Velocimetry (LDV) was used to measure the velocity field in the wake. This experiment demonstrates that attached ribbons can be used to reduce the drag force on vertical pipes for various directions of incoming flows. The ribbon-type device is very simple and easy to fabricate for field applications. The results are promising for the application to offshore structures.  相似文献   

Distribution,provenance, and dispersal pattern of clay minerals in surface sediments,Bransfield Strait,Antarctica     

H. I. Yoon  M. W. Han  B. K. Park  S. J. Han  J. K. Oh 《Geo-Marine Letters》1992,12(4):223-227

Clay minerals of the surface sediments of Bransfield Strait, Antarctica, exhibit distinctive geographical distributions: kaolinite has the highest concentration near the shore of the South Shetland Islands in the northern strait (20%); chlorite, near Smith Island in the northwestern strait; illite, on the continental shelf off the Antarctic Peninsula in the southern strait (80%); and smectite, close to the Penguin and Bridgeman islands in the northeastern strait (25%). This distribution pattern, combined with hydrographic and climatic data for the strait, are used to infer clay mineral provenance and dispersal patterns.  相似文献   

Synoptic distributions of thermal surface mixed layer and thermocline in the southern yellow and East China Seas     

Sunghyea Park  Peter C. Chu 《Journal of Oceanography》2007,63(6):1021-1028

Synoptic distributions of thermal surface mixed layer and thermocline were identified using four airborne expendable bathythermograph (AXBT) surveys (September 1992 and February, May, and September 1993) in the southern Yellow and East China Seas. Seasonality and a dominant driving mechanism of the surface mixed layer were examined. The dominant driving mechanisms differ between seasons and between on-shelf and off-shelf regimes. Currents, eddies, and migration of bottom cold waters (on the shelf) also affect the surface mixed layer. Thermocline thickness, temperature difference from thermocline top to bottom, and thermocline intensity in warm seasons were measured, and their synoptic features were also discussed.  相似文献   

Application of indigenous benthic amphipods as sediment toxicity testing organisms     

Jung-Suk Lee  Kyu-Tae Lee  Dong-Hoon Kim  Chan-Kook Kim  Jong-Hyeon Lee  Kun-Ho Park  Gyung-Soo Park 《Ocean Science Journal》2005,40(1):17-24

A series of experiments were conducted to develop standard test organisms and test protocols for measuring sediment toxicity using candidate amphipods such asMandibulophoxus mai, Monocorophium acherusicum, Haustorioides indivisus, andHaustorioides koreanus, which are indigenous to Korea. The relevant association of test species with sediment substrates was one of the important factors in sediment bioassay. The indigenous amphipodsM. mai andM. acherusicum were well associated with test sediments when they were exposed to various sediment substrates from sand to mud. The tolerant limits to various physico-chemical factors affecting bioassay results such as temperature, salinity and ammonia, as well as sensitivities to reference toxicant and contaminated sediments, were investigated usingM. mai andM. acherusicum in the present study. These amphipods were tolerant to relatively wide ranges of salinity (10~30 psu) and ammonia (<50 ppm), and displayed relevant sensitivity to temperature as well. They are more sensitive to Cd, the reference toxicant, when compared to the standard test species used in other countries. Field-sediment toxicity tests revealed thatM. mai would be more sensitive to sediment-associated pollutants thanM. acherusicum, while the sensitivity ofM. acherusicum was comparable to that ofLeptocheirus plumulosus, which has been used as a standard test species in the United States of America. Overall results of this first attempt to develop an amphipod sediment toxicity test protocol in Korea indicated thatM. mai andM. acherusicum would be applicable in the toxicity assessment of contaminated sediments, following the further evaluation encompassing various ecological and toxicological studies in addition to test method standardization.  相似文献   

Geostatistical integration of gravity and magnetotelluric data to enhance resolution of geologic structure     

Gyesoon Park  Seokhoon Oh  Heuisoon Lee  Jung-Ho Kim  Byung-Doo Kwon 《Journal of Applied Geophysics》2011,73(3):232-242

To enhance the spatial resolution, two types of complementary integration methods were developed using gravity and magnetotelluric (MT) data. The first method involves the enhancement processing of gravity vertical resolution using MT data. This is called a layer density correction (LDC) process which makes the density distribution more sensitive to geologic structure. The second method involves the spatial expansion processing of MT data using the enhanced gravity data. In this process, non-linear indicator transformation (NLIT) and simple kriging with varying local means (SKlm) methods were employed. The assumptions are that while the results are analyzed by different physical properties, each method senses the same underlying geologic structure and thus there is a relationship among the physical properties. The proposed geostatistical integration methods were tested using synthetic models and field data. The experiment illustrates that the integration method proposed in this study can provide improved structures. The method integrates constructively the gravity information having a wider spatial distribution and the MT information having higher vertical resolution.  相似文献   

Simulation of atmospheric states for a storm surge on the west coast of Korea: model comparison between MM5, WRF and COAMPS     

Ki-Young Heo  Jeong-Wook Lee  Kyung-Ja Ha  Ki-Cheon Jun  Kwang-Soon Park  Jae-Il Kwon 《Natural Hazards》2009,51(1):151-162

High-quality informations on sea level pressure and sea surface wind stress are required to accurately predict storm surges over the Korean Peninsula. The storm surge on 31 March 2007 at Yeonggwang, on the western coast, was an abrupt response to mesocyclone development. In the present study, we attempted to obtain reliable surface winds and sea level pressures. Using an optimal physical parameterization for wind conditions, MM5, WRF and COAMPS were used to simulate the atmospheric states that accompanied the storm surge. The use of MM5, WRF and COAMPS simulations indicated the development of high winds in the strong pressure gradient due to an anticyclone and a mesocyclone in the southern part of the western coast. The response to this situation to the storm surge was sensitive. A low-level warm advection was examined as a possible causal mechanism for the development of a mesocyclone in the generating storm surge. The low-level warm temperature advection was simulated using the three models, but MM5 and WRF tended to underestimate the warm tongue and overestimate the wind speed. The WRF simulation was closer to the observed data than the other simulations in terms of wind speed and the intensity of the mesocyclone. It can be concluded that the magnitude of the storm surge at Yeonggwang was dependent, not only on the development of a mesocyclone but on ocean effects as well.  相似文献   

A numerical study on rapid intensification of Hurricane Charley (2004) near landfall     

Kyungjeen Park  X. Zou  Gang Li 《Frontiers of Earth Science》2009,3(4):457-470

The rapid intensification of Hurricane Charley (2004) near landfall is studied using the fifth-generation Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Model (MM5) and its adjoint system for both vortex initialization and forecasts. A significant improvement in both track and intensity forecasts is achieved after an ill-defined storm vortex, derived from large-scale analysis, in the initial condition is replaced by the vortex generated by a four-dimensional data variational (4D-Var) hurricane initialization scheme. Results from numerical experiments suggest that both the inclusion of the upper-level trough and the use of high horizontal resolution (6 km) are important for numerical simulations to capture the observed rapid intensification as well as the size reduction during the rapid intensification of Hurricane Charley. The approach of the upper-level trough significantly enhanced the upper-level divergence and vertical motion within simulated hurricanes. Small-scale features that are not resolvable at 18 km resolution are important to the rapid intensification and shrinking of Hurricane Charley (2004). Numerical results from this study further confirm that the theoretical relationship between the intensification and shrinking of tropical cyclones based on the angular momentum conservation and the cyclostrophic approximation can be applied to the azimuthal mean flows.  相似文献   

Variations in sediment thickness and type along the northern Philippine Sea Plate at the Nankai Trough     

Toshihiro  Ike  Gregory F.  Moore  Shin'ichi  Kuramoto  Jin-Oh  Park  Yoshiyuki  Kaneda  Asahiko  Taira 《Island Arc》2008,17(3):342-357

Abstract   We documented regional and local variations in basement relief, sediment thickness, and sediment type in the Shikoku Basin, northern Philippine Sea Plate, which is subducting at the Nankai Trough. Seismic reflection data, tied with ocean drilling program drill cores, reveal that variations in the incoming sediment sequences are correlated with basement topography. We mapped the three-dimensional seismic facies distribution and measured representative seismic sequences and units. Trench-parallel seismic profiles show three regional provinces in the Shikoku Basin that are distinguished by the magnitude of basement relief and sediment thickness: Western (<200–400 m basement relief, >600 m sediment thickness), Central (>1500 m relief, ∼2000 m sediments), and Eastern (<600 m relief, ∼1200 m sediments) provinces. The total thickness of sediment in basement lows is as much as six times greater than that over basement highs. Turbidite sedimentation in the Shikoku Basin reflects basement control on deposition, leading to the local presence or absence of turbidite units deposited during the middle Oligocene to the middle Miocene. During the first phase of sedimentation, most basement lows were filled with turbidites, resulting in smooth seafloor morphology that does not reflect basement relief. A second phase of turbidite deposition in the Eastern Province was accompanied by significant amounts of hemipelagic sediments interbedded with turbidite layers compared to the other provinces because of its close proximity to the Izu–Bonin Island Arc. Both regional and local variations in basement topography and sediment thickness/type have caused lateral heterogeneities on the underthrusting plate that will, in turn, influence lateral fluid flow along the Nankai accretionary prism.  相似文献   

Accounting for high-order correlations in probabilistic characterization of environmental variables,and evaluation     

Kasemsan Manomaiphiboon  Sun-Kyoung Park  Armistead G. Russell 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(2):159-168

Probabilistic characterization of environmental variables or data typically involves distributional fitting. Correlations, when present in variables or data, can considerably complicate the fitting process. In this work, effects of high-order correlations on distributional fitting were examined, and how they are technically accounted for was described using two multi-dimensional formulation methods: maximum entropy (ME) and Koehler–Symanowski (KS). The ME method formulates a least-biased distribution by maximizing its entropy, and the KS method uses a formulation that conserves specified marginal distributions. Two bivariate environmental data sets, ambient particulate matter and water quality, were chosen for illustration and discussion. Three metrics (log-likelihood function, root-mean-square error, and bivariate Kolmogorov–Smirnov statistic) were used to evaluate distributional fit. Bootstrap confidence intervals were also employed to help inspect the degree of agreement between distributional and sample moments. It is shown that both methods are capable of fitting the data well and have the potential for practical use. The KS distributions were found to be of good quality, and using the maximum likelihood method for the parameter estimation of a KS distribution is computationally efficient.  相似文献   

Local enhancements in the horizontal distribution of the electron density at heights of the topside ionosphere near the dayside polar cap boundary     

V. V. Khegay  K. W. Min  H. J. Kim  J. Park  J. J. Lee  V. P. Kim 《Geomagnetism and Aeronomy》2008,48(5):615-621

The structure of the electron density horizontal distribution at heights of the topside ionosphere in the Northern Hemisphere under quiet magnetic conditions in the polar peak region has been analyzed based on the measurements conducted on board the STSAT-1, DMSP F13, and DMSP F15 satellites during the period of moderate solar activity. The sector near 1000 MLT (magnetic local time) for the spring equinox season has been studied most thoroughly. It has been obtained that the polar peak consists of localized irregularities in the electron density of a specific form, inside which the electron density exceeds its background values by several tens of percent. The characteristic dimensions of the irregularities vary from a few degrees to several tens of degrees in the meridional and zonal directions, respectively. The irregularities are centered along the dayside boundary of the polar cap and coincide with the region of “soft” electron precipitation (with the average energy lower than 500 eV and with the flux density above 10⁷ electrons cm^?2 s^?1 sr^?1).  相似文献