Numerical simulation of a short flexible pipe subject to forced motion and vortex-induced vibration   总被引：2，自引：0，他引：2  

CHEN Zhengshou  KIM Wu-joan  CHOI Yoon-rak 《海洋学报(英文版)》2009,28(6):70-83

A series of numerical simulations about a small scale(aspect ratio:63.2) flexible pipe undergoing forced harmonious oscillation and vortex-induced vibration(VIV) have been taken into account.The wake hydrodynamics and pipe deformation were accomplished by ANSYS MFX solution strategy designed for fluid-structure interaction(FSI) problem with well-performed LES model.The configuration of structured mesh,multi-domain design,different mesh stiffness admeasured by User Fortran ensured that the numerical task was competent to deal with large deformation related to this case.The introduction of instantaneous amplitude definition and modeless component decomposition method(Chen and Kim,2008) was helpful to reveal much more information from modal analysis.Most results from numerical simulation are generally consistent with those from model test(Choi and Hong,2000) via the comparison between them.As supplementary to model test,visualization of the vortex wake was also provided.It has been proved that the forced oscillation doesn't only excite a complicated dumbbell-like wake pattern around the outer thimble,but also results in inner flow inside the PVC pipe.The velocity of the inner flow increases with the frequency of forced oscillation.  相似文献   

Two climate factors in May that affect Korean rainfall in September     

CHOI Ki-Seon  MOON Il-Ju 《海洋学报(英文版)》2013,32(1):32-47

This study revealed a high positive correlation between rainfall in Korea during September and the trade wind (TW)/Arctic Oscillation (AO) index in May that combines two climate factors, low-level TWs and the AO. This correlation was identified on the basis of the difference in the 850 hPa streamline analysis between the positive and negative phases selected using the combined TW/AO index. In May, the spatial pattern of the anomalous pressure systems is similar to that in the positive AO phase. These anomalous pressure systems continue in June to August (JJA) and September, but the overall spatial distribution shifts a little to the south. Particularly in September, a huge anomalous anticyclone centered over the southeast seas of Japan strengthens in most of the western north Pacific region and supplies a large volume of warm and humid air to the region near Korea. This characteristic is confirmed by the facts that during the positive TW/AO phase, the subtropical western north Pacific high (SWNPH) is more developed to the north and that the continuous positioning of the upper troposphere jet over Korea from May to September strengthens the anomalous upward flow, bringing warm and humid air to all layers. These factors contribute to increasing September rainfall in Korea during the positive TW/AO phase. Because the SWNPH develops more to the north in the positive phase, tropical cyclones tend to make landfall in Korea frequently, which also plays a positive role in increasing September rainfall in Korea.The above features are also reflected by the differences in average rainfall between the six years that had the highest May Ni o 3.4 indices (El Ni o phase) and the six years that had the lowest May Ni o 3.4 indices (La Ni a phase).  相似文献   

1998年南海夏季风爆发过程中副热带高压减弱的诊断分析   总被引：3，自引：2，他引：1  

黄辰洁  蓝光东  徐敏贞  陈训来  王安宇  吴池胜 《热带气象学报》2010,26(3):349-356

1998年南海夏季风爆发于5月21日。利用NCEP再分析资料,用Zwack-Okossi涡度方程诊断分析引起季风爆发前后南海-西太平洋副热带反气旋脊迅速减弱的物理因子,结果表明:在夏季风爆发前,华东-华南沿岸附近高空槽前的正涡度平流区随高空槽的东南移动向南海和菲律宾中部附近地区推进;正涡度平流是引起上述地区850 hPa气旋性涡度增大的最主要的物理因子,其次是暖平流。在夏季风爆发后,潜热加热项的作用迅速增大至与正涡度平流项大小相当,这两项是引起区域平均气旋性涡度增加的最主要的物理因子;它们和暖平流项一起抵偿了辐散项和绝热项的负贡献,令季风区的气旋性涡度得以发展/维持。因此,正涡度平流是直接导致南海-西太平洋副热带反气旋脊迅速减弱最重要的物理因子。  相似文献   

Observational Diagnosis of Cloud Phase in the Winter Antarctic Atmosphere for Parameterizations in Climate Models     

Yong-Sang CHOI  Chang-Hoi HO  Sang-Woo KIM  Richard S. LINDZEN 《大气科学进展》2010,27(6):1233-1245

The cloud phase composition of cold clouds in the Antarctic atmosphere is explored using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instruments for the period 2000--2006. We used the averaged fraction of liquid-phase clouds out of the total cloud amount at the cloud tops since the value is comparable in the two measurements. MODIS data for the winter months (June, July, and August) reveal liquid cloud fraction out of the total cloud amount significantly decreases with decreasing cloud-top temperature below 0oC. In addition, the CALIOP vertical profiles show that below the ice clouds, low-lying liquid clouds are distributed over ～20% of the area. With increasing latitude, the liquid cloud fraction decreases as a function of the local temperature. The MODIS-observed relation between the cloud-top liquid fraction and cloud-top temperature is then applied to evaluate the cloud phase parameterization in climate models, in which condensed cloud water is repartitioned between liquid water and ice on the basis of the grid point temperature. It is found that models assuming overly high cut-offs (》-40oC) for the separation of ice clouds from mixed-phase clouds may significantly underestimate the liquid cloud fraction in the winter Antarctic atmosphere. Correction of the bias in the liquid cloud fraction would serve to reduce the large uncertainty in cloud radiative effects.  相似文献   

Preliminary Results of the Ground-Based Orographic Snow Enhancement Experiment for the Easterly Cold Fog （Cloud） at Daegwallyeong during the 2006 Winter     

Myoung-Joo LEE  Ki-Ho CHANG  Gyun-Myoung PARK  Jin-Yim JEONG  Ha-Young YANG  Ki-Deok JEONG  Joo-Wan CHA  Sung-Soo YUM  Jae-Cheol NAM  Kyungsik KIM  Byung-Chul CHOI 《大气科学进展》2009,26(2):222-228

The snow enhancement experiments, carried out by injecting AgI and water vapor into orographically enhanced clouds (fog), have been conducted to confirm Li and Pitter’s forced condensation process in a natural situation. Nine ground-based experiments have been conducted at Daegwallyeong in the Taebaek Mountains for the easterly foggy days from January–February 2006. We then obtained the optimized condi- tions for the Daegwallyeong region as follows: the small seeding rate (1.04 g min-1) of AgI for the easte...  相似文献   

The Quasi-Stationary Field in the Even-Charged Body Model of Seismic Electromagnetic Signals     

Bao Dexiu  Pan Erda  Luo Yaohuang  Wu Yonghan  and Zhang Shu Department of Physics of Yunnan University  Kunming  China 《中国地震研究》1996,(1)

Analytic expressions of a quasi-stationary field caused by an even-charged body in a three-layer medium are obtained from an electrostatic field.Analysis and studies on it are carried out to obtain some guiding results in observing and analyzing seismic electromagnetic precursor indications.  相似文献   

Three-Dimensional Numerical Model for Tsunami Propagation Passing Through An Obstacle     

Sung Jin HONG Byung Ho CHOI Fumihiko IMAMURA 《中国海洋工程》2006,20(3):509-516

1 .Introduction In the present numerical analysis of a tsunami ,atwo-dimensional numerical model based on non-linear shallowwater theoryis mainly used (Aburaya and Imamura ,2002 ;Imamura ,1995 ; Goto andOgawa ,1992) .Thoughthis model representstsunami hei…  相似文献   

Geochemical Evolution of Hydrothermal Fluids at the Daejang Cu–Zn–Pb Vein Deposit, Korea     

Sang Hoon CHOI 《Resource Geology》1998,48(3):171-182

Abstract: The Daejang mine is located within the Cretaceous Gyeongsang basin. Mineral paragenesis can be divided into four stages (stages I, II, III and IV) by major tectonic fracturing. Stages I, III and IV are economically barren. Stage II, at which the precipitation of major ore minerals occurred, is further divided into three substages with paragenetic time based on minor fractures and discernible mineral assemblages: substage IIa, marked by deposition of quartz and Fe–sulfides; substage IIb, by introduction of base-metal sulfides within carbonates and some quartz; substage IIc, by quartz and carbonates with various sulfosalts. Fluid inclusion data indicate a complex geochemical evolution of hydrothermal fluids. Both CO₂–rich and H₂O–rich fluids were trapped in fluid inclusions at stage I and substage IIa. It is suggested that a compositionally heterogeneous fluid was formed by fluid boiling and CO₂ immiscibility at temperatures of about 400° to 300°C. Composite lodes of base-metal sul–fides, carbonates and quartz at substage IIb were deposited in open spaces created by fracturing. The fracturing event prompted rapid decreases in pressure and temperature of residual fluids and resulted in retrograde fluid boiling at about 200 bars and 300°–250°C during substage IIb. The progressive loss of CO₂ by CO₂ effervescence and retrograde boiling from substage IIa and IIb fluids resulted in pH increase and related increase in carbonate activity, causing deposition of abundant carbonates. The change in pH also caused the decrease of stability of hydrogen sulfide with Cu, Zn and Pb chloride complexes (as main transporting agents at Daejang) and resulted in the pricipitation of base-metal minerals. Deposition of Ag– and Sb-bearing sul–fides and sulfosalts of substage IIc occurred at temperatures of about 250° to 150°C from a dominantly aqueous fluid with low salinity (down to 3. 0 equiv. wt % NaCl). At this substage, aqueous fluid formed by mixing with cooler and less saline meteoric groundwater. There is a systematic decrease in caculated δ¹⁸O_water values with the mineralization stage (and decreasing temperature) in the Daejang hydrothermal system, from values of about 11% for stage I, through about 4% for stages II and III, to about –3 per mil for stage IV. The result of stable isotope and fluid inclusion studies are interpreted to indicate progressive less evolved and/or unexchanged meteoric water influx of an early hydrothermal system formed by highly evolved meteoric waters.  相似文献   

Geochemistry of peridotite xenoliths in alkali basalts from Jeju Island, Korea   总被引：1，自引：0，他引：1  

SEONG HEE  CHOI  JONG IK  LEE  CHUNG-HWA  PARK  JACQUES  MOUTTE 《Island Arc》2002,11(4):221-235

Abstract   Ultramafic xenoliths in alkali basalts from Jeju Island, Korea, are mostly spinel lherzolites with subordinate amounts of spinel harzburgites and pyroxenites. The compositions of major oxides and compatible to moderately incompatible elements of the Jeju peridotite xenoliths suggest that they are residues after various extents of melting. The estimated degrees of partial melting from compositionally homogeneous and unfractionated mantle to form the residual xenoliths reach 30%. However, their complex patterns of chondrite-normalized rare earth element, from light rare earth element (LREE)-depleted through spoon-shaped to LREE-enriched, reflect an additional process. Metasomatism by a small amount of melt/fluid enriched in LREE followed the former melt removal, which resulted in the enrichment of the incompatible trace elements. Sr and Nd isotopic ratios of the Jeju xenoliths display a wide scatter from depleted mid-oceanic ridge basalt (MORB)-like to near bulk-earth estimates along the MORB–oceanic island basalt (OIB) mantle array. The varieties in modal proportions of minerals, (La/Yb)_N ratio and Sr-Nd isotopes for the xenoliths demonstrate that the lithospheric mantle beneath Jeju Island is heterogeneous. The heterogeneity is a probable result of its long-term growth and enrichment history.  相似文献   

Wintertime suspended sediment simulation in the Huanghai and East China Seas   总被引：1，自引：0，他引：1  

CHOI Byung Ho  MUN Jong Yoon  KO Jin Seok 《海洋学报(英文版)》2005,24(1):46-59

A simulation of suspended sediment movement relating to tidal and wave forcing during a winter monsoon in November 1983 in the Huanghai and East China Seas continental shelf is attempted by using the model describing the cohesive/non-cohesive sediment resuspension generated by interactions between currents and waves.model simulation showed that sediment concentration was increased by resuspension at shallow depths during the strong storm conditions due to high bottom stress interacted between currents and waves. This result is in general agreement with observations in horizontal distribution of suspended sediment distribution.At three current meter mooring positions off the southern Shandong Peninsula resuspension occurred only at a depth of 22m,nearest coastal position and at deeper parts at depths of 51 and 80m wave-current interaction effects were not significant. It has shown that the present model simulation demonstrated the capability of reproduction of suspended sediment movement under wintertime extreme event reasonably well.  相似文献