Impact test simulations of stiffened plates using the micromechanical porous plasticity model     

Joonmo Choung  Sang-Rai Cho  Kyung Su Kim 《Ocean Engineering》2010,37(8-9):749-756

This paper first reviews the physical meanings and the expressions of two representative strain rate models: CSM (Cowper–Symonds model) and JCM (Johnson–Cook model). Since it is known that the CSM and JCM are suitable for low-intermediate and intermediate-high rate ranges, many studies regarding marine accidents such as ship-to-ship collisions, ship-to-rock groundings, and explosions in FPSO have employed the former in particular. A formula to predict the material constant of the CSM is introduced from a literature survey. The validity of the formula is proved by comparing with strain rate test results of high strength marine structural steels of DH-36. Numerical simulations with two different material constitutive equations, the classical metal plasticity model based on the von Mises yield function and the micromechanical porous plasticity model based on the Gurson yield function, have been carried out for stiffened plates under impact loading. It is concluded that the porous plasticity model with the porosity fracture criterion can quantitatively predict plastic deformation process and final fracture under impact loading if the material constants are properly chosen.  相似文献   

Analytical solutions for long waves over a circular island     

Tae-Hwa Jung  Changhoon Lee  Yong-Sik Cho 《Coastal Engineering》2010

In this study, we derive an analytical solution for long waves over a circular island which is mounted on a flat bottom. The water depth on the island varies in proportion to an arbitrary power, γ, of the radial distance. Separation of variables, Taylor series expansion, and Frobenius series are used to find the solutions, which are then validated by comparing them with previously developed analytical solutions. We also investigate how different wave periods, radii of the island toe, and γ values affect the solutions. For a circular island with a small value of γ (e.g. γ = 2/3, as in the equilibrium beach (Bruun, 1954)), the wave rays approaching near the island center reach the coastline, whereas the rays approaching away from the center bend away from the coastline, leading to smaller wave amplitudes along the coast. However, for a circular island with a large value of γ, e.g. γ = 2, all the rays on the island reach the coast, giving large coastline wave amplitudes. If the island domain is small compared to the wavelength, the wave amplitudes on the coastline do not increase significantly; however, when the island domain is not small, the wave amplitudes increase significantly. If γ is also large, the amplitudes can be so large as to cause a disaster on the island.  相似文献   

A new type of troposphere zenith path delay product of the international GNSS service   总被引：3，自引：2，他引：1  

Sung H. Byun  Yoaz E. Bar-Sever 《Journal of Geodesy》2009,83(3-4):1-7

The International GNSS Service (IGS) has been producing the total troposphere zenith path delay (ZPD) product that is based on combined ZPD contributions from several IGS Analysis Centers (AC) since GPS week 890 in 1997. A new approach to the production of the IGS ZPD has been proposed that replaces the direct combination of diverse ZPD products with point positioning estimates using the IGS Combined Final orbit and clock products. The new product was formally adopted in 2007 after several years of concurrent production with the legacy product. We describe here the advantages of the new approach for the IGS ZPD product, which enhance the value of the new ZPD product for climate studies. We also address the impact the IGS adoption in November 2006 of new GPS antenna phase center standards has had on the new ZPD product. Finally we describe plans to further enhance the ZPD products.  相似文献   

A comparative study for the fatigue assessment of a ship structure by use of hot spot stress and structural stress approaches     

Myung Hyun Kim  Seong Min Kim  Sung Geun Kim  Gyeong Rae Kim 《Ocean Engineering》2009,36(14):1067-1072

Recently, a mesh-size insensitive structural stress definition (Battelle structural stress method) has been proposed. This method gives a stress state at a weld toe with a relatively coarse mesh, such as up to 2t (t=plate thickness) or irregular mesh shapes. The structural stress definition is based on the elementary structural mechanics theory and provides an effective measure of a stress state in front of a weld toe. In this present study, a fatigue strength assessment was carried out for a side shell connection of a container vessel using both the hot spot stress and the structural stress methods. A consistent approach to computing extrapolated hot spot stress for design purposes based on converged hot spot stresses is described and current fatigue guidance is evaluated. Fatigue strength predicted by the two methods, i.e. hot spot stress and structural stress approaches, at hot spot locations of a typical ship structure are compared and discussed.  相似文献   

Assimilation of sea surface temperature in the Northwest Pacific Ocean and its marginal seas using the ensemble Kalman filter   总被引：2，自引：0，他引：2  

Gwang-Ho Seo  Byoung-Ju Choi  Yang-Ki Cho  Young Ho Kim  Sangil Kim 《Ocean Science Journal》2010,45(4):225-242

Satellite-borne sea surface temperature (SST) data were assimilated with the ensemble Kalman filter (EnKF) in a Northwest Pacific Ocean circulation model to examine the effect of data assimilation. The model domain included the northwestern part of the Pacific Ocean and its marginal seas, such as the Yellow Sea and East/Japan Sea. The performance of the data assimilation was evaluated by comparing the simulated ocean state with that observed. Spatially averaged root-mean-squared errors in the SST and sea surface height (SSH) decreased by 0.44 °C and 4 cm, respectively, by the assimilation. The results of the numerical experiments substantiated the effectiveness of the SST assimilation via the EnKF for all marginal seas, as well as the Kuroshio region. The benefit of the data assimilation depended on the characteristics of each marginal sea. The variation of the SST in the East/Japan Sea and the Kuroshio extension (KE) region were improved 34% and those in the Yellow Sea 12.5%. The variation of the SSH was improved approximately 36% in the KE region. This large improvement was achieved in the deep-water regions because assimilation of SST data corrected the separation point of the western boundary currents, such as the Kuroshio and the East Korea Warm Current, and the associated horizontal surface currents. The SST assimilation via the EnKF also improved the subsurface temperature profiles. The effectiveness of SST assimilation was seasonally dependent, with the improvement being relatively larger in winter than in summer, which was related to the seasonal variation of the vertical mixing and stratification in the ocean surface layer.  相似文献   

The effects of the M/V Sea Prince accident on maritime safety management in Korea   总被引：1，自引：0，他引：1  

Dong-Oh Cho   《Marine Policy》2007,31(6):730-735

The Sea Prince accident was the first VLCC accident in Korea and a shock to the general public and government. Before the accident, any oil-spill management plan, such as National contingency plan (NCP) and regional contingency plans (RCPs), was not available and the resources for oil spills were lacking for the Sea Prince accident. About 5000 tons of oil spilled, polluting large areas of southern coastal waters, damaging the fisheries, including aquaculture. After the Sea Prince accident, Korea's government established various alternatives for dealing with oil spills, such as the NCP, RCPs, Typhoon Refuge Management Plan, and resources for oil-spill response. However, port safety management in emergency situations such as typhoons has not been solved.  相似文献   

Ediacaran mafic magmatism recorded in Cambrian eclogites of the Ross orogen,Antarctica: Implications for the Neoproterozoic rifting episodes along the Pacific-Gondwana margin     

Taehwan Kim  Yoonsup Kim  Wonseok Cheong  Moonsup Cho  Jong Ik Lee 《地学学报》2023,35(1):32-40

We report the first finding of Ediacaran mafic magmatism in northern Victoria Land of the Ross orogen, Antarctica, based on ca. 600–590 Ma magmatic zircon cores in Cambrian eclogites. The mafic magmatism could be either linked to ca. 615–590 Ma incipient convergent margin magmatism in central segment of the Ross orogen, or ca. 600–580 Ma continental rift-related volcanism widespread in eastern Australia. The latter is preferred based on the trace-element compositions distinctive from those of arc-related basalts and the depleted mantle-like Hf isotopic compositions of zircon. Our results suggest dual rifting episodes during both the Ediacaran and Cryogenian (ca. 670–650 Ma) in the East Antarctic margin, correlative with those in eastern Australia. A spatial distribution of coeval rifting and subduction along the Ediacaran margin of East Antarctica is readily accounted for by rift inheritance; the upper- and lower-plate geometry resulting from detachment and transform faulting.  相似文献   

A preliminary study of natural environmental change and its impact on early Late Paleolithic people in the northeast central Korean Peninsula during Marine Istope Stage 3 (40–30k cal a bp)     

Sangheon Yi  Chang-Gyun Han  Keun-Chang Oh  In Sun Seo  Dongwook Kim  Jaeyoung Lee  Min Han  Hanwoo Choi  Jaesoo Lim  Sujeong Park  Chang-Pyo Jun  Taesop Cho 《第四纪科学杂志》2022,37(1):100-113

We comprehensively analyzed sediments obtained from an archeological excavation. A trench sediment profile of Maedun Cave (MC), South Korea, was analyzed geoarchaeologically. Multi-proxy analyses (palynomorphs, grain size, magnetic susceptibility, animal bones and artifacts) reflected the vegetation, hydroclimate and lives of prehistoric people at Marine Isotope Stage (MIS) 3 (ca. 40–30k cal a bp ) in the early Late Paleolithic. The palynoflora consisted of pollen and non-pollen palynomorphs. Under the air-circulation system in the cave, anemophilous pollen flowed in during the day, whereas waterborne pollen and spores, and freshwater algae, were transported by flooding during the summer monsoon rainy season. Mixed conifer and deciduous broad-leaved forest with an understory of pteridophytes flourished around the north-east central Korean Peninsula during MIS 3. Freshwater algae and grass pollen records may reflect precipitation intensity. It is assumed that they had flowed in during flooding caused by high precipitation during the enhanced East Asian summer monsoon, corresponding to Dansgaard–Oeschger (D/O) events 5 and 8 of δ¹⁸O GISP2 and Hulu Cave. The prehistoric people hunted herbivorous animals in the area around MC and sheltered inside it seasonally. They also used the grains of oats growing near the dwelling as a source of food.  相似文献