• Ocean and Polar Research
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• 제40권3호
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• pp.127-143
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• 2018

This study analyzed the influence of climate change on the spawning ground area of the common squid, Todarodes pacificus. To estimate long term changes in the area of the spawning ground of the common squid, water temperature at 50 m deep that can be inferred from sea surface temperature (SST) based on both NOAA/AVHRR (1981.07-2002.12) and MODIS/AQUA (2003.01-2009.12) ocean color data was analyzed. In addition, five climate indices, Arctic Oscillation Index (AO), Siberian High Index (SH), Aleutian Low Pressure Index (ALP), East Asia Winter Monsoon Index (EAWM) and Pacific Decadal Oscillation (PDO) which are the main indicators of climate changes in the northwestern Pacific were used to study the relationship between the magnitude of the estimated spawning ground and climate indices. The area of the estimated spawning ground was highly correlated with the total catch of common squid throughout four decades. The area of the estimated spawning ground was negatively correlated with SH and EAWM. Especially, PDO was negatively correlated with the area of the spawning ground in the northwestern Pacific (r = -0.39) and in the southern part of the East Sea (r = -0.38). There was a positive relationship between the AO and the area of the spawning ground in the northwestern Pacific (r = 0.46) as well as in the southern part of the East Sea (r = 0.32). Temporally, the area of the winter spawning ground in the southern part of the East Sea in the 1980s was smaller than those areas in the 1990s and 2000s, because the area was disconnected with the western coastal spawning ground of Japan in the 1980s, while the area had been made wider and more continuous from the Korea strait to the western coastal water of Honshu in the 1990s and 2000s.

• Journal of Welding and Joining
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• 제33권1호
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• pp.35-40
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• 2015

Recently, there have been the increase of ship size and the development of oil and gas in arctic region. These trends have led to the requirements such as high strength, good toughness at low temperature and good weldability for prevent of brittle fracture at service temperature. There has been the key issue of crack arrestability in large size structure such as container ship. In this report for the first time, crack arrest toughness of thick steel plate welds was evaluated by large scale ESSO test for estimate of brittle crack arrestability in thick steel plate. For large structures using thick steel plates, fracture toughness of welded joint is an important factor to obtain structural integrity. In general, there are two kinds of design concepts based on fracture toughness: crack initiation and crack arrest. So far, when steel structures such as buildings, bridges and ships were manufactured using thick steel plates (max. 80~100mm in thickness), they had to be designed in order to avoid crack initiation, especially in welded joint. However, crack arrest design has been considered as a second line of defense and applied to limited industries like pipelines and nuclear power plants. Although welded joint is the weakest part to brittle fracture, there are few results to investigate crack arrest toughness of welded joint. In this study, brittle crack arrest designs were developed for hatch side coaming of large container ships using arrest weld, hole, and insert technology.

• 한국제4기학회지
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• 제25권2호
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• pp.1-15
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• 2011

국제공동해양시추사업(Ocean Drilling Program: ODP)는 DSDP, IPOD 그리고 현재의 IODP 등의 여러 가지 이름으로 바뀌어 왔지만 공고한 국제협동을 통해 지구과학의 발전에 크게 기여하여 왔다. 약 10 년 전에 시작된 IODP는 이제 2013년부터 2단계로 진입하면서 더욱더 견고한 국제협력, 새로운 과학 영역에 대한 도전, 그리고 새로운 과학적 목표를 향해 발전해 나갈 것이다. 이 논문은 그동안 수행된 ODP탐사로 얻어진 탁월한 연구성과와 새롭게 출범되는 IODP의 구조와 새로운 과학영역을 한층 발전시키기 위해 필요한 역할에 대해 정리하였다. 특히 2단계로 접어드는 IODP에서는 현재까지 이루어지지 않았던 북극해와 같은 지역에 대한 조사와 심해 생물권(biosphere) 등 미생물 영역에 대한 연구, 기후변화에 대한 연구가 더욱 활성화 될 것으로 기대된다. 이처럼 IODP는 가맹국들의 강력한 국제협력을 통해 IODP는 앞으로도 지구과학의 발전에 중요한 역할을 할 것으로 생각된다.

• 한국해양공학회지
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• 제29권6호
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• pp.454-462
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• 2015

An extended study was conducted on the fracture criterion by Choung et al. (2011; 2012) and Choung and Nam (2013), and the results are presented in two parts. The theoretical background of the fracture and the results of new experimental studies were reported in Part I, and three-dimensional fracture surface formulations and verifications are reported in Part II. How the corrected true stress can be processed from the extrapolated true stress is first introduced. Numerical simulations using the corrected true stress were conducted for pure shear, shear-tension, and pure compression tests. The numerical results perfectly coincided with test results, except for the pure shear simulations, where volume locking appeared to prevent a load reduction. The average stress triaxialities, average normalized lode parameters, and equivalent plastic strain at fracture initiation were extracted from numerical simulations to formulate a new three-dimensional fracture strain surface. A series of extra tests with asymmetric notch specimens was performed to check the validity of the newly developed fracture strain surface. Then, a new user-subroutine was developed to calculate and transfer the two fracture parameters to commercial finite element code. Simulation results based on the user-subroutine were in good agreement with the test results.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권4호
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• pp.301-311
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• 2016

This paper describes the whole procedures to determine ice-induced global loads on the ship using measured full-scale data in accordance with the method proposed by the Canadian Hydraulics Centre of the National Research Council of Canada. Ship motions of 6 degrees of freedom (dof) are found by processing the commercial sensor signals named Motion Pak II under the assumption of rigid body motion. Linear accelerations as well as angular rates were measured by Motion Pak II data. To eliminate the noise of the measured data and the staircase signals due to the resolution of the sensor, a band pass filter that passes frequencies between 0.001 and 0.6 Hz and cubic spline interpolation resampling had been applied. 6 dof motions were computed by the integrating and/or differentiating the filtered signals. Added mass and damping force of the ship had been computed by the 3-dimensional panel method under the assumption of zero frequency. Once the coefficients of hydrodynamic and hydrostatic data as well as all the 6 dof motion data had been obtained, global ice loads can be computed by solving the fully coupled 6 dof equations of motion. Full-scale data were acquired while the ARAON rammed old ice floes in the high Arctic. Estimated ice impact forces for two representative events showed 7e15 MN when ship operated in heavy ice conditions.

• 수산해양교육연구
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• 제29권2호
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• pp.612-625
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• 2017

To grasp the algal vegetation using the occurred species number, biomass and dominant species, this study was performed in the subtidal zone of Muan-gun, in the intertidal zone of Jindo-gun and in the intertidal zone and subtidal zone of Geomundo, the south-eastern coast of Jeollanamdo, Korea in the spring 2014. The total occurred species was 140 ones including 10 chlorophytes(7.14%), 54 phaeophytes(38.57%) and 76 rhodophytes(54.29%); the biomass was $70,484g{\cdot}w{\cdot}w/m^2$ in total. The flora charateristic using R/P ratio, geographical distribution pattern of algae, at the Station 9-1(intertidal zone) in Geomundo was tropical; the flora at the Station 6 (Maengseong-ri, Sanjodo, Jindo-gun) and the Station 9-2(subtidal zone) in Geomundo were mixed; the others were arctic to temperate. The physiognomic types were also shown. Each species was classified into six functional-form groups, and two ecological state groups(ESG) were evaluated based on these groups. The coarsely branched-group of functional-form groups was 44% of total occurred species. The ESG II in all study sites was high, and this is maybe due to the environmental stress such as pollution and disturbance, etc.

• 한국해양공학회지
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• 제30권4호
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• pp.277-286
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• 2016

The first part of this study found the tendencies of the mechanical properties of two arctic structural steels (EH32 and FH32). In the second part, the crashworthiness of stiffened panels scaled down from the side frame structure of a Korean research icebreaker was determined. A procedure for designing the shapes and sizes of the stiffened panels, mass and shape of a drop striker, and a large temperature chamber, and then manufacturing these, is introduced in detail. From impact bending tests for the stiffened panels, the residual permanent deformations and deformation histories over time were captured using manual measurement and video image analyses. Numerical simulations of the impact bending tests were carried out for three different finite element models, which were mainly composed of shell elements, solid elements, and solid elements, with welding beads. It was proven from a comparison of the test results and numerical simulation results that the solid element model with the welding bead consideration approached the test results in terms of the residual deformations as long as the strain rate effect was taken into account.

• 한국해양공학회지
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• 제22권2호
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• pp.42-49
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• 2008

Recently many countries have become interested in the development of cold or arctic regions. The construction of engineered structures in those regions demands an understanding of the deformation characteristics of frozen soil. However, an understanding of frozen soil behavior poses difficult problems owing to the complex interaction between the soil particles and the ice matrix. In this research, a series of laboratory tests was performed to investigate the variations in the unconfined compression strength and split tensile strength of weathered granite soil and mixed soil (standard sand and kaolinite) in 15 degrees below zero environments. In the frozen soil tests, specimens were prepared with various water and clay contents, and then the interrelationships between four factors (water content, clay content, unconfined compression strength, split tensile strength) were analyzed. The test results were summarized as follows; as the water content was increased, the unconfined compressive and split tensile strengths also increased in frozen soil. However as the clay content was increased, the unconfined compressive and split tensile strengths were lowered. In the case of frozen soil that contained little clay content, the strength decreased rapidly in mixed soil (standard sand and kaolinite) when the frozen specimen was broken. On the other hand, in the cases of mixed soil that contained a high clay content and weathered granite soil, the strength decreased relatively slowly.

• 대한조선학회논문집
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• 제53권2호
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• pp.85-91
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• 2016

The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

• 대기
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• 제32권3호
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• pp.207-221
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• 2022

In Jeju, on January 23, 2016, a cold surge accompanied by heavy snowfall with the most significant amount of 12 cm was the highest record in 32 years. During this period, the temperature of 850 hPa in January was the lowest in 2016. Notably, in 2016, the average surface temperature of January on the Polar cap was the highest since 1991, and 500 hPa geopotential height also showed the highest value. With this condition, the polar vortex in the northern hemisphere meandered and expanded into the subtropics regionally, covering the Korean Peninsula with very high potential vorticity up to 7 Potential Vorticity Unit. As a result, the strong cold advection, mostly driven by a northerly wind, around the Korean Peninsula occurred at over 2𝜎. Previous studies have not addressed this extreme synoptic condition linked to polar vortex expansion due to the unprecedented Arctic warming. We suggest that the occurrence of a strong Ural blocking event after the abrupt warming of the Barents/Karas seas is a major cause of unusually strong cold advection. With a specified mesoscale model simulation with SST (Sea Surface Temperature), we also show that the warmer SST condition near the Korean Peninsula contributed to the heavy snowfall event on Jeju Island.