• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.349-349
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• 2017

표준강수지수(Standardized precipitation index, SPI)는 가장 널리 사용되고 있는 가뭄지수로, 우리나라 뿐만 아니라 세계기상기구(World Meteorological Organization)에서도 추천하고 있는 대표적인 기상학적 가뭄 지수라고 할 수 있다. 현재 표준강수지수는 2변수 gamma 분포를 적용하여 강수 부족 상황을 지수화하여 나타내고 있는데, 일부 연구에서는 다른 확률분포형의 적용하기도 하였다(Guttman, 1999; Lloyd-Hughes and Saunders, 2002; Stagge et al., 2015). 우리나라에서는 유원희(2000)에 의해 Pearson type 3, 2변수 gamma, generalized logistic, GEV, 3변수 log-normal 분포에 따른 SPI 산정 결과를 비교한 연구가 수행되었는데, SPI 산정에는 분포형별 차이가 뚜렷하지 않다는 결론을 얻었다. 그러나 이때 금강유역 내 지점에 국한하여 적용하였고, 분포형별 적합도 검정을 수행하지 않고 SPI 산정결과만을 비교하여 우리나라에 일반적으로 적용하기에는 어려움이 있다. 따라서 본 연구에서는 우리나라의 강우특성을 반영할 수 있도록 다양한 확률분포형을 고려하여 표준강수지수를 분석하고자 한다. 이를 위해 관측기간이 30년 이상인 기상관측소의 월단위 강우자료를 구축하고, 월단위 강우자료에 다양한 확률분포형을 적용하고자 한다. 이때 적용하는 확률분포형은 2변수 gamma, Gumbel, normal 분포이다. 적정 확률분포형 선정을 위해 적합도 검정을 수행하고자 한다. 또한 각 분포형별로 산정된 표준강수지수를 기존 표준강수지수와 비교검토하고자 한다.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.2
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• pp.108-114
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• 2016

Recently, there has been a growing interest in marine leisure sports and high speed power boat for fishing. The prototype of 20 feet class power boat was developed and authors are joined in this government-led project. The research was performed to evaluate the optimal structure and design of the structural strength necessary to ensure the structural safety of the power boat. A new material ROCICORE fiber added to the mat and roving was adopted for high-power tenacity. ANSYS Workbench has been used to make the structural model, evaluate the strength and optimize the structural design. The response of the structure to quasi-static slamming loads according to the rules and regulations of ISO 12215-5, Lloyd’s Register of Shipping and Korean Register has been implemented and studied. An optimization study for the structural response is carried out by changing the plate thickness and section modulus of stiffeners. The power boat structure derived fuel efficiency is optimized by performing the best possible structural design to minimize the hull weight.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.5
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• pp.703-708
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• 2010

Recently, the development of the Marina port is determined as a national plan, and a variety of leisure boats and facilities on the field has been of critical interest. In particular, yachts are designed and produced mostly at small shipbuilding companies and research institute. The regulation and historic data, however, about the safety of structure are not readily available. Therefore, it is required to evaluate the strength of ship structure. This paper deals with the estimation of local strength of 40 feet sailing yacht by using finite element analysis. The forebody, mast and connection parts of a FRP yacht structure are evaluated. In addition, the results are compared with the regulation of Lloyd's register and Korean register.

• International Journal of Naval Architecture and Ocean Engineering
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• v.1 no.1
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• pp.39-49
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• 2009

The use of high-strength aluminum alloys is increasing in shipbuilding industry, particularly for the design and construction of war ships, littoral surface craft and combat ships, and fast passenger ships. While various welding methods are used today to fabricate aluminum ship structures, namely gas metallic arc welding (GMAW), laser welding and friction stir welding (FSW), FSW technology has been recognized to have many advantages for the construction of aluminum structures, as it is a low-cost welding process. In the present study, mechanical properties of friction stir welded aluminum alloys are examined experimentally. Tensile testing is undertaken on dog-bone type test specimen for aluminum alloys 5083 and 5383. The test specimen includes friction stir welded material between identical alloys and also dissimilar alloys, as well as unwelded (base) alloys. Mechanical properties of fusion welded aluminum alloys are also tested and compared with those of friction stir welded alloys. The insights developed from the present study are documented together with details of the test database. Part of the present study was obtained from the Ship Structure Committee project SR-1454 (Paik, 2009), jointly funded by its member agencies.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.458-465
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• 2018

Ice-going ships such as icebreakers, icebreaking tankers, and icebreaking LNG carriers are subjected to wave loads in open water and ice loads in ice-covered water. In terms of the ship's structural design, the local ice load is important. The fatigue failure due to repeated ice loads is also important. ISO 19906 specifies the assessment of the fatigue limit for a polar offshore structures. In addition, Lloyd's Register refers to fatigue damage based on ShipRight FDA ICE. In ShipRight FDA ICE, the fatigue damage indices due to wave and ice loads are simply presented as 0.5 for each load. It also states that the sum of the two fatigue damage indices should not exceed one. This study calculated and analyzed the fatigue damage index and fatigue life considering ARAON's voyage schedules and the assumed Antarctic voyage based on data measured during the Arctic voyage of ARAON in 2010.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.143-153
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• 2019

In this study, numerical simulations for the prediction of added resistance for KVLCC2 with varying wave steepness are performed using a Computational Fluid Dynamics (CFD) method and a 3-D linear potential method, and then the non-linearities of added resistance and ship motions are investigated in regular short and long waves. Firstly, grid convergence tests in short and long waves are carried out to establish an optimal mesh system for CFD simulations. Secondly, numerical simulations are performed to predict ship added resistance and vertical motion responses in short and long waves and the results are verified using the available experimental data. Finally, the non-linearities of added resistance and ship motions with unsteady wave patterns in the time domain are investigated with the increase in wave steepness in both short and long waves. The present systematic study demonstrates that the numerical results have a reasonable agreement with the experimental data and emphasizes the non-linearity in the prediction of the added resistance and the ship motions with the increasing wave steepness in short and long waves.

• Nuclear Engineering and Technology
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• v.51 no.2
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• pp.510-517
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• 2019

Increasing proliferation resistance of plutonium by way of increased $^{238}Pu$ content is of interest to the nuclear nonproliferation and international safeguards community. Considering the high alpha decay heat of $^{238}Pu$, increasing the isotopic fraction leads to a noticeably higher amount of heat generation within the plutonium. High heat generation is especially unattractive in the scenario of weaponization. Upon weaponization of the plutonium, the plutonium may generate enough heat to elevate the temperature in the high explosives to above its self-explosion temperature, rendering the weapon useless. In addition, elevated temperatures will cause thermal expansion in the components of a nuclear explosive device that may produce thermal stresses high enough to produce failure in the materials, reducing the effectiveness of the weapon. Understanding the technical limit of $^{238}Pu$ required to reduce the possibility of weaponization is key to reducing the current limit on safeguarded plutonium (greater than 80 at. % $^{238}Pu$). The plutonium vector evaluated in this study was found by simulating public information on Lightbridge's fuel design for pressurized water reactors. This study explores the temperature profile and maximum stress within a simple (first generation design) hypothetical nuclear explosive device of four unique scenarios over time. Analyzing the transient development of both the temperature profile and maximum stress not only establishes a technical limit on the $^{238}Pu$ content, but also establishes a time limit for which each scenario would be useable.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.4
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• pp.31-38
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• 2021

In this paper, we proposed an optimal design for determining the shape of a lifting lug freely by applying a multivariate function to the D-type lug, which is commonly used in shipyards. We derived the optimal aspect ratio of the lug through structural analysis and analyzed the safety and behavior of the lug aspect ratio. As a result, two types of final candidates, both lighter than the existing lug weight, were suitable for the ratio. They were found to have the greatest force at an angle of 45 degrees when a load of 100 tons was imposed. When the horizontal and vertical feature ratio of the lug was 1:3, it showed excellent results in terms of safety rates while maintaining weight reduction and functional aspects.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.34 no.4
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• pp.95-102
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• 2018

In this study, existential thoughts in Frank Lloyd Wright's notion of nature were investigated. Wright, a modern architect, presented the idea of creating organic architecture in harmony with nature. His naturalistic romanticism is considered to be the original inspiration for his concept of organic architecture. However, his understanding of architecture in harmony with nature stems from existential ideas in his notion of nature, including humanity. The proposed study analyzes his existential beliefs through his speeches and writings in four categories-love of nature, thoughts of abstract and concrete, nature as being intrinsic and "becoming," and thoughts on science and art. Our analyses reveal that, on the one hand, Wright was inspired by thoughts of naturalistic romanticism born from his disillusionment with city life and an urge to seek life in nature, while, on the other, he also believed that real nature is intrinsic to humans and manifests itself in the very core of their being. He sought to unite humanity, as the interior of nature, with its physical environment, as the exterior of nature. His notion of nature is a "becoming" one that changes with time and space, and varies based on individual humans. In line with these thoughts, Wright sought to create forms not only with respect to mathematical dimensions, but also in consideration of human significance. He considered art and architecture to be born out of an integral thought as a process of humanization. To him, nature is interpreted by humans.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.3
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• pp.24-32
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• 2021

The size of container ships is increasing to increase the cargo loading capacity. However, container ships are limited in terms of the hull longitudinal strength. To overcome this limitation, brittle crack arrest steel can be used. This study was aimed at examining the influence of the heat input on the welding procedures of flux cored arc welding and submerged arc welding. In the experiment, the crack tip opening displacement test, which pertains to a parameter of fracture mechanics, was performed, and a 3-point bending tester was adopted. Based on the results, the crack measurement method was presented, and the stress expansion coefficient value for the pre-fatigue crack length was derived according to the heat input after the pre-cracking length was measured. It was noted that the heat input affected the crack tip opening displacement of brittle crack arrest steel.