• 한국해양공학회지
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• 제36권2호
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• pp.101-107
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• 2022

Dean (1965) proposed the use of the root mean square error (RMSE) in the dynamic free surface boundary condition (DFSBC) and kinematic free-surface boundary condition (KFSBC) as an error evaluation criterion for wave theories. There are well known wave theories with RMSE more than 1%, such as Airy theory, Stokes theory, Dean's stream function theory, Fenton's theory, and trochodial theory for deep-water waves. However, none of them can be applied for deep-water breaking waves. The purpose of this study is to provide a closed-form solution for deep-water waves with RMSE less than 1% even for breaking waves. This study is based on a previous study (Shin, 2016), and all flow fields were simplified for deep-water waves. For a closed-form solution, all Fourier series coefficients and all related parameters are presented with Newton's polynomials, which were determined by curve fitting data (Shin, 2016). For verification, a wave in Miche's limit was calculated, and, the profiles, velocities, and the accelerations were compared with those of 5^th-order Stokes theory. The results give greater velocities and acceleration than 5^th-order Stokes theory, and the wavelength depends on the wave height. The results satisfy the Laplace equation, bottom boundary condition (BBC), and KFSBC, while Stokes theory satisfies only the Laplace equation and BBC. RMSE in DFSBC less than 7.25×10^-2% was obtained. The series order of the proposed method is three, but the series order of 5^th-order Stokes theory is five. Nevertheless, this study provides less RMSE than 5^th-order Stokes theory. As a result, the method is suitable for offshore structural design.

• 대한정형외과학회지
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• 제56권6호
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• pp.540-545
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• 2021

슬개골 횡골절은 수술이 필요한 전위된 슬개골 골절의 가장 흔한 형태이다. 이러한 슬개골 횡골절은 골절선을 지나 평행하게 삽입된 Kirschner-강선이나 나사못에 장력대 강선을 추가적으로 고정한 기법이 흔히 사용된다. 그러나 고식적인 고정 방법의 경우 삽입된 강선이나 핀의 돌출에 의한 합병증이 흔히 발생한다. 이러한 합병증은 내고정물의 제거를 위한 추가적인 수술을 필요로 하고, 의료비 상승 및 슬관절의 기능 제한을 일으킬 수 있다. 이에 슬개골 횡골절에 대해 안정적인 고정력을 제공하고 수술 시 연부조직 손상을 최소화하여 골절부 혈류를 보존하고 수술 후 통증을 감소시키며, 내고정물에 의한 자극과 그에 따른 통증을 감소시켜 관절 운동 제한 발생 위험을 감소 시키는 최소 침습 부하 분산 경피적 슬개건 봉합술을 이용하여 치료한 사례들을 수술 술기와 함께 보고하고자 한다.

• Computers and Concrete
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• 제28권5호
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• pp.521-532
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• 2021

Present paper focuses on the modeling of size effect on the compressive strength of normal concrete with the application of Discrete Element Method (DEM). Test specimens with different size and shape were cast and uniaxial compressive strength test was performed on each sample. Five different concrete mixes were used, all belonging to a different normal strength concrete class (C20/25, C30/37, C35/45, C45/55, and C50/60). The numerical simulations were carried out by using the PFC 5 software, which applies rigid spheres and contacts between them to model the material. DEM modeling of size effect could be advantageous because the development of micro-cracks in the material can be observed and the failure mode can be visualized. The series of experiments were repeated with the model after calibration. The relationship of the parallel bond strength of the contacts and the laboratory compressive strength test was analyzed by aiming to determine a relation between the compressive strength and the bond strength of different sized models. An equation was derived based on Bazant's size effect law to estimate the parallel bond strength of differently sized specimens. The parameters of the equation were optimized based on measurement data using nonlinear least-squares method with SSE (sum of squared errors) objective function. The laboratory test results showed a good agreement with the literature data (compressive strength is decreasing with the increase of the size of the specimen regardless of the shape). The derived estimation models showed strong correlation with the measurement data. The results indicated that the size effect is stronger on concretes with lower strength class due to the higher level of inhomogeneity of the material. It was observed that size effect is more significant on cube specimens than on cylinder samples, which can be caused by the side ratios of the specimens and the size of the purely compressed zone. A limit value for the minimum size of DE model for cubes and cylinder was determined, above which the size effect on compressive strength can be neglected within the investigated size range. The relationship of model size (particle number) and computational time was analyzed and a method to decrease the computational time (number of iterations) of material genesis is proposed.

• Structural Engineering and Mechanics
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• 제85권5호
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• pp.679-691
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• 2023

Many codes allow designers to use the bending moment diagram computed by elastic analysis and modify it by a certain amount of moment redistribution (MR) to account for plastic behaviour of continuous beams. However, several researchers indicated that the MR at the ultimate limit state (𝛽_u) for some beams deviate significantly from the specified values of various codes. This paper examines the applicability of the provisions on 𝛽_u in ACI 318-19 and Eurocode 2 through numerical investigations and comprehensively explores the influencing factors. The results show that some parameters not considered in those codes influence 𝛽_u to a certain extent, where the ratio of tensile reinforcement ratio at intermediate support to tensile reinforcement ratio at midspan (𝜌_s1/𝜌_s2) and load type are crucial parameters to consider. The specific combination of these two parameters may make the codes overestimate or significantly underestimate the 𝛽_u. On the other hand, the yield state of both critical sections is found to have an important influence on the influence degree of each parameter on 𝛽_u. The yield conditions are investigated, and an empirical judgment equation is proposed. In addition, the influence laws of the critical parameters on 𝛽_u have been further proved by theoretical derivation. Finally, due to 𝜀_t is found to have a better linear correlation with 𝛽_u than x_u/d, equations as a function of 𝜀_t for predicting the 𝛽_u of continuous beams under the two loads are proposed, respectively.

• 산업경영시스템학회지
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• 제45권4호
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• pp.42-52
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• 2022

North Korea continues to upgrade and display its long-range rocket launchers to emphasize its military strength. Recently Republic of Korea kicked off the development of anti-artillery interception system similar to Israel's "Iron Dome", designed to protect against North Korea's arsenal of long-range rockets. The system may not work smoothly without the function assigning interceptors to incoming various-caliber artillery rockets. We view the assignment task as a dynamic weapon target assignment (DWTA) problem. DWTA is a multistage decision process in which decision in a stage affects decision processes and its results in the subsequent stages. We represent the DWTA problem as a Markov decision process (MDP). Distance from Seoul to North Korea's multiple rocket launchers positioned near the border, limits the processing time of the model solver within only a few second. It is impossible to compute the exact optimal solution within the allowed time interval due to the curse of dimensionality inherently in MDP model of practical DWTA problem. We apply two reinforcement-based algorithms to get the approximate solution of the MDP model within the time limit. To check the quality of the approximate solution, we adopt Shoot-Shoot-Look(SSL) policy as a baseline. Simulation results showed that both algorithms provide better solution than the solution from the baseline strategy.

• 열처리공학회지
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• 제36권5호
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• pp.311-317
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• 2023

An autofilter is a device that removes impurities contained in heavy fuel oil used in diesel engines of ships or power plants, and also automatically removes impurities accumulated in the filter through a reverse washing function. The reducer-integrated motor serves to rotate the filter at low speed to enable reverse automatic cleaning in the autofilter device. To achieve a low speed of 0.65 to 0.75 rpm in a reducer-integrated motor, a small motor that can operate at 97rpm at a rated voltage of 110 V and 112.5 rpm at 220 V is required. Additionally, a large gear ratio of 1/150 is required. To ensure the durability and reliability of these reducers, the strength of the gear must be evaluated at the design stage. In general, there is a limit to evaluating the stress and strain state according to the vibration characteristics acting on each gear in the driving state of the reducer through quasi-static analysis. Therefore, in this study, the operation characteristics of the auto filter's reducer-integrated motor were first analyzed using the rigid body dynamics analysis method. Then, this rigid body dynamics analysis model was extended to a flexible multibody dynamics analysis model to analyze the stress and strain states acting on each gear and evaluate the design feasibility of the gear.

• 한국ITS학회 논문지
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• 제22권1호
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• pp.39-51
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• 2023

본 연구에서는 헤도닉 모형을 활용하여 공공주택가격(복합재화)에 영향을 주는 변수들을 분리하여 각각의 변수들에 대한 영향을 분석하고자 한다. 이때 변수로 주차장(세대당 주차면수)을 포함하여 금전적 가치를 추정하고 시사점을 도출하고자 한다. 주차장을 비시장재화로 보고 공동주택에서 주차가 갖는 금전적 가치를 공동주택의 실거래가를 활용하여 추정하고 제시했다는 점에서 기존의 연구들과 차별성을 보인다. 하남시를 대상으로 분석한 결과, 주차 1면의 증가는 약 2,597만원~5,968만원의 가격상승에 영향을 주며, 이는 주차 1면에 대한 경제적 가치로 해석될 수 있다. 본 연구를 시작으로 주차장에 대한 지속적인 연구가 이루어진다면, 재정투자사업 평가를 과학적이고 객관적으로 수행하는데 도움이 될 것으로 기대된다.

• Earthquakes and Structures
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• 제22권5호
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• pp.503-515
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• 2022

This paper presents the development of seismic fragility curves for a precast reinforced concrete bridge instrumented with a structural health monitoring (SHM) system. The bridge is located near an active seismic fault in the Dominican Republic (DR) and provides the only access to several local communities in the aftermath of a potential damaging earthquake; moreover, the sample bridge was designed with outdated building codes and uses structural detailing not adequate for structures in seismic regions. The bridge was instrumented with an SHM system to extract information about its state of structural integrity and estimate its seismic performance. The data obtained from the SHM system is integrated with structural models to develop a set of fragility curves to be used as a quantitative measure of the expected damage; the fragility curves provide an estimate of the probability that the structure will exceed different damage limit states as a function of an earthquake intensity measure. To obtain the fragility curves a digital twin of the bridge is developed combining a computational finite element model and the information extracted from the SHM system. The digital twin is used as a response prediction tool that minimizes modeling uncertainty, significantly improving the predicting capability of the model and the accuracy of the fragility curves. The digital twin was used to perform a nonlinear incremental dynamic analysis (IDA) with selected ground motions that are consistent with the seismic fault and site characteristics. The fragility curves show that for the maximum expected acceleration (with a 2% probability of exceedance in 50 years) the structure has a 62% probability of undergoing extensive damage. This is the first study presenting fragility curves for civil infrastructure in the DR and the proposed methodology can be extended to other structures to support disaster mitigation and post-disaster decision-making strategies.

• 융합보안논문지
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• 제22권2호
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• pp.3-8
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• 2022

보안 위협은 외부에서 발생하기도 하지만 내부에서 발생하는 비율이 더 높다. 특히 내부 사용자는 정보 서비스에 대한 정보를 인지하고 있기에 보안 위협에 의한 피해는 더욱 커진다. 이러한 환경에서 중요 정보 서비스에 접근하는 모든 사용자의 행위는 실시간으로 모니터링되고 기록되어야 한다. 그러나 현재 운영체제는 시스템과 Application 실행에 대한 로그만을 기록하고 있어, 사용자의 행위를 실시간으로 모니터링하기에는 한계가 있다. 이러한 보안 환경에서는 사용자의 비인가 행위로 인한 피해가 발생할 수 있다. 본 연구는 이러한 문제점을 해결하기 위하여, Linux 환경에서 사용자의 행위를 실시간으로 모니터링하는 아키텍처를 제안한다. 제안하는 아키텍처의 실효성을 확인하기 위하여 기능을 검증한 결과, 운영체제에 접근한 모든 사용자의 console 입력값과 출력값을 모두 실시간으로 모니터링하고 이를 저장한다. 제안한 아키텍처의 성능은 운영체제에서 제공하는 식별 및 인증 기능보다는 다소 늦지만, 사용자가 인지할 수준은 아닌 것으로 확인되어, 충분히 실효적이라고 판단되었다.

• 문화기술의 융합
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• 제8권3호
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• pp.463-468
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• 2022

COVID-19의 장기화는 다양한 산업의 패러다임에 새로운 시도와 변화를 주고 있다. 고객이 직접 피우에 닿고 사용하는 제품을 판매하는 산업에서는 그 현상이 날로 가중된다. 이러한 상황에 대응하고자 최근 Cosmetics 업계에서 다양한 언택트(비대면) 서비스들을 선보이고 있다. 기존 전통 오프라인 채널에서부터 다양한 온라인 채널 확보를 통하여 고객들의 수요와 참여를 끌어내고자 한다. 대표적으로 기존에는 온라인 문진 서비스를 이용하여 고객에게 맞춤 제품을 추천하는 서비스들을 제공하고 있지만 얼마 지나지 않아 한계에 도달하게 된다. 본 논문에서는 기존 정형화된 문진 서비스와 한걸음 더 나아가 AI 기술을 이용한 이미지 기반 피부진단 기능을 결합하는 새로운 방식의 피부진단 서비스에 대하여 연구하였다. 사용자는 촬영된 이미지를 이용하여 몇 가지 항목에 대한 진단을 받게 되고 최종 피부타입을 도출하기 위하여 부족한 진단 항목은 기존에 제안한 피부진단 서비스를 활용하였다. 이런 방식은 기존에 제공되고 있는 문진 서비스보다 재미 요소를 더할 뿐만 아니라 기술 트린드인 AI를 결합하여 더욱 고객 참여를 이끌어 낼 수 있고 가시적이고 정확도가 있는 지속적인 서비스를 만들어 내고자 함에 있다.