• Journal of Ocean Engineering and Technology
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• v.33 no.3
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• pp.236-244
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• 2019

Internal waves occur at the interface between two layers caused by a seawater density difference. The internal waves generated by a body moving in a two-layer fluid are also related to the generation of surface waves because of their interaction. In these complex flow phenomena, the experimental measurements and experimental set-up for the wave patterns of the internal waves and surface waves are very difficult to perform in a laboratory. Therefore, studies have mainly been carried out using numerical analysis. However, model tests are needed to evaluate the accuracy of numerical models. In this study, the various experimental conditions were evaluated using CFD simulations before experiments to measure the wave patterns of the internal waves and surface waves in a stratified two-layer fluid. The numerical simulation conditions included variations in the densities of the fluids, depth of the two-layer fluid, and moving speed of the underwater body.

• Structural Engineering and Mechanics
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• v.89 no.6
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• pp.601-615
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• 2024

Effect of ring and straight stiffeners in the buckling as well as vibration characteristics of metal-ceramic functionally graded plates with cutout subjected to various uniaxial and localized in-plane compressive edge loadings was explored in the present work. In the current work, the distinguishing characteristics of metal and ceramic are merged in a single volume, and power law was used for estimating the material composition throughout thickness. Buckling and free vibration characteristics were studied initially for unstiffened Al/SiC functionally graded plates with cutout. Subsequently, the influence of cutout ratio on buckling load as well as natural frequency for different power law indices was discussed. The functionally graded plate was stiffened by three different stiffener patterns, namely; ring stiffener, straight stiffener, as well as a combination of the ring and the straight stiffener, to enhance the buckling as well as vibration characteristics. The effect of stiffener depth ratio for different stiffener patterns was also presented for functionally graded plates having different cutout sizes under various loading conditions. Such studies on functionally graded material have potential applications in a variety of technological fields including the aerospace and defense sectors.

• Journal of Broadcast Engineering
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• v.23 no.1
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• pp.11-18
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• 2018

In these days, technologies of virtual reality (VR) and of augmented reality (AR) have applied to diverse areas such as medicine, defense, education that are closely related to real-life practice. In contrast to the previous applications of game or sports, the technologies of VR and AR tends to expand the areas of applications according to development of the imaging or video techniques. This paper introduces VR and AR techniques and some examples of applications. In addition, this paper introduces how the differences between VR and AR technologies affect to the applications of broadcasting systems. In the last, this paper introduces the results of interviews about suitability and future feasibility of VR and AR techniques for broadcasting systems from korean broadcasting companies.

• Journal of Distribution Science
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• v.19 no.2
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• pp.25-36
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• 2021

Purpose: This paper attempts to explore a Christian perspective on the process leading to growth after complex trauma caused by family violence experience. To achieve it, the article tackles the analysis of relationship between the inflictor father and victim, interpersonal relationship, and relationship with God in terms of growth after suffering from the trauma of family violence with a Christian perspective. Research design, data, and methodology: This study employed an in-depth interview as a methodology. Seven Christian adults who have experienced family violence in childhood are selected for the qualitative case study. 58 concepts, 24 low-level categories, and eight high-level categories are derived from each interview case. Results: The results of the case study show that the negative emotion caused by family violence during childhood is likely to lead to narcissistic rage. It is found that the reflection for posttraumatic growth starts with crying to God, simultaneously expressing pain and suffering. Conclusions: The interesting thing is that they are willing to forgive in the process of trauma therapy. It should be noted that the research results also demonstrate that relationship restoration entails the meaning reconstruction in the interpersonal relations.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.1
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• pp.123-132
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• 2021

In order for the underwater vehicle to perform various tasks, it is important to control the depth, course, and roll of the underwater vehicle. To design such a controller, it is necessary to construct a dynamic model of the underwater vehicle and select the appropriate hydrodynamic coefficients. For the controller design, since the dynamic model is linearized assuming a limited operating range, the control performance in the steady state is well satisfied, but the control performance in the transient state may be unstable. In this paper, in order to overcome the problems of the existing controller design, we propose a A2C(Advantage Actor-Critic) based roll controller for underwater vehicle with stable learning performance in a continuous space among reinforcement learning methods that can be learned through rewards for actions. The performance of the proposed A2C based roll controller is verified through simulation and compared with PID and Dueling DDQN based roll controllers.

• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2011-2022
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• 2022

According to the defense-in-depth concept, not only a preventive strategy but also an integrated cyberattack response strategy for NPPs should be established. However, there are limitations in terms of responding to penetrations, and the existing EOPs are insufficient for responding to intentional disruptions. In this study, we focus on manipulative attacks on process data. Based on an analysis of the related attack vectors and possible attack scenarios, we adopt the Kalman filter to detect process anomalies that can be caused by manipulations of process data. To compensate for these manipulations and secure MCR operators' situational awareness, we modify the Kalman filter such that it can filter out the effects of the manipulations adaptively. A case study was conducted using a hardware-in-the-loop system. The results indicated that the developed method can be used to verify whether the displayed safety-related state data are reliable and to implement the required safety response actions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.6
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• pp.81-88
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• 2022

Titanium alloy (Ti-6Al-4V) has excellent mechanical properties and high specific strength; therefore, it is widely used in aerospace, automobile, defense, engine parts, and bio fields. Particularly in the aerospace field, as it has a low specific gravity and rigidity, it is used for the purpose of increasing energy efficiency through weight reduction of parts, and most have a thin-walled structure. However, it is extremely difficult to machine thin-walled shapes owing to vibration and deformation. In the case of thin-walled structures, the cutting forces and vibrations rapidly increase depending on the cutting conditions, significantly affecting the surface integrity and tool life. In this study, machining experiments on thin-wall milling of a titanium alloy (Ti-6Al-4V) were conducted for each experimental condition with different axial depths of cut, radial depth of cut, and machining sequence. The machining characteristics were analyzed, and an effective machining method was derived by a comprehensive analysis of the machined surface conditions and cutting signals.

• Animal Systematics, Evolution and Diversity
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• v.39 no.3
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• pp.99-113
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• 2023

The nudibranch is one of the most colorful gastropod species found in oceans worldwide. Unlike many other gastropod groups, the nudibranch loses an external shell in the adult stage, but instead develops various chemical defense systems. More than 2,500 nudibranch species have been reported worldwide, and 73 species are currently recorded in Korean waters. In this study, we present morphological descriptions, DNA barcode information of mtDNA cox1 sequence, and taxonomic review for five nudibranch species: Apata pricei (MacFarland, 1966), Doto rosacea Baba, 1949, Janolus toyamensis Baba and Abe, 1970, Polycera abei (Baba, 1960), and Trinchesia sibogae (Bergh, 1905). Of these, we also provide in-depth discussion of taxonomic issue of A. pricei that was previously subdivided into two subspecies, A. pricei pricei and A. pricei komandorica. Our morphological examination and molecular analyses of the mtDNA cox1 sequences indicate that these two subspecies are not taxonomically warranted. The phylogenetic information for the other nudibranch species from mtDNA cox1 sequence analysis is also included, providing a molecular basis for species identification and inferring their local phylogenies within each of the species groups discussed herein.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.653-664
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• 2013

The design of computer-based instrumentation and control (I&C) systems is determined by the allocation of I&C functions to I&C systems and components. Due to the characteristics of computer-based technology, component failures can negatively affect several I&C functions, so that the reliability proof of the I&C systems requires the accomplishment of I&C system design analyses throughout the I&C life-cycle. On one hand, this paper proposes the restructuring of the sequential IEC 61513 I&C life-cycle according to the V-model, so as to adequately integrate the concept of verification and validation. On the other hand, based on a metamodel for the modeling of I&C systems, this paper introduces a method for the modeling and analysis of the effects with respect to the superposition of failure combinations and event sequences on the I&C system design, i.e. the temporal change of physical structure is analyzed. In the first step, the method is concerned with the modeling of the I&C systems. In the second step, the method considers the analysis of temporal change of physical structure, which integrates the concepts of the diversity and defense-in-depth analysis, fault tree analysis, event tree analysis, and failure mode and effects analysis.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.2
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• pp.116-123
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• 2012

This study aims to analyze the strength of pressure hull of a small submarine. The pressure hull of a submarine has to withstand very large differential pressure between hydrostatic pressure in submarine operating depth and atmospheric pressure in inner space of a submarine. To do that, the pressure hull is generally ring-stiffened cylindrical shell under external pressure. In this situation, there are some foreseeable failure modes of the pressure hull such as shell yielding, axisymmetric shell buckling, asymmetric shell buckling, overall buckling and buckling of end closure. We calculated collapse pressures of these failure modes with approximation and empirical formulas. And, to analyze critical buckling pressure, we performed eigenvalue analysis with finite element method tools.