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Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2012 (설비공학 분야의 최근 연구 동향 : 2012년 학회지 논문에 대한 종합적 고찰)

  • Han, Hwataik;Lee, Dae-Young;Kim, Sa Ryang;Kim, Hyun-Jung;Choi, Jong Min;Park, Jun-Seok;Kim, Sumin
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.25 no.6
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    • pp.346-361
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    • 2013
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2012. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. The conclusions are as follows : (1) The research works on thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and valves, fuel cells and power plants, ground-coupled heat pumps, and general heat and mass transfer systems. Research issues are mainly focused on new and renewable energy systems, such as fuel cells, ocean thermal energy conversion power plants, and ground-coupled heat pump systems. (2) Research works on the heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer, and industrial heat exchangers. Researches on heat transfer characteristics included the results for natural convection in a square enclosure with two hot circular cylinders, non-uniform grooved tube considering tube expansion, single-tube annular baffle system, broadcasting LED light with ion wind generator, mechanical property and microstructure of SA213 P92 boiler pipe steel, and flat plate using multiple tripping wires. In the area of pool boiling and condensing heat transfer, researches on the design of a micro-channel heat exchanger for a heat pump, numerical simulation of a heat pump evaporator considering the pressure drop in the distributor and capillary tubes, critical heat flux on a thermoexcel-E enhanced surface, and the performance of a fin-and-tube condenser with non-uniform air distribution and different tube types were actively carried out. In the area of industrial heat exchangers, researches on a plate heat exchanger type dehumidifier, fin-tube heat exchanger, an electric circuit transient analogy model in a vertical closed loop ground heat exchanger, heat transfer characteristics of a double skin window for plant factory, a regenerative heat exchanger depending on its porous structure, and various types of plate heat exchangers were performed. (3) In the field of refrigeration, various studies were executed to improve refrigeration system performance, and to evaluate the applicability of alternative refrigerants and new components. Various topics were presented in the area of refrigeration cycle. Research issues mainly focused on the enhancement of the system performance. In the alternative refrigerant area, studies on CO2, R32/R152a mixture, and R1234yf were performed. Studies on the design and performance analysis of various compressors and evaporator were executed. (4) In building mechanical system research fields, twenty-nine studies were conducted to achieve effective design of mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, renewable energy systems, and lighting systems in buildings. New designs and performance tests using numerical methods and experiments provide useful information and key data, which can improve the energy efficiency of buildings. (5) In the fields of the architectural environment, studies for various purposes, such as indoor environment, building energy, and renewable energy were performed. In particular, building energy-related researches and renewable energy systems have been mainly studied, reflecting interests in global climate change, and efforts to reduce building energy consumption by government and architectural specialists. In addition, many researches have been conducted regarding indoor environments.

Game Theoretic Optimization of Investment Portfolio Considering the Performance of Information Security Countermeasure (정보보호 대책의 성능을 고려한 투자 포트폴리오의 게임 이론적 최적화)

  • Lee, Sang-Hoon;Kim, Tae-Sung
    • Journal of Intelligence and Information Systems
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    • v.26 no.3
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    • pp.37-50
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    • 2020
  • Information security has become an important issue in the world. Various information and communication technologies, such as the Internet of Things, big data, cloud, and artificial intelligence, are developing, and the need for information security is increasing. Although the necessity of information security is expanding according to the development of information and communication technology, interest in information security investment is insufficient. In general, measuring the effect of information security investment is difficult, so appropriate investment is not being practice, and organizations are decreasing their information security investment. In addition, since the types and specification of information security measures are diverse, it is difficult to compare and evaluate the information security countermeasures objectively, and there is a lack of decision-making methods about information security investment. To develop the organization, policies and decisions related to information security are essential, and measuring the effect of information security investment is necessary. Therefore, this study proposes a method of constructing an investment portfolio for information security measures using game theory and derives an optimal defence probability. Using the two-person game model, the information security manager and the attacker are assumed to be the game players, and the information security countermeasures and information security threats are assumed as the strategy of the players, respectively. A zero-sum game that the sum of the players' payoffs is zero is assumed, and we derive a solution of a mixed strategy game in which a strategy is selected according to probability distribution among strategies. In the real world, there are various types of information security threats exist, so multiple information security measures should be considered to maintain the appropriate information security level of information systems. We assume that the defence ratio of the information security countermeasures is known, and we derive the optimal solution of the mixed strategy game using linear programming. The contributions of this study are as follows. First, we conduct analysis using real performance data of information security measures. Information security managers of organizations can use the methodology suggested in this study to make practical decisions when establishing investment portfolio for information security countermeasures. Second, the investment weight of information security countermeasures is derived. Since we derive the weight of each information security measure, not just whether or not information security measures have been invested, it is easy to construct an information security investment portfolio in a situation where investment decisions need to be made in consideration of a number of information security countermeasures. Finally, it is possible to find the optimal defence probability after constructing an investment portfolio of information security countermeasures. The information security managers of organizations can measure the specific investment effect by drawing out information security countermeasures that fit the organization's information security investment budget. Also, numerical examples are presented and computational results are analyzed. Based on the performance of various information security countermeasures: Firewall, IPS, and Antivirus, data related to information security measures are collected to construct a portfolio of information security countermeasures. The defence ratio of the information security countermeasures is created using a uniform distribution, and a coverage of performance is derived based on the report of each information security countermeasure. According to numerical examples that considered Firewall, IPS, and Antivirus as information security countermeasures, the investment weights of Firewall, IPS, and Antivirus are optimized to 60.74%, 39.26%, and 0%, respectively. The result shows that the defence probability of the organization is maximized to 83.87%. When the methodology and examples of this study are used in practice, information security managers can consider various types of information security measures, and the appropriate investment level of each measure can be reflected in the organization's budget.

Seasonal Circulation and Estuarine Characteristics in the Jinhae and Masan Bay from Three-Dimensional Numerical Experiments (3차원 수치모의 실험을 통한 진해·마산만의 계절별 해수순환과 염하구 특성)

  • JIHA KIM;BYOUNG-JU CHOI;JAE-SUNG CHOI;HO KYUNG HA
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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    • v.29 no.2
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    • pp.77-100
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    • 2024
  • Circulation, tides, currents, harmful algal blooms, water quality, and hypoxic conditions in Jinhae-Masan Bay have been extensively studied. However, these previous studies primarily focused on short-term variations, and there was limited detailed investigation into the physical mechanisms responsible for ocean circulation in the bays. Oceanic processes in the bays, such as pollutant dispersal, changes on a seasonal time scale. Therefore, this study aimed to understand how the circulation in Jinhae-Masan Bay varies seasonally and to examine the effects of tides, winds, and river discharges on regional ocean circulation. To achieve this, a three-dimensional ocean circulation model was used to simulate circulation patterns from 2016 to 2018, and sensitivity experiments were conducted. This study reveals that convective estuarine circulation develops in Jinhae and Masan Bays, characterized by the inflow of deep oceanic water from the Korea Strait through Gadeoksudo, while surface water flows outward. This deep water intrusion divides into northward and westward branches. In this study, the volume transport was calculated along the direction of bottom channels in each region. The meridional water exchange in the eastern region of Jinhae Bay is 2.3 times greater in winter and 1.4 times greater in summer compared to that of zonal exchange in the western region. In the western region of Jinhae Bay, the circulation pattern varies significantly by season due to changes in the balance of forces. During winter, surface currents flow southward and bottom currents flow northward, strengthening the north-south convective circulation due to the combined effects of northwesterly winds and the slope of the sea surface. In contrast, during summer, southwesterly winds cause surface seawater to flow eastward, and the elevated sea surface in the southeastern part enhances northward barotropic pressure gradient intensifying the eastward surface flow. The density gradient and southward baroclinic pressure gradient increase in the lower layer, causing a strong westward inflow of seawater from Gadeoksudo, enhancing the zonal convective circulation by 26% compared to winter. The convective circulation in the western Jinhae Bay is significantly influenced by both tidal current and wind during both winter and summer. In the eastern Jinhae Bay and Masan Bay, surface water flows outward to the open sea in all seasons, while bottom water flows inward, demonstrating a typical convective estuarine circulation. In winter, the contributions of wind and freshwater influx are significant, while in summer, the influence of mixing by tidal currents plays a major role in the north-south convective circulation. In the eastern Jinhae Bay, tidally driven residual circulation patterns, influenced by the local topography, are distinct. The study results are expected to enhance our understanding of pollutant dispersion, summer hypoxic events, and the abundance of red tide organisms in these bays.

A Dynamic Simulation on the Squeezing Flow of ER Fluids (전기유변 유체의 압착유동에 대한 동적 수치모사)

  • 김도훈;주상현;안경현;이승종
    • The Korean Journal of Rheology
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    • v.11 no.2
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    • pp.82-90
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    • 1999
  • Electrorheological(ER) fluid is a material that shows the dramatic change of rheological properties under an electric field and responds reversibly in a few milliseconds. ER fluid's response to an electric field along with its fast switching capability allows ER devices to be precisely controlled. The real application with ER fluid, however, has many limitations to be overcome; temperature fluctuation, moisture, dust, aggregation, precipitation, and low yield stress, for example. The magnitude and the characteristics of yield stress of ER fluid plays an important role in practical applications. In this research, a dynamic simulation on the squeezing flow of the ER fluid was carried out. Numerical simulation on isolated chains was performed to find out the effect of hydrodynamic and electrostatic force depending on the chain location, the squeezing rate, and the chain structure. Suspension model that is composed of a large number of particles was also investigated. The increase of normal stresses as well as the existence of a yield stress at an earlier stage could be observed, and the effective control of the normal stresses could be achieved at an optimal condition of the hydrodynamic force and the electrostatic force.

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The Effect of Cement Milk Grouting on the Deformation Behavior of Jointed Rock Mass (시멘트현탁액 주입에 의한 절리암반의 역학적 특성 변화)

  • 김태혁;이정인
    • Tunnel and Underground Space
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    • v.13 no.5
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    • pp.331-343
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    • 2003
  • Though the Grouting has been in use for a long time, it is still regarded as an technique rather than engineering. The study of ground improvement by grouting is rare especially in jointed rock mass. In this study, biaxial compression tests were performed in the jointed rock mass models with .ough surfBce joints assembled with blocks before and after grouting. The load-deformation curves of the jointed rock masses showed a non-linear relationship before grouting but showed a relatively linear deformaion behavior after grouting. Improvement ratio (deformation modulus after grouting/deformation modulus before grouting) decreased with increasing joint spacing and lateral stress. Improvement ratio decreased exponentially with increasing deformation modulus of the rock mass model before grouting. Three-dimensional FDM analysis was performed to a highway tunnel case using experimental data of grouted rock. The convergence of the tunnel predicted after grouting by the numerical modelling coincided with those attained from the field measurement.

Transformation of Dynamic Loads into Equivalent Static Load based on the Stress Constraint Conditions (응력 구속조건을 고려한 동하중의 등가정하중으로의 변환)

  • Kim, Hyun-Gi;Kim, Euiyoung;Cho, Maenghyo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.26 no.2
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    • pp.165-171
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    • 2013
  • Due to the difficulty in considering dynamic load in the view point of a computer resource and computing time, it is common that external load is assumed as ideal static loads. However, structural analysis under static load cannot guarantee the safety of design of the structures under dynamic loadings. Recently, the systematic method to construct equivalent static load from the given dynamic load has been proposed. Previous study has calculated equivalent static load through the optimization procedure under displacement constraints. However, previously reported works to distribute equivalent static load were based on ad-hoc methods. Improper selection of equivalent static loading positions may results in unreliable prediction of structural design. The present study proposes the selection method of the proper locations of equivalent static loads to dynamically applied loads when we consider transient dynamic structural problems. Moreover, it is appropriate to take into account the stress constraint as well as displacement constraint condition for the safety design. But the previously reported studies of equivalent static load design methods considered only displacement constraint conditions but not stress constraint conditions. In the present study we consider not only displacement constraint but also stress constraint conditions. Through a few numerical examples, the efficiency and reliability of proposed scheme is verified by comparison of the equivalent stress between equivalent static loading and dynamic loading.

Numerical Analysis of Intense Electric Current Pulse to Disperse Shaped Charge Metal Jet (성형작약탄 금속제트 산란을 위한 대전류 펄스의 수치해석적 연구)

  • Park, Hyeong Gyu;Kim, Dong Kyu;Kim, Si Woo;Joo, Jae Hyun;Song, Woo Jin;Kim, Jeong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.1
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    • pp.55-62
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    • 2015
  • The electromagnetic force induced by an intense electric current pulse, which generates an electromagnetic field around the metal jet originating from a shaped charge, can disperse and scatter the high-speed metal jet. An electric device consisting of an RLC circuit applies an intense electric current pulse that flows in the circuit while the metal jet passes between two electrodes. In this study, the metal jet formation was simulated using the ALE technique in 2-D, and a 3-D finite element model was mapped using 2-D simulation results to induce the electric current directly. The deformed shapes of the metal jet and the electromagnetic force were calculated using a finite element analysis by inducing the electric current directly, and the major parameters of the intense electric current pulse for breaking up the metal jet were examined.

Numerical Simulations of Dynamic Response of Cased Reactive System Subject to Bullet Impact (총탄 충격이 가해진 반응 시스템의 파괴 거동에 관한 수치적 연구)

  • Kim, Bohoon;Kim, Minsung;Doh, Youngdae;Kim, Changkee;Yoo, Jichang;Yoh, Jai-Ick
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.6
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    • pp.525-538
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    • 2014
  • Safety of reactive systems is one of the most important research areas in the field of weapon development. A NoGo response or at least a low-order explosion should be ensured to prevent unexpected accidents when the reactive system is impacted by high-velocity projectile. We investigated the shock-induced detonation of cased reactive systems subject to a normal projectile impact to the cylindrical surface based on two-dimensional hydrodynamic simulations using the I&G chemical rate law. Two types of energetic materials, namely LX-17 and AP-based solid propellant, were considered to compare the dynamic responses of the reactive system when subjected to the threshold impact velocity. It was found that shock-to-detonation transition phenomena occurred in the cased LX-17, whereas no full reaction occurred in the propellant.

Topology Design Optimization and Experimental Validation of Heat Conduction Problems (열전도 문제에 관한 위상 최적설계의 실험적 검증)

  • Cha, Song-Hyun;Kim, Hyun-Seok;Cho, Seonho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.28 no.1
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    • pp.9-18
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    • 2015
  • In this paper, we verify the optimal topology design for heat conduction problems in steady stated which is obtained numerically using the adjoint design sensitivity analysis(DSA) method. In adjoint variable method(AVM), the already factorized system matrix is utilized to obtain the adjoint solution so that its computation cost is trivial for the sensitivity. For the topology optimization, the design variables are parameterized into normalized bulk material densities. The objective function and constraint are the thermal compliance of the structure and the allowable volume, respectively. For the experimental validation of the optimal topology design, we compare the results with those that have identical volume but designed intuitively using a thermal imaging camera. To manufacture the optimal design, we apply a simple numerical method to convert it into point cloud data and perform CAD modeling using commercial reverse engineering software. Based on the CAD model, we manufacture the optimal topology design by CNC.

Study on Combined Use of Inclination and Acceleration for Displacement Estimation of a Wind Turbine Structure (경사 및 가속도 계측자료 융합을 통한 풍력 터빈의 변위 추정)

  • Park, Jong-Woong;Sim, Sung-Han;Jung, Byung-Jin;Yi, Jin-Hak
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.1
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    • pp.1-8
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    • 2015
  • Wind power systems have gained much attention due to the relatively high reliability, good infrastructures and cost competitiveness to the fossil fuels. Advances have been made to increase the power efficiency of wind turbines while less attention has been focused on structural integrity assessment of structural sub-systems such as towers and foundations. Among many parameters for integrity assessment, the most perceptive parameter may be the induced horizontal displacement at the hub height although it is very difficult to measure particularly in large-scale and high-rise wind turbine structures. This study proposes an indirect displacement estimation scheme based on the combined use of inclinometers and accelerometers for more convenient and cost-effective measurements. To this end, (1) the formulation for data fusion of inclination and acceleration responses was presented and (2) the proposed method was numerically validated on an NREL 5 MW wind turbine model. The numerical analysis was carried out to investigate the performance of the propose method according to the number of sensors, the resolution and the available sampling rate of the inclinometers to be used.