• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.181-183
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• 2002

The accurate permeability for preform is critical to model and design the impregnation of fluid resin in the composite manufacturing process. In this study, the in-plane and transverse permeability for a woven fabric are predicted numerically through the coupled flow model which combines microscopic with macroscopic flow. The microscopic and macroscopic flow which are flows within the micro-unit and macro-unit cell, respectively, are calculated by using 3-D CVFEM(control volume finite element method). To avoid checker-board pressure field and improve the efficiency on numerical computation, A new interpolation function for velocity is proposed on the basis of analytic solutions. The permeability of plain woven fabric is measured through unidirectional flow experiment and compared with the permeability calculated numerically. Based on the good agreement of the results, the relationships between the permeability and the structures of preform such as the fiber volume fraction and stacking effect can be understood. The reverse and the simple stacking are taken in account. Unlike past literatures, this study is based on more realistic unit cell and the improved prediction of permeability can be achieved. It is observed that in-plane flow is more dominant than transverse flow in the real flow through preform and the stacking effect of multi-layered preform is negligible. Consequently, the proposed coupled flow model can be applied to modeling of real composite materials processing.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2034-2046
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• 2023

Industrial control systems in nuclear facilities are facing increasing cyber threats due to the widespread use of information and communication equipment. To implement cyber security programs effectively through the RG 5.71, it is necessary to quantitatively assess cyber risks. However, this can be challenging due to limited historical data on threats and customized Critical Digital Assets (CDAs) in nuclear facilities. Previous works have focused on identifying data flows, the assets where the data is stored and processed, which means that the methods are heavily biased towards information security concerns. Additionally, in nuclear facilities, cyber threats need to be analyzed from a safety perspective. In this study, we use the system theoretic process analysis to identify system-level threat scenarios that could violate safety constraints. Instead of quantifying the likelihood of exploiting vulnerabilities, we quantify Security Control Measures (SCMs) against the identified threat scenarios. We classify the system and CDAs into four consequence-based classes, as presented in NEI 13-10, to analyze the adversary impact on CDAs. This allows for the ranking of identified threat scenarios according to the quantified SCMs. The proposed framework enables stakeholders to more effectively and accurately rank cyber risks, as well as establish security and response strategies.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3068-3073
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the performance study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and shadow graph. Numerical simulation was also performed to study flow characteristics and interactions between ramp tabs. This paper provides to analyze the location of normal shock wave and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• Journal of Power Electronics
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• v.16 no.6
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• pp.1991-2004
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• 2016

An LC filter is required to reduce the output current ripple in the auxiliary resonant snubber inverter (ARSI) for high-performance applications. However, if the traditional control method is used in the ARSI with LC filter, then unnecessary current flows in the auxiliary circuit. In addressing this problem, a novel load-adaptive control that fully uses the filter inductor current ripple to realize the soft-switching of the main switches is proposed. Compared with the traditional control implemented in the ARSI with LC filter, the proposed control can reduce the required auxiliary current, contributing to higher efficiency and DC-link voltage utilization. In this study, the detailed circuit operation in the light load mode (LLM) and the heavy load mode (HLM) considering the inductor current ripple is described. The characteristics of the improved ARSI are expressed mathematically. A prototype with 200 kHz switching frequency, 80 V DC voltage, and 8 A maximum output current was developed to verify the effectiveness of the improved ARSI. The proposed ARSI was found to successfully operate in the LLM and HLM, achieving zero-voltage switching (ZVS) of the main switches and zero-current switching (ZCS) of the auxiliary switches from zero load to full load. The DC-link voltage utilization of the proposed control is 0.758, which is 0.022 higher than that of the traditional control. The peak efficiency is 91.75% at 8 A output current for the proposed control, higher than 89.73% for the traditional control. Meanwhile, the carrier harmonics is reduced from -44 dB to -66 dB through the addition of the LC filter.

• The KSFM Journal of Fluid Machinery
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• v.10 no.6
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• pp.32-37
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and schlieren system. This paper provides the thrust spoilage, three directional forces and moments and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12B
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• pp.1112-1122
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• 2008

This paper reviews the Parlay X and proposes SIP multimedia session control mechanism which is able to be implemented over IMS using Extended Call Control APIs of Parlay X. Parlay X is one of the industrial standards of Open API in the telecommunication to open network resources and capabilities to third party service providers. In this paper, SIP session control mechanism is described by depicting call flows of basic and essential session handling methods including session initiation, transfer, restoration, and termination. We also show how easy Parlay X Extended Call Control APIs can be used for the purpose of complicated calls handling in the IT applications. To verify feasibility of the blended services based on convergence of telecommunication and internet with regard to performance, we accomplish experimental performance of Extended Call Control APIs from IT application through open service gateway. We show Open API could be applied to next generation network based on IMS without serious degradation of the network performance.

• Journal of Korea Multimedia Society
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• v.7 no.5
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• pp.698-712
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• 2004

DiffServ network architecture does not define a call admission control procedure explicitly. In this paper, a new DiffServ QoS control mechanism is suggested which, after the call admission control, can execute packet process according to the class while, at the same time, executing on the flow based call admission control in the DiffServ network. Routers on the path from the source to the destination estimate the aggregated class traffic of the existing flows and the new incoming flow and then, perform a call admission control in accordance with the type of classes efficiently based on the required bandwidth per each class that can meet the user's QoS requirements. In order to facilitate the packet process according to the class after the flow based call admission control, a mechanism is suggested that can adjust the network resources to classes dynamically. The performance analysis on this mechanism is carried out through a simulation.

• Journal of Communications and Networks
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• v.12 no.6
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• pp.568-576
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• 2010

The paper presents a control architecture aimed at implementing bandwidth optimization combined with call admission control (CAC) over a digital video broadcasting (DVB) return channel satellite terminal (RCST) under quality of service (QoS) constraints. The approach can be applied in all cases where traffic flows, coming from a terrestrial portion of the network, are merged together within a single DVB flow, which is then forwarded over the satellite channel. The paper introduces the architecture of data and control plane of the RCST at layer 2. The data plane is composed of a set of traffic buffers served with a given bandwidth. The control plane proposed in this paper includes a layer 2 resource manager (L2RM), which is structured into decision makers (DM), one for each traffic buffer of the data plane. Each DM contains a virtual queue, which exactly duplicates the corresponding traffic buffer and performs the actions to compute the minimum bandwidth need to assure the QoS constraints. After computing the minimum bandwidth through a given algorithm (in this view the paper reports some schemes taken in the literature which may be applied), each DM communicates this bandwidth value to the L2RM, which allocates bandwidth to traffic buffers at the data plane. Real bandwidth allocations are driven by the information provided by the DMs. Bandwidth control is linked to a CAC scheme, which uses current bandwidth allocations and peak bandwidth of the call entering the network to decide admission. The performance evaluation is dedicated to show the efficiency of the proposed combined bandwidth allocation and CAC.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.2
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• pp.227-234
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• 2020

This paper introduces the state definition and diagnostic algorithm for autonomic control of manufacturing facilities. Smart factory systems through cyber-physical systems and digital twin technology are increasing the productivity and stability of existing manufacturing plants, which has become an issue recently. A Smart factory system is one of the key technologies that make up a smart factory system, to improve productivity, enable workers to make better decisions, and to control abnormal process flows. However, performing an autonomic control process based on large number of integrated plat data requires significant advance work. Therefore, in this paper, we define an abstracted facility state for manufacturing facility autonomic control and propose an algorithm to diagnose the current state. This makes the autonomic control process simpler by autonomic control based on the facility status rather then integrated facility data.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1129-1136
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• 2009

The paper presents the performance characteristics for a cooling system using EEV. The water cooler was used to reduce thermal deformation and contraction due to high speed of machine tools and the EEV was used for capacity control for water cooler. The apparatus was designed for hot-gas bypass system which a hot-gas can flows from outlet of compressor to the inlet of evaporator. This experiment is the intermediary study for precise temperature control through PID control. The results show that the evaporator pressure increased and refrigeration capacity decreased as the EEV opening step of hot-gas bypass increased. These results can be used as basic data for the design of effective water cooler.