• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.407-412
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• 2008

Heat transfer from three-dimensional heat-generating modules was investigated. Simulated electronic module in an array configured with dummy module elements were used to measure the average heat transfer coefficients. Various module arrangements were tested using module spacings of 0.85 and 1.15 cm for six Reynolds numbers ranging from 500 to 975. The results show that a module placed in-line with and upstream of a heated module results in the heat transfer enhancement due to high turbulence intensity prompted by upstream modules. The highest enhancement occurs when the separation distance between modules is close to the module length in the flow direction. The laminar flow was observed on the front of the first module, slow recirculation regions on the sides parallel to the airstream, and turbulent flow on the back side. It appears that the first module serves to trip the air stream and produce a high level of turbulence, which enhances the heat transfer rate downstream.

• Journal of Korean Association for Spatial Structures
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• v.21 no.3
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• pp.69-76
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• 2021

Precast concrete (PC) modules have been increased its use in modular buildings due to their better seismic performance than steel modules. The main issue of the PC module is to ensure structural performance with appropriate connection methods. This study proposed a PC modular beam system for simple construction and improved structural and splicing performance. This modular system consisted of modules with steel plates inserted, and it is easy to construct by bolted connection. The steel plates play the role of tensile rebar and stirrup, which has the advantage of structural performance. The structural performance of the proposed PC modular beam system was evaluated by flexural test on one reinforced concrete (RC) beam specimen consisting of a monolithic, and two PC specimens with the proposed PC modular beam system. The results demonstrated that the proposed PC modular beam system achieved approximately 86% of the structural performance compared to the RC monolithic specimen, with similar ductility of approximately 1.06 fold greater.

• Journal of Power Electronics
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• v.19 no.5
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• pp.1259-1269
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• 2019

PV system performance is dependent on different irradiations and temperature values in addition to the capability of the employed PV inverter / maximum power point tracker (MPPT) circuit or algorithm. Therefore, it would be appropriate to use a PV simulator capable of producing identical repeatable conditions regardless of the weather to evaluate the performance of inverter / MPPT circuits and algorithms. In accordance with this purpose, a photovoltaic (PV) array simulator is presented in this paper. The simulator is designed to generate current-voltage (I-V) and power-voltage (P-V) curves of a PV panel. Series connected cascaded modules constitute the basic part of the simulator. This feature also allows for the modeling of PV arrays since the number of modules can be increased and high voltage values can be reached with the simulator. In addition, the curves obtained at the simulator output become similar to the actual curves of sample PV panels with an increase in the number of modules. In order to show the validity of the proposed simulator, it was simulated for various situations such as panels under full irradiance and partial shading conditions. After completing simulations, experiments were realized to support the simulation study. Both simulation and experimental results show that the proposed simulator will be very useful for researchers to carry out PV studies under laboratory conditions.

• Proceedings of the Korea Information Processing Society Conference
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• 2024.05a
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• pp.235-238
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• 2024

This paper investigates the integration of ARIA cryptography within hardware secure modules to bolster IoT security. We present a comparative analysis of two prominent IoT communication protocols, MQTT and LwM2M, augmented with ARIA cryptography. The study evaluates their performance, security, and scalability in practical IoT applications. Our experimental setup comprises FPGA-enabled hardware secure modules interfaced with Raspberry Pi acting as an MQTT and LwM2M client. We utilize the Mosquitto MQTT server and an LwM2M server deployed on AWS IoT. Through rigorous experimentation, we measure various performance metrics, including latency, throughput, and resource utilization. Additionally, security aspects are scrutinized, assessing the resilience of each protocol against common IoT security threats. Our findings highlight the efficacy of ARIA cryptography in bolstering IoT security and reveal insights into the comparative strengths and weaknesses of MQTT and LwM2M protocols. These results contribute to the development of robust and secure IoT systems, paving the way for future research in this domain.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.9
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• pp.703-712
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• 2003

This paper suggests a fuzzy expert system for fault diagnosis of rotating machinery, based on modulated databases. In the proposed system, alarm and trip levels are set based on ISO, considering operating condition, machinery type and maintenance history. Input signals for diagnosis, such as sub-and super-harmonic components of vibration and mean value, are normalized from 0 to 1 under the threshold level and otherwise equal to one so that chronic faults slightly below the threshold level can be monitored. The database for diagnosis consists of two modules: the well-known Sohre's chart module and if-then type rules. The Sohre's chart is utilized for the most common problems of high-speed turbomachinery, while the rule-based module, which was collected from many papers and reports, is for diagnosing peculiar faults according to the type of machinery. To infer the results from two modules, a fuzzy operation of Yager sum was adopted. Using a simulator constructed in laboratory, experimental verification was performed for the cases of unbalance and resonance which were intended. The experimental results show that the proposed fuzzy expert system has feasibility in practical diagnosis of rotating machinery.

• The KIPS Transactions:PartA
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• v.10A no.1
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• pp.15-24
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• 2003

In this paper, an optimization model for the clustered node allocation systems in the distributed computing environment is presented. In the presented model with a distributed file system framework, the dynamics of system behavior over times is carefully thought over the nodes and hence the functionality of the cluster monitor node to check the feasibility of the current set of clustered node allocation is given. The cluster monitor node of the node allocation system capable of distributing the parallel modules to clustered nodes provides a good allocation solution using Genetic Algorithms (GA). As a part of the experimental studies, the solution quality and computation time effects of varying GA experimental parameters, such as the encoding scheme, the genetic operators (crossover, mutations), the population size, and the number of node modules, and the comparative findings are presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.303-312
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• 2003

This paper suggests a fuzzy expert system for fault diagnosis of rotating machinery, based on modulated databases. In the proposed system, alarm and trip levels are set based on ISO, considering operating condition, machinery type and maintenance history. Input signals for diagnosis, such as sub- and super-harmonic components of vibration and mean value, are normalized from 0 to 1 under the threshold level and otherwise equal to one so that chronic faults slightly below the threshold level can be monitored. The database for diagnosis consists of two modules: the well-known Sohre's chart module and if-then type rules. The Sohre's chart is utilized for the most common problems of high-speed turbomachinery, while the rule-based module, which was collected from many papers and reports, is for diagnosing peculiar faults according to the type of machinery. To infer the results from two modules, a fuzzy operation of Yager sum was adopted. Using a simulator constructed in laboratory, experimental verification was performed for the cases of resonance and housing looseness which were intended. The experimental results show that the proposed fuzzy expert system has feasibility in practical diagnosis of rotating machinery.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.10
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• pp.915-920
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• 2013

Payload capacity and transition ability are essential for climbing robots to apply the robots to various applications such as inspection and exploration. This paper presents a new climbing robotic platform with multi-link structure of track-wheel modules to enhance payload capacity and transition ability, and its tracking controller design and experimental results. The compliances between track-wheel modules achieve stable internal and external transitions while the large adhesion area of the track-wheel module enhances the payload capacity of the robot. Kinematic model-based tracking controller is designed and implemented for autonomous internal transition, and the gains of the controller are optimized by experimental design. Experiments on the automatic internal transitions are performed and the results guarantee autonomous internal transition with little tracking error.

• Journal of Korean Association for Spatial Structures
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• v.19 no.2
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• pp.35-42
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• 2019

The purpose of this paper is to evaluate the structural performance of joints between modules with steel plate press forming type non-symmetric cross section. The main experimental variables are direction of load, whether vertical bolts are fastened, and whether the concrete inside the column is filled. A total of three experiments were performed for each variable. Experimental results show that the behavior of the joints dominated by the local buckling deformation of the upper and lower beam flanges of the module joints, and the final failure was the fracture of the column-beam welds. In case of short side direction, it is possible to secure the performance of intermediate moment frame (0.02 rad). In case of long side direction, it is evaluated that the performance of special moment frame (0.04 rad) is secured regardless of whether or not concrete is infilled in the column.

• ETRI Journal
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• v.43 no.5
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• pp.891-899
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• 2021

We propose a stray inductance extraction method on power modules of the few-kilovolts/several-hundred-amperes class using only low voltages and low currents. The method incorporates a double-pulse generator, a level shifter, a switching device, and a load inductor. The conventional approach generally requires a high voltage of more than half the power module's rated voltage and a high current of around half the rated current. In contrast, the proposed method requires a low voltage and low current environment regardless of the power module's rated voltage because the module is measured in a turn-off state. Both theoretical and experimental results are provided. A physical circuit board was fabricated, and the method was applied to three commercial power modules with EconoDUAL3 cases. The obtained stray inductance values differed from the manufacturer-provided values by less than 1.65 nH, thus demonstrating the method's accuracy. The greatest advantage of the proposed approach is that high voltages or high currents are not required.