• Journal of Ocean Engineering and Technology
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• v.20 no.2 s.69
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• pp.1-7
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• 2006

This paper, presents a comparison between numerical analysis and field test on a real offshore platform in Bohai Bay, China. This platform is a steel jacket offshore platform with vertical piles. The field testing under wave-induced force and wind force etc. was conducted, in order to obtain the dynamic parameters of the structure, including the frequencies of the jacket platform, as well as the corresponding damping ratios and mode shapes. The natural excitation technology (NexT) combined with eigensystem realization algorithm (ERA) and the peak picking (PP) method in frequency domain are carried out for modal parameter indentification under operational conditions. The three-dimeansional finite element model (FEM) is constructed by ANSYS and analytical modal analysis is performed to generate modal parameters. The analytical results were compared with experimental results. A good agreement was achieved between the finite element and analysis and field test results. It is further demonstrated that the numerical and experimental modal analysis provide a comprehensive study on the dynamic properties of the jacket platform. According to the analysis results, the modal parameters identification under ambient excitation can calibrate finite element model of the jacket platform structures, or can be used for the structural health monitoring system.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.494-499
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• 2007

The thermal reliability of the closed-type BLDC motor for the high speed axial fans is analyzed by a numerical method in this dissertation. Since the module and the motor part are combined in a closed case, the heat generated from a rotor in the motor and the electronic components in the PCB module can not be effectively removed to the outside. Therefore the module will easily fail by high temperature. The accelerated-life testing was accomplished to formulate the life equation and numerical method is used to predict the inside temperature of the PCB module, which is one of the life equation parameter according to the environment. The experiment for measuring the surface heat flux of the electronic components is carried out to apply the boundary condition of numerical study. When the environment temperature of BLDC motor is 21, 35 and $50^{\circ}C$, the temperature in the PCB space is predicted as 73.4, 87.5 and $102.4^{\circ}C$. Then the life time with the temperature are calculated as 2,239, 863 and 328.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1110-1122
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• 2018

This paper proposes an alternative method to evaluate the effect of wind power to the power system stability with small disturbance. Alternatively, available techniques for stability analysis of a power system based on deterministic methods are less accurate for high penetration of wind power. Numerical simulations of random behaviors are computationally expensive. A stochastic stability index (SSI) is proposed for the power system stability evaluation based on the theory of stochastic stability and energy function, specifically the stochastic derivative of the relative well-defined energy function and the critical energy. The SSI is implemented on the modified nine-bus system including wind turbines under different conditions. A doubly-fed induction generator (DFIG) wind turbine is characterized and modeled using measured wind data from several sites in Thailand. Each of the obtained wind power data is analyzed. The wind power effect is modeled considering the aggregated effect of wind turbines. With the proposed method, the system behavior is properly predicted and the stability is quantitatively evaluated with less computational effort compared with conventional numerical simulation methods.

• Structural Engineering and Mechanics
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• v.84 no.5
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• pp.665-673
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• 2022

Additive manufacturing is an emerging method to manufacture objects with complex shapes and intricate geometry, such as cellular structures. The cellular structures can widely be used in lightweight application as it provides a high strength-to-load ratio. Under the various testing condition, each topology shows different mechanical properties. This study investigates the structural response of various types of cellular structures in compression loading, both experimentally and numerically. For that purpose, honeycomb, modified honeycomb, and spiral-type topology were selected to investigate. Besides, structural properties change by changing the cell size for each topology is also investigated. The specimens were subjected to a compression test by a universal testing machine to determine the absorbed energy and other mechanical properties. An implicit numerical study was also conducted to determine cellular structure's mechanical characteristics. The experimental and numerical results show that the honeycomb structure absorbs the maximum energy compared to the other structures. The experimentally and numerically calculated absorbed energy for the 4.8 mm honeycomb structure was 32.2J and 30.63J, respectively. The results also show that the increase of cell size for a particular cellular structure reduces the energy-absorbing ability of that structure.

• Smart Structures and Systems
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• v.13 no.1
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• pp.137-154
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• 2014

Servohydraulic shaking tables are being increasingly used in the field of earthquake engineering. They play a critical role in the advancement of the research state and remain one of the valuable tools for seismic testing. Recently, the National Earthquake Engineering Research Center, CGS, has acquired a 6.1m x 6.1 m shaking table system which has a six degree-of-freedom testing capability. The maximum specimen mass that can be tested on the shaking table is 60 t. This facility is designed specially for testing a complete civil engineering structures, substructures and structural elements up to collapse or ultimate limit states. It can also be used for qualification testing of industrial equipments. The current paper presents the main findings of the experimental shake-down characterization testing of the CGS shaking table. The test program carried out in this study included random white noise and harmonic tests. These tests were performed along each of the six degrees of freedom, three translations and three rotations. This investigation provides fundamental parameters that are required and essential while elaborating a realistic model of the CGS shaking table. Also presented in this paper, is the numerical model of the shaking table that was established and validated.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.44 no.4
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• pp.154-168
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• 2021

COVID-19 has been spreading all around the world, and threatening global health. In this situation, identifying and isolating infected individuals rapidly has been one of the most important measures to contain the epidemic. However, the standard diagnosis procedure with RT-PCR (Reverse Transcriptase Polymerase Chain Reaction) is costly and time-consuming. For this reason, pooled testing for COVID-19 has been proposed from the early stage of the COVID-19 pandemic to reduce the cost and time of identifying the COVID-19 infection. For pooled testing, how many samples are tested in group is the most significant factor to the performance of the test system. When the arrivals of test requirements and the test time are stochastic, batch-service queueing models have been utilized for the analysis of pooled-testing systems. However, most of them do not consider the false-negative test results of pooled testing in their performance analysis. For the COVID-19 RT-PCR test, there is a small but certain possibility of false-negative test results, and the group-test size affects not only the time and cost of pooled testing, but also the false-negative rate of pooled testing, which is a significant concern to public health authorities. In this study, we analyze the performance of COVID-19 pooled-testing systems with false-negative test results. To do this, we first formulate the COVID-19 pooled-testing systems with false negatives as a batch-service queuing model, and then obtain the performance measures such as the expected number of test requirements in the system, the expected number of RP-PCR tests for a test sample, the false-negative group-test rate, and the total cost per unit time, using the queueing analysis. We also present a numerical example to demonstrate the applicability of our analysis, and draw a couple of implications for COVID-19 pooled testing.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.125-135
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• 2004

This paper describes the calculation technique for guided wave propagation with a semi-analytical finite element method (SAFEM) and shows some results of numerical calculation and guided wave simulation for plates, pipes and railway rails. The SAFEM calculation gives dispersion curves and wave structures for bar-like structures. Dispersion curve software for a pipe is introduced, and also dispersion corves for a rail are given and experimentally verified. The mode conversions in a plate with a defect and in a pipe with an elbow or a defect are shown as examples of our guided wave simulations.

• Communications for Statistical Applications and Methods
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• v.13 no.3
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• pp.551-566
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• 2006

In this paper, we consider a Bayesian model selection for the intraclass correlation coefficient in familiar data. In particular, we compare two nested models such as the independence and intraclass models using the reference prior. A criterion for testing is the Bayesian Reference Criterion by Bernardo (1999) and the Intrinsic Bayes Factor by Berger and Pericchi (1996). We provide numerical examples using simulation data sets for illustration.

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.405-408
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• 1989

A 1800KV testing chamber for gas insulation has been developed. To develop the chamber, all parts consisting of the chamber, namely, bushing, main chamber, shield, conductor bus, inspection window, feedthrough, and spacer have been designed based on numerical electric field analysis. This paper presents the detailed design philosophy and methods of the chamber.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.372.1-372
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• 2002

Although impact hammer is widely used as a convenient excitation tool in structural modal testing, little is known about the dynamic charateristics of its impulse mechanism. Transmission of the impulsive force to the structure depends on the dynamic properties of the impact hammer as well as the stiffness of the tip. An improved dynamic model of the impact hammer is proposed in this study with numerical simulations based on this model. (omitted)