• 한국안전학회지
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• 제31권4호
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• pp.35-41
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• 2016

In order to guarantee the process safety and prevent accidents, the deviations from normal operating conditions should be monitored and their root causes have to be identified as soon as possible. The statistical theories-based method among various fault diagnosis methods has been gaining popularity, due to simplicity and quickness. However, according to fault magnitudes, the scalar value generated by statistical methods can be changed and this point can lead to produce wrong information. To solve this difficulty, this work employs PCA (Principal Component Analysis) based method with qualitative information. In the case study of our previous study, the number of assumed faults is much smaller than that of process variables. In the case study of this study, the number of predefined faults is 19, while that of process variables is 6. It means that a fault diagnosis becomes more difficult and it is really hard to isolate a single fault with a small number of variables. The PCA model is constructed under normal operation data in order to get a loading vector and the data set of assumed faulty conditions is applied with PCA model. The significant changes on PC (Principal Components) axes are monitored with CUSUM (Cumulative Sum Control Chart) and recorded to make the information, which can be used to identify the types of fault.

• 한국전기전자재료학회논문지
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• 제19권2호
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• pp.162-168
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• 2006

Recently, diagnosis techniques have been investigated to detect a Partial Discharge associated with a dielectric material defect in a high voltage electrical apparatus, However, the properties of detection technique of Partial Discharge aren't completely understood because the physical process of Partial Discharge. Therefore, this paper analyzes the process on surface discharge of polymer insulator using wavelet transform. Wavelet transform provides a direct quantitative measure of spectral content in the time~frequency domain. As it is important to develop a non-contact method for detecting the kaolin contamination degree, this research analyzes the electromagnetic waves emitted from Partial Discharge using wavelet transform. This result experimentally shows the process of Partial Discharge as a two-dimensional distribution in the time-frequency domain. Feature extraction parameter namely, maximum and average of wavelet coefficients values, wavelet coefficients value at the point of $95\%$ in a histogram and number of maximum wavelet coefficient have used electromagnetic wave signals as input signals in the preprocessing process of neural networks in order to identify kaolin contamination rates. As result, root sum square error was produced by the test with a learning of neural networks obtained 0.00828.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전력기술부문
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• pp.27-29
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• 2006

This paper deals with the application of the concept of POM to analysis of power system behavior and describes a practical method of PRA for KEPCO system. This paper presents not only marginal power flow evaluation of KEPCO system in view point of physical and operation mode by using Physical and Operational Margins (POM Ver. 2.2), which is developed by V&R Energy System Research, but also by using Probabilistic Reliability Assessment (PRA Ver.3.1), which is developed by EPRI. The ability of the method to provide insights on root causes, weak points and regional causes and effects was shown. The approach offers fast and accurate determination of bottlenecks in the transmission network and optimal mitigation measures to alleviate the identified violations.

• 대한조선학회논문집
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• 제43권4호
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• pp.494-503
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• 2006

Inherent damage zone model is presented to explain the fatigue properties near the fatigue limit and the crack growth threshold consistently Inherent damage zone model assumes that the stress at a point which is located at a small distance, $r_0$, an inherent length of the material that represents the size of effective damage zone, from the crack initiation position governs the fatigue characteristics regardless of the geometric configuration of the specimen; smooth specimen, notched specimen or cracked specimens with short and long crack length. A special feature of the paper is using the exact stress distributions of notched and cracked specimens at the strength evaluations. Analytical elastic solutions by Neuber and Westergaard are employed for this purpose Relationship between fatigue limit of smooth specimen and threshold stress of cracked specimen, occurrence condition of non-propagating crack at the root of elliptic notch and circular hole and relationship between stress concentration factor and fatigue notch factor are discussed quantitatively based on the proposed model.

• Journal of Welding and Joining
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• 제22권6호
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• pp.57-63
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• 2004

Fracture toughness is an important parameter in designing offshore structures to ensure resistance to fracture at various temperatures. In this study, a series of experiments is carried out to obtain fracture toughness values (CTOD) of API 2W Gr.50B, welded using FCAW(Flux Cored Arc Weld). In particular, a comparison of absorbed impact energy and CTOD values are made with respect to two different welding groove shapes; double-V-groove and double-bevel-groove. Charpy impact tests are performed for specimens sampled near the root gap, and CTOD tests are carried out for three point bending specimens having the notch at weld zone. While Charpy impact test result is determined to be a good qualitative measure of fracture toughness, no quantitative correspondence between impact absorbed energy and CTOD values was found. Based on the experiment, it is observed that double-V-groove welds give lower transition temperature than those of double-bevel-groove.

• 산학경영연구
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• 제4권
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• pp.339-354
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• 1991

Araditionally, a business enterprise was a unit of individual economy which looked after it's own interesting. This business philosophy gave not only much wealth and advantages to the society but also caused many social problems, such as pollution, inferior goods, false advertisements, unreasonable packing and so on. Because of this criticism, it is necessary for us to fulfill the social responsibility of business and to make an accounts report about it. A business should examine itself that, for the long run, the philosophy, looking after its own interesting by means of unreasonable economical actions, is unfavorable to the business and be aware of the social responsibility of business. It is important that the business accounting should identifying, measuring and communicating on the former business actibities, but in order to help the persons interested in the business in the with their interests control and their appraising the degree of social contribution, its object should be the embodiment of social justice by giving the economic intelligences. We con get at the root of formation of corporate social accounting on this point, that it to say, we can lay it down that business activities deal with the affairs which are measured, reported, and appraised from the social view points. Givena definition of this corporate social accounting according to the general standard of business accounting. I think the persons interested in business can get useful accounting informations to make a reasonable decision from the social view points. Set forth the responsibility of accounting based on this, it is very meaningful to study in the social recognition.

• 한국분무공학회지
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• 제12권1호
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• pp.18-29
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• 2007

Feedwater heaters of many nuclear power plants have recently experienced severe wall thinning damage, which will increase as operating time progresses. Several nuclear power plants in Korea have experienced wall thinning damage in the area around the impingement baffle - installed downstream of the high pressure turbine extraction steam line - inside number 5A and 5B feedwater heaters. At that point, the extracted steam from the high pressure turbine is two phase fluid at high temperature, high pressure, and high speed. Since it flows in reverse direction after impinging the impingement baffle, the shell wall of the number 5 high pressure feedwater heater may be affected by flow-accelerated corrosion. This paper describes the comparisons between the numerical analysis results using the FLUENT code and the down scale experimental data in an effort to determine root causes of the shell wall thinning of the high pressure feedwater heaters. The numerical analysis and experimental data were also confirmed by actual wall thickness measured by an ultrasonic test.

• 터널과지하공간
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• 제12권4호
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• pp.268-276
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• 2002

In this study, a 3D coordinate measurement system equipped with a laser displacement meter for digitizing rock joint surface was established and the digitized data were used to calculate several roughness parameters. The parameters used in this study were micro avenge inclination $angle(i_{ave})$, average slope of joint $asperity(SL_{ ave})$, root mean square of $i-angle(i_{rms})$, standard deviation of height(SDH), standard deviation of $i-angle(SD_i)$, roughness profile $index(R_P)$, and fractal dimension(D). The relationships between the roughness parameters based on the digitzation of the surface profile were analyzed. Since the measured value varied according to the degree of reflection and the variation of colors at the measuring point, rock joint surface was painted in white to minimize the influence of the surface conditions. The comparison of the measured values and roughness parameters before and after painting revealed the better consequence from measurement on the painted surfaces. Also, effect of measuring interval was studied. As measured interval was increased, roughness parameters were exponentially decreased. The incremental sequence of degree of decrease was $SDH\; i_{ave},\; i_{rms},\; SD_i,\;and\; R_ p-1$. As a result of comparison of parameters from pin-type measurement system and laser type measurement system, all value of parameters were higher when laser-type measurement system was used, except SDH.

• 한국게임학회 논문지
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• 제19권6호
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• pp.99-106
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• 2019

본 논문에서는 두 타원체 사이의 중심 간 방향으로의 최단 접근 거리를 구하는 방법을 다룬다. 이는 타원체 사이의 충돌 검사 및 반응에 있어서 핵심 기술이다. 외부에서 서로 접하는 두 타원체의 중심 사이의 거리와 접촉점, 접촉방향에 관한 조건식을 세우고, 해를 포함하는 구간을 유지하는 이분법과 도함수를 이용하는 Newton 방법의 혼합을 통해 최단 접근 거리를 항상 안정적이며 효율적으로 구할 수 있게 한다. 또한 다양한 실험을 통해 제안된 방법의 안정성 및 효율성을 보인다.

• 대한전기학회논문지
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• 제44권10호
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• pp.1290-1294
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• 1995

In this paper, a new voltage collapse proximity index (VCPI) based on system apparent power loss sensitivity is proposed. The newly proposed index .lambda.$^{Sloss}$ reaches -.inf. at system voltage collapse point and can be represented by .root..lambda.$^{Ploss}$$^{2}$+.lambda.$^{Qloss}$$^{2}$ where .lambda.$^{Ploss}$ and .lambda.$^{Qloss}$ are the VCPI based on the system active and reactive power loss sensitivity respectively. These indices can be used for the system VAR investment. .DELTA.Q [VAR] is invested, step by step, by the priority of the VCPI index given for each bus. The indices use information from normal power flow equations and their Jacobians. Computation time for deriving .lambda.$^{Sloss}$ is almost same as that for power flow calculation. Two case studies prove the effectiveness of the .lambda.$^{Sloss}$ index and the VAR investment algorithm proposed.