• Journal of applied mathematics & informatics
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• 제29권5_6호
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• pp.1435-1451
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• 2011

In this paper the estimation of the parameters as well as survival and hazard functions are presented for the two-parameter Pareto distribution by using Bayesian and non-Bayesian approaches under upper record values. Maximum likelihood estimation (MLE) and interval estimation are derived for the parameters. Bayes estimators of reliability performances are obtained under symmetric (Squared error) and asymmetric (Linex and general entropy (GE)) losses, when two parameters have discrete and continuous priors, respectively. Finally, two numerical examples with real data set and simulated data, are presented to illustrate the proposed method. An algorithm is introduced to generate records data, then a simulation study is performed and different estimates results are compared.

• 드라이브 ㆍ 컨트롤
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• 제15권4호
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• pp.48-54
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• 2018

The hydraulic servo actuator has always operated very precisely with high frequency and small displacement, and is used continuously for a long time. The hydraulic servo actuator of the test equipment used in the accelerated life test in order to guarantee the service life of the automotive parts failed earlier than the products before finishing the test. This study performed an analysis on the cause of the failure of the hydraulic servo actuator used in the test equipment, changed the design of the actuator to solve the root cause of the main failure mode, and developed the improved servo actuator. Based on above process, this study established a better performances and longer lifetime of the servo actuator after testing.

• Journal of Power Electronics
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• 제15권5호
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• pp.1149-1157
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• 2015

As a key part in the wind turbine system, the power electronic converter is proven to have high failure rates. At the same time, the failure of the wind power converter is becoming more unacceptable because of the quick growth in capacity, remote locations to reach, and strong impact to the power grid. As a result, the correct assessment of reliable performance for power electronics is a crucial and emerging need; the assessment is essential for design improvement, as well as for the extension of converter lifetime and reduction of energy cost. Unfortunately, there still exists a lack of suitable physic-of-failure based evaluation tools for a reliability assessment in power electronics. In this paper, an advanced tool structure which can acquire various reliability metrics of wind power converter is proposed. The tool is based on failure mechanisms in critical components of the system and mission profiles in wind turbines. Potential methodologies, challenges, and technology trends involved in this tool structure are also discussed. Finally, a simplified version of the tool is demonstrated on a wind power converter based on Double Fed Induction Generator system. With the proposed tool structure, more detailed information of reliability performances in a wind power converter can be obtained before the converter can actually fail in the field and many potential research topics can also be initiated.

• 한국항공우주학회지
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• 제34권8호
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• pp.24-32
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• 2006

결정론적인 최적 설계 방법을 이용하는 경우 불확실성의 영향으로 인하여 제약조건의 위반이나 목표 성능의 저하를 초래할 수 있다. 이러한 까닭에 불확실성하에서 제약 조건에 대한 신뢰성을 보장하고 목적함수의 강건성을 확보하는 설계가 필요하다. 그러므로 본 연구에서는 강건성과 신뢰성을 평가하기 위하여 Monte Carlo Simulation(MCS)을 이용하였으며, 계산 효율의 증가를 위하여 MCS에 적합한 근사모델을 선정하는 과정을 거쳐 신경망 모델을 채택하게 되었다. 이를 공력-구조가 연동된 항공기 날개 설계 문제에 적용하여 봄으로써 그 가능성을 타진하였다. 불확실성을 고려한 최적 설계를 수행한 결과 요구되는 신뢰도 수준을 만족시키면서 baseline보다 강건한 최적해를 탐색하는 것이 가능하였다.

• 대한간호학회지
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• 제27권2호
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• pp.303-314
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• 1997

This is descripitive study conducted to identify educational needs of mothers of nephrotic syndrome patients and tie degree of nerses' educational performances perceived by mothers who look after mainly nephrotic syndrome patients. The study subjects were composed of 74 mothers of nephrotic syndrome patients whose children were hospitalized in 2 Pediatric wards of University Hospital in Seoul and 1 in Pen from June in 1996 to Januaryin 1997. A questionaire for this study was item Kikert type 5 point scale, developed on the basis of previous literature and researcher's clinical experience and the reliability of the used instruments was α=.97. The data analysis was done by SAS. t-test, and ANOVA were done to determine the effect of general characteristics of subjects on their educational needs. Pearson correlation was done to measure relations between general characterictics of subjects and their educational needs and Stepwise Multiple Regression was done to test a variable affecting educational needs. The results were as follows. 1. Mean score of educational needs of subjects was 137.06(Maximum 176). The score of the educational needs of home care was the highes, but the question numbers(of that category) are smaller than others. So, the educational need of the diagnosis art treatment was regarded as the highest in contents. 2. The mean score of nurses' educational performances was very low, 74.91(Maximum 176). Nurse's educational performances score in the diagnosis and treatment of the disease ranked as the highest Burt that score in the care during hoapitalization was the highest in contents as the educational needs was. 3. The number of children excepting the patient (r²=.215289. p=.006) and the age of patient(r²=.23770, p=.001) were emerged as important variables affecting the degree of mother's educational need.

• 한국병원경영학회지
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• 제22권4호
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• pp.74-86
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• 2017

Purposes: This study was performed to understand the recognition about accreditation motives, support within the hospital and accreditation survey process for the hospitals that participated in the accreditation program and to find out whether these factors are related to hospital management performances, so that the study can suggest plans for activation and development of the accreditation program. Methodology: This study was performed targeting 98 hospitals answered th the survey among 189 acute care hospitals that acquired accreditation from December 2010 to February 2014. For data analysis, frequency analysis, ${\chi}^2$-test, reliability analysis, ANOVA, Kruskal-Wallis H test and multiple regression analysis with SPSS 21.0 were used. Findings: The hospitals that had staff in charge of patient safety had bigger hospital culture change than those that didn't have(p<.05). In addition, the hospital culture change was bigger as internal motives were bigger, and as CEO's will was bigger(p<.05). Meanwhile, as maintenance rate of internal management after accreditation was higher, and as CEO's will was bigger, process improvement level was higher(p<.05). The quality improvement and patient satisfaction level were higher as CEO's will was bigger, and as suitability of survey process was recognized to be high(p<.05). As a result of analyzing the factors that affect hospital management performances with hospital culture change, process improvement and quality improvement combined, as internal management maintenance rate was higher, as CEO's will was bigger, and as suitability of survey process was higher, performances were higher(p<.05). Practical Implications: Hospitals need to reinforce internal motives to improve internal competences such as the whole system maintenance opportunity and staff training. In addition, the will of hospital director is most important, and if there is hospital director's interest in quality improvement and improvement intention definitely, employees voluntarily participate in and cooperate with the accreditation program, so that prompt medical service provision and high quality of medical services can be guaranteed, leading to hospitals' management performances.

• 대한지역사회영양학회지
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• 제11권1호
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• pp.116-123
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• 2006

The purposes of this study were to develop a tool for assessing internal branding performance and to identify the difference of internal branding performance between local and international hotels. The internal branding performance measure was developed through literature studies and face-to-face in-depth interviews with managers in various departments of 5 deluxe hotels. The questionnaires were distributed to 460 employees in food and beverage departments of 11 deluxe hotels in Seoul, and a total of 398 questionnaires were used for analysis ($86.5\%$). The statistical analyses were completed using SPSS Win (12.0) for descriptive analysis, reliability analysis and t-test, and AMOS (5.0) for confirmatory factor analysis. The results of this study showed that the measure developed in this study was reliable and valid for assessing internal branding performances of hotels. In addition, the internal branding performances of hotels were high at understanding of brand dimensions and relatively low at work and organizational culture and human resource management dimensions, and local hotels showed lower levels of performance than international hotels at the dimensions of work and organizational culture (t = -3.801, P < 0.001) and human resource management(t = -5.397, p < 0.001). In conclusion, it is considered that a strong internal branding strategy should be established for successful brand management, and the practical measure for internal branding performance would be a key factor.

• Earthquakes and Structures
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• 제15권4호
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• pp.431-441
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• 2018

This study provides fragility-based assessment of seismic performance of reinforced concrete bridges. Seismic fragility curves were created using nonlinear analysis (NA) and artificial neural networks (ANNs). Nonlinear response history analyses were performed, in order to calculate the seismic performances of the bridges. To this end, 306 bridge-earthquake cases were considered. A multi-layered perceptron (MLP) neural network was implemented to predict the seismic performances of the selected bridges. The MLP neural networks considered herein consist of an input layer with four input vectors; two hidden layers and an output vector. In order to train ANNs, 70% of the numerical results were selected, and the remained 30% were employed for testing the reliability and validation of ANNs. Several structures of MLP neural networks were examined in order to obtain suitable neural networks. After achieving the most proper structure of neural network, it was used for generating new data. A total number of 600 new bridge-earthquake cases were generated based on neural simulation. Finally, probabilistic seismic safety analyses were conducted. Herein, fragility curves were developed using numerical results, neural predictions and the combination of numerical and neural data. Results of this study revealed that ANNs are suitable tools for predicting seismic performances of RC bridges. It was also shown that yield stresses of the reinforcements is one of the important sources of uncertainty in fragility analysis of RC bridges.

• 한국자동차공학회논문집
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• 제12권2호
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• pp.123-130
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• 2004

The automobile suspension system is composed of parts that affect performances of a vehicle such as ride quality, handling characteristics, straight performance and steering effort, etc. Moreover, by using the finite element analysis the cost for the initial design step can be decreased. In the design of a suspension system, usually system vibration and structural rigidity must be considered simultaneously to satisfy dynamic and static requirements simultaneously. In this paper, we consider the weight reduction and the increase of the first eigen-frequency of a suspension part, the upper control arm, especially using topology optimization and size optimization. Firstly, we obtain the initial design to maximize the first eigen-frequency using topology optimization. Then, we apply the multi-objective parameter optimization method to satisfy both the weight reduction and the increase of the first eigen-frequency. The design variables are varying during the optimization process for the multi-objective. Therefore, we can obtain the deterministic values of the design variables not only to satisfy the terms of variation limits but also to optimize the two design objectives at the same time. Finally, we have executed reliability based optimal design on the upper control arm using the Monte-Carlo method with importance sampling method for the optimal design result with 98％ reliability.

• Smart Structures and Systems
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• 제14권5호
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• pp.847-867
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• 2014

There are continuous efforts to mitigate structural losses from earthquakes and manage risk through seismic risk assessment; seismic fragility curves are widely accepted as an essential tool of such efforts. Seismic fragility curves can be classified into four groups based on how they are derived: empirical, judgmental, analytical, and hybrid. Analytical fragility curves are the most widely used and can be further categorized into two subgroups, depending on whether an analytical function or simulation method is used. Although both methods have shown decent performances for many seismic fragility problems, they often oversimplify the given problems in reliability or structural analyses owing to their built-in assumptions. In this paper, a new method is proposed for the development of seismic fragility curves. Integration with sophisticated software packages for reliability analysis (FERUM) and structural analysis (ZEUS-NL) allows the new method to obtain more accurate seismic fragility curves for less computational cost. Because the proposed method performs reliability analysis using the first-order reliability method, it provides component probabilities as well as useful byproducts and allows further fragility analysis at the system level. The new method was applied to a numerical example of a 2D frame structure, and the results were compared with those by Monte Carlo simulation. The method was found to generate seismic fragility curves more accurately and efficiently. Also, the effect of system reliability analysis on the development of seismic fragility curves was investigated using the given numerical example and its necessity was discussed.