• Title/Summary/Keyword: prediction of lifetime

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Temperature distribution of ceramic panels of a V94.2 gas turbine combustor under realistic operation conditions

  • Namayandeh, Mohammad Javad;Mohammadimehr, Mehdi;Mehrabi, Mojtaba
    • Advances in materials Research
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    • v.8 no.2
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    • pp.117-135
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    • 2019
  • The lifetime of a gas turbine combustor is typically limited by the durability of its liner, the structure that encloses the high-temperature combustion products. The primary objective of the combustor thermal design process is to ensure that the liner temperatures do not exceed a maximum value set by material limits. Liner temperatures exceeding these limits hasten the onset of cracking which increase the frequency of unscheduled engine removals and cause the maintenance and repair costs of the engine to increase. Hot gas temperature prediction can be considered a preliminary step for combustor liner temperature prediction which can make a suitable view of combustion chamber conditions. In this study, the temperature distribution of ceramic panels for a V94.2 gas turbine combustor subjected to realistic operation conditions is presented using three-dimensional finite difference method. A simplified model of alumina ceramic is used to obtain the temperature distribution. The external thermal loads consist of convection and radiation heat transfers are considered that these loads are applied to flat segmented panel on hot side and forced convection cooling on the other side. First the temperatures of hot and cold sides of ceramic are calculated. Then, the thermal boundary conditions of all other ceramic sides are estimated by the field observations. Finally, the temperature distributions of ceramic panels for a V94.2 gas turbine combustor are computed by MATLAB software. The results show that the gas emissivity for diffusion mode is more than premix therefore the radiation heat flux and temperature will be more. The results of this work are validated by ANSYS and ABAQUS softwares. It is showed that there is a good agreement between all results.

Characterization and Fatigue Life Evaluation of Rubber/Clay Nanocomposites (고무-점토 나노복합체 물성 및 피로내구성 평가)

  • Woo, Chang-Su;Park, Hyun-Sung;Joe, Deug-Hwan;Jun, Young-Sig
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.10
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    • pp.1199-1203
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    • 2011
  • Nanocomposites were prepared through the compounding of rubber and clay. Measurements of the static and dynamic mechanical properties of different compositions over a temperature range $70-100^{\circ}C$ showed that the mechanical properties of these rubber/clay nanocomposites are superior to those of existing rubber materials. In this study, by using the parameter of the maximum Green.Lagrange strain appearing at certain locations, the relationship between fatigue life and maximum Green.Lagrange strain, and the correlations between test-piece tests and bench tests of actual rubber components are proved. In order to predict the fatigue life of rubber components at the design stage, a simple procedure of life prediction is suggested. The predicted fatigue lives of the rubber engine mounts agree fairly well with the fatigue lives determined experimentally.

Life-cycle estimation of HVDC full-bridge sub-module considering operational condition and redundancy (HVDC 풀-브리지 서브모듈의 동작 조건과 여유율을 고려한 수명예측)

  • Kang, Feel-soon;Song, Sung-Geun
    • Journal of IKEEE
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    • v.23 no.4
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    • pp.1208-1217
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    • 2019
  • The life-cycle prediction of the sub-module which is the unit system of MMC is very important from the viewpoint of maintenance and economic feasibility of HVDC system. However, the life-cycle prediction that considers only the type, number and combination of parts is a generalized result that does not take into account the operating condition of the sub-module, and may significantly differ from the life-cycle of the actual one. Therefore, we design a fault tree for the purpose of reflecting the operation characteristics of the full-bridge sub-module and apply the MIL-HDBK-217F to the failure rate of the basic event to predict the life-cycle of the full-bridge sub-module. It compares the life-cycle expectancy of the conventional failure rate analysis with the proposed fault-tree analysis and compares the lifetime according to whether the redundancy of the full-bridge sub-module is considered.

Prediction of Inhalation Exposure to Benzene by Activity Stage Using a Caltox Model at the Daesan Petrochemical Complex in South Korea (CalTOX 모델을 이용한 대산 석유화학단지의 활동단계에 따른 벤젠 흡입 노출평가)

  • Lee, Jinheon;Lee, Minwoo;Park, Changyong;Park, Sanghyun;Song, Youngho;Kim, Ok;Shin, Jihun
    • Journal of Environmental Health Sciences
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    • v.48 no.3
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    • pp.151-158
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    • 2022
  • Background: Chemical emissions in the environment have rapidly increased with the accelerated industrialization taking place in recent decades. Residents of industrial complexes are concerned about the health risks posed by chemical exposure. Objectives: This study was performed to suggest modeling methods that take into account multimedia and multi-pathways in human exposure and risk assessment. Methods: The concentration of benzene emitted at industrial complexes in Daesan, South Korea and the exposure of local residents was estimated using the Caltox model. The amount of human exposure based on inhalation rate was stochastically predicted for various activity stages such as resting, normal walking, and fast walking. Results: The coefficient of determination (R2) for the CalTOX model efficiency was 0.9676 and the root-mean-square error (RMSE) was 0.0035, indicating good agreement between predictions and measurements. However, the efficiency index (EI) appeared to be a negative value at -1094.4997. This can be explained as the atmospheric concentration being calculated only from the emissions from industrial facilities in the study area. In the human exposure assessment, the higher the inhalation rate percentile value, the higher the inhalation rate and lifetime average daily dose (LADD) at each activity step. Conclusions: Prediction using the Caltox model might be appropriate for comparing with actual measurements. The LADD of females was higher ratio with an increase in inhalation rate than those of males. This finding would imply that females may be more susceptible to benzene as their inhalation rate increases.

Statistical analysis on the fluence factor of surveillance test data of Korean nuclear power plants

  • Lee, Gyeong-Geun;Kim, Min-Chul;Yoon, Ji-Hyun;Lee, Bong-Sang;Lim, Sangyeob;Kwon, Junhyun
    • Nuclear Engineering and Technology
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    • v.49 no.4
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    • pp.760-768
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    • 2017
  • The transition temperature shift (TTS) of the reactor pressure vessel materials is an important factor that determines the lifetime of a nuclear power plant. The prediction of the TTS at the end of a plant's lifespan is calculated based on the equation of Regulatory Guide 1.99 revision 2 (RG1.99/2) from the US. The fluence factor in the equation was expressed as a power function, and the exponent value was determined by the early surveillance data in the US. Recently, an advanced approach to estimate the TTS was proposed in various countries for nuclear power plants, and Korea is considering the development of a new TTS model. In this study, the TTS trend of the Korean surveillance test results was analyzed using a nonlinear regression model and a mixed-effect model based on the power function. The nonlinear regression model yielded a similar exponent as the power function in the fluence compared with RG1.99/2. The mixed-effect model had a higher value of the exponent and showed superior goodness of fit compared with the nonlinear regression model. Compared with RG1.99/2 and RG1.99/3, the mixed-effect model provided a more accurate prediction of the TTS.

A Methodology of Customer Churn Prediction based on Two-Dimensional Loyalty Segmentation (이차원 고객충성도 세그먼트 기반의 고객이탈예측 방법론)

  • Kim, Hyung Su;Hong, Seung Woo
    • Journal of Intelligence and Information Systems
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    • v.26 no.4
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    • pp.111-126
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    • 2020
  • Most industries have recently become aware of the importance of customer lifetime value as they are exposed to a competitive environment. As a result, preventing customers from churn is becoming a more important business issue than securing new customers. This is because maintaining churn customers is far more economical than securing new customers, and in fact, the acquisition cost of new customers is known to be five to six times higher than the maintenance cost of churn customers. Also, Companies that effectively prevent customer churn and improve customer retention rates are known to have a positive effect on not only increasing the company's profitability but also improving its brand image by improving customer satisfaction. Predicting customer churn, which had been conducted as a sub-research area for CRM, has recently become more important as a big data-based performance marketing theme due to the development of business machine learning technology. Until now, research on customer churn prediction has been carried out actively in such sectors as the mobile telecommunication industry, the financial industry, the distribution industry, and the game industry, which are highly competitive and urgent to manage churn. In addition, These churn prediction studies were focused on improving the performance of the churn prediction model itself, such as simply comparing the performance of various models, exploring features that are effective in forecasting departures, or developing new ensemble techniques, and were limited in terms of practical utilization because most studies considered the entire customer group as a group and developed a predictive model. As such, the main purpose of the existing related research was to improve the performance of the predictive model itself, and there was a relatively lack of research to improve the overall customer churn prediction process. In fact, customers in the business have different behavior characteristics due to heterogeneous transaction patterns, and the resulting churn rate is different, so it is unreasonable to assume the entire customer as a single customer group. Therefore, it is desirable to segment customers according to customer classification criteria, such as loyalty, and to operate an appropriate churn prediction model individually, in order to carry out effective customer churn predictions in heterogeneous industries. Of course, in some studies, there are studies in which customers are subdivided using clustering techniques and applied a churn prediction model for individual customer groups. Although this process of predicting churn can produce better predictions than a single predict model for the entire customer population, there is still room for improvement in that clustering is a mechanical, exploratory grouping technique that calculates distances based on inputs and does not reflect the strategic intent of an entity such as loyalties. This study proposes a segment-based customer departure prediction process (CCP/2DL: Customer Churn Prediction based on Two-Dimensional Loyalty segmentation) based on two-dimensional customer loyalty, assuming that successful customer churn management can be better done through improvements in the overall process than through the performance of the model itself. CCP/2DL is a series of churn prediction processes that segment two-way, quantitative and qualitative loyalty-based customer, conduct secondary grouping of customer segments according to churn patterns, and then independently apply heterogeneous churn prediction models for each churn pattern group. Performance comparisons were performed with the most commonly applied the General churn prediction process and the Clustering-based churn prediction process to assess the relative excellence of the proposed churn prediction process. The General churn prediction process used in this study refers to the process of predicting a single group of customers simply intended to be predicted as a machine learning model, using the most commonly used churn predicting method. And the Clustering-based churn prediction process is a method of first using clustering techniques to segment customers and implement a churn prediction model for each individual group. In cooperation with a global NGO, the proposed CCP/2DL performance showed better performance than other methodologies for predicting churn. This churn prediction process is not only effective in predicting churn, but can also be a strategic basis for obtaining a variety of customer observations and carrying out other related performance marketing activities.

Prediction of Fretting Fatigue Life on 2024-T351 Al-alloy (2024-T351 알루미늄 합금판 프레팅 피로수명 예측)

  • Kwon, Jung-Ho;Hwang, Kyung-Jung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.7
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    • pp.601-611
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    • 2007
  • Most of mechanically jointed aircraft structures are always encountered the fretting damages on the contact surfaces between two jointed structural members or at the edges of fastener holes. The partial slip and contact stresses associated with fretting contact can lead to severe reduction in service lifetime of aircraft structures. Thus a critical need exists for predicting fretting crack initiation in mechanically jointed aircraft structures, which requires characterizing both the near-surface mechanics and intimate relationship with fretting parameters. In this point of view, a series of fretting fatigue specimen tests for 2024-T351 Al-alloy, have been conducted to validate a mechanics-based model for predicting fretting fatigue life. And included in this investigaion were elasto-plastic contact stress analyses using commercial FEA code to quantify the stress and strain fields in subsurface to evaluate the fretting fatigue crack initiation.

Comparative Study of AI Models for Reliability Function Estimation in NPP Digital I&C System Failure Prediction (원전 디지털 I&C 계통 고장예측을 위한 신뢰도 함수 추정 인공지능 모델 비교연구)

  • DaeYoung Lee;JeongHun Lee;SeungHyeok Yang
    • Journal of Korea Society of Industrial Information Systems
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    • v.28 no.6
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    • pp.1-10
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    • 2023
  • The nuclear power plant(NPP)'s Instrumentation and Control(I&C) system periodically conducts integrity checks for the maintenance of self-diagnostic function during normal operation. Additionally, it performs functionality and performance checks during planned preventive maintenance periods. However, there is a need for technological development to diagnose failures and prevent accidents in advance. In this paper, we studied methods for estimating the reliability function by utilizing environmental data and self-diagnostic data of the I&C equipment. To obtain failure data, we assumed probability distributions for component features of the I&C equipment and generated virtual failure data. Using this failure data, we estimated the reliability function using representative artificial intelligence(AI) models used in survival analysis(DeepSurve, DeepHit). And we also estimated the reliability function through the Cox regression model of the traditional semi-parametric method. We confirmed the feasibility through the residual lifetime calculations based on environmental and diagnostic data.

Biomarkers for Evaluation of Prostate Cancer Prognosis

  • Esfahani, Maryam;Ataei, Negar;Panjehpour, Mojtaba
    • Asian Pacific Journal of Cancer Prevention
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    • v.16 no.7
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    • pp.2601-2611
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    • 2015
  • Prostate cancer, with a lifetime prevalence of one in six men, is the second cause of malignancy-related death and the most prevalent cancer in men in many countries. Nowadays, prostate cancer diagnosis is often based on the use of biomarkers, especially prostate-specific antigen (PSA) which can result in enhanced detection at earlier stage and decreasing in the number of metastatic patients. However, because of the low specificity of PSA, unnecessary biopsies and mistaken diagnoses frequently occur. Prostate cancer has various features so prognosis following diagnosis is greatly variable. There is a requirement for new prognostic biomarkers, particularly to differentiate between inactive and aggressive forms of disease, to improve clinical management of prostate cancer. Research continues into finding additional markers that may allow this goal to be attained. We here selected a group of candidate biomarkers including PSA, PSA velocity, percentage free PSA, $TGF{\beta}1$, AMACR, chromogranin A, IL-6, IGFBPs, PSCA, biomarkers related to cell cycle regulation, apoptosis, PTEN, androgen receptor, cellular adhesion and angiogenesis, and also prognostic biomarkers with Genomic tests for discussion. This provides an outline of biomarkers that are presently of prognostic interest in prostate cancer investigation.

Service life prediction of chloride-corrosive concrete under fatigue load

  • Yang, Tao;Guan, Bowen;Liu, Guoqiang;Li, Jing;Pan, Yuanyuan;Jia, Yanshun;Zhao, Yongli
    • Advances in concrete construction
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    • v.8 no.1
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    • pp.55-64
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    • 2019
  • Chloride corrosion has become the main factor of reducing the service life of reinforced concrete structures. The object of this paper is to propose a theoretical model that predicts the service life of chloride-corrosive concrete under fatigue load. In the process of modeling, the concrete is divided into two parts, microcrack and matrix. Taking the variation of mcirocrack area caused by fatigue load into account, an equation of chloride diffusion coefficient under fatigue load is established, and then the predictive model is developed based on Fick's second law. This model has an analytic solution and is reasonable in comparison to previous studies. Finally, some factors (chloride diffusion coefficient, surface chloride concentration and fatigue parameter) are analyzed to further investigate this model. The results indicate: the time to pit-to-crack transition and time to crack growth should not be neglected when predicting service life of concrete in strong corrosive condition; the type of fatigue loads also has a great impact on lifetime of concrete. In generally, this model is convenient to predict service life of chloride-corrosive concrete with different water to cement ratio, under different corrosive condition and under different types of fatigue load.