• 제목/요약/키워드: SNB model

검색결과 16건 처리시간 0.028초

이산화탄소-수증기 혼합가스에 대한 파장별 회색가스가중합법에서 회색가스재조합에 대한 연구 (Study on Regrouping of Gray Gases in spectral WSGGM for Arbitrary Mixtures of CO2 and H2O Gases)

  • 박원희;김태국
    • 대한기계학회논문집B
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    • 제27권2호
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    • pp.227-235
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    • 2003
  • The WSGG-based narrow band model was employed to solve the radiative transfer equations along isothermal and non-isothermal paths through $CO_2-H_2O-N_2$ gas mixtures at 1 atm. When the WSGGM is applied for arbitrary gas mixtures by considering the multiplication property of transmissivity in overlapping bands, the number of gray gases is significantly increased. To reduce the computation time, three different regrouping methods for the gray gases are tested in obtaining the mean absorption coefficient for each gray gas group. Among them, the regrouping method by minimizing the regrouping error shows the best results. For the isothermal media, 10 gray gases show fairly good agreement with the results by statistical narrow band(SNB) model which are regarded as reference solutions. For non-isothermal media, 20 gray gases show good agreement with reference solutions.

Improving SARIMA model for reliable meteorological drought forecasting

  • Jehanzaib, Muhammad;Shah, Sabab Ali;Son, Ho Jun;Kim, Tae-Woong
    • 한국수자원학회:학술대회논문집
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    • 한국수자원학회 2022년도 학술발표회
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    • pp.141-141
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    • 2022
  • Drought is a global phenomenon that affects almost all landscapes and causes major damages. Due to non-linear nature of contributing factors, drought occurrence and its severity is characterized as stochastic in nature. Early warning of impending drought can aid in the development of drought mitigation strategies and measures. Thus, drought forecasting is crucial in the planning and management of water resource systems. The primary objective of this study is to make improvement is existing drought forecasting techniques. Therefore, we proposed an improved version of Seasonal Autoregressive Integrated Moving Average (SARIMA) model (MD-SARIMA) for reliable drought forecasting with three years lead time. In this study, we selected four watersheds of Han River basin in South Korea to validate the performance of MD-SARIMA model. The meteorological data from 8 rain gauge stations were collected for the period 1973-2016 and converted into watershed scale using Thiessen's polygon method. The Standardized Precipitation Index (SPI) was employed to represent the meteorological drought at seasonal (3-month) time scale. The performance of MD-SARIMA model was compared with existing models such as Seasonal Naive Bayes (SNB) model, Exponential Smoothing (ES) model, Trigonometric seasonality, Box-Cox transformation, ARMA errors, Trend and Seasonal components (TBATS) model, and SARIMA model. The results showed that all the models were able to forecast drought, but the performance of MD-SARIMA was robust then other statistical models with Wilmott Index (WI) = 0.86, Mean Absolute Error (MAE) = 0.66, and Root mean square error (RMSE) = 0.80 for 36 months lead time forecast. The outcomes of this study indicated that the MD-SARIMA model can be utilized for drought forecasting.

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비회색 가스 복사를 고려한 층류대향류 부분예혼합 화염에서의 $CO_2$$H_2O$ 첨가에 따른 영향 연구 (Effects of $CO_2$ and $H_2O$ Additions on Partially Premixed Counterflow Flame by Considering Nongray Gas Radiation)

  • 조범진;김태국
    • 한국연소학회지
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    • 제10권3호
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    • pp.10-16
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    • 2005
  • Detailed flame structures of the counterflow flames of $CH_4/Air$ formed with $CO_2$ and $H_2O$ addition are studied numerically. The detailed chemical reactions are modeled by using the OPPDIF and CHEMKIN-II code. Only the $CO_2$ and $H_2O$ are assumed to participate in radiative heat transfer while all other gases are assumed to be transparent. The discrete ordinates method(DOM) and the narrow band based WSGGM with a gray gas regrouping technique(WSGGM-RG) are applied for modeling the radiative transfer through non-homogeneous and non-isothermal combustion gas mixtures generated by the counter flow flames. The results compared with the SNB model show that the WSGGM-RG is successful in modeling the counterflow flames with non-gray gas mixture. The numerical results show that the addition of $CO_2$ and $H_2O$ to the oxidant nozzle lowers the peak temperature and the NO concentration in flame.

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회색가스 재조합에 의한 좁은밴드 회색가스가중합법을 이용한 3 차원 복사열전달 해석 연구 (3-Dimensional Radiative Transfer Analysis by Using the Narrow Band Based WSGGM with a Gray Gas Regrouping Technique)

  • 박원희;김태국;손봉세
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 추계학술대회
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    • pp.284-289
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    • 2003
  • The narrow band-averaged transmissivity of $CO_2-H_2O$ mixtures is expressed by multiplying the transmissivities of $CO_2$ and $H_2O$. Applying the multiplication property of narrow band transmissivities for gas mixtures of $CO_2-H_2O$, the number of gray gases, required for accurate representation of the absorption characteristics by using the narrow band based WSGGM, is significantly increased. To reduce the computational loads by reducing the number of gray gases, we propose a gray gas regrouping process where the gray gases used for the WSGGM are regrouped into a specified number of groups according to the magnitudes of absorption coefficients. To evaluate the proposed WSGGM for gas mixtures, the radiative transfer problems through three-dimensional gas media are considered. The radiative source terms and the radiative heat fluxes obtained by using the proposed method are fairly well compared to those obtained by using the SNB model. The regrouping technique results in an excellent computational efficiency with minor loss of accuracy.

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Effects of Additive and Preheat on the Partially Premixed $CH_4-Air$ Counter Flow Flames Considering Non-gray Gas Radiation

  • Park Won-Hee;Chang Hee-Chul;Kim Tae-Kuk
    • Journal of Mechanical Science and Technology
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    • 제20권2호
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    • pp.242-250
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    • 2006
  • Detailed structures of the counterflow flames formed for different inlet fluid temperatures and different amount of additives are studied numerically. The detailed chemical reactions are modeled by using the CHEMKIN-II code. The discrete ordinates method and the narrow band based WSGGM with a gray gas regrouping technique (WSGGM-RG) are applied for modeling the radiative transfer through non-homogeneous and non-isothermal combustion gas mixtures generated by the counterflow flames. The results compared with those obtained by using the SNB model show that the WSGGM-RG is very successful in modeling the counterflow flames with non-gray gas mixture. The numerical results also show that the addition of $CO_2\;or\;H_2O$ to the oxidant lowers the peak temperature and the NO concentration in flame. But preheat of fuel or oxidant raises the flame temperature and the NO production rates. $O_2$ enrichment also causes to raise the temperature distribution and the NO production in flame. And it is found that the $O_2$ enrichment and the fuel preheat were the major parameters in affecting the flame width.

하악 전방분절 절골술을 이용한 경미한 하악전돌증의 교정 (The Correction of Mild Mandibular Prognathism Using Mandibular Anterior Segmental Osteotomy)

  • 최재호;최준;김영환;윤성호;김영수;최영웅
    • Archives of Plastic Surgery
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    • 제34권6호
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    • pp.777-784
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    • 2007
  • Purpose: For a minor degree of mandibular prognathism, mandibular anterior segmental osteotomy (ASO), usually extracting the bilateral premolars, has been performed frequently to correct malocclusion of the anterior teeth. Preoperative planning using cephalometry and a dental model is very important for such a orthognathic surgery. Depending on the specific preoperative mock surgery with the dental model, ASO, with ipsilateral unitooth extraction, is defined to be feasible and performed for ten patients. The comparisons of its preoperative and postoperative analysis of clinical photographs, dental casts, and lateral cephalograms, for soft tissue profiles, skeletal and dental relationships are described in the following, and its clinical applications are noted. Methods: From March 1, 2004, to March 31, 2006, We performed 10 mandibular ASO by extraction of ipsilateral unitooth to improve their lower facial profiles and the lip relationships. Patient age ranged from 19 to 33 years, with a mean age of 25.6 years. Two were males and eight were females. Results: All patients were satisfied with aesthetic and occlusal changes postoperatively. Significant and persistent decrease in the SNB and interincisal angle were observed in the postoperative cephalometries. The soft tissue profiles also were improved and near Ricketts's esthetic line. Other combined procedures include nine genioplasties, two rhinoplasties, and one blepharoplasty. One patient complained of transient unilateral inferior mental nerve paresthesia. There were no other significant complications or relapses throughout the follow-up period(6-20 months). Conclusion: Mandibular ASO, extracting the ipsilateral unitooth, was performed for ten patients to correct mild mandibular prognathism. The amount of setback of the mandibular anterior portion was 2 to 3 mm, and satisfactory results were obtained combined with genioplasties.