칼라 등색선무늬용 광탄성실험 하이브릿법 개발에 관한연구

권오성(O-Sung Kwon),황재석(Jai-Sug Hawong),남정환(Jeong-Hwan Nam),한송령(Song-Ling Han),권건(Gun Kwon),류의(Yi Liu) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5

Isochromatics obtained from photoelastic experiment shows the stress distributions of full field of a structure under a load. Therefore stress distributions of the structure can be read at a glace through isochromatics. Many experimental data are obtained from isochromatics. And then, the various photoelastic experimental hybrid methods have been developed. Until now, monochromatic light has been used for photoelastic experimental hybrid method. Therefore the photoelastic experimental hybrid method used until now is called the photoelastic experimental hybrid method for black and white isochromatics. When stresses are analyed by photoelastic experimental hybrid method, many experimental data are needed. Therefore some fringe orders of isochromatics are needed for the photoelastic experimental hybrid method for white and black isochromatics. Therefore in this paper, the photoelastic experimental hybrid method for color isochromatics is developed. In this case, two fringe orders are enough for the experimental data of photoelastic experimental hybrid method for color isochromatics. Applying the method to stress concentration problems, its validity is confirmed. In the precision, the photoelastic experimental hybrid method for color isochromatics is better than the photoelastic experimental hybrid method for white and black isochromatics when fringe orders of isochromatics are few. When fringe orders are few, the photoelastic experimental hybrid method for color isochromatics can be used to analyze stress through few fringe orders of isochromatics.

study on the development of photoelastic experimental hybrid method for colour isochromatics (Ⅰ)

황재석,남정환,김교형,권오성,Gun Kwon,박성한 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.6

Isochromatics obtained from photoelastic experiment shows the stress distributions of the full field of a structure under load. Therefore, stress distributions of the structure can be read at a glance through isochromatics. Many experimental data can be obtained from isochromatics which are then used in various photoelastic experimental hybrid methods for stress analysis. Monochromatic light has however, until now been used in the photoelastic experimental hybrid method to produce black and white isochromatics. The use of black and white isochromatics in photoelastic experimental hybrid method for black and white isochromatics requires high fringe orders in order to obtain sufficient experimental data for photoelastic hybrid techniques. Accordingly,this paper develops the photoelastic experimental hybrid method for color isochromatics in which a fringe order of 1 is enough to gather the experimental data of the photoelastic experimental hybrid method. The method was applied to validate stress concentration problems. Experimental results from this study indicated that the photoelastic experimental hybrid method for color isochromatics is more precise than the photoelastic experimental hybrid method for black and white isochromatics. The use of few fringe orders in photoelastic experimental hybrid method for color isochromatics can offer significant advantages in stress analysis of real components using reflective-type photoelastic experimental method.

A study on the development of photoelastic experimental hybrid method for colour isochromatics (II)

남정환,황재석,Gun Kwon,신동철,Bruno R. Mose,박성한 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.7

Using the photoelastic experimental hybrid method, we can obtain stress intensity factors and separate the stress components near the crack tip of any material under various loading conditions from only isochromatics. However, monochromatic light has, until now been used in the photoelastic experimental hybrid method to produce black and white isochromatics. The existing photoelastic experimental hybrid method using black and white isochromatics requires high order fringes to obtain sufficient experimental data for photoelastic hybrid techniques. If a photoelastic experimental hybrid method for colour isochromatics is developed, isochromatics with a maximum fringe order of 2 will be adequate for gathering the necessary experimental data for stress analyses using photoelastic hybrid techniques. Therefore, in this work, photoelastic experimental hybrid method for colour isochromatics of a crack problem was developed, and its superiority demonstrated by comparing its results with the results from black and white isochromatics. The use of few fringe orders in photoelastic experimental hybrid method for colour isochromatics is an important feature of this method. Because of this feature, this method, specifically the reflection type photoelastic method where low fringe orders are produced compared to the transmission type photoelastic method, can be widely used in stress analysis of real components.

Topology optimization of bounded acoustic problems using the hybrid finite element-wave based method

Goo, S.,Wang, S.,Kook, J.,Koo, K.,Hyun, J. North-Holland Pub. Co 2017 Computer methods in applied mechanics and engineer Vol.313 No.-

This paper presents an alternative topology optimization method for bounded acoustic problems that uses the hybrid finite element-wave based method (FE-WBM). The conventional method for the topology optimization of bounded acoustic problems is based on the finite element method (FEM), which is limited to low frequency applications due to considerable computational efforts. To this end, we propose a gradient-based topology optimization method that uses the hybrid FE-WBM whereby the entire domain of a problem is partitioned into design and non-design domains. In this respect, the FEM is used as a design domain of topology optimization, and the WBM is used as a non-design domain to increase computational efficiency. The adjoint variable method based on the hybrid FE-WBM is also proposed as a means of computing design sensitivities. Numerical examples are presented to demonstrate the effectiveness of the proposed method. We compare the optimized design obtained from the proposed method to that obtained from the conventional method in terms of objective function values, optimized topologies and computational efficiency. The optimization results show that the proposed method can perform more efficient topology optimization than conventional method and can thus be applied to much higher frequency applications that conventional method takes considerable computation time to manage.

Lattice Boltzmann 방법을 사용한 자연대류 해석에서 열모델의 선택에 관한 연구

최석기(Seok-Ki Choi),김성오(Seong-O Kim) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.4

A comparative analysis of thermal models in the lattice Boltzmann method(LBM) for the simulation of laminar natural convection in a square cavity is presented. A HYBRID method, in which the thermal equation is solved by the Navier-Stokes equation method while the mass and momentum conservation are resolved by the lattice Boltzmann method, is introduced and its merits are explained. All the governing equations are discretized on a cell-centered, non-uniform grid using the finite-volume method. The convection terms are treated by a second-order central-difference scheme with a deferred correction method to ensure stability of the solutions. The HYBRID method and the double ?population method are applied to the simulation of natural convection in a square cavity and the predicted results are compared with the benchmark solutions given in the literatures. The predicted results are also compared with those by the conventional Navier-Stokes equation method. In general, the present HYBRID method is as accurate as the Navier-Stokes equation method and the double-population method. The HYBRID method shows better convergence and stability than the double-population method. These observations indicate that this HYBRID method is an efficient and economic method for the simulation of incompressible fluid flow and heat transfer problem with the LBM.

Lattice Boltzmann 방법을 사용한 층류 및 난류 자연대류 해석

최석기(Seok-Ki Choi),김성오(Seong-O Kim) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.11

A study on the computation of laminar and turbulent natural convection with the lattice Boltzmann method(LBM) is presented. First, a comparative analysis of thermal models in the LBM for the simulation of natural convection in enclosures is presented. A HYBRID method, in which the thermal equation is solved by the Navier-Stokes equation method while the mass and momentum conservation are resolved by the LBM, is introduced and its merits are explained. All the governing equations are discretized on a cell-centered, non-uniform grid using the finite-volume method. The convection terms are treated by a second-order central-difference scheme with a deferred correction method to ensure stability of the solutions. The HYBRID and double-population LBM are applied to the simulation of laminar natural convection in square cavity and the predicted results are compared with the benchmark solutions given in the literatures. The predicted results are also compared with those by the Navier-Stokes equation method. In general, the present HYBRID method is as accurate as the Navier-Stokes equation method and the double-population LBM. The HYBRID method shows better convergence and stability than the double-population LBM. The present HYBRID LBM is also applied to the prediction of a turbulent natural convection in a rectangular cavity and the computed results are compared with the experimental data. The elliptic-relaxation model is employed for the turbulence model and the turbulent heat fluxes are treated by the algebraic flux model. It is shown that the LBM with the present HYBRID thermal model predicts the mean velocity components and turbulent quantities accurately which are as good as those by the conventional finite-volume method.

Comparison of shaping ability between various hybrid instrumentation methods with ProTaper

Hong, Eun-Sook,Park, Jeong-Kil,Hur, Bock,Kim, Hyeon-Cheol 大韓齒科保存學會 2006 Restorative Dentistry & Endodontics Vol.31 No.1

이 연구의 목적은 ProTaper^(®) S1과 3가지 종류의 파일을 각각 같이 사용하는 혼합법의 근관성형 효율을 비교해 보는 것이다. 5년 이상의 임상경력을 가진 치과의사 20명이 Ni-Ti 파일 경험자군과 비경험자군으로 나뉘어, ProTaper^(®)만을 사용한 C군과 ProTaper^(®) S1과 함께 세 종류의 파일 시스템- ProFile^(®) (P군), HeroShaper^(®) (H군), K-Flexofile^(®) (S군)을 혼합 적용하여,각각의 방법으로 레진 근관을 성형하였다. 성형 전후 이미지를 중첩 시켜 근관형태 이상을 조사하고, 근단공부터 1, 2, 3 ㎜ 위치에서 근관 폭경의 변화량, 중심 변위율을 산출, 비교하여 다음의 결과를 얻었다. C군과 S군 모두 다른 실험군에 비해 성형시간이 많이 소요되었다. 경험자군에 비해 비경험자군에서는 C군과 H군에서 더 많은 시간이 소요되었다. P군의 중심변위율은 ProTaper^(®)만을 사용한 C군이나 SS 파일을 사용한 S군보다 양호 하였다. 마찬가지로, 경험자군의 경우에서는 P군에 추가하여 H군도 더 나은 결과를 보였다 (p < 0.05). 이 실험 조건하에, ProFile^(®)과 HeroShaper^(®)를 사용한 혼합법이 ProTaper^(®)만을 사용한 성형방법보다 더욱 추천된다. The purpose of this study was to compare and evaluate the shaping abilities of various hybrid instrumentation method using constant tapered file systems with ProTaper^(®) S1 and the difference between experts and inexperienced clinincians in use of NiTi file. Three hybrid methods used in this study were composed of ProTaper^(®) S1 and K- Flexofile^(®) (group S), ProTaper^(®) S1 and HeroShaper^(®) (group H), and ProTaper^(®) S1 and ProFile^(®) (group P), respectively. The ProTaper^(®) -alone method (group C) was introduced as a control group. After canal preparation, the lapse of time was recorded. The images of pre- and post-operative canal were scanned and superimposed. Amounts of instrumented canal widths and centering ratio were measured at apical 1, 2 and 3 ㎜ levels and statistical analysis was performed. In this study, both of the group C and S took more time to prepare canals than other groups. Inexperienced operators required more time for the entire preparation with the groups C and H than the experienced (p < 0.05). And the centering ratio of group P were preferable to ProTaper^(®) -alone method or the hybrid technique using stainless steel files. As such, within experienced operators, group H also showed better results in addition to the group P. Under these condition, the hybrid methods of each the ProFile^(®) system and HeroShaper^(®) with ProTaper^(®) are recommendable comparative to ProTaper^(®) -alone method. According to the results, the hybrid instrumentation method is a more appropriate method of canal preparation than single file system for narrow or curved canals.〔J Kor Acad Cons Dent 31(1):11-19, 2006〕

수도권 화물차량 기·종점자료 신뢰도 향상 방안

김채만,김락기,정용기 대한교통학회 2009 대한교통학회지 Vol.27 No.4

The main goal of this paper is to develop a methodology for increasing the reliability of truck OD matrices in Seoul Metropolitan Area. We propose a Hybrid Method made up of five processes by using Non-Traffic Assignment and Gradient Method. A Hybrid Method and Gradient Method have applied for comparison and estimation in Seoul Metropolitan Area. Mean Error and Root Mean Square Error of a Hybrid Method present lower than Gradient Method. The findings of this paper show that the new truck OD matrices created by a Hybrid Method are more reliable than the existing truck OD matrices in the Seoul Metropolitan Area. 본 연구는 도로상의 화물차량 관측교통량과 가장 잘 부합하는 화물차량 기·종점통행량을 생성하는 모형을 개발하는 것이다. 본 연구에서는 비통행배정과 통행배정(GM모형)을 순차적으로 사용한 통합모형(Hybrid Method)을 개발하고, 통합모형과 GM모형을 수도권에 적용하여 비교·평가한 결과 평균오차율과 %RMSE에서 통합모형이 더 신뢰도 높은 화물차량 기․종점통행량을 생성하는 것으로 나타났다. 통합모형으로 보정된 수도권 화물차량 기․종점통행량은 첫째, 화물차량을 차종별로 구분하여 제시함으로써 활용 영역을 확장시켰다. 둘째, 기존 화물차량 기·종점통행량 보다 평균오차율과 %RMSE가 낮은 신뢰도 높은 화물차량 기․종점통행량을 산출하였다. 셋째, 현재뿐만 아니라 장래 화물차량 기·종점 자료를 제시함으로써 타당성 조사 등에 활용이 가능하게 하였다.

CFD/DSMC 혼합해석기법을 이용한 축대칭 천이영역 유동 해석

최영재(Young-Jae Choi),권오준(Oh-Joon Kwon) 한국항공우주학회 2019 韓國航空宇宙學會誌 Vol.47 No.3

본 연구에서는 희박기체 환경의 유동 정보를 효과적으로 계산하기 위해 CFD 해석기법과 DSMC 해석기법 간 연계 해석을 수행하는 CFD/DSMC 혼합해석기법을 개발하였으며, 개발된 해석기법을 이용하여 천이영역에서의 고속 비행체 주위 유동에 대한 해석을 수행하였다. 해석 형상으로는 콘과 실린더 형태로 이루어진 FRESH-FX 형상으로 고려하였고, 혼합해석기법의 결과는 순수 CFD 및 DSMC 해석 결과와 비교하였다. 천이영역의 대기가 상대적으로 희박하여 초음속 유동에서 발생하는 충격파의 구배 및 세기가 약화된 것을 확인하였다. 순수 CFD 해석 결과와는 차이를 보였고, 순수 DSMC 해석 결과와 거의 일치하는 결과를 도출하는 것을 확인하였다. 또한, 순수 DSMC 계산시간보다 해석 시간이 감소하였다. 이를 통해 혼합해석기법의 결과에 대한 신뢰성 및 해석 시간에서의 효율을 확인하였다. In the present study, a CFD/DSMC hybrid method performed by a coupled analysis between the CFD method and the DSMC method was developed to obtain the flow information on the rarefied gas flows effectively. Flow simulations around the high speed vehicles on the transition flow regimes were conducted by using the developed method. The FRESH-FX vehicle made of cone and cylinder shapes was considered for the simulations. The results of the hybrid method were compared with the results of the pure CFD and the pure DSMC method to confirm the reliability and efficiency of the hybrid method. It was found that the gradient and the intensity of the shock waves were weakened due to the relatively low density on the transition flow regime. It was confirmed that the results of the hybrid analysis were different to those of the pure CFD analysis and almost identical to those of the pure DSMC analysis. In addition, the computational time of the hybrid method was reduced than that of the pure DSMC method. As a result, it was obtained that the validity and the efficiency of the CFD/DSMC hybrid method.

A Hybrid Stress Measurement Using only x-displacements by Phase Shifting Method with Fourier Transform (PSM/FT) in Laser Speckle Interferometry and Least Squares Method

백태현,Thomas J. Rudolphi 한국정밀공학회 2010 International Journal of Precision Engineering and Vol.11 No.1

Stress measurement around the edge of a circular hole at the center of a tensile-loaded plate was performed using an improved hybrid method. Phase-shifting method by Fourier transformation (PSM/FT) in laser speckle interferometry was utilized to measure micro-scale displacement of points away from the edge of the hole. Using few x-displacement and location data only, least-squares method integrated with a Laurent series representation of the stress function and local collocation was used to do reliable stress evaluation on the hole boundary. Traction-free conditions are satisfied at the geometric discontinuity using conformal mapping and analytic continuation. The results of the present improved hybrid method agree well with that of finite element method using commercial software, ABAQUS. Different values of number of term (m) in the complex stress functions were tested to see its effect. In the comparison between input x-displacement data and calculated the hybrid method is effective with an error below 1% in all values of m. On the other hand, it came out that at point of high stress concentration (θ =90°), well-comparable results was attained at decreasing value of m. The best value of m is consistently known to be equal to 1 which results are accurate by less than one percent. Results showed that the method is accurate and reliable as compared with the widely-used ABAQUS.