최적화 기법과 분산 컴퓨팅을 이용한 재료 성형공정의 역문제 에 관한 연구

최주호(JooHo Choi),오동길(DongGil Oh),하덕식(DukSik Ha),김준범(JunBum Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5

In this paper, an inverse problem of glass forming process is studied to determine a number of unknown<br/> heat transfer coefficients which are imposed as boundary conditions. An analysis program for transient heat<br/> conduction of axi-symmetric dimension is developed to simulate the forming and cooling process. The<br/> analysis is repeated until it attains periodic state, which requires at least 30 cycles of iteration. Measurements<br/> are made for the temperatures at several available time and positions of glass and moulds in operation. Heat<br/> removal by the cooling water from the plunger is also recorded. An optimization problem is formulated to<br/> determine heat transfer coefficients which minimize the difference between the measured data and analysis<br/> results. Significant time savings are achieved in finite difference based sensitivity computation during the<br/> optimization by employing distributed computing technique. The analysis results by the optimum heat transfer<br/> coefficients are found to agree well with the measured data.

초공동(초공동)하의 수중 주행체 캐비테이터 형상 최적설계

최주호(JooHo Choi),Ramana V. Grandhi 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11

When a projectile travels at high speed underwater, supercavitating flow arises, in which a huge cavity is<br/> generated behind the projectile so that only the nose, i.e., the cavitator, of the projectile is wetted, while the<br/> rest of it should be surrounded by the cavity. In that case, the projectile can achieve very high speed due to the<br/> reduced drag. Furthermore if the nose of the body is shaped properly, the attendant pressure drag can be<br/> maintained at a very low value, so that the overall drag is also reduced dramatically. In this study, shape<br/> optimization technique is employed to determine the optimum cavitator shape for minimum drag, given<br/> certain operating conditions. Shape optimization technique is also used to solve the potential flow problem for<br/> any given cavitator, which is a free boundary value problem having the cavity shape as unknown a priori.<br/> Analytical sensitivities are derived for various shape parameters in order to implement a gradient-based<br/> optimization algorithm. Simultaneous optimization technique is proposed for efficient cavitator shape<br/> optimization, in which the cavity and cavitator shape are determined in a single optimization routine.

Rattle 해석을 위한 확률적 접근방법

최주호(Jooho Choi),임체규(Chekyu Lim),허현준(Hyun-Jun Heo) 한국자동차공학회 2013 오토저널 Vol.35 No.5

초공동(超空洞) 하의 수중 주행체 캐비테이터 형상최적설계

최주호(Jooho Choi) 한국추진공학회 2008 한국추진공학회 학술대회논문집 Vol.2008 No.5

수중에서 발사체가 고속으로 주행할 때 발사체의 머리 즉, 캐비테이터 만이 물과 접촉한 상태에서 커다란 공동이 발생하여 몸체 전체를 뒤덮는 초공동현상이 발생한다. 초공동 상태에서는 발사체는 저항이 감소되어 매우 빠른 속도를 낼 수 있게 된다. 더욱이 캐비테이터가 적합한 형상을 가지게 되면 매우 낮은 압력저항을 유지하고 전체적인 저항도 획기적으로 줄일 수 있기 때문에 본 연구에서는 주어진 작용환경 하에서 저항을 최소화 하기위한 최적의 캐비테이터 형상최적설계 문제를 고려하였다. 그리고 효율적인 캐비테이터 형상최적화를 위해 공동과 캐비테이터 형상을 하나의 죄적화로 변환한 동시 최적화기법을 수행하였다. When a projectile travels at high speed underwater, supercavitating flowarises, in which a huge cavity is generated behind the projectile so that only the nose, i.e., the cavitator, of the projectile is wetted, while the rest of it should be surrounded by the cavity. In that case, the projectile can achieve very high speed due to the reduced drag. Furthermore if the nose of the body is shaped properly, the attendant pressure drag can be maintained at a very low value, so that the overall drag is also reduced dramatically. In this study, shape optimization technique is employed to determine the optimum cavitator shape for minimum drag, given certain operating conditions. Simultaneous optimization technique is proposed for efficient cavitator shape optimization, in which the cavity and cavitator shape are determined in a single optimization routine.

자동차 내장 폴리머 재료의 열화모델 개발

허현준(Hyun-Jun Heo),최주호(Jooho Choi) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

In the automotive industry, rattle noise is one of the important issues, which occurs in the cockpit or other interior components when the parts in close proximity impact against each other under the excessive vibration. As more polymers are employed in these parts and the polymer is prone to degradation, the noise becomes more pronounced in the aged cars. Diverse efforts are being directed to solve these problems, one of which is to conduct FEA to simulate rattle occurrence. In this study, degradation of the material properties is investigated for the polymers of the automotive, which includes elastic modulus, Poisson ratio and CTE on the static side and storage and loss moduli on the dynamic side. Empirical models are established that describes the degradation behavior as a function of time as well as the temperature and humidity, by using some suitable models including Arrhenius and Layton models. In order to account for the scattered data, statistical techniques are employed which are the maximum likelihood and bootstrap methods, from which the model is obtained in the form of probability distributions. Once the models are established, they are used to predict the degradation under arbitrary cycles by applying the concept of cumulative degradation which is given by the integration of the degradation rate over time. Finally, the prediction is validated by applying arbitrary cycles to the coupon, measuring the property and comparing with the predicted values.

Bayesian approach for reliability analysis of side load spring design problem

안다운(Dawn An),최주호(Jooho Choi),원준호(Junho Won) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Bayesian approach for the structural reliability analysis is proposed, which can deal with the epistemic uncertainty arising due to the limited number of data. Until recently, the conventional reliability analysis mostly dealt with the aleatory uncertainty in which the statistical properties are completely known. In practice, however, this is not the case due to the insufficient data for estimating the statistical information, which makes the existing methods less useful. In the Bayesian approach, the probability itself is a random variable conditioned by the observed data, and is represented by a PDF, which is obtained by conducting a double loop of reliability analyses. KDRM is employed for the efficient implementation of the reliability analysis, which can construct the PDF of the limit state function with favorable accuracy under a small number of analyses Mathematical examples are used to verify the proposed method. A reliability problem of a side load spring is solved as an example for practical application.

몬테 카를로 시뮬레이션을 이용한 하이브리드 로켓의 신뢰성 분석

문근환,김완범,이정표,최주호,김진곤,Moon, Keunhwan,Kim, Wanbeom,Lee, Jungpyo,Choi, Jooho,Kim, Jinkon 항공우주시스템공학회 2013 항공우주시스템공학회지 Vol.7 No.4

In this study, probabilistic reliability analysis was conducted for hybrid rocket performance using Monte-Carlo Simulation. For the accuracy, reliability analysis was performed with experimental data. To simplify the analysis process, the oxidizer was supplied with constant pressure, so that pressure variation with time can be eliminated. And time-space averaged regression rate model was used. The regression rate is obtained with a series of experiments. For reliability analysis of thrust, constant exponent of regression rate is assumed that has probabilistic character. So, the efficiency of characteristic velocity has also probabilistic values. As a results, probability distribution of the thrust is obtained by Monte-Carlo simulation using random samples of the input parameter and validated under the 95% confidence level.

모터 전류 신호를 이용한 출입문 부품의 고장진단

함석주(SeokJu-Ham),최주호(JooHo-Choi) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.2

현장데이터 기반 피로수명 예측을 위한 베이지안 접근법

안다운(Dawn An),최주호(Jooho Choi),김남호(Nam H. Kim),Pattabhiraman Sriram 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

In the design considering fatigue life of mechanical components, uncertainties arising from the materials and manufacturing processes should be taken into account for ensuring reliability. Common practice in the design is to apply safety factor in conjunction with the numerical codes for evaluating the lifetime. This approach. however, most likely relies on the designer's experience. Besides, the predictions often are not in agreement with the real observations during the actual use. In this paper, a more dependable approach based on the Bayesian technique is proposed, which incorporates the field failure data with the prior knowledge to obtain the posterior distribution of the unknown parameters of the fatigue life. Posterior predictive distributions and associated values are estimated afterwards. which represents the degree of our belief of the life conditional on the observed data. As more data are provided, the values will be updated to more confident information. The results can be used in various needs such as a risk analysis, reliability based design optimization. maintenance scheduling. or validation of reliability analysis codes. In order to obtain the posterior distribution. Markov Chain Monte Carlo (MCMC) technique is employed, which is a modern statistical computational method which draws effectively the samples of the given distribution. Field data of turbine components are exploited to illustrate om approach. which counts as a regular inspection the number of failed blades in a turbine disk.

마코프체인 몬테카를로 방법을 이용한 리튬 이온 배터리 물리 모델의 변수 추정

이재욱(Jaewook Lee),최주호(Jooho Choi),성우석(Wooseok Sung),유민영(Minyoung Yoo),진현철(Hyeoncheol Jin) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12