• Coupled systems mechanics
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• 제10권1호
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• pp.79-102
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• 2021

In this paper we deal with instability problems of structures under nonconservative loading. It is shown that such class of problems should be analyzed in dynamics framework. Next to analytic solutions, provided for several simple problems, we show how to obtain the numerical solutions to more complex problems in efficient manner by using the finite element method. In particular, the numerical solution is obtained by using a modified Euler-Bernoulli beam finite element that includes the von Karman (virtual) strain in order to capture linearized instabilities (or Euler buckling). We next generalize the numerical solution to instability problems that include shear deformation by using the Timoshenko beam finite element. The proposed numerical beam models are validated against the corresponding analytic solutions.

• Coupled systems mechanics
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• 제3권1호
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• pp.89-110
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• 2014

In this work we provide the theoretical formulation, discrete approximation and solution algorithm for instability problems combing geometric instability at large displacements and material instability due to softening under combined thermo-mechanical extreme loads. While the proposed approach and its implementation are sufficiently general to apply to vast majority of structural mechanics models, more detailed developments are provided for truss-bar model. Several numerical simulations are presented in order to illustrate a very satisfying performance of the proposed methodology.

• Archives of Pharmacal Research
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• 제18권1호
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• pp.31-37
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• 1995

S. pneumoniae (pneumococcus) gene cloning and library construction in E. coli multicopy plasmid has been hampered, in part, by instability problems. In this study, stability of pneumococcus gene library in cosmid vector and pACYC184 was examined. Pneumococcus library in the cosmid vector pHC79 was extermely unstable that most of the recobinant clones were degenerated rapidly. Only 2 out 849 clones were stable and had appropriate insert size. Pneumococcus library in pACYC184 was also so unstable that the pneumococcal inserg and/or part of the vector were deleted. However, the instability problems seemed to be resolved when transcription teminator plasmid was employed for pneumococcus library construction.

• Human Ecology Research
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• 제54권6호
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• pp.631-642
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• 2016

This study analyzed of the themes (wounding and healing); concerning the Sandplay therapy process applied to children with emotional instability and attention deficit problems. The subjects of the study were 30 elementary school children who agreed to a personal-interview with the author. They all were families of receiving basic livelihood welfare living in the same county. After the preliminary analysis, the main study data collected from subjects was analyzed by variance (t-test), frequency analysis, and correlation analysis using the standard table modified in accordance with Mitchell's classification system. Particular attention was made in the analyses of the characteristics of the subjects as members of low-income families. As the Sandplay therapy proceeded, it became evident that the wounding area showed a low frequency while the healing area featured a high frequency, and confirmed (as in previous studies) that the Sandplay therapy would be effective for children with emotional instability as well as for those with attention deficit problems. The analysis of difference between the types of children with both problems revealed that Sandplay therapy was more effective for children with emotional instability than for those with attention deficit problems. The analysis also revealed that Sandplay therapy was more effective for girls than for boys.

• Coupled systems mechanics
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• 제11권2호
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• pp.167-198
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• 2022

In this paper we deal with classical instability problems of heterogeneous Euler beam under conservative loading. It is chosen as the model problem to systematically present several possible solution methods from simplest deterministic to more complex stochastic approach, both of which that can handle more complex engineering problems. We first present classical analytic solution along with rigorous definition of the classical Euler buckling problem starting from homogeneous beam with either simplified linearized theory or the most general geometrically exact beam theory. We then present the numerical solution to this problem by using reduced model constructed by discrete approximation based upon the weak form of the instability problem featuring von Karman (virtual) strain combined with the finite element method. We explain how such numerical approach can easily be adapted to solving instability problems much more complex than classical Euler's beam and in particular for heterogeneous beam, where analytic solution is not readily available. We finally present the stochastic approach making use of the Duffing oscillator, as the corresponding reduced model for heterogeneous Euler's beam within the dynamics framework. We show that such an approach allows computing probability density function quantifying all possible solutions to this instability problem. We conclude that increased computational cost of the stochastic framework is more than compensated by its ability to take into account beam material heterogeneities described in terms of fast oscillating stochastic process, which is typical of time evolution of internal variables describing plasticity and damage.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.54-58
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• 2017

연소불안정은 로켓엔진과 가스터빈을 포함하는 연소장치의 개발에 있어서 가장 심각한 문제 중의 하나이다. 특히, 연소실에서의 연소와 음향섭동과의 공진에 의해 야기되는 고주파 연소불안정은 하드웨어에 심각한 손상을 초래한다. 왜냐하면 고주파 연소불안정은 높은 압력섭동과 연소실 벽면으로의 과도한 열유속을 동반하기 때문이다. 따라서 연소불안정은 액체로켓엔진 개발에 있어서 반드시 해결되어야 하는 문제 중의 하나이다. 본 논문에서는 액체추진과학로켓(KSR-III) 및 한국형발사체(KSLV-II) 엔진 연소기 개발에 있어서 연소불안정의 경험 사례를 소개한다.

• Structural Engineering and Mechanics
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• 제48권1호
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• pp.103-124
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• 2013

This paper studies the static and dynamic characteristics of composite plates subjected to an arbitrary periodic load in hygrothermal environments. The material properties of composite plates are depended on the temperature and moisture. The governing equations of motion of Mathieu-type are established by using the Galerkin method with reduced eigenfunction transforms. A periodic load is taken to be a combination of axial pulsating load and bending stress in the example problem. The regions of dynamic instability of laminated composite plates are determined by solving the eigenvalue problems based on Bolotin's method. The effects of temperature rise and moisture concentration on the dynamic instability of laminated composite plates are investigated and discussed. The influences of various parameters on the instability region and dynamic instability index are also investigated. The numerical results reveal that the influences of hygrothermal effect on the dynamic instability of laminated plates are significant.

• Journal of Yeungnam Medical Science
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• 제15권1호
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• pp.164-172
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• 1998

본 포항성모병원 정형외과에서는 1991년 5월부터 1995년 12월까지 척추불안정성과 관련된 요추부질환 중 연성고정술을 시행한 145례 중 문제점이 발생된 22례를 분석하여 다음과 같은 결론을 얻었다. 1. 총 145례 중 22례(15.1%)에서 연성고정술로 유발되는 문제점을 발견하였다. 2. 문제점으로 주위분절의 불안정성 증가 10례, 추간판 간격의 감소 8례, 척추경 나사못의 해리 3례, Graf band의 파열이 1례였다. 3. 추간판 간격의 감소 8례 중 초기 질환의 원 인으로 추간판이 파열된 경우가 6례로 의의있는 소견을 보였다. 이상과 같은 문제점이 관찰되었으나 주위분절의 불안정성 증가 및 척추경 나사못의 해리는 견고한 고정술에 비해 그 빈도가 낮은 것으로 보이며, 추간판 간격의 감소의 경우 역시 단순 수핵 제거술후 발생된 추간판 간격의 감소 보다 빈도가 적었으나, 보다 장기간의 추시 및 계속적인 관찰과 연구가 필요할 것으로 사료된다.

• 대한토목학회논문집
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• 제31권2A호
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• pp.71-77
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• 2011

본 논문은 고체의 동적 탄소성해석을 수행하기 위해 인장불안정이 제거된 SPH기법을 사용하였다. 인장불안정은 SPH 입자들이 인장력에 의해 서로 떨어져나가는 해석적 오류현상이며, 재료적 특성에 따라 해석결과에 큰 영향을 미치게 된다. 이와 같은 인장불안정을 제어하기 위한 방법으로 본 연구에서는 가상응력의 개념을 적용하였다. 본 연구에서 제시한 SPH에 의해 해석예제를 수행하여 해석법의 효율성을 검증하였으며, 해석예제로 원형 링의 충돌문제와, 절단, 균열과 같은 재료적 파괴문제를 수행하였다.

• 가정과삶의질연구
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• 제28권5호
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• pp.251-262
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• 2010

This study examines the relationship between a mother's psychological well-being and children's problematic behavior(withdrawal, depression anxiety, aggression and emotional instability). In order to expand the study on the relationships, special attention was given to the possible mediator effects of mother's coping style with children's negative emotions. The subjects were 305 mothers with children 4-5 years old residing in the cities of Cheonan and Seongnam. It was found that mother's psychological well-being was significantly related to the level of children's withdrawal, depression anxiety, aggression and emotional instability. The mother's coping style with children's negative emotions were also significantly related to the mother's psychological well-being. In addition the mother's coping style with children's negative emotions was found to be a significant mediator of the relationship between mother's psychological well-being and children's. This was especially so for internal problems behavior as like withdrawal, depression anxiety and emotional instability that were perfectly mediated by the mother's coping style with children's negative emotions. Aggression, external problems behavior was partially mediated by the mother's coping style.