• 콘크리트학회논문집
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• 제14권2호
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• pp.171-179
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• 2002

본 연구는 비부착 프리스트레스트 보강재를 갖는 PSC 부재의 휨거동과 프리스트레스트 보강재의 극한응력과의 관계분석을 위한 해석연구로서, Moon/Lim의 제안식을 검증하기 위한 일련의 연구에 포함된다. 프리스트레스트 보강재의 응력변화량이 부재의 변위와 밀접한 관계가 있다는 기존 실험연구의 결과를 토대로 변형률 적합 조건을 이용한 해석적 연구를 수행하였다. 제안식이 변형률 적합 조건을 사용하였기 때문에 동일한 방법을 사용하여 부재변위를 해석적으로 구하고 실험결과와 먼저 비교하였다. 그 결과를 통하여 변형률 적합조건을 사용하는 해석방법과 제안식의 타당성을 증명하였다. 흐리고 검증된 해석결과를 이용하여 비부착 프리스트레스트 보강재를 갖는 PSC 부재의 휨거동과 프리스트레스트 보강재의 극한응력과의 관계를 분석하였다. 또한 부재변위를 대상으로 한 변수별 효과분석을 통하여 기존연구의 결과와 유사한 결과를 얻을 수 있었다. 끝으로 제안식에 사용한 변수들도 적절하게 선정되었음도 검증하였다.

• 한국지반신소재학회논문집
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• 제7권4호
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• pp.47-55
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• 2008

본 연구에서는 제주도와 같이 투수성이 매우 높은 지반에서의 침투량을 산정하기 위하여 침투트렌치에 대한 모형시험 및 현장시험을 실시하였다. 모형실험결과를 토대로 비침투량 산정식을 제안하였다. 제안된 식에 의해 산정된 침투량은 기존식에 의해 산정된 침투량보다 약 2배 정도 크게 나타났다. 한편, 현장침투시험을 통해 얻어진 침투량을 제안식과 기존식에 의해 얻은 침투량과 비교 한 결과, 현장침투시험을 통해 얻은 침투량은 제안식에 의해 얻은 침투량과 거의 비슷하게 나타났다. 따라서 투수성이 높은 조립토 지반에 설치된 침투트렌치의 침투량을 산정함에 있어 본 연구에서 제안된 침투량 산정식을 적용하는 것이 타당하다.

• 콘크리트학회논문집
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• 제12권4호
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• pp.69-78
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• 2000

Creep of concrete is the most dominating factor affecting time-dependent deformations of concrete structures. Especially, creep deformation for design and construction in prestressed concrete structures should be predicted accurately because of its close relation with the loss in prestree of prestressed concrete structures. Existing creep-prediction models for special applications contain several impractical factors such as the lack ok accuracy, the requirement of long-term test and the lack of versatility for change in material properties, ets., which should be improved. In order to improve those drawbacks, a methodology to modify the creep-prediction equation specified in current Korean concrete structures design standard (KCI-99), which underestimates creep of concrete and does not consider change of condition in mixture design, is proposed. In this study, short-term creep tests were carried out for early-age concrete within 28 days after loading and their test results on influencing factors in the equation are analysed. Then, the prediction equation was modified by using the early-age creep test results. The modified prediction equation was verified by comparing their results with results obtained from long-term creep test.

• 소성∙가공
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• 제22권7호
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• pp.401-406
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• 2013

The use of roll-formed products increases every year due to its advantages, such as high production rates, reduced tooling cost and improved quality. However, till now, it is limited to part profiles with constant cross section. In recent years, the flexible roll forming process, which allows variable cross sections of profiles by adaptive roll stands, was developed. In this study, an attempt to optimize profile design for the flexible roll forming process was performed. An equation that predicts the longitudinal strain for part geometries with variable cross-sections was proposed. The relationship between geometrical parameters and the longitudinal strain was analyzed and investigations on the optimal profile design were performed. Experiments were conducted with a lab-scale roll forming machine to validate the proposed equation. The results show that the profile design method proposed in this study is feasible and parts with variable cross sections can be successfully fabricated with the flexible roll forming process.

• 한국강구조학회 논문집
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• 제25권6호
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• pp.587-599
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• 2013

본 연구에서는 EC4의 내화설계 관점에서 표준화재하의 무피복 콘크리트충전강관기둥의 내화성능을 해석적으로 예측하는 개선된 방안을 제시하고자 하였다. Lawson 등이 제안한 콘크리트충전강관기둥에 대한 단면온도평가식의 한계를 분석하고, 기존 실험결과와 유한요소 열전달해석을 바탕으로 콘크리트충전강관기둥의 단면온도분포 예측식을 새로이 제안하였다. 본 연구에서 제안한 온도분포 예측식과 EC4의 내화설계법을 이용하여 예측한 콘크리트충전강관기둥의 축강도는 기존 설계법과 비교하여 더욱 정확하고 설계목적에 합당하다고 판단된다. 본 연구의 결과는 무피복 콘크리트충전강관기둥의 내화설계 및 성능평가에 매우 편리하게 활용될 수 있다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.348-351
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• 1995

This note proposes a robust LQR method for systems with structured real parameter uncertainty based on Riccati equation approach. Emphasis is on the reduction of design conservatism in the sense of quadratic performance by utilizing the uncertainty structure. The class of uncertainty treated includes all the form of additive real parameter uncertainty, which has the multiple rank structure. To handle the structure of uncertainty, the scaling matrix with block diagonal structure is introduced. By changing the scaling matrix, all the possible set of uncertainty structures can be represented. Modified algebraic Riccati equation (MARE) is newly proposed to obtain a robust feedback control law, which makes the quadratic cost finite for an arbitrary scaling matrix. The remaining design freedom, that is, the scaling matrix is used for minimizing the upper bound of the quadratic cost for all possible set of uncertainties within the given bounds. A design example is shown to demonstrate the simplicity and the effectiveness of proposed method.

• 전기학회논문지
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• 제59권2호
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• pp.374-379
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• 2010

In this paper, we have mathematically analyzed lumped element type negative group delay circuit (NGDC) and derived general design equation. The applicability of the proposed design equation is validated with mathematical and circuit simulation as well as with experimental results for intentional mobile telecommunication 2000 (IMT-2000) downlink band. As a design example, single branch NGDC with -0.8ns of group delay (GD) for narrow bandwidth of the specific frequency is simulated and fabricated. Finally, $\pi$-network NGDC is proposed and validated to obtain wideband GD response of $-1.7{\pm}0.06$ nsec for 60 MHz.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.571-572
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• 2009

초고강도 콘크리트의 개발에 따라 철근 압축이음에 대한 연구 필요성이 높아지고 있다. 현행 설계 기준에서 콘크리트강도와 횡보강근의 영향을 고려하지 않기 때문에 압축이음길이가 인장이음길이보다 길어지는 기현상(奇現象)이 발생한다. 본 연구에서는 51개 실험체의 결과를 바탕으로 40MPa부터 70MPa까지 콘크리트에 대한 압축이음길이 설계식을 제안하였다. 본 연구에서 제안된 압축이음길이 설계식을 이용하여 고강도 콘크리트에서 압축이음길이가 인장이음길이보다 길어지는 이상 현상을 해소할 수 있다. 더불어 제안된 압축이음길이 설계식은 통계적 기법에 기반을 두어 재료강도와 동일한 수준의 신뢰성을 확보할 수 있다.

• Journal of Mechanical Science and Technology
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• 제16권10호
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• pp.1229-1238
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• 2002

In this paper, a method to obtain the sensitivity of eigenvalues and the random responses of the structure with uncertain parameters is proposed. The concept of the proposed method is that the perturbed equation of each uncertain substructure is obtained using the finite element method, and the perturbed equation of the overall structure is obtained using the mode synthesis method. By this way, the reduced order perturbed equation of the uncertain system can be obtained. And the response of the uncertain system is obtained using probability method. As a numerical example, a simple piping system is considered as an example structure. The damping and spring constants of the support are considered as the uncertain parameters. Then the variations of the eigenvalues, the correlation function and the power spectral density function of the responses are calculated. As a result, the proposed method is considered to be useful technique to analyze the sensitivities of eigenvalues and random response against random excitation in terms of the accuracy and the calculation time.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.1032-1037
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• 2003

Although the holes on the shell case are very important fer the acoustic performance, it is difficult to solve the problem because the case includes thin bodies. Hence, in the past, only the method of trial and error, which depends on the engineer's intuition and experience, was available fur the design of holes. Many researchers have tried to solve the thin-body acoustic problems, since the conventional boundary element method (BEM ) using the Helmholtz integral equation fails to yield a reliable solution fer the numerical modelling of radiation anti scattering of sound from thin bodies. In the area of the analysis of thin-body acoustic problem, three approaches are generally used; the multi-domain BEM, the indirect variational BEM, and the normal derivative integral equation And there has been just a f9w study reported on the design optimization for the acoustic radiation problems by using only the conventional BEM. For the thin-body acoustics, however, no further study in the optimization fields has been reported. In this research, the normal derivative integral equation is adopted as an analysis formulation in the thin-body acoustics, and then used fur the optimization. The analytical approaches for the design of holes are proposed by using a topology optimization technique and a genetic algorithm. The proposed approaches are implemented and validated using numerical examples.