• Structural Engineering and Mechanics
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• 제35권5호
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• pp.631-643
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• 2010

A numerical procedure for the geometrical and material nonlinear analysis of concrete beams prestressed with external tendons is described, where the effects of external prestressing are treated as the equivalent loads applied on the concrete beams. The geometrical nonlinearity is considered not only the eccentricity variations of external tendons (second-order effects) but also the large displacement effects of the structure. The numerical method can predict the nonlinear response of externally prestressed concrete beams throughout the entire loading history with considerable accuracy. An evaluation of second-order effects of externally prestressed concrete beams is carried out using the proposed analysis. The analysis shows that the second-order effects have significant influence on the response characteristics of externally prestressed concrete beams. They lead to inferior ultimate load and strength capacities and a lower ultimate stress increase in tendons. Based on the current analysis, it is recommended that, for simply-supported externally prestressed beams with straight horizontal tendons, one deviator at midspan instead of two deviators at one-third span be furnished to minimize these effects.

• 한국강구조학회 논문집
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• 제21권6호
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• pp.627-636
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• 2009

본 연구는 강구조 설계기준에서 제시하고 있는 하중증폭계수를 적용한 2차 해석법의 타당성을 해석적 방법을 통해 평가하는데 그 목적이 있다. 이를 위해 KBC 2005에서 제안하고 있는 B1 및 B2 계수를 적용한 2차 해석과 KBC 2009(안)에서 제안하고 있는 하중증폭계수를 적용한 직접해석을 3층 1스팬 및 5층 3스팬 비가새 강구조 골조에 대해 실시하고, 그 해석 결과를 2차 비선형 해석 결과와 비교하여 기준에서 제안된 2차 해석법들을 평가하였다. 해석의 주요 변수로는 골조의 규모, 기둥의 축력비, 해석방법 등이 적용되었다. 연구 결과 고축력 조건시 KBC 2005에서 제안된 하중증폭계수를 적용한 2차 해석은 2차 효과의 영향을 적절하게 고려하지 못하나 KBC 2009(안)에서 제안된 직접해석법의 경우 적절한 수준에서 2차 효과를 고려하고 있는 것으로 나타났다.

• 대한전기학회논문지:전력기술부문A
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• 제51권3호
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• pp.127-133
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• 2002

This paper presents an efficient improvement of the iterative eigenvalue calculation method of the AESOPS algorithm. The intuitively and heuristically approximated iterative eigenvalue calculation method of the AESOPS algorithm is transformed to the Second Order Newton Raphson Method which is generally used in numerical analysis. The equations of second order partial differentiation of external torque, terminal and internal voltages are derived from the original AESOPS algorithm. Therefore only a few calculation steps are added to transform the intuitively and heuristically approximated AESOPS algorithm to the Second Order Newton Raphson Method, while the merits of original algorithm are still preserved.

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.780-786
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• 2013

In the reliability-based design optimization of electromagnetic devices, the accurate and efficient reliability assessment method is very essential. The first-order sensitivity-assisted Monte Carlo Simulation is proposed in the former research. In order to improve its accuracy for wide application, in this paper, the second-order sensitivity analysis is presented by using the hybrid direct differentiation-adjoint variable method incorporated with the finite element method. By combining the second-order sensitivity with the Monte Carlo Simulation method, the second-order sensitivity-assisted Monte Carlo Simulation algorithm is proposed to implement reliability calculation. Through application to one superconductor magnetic energy storage system, its accuracy is validated by comparing calculation results with other methods.

• 한국구조물진단유지관리공학회 논문집
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• 제12권5호
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• pp.143-151
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• 2008

본 연구에서는 2차 비탄성해석과 단면점증법을 이용한 평면 강골조 구조물의 최적설계 방법을 제시하였다. 2차 비탄성해석은 구조시스템과 그에 속한 부재들의 기하학적 비선형과 재료적 비선형을 고려하기 때문에 2차 비탄성해석에 바탕을 둔 설계법에서는 해석 후 개별부재의 강도검토가 필요 없다. 본 논문에서 제안한 단면점증법을 최적화 기법으로 사용하였으며 목적함수로 구조물의 중량을 사용하였다. 제약조건식은 구조시스템의 하중-저항능력, 처짐 및 층간 수평변위 등을 고려하였으며 제안된 방법에 의한 설계결과를 다른 방법에 의한 것들과 비교하여 그 효율성을 증명하였다.

• 한국해양공학회지
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• 제12권2호통권28호
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• pp.33-42
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• 1998

In the presence of incident waves with different frequencies, the second order sum and difference frequency waves due to the nonlinearity of the incident waves come into existence. Although the magnitudes of the forces produced on a Tension Leg Platform(TLP) by these nonlinear waves are small, they act on the TLP at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency wave loads produced close to the natural frequencies of TLPs often give greater contributions to high and low frequency resonant responses. The second order wave exciting forces and moments have been obtained by the method based on direct integration of pressure acting on the submerged surface of a TLP. The components of the second order forces which depend on first order quantities have been evaluated using the three dimensional source distribution method. The numerical results of time domain analysis for the nonlinear wave exciting forces in regular waves are compared with the numerical ones of frequency domain analysis. The results of comparison confirmed the validity of the proposed approach.

• ETRI Journal
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• 제32권1호
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• pp.102-111
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• 2010

Recently power attacks on RSA cryptosystems have been widely investigated, and various countermeasures have been proposed. One of the most efficient and secure countermeasures is the message blinding method, which includes the RSA derivative of the binary-with-random-initial-point algorithm on elliptical curve cryptosystems. It is known to be secure against first-order differential power analysis (DPA); however, it is susceptible to second-order DPA. Although second-order DPA gives some solutions for defeating message blinding methods, this kind of attack still has the practical difficulty of how to find the points of interest, that is, the exact moments when intermediate values are being manipulated. In this paper, we propose a practical second-order correlation power analysis (SOCPA). Our attack can easily find points of interest in a power trace and find the private key with a small number of power traces. We also propose an efficient countermeasure which is secure against the proposed SOCPA as well as existing power attacks.

• 전산구조공학
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• 제7권3호
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• pp.115-122
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• 1994

불확정 구조계획의 선형 고유치 문제는 재료정수나 경게조건 및 외부하중 등에 결정론적으로 사용할 수 없는 확률량을 포함하고 있다. 변동량을 내포한 고유치 문제의 해석은 기대치에 대한 지배 방정식과 변동량 결정방정식을 고려해야 한다. 비선형성이 심한 구조계를 선형화할 대 일차 및 이차 변동값을 반영함으로 고유치의 정도를 향상시킬 수 있다. 매개변수에 불확정성을 포함한 고유치 문제는 최적설계 정식화에서 변동된 값을 고료해 줌으로 신뢰성 있는 설계가 된다. 최적설계 알고리즘 중에는 목적함수와 제한 조건식의 설계 민감도를 요한다. 이차 기울기에 근거를 둔 최적설계 수행시에 변동량에 고려하여 제한식으로 설정하고, 설계 민감도를 구할 수 있는 방법을 제시하였다.

• ETRI Journal
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• 제38권2호
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• pp.387-396
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• 2016

This paper introduces a new type of collision attack on first-order masked Advanced Encryption Standards. This attack is a known-plaintext attack, while the existing collision attacks are chosen-plaintext attacks. In addition, our method requires significantly fewer power measurements than any second-order differential power analysis or existing collision attacks.

• Journal of applied mathematics & informatics
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• 제18권1_2호
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• pp.171-182
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• 2005

An analysis of the non-homogeneous term involved in the free surface condition for second order wave diffraction on a pair of cylinders is presented. In the computations of the nonlinear loads on offshore structures, the most challenging task is the computation of the free surface integral. The main contribution to this integrand is due to the non-homogeneous term present in the free surface condition for second order scattered potential. In this paper, the free surface condition for the second order scattered potential is derived. Under the assumption of large spacing between the two cylinders, waves scattered by one cylinder may be replaced in the vicinity of the other cylinder by equivalent plane waves together with non-planner correction terms. Then solving a complex matrix equation, the first order scattered potential is derived and since the free surface term for second order scattered potential can be expressed in terms of the first order potentials, the free surface term can be obtained using the knowledge of first order potentials only.