• Wind and Structures
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• 제5권6호
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• pp.527-542
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• 2002

Wind-excited vibrations of slender structures can induce fatigue damage and cause structural failure without exceeding ultimate limit state. Unfortunately, the growing importance of this problem is coupled with an evident lack of simple calculation criteria. This paper proposes a mathematical method for evaluating the crosswind fatigue of slender vertical structures, which represents the dual formulation of a parallel method that the authors recently developed with regard to alongwind vibrations. It takes into account the probability distribution of the mean wind velocity at the structural site. The aerodynamic crosswind actions on the stationary structure are caused by the vortex shedding and by the lateral turbulence, both schematised by spectral models. The structural response in the small displacement regime is expressed in closed form by considering only the contribution of the first vibration mode. The stress cycle counting is based on a probabilistic method for narrow-band processes and leads to analytical formulae of the stress cycles histogram, of the accumulated damage and of the fatigue life. The extension of this procedure to take into account aeroelastic vibrations due to lock-in is carried out by means of ESDU method. The examples point out the great importance of vortex shedding and especially of lock-in concerning fatigue.

• Structural Engineering and Mechanics
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• 제8권5호
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• pp.513-529
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• 1999

A concept of hierarchical modeling, the newest modeling technology, has been introduced in early 1990's. This new technology has a great potential to advance the capabilities of current computational mechanics. A first step to implement this concept is to construct hierarchical models, a family of mathematical models sequentially connected by a key parameter of the problem under consideration and have different levels in modeling accuracy, and to investigate characteristics in their numerical simulation aspects. Among representative model problems to explore this concept are elastic structures such as beam-, arch-, plate- and shell-like structures because the mechanical behavior through the thickness can be approximated with sequential accuracy by varying the order of thickness polynomials in the displacement or stress fields. But, in the numerical, analysis of hierarchical models, two kinds of errors prevail, the modeling error and the numerical approximation error. To ensure numerical simulation quality, an accurate estimation of these two errors is definitely essential. Here, a local a posteriori error estimator for elastic structures with thin domain such as plate- and shell-like structures is derived using the element residuals and the flux balancing technique. This method guarantees upper bounds for the global error, and also provides accurate local error indicators for two types of errors, in the energy norm. Compared to the classical error estimators using the flux averaging technique, this shows considerably reliable and accurate effectivity indices. To illustrate the theoretical results and to verify the validity of the proposed error estimator, representative numerical examples are provided.

• Structural Engineering and Mechanics
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• 제59권6호
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• pp.1037-1054
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• 2016

Structural parameter evaluation and external force estimation are two important parts of structural health monitoring. But the structural parameter identification with limited input information is still a challenging problem. A new simultaneous identification method in time domain is proposed in this study to identify the structural parameters and evaluate the external force. Each sampling point in the time history of external force is taken as the unknowns in force evaluation. To reduce the number of unknowns for force evaluation the time domain measurements are divided into several windows. In each time window the structural excitation is decomposed by orthogonal polynomials. The time-variant excitation can be represented approximately by the linear combination of these orthogonal bases. Structural parameters and the coefficients of decomposition are added to the state variable to be identified. The extended Kalman filter (EKF) is augmented and selected as the mathematical tool for the implementation of state variable evaluation. The proposed method is validated numerically with simulation studies of a time-invariant linear structure, a hysteretic nonlinear structure and a time-variant linear shear frame, respectively. Results from the simulation studies indicate that the proposed method is capable of identifying the dynamic load and structural parameters fairly accurately. This method could also identify the time-variant and nonlinear structural parameter even with contaminated incomplete measurement.

• 한국통신학회논문지
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• 제19권4호
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• pp.685-690
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• 1994

벡터 양자화의 부호화에서 입력벡터에 가장 잘 정합되는 코드벡터를 탐색하는 과정에서 발생하는 계산의 복잡도는 코드북의 크기에 비례하여 지수직으로 증가하고 실질적으로 응용을 제한한다. 본 논문에서는 정합 가능성이 없는 코드벡터에 대한 왜곡의 계산을 제거하기 위한 조건의 시작 벡터로서 참조 벡터를 사용하는 단순, 고속의 효율적인 벡터 양자화의 부호화 알고리즘을 제안하였다. 이는 입력벡터에 정합 기능성을 갖는 참조 벡터를 선택하고 코드 벡터에 대한 왜곡의 계산을 제거하기 위한 조건을 결합하는 것이다. 제한된 방법은 전탐색 벡터 양자화에 비하여 단지 10~15%의 수학적 연산을 필요로 한다. 그리고 덧셈과 비교 연산의 수는 크게 줄어들지 않지만 곱셈은 벡터 양자화의 여러 고속부호화 방법의 70~80%까지 들었다.

• 한국지능시스템학회논문지
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• 제10권5호
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• pp.432-441
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• 2000

본 논문은 기존의 수학적인 모델링으로는 만족스러운 결과를 얻기 어려운 복잡하고 불확실한 비선형 시스템에 대한 퍼지 모델링 기법을 다룬다. 유전 알고리듬은 어느 정도 최적해를 전역적으로 찾을 수 있기 때문에 퍼지 모델링시에 파라미커와 구조를 동정하기 위하여 사용되었다. 하지만, 유전 알고리듬은 개체군이 유전적 다양성을 잃었을 경우 조기 수렴한다는 문제점이 있으며 바이러스-진화 유전 알고리듬은 이러한 지역수렴에 대한 방아닝 될 수 있다. 따라서, 본 논문에서는 바이러스 이론이 적용된 VEGA를 퍼지 모델링 할 때 이용할 수 있는 방법을 제안한다. 이 방법에서는 지역정보가 개체군 내에서 교환됨으로써 유전적 다양성을 유지하게 된다. 마지막으로, 본 논문에서 제안한 방법의 우수성과 일반성을 평가하기 위해 몇 가지의 수치적 예제를 제공한다.

• 한국군사과학기술학회지
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• 제18권6호
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• pp.797-807
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• 2015

The low-altitude PAC-2 Patriot missile system is the backbone of ROK air defense for intercepting enemy aircraft. Currently there is no missile interceptor which can defend against the relatively high velocity ballistic missile from North Korea which may carry nuclear, biological or chemical warheads. For ballistic missile defense, Korea's air defense systems are being evaluated. In attempting to intercept ballistic missiles at high altitude the most effective means is through a multi-layered missile defense system. The missile defense problem has been studied considering a single interception system or any additional capability. In this study, we seek to establish a mathematical model that's available for multi-layered missile defense and minimize total interception fail probability and proposes a solution based on genetic algorithms. We perform computational tests to evaluate the relative speed and solution of our GA algorithm in comparison with the commercial optimization tool GAMS.

• 한국실천공학교육학회논문지
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• 제3권1호
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• pp.40-44
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• 2011

공학교육에 있어 학생들의 성취도 수준차이는 교육방법을 어렵게 하는 가장 중요한 문제 중 하나이다. 이를 해결하기 위한 방법 중의 하나로 소그룹 협동학습을 통해 학생들 스스로 자율적인 교육과 학습이 이루어지도록 유도함으로서 학생들의 수업이해도를 높일 수 있다. 그러나 대부분의 그룹과제에 있어 학생들 간의 실질적인 협력을 유도하는 것은 쉽지 않을 일이다. 본 논문에서는 수학적 연습을 요구하는 공학교과목에 있어 실질적인 협동학습을 유도하기위한 방안을 제안한다. 제안된 협동학습방법은 학생개별평가결과를 그룹 내 학생들에게 모두 반영함으로서 학생들 간의 활발한 협동학습을 유도하여 학생들의 학습 성취도 편차를 감소시키고 전반적인 이해도를 향상시킬 수 있다.

• 전력전자학회논문지
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• 제23권3호
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• pp.208-216
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• 2018

In this paper, an LLC resonant converter employing two coupled inductors on the secondary side of the converter is proposed. The conventional LLC converter exhibits serious power loss during secondary winding of the transformer because of generation of tremendous output current ripples. To overcome this problem, an LLC resonant converter with a current doubler as a rectifying circuit was recently proposed. However, the current-doubler rectifying circuit requires coupled inductors with a high coupling ratio to retain the designed resonance characteristics. Therefore, an additional hardware filter is required at the output stage to address large output current ripples. Additional design procedures are also necessary because the inductance component of the added filter affects the designed resonant network. To solve this issue, an LLC resonant converter employing two coupled inductors is proposed in this paper. Mathematical analysis shows that the proposed secondary-side current-doubler circuit does not affect the designed resonance characteristics. The operating principles and theoretical analyses are proven through a simulation and experiments with a 54 V/28 A prototype.

• Journal of Power Electronics
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• 제17권1호
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• pp.253-261
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• 2017

For a single-phase active power filter (APF), designing a more efficient algorithm to guarantee accurate and fast harmonics extraction with a lower computing cost is still a meaningful topic. The common idea still employs a IRPT-based Park transform, which was originally designed for 3-phase applications. Therefore, an additional virtual signal generation (VSG) link is necessary when it is used in the single-phase condition. This method, with virtual signal generation and transform, is obviously not the most efficient one. Regarding this problem, this paper proposes a novel harmonics extraction algorithm to further improve efficiency. The new algorithm is based on the principle of trigonometric orthogonal functions (TOF), and its mathematical principle and physical meaning are introduced in detail. Its implementation and superiority in terms of computation efficiency are analyzed by comparing it with conventional methods. Finally, its effectiveness is well validated through detailed simulations and laboratory experiments.

• 융합보안논문지
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• 제16권7호
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• pp.85-91
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• 2016

블록암호는 암호시스템 중에서 두드러지면서 중요한 부분이며, 최소의 구조를 갖는 것에 관한 연구는 암호학 연구에서 주요한 주제 중의 하나이다. 최소의 구조에 관해 관심을 갖던 Even과 Mansour는 1990년대 초반에 Even-Mansour 스킴이라고 불리는 일종의 블록암호를 제안하였다. Even-Mansour 스킴은 하나의 치환과 두 개의 비밀키를 가지는 매우 간단한 암호이다. 이러한 Even-Mansour 스킴과 그의 안전성 분석에 관한 많은 연구들이 이루어져 왔다. 우리는 Even-Mansour 스킴을 설명하고 이 스킴의 공격방법에 대해 수학적인 언어를 이용하여 단순화한다. 추가적으로, 우리는 이산로그를 공격할 때 사용하는 Pollard rho 공격과 동일한 계산량으로 Pollard rho 공격을 Even-Mansour 스킴의 공격에 적용할 수 있음을 보인다.