• 융합신호처리학회논문지
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• 제14권3호
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• pp.169-180
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• 2013

The modification of conditional Fuzzy C-Means (CFCM) with Gaussian weights (CFCM_GW) is accomplished for blind equalization of channels in this paper. The proposed CFCM_GW can deal with both of linear and nonlinear channels, because it searches for the optimal desired states of an unknown channel in a direct manner, which is not dependent on the type of channel structure. In the search procedure of CFCM_GW, the Bayesian likelihood fitness function, the Gaussian weighted partition matrix and the conditional constraint are exploited. Especially, in contrast to the common Euclidean distance in conventional Fuzzy C-Means(FCM), the Gaussian weighted partition matrix and the conditional constraint in the proposed CFCM_GW make it more robust to the heavy noise communication environment. The selected channel states by CFCM_GW are always close to the optimal set of a channel even when the additive white Gaussian noise (AWGN) is heavily corrupted. These given channel states are utilized as the input of the Bayesian equalizer to reconstruct transmitted symbols. The simulation studies demonstrate that the performance of the proposed method is relatively superior to those of the existing conventional FCM based approaches in terms of accuracy and speed.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.81-84
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• 1996

We propose the robust nonlinear controller design methodology, the $H_{\infty}$ constrained quasi - linear quadratic Gaussian control (QLQG/ $H_{\infty}$), for the statistically-linearized multivariable system with hard nonlinearties such as Coulomb friction, deadzone, etc. The $H_{\infty}$ performance constraint is involved in the optimization process by replacing the covariance Lyapunov equation with the Riccati equation whose solution leads to an upper bound of the QLQG performance. Because of the system's nonlinearity, however, one equation among three Riccati equations contain the nonlinear correction terms that are very difficult to solve numerically. To treat this problem, we use simple algebraic techniques. With some analytic transformation for Riccati equations, the nonlinear correction terms can be so eliminated that the set of a linear controller to the different operating points are designed. Synthesizing these via inverse random input describing function (IRIDF) technique, the final nonlinear controller can be designed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권11호
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• pp.4463-4482
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• 2020

Mesh model generated from 3D reconstruction usually comes with lots of noise, which challenges the performance and robustness of mesh simplification approaches. To overcome this problem, we present a novel method for mesh simplification which could preserve structure and improve the accuracy. Our algorithm considers both the planar structures and linear features. In the preprocessing step, it automatically detects a set of planar structures through an iterative diffusion approach based on Region Seed Growing algorithm; then robust linear features of the mesh model are extracted by exploiting image information and planar structures jointly; finally we simplify the mesh model with plane constraint QEM and linear feature preserving strategies. The proposed method can overcome the known problem that current simplification methods usually degrade the structural characteristics, especially when the decimation is extreme. Our experimental results demonstrate that the proposed method, compared to other simplification algorithms, can effectively improve the quality of mesh and yield an increased robustness on noisy input mesh.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2007년도 공동학술대회 논문집
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• pp.209-214
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• 2007

In Korean geology that crystalline rock is dominant, the properties of subsurface including the anisotropy are distributed complexly and changed abruptly. Because of such geological environments, cross-hole seismic traveltime tomography is widely used to obtain the high resolution image of the subsurface for the engineering purposes in the geotechnical sites. However, because the cross-hole tomography has a wide propagation angle coverage relatively, its data tend to include the seismic velocity anisotropy comparing with the surface seismic methods. It can cause the misinterpretation that the cross-hole seismic data including the anisotropic effects are analyzed and treated with the general processing techniques assuming the isotropy. Therefore, we need to consider the seismic anisotropy in cross-hole seismic traveltime tomography. The seismic anisotropic tomography algorithm, which is developed for evaluation of the velocity anisotropy, includes several inversion schemes in order to make the inversion process stable and robust. First of all, the set of the inversion parameters is limited to one slowness, two ratios of slowness and one direction of the anisotropy symmetric axis. The ranges of the inversion parameters are localized by the pseudo-beta transform to obtain the reasonable inversion results and the inversion constraints are controlled efficiently by ACB(Active Constraint Balancing) method. Especially, the inversion using the Fresnel volume is applied to the anisotropic tomography and it can make the anisotropic tomography more stable than ray tomography as it widens the propagation angle coverage.

• 한국통신학회논문지
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• 제26권11A호
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• pp.1946-1956
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• 2001

본 논문에서는 관계 벡터 공간상의 특징 대응에 관한 확률적 해석에 기반한 새로운 부분 인식 기법을 제안한다. 효과적인 인식을 위해 물체를 관계 속성 그래프(Attributed Relational Graph; ARG)와 관계 벡터 공간들의 집합으로 표현한다. 또한 잡음이나 특징 소실로 인한 왜곡을 관계 벡터 공간에서의 관계 벡터 분포에 대한 왜곡으로 확률적으로 모델링한다. 제안하는 부분 인식 기법은 두 단계로 이루어진다. 우선 지역적인 특징(local feature)과 구조적인 일관성(structural consistency)을 사용하여 후보집합을 추출한다. 이렇게 추출된 후보집합 각각에 대해 관계 벡터 공간상에서의 에러 분석과 반복적인 voting 알고리즘을 통해 특징 소실을 검출한다. 실제 영상에 대한 실험 결과를 통해 제안한 알고리즘이 잡음이나 가리어짐이 심한 경우에도 강건한 성능을 보임을 알 수 있으며, 릴렉세이션(relaxation) 기법과 수행 시간 비교 분석을 통해 계산량 측면에서의 성능 향상을 확인할 수 있다.

• 한국전산구조공학회논문집
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• 제27권1호
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• pp.9-16
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• 2014

레벨셋 기법과 위상민감도를 이용하여 선형 탄성 구조물에 대하여, 초기 설계형상에 의존성이 없는 위상 및 형상 최적설계 기법을 개발하였다. 레벨셋 기법에서는 복잡한 위상 형상변화를 쉽게 다루기 위해 초기 영역은 고정한 채 레벨셋 함수로 표현되는 암시적 이동경계로 경계를 표현한다. 해밀턴-자코비(H-J) 방정식과 수치적으로 강건한 기법인 'up-wind scheme'은 컴플라이언스 목적함수를 최소화시키고 허용체적 제약조건을 만족시키면서, 초기 암시적 경계를 법선 속도장에 따라 최적의 형상으로 이끌어 낸다. 점근적인 정규화 개념에 근거하여, 구멍의 반지름을 0으로 접근시켜 형상 미분의 극한을 취한 위상민감도를 고려하였다. 최적조건으로부터 유도된 라그란지안의 감소 방향을 이용하여 H-J 방정식을 갱신하기 위한 속도장을 결정하였다. 개발한 방법에서는 위상민감도로부터 얻어지는 지표를 이용하여 구멍을 언제든지 어디에서나 생성가능하기 때문에 초기 구멍이 최적 형상을 얻기 위해 요구되지 않는다는 사실을 확인하였다. 또한 효율적인 최적화 과정을 위해서는 구멍 생성을 위한 조정변수의 적절한 선택이 중요함을 확인하였다.

• 한국안전학회지
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• 제27권5호
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• pp.148-157
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• 2012

Reliability-based design optimization (RBDO) problem is usually formulated as an optimization problem to minimize an objective function subjected to probabilistic constraint functions which may include deterministic design variables as well as random variables. The challenging task is that, because the probability models of the random variables are often assumed based on limited data, there exists a possibility of selecting inappropriate distribution models and/or model parameters for the random variables, which can often lead to disastrous consequences. In order to select the most appropriate distribution model from the limited observation data as well as model parameters, this study takes into account a set of possible candidate models for the random variables. The suitability of each model is then investigated by employing performance and risk functions. In this regard, this study enables structural design optimization and fitness assessment of the distribution models of the random variables at the same time. As the first paper of a two-part series, this paper describes a new design method considering probability model uncertainties. The robust performance of the proposed method is presented in Part 2. To demonstrate the effectiveness of the proposed method, an example of ten-bar truss structure is considered. The numerical results show that the proposed method can provide the optimal design variables while guaranteeing the most desirable distribution models for the random variables even in case the limited data are only available.

• Wind and Structures
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• 제31권3호
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• pp.241-253
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• 2020

The inerter-based vibration absorber (IVA) is an enhanced variation of Tuned Mass Damper (TMD). The parametric optimization of absorbers in the previous research mainly considered only two decision variables, namely frequency ratio and damping ratio, and aimed to minimize peak displacement and acceleration individually under the excitation of the across-wind load. This paper extends these efforts by minimizing two conflicting objectives simultaneously, i.e., the extreme displacement and acceleration at the top floor, under the constraint of the physical mass. Six decision variables are optimized by adopting a constrained multi-objective evolutionary algorithm (CMOEA), i.e., NSGA-II, under fluctuating across- and along-wind loads, respectively. After obtaining a set of optimal individuals, a decision-making approach is employed to select one solution which corresponds to a Tuned Mass Damper Inerter/Tuned Inerter Damper (TMDI/TID). The optimization procedure is applied to parametric optimization of TMDI/TID installed in a 340-meter-high building under wind loads. The case study indicates that the optimally-designed TID outperforms TMDI and TMD in terms of wind-induced vibration mitigation under different wind directions, and the better results are obtained by the CMOEA than those optimized by other formulae. The optimal TID is proven to be robust against variations in the mass and damping of the host structure, and mitigation effects on acceleration responses are observed to be better than displacement control under different wind directions.

• 지구물리와물리탐사
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• 제10권4호
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• pp.229-240
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• 2007

이 연구에서는 지하 매질의 속도 이방성을 규명하고 이를 고려하여 지하 단면을 해석하는 탄성파 이방성 토모그래피(seismic anisotropic tomography) 알고리듬을 개발하였다. 이는 지하 매질을 대칭축이 기울어진 횡등방성(Tilted Transversely Isotropic) 매질로 가정하여 지하의 속도 구조와 더불어 이방성 구조를 함께 파악할 수 있도록 고안되었다. 개발된 알고리듬은 이방성 토모그래피에서 흔히 나타날 수 있는 역산의 안정성 문제를 해결하기위해여 역산 매개 변수를 역속도비, 역속도 그리고 이방성 대칭축 방향으로 설정하였고, 의사 베타 변환(pseudo-beta transform)을 통해 이방성 계수의 범위를 제한하였으며, ACB (Active Constraint Balancing) 법을 이용하여 효율적으로 역산 제한조건을 적용하였다. 특히, 기존의 등방성 토모그래피에서 사용하던 프레넬대(Fresnel volume)를 고려한 역산 기법을 이방성 토모그래피로 확장하여 파선 토모그래피에 비해 넓은 범위의 전파각 영역을 확보함으로써 이방성 토모그래피의 안정성을 높일 수 있었다. 개발된 이방성 토모그래피 알고리듬을 복잡한 수치 모델에 적용하여 알고리듬의 타당성을 검증하였으며 현장 자료에 적용하여 시추 결과 및 지질 정보들과 일치하는 향상된 결과를 얻었다. 개발된 이방성 토모그래피 알고리듬을 통해 지하매질의 속도 정보와 이방성 정보를 함께 고려함으로써 보다 정확한 지하 구조의 해석이 가능할 것으로 기대된다.