For a member model in nonlinear structural analysis, a lumped plastic model that idealizes its flexural bending, shear, and axial behaviors by springs with the nonlinear hysteretic model is widely adopted because of its simplicity and transparency compared to the other rigorous finite element methods. On the other hand, a challenging task in its numerical solution is to satisfy the equilibrium condition between nonlinear flexural bending and shear springs connected in series. Since the local forces between flexural and shear springs are not balanced when one or both springs experience stiffness changes (e.g., cracking, yielding, and unloading), the additional unbalanced force due to overshooting or undershooting each spring force is also generated. This paper introduces an iterative scheme for numerical solutions satisfying the equilibrium conditions between flexural bending and shear springs. The effect of equilibrium iteration on analysis results is shown by comparing the results obtained from the proposed method to those from the conventional scheme, where the equilibrium condition is not perfectly satisfied.

본 논문에서는 축하중과 폭발하중을 동시에 받는 철근콘크리트 부재의 구조 거동을 분석하였다. 기본적인 폭발하중을 받는 패널 실험 데이터, 축하중과 폭발하중을 받는 철근콘크리트 기둥 실험데이터를 이용하여 비선형 동적해석 모델링을 검증하였다. 축하중의 적용에 있어서 Autodyn은 동적해석만을 위한 프로그램이기 때문에 축하중과 같은 정적 하중에 대한 초기 응력 상태를 모사하는 해석 절차를 제시하였다. 축하중비 0%~70% 구간과 TNT 등가량에 의존한 환산거리 1.1~2.0에 해당하는 매개변수를 선정하여 총 80개의 비선형 동적 유한요소해석을 진행하였다. 축하중비와 환산거리의 변화를 통해 손상정도와 최대 변위 및 회전각으로 구조 거동을 비 교 분석한 결과로 원거리 폭발하중에서 축하중을 받는 기둥의 강성 증가로 최대 변위가 감소한다. 결과적으로 축하중비 10%~30%, 30%~50%, 50% 이상의 영역 3가지로 구조적 거동 분류가 가능함에 따라 내폭 설계 모델 개발에 활용될 수 있을 것으로 보인다.

본 연구는 우리나라 Jersey 암소 41두로부터 측정된 체중 데이터를 이용해 Gompertz, von Bertalanffy 및 Logistic 모형의 성장 곡선을 추정하고, 추정된 성장 곡선의 모수를 활용하여 Jersey 암소의 성장 특성에 대해 알아보고자 실시하였다. 추정된 Gompertz, von Bertalanffy 및 Logistic 모형의 성장 곡선 함수식은 각각    ,         및          이었다. Gompertz, von Bertalanffy 및 Logistic 모형에 대해 변곡점은 각각 10.719, 8.4292 및 14.618 개월로 추정되었고, 변곡점 체중은 각각 208.514, 211.347 및 203.548kg으로 추정되었으며, 최대 증체율은 각각 20.851, 21.192 및 21.993 (kg/월)로 추정되었다. 오차 평균 제곱합과 모형 결정 계수의 결과를 종합해보면 von Bertalanffy, Gompertz 그리고 Logistic 모형 순으로 Jersey 암소 성장 곡선에 적합도가 높은 것으로 판단된다.

본 연구에서는 유리섬유보강근(GFRP rebar)를 적용한 SB6 등급 콘크리트 방호벽의 비선형 동적 해석을 수행하였다. ACI 설계기준에 근거한 새로운 방호벽 구조에 대하여 소형차와 트럭의 충돌에 대한 유한요소 모델링을 수행하였다. 트럭 충돌 에 대하여 제안한 모델은 기존의 철근을 적용한 모델과 비교하였을 때 구조적으로 만족할 만한 성능을 보였다. 또한, 소형차 충 돌 해석으로부터 산출한 탑승자 보호지수는 한계기준 범위 안에서 만족하였다. 이러한 결과로부터, 제안한 방호벽 구조는 기존 철근을 적용한 방호벽을 대체하여 실용적으로 적용이 가능할 것으로 기대된다.

In this study, the frequency response analysis of a bistable electromagnetic vibration energy harvester is performed, based on an electromagnetic oscillator model, to investigate its nonlinear dynamic behaviors. The displacement and current responses are obtained, by the direct integration of the model, with the variations of mechanical and electromagnetic parameters. It is shown that the operating frequency band of the system can be broadened by the increase in mechanical parameters(inertial mass and Q-factor), but it does not depend significantly on any electromagnetic parameters(an external load resistance and the internal resistance of a coil). On the other hand, the output current of the energy harvester is affected only by the electromagnetic parameters (specifically, the sum of two resistances). Thus, the mechanical and electromagnetic parameters of the electromagnetic energy harvester must be designed properly, respectively, for broader and more efficient performance.

강진 시 원자력발전시설의 비선형 응답이 중요하기 때문에 이 시설의 내진성능에 대한 관심이 증가하였다. 이 연구에서는 원자력 발전소 철근콘크리트 전단벽의 유한요소해석을 위한 재료모델의 적절한 변수를 제시하였다: 최대인장강도, 팽창각, 손상계수. 이를 위해 상용 유한요소 해석프로그램인 ABAQUS를 사용하여 낮은 형상비를 가진 철근콘크리트 전단벽의 비선형 거동과 전단 파괴모드 에 대한 이 주요 변수의 효과에 대한 연구를 수행하였다. 연구결과에 기반하여 비선형 시간이력해석을 통해 강진 하의 원자로건물의 비선형 응답을 평가하였다.

This study aims to develop a form-finding algorithm for a single-layered pneumatic membrane. The initial shape of this pneumatic membrane, which is an air-supported type pneumatic membrane, is to find a state in which a given initial tension and internal pneumatic pressure are in equilibrium. The algorithm developed to satisfy these conditions is that a nonlinear optimization problem based on the force method considering the deformed shape is formulated, and, it’s able to find the shape by iteratively repeating the process of obtaining a solution of the governing equations. An computational technique based on the Gauss-Newton method was used as a method for obtaining solutions of nonlinear equations. In order to verify the validity of the proposed form-finding algorithm, a single-curvature pneumatic membrane example and a double-curvature air pneumatic membrane example were adopted, respectively. In the results of these examples, it was possible to well observe the step-by-step convergence process of the shape of the pneumatic membrane, and it was also possible to confirm the change in shape according to the air pressure. In addition, the calculation results of the shape and internal force after deformation due to initial tension, air pressure, and self-weight were obtained.

In this paper, we propose dead pixel detection and compensation method using nonlinear estimator for infrared camera. Infrared camera has dead pixel that is abnormal output values due to complex factors such as manufacturing process, electronic parts and so on. Dead pixels are able to affect detecting a small target. So, It needs detection and Compensation process. However, after Compensation, some dead pixels are remained and detected by the human. They are soft dead pixel. The key idea of this proposed method, detecting soft dead pixels, is that design a nonlinear estimator using image data characteristics. This propose is able to not only detect soft dead pixels but also pixel Compensation that reflects infrared camera output characteristics well.

Conditional spectra (CS) are applied to the seismic fragility assessment of a nuclear power plant (NPP) containment building for comparison with a relevant conventional uniform hazard response spectrum (UHRS). Three different control frequencies are considered in developing conditional spectra. The contribution of diverse magnitudes and epicentral distances is identified from deaggregation for the UHRS at a control frequency and incorporated into the conditional spectra. A total of 30 ground motion records are selected and scaled to simulate the probability distribution of each conditional spectra, respectively. A set of lumped mass stick models for the containment building are built considering nonlinear bending and shear deformation and uncertainty in modeling parameters using the Latin hypercube sampling technique. Incremental dynamic analysis is conducted for different seismic input models in order to estimate seismic fragility functions. The seismic fragility functions and high confidence of low probability of failure (HCLPF) are calculated for different seismic input models and analyzed comparatively.

The connection of the steel structure serves to transmit external forces to the main components. The same is true for the behavior of modular systems composed mainly of steel or composite members. In this study, the joint performance of the composite and steel modules proposed was evaluated. The analytical models of the two joint types were constructed and were subjected to cyclic loading to assess the safety and the energy dissipation capacity of the joint types. The analysis results of the joints showed that the joints of the modular systems remain stable when the joint rotation reached the seismic performance limit state of the 0.02 rad required for steel intermediate moment frame. It was also observed that the joint of the composite modular system showed higher energy dissipation capacity compared with the steel modular system.

In this paper, nonlinear finite element analysis was conducted based on the experimental results on buckling restrained brace. The reliability of the analytical model was verified by comparing the results of experimental studies with hysteresis loop, bi-linear curve, cumulative energy dissipation capacity, and equivalent viscous damping. A valid finite element model has been secured and will be used as basic data for finite element analysis of buckling restrained braces in the future.

Structures of domestic nuclear power plants are designed to perform elastic behavior against beyond design earthquakes, but studies on the nonlinear behavior of structures have been insufficient since the beyond design earthquake. Accordingly, it is judged that it will be necessary to develop an evaluation method that considers the nonlinear behavioral characteristics to check the safety margin for a standard nuclear power plant structure. It is confirmed that the restoring force characteristics for each member level can be identified through the calculation formula, and the lateral stiffness for each story can also be easily calculated by JEAC 4601. In addition, as a result of applying the evaluation method of JEAC 4601 as a nonlinear restoring force model of the nuclear power plant, a certain degree of safety margin can be identified.

This study pursues to solve a batch of nonlinear parameter estimation (NPE) problems where a model interpreting the independent and the dependent variables is given and fixed but corresponding data sets vary. Specifically, we assume that the model does not have an explicit form and the discrepancy between a value from a data set and a corresponding value from the model is unknown. Due to the complexity of the problem, one may prefer to use heuristic algorithms rather than gradient-based algorithms, but the performance of the heuristic algorithms depends on their initial settings. In this study, we suggest two schemes to improve the performance of heuristic algorithms to solve the target problem. Most of all, we apply a Bayesian optimization to find the best parameters of the heuristic algorithm for solving the first NPE problem of the batch and apply the parameters of the heuristic algorithm for solving other NPE problems. Besides, we save a list of simulation outputs obtained from the Bayesian optimization and then use the list to construct the initial population set of the heuristic algorithm. The suggested schemes were tested in two simulation studies and were applied to a real example of measuring the critical dimensions of a 2-dimensional high-aspect-ratio structure of a wafer in semiconductor manufacturing.

본 연구에서는 국부 비선형 정적 해석을 효율적으로 수행하기 위하여 강성응축(Static condensation)을 활용한 해석기법을 제시하였다. 강성응축기법은 자유도 기반의 유한요소 모델 축소기법이며, 해석 모델을 관심 대상(Target) 부분과 응축되어 생략될(Omitted) 부분으 로 구분한다. 본 연구에서는, 관심 대상 부분에는 비선형 영역, 생략될 부분에는 선형 영역으로 지정하였고, 선형 영역에 대응되는 강성 행렬 및 하중 벡터를 비선형 영역, 즉 관심 대상 부분으로 모두 응축하였다. 모델 응축 후에는 비선형 영역에 대한 강성 행렬 및 하중 벡터만으로 이루어진 축소 모델을 구성하였으며, 이 축소 모델만을 뉴턴-랩슨 반복(Newton-Raphson iteration)을 통해 갱신하여 효율적으로 비선형 해석을 수행하였다. 끝으로, 제안된 기법을 다양한 수치 예제에 적용하여 해석기법의 효율성과 신뢰성을 제시하였다.

The seismic deformation method is conventionally used as a seismic design for a multi-utility tunnel in Korea. In the seismic deformation method, the soil ground’s natural period is one of the most critical factors for calculating the ground displacement using cosine functions. Correction factors for the natural period and shear wave velocity have been used to consider the non-linearity of dynamic soil properties. However, the correction factors have been issued because the correction factors have not been sufficiently studied to consider Korea’s regional conditions. This paper aims to evaluate the natural periods for the seismic deformation method considering Korea’s ground conditions. Ground response analysis was performed using seven real earthquake records on twelve sites with different soil conditions where actual multi-utility tunnels are installed. As a result, natural periods of the sites were analyzed and new correction factors were proposed according to seismic performance and Korea’s regional conditions.

In this paper, we proposed an auto-encoder model of observation-wise linear transformation to reduce the dimensionality of data. While nonlinear models can reduce the dimensionality more effectively than linear models, such as the principal component analysis, the non-linear methods can hardly provide a simple linear relationship between the original and the dimensionally reduced data. The proposed model overcomes this difficulty while maintaining the effectiveness of the dimensionality reduction. We assessed the proposed model and compared with PCA and a typical auto-encoder model in terms of the loss function and the degree of reconstruction of the original data. By applying the proposed method to a public data of MNIST and Fashion-MNIST, we showed the effectiveness in the dimensionality reduction and relationship between the original data to the reduced data.