• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2642-2649
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• 2023

A real-time unmeasured dynamic response prediction process for the nuclear power plant pressure pipeline is proposed and its performance is tested in the test-loop system (KAERI). The aim of the process is to predict unmeasurable or unreachable dynamic responses such as acceleration, velocity, and displacement by using a limited amount of directly measured physical responses. It is achieved by combining a well-constructed finite element model and robust inverse force identification algorithm. The pressure pipeline system is described by using the displacement-pressure vibro-acoustic formulation to consider fully filled liquid effect inside the pipeline structure. A robust multiphysics modal projection technique is employed for the real-time sensor synchronized prediction. The inverse force identification method is also derived and employed by using Bathe's time integration method to identify the full-field responses of the target system from the modal domain computation. To validate the performance of the proposed process, an experimental test is extensively performed on the nuclear power plant pressure pipeline test-loop under operation conditions. The results show that the proposed identification process could well estimate the unmeasured acceleration in both frequency and time domain faster than 32,768 samples per sec.

• 소음진동
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• 제2권3호
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• pp.193-202
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• 1992

The unbalance response analysis is one of the essential area in the forced vibration analysis of rotor bearing systems because of it usefulness in balancing and diagnosis as well as identification of parameters involved in rotor bearing systems. However some unbalance responses are not measurable due to the fact that rotor bearing systems are often encapsulated by fixtures or safety protectors. In the present paper, an efficent estimation scheme for unmeasured unbalance responses in rotor bearing systems is developed. The fundamental fearture of the proposed method is characterized by the linear formulae to estimate the unbalance responses from the measured unbalance responses and the finite element auxilliary model equation which is constructed to be identical to the prototype excluding the uncertain parameters such as bearing coefficients. The identification formulae for bearing parameters are also derived by using the unbalance response and the finite elements auxiliary model. Simulation is provided to verify the effectiveness of the proposed method.

• Smart Structures and Systems
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• 제15권2호
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• pp.489-503
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• 2015

Response estimation at unmeasured locations using the limited number of measurements is an attractive topic in the field of structural health monitoring (SHM). Because of increasing complexity and size of civil engineering structures, measuring all structural responses from the entire body is intractable for the SHM purpose; the response estimation can be an effective and practical alternative. This paper investigates a response estimation technique based on the Kalman state estimator to combine multi-sensor data under non-zero mean input excitations. The Kalman state estimator, constructed based on the finite element (FE) model of a structure, can efficiently fuse different types of data of acceleration, strain, and tilt responses, minimizing the intrinsic measurement noise. This study focuses on the effects of (a) FE model error and (b) combinations of multi-sensor data on the estimation accuracy in the case of non-zero mean input excitations. The FE model error is purposefully introduced for more realistic performance evaluation of the response estimation using the Kalman state estimator. In addition, four types of measurement combinations are explored in the response estimation: strain only, acceleration only, acceleration and strain, and acceleration and tilt. The performance of the response estimation approach is verified by numerical and experimental tests on a simply-supported beam, showing that it can successfully estimate strain responses at unmeasured locations with the highest performance in the combination of acceleration and tilt.

• 한국지진공학회논문집
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• 제21권6호
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• pp.287-293
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• 2017

Sometimes, it is impossible to install a sensor on a certain location of a structure due to the size of a structure or poor surrounding environments. Even if possible, sensors can be frequently malfunctioned or improperly operated due to lack of adequate maintenance. These kind of problems are solved by the virtual sensing methods in various engineering fields. Virtual sensing technology is a technology that can measure data even though there is no physical sensor. It is expected that this technology can be also applied to the construction field effectively. In this study, a virtual sensing technology based on ARX model is proposed. An ARX model is defined by using the simulated data through a structural analysis rather than by actually measured data. The ARX-based virtual sensing model can be applied to estimate unmeasured response using a transfer function that defines the relationship between two point data. In this study, a simulation and experimental study were carried out to examine the proposed virtual sensing method with a laboratory test on a cable-stayed model bridge. Acceleration measured at a girder is transformed to estimate a cable tension through the ARX model-based virtual sensing.

• 대한기계학회논문집A
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• 제26권5호
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• pp.872-880
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• 2002

The finite element analysis is frequently used to predict dynamic responses of complex structures. Since the predicted responses often differ from experimentally measured ones, updating of the finite element models is performed to make the finite element results agree with the measured ones. Among several model updating methods, one is to use FRF(frequency response function) data without a modal analysis. This paper investigates characteristics of the model updating method in order to improve the method. The investigation is focused on how to obtain FRFs for unmeasured rotational displacements and how to consider damping. For the investigation simulated data and experimental data for a cantilever beam are used.

• 한국인터넷방송통신학회논문지
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• 제19권5호
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• pp.129-133
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• 2019

넓은 BW를 사용하는 위성 통신 시스템에서 주파수 자원을 최대한 효율적으로 사용하는 것은 매우 중요하다. 주파수 자원의 낭비를 초래하는 원인들 중 하나는 사용 대역의 평탄도가 좋지 못하는 경우이다. 사용 대역의 평탄도가 좋지 못한 위성 단말 송신부는 ACI와 가드밴드로 인해 주파수 자원 효율이 낮아지게 된다. 이를 극복하기 위해 본 논문에서는 위성 단말 송신부의 평탄도를 보정하는 방법을 제안한다. 우선, 선별하여 측정한 데이터로부터 최소 자승법을 만족하는 다항식을 생성하고 측정하지 않은 주파수 응답 특성을 보간 하였다. 그리고 최소 자승법을 만족하는 다항식을 이용하여 모뎀의 출력 레벨을 조절하였다. 시뮬레이션 결과 보정된 데이터는 보정 전 데이터 대비 pk-pk와 표준편차가 낮아졌고 이를 통해 평탄도가 보정되었음을 확인하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 봄 학술발표회 논문집
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• pp.113-119
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• 1994

Vibration control of offshore structures subjected to wave loads is studied. The reduction of the dynamic responses of offshore towers subjected to wind generated random ocean waves is an important issue in the aspect of serviceability, fatigue life and safety of the structure. In this thesis, the effectiveness of the active tuned mass damper(ATMD) compared with the tuned mass damper(TMD) is mainly considered. Instantaneous optimal control scheme is employed for the active vibration control and Kalman filtering technique is used for the estimation of unmeasured response of structures. In practice, displacements and velocities could not be measured as easily as accelerations. So the state estimation methods like Kalman filter is very important. Numerical simulation is conducted for guarantee the effectiveness of ATMD for offshore structures.

• Clinical and Experimental Pediatrics
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• 제63권5호
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• pp.164-170
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• 2020

The prognosis of patients who are comatose after resuscitation remains uncertain. The accurate prediction of neurological outcome is important for management decisions and counseling. A neurological examination is an important factor for prognostication, but widely used sedatives alter the neurological examination and delay the response recovery. Additional studies including electroencephalography, somatosensory-evoked potentials, brain imaging, and blood biomarkers are useful for evaluating the extent of brain injury. This review aimed to assess the usefulness of and provide practical prognostic strategy for pediatric postresuscitation patients. The principles of prognostication are that the assessment should be delayed until at least 72 hours after cardiac arrest and the assessment should be multimodal. Furthermore, multiple factors including unmeasured confounders in individual patients should be considered when applying the prognostication strategy.

• 한국환경보건학회지
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• 제37권5호
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• pp.358-368
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• 2011

Objectives: In order to evaluate the association between occupational exposure to chloroethylene (TCE) and risk of non-Hodgkin lymphoma (NHL), we conducted a meta-analysis of retrospective cohort studies and casecontrol studies and attempted to summarize the evidence of the association from molecular-epidemiological studies and experiments with human cells. Methods: In the meta-analysis, we restricted the analysis to those studies with data for chlorinated solvents, degreasers, or TCE. Studies involving dry cleaners or launderers were excluded from the analysis because use of TCE as a dry cleaning fluid has been rare since the 1960s. The data were combined using a random-effects model to estimate the summary risks (OR and RR) and 95% confidence intervals (CIs). Molecular evidence of the effect of TCE on human immune system were also reviewed and summarized. Results: Occupational exposure to TCE was strongly associated with NHL among cohort studies (number of studies=13, summary RR=1.33, 95% CI=1.04-1.70) whereas the association was not statistically significant among case-control studies (number of studies=15, summary OR=1.10, 0.98-1.23). When exposure level was considered, it became statistically significant for the highest exposure level (number of studies=5, summary OR=1.70, 1.25-2.32). Molecular evidences showed that TCE exposure in human or cultured human cells may cause a significant decrease immune cell subsets and changes in hormone levels related to immune response. Conclusions: Our results from meta-analysis and additional molecular evidence suggest that occupational exposure to TCE may cause NHL. However, unmeasured potential confounding and unclear dose-response relationships warrant further study on the role of TCE exposure in NHL carcinogenesis.

• 한국전산구조공학회논문집
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• 제13권4호
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• pp.395-404
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• 2000

강제진동을 가한 구조물의 제한된 위치에서 측정한 가속도를 사용하여 손상을 확인하고 평가하는 알고리듬을 개발하였다. 개발된 알고리듬에서는 선형적 구속-비선형 최적화에 의해 최적의 구조변수를 구하여 구조물을 인식하는 시간영역-시스템 인식기법을 사용하였다. 동적운동방정식의 오차를 최소화하도록 최적의 변수를 추정하였으며, 제한된 위치에서 측정된 가속도 자료를 이용하여 손상된 부재를 찾기 위하여 적합적 변수모음법을 적용하였다. 손상은 측정된 가속도의 시간이력에 시간창의 개념을 적용하여 통계적으로 평가하였다. 가속도가 측정된 자유도에서의 변위와 속도는 측정된 가속도를 적분하여 계산하였으며, 미측정 자유도에서는 변위를 추가의 미지변수로 추정하고, 속도와 가속도는 추정된 변위의 차분에 의해 수치적으로 계산하였다. 개발된 알고리듬의 효율성을 검증하기 위하여 트러스에 대한 수치모의실험을 실시하였다. 손상지수의 한계치를 정하고 각 부재에서의 손상가능도를 계산하기 위하여 자료교란법을 적용하였다.