• 한국정밀공학회지
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• 제16권8호
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• pp.186-192
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• 1999

This paper introduces a study of a method for the forward kinematic analysis, which finds the 6 DOF motions and velocities from the given six cylinder lengths in the Stewart platform. From the viewpoints of kinematics, the solution for the inverse kinematic is easily found by using the vectors of the links which are composed of the joint coordinates in base and plate frames, to act contrary to the serial manipulator, but forward kinematic is difficult because of the nonlinearity and complexity of the Stewart platform dynamic equation with the multi-solutions. Hence we, first in this study, introduce the linear estimator using the Luenberger's observer, and the estimator using the nonlinear measured model for the forward kinematic solutions. But it is difficult to find the parameter of the design for the estimation gain or to select the estimation gain and the constant steady state error exists. So this study suggests the estimator with the estimation gain to be learned by the neural network with the structure of multi-perceptron and the learning method using back propagation and shows the estimation performance using the simulation.

• 한국소음진동공학회논문집
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• 제20권10호
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• pp.923-930
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• 2010

Finite element models of dynamic systems can be updated in two stages. In the first stage, mass and stiffness matrices are updated neglecting damping, and in the second stage, damping matrices are estimated with the mass and stiffness matrices fixed. Three methods to estimate damping matrices for this purpose are proposed in this paper. The methods include one for proportional damping systems and two for non-proportional damping systems. Method 1 utilizes orthogonality of normal modes and estimates damping matrices using the modal parameters extracted from the measured responses. Method 2 estimates damping matrices from impedance matrices which are the inverse of FRF matrices. Method 3 estimates damping using the equation which relates a damping matrix to the difference between the analytical and measured FRFs. The characteristics of the three methods are investigated by applying them to simulated discrete system data and experimental cantilever beam data.

• The Journal of Asian Finance, Economics and Business
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• 제9권10호
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• pp.215-225
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• 2022

This study investigates employees' online reviews, conducts in-depth text topic mining, effectively summarizes the dimensions of employer brand value, and seeks effective ways to build employer brands from a multi-dimensional perspective. This study employs samples of employer reviews, filter keywords according to word frequency-inverse document frequency, builds a review network containing the same keywords, explore the community and summarize the theme dimensions. Simultaneously, it makes a dynamic comparison and analysis of the employer brand value dimension of different industries and enterprises. The study shows that the community exploration theme can be summarized into 11 dimensions of employer brand value, and the dimensions of employer brand value are significantly different across industries and among different enterprises within the industry. The attention to the employer brand value dimension has a significant time change. Various industries pay increasing attention to the dimension of work intensity and career development, while employers pay steady attention to the dimension of welfare benefits. The findings of this study suggest that seeking the heterogeneity of employer brand resources from the multi-dimensional differences and changes is an effective way to improve the competitiveness of enterprises in the human capital market.

• Structural Engineering and Mechanics
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• 제91권2호
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• pp.227-238
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• 2024

Sparse regularization methods have proven effective in addressing the ill-posed equations encountered in moving force identification (MFI). However, the complexity of vehicle loads is often ignored in existing studies aiming at enhancing MFI accuracy. To tackle this issue, a double 𝑙₁ regularization method is proposed for MFI based on a response spectrum-based weighted dictionary in this study. Firstly, the relationship between vehicle-induced responses and moving vehicle loads (MVL) is established. The structural responses are then expanded in the frequency domain to obtain the prior knowledge related to MVL and to further construct a response spectrum-based weighted dictionary for MFI with a higher accuracy. Secondly, with the utilization of this weighted dictionary, a double 𝑙₁ regularization framework is presented for identifying the static and dynamic components of MVL by the alternating direction method of multipliers (ADMM) method successively. To assess the performance of the proposed method, two different types of MVL, such as composed of trigonometric functions and driven from a 1/4 bridge-vehicle model, are adopted to conduct numerical simulations. Furthermore, a series of MFI experimental verifications are carried out in laboratory. The results shows that the proposed method's higher accuracy and strong robustness to noises compared with other traditional regularization methods.

• KIEAE Journal
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• 제7권4호
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• pp.147-152
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• 2007

Numerous non-destructive tests(NDT) to assess the safety of real structures have been developed. System identification(SI) techniques using dynamic responses and behaviors of structural systems become an outstanding issue of researchers. However the conventional SI techniques are identified to be non-practical to the complex and tall buildings, due to limitation of the availability of an accurate data that is magnitude or location of external loads. In most SI approaches, the information on input loading and output responses must be known. In many cases, measuring the input information may take most of the resources, and it is very difficult to accurately measure the input information during actual vibrations of practical importance, e.g., earthquakes, winds, micro seismic tremors, and mechanical vibration. However, the desirability and application potential of SI to real structures could be highly improved if an algorithm is available that can estimate structural parameters based on the response data alone without the input information. Thus a technique to estimate structural properties of building without input measurement data and using limited response is essential in structural health monitoring. In this study, shaking table tests on three-story plane frame steel structures were performed. Out-put only model analysis on the measured data was performed, and the dynamic properties were inverse analyzed using least square method in time domain. In results damage detection was performed in each member level, which was performed at story level in conventional SI techniques of frequency domain.

• 한국해안·해양공학회논문집
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• 제35권2호
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• pp.41-48
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• 2023

본 연구에서는 바닥의 움직임에 따른 파랑의 생성 및 변화를 모의할 수 있는 간단한 선형 수치해석 기법을 소개한다. 연속방정식과 선형의 동역학적 및 운동학적 자유수면 경계조건, 선형의 운동학적 바닥 경계조건을 공간에 대해 푸리에 변환한 후 파수 영역에서 수치해석을 수행하며, 결과는 푸리에 역변환을 통해 공간영역에서 표현된다. 파수 영역에서 동역학적 자유수면 경계조건과 운동학적 자유수면 경계조건이 수치적으로 계산되며, 이 때 평균수면 (z = 0)에서의 속도포텐셜은 연속방정식과 운동학적 바닥 경계조건을 만족한다. 삼각형 및 사각형 형상의 바닥이 주기적으로 움직이는 경우의 파랑 생성 및 전파에 대해 검토하였다. 간편 수치해석 기법을 이용한 결과는 기존의 선형 해석해와 비교하였으며, 거의 일치하는 결과를 보였다. 계산 시간간격(Δt)과 계산 파수간격(Δk)에 따른 수치해석 결과의 안정성에 대해서도 검토하였다. 검토 결과 Δt ≤T(주기)/1000, Δk ≤ π/100 일 때 수치해석에 의한 결과가 적절하게 도출되는 것으로 나타났다.

• 대한기계학회논문집A
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• 제34권4호
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• pp.431-437
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• 2010

본 연구의 목적은 편마비 환자와 같이 정상 보행이 아닌 경우의 보행 실험에서 힘측정판을 이용한 지면반발력의 측정이 매우 어려웠던 경험에서 출발하여 힘측정판을 사용하지 않고 운동학적 데이터만으로 보행 중 발생하는 지면반발력을 계산하는 것이다. 3차원 동작분석 시스템과 동기화된 힘측정판을 이용하여 보행실험을 실시하여 3차원 동작분석 시스템으로부터 보행의 운동학적 데이터를 추출하였고 이로부터 보행주기를 검출하였다. 인체를 13개의 체절로 모델링하고 각 체절의 거동이 추출한 운동학적 데이터를 따르도록 하였다. 각 체절의 질량과 질량 중심은 인체측정학의 자료를 이용하였다. 보행실험에서 측정한 지면반발력과 운동학적 데이터만을 이용한 계산 결과의 비교에서 크기가 가장 큰 수직방향은 잘 일치하였고 전후방향이나 횡방향도 유사한 경향을 보였다. 본 계산 결과는 보행에 관한 역동역학 해석의 기본 자료로 활용할 수 있다.

• 대기
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• 제26권2호
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• pp.301-319
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• 2016

The evolutionary process of the polar low, which caused the heavy snowfall in the East Coast area on 11~12 February 2011, was investigated to describe in detail using synoptic weather charts, satellite imageries, and ERA (European Centre for Medium-Range Weather Forecasts Re-Analysis) -Interim reanalysis data. It was revealed that 1) the polar low was generated over the sea near Busan where a large cyclonic shear in the inverted trough branched from the parent low existed, 2) during the developing and mature stages, there was a convectively unstable region in the lower layer around the polar low and its south side, 3) the polar low was developed in the region where the static stability in the 500~850 hPa layer was the lowest, 4) the result from the budget analysis of the vorticity equation indicated that the increase in the vorticity at the lower atmosphere, where the polar low was located, was dominated mainly by the stretching term, 5) the warm core structure of the polar low was identified in the surface-700 hPa layer during the mature stage, 6) there was a close inverse relationship between a development of the polar low and the height of the dynamic tropopause over the polar low, and 7) for generation and development of the polar low, large-scale circulation systems, such as upper cold low and its combined short wave trough, major low (parent low), and polar air outbreak, should be presented, indicating that the polar low has the nature of the baroclinic disturbance.

• 한국구조물진단유지관리공학회 논문집
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• 제17권1호
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• pp.124-132
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• 2013

손상된 구조물의 동적응답신호를 역해석함으로써 손상위치와 정도를 파악할 수 있다. 일반적으로 손상 전 후 고유진동수의 변화로부터 강성의 감소량을 구하고, 모드형상의 변화로부터 손상위치를 파악할 수 있다. 토목구조물의 경우 동적 응답신호로부터 손상을 검출코자 하는 연구가 상당히 진행되었으며 실용화 되었다. 그러나 건축구조물의 경우 몇 가지 문제로 인하여 이에 대한 연구가 활발히 진행되지 못하고 있다. 본 연구에서는 모드형상을 이용한 전단형 건물의 손상위치 추적방안을 제시 하고자 한다. 전단형 건물의 손상 전 후 1차 모드강성의 차이를 이용한 손상위치 추적지수를 이론적으로 고찰하였으며, 이를 Matlab 또는 MIDAS GENw와 같은 수치해석모델에 적용함으로써 손상위치추적기법의 타당성을 검증하였다. 또한 소형 진동대 실험을 수행하고 실측된 동적응답신호를 이용하여 손상위치를 추적함으로써 실구조물에 대한 적용성을 검토하였다. 진동대 실험결과 층강성이 25% 감소할 때 1차 모드 진동수는 12%증가 하였으며, 손상위치 지수는 손상 층에서 마이너스 값을 나타내었다.

• 한국항행학회논문지
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• 제26권6호
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• pp.404-411
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• 2022

위성항법시스템 운용 시 주요 기능은 항법위성의 궤도를 정확히 결정하여 항법메시지로 전송하는 것이다. 본 연구에서는 확장 칼만필터와 정밀동역학모델을 결합하여 항법위성의 궤도결정을 수행하는 소프트웨어를 개발하였다. IGS (international gnss service) 지상국의 실제 관측값을 사용하여 GPS (global positioning system)와 QZSS (quasi-zenith satellite system)의 궤도결정을 수행하고, IGS 정밀궤도력과 비교하여 항법시스템의 주요 성능지표인 URE (user range error)를 계산하였다. 항법위성에 탑재된 시계오차를 추정할 경우 radial 방향 궤도오차와 시계오차가 높은 역상관 관계를 가지는데 서로 상쇄되어 GPS와 QZSS의 궤도결정 URE 표준편차는 1.99 m, 3.47 m로 낮은 수준을 유지하였다. 항법위성 시계오차를 추정하는 대신 항법메시지의 시계오차를 모델링한 값으로 대체하여 궤도결정을 수행하였으며, URE와 지역적 상관관계 및 지상국 배치에 의한 영향을 분석하였다.