• 대한기계학회논문집A
• /
• 제36권7호
• /
• pp.777-787
• /
• 2012

본 논문에서는 여러 가지 충격하에서 압저항 고충격 미소가속도계의 과도 출력전압의 계산시 발생하는 방대한 계산 시간 문제를 모드중첩법 및 최소자승법을 이용하여 압저항 미소가속도계의 실시간 출력전압 계산이 가능하도록 효율적인 출력전압 과도해석 방법을 제안한다. 우선 정적 압저항-구조 해석을 통하여 미소가속도계의 변위와 출력전압을 계산하고 출력전압을 특정 위치의 변위에 관한 2차 다항식으로 근사화하여 그 회귀계수를 최소자승법을 통하여 결정한다. 이후에 모드중첩법을 통하여 여러 방향의 고충격하에서 미소가속도계의 과도 변위응답을 계산하고, 이 변위응답을 변위로 표현되는 출력전압 근사식에 대입하여 과도 출력전압을 예측한다. 100,000 G 고충격파, 사인파, 계단파 및 사각파 등의 여러 가지 고충격 입력에 대한 압저항 미소가속도계의 수치예제를 통하여 제안한 방법의 정확성 및 효율성을 검증하였다.

• 대한조선학회논문집
• /
• 제52권6호
• /
• pp.435-443
• /
• 2015

Offshore structure may be considerably vulnerable to fatigue failure while initial flaw propagates under cyclic loading, so crack propagation analysis/fracture/yield assessments about initial flaw detected by NDT are necessarily required. In this paper, case studies have been conducted by flaw assessment program using engineering criticality analysis (ECA) approach. Variables such as flaw geometry, flaw size, structure geometry, dynamic stress, static stress, toughness, crack growth rate, stress concentration factor (SCF) affected by weld are considered as analysis conditions. As a result, the safety of structure was examined during fatigue loading life. Also, critical initial flaw size was calculated by sensitivity module in the developed program. The flaw assessments analysis using ECA approach can be very useful in offshore industries owing to the increasing demand on the engineering criticality analysis of potential initial flaws.

• Structural Engineering and Mechanics
• /
• 제51권3호
• /
• pp.447-470
• /
• 2014

Numerical simulation of the non-linear behavior of (RC) structural walls subjected to severe earthquake ground motions requires a reliable modeling approach that includes important material characteristics and behavioral response features. The objective of this paper is to optimize a simplified method for the assessment of the seismic response and damage development analyses of an RC structural wall building using macro-element model. The first stage of this study investigates effectiveness and ability of the macro-element model in predicting the flexural nonlinear response of the specimen based on previous experimental test results conducted in UCLA. The sensitivity of the predicted wall responses to changes in model parameters is also assessed. The macro-element model is next used to examine the dynamic behavior of the structural wall building-all the way from elastic behavior to global instability, by applying an approximate Incremental Dynamic Analysis (IDA), based on Uncoupled Modal Response History Analysis (UMRHA), setting up nonlinear single degree of freedom systems. Finally, the identification of the global stiffness decrease as a function of a damage variable is carried out by means of this simplified methodology. Responses are compared at various locations on the structural wall by conducting static and dynamic pushover analyses for accurate estimation of seismic performance of the structure using macro-element model. Results obtained with the numerical model for rectangular wall cross sections compare favorably with experimental responses for flexural capacity, stiffness, and deformability. Overall, the model is qualified for safety assessment and design of earthquake resistant structures with structural walls.

• Composites Research
• /
• 제24권3호
• /
• pp.12-16
• /
• 2011

경량복합소재의 고속인장시험을 수행하여 변형률속도에 따른 강도변화를 측정하고자 한다. 준 정적 시험인 경우 섬유강화 복합소재의 인장시험은 ASTM D3039에 따른 시편 형상이 사용되지만 고속 인장시험인 경우 표준화된 시편 형상에 대한 연구가 진행되어 있지 않다. 본 연구에서는 ASTM D638에 나타난 시편 형상을 기본으로 몇 가지 변형된 형태의 시편을 가지고 고속인장 시험을 수행하여 변형률 속도에 따른 경량복합소재의 강도 변화를 측정하였다. 낙하방식의 고속인장 시험기를 제작하여 변형률 속도 15/s, 100/s에서 시편의 형상에 따른 섬유강화 복합소재의 인장거동을 측정하였으며 시편의 폭이 6mm, 8mm, 10mm인 경우에 대하여 시험을 수행하였다. 측정 결과 시편의 폭이 8mm인 경우 섬유강화 복합소재의 강도를 정확하게 평가할 수 있는 것으로 나타났다.

• The Korean Journal of Physiology and Pharmacology
• /
• 제1권3호
• /
• pp.263-273
• /
• 1997

The purpose of this study was to evaluate the effects of electrical stimulation on vestibular compensation following ULX in rats. Electrical stimulation (ES) with square pulse ($100{\sim}300uA$, 1.0 ms, 100 Hz) was applied to ampullary portion bilaterally for 6 and 24 hours in rats receiving ULX. After ES, animals that showed the recovery of vestibular symptoms by counting and comparing the number of spontaneous nystagmus were selected for recording resting activity of type I, II neurons in the medial vestibular nuclei (MVN) of the lesioned side. And then the dynamic neuronal activities were recorded during sinusoidal rotation at a frequency of 0.1 Hz and 0.2 Hz. The number of spontaneous nystagmus was significantly different 24 hours (p<0.01, n=10), but not 6 hours after ULX+ES. As reported by others, the great reduction of resting activity only in the type I neurons ipsilateral to lesioned side was observed 6, 24 hours after ULX compared to that of intact labyrinthine animal. However, the significant elevation (p<0.01) of type I and reduction (p<0.01) of type II neuronal activity were seen 24 hours after ULX+ES. Interestingly, gain, expressed as maximum neuronal activity(spikes/sec)/maximum rotational velocity(deg/sec), was increased in type I cells and decreased in type II cells 24 hours after ULX+ES in response to sinusoidal rotation at frequencies of both 0.1 Hz and 0.2 Hz. This result suggests that accompanying the behavioral recovery, the electrical stimulation after ULX has beneficial effects on vestibular compensation, especially static symptoms (spontaneous nystagmus), by enhancing resting activity of type I neurons and reducing that of type II neurons.

• 대한기계학회논문집B
• /
• 제38권9호
• /
• pp.731-737
• /
• 2014

와류실은 압축된 공기를 이용하여 고온과 저온 가스로 분리할 수 있는 단순한 장치로, 차세대 새로운 열교환기로 각광받고 있으나, 와류실 내부에서 발행하는 물리적 유동특성에 대해 아직까지 많이 알려지지 않았다. 본 연구에서는 온도 분리 현상을 조사하기 위해 실험 및 수치해석을 수행하였다. 공급 압력에 따른 온도 변화를 측정하기 위하여 다수의 압력 및 온도 센서를 사용하였으며, CFD 기법을 적용하여 3차원 비정상 압축성 유동장을 조사하였다. 연구를 통해 온도 분리 현상은 점성일과 밀접한 관계가 있는 공급 압력과 와류실의 직경에 영향을 받았으며, 와류실에서 발생하는 온도분리 현상은 압력구배파의 개념으로 확증할 수 없었다.

• 대한조선학회논문집
• /
• 제57권4호
• /
• pp.182-190
• /
• 2020

This study reports a series of drop impact tests performed to generate denting damages on stiffened plates and their residual ultimate strength tests under axial compression. The models were fabricated of general structural steel, and each model has six longitudinal stiffeners and two transverse frames. Among six fabricated models, four were damaged, and two were left intact for reference. To investigate the effects of collision velocity and impact location on the extent of damage, the drop height and the impact location were changed in each impact test. After performing the collision tests, the ultimate axial compression tests were conducted to investigate the residual strengths of the damaged stiffened plates. Finite element analyses were also carried out using a commercial package Abaqus/Explicit. The material properties obtained from a quasi-static tensile tests were used, and the strain-rate sensitivity was considered. After importing the collision simulation results, the ultimate strength calculations were carried out and their results were compared with the test data for the validation of the finite element analysis method.

• 한국시뮬레이션학회논문지
• /
• 제29권2호
• /
• pp.83-93
• /
• 2020

BMORE(Bivariate measure of risk and error) 도표는 본래 확률적 시뮬레이션에서의 이변량 성과 데이터와, 그와 관계된 표본 평균, 중앙값, 이상점, 특정 백분위 내의 결과 데이터의 범위 등과 같은 통계량들을 시각화하기 위해 설계되었으며, 정적인 정보들만 제공하는 것에 비해 사용자들이 시뮬레이션 결과 데이터에 담긴 가변성을 더욱 직관적으로 쉽게 이해할 수 있도록 돕는다. 본 연구에서는 BMORE 도표를 단순히 한 시스템의 가변성을 시각화하기 위한 것이 아닌, 특정 확률적 제약 아래 대상 시스템들의 실행 가능성을 타진하고, 통계적 배경 아래 여러 시스템들의 성과 비교를 행하며, 매개변수들의 민감도 분석을 실시하기 위한 의사결정 도구로써 활용할 수 있음을 보이고 이를 위한 여러 방안을 제안한다. 그 활용 예시를 보이고자 본 연구에서는 간단한 재고 관리 문제를 차용하였으나, 제시된 방안들 자체는 이변량 성과 척도를 가지는 시뮬레이션/실험 데이터를 근거로하여 여러 시스템들을 비교하는 문제라면 어디든 사용될 수 있음을 밝혀둔다.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제7권2호
• /
• pp.227-243
• /
• 2015

In this paper, the effects of nonlinear soft clay on dynamic embedment of offshore pipeline were investigated. Seabed embedment by pipe-soil interactions has impacts on the structural boundary conditions for various subsea structures such as pipeline, riser, pile, and many other systems. A number of studies have been performed to estimate real soil behavior, but their estimation of seabed embedment has not been fully identified and there are still many uncertainties. In this regards, comparison of embedment between field survey and existing empirical models has been performed to identify uncertainties and investigate the effect of nonlinear soil parameter on dynamic embedment. From the comparison, it is found that the dynamic embedment with installation effects based on nonlinear soil model have an influence on seabed embedment. Therefore, the pipe embedment under dynamic condition by nonlinear parameters of soil models was investigated by Dynamic Embedment Factor (DEF) concept, which is defined as the ratio of the dynamic and static embedment of pipeline, in order to overcome the gap between field embedment and currently used empirical and numerical formula. Although DEF through various researches is suggested, its range is too wide and it does not consider dynamic laying effect. It is difficult to find critical parameters that are affecting to the embedment result. Therefore, the study on dynamic embedment factor by soft clay parameters of nonlinear soil model was conducted and the sensitivity analyses about parameters of nonlinear soil model were performed as well. The tendency on dynamic embedment factor was found by conducting numerical analyses using OrcaFlex software. It is found that DEF was influenced by shear strength gradient than other factors. The obtained results will be useful to understand the pipe embedment on soft clay seabed for applying offshore pipeline designs such as on-bottom stability and free span analyses.

• 한국정보시스템학회지:정보시스템연구
• /
• 제17권3호
• /
• pp.205-233
• /
• 2008

This study suggests the dynamic value chain model, that will be able to not only show changing processes to organization's significant capital by integrating an individual, implicit, and explicit knowledge which affect organizational decision making, but also distinguish the key driver for raising organizational competitive power because it makes possible to analyze sensitivity of performance along with decision making alternatives and policy changes from dynamic view by connecting knowledge management capability, knowledge management activity, and relations with organizational performance with specific strategic map. Recently, a lot of organizations show interest in measuring and evaluating their performance synthetically. In organizations taking knowledge management, they introduce effective value chain model like a dynamic balanced scorecard (DBSC), and therefore they can reflect their knowledge management condition as well as show their changes by checking performance of established vision and strategy periodically. Furthermore, they can ask for their inner members' understanding and participation by communicating with and inspiring their members with awareness that members are one of their group, present a base of benchmarking, and offer significant information for later decision making. The BSC has been a successful framework for measuring an organization's performance in various perspectives through translating an organization's vision and strategy into an interrelated set of key performance indicators and specific actions. The BSC, while having significant strengths over traditional performance measurement methods, however, has its own limitations, due to its static nature, such as overlooking two-way causation between performance indicators and neglecting the impact of delayed feedback flowing from the adoption of new strategies or policy changes. To overcome these limitations, this study employs SD, a methodology for understanding complex systems where dynamic feedback among the interrelated system components significantly impact on the system outcomes. The SD simulation model in the form of DBSC would serve as a useful strategic teaming tool for facilitating an organization's communication process through various scenario analyses as well as predicting the dynamic behavior pattern of their key performance measures over a future time frame. For the demonstration purpose, this study applied the DBSC model to Prototype of Korea manufacturing and service firm.