• Tribology and Lubricants
• /
• 제30권5호
• /
• pp.284-290
• /
• 2014

The influence of round embossed surface on slider bearing characteristics and its load carrying capacity is discussed for thin film effect of embossed slider bearing. For the numerical computation of lubrication parameters such as pressure, load capacity and shear stress that are normalized and a Reynolds equation is used for the analysis of embossed slider bearing characteristics. For this purpose, the finite difference method of central difference scheme is used in this study. In a slider bearing with embossed form, several simulation parameters such as pressure, load capacity and shear stress of the bearing can be obtained according to independent parameters such as the slope of the slider bearing and number of embossing in the upper slider. Also this results can be summarized and be stored in sequential data file for latter analysis. After all, their distribution of the pressure and shear stress parameters can be displayed and be analyzed easily by using the developed program with matlab GUI technique. The independent parameters such as a number of embossing and a slope of the embossed surface slider are used for discussing simulation parameters of pressure distribution, shear stress and load carrying capacity of the round embossing. These study results reported in this paper should be applied to the other shaped slider bearing with a rectangular embossed surface or rectangular waved surface.

• International Journal of Aeronautical and Space Sciences
• /
• 제17권2호
• /
• pp.184-194
• /
• 2016

In existing identification methods for on-orbit spacecraft, such as eigensystem realization algorithm (ERA) and subspace method identification (SMI), singular value decomposition (SVD) is used frequently to estimate the modal parameters. However, these identification methods are often used to process the linear time-invariant system, and there is a lower computation efficiency using the SVD when the system order of spacecraft is high. In this study, to improve the computational efficiency in identifying time-varying modal parameters of large spacecraft, a faster recursive algorithm called fast approximated power iteration (FAPI) is employed. This approach avoids the SVD and can be provided as an alternative spacecraft identification method, and the latest modal parameters obtained can be applied for updating the controller parameters timely (e.g. the self-adaptive control problem). In numerical simulations, two large flexible spacecraft models, the Engineering Test Satellite-VIII (ETS-VIII) and Soil Moisture Active/Passive (SMAP) satellite, are established. The identification results show that this recursive algorithm can obtain the time-varying modal parameters, and the computation time is reduced significantly.

• Smart Structures and Systems
• /
• 제6권8호
• /
• pp.905-920
• /
• 2010

Changes in temperature, loads and boundary conditions may have effects on the dynamic properties of large civil structures. Taking the Run Yang Suspension Bridge as an example, modal properties obtained from ambient vibration tests and from the structural health monitoring system of the bridge are used to identify and evaluate the modal parameter variability. Comparisons of these modal parameters reveal that several low-order modes experience a significant change in frequency from the completion of the bridge to its operation. However, the correlation analysis between measured modal parameters and the temperature shows that temperature has a slight influence on the low-order modal frequencies. Therefore, this paper focuses on the effects of the boundary conditions on the dynamic behaviors of the suspension bridge. An analytical model is proposed to perform a sensitivity analysis on modal parameters of the bridge concerning the stiffness of expansion joints located at two ends of bridge girders. It is concluded that the boundary conditions have a significant influence on the low-order modal parameters of the suspension bridge. In addition, the influence of vehicle load on modal parameters is also investigated based on the proposed model.

• 한국지반공학회논문집
• /
• 제30권10호
• /
• pp.45-54
• /
• 2014

비탈면 붕괴를 최소화 하기 위하여 조사, 설계, 해석, 대책방안 등의 연구가 많이 수행되고 있다. 그러나, 최근 태풍 및 집중호우로 인하여 비탈면 및 자연 사면의 산사태 발생빈도는 줄지 않고 있다. 단순한 설계 기준의 강화만으로는 적절한 대책을 마련하기 어려운 실정이다. 따라서, 지반과 강우를 고려한 최적의 조건에서 설계 및 안정해석을 실시하여야 한다. 본 연구는 비탈면 해석시 강우 및 해석조건에 대하여 각 변수의 영향을 살펴보고자 안전율의 변화를 다각도로 검토한 것이다. 연구방법으로는 비탈면 안정에 가장 민감하게 반응한다고 판단되는 강우조건과 지반조건을 선정하였고, 각각의 조건변수를 변화시켜가면서 수치해석적 검토를 수행하였다. 강우특성으로는 국내의 확률강우특성을 기반으로 해석을 수행하였으며 지반조건으로는 불포화토를 대상으로 검토를 실시하였다. 연구결과, 지역별 강우특성과 불포화토의 매개변수 적용이 비탈면 안전율 변화에 민감하게 반응하는 것으로 나타났다. 따라서, 설계시 입력변수에 대한 충분한 검토가 선행되어야 할 것이다.

• Structural Engineering and Mechanics
• /
• 제72권6호
• /
• pp.675-687
• /
• 2019

As the bridges are an integral part of the transportation network, their function as one of the most important vital arteries during an earthquake is fundamental. In a design point of view, the bridges piers, and in particular the wall piers, are considered as effective structural elements in the seismic response of bridge structures due to their cantilever performance. Owing to reduced seismic load during design procedure, the response of these structural components should be ductile. This ductile behavior has a direct and decisive correlation to the development of plastic hinge region at the base of the wall pier. Several international seismic design codes and guidelines have suggested special detailing to assure ductile response in this region. In this paper, the parameters which affect the length of plastic hinge region in the reinforced concrete bridge with wall piers were examined and the sensitivity of these parameters was evaluated on the length of the plastic hinge region. Sensitivity analysis was accomplished by independently variable parameters with one standard deviation away from their means. For this aim, the Monte Carlo simulation, tornado diagram analysis, and first order second moment method were used to determine the uncertainties associated with analysis parameters. The results showed that, among the considered design variables, the aspect ratio of the pier wall (length to width ratio) and axial load level were the most important design parameters in the plastic hinge region, while the yield strength of transverse reinforcements had the least effect on determining the length of this region.

• Structural Engineering and Mechanics
• /
• 제83권3호
• /
• pp.327-340
• /
• 2022

The Collapse Margin Ratio (CMR) is a notable index used for seismic assessment of the structures. As proposed by FEMA P695, a set of analyses including the Nonlinear Static Analysis (NSA), Incremental Dynamic Analysis (IDA), together with Fragility Analysis, which are typically time-taking and computationally unaffordable, need to be conducted, so that the CMR could be obtained. To address this issue and to achieve a quick and efficient method to estimate the CMR, the Artificial Neural Network (ANN), Response Surface Method (RSM), and Adaptive Neuro-Fuzzy Inference System (ANFIS) will be introduced in the current research. Accordingly, using the NSA results, an attempt was made to find a fast and efficient approach to derive the CMR. To this end, 5016 IDA analyses based on FEMA P695 methodology on 114 various Reinforced Concrete (RC) frames with 1 to 12 stories have been carried out. In this respect, five parameters have been used as the independent and desired inputs of the systems. On the other hand, the CMR is regarded as the output of the systems. Accordingly, a double hidden layer neural network with Levenberg-Marquardt training and learning algorithm was taken into account. Moreover, in the RSM approach, the quadratic system incorporating 20 parameters was implemented. Correspondingly, the Analysis of Variance (ANOVA) has been employed to discuss the results taken from the developed model. Additionally, the essential parameters and interactions are extracted, and input parameters are sorted according to their importance. Moreover, the ANFIS using Takagi-Sugeno fuzzy system was employed. Finally, all methods were compared, and the effective parameters and associated relationships were extracted. In contrast to the other approaches, the ANFIS provided the best efficiency and high accuracy with the minimum desired errors. Comparatively, it was obtained that the ANN method is more effective than the RSM and has a higher regression coefficient and lower statistical errors.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
• /
• pp.355-360
• /
• 2000

There are many changed while a design is completed. Therefore, if the impact of the design changes is estimated, it may result in the improvement of design efficiency. But, the design changes have various types and affect other parts of the design system. Hence, it is difficult to deal with design changes directly. The purpose of this research is to develop a systematic change propagation tracing algorithm and a method of change impact analysis and then, to implement a change impact analysis system. Process based design is set up for the field of this research. Also the design, composed of design parameters and constraints, is set up for the subject of the research. Change propagation tracing algorithm traces change propagation based on the following concept : If the design parameters are changed, other parameters within the constrains including them may be changed. Using the result of change propagation tracing algorithm, changeable parameters, constraints and tasks can be found. The method of change impact analysis, to calculate change impact value from this changeable tasks, is developed. Change propagation tracing algorithm and the method of change impact analysis are implemented into change impact analysis system and it is applied to the redesign of 2 stage gear drives. It can support different kinds of design activities systematically. especially, at the redesign step, where many design change alternatives exist, change impact value of each alternative exist, change impact value of each alternative is calculated and design change is performed toward direction to minimize the impact of design change. Consequently, it is expected to improve the efficiency of the whole design.

• 한국수자원학회논문집
• /
• 제51권6호
• /
• pp.491-501
• /
• 2018

본 연구는 도시 유역의 물 순환을 개선시키기 위해 최근 활발하게 적용되고 있는 저영향개발(low impact development, LID) 시설의 설계 및 계획 매개변수를 선정하기 위한 방법을 제시하였다. 이때 Storm Water Management Model (SWMM) 모형의 LID 시설 모의 기능을 활용하여 다양한 매개변수에 대해 민감도 분석 및 다양한 시나리오를 자동으로 수행하여 비교할 수 있도록 개발된 Water Management Analysis Module (WMAM)을 이용하였다. 본 연구는 최근 도시화가 진행되고 있는 서울의 한 유역에 적용하였다. 적용 결과 LID 중 하나인 투수성포장 시설이 없는 경우와 임의로 결정된 설계 및 계획 시나리오 보다 본 방법을 통해 도출된 시나리오가 총유출량 및 첨두유량 감소와 침투량 증가에 더 좋은 효과를 보였다. 향후 경제성을 고려한 방법을 개발한다면 실무에서도 활용될 수 있을 것으로 예상된다.

• 한국정밀공학회지
• /
• 제20권1호
• /
• pp.151-158
• /
• 2003

Design changes frequently occur while design activities are performed. If the impact of design changes is estimated, design efficiency can be improved. But, the types of design changes are various and they can affect other design parts. Hence, it is difficult to deal with design changes directly. The purpose of this research is to develop systematic algorithms for change propagation tracing and change impact analysis, and then to implement a change impact analysis system. We have selected a process-based design and a design environment which is composed of design parameters and constraints. The algorithm for change propagation tracing tracks the change propagation of design parameters and finds design parameters, constraints and tasks which are probably changed. In the algorithm for change impact analysis, a change impact value is calculated from the list of changeable tasks. These two algorithms have been implemented into change impact analysis system (CIAS). CIAS has been applied to the redesign of 2 stage gear drives. CIAS can improve the efficiency of design activities. If there are many alternatives for a design change at the redesign step, designers can calculate the change impact value of each alternative and perform design change activities in the direction of minimizing design change impact.

• Tribology and Lubricants
• /
• 제37권3호
• /
• pp.112-116
• /
• 2021

Appropriate friction model usage is important for impact analysis because the relative motions between parts that are in contact for very short durations can vary greatly depending on the friction model. Vehicle seat components that have significant effects on impact analysis are also considered. This paper presents an experimental investigation of various material contact pairs to obtain the friction parameters of the Benson exponential friction model for impact simulation. The Coulomb friction model has limitations for impact analysis because of singularity at zero velocity. Metal/nonmetal materials are prepared, and friction tests are conducted for various sliding speeds, loads, and lubrication conditions. The obtained data are used in the friction model to implement finite element analysis. The parameters of the friction model are obtained by the curve-fitting method. The experimental results show that the friction coefficient with metal/nonmetal contact pairs is stable regardless of the working conditions. The friction model used in this study can also be applied for finite element analysis of the crash conditions, where the friction changes abruptly at the contact interface; the obtained friction parameters are also expected to be more accurate with more precise tests under different working conditions. These results can help improve the accuracy of the finite element analysis.