• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.2
• /
• pp.87-93
• /
• 2007

Generally, the analysis using Computational Fluid Dynamics(CFD) is necessary for aircraft design. However, the analysis using CFD, it requires a lot of computational time and cost. But we can reduce grid reconstruction time of analyzing the various models if we use dynamic mesh. In addition, dynamic mesh can be an efficient technique in aeroelastic analysis and design optimization problem because these problems need grid reconstruction process frequently.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2004.10a
• /
• pp.355-362
• /
• 2004

An efficient boundary-based technique is developed for addressing shape design sensitivity analysis in various problems. An analytical sensitivity formula in the form of a boundary integral is derived based on the continuum formulation for a general functional defined in problems. The formula, which is expressed in terms of the boundary solutions and shape variation vectors, can be conveniently used for gradient computation in a variety of shape design problems. While the sensitivity can be calculated independent of the analysis means, such as the finite element method (FEM) or the boundary element method (BEM), the FEM is used for the analysis in this study because of its popularity and easy-to-use features. The advantage of using a boundary-based method is that the shape variation vectors are needed only on the boundary, not over the whole domain. The boundary shape variation vectors are conveniently computed by using finite perturbations of the shape geometry instead of complex analytical differentiation of the geometry functions. The supercavitating flow problem and fillet problem are chosen to illustrate the efficiency of the proposed methodology. Implementation issues for the sensitivity analysis and optimization procedure are also addressed in these problems.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.3 s.108
• /
• pp.255-262
• /
• 2006

Frequency spectrum using the conventional Fourier analysis gives adequate information about the dynamic characteristics of the slider air bearing for the linear and stationary cases. The intermittent contacts for the extremely low flying height, however, generate nonlinear and nonstationary vibration at the instant of contact. Nonlinear dynamic model should be developed to simulate the impulse response of the air bearing during slider-disk contact. Time-frequency analysis is widely used to investigate the nonstationary signal. Several time-frequency analysis methods are employed and compared for the slider vibration signal caused by the impact against an artificially induced scratch on the disk. The representative Wigner-Ville distribution leads to the severe interference problem by cross terms even though it gives good resolution both in time and frequency. The smoothing process improves the interference problem at the expense of resolution. In order to get the results with good resolution and little interference, the reassignment method is proposed. Among others the reassigned Gabor spectrogram shows the best resolution and readability with negligible interference.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.13 no.2
• /
• pp.75-80
• /
• 2004

Vehicle structures are composed of many substructure connected to one another by various types of mechanical joints. In vehicle engineering it is important to study these connected structures under various dynamic forces for the evaluations of fatigue life and stress concentration exactly. It is difficult to obtain the accurate load history of specified positions because of the errors such as modeling, measurement and etc. In the beginning of design exact load data are actually necessary for the fatigue strength and life analysis to minimize the cost and time of designing. In this paper, the procedure of practical dynamic force determination is developed by the combination of the principal stresses of F. E. Analysis and experiment. Least square pseudo inverse matrix is adopted to obtain in inverse matrix of analyzed stresses matrix. The error minimization method utilizes the inaccurate measured error and the shifting error that the whole data is stiffed over real data. The least square criterion is adopted to avoid these non. Finally, to verify the proposed procedure, a bus is analyzed. This measurement and prediction technology can be extended to the structural modification of any geometric shape in complex structure.

• Journal of KSNVE
• /
• v.6 no.1
• /
• pp.71-82
• /
• 1996

The finite element analysis for rotor bearing systems has been an essential tool for design, identification, and diagnosis of rotating machinery. Among others, the unbalance response analysis is fundamental in the vibration analysis of rotor bearing systems because rotating unbalance is recognized as a common sourve of vibration in rotating machinery. However there still remains a problem in the aspect of computational efficiency for unbalance response analysis of large rotor bearing systems. Gyroscopic terms and local bearing parameters in rotor bearing systems often make matters worse in unbalance response computation due to the complicated dynamic properties such as rotational speed dependency and/or anisotropy. The present paper proposes an efficient method for unbalance responses of multi-span rotor bearing systems. An improved substructure synthesis scheme is introduced which makes it possible to compute unbalance responses of the system by coupling unbalance responses of substructures that are of self adjoint problem with small order matrices. The present paper also suggests a scheme to easily deal with gyroscopic tems and local, coupling or bearing parameters. The proposed method causes no errors even though the computational effort is reduced drastically. The present method is demonstrated through three test examples.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.4 no.2
• /
• pp.185-191
• /
• 2000

The safety problem of aged tunnels has been emphasized. For the effective maintenance, site inspection of tunnel structures and surrounding grounds are required periodically. Also, the determination of safety of tunnels is not a simple problem. So the role experienced engineer in the maintenance is very important and development of an expert system that can perform as the engineers, has been needed. In this study, from the results of numerical analysis in several case, new precision inspection rules which can substitute actual numerical analysis are determined by a commercial program FLAC and regression analysis under various parameters such as material property, lining thickness, overburden and laterial coefficients. They are added to the knowledge base to determine safety of tunnel lining. To verify the expert system, the results are compared with an existing tunnel diagnosis report. It can be concluded that the new rule are well represented the actual numerical analysis under various site conditions. Therefore it is expected that the systematic management for effective maintenance of tunnel structure will be possible.

• Journal of Korea Society of Digital Industry and Information Management
• /
• v.17 no.4
• /
• pp.161-175
• /
• 2021

This study analyzed the efficiency and influence factors according to the main research institute type of R&D Program for the local community problem-solving. This study applied data envelopment analysis (DEA) method and Tobit regression analysis by using 20 institutions that participated in R&D Program. The results are summarized as follows. First, Analysis results according to the research institute type of R&D project, Efficient DMUs showed more regional innovation institutions than social economy enterprises. But regional innovation institutions were the lowest in the CCR and BCC model. However, efficiency dose not differ between regional innovation institutions and social economy enterprises. Second, as a result of the analysis relation between efficiency and allocation characteristics of R&D input, the participation of regional innovation organizations as participating organizations has a negative effect on efficiency. It was found that the higher the proportion of government subsidies and the higher the employment rate of the vulnerable, which is a social achievement, the positive effect on efficiency. The implication of this study is that the participation of social economy enterprises as the main R&D institution and government R&D support can provide social economy enterprises with opportunities to accumulate R&D capabilities and experience successful commercialization.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.13 no.1
• /
• pp.50-56
• /
• 2021

An accurate evaluation of three-dimensional (3D) Time-Domain Green Function (TDGF) in infinite water depth is essential for ship's hydrodynamic analysis. Various numerical algorithms based on the TDGF properties are considered, including the ascending series expansion at small time parameter, the asymptotic expansion at large time parameter and the Taylor series expansion combines with ordinary differential equation for the time domain analysis. An efficient method (referred as "Present Method") for a better accuracy evaluation of TDGF has been proposed. The numerical results generated from precise integration method and analytical solution of Shan et al. (2019) revealed that the "Present method" provides a better solution in the computational domain. The comparison of the heave hydrodynamic coefficients in solving the radiation problem of a hemisphere at zero speed between the "Present method" and the analytical solutions proposed by Hulme (1982) showed that the difference of result is small, less than 3%.

• Journal of the Korean Society of Industry Convergence
• /
• v.25 no.6_3
• /
• pp.1303-1313
• /
• 2022

Modern cities need to revitalize the downtown area, which is declining due to population decline, economic recession, and deterioration of the residential environment, economically, socially, and physically by introducing and creating new functions. In addition, the hollowing out of the existing city center is getting worse due to the development of the outskirts of the city. Therefore, the discussion for the development of urban regeneration is the core task of modern cities. This study analyzed based on a basic understanding of urban regeneration projects, and through this, the problems of domestic urban regeneration projects were derived. In addition, the problem factors and major improvement plans of the urban regeneration project were analyzed from the expert's point of view using the AHP analysis technique. Based on this, the purpose is to present policy alternatives for the future development of urban regeneration projects. The problems derived to present the policy alternatives and improvement directions of the urban regeneration project were classified into problems related to goal achievement, problems related to the business itself, and problems related to project results. It was subdivided into sub-categories. This study analyzed the problem factors and major improvements from the expert's point of view by using the AHP analysis technique for the problems of the urban regeneration project. Based on the AHP analysis results and experts' opinions, five policy alternatives for the development of urban regeneration projects were presented.

• International Journal of Advanced Culture Technology
• /
• v.11 no.2
• /
• pp.36-43
• /
• 2023

This study aims to derive discourse's linguistic meaning, production method, and social practice implications by analyzing news reports on de-facility for people with disabilities. To this end, the discourse was analyzed by applying Fairclough's framework of critical discourse analysis. The subject of analysis is a news article on the de-facility of the disabled on the N portal site, and the analysis period is one year, from January 1 to December 31, 2022. First, as a result of the study, the surface meaning of the news discourse on the de-facility for disabled people was ideological through the seriousness of the problem for disabled people, the poor environment, and the policy of de-facility for disabled people separated from reality. Second, the social meaning of the de-facility news discourse for disabled people appeared from a realistic perspective, such as the structural cause of the problem for disabled people and the need for sensible government policies and measures to practice de-facility for disabled people. Finally, the socio-cultural practical implications of the de-facility news discourse for people with disabilities proposed the development of a systematic and realistic de-facility management manual for the disabled, practical government policy support, and changes in self-support perception for disabled people. The results of this study are expected to help find an alternative direction to reduce the gap between actual policies for de-facility for disabled people and practice in the field in the future.