• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.12
• /
• pp.3804-3821
• /
• 1996

The configuration optimization is a structural optimization method which includes the coordinates of a structure as well as the sectional properties in the design variable set. Effective reduction of the weight of discrete structures can be obrained by changing the geometry while satisfying stress, Ei;er bickling, displacement, and frequency constraints, etc. However, the nonlinearity due to the configuration variables may cause the difficulties of the convergence and expensive computational cost. An efficient approximation method for the configuration optimization has been developed to overcome the difficulties. The method approximates the constraint functions based onthe second-order Taylor series expansion with reciprocal design variables. The Hessian matrix is approzimated from the information on previous design points. The developed algotithms are coded and the examples are solved.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.11a
• /
• pp.898-901
• /
• 2004

Since soil-structure interactions are one of the most important subjects in the structural/foundation engineering, much study concerning the soil-structure interactions had been carried out. One of typical structures related to the soil-structure interactions is the strip foundation which is basically defined as the beam or strip rested on or supported by the soils. At the present time, lack of studies on dynamic problems related to the strip foundations is still found in the literature. From these viewpoint, this paper aims to theoretically investigate dynamics of the circular strip foundations and also to present the practical engineering data for the design purpose. Differential equations governing the free, out-of-plane vibrations of such strip foundations are derived, in which effects of the rotatory and torsional inertias and also shear deformation are included although the warping of the cross-section is excluded. Governing differential equations subjected to the boundary conditions of corresponding end constraints are numerically solved for obtaining the natural frequencies and mode shapes by using the numerical integration technique and the numerical method of non-linear equation.

• Journal of Korean language education
• /
• v.23 no.1
• /
• pp.1-23
• /
• 2012

The development of corpus in recent years has attracted increased research on spoken Korean. Nevertheless, these research outcomes are yet to be meaningfully and adequately reflected in Korean language textbooks. The reported speech marker '-dae' is one of these areas that need more attention. This study investigates whether or not in textbooks '-dae' is clearly explained to English-speaking learners to prevent confusion and misuse. Based on a contrastive analysis of Korean and English, this study argues three points: Firstly, '-dae' should be introduced to Korean learners as an independent sentence ender rather than a contracted form of '-dago hae'. Secondly, it is necessary to teach English-speaking learners that '-dae' is not equivalent to the English report speech form. It functions more or less as a third person marker in Korean. Learners should be informed that '-dae' is used for statements in English, if those statements were hearsay but the source of information does not need to be specified. This is a very distinctive difference between Korean and English and should be emphasized in class when 'dae' is taught. Thirdly, '-dae' should be introduced before indirect speech constructions, because it is mainly used in simple statements and the frequency of '-dae' is very high in spoken Korean.

• Wind and Structures
• /
• v.14 no.6
• /
• pp.559-582
• /
• 2011

This paper presents an integrated wind-induced dynamic analysis and computer-based design optimization technique for minimizing the structural cost of general tall buildings subject to static and dynamic serviceability design criteria. Once the wind-induced dynamic response of a tall building structure is accurately determined and the optimal serviceability design problem is explicitly formulated, a rigorously derived Optimality Criteria (OC) method is to be developed to achieve the optimal distribution of element stiffness of the structural system satisfying the wind-induced drift and acceleration design constraints. The effectiveness and practicality of the optimal design technique are illustrated by a full-scale 60-story building with complex 3D mode shapes. Both peak resultant acceleration criteria and frequency dependent modal acceleration criteria are considered and their influences on the optimization results are highlighted. Results have shown that the use of various acceleration criteria has different implications in the habitability evaluations and subsequently different optimal design solutions. The computer based optimization technique provides a powerful tool for the lateral drift and occupant comfort design of tall building structures.

• Smart Structures and Systems
• /
• v.24 no.1
• /
• pp.27-35
• /
• 2019

This paper proposes a quantitative criterion for optimization of actuator placement for the Prestress-Accumulation Release (PAR) strategy of mitigation of vibrations. The PAR strategy is a recently developed semi-active control approach that relies on controlled redistribution of vibration energy into high-order modes, which are high-frequency and thus effectively dissipated by means of the natural mechanisms of material damping. The energy transfer is achieved by a controlled temporary removal of selected structural constraints. This paper considers a short-time decoupling of rotational degrees of freedom in a frame node so that the bending moments temporarily cease to be transferred between the involved beams. We propose and test a quantitative criterion for placement of such actuators. The criterion is based on local modal strain energy that can be released into high-order modes. The numerical time complexity is linear with respect to the number of actuators and potential placements, which facilitates quick analysis in case of large structures.

• Advances in aircraft and spacecraft science
• /
• v.6 no.1
• /
• pp.31-49
• /
• 2019

Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, helicopter blades, engine rotors, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness and inertia forces on a structure. The conventional method for designing a rotor blade to be free from flutter instability throughout the helicopter's flight regime is to design the blade so that the aerodynamic center (AC), elastic axis (EA) and center of gravity (CG) are coincident and located at the quarter-chord. While this assures freedom from flutter, it adds constraints on rotor blade design which are not usually followed in fixed wing design. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called "stop-bands". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. In this work, we analyze the flutter characteristics of a helicopter blades with a periodic change in their sandwich material using a finite element structural model. Results shows great improvements in the flutter forward speed of the rotating blade obtained by using periodic design and increasing the number of periodic cells.

• Journal of Astronomy and Space Sciences
• /
• v.37 no.4
• /
• pp.219-228
• /
• 2020

A CubeSat platform has become a popular choice due to inexpensive commercial off-the-shelf (COTS) components and low launch cost. However, it requires more power-efficient and higher-data rate downlink capability for space applications related to remote sensing. In addition, the platform is limited by the size, weight and power (SWaP) constraints as well as the regulatory issue of licensing the radio frequency (RF) spectrum. The requirements and limitations have put optical communications on promising alternatives to RF communications for a CubeSat platform, owing to the power efficiency and high data rate as well as the license free spectrum. In this study, we analyzed the performance of optical downlink communications compatible with CubeSat platforms in terms of data rate, bit error rate (BER) and outage probability. Mathematical models of BER and outage probability were derived based on not only the log-normal model of atmospheric turbulence but also a transmitter with a finite extinction ratio. Given the fixed slot width, the optimal guard time and modulation orders were chosen to achieve the target data rate. And the two performance metrics, BER and outage data rate, were analyzed and discussed with respect to beam divergence angle, scintillation index and zenith angle.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.25 no.6
• /
• pp.561-571
• /
• 2022

An optical mirror assembly is an opto-mechanically coupled system as the optical and mechanical behaviors interact. In the assembly, a flexure mount attached to an optical mirror should be flexible in the radial direction, but rigid for the remaining degrees of freedom for supporting the mirror rigidly and suppressing the wavefront error of the optical mirror. This work presents an optimal design of the flexure mount using topology optimization with thermal stress constraint. By simplifying the optical mirror assembly into finite shell elements, topology optimization model was built for efficient design and good machinability. The stress at the boundary between the optical mirror and the mount together with the first natural frequency were applied as constraints for the optimization problem, while the objective function was set to minimize the strain energy. As a result, we obtained the optimal design of the flexure mount yielding the improved wavefront error, proper rigidity, and machinability.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.6A
• /
• pp.827-833
• /
• 2008

This paper deals with the free vibrations of elastica shaped arches. The elastica shaped arches are formed by the post-buckled column whose arc length is always constant. The equations governing free, planar vibration of general arch in open literature are modified for applying the free vibrations of elastica shaped arch and solved numerically to obtain frequencies and mode shapes for hinged-hinged, clamped-hinged and clamped-clamped end constraints. The effects of rotatory inertia, rise ratio and slenderness ratio on natural frequencies are presented. The frequencies of elastica shaped arches are greater than those of parabolic shaped ones. Also, typical mode shapes are presented in figures.

• Journal of the Korea Fashion and Costume Design Association
• /
• v.26 no.2
• /
• pp.129-140
• /
• 2024

Omni-channel refers to a distribution channel through which consumers can purchase products without time and place constraints through the fusion of existing online and offline stores. Therefore, a study on the effect of the four characteristics of Omni-channel on customer satisfaction and preference was conducted among 350 and 365 Korean and Chinese consumers, respectively on customers of Olive Young and Watson China, representative drug store brands in Korea and China. Analysis was conducted using IBM SPSS 26.0's statistical package program. Frequency analysis, factor analysis, Cronbach alpha, correlation analysis, and regression analysis were performed. As a result of verifying the effect of Omni-channel characteristics on customer satisfaction, it was found that convenience, accessibility, and price fairness had a significant positive (+) effect on customer satisfaction for Korean and Chinese consumers. Customer satisfaction was found to have a significant positive (+) effect on preference. This is because Korean and Chinese consumers generally had high satisfaction and preference for Olive Young and Watsons.