• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.978-981
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• 2005

The vibration analysis of damped sandwich beam is conducted using finite element method. The equation of motion presented by Mead and Markus is used to formulate FEM. Also as the thickness of the core in the damped sandwich beam goes to zero, conventional beam theory based on the transformed-section method and the equation of Mead and Markus are compared. According to the change of thickness and loss factor of the core, the forced frequency response of beam is calculated and discussed. And then using the half-power band width method, the damping ratio of each mode is calculated and discussed about each case.

• Steel and Composite Structures
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• 제26권5호
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• pp.649-662
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• 2018

In this study, based on the three-dimensional theory of elasticity, free vibration characteristics of sandwich sectorial plates with multiwalled carbon nanotube-(MWCNT)-reinforced composite core are considered. Modified Halpin-Tsai equation is used to evaluate the Young's modulus of the MWCNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. The exponential shape factor modifies the Halpin-Tsai equation from expressing a straight line to a nonlinear one in the MWCNTs wt% range considered. In this paper, free vibration of thick functionally graded sandwich annular sectorial plates with simply supported radial edges and different circular edge conditions including simply supported-clamped, clamped-clamped, and free-clamped is investigated. A semi-analytical approach composed of two-dimensional differential quadrature method and series solution are adopted to solve the equations of motion. The material properties change continuously through the core thickness of the plate, which can vary according to a power-law, exponentially, or any other formulations in this direction. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of laminated sectorial plates.

• Asia pacific journal of information systems
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• 제13권3호
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• pp.41-62
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• 2003

This study investigated the current status and characteristics of strategic alliances attempted by domestic internet businesses. Specifically, this study surveyed competitive environmental characteristics of partner companies involved, alliance period, types of partner companies, motives of alliances, types of alliances, success and failure factors and satisfaction toward the alliances. Major findings were: first, alliances between portal companies and content producers; portal companies and internet services; e-commercial sites and internet services were the most frequent partnerships engaged. Second, the most important motive for and type of the strategic alliance were: 'the commercialization and marketing of new product' and 'joint distribution and marketing agreement' respectively. Third, the most important factor for the successful alliance was 'a close examination of partners' core business value and competence'; and the factor most hindering the successful alliance was 'a discrepancy on capabilities of partners' core personnel. Finally types of internet business were significantly related to perceived satisfaction toward strategic alliance.

• 한국IT서비스학회지
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• 제10권1호
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• pp.151-165
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• 2011

Recently building up of u-learning oriented teaching and learning system has been expanded rapidly, However domestic junior college's challenging for adapting it might be slower than other educational body's doing, and in that result it might be paid more or be taken longer time to improve their old system effectively. Now, it is very time for them to develop and implement u-learning oriented teaching and learning system quickly. This paper offers and draws the core factors to design ubiquitous teaching and learning model systematically through investigation of worldwide recent technology and R&D, patent, service and standardization tendency related with u-learnig modeling.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 추계학술대회논문집; 한국과학기술회관, 8 Nov. 1996
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• pp.217-223
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• 1996

A structure's vibration characteristic is determined by modal property of the system. Through proper vibration analysis or experiments, the structure can be modified to reduce of vibration and noise. This paper is concerned with the natural frequency and modal loss factor of sandwich plates with viscoelastic core. The effects of shear and normal strain in the viscoelastic layer are investigated on modal properties, natural frequency and modal loss factor, by changing geometry parameter and viscoelastic material property of sandwich plates. The errors of modal parameters resulting from neglecting the extension or compression in the core material for simply supported(S-S-S-S) case are compared with those for clamped(C-C-C-C) boundary condition. Finite difference method(FDM) is utilized as numerical analysis technique of square sandwich plates for fixed boundary conditions. In order to reduce computation time and increase accuracy, improved finite difference expression with fourth order truncation error was used.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(5)
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• pp.315-318
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• 2002

In this paper, we have studied about the determination methode of the operating frequency, and the design technique for the self-exited electronic ballast. Because we use the saturation characteristics of the ferrite core, the variation of the B/H curve characteristics for the selected core in the most important factor for the stabilization. Although it is impossible to fix the operation frequency, the self-exited electronic ballast is widely used because of its cost and the simplicity of its structure.

• Steel and Composite Structures
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• 제19권5호
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• pp.1321-1331
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• 2015

A square steel sandwich plate with lattice corrugated core is explored for damping improvement. A range of damping materials are filled inside the openings provided by the corrugated core, or are applied on the surfaces of the facesheets. The dynamic properties such as natural frequency and damping factor are experimentally measured for the sandwich plate with each filling solution. The relative performance of each insertion is compared in terms of damping capacity and added mass.

• Composites Research
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• 제24권1호
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• pp.17-23
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• 2011

풀아웃 하중을 받는 복합재 샌드위치 체결부의 파손 거동을 시험으로 연구하였다. 체결의 방식과 코어의 종류를 달리하여 5종류, 총 30개의 시편에 대해 시험을 수행하였다. 시험 결과, 노멕스 하니콤 코어를 사용할 경우 코어의 강성에 의해 지배되는 전단좌굴이 먼저 발생하고, 이후 50~200% 정도의 추가적인 하중을 지지하다가, 면재가 찢어지는 최종파손이 발생하였다. 반면에 PMI 폼을 사용하면 하중 초기에 코어의 전단파손이 발생하며 지지하중도 크게 저하되는 것을 확인하였다. 파손모드를 고려한 설계의 관점에서 볼 때, 노멕스 코어를 사용할 경우 코어의 강성과 면재의 강성 및 강도를 동시에 고려해야 하는 반면, 폼 코어를 사용할 경우 코어의 전단파손 하중을 높이는 것이 가장 중요한 것으로 나타났다.

• Earthquakes and Structures
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• 제19권3호
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• pp.197-214
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• 2020

Diagrid structures have been introduced as a fairly modern lateral load-resisting system in the design of high-rise buildings. In this paper, a novel diagrid system called tube-in-tube diagrid building is introduced and assessed through pushover and incremental dynamic analyses. The main objectives of this paper are to find the optimum angle of interior and exterior diagrid tube and evaluate the efficiency of diagrid core on the probability of collapse comparing to the conventional diagrid system. Finally, the seismic performance factors of the proposed system are validated according to the FEMA P695 methodology. To achieve these, 36-story diagrid buildings with various external and internal diagonal angles are designed and then 3-D nonlinear models of these structures developed in PERFORM-3D. The results show that weight of steel material highly depends on diagonal angle of exterior tube. Adding diagrid core generally increases the over-strength factor and collapse margin ratio of tall diagrid buildings confirming high seismic safety margin for tube-in-tube diagrid buildings under severe excitations. Collapse probabilities of both structural systems under MCE records are less than 10%. Finally, response modification factor of 3.0 and over-strength factor of 2.0 and 2.5 are proposed for design of typical diagrid and tube-in-tube diagrid buildings, respectively.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.672-675
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• 2006

It is becoming more significant to develop a rotary VCM type actuator for small form factor ODD, as portables are getting more and more popularized nowadays. In this paper, the procedure of development of the actuator which is applicable to compact flash II card and is fit in the specification of BD 1X is explained. This is based on the rotary VCM type actuator, which is good for reducing thickness. Air core solenoid coil is used in order to do focusing mechanism. And the total weight is reduced by using the structure of steel-aluminium-steel triple layer, so, the stiffness is still adequate. Additionally, the tracking coil is moved next to the actuator, so the total length was reduced, then the actuator become applicable to compact flash II card. The force of Magnetic Circuit is improved by using Magnetic Circuit DOE. And flexible mode frequency improved through the DOE of structure part. Modeling was exactly done in consideration of air core solenoid coil and pivot bearing. It is confirmed that the designed model is satisfied with the specification of BD 1X and is applicable to Compact Flash II card.