• Journal of the Earthquake Engineering Society of Korea
• /
• v.6 no.4
• /
• pp.15-22
• /
• 2002

In the course of seismic probabilistic risk assessment(SPRA), seismic fragility analysis(SFA) is utilized as a tool to evaluate the actual seismic capacity of structures. This paper introduces a methodology of SFA and its evaluation procedures, especially focusing on the basic fragility variables. A new definition of the response spectrum shape factor as one of the most critical basic variables is suggested. The new factor is expressed as a term of linear algebraic sum using the modal contribution factor. The efficiency of new response spectrum shape factor is evaluated and validated to use in practice through the case study of the nuclear power plant structures. The case study results show that the proposed method can be effectively applicable to multi-mode structures with composite modal damping.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.3
• /
• pp.617-631
• /
• 2019

In the four-step demand model, a gravity mode is used most commonly at the trip distribution stage. The purpose of this study was to develop a new friction factor that can express the accessibility property as a single friction factor to compensate for the variable limits of the gravity model parameters (travel time, travel cost). To derive a new friction factor, a new friction factor was derived using the space syntax that can quantify the characteristics of the urban space structure, deriving the link-unit integration degree and then using the travel time and travel distance relationship. Calibration of the derived friction factor resulted in a similar level to that of the existing friction factor. As a result of verifying the various indicators, the explanatory power was found to be excellent in the short - and long - distance range. Therefore, it is possible to derive and apply the new friction factor using the integration index, which can complement the accessibility beyond the limit of the existing shortest distance, and it is believed to be more advantageous in future utilization.

• Structural Engineering and Mechanics
• /
• v.24 no.5
• /
• pp.621-639
• /
• 2006

Stability of a cylindrical shell subject to a uniform axial compression, which is a power function of time, is examined within the framework of small strain elasto-plasticity. The material of the shell is incompressible and the effect of the elastic unloading is considered. Initially, employing the infinitesimal elastic-plastic deformation theory, the fundamental relations and Donnell type stability equations for a cylindrical shell have been obtained. Then, employing Galerkin's method, those equations have been reduced to a time dependent differential equation with variable coefficient. Finally, for two initial conditions applying a Ritz type variational method, the critical static and dynamic axial loads, the corresponding wave numbers and dynamic factor have been found. Using those results, the effects of the variations of loading parameters and the variations of power of time in the axial load expression as well as the variations of the radius to thickness ratio on the critical parameters of the shells for two initial conditions are also elucidated. Comparing results with those in the literature validates the present analysis.

• Journal of the Korean Home Economics Association
• /
• v.46 no.8
• /
• pp.121-133
• /
• 2008

The purpose of this study was to decipher the BRQ (Brand Relationship Quality) Construct of fashion product consumers and to identify influencing variables. Consumption values of consumers, fashion product attributes and marketing communication instruments were investigated as affecting variables. A questionnaire was distributed to 350 women between the age of 20 and 50 living in Seoul and other metropolitan areas from Mar. 5 to Mar. 18, 2008. Collected data were analyzed by factor analysis, reliability, multiple regression, frequency and percentage using SPSS (Version 15,0) statistical Package. The results were as follows: Firstly, the BRQ Construct of fashion product consumers was proved to be composed of five factors; 'self-connective love', 'pursuing symbol', 'trust', 'intimacy', and 'knowledge'. Secondly, consumption values had a significant effect on the BRQ Construct and their explanatory power was 32%, 'Epistemic value' was the most significant variable affecting BRQ. 'Functional value' had a significant influence on some BRQ factors. Thirdly, explanatory power of fashion product attributes affecting BRQ was 45%. 'Aesthetic attribute' had significant effect on all BRQ factors, while 'functional attribute' showed significant effect on only 'pursuing symbol', 'trust', and 'intimacy'. Finally, marketing communication mixes showed 21% explanatory power and 'word of mouth' and 'display' among marketing communication mixes were found as the most influential variables affecting the BRQ Construct.

• Journal of Power Electronics
• /
• v.18 no.6
• /
• pp.1642-1649
• /
• 2018

A single-stage flyback LED AC-DC converter based on primary-side control under constant current mode is proposed in this study. The proposed converter features low total harmonic distortion (THD) and high power factor (PF). It also consists of a zero-crossing distortion compensation circuit and a variable duty ratio control compensation circuit to deal with the line current distortions caused by fixed duty ratio control. The system model and layout are built in Simplis and Cadence, respectively. The feasibility and performance of the proposed circuit is verified by designing and fabricating an IC controller in the HHNEC $0.35{\mu}m$ 5 V/40 V HVCMOS process. Experimental results show that the PF can reach a level in the range of 0.985-0.9965. Moreover, the average THD of the entire system is approximately 10%, with the minimum being 6.305%, as the input line voltage changes from 85 VAC to 265 VAC.

• Journal of Power Electronics
• /
• v.6 no.1
• /
• pp.52-66
• /
• 2006

This paper proposes a wind energy conversion system connected to a grid using a self-excited induction generator (SEIG) based on the maximum power point tracking (MPPT) control scheme. The induction generator (IG) is controlled by the MPPT below the base speed and the maximum energy can be captured from the wind turbine. Therefore, the stator currents of the IG are optimally controlled using the indirect field orientation control (IFOC) according to the generator speed in order to maximize the generated power from the wind turbine. The SEIG feeds a (CRPWM) converter which regulates the DC-link voltage at a constant value where the speed of the IG is varied. Based on the IG d-q axes dynamic model in the synchronous reference frame at field orientation, high-performance synchronous current controllers with satisfactory performance are designed and analyzed. Utilizing these current controllers and IFOC, a fast dynamic response and low current harmonic distortion are attained. The regulated DC-link voltage feeds a grid connected CRPWM inverter. By using the virtual flux orientation control and the synchronous frame current regulators for the grid connected CRPWM inverter, a fast current response, low harmonic distortion and unity power factor are achieved. The complete system has been simulated with different wind velocities. The simulation results are presented to illustrate the effectiveness of the proposed MPPT control scheme for a wind energy system. In the simulation results, the d-q axes current controllers and DC-link voltage controller give prominent dynamic response in command tracking and load regulation characteristics.

• Journal of Energy Engineering
• /
• v.23 no.1
• /
• pp.7-20
• /
• 2014

The optimal woodchip production system was developed and the production cost of a forest woodchip fuel was calculated for utilizing the pitch pine, which covers around 480,000ha nationwide. the marginal price of the woodchip fuel considering the factor of supply price, electricity and heat selling price as well as capacity factor were suggested and the economic sensitivity analysis was conducted for various scenario. The most important variable which determine economic feasibility was a fuel cost for the power generation facility. If the electricity price is higher than the current SMP(System Marginal Price) or the capacity factor is higher than 80%, there fully is a benefit to consume the woodchip fuels produced in the suggested production system in this study. In addition, the additional benefit becomes more obvious when considering REC(Renewable Energy Certificate) and CDM(Clean Development Mechanism). Therefore, it is strongly suggested for domestic power generation sector to utilize the forest biomass fuel to achieve the obligatory target of RPS.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.20 no.4
• /
• pp.440-445
• /
• 2011

This paper presents a new regenerative brake system of electric vehicles that employs a continuous variable transmission(CVT) and a flywheel. The developed device has advantages over existing regenerative brakes from a standpoint of reliability and versatility in actual driving conditions. The system consists of a CVT, two wheels, a flywheel, a coupling and auxiliary powertrain components. The CVT is designed as a combination of two cones and a roller, which causes the velocity difference between the wheel and the flywheel. The power flow of the flywheel system is controlled by the CVT roller and the coupling through step motors. A prototype has been developed and then its performance has been investigated for various operating conditions. Results show that the storage efficiency of the flywheel is much affected by the vehicle's velocity and it is reduced below 20% for high speed, as compared to the 25% efficiency for an ideal condition. The CVT is a primary factor for lowering the flywheel efficiencies due to large friction and slipping between the cone and the roller.

• Steel and Composite Structures
• /
• v.13 no.1
• /
• pp.91-107
• /
• 2012

In this research, mechanical buckling of hybrid functionally graded plates is considered using a new four variable refined plate theory. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The plate properties are assumed to be varied through the thickness following a simple power law distribution in terms of volume fraction of material constituents. Governing equations are derived from the principle of minimum total potential energy. The closed-form solution of a simply supported rectangular plate subjected to in-plane loading has been obtained by using the Navier method. The effectiveness of the theories is brought out through illustrative examples.

• Journal of Drive and Control
• /
• v.16 no.2
• /
• pp.43-50
• /
• 2019

The objective of this study was to reverse engineer a swash plate type piston pump mounted on a wheeled armored vehicle and to analyze the structure of the pump case. From the analysis, the weak parts were identified and corrected in the final design. Each element corresponding to the piston pump case was analyzed. The analytical method was given static boundary conditions, load conditions and confirmed displacement, strain, stress, and safety factor. Plastic deformation and damage were also confirmed and the component elements redesigned through structural analysis Structural analysis and vibration analysis were carried out for the components of the piston pump case. The piston pump model was finally modified by structural analysis and vibration analysis results for each component assembly, and a prototype was designed. Durability test and environmental test were carried out and the test results satisfied all of the requirements. Therefore, the analytical method presented in this study can be utilized as a methodology for element component design in the development of various piston pumps.