• Journal of Korean Society of Steel Construction
• /
• v.13 no.6
• /
• pp.703-713
• /
• 2001

Derivation procedures of exact dynamic stiffness matrices of thin-walled straight beams subjected to eccentrically axial forces are rigorously presented for the spatial free vibration analysis. An exact dynamic stiffness matrix is established from governing equations for a uniform beam element with nonsymmetric thin-walled cross section. First this numerical technique is accomplished via a generalized linear eigenvalue problem by introducing 14 displacement parameters and a system of linear algebraic equations with complex matrices. Thus, the displacement functions of displacement parameters are exactly derived and finally exact stiffness matrices are determined using element force-displacement relationships. The natural frequencies of nonsymmetric thin-walled straight beams are evaluated and compared with analytical solutions or results by thin-walled beam element using the cubic Hermitian polynomials and ABAQU's shell elements in order to demonstrate the validity of this study.

• Journal of Korean Society of Steel Construction
• /
• v.14 no.4
• /
• pp.509-518
• /
• 2002

In order to perform the spatial buckling and static analysis of the nonsymmetric thin-walled beam-column element, improved exact static stiffness matrices were evaluated using equilibrium equation and force-deformation relationships. This numerical technique was obtained using a generalized linear eigenvalue problem, by introducing 14 displacement parameters and system of linear algebraic equations with complex matrices. Unlike the evaluation of dynamic stiffness matrices, some zero eigenvalues were included. Thus, displacement parameters related to these zero eigenvalues were assumed as polynomials, with their exact distributions determined using the identity condition. The exact displacement functions corresponding to three loadingcases for initial stress-resultants were then derived, by consistently combining zero and nonzero eigenvalues and corresponding eigenvectors. Finally, exact static stiffness matrices were determined by applying member force-displacement relationships to these displacement functions. The buckling loads and displacement of thin-walled beam were evaluated and compared with analytic solutions and results using ABAQUS' shell element or straight beam element.

• KEPCO Journal on Electric Power and Energy
• /
• v.6 no.4
• /
• pp.393-397
• /
• 2020

Shunt reactor, a facility for reactive power compensation, is switched several times a day depending on the load pattern. When the circuitbreaker opens the shunt reactor over-voltage is generated by several factors which degrade the insulating performance of internal parts of the circuit-breaker and cause severe voltage stress on the equipment in the power system. Transient phenomenon occurring during the switching of shunt reactor are available in laboratories that verify the performance of the circuit-breaker by simulating the power system. However, it is difficult to measure the transient phenomenon that occurs during actual operation in actual power system due to many limitations. Therefore, this paper deals with the modeling using EMTP to analyze the reignition and current chopping which causes more severe transient recovery voltage in the small inductive current breaking in actual power systems. In addition, this paper analyzes the main phenomenon that cause circuit-breaker failure in opening shunt reactor using EMTP model.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.6C
• /
• pp.219-229
• /
• 2010

Slope failure in South Korea generally occurs by the localized heavy rain in a rainy season and typhoon, and it annually causes huge losses of both life and property because nearly 70% of territory in South Korea is covered with mountains. It is required to measure the risk of slope failure quantitatively before proper prevention methods are provided. However, there is no way to estimate the risk based on realtime rainfall, geological characteristics, and geotechnical engineering properties. This study presents the development of digital terrion model to predict slope stability using infinite slope stability theory combined with temporal groundwater change. Case studies were performed to investigate factors to affect slope stability in Japan.

• The Korean Journal of Applied Statistics
• /
• v.32 no.5
• /
• pp.653-669
• /
• 2019

The development of new media has gradually decreased the use of newspapers, which had previously occupied the largest share of media. Subscriptions have declined gradually and fell to 14 percent in 2016. This study explores the effects of Newspaper reader's characteristics on regular newspaper subscriptions. The data used for analysis was provided by the Korean Press Foundation and Media Audience Awareness Survey Data in 2016 and 2017. We considered gender, age, education, income, number of days of reading, reading time and amount of reading as the characteristics of the reader. Multiple logistic regression was fitted and interpreted to see what characteristics affect regular subscription.

• Journal of the Korean Society of Industry Convergence
• /
• v.22 no.3
• /
• pp.373-379
• /
• 2019

Nowadays, the IoT portable electronic devices have become more useful and diverse, so they require various supply voltage levels to operate. This paper presents a DC-DC buck converter with pulse width modulation (PWM) for portable electronic devices. The proposed step-down DC-DC converter consists of passive elements such as capacitors, inductors, and resistors and an integrated chip (IC) for signal control to reduce power consumption and improves ripple voltage with the resolution. The proposed DC-DC converter is simulated and analyzed in PSPICE circuit design platform, and implemented on the prototype PCB board with a Texas Instruments LM5165 IC. The proposed buck converter is showed 92.6% of peak efficiency including a load current range of 4-10 mA, 3.29 mV of the voltage ripple at 5 V output voltage for the supply voltage 12 V. Measured and Simulated power efficiency are made good agreement with each other.

• Composites Research
• /
• v.31 no.2
• /
• pp.69-75
• /
• 2018

In this study, a grid panel structure in which the woven CFRP composites were stacked in the orthogonal array was proposed and the mechanical properties were analyzed and studied. The grid parts were fabricated by cutting prepregs and laminating them. The grid panel structure was fabricated by co-curing with lower laminate plate in auto-clave process. The behavior of the proposed grid panel structure was evaluated by tests under tensile, compressive, shear, and bending loads. The effect of increasing the stiffness of the orthogonal grid structure was verified through these tests. In addition, the finite element model was constructed and compared with the test results, confirming the validity and reliability of the test and analysis.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.5
• /
• pp.515-526
• /
• 2009

There are three main production processes in the manufacture of concrete-filled square steel columns. The first process is known as the 'box-type process' or 'four-seam method,' wherein four beams are welded together at the seams. The second is the 'cold-forming process' or 'two-seam method,' wherein the seams of two channel beams are welded together. The third is the 'pressing process' or 'one-seam method,' wherein a circular column is pressed until it becomes a square column. In calculating the production cost for the making of a steel tube, it is very important to consider the welding process to be used and the desiredthickness of the steel tube, such as a square column that was developed under a new method, formed through the four-seam flare welding method at the center of the steel column width, following the L-shape formation. Certain tests were suggested in this study to evaluate the welding amount of concrete-filled square steel columns. With the parameters of the production method of a square steel column, the thickness of the steel square columns, and the welding amount, six specimens were produced. A structural test and finite-element analysis were conducted to assess the behavior of the steel column according to the water pressure inside the steel columns.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.8
• /
• pp.929-934
• /
• 2012

This study was carried out to analyze the dynamic characteristics of laser tailor-welded blanks (TWBs) made of dissimilar materials. The analysis was performed using Hyper Works 10.0 with Solver LS-DYNA v.971. 2D-Shell was used as the modeling element, and the number of elements and nodes was 35,641 and 36,561, respectively. The impact speed was 10 km/h. To analyze the impact characteristics according to the height of the weld line for the upper and lower parts of the center pillar, the length of the lower part was set as 300 and 400 mm. When the lower part was made of SPFC980 steel with a length of 300 mm, the deformation was the smallest and the absorbed energy of the impact force was the largest. On based the lower part of center pillar, the position of TWB shows the shorter and the better value. In other words, the performance depended on the proportion of the upper part made of high-strength SABC1470 steel. A lower part made of SPFH590 steel showed large deformation. In contrast, a lower part made of SPFC980 steel showed significantly lesser deformation. Therefore, the impact performance of a lower part made of SPFC980 steel with a length of 300 mm showed the best analysis result.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.8 no.1
• /
• pp.33-40
• /
• 1988

The new technique has been used to determine the soil-reinforcement interaction. The testing apparatus is essentially a triaxial cell fitted with the capability to house a hollow cylinderical sample. A hollow cylinderical sand specimen with a concentrical layer of reinfarcing material sandwitched in the middle is used in this investigation. The reinforcement is fastened at the base. The hollow specimen can be viewed as a "unit sheet" of a soil-reinforcement composite system of infinite horizontal extent. Axial load as well as inner and outer chamber pressures can be applied to perform a test. The specimen is first subjected to an isotropic stress state corresponding to the overburden pressure. Next, an extension test by reducing the axial load is carried out. The specimen is "loaded" to failure by either the breakage of reinforcing material (tensile failure) or slippage which takes place at the soil-reinforcement interface (i.e. the overcoming of the bonding capacity). Since the reinforcement is fastened at its lower end to the base, any tendency of relative movement between the reinforcement and the sand during an extension test can induce tensile force in the reinforcement thus forming a "reversed pull-out" test condition. Preliminary test results have demonstrated positively of the new approach to test the soil-reinforcement interaction. Reinforcing elements of different extensibility were used to study the deformbility of reinforced soil. Furthermore, both the breakage and the pull-out modes of failure were observed.