• Journal of the Korea Society for Simulation
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• v.8 no.3
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• pp.39-48
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• 1999

A finite element model of geared rotor system with flexible bearings were used to simulate the critical speeds and to investigate the effects of bearing coefficients on the dynamic behaviors of the systems. The finite element model includes the effects of tooth mesh stiffness, gyroscopic moment, rotary inertia, shear, and torque of the shaft. The gear mesh was modelled as a pair of rigid disks connected by a spring of time varying stiffness. The time varying mesh stiffness results in the abrupt change of the critical speeds of spur geared systems. As the bearing stiffness increases, critical speeds increase rapidly in case of stiff shafts, compared with flexible shafts.

• Wind and Structures
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• v.28 no.3
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• pp.171-180
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• 2019

This paper presents a restart iterative approach for time-domain flutter analysis of long-span bridges using the commercial FE package ANSYS. This approach utilizes the recursive formats of impulse-response-function expressions for bridge's aeroelastic forces. Nonlinear dynamic equilibrium equations are iteratively solved by using the restart technique in ANSYS, which enable the equilibrium state of system to get back to last moment absolutely during iterations. The condition for the onset of flutter instability becomes that, at a certain wind velocity, the amplitude of vibration is invariant with time. A long-span suspension bridge was taken as a numerical example to verify the applicability and accuracy of the proposed method by comparing calculated results with wind tunnel tests. The proposed method enables the bridge designers and engineering practitioners to carry out time-domain flutter analysis of bridges in commercial FE package ANSYS.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.3
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• pp.360-368
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• 2019

A study on aerodynamic modeling was performed to predict the hinge moments required for initial design of missile. Fin aerodynamic coefficients were modeled using the equivalent angle of attack method based on the wind tunnel test. In addition, CFD analysis was performed to calculate the dynamic pressure around the body and improve the accuracy of aerodynamic coefficients. The aerodynamic coefficient accuracy was verified by comparisons of the coefficient acquired from wind tunnel test and prediction of flow conditions, not involved in the model built-up. It was confirmed that fin aerodynamic coefficients can be predicted effectively by using the proposed method.

• Computers and Concrete
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• v.23 no.3
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• pp.203-215
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• 2019

Precast reinforced concrete structure (PRCS) consists of prefabricated members assembled at worksites and has more connections limitations in comparison with the equivalent in-situ reinforced concrete structure (IRCS). As a result of these limitations, PRCSs have less ductility in comparison with IRCSs. Recent studies indicate that the most noticeable failure in PRCSs have occurred in their connection zone. The objective of this study is introducing a type of precast beam-to-column connection (PBC) which in spite of being simple is of the same efficiency and performance as in-situ beam-to-column connection (IBC). To achieve this, the performance of proposed new PBC at exterior joint of a four story PRCS was analyzed by pseudo dynamic analysis and compared with that of IBC in equivalent IRCS. Results indicated that the proposed connection has even better performance in terms of strength, energy dissipation and stiffness, than that of IBC.

• Bulletin of the Korean Chemical Society
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• v.17 no.4
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• pp.358-362
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• 1996

The ionic strength dependent binding mode of 9-aminoacridine (9AA), a well-known DNA intercalator, to DNA is studied by flow linear dichroism, circular dichroism, fluorescence techniques and equilibrium dialysis. The DNA-bound 9AA exhibits spectral properties corresponding to the intercalative binding mode disregarding the salt concentrations; the angle between the long-axis transition moment of the 9AA molecule and DNA helix axis is calculated to be about 65°, indicating a significant deviation from the classical intercalation. At low salt concentrations, however, upwards bending curve in Stern-Volmer plot is observed (where 9AA is a fluorophore and DNA a quencher), indicating the coexistence of both static and dynamic quenching mechanisms or the existence of an additional binding site.

• Journal of applied mathematics & informatics
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• v.42 no.2
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• pp.223-235
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• 2024

In this paper, our primary focus revolves around the examination of a set of fractional stochastic models. Through our investigation, we can establish the presence of a solution and its distinctiveness. Additionally, we employ a moment-based algorithm to estimate the coefficients within these models and provide evidence that these estimations maintain their asymptotic characteristics. To support this claim, we conduct experimental studies using simulations and numerical examples.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.63-70
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• 2015

This paper proposes a novel airfoil named "KA2" for the blade of the wind turbine systems. Dynamic loads characteristics are analyzed and compared using aerodynamic data of ten airfoils including the proposed airfoil. The blade is divided into the sixteen elements in the longitudinal direction of the blade for applying the Blade Element Method Theory (BEMT) method, and in each element, torque, thrust, and pitching moment are calculated using turbulent time varying wind speed and aerodynamic data of each wing. Additionally, each force and torque is accumulated in the whole region of the blade for the estimation of representative values. The magnitude of such forces is comparatively analyzed for different airfoils. The angle of attack is constant below the rated wind speed due to the fact that the tip speed ratio is kept at the constant value, and it increases in the region of over rated wind speed as the tip speed ratio decreasing with constant rated rpm and increasing wind speed. Such increase in the angle of attack causes the changes of the force acting on the airfoil with different characteristics of lift and drag in the stall region of each different airfoil. Even though the mean wind speed is in the rated speed in a given time, because of the turbulence, it has either the over rated or under rated speed most of the time. Furthermore, the dynamic properties of each force are analyzed in this rated wind speed in order to objectively understand the dynamic properties of the blades which are designed based on the different airfoils. These dynamic properties are also compared by the standard deviation of time varying characteristics. Moreover, the output characteristics of the wind turbine are investigated with different airfoils and wind speeds. Based on these investigations, it was revealed that the proposed airfoil (KA2) is well applicable to the blade with passive pitch control system.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.93-102
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• 2023

Despite recent modifications to building structural standards emphasizing the seismic stability of building foundations, the current design focus remains solely on vertical support, resulting in insufficient consideration of horizontal loads during earthquakes. In this study, we evaluated the dynamic behavior of inclined tripod micropiles (ITMP), which provide additional seismic resistance against horizontal and vertical loads during earthquakes. A comparison of the dynamic characteristics, such as acceleration, displacement, bending moment, and axial force, of ITMP with a 15° installation angle and normal vertical micropiles with a 0° installation angle was performed using dynamic centrifuge model tests. Results show that under moderate seismic loads, the proposed ITMP exhibited lower acceleration responses than the vertical micropiles. However, when subjected to a long-period strong seismic excitation, such as sine (2 Hz), ITMP showed greater responses than the vertical micropiles in terms of acceleration and settlement. These results indicate that the use of ITMP reduces the amplif ication of short-period (high-f requency) contents compared with the use of vertical micropiles. Therefore, ITMP can be used to enhance seismic performance of structures.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.629-636
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• 2011

It has been suggested that buildings designed for strong ground motions will also have improved resistance to air blast loads. As an initial attempt to quantify this behavior, the responses of a ten story steel building, designed for the 1994 building code, with lateral resistance provided by perimeter moment frames, is considered. An analytical model of the building is developed and the magnitude and distribution of blast loads on the structure are estimated using available computer software that is based on empirical methods. To obtain the relationship between pressure, time duration, and standoff distance, these programs are used to obtain an accurate model of the air blast loading. A hemispherical surface burst for various explosive weights and standoff distances is considered for generating the air blast loading and determining the structural response. Linear and nonlinear analyses are conducted for these loadings. Air blast demands on the structure are compared to current seismic guidelines. These studies present the displacement responses, story drifts, demand/capacity ratio and inelastic demands for this structure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.6
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• pp.649-654
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• 2010

A three-dimensional numerical study of the WIG-effect vehicle with a direct-underside-pressurization (DUP) system and a propeller is performed to analyze the aerodynamic forces and moments acting on the vehicle. The computational model includes all the compartments of a WIG-effect vehicle, including a propeller in the middle of the fuselage and an air chamber under the fuselage. The DUP system and propeller help considerably reduce the take-off speed and minimize the effect of the hump drag when the vehicle accelerates to take off on water. The airflow is accelerated by a propeller, and the air then enters the air chamber through a channel in the middle of the fuselage, this air helps increase the lift since the dynamic pressure of air is converted to static pressure. However, the air accelerated by the propeller produces excessive drag and creates yawing moment. It is found that the effect of yawing and rolling moments on static stability is negligible.