• Journal of the Earthquake Engineering Society of Korea
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• v.23 no.5
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• pp.261-268
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• 2019

This paper proposes damage indices efficient on evaluating the seismic safety of cable-stayed bridges, especially dual-plane, cable-stayed bridges with H-type pylons. The research assumes that the location of accelerometers is already defined as given in the 2017 Ministry of the Interior and Safety (MOIS) guideline. In other words, the paper does not attempt to suggest optimal sensor location for the seismic safety evaluation of cable-stayed bridges. The proposed damage indices are based on those for building structures widely applied in the field already. Those include changes in natural frequencies and changes in relative lateral displacements. In addition, the study proposes other efficient damage indices as the rotation changes at the top of pylons and in the midspan of the girder system. Sensitivity analysis for various damage indices is performed through dynamic analysis using selected earthquake ground motions. The paper compares the effectiveness of the damage indices.

• Journal of The Korean Astronomical Society
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• v.56 no.2
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• pp.149-157
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• 2023

The propagation speed of a circumstellar pattern revealed in the plane of the sky is often assumed to represent the expansion speed of the wind matter ejected from a post-main-sequence star at the center. We point out that the often-adopted isotropic wind assumption and the binary hypothesis as the underlying origin for the circumstellar pattern in the shape of multilayered shells are, however, mutually incompatible. We revisit the hydrodynamic models for spiral-shell patterns induced by the orbital motion of a hypothesized binary, of which one star is losing mass at a high rate. The distributions of transverse wind velocities as a function of position angle in the plane of the sky are explored along viewing directions. The variation of the transverse wind velocity is as large as half the average wind velocity over the entire three dimensional domain in the simulated models investigated in this work. The directional dependence of the wind velocity is indicative of the overall morphology of the circumstellar material, implying that kinematic information is an important ingredient in modeling the snapshot monitoring (often in the optical and near-infrared) or the spectral imaging observations for molecular line emissions.

• Journal of Korean Society of Steel Construction
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• v.13 no.5
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• pp.599-608
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• 2001

Many papers which deal with the dynamic instability of shell-like structures under the STEP load has been published but there have been few papers related to the dynamic instability of hybrid cable domes. And also there are a few researches which treat the essential phenomenon of the dynamic buckling using the phase for investigating occurrence of chaos. In this study the indirect buckling of hybrid cable domes considering geometric nonlinearity are investigated numerically and compared it with the static critical load The dynamic critical loads are determined by the numerical integration of the geometric nonlinear equation of motion and the mechanism of the indirect buckling is examined by using the phase curves.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.11
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• pp.1085-1091
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• 2014

This paper presents the guidance and control design for automatic carrier landing of a UAV (Unmanned Aerial Vehicle). Differently from automatic landing on a runway on the ground, the motion of a carrier deck is not fixed and affected by external factors such as ship movement and sea state. For this reason, robust guidance/control law is required for safe shipboard landing by taking the relative geometry between the UAV and the carrier deck into account. In this work, linear quadratic optimal controller and longitudinal/lateral trajectory tracking guidance algorithm are developed based on a linear UAV model. The feasibility of the proposed control scheme and guidance law for the carrier landing are verified via numerical simulations using X-Plane and Matlab/simulink.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.8
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• pp.669-681
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• 2016

Mechanical designers often make mistakes that result in unwanted over-constraints, causing difficulty in assembly operations and residual stress due to interference among parts. This study is concerned with detection and elimination of over-constraints. Screw theory is a general method that is used for constraint analysis of an assembly and motion analysis of a mechanism. Mechanical assemblies with plane-plane, pin-hole, and pin-slot constraint pairs are analyzed using screw theory to illustrate its utility. As a real-world problem, a ball valve design is analyzed using the same method, and several unwanted over-constraints are detected. Elimination measures are proposed. Nominal dimensions of some parts are adjusted, and dimensions and tolerances of the pins and holes are modified using the virtual condition boundary concept. The revised design is free of over-constraints. General procedure for applying screw theory to constraint analysis is established and demonstrated; it will contribute to improving quality of assembly designs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.3 s.234
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• pp.439-446
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• 2005

The theoretical method is developed to investigate the vibration characteristics of the combined cylindrical shells with an annular plate joined to the shell at any arbitrary axial position. The structural rotational coupling between shell and plate is simulated using the rotational artificial spring. For the translational coupling, the continuity conditions for the displacements of shell and plate are used. For the uncoupled annular plate, the transverse motion is considered and the in-plane motions are not. And the additional transverse and in-plane motions of the coupled annular plate by shell deformation are considered in analysis. Theoretical formulations are based on Love's thin shell theory. The frequency equation of the combined shell with an annular plate is derived using the Rayleigh-Ritz approach. The effect of inner-to-outer radius ratio, axial position and thickness of annular plate on vibration characteristics of combined cylindrical shells is studied. To demonstrate the validity of present theoretical method, the finite element analysis is performed.

• Journal of the Korean Society of Visualization
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• v.17 no.3
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• pp.12-18
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• 2019

Direct numerical simulation of a fully developed turbulent plane Couette-Poiseuille flow with a two-dimensional (2-D) rod-roughened wall is performed to investigate the impacts of the surface roughness. It is shown that the logarithmic region in the mean velocity profile over the rough wall Couette-Poiseuille flow is significantly shortened by the surface roughness compared to that over a turbulent Couette-Poiseuille flow with smooth wall. The Reynolds shear stress over the rough wall Couette-Poiseuille flow is decreased compared to that for a smooth case in the outer layer. These results are attributed to weakened turbulence activity or roll-cell mode over the rough wall Couette-Poiseuille flow near the channel centerline due to suppressed development of u'-structure on the top wall, as documented through spanwise energy spectra of the streamwise velocity fluctuations. Inspection of congregation motion near the bottom wall and time evolution of u'-structure reveal weakened co-supporting cycle for the rough wall case.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.713-722
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• 2020

This article aims to illustrate the damped dynamic responses of layered functionally graded (FG) thick 2D beam under dynamic pulse sinusoidal load by using finite element method, for the first time. To investigate the response of thick beam accurately, two-dimensional plane stress problem is assumed to describe the constitutive behavior of thick beam structure. The material is distributed gradually through the thickness of each layer by generalized power law function. The Kelvin-Voigt viscoelastic constitutive model is exploited to include the material internal damping effect. The governing equations are obtained by using Lagrange's equations and solved by using finite element method with twelve -node 2D plane element. The dynamic equation of motion is solved numerically by Newmark implicit time integration procedure. Numerical studies are presented to illustrate stacking sequence and material gradation index on the displacement-time response of cantilever beam structure. It is found that, the number of waves increases by increasing the graduation distribution parameter. The presented mathematical model is useful in analysis and design of nuclear, marine, vehicle and aerospace structures those manufactured from functionally graded materials (FGM).

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.5
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• pp.203-209
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• 2022

A simplified method for earthquake response analysis of a rectangular liquid storage tank is proposed with fluid-structure interaction considered. In order to simplify the complex three-dimensional structural behavior of a rectangular liquid storage tank, it is assumed that structural deformation does not occur in the plane parallel to the direction in which the earthquake ground motion is applied but in the plane perpendicular to the direction. The structural deformation is approximated by combining the natural modes of the simple beam and the cantilever beam. The hydrodynamic pressure, the structure's mass and stiffness, and the hydrodynamic pressure's added mass are derived by applying the Rayleigh-Ritz method. The natural frequency, structural deformation, pressure, effective mode mass, and effective mode height of the rectangular liquid storage tank are obtained. The structural displacement, hydrodynamic pressure, base shear, and overturning moment are calculated. The seismic response analysis of an example rectangular liquid storage tank is performed using the proposed simplified approach, and its accuracy is verified by comparing the results with the reference solution by the finite element method. Existing seismic design codes based on the hydrodynamic pressure in rigid liquid storage tanks are observed to produce results with significant errors that cannot be ignored.

• Journal of the Korean Society of Physical Medicine
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• v.14 no.3
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• pp.21-27
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• 2019

PURPOSE: This study examined the changes in the kinematic variables during walking on a downhill ramp according to the shoe heel height. METHODS: The subjects were 10 adult women with no history of musculoskeletal disorders who agreed to participate in the study. Data were collected using a motion analysis system (VICON) consisting of six infrared cameras. The slope was 120 cm in width, 200 cm in length, and 15 in inclination. To confirm the change in gait parameters (stride length, gait speed) and lower extremity joint angle according to the heel heights of the shoes, flat, 5 cm, and 10 cm heel shoes were prepared and walked alternately. RESULTS: As a result, both the stride length and walking speed showed significant differences according to the heel height between flat and 10 cm (p<.05). In the sagittal plane, there was no significant difference in the hip joint and knee joint, but a significant difference was observed in all events in the ankle joint on all heel heights (p<.05). In particular, the heel strike and mid stance events showed significant differences among all height conditions (p<.05). No significant difference was observed in any of the joint angle changes in the frontal plane (p>.05). CONCLUSION: As the shoe heel height increased, the instability increased and efforts to secure the stability were made, leading to a shortened stride length, walking speed, and angle of the ankle joint.