• Computers and Concrete
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• v.10 no.5
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• pp.489-505
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• 2012

This paper presents a simplified grid beam model for simulating the nonlinear response of reinforced concrete flat-plate structures. The beam elements are defined with nonlinear behavior for bending moment and torsion. The flexural stiffness and torsional strength of the beam elements are defined based on experimental data to implicitly account for slab two-way bending effects. A failure criterion that considers the interaction between the punching strength and slab flexural behavior is incorporated in the model. The effects of bond-slip of slab reinforcement on connection stiffness are examined. The proposed grid beam model is validated by simulating large-scale tests of slab-column connections subjected to concentric gravity loading and unbalanced moment. This study also determines the critical parameters for a hysteretic model used to simulate flat-plates subjected to cyclic lateral loading.

• 한국HCI학회:학술대회논문집
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• 2007.02a
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• pp.612-615
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• 2007

This research studies the Virtual Reality simulation of Newton's physics law on rigid body type of objects for physics learning. With network support, collaborative interaction is enabled so that people from different places can interact with the same set of objects in Collaborative Virtual Environment. The taxonomy of the interaction in different levels of collaboration is described as: distinct objects and same object, in which there are same object - sequentially, same object - concurrently - same attribute, and same object - concurrently - distinct attributes. The case studies are the interaction of users in two cases: destroying and creating a set of arranged rigid bodies. We identify a specific type of application for contents authoring with modeling systems integrated with real-time physics and implemented in VR system. In our application called Virtual Dollhouse, users can observe physics law while constructing a dollhouse using existing building blocks, under gravity effects.

• Journal of The Korean Astronomical Society
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• v.46 no.6
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• pp.261-268
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• 2013

Magnetohydrostatic equilibria, in which the Lorentz force, the plasma pressure force and the gravitational force balance out to zero, are widely adopted as the zeroth order states of many astrophysical plasma structures. A magnetic flux-current surface is a surface, in which both magnetic field lines and current lines lie. We for the first time derive the necessary and sufficient condition for existence of magnetic flux-current surfaces in magnetohydrostatic equilibria. It is also shown that the existence of flux-current surfaces is a necessary (but not sufficient) condition for the ratio of gravity-aligned components of current density and magnetic field to be constant along each field line. However, its necessary and sufficient condition is found to be very restrictive. This finding gives a significant constraint in modeling solar coronal magnetic fields as force-free fields using photospheric magnetic field observations.

• Structural Engineering and Mechanics
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• v.51 no.2
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• pp.267-276
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• 2014

Wharfs are essential to shipping and support very large gravity loads on both a short-term and long-term basis which cause quite large seismic internal forces. Therefore, these structures are vulnerable to seismic activities. As they are supported on vertical and/or batter piles, soil-pile interaction effects under earthquake events have a great importance in seismic resistance which is not yet fully understood. Seismic design codes have become more stringent and suggest the use of new design methods, such as Performance Based Design principles. According to Turkish Code for Coastal and Port Structures (TCCS 2008), the interaction between soil and pile should somehow be considered in the nonlinear analysis in an accurate manner. This study aims to explore the lateral load carrying capacity of recently designed wharf structures considering soil-pile interaction effects for different soil conditions. For this purpose, nonlinear structure analysis according to TCCS (2008) has been performed comparing simplified and detailed modeling results.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.26-33
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• 2005

In this paper, a computational model for nonlinear crack damage analysis of concrete gravity dam-foundation boundary region subjected to earthquake loading is suggested. An enhanced model based on the Lee-Fenves plastic-damage model is used as the inelastic material model for a concrete dam structure and rock foundation. The suggested model is implemented numerically and used for computational earthquake simulation of Koyna dam, which was severly damaged from the strong earthquake in 1967. From the numerical result it is demonstrated that the suggested computational model can realistically represent crack initiation and propagation in the dam-foundation boundary region.

• Journal of the Korea Institute of Military Science and Technology
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• v.11 no.3
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• pp.169-175
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• 2008

A fine carbon fibers dispersion model is implemented to calculate the scattering range and ground level concentration of carbon fibers emitted at certain altitudes of atmospheric boundary layer. This carbon fibers dispersion model was composed by coupling a commonly used atmospheric dispersion model and an atmospheric boundary layer model. The atmospheric boundary layer model, applying the Monin-Obukov Similarity Rule obtained from measurement input data at ground level, was used to create the atmospheric boundary layer structure. In the atmospheric dispersion model, the Lagrangian Particle Model and the Markov Process were applied to calculate the trajectory of scattered carbon fibers relative to gravity and aerodynamic force, as well as carbon fibers specification.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.11a
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• pp.74-77
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• 2000

Infiltration and water flow in the upper soil layer of a deep water table aquifer are modeled for multistorm runoff events. The infiltration process is developed using the sharp wetting front model of Green and Ampt, and the following redistribution process is modeled using the gravity drained rectangular approximation. The Brooks-Corey model [Brooks and Corey, 1966] is adopted to relate the effective soil saturation, the tension head, and the unsaturated hydraulic conductivity Firstly, the infiltration and redistribution model is developed for a single stom runoff event. Then a couple of events combined for multistorm runoff events. In the later case, infiltration rate of the second rainfall is strongly influenced by the length of the rainfall hiatus and soil moisture profile.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.548-553
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• 2002

Most tasks of the large vertical or ceiling structures have been carried out by human power. Those tasks require us much operation costs and times, safety devices, etc. So the need of automation for those tasks have been rising. That automation needs a wall-climbing mobile vehicle. Most former researches are things about attachment devices and moving mechanisms. A wall-climbing mobile vehicle must be designed by a method different from the case of the vehicle of the horizontal environment. That is because gravity acts as a negative role on the stability of a wall-climbing vehicle. In this thesis, the particular shape characteristics of a wall-climbing mobile vehicle are derived by the wall-environment modeling. In addition, some design constraints of the permanent magnetic wheel as an attachment device was studied. According to those requirements and constraints, one specific wall-climbing mobile vehicle was designed and some experiments were made on the attachment ability of that vehicle.

• Korean Journal of Computational Design and Engineering
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• v.15 no.1
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• pp.70-83
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• 2010

Recently, floating cranes are mainly used to erect heavy blocks or cargos for constructing ships in many shipyards. It is important to estimate the dynamic motion of the heavy cargo suspended by a floating crane and the tension of the wire ropes between the floating crane and the heavy cargo. In this paper, the coupled dynamic equations of motion are set up for considering the 6 degree-of-freedom floating crane and the 6-degrees-of-freedom heavy cargo based on multibody system dynamics. Depending on the cargo weight, the motion of the floating crane would be changed to nonlinear state. The nonlinear terms in the equation of motion are considered. In addition, the nonlinear hydrostatic force, the linear hydrodynamic force, wire rope force, mooring force and gravity force are considered as the external forces. As the result of this paper, we analyze the engineering effect for erecting the heavy cargo by using the floating crane.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.1940-1942
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• 2001

Magnetic Levitation System(MLS) levitates a steel ball to the desired position in the gravity field using electromagnetic force. MLS consists of light sensor to measure the position of steel ball and an electromagnet to control the position of the ball, that composes a feedback control system. This work does not use a steel ball with constant mass but variable mass steel balls as magnetic levitation targets. Differential equation of electric circuit for electromagnet and motion equation of the movement of steel ball are derived for modeling nonlinear system, that will be linearized at the nominal operating point. We propose a digital control that can levitate a steel ball of which weight is not known for ED-4810 system. Algorithm for estimating ball weight and feedback control are implemented in digital scheme under pentium PC equiped with A/D and D/A converter, ACL-8112, using C-language. Simulation and experimental results are given to show the usefulness of the proposed controller.