• Structural Engineering and Mechanics
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• v.53 no.5
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• pp.997-1016
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• 2015

The contribution of tensioned concrete between cracks (tension-stiffening) cannot be ignored when analysing deformation of reinforced concrete elements. The tension-stiffening effect is crucial when it comes to adequately estimating the load-deformation response of steel reinforced concrete and the more recently appeared fibre reinforced polymer (FRP) reinforced concrete. This paper presents a unified methodology for numerical modelling of the tension-stiffening effect in steel as well as FRP reinforced flexural members using the concept of equivalent deformation modulus and the smeared crack approach to obtain a modified stress-strain relation of the reinforcement. A closed-form solution for the equivalent secant modulus of deformation of the tensioned reinforcement is proposed for rectangular sections taking the Eurocode 2 curvature prediction technique as the reference. Using equations based on general principles of structural mechanics, the main influencing parameters are obtained. It is found that the ratio between the equivalent stiffness and the initial stiffness basically depends on the product of the modular ratio and reinforcement ratio ($n{\rho}$), the effective-to-total depth ratio (d/h), and the level of loading. The proposed methodology is adequate for numerical modelling of tension-stiffening for different FRP and steel reinforcement, under both service and ultimate conditions. Comparison of the predicted and experimental data obtained by the authors indicates that the proposed methodology is capable to adequately model the tension-stiffening effect in beams reinforced with FRP or steel bars within wide range of loading.

• Structural Engineering and Mechanics
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• v.49 no.4
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• pp.427-448
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• 2014

At present, the time of easy oil and gas is over. Now, the largest part of fossil fuels is concentrated in the deepest levels of tectonic structures and in the sea shelves. One of the most cumbersome operations of their extraction is the bore-hole drilling. In connection with austere tectonic and climate conditions, their drivage every so often is associated with great and diversified technological difficulties causing emergencies on frequent occasions. As a rule, they are linked with drill string accidents. A key role in prediction of these situations should play methods of theoretical modelling. For this reason, there is a growing need for development and implementation of new numerical methods for computer simulation of critical and post-critical behavior of drill strings (DSs). In this paper, the processes of non-linear deforming of a DS in cylindrical cavity of a deep bore-hole are considered. On the basis of the theory of curvilinear flexible rods, non-linear constitutive differential equations are deduced. The effects of the longitudinal non-uniform preloading, action of torque and interaction between the DS and the bore-hole surface are taken into account. Owing to the use of curvilinear coordinates in the constraining cylindrical surface and a specially chosen concomitant reference frame, it became possible to separate the desired variables and to reduce the total order of the equation system. To solve it, the method of continuation the solution by parameter and the transfer matrix technique are applied. As a result of the completed numerical analysis, the critical states of the DS loading in the cylindrical channels of inclined bore-holes are found. It is shown that the modes of the post-critical deforming of the DS are associated with its irregular spiral curving prevailing in the zone of bottom-hole-assembly. The possibility of invariant state generation during post-critical deforming is established, condition of its bifurcation is formulated. It is shown that infinite variety of loads can correspond to one geometrical configuration of the DS. They differ each from other by contact force functions.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.4
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• pp.185-191
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• 2004

A mooring system can be applied to keep the position of a floating structures. In this study, the structural analysis is carried out to analyze the dynamic characteristics of a mooring line for a floating breakwater. A three-dimensional equations of motion for a submerged chain are derived. Bending stiffness is considered for the necessary restoring force in the regions of zero tension. A fortran program is to be developed by employing finite difference method. In the algorithm, an implicit time integration and Newton-Raphson iteration are adopted. The results of simulation show good agreement in tension response pattern with the experimental results of a reference. The results of this study can contribute for the design of mooring system for a floating breakwater.

• Korean Journal of Applied Biomechanics
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• v.16 no.3
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• pp.53-63
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• 2006

The general objective of this study was to investigate biomechanical characteristics of bowling swing using three-dimensional cinematography. This study focused specifically on movements of the upper body segments during a bowling swing. Eight elite female bowling players participated in this study. Subjects performed bowling swing and their performance was sampled at 60 frame/sec using two high-speed video cameras with a synchronizer. After digitizing images from two cameras, the two-dimensional coordinates were used to produce three-dimensional coordinates of the 12 body segments (20 joint reference makers). The obtained three-dimensional coordinates were fed to a custom-written kinematic and kinetic analyses program (LabView 6.1, National Instrument, Austin, TX, USA). The analyses determined the linear and angular kinematic variables of the body segments with which joint force and torque of the lower and upper trunks and the shoulder were estimated based on the Newton-Euler equations. It was found that during the bowling swing the peak linear velocities of the body segments were reached in sequence the trunk, the shoulder, the elbow, the wrist, and the bowl. This result indicates that linear momentum of the lower body and the trunk transmits to the arm segment during the bowling swing. The joint torques of the torso and the arm occurred almost simultaneously, indicating that bowling swing seem to be a push-like motion, rather than a proximal-distal sequence motion in which many of throwing motions are categorized. The ultimate objective of the bowling swing is to release a heavy-weight bowl with power and consistency. Therefore, the bowling swing observed in this study well agrees with that bowlers use the stepping to increase the linear velocity of the bowl, the simple pendulum system and the push-like segmental motion in the torso and the arm segment to enhance the power at the release of the bowl.

• Journal of the Korean Geotechnical Society
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• v.33 no.3
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• pp.17-28
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• 2017

We performed laboratory spudcan penetration and extraction tests considering various geometries. Jumunjin sand, representative standard sand in South Korea, and kaolinite were used for uniform sand and clay layers, respectively. The measured vertical bearing and pull-out capacities were compared to empirical equations for shallow foundations. The results showed good agreement between measured and calculated bearing capacity from laboratory test and previous study at shallow depths. The effect of spudcan geometry is shown to depend on site condition. The influence of a sharp spigot is not significant in clays. The slope of the spudcan surface is shown to influence the pull-out capacity. The characteristics of spudcan penetration and extraction behavior considering various geometries can be a useful reference for determining spudcan geometries.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.2
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• pp.154-162
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• 2007

In this paper, we propose a new AC-DC converter control method to comply with harmonics regulation(IEC 61000-3) effective for the inverter system of an air conditioner whose power consumption is less than 2,500W. There are many different ways of AC-DC converter control, but this paper focuses on the converter control method that is adopting an input reactor with low cost silicon steel core to strengthen cost competitiveness of the manufacturer. The proposed control method controls input current every half cycle of the line frequency to get unit power factor and at the same time to reduce switching loss of devices and acoustic noise from reactor. This kind of converter is known as a Partial Switching Converter(PSC). In this study, theoretical analysis of the PSC has been performed using Matlab/Simulink while a 16-bit micro-processor based converter has been used to perform the experimental analysis. In the theoretical analysis, electrical circuit models and equations of the PSC are derived and simulated. In the experiments, micro-processor controls input current to keep the power factor above 0.95 by reducing the phase difference between input voltage and current and at the same time to maintain a reference DC-link voltage against voltage drop which depends on DC-link load. Therefore it becomes possible to comply with harmonic regulations while the power factor is maximized by optimizing the time of current flow through the input reactor for every half cycle of line frequency.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5930-5938
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• 2013

The sigmoid functionally graded mateiral(S-FGM) theory is reformulated using the nonlocal elatictiry of Erigen. The equation of equilibrium of the nonlocal elasticity are derived. This theory has ability to capture the both small scale effects and sigmoid function in terms of the volume fraction of the constituents for material properties through the plate thickness. Navier's method has been used to solve the governing equations for all edges simply supported boundary conditions. Numerical solutions of biaxial buckling of nano-scale plates are presented using this theory to illustrate the effects of nonlocal theory and power law index of sigmoid function on buckling load. The relations between nonlocal and local theories are discussed by numerical results. Further, effects of (i) power law index, (ii) length, (iii) nonlocal parameter, (iv) aspect ratio and (v) mode number on nondimensional biaxial buckling load are studied. To validate the present solutions, the reference solutions are discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.711-721
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• 2014

PPWS, a large number of which a main cable of a suspension bridge consists of, must be precisely erected at a target location under construction considering the differences among design conditions. The absolute sag is measured for several PPWSs, which are reference strands and the relative sag is surveyed from them to other PPWSs, which are divided into several groups. And the adjustment of PPWS length is performed to erect it at target configuration. When PPWS is being under erection in a real bridge site, the procedures are as follows; evaluate sag sensitivities according to sag variation factors, calculate an adjustment length of PPWS corresponding to them and adjust a sag of PPWS by controlling the calculated amount of PPWS length. In this study, the differential-related equations of sag sensitivity were proposed for support movement of PPWS. Before site demonstration study of a series of them, we established a catenary model system and accomplished verification tests of them. From test results, the validation of them was done.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.1
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• pp.1-10
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• 2005

An aerodynamic shape optimization technique has been developed for helicopter rotor blades in hover based on a continuous adjoint method on unstructured meshes. The Euler flow solver and the continuous adjoint sensitivity analysis were formulated on the rotating frame of reference for hovering rotor blades. In order to handle the repeated evaluation of the design cycle efficiently, the flow and adjoint solvers were parallelized using a domain decomposition strategy. A solution-adaptive mesh refinement technique was adopted for the accurate capturing of the tip vortex. Applications were made for the aerodynamic shape optimization of Caradonna-Tung rotor blades and UH60 rotor blades in hover. The results showed that the present method is an effective tool to determine optimum aerodynamic shapes of rotor blades requiring less torque while maintaining the desired thrust level.

• Korean Journal of Food Science and Technology
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• v.12 no.4
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• pp.285-291
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• 1980

The hydration and cooking rate of two rice varieties, Akibare (Japonica) and Milyang 23 (Indica), were investigated in terms of mathematical rate equations. The hydration rate at temperatures of $10{\sim}40^{\circ}C$ was examined by weighing method. The absorption of liquid water by rice grain was directly proportional to the square root of the hydration time. The diffusion coefficient was given by the Arrhenius relation : $D=3.151{\times}10^{-3}\exp\;(-4000/RT)$ for Akibare and $D=5.853{\times}10^{-3}\exp\;(-5700/RT)$ for Milyang 23. Milyang 23 was cooked at a faster rate than Akibare. The activation energies for cooking were in the range of 18 000 cal/mole at $90{\sim}100^{\circ}C$ and 9,000cal/mole at $100{\sim}120^{\circ}C$. However, Milyang 23 showed slightly higher activation energy of cooking at $90{\sim}100^{\circ}C$. Adhesiveness and amylograph viscosities at all reference points for Milyang 23 were higher than those for Akibare.