• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.667-673
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• 2010

This paper proposes a control method based on a pseudo-impedance model to control the motion of biped robots walking on an uneven surface. The pseudo-impedance model simulates the action of the ankle of a foot landing on the ground when a human walks. When the foot is in contact with the ground, the human ankle goes through two different phases. In the first phase, the human exerts little or no effort and applies no torque on the ankle so that the orientation of the foot is effortlessly and passively adjusted with respect to the ground. In the second phase of landing, the ankle generates a significant amount of torque in order to rotate and move the main part of the human body forward and to support the weight of the human; this phase is called the weight acceptance phase. Computer simulations of a 12-DOF biped robot with a 6-DOF environment model were performed to determine the effectiveness of the proposed pseudo-impedance control. The simulation results show that stable locomotion can be achieved on an irregular surface by using the proposed model.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.981-987
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• 2010

The split Hopkinson pressure bar (SHPB) technique is extensively used to characterize material deformation behavior under high strain rate condition. In this study, the dynamic deformation behavior of aluminum 7075-T6 under a high strain rate and at a high temperature is investigated by using a modified SHPB set-up with the pulse shaper technique. The parameters used in the Johnson-Cook constitutive equation are determined by using the SHPB experimental results including the data on the effects of strain rate, temperature, strain hardening, and thermal softening of the material.

• Fire Science and Engineering
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• v.22 no.4
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• pp.85-94
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• 2008

The purpose of this study is to obtain the fundamental fire resistance performance of engineered cementitious composites (ECC) under fire temperature in order to use the fire protection material in high-strength concrete structures. The present study conducted the experiment to simulate fire temperature by employing of ECC and investigated experimentally the explosion and cracks in heated surface of these ECC. In the experimental studies, 5 HSC specimens are being exposed to fire, in order to exami ne the influence of vari ous parameters (such as depth of layer=20, 30, 40 mm; construction method=lining and repairing type) on the fire performance of HSC structures. Employed temperature curve were ISO 834 criterion (3 hr), which are severe in various criterion of fire temperature in building structures. The numerical regressive analysis and proposed equation to calculate ambient temperature distribution is carried out and verified against the experimental data. By the use of proposed equation, the HSC members subjected to fire loads were designed and discussed.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.155-161
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• 2000

It is very important to control the final load that acts on a support system, in tunnel engineering. A reliable analysis is needed to carry out technically reasonable design and safe construction. Also, a series of procedures of construction and the rock-support interaction behavior must be considered. Most existing studies have been performed as the limited analysis based on the simplified assumption. In this study, through the analysis of a circular tunnel using a 2-D finite differential code, the rook-support interaction behaviors in the variation of rock and stress conditions are analyzed and compared with the results from the closed form solutions. Consequently, more realistic rock-support interaction curves are obtained by including the effects of initial stresses and rock condition. These cures are very useful to predict the required support pressure in the initial design stage.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.403-409
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• 2000

It is very important to control the final load that acts on a support system, in tunnel engineering. A reliable analysis is needed to carry out technically reasonable design and safe construction. Also, a series of procedures of construction and the rock-support interaction behavior must be considered. Most existing studies have been performed as the limited analysis based on the simplified assumption. In this study, through the analysis of a circular tunnel using a 2-D finite differential code, the rock-support interaction behaviors in the variation of rock and stress conditions are analyzed and compared with the results from the closed form solutions. Consequently, more realistic rock-support interaction curves are obtained by including the effects of initial stresses and rock condition. These curves are very useful to predict the required support pressure in the initial design stage.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.255-266
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• 1999

The objective of this experiment is to observe the elastic and inelastic behaviors of high-rise reinforced concrete frames having non-seismic details. To do this, a building frame designed according to Korean seismic code and detailed in the Korean conventional practice was selected. A 1:12 scale plane frame model was manufactured according to similitude law. A reversed lateral load test and a monotonic pushover test were performed under the displacement control. To simulate the earthquake effects, the lateral force distribution was maintained to be an inverse triangle by using a whiffle tree. From the tests, base shears, crack pattern, local rotations in the ends of critical members and the relations between interstory drift versus story shear are obtained. Based on test results, conclusions are drawn on the implications of the elastic and inelastic behaviors of a high-rise reinforced concrete frame having non-seismic details.

• Composites Research
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• v.13 no.6
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• pp.23-29
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• 2000

The internal residual stresses within the multilayered structure with sharp interface induced by the difference in thermal expansion coefficient between the materials of adjacent layers often provide the source of failure such as delamination of interfaces etc. Recent development of the multilayered structure with functionally graded interface would be the solution to prevent this kind of failure. However a systematic thermo-mechanical analysis is needed for the customized structural design of multilayered structure. In this study, theoretical model for the thermo-mechanical analysis is developed for multilayered structures of the $Al-SiC_p$ functionally graded composite for electronic packaging. The evolution of curvature and internal stresses in response to temperature variations is presented for the different combinations of geometry. The resultant analytical solutions are used for the optimal design of the multilayered structures with functionally graded interface as well as with sharp interface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.4
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• pp.417-424
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• 2011

A fuel assembly consists of five major components, i.e., a top end piece (TEP), a bottom end piece (BEP), spacer grids (SGs), guide tubes (GTs) and an instrumentation tube (IT); in addition, it also includes fuel rods (FRs). The TEP/BEP should satisfy stress intensity limits according to the conditions A and B of ASME, Section III, Division 1-Subsection NB. In a dual-cooled fuel assembly, the array and position of fuel rods are different from those in a conventional PWR fuel assembly; these changes are necessary for achieving power uprating. The flow plates of the TEP and BEP have to be modified accordingly. The pattern and shape of the flow holes were newly designed. To verify the strength compatibility, the Tresca stress limit according to the ASME code was investigated in the case of an axial load of 22.241 kN. In this paper, the stress linearization procedure for strength evaluation of a newly designed TEP is presented.

• Journal of Advanced Navigation Technology
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• v.15 no.2
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• pp.181-188
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• 2011

A small UAVs(Unmaned Aerial Vehicles) have limited by the payload capacity which requires miniaturization of a navigation system. In this paper, the performance of the lightweight and small sized AHRS(Attitude Heading Reference System), which is self-developed, is evaluated at low acceleration environment. The designed AHRS adopts the commercial low-cost MEMS sensors. A quaternion-based attitude calculation method, which eliminates singularity with relatively simple algebra, is used. In an attitude correction algorithm, the Kalman filter is used with accelerometers and magnetometers combined. The fabricated AHRS is also evaluated with reference to a COTS(Commercial Off-The-Shelf) AHRS which reports a number of successful applications to a small UAVs. The test results show that the measurements from the fabricated AHRS provide proper attitude output data with acceptable amount of differences(horizontal axis 0.5$^{\circ}$, vertical axis 1.5$^{\circ}$) in test environment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.1-6
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• 2018

Hydro-forming technology has spread dramatically throughout automotive industry over the last 20 years. This technology has many advantages for automotive applications in terms of better structural integrity of the parts, lower cost from fewer parts, material savings, weight reduction, lower springback, improved strength, durability, and design flexibility. In this study, various simulation technologies were developed to investigate the formability of hydro-forming components. Through this technology, to establish the effective forming process for appropriate components design, the bending process, pre-forming process, die closing process, etc. were considered for good forming. This paper proposes the forming amount, section length (corresponding to the hydro-forming press capacity), and minimum curvature (curvature effect evaluation according to the hydro-forming pressure) among the considerations in the design of the hydro-forming part. In addition, a design method is proposed for hydro-forming molding by carrying out cross section analysis of a real sub-frame part for automobiles. The effects of pre-bending, axial feed, hydraulic pressure, press load, and friction among the hydro-forming process parameters were analyzed. Therefore, whether these processes are necessary factors for hydro-forming were examined.