• Structural Engineering and Mechanics
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• 제68권4호
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• pp.409-421
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• 2018

In the present paper, functionally graded (FG) materials are presented to investigate the bending analysis of simply supported plates. It is assumed that the material properties of the plate vary through their length according to the power-law form. The displacement field of the present model is selected based on quasi-3D hyperbolic shear deformation theory. By splitting the deflection into bending, shear and stretching parts, the number of unknowns and equations of motion of the present formulation is reduced and hence makes them simple to use. Governing equations are derived from the principle of virtual displacements. Numerical results for deflections and stresses of powerly graded plates under simply supported boundary conditions are presented. The accuracy of the present formulation is demonstrated by comparing the computed results with those available in the literature. As conclusion, this theory is as accurate as other shear deformation theories and so it becomes more attractive due to smaller number of unknowns. Some numerical results are provided to examine the effects of the material gradation, shear deformation on the static behavior of FG plates with variation of material stiffness through their length.

• Computers and Concrete
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• 제30권4호
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• pp.277-287
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• 2022

Due to the scarcity of extortionate experimental data, fatigue failure of the reinforced concrete (RC) element might be achieved economically adopting nonlinear finite element (FE) analysis as an alternative approach. However, conventional implicit dynamic analysis is expensive, quasi-static method overlooks interaction effects and inertia, direct cyclic analysis computes stabilized responses. Apart from this, explicit dynamic analysis may provide a numerical operating system for factual long-term responses. The study explores the fatigue behavior based on a simplified explicit dynamic solution employing nonlinear time domain analysis. Among fourteen RC beams, one beam is selected to validate under static loading, one under fatigue with the experimental study and other twelve to check the detail fatigue behavior. The SWOT (Strength, Weakness, Opportunities, Threats) analysis has been carried out to pinpoint the detail scenario in the adoption of numerical approach as an alternative to the experimental study. Excellent agreement of FE and experimental results is seen. The 3D nonlinear RC beam model at service fatigue limits is truthful to be used as an expedient contrivance to envisage the precise fatigue behavior. The simplified analysis approach for RC beam under fatigue offers savings in computation to predict responses providing acceptable accuracy rather than the complicated laboratory investigation. At higher frequency, the flexural failure occurs a bit earlier gradually compared to the repeated loading case of lower frequency. The deflection increases by 6%-10% at the end of first cycle for beams with increasing frequency of cyclic loading. However, at the end of fatigue loading, greater deflection occur earlier for higher load range because of more rapid stiffness degradation. For higher frequency, a slight boost in concrete compressive strains at an initial stage of loading has been seen indicating somewhat stepper increment. Stiffness degradation in larger loading cycle at same duration escalates the upsurge of the rate of strain in case of higher frequency.

• Steel and Composite Structures
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• 제44권4호
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• pp.503-517
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• 2022

This paper presents the mechanical buckling of bi-directional functionally graded sandwich beams (BFGSW) with various boundary conditions employing a quasi-3D beam theory, including an integral term in the displacement field, which reduces the number of unknowns and governing equations. The beams are composed of three layers. The core is made from two constituents and varies across the thickness; however, the covering layers of the beams are made of bidirectional functionally graded material (BFGSW) and vary smoothly along the beam length and thickness directions. The power gradation model is considered to estimate the variation of material properties. The used formulation reflects the transverse shear effect and uses only three variables without including the correction factor used in the first shear deformation theory (FSDT) proposed by Timoshenko. The principle of virtual forces is used to obtain stability equations. Moreover, the impacts of the control of the power-law index, layer thickness ratio, length-to-depth ratio, and boundary conditions on buckling response are demonstrated. Our contribution in the present work is applying an analytical solution to investigate the stability behavior of bidirectional FG sandwich beams under various boundary conditions.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.835-841
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• 2013

Modern solid-state gyroscopes (HRG) with hemispherical resonators from high-purity quartz glass and special surface superfinishing and ultrathin gold coating become the best instruments for precise-grade inertial reference units (IRU) targeting long-term space missions. Designing of these sensors could be a notable contribution into development of Korea as a space nation. In participial, 40mm diameter thin-shell resonator from high-purity fused quartz, fabricated as a single-piece with its supporting stem has been designed, machined, etched, tuned, tested, and delivered by STM Co. (ATS of Ukraine) several years ago; an extremely-high Q-factor (upto 10~20 millions) has been shown. Understanding of the best way how to match such a unique sensor with inner glass assembly of the gyro means how to use the high potential in a maximal extent; and this has become the urgent task. Inner quartz glass assembly has a very thin indium (In) layer soldered the resonator and its silica base (case), but effects of internal resonances between operational modal pair of the shell-cup and its side (parasitic) modes can notable degrade the potential of the sensor as a whole, instead of so low level of resonator's intrinsic losses. Unfortunately, there are special combinations of dimensions of the parts (so-called, "resonant sizes"), when intensive losses of energy occurs. The authors proposed to use the length of stem's fixture as an additional design parameter to avoid such cases. So-called, a cyclic scheme of finite element method (FEM) and ANSYS software were employed to estimate different combinations of gyro assembly parameters. This variant has no mismatches of numerical origin due to FEM's discrete mesh. The optimum length and dangerous "resonant lengths" have been found. The special attention has been paid to analyses of 3D effects in a cup-stem transient zone, including determination of a difference between the positions of geometrical Pole of the resonant hemisphere and of its "dynamical Pole", i.e., its real zone of oscillation node. Boundary effects between the shell (cup) and 3D short "beams" (inner and outer stems) have been ranged. The results of the numerical experiments have been compared with the classic model of a quasi-hemispherical shell band with inextensional midsurface, and the solution using Rayleigh's functions of the $1^{st}$ and $2^{nd}$ kinds. To guarantee the truth of the recommended sizes to a designer of the real device, the analytical and FEM results have been compared with experimental data for a party of real resonators. The consistency of the results obtained by different means has been shown with errors less than 5%. The results notably differ from the data published earlier by different researchers.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.53-60
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• 2002

Motion of lung tumors from respiration has been reported in the literature to be as large as of 1-2 cm. This motion requires an additional margin between the Clinical Target Volume (CTV) and the Planning Target Volume (PTV). While such a margin is necessary, it may not be sufficient to ensure proper delivery of Intensity Modulated Radiotherapy (IMRT) to the CTV during the simultaneous movement of the DMLC. Gated treatment has been proposed to improve normal tissues sparing as well as to ensure accurate dose coverage of the tumor volume. The following questions have not been addressed in the literature: a) what is the dose error to a target volume without gated IMRT treatment\ulcorner b) what is an acceptable gating window for such treatment. In this study, we address these questions by proposing a novel technique for calculating the 3D dose error that would result if a lung IMRT plan were delivered without gating. The method is also generalized for gated treatment with an arbitrary triggering window. IMRT plans for three patients with lung tumor were studied. The treatment plans were generated with HELIOS for delivery with 6 MV on a CL2100 Varian linear accelerator with a 26 pair MLC. A CTV to PTV margin of 1 cm was used. An IMRT planning system searches for an optimized fluence map ${\Phi}$ (x,y) for each port, which is then converted into a dynamic MLC file (DMLC). The DMLC file contains information about MLC subfield shapes and the fractional Monitor Units (MUs) to be delivered for each subfield. With a lung tumor, a CTV that executes a quasi periodic motion z(t) does not receive ${\Phi}$ (x,y), but rather an Effective Incident Fluence EIF(x,y). We numerically evaluate the EIF(x,y) from a given DMLC file by a coordinate transformation to the Target's Eye View (TEV). In the TEV coordinate system, the CTV itself is stationary, and the MLC is seen to execute a motion -z(t) that is superimposed on the DMLC motion. The resulting EIF(x,y)is inputted back into the dose calculation engine to estimate the 3D dose to a moving CTV. In this study, we model respiratory motion as a sinusoidal function with an amplitude of 10 mm in the superior-inferior direction, a period of 5 seconds, and an initial phase of zero.

• 농약과학회지
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• 제10권4호
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• pp.296-305
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• 2006

토양 중 pencycuron의 온도, 수분함량 및 토성에 따른 흡착, 잔류 특성을 구명하고자 실내 및 포장실험과 환경의 영향에 대하여 실험을 수행하였다. 2종 토양에서 진탕 시간과 약제의 흡착량사이에 높은 유의성이 있는 power function의 상관관계가 인정되었다. 흡착속도는 진탕 1시간 이내에 사질식양토에서 최대 흡착량의 60%가, 미사질식양토에서 65%가 흡착되었고, 12시간 후에는 의사평형에 도달하였다. Pencycuron의 농도별 흡착은 Freundlich 등온식에 부합되었으며, 흡착분배계수 $K_d$값은 사질식양토에서 2.31, 미사질식양토에서 2.92었다. 토양 중 유기탄소에 대한 분배계수 $K_{oc}$는 사질식양토에서 292.9이었고, 미사질식양토에서 200.5이었다. 흡착강도 및 비선형도를 성명하는 상수값은 사질식양토에서 1.45, 미사질식양토에서 1.68이었다. 실내 실험에 있어서 pencycuron의 잔류는 1차 반응식에 부합되었고, 반감기는 $12^{\circ}C{\sim}28^{\circ}C$에서 95일${\sim}$20일로, 토양 수분함량이 포장용수량의 $30{\sim}70%$인 토양에서 38일에서 21일로 짧아졌다. 토양 종류에 따른 pencycuron의 반감기는 토성이 현저히 달랐음에도 사질식양토에서 25일, 미사질식양토에서 22일로 나타났다. 포장 실험에서도 pencycuron의 반감기는 사질식양토에서 26일, 미사질식양토에서 23일이었다. 포장에서 10%까지 잔류되는 기간은 미사질식양토에서 57일, 사질식양토에서 69일로 나타났다.

• 재무관리연구
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• 제24권1호
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• pp.29-58
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• 2007

본 연구에서는 기업의 성장기회에 대한 대용변수를 개발하기 위하여 신규투자의 투자수익률과 성장기회 가치를 추정할 수 있는 방법론을 제시하였다. M-M(1961, 1963), 이원흠(2006)의 기업가치 평가모형을 바탕으로 횡단면평균 투자수익률 및 개별기업의 가중평균자본비용을 추정하는 방법론을 제안하였고, 신규투자수익률 및 성장기회가치를 추정하는 방법론도 제안하였다. IMF 외환위기를 겪으면서 우리 기업들은 재무구조, 사업구조, 기업지배구조 조정 등 다방면으로 자구책을 시행한 바 있으나 그 실질적인 효과가 사업투자의 증대와 부가가치 창출로 이어지지 못하고, 기업투자 부진이 한국경제의 장기적 성장동력을 잠식시키고 있다는 우려가 높다. 이런 우려가 현실적으로 어떤 원인에서 연유하는가를 평가해 볼 수 있는 성장기회의 대용변수를 개발하였다. 새롭게 개발한 대용변수를 통해 한국 기업의 시기별, 산업별 성장기회가 변화한 모습을 추정한 결과를 종합하여 정리하면 다음과 같다. 첫째, 상장기업은 신규투자 성공률이 높지 못하다. 분석기간의 전체기업 중 약 $50{\sim}60%$에 불과한 기업들이 성장기회가 있을 때 신규투자 규모를 증가시키고 있다. 둘째, IMF 외환위기 진행시기에는 성장기회스프레드가 -2%에 달하는 음(-)의 값을 갖는 산업에서 신규투자 증가가 발생하여 산업의 성장가치를 훼손하였다. 이런 기업이 상장기업의 약 1/3에 달하였었다. 2000년대 들어서는 성장기회스프레드가 전 산업에 걸쳐 양(+)의 값으로 전환됨으로써 이를 잘 활용하여 투자액을 늘리면 성장가치가 증식될 수 있는 환경으로 변하였다. 이는 IMF 외환위기 극복과정에서 기업들이 시행한 사업구조 및 재무구조 개선 노력의 결과인 것으로 이해된다. 셋째, IMF 외환위기를 전후한 시기의 성장기회수익률과 성장기회스프레드를 비교해 보면 미미하지만 점차 양호해 진 것을 알 수 있다. 신규투자에서 기대되는 투자수익률을 측정하는 성장기회수익률이 11%에서 12.5%로 상승하였고, 신규투자의 초과이익률을 측정하는 성장기회스프레드는 -0.87%에서 +0.86%로 증가하였다. 넷째, 성장가치 면에서 살펴보면 오히려 절대값이 하락하였다. 성장가치를 무형자산가치비중과 성장기회가치비중으로 구분하여 살펴 본 결과, 무형자산가치비중은 분석기간 중 큰 변화가 없이 18% 수준을 유지하였으나, 성장기회가치비중은 IMF외환위기 진행기에는 15%에 달하던 것이 극복기가 되면 -2%로 대폭 하락한 것으로 분석된다. 다섯째, 연구개발, 고객만족 등 무형자산의 중요성이 강조되면서 그에 대한 투자가 활성화되었음에도 불구하고 무형자산가치비중이 크게 증가하지 못하고 있다는 점은 무형자산투자 관리에 더 노력하여야 한다는 점을 시사해 준다.