• 한국건축시공학회지
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• 제19권5호
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• pp.449-456
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• 2019

최근 비정형 건축물의 비중이 증가함에 따라 거푸집 재사용이 불가하여 건설폐기물이 증가하고 있는 추세이다. 또한 비정형 건축물 건축 시 생산자의 숙련도에 따라 비정형 패널의 품질이 결정되며 이에 따른 정확한 공사비 측정불가 및 인건비 증대라는 문제점이 있다. 본 연구는 이러한 비정형 건축물의 문제점을 보완하기 위하여 오차율이 적고 작업성이 좋은 최적의 배합을 찾는 것을 목표로 실험을 진행한다.

• Wind and Structures
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• 제30권6호
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• pp.663-678
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• 2020

Robust semi-active vibration control of wind turbines using tuned mass dampers (TMDs) is a promising technique. This study investigates a 1.5 megawatt wind turbine controlled by eight different types of tuned mass damper systems of equal mass: a passive TMD, a semi-active varying-spring TMD, a semi-active varying-damper TMD, a semi-active varying-damper-and-spring TMD, as well as these four damper systems paired with an additional smaller passive TMD near the mid-point of the tower. The mechanism and controllers for each of these TMD systems are explained, such as employing magnetorheological dampers for the varying-damper TMD cases. The turbine is modelled as a lumped-mass 3D finite element model. The uncontrolled and controlled turbines are subjected to loading and operational cases including service wind loads on operational turbines, seismic loading with service wind on operational turbines, and high-intensity storm wind loads on parked turbines. The displacement and acceleration responses of the tower at the first and second mode shape maxima were used as the performance indicators. Ultimately, it was found that while all the semi-active TMD systems outperformed the passive systems, it was the semi-active varying-damper-and-spring system that was found to be the most effective overall - capable of controlling vibrations about as effectively with only half the mass as a passive TMD. It was also shown that by reducing the mass of the TMD and adding a second smaller TMD below, the vibrations near the mid-point could be greatly reduced at the cost of slightly increased vibrations at the tower top.

• 한국항공우주학회지
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• 제35권7호
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• pp.619-626
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• 2007

고무 블록의 마찰에너지에 관한 연구는 고무 마모 연구를 위한 기초 연구이자 마찰과 마모의 관계를 규정짓는 중요한 연구이며, 지금까지의 마모 이론은 대부분 마찰에너지에 근거하여 전개되어 오고 있다. 하지만, 대부분이 실험이나 유한요소 해석에 기초한 연구이며, 해석적 방법에 의한 연구는 많이 이루어지지 않았다. 따라서 본 논문에서는 에너지 방법을 이용하여 재료 물성, 블록의 형상, 수직 및 전단하중, 블록 이동 속도의 함수로 표현되는 마찰에너지를 해석적으로 구하고 그 결과를 시험 결과와 비교 검토하였으며, 이를 통해 마모 특성 해석의 정확도를 높일 수 있는 기반을 마련하였다

• 한국임상수의학회지
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• 제31권1호
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• pp.54-56
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• 2014

9살 된 한우 싸움소가 왼쪽 뒷다리 파행 때문에 경북대학교 수의과대학 부속동물병원에 진료가 의뢰되었다. 환축은 좌측다리에 체중을 싣지 못하고 있었으며 파행이 발견되었다. 촉진하였을 때, 무릎관절은 부어 있었고 미열이 느껴졌다. 방사선 사진에서, 관절액의 증가, 연골하골의 미란, 도르레 융기선의 골편 형성, 무릎인대하 지방체의 변화를 보였으며, 정강뼈와 융기사이융기의 앞쪽 변위를 볼 수 있었다. 병력, 신체검사에 기초하여 전십자인대 파열을 잠정 진단하였으며 방사선 사진으로 확진하였다. 대상 환축은 심한 통증을 호소하면서 정상 보행이 불가능한 상태일 뿐 아니라 투우로서 효용성을 상실하고 현실적으로 치료가 불가능하여 신속히 도태 처분하였다.

• Structural Engineering and Mechanics
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• 제45권5호
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• pp.677-691
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• 2013

A semi-analytical finite strip method is developed for analyzing the post-buckling behavior of rectangular composite laminated plates of arbitrary lay-up subjected to progressive end-shortening in their plane and to normal pressure loading. In this method, all the displacements are postulated by the appropriate harmonic shape functions in the longitudinal direction and polynomial interpolation functions in the transverse direction. Thin or thick plates are assumed and correspondingly the Classical Plate Theory (CPT) or Higher Order Plate Theory (HOPT) is applied. The in-plane transverse deflection is allowed at the loaded ends of the plate, whilst the same deflection at the unloaded edges is either allowed to occur or completely restrained. Geometric non-linearity is introduced in the strain-displacement equations in the manner of the von-Karman assumptions. The formulations of the finite strip methods are based on the concept of the principle of the minimum potential energy. The Newton-Raphson method is used to solve the non-linear equilibrium equations. A number of applications involving isotropic plates, symmetric and unsymmetric cross-ply laminates are described to investigate the through-thickness shearing effects as well as the effect of pressure loading, end-shortening and boundary conditions. The study of the results has revealed that the response of the composite laminated plates is particularly influenced by the application of the Higher Order Plate Theory (HOPT) and normal pressure loading. In the relatively thick plates, the HOPT results have more accuracy than CPT.

• Structural Engineering and Mechanics
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• 제42권5호
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• pp.715-728
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• 2012

This paper deals with determining the fundamental frequency of tall buildings that consist of framed tube, shear core, belt truss and outrigger systems in which the framed tube and shear core vary in size along the height of the structure. The effect of belt truss and outrigger system is modeled as a concentrated rotational linear spring at the belt truss and outrigger system location. Many cantilevered tall structures can be treated as cantilevered beams with variable cross-section in free vibration analysis. In this paper, the continuous approach, in which a tall building is replaced by an idealized cantilever continuum representing the structural characteristics, is employed and by using energy method and Hamilton's variational principle, the governing equation for free vibration of tall building with variable distributed mass and stiffness is obtained. The general solution of governing equation is obtained by making appropriate selection for mass and stiffness distribution functions. By applying the separation of variables method for time and space, the governing partial differential equation of motion is reduced to an ordinary differential equation with variable coefficients with the assumption that the transverse displacement is harmonic. A power-series solution representing the mode shape function of tall building is used. Applying boundary conditions yields the boundary value problem; the frequency equation is established and solved through a numerical process to determine the natural frequencies. Computer program has been developed in Matlab (R2009b, Version 7.9.0.529, Mathworks Inc., California, USA). A numerical example has been solved to demonstrate the reliability of this method. The results of the proposed mathematical model give a good understanding of the structure's dynamic characteristics; it is easy to use, yet reasonably accurate and suitable for quick evaluations during the preliminary design stages.

• Geomechanics and Engineering
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• 제27권5호
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• pp.447-463
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• 2021

Caisson-type structures are widely used as quay walls in coastal areas. In Korea, for a long time, many caisson-type quay walls have been constructed with a low front water depth. These facilities can no longer meet the requirements of current development. This study developed a new technology for deepening existing caisson-type quay walls using grouting and rubble mound excavation to economically reuse them. With this technology, quay walls could be renovated by injecting grout into the rubble mound beneath the front toe of the caisson to secure its structure. Subsequently, a portion of the rubble mound was excavated to increase the front water depth. This paper reports the results of an investigation of the seismic behavior of a renovated quay wall in comparison to that of an existing quay wall using centrifuge tests and numerical simulations. Two centrifuge model tests at a scale of 1/120 were conducted on the quay walls before and after renovation. During the experiments, the displacements, accelerations, and earth pressures were measured under five consecutive earthquake input motions with increasing magnitudes. In addition, systematic numerical analyses of the centrifuge model tests were also conducted with the PLAXIS 2D finite element (FE) program using a nonlinear elastoplastic constitutive model. The displacements of the caisson, response accelerations, deformed shape of the quay wall, and earth pressures were investigated in detail based on a comparison of the numerical and experimental results. The results demonstrated that the motion of the caisson changed after renovation, and its displacement decreased significantly. The comparison between the FE models and centrifuge test results showed good agreement. This indicated that renovation was technically feasible, and it could be considered to study further by testbed before applying in practice.

• 치과방사선
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• 제16권1호
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• pp.49-58
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• 1986

This study was designed to investigate the irradiation effects on the rat parotid gland, applied to the head and neck region. For this experiment, twenty-four rats, feeded under the even condition, were used as experimental animals. Twenty rats were used for experimental group and the rest were assigned to the control group. The experimental group was singly irradiated with 10Gray through Cobalt-60 radiotherapy device, Picker model 4M 60 (Field size; l2×5㎝, SSD; 50㎝, Depth; 1㎝). The experimental animals of both group were sacrificed each four animals in 2 days, 1week, 2weeks, 3weeks and 4weeks after irradiation. The specimens were examined through the light microscope using the H-E stain and H stain by routin procedure. The other specimens were observed under the fluorescence microscope using the B-O dichroic mirror and Y455 barrier filter after PA-ACH stain. 1. The results of this study were obtained as follows, The parotid acini were severely degenerated and the intraacinar spaces were widened. Within the acini, retained secretory granules and increased fibrosis were observed. Also the shape and the size of the acini showed very irregular atrophic degenerations. 2. The nuclei showed severe pyknosis, displacement and irregular aggregated appearance. 3. The tissue changes of the parotid acini were initiated after 2 days of irradiation and most severely appeared at the second week of irradiation, but almost returned to normal. 4. The salivary ducts of the parotid gland were severely atrophied, discontinued but initiated to regenerated after 3 weeks of irradiation.

• 한국지반신소재학회논문집
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• 제17권1호
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• pp.45-54
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• 2018

본 연구에서는 최근 도심지에서 발생하고 있는 지반함몰에 대하여 도로의 붕괴 가능성을 높이는 지하공동 영향인자에 대한 수치해석적 분석을 수행하였다. 지하공동으로 인한 지반함몰 영향 인자는 서울시에서 제안한 공동관리 등급제를 참고하여 아스팔트 포장층의 두께, 토피고, 공동 폭을 고려하였고, 본 연구에서 추가로 공동의 높이를 선정하였다. 이들 영향 인자들을 다양한 범위 내에서 변화시킨 조건에서 지하공동이 있는 아스팔트 포장층 상단에 집중하중과 등분포하중을 각각 변위제어하여 도로 파괴하중을 분석하였다. 분석된 파괴하중을 토대로 서울형 공동관리 등급제에 대한 적용성을 평가하였다. 해석 결과 공동의 높이가 파괴에 미치는 영향은 크지 않았으며 이외의 다른 인자에 따라 복합적으로 파괴하중이 결정되었다. 또한 파괴하중을 기준으로 한 공동분류 방법은 공동 조건을 기준으로 한 분류 방법보다 더 세밀한 분류가 가능하며 파괴 시 물리적인 현상을 반영할 수 있어 더 합리적인 방법이다.

• Restorative Dentistry and Endodontics
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• 제26권5호
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• pp.399-408
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• 2001

Tooth bleaching has been prevailing recently for its ability to recover the color and shape of natural teeth without reduction of tooth material. However, it has been reported that bleaching procedure adversely affects the adhesive bond strength of composite resin to tooth. At the same time the bond strength was reported to be regained by application of some chemical agents. The purpose of this in vitro study was to investigate the effect of the removal of residual peroxide on the composite- enamel adhesion and also evaluated fracture mode between resin and enamel after bleaching. Sixty extracted human anterior and premolars teeth were divided into 5 groups and bleached by combined technique using of office bleaching with 35 % hydrogen peroxide and matrix bleaching with 10% carbamide peroxide for 4 weeks. After bleaching, the labial surfaces of each tooth were treated with catalase, 70% ethyl alcohol, distilled water and filled with composite resin. Shear bond strength was tested and the fractured surfaces were also examined with SEM. Analysis revealed significantly higher bond strength values. (p＜0.05) for catalase-treated specimens, but water-treated specimens showed reduction of bond strength, alcohol- treated specimens had medium value between the two groups(p＜0.05). The fracture mode was shown that the catalase group and the alcohol group had cohesive failure but the water sprayed group had adhesive failure. It was concluded that the peroxide residues in tooth after bleaching seems to be removed by gradual diffusion and the free radical oxygen from peroxide prevents polymerization by combining catalyst in the resin monomer. Therefore it may be possible to eliminate the adverse effect on the adhesion of composite resin to enamel after bleaching by using water displacement solution or dentin bonding agent including it for effective removal of residual peroxide.