• 한국지반공학회논문집
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• 제15권2호
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• pp.17-27
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• 1999

도심지에서의 대규모. 대심도 굴착공사가 빈번해짐에 따라서 굴착이 배면지반은 물론, 인접 구조물에 미치는 영향을 정확히 평가하는 것이 중요한 문제로 대두되고 있다. 그러나 일상적으로 굴착의 영향을 평가할 때 구조물의 존재 유무에 관계없이 주위 지반 침하량을 산정하고 있는데 이는 옳지 않다고 판단된다. 본 연구에서는 굴착시 구조물이 토류벽체에 인접하여 놓여있는 경우에 각기 다른 지보강성과 벽면마찰각을 갖는 다양한 조건하에서 굴착으로 인한 주위 지반 및 구조물의 거동을 평가하기 위하여 구조물의 평면 및 단면상에서의 위치를 변화시켜가면서 모형실험을 실시하였다. 그 결과로부터 인접 구조물이 지표면에 위치할 경우에 이격거리가 굴착깊이의 0.3배 이내이면 구조물이 없을 때와 비교하여 최대 181%의 추가 침하가 발생하며, 1.0배 이상 떨어지면 구조물에 의한 추가적인 영향은 없다는 결론을 얻었다. 그리고 구조물 기초의 근입깊이가 깊어질수록 추가로 영향받는 영역이 줄어들고 기초의 근입깊이가 굴착깊이의 0.75배 이상이면 추가 침하는 거의 발생하지 않았다.

• International Journal of Fluid Machinery and Systems
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• 제3권1호
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• pp.67-79
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• 2010

Severe flexural vibration of the rotor shaft of a Francis turbine runner was experienced in the past. It was shown that the vibration was caused by the fluid forces and moments on the backshroud of the runner associated with the leakage flow through the back chamber. The aim of the present paper is to study the self-excited rotor vibration caused by the fluid force moments on the backshroud of a Francis turbine runner. The rotor vibration includes two fundamental motions, one is a whirling motion which only has a linear displacement and the other is a precession motion which only has an angular displacement. Accordingly, two types of fluid force moment are exerted on the rotor, the moment due to whirl and the moment due to precession. The main focus of the present paper is to clarify the contribution of each moment to the self-excited vibration of an overhung rotor. The runner was modeled by a disk and the whirl and the precession moments on the backshroud of the runner caused by the leakage flow were evaluated from the results of model tests conducted before. A lumped parameter model of a cantilevered rotor was used for the vibration analysis. By examining the frequency, the damping rate, the amplitude ratio of lateral and angular displacements for the cases with longer and shorter overhung rotor, it was found that the precession moment is more important for smaller overhung rotors and the whirl moment is more important for larger overhung rotors, although both types of moment due to the leakage flow can cause self-excited vibration of an overhung rotor.

• 한국터널지하공간학회 논문집
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• 제19권2호
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• pp.231-248
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• 2017

서울시는 도심지 교통체증을 해결하기 위해 최근 경부고속도로의 일부 구간을 복층터널로 계획하는 방안을 검토하고 있다. 도심지에 복층터널을 건설할 경우, 교통난 해소뿐만 아니라 말레이시아 스마트 터널과 같이 홍수 시 침수방지를 위한 저류시설로도 활용할 수 있을 것으로 본다. 그러나 도로터널을 복층터널로 계획할 경우에는 각 지역을 연결하는 분기터널이 필요하며, 분기터널은 토피가 낮은 구간에 편평율이 큰 대단면 또는 복잡한 터널 단면형상으로 이루어지게 된다. 이때 토피가 낮은 지역에서는 지하 공동구나 건물 기초 등에 인접하여 위치하게 되며 터널 건설로 인해 지장물에 미치는 영향에 대해 반드시 검토해야 한다. 본 연구에서는 복층터널에서 분기되는 터널 굴착 시, 지하 공동구에 미치는 영향을 수치해석을 통해 분석하였다. 변위조절모델(Displacement Controlled Model)을 이용하여 터널 주변의 지반손실률을 1.0%, 3.0%, 그리고 5.0%까지 모사하였다. 복층터널에서 분기되는 각도를 $45^{\circ}$와 $36^{\circ}$로 다르게 설정하여 공동구 측면 및 하부로의 접근을 고려할 수 있도록 하였다. 그 결과, 일반적으로 분기터널이 공동구에 근접할수록 그리고 지반손실률이 클수록 변위, 각변위 그리고 안정성에 미치는 영향이 큰 것으로 타나났다. 공동구 바닥부의 침하와 공동구 부재의 안정성에는 이격거리 보다는 공동구의 하부에 근접하여 큰 변위와 부등침하를 유발할 수 있는 각도 $36^{\circ}$, 이격거리 10 m가 가장 취약한 것으로 나타났다. 본 연구를 통해 근접시공 시 구조물의 안정성 평가를 위한 각변위-거리/직경 관계를 제시하였으며, 지하 공동구 안정성에 영향을 미치는 한계 임계 지반손실률을 산정하였다.

• 대한인간공학회지
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• 제26권1호
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• pp.19-27
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• 2007

Despite the widespread use of laterally wedged insoles for patients with knee osteoarthritis and medially wedged insoles for controlling rearfoot pronation, an understanding of the effects of wedged insoles was limited and sometimes controversial. The objective of this study was to evaluate the effect of wedged insoles on the kinematics and kinetics of normal gait. Ten male subjects without history of lower limb disorders were recruited. Each subject performed four gait cycles under each of seven conditions; shod with 5$^{\circ}$, 8$^{\circ}$ and 15$^{\circ}$, 8$^{\circ}$ and 15$^{\circ}$ laterally wedged insoles. In order to determine statistical differences among seven conditions, the measured temporal spatial variables, angular displacements, joint moments, and ground reaction forces were compared with a one-way analysis of variance. Some significant changes induced by wedged insoles were apparent in joint moments and ground reaction forces. The medially wedged insole increased the laterally directed ground reaction force and varus moments at the ankle force and varus moments at the ankle and the knee.

• Advances in nano research
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• 제6권1호
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• pp.21-37
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• 2018

In the present article, wave dispersion behavior of a temperature-dependent functionally graded (FG) nanobeam undergoing rotation subjected to thermal loading is investigated according to nonlocal strain gradient theory, in which the stress numerates for both nonlocal stress field and the strain gradient stress field. The small size effects are taken into account by using the nonlocal strain gradient theory which contains two scale parameters. Mori-Tanaka distribution model is considered to express the gradually variation of material properties across the thickness. The governing equations are derived as a function of axial force due to centrifugal stiffening and displacements by applying Hamilton's principle according to Euler-Bernoulli beam theory. By applying an analytical solution, the dispersion relations of rotating FG nanobeam are obtained by solving an eigenvalue problem. Obviously, numerical results indicate that various parameters such as angular velocity, gradient index, temperature change, wave number and nonlocality parameter have significant influences on the wave characteristics of rotating FG nanobeams. Hence, the results of this research can provide useful information for the next generation studies and accurate deigns of nanomachines including nanoscale molecular bearings and nanogears, etc.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2457-2465
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• 2002

Numerical modeling of a nondestructive testing system plays an important role in many aspects of quantitative nondestructive evaluation (QNDE). The ultimate goal of a model is to predict test results for a specific flaw in a material. Thus, in ultrasonic testing, a system model should include the transducer, its radiation pattern, the beam reflection and propagation, and scattering from defects. In this paper attention is focused on the scattering model and the scattered fields by defects are observed by an elastodynamic boundary element method. Flaw types addressed are void-like and crack-like flaws. When transverse ultrasonic waves are obliquely incident on the flaw, the angular distribution of far-field scattered displacements are calculated and presented in the form of A-scan mode. The component signals obtained from each scattering problem are identified and their differences are addressed. The numerical results are also compared with those obtained by high frequency approximate solutions.

• 한국정밀공학회지
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• 제33권4호
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• pp.295-301
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• 2016

The out-of-squareness is one of the error sources that affect the positioning accuracy of machine tools and coordinate measuring machines. Laser interferometer is widely used to measure the position and angular errors, and can measure the squareness using an optical square. However, the squareness measurement using the laser interferometer is difficult, as compared to other errors due to complicated optics setup and Abbe's error occurrence. The effect of out-of-squareness mainly appears at the face-diagonal of the movable plane. The diagonal displacements are also affected by the position dependent geometric errors. In this study, the squareness estimation techniques via diagonal displacement measurement using the laser interferometer without an optical square were proposed. For accurate estimation and measurement time reduction, the errors selected from proposed discriminant were measured. Discrepancy between the proposed technique with the laser interferometer (with an optical square) result was $0.6{\mu}rad$.

• 한국기계가공학회지
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• 제13권3호
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• pp.83-88
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• 2014

FSI (Fluid Structure Interaction) method, in this study, has been applied to analyzing thermal characteristics of a high speed machine tool spindle system. The spindle is composed of angular contact ceramic ball bearings, a high speed built-in motor, a cooling jacket, and so on. The cooling jacket has three inlets and outlets. Using the FSI method, temperature distributions and thermal displacements of the spindle system were computed considering the heating of the front and rear bearings and the built-in motor. The results computed using the FSI method were compared with those determined by experiment and using the conventional numerical approach. The results determined using the FSI method were similar to those from the conventional numerical approach but showed better agreement with the experimental results. Therefore, it is concluded that the FSI method is useful for analyzing the thermal characteristics of high speed spindles and can be applied to the design of high speed spindles.

• Steel and Composite Structures
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• 제22권5호
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• pp.1193-1214
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• 2016

In this paper, the 3D stress state and inter-laminar stresses in a rotating thin laminated cylinder shell are studied. The thickness of the cylinder is supposed to be thin and it is made of laminated composite material and can have general layer stacking. The governing equations of the cylindrical shell are obtained by employing the Layerwise theory (LWT). The effect of rotation is considered as rotational body force which is induced due to the rotation of the cylinder about its axis. The Layerwise theory (LWT), is used to discrete the partial differential equations of the problem to ordinary ones, in terms of the displacements of the mathematical layers. By applying the Free boundary conditions the solution of the governing equations is completed and the stress state, the inter-laminar stresses, and the edge effect in the rotating cylindrical shells are investigated in the numerical results. To verify the results, LWT solution is compared with the results of the FEM solution and good agreements are achieved. The inter-laminar normal and shear stresses in rotating cylinder are studied and effects of layer stacking and angular velocity is investigated in the numerical results.

• 한국소음진동공학회논문집
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• 제16권1호
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• pp.57-65
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• 2006

In this paper, we present the principle of virtual work, from which the exact non-linear equations of motion of a rotating ring can be derived, by using the theory of finite deformation. For a thin ring of which the effect of variation in curvature across the cross-section is neglected, the radial displacement and the extensional stress are determined from the principle of virtual work at the steady state where the ring is rotating with a constant angular velocity. And also we formulate systematically the governing equations concerned to the in-plane vibrations and the out-of-plane vibrations at the disturbed state by using the principle of virtual work which is expressed with the disturbed displacements about the steady state. The formulated governing equations are classified by four models along the cases of considering or neglecting all or partly the secondary effects of flexural shear, rotary inertia, circumferential extension, and twist inertia. The natural vibrations of thin rings are analyzed, and its results are compared and discussed.