• 한국지반환경공학회 논문집
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• 제24권10호
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• pp.51-58
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• 2023

지진 시 상부구조물을 지지하는 무리말뚝의 동적거동은 상부구조물의 관성력과 지반의 운동력에 의해 서로 다른 복잡한 동적 메커니즘에 영향을 받는다. 지진 시 상부구조물의 관성력과 지반의 운동력에 의한 지반, 말뚝기초, 상부구조물의 상호작용을 고려하여 말뚝기초의 동적거동을 분석하는 방법으로 동적 p-y 곡선이 사용되고 있다. 말뚝기초의 동적 p-y 곡선을 확인하기 위한 대부분의 연구는 사질토 및 점성토로 이루어진 단일지반에 설치된 말뚝기초를 대상으로 확인되었을 뿐 다층지반에 설치된 말뚝기초의 동적 p-y 곡선을 확인하기 위한 연구는 미비한 실정이다. 이에 본 연구에서는 서로 다른 상대밀도를 갖는 이층지반의 상·하지반의 지층비가 상부구조물을 지지하는 무리말뚝의 동적거동에 미치는 영향을 확인하기 위해 1g 진동대 모형실험을 수행하였다. 그 결과 지층비가 증가할수록 지반, 말뚝캡, 상부구조물에서의 최대가속도는 증가하고, 말뚝기초의 최대휨모멘트의 발생 위치는 변화하는 것으로 나타났다. 그리고 말뚝기초의 동적 p-y 곡선의 기울기는 지층비에 따라 감소 및 증가하는 것으로 확인되었다.

• Tribology and Lubricants
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• 제28권1호
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• pp.12-18
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• 2012

This application study of a swash-plate type axial piston pump was concerned about the lubrication characteristics between cylinder barrel and valve plate which are the main rotating body and its opposite sliding part respectively. A computer simulation was implemented to assess bearing and sealing functions of the fluid film between cylinder barrel and valve plate. A numerical algorithm was developed to facilitate simultaneous calculations of dynamic cylinder pressure, 3 degree-of-freedom barrel motions considering inertia effect, and fluid film pressure assuming full fluid film lubrication regime. Central clearance, tilt angle, and azimuth angle of the rotating body were calculated for each time step. Surface waviness was found to be an influential factor due to the small fluid film thickness which can appear in flat land bearings. Five surface lays which can form on the lubrication surface in accordance with machining process were defined and analyzed using the simulation tool. Oil leakage flow and frictional torque in the fluid film between cylinder barrel and valve plate were also calculated to discuss in the viewpoint of energy loss. The simulation results showed that in actual sliding conditions proper surface non-flatness can make a positive effect on the energy efficiency and reliability of the thrust bearing.

• 대한토목학회논문집
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• 제14권1호
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• pp.63-70
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• 1994

본 연구에서는 다경간 연속교의 내진해석시 가동받침의 마찰을 고려할 수 있는 비선형 동적해석 방법을 제시하고 가동받침의 마찰계수에 따른 연속교의 내진응답을 고찰하였다. 연구결과 국내와 같은 소규모 설계지진시에는 가동받침의 마찰은 마찰계수가 작더라도 에너지 감쇠에 의한 상부구조의 변위감소와 마찰력에 의한 상부구조의 관성력의 각 하부구조로 분배에있어 상당한 효과가 있음을 알 수 있었다. 또한 이러한 가동받침의 마찰효과는 마찰계수가 클수록, 입력지진의 규모가 작을수록 커짐을 보였다. 따라서 경간수가 많고 상부구조의 중량이 큰 다경간 연속교에 있어서 가동반침의 마찰계수를 적절히 사용함으로써 중소규모 설계지진 작용시 상부구조의 수평변위를 조절할 수 있고 상부구조의 교축방향 관성력을 각 하부구조로 분배하는 효과에 의해 경제성과 전체교량의 내진 안전성을 확보할 수 있다.

• Earthquakes and Structures
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• 제11권2호
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• pp.217-243
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• 2016

The linear and nonlinear seismic responses of steel buildings with perimeter moment resisting frames and welded connections (WC) are estimated and compared with those of buildings with post-tensioned connections (PC). Two-dimensional (2D) and three-dimensional (3D) structural representations of the buildings as well as global and local response parameters are considered. The seismic responses and structural damage of steel buildings with PC may be significantly smaller than those of the buildings with typical WC. The reasons for this are that the PC buildings dissipate more hysteretic energy and attract smaller inertia forces. The response reduction is larger for global than for local response parameters. The reduction may significantly vary from one structural representation to another. One of the main reasons for this is that the energy dissipation characteristics are quite different for the 2D and 3D models. In addition, in the case of the 3D models, the contribution of each horizontal component to the axial load on an specific column may be in phase each other during some intervals of time, but for some others they may be out of phase. It is not possible to observe this effect on the 2D structural formulation. The implication of this is that 3D structural representation should be used while estimating the effect of the PC on the structural response. Thus, steel frames with post-tensioned bolted connections are a viable option in high seismicity areas due to the fact that brittle failure is prevented and also because of their reduced response and self-centering capacity.

• 한국건설관리학회논문집
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• 제7권3호
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• pp.45-55
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• 2006

본 연구는 건설경영자의 경영Mind정립과 합리적 의사결정에 필요한 사고체계 구축에 필요한 논리와 기업경영에서 돌출될 수 있는 외부적 간섭인자를 효과적으로 분석할 수 있는 방향을 제시하는 것이 목적이다. 따라서 경영Mind 정립에 적용되는 간섭인자들이 경영 의사결정에 많은 영향을 주기 때문에 Mind정립과 경영환경에 대한 합리적 접근방법을 제시하고, 시간의 동태성에 따른 환경 요인들을 경영학, 심리학, 철학적 개념에서 논리적 단계로 분석했다. 끝으로 의사결정 요소에 대한 원칙적 한계 및 접근단계와 평가기준을 정립해보았다. 본 연구를 수행한 결과를 다음과 같이 요약해 본다. (1) 경영자의 의사결정 접근방법 (3) 시간의 동태성과 경영Mind (3) 의사결정의 외부 환경적 요인 (4) 경영Mind의 Synergy화 방법 (5) Mind 정립의 기대효과.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.381-387
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• 2002

In this work, the dynamic characteristics of an oil-lubricated, short SFD with a central feeding groove are derived based on a theoretical analysis considering the effect of a groove. The validity of the analysis is investigated experimentally using an Active Magnetic Bearing (AMB) system as an exciter. For the theoretical solution, the fluid film forces of a grooved SFD are analytically derived so that the dynamic coefficients of a SFD are expressed in terms of its design parameters. For the experimental validation of the analysis, a test rig using AMB as an exciter is proposed to identify the dynamic characteristics of a short SFD with a central groove. As an exciter, the AMB represents a mechatronic device to levitate and position the test journal without any mechanical contact, to generate relative motions of the journal inside the tested SFD and to measure the generated displacements during experiments with fairly high accuracy. Using this test rig, experiments are extensively conducted with different clearance, which is one of the most important design parameters, in order to investigate its effect on the dynamic characteristics and the performance of SFDs. Damping and inertia coefficients of the SFD that are experimentally identified are compared with the analytical results to demonstrate the effectiveness of the analysis. It is also shown that AMB is an ideal device for tests of SFDs.

• Structural Engineering and Mechanics
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• 제61권2호
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• pp.245-253
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• 2017

The increasing lack of good quality soils allowing the development of roadway, motorway, or railway networks, as well as large scale industrial facilities, necessitates the use of reinforcement techniques. Their aim is the improvement of the global performance of compressible soils, both in terms of settlement reduction and increase of the load bearing capacity. Among the various available techniques, the improvement of soils by incorporating vertical stiff piles appears to be a particularly appropriate solution, since it is easy to implement and does not require any substitution of significant soft soil volumes. The technique consists in driving a group of regularly spaced piles through a soft soil layer down to an underlying competent substratum. The surface load being thus transferred to this substratum by means of those reinforcing piles, which illustrates the case of a piled embankment. The differential settlements at the base of the embankment between the soft soil and the stiff piles lead to an "arching effect" in the embankment due to shearing mechanisms. This effect, which can be accentuated by the use of large pile caps, allows partial load transfer onto the pile, as well as surface settlement reduction, thus ensuring that the surface structure works properly. A technique for producing rigid piles has been developed to achieve in a single operation a rigid circular pile associated with a cone shaped head reversed on the place of a rigid circular pile. This technique has been used with success in a pile-supported road near Bourgoin-Jallieu (France). In this article, a numerical study based on this real case is proposed to highlight the functioning mode of this new technique in the case of industrial slabs.

• 한국항공우주학회지
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• 제44권5호
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• pp.416-422
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• 2016

본 논문에서는 연세대학교 천문우주학과 우주비행제어연구실에서 개발 중인 인공위성 편대비행 테스트베드에 대한 예비 성능분석 결과를 제시하였다. 동역학 모델에 포함되지 않은 동특성과 측정 잡음 등에 의한 불확실성의 영향을 받는 반작용 휠의 응답 성능을 향상시키기 위하여 간단한 1차 선형시스템을 기준 모델로 하는 적응제어기를 설계하였다. 또한 자세 측정값에 잡음이 포함된 환경에서도 원활한 제어를 수행하기 위해 최소제곱법 기반의 실시간 파라미터 추정기법을 이용하여 관성모멘트를 추정하였다. 수치 시뮬레이션과 하드웨어 실험을 통해 설계된 모델 기준 적응제어기의 적합성과 향후 적용가능성을 검토하였고, 전 시간에 걸친 자세 추적오차가 $0.25^{\circ}$ 이내에 머무는 것을 확인하였다. 하지만 하드웨어 실험을 통해 드러난 제어 입력에 대한 데드존의 영향을 줄이기 위해서는 인공위성 시뮬레이터의 설계 변경이 필요하다고 판단된다.

• Structural Engineering and Mechanics
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• 제59권3호
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• pp.503-526
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• 2016

In-plane and out-of-plane free vibration analysis of Timoshenko curved beams is addressed based on the isogeometric method, and an effective scheme to avoid numerical locking in both of the two patterns is proposed in this paper. The isogeometric computational model takes into account the effects of shear deformation, rotary inertia and axis extensibility of curved beams, and is applicable for uniform circular beams, and more complicated variable curvature and cross-section beams as illustrated by numerical examples. Meanwhile, it is shown that, the $C^{p-1}$-continuous NURBS elements remarkably have higher accuracy than the finite elements with the same number of degrees of freedom. Nevertheless, for in-plane or out-of-plane vibration analysis of Timoshenko curved beams, the NURBS-based isogeometric method also exhibits locking effect to some extent. To eliminate numerical locking, the selective reduced one-point integration and $\bar{B}$ projection element based on stiffness ratio is devised to achieve locking free analysis for in-plane and out-of-plane models, respectively. The suggested integral schemes for moderately slender models obtain accurate results in both dominated and non-dominated regions of locking effect. Moreover, this strategy is effective for beam structures with different slenderness. Finally, the influence factors of structural parameters of curved beams on their natural frequency are scrutinized.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.319-324
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• 2003

In general industrial rotating machinery is operated under 3,600 rpm as rotating speed and designed to have critical speed that is above operating speed. So, there was no problem to operate rotating machine under critical speed. But nowadays, they should be operated more than the frist critical speed as usual with the trend of high speed, large scale and hish precision in industries. In case of the large rotor assembly as the trend of large scale, using fitting method of disk or cylinder on shaft is rising for the convenience of assembly and cutting down of manufacturing cost. The shrink fitting is used to assemble lamination part on shaft for manufacturing of rotor of motor or generator in many cases and also is widely used for other machinery. In rotating system, which is compose of rotor and bearing, the critical speed is determined from inertia and stiffness for the rotor and bearings. In case of fitting assembly, analysis and design of the rotor is not easy because the rotor stiffness is determined depend on a lot of factors such as shaft material/dimension, disk material/dimension and assembled interference etc. Therefore designer who makes a plan for hish-speed rotating machine should design that the critical speed is located out of operating range, as dangerous factors exist in it. In order to appropriate design, an accurate estimation of stiffness and damping is very important. The stiffness variation depend on fitting interference is a factor that changes critical speed and if it's possible to estimate it, that Is very useful to design rotor-bearing system. In this paper, the natural frequency variation of the rotor depends on fitting interference between basic shaft and cylinder is examined by experimentation. From the result, their correlation is evaluated quantitatively using numerical analysis that is introduced equivalent diameter end the calculation criteria is presented for designer who design fitting assembly to apply with ease for determination of appropriate interference.