• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.253-256
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• 2009

과팽창 상태 추력 노즐 내부의 측력(Lateral Force)발생에 대한 기초적 연구 분석을 실험적, 수치 해석적 방법으로 수행하였다. 엔진 정지 과정시 추력 노즐 내에 발생하는 압력진동을 조사하였다. 구동 압력비 변화에 따른 벽 압력 분포를 측정 및 쉴리렌 가시화를 수행하였다. RSS(Restricted Shock Separation)에서 FSS(Free Shock Separation)로 천이하는 순간 벽 압력 피크값이 발생하였다.

• Journal of Welding and Joining
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• 제19권3호
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• pp.298-304
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• 2001

Turbine blade is subject to force of three types ; the torsional force by torsional mount, the centrifugal force by the rotation of rotor and the cyclic bending force by steam pressure. The cyclic bending force was a main factor on fatigue strength. SEM fractography in root of turbine blade showed micro-clack width was not dependent on stress intensity factor range. Especially, fatigue did not exist on SEM photograph in root of turbine blade. To clear out the fracture mechanism of turbine blade, nanofractography was needed on 3-dimensional crack initiation and crack growth with high magnification. Fatigue striation partially existed on AFM photograph in root of turbine blade. Therefore, to find a fracture mechanism of the torsion-mounted blade in nuclear power plant, the relation between stress intensity factor range and surface roughness measured by AFM was estimated, and then the load amplitude ΔP applied to turbine blade was predicted exactly by root mean square roughness.

• 한국전산유체공학회지
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• 제21권4호
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• pp.96-101
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• 2016

A two-dimensional Stokes flow past a circular disk in a circular tube is analyzed. The circular disk is located coaxially with the circular tube and the Hagen-Poiseuille flow exists at upstream and downstream far from the circular disk. The Stokes approximation is used and the flow is investigated analytically by using the method of eigenfunction expansion and the method of least square. From the analysis, the stream function and the pressure of the flow field are obtained, and the streamlines and pressure distribution are shown. Also, the pressure and shear stress distributions on the circular disk and circular tube wall are calculated, and shown for some typical radii of the circular disk. The additional pressure drop induced by the disk and the drag force exerted on the disk are compared as functions of the radius of the circular disk, and it is shown that the shear force on the wall of the tube increases due to the disk.

• Wind and Structures
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• 제24권2호
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• pp.145-169
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• 2017

The auxiliary structures of a high-rise building, such as balconies, ribs, and grids, are usually much smaller than the whole building; therefore, it is difficult to simulate them on a scaled model during wind tunnel tests, and they are often ignored. However, they may have notable effects on the local or overall wind loads of the building. In the present study, a series of wind pressure wind tunnel tests and high-frequency force balance (HFFB) wind tunnel tests were conducted on rigid models of an actual super high-rise building with vertical ribs protruding from its facades. The effects of the depth and spacing of vertical ribs on the mean values, fluctuating values and the most unfavorable values of the local wind pressure coefficients were investigated by analyzing the distribution of wind pressure coefficients on the facades and the variations of the wind pressure coefficients at the cross section at 2/3 of the building height versus wind direction angle. In addition, the effects of the depth and spacing of vertical ribs on the mean values, fluctuating values and power spectra of the overall aerodynamic force coefficients were studied by analyzing the aerodynamic base moment coefficients. The results show that vertical ribs significantly decrease the most unfavorable suction coefficients in the corner recession regions and edge regions of facades and increase the mean and fluctuating along-wind overall aerodynamic forces.

• 한국정밀공학회지
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• 제30권3호
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• pp.260-265
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• 2013

To increase the machine accuracy by improving the stiffness of spindle bearings, preload was applied to the spindle bearings. The methods of fixed position preload, convertible preload, constant pressure preload, and variable preload are used to apply the preload to the spindle bearing. The previous studies performed by the author of this study were variable preload methods using rubber pressure and centrifugal force based on mechanical systems. This study proposed a toggle joint mechanism that could be applied to variable preload method using centrifugal force and rubber pressure to increase the preload. Also, a finite element analysis was conducted to predict the deformation of the rubber and change of the preload. And the analysis results showed that the preload by the device using rubber pressure only was increased by the toggle joint mechanism using rubber pressure.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2023년도 학술발표회
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• pp.438-438
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• 2023

최근 전 세계적으로 기후변화가 심해지고 있어 자연재해 또한 늘어나고 있다. 많은 자연재해 중 겨울철 재해인 대설 피해는 2012년부터 2021년까지 10년동안 약 1,200억의 피해액이 발생하였고 많은 재산 피해의 위험이 있어 지속적인 연구가 필요하다. 그 중 충남지역의 피해액은 약 200 억으로 우리나라의 피해액 중 두 번째로 많다. 따라서 본 연구에서는 PSR(Pressure Index, State Index, Response Index)과 DPSIR(Driver force Index, Pressure Index, State Index, Impact Index, Response Index) 방법을 이용하여 충남지역의 대설에 대한 취약성을 분석하여 더 신뢰할 수 있는 대설 위험지역을 제시하였다. PSR 방법은 압력지수, 상태지수, 반응지수로 구분되고, DPSIR 방법은 추진력, 압력, 상태, 영향, 대책 지수로 나뉜다. 각 지표에 해당하는 데이터베이스를 구축하고 엔트로피 방법을 이용하여 가중치를 산정하고 충남지역의 대설 취약성 지수를 산출하였다. 2018년부터 2022년까지 최근 5년 동안의 충남지역의 대설피해를 기준으로 PSR(Pressure Index, State Index, Response Index)과 DPSIR(Driver force Index, Pressure Index, State Index, Impact Index, Response Index) 방법을 이용하여 산출한 지수를 비교한 결과 DPSIR(Driver force Index, Pressure Index, State Index, Impact Index, Response Index) 방법을 이용하여 산출된 취약성 지수가 더 신뢰할 수 있는 결과를 보였다. 본 연구의 결과 대설피해 발생 시 대설 위험지수가 높은 지역을 선제적으로 대비할 수 있고 효율적인 제설대응체계를 구축할 수 있을 것으로 기대된다.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2642-2649
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• 2023

A real-time unmeasured dynamic response prediction process for the nuclear power plant pressure pipeline is proposed and its performance is tested in the test-loop system (KAERI). The aim of the process is to predict unmeasurable or unreachable dynamic responses such as acceleration, velocity, and displacement by using a limited amount of directly measured physical responses. It is achieved by combining a well-constructed finite element model and robust inverse force identification algorithm. The pressure pipeline system is described by using the displacement-pressure vibro-acoustic formulation to consider fully filled liquid effect inside the pipeline structure. A robust multiphysics modal projection technique is employed for the real-time sensor synchronized prediction. The inverse force identification method is also derived and employed by using Bathe's time integration method to identify the full-field responses of the target system from the modal domain computation. To validate the performance of the proposed process, an experimental test is extensively performed on the nuclear power plant pressure pipeline test-loop under operation conditions. The results show that the proposed identification process could well estimate the unmeasured acceleration in both frequency and time domain faster than 32,768 samples per sec.

• 한국컴퓨터그래픽스학회논문지
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• 제1권2호
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• pp.201-212
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• 1995

This paper presents a new method of dynamics-based synthesis of bipedal, especially human, walking. The motion of the body at a time point is determined by ground reaction force and torque under the support foot and joint torques of the body at that time point. Motion synthesis involves specifying conditions that constrain ground reaction force and torque, and joint torques so that a given desired motion may be achieved. There are conditions on a desired motion which end-users can think of easily, e.g. the goal position and orientation of the swing foot for a single step and the time period of a single step. In this paper, we specify constraints on the motion of the support foot, which end-users would find difficult to specify. They are constraints which enforce non-sliding, non-falling, and non-spinning the support foot. They are specified in terms of joint torques and ground reaction force and torque. To satisfy them, both joint torques and ground reaction force and torque should be determined appropriately. The constraints on the support foot themselves do not give any good clues as to how to determine ground reaction force and torque. For that purpose, we specify desired trajectories of the application point of vertical ground reaction force (ground pressure) and the application point of horizontal ground reaction (friction) force. The application points of vertical pressure and friction force are good control variables, because they are indicators to kinds of walking motions to synthesize. The synthesis of a bipedal walking motion, then, consists of finding a trajectory of joint torques to achieve a given desired motion, so that the constraints are satisfied under the condition of the prescribed center of pressure and center of friction. Our approach is distinguished from many other approaches, e.g. the inverted-pendulum approach, in that it captures and formulates dynamics of the support foot and reasonable constraints on it.

• 한국산학기술학회논문지
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• 제20권5호
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• pp.510-519
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• 2019

본 연구에서는 보강토교대로 지지된 슬래브교의 설계 활하중을 도로교설계기준(2010)의 DB-24와 도로교설계기준(한계상태설계법)(2015)의 KL-510으로 구조해석을 수행하였다. 구조해석 결과로부터 산정된 슬래브교의 반력과 보강토교대에 작용하는 접지압에 대해 비교검토를 수행하였다. 교대에 작용되는 반력은 교각의 유무와 개수에 따라 다르게 산정되었다. 단경간에 비해 연속교에서 교대에 작용되는 반력이 감소되는 것으로 나타났다. 구조해석 결과, 활하중보다는 고정하중에 의한 반력이 약 2배 이상 크게 산정되었으며, 활하중이 전체 반력에 미치는 영향이 상대적으로 작았다. 보강토교대에 작용하는 접지압은 단경간에서 가장 크게 산정되었다. 이동하중의 종류에 따른 영향은 상대적으로 크지 않았다. 따라서, 연속교에서 교대에 작용되는 반력과 접지압이 작게 산정되기 때문에, 단경간 교량보다는 연속 교량에 보강토교대를 적용하는 것이 유리한 것으로 판단되었다. 보강토교대에 작용되는 반력과 하중 분담률은 다양한 조건에 따라 달라지므로, 다양한 교량 형식과 제원에서의 접지압 검토가 향후 필요하다.

• International Journal of Fluid Machinery and Systems
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• 제4권4호
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• pp.375-386
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• 2011

The turbo-type blood pump studied in this paper has an impeller that is magnetically suspended in a double volute casing. The impeller rotates with minimal fluctuations caused by fluid and magnetic forces. In order to improve stability of the rotating impeller and to facilitate long-term use, a careful investigation of the pressure fluctuations and of the fluid force acting on the impeller is necessary. For this purpose, two models of the pump with different volute cross-sectional area are designed and studied with computational fluid dynamics software. The results show that the fluid force varies with the flow rate and shape of the volute, that the fluctuations of fluid force decrease with increasing flow rate and that the vibratory movement of the impeller is more efficiently suppressed in a narrow volute.