• 제목/요약/키워드: Dimensionless Variables

검색결과 97건 처리시간 0.037초

채널 유동에서 점성이 단일 입자 혼합 유동의 suspension에 미치는 영향 (Effect of Fluid Viscosity on the Suspension of a Single Particle in Channel Flow)

  • 최형권
    • 대한기계학회논문집B
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    • 제33권3호
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    • pp.194-200
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    • 2009
  • Suspension of a single solid particle in a channel flow with a constant pressure gradient is studied numerically. The interaction of a circular particle with a surrounding Newtonian fluid is formulated using a combined formulation. Numerical results are presented using two dimensionless variables: the sedimentation Reynolds number and the generalized Froude number. From the present results, it has been shown that a solid particle is suspended at a smaller generalized Froude number as the viscosity of the surrounding fluid increases. The time taken for equilibrium position is found to be smaller as fluid viscosity increases when both : the sedimentation Reynolds number and the generalized Froude number are the same while, at the same situation, the dimensionless time taken for equilibrium position is to be nearly the same regardless of fluid viscosity when a dimensionless time variable is introduced

초기 비틀림각을 갖는 회전하는 다중 패킷 블레이드 시스템의 고유 진동 해석 (Modal Analysis of a Rotating Multi-Packet Pre-twisted Blade System)

  • 김민권;유홍희
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2008년도 춘계학술대회논문집
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    • pp.393-399
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    • 2008
  • A modeling method for the modal analysis of a pre-twisted multi-packet blade system undergoing rotational motion is presented in this paper. Blades are idealized as pre-twisted cantilever beams that are fixed to a rotating disc. The stiffness coupling effects between blades due to the flexibilities of the disc and the shroud are modeled with discrete springs. The coupling effect between chordwise and flapwise bending deflection is also considered. Hybrid deformation variables are employed to derive the equations of motion. To obtain more general information, the equations of motion are transformed into dimensionless forms in which dimensionless parameters are identified. The effects of the dimensionless parameters and the number of packets as well as blades on the modal characteristics of the rotating multi-packet pre-twisted blade system are investigated with some numerical examples.

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회전하는 테이퍼 단면 다중 패킷 블레이드 시스템의 진동 해석 (Vibration Analysis of a Rotating Multi-Packet Blade System Having Tapered Cross Section)

  • 김민권;유홍희
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2008년도 추계학술대회A
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    • pp.832-837
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    • 2008
  • A modeling method for the modal analysis of a multi-packet blade system having tapered cross section undergoing rotational motion is presented in this paper. Blades are idealized as tapered cantilever beams that are fixed to a rotating disc. The stiffness coupling effects between blades due to the flexibilities of the disc and the shroud are modeled with discrete springs. Hybrid deformation variables are employed to derive the equations of motion. To obtain more general information, the equations of motion are transformed into dimensionless forms in which dimensionless parameters are identified. The effects of the dimensionless parameters including tapered ratio and the number of packets as well as blades on the modal characteristics of the system are investigated with some numerical examples.

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크랙과 집중질량을 갖는 회전 외팔보의 진동 해석 (Vibration Analysis of a Cracked Beam with a Concentrated Mass Undergoing Rotational Motion)

  • 김민권;유홍희
    • 한국소음진동공학회논문집
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    • 제19권1호
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    • pp.10-16
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    • 2009
  • Modal characteristics of a cracked beam with a concentrated mass undergoing rotational motion are investigated in this paper. Hybrid deformation variables are employed to derive the equations of motion of a rotating cantilever beam. The flexibility due to crack, which is assumed to be open during the vibration, is calculated basing on a fracture mechanics theory. To obtain more general information, the equations of motion are transformed into a dimensionless form in which dimensionless parameters are identified. The effects of the dimensionless parameters related to the angular speed, the depth and location of a crack and the size and location of a concentrated mass on the modal characteristics of the beam are investigated numerically.

Effect of Functional Ankle Instability and Surgical Treatment on Dynamic Postural Stability and Leg Stiffness Variables during Vertical-Drop Landing

  • Jeon, Kyoung Kyu;Kim, Kew Wan;Ryew, Che Cheong;Hyun, Seung Hyun
    • 한국운동역학회지
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    • 제28권2호
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    • pp.135-141
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    • 2018
  • Objective: The purpose of this study was to investigate the effect of functional ankle instability (FAI) and surgical treatment (ST) on postural stability and leg stiffness during vertical-drop landing. Method: A total of 21 men participated in this study (normal [NOR]: 7, FAI: 7, ST: 7). We estimated dimensionless leg stiffness as the ratio of the peak vertical ground reaction force and the change in stance-phase leg length. Leg length was calculated as the distance from the center of the pelvis to the center of pressure under the foot. Furthermore, the analyzed variables included the loading rate and the dynamic postural stability index (DPSI; medial-lateral [ML], anterior-posterior [AP], and vertical [V]) in the initial contact phase. Results: The dimensionless leg stiffness in the FAI group was higher than that of the NOR group and the ST group (p = .018). This result may be due to a smaller change in stance-phase leg length (p = .001). DPSI (ML, AP, and V) and loading rate did not show differences according to the types of ankle instability during drop landing (p > .05). Conclusion: This study suggested that the dimensionless leg stiffness was within the normal range in the ST group, whereas it was increased by the stiffness of the legs rather than the peak vertical force during vertical-drop landing in the FAI group. Identifying these potential differences may enable clinicians to assess ankle instability and design rehabilitation protocols specific for the impairment.

한 개의 크랙을 가진 회전하는 패킷 블레이드 시스템의 진동해석 (Modal Analysis of a Rotating Packet Blade System having a crack)

  • 권승민;유홍희
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2009년도 춘계학술대회 논문집
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    • pp.266-271
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    • 2009
  • A modeling method for the modal analysis of a multi-packet blade system having a crack undergoing rotational motion is presented in this paper. Each blade is assumed as a slender cantilever beam. The stiffness coupling effects between blades due to the flexibilities of the disc and the shroud are modeled with discrete springs. Hybrid deformation variables are employed to derive the equations of motion. The flexibility due to crack, which is assumed to be open during the vibration, is calculated basing on a fracture mechanics theory. To obtain more general information, the equations of motion are transformed into dimensionless forms in which dimensionless parameters are identified. The effects of the dimensionless parameters related to the angular speed, the depth and location of a crack on the modal characteristics of the system are investigated with some numerical examples.

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Numerical simulation of air discharged in subcooled water pool

  • Y. Cordova ;D. Blanco ;Y. Rivera;C. Berna ;J.L. Munoz-Cobo ;A. Escriva
    • Nuclear Engineering and Technology
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    • 제55권10호
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    • pp.3754-3767
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    • 2023
  • Turbulent jet discharges in subcooled water pools are essential for safety systems in nuclear power plants, specifically in the pressure suppression pool of boiling water reactors and In-containment Refueling Water Storage Tank of advanced pressurized water reactors. The gas and liquid flow in these systems is investigated using multiphase flow analysis. This field has been extensively examined using a combination of experiments, theoretical models, and Computational Fluid Dynamics (CFD) simulations. ANSYS CFX offers two approaches to model multiphase flow behavior. The non-homogeneous Eulerian-Eulerian Model has been used in this work; it computes global information and is more convenient to study interpenetrated fluids. This study utilized the Large Eddy Simulation Model as the turbulence model, as it is better suited for non-stationary and buoyant flows. The CFD results of this study were validated with experimental data and theoretical results previously obtained. The figures of merit dimensionless penetration length and the dimensionless buoyancy length show good agreement with the experimental measurements. Correlations for these variables were obtained as a function of dimensionless numbers to give generality using only initial boundary conditions. CFD numerical model developed in this research has the capability to simulate the behavior of non-condensable gases discharged in water.

衝突水噴流에 의한 高溫面의 沸騰熱流束에 관한 硏究 (A study on the boiling heat flux on high temperature surface by impinging water jet)

  • 이기우;김유
    • 대한기계학회논문집
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    • 제12권1호
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    • pp.81-94
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    • 1988
  • 본 연구에서는 표면상태가 다양한 고온면을 충돌온류에 의하여 냉각하는 방식이 광범위하게 응용되고 있는 점에 유의하여 표면조도, 노즐직경 및 분류속도를 변화시키고 노즐끝에 전열면의 직경과 동일한 원형판을 부착하여 비철액체를 막고 문극내에 온류액체를 강제유동시킴으로써 열전달에 미치는 모든 영향을 실험에 의해 고찰하고 고찰하고 포화수온류에 의한 열류속의 무차원관계식을 도출하는 것을 본 연구의 목적으로 하였다.

볼 베어링의 무차원 형상변수를 이용한 최적 턱 높이 설계 (Optimum Shoulder Height Design using Non-dimensional Shape Variables of Ball Bearing)

  • 최동철;김태완
    • Tribology and Lubricants
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    • 제35권1호
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    • pp.37-43
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    • 2019
  • This paper presents an optimization method to determine the shoulder height of an angular contact ball bearing by 3D contact analysis using nondimensional-shaped variables. The load analysis of the ball bearing is performed to calculate the internal load distributions and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between the ball and inner/outer raceway, 3D contact analyses using influence function are conducted. The nondimensional shoulder height and nondimensional load are defined to give the generalized results. The relationship between the shoulder height and radius of curvature of the shoulder under various loading conditions is investigated in order to propose a design method for the two design parameters. Using nondimensional parameters, the critical shoulder heights are optimized with loads, contact angles, and conformity ratios. We also develop contour maps of the critical shoulder height as functions of internal loads and contact angles for the different contact angles using nondimensional parameters. The results show that the dimensionless shoulder height increased as the contact angle and dimensionless load increased. Conversely, when the conformity ratio increased, the critical shoulder height decreased. Therefore, if the contact angle is reduced and the conformity ratio is increased within the allowable range, it will be an efficient design to reduce the shoulder height of ball bearings.

Effects of Hydraulic Variables on the Formation of Freshwater-Saltwater Transition Zones in Aquifers

  • Park, Nam-sik
    • Korean Journal of Hydrosciences
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    • 제7권
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    • pp.1-8
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    • 1996
  • The location and the shape of a freshwater transition zone in a coastal aquifer are affected by many hydraulic variables. To data most works to determine the effects of these variables are limited to qualitative comparison of transiton zones. In this work characteristics of transition zones are analyzed quantitatively. The investigation is limited to a steady-state transition zones. Three dimensionless variables are defined to represent characteristics of steady-state transition zones. They are maximum introsion length, thickness, and degree of stratification. Effects of principal hydraulic variables (velocity and dispersivity) on these characteristics are studied using a numerical model. Dimensional analysis is used to systematically analyze entire model results. Effects of velocity and dispersivity are seem clearly. From this study, increase in velocity is found to cause shrinkage of transition zones. This observation contradicts claims by some that, because dispersion is proportional to velocity, increase in velocity would cause expansion of transition zones.

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