• Title/Summary/Keyword: Hydrodynamic pressure

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Hydrodynamic Investigation of a Floating-type Monoleaflet Polymer Valve under Steady Flow Condition (정상유동에서 유동형 단엽폴리머 인공판막의 수력학적 성능평가)

  • 김준우;박복춘
    • Journal of Biomedical Engineering Research
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    • v.17 no.1
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    • pp.49-60
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    • 1996
  • An experimental investigation was performed under steady flow condition to assess hydrodynamic performance of floating-type monoleaflet polymer valves (MLPV) withdifferent leaflet thickness. The St. Jude Medical valve (SJMV) was also used for comparison test. Pressure drops of MLPVS are larger than those for other types of polymer valves and mechanical valves. Furthermore, the thicker is the leaflet thickness of the polymer valve, the larger are the corresponding pressure drop. The velocity profiles for MLPs reveal a large reversed flow region downward to the valve position. The maximum wall shear stresses of MLPVS at a flow rate of $30{\ell}$/min are in the range 50-130 dyn/$cm^2$, and the corresponding maximum Reynolds shear stresses are in the range of 100-500 dyn/$cm^2$, respectively, which are beyond the allowable limit clinically. In contrast, floating-type monoleaflet polymer valves show better hydrodynamic performance in leakage volume. From the designing point of view, it may be concluded that the optimum thickness of leaflet for better hydrodynamic performance is one of the Important parameters.

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Hydrodynamic Investigation of a Floating-type Monoleaflet Polymer Heart Valve under Steady Flow Condition (정상유동에서 유동형 단엽폴리머 인공심장판막의 수력학적 성능평가)

  • Pak, Bock-Choon;Kim, Joon-Woo;Baek, Byoung-Joon;Min, Byoung-Goo
    • Proceedings of the KOSOMBE Conference
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    • v.1995 no.05
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    • pp.241-246
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    • 1995
  • An experimental investigation was performed under steady flow condition to assess hydrodynamic performance of floating-type monoleaflet polymer valves (MLPV) with different leaflet thickness. The St. Jude Medical valve (SJMV) was also used for comparison tests. Pressure drops of MLPVs are larger than those for other types of polymer valves and mechanical valves. Furthermore, the thicker is the leaflet thickness of a polymer valve, the larger arc the corresponding press drop. The velocity profiles for MLPV reveal a large reversed flow region downward to the valve position. The maximum wall shear stresses of MLPVs at a flow rate of 30 l/min are in the range $54-130\;dyn/cm^2$, and the corresponding maximum. Reynolds shear stresses are in the range of $100-500\;dyn/cm^2$, respectively. Both arc beyond the allowable limit clinically. In contrast, floating-type monoleaflet polymer valves show better hydrodynamic performance in leakage volume. From the designing point of view, it can be concluded that the optimum thickness of leaflet for better hydrodynamic performance is one of the important parameters.

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An investigation into the thermo-elasto-hydrodynamic effect of notched mechanical seals

  • Meng, Xiangkai;Qiu, Yujie;Ma, Yi;Peng, Xudong
    • Nuclear Engineering and Technology
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    • v.54 no.6
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    • pp.2173-2187
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    • 2022
  • A 3D thermo-elasto-hydrodynamic model is developed to analyze the sealing performance of a notched mechanical seal applied in the reactor coolant pump. In the model, the generalized Reynolds equation, the energy equation coupled with notch heat balance equation, the heat conduction equations, and the deformation equations of the sealing rings are iteratively solved by the finite element method. The film pressure and temperature distribution are obtained, and the deformation of the sealing rings is revealed to study the mechanism of the notched mechanical seals. A parameterized study is conducted to analyze the sealing performance under different operating conditions. As a comparison, the sealing performance of non-notched seals is also studied. The results show that the hydrostatic effect is dominant in the load-carrying capacity of the fluid film due to the radial mechanical and thermal deformations. The notch can cool the fluid film and influence the thermal deformation of seal rings. The sealing performance is sensitive to the pressure difference, ambient temperature, and rotational speed. It is suggested to set the notches on the softer sealing rings to acquire the greater hydrodynamic effect. Compared with the non-notched, the notched end face holds a better lubrication performance, especially under lower rotational speed.

A Study on Hydrodynamic Stiffness Characteristics of Air Bearing for High Speed Spindle

  • Lee, J.Y.;Lee, D.W.;Seong, S.H.;Lee, Y.C.
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2002.10b
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    • pp.115-116
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    • 2002
  • This study was carried out as one of efforts to overcome difficulties in air bearing design due to low stiffness and low damping. Hydrodynamic effects on hydrodynamic stiffness of a fluid film in a high speed air bearing with tow-row air sources are investigated. The hydrodynamic effects by the high speed over DN 1,000,000 and eccentricity of a proceeding which are not considered in conventional design of an air bearing need to be reconsidered. The hydrodynamic effects, which dominantly influence on the load capacity of air bearing, are caused mainly by proceeding speed, eccentricity, and the source positions. The two-row source arrangement in the air bearing produces quite unique hydrodynamic effects with respect to pressure distribution of the air film. Optimal arrangement of the two-row sources improves performance of an air bearing in film reaction force and loading capacity of high speed spindles. This study compares the pressure distribution by numerical simulation as a function of eccentricity of proceeding and the source positions. The air source position 1/7L form one end of an air bearing was found to be superior to source position of 1/4L. The dynamic stiffness were obtained using a two-dimensional cutting method which can directly measure the cutting reaction forces and the displacements of the spindle in two directions using a tool dynamometer and transducer sensors. Heat generation in the air film can not be negligible over the speed of DN 2,000,000. In order to analysis effects of heat generation on the characteristics of air bearing, high cooling bearing spindle and low cooling bearing spindle were tested and compared. Characteristics of the frequency response of shaft and motion of run out errors were different for the spindle. The test results show that, in the case of low cooling bearing spindle, the stiffness became smaller due to heat generation. The results, which were obtained for high speed region, may be used as a design information for spindle which can be applied to precision devices such as ultra precision grinding and ultra high speed milling.

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Application of Hydrodynamic Pressure for Three­dimensional Earthquake Safety Analysis of Dam Intake Towers (댐 취수탑 3차원 내진안전성 평가에서의 동수압 적용방법에 관한 연구)

  • Song, Gwang-Seok;Min, Kyoung-Uk;Bea, Jungju;Lee, Jeeho
    • Journal of the Earthquake Engineering Society of Korea
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    • v.22 no.3
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    • pp.139-147
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    • 2018
  • In the present study, effective hydrodynamic pressure modeling methods for three-dimensional earthquake safety analysis of a dam intake tower structure are investigated. Time history analysis results using the Westergaard added mass and Chopra added mass methods are compared with the one by the CASI (Coupled Acoustic Structural Interaction) method, which is accepted as giving almost exact solutions, to evaluate the difference in displacement response, stress and dynamic eccentricity. The 3D time history analysis of a realistic intake tower, which has the standard geometry widely used in Korea, shows that the Chopra added mass method gives similar results in displacement and stress and less conservative results in dynamic eccentricity to CASI ones, while the Westergaard added mass yields much more conservative results in all measures. This study suggests to use the CASI method directly for three-dimensional earthquake safety analysis of a dam intake tower, if computationally possible.

Finite Element Analysis of a Coupled Hydrodynamic Journal and Thrust Bearing in a Computer Hard Disk Drive (컴퓨터 하드디스크 드라이브에 사용되는 저널과 스러스트가 연성된 유체 동압 베어링의 유한 요소 해석)

  • Kim, Hakwoon;Lee, Sanghoon;Jang, Gunhee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.1 s.94
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    • pp.87-95
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    • 2005
  • This paper proposes a method to calculate the characteristics of a coupled hydrodynamic journal and thrust bearing of a HDD spindle motor. The governing equations for the journal and thrust bearings are the two dimensional Reynolds equations in $\theta z$ and $ r\theta$ planes, respectively. Finite element method is appropriately applied to analyze the coupled journal and thrust bearing by satisfying the continuity of mass and pressure at the interface between the journal and thrust bearings. The pressure in a coupled bearing is calculated by applying the Reynolds boundary condition and compared with that by using the Half-Sommerfeld boundary condition. The static characteristics are obtained by integrating the pressure along the fluid film. The flying height of spindle motor is measured to verify the proposed analytical result. This research shows that the proposed method can describe HDB in a HDD system more accurately and realistically than the separate analysis of a journal or thrust bearing.

Analysis of Earthquake Responses of a Floating Offshore Structure Subjected to a Vertical Ground Motion (해저지진의 수직지반운동에 의한 부유식 해양구조물의 지진응답 해석기법 개발)

  • Lee, Jin Ho;Kim, Jae Kwan;Jin, Byeong Moo
    • Journal of the Earthquake Engineering Society of Korea
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    • v.18 no.6
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    • pp.279-289
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    • 2014
  • Considering a rigorously fluid-structure interaction, a method for an earthquake response analysis of a floating offshore structure subjected to vertical ground motion from a seaquake is developed. Mass, damping, stiffness, and hydrostatic stiffness matrices of the floating offshore structure are obtained from a finite-element model. The sea water is assumed to be a compressible, nonviscous, ideal fluid. Hydrodynamic pressure, which is applied to the structure, from the sea water is assessed using its finite elements and transmitting boundary. Considering the fluid-structure interaction, added mass and force from the hydrodynamic pressure is obtained, which will be combined with the numerical model for the structure. Hydrodynamic pressure in a free field subjected to vertical ground motion and due to harmonic vibration of a floating massless rigid circular plate are calculated and compared with analytical solutions for verification. Using the developed method, the earthquake responses of a floating offshore structure subjected to a vertical ground motion from the seaquake is obtained. It is concluded that the earthquake responses of a floating offshore structure to vertical ground motion is severely influenced by the compressibility of sea water.

Dynamic Characteristics of a Coupled Journal and Thrust Hydrodynamic Bearing in a HDD Spindle System Due to Groove Location (HDD 스핀들 시스템에 사용되는 저널과 트러스트가 결합된 유체 동압 베어링의 홈 위치에 따른 동특성 해석)

  • 윤진욱;장건희
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11a
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    • pp.304-311
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    • 2001
  • This research numerically analyzes the dynamic characteristics of a coupled journal and thrust hydrodynamic bearing due to its groove location which has the static load due to the weight of a rotor in the axial direction and the dynamic load due to its mass unbalance in the radial direction. The Reynolds equation is transformed to solve a plain member rotating type of journal bearing(PMRJ), a grooved member rotating type of journal bearing (GMRJ), a plain member rotating type of thrust bearing (PMRT) and a grooved member rotating type of thrust bearing (GMRT). FEM is used to solve the Reynolds equations in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or floating height of a rotor, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This research shows that the groove location affects the pressure distribution in the fluid film and consequently the dynamic performance of a HDD spindle system.

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Finite Element Analysis of a Coupled Hydrodynamic Journal and Thrust Bearing in a Computer Hard Disk Drive (컴퓨터 하드디스크 드라이브에 사용되는 저널과 스러스트가 연성된 유체 동압 베어링의 유한 요소 해석)

  • Kim, Hak-Woon;Lee, Sang-Hoon;Jang, Gun-Hee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2004.11a
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    • pp.846-852
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    • 2004
  • This paper proposes a method to calculate the characteristics of a coupled hydrodynamic journal and thrust bearing of a HDD spindle motor. The governing equations for the journal and thrust bearings are the two dimensional Reynolds equations in ${\theta}z$ and $r\theta$ planes, respectively. Finite element method is appropriately applied to analyze the coupled journal and thrust bearing by satisfying the continuity of mass and pressure at the interface between the journal and thrust bearings. The pressure in a coupled bearing is calculated by applying the Reynolds boundary condition and compared with that by using the Half-Sommerfeld boundary condition. The static characteristics are obtained by integrating the pressure along the fluid film. The flying height of spindle motor is measured to verify the proposed analytical result. This research shows that the proposed method can describe HDB in a HDD system more accurately and realistically than the separate analysis of a journal or thrust bearing.

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Seismic performance of hybrid isolation plate-shell integrated concrete LSS

  • Lei Qi;Xuansheng Cheng;Shanglong Zhang;Yuyue Bu;Bingbing Luo
    • Earthquakes and Structures
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    • v.27 no.1
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    • pp.57-67
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    • 2024
  • To assess the seismic performance of Plate-Shell Integrated Concrete Liquid-Storage Structure (PSICLSS), a scaled test model was constructed. This model incorporated a hybrid isolation system, which combined shape memory alloy (SMA), lead-cored rubber isolation bearing (LRB) and sliding isolation bearing (SB). By conducting shaking table test, the dynamic responses of both non-isolated and hybrid-isolated PSICLSS were analyzed. The results show that the hybrid isolation system can effectively reduce the acceleration and displacement responses of the structure. However, it also results in an increase in local hydrodynamic pressure and liquid sloshing height. Under extreme earthquake action, the displacement of isolation layer is small. When vertical ground motion is taken into account, the shock absorption rate of horizontal acceleration decreases. The peak hydrodynamic pressure increases significantly, and the peak hydrodynamic pressure position also changes. The maximum displacement of isolation layer increases, the residual displacement decreases.