• Title/Summary/Keyword: Reattachment

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THE EARLY EFFECT OF DIFFERENT ROOT TREATMENT MODALITIES ON CONNECTIVE TISSUE ATTACHMENT IN RATS (치근면 처치시 결합조직 부착에 관한 초기효과의 조직병리학적 연구)

  • Moon, Sang-Joon;Lee, Chong-Heon;Lee, Jae-Hyun
    • Journal of Periodontal and Implant Science
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    • v.24 no.1
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    • pp.109-119
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    • 1994
  • An essential fact in the regeneration of new periodontal tissue after periodontal therapy is the reattachment of collagen fibers to the tooth. Two phenomena play a fundamental role in preventing new connective tissue attachment to the exposed root surface ; 1) The apical migration of the junctional epithelium 2) The contamination of cementum by toxic substances, especially endotoxins. Authors have used rat submucosal implantation of root sections to study the connective tissue healing to periodontally diseaed root, previously planed and demineralized with citric acid and tetracycline- HCl. The results were obtained as follows. 1. The connective tissue attachment was increased in tetracycline, citric acid, non disease, scaling and root planing order and inflammatory reaction was seen in the rat teeth, no treatment group. 2. Collagen fiber attachment at the dentin surface was more increased than cementum surface 3. In 2 week of citric acid and tetracycline-HCl specimens, osteoid was seen near the fibrotic band. 4. In the MT view, collagen fiber formation was increased with time and the numerous collagen fiber and connective tissue was more densly attached to the tooth surfaces in the tetracycline-HCl group than the citric acid group.

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Rectangular prism pressure coherence by modified Morlet continuous wavelet transform

  • Le, Thai-Hoa;Caracoglia, Luca
    • Wind and Structures
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    • v.20 no.5
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    • pp.661-682
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    • 2015
  • This study investigates the use of time-frequency coherence analysis for detecting and evaluating coherent "structures" of surface pressures and wind turbulence components, simultaneously on the time-frequency plane. The continuous wavelet transform-based coherence is employed in this time-frequency examination since it enables multi-resolution analysis of non-stationary signals. The wavelet coherence quantity is used to identify highly coherent "events" and the "coherent structure" of both wind turbulence components and surface pressures on rectangular prisms, which are measured experimentally. The study also examines, by proposing a "modified" complex Morlet wavelet function, the influence of the time-frequency resolution and wavelet parameters (i.e., central frequency and bandwidth) on the wavelet coherence of the surface pressures. It is found that the time-frequency resolution may significantly affect the accuracy of the time-frequency coherence; the selection of the central frequency in the modified complex Morlet wavelet is the key parameter for the time-frequency resolution analysis. Furthermore, the concepts of time-averaged wavelet coherence and wavelet coherence ridge are used to better investigate the time-frequency coherence, the coherently dominant events and the time-varying coherence distribution. Experimental data derived from physical measurements of turbulent flow and surface pressures on rectangular prisms with slenderness ratios B/D=1:1 and B/D=5:1, are analyzed.

A Study on the Mass Transfer from a Square Cylinder Using Naphthalene Sublimation Technique (나프탈렌승화법을 이용한 사각관 주위에서의 물질전달에 관한 연구)

  • 유성연
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1300-1310
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    • 1990
  • Naphthalene sublimation technique is employed to investigate the mass transfer processes from a square cylinder at various Reynolds numbers and various angles of attack. Distribution of the local mass transfer coefficients on each face of the cylinder changes dramatically with the angle of attack. Such variation of local mass transfer rates closely connected with the complex flow phenomena such as stagnation, acceleration, separation, reattachment and vortex shedding. The average Sherwood number has a minimum value at 12.deg.-13.deg., and a maximum value at a=20.deg.-25.deg. A comparison of present mass transfer measurement with other heat transfer measurements, using the heat/mass transfer analogy, shows good agreement in average transfer rates, same trend but notable differences in local values. Therefore, naphthalene sublimation technique can be adopted to explore heat transfer processes in the complex flow situations, which is considered to be hardly possible with the conventional heat transfer measurements.

Effects of Reynolds Number on Flow and Heat/Mass Characteristics Inside the Wavy Duct (Reynolds 수에 따른 꺾어진 덕트에서 열/물질전달 특성 고찰)

  • 장인혁;황상동;조형희
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.10
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    • pp.809-820
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    • 2003
  • The present study investigates effects of flow velocity on the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewall are determined by using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The aspect ratio and corrugation angle of the wavy duct is fixed at 7.3 and 145$^{\circ}$ respectively, and the Reynolds numbers, based on the duct hydraulic diameter, vary from 100 to 5,000. The results show that there exist complex secondary flows and transfer processes resulting in non-uniform distributions of the heat/mass transfer coefficients on the duct side walls. At low Re (Re<1000), relatively high heat/mass transfer regions like cell shape appear on both pressure and suction side wall due to the secondary vortex flows called Taylor-Gortler vortices perpendicular to the main flow direction. However, at high Re (Re>1000), these secondary flow cells disappear and boundary layer type flow characteristics are observed on pressure side wall and high heat/mass transfer region by the flow reattachment appears on the suction side wall. The average heat/mass transfer coefficients are higher than those of the smooth circular duct due to the secondary flows inside wavy duct. And also friction factors are about two times greater than those of the smooth circular duct.

Behavior and flow characteristics of pulsating flow in the jetflow region through cylindrical chokes (유압관로내 원통형 초크의 분류영역에서 맥동유동의 거동과 유동특성에 관한 연구)

  • ;;Moh, Y. W.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.11
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    • pp.3041-3053
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    • 1995
  • Cylindrical chokes are used widely as components of hydraulic equipments. The dynamic characteristics between flowrate and pressure drop through the cylindrical chokes were discussed by the frequency characteristics of the chokes. It was assumed no pressure recovery occurred near the downstream of the choke. The pulsating jetflow from the outlet of cylindrical chokes show very complex behaviours which are quite different from the steady jet flow but it's not clarified quantitatively. In order to utilize the chokes as a flowmeter, it is indispensable to discuss the estimation of the dynamics of pressure drop in the downstream jetflow region of cylindrical chokes. In this experimental study, it is clarified that the reattachment length depended on pressure wave is compared with it depended on velocity wave. A pulsating flow is verified by visualization method. In the present study, the flow characteristic variables of laminar pulsating flow are investigated analytically and experimentally in a circular pipe. Characteristic parameters of the ratios of inertia(.PHI.$_{t,1}$) and viscous(.PHI.$_{z,1}$) term to pressure term are introduced to describe the flow pattern of laminar pulsating flow. flow.low.

Effects of Length-to-Diameter Ratio on the Three-Dimensional Flow Within an Injection Hole Normally Oriented to the Mainflow (분사구멍의 길이가 수직 분사구멍 내부에서의 3차원 유동에 미치는 영향)

  • Lee, Sang Woo;Joo, Seong Kuk
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.9
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    • pp.1255-1266
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    • 1998
  • Effects of a length-to-diameter ratio, L/D, on the three-dimensional flow and aerodynamic loss within an injection hole, which is normally oriented to the mainflow, have been investigated by using a straight five-hole probe. The length-to-diameter ratio of the injection hole is varied to be 0.5 and 2.0 for blowing ratios of 0.5, 1.0 and 2.0. Regardless of the blowing ratio, flows within the hole and at the jet exit are strongly affected by the length-to-diameter ratio. In the case of L/D=0.5, the inside flow is considerably influenced by the mainflow, and the exit flow variation is found to be the greatest. The aerodynamic loss in this case is usually attributed to jet -mainflow interactions. In the case of L/D=2.0, the flow separation and reattachment in the inlet region are completely separated from the complicated exit flow, and the aerodynamic-loss production is mainly due to the inlet flow separation.

Hypersonic Aero-Heating Ground-Test Simulation Technique

  • Li, Ruiqu;Yao, Dapeng;Sha, Xinguo;Gong, Jian
    • International Journal of Aerospace System Engineering
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    • v.2 no.2
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    • pp.50-53
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    • 2015
  • It would encounter some complicated flow fields, such as transition, separation, reattachment and disturbances, in the hypersonic flight. Thus, it is difficult to theoretically analyze the hypersonic aerothermodynamics effects, so that the ground-test simulation is thought of as one of the most important methods to improve the understanding level of the hypersonic aerothermodynamics. However, the aero-heating tests could not simulate all aerodynamics and geometry parameters in the real flight due to the differences between the experimental environments supplied by the ground facilities and the flight, so that the feasible technique for the ground-test simulation of the hypersonic aerothermodynamics effects is required to be advanced. The key parameters that are especially required to simulate for aero-heating tests are analyzed and one detailed approach is suggested to perform the experimental investigation on the hypersonic aero-heating effects in the ground facilities in this paper, and the tests are performed in the FD-20 gun tunnel of CAAA (China Academy of Aerospace Aerodynamics) to give out the data which could be used to confirm the equation from the theoretical analysis.

Numerical Analysis on the Turbulent Flow of Compressor Cascades at High Incidence Angle

  • Jeong, Soo-in;Jeong, Gi-ho;Kim, Kui-soon
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.03a
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    • pp.825-830
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    • 2004
  • A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc (DCA) compressor cascades. Two types of double-circular-arc cascades were used in this analysis. The appropriate turbulence model for compressor analysis was selected among the conventional turbulence models such as Baldwin-Lomax, k-$\varepsilon$ and k-$\varepsilon$ models. The results of current study were compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE/PWIM algorithm for collocated grid and hybrid scheme for the convective terms were the main features of numerical tools. As commonly known, turbulence modeling is very important for the prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. For selection of turbulence model, 2-D analysis was performed. And then, k-$\varepsilon$ turbulence model with wall function chosen as the reasonable turbulence model for 3-D calculation was used to increase the efficiency of computation times. A reasonable result of 3-D flow pattern passing through the double-circular-arc cascade was obtained.

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Design Modification and Correlation Verification between Reattachment Flow of Dispersed Jet and Local Thinning of Feedwater Heater (충돌로 인해 분산된 2상 제트스팀의 재부착 현상과 국부 감육 상관관계 규명 및 설계개선에 관한 연구)

  • Kim, Hyung-Joon;Kim, Kyung-Hoon;Hwang, Kyeong-Mo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.21 no.9
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    • pp.483-495
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    • 2009
  • Feedwater heaters of many nuclear power plants have recently experienced severe wall thinning damange, which will increase as operating time progresses. Several nuclear power plants in Korea have experienced wall thinning damage in the area around the impingement baffle-installed downstream of the high pressure turbine extraction stream line-inside number 5A and 5B feedwater heaters. At that point, the extracted steam from the high pressure turbine is two phase fluid at high temperature, high pressure, and high speed. Since it flows in reverse direction after impinging the impingement baffle, the shell wall of the number 5 high pressure feedwater heater may be affected by flow-accelerated corrosion. This paper describes operation of experience and numerical analysis composed similar condition with real high pressure feedwater heater. This study applied squared, curved and new type impingement baffle plates to feedwater heater same as previous study. In addition, it shows difference of pressure distribution and value between single phase and two phase based on experience and numerical analysis.

An investigation on heat transfer effects of two dimensional plane jet attaching offseted obliqued wall (단이 진 경사벽면에 부착되는 2차원 평면제트의 열전달 효과에 관한 연구)

  • Yun, Sun-Hyeon;Lee, Dae-Hui;Sim, Jae-Gyeong;Song, Heung-Bok
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.10
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    • pp.1314-1325
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    • 1997
  • Experiments have been conducted to determine the flow and heat transfer characteristics for a two-dimensional turbulent wall attaching offset jet at different oblique angles to a flat surface. The distributions of the wall static pressure coefficient and time-averaged reattachment position for various offset ratios and oblique angles have been measured. The local Nusselt number distributions on the plate surface were also measured using liquid crystal as a temperature indicator. The new hue-capturing technique utilizing a true color image processing system was used to accurately determine the temperature of the liquid crystal. The experiments were carried out at Reynolds number, Re (based on D) of from 7300 to 21,300 with offset ratio, H/D from 2.5 to 10, and oblique angle, .alpha. from 0 deg. to 400 deg..