• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1674-1685
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• 2022

The ball valve is an important device in the pipeline transportation system of nuclear power plants. Its operational stability and safety directly affect the normal working of nuclear power plants. In this study, the transient numerical simulation of the opening and closing process of a ball valve was conducted on the basis of the flow interruption capability experiment of the ball valve by using the moving mesh method and inlet and outlet variable boundary conditions. The flow rate and pressure difference with time of the opening and closing process of the ball valve were studied. The internal flow characteristics of the ball valve under different relative openings were analyzed in conjunction with the typical back-step flow structure. Results show that the transient numerical results agree well with the experimental results. The internal flow characteristics of the ball valve are similar at the same opening during opening and closing process. At small opening, the spool and outlet channels easily form a back-step flow structure. The disappearance and generation of backflow vortices during opening and closing occur at 85% opening and 75% opening, respectively. With the decrease in opening degree, the difference in vortex core area in the flow channel of the ball valve spool in the opening and closing process gradually appears. The research results provide some reference value for the design and optimization of ball valves.

• Journal of Advanced Marine Engineering and Technology
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• 제32권6호
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• pp.923-930
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• 2008

The butterfly valve is widely used in the industrial field as an on-off or a flow control valve. When the butterfly valve is used as a flow control valve. cavitation sometimes occurs in the range of high flow rate because of the small valve opening. Therefore. the pressure loss and the cavitation characteristics are investigated by use of a commercial CFD code. The results show that the possibility of cavitation occurrence in the cryogenic butterfly valve is very high in the case of valve opening angle below 10 degree and incident velocity over 6m/s. By increasing the inlet velocity at 10 degree of valve opening angle. the value of loss coefficient increased. However. by increasing the inlet velocity at 50 degree of valve opening angle. the value of loss coefficient decreased.

• Steel and Composite Structures
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• 제18권3호
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• pp.641-657
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• 2015

Application of reduced web beam section (RWBS) as a sacrificial fuse element has become a popular research field in recent years. Weakening of beam web in these connections may cause local web buckling around the opening area which can affect cyclic behavior of connection including: maximum load carrying capacity, strength degradation rate, dissipated energy, rotation capacity, etc. In this research, effect of local web buckling on the cyclic behavior of RWBS connections is investigated using finite element modeling (FEM). For this purpose, a T-shaped moment connection which has been tested under cyclic loading by another author is used as the reference model. Fracture initiation in models is simulated using Cyclic Void Growth Model (CVGM) which is based on micro-void growth and coalescence. Included in the results are: effect of opening corner radii, opening dimensions, beam web thickness and opening reinforcement. Based on the results, local web buckling around the opening area plays a significant role on the cyclic behavior of connection and hence any parameter affecting the local web buckling will affect entire connection behavior.

• 한국정밀공학회지
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• 제14권4호
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• pp.136-144
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• 1997

The characteristics of fatigue crack growth subject to out-of-plane bending fatigue are studied in terms of crack opening behavior by using pre-cracked smooth specimens. Crack opening stress is measured by an elastic compliance method which may precisely and continuously provide many date using strain gages during experiment. The results of the short crack and the long crack arranged by crack closure concept show that the effective stress gange ratio of short crack is grester than that of long crack, and ano- malous growth behavior of short crack may be elucidated by the variation of crack opening stress. When the variation of fatigue crack growth rate is arranged versus effective stress intensity factor range. Iinear relation is held also for the short crack. It shows that growth behavior of short crack can be quantitatively represent- ed by the fracture mechanics parameter using effective stress intensity factor range.

• Journal of Periodontal and Implant Science
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• 제35권4호
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• pp.813-822
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• 2005

The predictable outcome of implant placement in the atrophic maxilla with sinus floor elevation procedure(osteotome sinus floor elevation technique and window opening technique) is well documented. Aim of this study was to evaluate the efficacy of $Br{\aa}nemark$ Ti-Unite implant system and ITI SLA implant system placed in the atrophic posterior maxilla with sinus floor elevation procedure. Eighty patients received placement of $Br{\aa}nemark$ Ti-Unite implants(195 implants) in their atrophic posterior Maxilla with sinus floor elevation procedure(153 osteotome sinus floor elevation technique and 42 window opening procedure). Fifty patients received placement of ITI SLA implants(83 implants) in their atrophic posterior Maxilla with sinus floor elevation procedure(77 osteotome sinus floor elevation technique and 6 window opening procedure). Chart review were taken from each patient. The total failed implants were seven and the total implant survival rate was 96.4% in $Br{\aa}nemark$ Ti-Unite system. The total failed implants were one and the total implant survival rate was 98.8% in ITI SLA system. The implant survival rate with osteotome technique was 96% and 97.6% with window opening in $Br{\aa}nemark$ Ti-Unite system. The implant survival rate with osteotome technique was 98.7% and 100% with window opening. The implant survival rate with osteotome technique was 96% and 97.6% with window opening in ITI SLA system. The results of this evaluation show that the placement of $Br{\aa}nemark$ Ti-Unite system as well as ITI SLA system is a reasonable treatment option for patients with the atrophic posterior maxillary area.

• 한국터널지하공간학회 논문집
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• 제23권4호
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• pp.265-280
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• 2021

도시화로 인한 인구의 집중은 도심지 지하공간 개발을 촉발시켰으며, 그로인해 진동과 소음으로 인한 환경문제 및 민원이 많은 발파공법보다 진동과 소음에 대한 영향이 없는 TBM공법에 많은 관심을 가지게 되었다. 이런 이유로 TBM에 대한 많은 연구가 진행되었으나 TBM 장비의 커터헤드 개구부가 굴착되는 지반조건에 따라 폐색되는 특성에 대한 연구는 미비한 실정이다. 그렇기 때문에 쉴드 TBM 굴진 시 커터헤드 개구부의 폐색현상을 연구하기 위해 축소모형시험을 진행하였다. 쉴드 TBM 장비의 커터헤드 개구부 폐색현상을 규명하기 위해 점토비(10%, 30%, 50%), 커터헤드 개구율(30%, 50%, 60%), 커터헤드 회전방향(일방향, 양방향) 및 회전속도(3 RPM, 6 RPM)을 변수로 실험조건을 달리하여 36가지의 Case에 대해 축소모형실험을 진행하였다. 쉴드 TBM 폐색현상에 대한 축소모형실험 결과, 점토가 함유된 지반 조건은 양방향 회전이 일방향 회전보다 폐색영향이 증가하고 커터헤드의 회전속도가 낮을수록 폐색영향이 적은 것으로 나타났다. 그에 따라 지반 굴착 시 지반조건을 고려하여 커터헤드 회전 방향, 회전 속도 및 개구율을 산정한다면 폐색 영향을 저감할 수 있을 것이다. 폐색영향이 저감됨에 따라 공사기간의 단축에 효과적일 것으로 사료된다. 따라서 본 연구는 해당연구가 전무한 국내 쉴드 TBM 시공 시 그 활용에 있어 중요한 자료가 될 것으로 판단된다.

• 한국유체기계학회 논문집
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• 제9권3호
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• pp.22-28
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• 2006

The discharge coefficient in segmental wedge haying ninety degrees yeller angle for the five kinds of opening ratio with differential pressure taps located at both upstream and downstream of one diameter of pipe was measured. Main purpose of this work is placed on specifying the characteristic of discharge coefficient of a segmental wedge used as a primary element of flow metering devices, and suggestion for the fixed location of pressure taps useful. Although the range of the opening ratio over this work is more expanded than previous studies. The opening ratios of segmental wedge, namely 0.3, 0.4, 0.5, 0.6 and 0.7 were investigated. The Reynolds number based on the spool inside diameter ranges from 12,000 to 380,000.

• 대한전자공학회논문지
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• 제21권1호
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• pp.13-24
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• 1984

본고는 기존의 시내및 시외전화교환망을 데이터 통신에 개방할 목적으로 이 교환망의 정송품질을 측정하고 또한 분석한 것을 소개한 것이다. 시험에 있어서 전화교환경에서 발생하는 랜덤잡음 및 임펄스성 잡음을 조사하고 또 기존전화망의 전송품질을 나타내는 빌오율 및 부록오율을 측정하였다. 본 측정 및 분석을 기초로 하여 전체교환주에서의 실시 가능한 최고 데이터 전송속도를 권고하고 또 공중교환전화망을 데이터 전송에 개방하는데 있어서의 그 가능성을 조사하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.25-28
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• 2004

The purpose of this paper is to present essential numerical data of FCV(Flow rate Control Valve) which is used in a projectile ejection system for a underwater vehicle. A commercial CFD code is applied to analyze the 3 dimensional viscous compressible flow field within the FCV as four cases of opening rate, 25, 50, 75, and $100\%$. The flow coefficient of each cases are mainly calculated. And other characteristics such as the location of shock wave and total temperature distribution are also determined.

• 한국자동차공학회논문집
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• 제4권3호
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• pp.92-101
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• 1996

In a gasoline engine, the characteristics of air flow is very important not only for the design of the intake system geometry bout also for the accurate measurement of the induction air mass. In this study, an air flow rate measurement of the induction air mass. In this study, an air flow rate measurement was conducted by using the hot wire flow meter at the upstream of the intake port and the throttle. At the upstream of the throttle, the overshoot phenomena of the air flow rate by fast throttle opening were analyzed with choked flow. At the upstream of the intake port, the cylinder variation of the air flow rate and the difference between fast throttle opening and closing were showed during the unsteady state by the throttle step change. The results of this study can be used for the design of the throttle valve geometry and cylinder by cylinder control.