• 제목/요약/키워드: internal stability

검색결과 1,118건 처리시간 0.025초

Sloshing suppression by floating baffle

  • Kang, Hooi-Siang;Md Arif, Ummul Ghafir;Kim, Kyung-Sung;Kim, Moo-Hyun;Liu, Yu-Jie;Lee, Kee-Quen;Wu, Yun-Ta
    • Ocean Systems Engineering
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    • 제9권4호
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    • pp.409-422
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    • 2019
  • Sloshing is a phenomenon which may lead to dynamic stability and damages on the local structure of the tank. Hence, several anti-sloshing devices are introduced in order to reduce the impact pressure and free surface elevation of liquid. A fixed baffle is the most prevailing anti-sloshing mechanism compared to the other methods. However, the additional of the baffle as the internal structure of the LNG tank can lead to frequent damages in long-term usage as this structure absorbs the sloshing loads and thus increases the maintenance cost and downtime. In this paper, a novel type of floating baffle is proposed to suppress the sloshing effect in LNG tank without the need for reconstructing the tank. The sloshing phenomenon in a membrane type LNG tank model was excited under sway motion with 30% and 50% filling condition in the model test. A regular motion by a linear actuator was applied to the tank model at different amplitudes and constant period at 1.1 seconds. Three pressure sensors were installed on the tank wall to measure the impact pressure, and a high-speed camera was utilized to record the sloshing motion. The floater baffle was modeled on the basis of uniform-discretization of domain and tested based on parametric variations. Data of pressure sensors were collected for cases without- and with-floating baffle. The results indicated successful reduction of surface run-up and impulsive pressure by using a floating baffle. The findings are expected to bring significant impacts towards safer sea transportation of LNG.

심한 하악골 전돌증 환자의 외과적 치험례 (SURGICAL CORRECTION OF SEVERE MANDIBULAR PROGNATHISM BY OBWEGESER II AND RIGID INTERNAL FLXATION)

  • 이근호;권대근;장도근;이상한
    • Maxillofacial Plastic and Reconstructive Surgery
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    • 제16권1호
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    • pp.33-42
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    • 1994
  • 본교실에서는 심한 하악골 전동증 환자 5례에서 Obwegeser II method와 과두 위치 보존술 및 견고한 골간 고정을 상요하여 추적조사결과 다음과 같은 결과를 얻었다. 1. Obwegeser II method는 15mm이상의 하악골 후방이동이 요구되거나 심한 개교합의 외과적교정시에 원심골편을 수동적으로 이동시킬 수 있는 방법이라 판단된다. 2. 술후 하악과두의 위치 변화가 많은 증례 V에서 술직후 비교적 많은 재발을 경험하였다. 3. 하악과두위치의 보존과 견고한 골간고정을 통하여 악간고정기간의 단축과 술후 안정성 및 심미적 기능적 개선을 얻었다.

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초고온가스로용 Alloy 617의 불순물 함유 헬륨/공기 중에서 고온부식 특성 (High Temperature Corrosion of Alloy 617 in Impure Helium and Air for Very High-Temperature Gas Reactor)

  • 정수진;이경근;김동진;김대종
    • Corrosion Science and Technology
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    • 제12권2호
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    • pp.102-112
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    • 2013
  • A very high-temperature gas reactor (VHTR) is one of the next generation nuclear reactors owing to its safety, high energy efficiency, and proliferation-resistance. Heat is transferred from the primary helium loop to the secondary helium loop through an intermediate heat exchanger (IHX). Under VHTR environment Alloy 617 is being considered a candidate Ni-based superalloy for the IHX of a VHTR, owing to its good creep resistance, phase stability and corrosion resistance at high temperature. In this study, high-temperature corrosion tests were carried out at 850 - $950^{\circ}C$ in air and impure helium environments. Alloy 617 specimens showed a parabolic oxidation behavior for all temperatures and environments. The activation energy for oxidation was 154 kJ/mol in helium environment, and 261 kJ/mol in an air environment. The scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS) results revealed that there were a Cr-rich surface oxide layer, Al-rich internal oxides and depletion of grain boundary carbide after corrosion test. The thickness and depths of degraded layers also showed a parabolic relationship with the time. A corrosion rate of $950^{\circ}C$ in impure helium was higher than that in an air environment, caused by difference in the outer oxide morphology.

임상간호사의 직무만족 측정도구 개발 (Development of Job Satisfaction Scale for Clinical Nurses)

  • 이병숙;어용숙;이미애
    • 대한간호학회지
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    • 제48권1호
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    • pp.12-25
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    • 2018
  • Purpose: This study was performed to develop the Job Satisfaction Scale for Clinical Nurses (JSS-CN) and verify its validity and reliability. Methods: A preliminary 42-item version of the JSS-CN was developed through literature reviews and in-depth interviews. The draft scale was developed using thirty-seven items selected following content validity evaluation. Finally, thirty-three items with response options on a 5-point Likert scale were selected based on internal consistency reliability and construct validity. Subsequently, the test-retest reliability and convergent validity of the JSS-CN were verified. Results: Six factors, namely, recognition from the organization and professional achievement, personal maturation through the nursing profession, interpersonal interaction with respect and recognition, accomplishment of accountability as a nurse, display of professional competency, and stability and job worth, were identified, which explained 59.7% of the total variance. The JSS-CN's Cronbach's ${\alpha}$ for the total scale was .95, and the intra-class correlation coefficient was .90. The correlation coefficient between the scores of the JSS-CN and Slavitt's scale was .75, and that between the JSS-CN and job performance was .53. Conclusion: Results showed that the JSS-CN has good reliability and validity. Therefore, it is concluded that the JSS-CN could be a useful tool for the measurement of the job satisfaction of clinical nurses in Korea.

An improved Maxwell creep model for salt rock

  • Wang, Jun-Bao;Liu, Xin-Rong;Song, Zhan-Ping;Shao, Zhu-Shan
    • Geomechanics and Engineering
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    • 제9권4호
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    • pp.499-511
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    • 2015
  • The creep property of salt rock significantly influences the long-term stability of the salt rock underground storage. Triaxial creep tests were performed to investigate the creep behavior of salt rock. The test results indicate that the creep of salt rock has a nonlinear characteristic, which is related to stress level and creep time. The higher the stress level, the longer the creep time, the more obvious the nonlinear characteristic will be. The elastic modulus of salt rock decreases with the prolonged creep time, which shows that the creep damage is produced for the gradual expansion of internal cracks, defects, etc., causing degradation of mechanical properties; meanwhile, the creep rate of salt rock also decreases with the prolonged creep time in the primary creep stage, which indicates that the mechanical properties of salt rock are hardened and strengthened. That is to say, damage and hardening exist simultaneously during the creep of salt rock. Both the damage effect and the hardening effect are considered, an improved Maxwell creep model is proposed by connecting an elastic body softened over time with a viscosity body hardened over time in series, and the creep equation of which is deduced. Creep test data of salt rock are used to evaluate the reasonability and applicability of the improved Maxwell model. The fitting curves are in excellent agreement with the creep test data, and compared with the classical Burgers model, the improved Maxwell model is able to precisely predict the long-term creep deformation of salt rock, illustrating our model can perfectly describe the creep property of salt rock.

세장비 변화에 따른 3차원 공동 주위의 난류유동 및 음향 특성에 관한 수치적 연구 (NUMERICAL ANALYSIS FOR TURBULENT FLOW OVER A THREE DIMENSIONAL CAVITY WITH LARGE ASPECT RATION)

  • 문바울;김재소
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2009년 추계학술대회논문집
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    • pp.13-18
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    • 2009
  • Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 2.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}106$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental data in the low aspect ratio cavity (L/D = ~ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed using the Correlation of Pressure Distribution (CPD).

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암반사면의 평면파괴에 대한 신뢰성해석 (Reliability Analysis of Plane Failure in Rock Slope)

  • 장연수;오승현;김종수
    • 한국지반공학회논문집
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    • 제18권4호
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    • pp.119-126
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    • 2002
  • 본 논문에서는 암반사면의 절토시 현장지반 시추조사의 불충분한 자료와 비균질한 지반특성에서 오는 불확실성이 암사면의 파괴확률에 미치는 영향을 알아보기 위하여 신뢰성해석을 실시하였고 이를 확정론적 해석결과와 비교하였다. 해석에 사용된 확률변수는 절리면의 점착력과 마찰각, 암반의 단위중량 이었으며 절리면의 경사각은 확률변수로 적용한 경우와 그렇지 않은 경우로 나누어 해석하였다. 해석 결과 대상 절토사면의 경우 확정론적 해석시 안정하게 나타남에도 신뢰도 해석에서는 연약 지질층의 영향에 의한 높은 불명확성으로 인하여 높은 파괴확률을 갖는 것으로 나타났다. 각 확률변수의 평균값과 분산에 대한 파괴확률의 민감도는 점착력이 가장 큰 것으로 나타났으며 평균값이 미치는 민감도가 분산의 경우보다 크게 나타나 현장 지반물성치들에 대한 평균값의 정확한 산출이 중요한 것으로 나타났다.

초기 진단에 어려움이 있는 불안정성 족근 중족 관절 미세 손상에 대한 도수 정복 및 내고정술 후 임상적 결과 (Clinical Results after Closed Reduction and Internal Fixation for Unstable Subtle Injuries of Lisfranc Joint)

  • 유선오;박용욱;김주성;이기준
    • 대한족부족관절학회지
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    • 제8권1호
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    • pp.71-75
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    • 2004
  • Purpose: The purpose of this study was to evaluate retrospectively the clinical results of closed reduction and percutaneous screw fixation for unstable injuries on stress radiographs in subtle injuries of Lisfranc joint. Materials and Methods: From June 1997 to March 2003, 6 cases of unstable injuries on stress radiograph in subtle injuries of Lisfranc joint were treated by percutaneous cannulated screw fixation after closed reduction. All cases were injuried by indirect force (twisting injury). The average diastasis between the 1st and 2nd metatarsal base was 3 mm (2-4 mm) on initial nonweight bearing AP radiograph. The average follow-up period was 20 months. Clinical evaluation was assessed according to the American Orthopedic Foot and Ankle Society (AOFAS) midfoot score. Results: The AOFAS midfoot score was average 86 (80-90) points. The average diastasis between 1st and 2nd metatarsal base was 2 mm (1-3 mm) on weight bearing AP radiograph in final follow up. The final diastasis was increased slightly than diastasis in initial postoperative radiographs. But the clinical results were good. There was no correlation between the degree of diastasis and the clinical results. On weight bearing lateral radiograph, the average difference with normal foot in the distance between plantar aspect of 5th metatarsus and medial cuneiform was 2 mm (0-3 mm). One case had mild arthritic change on the radiographs. Conclusion: When the Lisfranc injuries, especially in the subtle injuries were suspicious, the stress views are helpful to assess stability of the Lisfranc injuries and planning of treatment. For unstable injuries on stress radiographs in subtle injuries of Lisfranc joint, closed reduction and percutaneous screw fixation is useful method to expect good clinical results.

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Comparison of the Muscle Activity of Lumbar Stabilizers Between Stoop and Semi-Squat Lifting Techniques at Different Lifting Loads

  • Yang, Hoe-Song;Kwon, Oh-Yun;Lee, Yeon-Seop
    • 한국전문물리치료학회지
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    • 제19권3호
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    • pp.105-114
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    • 2012
  • This study was performed to compare the muscle activity of lumbar stabilizers between stoop and semi-squat lifting techniques at different lifting loads. Twenty healthy subjects (9 males, 11 females) were recruited for this study. Muscle activity of external obliques (EO), internal obliques (IO) and lumbar multifidus (LM) muscle was measured by surface electromyography during stoop and semi-squat lifting at different lifting loads (10%, 20%, and 30% of the subject's body weight). A one-way repeated measure ANOVA was applied. The results showed that EMG activity of EO was significantly increased with a load of 30% of body weight compared to 10% and 20% of body weight in both lifting techniques (p<.05). Muscle activity of LM was significantly increased in 20% compared to 10% and 30% compared to 10% of subject's body weight in stoop lifting and the muscle activity of LM was significantly increased in 20% compared to 10%, 30% compared to 20%, and 30% compared to 10% of the subject's body weight in semi-squat lifting (p<.05). However, there was no significant difference in activity of IO according to lifting loads in both lifting techniques. There were no significant differences in muscle activity of EO, IO, and LM between stoop and semi-squat technique (p>.05). Therefore, the results of this study suggested that the EO can contribute to increase the lumbar stability during stoop and semi-squat lifting at 30% of body weight rather than at lower loads, and the LM seems to act as counteractor to imposed loads during stoop and semi-squat lifting with increasing loads.

빅데이터 분석 기법을 활용한 도서관발전종합계획 동향 분석 연구 (Analysis Study on Trends of Library Development Plan by Using Big Data Analysis)

  • 김동석;노영희
    • 한국비블리아학회지
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    • 제29권2호
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    • pp.85-108
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    • 2018
  • 본 연구에서는 도서관발전종합계획에 대한 언론보도를 빅데이터 분석 기법을 활용하여 시기별 동향과 시사점을 도출하고자 하였다. 이를 위해 국내 주요 포털 사이트를 통해 2009년부터 2017년까지 관련 데이터를 수집하였다. 수집된 데이터는 텍스트 마이닝 과정을 통해 정제된 단어를 도출하였고 이를 바탕으로 빈도분석 및 중심성 분석, 구조적 등위성 분석 등을 수행하였다. 분석 결과 제1 2차 도서관발전종합계획이 시행되는 동안 도서관 정책의 흐름이 외연적 성장에서 도서관 운영의 내실화 고도화의 흐름으로 변화하고 있었으며, 도서관 시설 확충과 같은 특정 정책에 국한되어 언론보도가 이루어짐을 확인할 수 있었다. 이러한 연구 결과는 도서관발전종합계획으로 대변되는 도서관 정책을 어떤 관점에서 인식하고 이해하고 있는지 확인하는데 유용한 자료로 사용될 수 있으며, 향후 도서관발전종합계획의 비전을 모색하는데 활용되기를 바란다.