• Title/Summary/Keyword: Fatigue strength analysis

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원심압축기 밀폐형 임펠러 형상에 따른 성능특성 파악을 위한 유동해석 (Flow Analysis for Performance Characteristics with Closed Type Impeller Shapes of a Centrifugal Compressor)

  • 조종재;윤용상;조명환;강석철
    • 한국추진공학회지
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    • 제21권1호
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    • pp.26-35
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    • 2017
  • 원심압축기 운전 중에 발생하는 고주기 피로균열이나 공진 등은 임펠러 파손의 주된 원인이다. 이러한 파손을 회피하기 위해 공진영역 운전에서도 견딜 수 있는 충분한 강도의 임펠러를 설계하거나, 공진이 발생하지 않도록 임펠러를 튜닝 한다. 이러한 회피설계는 임펠러 내부유동 및 성능특성 변화를 야기하게 된다. 본 연구에서는 밀폐형 임펠러에 대해 블레이드 두께를 증가시킨 모델과 스켈럽을 적용한 모델에 대한 유동 및 성능특성을 파악하기 위해 전산해석을 수행하였다. 전산해석 결과, 블레이드 두께 증가 모델 경우는 기본모델 대비 압력계수가 0.5% 감소하였으며, 전효율은 0.1% 감소하였다. 스켈럽 적용모델은 압력계수가 0.4% 증가하였으며, 전효율은 1.6% 감소하였다.

복소퍼텐셜을 이용한 타원공 또는 균열을 가진 복합재 평판 응력해석 (Stress Analysis of Composite Plate with an Elliptical Hole or a Crack Using Complex Potentials)

  • 권정호;황경정
    • Composites Research
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    • 제20권5호
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    • pp.56-63
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    • 2007
  • 복소퍼텐셜을 이용하여 타원공 또는 균열을 내재한 복합재 적층판구조 해석법을 고찰하였다. 복합재 적층판은 충격에 취약하며 이러한 충격손상은 타원공이나 균열형태의 노치로 모델화된 바 있다. 이와 같이 컷아웃부를 내재한 복잡한 형태의 복합재 적층판 해석에 유한요소해석법이 널리 사용되고 있으나 피로하중 하에서의 손상허용성 평가와 같이 손상진전에 따라 반복적으로 유한요소모델링을 수정하여 해석을 수행하여야 하는 경우 매우 번거로운 작업이 요구된다. 이러한 관점에서 복소퍼텐셜을 이용한 해석적 기법은 매우 간편하고 사용하기 손쉬운 기법이라고 할 수 있다. 이러한 해석법에 의한 계산결과를 유한요소해석 결과와 비교 분석함으로써 계산과정의 유효성과 용이성을 검증하였다.

소형 위그선의 탄소/에폭시 복합재 주익의 구조 설계 및 해석에 관한 연구 (Structural Design and Analysis for Carbon/Epoxy Composite Wing of A Small Scale WIG Vehicle)

  • 박현범;강국진;공창덕
    • Composites Research
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    • 제19권5호
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    • pp.12-19
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    • 2006
  • 본 논문에서 한국해양연구원에서 개발 중인 20인승급 소형 위그선의 주익 구조 설계 및 해석에 관한 연구를 수행하였다. 경량화를 위해 탄소/에폭시 복합재료를 적용하였으며, 구조 형태는 스킨 스파 폼 샌드위치 구조를 사용하였다. 개념 설계에는 복합재 설계 개념을 반영하였고, 상세 설계 및 경량화 구조 설계에는 상용 유한 요소 코드인 NASTRAN을 이용하여 구조 설계를 수행하였다. 여러 단계의 구조 설계 변경을 통해 최종 구조 설계 결과는 설계 요구 조건을 만족하는 결과임을 확인하였다. 또한 주익을 동체에 고정하기 위해 8개의 고강도 볼트를 이용한 삽입 볼트형 구조가 용이한 장탈과 20넌 이상의 피로 수명의 고려를 통해 채택되었다.

관절염 환자의 운동행위 예측모형 (Pender의 재개정된 건강증진 모형에 의한) (Prediction Model of Exercise Behaviors in Patients with Arthritis (by Pender's revised Health Promotion Model))

  • 임난영;서길희
    • 근관절건강학회지
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    • 제8권1호
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    • pp.122-140
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    • 2001
  • The aims of this study were to understand and to predict the determinent factors affecting the exercise behaviors and physical fitness by testing the Pender's revised health promotion model, and to help the patients with rheumatoid arthritis and osteoarthritis perform the continous exercise program, and to help them maximize the physical effect such as muscle strength, endurance, and functional status and mental effects including self efficacy and quality of life, and improve the physical and mental well being, and to provide a basis for the nursing intervention strategies. Of the selected variables in this study, the endogenous variables included the physical fitness, exercise score, exercise participation, perceived benefits of action, perceived barriers of action to exercise, activity-related affect(depression) and perceived self-efficacy, interpersonal influences(family support), situational factors(duration of arthritis, fatigue) and the exogenous variables included personal sociocultural factor(education level), personal biologic factor(body mass index), personal psychologic factor(perceived health status) and prior related behavior factors(previous participation in exercise, life-style). We analyzed the clinical records of 208 patients with rheumatoid arthritis and degenerative arthritis who visited the outpatient clinics at H university hospital in Seoul. Data were composed of self reported qustionnaire and good of fitness score which were obtained by padalling the ergometer of bicycle for 9 minutes. SPSS Win 8.0 and Window LISREL 8.12a were used for statistical analysis. Of 75 hypothetical paths that influence on physical fitness, exercise participation, exercise score, perceived benefits of action, perceived barriers of action to exercise, activity-related affect(depression) and perceived self-efficacy, interpersonal influences(family support), situational factors(duration of arthritis, fatigue), 40 were supported. The physical fitness was directly influenced by life-style, perceived health status, education level, family support, fatigue, which explained 12% of physical fitness. The exercise participation were directly influenced by life-style, education level, past exercise behavior, perceived benefits of action, perceived barriers of action, depression and duration of arthritis, which explained 47% of exercise participation. Exercise score were directly affected by perceived self efficacy. BMI, life-style, past exercise behavior, perceived benefits of action, family support, perceived health status. perceived barriers of action, and fatigue, which explained 70%. Perceived benefits of action was directly influenced by BMI, life-style, which explained 39%. Perceived barriers of action were directly influeced by past exercise behavior, perceived health status, which explained 7%. Perceived self efficacy were directly influeced by level of education, perceived health status, life-style, which explained 57%. Depression were directly influeced by past exercise behavior, BMI, life-style, which explained 27%. Family support were directly influeced by life-style, perceived health status, which explained 29%. Fatigue were directly influeced by BMI, life-style, perceived health status. which explained 41%. Duration of arthritis were directly influeced by life-style, past exercise behavior, BMI, which explained 6%. In conclusion, important variables for physical fitness were life-style, and variable affecting exercise participation were life-style. Perceived self-efficacy of exercise was a significant predictor of exercise score. BMI, Life-style, perceived benefits of action, family support, past exercise behavior showed direct effects on perceived self-efficacy. Therefore, disease related factor should be minimized for physical performance and well being in nursing intervention for patients with rheumatoid arthritis, and plans to promote and continue exercise should be seeked to reduce disability. In addition, Exercise program should be planned and performed by the exact evaluation of exercise according to the ability of the patients and the contents to improve the importance of exercise and self efficacy in self control program, dedicated educational program should be involved. This study suggest that the methods to reduce the disease related factors, the importance of daily life-style, recognition of benefit of exercise, and educational program to promote self efficacy should be considered in the exercise behavior promotion and nursing intervention for continous performance. The significance of this study is also thought to provide patients with chronic arthritis the specific data for maximal physical and mental well being through exercise, chronic therapeutic procedure, daily adaptation and confrontation in nursing intervention.

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국내 남녀 중고 골프 선수들의 운동 상해 빈도 조사 (The Frequency of Sport Injury for the Junior Elite Golf Players in Korea)

  • 임영태;서희진;박찬희
    • 한국운동역학회지
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    • 제13권3호
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    • pp.151-162
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    • 2003
  • The purpose of this study was to investigate the frequency of sports injury among Korean junior elite golf players. The survey was made through the questionnaire which consist of eight categories and 280 valid answers were used to perform frequency analysis. The results indicated that 197 out of 280 participants experienced golf injuries (30%: during a game, 70%: during a practice) and 70% of them also experienced injuries within a year. The frequency analysis for the site of injury has shown that back was the most vulnerable area for all players(33%), followed by the right wrist, left shoulder and elbow for male players. Among female players, left wrist was the second weak site of injury, followed by the right wrist, right thoracic spine, and left shoulder. A few of them also have shown abnormal symptoms of ruptured lumbar disk, scoliosis, and lordosis and these injuries might be caused by the lack of flexibility and the fatigue due to over-practice. High frequency of wrist injury also demonstrated that excessive chopping or punching shot and poor environmental course conditions may cause this injury to be common. Overall, lack of warm up time, lack of strength and flexibility, and excessive amount of practice were the major reasons of injury for the junior elite golfers in Korea. The study also proved that these young Korean golfers actually had more chances to be faced with the injury than average. Thus, it is necessary to develop systematic and scientific methods of training, and prevention, treatment of these injuries with medical professionals.

긴장재 느슨해짐에 따른 해중 터널의 동적 불안정 거동 (Dynamic Instability of Submerged Floating Tunnels due to Tendon Slack)

  • 원덕희;김승준
    • 한국강구조학회 논문집
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    • 제29권6호
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    • pp.401-410
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    • 2017
  • 본 연구에서는 긴장재로 계류된 해중 터널에서 긴장재의 느슨해짐에 따른 동적 불안정 거동에 대해 다룬다. 해중 터널의 설계는 파랑 및 조류 등 유체력에 의해 지배받는다. 특히 시간에 따라 지속적으로 크기 및 작용방향이 변하는 파랑은 해중 터널의 동적 거동을 직접적으로 야기하게 되는데, 파랑에 의한 부유 튜브의 운동은 계류선 내력의 동적 변동을 유발하게 되고, 이 힘의 변화는 계류선의 강도설계 뿐 만 아니라 피로 설계에도 직접적인 영향을 미친다. 파랑에 의한 터널의 운동이 극심할 경우, 계류선의 장력은 모두 소실될 수 있는데, 이 때 계류선이 느슨해짐에 따라 일시적으로 부유 터널의 운동에 대한 저항성이 사라져 동적 불안정 거동이 유발 될 수 있다. 이에 본 연구에서는 유체-구조동역학 해석기법을 통해 해중 터널 긴장재의 느슨해짐 발생 시 부유 튜브의 동적 불안정 거동에 대해 분석하였다. 특히 해중터널의 중요 설계 인자인 흘수, 부력-자중 비율(Buoyancy-Weight Ratio, BWR), 긴장재 기울임이 동적 불안정 거동에 미치는 영향에 대해 분석하였다.

Dynamic numerical simulation of plastic deformation and residual stress in shot peening of aluminium alloy

  • Ullah, Himayat;Ullah, Baseer;Muhammad, Riaz
    • Structural Engineering and Mechanics
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    • 제63권1호
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    • pp.1-9
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    • 2017
  • Shot peening is a cold surface treatment employed to induce residual stress field in a metallic component beneficial for increasing its fatigue strength. The experimental investigation of parameters involved in shot peening process is very complex as well as costly. The most attractive alternative is the explicit dynamics finite element (FE) analysis capable of determining the shot peening process parameters subject to the selection of a proper material's constitutive model and numerical technique. In this study, Ansys / LS-Dyna software was used to simulate the impact of steel shots of various sizes on an aluminium alloy plate described with strain rate dependent elasto-plastic material model. The impacts were carried out at various incident velocities. The influence of shot velocity and size on the plastic deformation, compressive residual stress and force-time response were investigated. The results exhibited that increasing the shot velocity and size resulted in an increase in plastic deformation of the aluminium target. However, a little effect of the shot velocity and size was observed on the magnitude of target's subsurface compressive residual stress. The obtained results were close to the published ones, and the numerical models demonstrated the capability of the method to capture the pattern of residual stress and plastic deformation observed experimentally in aluminium alloys. The study can be quite helpful in determining and selecting the optimal shot peening parameters to achieve specific level of plastic deformation and compressive residual stress in the aluminium alloy parts especially compressor blades.

시일과 스틸면 사이에 구형입자가 있는 접촉문제의 해석 (Contact Analysis of a Spherical Particle Between Elastomeric Seal and Steel Surface)

  • 박태조;조현동
    • 대한기계학회논문집A
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    • 제34권2호
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    • pp.161-166
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    • 2010
  • 본 논문에서는 시일 설치면에서의 마멸발생기구를 정확하게 조사하기 위한 연구의 일환으로 미세입자가 시일과 스틸면 사이에 존재하는 경우의 접촉문제를 비선형문제해석 프로그램인 MARC를 사용하여 해석하였다. 이 결과, 시일의 재질은 스틸면에서의 응력분포와 변형형상에 아주 큰 영향을 미쳤다. 특히, PTFE와 같이 탄성계수가 높은 시일인 경우에 스틸 표면은 국부적으로 항복상태에 도달할 뿐만 아니라 시일을 제거한 후에도 영구변형과 함께 상당한 크기의 압축/인장 잔류응력이 존재하였다. 따라서, 시일과 스틸면 사이에 경질입자가 존재할 경우에는 연삭마멸과 함께 피로마멸이 발생할 수 있음을 확인하였으며, 다양한 설계변수에 대한 추가연구가 요구된다.

LNG 선박용 벨로우즈의 제작시 성형방법에 따른 성능 평가 I - 벨로우즈의 제작방법 및 기계적 특성 비교 - (Performance evaluation of the forming methods used in the production of bellows for LNG carriers I - Comparison of design methods and mechanical properties of bellows -)

  • 김평수;김종도
    • Journal of Advanced Marine Engineering and Technology
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    • 제40권7호
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    • pp.587-592
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    • 2016
  • LNG 선박용 벨로우즈는 극한의 환경에서 지속적인 진동 그리고 큰 온도변화에 따른 수축과 팽창을 견뎌내야 하는 피로수명과 해수환경에서의 내식성을 가져야 한다. 이러한 특성을 갖기 위해서는 저온에서의 인성이 강하고 내부식성이 강한 재료를 사용하여 최적화된 성형조건을 유지하는 것이 매우 중요하다. 이를 위해서는 벨로우즈의 최적화된 설계 조건과 성형방법이 뒷받침되어야 한다. 본 연구에서는 기계적 강성과 신뢰성이 높은 극저온용 벨로우즈를 개발하기 위하여 유한요소 해석을 통해 벨로우즈를 설계하였다. 또한 두 가지의 성형방법을 통해 설계된 벨로우즈를 제작하여 최적화된 성형조건을 도출하고자 하였다. 기계식 성형방법과 하이드로포밍 방법을 통해 벨로우즈를 성형하고 성형방법에 따른 벨로우즈의 기계적 특성을 비교하기 위하여 성형부의 높이, 두께 및 비커스 경도 값을 측정하였다. 이를 통해 기계식 성형방법으로 제작된 벨로우즈의 경도 값이 하이드로포밍 제작 벨로우즈보다 더 높은 것을 확인하였다.

박용엔진 피스톤 스커트 프로파일 변경에 의한 마찰손실(FMEP) 저감 연구 (Friction Power Loss Reduction for a Marine Diesel Engine Piston)

  • 안성찬;이상돈;손정호;조용주
    • Tribology and Lubricants
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    • 제32권4호
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    • pp.132-139
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    • 2016
  • The piston of a marine diesel engine works under severe conditions, including a combustion pressure of over 180 bar, high thermal load, and high speed. Therefore, the analyses of the fatigue strength, thermal load, clamping (bolting) system and lubrication performance are important in achieving a robust piston design. Designing the surface profile and the skirt ovality carefully is important to prevent severe wear and reduce frictional loss for engine efficiency. This study performs flexible multi-body dynamic and elasto-hydrodynamic (EHD) analyses using AVL/EXCITE/PU are performed to evaluate tribological characteristics. The numerical techniques employed to perform the EHD analysis are as follows: (1) averaged Reynolds equation considering the surface roughness; (2) Greenwood_Tripp model considering the solid_to_solid contact using the statistical values of the summit roughness; and (3) flow factor considering the surface topology. This study also compares two cases of skirt shapes with minimum oil film thickness, peak oil film pressure, asperity contact pressure, wear rate using the Archard model and friction power loss (i.e., frictional loss mean effective pressure (FMEP)). Accordingly, the study compares the calculated wear pattern with the field test result of the piston operating for 12,000h to verify the quantitative integrity of the numerical analysis. The results show that the selected profile and the piston skirt ovality reduce friction power loss and peak oil film pressure by 7% and 57%, respectively. They also increase the minimum oil film thickness by 34%.