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Assessment of Structural Soundness and Joint Load of the Rotorcraft External Fuel Tank by Sloshing Movement

슬로싱 운동에 의한 회전익항공기 외부연료탱크 체결부 하중 및 구조건전성 평가

  • Accepted : 2019.05.03
  • Published : 2019.05.31

Abstract

The fuel sloshing due to the rapid manoeuvre of the aircraft causes significant loads on internal components, which may break components or piping. In particular, a significant load is applied to the joint of the external fuel tank by sloshing movement, which may affect the safety of the aircraft when the joint of the external fuel tank is damaged. Therefore, in order to improve the survivability of aircraft and crew members, the design of external fuel tanks, and joints should be performed after evaluating the sloshing load through a numerical analysis of the fuel sloshing conditions. In this paper, a numerical analysis was performed on the sloshing test of the external fuel tank for rotorcraft. ALE (Arbitrary Lagrangian Eulerian) technique was used, and the test conditions specified in the U.S. Military Specification (MIL-DTL-27422D) was applied as the conditions for numerical analysis. As a result of the numerical analysis, the load on the joint of the external fuel tank was calculated. Moreover, the effects of sloshing movement on structural soundness were assessed through analysis of stress levels and margin of safety on metal fittings and composite containers.

항공기가 급격한 기동을 하는 경우에는 연료의 쏠림에 의해 상당한 하중이 관련 구성품들에 작용하는데 심각한 상황에서는 구성품이나 배관의 파손이 발생하여 연료탱크 외부로 연료가 누설될 수 있다. 특히, 외부 연료탱크가 장착된 경우에는 슬로싱 운동에 의해 외부 연료탱크 체결부에 상당한 하중이 작용하게 되는데, 해당 하중을 반영하지 않은 설계로 인하여 체결부의 파손이 발생하게 되면 항공기 안전 뿐만 아니라 승무원의 생존에도 악영향을 미칠수가 있다. 따라서, 따라서, 항공기 및 승무원의 생존성 향상을 위해서는 연료 슬로싱 운동에 의한 하중을 고려하여 연료탱크와 내부 부품뿐만 아니라 체결부에 대한 설계가 수행되어야 한다. 본 논문에서는 회전익항공기용 외부 연료탱크의 슬로싱 시험에 대한 수치해석을 수행하였다. 수치해석 기법으로 유체-구조 연성해석의 하나인 ALE 방법을 사용하였고 미군사 규격에서 요구하는 시험조건을 수치해석에 적용하였다. 수치해석 결과로 외부 연료탱크 체결부 하중을 계산하여 체결부 설계시 고려해야 하는 하중 수준을 검토하였다. 또한, 슬로싱 운동에 의해 금속피팅부와 복합재 컨테이너에 작용하는 응력수준과 안전여유 분석을 통해 구조건전성에 미치는 영향을 평가하였다.

Keywords

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Fig. 1. General concept of slosh test and external fuel tank

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Fig. 2. Concept of sloshing test for external fuel tank

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Fig. 3. Euler and lagrangian model for external fuel tank system

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Fig. 4. External auxiliary fuel tank

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Fig. 5. Application area of foam in composite container and material coordinator

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Fig. 6. Internal fluid inside of fuel tank

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Fig. 7. Numerical model of external fuel tank system and test fixture

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Fig. 8. Bolt modeling and four position of bolt joint

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Fig. 9. Angular velocity condition on the test fixture

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Fig. 10. Locations of Joints for assembly

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Fig. 11. Axial force in joint 01~04

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Fig. 12. Shear force in joint 01~04

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Fig. 13. Behavior of internal fluid by sloshing movement

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Fig. 14. Max. equivalent stress on metal fitting

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Fig. 15. Max. stress of compression in x-dir

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Fig. 16. Max. stress of compression in y-dir

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Fig. 17. Max. stress of compression in xy-dir

Table 1. Material data for composite

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