• Title/Summary/Keyword: 섭동하중

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Numerical Prediction of Acoustic Load Around a Hammerhead Launch Vehicle at Transonic Speed (해머헤드 발사체의 천음속 음향하중 수치해석)

  • Choi, Injeong;Lee, Soogab
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.49 no.1
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    • pp.41-52
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    • 2021
  • During atmospheric ascent of a launch vehicle, airborne acoustic loads act on the vehicle and its effect becomes pronounced at transonic speed. In the present study, acoustic loads acting on a hammerhead launch vehicle at a transonic speed have been analyzed using ��-ω SST based IDDES and the results including mean Cp, Cprms, and PSD are compared to available wind-tunnel test data. Mesh dependency of IDDES results has been investigated and it has been concluded that with an appropriate turbulence scale-resolving computational mesh, the characteristic flow features around a transonic hammerhead launch vehicle such as separated shear flow at fairing shoulder and its reattachment on rear body as well as large pressure fluctuation in the region of separated flow behind the boat-tail can be predicted with reasonable accuracy for engineering purposes.

Damage Assessment and Aseismic Capacity Evaluation of Existing Structures (기설구조물의 손상도 및 내진능력 평가방법)

  • 윤정방;송종걸;김유진
    • Computational Structural Engineering
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    • v.11 no.3
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    • pp.199-212
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    • 1998
  • 본 연구에서는 기설구조물에 대한 손상도 추정기법과 내진능력평가 방법에 대하여 연구하였다. 구조물의 손상도를 추정하는 방법으로는 소수의 계측 데이터를 이용한 모드섭동법(inverse modal perturbation)을 이용하였다. 구조물의 손상은 강성행렬의 감소로 표현하여, 각 요소행렬에 대한 손상을 손상지수를 사용하여 나타내었다. 구조적 손상과 이에 기인한 고유진동 특성의 변화량과의 관계를 섭동방정식으로부터 구한 후, 이로부터 손상지수와 고유진동 특성의 변화량과의 관계를 유동하였다. 따라서 손상 전과 후에서 구조물의 고유진동수와 모드형상을 측정하여 섭동식의 해를 구함으로써 구조물의 강성행렬의 감소로 나타나는 구조물의 손상도를 추정하게 된다. 손상도 추정에 의해 평가된 강성의 변화량에 기인한 손상 후의 기설구조물의 지진응답, 내진능력과 지진손상도의 평가를 손상전과 비교하였다. 내진능력은 구조부재에서 회전연성도 능력의 경험식을 이용하여 평가하였고, 지진손상도의 평가는 가장 많이 사용되는 방법인 Park & Ang 방법을 사용하였다. 예제해석은 다른 지진하중을 받는 2층과 8층의 예제구조물에 대해서 수행하였다.

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Prediction of Pressure Fluctuations on Hammerhead Vehicle at Transonic Speeds Using CFD and Semi-empirical Formula Considering Spatial Distribution (CFD와 공간분포를 고려한 반경험식을 이용한 해머헤드 발사체의 천음속 압력섭동 예측)

  • Kim, Younghwa;Nam, Hyunjae;Kim, June Mo;Sun, Chul
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.49 no.6
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    • pp.457-464
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    • 2021
  • To analyze the buffet phenomenon that causes serious vibration loads on a satellite launch vehicle, the pressure fluctuations on a hammerhead launch vehicle at transonic speeds are predicted by coupling CFD analysis and semi-empirical methods. From the RANS simulation, shock oscillation region, separation region, and separation reattachment region are identified, and the boundary layer thickness, the displacement thickness, and flow properties at boundary layer edge are calculated. The pressure fluctuations and power spectra on the hammerhead fairing are predicted by coupling RANS results and semi-empirical methods considering spatial distribution, and compared with the experimental data.

Improvement of Euler-Bernoulli Beam Theory for Free Vibration and Buckling Analyses via Saint-Venant's Principle (생브낭 원리를 이용한 고전 보 이론의 고유진동수 및 좌굴하중 예측 개선)

  • Jeong, Yong-Min;Kim, Jun-Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.4
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    • pp.381-387
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    • 2016
  • In this paper, the methodology applied to the improvement of stress analyses is extended to free vibration and buckling analyses. The essence of the methodology is the Saint-Venant's principle that is applicable to beam and plate models. The principle allows one to dimensionally reduce three-dimensional elasticity problems. Thus the methodology can be employed to vibration and buckling as well as stress analysis. First, the principle is briefly revisited, and then the formations of classical beam theories are presented. To improve the predictions, the perturbed terms (unknowns) are introduced together with the warping functions that are calculated by stress equilibrium equations. The unknowns are then calculated by applying the equivalence of stress resultants (i.e., Saint-Venant's principle). As numerical examples, cantilever and simply supported beams are analytically solved. The results obtained are compared with those of the classical beam theories. It is shown that the methodology can be used to improve the predictions without introducing shear correction factors.

Study on Deriving the Buckling Knockdown Factor of a Common Bulkhead Propellant Tank (공통격벽 추진제 탱크 구조의 좌굴 Knockdown Factor 도출 연구)

  • Lee, Sook;Son, Taek-joon;Choi, Sang-Min;Bae, Jin-Hyo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.26 no.3
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    • pp.10-21
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    • 2022
  • The propellant tank, which is a space launch vehicle structure, must have structural integrity as various static and dynamic loads are applied during ground transportation, launch standby, take-off and flight processes. Because of these characteristics, the propellant tank cylinder, the structural object of this study, has a thin thickness, so buckling due to compressive load is considered important in the cylinder design. However, the existing buckling design standards such as NASA and Europe are fairly conservative and do not reflect the latest design and manufacturing technologies. In this study, nonlinear buckling analysis is performed using various analysis models that reflect initial defects, and a method for establishing new buckling design standards for cylinder structures is presented. In conclusion, it was confirmed that an effective lightweight design of the cylinder structure for common bulkhead propulsion tank could be realized.

A study on in-flight acoustic load reduction in launch vehicle fairing by FE-SEA hybrid method (FE-SEA 하이브리드 기법을 이용한 비행 중 발사체 페어링 내부 음향하중 저감에 관한 연구)

  • Choi, Injeong;Park, Seoryong;Lee, Soogab
    • The Journal of the Acoustical Society of Korea
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    • v.39 no.4
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    • pp.351-363
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    • 2020
  • Launch vehicles are subject to airborne acoustic loads during atmospheric flight and these effects become pronounced especially in transonic region. As the vibration due to the acoustic loads can cause malfunction of payloads, it is essential to predict and reduce the acoustic loads. In this study, a complete process has been developed for predicting airborne vibro-acoustic environment inside the payload pairing and subsequent noise reduction procedure employing acoustic blankets and Helmholtz resonators. Acoustic loads were predicted by Reynolds-Averaged Navier-Stokes (RANS) analysis and a semi-empirical model for pressure fluctuation inside turbulent boundary layer. Coupled vibro-acoustic analysis was performed using VA One SEA's Finite Element Statistical Energy Analysis (FE-SEA) hybrid module and ANSYS APDL. The process has been applied to a hammerhead launch vehicle to evaluate the effect of acoustic load reduction and accordingly to verify the effectiveness of the process. The presently developed process enables to obtain quick analysis result with reasonable accuracy and thus is expected to be useful in the initial design phase of a launch vehicle.

A Study on the Design of Robust Simulation Controller of Magnetic Levitation System(I) (자기부상 시스템의 강인한 제어기 설계에 관한 연구(I) -시뮬레이션을 중심으로-)

  • 양주호;김창화;정석권;김영복
    • Journal of Advanced Marine Engineering and Technology
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    • v.19 no.3
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    • pp.84-90
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    • 1995
  • The magnetic levitation system has great advantages, such as little friction, no lubrication no noise and so on. The magnetic levitation system need a stabilizing controller because it is a unstable system in natural. This paper presents the robust stabilizing controller design of the magnetic levitation system. The controller which is designed in this paper by $H_{infty}$ control theory is robust servo controller which has zero offset in spite of the model uncertainties. The validity of controller was investigater through the response simulation. In the future, we will use the result of this study at the actual magnetic levitation system.

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Buckling of Composite Cylindrical Shells Sugjected ot Torsion of Lateral Pressure (비틀림 및 횡압럭을 받고 있는 복합재 원통쉘의 좌굴)

  • Han, Byeong-Gi;Lee, Seong-Hui;Yu, Taek-In
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.5
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    • pp.1436-1444
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    • 1996
  • The problem ofinstability of laminated circular cylindrical shell under the action of torsio or lateral pressure is investigated. The analysis is based on the Sander's theory for finite deformations of thin shell. The buckling is elastic for thin compoisite shell nad the geometry is assumed to be free of initial imperfections. The equilibrium equations are obrained by usitn the p[erturbation technique. Solution procedure is based on the Galerkin mehtod. The computer program for numerical results is made for several stacking sequence, length-to-radius ratio, and radius-to-thickness ratio. The numerical results of buckling load are present.

Speed Control of the Low Speed Diesel Engine by $H_{\infty}$ Controller Design Method ($H_{\infty}$ 제어기법을 이용한 저속디젤기관의 속도제어)

  • 양주호;정병건
    • Journal of Advanced Marine Engineering and Technology
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    • v.17 no.5
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    • pp.63-70
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    • 1993
  • In 1980's to 1990's the marine propulsion diesel engines have been developed into lower speed and longer stroke for the energy saving(small S.F.O.C.). As these new trends the convetional mechnical-hydraulic governors were not adapted to the new requirements and the digital governors have been adopted in the marine use. The digital governors usually use the control algorithms such as the PID control, optimal control, adaptive control and etc. While the engine has delay time and parameter variations these control algorithms have difficulty in considering the stability and the robustness for the model uncertainty. In this study, the $H_{\infty}$ controller design method are applied to the speed control of the low speed marine diesel engine. By comparison the $H_{\infty}$ control results with the PID control results, the validity of the $H_{\infty}$ controller under the delay time and parameter variations is confirmed.

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A Study on the Dynamic Stability of the Long Vertical Beam Subjected to the Parametric Excitation (파라메터 기진에 의한 긴수직보의 동적안정성에 관한 연구)

  • Y.C. Kim;J.S. Hong
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.1
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    • pp.69-82
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    • 1991
  • The dynamic stability of the long vertical beam subjected to the periodic axial load is investigated. As a solution method, the Galerkin's method is used to obtain a set of coupled Mathieu type equations. To obtain the stability chart, both the perturbation method and numerical method are used, and the results of the both methods are compared with each other. The stability regions for the various boundary conditions are obtained, Also the effects of the viscous damping, the mean tension and the multi-frequency parametric excitation are studied in detail.

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