• Steel and Composite Structures
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• 제46권5호
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• pp.611-619
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• 2023

In the present work, the flutter characteristics of porous nanocomposite cylindrical shells, reinforced with graphene platelets (GPLs) in supersonic airflow, have been investigated. Different distributions for GPLs and porosities have been considered which are named uniform and non-uniform distributions thorough the shell's thickness. The effective material properties have been determined via Halpin-Tsai micromechanical model. The cylindrical shell formulation considering supersonic airflow has been developed in the context of first-order shell and first-order piston theories. The governing equations have been solved using Galerkin's method to find the frequency-pressure plots. It will be seen that the flutter points of the shell are dependent on the both amount and distribution of porosities and GPLs and also shell geometrical parameters.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2007년도 춘계학술발표대회 및 제12회 신소재 심포지엄
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• pp.42-42
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• 2007

• 한국가시화정보학회지
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• 제9권3호
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• pp.30-37
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• 2011

The thrust vectoring concept has been used for use in new advanced supersonic aircraft. This study presents the performance characteristics of the thrust vectoring nozzle by visualizing the shock behaviors with Schlieren method. The scaled models were designed and manufactured to see the shock behaviors of the various airflow condition. Also we executed experimental tests to see the geometrical effects of the thrust vector nozzle by changing pitch angle and length of pitch flaps. From this study we could understand the supersonic flow characteristics of the thrust vector nozzle. The total thrust of thrust vector nozzle is diminished by increasing the flap angle. But there is an optimum flap length ratio for attaining the highest thrust level and proper pitch effect.

• 한국연소학회지
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• 제7권3호
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• pp.32-36
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• 2002

A numerical study was carried out to investigate combustion phenomena in a model Scramjet engine, which had been experimentally studied at the University of Tokyo using a high-enthalpy supersonic wind tunnel. The main airflow was Mach number 2.0 and the total temperature of hot flow was 1800K. Equivalence ratio was set to be 0.26 which is higher than that of experiment to investigate the effect of strong precombustion shock. The results showed that self-ignition occurred at the rear bottom wall of the combustor and combined with the shear layer flame between fuel jet and main airflow. Then, precombustion shock was generated at the step location and reversely enhanced the mixing and combustion process behind the shock. Due to the high equivalence ratio, the precombustion shock moved upstream of the step compared with that of experiment.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2001년도 제22회 KOSCI SYMPOSIUM 논문집
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• pp.127-132
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• 2001

A numerical study was carried out to investigate the combustion phenomena in a model Scramjet engine, which had been experimentally studied in the University of Tokyo using a high-enthalpy supersonic wind tunnel. The main airflow was 2.0 in Mach number and the total temperature of hot flow was 1800K. Equivalence ratio was set to be rather higher value of 0.26 than that of experiment to investigate the effect of strong precombustion shock. The results showed that self-ignition occurred at the rear bottom wall of the combustor and combined with the shear layer flame between fuel jet and main airflow. Then, precombustion shock was generated at the step location and reversely enhanced the mixing and combustion process behind the shock. Due to the high equivalence ratio, the precombustion shock moved upstream of the step compared with that of experiment.

• Advances in aircraft and spacecraft science
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• 제5권4호
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• pp.445-458
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• 2018

Turbulent airflow in channels of rectangular cross section with symmetric centerbodies is studied numerically. Shock wave configurations formed in the channel and in front of the entrance are examined. Solutions of the unsteady Reynolds-averaged Navier-Stokes equations are obtained with finite-volume solvers of second-order accuracy. The solutions demonstrate an expulsion/swallowing of the shocks with variations of the free-stream Mach number or angle of attack. Effects of the centerbody length and thickness on the shock wave stability and flow bifurcation are examined. Bands of the Mach number and angle of attack, in which there exist non-unique flow fields, are identified.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.437-452
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• 2022

For the first time, the higher-order shear and normal deformable plate theory (HOSNDPT) is used for the vibration and flutter analyses of the multilayer functionally graded graphene platelets reinforced composite (FG-GPLRC) plates under supersonic airflow. For modeling the supersonic airflow, the linear piston theory is adopted. In HOSNDPT, Legendre polynomials are used to approximate the components of the displacement field in the thickness direction. So, all stress and strain components are encountered. Either uniform or three kinds of non-uniform distribution of graphene platelets (GPLs) into polymer matrix are considered. The Young modulus of the FG-GPLRC plate is estimated by the modified Halpin-Tsai model, while the Poisson ratio and mass density are determined by the rule of mixtures. The Hamilton's principle is used to obtain the governing equations of motion and the associated boundary conditions of the plate. For solving the plate's equations of motion, the Galerkin approach is applied. A comparison for the natural frequencies obtained based on the present investigation and those of three-dimensional elasticity theory shows a very good agreement. The flutter boundaries for FG-GPLRC plates based on HOSNDPT are described and the effects of GPL distribution patterns, the geometrical parameters and the weight fraction of GPLs on the flutter frequencies and flutter aerodynamic pressure of the plate are studied in detail. The obtained results show that by increasing 0.5% of GPLs into polymer matrix, the flutter aerodynamic pressure increases approximately 117%, 145%, 166% and 196% for FG-O, FG-A, UD and FG-X distribution patterns, respectively.

• Composites Research
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• 제13권5호
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• pp.50-59
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• 2000

본 논문에서는 복합재료 패널 플러터를 억제할 수 있는 두 가지 방법에 대해서 연구하였다. 첫번째, 능동제어 방법에서는 선형 제어 이론을 바탕으로 제어기를 설계하였으며 제어입력이 작동기에 가해진다. 여기서 작동기로는 PZT를 사용하였다. 두 번째, 인덕터와 저항으로 구성되어진 션트회로를 사용하여 시스템의 감쇠를 증가시킴으로써 패널 플러터를 억제할 수 있는 새로운 방법인 수동감쇠기법에 대한 연구가 수행되었다. 이 수동감쇠기법은 능동적 제어보다 강건(robust)하며 커다란 전원 공급이 필요하지 않고 제어기나 감지 시스템과 같이 복잡한 주변 기기가 필요 없이도 실제 패널 플러터 억제에 쉽게 응용할 수 있는 장점을 가지고 있다. 최대의 작동력/감쇠 효과를 얻기 위해서 유전자 알고리듬을 사용하여 압전 세라믹의 형상과 위치를 결정하였다. 해밀턴 원리를 사용해서 지배 방정식을 유도하였으며, 기하학적 대변형을 고려하기 위해 von-Karman의 비선형 변형률-변위 관계식을 사용하였으며 공기력 이론으로는 준 정상 피스톤 1차 이론을 사용하였다. 4절점 4각형 평판 요소를 이용하여 이산화된 유한 요소 방정식을 유도하였다. 효율적인 플러터 억제를 위해 패널 플러터에 중요한 영향을 미치는 플러터 모드를 이용한 모드축약기법을 사용하였으며, 이를 통해 비선형 연계 모달 방정식이 얻어지게 된다. 능동적 제어 방법과 수동 감쇠 기법에 의해 수행되어진 플러터 억제 결과들을 Newmark 비선형 시분할 적분법을 통해 시간 영역에서 살펴 보았다.