• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.2
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• pp.159-170
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• 2023

In the present study, the dynamic behavior characteristics of an amphibious assault vehicle during water entry were analyzed using STAR-CCM+, a commercial computational fluid dynamics(CFD) code. All computations were performed using an overset mesh system and a RANS based flow-solver coupled with dynamic fluid-body interaction(DFBI) solver for simulating three degrees of freedom motion. For numerical validation of the solver, a water entry simulation of inclined circular cylinder was conducted and it was compared between an existing experiment data and CFD results. The pitch angle variation and the trajectory of the circular cylinder during water entry shows good agreement with previous experimental and numerical studies. For the water entry simulations of the amphibious assault vehicle, the analysis of dynamic behaviors of the amphibious assault vehicle with different slope angles, submerged depths and initial velocities were conducted. It is confirmed that the steep slope angle increases the submerged volume of the amphibious assault vehicle, so the buoyancy acting on the vehicle is increased and the moved distance for the re-flotation is decreased. It is also revealed that the submerged volume is increased, bow-up phenomenon occur earlier.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.627-636
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• 2021

This paper deals with a study for the guidance control of reusable launch vehicle. For this purpose, modeling of the equation of motion of a reusable launch vehicle with 6 degrees of freedom was performed. With this model, an optimal re-entry path was created and a path-following guidance control simulation was performed to follow the optimal re-entry path. For the design of the path-following guidance controller, the attitude controller applying a time-delay technique that is resistant to modeling uncertainty, disturbance and failure. And the nonlinear path-following guidance law were used. Guidance control simulation using a classical PD controller was performed and compared with the guidance control simulation of a reusable launch vehicle applying a time delay technique.

• Journal of computational fluids engineering
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• v.19 no.1
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• pp.7-14
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• 2014

Aerothermodynamic characteristics of re-entry vehicles in hypersonic speed regimes are investigated by applying CFD methods based on the Navier-Stokes-Fourier equations. A special emphasis is placed on the effects of high temperature chemically reacting gases on shock stand-off distance and thermal characteristics of the flowfields. A ten species model is used for describing the kinetic mechanism for high temperature air. In particular, the hypersonic flows around a cylinder are computed with and without chemically reacting effects. It is shown that, when the chemically reacting effects are taken into account, the shock stand-off distance and temperature are significantly reduced.

• Journal of Mechanical Science and Technology
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• v.16 no.6
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• pp.745-756
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• 2002

The re-entry problem consists of guidance design and trajectory control. This paper summarizes the detailed relationships between the velocity, drag acceleration and altitude in determining reference trajectories. The computational issues are also addressed, and the performance of the proposed simple nonlinear control of a bank angle for the longitudinal/ lateral trajectory is demonstrated. In particular, the fixed bank angle methods that can reduce the drag acceleration errors at low-speeds are proposed. The importance of bank reversals with respect to the azimuth errors Is also elucidated.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.3
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• pp.247-255
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• 2013

The flight control of re-entry vehicles poses a challenge to conventional gain-scheduled flight controllers due to the widely spread aerodynamic coefficients. In addition, a wide range of uncertainties in disturbances must be accommodated by the control system. This paper presents the design of a roll channel controller for a non-axisymmetric reentry vehicle model using the trajectory linearization control (TLC) method. The dynamic equations of a moving mass system and roll control model are established using the Lagrange method. Nonlinear tracking and decoupling control by trajectory linearization can be viewed as the ideal gain-scheduling controller designed at every point along the flight trajectory. It provides robust stability and performance at all stages of the flight without adjusting controller gains. It is this "plug-and-play" feature that is highly preferred for developing, testing and routine operating of the re-entry vehicles. Although the controller is designed only for nominal aerodynamic coefficients, excellent performance is verified by simulation for wind disturbances and variations from -30% to +30% of the aerodynamic coefficients.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.1
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• pp.10-17
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• 2000

본 논문은 우주 발사 비행체가 지구 재진입 할 때의 유도제어에 관한 것이다. 우주 발사 비행체의 재진입궤적은 재진입 할 때의 특징에 따라 여러 단계로 나누어진다. 저항가속도는 각 단계에 따라 알맞은 파라메터로 표현되며, 해석적인 저항가속도로 단순화된 궤적으로 표현한다. 본 연구는 현재의 이란적인 궤적방법과 예측방법의 각각의 장점에 의한 혼합유도방법을 표현하였다. 제안된 유도방법을 이용한 우주 발사 비행체의 재진입 모의실험의 결과는 혼합유도방법이 지구대기 재진입 할 때 간단하고 효과적인 유도방법임을 보여주었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1653-1665
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• 2002

One of the most significant problems in the processing of composite materials is residual stresses. The residual stresses may be high enough to cause cracking in the matrix even before external loads are applied and can degrade the integrity of composite structures. In this study, thermo-viscoelastic residual stresses occurred in the polymeric composite cylinder are investigated. This type of structure is used for the launch vehicle fuselage. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. These equations are solved with the finite element method to predict the residual stresses in the composite structures during cure. A launch vehicle experiences high thermal loads during flight and re-entry due to aerodynamic heating or propulsion heat, and the thermal loads may cause thermal buckling on the structure. In this study the thermal buckling analysis of composite cylinders are performed. Two boundary conditions such as all clamped and all simply supported are used for the analysis. The effects of laminates stacking sequences, shapes and residual stresses on the critical buckling temperatures of composite cylinders are investigated. The thermal buckling analysis is performed using ABAQUS.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.681-688
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• 2021

This paper considers the trajectory and impact point dispersion analysis of the test launch vehicle (TLV). The analysis, which performed before and after its flight test on November 28, 2018, is described and verified by comparing with the flight test results. The six degree-offreedom (DOF) simulation is used to compute the dispersion of the trajectory, attitude, and impact point, where the launch vehicle performance variations and wind effects during the atmospheric phase are included. The impact area to guarantee the flight safety is determined using the results of the dispersion analysis. The flight test results confirm that the safe flight of TLV is performed within the predicted dispersion boundary.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.4
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• pp.370-377
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• 1995

The recombination of oxygen and nitrogen atoms on the surfaces of two coating m materials of the Space Shuttle Orbiter (SSO), a reaction cured glass (RCG) and a spinel (C742), was investigated. The recombination probability, $\gamma$, i.e., the probability that atoms im p pinging on the surface will recombine, was measured in a diffusion reactor. Value of $\gamma$ for oxy g gen atom on C742 ($3 {\times} 10^{-2}$) was much higher than that on RCG ($4 {\times} 10^{-4}$) at the tempera t ture of SSO re-entry (ca. 1000K). The higher value of $\gamma$ on C742 indicates a higher number d density of active sites than RCG. It suggests the possibility of designing less active surfaces by i inducing the desorption at lower temperature.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.731-743
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• 2020

The hypersonic glide vehicle ascends to a high altitude by a rocket booster, separates it from the booster, and glides at a hypersonic speed of Mach 5 or higher at an altitude of about 30~70 km, changing its direction in the atmosphere. Since it moves on an unpredictable flight path rather than a parabolic trajectory, it is difficult to intercept with current missile defense systems. The U.S. conducted HTV-2 and AHW flight tests in the early 2010s to confirm the possibility of hypersonic gliding flights, and recently it has been developing hypersonic glide vehicle systems such as LRHW and ARRW. China has conducted several flight tests of the DF-ZF (WU-14) glide vehicle since 2014 and has been operating it with DF-17 missiles. Russia has conducted hypersonic glide vehicle research since the former Soviet Union, but it has repeatedly failed, and recently it has been successfully tested with the Avangard (Yu-71) glide vehicle mounted on the SS-19 ICBM. In this paper, the characteristics, flight test cases, and development trends of hypersonic glide vehicles developed or currently being developed in the United States, China, Russia, Japan, India, and Europe are reviewed and summarized.