• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.41-46
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• 2006

When new weapons are introduced, the target points estimation is one of the important objectives in the flight test as well as the safe separation. The prediction methods help to design the flight test schedule. However, the incremental aerodynamic coefficients in the aircraft flow field so-called BSE are difficult to predict. Generally, the semiempirical methods such as the grid methods, IFM and Flow TGP using database are used for estimation of BSE. However, these methods are quasi-steady methods using static aerodynamic loads. Nowadays the time-accurate CFD method is often used to predict the store separation event. In the current process, the incremental aerodynamic coefficients in BSE regime are calculated directly, and the elimination of delta coefficients is checked simultaneously. This stage can be used for the initial condition of Flow TGP with freestream database. Two dimensional supersonic and subsonic store separation problems have been simulated and incremental coefficients are calculated. The results show the time when the store gets out of BSE region.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2004년도 한국우주과학회보 제13권2호
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• pp.239-242
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• 2004

The fairing of the launch vehicles has a role of protecting the spacecraft from outer thermal, acoustical, and mechanical loads during flight. Among them, the thermal load is analyzed in the present study. The ascent thermal analyses include aerodynamic heating rate on every point of the fairing, heat transfer through the fairing and spacecraft, and the final temperature during ascent flight phase. A design code based on theoretical/experimental database is applied to calculate the aerodynamic heating rate, and a thermal math program, SINDA/Fluint, is considered for conductive heat transfer of the fairing. The results show that the present design satisfies the allowing temperature of the structure. Another important thermal problem, pyro explosive fairing separation device, is calculated because the pyro system is very sensitive to the temperature. The results also satisfies the pyro thermal condition.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.321-326
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• 2007

The joined-wing is a new concept of the airplane wing. The fore-wing and the aft-wing arc joined together in the joined-wing. The range and loiter are longer than those of a conventional wing. The joined-wing can lead to increased aerodynamic performances and reduction of the structural weight. The structural behavior of the joined-wing has a high geometric nonlinearity according to the external loads. The gust loads are the most critical loading conditions in the structural design of the joined-wing. The nonlinear behavior should be considered in the optimization of the joined-wing. It is well known that conventional nonlinear response optimization is extremely expensive: therefore, the conventional method is almost impossible to use in large scale structures such as the joined-wing. In this research, geometric nonlinear response structural optimization is carried out using equivalent loads. Equivalent loads are the load sets which generate the same response field in linear analysis as that from nonlinear analysis. In the equivalent loads method, the external loads are transformed to the equivalent loads (EL) for linear static analysis, and linear response optimization is carried out based on the EL.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.340-346
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• 2013

This paper describes a helicopter vibration induced by main rotor in forward flight. The hub loads in the fixed frame, which are dominant source of helicopter vibration, are obtained by multi-blade summation of rotating blades loadings. The components of 3/rev, 4/rev, and 5/rev blades loadings are transmitted by blades to 4/rev hub loads in the fixed frame. The vertical vibrations of helicopter at pilot seat and copilot seat are calculated through rigid body transfer functions considering airframe to be rigid body. The blades are assumed to be elastic and undergo the flap, lag, and torsion motion and free wake aerodynamic model is used to calculate the precise blade loadings in the analysis. The 4/rev vertical vibration responses are analyzed from rotating blade loadings and fixed hub loadings.

• Wind and Structures
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• 제5권5호
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• pp.393-406
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• 2002

Aerodynamic pressures and forces were measured on a model of a solar panel containing six slender, parallel modules. Of particular importance to system design is the aerodynamically induced torque. The peak system torque was generally observed to occur at approach wind angles near the diagonals of the panel ($45^{\circ}$, $135^{\circ}$, $225^{\circ}$ and $315^{\circ}$) although large loads also occurred at $270^{\circ}$, where wind is in the plane of the panel, perpendicular to the individual modules. In this case, there was strong vortex shedding from the in-line modules, due to the observation that the module spacing was near the critical value for wake buffeting. The largest loads, however, occurred at a wind angle where there was limited vortex shedding ($330^{\circ}$). In this case, the bulk of the fluctuating torque came from turbulent velocity fluctuations, which acted in a quasi-steady sense, in the oncoming flow. A simple, quasi-steady, model for determining the peak system torque coefficient was developed.

• Wind and Structures
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• 제37권2호
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• pp.163-178
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• 2023

The paper reviews and discusses the substantive changes to the ASCE 49-21 Standard, Wind Tunnel Testing for Buildings and Other Structures. The most significant changes are the requirements for wind field simulations that utilize (i) partial turbulence simulations, (ii) partial model simulations for the flow around building Appurtenances, along with requirements for determining wind loads on products that are used at multiple sites in various configurations. These modifications tend to have the effect of easing the precise scaling requirements for flow simulations because it is not generally possible to construct accurate models for small elements placed, for example, on large buildings at the scales typically available in boundary layer wind tunnels. Additional discussion is provided on changes to the Standard with respect to measurement accuracy and data acquisition parameters, such as duration of tests, which are also related to scaling requirements. Finally, research needs with respect to aerodynamic mechanisms are proposed, with the goal of improving the understanding of the role of turbulence on separated-reattaching flows on building surfaces in order to continue to improve the wind tunnel method for determining design wind loads.

• International Journal of Aeronautical and Space Sciences
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• 제15권4호
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• pp.345-355
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• 2014

This paper focuses on aerodynamic and inertial modeling of the propeller for its applications in flight dynamics analyses of a propeller-driven airplane. Unsteady aerodynamic and inertial loads generated by the propeller are formulated using the blade element method, where the local velocity and acceleration vectors for each blade element are obtained from exact kinematic relations for general maneuvering conditions. Vortex theory is applied to obtain the flow velocities induced by the propeller wake, which are used in the computation of the aerodynamic forces and moments generated by the propeller and other aerodynamic surfaces. The vortex lattice method is adopted to obtain the induced velocity over the wing and empennage components and the related influence coefficients are computed, taking into account the propeller induced velocities by tracing the wake trajectory trailing from each of the propeller blades. Aerodynamic forces and moments of the fuselage and other aerodynamic surfaces are computed by using the wind tunnel database and applying strip theory to incorporate viscous flow effects. The propeller models proposed in this paper are applied to predict isolated propeller performances under steady flight conditions. Trimmed level forward and turn flights are analyzed to investigate the effects of the propeller on the flight characteristics of a propeller-driven light-sports airplane. Flight test results for a series of maneuvering flights using a scaled model are employed to run the flight dynamic analysis program for the proposed propeller models. The simulations are compared with the flight test results to validate the usefulness of the approach. The resultant good correlations between the two data sets shows the propeller models proposed in this paper can predict flight characteristics with good accuracy.

• 한국군사과학기술학회지
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• 제10권4호
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• pp.81-87
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• 2007

In this study, analysis of structural design criteria for the canopy actuating device has been conducted considering the aerodynamic breakaway capabilities of jettisonable canopy system. Unsteady aerodynamic loads for the opened canopy configuration at passively controlled jettision mode were computed using CFD method. The general purpose multi-body finite element code, SAMCEF Mecano, is used in the implemented analyses for the passive jettision condition. The recommended altitude and speed of aircraft was suggested as design criteria of aerodynamic breakaway capability of jettisonable canopy system as a bakup egress method when normal canopy jettison sequence malfunctioned. Aerodynamic breakaway condition of jettisonable canopy was also simulated and the fracture load conditions of canopy actuator were investigated.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.877-880
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• 2017

원심압축기 임펠러의 블레이드는 고속회전과 정상유동 압력에 의한 정적하중이 가해진다. 동시에 임펠러와 디퓨저 베인 간 상호작용에 의해 발생하는 비정상 유동의 공력가진력이 공진조건에서 주기적으로 임펠러를 가진함에 따라 임펠러 블레이드의 고주기피로 파손이 발생할 수 있다. 이에 대한 정밀한 구조응답 예측을 위해 ANSYS를 이용한 비정상 유동 해석과 모드해석을 각기 수행하여 공력가진력과 주요 공진조건을 도출하였다. 이 후 공력-구조를 연계하는 단일방향의 강제진동 해석을 수행하고, 결과들을 토대로 고주기피로에 대한 안전도를 평가하였다.

• Wind and Structures
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• 제31권6호
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• pp.561-573
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• 2020

Unsteady self-excited forces are commonly represented by parametric models such as rational functions. However, this requires complex multiparametric nonlinear fitting, which can be a challenging task that requires know-how. This paper explores the alternative nonparametric modeling of unsteady self-excited forces based on relations between flutter derivatives. By exploiting the properties of the transfer function of linear causal systems, we show that damping and stiffness aerodynamic derivatives are related by the Hilbert transform. This property is utilized to develop exact simplified expressions, where it is only necessary to consider the frequency dependency of either the aeroelastic damping or stiffness terms but not both simultaneously. This approach is useful if the experimental data on aerodynamic derivatives that are related to the damping are deemed more accurate than the data that are related to the stiffness or vice versa. The proposed numerical models are evaluated with numerical examples and with data from wind tunnel experiments. The presented method can evaluate any continuous fitted table of interpolation functions of various types, which are independently fitted to aeroelastic damping and stiffness terms. The results demonstrate that the proposed methodology performs well. The relations between the flutter derivatives can be used to enhance the understanding of experimental modeling of aerodynamic self-excited forces for bridge decks.