• Journal of computational fluids engineering
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• v.17 no.4
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• pp.56-68
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• 2012

Nowadays, Unmanned Combat Air Vehicle(UCAV) has become an important aircraft system for the national defense. For its efficiency and survivability, shape optimization of UCAV is an essential part of its design process. In this paper, shape optimization of UCAV was processed for aerodynamic performance improvement and Radar Cross Section(RCS) reduction using Multi Objective Genetic Algorithm(MOGA). Lift and induced drag, friction drag, RCS were calculated using panel method, boundary layer theory, Physical Optics(PO) approximation respectively. In particular, calculation applied Radar Absorbing Material(RAM) was performed for the additional RCS reduction. Results are indicated that shape optimization is performed well for improving aerodynamic performance, reducing RCS. Further study will be performed with higher fidelity tools and consider other design segments including structure.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.100-110
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• 2007

A new design approach for a delicate treatment of complex geometries such as a wing/body configuration is arranged using overset mesh technique under large scale computing environment for turbulent viscous flow. Various pre- and post-processing techniques which are required of overset flow analysis and sensitivity analysis codes are discussed for design optimization problems based on gradient based optimization method (GBOM). The overset flow analysis code is validated by comparing with the experimental data of a wing/body configuration (DLR-F4) from the 1st Drag Prediction Workshop (DPW-I). In order to examine the applicability of the present design tools, careful design works for the drag minimization problem of a wing/body configuration are carried out by using the developed aerodynamic shape optimization tools for the viscous flow over multiple-body aircraft geometries.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.347-354
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• 2008

We introduce a series of studies on turbulent skin friction drag reduction in wall-turbulence. First, an identity equation relating the skin friction drag and the Reynolds shear stress (the FIK identity) is introduced. Based on the implication of the FIK identity, a new analytical suboptimal feedback control law requiring the streamwise wall-shear stress only is introduced and direct numerical simulation (DNS) results of turbulent pipe flow with that control is reported. We also introduce DNS of an anisotropic compliant surface and parameter optimization using an evolutionary optimization technique.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.347-354
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• 2008

We introduce a series of studies on turbulent skin friction drag reduction in wall-turbulence. First, an identity equation relating the skin friction drag and the Reynolds shear stress (the FIK identity) is introduced. Based on the implication of the FIK identity, a new analytical suboptimal feedback control law requiring the streamwise wall-shear stress only is introduced and direct numerical simulation (DNS) results of turbulent pipe flow with that control is reported. We also introduce DNS of an anisotropic compliant surface and parameter optimization using an evolutionary optimization technique.

• Journal of computational fluids engineering
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• v.4 no.1
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• pp.34-40
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• 1999

Drag reduction on vehicles are the main concern for the body shape designers in order to lower the fuel consumption rate and to aid the driving stability. The drag of bluff bodies like transportation vehicles is mostly pressure drag due to the flow separation, which can be minimized by controlling the location and size of the separation bubble. In the present study, the TURBO-3D code is incorporated with optimal algorithm based on analytical approximation method to obtain an optimal afterbody shape of the MIRA Model corresponding to the lowest drag coefficient. For this purpose three mutually independent afterbody angles are chosen as design variables, while the drag coefficient is chosen as an objective function. It is demonstrated in the present study that an optimal body shape having the lowest drag coefficient which is about 6% lower than that of the original shape has been successfully obtained within number of iterations of tile optimal design loop.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.111-118
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• 2000

The design of reference trajectory with respect to drag acceleration is necessary to decelerate from hypersonic speed safely after atmosphere re-entry of space vehicle. The re-entry guidance design involves trajectory optimization, generation of a reference drag acceleration profile with the satisfaction of 6 trajectory constraints during the re-entry flight. This reference drag acceleration profile can be considered as the reference trajectory. The cost function is composed of the accumulated total heating on vehicle due to the reduction of weight. And a regularization is needed to prevent optimal drag profile from varying too fast and achieve realized trajectory. This paper shows the relations between velocity, drag acceleration and altitude in drag acceleration profile, and how to determine the reference trajectory.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.3
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• pp.423-431
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• 2016

In this study, wing design optimization for long-endurance unmanned aerial vehicles (UAVs) is investigated. The fluid-structure integration (FSI) analysis is carried out to simulate the aeroelastic characteristics of a high-aspect ratio wing for a long-endurance UAV. High-fidelity computational codes, FLUENT and DIAMOND/IPSAP, are employed for the loose coupling FSI optimization. In addition, this optimization procedure is improved by adopting the design of experiment (DOE) and Kriging model. A design optimization tool, PIAnO, integrates with an in-house codes, CAE simulation and an optimization process for generating the wing geometry/computational mesh, transferring information, and finding the optimum solution. The goal of this optimization is to find the best high-aspect ratio wing shape that generates minimum drag at a cruise condition of $C_L=1.0$. The result shows that the optimal wing shape produced 5.95 % less drag compared to the initial wing shape.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.5
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• pp.785-794
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• 2015

To obtain low resistance and high efficiency energy-saving ship, minimum total resistance hull form design method is studied based on potential flow theory of wave-making resistance and considering the effects of tail viscous separation. With the sum of wave resistance and viscous resistance as objective functions and the parameters of B-Spline function as design variables, mathematical models are built using Nonlinear Programming Method (NLP) ensuring the basic limit of displacement and considering rear viscous separation. We develop ship lines optimization procedures with intellectual property rights. Series60 is used as parent ship in optimization design to obtain improved ship (Series60-1) theoretically. Then drag tests for the improved ship (Series60-1) is made to get the actual minimum total resistance hull form.

• Journal of the Korean Society for Railway
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• v.18 no.4
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• pp.279-288
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• 2015

Using the Vehicle Modeling Function, which can model various 3D nose shapes, nose shape optimization is performed to reduce the aerodynamic drag of the KTX Sancheon. 2D characteristic shapes of the KTX Sancheon nose were extracted and a base model of the KTX Sancheon was constructed for design optimization using the Vehicle Modeling Function. The design space was constructed with the base model and does not violate the shape constraints of commercial trains. Through nose shape optimization with the Broyden-Fletcher-Goldfarb-Shanno algorithm, the aerodynamic drag of the optimized shape was reduced by 6% compared to that of the base model. The longer nose and sharper edge of the optimized shape weaken the vortices behind the last car and can reduce the aerodynamic drag.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.18-18
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• 2000

In the high lift devices specifications for surface smoothness requirements, as manufacturing tolerances, arise out of aerodynamic consideration to minimize drag. True optimization of tolerances is a multi-disciplinary problem involving fluid mechanics, device performance, manufacturing philosophy and life cycle costing. One of the reasons for degradation of wetted surface is discrete roughness as a consequence of manufacturing defects, collectively termed as one of the excrescences effect. Usually, excrescence drag arising out of discrete roughness is of considerable lower order of magnitude as compared to the total drag of the flight bodies. Nor was there adequate predicting tool to account for the extent of drag degradation. Estimation of excrescence drag remained as a state-of-the art based on experimental results.