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Minjung Park - One of the best experts on this subject based on the ideXlab platform.

  • optimization of ski jumper s posture considering lift to Drag Ratio and stability
    Journal of Biomechanics, 2012
    Co-Authors: Minjung Park
    Abstract:

    An optimization analysis of a ski jumper’s posture has been performed to improve the lift-to-Drag Ratio, and to examine aerodynamic stability to ensure flight control and safety. Three-dimensional Reynoldsaveraged Navier–Stokes equations were discretized using finite volume approximations for the flow analysis, and the shear stress transport k-o turbulence model was used for a turbulence closure. The Airfoil theory and principles of aircraft stability were used to examine the stability mechanism. Two ski jumper posture angles were chosen as design variables through a preliminary test, and the lift-to-Drag Ratio was used as an objective function for the optimization problem. Thirteen design points within design spaces are selected by Latin hypercube sampling. In order to predict the objective function values in the design space, the Kriging model was constructed using the numerical results on the design points. By the sequential quadratic programming, the optimal point was found from the constructed the Kriging model. The Kriging model predicted the objective function value at the optimum point with a 1.1% error compared to the value obtained by numerical analysis. The optimum design showed a considerable lift-to-Drag Ratio improvement compared to the reference design.

  • Optimization of Ski Jumper’s Posture Considering Lift-to-Drag Ratio and Aerodynamic Stability in Pitch
    Volume 6: Fluids and Thermal Systems; Advances for Process Industries Parts A and B, 2011
    Co-Authors: Minjung Park, Ki-don Lee, Kwang-yong Kim
    Abstract:

    In the present study, an optimization of ski jumper’s posture using a surrogate model has been numerically performed to improve lift-to-Drag Ratio and to examine aerodynamic stability in pitch to ensure flight control and safety. Three-dimensional Reynolds-averaged Navier-Stokes equations are discretized by finite volume approximations for the flow analysis, and the shear stress transport turbulence model is used as the turbulence closure. Airfoil theory and principles of aircraft stability are used to examine the stability mechanism. To enhance aerodynamic stability in ski jumping, the ranges of design variables are determined to have a static margin value within 5∼25%. Two angles of ski jumper’s posture are chosen as design variables through a preliminary test and the lift-to-Drag Ratio is used as an objective function for the present optimization problem. Twelve design points within design spaces are selected by Latin hypercube sampling. To approximate the objective function in the design space, the Kriging model is constructed using the numerical results on the design points, and the optimal point is found by sequential quadratic programming. The predicted values of the design variables and the objective function for the optimal and the reference design, as well as corresponding results of numerical calculation. The Kriging model predicts the objective function values at the optimum points with only 1.61% error in comparison with the values obtained the RANS analysis. And, the optimum design shows not only improved lift-to-Drag Ratio but also increased longitudinal stability in ski jumping as compared to the reference design.© 2011 ASME

  • optimization of ski jumper s posture considering lift to Drag Ratio and aerodynamic stability in pitch
    Volume 6: Fluids and Thermal Systems; Advances for Process Industries Parts A and B, 2011
    Co-Authors: Minjung Park, Ki-don Lee, Kwang-yong Kim
    Abstract:

    In the present study, an optimization of ski jumper’s posture using a surrogate model has been numerically performed to improve lift-to-Drag Ratio and to examine aerodynamic stability in pitch to ensure flight control and safety. Three-dimensional Reynolds-averaged Navier-Stokes equations are discretized by finite volume approximations for the flow analysis, and the shear stress transport turbulence model is used as the turbulence closure. Airfoil theory and principles of aircraft stability are used to examine the stability mechanism. To enhance aerodynamic stability in ski jumping, the ranges of design variables are determined to have a static margin value within 5∼25%. Two angles of ski jumper’s posture are chosen as design variables through a preliminary test and the lift-to-Drag Ratio is used as an objective function for the present optimization problem. Twelve design points within design spaces are selected by Latin hypercube sampling. To approximate the objective function in the design space, the Kriging model is constructed using the numerical results on the design points, and the optimal point is found by sequential quadratic programming. The predicted values of the design variables and the objective function for the optimal and the reference design, as well as corresponding results of numerical calculation. The Kriging model predicts the objective function values at the optimum points with only 1.61% error in comparison with the values obtained the RANS analysis. And, the optimum design shows not only improved lift-to-Drag Ratio but also increased longitudinal stability in ski jumping as compared to the reference design.© 2011 ASME

V. B. Kharchenko - One of the best experts on this subject based on the ideXlab platform.

S. A. Isaev - One of the best experts on this subject based on the ideXlab platform.

Guo-liang Liu - One of the best experts on this subject based on the ideXlab platform.

  • Hydrodynamic performance and calculation of lift–Drag Ratio on underwater glider
    Journal of Marine Science and Technology, 2020
    Co-Authors: Zhang Yanqin, Zhang Zhiquan, Quan Zhen, Guo-liang Liu
    Abstract:

    The hydrodynamic performance and lift-Drag Ratio of the underwater glider affected the state of its own opeRation. Therefore, a three-dimensional physical model and a mathematical model of a certain type of underwater glider are established. According to the principles of aircraft performance characterization, the fluid dynamics method was used to simulate the pressure distribution of the underwater glider pressure field and the overall outflow field, under the attack angle from − 10° to 10° and the gliding speeds were 0.25 m/s, 0.5 m/s, 0.75 m/s, and 1 m/s. Finally, the Drag experiment of this type of underwater glider is verified. It is concluded that as the gliding speed increases, the pressure of the high-pressure area of is increases, the pressure of the low-pressure area decreases, and the pressure difference resistance increases continuously. In the case of small attack angle (  8°), the lift–Drag Ratio tends to decrease slightly with increase in attack angle. The maximum lift–Drag Ratio is produced at an attack angle about 8° and the underwater glider can get maximum hydrodynamic efficiency at this attack angle.

  • hydrodynamic performance and calculation of lift Drag Ratio on underwater glider
    Journal of Marine Science and Technology, 2020
    Co-Authors: Zhiquan Zhang, Yanqin Zhang, Zhen Quan, Guo-liang Liu
    Abstract:

    The hydrodynamic performance and lift-Drag Ratio of the underwater glider affected the state of its own opeRation. Therefore, a three-dimensional physical model and a mathematical model of a certain type of underwater glider are established. According to the principles of aircraft performance characterization, the fluid dynamics method was used to simulate the pressure distribution of the underwater glider pressure field and the overall outflow field, under the attack angle from − 10° to 10° and the gliding speeds were 0.25 m/s, 0.5 m/s, 0.75 m/s, and 1 m/s. Finally, the Drag experiment of this type of underwater glider is verified. It is concluded that as the gliding speed increases, the pressure of the high-pressure area of is increases, the pressure of the low-pressure area decreases, and the pressure difference resistance increases continuously. In the case of small attack angle (  8°), the lift–Drag Ratio tends to decrease slightly with increase in attack angle. The maximum lift–Drag Ratio is produced at an attack angle about 8° and the underwater glider can get maximum hydrodynamic efficiency at this attack angle.

Elizarov A. - One of the best experts on this subject based on the ideXlab platform.

  • Maximization of the lift/Drag Ratio of airfoils with a turbulent boundary layer: Sharp estimates, approximation, and numerical solutions
    2020
    Co-Authors: Elizarov A., Kalimullina A.
    Abstract:

    The lift/Drag Ratio of an airfoil placed in an incompressible attached flow is maximized taking into account the viscosity in the boundary-layer approximation. An exact solution is constructed. The situation when the resulting solutions are not in the admissible class of univalent flows is discussed. A procedure is proposed for determining physically feasible airfoils (with a univalent flow region) with a high lift/Drag Ratio. For this purpose, a class of airfoils is constructed that are determined by a twoparameter function approximating the found exact solution to the variational problem. For this class, the ranges of free parameters leading to physically feasible flows are found. The results are verified by computing a turbulent boundary layer using Eppler's method, and airfoils with a high lift/Drag Ratio in an attached flow are detected. © 2009 Pleiades Publishing, Ltd

  • Maximizing the lift-Drag Ratio of wing airfoils with a turbulent boundary layer: Exact solutions and approximations
    2020
    Co-Authors: Elizarov A.
    Abstract:

    Exact solutions and approximations for maximizing the lift-Drag Ratio of wing airfoils with a turbulent boundary layer is discussed. The employment of the inviscid incompressible-fluid and boundary-layer models enables to write the optimized functional and the optimization constraints in the explicit form. The need of the smooth and sepaRationless flow is a necessary assumption in the formulation of the problem. The consideRation of the fact that the calculation of the whole layer as fully turbulent yields more reliable values of the airfoil loss coefficients, with the consideRation of the fully turbulent flow around the airfoil. The wing airfoil shape is also numerically optimized to obtain the global maximum of the lift-Drag Ratio under the conditions of the absence of turbulent boundary layer-sepaRation and the airfoil contour simplicity