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optimization OF ROTOR PERFORMANCE IN HOVER USING A FREE WAKE ANALYSIS

JOURNAL OF AIRCRAFT 1991年第3期28卷 200-207页

作者： QUACKENBUSH, TR WACHSPRESS, DA KAUFMAN, AE Continuum Dynamics Inc. Princeton New Jersey 08543

Performance optimization for rotors in hover is a topic of continuing importance to rotorcraft designers. The aim of this research was to demonstrate that a free wake hover performance prediction code could be coupled to a numerical optimization algorithm. The hover code, dubbed EHPIC (evaluation of hover performance using influence coefficients), uses a quasilinear wake relaxation to solve for the rotor performance and is well suited to optimization applications. The coupling was accomplished by expanding the matrix of influence coefficients in EHPIC to accommodate design variables and by deriving new coefficients for linearized equations governing perturbations in power and thrust. These coefficients formed the input to a numerical optimization analysis, which used the flow tangency conditions on the blade and in the wake along with specified inequality constraints to constrain the design. It was found that this linearized analysis could be invoked to predict a design change that would produce significant reductions in power required at constant thrust. Thus, improved versions of the baseline design can be found efficiently while retaining the accuracy inherent in a free wake performance analysis. Sample problems were undertaken to demonstrate the success of this approach in reducing the power required at a specified thrust for several representative rotor configurations.

关键词： Free Wake Analysis Influence Coefficients Aerodynamic Vehicle Coaxial Rotor Numerical optimization Thrust Equation Vortex Filaments optimization algorithm Lift Coefficient Blade Vortex Interaction

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INTEGRATED STRUCTURAL-ANALYSIS AND DESIGN USING 3-DIMENSIONAL FINITE-ELEMENTS

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AIAA JOURNAL 1991年第5期29卷 791-797页

作者： BARTHELEMY, B HAFTKA, RT MADAPUR, U SANKARANARAYANAN, S VIRGINIA POLYTECH INST & STATE UNIV DEPT AEROSP & OCEAN ENGNBLACKSBURGVA 24061

A design approach that combines iterative structural analysis with a traditional iterative optimization algorithm is applied to the optimum design of the shape of a hole in a plate in tension. The plate is modeled by three-dimensional finite elements, and an element-by-element preconditioned conjugate gradient iterative algorithm is used for solving the equations of equilibrium. Several parameterizations of the optimum shape are considered, and it is shown that a sine series can describe the optimum shape with only three design variables, whereas other series require seven variables for similar results. The optimum shape compares well with an experimental optimum obtained by A. J. Durelli. An investigation is performed to determine the best way of obtaining finite-difference derivatives of the stresses with respect to design variables. It is shown that a method based on modifying the equations of equilibrium for the perturbed problem performs best. The benefit of the integrated approach is determined by comparing convergence with different initial iterates for the displacement field. It is shown that using the final iterate of the previous solution can reduce the number of analysis iterations by about 40% compared to starting with a zero initial iterate.

关键词： Structural Analysis optimization algorithm Iterative algorithm Finite Element Modeling Gaussian Elimination Iterative Solution Structural optimization Sequential Linear Programming Interlaminar Stress Stress Concentration

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OPTIMAL AIRCRAFT PERFORMANCE DURING MICROBURST ENCOUNTER

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1991年第2期14卷 440-446页

作者： PSIAKI, ML STENGEL, RF PRINCETON UNIV MECH & AEROSP ENGNPRINCETONNJ 08544

The effects of microburst characteristics on the optimal penetration performance of jet transport and general aviation aircraft are presented. The purpose is to determine the best possible performance that can be achieved in a broad range of microbursts. A secondary goal is to illustrate good strategies for dealing with a range of microbursts during takeoff and landing. Over 1100 optimal trajectories were computed for two aircraft types flying through idealized microbursts using a Successive Quadratic Programs trajectory optimization algorithm. Contours of safety metrics are plotted as functions of the length scales, magnitudes, and locations of horizontal wind shears and vertical downdrafts. These performance contours show three length-scale regimes for optimal microburst penetration. At short length scales, hazards usually associated with gustiness predominate (e.g., high normal load factor, rotational upset). At intermediate length scales, a degraded ability to maintain flight path and/or vertical velocity poses the most serious threat. At very long microburst length scales, excessive touch-down velocities may result. The ability to transit a microburst successfully also varies strongly with microburst location. The results show that both aircraft types could penetrate some very severe microbursts if optimal control histories were followed. Nevertheless, these control strategies assume perfect prior knowledge of the wind, and practical limits to successful encounter with real-time control capabilities would, be lower. The optimally controlled jet transport can successfully penetrate higher intensity microbursts than can the general aviation aircraft.

关键词： Microburst Aircraft Performance Algebraic Riccati Equation General Aviation optimization algorithm Takeoff and Landing Airspeed Angle of Attack Aerodynamic Properties Phugoid

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DESIGN OF A VISCOUS RING NUTATION DAMPER FOR A FREELY PRECESSING BODY

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1991年第6期14卷 1136-1144页

作者： CHANG, CO CHOU, CS WANG, SZ CHUNG SHAN INST SCI & TECHNOL LONG TANGTAIWAN

A ring damper partially filled with mercury for removing the wobble motion of a freely precessing body is analyzed. Coupled equations of motion of the rotor and mercury are derived in terms of Euler parameters and quasicoordinates for the purposes of computational efficiency and singularity-free solution when the nutation angle approaches zero. An experiment is made to verify the theoretical solution of the nutation angle obtained by numerical integration of the equations of motion. The best choice of parameters of the damper is obtained by solving a minimum-time optimization problem that minimizes the time elapsed in the nutation-synchronous mode as well as the residual nutation angle in the spin-synchronous mode. The results show that the decay of the nutation angle can be accelerated to a great extent if the damper is properly designed.

关键词： Viscous Ring Nutation Damper Numerical Integration Gyroscopes Kinetic Energy Shear Stress Turbulent Flow Cartesian Coordinate System optimization algorithm Kinematic Viscosity Quaternions

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CONSERVATIVE METHODS FOR STRUCTURAL optimization

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AIAA JOURNAL 1990年第8期28卷 1491-1496页

作者： BENNETT, JA LUST, RV General Motors Research Laboratories Warren Michigan 48090-9055

Several methods can be used to generate conservative designs when using structural optimization techniques. A method is introduced which adds a padding term to each constraint that is proportional to the gradient of the constraint. One way to implement this approach is to determine the gradients of the constraints at the unpadded optimum design, to modify the constraint allowables, and then to restart the optimization. This approach assumes that these gradients will not change significantly when the new optimum is located. A second implementation is proposed which imbeds the padding calculation into the optimization process by updating the padding term periodically during the optimization process. Numerical experiments indicated that the additional nonlinearity introduced by this method did not affect the solution progress. Finally an implementation which uses nonlinear constraint approximations and a second order update method is described. It was shown that all implementations produced more mass efficient designs than does the more traditional method of adding a constant safety factor to each constraint. © 1990 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Structural optimization optimization algorithm Structural Integrity Structural Response Taylor Series Yield Stress

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STRUCTURAL MODEL VERIFICATION WITH LINEAR QUADRATIC optimization THEORY

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AIAA JOURNAL 1990年第8期28卷 1497-1503页

作者： LAPIERRE, H OSTIGUY, G UNIV MONTREAL ECOLE POLYTECHDEPT MECH ENGNMONTREAL H3C 3J7QUEBECCANADA

A graphic tool is developed and validated for the verification and updating of large structure finite element models (FEM) for better correlation with modal test data. The elaborated Linear Quadratic optimization (LQO) theory consists of a linearization and solution of the conventional matrix optimization problem that respect the connectivity of the structure and the symmetry of the stiffness matrix. The LQO theory is validated through a numerical and experimental sensitivity analysis. The results demonstrate the ability of the LQO algorithm to identify and update the stiffness coefficients associated with the inappropriately modeled load paths in the structure. © 1990 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Structural Modeling Finite Element Modeling Lagrange Multipliers Accelerometer Structural Damping Singular Value Decomposition Propellant Nastran optimization algorithm Sensitivity Analysis

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REANALYSIS FOR STRUCTURAL MODIFICATIONS IN BOUNDARY-ELEMENT RESPONSE AND DESIGN SENSITIVITY ANALYSIS

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AIAA JOURNAL 1990年第2期28卷 323-328页

作者： SAIGAL, S Carnegie Mellon University Pittsburgh Pensylvania

A reanalysis technique is presented for obtaining changes in response variables due to changes in design parameters with the boundary-element method. The approach is considered for static response analysis and design sensitivity analysis. Two iterative schemes, one based on total quantities and another based on incremental quantities, are developed. These schemes avoid the computationally expensive step of factorization of the coefficient matrix for the modified structure. Numerical results are obtained for analyses using 1) single-zone discretization, 2) multizone discretization, and 3) multizone discretization with condensation. The convergence trends for both iterative algorithms are presented for the response analysis and the design sensitivity analysis. A substantial economy in computer time is obtained using the present developments and is demonstrated here through CPU timings. © 1990 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Sensitivity Analysis Condensation Boundary Element Method Iterative algorithm Shape optimization Finite Element Method Internal Pressure Static Analysis optimization algorithm Numerical Integration

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CORRECTING FINITE-ELEMENT MODELS USING A SYMMETRICAL EIGENSTRUCTURE ASSIGNMENT TECHNIQUE

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AIAA JOURNAL 1990年第9期28卷 1670-1676页

作者： ZIMMERMAN, DC WIDENGREN, M ROYAL INST TECHNOL DEPT MECHS-10044 STOCKHOLM 70SWEDEN

Improvement of structural models by incorporating measured structural modal parameters is approached from a controls aspect. The approach is developed for linear structures that exhibit nonproportional damping. Residual damping and stiffness matrices are determined such that the unproved analytical model eigenstructure matches more closely that obtained experimentally. The method is based on the development of a symmetric eigenstructure assignment algorithm. Examples will be presented that demonstrate the algorithm. © 1990 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Finite Element Modeling Algebraic Riccati Equation Nonlinear Programming Structural Modeling Riccati Equations Closed Loop optimization algorithm Flexible Structures Feedback Control Damping Ratio

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APPROXIMATION OF ANALOG CONTROLLERS FOR SAMPLED-DATA SYSTEMS

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1990年第6期13卷 1155-1157页

作者： PENA, RSS Instituto de Investigaciones Aeronauticas y Espaciales Centro Espacial San Miguel Buenos Aires Argentina

For a sampled data feedback system, the compensator consists of a prefilter F(s), a sampler with a sample period T, a digital computer D(z), and a hold device H(s). The objective of a feedback controller design is to choose these elements to stabilize the plant G(s) and to meet various performance specifications. In this paper, an improvement to other methods is given by guaranteeing closed-loop stability, approximating a performance cost function, and improving the numerical condition of the problem. The general formulation will be stated. The work describes a solution that is suboptimal but computationally less expensive than the general approach stated. Examples for both approaches are presented,

关键词： Sampled Data Systems Closed Loop System Nonlinear Programming optimization algorithm Digital Computers Gradient Method Newton's Method

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OPTIMAL AUTOROTATIONAL DESCENT OF A HELICOPTER WITH CONTROL AND STATE INEQUALITY CONSTRAINTS

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1990年第5期13卷 922-924页

作者： LEE, AY Jet Propulsion Laboratory California Institute of Technology Pasadena California 91106

Gliding descent in autorotation is used by helicopter pilots in case of engine failure. A successful landing following an autorotation descent requires considerable skill, and since it is seldom practiced, it is considered quite dangerous. Methods and devices have been proposed to improve helicopter autorotational landing characteristics. In this paper a point-mass model of an OH-58A helicopter is used to determine its autorotation profiles that minimize the impact velocity of the helicopter while staying within bounds on the rotor's collective pitch and angular speed. The optimal control strategies obtained are similar to those used by pilots in autorotational landings. The study indicates that there is a potential for reducing the H-V restriction zone of OH-58A helicopters using optimal energy management techniques.

关键词： Helicopters Pilot Rotor Blades Optimal Control Nelder Mead Simplex Energy Management Drag Coefficient Flight Testing optimization algorithm Momentum Theory

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