On repetitive flutter calculations in structural design

Haftka, Raphael T.; Yates, E. C.

doi:10.2514/6.1974-141

Cited by 7 publications

(11 citation statements)

References 2 publications

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“…The use of fixed-basis modal design models for the dynamic aeroelastic disciplines started long before their usage in the static disciplines [16]. Other than using a fixed basis, the formulation in [16] was that of a classic frequencydomain flutter analysis with transcendental unsteady aerodynamic force coefficient matrices [5, 6].…”

Section: Introductionmentioning

confidence: 99%

“…Other than using a fixed basis, the formulation in [16] was that of a classic frequencydomain flutter analysis with transcendental unsteady aerodynamic force coefficient matrices [5, 6]. Some control system effects can be accommodated by the frequency-domain approach, but the application of various modern control design techniques requires the aeroservoelastic equations of motion to be transformed into a first-order, time-domain (statespace) form.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the modal basis can be expanded during the optimization process by including static modes. Local effects due to concentrated loads or large structural changes can be treated by fictitious-mass techniques [13,15].The use of fixed-basis modal design models for the dynamic aeroelastic disciplines started long before their usage in the static disciplines [16]. Other than using a fixed basis, the formulation in [16] was that of a classic frequencydomain flutter analysis with transcendental unsteady aerodynamic force coefficient matrices [5, 6].…”

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confidence: 99%

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Procedures and Models for Aeroservoelastic Analysis and Design

Karpel

2001

Z. angew. Math. Mech.

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The multi‐disciplinary area that deals with the interaction of the structural, aerodynamic, and control systems of flight vehicles is called aeroservoelasticity. The various aircraft design aspects which are affected by aeroservoelastic interaction are presented with a common modal‐based formulation. The disciplinary and interaction techniques are reviewed and combined for an integrated design optimization scheme where stress, static‐aeroelastic, closed‐loop flutter, control margins, time response, and continuous gust constraints are treated with a common basic model. The structure is represented in the basic model by a set of low‐frequency normal modes of a baseline design. Design changes are adequately addressed without changing the generalized coordinates. Typical difficulties of the modal approach are alleviated by various optional fictitious‐mass and modal perturbation techniques. Static modes can be added during the optimization process for better convergence to the optimal solution. Minimum‐state rational approximation of the unsteady aerodynamics leads to an efficient state‐space model which can be augmented by any combination of linear control components. Physical weighting algorithm is used to improve the aerodynamic approximations and to select modes for truncation or residualization. Linear reduced‐size models and the associated analytic sensitivities to design changes facilitate extremely efficient and adequately accurate on‐line design sessions. The linear models can be integrated with computational aerodynamics codes for the evaluation of important non‐linear aerodynamic effects early in the design process.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Procedures and Models for Aeroservoelastic Analysis and Design

Karpel

2001

Z. angew. Math. Mech.

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“…[35] it was shown that there is a substantial difference in the derivatives of aircraft flutter speeds when fixed modes are used rather than the updated modes.…”

Section: Fixed Versus Updated Modes In Sensitivity Calculationsmentioning

confidence: 99%

Computational aspects of sensitivity calculations in linear transient structural analysis

Greene

Haftka

1991

Structural Optimization

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A study has been performed focusing on the calculation of sensitivities of displacements, velocities, accelerations, and stresses in linear, structural, transient response problems. One significant goal of the study was to develop and evaluate sensitivity calculation techniques suitable for large-order finite element analyses. Two types of sensitivity calculation techniques were developed and evaluated.The first type of technique is an overall finite difference method where the analysis is repeated for perturbed designs. The second type of technique is termed semianalytical because it involves direct, analytical differentiation of the equations of motion with finite difference approximation of the coefficient matrices. To be computationally practical in large-order problems, the overall finite difference methods must use the approximation vectors from the original design in the analyses of the perturbed models. In several cases this fixed mode approach resulted in very poor approximations of the stress sensitivities. Almost all of the original modes were required for an accurate sensitivity and for small numbers of modes, the accuracy was extremely poor. To overcome this poor accuracy, two semi-analytical techniques were developed. The first technique accounts for the change in eigenvectors through approximate eigenvector derivatives. The second technique applies the mode acceleration method of transient analysis to the sensitivity calculations. Both result in accurate values of the stress sensitivities with a small number of modes. In both techniques the computational cost is much less than would result if the vibration modes were recalculated and then used in an overall finite difference method.

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“…Haftka has in a series of papers (Haftka 1973;Haftka and Yates 1976) presented several differen¢ methods based on optimality criteria methods as well as more rigorous methods of optimization. In particular, Haftka and Yates (1976) discuss the use of a fixed modal subspace as opposed to using a design dependent subspace. Wilkinson et al (1977) have developed the software system FASTOP for design optimization subject to strength and flutter speed constraints.…”

Section: Introductionmentioning

confidence: 99%

On structural optimization with aeroelasticity constraints

Ringertz

1994

Structural Optimization

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The optimal design of a cantilever wing in incompressible flow is considered. The wing is modelled as a full depth sandwich wing using finite element analysis. A doublet lattice panel method is used for computation of the unsteady aerodynamic loads. The weight of the wing is minimized using the thicknesses of the composite face sheets as design variables subject to constraints on flutter and divergence speed. Imperfection sensitivity of the final design is analysed and general aspects of imperfection sensitivity in optimization subject to aeroelasticity constraints are discussed in some detail.

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On repetitive flutter calculations in structural design

Cited by 7 publications

References 2 publications

Procedures and Models for Aeroservoelastic Analysis and Design

Procedures and Models for Aeroservoelastic Analysis and Design

Computational aspects of sensitivity calculations in linear transient structural analysis

On structural optimization with aeroelasticity constraints

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