Aeroelastic Design Sensitivity and Optimization

LDP advanced expertise in the structural and aerodynamic modelling, in conjunction with its know-how of critical engineering topics, allows studies of aeroelastic design sensitivity and optimization. This is a multidisciplinary analysis.

For an optimization procedure to be of maximum benefit, it must be able to simultaneously take into account of all the conditions that impact the design. For this reason, the design sensitivity and optimization capability of LDP Aerospace is based on a multidisciplinary analysis capability that includes statics, normal modes, buckling, direct and modal frequency, modal transient, static aeroelastic, and flutter analyses. The static aeroelastic and flutter analysis capabilities present in the multidisciplinary analysis and design solution sequence contain the full capabilities of the static aeroelastic and flutter solution sequences. It is necessary in this kind of study to designate the type of analysis being performed for each subcase using the extreme care and experience.

Response Evaluation

Responses are quantities available for sensitivity analysis or optimization.For a sensitivity value to be computed, LDP Engineers must designate it as entry and either constrain it as entry or identify it as the design objective. For static aeroelasticity, LDP can invoke standard static analysis responses, as well as two responses, developed inside LDP, that are unique to static aeroelasticity. The response requests a stability derivative response and therefore selects one of the components of an aerodynamic extra point. The selected response type can correspond to a restrained or unrestrained derivative, based on the value of the computational field.The utility of this request is that it is possible to determine how a key aeroelastic parameter, such as lift curve slope, varies when a structural change is made. More significant perhaps, it is possible to include design requirements on these stability derivatives in a design optimization study. It is to be expected that the sensitivity of this response to a particular structural parameter is small. The response can have utility in limiting the range over which an aerodynamic value can vary during an optimization task; e.g., by limiting an elevator rotation.

Sensitivity Analysis

Sensitivity information can guide the aeroelastician in making design changes. The specification of response quantities as described precedently is a means towards the end of obtaining information for the structural design task. The first type of information that is available is sensitivity results wherein the rate of change of a particular response quantity, with respect to a change in a design variable, is produced. Design Sensitivity andOptimization is a detailed study of design sensitivity analysis while Aeroelastic Analysis, is more broadly a description of the calculations required to provide these sensitivities for aeroelastic responses. Implementation of design sensitivity analysis requires that the responses must be "constrained" in order for design sensitivity to occur. Further, the constrained responses have to pass through screening criteria that are applied in order to limit the number of responses that are used in a design sensitivity and/or optimization task. The screening procedure of LDP then selects the constraints that are greater than a threshold value with a further limitation that only a limited number of responses of a given type will be retained. LDP Engineers can force a response to be retained for later use by using appropriate routines.

Optimization

Optimization can take the place of tedious "cut and try" procedures. Once LDP Engineers has specified the design variables, a design objective, and design constraints, the design that provides the minimum (or maximum) value of the objective while satisfying the imposed constraints can be determined. This is a powerful tool for the aeroelastician in that it provides a systematic means of finding an improved design. It can also be appreciated that, particularly in the context of aeroelasticity, LDP Engineers must be involved with the optimization task and apply "reasonableness" tests to the designs that are achieved. An optimization task exploits any deficiencies in the analysis in a way that helps it achieve its goals.