Dynamic Aeroelastic Response Analysis

The purpose of dynamic aeroelastic response analysis is to study the reactions of an aeroelastic system to prescribed loads and displacements, and to atmospheric gust fields. The effects of a control system can also be assessed if its equations (transfer functions) have been included in the (aeroservoelastic) model. As in flutter analysis, the modal method is employed to reduce the computational effort. LDP can solve for frequency response, random response, and transient response problems in the presence of an airstream. Examples of response problems in which aerodynamic effects should usually not be neglected include high speed landing loads, in-flight store ejection loads, and loads and accelerations in a gust field.

LDP Aerospace utilizes two techniques in solving for the response to an enforced displacement: one is the large mass method, and the other is the Lagrange multiplier method. The Lagrange multiplier method requires less judgment and is computationally efficient with a small number of modes, so it is utilized effectively in some dynamic aeroelastic response analyses.

Frequency Response Analysis

All dynamic aeroelastic analyses require a modal frequency analysis. A frequency response analysis is an integral part of random response analysis and transient analysis, and it can be of interest in its own right to obtain transfer functions for designing control systems. If only the frequency response is desired, LDP Engineers must specify the frequency content of the loading. If the loading is more conveniently specified in the time domain, specifically, the solution sequence will lead to the transient response and the intermediate result of the frequency response. Particular care is required to output the frequency response data in this case. The input data for a dynamic aeroelastic response analysis are similar to those required for a flutter analysis.

Random Response Analysis

LDP performs random response analyses. For a random response analysis, the loading is specified in the frequency domain, or by an enforced motion. To proceed with the random response analysis subsequent to the frequency response analysis, it is only necessary to specify the power spectral density of the excitation. A prescribed random loading is obtained by using dedicated routines developed inside LDP Aerospace, that specify also the input excitation power spectrum. For gust loading, it can be specified either the von Karman or Dryden spectrum or a tabulated power spectrum. The output power spectral density is requested by specific plot commands. The root mean square values of each selected output response and its expected frequency, are generated when output power spectra are requested.

Transient Response Analysis

LDP performs transient response analyses. For transient response analysis under a prescribed loading condition, the loading is specified in conjunction with specific models developed inside LDP, or by an enforced displacement. To proceed with the transient response analysis subsequent to the frequency response analysis, it is only necessary to specify the time history of the excitation.