Research Of Structural Modal Parameters And Dynamic Internal Forces Identification For High Speed Vehicles Under Flying Environments

In recent years, hypersonic aircraft, as represented by X51WaveRider from U.S., has attracted worldwide attention. Distinguished from any other aircraft, a hypersonic aircraft can reach anywhere on earth carrying warheads in a single hour.As to the traditional aircraft design, modal analysis as well as design of strength and stability in each cross section should be considered. Generally, people can analyze the modes of an aircraft by using a simulation model and computer aided engineering technique. However, in some specific situation, this approach doesn’t work well. For a hypersonic aircraft in flight condition, is a complex time-varying system, computer aided engineering method couldn’t handle this problem easily. For this reason, identifying modal parameters by using flight data is irreplaceable for modal analysis. Common methods for time-invariant modal parameter identification have been widely used. For example, some frequency-domain methods, such as, PolyMax, have been applied to solve modal problems in the field of civil engineering automatically, and there are also software using PolyMax method. No matter inside China or not, compared with time-invariant modal parameter identification methods, the depth of time-varying modal parameter identification still has a long way to go.In this paper, two approaches in time-varying modal parameter estimation based on subspace tracking are introduced. Both of the two methods can be treated as a combination of power iteration algorithm and optimization problem. The difference between the two methods is that the column vectors of the subspace in NPI method are naturally orthotropic. This kind of feature is reflected in the modal result: NPI approach yields a much better consequence than PAST approach. Based on a large scale of simulation and calculation, we provide useful experiences in Hankel matrix forming.Also, an internal force estimation method based on flight data and modal parameters is introduced and applied to a free-free beam. While handling with the flight data, some signal process techniques are introduced so that the data can be used in this approach, such as FIR low pass filter and wavelet decomposition.