Development of airborne laser Doppler vibrometry for improved dynamic characterization of large engineering structures

DFG Projektnummer 496079937

Motivation

Large structures are subjected to strong wind loads, which can lead to damage and thus cause a financial burden, but also represent a safety risk. This concerns, for example, historic buildings for which little information is available regarding the aging processes. One method to minimize the risk of material failure is structural health monitoring (SHM). Various methods, such as ambient vibration testing (AVT), can be used to obtain information about the current condition. This makes it possible to detect damage at an early stage.

In this context, laser Doppler vibrometers (LDV) are increasingly used to perform AVT on large structures such as bridges and towers. In contrast to conventional measurements with several deflection sensors, LDVs are much more suitable due to their high resolution and low installation effort.

Currently, LDV measurements are limited by some surfaces on large structures being inaccessible and poor angles of incidence limiting signal quality. Optical disturbances due to turbulence in the air are another limitation.

Methods

The goal of this DFG-funded project is to address these limitations by using a novel measurement method: drone-based vibration measurement. This is made possible by the combination of an optimized LDV on the ground and a drone-mounted steerable mirror unit. The LDV's measurement beam is positioned on the drone with the help of a control unit and can be positioned anywhere on a measurement object using the mirror.

Another important goal of the project is the suppression of the occurring environmental influences and vibrations caused by the drone rotors. In collaboration with the project partner at the german aerospace center (Deutsches Zentrum für Luft- und Raumfahrt DLR), we already published two DFG-funded papers on this topic:

• M. Schewe, M.A.A. Ismail and C. Rembe:
  Towards airborne laser Doppler vibrometry for structural health monitoring of large and curved structures
  ^{In: Insight - Non-Destructive Testing and Condition Monitoring 2021, 63(5), 280-282, DOI: 10.1784/insi.2021.63.5.280.}
• M. Schewe, M. Ismail und C. Rembe:
  Differentielle Laser-Doppler-Vibrometrie für luftgestützte Vibrationsmessungen mit Drohnen
  ^{In: tm - Technisches Messen. Vol. 88, Issue s1, pp. 42-47, Aug. 2021. DOI: 10.1515/teme-2021-0071.}