TY - CHAP
T1 - Investigations of Mode Shapes of Closely Spaced Modes from a Lattice Tower Identified Using Stochastic Subspace Identification
AU - Liesecke, Leon
AU - Jonscher, Clemens
AU - Grießmann, Tanja
AU - Rolfes, Raimund
N1 - This research has been financed by the Federal Ministry of Economic Affairs and Energy of the Federal Republic of Germany (project: German Research Facility for Wind Energy-Phase 2, FKZ 0325936I) and Deutsche Forschungsgemeinschaft (project: SFB 1463-Integrated Design and Operation Methodology for Offshore Megastructures). We would like to gratefully acknowledge their support.
PY - 2023
Y1 - 2023
N2 - In this work, the complex mode shapes of closely spaced modes of a slender lattice tower structure identified with stochastic subspace identification (SSI) are investigated. The SSI delivers its results in the form of complex eigenvalues and eigenvectors. For a proportionally damped structure, the mode shape components of a single mode shape lie almost on a line in the complex plane, referred to as the mean phase. For closely spaced modes it is known, that the mode shape components are not necessarily on a line in the complex plane. The mean phase deviation as an identification quality criterion for the identification of mode shapes has less significance in connection with close modes, so that a different examination of these mode shapes is necessary. This study is performed using experimental data of a lattice tower under environmental variability. For the mode shapes of the closely spaced modes of the structure, two dominant phases are observed in the complex plane corresponding to the two measurement directions. The influence of the environmental conditions and different structural states of the structure on the corresponding mode shapes is investigated. A new approach in dealing with complex mode shapes of closely spaced modes was developed and allows a better interpretation of the identification results and can be useful in assessing the state of the structure.
AB - In this work, the complex mode shapes of closely spaced modes of a slender lattice tower structure identified with stochastic subspace identification (SSI) are investigated. The SSI delivers its results in the form of complex eigenvalues and eigenvectors. For a proportionally damped structure, the mode shape components of a single mode shape lie almost on a line in the complex plane, referred to as the mean phase. For closely spaced modes it is known, that the mode shape components are not necessarily on a line in the complex plane. The mean phase deviation as an identification quality criterion for the identification of mode shapes has less significance in connection with close modes, so that a different examination of these mode shapes is necessary. This study is performed using experimental data of a lattice tower under environmental variability. For the mode shapes of the closely spaced modes of the structure, two dominant phases are observed in the complex plane corresponding to the two measurement directions. The influence of the environmental conditions and different structural states of the structure on the corresponding mode shapes is investigated. A new approach in dealing with complex mode shapes of closely spaced modes was developed and allows a better interpretation of the identification results and can be useful in assessing the state of the structure.
KW - SSI
KW - closely spaced modes
KW - complex mode shapes
KW - lattice tower
UR - http://www.scopus.com/inward/record.url?scp=85172284670&partnerID=8YFLogxK
U2 - 10.1007/978-3-031-39109-5_54
DO - 10.1007/978-3-031-39109-5_54
M3 - Contribution to book/anthology
SN - 978-3-031-39108-8
T3 - Lecture Notes in Civil Engineering
SP - 529
EP - 538
BT - Experimental Vibration Analysis for Civil Engineering Structures
A2 - Limongelli, Maria Pina
A2 - Giordano, Pier Francesco
A2 - Gentile, Carmelo
A2 - Quqa, Said
A2 - Cigada, Alfredo
ER -