Linear Aeroelastic Stability Analysis of LT1500 Installation Crane
Translated title
Lineær Aeroelastisk Stabilitets Analyse af LT1500 Installationskran
Authors
Eilers, Mikkel Alexander Ihe ; Pristed, William Balslev
Term
4. term
Education
Publication year
2025
Submitted on
2025-05-30
Pages
59
Abstract
Denne afhandling undersøger den lineære aeroelastiske stabilitet af Liftras LT1500 installationskran, der anvender vindmølletårnet som bærestruktur. Baggrunden er feltobservationer af vindinducerede vibrationer i tårne, som kan påvirke kranens drift under installation og service. For at belyse, hvornår ustabilitet kan opstå, opstilles en model af kranens bom, hvor de konservative, indre kræfter beskrives med en tyndvægget bjælkemodel med én symmetriakse baseret på energimetoder, og de ikke‑konservative aerodynamiske påvirkninger modelleres med tovejskobling mellem torsion og vindlast. Systemet linearisers og omskrives til dimensionsløs form, hvorefter bølgetal og bølgemodale koefficienter bestemmes til at beregne egenfrekvenser og svingningsformer for en given konfiguration. Tårnets fleksibilitet indarbejdes via elastiske randbetingelser, så stabiliteten kan vurderes både med og uden denne eftergivelighed. Resultaterne peger på, at kranbomens tværsnitsegenskaber har væsentlig betydning for den kritiske vindhastighed, hvor ustabilitet indtræffer, og den udviklede metode giver et grundlag for at vurdere driftsbetingelser og designparametre for LT1500‑systemet.
This thesis examines the linear aeroelastic stability of Liftra’s LT1500 installation crane, which uses the wind turbine tower as its support structure. Motivated by field observations of wind‑induced tower vibrations that may affect crane operations during installation and service, the study aims to identify when instability can occur. A model of the crane boom is developed in which conservative internal forces are described by an energy‑based thin‑walled beam formulation with a single axis of symmetry, while non‑conservative aerodynamic effects are represented with a two‑way coupling between torsion and wind load. The system is linearized and cast in dimensionless form, and wave numbers and wave modal coefficients are determined to compute eigenfrequencies and mode shapes for a given configuration. Tower flexibility is incorporated through elastic boundary conditions, enabling stability assessment with and without this compliance. The findings indicate that the boom’s cross‑sectional properties have a significant influence on the critical wind speed at which instability occurs, and the framework provides a basis for evaluating operating conditions and design parameters for the LT1500 system.
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