Change of surface design of monopile (Revised)
Author
Bak-Jensen, Mads
Term
4. term
Education
Publication year
2018
Submitted on
2018-11-11
Pages
78
Abstract
Dette speciale undersøger et forslag fra Vattenfall om at ændre monopælens ydre overflade fra glat til takket for potentielt at reducere materialeforbruget via øget skindfriktion. To 3D-modeller af de alternative overfladedesigns er opstillet i PLAXIS 3D med en Mohr–Coulomb-materialebeskrivelse og en enkel lagdelt jordprofil bestående af løst sand, ler og middeltæt sand. For at forenkle analysen er der desuden udviklet to tilsvarende 1D-modeller, som er kalibreret ved at matche forskydninger og last-flytning-kurver (p–y, t–z og Q–z) fra 3D-resultaterne; laterale påvirkninger er modelleret med bjælkeelementer og vertikale med stangelementer. Sammenligninger viser, at 1D-modellerne reproducerer 3D-modellernes respons, og at der under statisk belastning ikke er nogen væsentlig forskel i deformationer mellem glat og takket overflade. Last–forskydningskurverne indikerer desuden, at den glatte løsning kræver højere kræfter for at opnå samme forskydning end den takkede, og den samlede vurdering er, at den takkede overflade ikke giver en meningsfuld materialebesparelse i denne undersøgelse; den nuværende glatte overflade fremstår som den mest materialeeffektive.
This thesis examines a proposal from Vattenfall to change the exterior surface of a monopile from smooth to jagged to potentially reduce material use through increased skin friction. Two alternative surface designs were modeled in PLAXIS 3D using the Mohr–Coulomb material model and a simple layered soil profile comprising loose sand, clay, and medium-dense sand. To simplify the analysis, two corresponding 1D models were developed and calibrated to reproduce displacements and load–displacement behavior (p–y, t–z, and Q–z curves) from the 3D results; lateral effects were modeled with beam elements and vertical effects with bar elements. Comparisons show that the 1D models replicate the 3D response and that, under static loading, there is no significant difference in deformations between the smooth and jagged surfaces. The load–displacement curves further indicate that the smooth design requires higher forces to achieve the same displacement than the jagged one, and the overall assessment is that the jagged surface does not yield a meaningful material saving in this study; the current smooth surface appears to be the most material-efficient.
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