Triennial Report 2003 - CHARMEC

Vibrations and noise – Vibrationer och buller (VB) – Schwingungen und Geräusche – Vibrations et bruitsVB5. WAVE PROPAGATION UNDER HIGH-SPEED TRAINSVågutbredning under höghastighetstågWellenausbreitung unter HochgeschwindigkeitszügenPropagation d’ondes sous des trains à grande vitesseProject leaderand supervisorDoctoral candidateProfessor Nils-Erik Wiberg,Structural MechanicsMr Torbjörn Ekevid(from 1999-01-01;Lic Eng December 2000;PhD December 2002)Period 1999-01-01 – 2003-06-30(– 2003-12-31)Chalmers budget Stage 2: ksek 710(excluding university Stage 3: ksek 1585basic resources) Stage 4: ksek 385Industrial interests Stage 2: ksek 500in-kind budget Stage 3: ksek 300(Banverket) Stage 4: ksek 150Note: VB5 has had an additional funding of kSEK 250for each one of the first four years from the SwedishFoundation for Strategic Research (SSF) through itsNational Graduate School in Scientific Computation(NGSSC).At places in Sweden where ground conditions are poorwith deep layers of loose clay, high vibration levels havebeen observed on the embankment and surroundingground when high-speed trains passed. A shock, similarto that experienced when an aircraft breaks the soundbarrier, occurs when the increasing speed of the trainexceeds the shear wave speed in the ground. On certainstretches of track in Sweden, the maximum permissibletrain speed has had to be reduced. By means of numericalsimulations and parallel in-field measurements, the vb5project has aimed at providing an understanding of whichfactors affect the vibration levels. It should then be possibleto propose measures to reduce these levels.Numerical models in space and time have been developedusing adaptive finite element technology. By useof the Scaled Boundary Finite Element Method (sbfem),reflections at the boundaries of the models have beenavoided and the spatial extension of the models limited.A so-called multigrid technique has been developed.This technique enables computers with a relatively smallstorage capacity to handle large and detailed modelsreasonably quickly. The complexity (calculation time)then only increases linearly with the resolution (numberof equations), a fact which can be regarded as a uniqueproperty. The technique has also proved to be applicablenot only to linear problems but also to problems thatinclude non-linear effects (at least material such effects).Simulations in two and three dimensions have been carriedout. The in-field measurements at Ledsgård southof Gothenburg in the spring of 2000 have been evaluatedand exploited. Parametric studies have shown that theExample in project VB5 of three-dimensional simulation of wavepropagation. The length of the model is 89 m. It is enclosed by anon-reflecting layer of scaled boundary finite elements. The trainhas ten bogies (twenty wheelsets). The two train speeds consideredare 50 m/s (below the critical value) and 70 m/s (abovethe critical value). Snapshots are shown of the displacement fieldwhen the train has reached the same position in the two cases.The displacements have been magnified by the factor 20026