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STRUCTURAL ANALYSIS OF TRUSS CONSTRUCTION FOR WIND TURBINE BLADES

Weddig, Björn LU (2016) In TVSM-5000 VSM820 20151
Department of Construction Sciences
Structural Mechanics
Abstract
The usage of wind turbines during the latest years has grown substantially and are becoming
an increasingly important source of renewable energy, as many countries are trying to reduce
their reliance on fossil fuels. In order to increase the effect of the wind turbines the length of
the blades has been increased, which has also led to an increase of the cross-section
dimensions. This has led to making the weight of the blade a more dominating load.
Therefore, it is of great interest to reduce the weight of wind turbine blades to continue
constructing longer blades. To accomplish this Winfoor are developing a wind turbine blade
that combines traditional horizontal-axis wind turbine (HAWT), with a truss system
containing truss bars... (More)
The usage of wind turbines during the latest years has grown substantially and are becoming
an increasingly important source of renewable energy, as many countries are trying to reduce
their reliance on fossil fuels. In order to increase the effect of the wind turbines the length of
the blades has been increased, which has also led to an increase of the cross-section
dimensions. This has led to making the weight of the blade a more dominating load.
Therefore, it is of great interest to reduce the weight of wind turbine blades to continue
constructing longer blades. To accomplish this Winfoor are developing a wind turbine blade
that combines traditional horizontal-axis wind turbine (HAWT), with a truss system
containing truss bars and a plate connected to the blades. Winfoor has the ambition to evolve
the wind blade industry by modify the shape of a HAWT blade into a Triblade. The results
and conclusions form this thesis are one of many things that has to be taken into account
when the final design is developed.
As the truss bars are long and slender, the bars that are being compressed are more likely to
buckle. The structural response of a dynamic load applied to the structure was also studied
in this thesis.
Identification and evaluation of the variables, such as Young’s module, influence on the load
capacity was computed with non-linear numerical analysis. In order to find a design proposal
containing both section dimensions and material properties was two parameter studies
completed. In structural design, the load capacity was often evaluated using finite element
method (FEM). This thesis includes non-linear FE analysis, which considers large
deformations.
The blades structural dynamic response was evaluated using both modal, and frequency
response analysis. Additionally are the response of an impulse studied using full transient
analysis.
The main conclusion from this thesis where that buckling truss bars are problematic when
an impulse was added to the structure. The impulse created from the tower passage was big
enough to change the buckling mode of the truss bar. This generates a great variation in
stresses for these truss bars, which cause it to that fatigue, damage, and this may decrease its
life span.
An additionally conclusion was that the eigenfrequency for each truss bar should not overlap
with the eigenfrequency for the global bending mode of the Triblade. (Less)
Popular Abstract (Swedish)
I takt med att det globala klimatet förändras ökar viljan att utveckla och effektivisera energi utvinningen av förnybara energier så som vindkraft. Utveckling inom vindkraftsindustrin har under de senaste åren varit att bladlängden blir längre. Detta eftersom längden på bladen ökar effekten vindkraftverket kan producera. Problemet med den ökade vindlängden har varit dels varit att vikten av bladet självt har blivit för tungt (över 10 ton) och dels att deformationer längs ut på vingen har blivit så stora att rotationsplan måste placeras längre ifrån vindkraftstornet.
Som en lösning till dessa problem har Winfoor börjat utveckla en ny typ utav vindkraftverksblad, Triblade. En Triblade består utav tre traditionella blad som är förstärkt med... (More)
I takt med att det globala klimatet förändras ökar viljan att utveckla och effektivisera energi utvinningen av förnybara energier så som vindkraft. Utveckling inom vindkraftsindustrin har under de senaste åren varit att bladlängden blir längre. Detta eftersom längden på bladen ökar effekten vindkraftverket kan producera. Problemet med den ökade vindlängden har varit dels varit att vikten av bladet självt har blivit för tungt (över 10 ton) och dels att deformationer längs ut på vingen har blivit så stora att rotationsplan måste placeras längre ifrån vindkraftstornet.
Som en lösning till dessa problem har Winfoor börjat utveckla en ny typ utav vindkraftverksblad, Triblade. En Triblade består utav tre traditionella blad som är förstärkt med en fackverkskonstruktion. Fackverks konstruktions består utav 6 stycken plattor och 30 stycken stag som tillsammans stabiliserar och minskar spänningarna i vingarna och på så viss förstärker konstruktionen.

Problemet med denna konstruktion är att stagen är upp till 17 meter långa viket medför att det krävs en väldigt liten tryckande kraft för att de ska bli ostabila och börjar buckla. Då en stång bucklar kommer denna inte att ta någon mer last och i värsta fall gå i sönder. I detta examensarbete har detta fenomenet undersökt och även hur bladet deformeras efter att dessa stänger har börjat buckla. Detta gjordes med en olinjär finita element analys. Denna analys används för att kunna räkna ut den högsta som kan belastas på bladet innan bladet blir ostabilt, denna last kallas också kritisk bucklingslast.
En slutsats från denna analys var att efter de stag som bucklat sker det inte någon ytterligare ökning av spänningen i stagen sig självt, istället ökar spänningsbelastning på de plattor som håller ihop bladen. Då spänningen ökar i dessa plattor finns det risk att även dessa plattor bucklar. Det är betydligt alvarligare om dessa plattor bucklar jämfört med om stängerna bucklar eftersom bucklingen hos plattorna skulle medföra att hela vingen blir ostabil. Därför behövdes dessa plattor förstärkas ytterligare jämfört.
Eftersom vinden varierar i styrka har det även i detta examensarbetet studerats hur Tribladet reagerar till en dynamisk last. Det visade sig att det är viktigt att stagen inte har samma egenfrekvens som de lägsta egenfrekvenserna för hela bladet. (Less)
Please use this url to cite or link to this publication:
author
Weddig, Björn LU
supervisor
organization
course
VSM820 20151
year
type
M3 - Professional qualifications ( - 4 Years)
subject
keywords
Wind turbine blade, FRP, Truss system, Instability, Buckling, Non-Linear, Eigenvalue problem, Frequency response analysis, Transient dynamic response
publication/series
TVSM-5000
report number
TVSM-5215
ISSN
0281-6679
language
English
id
8876435
alternative location
http://www.byggmek.lth.se/english/publications/tvsm-5000-masters-dissertations/
date added to LUP
2016-06-28 14:27:12
date last changed
2016-06-28 14:27:12
@misc{8876435,
  abstract     = {The usage of wind turbines during the latest years has grown substantially and are becoming
an increasingly important source of renewable energy, as many countries are trying to reduce
their reliance on fossil fuels. In order to increase the effect of the wind turbines the length of
the blades has been increased, which has also led to an increase of the cross-section
dimensions. This has led to making the weight of the blade a more dominating load.
Therefore, it is of great interest to reduce the weight of wind turbine blades to continue
constructing longer blades. To accomplish this Winfoor are developing a wind turbine blade
that combines traditional horizontal-axis wind turbine (HAWT), with a truss system
containing truss bars and a plate connected to the blades. Winfoor has the ambition to evolve
the wind blade industry by modify the shape of a HAWT blade into a Triblade. The results
and conclusions form this thesis are one of many things that has to be taken into account
when the final design is developed.
As the truss bars are long and slender, the bars that are being compressed are more likely to
buckle. The structural response of a dynamic load applied to the structure was also studied
in this thesis.
Identification and evaluation of the variables, such as Young’s module, influence on the load
capacity was computed with non-linear numerical analysis. In order to find a design proposal
containing both section dimensions and material properties was two parameter studies
completed. In structural design, the load capacity was often evaluated using finite element
method (FEM). This thesis includes non-linear FE analysis, which considers large
deformations.
The blades structural dynamic response was evaluated using both modal, and frequency
response analysis. Additionally are the response of an impulse studied using full transient
analysis.
The main conclusion from this thesis where that buckling truss bars are problematic when
an impulse was added to the structure. The impulse created from the tower passage was big
enough to change the buckling mode of the truss bar. This generates a great variation in
stresses for these truss bars, which cause it to that fatigue, damage, and this may decrease its
life span.
An additionally conclusion was that the eigenfrequency for each truss bar should not overlap
with the eigenfrequency for the global bending mode of the Triblade.},
  author       = {Weddig, Björn},
  issn         = {0281-6679},
  keyword      = {Wind turbine blade,FRP,Truss system,Instability,Buckling,Non-Linear,Eigenvalue problem,Frequency response analysis,Transient dynamic response},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVSM-5000},
  title        = {STRUCTURAL ANALYSIS OF TRUSS CONSTRUCTION FOR WIND TURBINE BLADES},
  year         = {2016},
}