Tubular, lattice and hybrid steel turbine towers for offshore wind energy. A numerical investigation

The increasing world power demand combined with the need of environment protection and sustainable energy production, has led recently to the use of alternative means of energy production minimizing CO2 emissions including wind energy harvesting. The new trend to expand to offshore wind power installations in order to increase the amount of world sustainable energy production has led to the development of multiple structural solutions both for the foundations and the upper structure of wind power generators. Research on the structural optimization of wind turbine towers is of great interest and importance due to their high manufacturing and erection costs and certain transportation limitations that prevent them from reaching greater heights. The present work addresses the comparison of a classic tapered steel wind turbine tower configuration with a hybrid lattice tower of the same height and energy production potential. Aiming to contribute to better understanding of the structural behaviour of both types of wind turbine towers, the present research work focuses on the development of reliable numerical models along with the use of analytical equations in order to predict accurately and interpret the aforementioned structural response of the two tower configurations by conducting a comparative study between them.</p

A comparative life-cycle analysis of tall onshore steel wind-turbine towers

Earth has lately been suffering from unforeseen catastrophic phenomena related to the consequences of the greenhouse effect. It is therefore essential not only that sustainability criteria be incorporated into the everyday lifestyle, but also that energy-saving procedures be enhanced. According to the number of wind farms installed annually, wind energy is among the most promising sustainable-energy sources. Taking into account the last statement for energy-saving methods, it is essential to value the contribution of wind energy not only in eliminating CO2 emissions when producing electricity from wind, but also in assessing the total environmental impact associated with the entire lifetime of all the processes related with this energy-production chain. In order to quantify such environmental impacts, life-cycle analysis (LCA) is performed. As a matter of fact, there are a very limited number of studies devoted to LCA of onshore wind-energy-converter supporting towers - a fact that constitutes a first-class opportunity to perform high-end research. In the present work, the life-cycle performance of two types of tall onshore wind-turbine towers has been investigated: a lattice tower and a tubular one. For comparison reasons, both tower configurations have been designed to sustain the same loads, although they have been manufactured by different production methods, different amounts of material were used and different mounting procedures have been applied; all the aforementioned items diversify in their overall life-cycle performance as well as their performance in all LCA phases examined separately. The life-cycle performance of the two different wind-turbine-tower systems is calculated with the use of efficient open LCA software and valuable conclusions have been drawn when combining structural and LCA results in terms of comparing alternative configurations of the supporting systems for wind-energy converters.</p

Finite Element Modelling and Parametric Studies of Semi-Closed Thin-Walled Steel Polygonal Columns For The Application on Steel Lattice Towers

The trend of structural engineering in the recent years is toward the use of lighter and more economical structural elements. In steel construction, peculiarly, main structural member composed by thin-walled elements are being explored by researchers due to their potential to offer better solution with economical features. However, the use of slender profiles and a complex cross sections shape lead to requirements to study instability phenomenon in a form of local, distortional, flexural, torsional and coupled instability. Such complex structural behaviour is inevitably accompanied by demand to improve calculation methods and design provisions. In this context an innovative solution of structural element composed of thin-walled plates is proposed for the application on lattice support structure of wind turbine. A semi-closed section is made by assembling series of folded plates into polygonal profiles with mechanical fasteners, loaded in compression and bending moment which occurs as the effect of forces acting on the connection. The expected structural behaviour of the column is a mixture between the open and closed cross-section. These cases will be investigated through numerical analysis and parametric studies of the proposed profiles for the investigation of buckling behaviour and ultimate resistance, respectively

Elastic and inelastic buckling of steel cellular beams under strong-axis bending

This paper presents an extensive parametric study of elastic and inelastic buckling of cellular beams subjected to strong axis bending in order to investigate the effect of a variety of geometric parameters, and further generate mass data to validate and train a neural network-based formula. Python was employed to automate mass finite element (FE) analyses and reliably examine the influence of the parameters. Overall, 102,060 FE analyses were performed. The effects of the initial geometric imperfection, material nonlinearity, manufacture-introduced residual stresses, web opening diameter, web-post width, web height, flange width, web and flange thickness, end web-post width, and span of the beams and their combinations were thoroughly examined. The results are also compared with the current state-of-the-art design guidelines used in the UK. It was concluded that the critical elastic buckling load of perforated beams corresponds to the lateral movement of the compression flange while the most critical parameters are the web thickness and the geometry of the flange. However, from the inelastic analysis, the geometry and position of the web opening influence the collapse load capacity in a similar fashion to the geometry of the flange and thickness of the web. It was also concluded that the effect of the initial conditions was insignificant

Stability analysis of newly developed polygonal cross-sections for lattice wind towers

The pursuit for cheaper energy is leading the current wind tower design to increased heights. Common wind turbine tower designs would generate unjustified costs for transportation and erection leading to inefficient use of materials. In order to reduce these costs, several simplified erection methods have been proposed. One of such is the hybrid lattice-tubular steel tower. For economic feasibility, built-up cold-formed polygonal cross-sections have been proposed for the lattice part. This article presents a numerical investigation of the failure modes of closed polygonal cross-sections. The first part contains a presentation of structural systems which incorporate elements composed of plates and cold-formed members. The evaluation of the polygonal sections is done by means of finite element analysis considering local and global geometrical imperfections and residual stresses generated in the fabrication procedure. A comparative study is performed between several finite element models to propose a corresponding European buckling curve for calculating the flexural buckling resistance. The results show that the design of polygonal sections can be done according to European buckling curves methodology.2018-08-02 (rokbeg);konferensartikel i tidskrift</p

Structural response of stainless steel cross-sections under combined compression and biaxial bending

The Continuous Strength Method (CSM) was developed and calibrated against experimental and numerical results as a design approach, which allows for a rational exploitation of the significant strainhardening exhibited by stocky stainless steel cross-sections, thereby leading to more economic design. In order to extend its scope of application beyond the fundamental loading cases of concentric compression and uniaxial bending, a comprehensive numerical parametric study has been conducted and the obtained numerical results have been utilized to determine suitable interaction equations for cross-sections subjected to combined loading. This paper focuses on the ultimate response of I-sections under combined loading and complements a recent relevant study on RHS under combined loading. It is concluded that the current design guidance for stainless steel cross-sections under combined compression and biaxial bending is overly conservative and significant gains can be made if the effect of strain-hardening on ultimate capacity is taken into account.</p

Structural analysis and optimal design of steel lattice wind turbine towers

Wind energy has shown its dominance among the means of sustainable energy production by the accelerating rise in total installed capacity and increase in size of wind energy structures. Taking into consideration the fact that the supporting structure of onshore wind power generators constitutes approximately one-third of the initial construction cost, structural optimisation of the tower is considered crucial towards the minimisation of capital expenditure during construction. Contemporary energy needs employ the construction of constantly taller and more powerful wind power converters, whose robust design in parallel with compression of initial capital expenditure cannot be neglected. The dominant structural configuration for onshore wind power generators is the tapered steel tower, but lattice towers using enhanced special cross-sections can be a rather promising solution towards economy of material use. The present paper addresses the structural performance and optimisation of tubular and lattice steel wind turbine towers, examining alternative configuration solutions for a given height and rotor characteristics. The finite-element software Abaqus has been used for the implementation of the structural models and an algorithm has been elaborated in Mathematica software in order to allow for optimisation of the use of the cross-section in the case of lattice towers. </jats:p

Statistical evaluation of the bearing capacity of short polygonal columns

Regular convex polygon sections (RCPS) are commonly used as towers supporting transmission lines, stadium lightning and street lamps. Their use provides advantages in the bearing capacity and can simplify erection. Over the last 50 years experimental studies have been conducted to check the applicability of the plate theory to stocky polygonal columns. The paper presents the processed data gathered from compression tests found in the literature. Results from 70 specimens tested under pure compression were statistically analysed. Specimens with yield strength varying from 235 to 700 MPa and angles varying from 144 to 175.5 (5 to 40 sides) were investigated. The local non-dimensional slenderness was calculated using buckling lengths according to EN 1993-1-3 and EN 1993-1-5 with values ranging from 0.55 to 4.52. The objective of the paper was to compare the plate buckling resistance predictions to the experimental results. The paper concludes with a buckling width recommendation for evaluating the critical stress as calculated according to EN 1993-1-3 or EN 1993-1-5.ISBN för värdpublikation: 9780429320248</p