In recent years, offshore wind power generation technology has developed rapidly around the world, making important contributions to the further development of renewable energy. When designing an ...Offshore Wind Turbine (OWT) system, the uncertainties in parameters and different types of constraints need to be considered to find the optimal design of these systems. Therefore, the Reliability-Based Design Optimization (RBDO) method is usually adopted to ensure the stability and reliability of the design scheme. However, the calculation cost is huge in the RBDO problem considering mixed uncertainties. The Kriging model is a widely used approximation technique to reduce the computational cost in RBDO. However, establishing a sufficiently accurate Kriging model for a complex engineering system often requires the collection of more sample data and more time-consuming performance evaluation. In order to solve this problem, this study proposes a hybrid RBDO method based on a Portfolio allocation strategy. Based on ensuring the accuracy of the Kriging model, this method requires fewer iterations than the previous method of iteratively establishing the Kriging model using the same learning function. Furthermore, the optimal design of the system can be completed in a shorter time. This has great application potential to reduce the time labor and material costs spent in the design process of OWT. Two mathematical examples and two engineering examples are used to verify the accuracy of the method. Then, the proposed method is used in the design and optimization of a typical OWT support structure, showing the method's feasibility and superiority.
•An optimization method for offshore wind turbine support structures is proposed.•A new surrogate model building strategy is proposed.•Reduce the time cost required to build surrogate models.
•An efficient methodology for local stress analysis is presented.•Combining submodelling techniques with modal superposition principles, the multiscale problem may be efficiently overcome.•The ...proposed workflow allows the accurate modelling of the structural behaviour at different scales, addressing the real local response of the mechanism of loading transference.•The calculation of local mechanical quantities makes it possible to apply local fatigue methods to multiple geometries, characterised with different materials, overcoming relevant limitations of global S-N approaches.•The suggested multiscale methodology provides tools for disseminating the implementation of local fatigue approaches in current engineering safety checks.
This paper presents an advanced submodelling methodology for local stress analysis of complex details of existing metallic railway bridges. The fatigue assessment of connections of large structures based on local methods leads inherently to a multiscale problem that can only be solved by adopting efficient numerical procedures. Aiming to overcome such limitations that influence the analysis process, submodelling techniques and modal superposition principles are combined to fully represent numerically the local geometrical, material and contact properties of the fatigue-critical details. The results of experimental in situ tests are proposed to characterise the numerical models and respective multiscale relation, implementing optimisation and validation procedures. In this work, the suggested efficient multiscale methodology for stress analysis aims to allow the subsequent local fatigue assessment, according to the real mechanism of loading transference, reducing sources of conservatism. All numerical procedures and respective validation thru experimental techniques are illustrated using a real case study.
PurposeIn the last decades, the demand and use of renewable energies have been increasing. The increase in renewable energies, particularly wind energy, leads to the development and innovation of ...powerful wind energy converters as well as increased production requirements. Hence, a higher supporting structure is required to achieve higher wind speed with less turbulence. To date, the onshore wind towers with tubular connections are the most used. The maximum diameter of this type of tower is limited by transportation logistics. The purpose of this paper is to propose an alternative wind turbine lattice structure based on half-pipe steel connections.Design/methodology/approachIn this study, a new concept of steel hybrid tower has been proposed. The focus of this work is the development of a lattice structure. Therefore, the geometry of the lattice part of the tower is assessed to decrease the number of joints and bolts. The sections used in the lattice structure are constructed in a polygonal shape. The elements are obtained by cold forming and bolted along the length. The members are connected by gusset plates and preloaded bolts. A numerical investigation of joints is carried out using the finite element (FE) software ABAQUS.FindingsBased on the proposed study, the six “legs” solution with K braces under 45° angle and height/spread ratio of 4/1 and 5/1 provides the most suitable balance between the weight of the supporting structure, number of bolts in joints and reaction forces in the foundations, when compared with four “legs” solution.Originality/valueIn this investigation, the failure modes of elements and joints of an alternative wind turbine lattice structures, as well as the rotation stiffness of the joints, are determined. The FE results show good agreement with the analytical calculation proposed by EC3-1-8 standard.
► The mechanical behavior of reinforced solid wood beams is investigated. ► The effects of glued CFRP laminates of distinct lengths are analyzed. ► The interfacial stresses are investigated using ...analytical and FE models. ► The shear deformation of the wood has a significant effect on interfacial stresses.
This paper investigates the mechanical behavior of solid wood beams reinforced with CFRP laminates. Experimental, numerical and analytical approaches are explored in order to assess the effect of the reinforcement length on the interfacial shear and peeling stresses which are critical for a failure prediction. The experimental program aimed the characterization of the base materials and the comparison of the performance of wood beams with distinct reinforcement lengths and beams without any reinforcement. Finite element models were proposed and calibrated using the experimental data. Finally, analytical models for the interfacial stresses were applied and their performance assessed and compared with the numerical results. The success of the analytical models depends on consideration of shear deformation of the adherents, in particular of the wood, which shows relative low shear modulus.
•Proposed non-linear fatigue damage accumulation model for fatigue life prediction under multiple load levels.•The isodamage curves converge into one point due to the exhaustion of static ...toughness.•The proposed model yields better life predictions than the other four models for the five materials.
Cumulative fatigue damage is a continuous and irreversible process that refers to the degradation of the component mechanical properties under cyclic loadings. In this work, using the concept of isodamage curves, a new non-linear fatigue damage accumulation model is proposed to account for fatigue damage evolution under multiple load levels. In particular, a computational process is established in which the isodamage curves converge into one point due to the exhaustion of static toughness. Experimental data of five materials are used for model validation and comparison. Results indicate that the proposed model provides better life predictions than the other four models.
•The fatigue crack initiation can be assess using the modal superposition technique.•The modal superposition allows efficient and detailed numerical analyses.•Submodeling combined with the modal ...superposition are a robust computational tool.
Local fatigue approaches, such as, the stress-life, strain-life or energetic approaches defines a framework to estimate the fatigue crack initiation from notches of structural details. Various engineering structures, such as, bridges, wind towers, among others, are subjected to cyclic dynamic loadings which may substantially reduce the strength of these structures. Nowadays, the structural systems tend to be more complex being necessary to find computationally efficient solutions to perform their fatigue analysis, accounting for dynamic actions corresponding to long complex loading events (e.g. diversity of trains crossing a bridge), mainly if local approaches are envisaged. Thus, this paper aims at presenting and validating a generalization of a methodology based on modal superposition technique, for fatigue damage parameters evaluation, which can be applied in fatigue analysis using local approaches. This technique was applied recently in the context of fatigue crack propagation based on fracture mechanics, although it can be extended to compute the history of local notch stresses and strains at notches. A very important conclusion is that the technique can be explored for the case of local confined plasticity at notches whenever the global elastic behaviour of the component prevails. Local submodelling can be explored with this technique to avoid the necessity of large computational models. Local models are only needed to be run under linear elastic conditions for the selected modal shapes of the structure, being the local time history of fatigue damage variable computed by modal superposition for each loading event. That time history may be further post-processed for elastoplastic conditions using Neuber or Glinka’s analyses. Comparisons with direct integration elastoplastic dynamic analysis confirmed the feasibility of the proposed approach.
Purpose
The purpose of this paper is twofold: first, to observe an influence of different Composite Fibre-Reinforced Polymer (CFRP) patches, whose application to metals is very easy, in suppling and ...significantly elongating the service time; and second, the numerical calculation of the reduced stress intensity factor (SIF) range for strengthened cracked steel specimens.
Design/methodology/approach
One of the successful strengthening methods is the CFRP patching along the fatigue crack paths. The presented approach has been studied and discussed in this paper on the background of the numerical and experimental data. As it was expected, the proposed strengthening method is efficient and promising in case of the “immediate” repairs of critical members with cracks. The manufacturing process of specimens and test methodology as well as numerical approach to calculate SIFs for various reinforcements of steel specimens are presented. For this purpose, the Extended Finite Element Method was involved and described.
Findings
The main mechanism of fatigue crack growth retardation is associated with local ΔK reduction due to CFRP patches; any type of reinforcement results in an increase in af and a significant decrease in SIF values. The beach-marking method is described as a good, reliable and comprehensive method to capture the crack propagation in structures consisting of various materials and could be applied successfully for mixed mode testing.
Originality/value
A detailed experimental-numerical approach for fatigue crack growth in long-term operated structures made of steel is presented. The strengthening methodology is presented with consideration of the various CFRP patches configurations.
This paper presents an innovative computational approach for fatigue assessment of riveted connections. Such methodology is based on modal superposition principles, submodelling techniques and an ...elastoplastic post-processing to efficiently evaluate fatigue damaging events considering local geometrical, material and contact nonlinearities. The computational burden, intrinsic to localized detailed numerical analyses, is mitigated implementing a sub-algorithm based on network parallel computing. The developed computational methodology overcomes relevant drawbacks of S–N global approaches suggested in international standards and guidelines and it is an accurate methodology to analyse complex riveted fatigue-critical details, in particular the ones part of large structures, e.g. railway bridges.
An idealised riveted beam case-study was investigated and local damage parameters were calculated in reduced computational times. The accuracy of such results proved that the proposed approach allows fully analysing the fatigue life of riveted connections, being applicable to unlimited geometrical configurations submitted to variable loadings.
•An innovative approach to compute fatigue damages in metallic connections is proposed.•The focus is put on riveted connections due to their complex local nonlinear behaviour.•A computational algorithm considering submodelling techniques is developed.•Modal superposition and network parallel computing are considered to increase the computational efficiency.•Such approach allows overcoming relevant drawbacks of the global S–N approaches for fatigue analyses of large structures.
The fracture assessment of notched components based on cracked components approaches leads to over‐conservative failure predictions. In the research literature, several approaches are proposed to ...overcome this problem using an apparent fracture toughness,
KmatN. Nevertheless, most of these approaches are based on deterministic assumptions despite the large and variable scatter exhibited by
KmatN for different notch radii (ρ) or temperatures (T). This paper proposes a methodology for deriving a probabilistic
KmatN−ρ field including the effect of temperature on the failure of notched components. First, the theory of critical distances is applied to transform each apparent fracture toughness into the equivalent fracture toughness for ρ = 0. Then, the temperature is supposed to act as a scale effect in the Weibull cumulative distribution function of the equivalent fracture toughness, and the corresponding scale effect function is derived. Finally, the applicability of the proposed methodology is illustrated by an example using two ferritic‐pearlitic steels: S275JR and S355J2.
Cold-formed thin-walled steel profiles are used in Storage-and-Retrieval (S&R) logistic systems due to their lightweight design, cost-effective production, and mechanical performance. Moreover, ...modern S&R systems are automated, where carrier-shuttles and stacker-cranes move heavy palleted products through a racking structure, subjecting its structural members to fatigue phenomena, which may be aggravated due to manufacturing residual stresses. Hence, this work describes experimental and numerical procedures for determining manufacturing residual stresses, whose results are directly compared, validating the predicting capabilities of the numerical models. Finally, stresses due to pre-forming coiling/uncoiling cycles are also investigated and found to impact the final residual stress field.
•Manufacturing residual stresses are determined for cold-formed thin-walled profiles.•Manufacturing residual stresses are obtained via experimental and numerical methods.•Experimental data is used to validate the predicting capabilities of the FE models.•Residual stresses due to coiling/uncoiling are combined with cold-forming stresses.•Parametric studies of the forming and pre-forming processes are also presented.
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