Showing papers by "Peter Davies published in 2018"

A Review and Methodology Development for Remaining Useful Life Prediction of Offshore Fixed and Floating Wind turbine Power Converter with Digital Twin Technology Perspective

Abstract: The growing number of Offshore wind farms demands highly reliable wind turbines to curtail the maintenance cost and to shorten the downtime. Power converter is one of the critical components that undergoes high rate of medium and short term thermal cycles especially in Offshore floating wind turbines compared to fixed bottom turbines. The current study proposes a novel methodology to predict the remaining useful life of an offshore wind turbine power converter in digital twin frame work as a means of predictive maintenance strategy. The remaining useful life is estimated for both diagnostic and prognostic health monitoring specific for offshore operating environment.

An experimental study of water diffusion in carbon/epoxy composites under static tensile stress

Abstract: The coupling between tensile stress and water diffusion in composites represents a major issue in many marine applications. Even if these two behaviours are well documented as separate subjects, there are still very few data on fully coupled mechanisms. The aim of this study is to understand what governs the coupled behaviour, by investigating the water diffusion in carbon/epoxy. The coupling is first evaluated on neat resin samples to characterise the matrix behaviour. Then the study focuses on composites with two types of woven fibre orientation: one at ±45°, in order to understand the coupling effects on materials loaded away from the reinforcement direction and another quasi-isotropic to obtain properties along the fibres. For each material the same approach was applied: first, the tensile behaviour, damage development and water diffusion were studied uncoupled. Then, semi-coupled effects were investigated. The final part of the paper combines both behaviours as fully coupled phenomena.

Evaluation of Basalt Fibre Composites for Marine Applications

Abstract: Basalt fibres offer potential for use in marine structures, but few data exist to evaluate the influence of seawater immersion on their mechanical behaviour. This paper provides the results from a study in which basalt fibre reinforced epoxy composites were aged in natural seawater at different temperatures. Tests were performed under quasi-static and cyclic loading, first in the as-received state then after saturation in natural seawater. Results are compared to those for an E-glass reinforced composite with the same epoxy matrix. They indicate similar mechanical performance for both materials after seawater saturation.

Habitat disruption and the identification and management of functional trait changes

Abstract: Aquatic ecosystems are facing escalating threats from urbanization, habitat loss and projected impacts of climate change, which both individually and in combination have the potential to fundamentally alter ecosystem functioning. While it is well established that habitat disturbances can affect the composition and diversity of aquatic communities, only recently have studies considered whether such impacts result in changes in species’ functional traits. We consider how functional traits of freshwater and marine fishes respond to environmental change, and how shifts in the expression of these traits can impact community dynamics and key ecological processes, including trophic interactions and nutrient transfer. We find that a multitude of functional traits, including behavioural and sensory traits, is sensitive to habitat disturbances. We demonstrate how these trait changes can be used to reveal hidden “ecological diversity” as well as serving as early indicators of environmental perturbation. We conclude that management strategies that consider the fundamental biological responses of fishes to habitat disturbance will be particularly effective in determining causal relationships within the ecological network. While detailed information on trait function is often lacking, even some general understanding of trait function and importance will facilitate targeted and efficient ecosystem management. We urge fisheries biologists and aquatic ecosystem managers to consider the role of functional traits in facilitating effective habitat restoration and management.

Influence of water on the short and long term mechanical behaviour of polyamide 6 (nylon) fibres and yarns

Abstract: Polyamide fibres are known to be sensitive to water, and this has limited their marine applications. However, their low stiffness and high strength could be attractive for shallow water mooring line ropes, particularly for floating wind turbines. Such applications require the influence of water on mechanical behaviour to be fully understood, and this paper presents results describing how water affects static and creep response of polyamide 6 fibre yarns. First, the effect of water on fibre Tg is quantified, then tensile behaviour is examined. Finally, a model based on Schapery’s non-linear creep analysis is identified for different humidity conditions. The results show that while moisture has a small effect on short-term tensile behaviour, long term response is strongly affected and this must be considered in any marine application.

Correlative Imaging and Bio-inspiration: Multi-scale and Multi-modal Investigations of the Acorn Barnacle (Semibalanus balanoides)

Abstract: Natural-forming biomaterials can be subject to extremes of moisture, chemistry, loading, temperature flux, and predation. Yet, those forming in the marine environment for example, form in ambient conditions using only the habitat-dependent resources available to the organism (e.g., elemental composition of seawater for precipitation of CaCO3 hard parts). Through evolution and adaptation, organisms have developed an incredibly diverse range of strategies to survive despite these unpredictable habitatdependent conditions; this includes the development of complex chemical-biological-structural relationships [1-2], which not only enhance structural integrity but also make the most of the resources available to them. Studying these relationships is pivotal to developing bio-inspiration strategies that can contribute to novel human-made engineering and material science development and innovation.

Hierarchical multi‐taxa models inform riparian vs. hydrologic restoration of urban streams in a permeable landscape

Abstract: The degradation of streams caused by urbanization tends to follow predictable patterns; however, there is a growing appreciation for heterogeneity in stream response to urbanization due to the local geoclimatic context. Furthermore, there is building evidence that streams in mildly sloped, permeable landscapes respond uncharacteristically to urban stress calling for a more nuanced approach to restoration. We evaluated the relative influence of local-scale riparian characteristics and catchment-scale imperviousness on the macroinvertebrate assemblages of streams in the flat, permeable urban landscape of Perth, Western Australia. Using a hierarchical multi-taxa model, we predicted the outcomes of stylized stream restoration strategies to increase the riparian integrity at the local scale or decrease the influences of imperviousness at the catchment scale. In the urban streams of Perth, we show that local-scale riparian restoration can influence the structure of macroinvertebrate assemblages to a greater degree than managing the influences of catchment-scale imperviousness. We also observed an interaction between the effect of riparian integrity and imperviousness such that the effect of increased riparian integrity was enhanced at lower levels of catchment imperviousness. This study represents one of few conducted in flat, permeable landscapes and the first aimed at informing urban stream restoration in Perth, adding to the growing appreciation for heterogeneity of the Urban Stream Syndrome and its importance for urban stream restoration.

Taking a deeper look: Quantifying the differences in fish assemblages between shallow and mesophotic temperate rocky reefs

Abstract: The spatial distribution of a species assemblage is often determined by habitat and climate. In the marine environment, depth can become an important factor as degrading light leads to changes in the biological habitat structure. To date, much of the focus of ecological fish research has been based on reefs in less than 40 m with little research on the ecological role of mesophotic reefs. We deployed baited remote underwater stereo video systems (stereo-BRUVS) on temperate reefs in two depth categories: shallow (20-40m) and mesophotic (80-120m), off Port Stephens, Australia. Sites were selected using data collected by swath acoustic sounder to ensure stereo-BRUVS were deployed on reef. The sounder also provided rugosity, slope and relief data for each stereo-BRUVS deployment. Multivariate analysis indicates that there are significant differences in the fish assemblages between shallow and mesophotic reefs, primarily driven by Ophthalmolepis lineolatus and Notolabrus gymnogenis only occurring on shallow reefs and schooling species of fish that were unique to each depth category: Atypichthys strigatus on shallow reefs and Centroberyx affinis on mesophotic reefs. While shallow reefs had a greater species richness and abundance of fish when compared to mesophotic reefs, mesophotic reefs hosted the same species richness of fishery targeted species. Chrysophrys auratus (pink snapper) and Nemodactylus douglassii (grey morwong) are two highly targeted species in this region. While C. auratus was numerically more abundant on shallow reefs, mesophotic reefs provide habitat for larger fish. In comparison, N. douglassii were evenly distributed across all sites sampled. Generalized linear models revealed that depth and habitat type provided the most parsimonious model for predicting the distribution of C. auratus, while habitat type alone best predicted the distribution of N. douglassii. These results demonstrate the importance of mesophotic reefs to fishery targeted species and therefore have implications for informing the management of these fishery resources on shelf rocky reefs.

Long-term durability of CFRP under fatigue loading for marine applications

Abstract: Composite propellers are a major new development in the marine transport industry. The use of composite materials in seawater turbines is also of great interest to the marine renewable energy industry. Those systems present similarities being both constantly immersed in seawater, under fatigue loadings, of large dimensions, and they are often designed using Carbon Fibre Reinforced Polymer (CFRP). Previous studies have shown sensitivity of some composite materials to the seawater environment mainly in the quasi-static loading domain. However, investigations now need to be performed on the behaviour of CFRP under seawater environment and fatigue loadings. In this study, CFRP samples were aged in natural seawater until saturation, in order to investigate the influence of water absorption on the fatigue properties of the material. Results showed a small decrease in fatigue lifetime under tension but a more significant drop for sample subjected to four point flexural fatigue.

Marine Ageing Behaviour of New Environmentally Friendly Composites

Abstract: In recent years several new materials have been proposed for marine applications. These include liquid infusible acrylics, basalt fibre and plant fibre-reinforced composites, and thermoplastic polyamide composites. In order to assess the long-term durability of such materials accelerated tests are used but the validity of this approach, widely accepted for traditional marine composites, must be checked. This presentation will describe results from ageing tests on these four materials, specifically developed for particular applications: acrylic composites and basalt and flax fibre composites for surface structures, and carbon-reinforced polyamides for deep sea pressure vessels.

Fatigue of polyamide mooring ropes for floating wind turbines

Abstract: This paper describes a study of the fatigue characterization of polyamide mooring ropes for floating wind turbines. Under some conditions polyester ropes, which are favoured for offshore platform station-keeping, are too stiff for wind turbine moorings, and polyamide may be a suitable alternative. While early studies on fatigue of braided nylon ropes showed very short lifetimes some recent results have indicated that it is possible to significantly enhance lifetime by modifying rope construction and improving fibre coatings [1]. The fatigue results presented here for ropes from a different supplier, confirm this result. In order to develop an accelerated evaluation of the fatigue performance, heat build-up tests have been performed, and promising first results are shown. Finally, the influence of coating is examined by microscopy and yarn-on-yarn tests, in order to improve understanding of the fatigue mechanisms leading to failure.

Modelling of the damage development in carbon/epoxy laminates subjected to combined seawater ageing and mechanical loading

Abstract: In this study, a damage model that accounts for the effect of seawater ageing is proposed. The model is based on a failure criterion that takes into account the effect of the ply thickness, while t...

CFD Validation of Scaled Floating Offshore Wind Turbine Rotor

Abstract: Offshore wind turbines are lucrative than land based turbines for its high and consistent wind speed. Since the floating wind turbines are economical than gravity based or fixed bottom type wind turbines, offshore wind industry is exploring all possible ways to adopt well established oil and gas floating platform technologies. Unlike fixed bottom wind turbines, floating platform is subjected to complex motions in all 6 degrees of freedom that introduces new challenges in predicting the aerodynamic forces on the rotor. The conventional approach to determine the aerodynamic forces is not applicable for offshore floating turbines that is subjected to hydrodynamic and all other forces. The current study is focused on computationally validating the scaled model of NREL 5MW wind turbine that is experimentally investigated for various frequencies of platform surge motions at University of Strathclyde. The thrust forces and rotor torque are computed by numerically simulation and compared with experimental outcome showing a good agreement in the trend. The minor deviation in the aerodynamic forces is attributed to the higher prediction of lift and drag forces by XFOIL.

Composite Materials in Tidal Energy Blades

Abstract: Composite materials are the natural choice for the construction of tidal energy blades; their high strength, good environmental resistance and the ease with which they may be used to form complex shapes means that they are well suited to the application. The design of MW-scale tidal energy blades has evolved over a number of years, keeping step with the requirements of turbine developers as their emphasis shifts from prototyping to production. In parallel, it has been necessary to develop a rigorous approach to materials testing and qualification. The specifics of the blade structure and the operational environment mean that it has been necessary to solve a number of complications that arise during such a qualification programme. These issues are discussed and efforts to mitigate their consequences are explained. Although this chapter is written particularly with tidal energy blades in mind, much of the content will be applicable to a wide range of other applications where composite materials are used in the marine environment.

Improved Bend Over Sheave Durability of HMPE Ropes for Deep Sea Handling

Abstract: The use of synthetic fiber ropes for subsea installation is extending, as the offshore industry explores deeper waters, but there are few data available to evaluate the lifetime of these materials. In a previous OMAE presentation the authors described results from the first phase (2010-2013) of a JIP aiming to understand the mechanisms controlling the long term behavior of HMPE fibre ropes [1]. This presentation will describe the results from the second phase of this study (2014-2018) in which predictive models have been developed and applied to a range of improved braided rope materials. Two modeling approaches will be discussed, an empirical method based on residual strength after cycling, and a numerical approach using finite element software specifically adapted to fibre materials [2]. An extensive test program, which has generated a database of CBOS (cyclic bend over sheave) results for various grades of HMPE and different constructions, will be described. Comparisons have been made with steel wire handling lines in order to quantify the benefits of fibre ropes for these deepwater applications.

Durability of Polymers and Composites: The Key to Reliable Marine Renewable Energy Production

Abstract: Recovery of marine energy is progressing from the prototype stage to arrays, and all of the systems currently being developed include critical elements manufactured from polymers and composites. Structural MRE (Marine Renewable Energy) components range from composite turbine blades, for floating wind and tidal turbines, to polymer fiber ropes for wave, tidal and floating wind mooring systems. Elastomeric components are also widely used for sealing and protection. In all cases it is essential to understand how seawater diffuses into these polymers and how it affects mechanical properties; this allows appropriate safety factors to be applied without excessive over-conservative design, and can result in significant cost reduction. This paper will present a methodology for evaluating the long term behavior of such components based on accelerated testing. Three examples will be shown to illustrate the approach; tidal turbine blade composites, synthetic fiber rope moorings, and rubber components. In each case the seawater diffusion kinetics will be described first, then the influence of water on mechanical behavior will be quantified for the particular loadings of interest, and finally results from fully coupled fatigue tests in seawater will be discussed.