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A significant challenge designers of tidal stream turbines face is ensuring that the device can survive the harsh operating environment. Understanding the effect of the onset flow structure on the loading spectrum of the blades will lead to improved blade designs. The results of a preliminary parametric analysis suggest that the mean flow speed, longitudinal turbulence intensity, wave state and depth of hub relative to the channel depth are dominant drivers of the blade loads for horizontal-axis tidal turbines. They should therefore be accurately modeled in both fatigue and extreme load analyses.

Resin Infusion (RI) is one of the Liquid Composite Moulding processes, and is increasingly being used to manufacture high performance composite structures. Application of a flexible bag as one part of the mould results in laminate thicknesses varying significantly during filling, and in the period after filling, during which final laminate quality is reached. A 2.5D RI simulation has been developed, and is compared to detailed experiments for three moderately complex preform shapes. Evolution of resin pressure is predicted with good accuracy, and laminate thicknesses changes are moderately underestimated. SimLCM is demonstrated to be superior to a constant thickness Resin Transfer Moulding simulation, and is currently being extended to model the post-filling period. ispartof: pages:1-4 ispartof: Proceedings of the 7th Asia-Australasian conference on Composite Materials, CDROM pages:1-4 ispartof: ACCM location:Taipei date:15 Nov - 18 Nov 2010 status: published

Resin Infusion (a.k.a. VARTM) is one of the Liquid Composite Moulding processes, for which liquid resin is drawn into dry fibre reinforcement. Resin Infusion is a closed mould process in which half of the mould is formed by a flexible vacuum bag. Significant cavity thickness changes occur during processing, due to the flexibility of the vacuum bag and the complex stress balance within the laminate. While the magnitude of thickness change is often small, the influence is significant on reinforcement fibre volume fraction. Dynamic changes in permeability during mould filling and post-filling have the potential to significantly affect the process. To simulate this behaviour, it is important to accurately model the compaction and relaxation of reinforcement in the dry and wet state. A series of tests have been completed to determine the compaction behaviour of an isotropic glass fibre mat. From these tests several non-linear elastic compaction models have been determined, and applied within a new Resin Infusion simulation. The process simulation, which addresses the pre-filling, filling and post-filling stages, is compared to an experiment employing a full field cavity thickness measurement apparatus, as well as measurement of resin pressure at three discrete points within the laminate.

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This paper presents results from an experimental investigation into real-time sensing and control of resin flow in an resin transfer molding (RTM) process. The objective of the research was to develop intelligent process control methodologies using in-situ sensors and process models, for real-time control of the RTM process. The real time control of the RTM process enables an increase in throughput, high yields, low defects, and consistent repeatability of quality between the parts. We concentrated on controlling the resin flow using multiple injection ports and vent locations. The results from the preliminary investigations indicate the feasibility of implementing real-time control on the RTM production floor.

A sensor placement algorithm uses process data to determine the optimal distribution of sensors in a distributed parameter manufacturing system. An automatic classification procedure maps any problems in the process to a predetermined set of process disturbances. A control procedure uses process data to determine the best control action that will ensure good system response. Methods for sensor placement, automatic decision tree classification, corrective action control and the apparatus to effectuate these respective methods are integrated into a design methodology.

This paper analyses a set of velocity time histories which were obtained at a fixed point in the bottom boundary layer of a tidal stream, 5 m from the seabed, and where the mean flow reached 2.5 m s −1 . Considering two complete tidal cycles near spring tide, the streamwise turbulence intensity during non-slack flow was found to be approximately 12–13%, varying slightly between flood and ebb tides. The ratio of the streamwise turbulence intensity to that of the transverse and vertical intensities is typically 1 : 0.75 : 0.56, respectively. Velocity autospectra computed near maximum flood tidal flow conditions exhibit an f −2/3 inertial subrange and conform reasonably well to atmospheric turbulence spectral models. Local isotropy is observed between the streamwise and transverse spectra at reduced frequencies of f >0.5. The streamwise integral time scales and length scales of turbulence at maximum flow are approximately 6 s and 11–14 m, respectively, and exhibit a relatively large degree of scatter. They are also typically much greater in magnitude than the transverse and vertical components. The findings are intended to increase the levels of confidence within the tidal energy industry of the characteristics of the higher frequency components of the onset flow, and subsequently lead to more realistic performance and loading predictions.

International audience; Introduction With the increased use of Liquid Composite Moulding (LCM) processes in the aeronautical and automotive industries, the complexity of the parts and quality requirements have increased tremendously. The development of fabric forming models and the refinement of mould filling simulations, calls for improved material models to achieve the predictions expected by the industry. Accurate permeability data of reinforcing materials is essential in order to conduct LCM simulations and design the manufacturing process more efficiently [1]. Permeability is predominantly a function of the reinforcement architecture and its fibre volume fraction, both of which are affected by textile deformation when used to manufacture complex 3D parts. The push for more sustainable materials either biodegradable or fully recyclable has also pushed the composite industry to look increasingly at bio-based reinforcements and resins. The bio-based reinforcement being formed from the assembly of short fibrils of variable geometry into continuous strands have very different forming and permeability properties than traditional composite reinforcements formed by assembling continuous fibre with smooth geometry.

International audience

The Resin Infusion process (RI, also known as VARTM) is a subclass of the Liquid Composite Moulding (LCM) collective, which is increasingly applied in industry. As opposed to the other LCM processes, RI utilises only one rigid mould half, the upper mould half of the mould being a flexible plastic bag. This greatly reduces tooling costs, and makes the process suitable for medium to very large sized parts. However, the interaction between a flexible bag and the infusion of the laminate within, presents a significant challenge to model and understand. The University of Auckland LCM research group is developing SimLCM as a generic LCM mould filling simulation. SimLCM has recently been extended to simulate RI, focusing on resin flow and laminate thickness predictions throughout the process. To accurately predict filling times, and the evolution of fluid pressure and laminate thickness during filling and post-filling phases, a detailed knowledge is required of the complex compaction response of the fibre reinforcement. While significant research has been published on modelling of the filling in RI, the post-filling period has received much less attention. This phase is, however, significant as spatial variations in laminate thickness are removed, preferably before the infused resin gels. Extending on previous work on rectilinear filling, this paper will present a program of RI experiments in a range of 2D flow geometries and the results will be compared to the predictions made using SimLCM. Special attention is given to the post-filling stage, and the validation of the new models developed for SimLCM. A selection of radial, peripheral and more complex filling situations have been addressed.

International audience; With the increased use of Liquid Composite Moulding (LCM) processes in the aeronautical and automotive industries, the complexity of the parts and quality requirements have increased tremendously. The development of fabric forming models and the refinement of mould filling simulations, calls for improved material models to achieve the predictions expected by the industry. Accurate permeability data of reinforcing materials is essential in order to conduct LCM simulations and design the manufacturing process more efficiently [1]. Permeability is predominantly a function of the reinforcement architecture and its fibre volume fraction, both of which are affected by textile deformation when used to manufacture complex 3D parts. The push for more sustainable materials either biodegradable or fully recyclable has also pushed the composite industry to look increasingly at bio-based reinforcements and resins. The bio-based reinforcement being formed from the assembly of short fibrils of variable geometry into continuous strands have very different forming and permeability properties than traditional composite reinforcements formed by assembling continuous fibre with smooth geometry. This study compares the permeability characteristics of two different flax fibre fabrics with different tow size and a glass fibre fabric with an equivalent tow dimension. In order to gather information on the behaviour of such reinforcements during LCM manufacturing processes, the permeability behaviour of sheared textiles was determined. The fabrics were sheared before conducting the permeability tests, simulating the textile deformation that is present when preforming textiles in 3D moulds and the effects of these deformations on the textile properties were observed.

Resin Transfer Molding (RTM) is a composite material manufacturing process during which resin is injected into a mold cavity filled with a fibrous reinforcing preform. Application of woven and stitched fiber mats in fabricating preforms for RTM is a highly viable means of manufacturing affordable composites. Draping, in this paper, refers to the act of bringing a flat workpiece into contact with an arbitrary tool surface. As a result, the draping of woven and stitched mats tends to cause the mat to deform to the tool geometry. This paper details an experimental study designed to demonstrate the effect of draping preforms on mold filling, and final structure of the composite product. A mold was built providing a conical mold cavity. Flow visualization experiments were performed, as well as shearing angle and preform fiber volume fraction measurements from manufactured cone parts. Experimental results show that draping does significantly change fiber orientation, fiber volume fraction, permeability and hence the injection pressure or flow rate required to fill a mold. This data was compared with numerical prediction codes for preform deformation, permeability calculation, and mold filling. Preform deformation predictions were found to overpredict in areas of high deformation, due to the assumptions made by the numerical algorithm used. Permeability components calculated are reasonable, but are affected by overpredicted preform deformation, and interpolation methods used. Prediction of injection pressure and flow rate histories are good, while predicted flow front shapes fail to capture some experimental features. Difficulties in predicting flow front shapes are attributed to three mechanisms; a decrease in permeability magnitudes due to increased volume fraction, a smaller volume of fluid required due to increased volume fraction, and reorientation of fiber tows changing the direction of principle permeability components.

The out-of-plane permeability of two glass fibre fabrics was measured by 26 institutions using silicone oil as a test fluid. Participants in this study were free to select the test procedure, specimen dimensions and data analysis method, provided that testing was carried out at three target fibre volume fractions, 46 %, 50 % and 54 %. While results showed a variability of two orders of magnitude between participants, most values were within a significantly narrower band. A majority of participants used 1D saturated test method. A few selected 1D unsaturated and 3D unsaturated flow method which gave very similar results. Focusing on analysis of data and results of 1D saturated flow measurements, results are not conclusive, but they are consistent with number of layers in a specimen, fibre volume fraction, injection pressure and sealing of specimen edges all having an effect on the measured permeability. Specifying limits for these parameters is expected to result in reduced scatter in measured permeability., Composites Part A: Applied Science and Manufacturing, 148, ISSN:1359-835X, ISSN:1878-5840

This study investigates the influences of dissolved gasses on vacuum assisted resin infusion, providing a methodology which can be applied to assist in the development of robust high-performance infusion manufacturing processes. Resin degassing pressure was found to be influential on the effectiveness of degassing. Pressures under 5 mBar are recommended to ensure rapid and thorough removal of dissolved gasses. The saturation point of dissolved oxygen in resin was found to linearly correlate with resin pressure. The binary saturation condition of the resin during vacuum assisted resin infusion processes was found to directly impact void content within a cured laminate. Resin that was oversaturated with dissolved gas relative to the set post-fill fluid pressure was found to result in average void contents ranging from 1 to 2% across the laminate. Undersaturated resin resulted in consistently low void contents, being less than 0.2% across the laminate. This demonstrates the significance of resin dissolved oxygen content.