An on-line neural network-based harmonic analyzer

This paper introduces a simple solution, based on neural networks, to the problem of the on-line and adaptive harmonic component analysis in power systems. A single neuron is used whose synaptic weights are directly related to the signal's dc component and to the magnitudes and phases of the harmonic components present in the signal. In addition, deviation from the nominal fundamental frequency is accounted for in the same context. The simulation of a realistic test case shows a very efficient and precise estimation of the present harmonic

An on-line neural network-based harmonic analyzer

This paper introduces a simple solution, based on neural networks, to the problem of the on-line and adaptive harmonic component analysis in power systems. A single neuron is used whose synaptic weights are directly related to the signal's dc component and to the magnitudes and phases of the harmonic components present in the signal. In addition, deviation from the nominal fundamental frequency is accounted for in the same context. The simulation of a realistic test case shows a very efficient and precise estimation of the present harmonic

Master curve approach to axial stiffness calculation for non-crimp fabric biaxial composites with out-of-plane waviness

International audienceThe effect of 0 degrees-tow out-of-plane waviness on the biaxial non-crimp-fabric (NCF) composite axial stiffness is investigated. Homogenizing, the bundle mesostructure of the NCF composite is replaced by layers. Then the composite is represented by a laminate with flat layers with effective stiffness properties representing the curved 0 degrees-layer and the 90 degrees-layer with varying thickness. It is shown that the NCF composite knock-down factor characterizing the stiffness degradation has almost the same dependence on wave parameters as the knock-down factor for the curved 0 degrees-layer. Numerical analysis showed that 90 degrees-layer knock-down factor versus amplitude curves for different wavelength can be reduced to one master curve which can be described by a one-parameter expression with the parameter dependent on the used material. This observation is used to obtain high accuracy for analytical predictions for knock-down factors for cases with different wavelength and amplitudes based on two FE calculations only

Effective stiffness of curved 0 degrees-layers for stiffness determination of cross-ply non-crimp fabric composites

International audienceThe effect of the 0 degrees-tow waviness on axial stiffness of cross-ply non-crimp fabric composites is analysed using multiscale approach. The curved 0 degrees- and 90 degrees-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0 degrees-layer stiffness is calculated analysing isolated curved 0 degrees-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0 degrees-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0 degrees-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties in the 90 degrees-layers with bundle structure can be replaced by the transverse stiffness of the homogenised 90 degrees-layer material

Microdamage analysis in thermally aged CF/polyimide laminates

Microdamage in layers of CF Thornel® T650 8-harness satin woven composite with thermosetting polyimide NEXIMID® MHT-R resin was analysed. After cooling to room temperature multiple intra-bundle cracking due to tensile transverse thermal stresses was observed in the studied [(+45/-45)/(90/0)]2s composite. The composite was subjected to thermal cycling quantifying the increase of crack density in layers. Comparison of two ramps with the same lowest temperature shows that the highest temperature in the cycle has a significant detrimental effect. Exposure for 40 days to 288°C caused many new cracks after cooling down to room temperature. Both aged and not aged specimens were tested in uniaxial quasi-static tension. Cracking was analysed using fracture mechanics and probabilistic approaches. Cracking in off-axis layers was predicted based on Weibull analysis of the 90- layer. The thermal treatment degraded the cracking resistance of the surface layer and of the next layer