Shakedown and limit analysis of 90° pipe bends under internal pressure,cyclic in-plane bending and cyclic thermal loading

The Linear Matching Method is used to create the shakedown limit and limit load interaction curves of 90° pipe bends for a range of bend factors. Two load cases are considered i) internal pressure and in-plane bending (which includes opening, closing and reversed bending) and ii) internal pressure and a cyclic through wall temperature difference giving rise to thermal stresses. The effects of the ratios of bend radius to pipe mean radius (R/r) and mean radius to wall thickness (r/t) on the limit load and shakedown behaviour are presented.     

Effect of hydrofoil flexibility on the power extraction of a flapping tidal generator via two- and three-dimensional flow simulations

In this study, we investigate the effect of hydrofoil flexibility on the power extraction of a flapping tidal stream generator with hydrofoils down-scaled for a water channel in an experiment with a typical Strouhal number and frequency. The described deformations in the chord and spanwise directions are imposed onto the surfaces of the hydrofoil to analyze the flexibility effect. In a two-dimensional (2D) simulation, parameter studies of the chordwise flexure are conducted and a 30% improvement in the rate of the power-extraction efficiency is then achieved when the chordwise flexure is 20% of the chord length. In a three-dimensional (3D) simulation, the chordwise flexure of 20% achieves a 15% improvement in the rate of the power-extraction efficiency for the hydrofoil with an aspect ratio (AR) of 5, which is less than that in the 2D simulation due to 3D effects such as tip loss and a spanwise vortex. Meanwhile, the effect of the spanwise flexure on the power extraction is minor as compared to that of the chordwise flexure. It was also found throughout the parametric study of the AR variation that the 3D effect of the chordwise flexible hydrofoil is slightly stronger than that of the rigid hydrofoil.     

Molecular dynamics simulation of the nonlinear behavior of the CNT-reinforced calcium silicate hydrate (C–S–H) composite

Calcium–Silicate–Hydrate (C–S–H), which is the major constituent of the cement at the nanoscale, is responsible for the strength and fracture properties of concrete. This research is dedicated to the numerical study of enhanced mechanical properties of C–S–H reinforced by embedding carbon nanotube (CNT) in its molecular structure. Series of molecular dynamics (MD) simulations indicate that the tensile strength of CNT-reinforced C–S–H is substantially enhanced along the direction of CNT as compared to the pure C–S–H. The results of tensile loading reveal that CNT can efficiently bridge the two sides of cracked C–S–H. In addition, CNTs can severely intensify the “transversely isotropic” response of the CNT-reinforced C–S–H. Furthermore, the pull-out behavior of CNT reveals that the force-displacement response can be estimated by a bilinear model, which can later be used for simulation of cohesive crack propagation and multiscale simulation of crack bridging at macro scale specimen of CNT-reinforced cement.     

Mode I and Mode II interlaminar fracture toughness of composite laminates interleaved with electrospun nanofibre veils

In this study, the effects of interleaved nanofibre veils on the Mode I and Mode II interlaminar fracture toughness (ILFT) of autoclave cured unidirectional carbon/epoxy composite laminates were investigated. Various electrospun nanofibre veils consisting of a range of different polymer types, fibre diameters and veil architectures were placed in the laminate mid-planes, which were subsequently subjected to double cantilever beam and end-notch flexure tests. It was found that the polymer type and veil areal weight were the most important factors contributing to laminate performance. A 4.5 g/m² PA66 veil provided the best all-round performance with fracture toughness improvements of 156% and 69% for Mode I and Mode II, respectively.     

Nondestructive evaluation of multilayered paint films in ambient atmosphere using terahertz reflection spectroscopy

The reliability of material characterization with terahertz (THz) waves is typically compromised by irrelevant signals present in the THz measurements. These are well observed in the investigation of layered materials in humid environments, causing difficulty in accurate analyses. In this article, we suggest a realistically employable method of analyzing angled THz reflection measurements in ambient atmosphere for qualitative monitoring and evaluation of multilayered paint films. In particular, we present successive decomposition of THz sample signals for individual identification of each constituent layer in the samples. It is shown that the extracted spectrum of each paint layer presents sufficient information for effective monitoring of the multilayered structures. In this process, THz spectra of the marine paints EH2350, Interthane 989, BEA777, and ENA300 are reported for the first time. Our experimental findings show promise in highly effective nondestructive inspection of layered structures for real-world evaluation applications.     

基于引力搜索神经网络的风电机组传动链故障识别

针对风电机组传动链故障识别由风电场制定合理维修策略可减少停机时间、降低维修费用问题,将引力搜索算法用于BP神经网络初始权值及阈值优化,提出基于引力搜索神经网络的风电机组传动链故障识别方法。算例结果表明,所提方法精度较BP神经网络高,能准确识别齿轮磨损、齿轮断齿、轴承松动等风电机组传动链典型故障,验证该方法的有效性。     

Regional energy rebound effect: The impact of economy-wide and sector level energy efficiency improvement in Georgia,USA

Rebound effect is defined as the lost part of ceteris paribus energy savings from improvements on energy efficiency. In this paper, we investigate economy-wide energy rebound effects by developing a computable general equilibrium (CGE) model for Georgia, USA. The model adopts a highly disaggregated sector profile and highlights the substitution possibilities between different energy sources in the production structure. These two features allow us to better characterize the change in energy use in face of an efficiency shock, and to explore in detail how a sector-level shock propagates throughout the economic structure to generate aggregate impacts. We find that with economy-wide energy efficiency improvement on the production side, economy-wide rebound is moderate. Energy price levels fall very slightly, yet sectors respond to these changing prices quite differently in terms of local production and demand. Energy efficiency improvements in particular sectors (epicenters) induce quite different economy-wide impacts. In general, we expect large rebound if the epicenter sector is an energy production sector, a direct upstream/downstream sector of energy production sectors, a transportation sector or a sector with high production elasticity. Our analysis offers valuable insights for policy makers aiming to achieve energy conservation through increasing energy efficiency.     

Investigation of the performance of a ventilated wall

The need for environmental friendly and energy efficient building design has stimulated the design of new facade technologies, including various configurations of double skin facades. This paper investigates the thermal performance of a ventilated wall, both for heating and cooling. A thermal analysis was carried out, paying special attention to the characterization of the heat convection resulting from the buoyancy-induced flow in the open air channel which proved to be a critical aspect of the ventilated wall's behaviour. An integrated thermal and air flow model for the entire system was developed. A model of the ventilated wall construction was developed with the ESP-r simulation program and checked against experimental data from a real-scale test cell facility.The thermal benefits of adding a radiant barrier layer were also investigated. The results showed that this layer was beneficial in terms of the energy performance of the construction. Also, the comparison between the experimental and simulation model results showed satisfactory levels of convergence with the exception of the night hours during the summer period. A sensitivity analysis was also undertaken in order to investigate the main factors and the extent of their effect on the temperature variation inside the ventilated facades.