19684 research outputs found
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Visual measurement of laser-transferred structural vibrations
No full textVision-based vibration measurement techniques are receiving increasing attention as a typical means of non-contact vibration measurement. Vibration measurements of towering structures using vision-based methods often suffer from low spatial resolution of the camera due to the long shooting distance, which in turn limits the ability to recognize small-amplitude vibrations. Such shortcomings can be compensated to some extent by increasing the focal length of the camera, but longer focal length lenses not only increase the cost, but also place higher demands on the stability of the camera itself. With the progress of UAV technology, the spatial resolu-tion of the camera can also be improved by taking close-up shots of large structures with the on-board camera, but the stability of the UAV itself is still difficult to meet the requirements of high-precision vibration measurement. In this paper, a vibration measurement method is pro-posed by attaching a laser pointer to a towering structure, which converts the structural vibra-tion into the movement of the laser spot on the ground and realizes the accurate measurement of structural vibration by using the camera to detect the movement of the laser spot at a close distance. For ease of analysis, the method is known as Laser-assisted Visual Measurement of Structural Vibration i.e. LAVM-Vib. Its operating principle is derived firstly. Then its meas-urement accuracy is examined numerically for different measurement setups. Finally, the method is evaluated by monitoring the vibration of a micro-wind turbine system. The results obtained by LAVM-Vib are close to that of both the laser displacement sensors and accelerome-ters mounted on the structure, showing satisfactory results in monitoring faults in tower foundations
Development of a mechatronic pantograph for improved contact with railway catenaries in conventional networks
No full textThe pantograph-catenary system is crucial for transferring electrical traction power in railway networks. A current challenge in enhancing the competitiveness of railway systems is to increase their operational speed, which is limited by strict contact quality requirements. As their designs become optimised, the potential for dynamic improvements narrows for passive pantographs. An alternative approach is to introduce active control on the pantograph, upgrading it into a mechatronic system. In this work, control strategies are developed for the pantograph, with the goal of improving the contact quality and, consequently, the operational speed. To this effect, a realistic numerical environment is achieved by combining a three-dimensional multibody pantograph model, based on a physical prototype, with a finite element model of a Portuguese catenary designed for normal and elevated speeds. Since the pantograph and catenary models require different time integration formulations, they are simulated in separate programs and synchronised through a co-simulation procedure. An optimal controller is implemented, based on an identification process which assesses how variations in actuation affect the contact force. The dynamic simulations demonstrate that, for scenarios involving single or double pantographs, the contact quality parameters are improved with the mechatronic pantograph, with the operation speed increasing 10–15%.</p
Theoretical modeling of ultrasonic cavitation micro-jet impact and experimental study on deburring of crossed V-groove edges
No full textV-groove microstructures are widely used in optics, energy, and electronics due to their excellent functional properties. However, burr formation during ultra-precision machining can significantly compromise surface quality and machining accuracy. This study explores an ultrasonic cavitation deburring method specifically designed for the crossed edges of V-grooves. A theoretical model was established to describe the relationship between the maximum micro-jet impact pressure generated by cavitation bubble collapse and the key process parameters, namely the working gap and ultrasonic amplitude. This model clarifies the burr removal mechanism and defines the critical conditions required for effective deburring. Experiments were conducted to optimize three major parameters: deburring time, ultrasonic amplitude, and working gap. In addition, the influence of cavitation erosion on the surface quality of micro V-grooves was analyzed. The results showed that a burr removal rate of up to 92.1 % was achieved within 40 s, while surface roughness variation was controlled within 15 %.</p
A numerical study of horizonal axis wind turbine blade Contamination:Aerodynamic and sustainable impacts
No full textWind turbine blade contamination, particularly on the suction side, can significantly degrade aerodynamic performance and reduce output power, making it essential to understand its effects for efficient wind energy generation. This study investigates the influence of varying contamination extents on the aerodynamic performance of horizontal-axis wind turbine blades and quantifies the resulting environmental and economic impacts. To analyse these effects, computational fluid dynamics simulations were conducted at two Reynolds numbers under both clean and contaminated blade conditions. This was followed by a blade element momentum analysis to assess annual energy production. The results show that contamination increases drag, reduces lift, and shifts the transition onset upstream, thereby decreasing aerodynamic efficiency. The blade element momentum analysis confirms that greater contamination extent up to 10 % reduces annual energy production, contributing to higher carbon emissions and economic losses exceeding 7 % relative to the minimum contamination extent.</p
Thermoacoustic Wave-Actuation of a Synthetic Jet:Effect of Thermoacoustic Parameters on the Jet Performance
No full textThermoacoustic systems are primarily used for power generation from low- to medium-grade heat sources, but they also offer seamless integration with complementary technologies. A thermoacoustic engine coupled with a synthetic jet as an actuation mechanism. Variations in resonator size and stack location, controlled by sliding pistons, were studied concerning jet performance. System functionality was evaluated using temperature difference (ΔT), drive ratio (DR), and peak jet velocity. The results provide the first clear evidence that an acoustically driven synthetic jet can operate as a high-performance cooling solution with significant potential for thermal management applications. At resonator length of 1070 mm and relative stack position of 10 %, a jet velocity of 78 m/s was achieved at a minimum ΔT of 256 °C. Integrating an elastic membrane had a powerful effect on the acoustic filed. Discrepancy in phase between membrane vibration and acoustic pressure fluctuations had the potential to delay the start of oscillations within the engine. This effect can be controlled through adjustments in resonator length or operating frequency. Higher velocities, up to 92 m/s, were obtained when the stack was positioned closer to the pressure antinode. However, this necessitated a greater ΔT while simultaneously introducing non-linear phenomena like the membrane’s panting response. The findings not only highlight the potential of this system as a future thermal management solution but also demonstrate the critical role of thermoacoustic design parameters in optimising the jet performance
Women Design for the Belgian Lace Industry, ca. 1890-1920
No full textThe lace industry was traditionally a female affair. In Flanders, where lace had been manufactured from the sixteenth century on, it was likewise mainly women who were working in the lace industry. It was thanks to their endeavours that the region developed into an internationally renowned production centre for luxury textiles. Lace even became part of the national identity after the independence of Belgium in 1830. Yet at the same time the national lace industry declined in the course of the nineteenth century because of the introduction of machine-made lace. The national lace industry even in danger of disappearing completely during World War I. One of the ways to counteract the decline and demise of the textile industry was to commission artists to draw lace designs, which is what happened during the war years. However, the most prestigious commissions, as well as associated publicity and later art-historical research, were focused on male artists Isidore De Rudder (1855-1943) and Fernand Khnopff (1858-1921) and their lace designs. Other men and especially women who drew lace designs, remain largely unknown. This article discusses women who drew designs for the Belgian lace industry between c. 1890 and 1920. At the same time it outlines the challenges faced by the national lace industry and how individual women responded to them. The first part focuses on Jenny Minne (1844-1909) and Irène d’Olszowska (b. 1880), two women who drew professional lace designs in the pre-war period. They and some of their lace work have been discussed before, but their lives and their artistic, social and merits have been largely overlooked. The second part looks at the lace-aid programmes that saved the Belgian lace industry during World War I and ensured employment for lacemakers. It discusses the women who drew lace designs for these humanitarian programmes. The results show that lace design was not a full-time occupation for this group of women, but was instead combined with other tasks within the lace industry, or other types of work elsewhere, or regarded as one of the duties of privileged women. These women’s names and achievements will fill gaps in the histories of lace, of art and of women
Spenser, Marine Life, and the Metaphysics of Extinction:Overfishing and the True Monsters of the Deep
No full textThis chapter plumbs Spenser’s representations of the sea and sea-life in the context of mounting anxiety about the decline of Britain’s fisheries. It reads the fisherman’s attempted rape of Florimell in Book 3 as a barbed critique of unsustainable fishing practices. The Faerie Queene contrasts Lucretian views of the ocean as the site par excellence of ecological instability with a Neoplatonic vision of the ‘fruitful’ ocean as a nursery of immeasurable fecundity and inexhaustible biodiversity. The crash of Britain’s fish stocks seemed to support Lucretius’ troubling theory that species could go extinct, but Spenser’s Neoplatonism spawns hope for the fisheries’ recovery. The chapter then turns to Guyon’s encounters with fish devouring sea-birds on the Rock of Vile Reproach (based on ‘Ireland’s Eye’) and the armada of sea monsters inspired by the drawings of Olaus Magnus. The episode both reinforces and debunks early modern notions of the monstrous alterity of marine life in ways that could alternately deter or encourage Britain’s incipient whaling industry and the expansion of fishing into the North Atlantic. Despite his recoiling from the idea of extinction, Spenser’s willingness to confront environmental problems and to navigate between stable-state and post-equilibrium ecologies makes him an important poet for eco-theory
Ranking based on average and ideal solution method for stakeholder engagement in building energy retrofitting
No full textEnergy retrofitting of residential buildings remains a pivotal strategy for reducing operational costs, curbing greenhouse gas emissions, and enhancing occupant well-being. Yet, existing multi-criteria decision-making approaches can struggle to capture both the complexity of technical trade-offs and the diversity of stakeholder viewpoints. In response, this paper proposes a novel framework, the ranking based on average and ideal solution (RAIS) method that addresses these challenges in a systematic and transparent manner. RAIS begins by combining subjective criterion weights, obtained through the rank order centroid (ROC) technique, with objective weights calculated via the logarithmic percentage change-driven objective weighting (LOPCOW) method. These weights are then fused using the Aczél–Alsina operator, ensuring that neither expert opinion nor data-driven measures exclusively dictate the outcome. Subsequently, each retrofit alternative is evaluated against a dual benchmark consisting of a weighted average solution and an ideal solution, thereby distinguishing retrofits that deliver high performance without deviating too far from conventional practice. This step reveals which options offer compelling benefits across cost, environmental impact, occupant comfort, and policy alignment factors that often compete in retrofit decisions. Through a residential case study, we demonstrate how RAIS can illuminate hidden opportunities, guiding decision-makers towards strategies that are simultaneously innovative and feasible. The findings underscore the method’s ability to reconcile conflicting priorities, offering a rigorously tested, adaptable tool for stakeholders. Ultimately, RAIS lays the groundwork for more nuanced retrofitting models that accommodate lifecycle analysis, equity considerations, and evolving regulatory contexts, all while preserving the clarity and balance central to robust decision-making.</p
Forced Transverse Nonlinear Vibration of an Axially Moving Graphene Sheet Over an Adjacent Substrate
No full textBackground: Squeeze film damping effect has been found to have a significant effect on the dynamic performance of the nano-sheet. Yet, it was not considered in previous works for axially moving nanosheets. Objectives: The objectives of this research are to study the squeez thin film effects on the dynamic behavior of an axially moving graphene sheets over a close parallel substrate and under the effect of a uniformly distributed harmonic load. The study includes frequency response, time domain response, and chaotic behavior. Methods: Within the context of the modified couple stress theory of nano-scale Euler–Bernoulli beams, the Galerkin method is utilized to develop a mathematical model that describes the dynamic behavior of the axially moving simply supported nano-beam, resembling a graphene sheet. Results: Frequency response curves are obtained to study the forced vibration of the axially moving small-size beam and understand the influence of squeeze film damping, nano-induced nonlinear damping, width-to-gap ratio, the axial motion of the nano-beam, and applied external force. Bifurcation diagrams are also studied to investigate transitions and chaotic behavior. Phase portrait and Poincaré section are studied for selected frequencies. Conclusions: Results show that the squeeze film damping has a significant impact on amplitude reduction as it damps the system and avoids failure at resonant frequencies. It is also shown that when the small size effect is considered, the natural frequency becomes higher than those of the classical beam theory. Increasing the vibration amplitude leads to a nonlinear hardening behavior in the system. Significant increasing the axial velocity of the nano-beam is found to alter frequency response, while no change in the frequency response is observed when changing the axial acceleration of the beam.</p
PaeNet:parallel attention enhancement network for ophthalmic image segmentation
No full textImage segmentation plays a critical role in medical image analysis. In recent years, U-Net-based semantic segmentation networks have gained wide popularity in various medical image segmentation tasks, including optic disc and optic cup segmentation, corneal nerve segmentation, and blood vessel detection. However, the existing segmentation methods often miss many details and require more robust feature extraction capabilities. Additionally, the continuous convolution and pooling operations result in the loss of spatial information, hindering more accurate segmentation of the target region. To address these issues, a novel Parallel Attention Enhancement Network (PaeNet) is proposed. Specifically, PaeNet introduces a dual-scale feature enhancement attention module that enhances the contextual information by fusing the feature information between adjacent feature layers and reconstructing the skip connections. Furthermore, PaeNet integrates a multi-scale parallel weight-shared fusion module that employs dense dilated convolution to capture deeper semantic information. To extract clear target boundary information, we introduce a new multi-label loss function to improve the ratio of foreground and background pixels. Finally, experiments are conducted on several public optic image datasets to evaluate the performance of PaeNet. The comprehensive results demonstrate that PaeNet outperforms state-of-the-art methods in the optic disc and cup segmentation, corneal nerve segmentation, and blood vessel detection.</p
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