242 research outputs found
Investigation on Darrieus type straight blade vertical axis wind turbine with flexible blade
In this study, a three-dimensional VAWT with a spanwise passively deformable flexible blade has been modelled. The study mainly focuses on the analysis of blade structure characteristics associated with the bending and twist deflection. Two types of flexible blade material and two strut locations supporting H-type blades are being investigated. The unsteady external loads and energy efficiency of VAWT with such designed flexible blade are also being analysed. The simulation results show that the bending and twist deflection peak is positively correlated with the turbine tip speed ratio λ. For a flexible blade, an unevenly distributed structural stress along the blade with a high stress regime in the vicinity of strut location has also been observed. Due to the rotational motion of a VAWT, the centrifugal force acting on VAWT blade plays an important role on the blade structure characteristics. Reduction of the blade stiffness results in an increase of the blade stress. Changing the strut location from middle to tip will cause a large area under high stress. The results also indicate that the VAWT with a highly flexible blade is not an efficient energy extraction device when it is compared to a less flexible or a rigid blade
A case study on tandem configured oscillating foils in shallow water
Previous research on the oscillating-foil turbine system has demonstrated its great potential for energy extraction. However, not much is known about the interaction of this device with its working environment. To determine the performance and environmental impact of an oscillating-foil turbine in shallow water, a case study have been conducted which was made of the dual oscillating energy extraction foils system with a tandem configuration which operates at two different water depths: i.e., D = 5c and D = 10c. The performance and the environmental effects of the device were compared between shallow-water and deep-water cases. The results show a 10% efficiency loss in the D = 5c case compared with that of the deep water case, because of the interaction between the oscillating-foils and the seabed. It is also observed that the foil vortices dissipation rate of the D = 5c case is 13% less than that of the deep-water case due to the free-surface effect. The water level also rises 23% around the oscillating-foils location of the D = 5c case because of the blockage effect of the device
Sense: Model Hardware Co-design for Accelerating Sparse CNN on Systolic Array
Sparsity is an intrinsic property of convolutional neural network(CNN) and
worth exploiting for CNN accelerators, but extra processing comes with hardware
overhead, causing many architectures suffering from only minor profit.
Meanwhile, systolic array has been increasingly competitive on CNNs
acceleration for its high spatiotemporal locality and low hardware overhead.
However, the irregularity of sparsity induces imbalanced workload under the
rigid systolic dataflow, causing performance degradation. Thus, this paper
proposed a systolicarray-based architecture, called Sense, for sparse CNN
acceleration by model-hardware co-design, achieving large performance
improvement. To balance input feature map(IFM) and weight loads across
Processing Element(PE) array, we applied channel clustering to gather IFMs with
approximate sparsity for array computation, and co-designed a load-balancing
weight pruning method to keep the sparsity ratio of each kernel at a certain
value with little accuracy loss, improving PE utilization and overall
performance. Additionally, Adaptive Dataflow Configuration is applied to
determine the computing strategy based on the storage ratio of IFMs and
weights, lowering 1.17x-1.8x DRAM access compared with Swallow and further
reducing system energy consumption. The whole design is implemented on
ZynqZCU102 with 200MHz and performs at 471-, 34-, 53- and 191-image/s for
AlexNet, VGG-16, ResNet-50 and GoogleNet respectively. Compared against sparse
systolic-array-based accelerators, Swallow, FESA and SPOTS, Sense achieves
1x-2.25x, 1.95x-2.5x and 1.17x-2.37x performance improvement on these CNNs
respectively with reasonable overhead.Comment: 14 pages, 29 figures, 6 tables, IEEE TRANSACTIONS ON VERY LARGE SCALE
INTEGRATION (VLSI) SYSTEM
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Investigation of bamboo pulp fiber-reinforced unsaturated polyester composites
Mechanical pulp fibers (MPFs) and chemical pulp fibers (CPFs) from moso bamboo have been characterized in terms of their length and width distributions, and their reinforcing effects in unsaturated polyester (UPE) composites have also been investigated. CPF-UPE composites had much higher tensile strength, flexural strength, and flexural modulus than MPF-UPE composites. CPF-UPE composites also absorbed less water than MPF-UPE composites. Treatments of the fibers with a combination of 1,6-diisocyanatohexane (DIH) and 2-hydroxyethyl acrylate (HEA) significantly increased the tensile strength, flexural strength, flexural modulus, and water resistance of the resulting composites. Fourier transform infrared and X-ray photoelectron spectroscopy analyses indicated that DIH-HEA was bound onto bamboo fibers (BFs) via carbamate linkages. The scanning electron microscopy images of the tensile-fractured surfaces of the composites revealed that the DIH-HEA treatments for BFs greatly improved the interfacial adhesion between the fibers and UPE resins.Keywords: water resistance, unsaturated polyester, mechanical properties, surface treatments, bamboo fibers, interfacial adhesionKeywords: water resistance, unsaturated polyester, mechanical properties, surface treatments, bamboo fibers, interfacial adhesio
High temperature superconductivity of quaternary hydrides XM3Be4H32 (X, M = Ca, Sr, Ba, Y, La, Ac, Th) under moderate pressure
The compressed hydrogen-rich compounds have received extensive attention as
promising candidates for room temperature superconductivity, however, the high
pressure required to stabilize such materials hinders their wide practical
application. In order to search for potential superconducting hydrides that are
stable at low pressures, we have investigated the crystal structures and
properties of quaternary hydrides, XM3Be4H32 (X, M = Ca, Sr, Ba, Y, La, Ac, Th)
based on the first-principles calculations. We identified nine dynamically
stable compounds at moderate pressure of 20 GPa. Strikingly, their
superconducting transition temperatures are much higher than that of liquid
nitrogen, especially CaTh3Be4H32 (124 K at 5 GPa), ThLa3Be4H32(134 K at 10
GPa), LaAc3Be4H32 (135 K at 20 GPa) and AcLa3Be4H32 (153 K at 20 GPa) exhibit
outstanding superconductivity at mild pressures. Metal atoms acting as
pre-compressors donate abundant electrons to hydrogen, weakening the H-H
covalent bond and thus facilitating the metallization of the hydrogen
sublattice. At the same time, the appropriate combination of metal elements
with different ionic radius and electronegativity can effectively tune the
electronic structure near the Fermi level and improve the superconductivity.
These findings fully reveal the great promise of hosting high-temperature
superconductivity of quaternary hydrides at moderate pressures and will further
promote related exploration.Comment: 14 pages, 6 figure
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