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91.
Sophie Ramananarivo Ramiro Godoy-Diana Benjamin Thiria 《Journal of the Royal Society Interface》2013,10(88)
Swimmers in nature use body undulations to generate propulsive and manoeuvring forces. The anguilliform kinematics is driven by muscular actions all along the body, involving a complex temporal and spatial coordination of all the local actuations. Such swimming kinematics can be reproduced artificially, in a simpler way, by using the elasticity of the body passively. Here, we present experiments on self-propelled elastic swimmers at a free surface in the inertial regime. By addressing the fluid–structure interaction problem of anguilliform swimming, we show that our artificial swimmers are well described by coupling a beam theory with the potential flow model of Lighthill. In particular, we show that the propagative nature of the elastic wave producing the propulsive force is strongly dependent on the dissipation of energy along the body of the swimmer. 相似文献
92.
Wen Shifeng Li Shuai Wei Qingsong Chunze Yan Zhang Sheng Shi Yusheng 《Journal of Materials Processing Technology》2014,214(11):2660-2667
Selective laser melting (SLM) manufactures components through the overlapping of multi-track and multi-layer molten pools of metal powders, resulting in two types of molten pool boundaries (MPBs), “layer–layer” and “track–track” MPBs, remaining in SLM parts. The microstructure of MPBs exhibits a complex and regular spatial topological structure. There is a coarse grain zone below the MPBs and nonmetallic elements (C, O, Si) near the MPBs are in an unstable state. Long and thin columnar grains with the same orientations distribute on two sides of the “layer–layer” MPBs, whereas the columnar grains on both sides of “track–track” MPBs have different orientations. The “track–track” MPBs are short and intersect with “layer–layer” MPBs at some points and form acute angles, where cracks are initiated when applied with external loads. The effect of the MPBs on microscopic slipping, macroscopic ductility and fracture mechanism of the SLM parts made along different directions, which were exerted a tensile loading in the as-built condition without heat treatment, was analyzed and evaluated using slip theory and experiments. The results reveal that the MPBs have a significant impact on the microscopic slipping at the loading, macroscopic plastic behavior and fracture mode, and are one of the main reasons for the obvious anisotropy and low ductility of SLM parts. 相似文献
93.
M. Nekouie Esfahani J. CouplandS. Marimuthu 《Journal of Materials Processing Technology》2014,214(12):2941-2948
This article reports on an experimental investigation to understand and subsequently control the alloying composition in laser welding of austenitic stainless steel and low carbon steel. An energy dispersive spectrometer was used to analyse the alloying composition, while microscopy and tensile tests were used to study the microstructure, and mechanical performance of the welded joint respectively. The investigation revealed that above a certain specific point energy the material within the melt pool is well mixed and the laser beam position can be used to control the mechanical properties of the joint. This finding was confirmed using a numerical model based on computational fluid dynamics (CFD) of melt pool dynamics. Strategies to control the composition leading to dramatic changes in hardness, microstructure and mechanical properties of the dissimilar laser welded joint are discussed. 相似文献
94.
95.
Won-Ik ChoSuck-Joo Na Claus ThomyFrank Vollertsen 《Journal of Materials Processing Technology》2012,212(1):262-275
A single-phase problem is solved rather than a multiphase problem for numerical simplicity: and the solution is based on the assumption that the region of gas or plasma can be treated as a void because solid or liquid steel has a greater density level than gas or plasma. The volume-of-fluid method, which can calculate the free surface shape of the keyhole, is used in conjunction with a ray-tracing algorithm to estimate the multiple reflections. Fresnel's reflection model is simplified by the Hagen-Rubens relation for handling a laser beam interaction with materials. Factors considered in the simulations include buoyancy force, Marangoni force and recoil pressure; furthermore, pore generation is simulated by means of an adiabatic bubble model, which can also lead to the phenomenon of a keyhole collapse. Models of the shear stress on the keyhole surface and of the heat transfer to the molten pool via a plasma plume are introduced in simulations of the weld pool dynamics. Analysis of the temperature profile characteristics of the weld bead and molten pool flow in the molten pool is based on the results of the numerical simulations. The simulation results are used to estimate the weld fusion zone shape; and the results of the simulated fusion zone formation are compared with the results of the experimental fusion zone formation and found to be in good agreement. The effects of laser beam profile (Gaussian vs. measured), vapor shear stress, vapor heat source and sulfur content on the molten pool behavior and fusion zone shape are analyzed. 相似文献
96.
《Journal of Nuclear Science and Technology》2013,50(5):734-743
Experiments were carried out to observe boiling behaviors of water on horizontal and vertical surfaces at pressures from 0.35 to 5 MPa. The growth curves of the primary bubbles are well described by the t1/2 variation over the whole range of pressures. The growth rates of primary bubbles are proportional to the square root of the Jakob number, and agree with the correlation by Labuntsov with the arbitrary constant β = 3. The conventional correlations of bubble growth rates, which are directly proportional to the Jakob number, predict slower growth rates at higher pressures. The coalescence behaviors of the primary bubbles were also measured on the vertical surface at 3.66 MPa. The coalesced bubbles, which were formed by the coalescence of two primary bubbles, grow at rates similar to the rates of the primary bubbles. The nucleation site densities measured on the vertical surface at pressures up to 5 MPa increase in proportion to about the 1.5th power of the pressure under equivalent heat flux conditions. The dependence of the nucleation site densities on the heat flux is very similar to the results obtained near atmospheric pressure where the nucleation site density is proportional to the 1.5th power of the heat flux. The nucleation site densities measured in the range of pressures of 0.35 to 5 MPa and at heat fluxes of 0.05 to 0.35MW/m2 agree fairly well with the available correlations. 相似文献
97.
In this paper, we analyze a new method to deal with users' biometric data, by incorporating them in an incomplete aggregation framework, to make an optimal decision for the normalization process. This latter invokes the experts' opinions concept, where the opinions are represented by the user-specific scores. This aggregation of opinions needs more experts for a trusted and informative partial consensus. The key idea of this new approach is based upon the employment of a convex mixture of users' score dispersion. This procedure is used to revise the users' scores, then to update specific statistical parameters which are the principal elements of our score normalization formula. Applying this concept to various scenarios gives an interesting outcome compared to other alternatives. The main contribution of this work for aggregation framework on native space is to introduce this new user-specific concept of scores' normalization, followed by a thorough evaluation of the performance. The validation of this approach is ensured by using a unique modality followed by the exploitation of the fusion of different modalities, to achieve a viable reliability of the final decision. The benchmarking was conducted under Nist2005, Biosecure DS2, and XM2VTS score databases. 相似文献
98.
大坝的建设将天然河道分隔成上、下两个环境单元,改变了河道的流量、流速和水位等水文要素,使原有的水力条件及生态环境都发生了变化,对鱼类的洄游、繁殖和生长等都产生较大影响。以江河湖泊常见鱼种—成年鲤为研究对象,以0.02 m~3/s为基础流量,按照0.01 m~3/s的流量递增进行大坝泄水模拟实验;采用声学信号监测技术监测成年鲤在不同泄水量下的洄游能力及游泳轨迹,分析不同泄水量的河道流场并与鱼类游泳轨迹进行拟合,研究不同流速对鱼类洄游能力的影响。结果表明:成年鲤的洄游距离、游泳速度随着河道流速增大而逐渐减小,成年鲤洄游开始出现困难、开始出现逆流后退以及无法洄游时河道流速分别为0.42,0.48 m/s和0.62 m/s;泄水量每增加一个0.01 m~3/s流量梯度,成年鲤洄游距离约减少1.5 m,说明随着河道流速增大鱼类洄游轨迹变化是一个逐渐收敛的过程。大坝泄水过程同时还会造成氮气和氧气过饱和、改变水体温度和浊度从而对鱼类生存环境、繁殖及鱼类资源造成影响。 相似文献
99.
Understanding fish migratory patterns and movements often relies on tags that are externally or internally implanted. Energy harvesting from fish swimming may benefit the state of the art of fish-tags, by increasing their battery lifetime and expanding their sensory capabilities. Here, we investigate the feasibility of underwater energy harvesting from the vibrations of a biomimetic fish tail though piezoelectric materials. We propose and experimentally validate a modeling framework to predict the underwater vibration of the tail and the associated piezoelectric response. The tail is modeled as a geometrically tapered beam with heterogeneous physical properties, undergoing large amplitude vibration in a viscous fluid. Fluid-structure interactions are described through a hydrodynamic function, which accounts for added mass and nonlinear hydrodynamic damping. To demonstrate the practical benefit of energy harvesting, we assess the possibility of powering a wireless communication module using the underwater vibration of the tail hosting the piezoelectrics. The electrical energy generated by the piezoelectrics during the undulations of the tail is stored and used to power the wireless communication device. This preliminary test offers compelling evidence for future technological developments toward self-powered fish-tags. 相似文献
100.
Assessment of chemical and microbiological parameters of indoor swimming pool atmosphere using multiple comparisons
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The aim of this study was to evaluate the air quality of an indoor swimming pool, analyzing diurnal and seasonal variations in microbiological counts and chemical parameters. The results indicated that yeast and bacteria counts, as well as carbon dioxide (CO2), nitrogen oxides (NOx) and O3 concentrations, showed significant diurnal difference. On the other hand, temperature, relative humidity (R.H.), yeast counts and concentrations of CO2, particles, O3, toluene, and benzene showed seasonal differences. In addition, the relationship between indoor and outdoor air and the degree of correlation between the different parameters have been calculated, suggesting that CO2, fine particles and NOx would have indoor origin due to the human activity and secondary reactions favored by the chemical and environmental conditions of the swimming pool; while O3, benzene and toluene, would come from outside, mainly. The overall results indicated that indoor air quality (IAQ) in the swimming pool building was deficient by the high levels of CO2 and microorganisms, low temperatures, and high R.H., because frequently the limits established by the legislation were exceeded. This fact could be due to the poor ventilation and the inadequate operation of heating, ventilation, and air‐conditioning systems. 相似文献