Papers by Keyword: Gradient

Abstract: Benefit from the gradient distribution of microstructure, gradient nanograined (GNG) metals have broad application prospect owing to their advantages of both high strength and good tensile ductility. Meanwhile, the fracture behavior of gradient nanograined metals is different from that of traditional homogeneous materials. Using molecular dynamics (MD) method, we simulated the propagation of a crack in a pre-cracked GNG Cu. Voronoi method was adopted to generate the polycrystalline topology with gradient grain size, and FCC copper atoms were filled into the topological structure. The crack was introduced by removing three layers of atoms. Then, the MD specimen was loaded to simulate the crack growth and/or blunting. The micro-defects were identified by the common neighbor analysis parameter. The effects of the grain size gradient and the crack tip initial position on the crack growth were also investigated.

Abstract: 3D printing of plastic materials is very popular nowadays, while printing of wear resistant hard materials is still an issue. Gradient or functionally graded structures are providing improved performance in impact-abrasive application (tunnelling, geothermal drilling, mining, etc.) through the optimal positioning of areas providing high wear resistance and high resistance against impacts. However, printing of such structures by widely used powder bed selective laser sintering leads to the high consumption of raw materials (powders) that cannot be used again for next printing. A method to overcome this problem is explored in current work. The cermets were produced from following powders: (1) commercial, (2) obtained by disintegration of cutting tool inserts (recycled) and (3) reused recycled ones. Tungsten and cobalt used for the production of the majority of cermets are critical raw materials and their consumption should be reduced while the rate of recycling needs to be increased. The surfaces were studied with the help of optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The hardness and wear rate of samples in abrasive conditions were measured.

Abstract: Heat removal from nuclear reactor core has been one of the major Engineering considerations in the construction of nuclear power plant. At the center of this consideration is the nuclear fuel pellet whose burning efficiency determines the rate of heat transfer to the coolant. This research, focuses on the study of temperature distribution of solid fuel, temperature distribution of annular fuel with external cooling and the temperature distribution of annular fuel with internal and external cooling. We analyzed the different distribution and made a conclusion on the possibility of improving temperature management of Nuclear fuel rod, by designing fuel pellets based on this geometrical and thermal Analysis. To date, a lot of studies has been done on the thermal and geometrical properties of Nuclear fuel pellet, it is observed that annular fuel pellet with simulteneous internal and external cooling can achieve better temperature distribution which leads to high linear heat generation rate, thus generating more power in the design [1]. It has also been observed that annular fuel pellets has low fission gas release [10]. In large LOCA, the peak cladding temperature of annular fuel is about 600 which is significantly less than that of solid fuel (920 ), this is due to the fact that annular fuel cladding has lower initial temperature and the thinner annular fuel can be cooled more efficiently than the solid fuel. One of drawbacks of annular fuel technology is “the fuel gap conductance assymmetry” which is caused by outward thermal expansion, it has a potential effect on the MDNBR (Minimum Departure from Nucleate Boiling Ratio), which is the minimum ratio of the critical to actual heat flux found in the core [10]. In this model, we used the ceramic fuel pellet of UO₂ as our case study. All the parameters in this model are assumed parameters of UO₂. The Heat Transfer tool (ANSYS APDL) was used to validate the Analytical Model of this research.

Abstract: The sliding mode based differential flatness control is used to stabilize the error dynamics in view of unmodeled dynamics employing position, velocity and acceleration as reference values but feeding back to system only the position and velocity measurements. This controller is able to plan trajectories of control gains within the proposed scheme of the controller. By above this paper describes a sliding mode based differential flatness control to a leg-wheel hybrid robot, in order to design a robotic prototype with the ability to move an uneven ground. To prove the controller working a simulation in Matlab-Simulink using Simmechanics is made. The result of this work shows a controller that is able to follow the reference trajectories without overshoots and small chattering.

Abstract: This paper describes the behavior of adaptive control using the MIT rule for a polar aligned single axis tracking system, it´s for increase the efficiency of solar energy capturing compared to a polar fixed system, where the response of system is analyzed by simulation in Simulink – MATLAB® software. The data input for estimate the energy in the photovoltaic panels is the radiation data, that is obtained by weather station of the CAR (regional autonomous corporation) situated in the zone of study. The objective of the integration between the photovoltaic panel and the mechanics tracking system is to keep the perpendicular sunlight during the day. The MIT adaptive control tries to reduce possible errors, such a sun position data deviations, friction and environmental changes in the conventional solar tracking. This control was designed according to a typical polar aligned single axis tracker.

Abstract: In this work Al-Si-Cu Functionally Graded Material (FGM) is developed using centrifuge technique. The method used in this work to produce FGM is totally different compared to other centrifugal process which helped in producing solid cylindrical parts. The FGM is characterized through Microstructure and Hardness and it is found that the Cu segregated at the bottom of the casting and Si at the top due to the density difference. Similarly the hardness and the ultimate tensile strength at the bottom of the casting and at the top of the casting region is more when compared to region in-between the top and bottom of the casting.

Abstract: The injection impurity element into ZnO has added new dimension to its versatile applications particularly in spintronics and optoelectronics. In this work, we are reporting effect of non magnetic Ti, and magnetic V impurities in ZnO. The substitution of impurity atoms have been done in ground state wurtzite (WZ) and meta stable zinc-blende (ZB) structure. Our investigations have revealed a small difference in WZ and ZB geometries of contaminated ZnO reflecting on the possibility of their experimental fabrication. Spin polarized electronic structures resembled nonmagnetic nature of Ti:ZnO in WZ and magnetic nature in ZB geometry. Similarly introduction of V in to ZnO induced magnetization in ZnO in both WZ and ZB geometry. For these investigations, we have adapted DFT approach using FP-L(APW+lo) method implemented in WIEN2k code.

Abstract: Most patch-based texture synthesis algorithms using Markov Random Field for composite materials only considers color similarity between the corresponding pixels. The traditional algorithms are lack of adaptability, so the size of patches needs to be defined artificially in advance as the result of blurring of image texture features for composite materials. In order to improve above problems, a new patch-based sampling algorithm for synthesizing textures from an input sample image texture of composite materials is presented in this paper. By using patches of the sample texture as building blocks for image texture synthesis of composite materials, this algorithm makes high-quality texture synthesis for a wide variety of textures ranging regular to stochastic. The method is effective by our experimental results.

Abstract: As a transparent conducting oxide, Cd:ZnO system is considered potential candidate for optoelectronic applications alternate to Al:ZnO. However instability issue of the Cd:ZnO system is under debate. Here we investigate effect of Cd impurities on physical properties of ZnO in wurtzite (WZ) as well as zincblende (ZB) geometries. Density functional theory (DFT) based full potential linearized augmented plane wave plus local orbital FP-L(APW+lo) method has been adapted for these investigations. To calculate the total energy of the system, exchange correlation energy term is evaluated at the level of GGA. For the more realistic band gap calculation, GGA in addition to mBJ exchange potential has been employed. From our calculations, it is observed, Cd:ZnO is more stable in ZB structure than that of WZ. The Cd substitution ZnO has a tendency to convert the hexagonal geometry into cubic. It is also observed, doping of the Cd impurities strongly influence the electronic structures resulting into the narrowing energy band gap.

Abstract: With the robustness of a single color which is not high in standard particle filter tracking, a fusion of color and gradient particle filter algorithm is proposed. By the advantages of color described the target ’global and gradients described the shape of structure, they are weighted fusion to form a new integrated histogram and applied to the particle filter framework. The experimental results show that compared with the traditional particle filter algorithm, the text of the algorithm can achieve relatively reliable target tracking under complicated background and illumination changes, with better robustness and reliability.