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排序方式: 共有53条查询结果,搜索用时 281 毫秒
1.
Darothi Bairagi Venkataramana Munukuti Pallabi Bhuyan Rajib Saha Sumantra Mandal 《工业材料与腐蚀》2021,72(5):829-838
The influence of cementite spheroidization on the impact toughness and electrochemical properties of a high-carbon steel has been thoroughly investigated in this study. Heavy warm rolling, followed by 2 h of annealing, has resulted in near-complete spheroidization, leading to a microstructure consisting of nano-cementite globules dispersed in the ultrafine-grained ferritic matrix. The Charpy impact test exhibited superior impact toughness with increased spheroidization. It is validated by the presence of abundant dimples in the fractographs of spheroidized specimens, in contrast to the as-received one that experienced a brittle failure due to its lamellar pearlitic structure. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) carried out in a 3.5% NaCl solution revealed that the corrosion resistance of the alloy gets improved with the increase in the degree of spheroidization. This is attributed to the lower susceptibility of the spheroidized specimen to microgalvanic corrosion owing to the minimum area of contact between nano-spheroidized cementite and ferrite, as elucidated with the help of EIS results aided by equivalent electrical circuit model. 相似文献
2.
The dynamic characteristics involved in the loading process in the ocean environment are extremely complicated and difficult
for exact evaluation. In this paper, parametric studies are presented to assess the influence of uncertainties associated
with various assumptions and approximations, involved in modelling the dynamic loading processes of ocean environment, for
the evaluation of dynamic response of offshore structures. These uncertainties are represented by the inertia coefficient
and the drag coefficient of the Morison equation which defines the wave forcing function, the mean height of the input sea
waves and the shear wave velocity of the soil. The results show that the effects of uncertainties are closely related to the
natural frequency of the structure and the predominant frequency of the wave force. These uncertainties, except the variation
in the shear wave velocity in the soil, contribute significantly to the dynamic response and the first passage probability
evaluation of the offshore structure systems. 相似文献
3.
The conventional proportional integral controlled direct torque control of an induction motor using the space vector pulse-width modulation technique may provide satisfactory dynamic response. However, the proportional integral controller (PIC) does not provide efficient dynamic performance in the induction motor drive during sudden changes in the load or speed. To improve dynamic performance of the induction motor drive, the PICs are replaced by type-2 fuzzy logic control. The type-2 fuzzy improves the starting transient performance as well as the steady-state response. In addition, the type-2 fuzzy direct torque control provides lesser current total harmonic distortion, flux distortion, and torque pulsation of the induction motor drive compared to conventional direct torque control. A MATLAB Simulink (The MathWorks, Natick, Massachusetts, USA) model for direct torque control with type-2 fuzzy logic control is developed to simulate the response of an induction motor drive with different operating conditions. The space vector pulse-width modulation technique is used to drive the inverter, as it produces lesser total harmonic distortion in inverter current and voltage waveforms for a given switching transition due to the single switching frequency for the movement of each state vector. A prototype type-2 fuzzy-based direct torque control induction motor with space vector pulse-width modulation is developed to validate the simulated response. The control signals for the inverter are generated by the DSPACE DS1104 (DSPACE GmbH, Germany) to drive a two-HP induction machine. 相似文献
4.
Achieving End-to-end Fairness in 802.11e Based Wireless Multi-Hop Mesh Networks Without Coordination
Tianji Li Douglas J. Leith Venkataramana Badarla David Malone Qizhi Cao 《Mobile Networks and Applications》2011,16(1):17-34
To mitigate the damaging impacts caused by interference and hidden terminals, it has been proposed to use orthogonal channels
in wireless multi-hop mesh networks. We demonstrate however that even if these issues are completely eliminated with perfectly
assigned channels, gross unfairness can still exist amongst competing flows which traverse multiple hops. We propose the use
of 802.11e’s TXOP mechanism to restore/enforce fairness. The proposed scheme is simple, implementable using off-the-shelf
devices and fully decentralised (requires no message passing). 相似文献
5.
V. D. Manvatkar A. A. Gokhale G. Jagan Reddy A. Venkataramana A. De 《Metallurgical and Materials Transactions A》2011,42(13):4080-4087
Laser engineered net shaping (LENS) and other similar processes facilitate building of parts with freeform shapes by melting
and deposition of metallic powders layer by layer. A-priori estimation of the layerwise variations in peak temperature, build dimension, cooling rate, and mechanical property is requisite
for successful application of these processes. We present here an integrated approach to estimate these build attributes.
A three-dimensional (3-D) heat transfer analysis based on the finite element method is developed to compute the layerwise
variation in thermal cycles and melt pool dimensions in the single-line multilayer wall structure of austenitic stainless
steel. The computed values of cooling rates during solidification are used to estimate the layerwise variation in cell spacing
of the solidified structure. A Hall–Petch like relation using cell size as the structural parameter is used next to estimate
the layerwise hardness distribution. The predicted values of layer widths and build heights have depicted fair agreement with
the corresponding measured values in actual deposits. The estimated values of layerwise cell spacing and hardness remain underpredicted
and overpredicted, respectively. The slight underprediction of the cell spacing is attributed to the possible overestimation
of the cooling rates that may have resulted due to the neglect of convective heat transport within the melt pool. The overprediction
of the layerwise hardness is certainly due to the underprediction of corresponding cell spacing. The application of Hall–Petch
coefficients, which is strictly valid for wrought and annealed grain structures, to estimate the hardness of as-solidified
cellular structures may have also contributed to the overprediction of the layerwise hardness. 相似文献
6.
A study of dynamic response of offshore structures in random seas to inputs of earthquake ground motions is presented. Emphasis
is placed on the evaluation of nonlinear hydrodynamic damping effects due to sea waves for the earthquake response. The structure
is discretized using the finite element method. Sea waves are represented by Bretschneider’s power spectrum and the Morison
equation defines the wave forcing function. Tajimi-Kanai’s power spectrum is used for the horizontal ground acceleration due
to earthquakes. The governing equations of motion are obtained by the substructure method. Response analysis is carried out
using the frequency-domain random-vibration approach.
It is found that the hydrodynamic damping forces are higher in random seas than in still water and sea waves generally reduce
the seismic response of offshore structures. Studies on the first passage probabilities of response indicate that small sea
waves enhance the reliability of offshore structures against earthquakes forces. 相似文献
7.
A high precision triangular plate bending element for the analysis of thick plates is developed in thin paper. The element has three nodes and 12 degrees of freedom per node. Explicit expressions for stiffness coefficients are derived. The superiority of the element is demonstrated by the accuracy of the results obtained by applying it to some typical thick plate problems. 相似文献
8.
Thick shells of revolution find application in nuclear pressure vessel technology. In this paper, a finite ring shell element, based on the stress-strain relations of moderately thick shells, is developed. The element has 20 degrees of freedom. Cubic polynomials are assumed for all the generalized displacements, i.e. the in-plane forces, the normal displacements and the total rotations of the normal about the co-ordinate lines. This ensures faster convergence and better accuracy in the results. The effectiveness of the element is demonstrated by numerical examples. 相似文献
9.
K Srinivasa Rao P Syamasundara Rao G Venkataramana 《Canadian Metallurgical Quarterly》1976,28(1):69-72
Supernatants of alloantigen-activated T cells contain a number of factors, including an immunoglobulin-binding factor (IBF) which inhibits complement-induced hemolysis of sheep erythrocytes coated with anti-Forssman IgG antibodies and a factor which suppresses IgM antibody synthesis in vitro. These two factors may be identical, since they are simultaneously retained on Sepharose beads to which IgG has been coupled and can be recovered by elution at pH 2.8. They do not bind to Sepharose beads to which IgM of F(ab')2 fragment of IgG has been coupled, demonstrating that they have a selective affinity for the Fc region of IgG. In addition, the fixation of IBF on the Fc portion of IgG reversibly inhibits subsequent binding of the first component of complement (C1), thus indicating that IBF does not irreversibly alter the C1 binding site(s) of IgG. 相似文献
10.
J. Venkataramana 《Nuclear Engineering and Design》1974,30(3):369-378
The application of a thick shell theory in the design of nuclear pressure vessels is given. A derivation for thick shells of revolution with the inclusion effects of transverse shear stress and normal stress, in which the Young's modulus is considered dependent on temperature, is presented. The set of equations so obtained are solved by a numerical integration method. The example of a spherical shell is solved and the results compared with the case in which the Young's modulus is assumed to be constant. It is shown that under large temperature gradients through the thickness, the change in deflections and stresses can be significant, if the present derivation is used. 相似文献