We deploy a finite volume numerical computation to investigate the two-dimensional hydromagnetic natural convection in a cooled square enclosure in the presence of four inner heated circular cylinders with identical s...
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We deploy a finite volume numerical computation to investigate the two-dimensional hydromagnetic natural convection in a cooled square enclosure in the presence of four inner heated circular cylinders with identical shape. The inner circular cylinders are placed in a rectangular array with equal distance away from each other within the enclosure and moving along the diagonals of the enclosure. All the walls of the enclosure are kept isothermal with temperatures less than that of the cylinders. A uniform magnetic field is applied along the horizontal direction normal to the vertical wall. All solid walls are assumed electrically insulated. Simulations are performed for a range of the controlling parameters such as the Rayleigh number 10(3) to 10(6), Hartmann number 0 to 50, and the dimensionless horizontal and vertical distance from the center of a cylinder to center of another cylinder 0.3 to 0.7. The study specifically aims to understand the effects of the location of the cylinders in the enclosure on the magnetoconvective transport, when they moved along the diagonals of the enclosure. It is observed that the unsteady behavior of the flow and thermal fields at relatively larger Rayleigh numbers and for some cylinder position are suppressed by imposition of the magnetic field. The heat transfer strongly depends on the position of the cylinders and the strength of the magnetic field. Hence, by controlling the position of the objects and the magnetic field strength, a significant control on the hydrodynamic and thermal transport can be achieved.
Axial flows over cylinders are frequently encountered in practice, e.g. in tubular heat exchangers and reactors. Using the Integral method, closed-form relationships are developed for heat transfer coefficients or Nus...
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Axial flows over cylinders are frequently encountered in practice, e.g. in tubular heat exchangers and reactors. Using the Integral method, closed-form relationships are developed for heat transfer coefficients or Nusselt number inside a fluid flowing axially between a rectangular/square array of parallel cylinders with unequal temperatures. The model considers the temperature variations of cylinders from one row to another while assuming the same temperature for all the cylinders in each row. The model could well capture several sets of numerical data, which can be regarded as excellent in light of the simplicity and comprehensiveness of the model. The compact and accurate formulae developed in this work can be readily employed, and also implemented into any software or tools, for the estimation of Nu in tubular heat exchangers, fins systems, porous media and composite manufacturing. (C) 2015 Elsevier Masson SAS. All rights reserved.
When the data are sparse but not exceedingly so, we face a trade-off between bias and precision that makes the usual choice between conducting either a fully unconditional inference or a fully conditional inference un...
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When the data are sparse but not exceedingly so, we face a trade-off between bias and precision that makes the usual choice between conducting either a fully unconditional inference or a fully conditional inference unduly restrictive. We propose a method to relax the conditional inference that relies upon commonly available computer outputs. In the rectangular array asymptotic setting, the relaxed conditional maximum likelihood estimator has smaller bias than the unconditional estimator and smaller mean square error than the conditional estimator.
The concept of spatial smoothing is first extended to a rectangular planar array and a two-dimensional (2-D) search function is formed to estimate the source of directions. To avoid performing a 2-D search, an approac...
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The concept of spatial smoothing is first extended to a rectangular planar array and a two-dimensional (2-D) search function is formed to estimate the source of directions. To avoid performing a 2-D search, an approach based on two one-dimensional (1-D) searches is also discussed. This approach uses rows and columns of the rectangular array to perform 1-D searches. To match the data obtained, a 2-D verification is then performed. Computer simulation results for both approaches, based on the MUSIC method, are presented.
A micromodeling analysis of unidirectionally reinforced Ti-6-4/SM1140+ composites subjected to transverse tensile loading has been performed using the finite-element method (FEM). The composite is assumed to be infini...
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A micromodeling analysis of unidirectionally reinforced Ti-6-4/SM1140+ composites subjected to transverse tensile loading has been performed using the finite-element method (FEM). The composite is assumed to be infinite and regular, with either hexagonal or rectangular arrays of fibers in an elastic-plastic matrix. Unit cells of these arrays are applied in this modeling analysis. Factors affecting transverse properties of the composites, such as thermal residual stresses caused by cooling from the composite processing temperature, fiber-matrix interface conditions, fiber volume fraction, fiber spacing, fiber packing, and test temperature are discussed. Predictions of stress-strain curves are compared with experimental results. A hexagonal fiber-packing model with a weak fiber-matrix interfacial strength predicts the transverse tensile behavior of the composite Ti-6-4/SM1140+ most accurately.
We investigate the flux pinning and dynamic properties of superconducting vortices in an Al film with an array of magnetic bars deposited on top. The dimensions of each bar are chosen in such a way that they host a si...
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We investigate the flux pinning and dynamic properties of superconducting vortices in an Al film with an array of magnetic bars deposited on top. The dimensions of each bar are chosen in such a way that they host a single magnetic domain. These micromagnets are distributed periodically in a rectangular array with 0.5 mu m separation parallel to the longest side of the bars and displaced laterally by a distance w. We show that, for w > Lambda, where Lambda is the effective field penetration depth, the pinning strength is almost independent of w whereas the critical temperature at zero field, T-c(0), decreases as similar to w(-1). For w < Lambda the opposite behavior is observed, i.e. T-c(0) seems to saturate to a nearly w-independent value and the transition from large to small w is accompanied by a large suppression of the critical current j(c) together with a clear change in the shape of the current-voltage characteristics. In particular, the substantial weakening of the pinning potential for w < Lambda gives rise to an unexpected flux flow response. The field evolution of this regime allows us to determine whether the magnetic bars induce vortex-antivortex pairs in the system. The present findings suggest that practical application of magnetic pinning centers are restricted to low field values.
In the past few years, we have developed techniques for inserting multiple discrete and wide continuous nulls for uniform linear array (ULA), and introduced for this purpose the use of quasi- and mixed- matrices and t...
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ISBN:
(纸本)9781728116792
In the past few years, we have developed techniques for inserting multiple discrete and wide continuous nulls for uniform linear array (ULA), and introduced for this purpose the use of quasi- and mixed- matrices and their factorizations. The techniques give an optimal solution, based on least squares criteria and a low-rank approximation to balance the null-depth and pattern distortion. The technique is extended to two-dimensional (2-D) uniform rectangular array (URA) in this paper. A fast algorithm is developed based on some efficient matrix properties of the Kronecker Product (KP). Essentially, we have converted a MN x MN matrix problem to M x M and N x N matrix problems to enable efficient implementation of 2-D deterministic nulling where M x N is the dimension of the URA.
This paper analyzes the radiation characteristics of fishbone antenna arrays and concludes its optimum set of array formation. In order to study the feasibility of apply fishbone antenna into pashed array, the common ...
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ISBN:
(纸本)9783038351153
This paper analyzes the radiation characteristics of fishbone antenna arrays and concludes its optimum set of array formation. In order to study the feasibility of apply fishbone antenna into pashed array, the common fishbone antenna array is analyzed and simulated by the method of moments. It mainly calculated the radiation properties of two-element array, four-element array and six-element array under the linear array, rectangular array and sector array respectively. Comparing characteristics of different number of array element under the same array type and the different array types under the same number of array element, it suggests that two-element array is the most appropriate array type when sector arrayed, and the array types of 3 x 2, 2 x 2 and 1 x 2 have relatively good effect of beam scanning in low frequency with phase shift.
Occurrence of partial discharges (PD) is one of the basic criteria of high voltage devices insulation evaluation. Precise PD source location is crucial for undertaking maintenance of mentioned equipment. This paper co...
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ISBN:
(纸本)9781479966134
Occurrence of partial discharges (PD) is one of the basic criteria of high voltage devices insulation evaluation. Precise PD source location is crucial for undertaking maintenance of mentioned equipment. This paper concerns the issue of partial discharges sources location using phased rectangular arrays technique and high-resolution direction of arrival estimation technology. In addition to the theoretical assumptions of both techniques, the simulation result, in which an Uniform rectangular array (URA) was used for registration of the electromagnetic signals generated by defects in power transformer insulation system, were shown. To estimate the Direction of Arrival (DOA) of electromagnetic signals, that propagate from the discharge-generating defect to the transducer array installed on transformer tank, Minimum Variance Distortionless Response (MVDR) algorithm was chosen. The location of defect was determined using two intersecting lines defined by the DOAs from two URAs. With the ability to locate multisource discharges (even at very low signal to noise ratio - SNR), the adopted solution has advantages over conventional techniques.
A new two-dimensional direction finding algorithm called 2D-11-SVD is proposed in this paper. It is designed for rectangular arrays and can also be extended to rectangular arrays with faulty or missing elements. The k...
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ISBN:
(纸本)9781479967704
A new two-dimensional direction finding algorithm called 2D-11-SVD is proposed in this paper. It is designed for rectangular arrays and can also be extended to rectangular arrays with faulty or missing elements. The key idea is to represent direction-of-arrival with two decoupled angles and then successively estimate them. Therefore two dimensional direction finding can be realized by applying several times of one dimensional sparse reconstruction based direction finding methods instead of directly extending them to two dimensional situation. Performance analysis and simulation results reveal that the proposed method has a much lower computational complexity and a similar performance compared with the wellknown 11-SVD algorithm, which has several advantages over conventional direction finding techniques due to the application of sparse signal reconstruction.
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