48 research outputs found

    Simulation of Nonlinear Free Surface Waves using a Fixed Grid Method

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    The simulation of nonlinear surface waves is of significant importance in safety studies of fluid containers and reservoirs. In this paper, nonlinear free surface flows are simulated using a fixed grid method which employs local exponential basis functions (EBFs). Assuming the flow to be inviscid and irrotational, the velocity potential Laplace’s equation is spatially discretized and solved by considering the nonlinear Bernoulli’s equation for irrotational flow as the boundary condition on the free surface. The nonlinear boundary conditions are imposed through a semi-implicit iterative time marching. The fixed grid feature of the method, based on a Lagrangian description of fluid flow, allows for retaining the portion of the discretization performed in the first time step for the bulk of the fluid. Thus, the portion which pertains to the regions near the moving boundaries is reprocessed during the time marching.  The accuracy and efficiency of the existing solution is shown by simulating various problems such as liquid sloshing induced by external excitation of the reservoir or initial deformed shape of liquid, seiche phenomena and solitary wave propagation in a basin with constant depth or with a step, and comparing the results with those which are analytically available or those from available codes such as Abaqus.  The proposed method shows far better stability of the results when compared with those of Abaqus which sometimes exhibit divergence after a relatively large number of time steps. For instance, in the propagation of the considered solitary wave in an infinite-like domain problem, the wave height is calculated by the maximum error of 1.6% and 9% using the present method and Abaqus, respectively

    Three-Dimensional Optimization of Blade Lean and Sweep for an Axial Compressor to Improve the Engine Performance

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    Nowadays, optimization methods have been considered as a practical tool to improve the performance of turbo-machines. For this purpose, the numerical study of the aerodynamic flow of the NASA Rotor-67 axial compressor has been investigated, and the results of this three-dimensional simulation show good agreement with experimental data. Then, the blade stacking line is changed using lean and sweep for Rotor-67 to improve the compressor performance. The third-order polynomial is selected to generate the lean and sweep changes from the hub to the shroud. The compressor flow field is solved by a Reynolds averaged Navier-Stokes solver. The genetic algorithm, coupled with the artificial neural networks, is implemented to find the optimum values for blade lean and sweep. Considering the three objective functions of pressure ratio, mass flow rate, and isentropic efficiency, the optimized rotor is obtained using the optimization algorithm. Two geometries are obtained using the optimization algorithm. The results of the optimized compressor include improving the isentropic efficiency, pressure ratio, and mass flow equal to 0.57%, 0.93%, and 1.8%, respectively. After compressor optimization, the effect of the changes in the compressor performance parameters is studied on a single spool turbojet engine. The engine is modeled by analyzing the Brayton thermodynamic cycle of the assumed turbojet engine under design point operating conditions. Results show that for the best test case, the engine with the optimized rotor, the thrust, and SFC are improved by 1.86% and 0.21%, respectively

    Optimal, scalable forward models for computing gravity anomalies

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    We describe three approaches for computing a gravity signal from a density anomaly. The first approach consists of the classical "summation" technique, whilst the remaining two methods solve the Poisson problem for the gravitational potential using either a Finite Element (FE) discretization employing a multilevel preconditioner, or a Green's function evaluated with the Fast Multipole Method (FMM). The methods utilizing the PDE formulation described here differ from previously published approaches used in gravity modeling in that they are optimal, implying that both the memory and computational time required scale linearly with respect to the number of unknowns in the potential field. Additionally, all of the implementations presented here are developed such that the computations can be performed in a massively parallel, distributed memory computing environment. Through numerical experiments, we compare the methods on the basis of their discretization error, CPU time and parallel scalability. We demonstrate the parallel scalability of all these techniques by running forward models with up to 10810^8 voxels on 1000's of cores.Comment: 38 pages, 13 figures; accepted by Geophysical Journal Internationa

    An Investigation into Enterobacteriaceae Responsible for Early Mortality in Japanese Quail Chicks and Their Antibiotic Susceptibility Patterns

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    Quail is an alternative source of protein for humans. These birds can be affected by common bacterial infections. Bacterial contamination of egg is the most common cause of mortality in Japanese quail chicks. In order to study the role of some members of Enterobacteriaceae responsible for early mortality in Japanese quail chicks, 100 dead or moribund quail chicks were obtained from 10 different farms in Ahvaz, Iran. Samples were taken from the liver and yolk sac of the birds and bacterial isolation from samples was conducted by streaking them on MacConkey, Brilliant Green, Salmonella-Shigella and Xylose Lysine Deoxycholate agar plates. The plates were incubated at 37 °C for 24-48 hours, and by standard biochemical tests bacterial isolates were identified. Final confirmation of Salmonella serotypes was performed by Razi Institute. All the isolates were examined for susceptibility to 12 different antibiotics (Padtan-Teb Co., Tehran, Iran) by the disk diffusion (Kirby Bauer) method. The results showed that 78% of the quail chicks were infected. The isolated bacteria were Escherichia coli (44%), Klebsiella pneumonia (8%), Salmonella serovar ruzizi (5%), Salmonella serovar typhimurium (3%), Enterobacter cloacae (4%), Enterobacter aerogenes (4%), Proteus vulgaris (5%) and Proteus mirabilis (5%). One hundred percent susceptibility was observed to gentamycin, soltrim, tetracycline, fosfomycin, florfenicol, cephalexin and ceftriaxone. E. coli isolates were susceptible to soltrim and ceftriaxone, Salmonella isolates were susceptible to fosfomycin, Enterobacter isolates were susceptible to ceftriaxone and Proteus and Klebsiella isolates showed susceptibility to ceftriaxone. It is concluded that the members of Enterobacteriaceae family, specifically the genera Escherichia and Salmonella, are the major causes of early mortality in newly-hatched Japanese quail chicks

    The survey of the nutritional status of 25-36 month old rural children and some factors affecting it in the rural areas of Kerman

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    A survey was carried out to assess the nutritional status of 2-3 year old rural children and some factors affecting it in the rural areas of Kerman. All of the 25-36 month old children (i.e. 1015 children) under coverage of primary health care center were included in the study. About one-third of the children’s mothers (334 mothers) were questioned. The data were collected using questionnaires and face-to-face interviews with the mothers. In addition, weight (Wt) and height (Ht) of the children were measured. The nutritional status was determined using various classifications based on weight for age (Wt/A), height for age (Ht/A), and weight for height (Wt/Ht) and the effects of various factors on nutritional status was assessed. Based on the Z-score, cut-off point under -2SD from median of the reference population (NCHS), 16.1% of the children were underweight (Wt/A), 15.6% stunted (Ht/A), and 7.2% wasted (Wt/Ht). According to percentile classification, 20% of the children were underweight (Wt/A), 19.2% stunted (Ht/A), and 8.8% wasted (Wt/Ht). A statistically significant relationship was found between Wt/A and birthweight of the child, health and maternal nutritional practices. A statistically significant relationship was also found between Ht/A and family size, birth weight child, food budget and maternal nutritional practices. Similarly, a statistically significant relationship was found between Wt/Ht and food budget. The results showed a correlation between Ht/A and family size, birth height of the child. A correlation was also found between Wt/A and number of rooms per person. Keywords: Nutritional status, 25-36 month old children, Rural areas, Kerma

    Topology optimization of plates

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    In this report we propose a stabilization method for topology optimization of planes. The method can be classified in the category of continuation methods. The new continuation method is based on using continuous of design variables (DV) defined on a set meshes different from the one used for the finite element solution. The optimization procedure stars with using a coarse DV-mesh compared to finite element one. Once the convergence is obtained in the optimizations steps, a finer DV-mesh is nominated for further steps. With such a continuation method one can control the bounds of the gradients of the DV while simultaneously smooth the values in a more logical fashion, compared to what conventional filters perform. The DV-mesh refinement can be continued until the final mesh becomes similar to the finite element mesh. Depending on the formulation and elements used for the plate problems, e.g. with Kirchhoff or Mindlin-Reissner hypothesis, the refinement may further be continued so that the DV elements become smaller than the plate elements. Application of the method is shown over a wide range of plate problems. Linear and nonlinear plate behaviors formulated by Kirchhoff or Mindlin Reissner hypothesis, while using several forms of DV, are considered to show the performance of the proposed method. As one of the main DV, density is used in a power-law approach (or in an artificial material approach). This is performed in two forms, on in obtaining the topology of Thickness is also used as a realistic design variable in order to show the performance of the method in a rather well-posed optimization problem. We have also included results from a homogenization approach. Comparison in made with conventional element/nodal based approaches using filter. The results show excellent and robust performance of the proposed method. Due to the wide range of cases studied, some inserting side conclusions are also given in this report. &nbsp

    Improving the Performance of ICA Algorithm for fMRI Simulated Data Analysis Using Temporal and Spatial Filters in the Preprocessing Phase

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    Introduction: The accuracy of analyzing Functional MRI (fMRI) data is usually decreases in the presence of noise and artifact sources. A common solution in for analyzing fMRI data having high noise is to use suitable preprocessing methods with the aim of data denoising. Some effects of preprocessing methods on the parametric methods such as general linear model (GLM) have previously been evaluated. In this study, besides the comparison of simple and noisy Independent Component Analysis (ICA) algorithms, the quantity effects of some spatial and temporal filtering have been evaluated on the functionality of ICA algorithms. Noisy ICA algorithms perform with a higher accuracy (up to 16%) in comparison to simple ICA for noisy fMRI data, although it is more time consuming than simple ICA. The accuracy of the results is improved by 8-10% using spatial and temporal filtering prior to simple ICA. Materials and Methods: Simple ICA and noisy ICA methods have been compared for analyzing simulated fMRI data sets. The impact of some temporal and spatial filters on the functionality of simple ICA algorithms has been evaluated. Implemented filters have been proposed in low and high pass group. Results: The sensitivity, specificity and temporal accuracy of simple ICA algorithms has been improved by using high pass filters. Although low pass filtering has some positive effects on the performance of simple ICA algorithms in the low SNR levels, in the high signal-noise Ratio (SNR) levels these low pass filters may cause a decrease in the sensitivity, specificity and temporal accuracy of simple ICA methods. Discussion and Conclusion: The results obtained from simple and noisy ICA algorithms for analyzing fMRI data having high SNR levels are approximately similar. Infomax algorithm uses Gradient based methods for estimating unmixing matrix has better sensitivity, specificity and temporal accuracy than Fast ICA for analyzing noisy ICA data. An alternative to the complicated and time consuming noisy ICA algorithms is to preprocess and denoise fMRI data prior to analyzing it by simple ICA algorithms

    On application of the finite point method to heat and elasticity problems

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    A stabilized version of the Finite Point Method (FPM) is presented. A source of instability due to the evaluation of the base function using a least square procedure is discussed. A suitable mapping is proposed and employed to eliminate the ill-conditioning effect due to directional arrangement of the points. A step by step algorithm is given for finding the local rotated axes and the dimensions of the cloud using local average spacing and inertia moments of the points distribution. It is shown that the conventional version of FPM may lead to wrong results when the proposed mapping algorithm is not used.It is shown that another source for instability and non-monotonic convergence rate in collocation methods lies in the treatment of Neumann boundary conditions. Unlike the conventional FPM, in this work the Neumann boundary conditions and the equilibrium equations appear simultaneously in a weight equation similar to that of weighted residual methods. The stabilization procedure may be considered as an interpretation of the Finite Calculus (FIC) method. The main difference between the two stabilization procedures lies in choosing the characteristic length in FIC and the weight of the boundary residual in the proposed method. The new approach also provides a unique definition for the sign of the stabilization terms. The reason for using stabilization terms only at the boundaries is discussed and the two methods are compared. Several numerical examples are presented to demonstrate the performance and convergence of the proposed methods
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