A gas-kinetic BGK solver for two-dimensional turbulent compressible flow

In this paper, a gas kinetic solver is developed for the Reynolds Average Navier-Stokes (RANS) equations in two-space dimensions. To our best knowledge, this is the first attempt to extend the application of the BGK (Bhatnagaar-Gross-Krook) scheme to solve RANS equations with a turbulence model using finite difference method. The convection flux terms which appear on the left hand side of the RANS equations are discretized by a semi-discrete finite difference method. Then, the resulting inviscid flux functions are approximated by gas-kinetic BGK scheme which is based on the BGK model of the approximate collisional Boltzmann equation. The cell interface values required by the inviscid flux functions are reconstructed to higher-order spatial accuracy via the MUSCL (Monotone Upstream-Centered Schemes for Conservation Laws) variable interpolation method coupled with a minmod limiter. As for the diffusion flux terms, they are discretized by a second-order central difference scheme. To account for the turbulence effect, a combined k-ε / k-ω SST (Shear-Stress Transport) two-equation turbulence model is used in the solver. An explicit-type time integration method known as the modified fourth-order Runge-Kutta method is used to compute steady-state solutions. The computed results for a supersonic flow past a flat plate where the transition is artificially triggered at 50% of plate length are presented in this paper. Validating the computed results against existing analytical solutions and also comparing them with results from other well-known numerical schemes show that a very good agreement is obtained

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Implementation of coverage problem in wireless sensor network based on unit Disk model

Wireless sensor networks (WSNs) have a wide range of applicability in many industrial and civilian applications such as industrial process monitoring and control, environment and habitat monitoring, machine health monitoring, home automation, health care applications, nuclear reactor control, fire detection, object tracking and traffic control. A WSN consists of spatially distributed autonomous sensors those cooperatively monitor the physical or environmental conditions including temperature, sound, vibration, motion, pressure or pollutants. In sensor networks where the environment is needed to be remotely monitored, the data from the individual sensor nodes is sent to a central base station (often located far from the network), through which the end-user can access data. The number of sensor nodes in a Wireless Sensor Network can vary in the range of hundreds to thousands. Such a network may have many challenges like low energy consumption, functional independence, efficient distributed algorithms, transmission routes, coverage, synchronization, topology control, robustness and fault tolerance, cost of maintaining the sensors and lifetime of the network

DFF-ResNet : An Insect Pest Recognition Model Based on Residual Networks

Insect pest control is considered as a significant factor in the yield of commercial crops. Thus, to avoid economic losses, we need a valid method for insect pest recognition. In this paper, we proposed a feature fusion residual block to perform the insect pest recognition task. Based on the original residual block, we fused the feature from a previous layer between two 1×1 convolution layers in a residual signal branch to improve the capacity of the block. Furthermore, we explored the contribution of each residual group to the model performance. We found that adding the residual blocks of earlier residual groups promotes the model performance significantly, which improves the capacity of generalization of the model. By stacking the feature fusion residual block, we constructed the Deep Feature Fusion Residual Network (DFF-ResNet). To prove the validity and adaptivity of our approach, we constructed it with two common residual networks (Pre-ResNet and Wide Residual Network (WRN)) and validated these models on the Canadian Institute For Advanced Research (CIFAR) and Street View House Number (SVHN) benchmark datasets. The experimental results indicate that our models have a lower test error than those of baseline models. Then, we applied our models to recognize insect pests and obtained validity on the IP102 benchmark dataset. The experimental results show that our models outperform the original ResNet and other state-of-the-art methods

Higher order global differentiability local approximations for 2-D and 3-D distorted element geometries

The primary focus of this thesis is to present a framework to develop higher order global differentiability local approximations for 2-D and 3-D distorted element geometries. The necessity and superiority of higher order global differentiability approximations in designing finite element computational processes has been demonstrated by Surana and co-workers [1-4]. It has been shown by Surana et al. [5] that when the element geometry is rectangular, higher order global differentiability approximations can be easily derived using tensor product of 1-D higher order continuity approximations. When the element geometries are distorted, the tensor product approach cannot be utilized in deriving these approximation functions. This thesis presents a systematic procedure for deriving desired order global differentiability approximations for 2-D and 3-D elements of distorted geometries. The curved element in 2-D or 3-D physical coordinate space is mapped to a master element in 2-D or 3-D natural coordinate space. The master elements considered for 2-D quadrilateral, 2-D triangular and 3-D hexahedral elements are a 2 unit square, a 2 unit equilateral triangle and a 2 unit cube respectively. For the master element, 2-D C00 or 3-D C000 p-version local approximations are considered and appropriate degrees of freedom and the corresponding approximation functions from appropriate nodes are borrowed to derive the higher order approximations and the corresponding derivative degrees of freedom at the corner nodes. These degrees of freedom can be transformed from natural coordinate space to the physical coordinate space by using Jacobians of transformations for the derivatives of various orders. The choice of these degrees of freedom and the corresponding functions being borrowed in deriving these desired functions for the derivative dofs is not arbitrary and must be made in such a way that all lower degree admissible functions and the corresponding dofs are borrowed before considering the higher degree functions and the corresponding dofs. Pascal's rectangle, Pascal's triangle and Pascal's pyramid provide a systematic selection process for accomplishing this selection process for 2-D quadrilateral, 2-D triangular and 3-D hexahedral geometries respectively. Numerical studies are presented to illustrate the behavior and performance of the approximations developed. The applicability of the developed approximation functions to all physical problems is demonstrated by solving model problems which are described by self-adjoint, non self-adjoint and non-linear differential operators. In all cases, various finite element quantities of interest (error or residual functional, error norms) are computed and a study of their convergence rates with h, p and k refinement is made

Bone fracture detection through X-ray using Edge detection Algorithms

Human beings are highly prone to bone fractures, to a great extent as an outcome of accidents or other factors such as bone cancer. Manual fracture detection takes a lengthy time and comes with a considerable chance of error. As a result, establishing a computer-based method to reduce fracture bone diagnosis time and risk of error is critical. The most common method for segmenting images based on sharp changes in intensity is edge detection. Sobel, Robert, Canny, Prewitt, and LoG (Laplacian of Gaussian) are some of the edge detection approaches that are examined for the study of bone fracture detection. The focal point of this paper is an endeavor to study, analyze and compare the Sobel, Canny, and Prewitt Techniques for detecting edges and identifying the fracture

A survey on privacy issues in digital forensics

Privacy issues have always been a major concern in computer forensics and security and in case of any investigation whether it is pertaining to computer or not always privacy issues appear. To enable privacy’s protection in the physical world we need the law that should be legislated, but in a digital world by rapidly growing of technology and using the digital devices more and more that generate a huge amount of private data it is impossible to provide fully protected space in cyber world during the transfer, store and collect data. Since its introduction to the field, forensics investigators, and developers have faced challenges in finding the balance between retrieving key evidences and infringing user privacy. This paper looks into developmental trends in computer forensics and security in various aspects in achieving such a balance. In addition, the paper analyses each scenario to determine the trend of solutions in these aspects and evaluate their effectiveness in resolving the aforementioned issues

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List of predatory journals and publishers

The predatory publications are a big challenge, especially in developing countries including Nepal. Predatory publishing not only harms or degrades academic reputations but also wastes time, money, resources, and efforts (Shrestha et al., 2020). Predatory publications pose a danger that could undermine the quality, integrity, and reliability of published scientific research works. Predatory publications also harm the reputation of the universities and research organizations which are connected with these publications. Universities and research organizations should educate researchers, especially juniors, about the existence of predatory journals, the dangers they pose, and ways to avoid them (Shrestha, 2020). The problem of potential open access predatory or fake publications is an important issue that must be actively discussed at national, regional and world level within academic communities (Shrestha et al., 2018b). Predatory publications must be avoided or excluded while evaluating CV or biodata of researchers for job promotion and releasing the research grants. The authors should be careful about predatory or fake journals/publishers for communicating their scientific works (Shrestha et al., 2018a). The researchers should be aware of the quality of journals while publishing their research results (Shrestha et al., 2020). There is an international initiative called “Think. Check. Submit.” (http://thinkchecksubmit.org) that helps the researchers to identify trusted journals for publication. It contains a simple checklist researchers can use to assess the credentials of a journal or publisher. Authors should look at the journal website some of the articles published in the journals to assess their quality; this quick review may be all that is needed to identify predatory journals (Forero et al., 2018).The below list of predatory journals and publishers is copied from https://predatoryjournals.com/ (Anonymous, 2020a) and https://beallslist.net/ (Anonymous, 2020b). The purpose of this article is to create awareness about the predatory publications

k - Version of Finite Element Method for Polymer flows using Giesekus Constitutive Model

One of the fundamental differences in the polymer flows compared to Newtonian or generalized Newtonian flow is the presence of elasticity due to polymer in addition to the viscosities of the solvent and the polymer. While for Newtonian and generalized Newtonian fluids viscous stresses are explicitly defined in terms of strain rates and transport properties, and thus can be completely eliminated from the governing differential equations (GDEs) by their substitution in the momentum and energy equations. This however is not possible in the case of polymer flows. The mathematical models for polymer flows are derived using conservation laws in which many different choices of stresses as dependent variables are possible. In the published works it is generally accepted that GDEs in elastic stresses are meritorious in Galerkin method with weak form over other choices. However, regardless of the choices of stresses the GDEs always remain non-linear and hence, the Galerkin method with weak form yields variationally inconsistent integral forms for all possible choices of the stresses. Thus, one of the investigation in this study is to show the influence of the choices of stresses in the mathematical models on the computational processes when the integral forms are variationally consistent (VC). Another significant issue in polymer flows is the issue of numerical solutions for higher Deborah numbers. For a given fluid and a given geometric configuration the choices of length ( Lo ) and relaxation time are generally fixed and hence high Deborah number flows are invariably associated with higher flow rates and thus higher velocities. In many standard model problems such as couette flow, lid driven cavity, expansion, contraction etc, severe deborah number (De) limitations are reported in the computational processes based on Galerkin method with weak form while there appears to be no such apparent limitation in the constitutive model such as Giesekus model. In this work we investigate if such Deborah number limitations exist in hpk framework or are such limitations a consequence of VIC integral form and C0 local approximations. The work presented here considers boundary value problems ( BVPs ) as well as initial value problems ( IVPs ) using Giesekus constitutive model. For BVPs, numerical studies are presented for (i) One dimensional fully developed flow between parallel plates (ii)developing flow between parallel plates and (iii) lid driven square cavity. In case of one dimensional fully developed flow solutions are reported for Deborah numbers up to 6514.52 and there does not seem to be any limit of deborah number in 'hpk' framework. Solutions are reported for developing flow between parallel plates upto deborah number of 20.13. Excellent agreement is obtained between for one dimensional fully developed flow between parallel plates and developing flow between parallel plates. For lid driven square cavity, mathematical idealization of the physics at the corners where stationary walls intersect the lid is presented. It is shown that in the hpk framework when hd goes to 0 and k goes to infinity, physics is approached where the lid meets the stationary vertical walls. Various numerical studies are presented upto deborah number of 2.4 for hd = 0.1 and 0.05. The converged solutions independent of h, p and k are reported. The convergence of the Newton's method with line search slows down for high deborah numbers primarily due to the fact that the stokes flow is not in the close neighborhood of the solution sought. This problem is overcome by using the solution at lower deborah number as the initial solution for high deborah number i.e. continuation in Deborah number. The numerical solutions of boundary value problem (BVP) and initial value problem (IVP) arising in Fiber spinning of polymers are presented using Least squares and space-time least squares finite element process in H(k,p) scalar product spaces. The parameter k, the order of the space defines the global differentiability of order (k-1) and is an independent parameter in all finite element computations in addition to characteristic length h and degree p of the approximations. This work discusses various mathematical models, assumptions employed in their derivations, integral forms and approximation spaces. The need and the importance of higher order spaces in space and time and the meritorious features of the variationally consistent (VC) integral forms are demonstrated. Numerical studies consist of four different benchmark problems used most frequently in the published work. Numerical studies are presented for different draw ratios and lengths of the physical domain. In all cases stationary states of the evolutions are compared with the solution of the corresponding BVP. Numerical studies show that for a given polymer there is a limiting value of draw ratio for a fixed length beyond which computations will fail due to excessive stresses in the polymeric liquid indicating possibility of the onset and progression of damage. The higher order global differentiability of the approximations in space and time and VC (or STVC) integral forms are essential for incorporating the desired physics in the computational process and for unconditional stability of the computational processes