International Journal of Modeling, Simulation, and Scientific Computing

In this paper, a class of multi-term time fractional advection diffusion equations (MTFADEs) is considered. By finite difference method in temporal direction and finite element method in spatial direction, two fully discrete schemes of MTFADEs with different definitions on multi-term time fractional derivative are obtained. The stability and convergence of these numerical schemes are discussed. Next, a V-cycle multigrid method is proposed to solve the resulting linear systems. The convergence of the multigrid method is investigated. Finally, some numerical examples are given for verification of our theoretical analysis.

Consideration is given to results of experimental and theoretical investigations how alpha-epsilon phase transition in the unalloyed iron and the 30 KhGSA steel and its absence in the austenitic 12Kh18N10T stainless steel influence processes under explosive deformation of spheres made of these materials. Polymorphous transition is shown to significantly effect on: amount of explosion-products energy transferred to a sphere, evolution of the converging-wave structure and its parameters, profiles of stress wave and temperature T(R, t) for some Lagrangian particles along the sphere radius, character of energy cumulation under spherical convergence of waves.

Short messages are an important part of social media network. Besides traditional communications, short messages can also be used for education, entertainment and even business. Nowadays, much work has been devoted to mining useful information and knowledge from short messages via classification and clustering approaches. However, in many situations, it is vital to identify some influential users whose messages will result in a large amount of forwarding, these users are called seed users. In this paper, studies on the forwarding behavior of mobile phone users are carried out first, then, a directed graph-based short message forwarding model is setup, together with a "Reverse PageRank" scoring policy. Finally, the forwarding model and scoring policy have been applied to a real short message record dataset from some telecom operator. By some exploratory data analysis of the dataset, parameters of the forwarding model are determined. Experimental results show that the model and the scoring policy are effective in finding out seed users.

Cavitating flows inside a diesel injection nozzle hole were simulated using a mixture model. A two-dimensional (2D) numerical model is proposed in this paper to simulate steady cavitating flows. The Reynolds-averaged Navier–Stokes equations are solved for the liquid and vapor mixture, which is considered as a single fluid with variable density and expressed as a function of the vapor volume fraction. The closure of this variable is provided by the transport equation with a source term Transport-equation based methods (TEM). The processes of evaporation and condensation are governed by changes in pressure within the flow. The source term is implanted in the CFD code ANSYS CFX. The influence of numerical and physical parameters is presented in detail. The numerical simulations are in good agreement with the experimental data for steady flow.

People gained limited progress on refinement of super-hard powder using the vibration mill for many years. According to various amplitude–frequency combination working conditions of vibration mill prototype, simulation research on dynamic characteristic of grinding medium flow field based on PFC is proposed in the paper, and a dynamics model of grinding medium flow field in barrel is established. Furthermore, trajectory image of medium flow, kinetic energy and strain energy and collision frequency can be obtained. The simulation analysis shows that collision between media as well as between media and the barrel can cause the changes of kinetic energy and strain energy of grinding medium flow under various amplitude–frequency combination conditions, and an energy-lacking region exists in the barrel. Contrast experiments under various working conditions show that kinetic energy and strain energy of grinding medium flow have large increment and energy-lacking regions become smaller, and then energy consumption decreases on working condition of high-amplitude and middle-frequency. The conclusion has practical value to refine powder by high-intensity vibration mill with certain frequency.

Aeroload simulator (ALS) is an important hardware-in-loop simulation equipment. In ALS system, surplus torque is the main cause of loading error. And the elimination of surplus torque has become research hotspot for a while, but study about cause of surplus torque has not made much progress. In this paper, a theory about the origin and mechanism modeling method of surplus torque is raised and the model is simulated based on permanent magnet synchronous motor (PMSM) system. Validity of newly launched model is proved by comparison with initial model and the source of error is analyzed afterwards. Moreover, to determine control strategy for eliminating loading error, influential factors of surplus torque are analyzed based on the mechanism model.

A novel technique for reconstructing fluid surface from video is introduced. Both fluid motion vectors as well as Lattice Boltzmann Method (LBM) are employed in the study. Region-based correlation method is used to initialize motion vectors field, after clustering fluid motion vector results can be obtained. Then the height geometry information of fluid surface can be calculated from fluid motion vector further. At last, the distribution of fluid particle is interpolated and the height field can be further refined. Reconstruction results are demonstrated with several challenge videos. The experimental results show that the method is convenient and efficient. The calculation results can reflect the characteristics of the fluid movement, and it is a valid method for reconstructing fluid surface.

In the present era, the competitive producers are forced to use maximally newer advanced technology and its effective fast implementation using various available tools for synthesis of new product requirement. Use of current state of art computer aided technology supports the creation of flexible assemblies and their built up though unified modular approach. The design of robotic mechanism is a complex process involving geometric, kinematic, singularity analyses during its synthesis phase. The present work is aimed at the effective utilization of CAx system Pro/Engineer tools for creation, ease in modification and analysis of spatial parallel manipulator. Three degrees of freedom of 3-PRS parallel manipulator is obtained using mobility analysis. Parallel manipulator with 3-DOF with 3-PRS configuration is investigated. The kinematics simulation of the robot is carried out using mechanism simulation and compared with closed form solutions. The concept of reachable, orientation and dexterous workspace is expressed. Tool tip coordinates obtained through simulation are plotted for workspace development. Inner and outer workspace boundaries are developed and analyzed for four different cases to understand the problem of interior singularity within workspace.

The regularization of ill-posed problems has become a useful tool in studying initial value problems that do not adhere to certain desired properties such as continuous dependence of solutions on initial data. Because direct computation of the solution becomes difficult in this situation, many authors have alternatively approximated the solution by the solution of a closely defined well posed problem. In this paper, we demonstrate this process of regularization for nonautonomous ill-posed problems including the backward heat equation with a time-dependent diffusion coefficient. In the process, we provide two different approximate well posed models and numerically compare convergence rates of their solutions to a known solution of the original ill-posed problem.

The main problem addressed in this paper is the quaternion-based trajectory control of a microcopter consisting of six rotors with three pairs of counter-rotating fixed-pitch blades, known as hexacopter. If the hypothesis of rigid body condition is assumed, the Newton–Euler equations describe the translational and rotational motion of the drone. The standard Euler-angle parametrization of three-dimensional rotations contains singular points in the coordinate space that can cause failure of both dynamical model and control. In order to avoid singularities, all the rotations of the microcopter are thus parametrized in terms of quaternions and an original proportional derivative (PD) regulator is proposed in order to control the dynamical model. Numerical simulations will be performed on symmetrical flight configuration, proving the reliability of the proposed PD control technique.

The pressing process, as compared to the machining process, makes good utilization of work piece material and shortens the production time, and as such it is increasingly used for production of complex shaped parts. A particular type of pressing is sheet-extrusion which controls the flow of material into special punch and die sets to produce an extruded shape. However, some particularly complex shaped parts cannot be made by sheet-extrusion due to the formation of piping defects. In this study, the finite element method (FEM) was used to investigate the formation of piping defects. In addition, the relationship between the characteristic dimensions of the extruded shape and the piping defect was also examined. Laboratory pressing experiments were performed to validate the accuracy of the FEM simulation results. Based on the stress distribution and velocity profiles within the extruded work piece, the relationship between the extruded shape and the piping defect was clearly identified. Furthermore, the FEM simulation results showed good agreement with the experimental results with regards to the dimensions of the extruded shape and the piping defect.

To pursue VNIIEF–VNIITF joint investigations, this paper briefly describes the experimental setup and provides numerical 3D-computation results (LEGAK-3D technique) on special features in the convergence dynamics of steel shells under their quasi-spherical explosive loading in the system with the 40-mm outer radius of the explosive layer.

The computation results were compared with the data experimentally registered for shells of the 30KhGSA steel, both as-received and quenched to HRC 35…40, and the austenitic 12Kh18N10T stainless steel. The comparison was also made with laser-interferometry results obtained directly under explosive loading, as well as with gamma-tomography and scanning electron microscopy investigations of the recovered shells.

Phase measurement unit (PMU) is the key equipment for electric power system, which has been used to monitor and control power grid. But it is too expensive to deploy on each bus. So, we need to investigate how to deploy PMU to satisfy our observation requirements with minimum PMU numbers. This problem is called the optimal PMU placement (OPP). In this paper, we employ differential evolution (DE) algorithm to solve the OPP problem. Our optimization target is to make the power grid completely observable with maximum redundancy and minimum number of PMU. The proposed method is tested on IEEE 14-bus system, IEEE 30-bus system and IEEE 57-bus system respectively with considering the zero injection.