High-precision Simulation Research Articles

COMPUTER SIMULATION OF ELECTROMAGNETIC FIELD WITH APPLICATION THE FREQUENCY ADAPTATION METHOD

Context. A modern stage of powerful radio-electronic and electrotechnical systems development, with a power more than 1 MW, imposes increased requirements to their energy equipment, uninterrupted operation and power supply reliability in various operational modes. Field simulation of such systems class is based on modern numerical realization methods of boundary value problems for Helmholtz and Maxwell equations, both in single-connected and multi-connected domains. It imposes increased requirements to resources, computer hardware speed and software computing efficiency, defining the relevance of a new mathematical apparatus development or its elaboration, including combinations of analytical and approximate numerical methods.Objective. The purpose of work is the elaboration a new numerical realization methods of field models taking into account ACelectrophysical processes with high frequency on the basis of Helmholtz equations in frequency formulations, adapted to software packagesuse with a free license.Method. A new method of frequency adaptation is elaborated, which provides systems of Helmholtz equations reduction in vectormagnetic potential formulations to the recurrent modified Maxwell’s equations, in analogies of DC formulation, and also provides highprecision and field simulation efficiency.Results. The generalized spatial mathematical model of interrelated electromagnetic and electrothermal processes AC energy conversionin current-conducting wires of powerful radio-electronic and electrotechnical systems is offered. This model considers operational modes, nonlinear dependences of electrophysical properties in electrotechnical materials, replacement effects and outer superficial effects, self- and mutual induction. A new method of frequency adaptation is elaborated, based on Helmholtz system of equations reduction in the vector magnetic potential formulations, in frequency domain, to the recurrent modified Maxwell’s equations, in analogies of DC formulation, and also provides high precision and field simulation efficiency. At numerical realization of frequency adaptation methods and finite elements, the number of freedom degrees decreases twice. It is caused by step-by-step solution the recurrent modified Maxwell’s equations, in analogies of DC formulations, for real and imaginary components of electric and vector magnetic potentials.Conclusions. The elaborated new frequency adaptation method significantly expands possibilities of production design preparation forpowerful radio engineering systems. It allows using the software packages with a free license, reduces requirements to computing resources, reduces time costs and provides high precision in electromagnetic fields simulation.

Stand basal area modelling for Chinese fir plantations using an artificial neural network model

Artificial neural network models are a popular estimation tool for fitting nonlinear relationships because they require no assumptions about the form of the fitting function, non-Gaussian distributions, multicollinearity, outliers and noise in the data. The problems of back-propagation models using artificial neural networks include determination of the structure of the network and over-learning courses. According to data from 1981 to 2008 from 15 permanent sample plots on Dagangshan Mountain in Jiangxi Province, a back-propagation artificial neural network model (BPANN) and a support vector machine model (SVM) for basal area of Chinese fir (Cunninghamia lanceolata) plantations were constructed using four kinds of prediction factors, including stand age, site index, surviving stem numbers and quadratic mean diameters. Artificial intelligence methods, especially SVM, could be effective in describing stand basal area growth of Chinese fir under different growth conditions with higher simulation precision than traditional regression models. SVM and the Chapman–Richards nonlinear mixed-effects model had less systematic bias than the BPANN.

High-precision simulation of the height distribution for the KPZ equation

The one-point distribution of the height for the continuum Kardar-Parisi-Zhang (KPZ) equation is determined numerically using the mapping to the directed polymer in a random potential at high temperature. Using an importance sampling approach, the distribution is obtained over a large range of values, down to a probability density as small as in the tails. Both short and long times are investigated and compared with recent analytical predictions for the large-deviation forms of the probability of rare fluctuations. At short times the agreement with the analytical expression is spectacular. We observe that the far left and right tails, with exponents 5/2 and 3/2, respectively, are preserved also in the region of long times. We present some evidence for the predicted non-trivial crossover in the left tail from the tail exponent to the cubic tail of the Tracy-Widom distribution, although the details of the full scaling form remain beyond reach.

Kernel Solver Design of FPGA-Based Real-Time Simulator for Active Distribution Networks

The field-programmable gate array (FPGA)-based real-time simulator takes advantage of many merits of FPGA, such as small time-step, high simulation precision, rich I/O interface resources, and low cost. The sparse linear equations formed by the node conductance matrix need to be solved repeatedly within each time-step, which introduces great challenges to the performance of the real-time simulator. In this paper, a fine-grained solver of the FPGA-based real-time simulator for active distribution networks is designed to meet the computational demand. The framework of the solver, offline process design on PC and online process design on FPGA are proposed in detail. The modified IEEE 33-node system with photovoltaics is simulated on a 4-FPGA-based real-time simulator. Simulation results are compared with PSCAD/EMTDC under the same conditions to validate the solver design.

A Novel Piecewise Affine Model for Vehicle Lateral Dynamics

The lateral tire force is of crucial importance for the vehicle lateral dynamics modeling. Linear and nonlinear models have been proposed to describe the characteristic of the force. Due to its simplicity, the linear model is widely used in a vehicle controller and an observer design at present. However, this model has a limited application area since it is accurate only when tires operate in the linear region and fails to reflect the nonlinear behavior of the tire force. Contrary to the linear model, nonlinear models can represent the behavior entirely with complex nonlinear functions, which are difficult to be used for the controller or the observer design. Aiming at these problems, a piecewise affine (PWA) model for the lateral tire force is proposed in this paper. According to the relationship between the tire lateral force and the tire slip angle, the lateral tire force is approximated by a five-segment PWA model with different slopes. Model parameters are calculated by the tire analysis tool of the high-precision real-time simulation software of vehicle dynamics called veDYNA. Combining the PWA model with the lateral dynamic model, a novel two-degree-of-freedom model is obtained to describe the vehicle lateral dynamics. Based on veDYNA, simulation results with different maneuvers show that the proposed model is valid and has a higher precision.

Acceleration of Gas Reservoir Simulation Using Proper Orthogonal Decomposition

High-precision and high-speed reservoir simulation is important in engineering. Proper orthogonal decomposition (POD) is introduced to accelerate the reservoir simulation of gas flow in single-continuum porous media via establishing a reduced-order model by POD combined with Galerkin projection. Determination of the optimal mode number in the reduced-order model is discussed to ensure high-precision reconstruction with large acceleration. The typical POD model can achieve high precision for both ideal gas and real gas using only 10 POD modes. However, acceleration of computation can only be achieved for ideal gas. The obstacle of POD acceleration for real gas is that the computational time is mainly occupied by the equation of state (EOS). An approximation method is proposed to largely promote the computational speed of the POD model for real gas flow without decreasing the precision. The improved POD model shows much higher acceleration of computation with high precision for different reservoirs and different pressures. It is confirmed that the acceleration of the real gas reservoir simulation should use the approximation method instead of the computation of EOS.

Fast and high-precision simulation of hydrodynamic and water quality process in river networks

To realize a fast and high-precision simulation of unsteady flows and water quality process in river networks, a 1-D mathematical modelling system for free-surface flows and water quality process is developed. In the hydrodynamic model, aθsemi-implicit method is used to discretize the free-surface gradient term in the momentum equation while the Eulerian-Lagrangian method is employed to solve the advection term. To achieve good mass conservation, the finite-volume method is used to discretize continuity equation. Moreover, the resulting hydrodynamic model is unconditionally stable with respect to the gravity wave speed and flow advection. In solving the scalar transport equation, the forward difference is used for discretization in time while the centre-difference is in space. A sub-cycling is introduced to divide the computational time step and improve the stability of water quality model. Therefore, large time steps are allowed in both the hydrodynamic and the transport models. The coupling of the branches of the river networks is solved using a predictioncorrection method. Then, a Gaussian pulse test and a rectangular wave test are employed to demonstrate the accuracy and the efficiency of the system, which will also provide powerful supports for ecological operations of cascade reservoirs in drainage basins.

Development of software for analysis and optimization of operating modes of underground gas stores

The object of research is underground gas storage facilities (UGS) and their technological facilities that are involved in the processes of gas injection, storage and extraction. One of the most important identified problems is the provision of reliable and economical operation of UGS in the gas transportation system (GTS) of Ukraine. One of the ways to solve the problem is development of effective software as decision-making tools, which, in the course of the studies, are not available in the dispatching services for managing the GTS.The analysis of existing programs on the market of software products shows their inconsistency with the necessary requirements for functionality, set and speed of solving problems. Basically, the developed software is oriented to the exploitation of coal-mining enterprises and could not be adapted for the operation of UGS facilities, where processes, especially filtration in reservoirs, are much faster.The development of a new multifunctional software product is aimed at providing modeling processes for gas dynamic and filtration processes in UGS facilities, identifying their technical and technological status and planning operational parameters of UGS facilities.The developed software product provides clarification of geophysical parameters of the reservoirs of the most UGS GTS reservoirs. The obtained estimates of the magnitude of the effect from the UGS reconstruction in cases of physico-chemical cuts of wells, the replacement of compressor stations of gas compressor units with imported ones with the best efficiency, in the transition from flow line-collector system of gas collection to fully flow lines. The developed software is also used for high-precision simulation of operating modes in extreme conditions of UGS operation.The systemic effect of the operation of the developed software is achieved by conducting studies to form pre-project solutions. As well as numerical experiments to study and evaluate the optimization potential, and to optimize the planning of promising solutions and operational operation.

Modeling population density based on nighttime light images and land use data in China

Population change is a key variable that influences climate change, ecological construction, soil and water use, and economic growth. Census data are always point data, whereas planar data are often required in scientific research. By using nighttime light (NTL) images and land use data, combined with the fifth and sixth census data of China at the county level, we carried out spatial matching on the population of each county, respectively, and established population density diagrams of China for 2000 and 2010, which had a spatial resolution of 1 × 1 km. The method proposed in this paper is relatively simple and has a high simulation precision. The results showed that during the first ten years of the 21st century, there are some remarkable characteristics in Chinese population spatial pattern change: 1) the “disappearance” of intermediate-density regions; namely, areas with a population density between 500 and 1500 persons/km2 have decreased by 41% during the ten years; 2) continuous growth of high-density regions; namely, areas with a population density of more than 1500 persons/km2 have increased by 76%; 3) an expansion tendency of low-density regions similar to high-density regions.

Impact of mechanism vibration characteristics by joint clearance and optimization design of its multi-objective robustness

Joint clearances and friction characteristics significantly influence the mechanism vibration characteristics; for example: as for joint clearances, the shaft and bearing of its clearance joint collide to bring about the dynamic normal contact force and tangential coulomb friction force while the mechanism works; thus, the whole system may vibrate; moreover, the mechanism is under contact-impact with impact force constraint from free movement under action of the above dynamic forces; in addition, the mechanism topology structure also changes. The constraint relationship between joints may be established by a repeated complex nonlinear dynamic process (idle stroke - contact-impact - elastic compression - rebound – impact relief - idle stroke movement - contact-impact). Analysis of vibration characteristics of joint parts is still a challenging open task by far. The dynamic equations for any mechanism with clearance is often a set of strong coupling, high-dimensional and complex time-varying nonlinear differential equations which are solved very difficultly. Moreover, complicated chaotic motions very sensitive to initial values in impact and vibration due to clearance let high-precision simulation and prediction of their dynamic behaviors be more difficult; on the other hand, their subsequent wearing necessarily leads to some certain fluctuation of structure clearance parameters, which acts as one primary factor for vibration of the mechanical system. A dynamic model was established to the device for opening the deepwater robot cabin door with joint clearance by utilizing the finite element method and analysis was carried out to its vibration characteristics in this study. Moreover, its response model was carried out by utilizing the DOE method and then the robust optimization design was performed to sizes of the joint clearance and the friction coefficient change range so that the optimization design results may be regarded as reference data for selecting bearings and controlling manufacturing process parameters for the opening mechanism. Several optimization objectives such as x/y/z accelerations for various measuring points and dynamic reaction forces of mounting brackets, and a few constraints including manufacturing process were taken into account in the optimization models, which were solved by utilizing the multi-objective genetic algorithm (NSGA-II). The vibration characteristics of the optimized opening mechanism are superior to those of the original design. In addition, the numerical forecast results are in good agreement with the test results of the prototype.

Simulation of Fluidity and Misrun Prediction for the Casting of 356.0 Aluminum Alloy into Sand Molds

The basic parameters for the high-precision simulation of misrun formation in castings are the interface heat transfer coefficient (IHTC) between the casting and the mold and the critical solid fraction (f S cr ) at which the alloy flow in the mold is choked off. The values for IHTC were obtained by comparing the simulated spiral lengths at different IHTC values with those obtained from experimental results. The IHTC values above the liquidus temperature (IHTCL = 1200 W m−2 K−1) and below the solidus temperature (IHTCS = 600 W m−2 K−1), as well as the critical solid fraction (f S cr = 0.1–0.15), were determined. The obtained values of IHTCL, IHTCS, and f S cr were used to simulate the casting process of 356.0 aluminum alloy into sand molds. Comparison of the misruns obtained in the cylindrical casting with misruns predicted by the simulation confirmed the accuracy of the IHTCL and IHTCS values obtained using the spiral test and allowed the value of the critical solid fraction (f S cr = 0.1) to be defined more accurately.

Modeling and Simulation of Complex Fluid Networks in the Flue Gas System of a Boiler

Under the conditions of high demand for energy saving and environmental protection, the thermal power unit is required to phase out the traditional extensive operation mode—a method of oxygen-enriched combustion in a furnace, considering safety first. Achieving efficient and economic operation with an optimal proportion of air distribution in these thermal power units is crucial. The high-precision simulation equipment could provide an experimental basis for optimal operation of field units. This paper starts by improving the accuracy of simulation equipment. In this work, the method of dividing nodes and branches in the boiler was based on signal flow graph theory. According to the flow characteristics of the working substance, the method for calculating the node and branch pressure drop was analyzed and set up. Subsequently, a fluid network model of the multi-dimensional flue gas system was constructed. With the help of our self-developed simulation model and data-driven platform, a modular simulation algorithm was designed. The simulation analysis of the boiler showed the accuracy of the model.

A novel quasi-3D thermodynamic model of oil film bearing with non-Newtonian and temperature-viscosity effects

PurposeThe purpose of this paper is to propose a quasi-three-dimensional (3D) thermohydrodynamic (THD) model for oil film bearings with non-Newtonian and temperature-viscosity effects. Its performance factors, including precision and time consumption, are investigated.Design/methodology/approachTwo-dimensional (2D), 3D and quasi-3D numerical models are built. The thermal and mechanical behaviors of two types of oil film bearings are simulated. All the results are compared with solutions of commercial ANSYS CFX.FindingsThe 2D THD model fails to predict the temperature and pressure field. The results of the quasi-3D THD model coincide well with those of the 3D THD model and CFX at any condition. Compared with the 3D THD model, the quasi-3D THD model can greatly reduce the CPU time consumption, especially at a high rotational speed.Originality/valueThis quasi-3D THD model is proposed in this paper for the first time. Transient mechanical and thermal analyses of high-speed rotor-bearing system are widely conducted using the traditional 3D THD model; however, the process is very time-consuming. The quasi-3D THD model can be an excellent alternative with high precision and fast simulation speed.

Generalized High-Precision Simulation for TT&C Channels Using B-Spline Signal Processing

Generalized High-Precision Simulation for TT&C Channels Using B-Spline Signal Processing

Helical vortices: Quasiequilibrium states and their time evolution

Helical vortices are found, e.g., in wind turbine wakes. An accurate description of viscous helical solutions is needed for instability studies and control. New generic quasisteady states are elaborated in the helical framework and characterized based on high-precision direct numerical simulation results.

A three-dimensional time-dependent Schrödinger equation solver: an application to hydrogen atoms in an elliptical laser field

We extended the two-dimensional generalized pseudo-spectral time-propagator to a three-dimensional time-propagator. With this time-propagator, we theoretically investigated the above-threshold ionization of hydrogen atoms in an elliptical field by solving the time-dependent Schrödinger equation. We found that the total ionization probabilities are suppressed about one order, while the excitation probabilities drop about eight orders from a linearly polarized laser to a circularly polarized one with a given laser intensity. The width of the lateral (perpendicular to the laser polarization plane) momentum distribution increases as the ellipticity increases, which is against our intuition that the large peak laser field results in a broad distribution in the lateral direction. Further analysis shows that the narrow lateral momentum distribution for linearly polarized laser fields originates from Coulomb focusing, which is as less or not important for the circularly polarized field. Such a high precision simulation can be used to calibrate the infrared laser intensity to a high precision.

Shielding calculations of PWR using JSNT code

Reactor shielding calculations is the foundation for assessing nuclear plant safety performance. It is also an important method to provide guidelines for constructions and operations of nuclear plant. JSNT is a massively parallel discrete ordinates transport code developed by CAEP software center for high performance numerical simulation, with high simulation precision and efficiency. In this paper, a commercial PWR has been modeled and simulated using JSNT code. Flux distributions are obtained and compared with experimental measuring results. Comparisons show that results obtained by both S8 and S16 calculations could satisfy engineering demand. Moreover, in comparison to S8 calculation, S16 could improve the calculation precision significantly and decrease relative errors of some detectors under 1%.

A formula for crossing probabilities of critical systems inside polygons

In this article, we use our results from Flores and Kleban (2015 Commun. Math. Phys. 333 389–434, 2015 Commun. Math. Phys. 333 435–81, 2015 Commun. Math. Phys. 333 597–667, 2015 Commun. Math. Phys. 333 669–715) to generalize known formulas for crossing probabilities. Prior crossing results date back to Cardy’s prediction of a formula for the probability that a percolation cluster in two dimensions connects the left and right sides of a rectangle at the percolation critical point in the continuum limit (Cardy 1992 J. Phys. A: Math. Gen. 25 L201–6). Here, we predict a new formula for crossing probabilities of a continuum limit loop-gas model on a planar lattice inside a 2N-sided polygon. In this model, boundary loops exit and then re-enter the polygon through its vertices, with exactly one loop passing once through each vertex, and these loops join the vertices pairwise in some specified connectivity through the polygon’s exterior. The boundary loops also connect the vertices through the interior, which we regard as a crossing event. For particular values of the loop fugacity, this formula specializes to FK cluster (resp. spin cluster) crossing probabilities of a critical Q-state random cluster (resp. Potts) model on a lattice inside the polygon in the continuum limit. This includes critical percolation as the Q = 1 random cluster model. These latter crossing probabilities are conditioned on a particular side-alternating free/fixed (resp. fluctuating/fixed) boundary condition on the polygon’s perimeter, related to how the boundary loops join the polygon’s vertices pairwise through the polygon’s exterior in the associated loop-gas model. For , we compare our predictions of these random cluster (resp. Potts) model crossing probabilities in a rectangle (N = 2) and in a hexagon (N = 3) with high-precision computer simulation measurements. We find that the measurements agree with our predictions very well for and reasonably well if Q = 4.

Identifying the structure of 4-chlorophenyl isocyanide adsorbed on Au(111) and Pt(111) surfaces by first-principles simulations of Raman spectra.

Surface Raman spectroscopy has become one of the most powerful analytical tools for interfacial structures. However, theoretical modeling for the Raman spectra of molecular adsorbate on metallic surfaces is a long-standing challenge because accurate descriptions of the electronic structure for both the metallic substrates and adsorbates are required. Here we present a quasi-analytical method for high-precision surface Raman spectra at the first principle level. Using this method, we correlate both geometrical and electronic structures of a single 4-chlorophenyl isocyanide (CPI) molecule adsorbed on a Au(111) or Pt(111) surface with its Raman spectra. The "finger-print" frequency shift of the CN stretching mode reveals the in situ configuration of CPI is vertical adsorption on the top site of the Au(111) surface, but a bent configuration when it adsorbs on the hollow site of the Pt(111) surface. Electronic structure calculations reveal that a π-back donation mechanism often causes a red shift to the Raman response of CN stretching mode. In contrast, σ donation as well as a wall effect introduces a blue shift to the CN stretching mode. A clear relationship for the dependence of Raman spectra on the surface electronic and geometrical information is built up, which largely benefits the understanding of chemical and physical changes during the adsorption. Our results highlight that high-precision theoretical simulations are essential for identifying in situ geometrical and electronic surface structures.

Radiative corrections ine+e−collisions with the BabaYaga event generator

The Monte Carlo event generator BabaYaga has been developed in the last decade for high precision simulation of QED processes (e + e − → e + e − , e + e − → μ + μ − and e + e − → γγ ) at flavour factories, mainly for luminometry purposes, with an estimated theoretical accuracy at the 0.1% level or better. The relevant QED radiative corrections are included by means of a QED Parton Shower matched with exact next-to-leading order corrections to reach the required accuracy. The main theoretical framework is overviewed and the status of the generator is summarized.