Efficient Simulation Model Research Articles

Efficient two-phase mass-conserving level set method for simulation of incompressible turbulent free surface flows with large density ratio

An efficient three-dimensional two-phase flow model for simulation of free surface flows is developed. The method is based in the solution of Navier-Stokes equation for quasi-incompressible flows. The equations in generalized coordinates are solved by extension of the fully explicit MacCormack scheme, second order in time and fourth order in space. The free surface is implicitly captured by the zero Level Set of a smooth function and by the Ghost Fluid Method to capture accurately shape discontinuities for properties in the vicinity of the interface. Finally, the Volume of Fluid method is used to ensure mass conservation. Turbulence is described by large eddy simulation, where only the large-scale eddies are solved, while the small scales are modeled by using the selective structure function subgrid-scale model. Boundary shapes are represented through the immersed boundary method on the Cartesian grid. The numerical model is validated by some free surface problems. Numerical predictions by all cases are in good agreement with experimental data.

Stochastic Analysis of Profitability of the Pig Breeding Process

This study deals with the economy of agricultural production, specifically in animal farming. The main goal is to find and apply an efficient simulation model of pig breeding process in order to investigate the impact of various changes in the production settings on the economy of a particular pig breeding. For this reason, it is necessary to take values given in the study as model ones. Costs at particular parts of the breeding process were used as the main simulation inputs, together with number of parities, length of farrowing interval, number of weaned piglets depending on a parity number, lactation length, and the gestation length of sows. Additional inputs were price of produced piglets, price of insemination doses etc. Statistical distributions for the simulations of the inputs were obtained with theoretical curve fitting of sample data, which were provided from research projects focused on piglet production efficiency. The empirical distribution of sow profitability depending on the number of parities, which can help to decide about the culling of sows from the herd, was also determined in the research. A simulation was performed using the program @RISK. The obtained results and recommendations are discussed at the end of the paper.

A New Total Variation Diminishing Predictor Corrector Approach for Two-Dimensional Shallow Water Flow

This paper presents a new efficient and robust hydrodynamic model for simulation of unsteady shallow water flow. The governing equations of shallow water flows in two dimensional forms are solved using a new total variation diminishing (TVD) MacCormack predictor corrector scheme. In this numerical technique an additional TVD term is added after the traditional predictor corrector steps. The advantage of the present TVD term is that it is very simple and gives accurate results at the same time removing the numerical oscillations. Further, application of semi implicit treatment of the friction slope term helps in flow simulation even with very low water depth. Finally the model is used to analyze a wide variety of hydraulic problems including quiescent water above irregular bed, steady flow over irregular bed, steady flow over irregular bed with a shock, dam break flow over dry bed and dam break flow over wet bed. For each of the cases numerical results are compared with available analytical solution and known experimental data. The agreements between the results are satisfactory.

A simple and efficient quasi 3-dimensional viscoelastic model and software for simulation of tapping-mode atomic force microscopy.

This paper introduces a quasi-3-dimensional (Q3D) viscoelastic model and software tool for use in atomic force microscopy (AFM) simulations. The model is based on a 2-dimensional array of standard linear solid (SLS) model elements. The well-known 1-dimensional SLS model is a textbook example in viscoelastic theory but is relatively new in AFM simulation. It is the simplest model that offers a qualitatively correct description of the most fundamental viscoelastic behaviors, namely stress relaxation and creep. However, this simple model does not reflect the correct curvature in the repulsive portion of the force curve, so its application in the quantitative interpretation of AFM experiments is relatively limited. In the proposed Q3D model the use of an array of SLS elements leads to force curves that have the typical upward curvature in the repulsive region, while still offering a very low computational cost. Furthermore, the use of a multidimensional model allows for the study of AFM tips having non-ideal geometries, which can be extremely useful in practice. Examples of typical force curves are provided for single- and multifrequency tapping-mode imaging, for both of which the force curves exhibit the expected features. Finally, a software tool to simulate amplitude and phase spectroscopy curves is provided, which can be easily modified to implement other controls schemes in order to aid in the interpretation of AFM experiments.

Application of an efficient exponential wide band model for the natural gas combustion simulation in a 300 kW BERL burner furnace

Methane is one of the most important radiation participating medium. However, the weighted-sum-of-gray-gas (WSGG) model which is widely used in the recent commercial computational fluid dynamics (CFD) software cannot address the contribution of methane to the effective absorption coefficient (EAC) when simulating the natural gas combustion. In this work, an efficient exponential wide band (E-EWB) model which accounts for the effects of many species including H2O, CO2, CO and CH4 on EAC is proposed and numerical simulations are carried out for the natural gas combustion in a 300 kW BERL (Burner Engineering Research Laboratory) burner. The results including the distributions of axial velocity, gas temperature and the O2 mass fraction in the furnace obtained by the simulations with both the WSGG model and the E-EWB model are then analyzed and validated against the experimental data. The calculation efficiencies of the two simulations with the WSGG and E-EWB models are also compared. It is found that simulation with the E-EWB model generates much better results, although its calculation speed is about 1.8 times slower than that of the simulation with the WSGG model.

A Computationally-Efficient Numerical Model to Characterize the Noise Behavior of Metal-Framed Walls

Architects, designers, and engineers are making great efforts to design acoustically-efficient metal-framed walls, minimizing acoustic bridging. Therefore, efficient simulation models to predict the acoustic insulation complying with ISO 10140 are needed at a design stage. In order to achieve this, a numerical model consisting of two fluid-filled reverberation chambers, partitioned using a metal-framed wall, is to be simulated at one-third-octaves. This produces a large simulation model consisting of several millions of nodes and elements. Therefore, efficient meshing procedures are necessary to obtain better solution times and to effectively utilise computational resources. Such models should also demonstrate effective Fluid-Structure Interaction (FSI) along with acoustic-fluid coupling to simulate a realistic scenario. In this contribution, the development of a finite element frequency-dependent mesh model that can characterize the sound insulation of metal-framed walls is presented. Preliminary results on the application of the proposed model to study the geometric contribution of stud frames on the overall acoustic performance of metal-framed walls are also presented. It is considered that the presented numerical model can be used to effectively visualize the noise behaviour of advanced materials and multi-material structures.

Experimental and numerical investigation of processes that occur during high velocity hydroforming technologies: An example of tubular blank free bulging during hydrodynamic forming

Frequent use of hydroforming in automotive and aerospace industries requires intensive research of all aspects of this relatively new technology. In this paper we have studied the characteristics of aluminum tubular blank free bulging during hydrodynamic forming; both experimentally, and through numerical finite element analysis using LS-DYNA. We obtained the quantitative description of a pressure wave in working liquid, which directly relates to the load on the blank. The finite element analysis examined how a computationally efficient simulation model could be achieved, to replicate the experimental testing results. It was intended to correlate the simulation with experimental results; we were successful in demonstrating that the simulation can achieve an acceptable level of correlation with the experimental results.

A simplified and efficient hybrid finite element model (HYMOD) for non-linear 3D simulation of RC structures

Purpose– The purpose of this paper is to present a simplified hybrid modeling (HYMOD) approach which overcomes limitations regarding computational cost and permits the simulation and prediction of the nonlinear inelastic behavior of full-scale RC structures.Design/methodology/approach– The proposed HYMOD formulation was integrated in a research software ReConAn FEA and was numerically studied through the use of different numerical implementations. Then the method was used to model a full-scale two-storey RC building, in an attempt to demonstrate its numerical robustness and efficiency.Findings– The numerical results performed demonstrate the advantages of the proposed hybrid numerical simulation for the prediction of the nonlinear ultimate limit state response of RC structures.Originality/value– A new numerical modeling method based on finite element method is proposed for simulating accurately and with computational efficiency, the mechanical behavior of RC structures. Currently 3D detailed methods are used to model single structural members or small parts of RC structures. The proposed method overcomes the above constraints.

Integrating heterogeneous engineering knowledge and tools for efficient industrial simulation model support

Design of simulation models and their integration into industrial automation systems require knowledge from several heterogeneous data sources and tools. Due to the heterogeneity of engineering data, the integration of the tools and data are time-consuming and error-prone tasks nowadays. The key goal of this article is to provide an effective and efficient integration of heterogeneous data sources and tools as a knowledge basis to support dynamic simulation for industrial plants. The integrated knowledge is utilized both (i) in the design phase of simulation models for defining structure and interfaces of the models and (ii) in the runtime phase of industrial systems for model-driven configuration of the integrated environment. Reaching such goals with a manual approach or point-to-point integration is not beneficial as it may be possible for a few tools and data sources, but quickly gets very complex. A growing number of elements increases the risk of errors and the effort needed for integration. The proposed solution is based on a specification of a common data model to represent engineering knowledge and a service-oriented tool integration with the Engineering Service Bus. Engineering knowledge is integrated in a knowledge base implemented with ontologies in Web Ontology Language-Description Logic (OWL-DL). The proposed approach is demonstrated and evaluated on an educational hydraulic system. Major results of the article are: (i) a data model to represent engineering knowledge for dynamic industrial systems, (ii) the integration platform that, based on this model, integrates the tools for system design and runtime, and (iii) basic design-time and runtime processes for the integrated industrial simulations.

An efficient lane model for complex traffic simulation

AbstractTraffic simulation heavily relies on lane model. This paper presents a novel method to model lanes based on the road axis under the Frenet frame. The road axis is generated from the geographic information system data after curve approximation, discretization, and compression. This lane model couples mileage information with three‐dimensional geometric information, so it offers an easy and fast position transformation from mileage to the Cartesian coordinate. It also keeps strictly consistent for mileage among neighboring lanes so that it facilitates lane‐change processing. Compared with existing methods that depict lanes as simple polylines or curves, the proposed lane model is more functional and more efficient, especially for complex traffic simulation with a large number of lane‐changes. Copyright © 2015 John Wiley & Sons, Ltd.

Generic Mathematical Model for Efficient Milling Process Simulation

The current challenge in metal cutting models is to estimate cutting forces in order to achieve a more accurate and efficient machining process simulation and optimization system. This paper presents an efficient mathematical model for process simulation to evaluate the cutting action with variable part geometries of helical cutters and predict the cutting forces involved in the process. The objective of this paper has been twofold: to improve both the accuracy and computational efficiency of the algorithm for cutting force estimation in peripheral milling. Runout effect and the real tool tooth trajectory are taken into account to determine the instantaneous position of the cutting flute. An expression of average chip thickness for the engaged flute in the cut is derived for cutting force calculations resulting in a more efficient process simulation method in comparison with previous models. It provides an alternative to other studies in scientific literature commonly based on numerical integration. Experiments were carried out to verify the validity of the proposed method.

Vehicle Mobility and Communication Channel Models for Realistic and Efficient Highway VANET Simulation

Developing real-time safety and nonsafety applications for vehicular ad hoc networks (VANETs) requires understanding of the dynamics of the network topology characteristics since these dynamics determine both the performance of routing protocols and the feasibility of an application over VANETs. Using various key metrics of interest, including node degree, neighbor distribution, number of clusters, and link duration, we provide a realistic analysis of the VANET topology characteristics over time and space for a highway scenario. In this analysis, we integrate real-world road topology and real-time data extracted from the freeway Performance Measurement System (PeMS) database into a microscopic mobility model to generate realistic traffic flows along the highway. Moreover, we use a more realistic, recently proposed, obstacle-based channel model and compare the performance of this sophisticated model to the most commonly used and more simplistic channel models, including unit disk and lognormal shadowing models. Our investigation on the key metrics reveals that both lognormal and unit disk models fail to provide realistic VANET topology characteristics. We therefore propose a matching mechanism to tune the parameters of the lognormal model according to the vehicle density and a correlation model to take into account the evolution of the link characteristics over time. The proposed method has been demonstrated to provide a good match with the computationally expensive and difficult-to-implement obstacle-based model. The parameters of the proposed model have been validated to depend only on the vehicle traffic density based on the real data of four different highways in California.

Parametric modelling and automatic optimisation of high-speed hard cutting process

In traditional finite element method (FEM) simulation model of cutting process, settings of material parameters and boundary conditions take up a lot of time. The optimal cutting parameters are not easily obtained by simulation results; also the target of solution process is blind. Based on optimisation theory and secondary development of finite element software, in this research, a parametric model is established by combining python with Abaqus for PCBN tool cutting steel orthogonally. Numerical values of tool angle, tool size, workpiece size and process can be set in the interface of two-dimensional model in a parameterised way. By combining Abaqus and Isight, the average value of cutting force and highest value of cutting temperature could be extracted from the simulation model automatically. To get the minimum of cutting force and temperature under the selected parameter, the model takes cutting feed and speed as design variables to optimise. Under experimental validation, the precision of optimisation results is acceptable. This research result lays a foundation for establishment of high efficiency and high accuracy FEM simulation model. Also, it provides a feasible and effective way for the optimisation of cutting parameters and development of new tools. [Received 09 November 2014; Revised 09 February 2015; Accepted 14 February 2015]

Asynchronous coupling of hybrid models for efficient simulation of multiscale systems

We present a new coupling approach for the time advancement of multi-physics models of multiscale systems. This extends the method of E et al. (2009) [5] to deal with an arbitrary number of models. Coupling is performed asynchronously, with each model being assigned its own timestep size. This enables accurate long timescale predictions to be made at the computational cost of the short timescale simulation. We propose a method for selecting appropriate timestep sizes based on the degree of scale separation that exists between models. A number of example applications are used for testing and benchmarking, including a comparison with experimental data of a thermally driven rarefied gas flow in a micro capillary. The multiscale simulation results are in very close agreement with the experimental data, but are produced almost 50,000 times faster than from a conventionally-coupled simulation.

Methodology for Predicting BGA Warpage by Incorporating Metal Layer Design

This paper presents a methodology to predict warpage of ball grid array packages (BGAs) that takes into account details of metal designs in the multi layered substrate. Composite theory along with local homogenization methods are used to resolve the distribution of material properties in each layer of the substrate that enables an efficient simulation model with moderate computational size. Associated procedures have been implemented and tested for finite element simulation tool. Verification examples were prepared to demonstrate the warpage predictions on BGA packages. Key substrate parameters including package mold compound shrinkage during post mold cure and the resultant impact on deformation behavior and mechanical reliability of BGA assemblies. A comparison of simplified homogenization methods and representative unit cell models of multi layered composite structures are discussed and show the significance of incorporating detailed metal layer design in simulation model for accurate warpage prediction.

LINTRAN v2.0: A linearised vector radiative transfer model for efficient simulation of satellite-born nadir-viewing reflection measurements of cloudy atmospheres

Radiance measurements of solar radiation that is backscattered by the Earth׳s atmosphere or surface contain information about the atmospheric composition and the state of the Earth׳s surface. Retrieving such information from satellite-based observations in nadir geometry employs a radiative transfer forward model. The forward model simulates the observed quantity, aiming to reproduce the observation.LINTRAN v2.0 is a linearised vector radiative transfer forward model, employing forward-adjoint theory, that is capable of modelling cloud contaminated satellite observations and their derivatives with respect to the state of the atmosphere and the Earth׳s surface in a numerically efficient manner. A significant gain in efficiency with respect to its predecessor (LINTRAN v1.0) is achieved through a mathematical framework that combines an approximate iterative solving method using the forward-adjoint perturbation theory with separation of the first N orders of scattering from the diffuse intensity vector field. Contributions to the observable up to order of scattering N are recursively solved in an analytical manner. Contributions from higher orders of scattering are subsequently solved in a numerical manner, assuming that the intensity field varies linearly with the vertical coordinate within an optically homogeneous model layer. This method is implemented in LINTRAN v2.0, choosing N=2, within the general framework of forward-adjoint perturbation theory.This new approach allows us to decrease the number of model layers and the degree of angular quadrature within the numerical solver by a factor of 10 and 1.4 respectively, compared to the previous model version, assuming a homogeneous atmosphere loaded with scattering Mie particles (size parameter χ≈35). In this homogeneous atmosphere, the reduced discretisation sampling in turn reduces the numerical effort associated with the numerical matrix solver by a factor of 42 relative to the previous model version, without a loss in model accuracy.

Development of innovative and efficient hydraulic fracturing numerical simulation model and parametric studies in unconventional naturally fractured reservoirs

The most effective method for stimulating unconventional reservoirs is using properly designed and successfully implemented hydraulic fracture treatments. The interaction between pre-existing natural fractures and the engineered propagating hydraulic fracture is a critical factor affecting the complex fracture network. However, many existing numerical simulators use simplified model to either ignore or not fully consider the significant impact of pre-existing fractures on hydraulic fracture propagation. Pursuing development of numerical models that can accurately characterize propagation of hydraulic fractures in naturally fractured formations is important to better understand their behavior and optimize their performance.In this paper, an innovative and efficient modeling approach was developed and implemented which enabled integrated simulation of hydraulic fracture network propagation, interactions between hydraulic fractures and pre-existing natural fractures, fracture fluid leakoff and fluid flow in reservoir. This improves stability and convergence, and increases accuracy, and computational speed. Computing time of one stage treatment with a personal computer is now reduced to 2.2min from 12.5min than using single porosity model.Parametric studies were then conducted to quantify the effect of horizontal differential stress, natural fracture spacing (the density of pre-existing fractures), matrix permeability and fracture fluid viscosity on the geometry of the hydraulic fracture network. Using the knowledge learned from the parametric studies, the fracture–reservoir contact area is investigated and the method to increase this factor is suggested. This new knowledge helps us understand and improve the stimulation of naturally fractured unconventional reservoirs.

Development of a 3D finite element acoustic model to predict the sound reduction index of stud based double-leaf walls

Building standards incorporating quantitative acoustical criteria to ensure adequate sound insulation are now being implemented. Engineers are making great efforts to design acoustically efficient double-wall structures. Accordingly, efficient simulation models to predict the acoustic insulation of double-leaf wall structures are needed. This paper presents the development of a numerical tool that can predict the frequency dependent sound reduction index R of stud based double-leaf walls at one-third-octave band frequency range. A fully vibro-acoustic 3D model consisting of two rooms partitioned using a double-leaf wall, considering the structure and acoustic fluid coupling incorporating the existing fluid and structural solvers are presented. The validity of the finite element (FE) model is assessed by comparison with experimental test results carried out in a certified laboratory. Accurate representation of the structural damping matrix to effectively predict the R values are studied. The possibilities of minimising the simulation time using a frequency dependent mesh model was also investigated. The FEA model presented in this work is capable of predicting the weighted sound reduction index Rw along with A-weighted pink noise C and A-weighted urban noise Ctr within an error of 1dB. The model developed can also be used to analyse the acoustically induced frequency dependent geometrical behaviour of the double-leaf wall components to optimise them for best acoustic performance. The FE modelling procedure reported in this paper can be extended to other building components undergoing fluid–structure interaction (FSI) to evaluate their acoustic insulation.

Compact modeling of STT-MTJ devices

STT-MTJ is a promising device for future high-density and low-power integrated systems. To enable design exploration of STT-MTJ, this paper presents a fully compact model for efficient SPICE simulation. Derived from the fundamental LLG equation, the new model consists of RC elements that are compact equations of device geometry and material properties. They support transient SPICE simulations, providing necessary details beyond the macromodel and enable resilient memory design. The accuracy of the model is validated with numerical results and published data. Scaling analysis shows the sensitivity of STT-MTJ to its geometry. We also did variability analysis with Monte Carlo simulation of the basic 1T1MTJ memory cell to study the bit error rate performance for different transistor size and programming current profile. We show that there is a tradeoff between programming energy and cell area for the same bit error rate constraint. Finally we derive the cell size that achieves minimum energy consumption for a given bit error rate constraint (primary) and latency or area constraint (secondary).

Implicit Geometry Meshing for the simulation of Rotary Friction Welding

The simulation of Rotary Friction Welding (RFW) is a challenging task, since it states a coupled problem of phenomena like large plastic deformations, heat flux, contact and friction. In particular the mesh generation and its restoration when using a Lagrangian description of motion is of significant severity. In this regard Implicit Geometry Meshing (IGM) algorithms are promising alternatives to the more conventional explicit methods. Because of the implicit description of the geometry during remeshing, the IGM procedure turns out to be highly robust and generates spatial discretizations of high quality regardless of the complexity of the flash shape and its inclusions.A model for efficient RFW simulation is presented, which is based on a Carreau fluid law, an Augmented Lagrange approach in mapping the incompressible deformations, a penalty contact approach, a fully regularized Coulomb-/fluid friction law and a hybrid time integration strategy. The implementation of the IGM algorithm using 6-node triangular finite elements is described in detail. The techniques are demonstrated on a fairly complex friction welding problem, demonstrating the performance and the potentials of the proposed method. The techniques are general and straight-forward to implement, and offer the potential of successful adoption to a wide range of other engineering problems.