Traditional Simulation Methods Research Articles

Predicting buckling behavior of microtubules based on an atomistic-continuum model

An atomistic-continuum model is proposed for microtubules. A higher-order gradient continuum constitutive relationship is established, and elasticity and global buckling of microtubules are studied intensively. As a typical macromolecular bio-system, atomic components and structures are much more complicated. Traditional atomistic simulation methods and classical continuum approaches have their own fundamental drawbacks in dealing with this large atomic system. Adopting a homogenization technique, this paper proposes a concept of fictitious bonds for microtubules to link the large atomic structure with continuum description. After selecting a representative unit, the fictitious bond energy equals to the energy stored in the continuum model. The higher-order Cauchy–Born rule is used to approximate the deformation of fictitious bonds under arbitrary loading conditions. A mesh-free numerical scheme is specifically developed for modeling computation. The elastic modulus and critical compressive force are predicted. Representative case studies are presented, and some results are obtained and discussed.

Bridge Buffeting Analysis Based on POD and Aeroelastic Coupling Method

The bridge buffeting response is a type of response varying with the time, space and frequency, in this paper, the bridge buffeting response analysis method based on Proper Orthogonal Decomposition (POD) and aeroelastic coupling is proposed, which can consider the contribution of effective turbulence on the bridge buffeting response. To test the proposed technique, a cable-stayed bridge is used to compare current analysis with the results using the traditional buffeting simulation method.

Efficient Simulation Method for General Assembly Systems With Material Handling Based on Aggregated Event-Scheduling

Performance evaluation of complex manufacturing systems is challenging due to many factors such as system complexity, parameter uncertainties, problem size, just to name a few. In many cases when a system is too complex to model using mathematical formulas, simulation is used as an effective alternative to conduct system analysis. A manufacturing system is a good example of such cases where both system performance and system complexity are greatly impacted by material handling (MH) strategy, management, and operational control. In this paper, we study vehicle general assembly (GA) system with MH, and focus on developing an efficient simulation method for modeling and analysis where traditional simulation methods may suffer from computation intensity. Making use of the partial system decomposability, we introduce an aggregated event-scheduling simulation method with two-level framework. A dividing mechanism with boundary conditions is employed in top-level simulation to divide the global event list into small sizes. A timing-focuses strategy based on max-plus algebra is applied in bottom-level local simulation to further reduce local event lists. With this new method it is possible to mimic real production systems fast and accurately within a reasonable computational time frame. The effectiveness and efficiency of the new simulation method are validated through experimental results.

Traditional Chinese Medicine Pulse-Condition Simulation and Wavelet Recognition Method

The human pulse-condition diagnosis is an important part of the traditional Chinese medicine (TCM) which is difficult to recognize accurately by doctor’s subjective experience. Objective identification of pulse-conditions has important meanings for modernization of TCM. In this paper human pulse-condition system transfer function model and model parameter estimation were introduced, which are used to construct four kinds of typical pulse-conditions simulation signals. There are normal pulse, taut pulse, slippery pulse and thready pulse. And then, discrete wavelet transform for extracting the multi-scale energy characteristics and wavelet packet decomposition for extracting the multi-band energy characteristics are proposed so as to recognize the pulse-conditions simulation signals. The results show that the recognition effect of discrete wavelet transform method is better. Moreover, the data features of characteristic parameters demonstrate the reality of simulation signals.

Example-based wrinkle synthesis for clothing animation

This paper describes a method for animating the appearance of clothing, such as pants or a shirt, that fits closely to a figure's body. Compared to flowing cloth, such as loose dresses or capes, these types of garments involve nearly continuous collision contact and small wrinkles, that can be troublesome for traditional cloth simulation methods. Based on the observation that the wrinkles in close-fitting clothing behave in a predominantly kinematic fashion, we have developed an example-based wrinkle synthesis technique. Our method drives wrinkle generation from the pose of the figure's kinematic skeleton. This approach allows high quality clothing wrinkles to be combined with a coarse cloth simulation that computes the global and dynamic aspects of the clothing motion. While the combined results do not exactly match a high-resolution reference simulation, they do capture many of the characteristic fine-scale features and wrinkles. Further, the combined system runs at interactive rates, making it suitable for applications where high-resolution offline simulations would not be a viable option. The wrinkle synthesis method uses a precomputed database built by simulating the high-resolution clothing as the articulated figure is moved over a range of poses. In principle, the space of poses is exponential in the total number of degrees of freedom; however clothing wrinkles are primarily affected by the nearest joints, allowing each joint to be processed independently. During synthesis, mesh interpolation is used to consider the influence of multiple joints, and combined with a coarse simulation to produce the final results at interactive rates.

The Transient Stability Preventive Control of Power System Based on RBF Neural Network

The transient stability preventive estimation and control is one of the most important tasks of the power system. The traditional time domain simulation method cannot meet the standard of on-line estimation because of its heavy computation burden. In this paper, we realize the on-line estimation of transient stability limits on critical lines of a power system using the favorable approximation ability of RBF network. We choose right samples by off-line count to train the RBF network in order to make the error satisfy demand. Preventive control direction and amount are determined based on first-order sensitivities of transient stability limits to generator outputs. The sensitivities are derived from partial derivatives of RBF network outputs to inputs. In the end, we take a practical power system for an example to demonstrate the efficiency of RBF network in estimation of the transient stability limit on critical lines and ability to provide preventive control strategy.

Real-time simulation of fog on GPU

Fog simulation is an important research topic in the field of three-dimensional simulation.It puts forward high requirements on real-time performance as well as realistic rendering results for complex three-dimensional simulation system.By analyzing the traditional simulation methods of fog,the authors proposed a Graphic Processing Unit(GPU)-based method to simulate the fog effect in real-time.The basic idea was to employ an exponential function to simulate the fade of fog with height.Then a GPU implementation of this formula was presented.And finally the fog color was blended with the fragment color according to the fog factor.The experimental results show that the proposed method can generate strongly realistic fog in real-time.

Proxel-based simulation of queuing systems with attributed customers

This paper describes a state space-based simulation method for queuing systems with attributed customers. Motivation was the need for exact solutions of queuing systems where no analytical solution is available. The original Proxel-based queuing simulation method is extended to incorporate attributed customers, concentrating on efficient coding and storage strategies to dampen state space explosion. The attributes classes priority, deadline and processing time are implemented and tested. Some interesting result statistics obtained would be hard to obtain using traditional simulation methods. The presented method can yield deterministic results for a larger number of queuing systems that cannot easily be solved analytically.

Brain Springs: Fast Physics for Large Crowds in WALL•E

A major challenge of making WALL*E was creating believable physics for human and robot crowds. To do this, Pixar technical directors combined a custom spring-physics system in the Massive software platform with traditional simulation methods. The performance was fast enough to scale for large crowds and maintain interactivity for previews.

A Novel Feature Selection Methodology for Automated Inspection Systems

This paper proposes a new feature selection methodology. The methodology is based on the stepwise variable selection procedure, but, instead of using the traditional discriminant metrics such as Wilks' Lambda, it uses an estimation of the misclassification error as the figure of merit to evaluate the introduction of new features. The expected misclassification error rate (MER) is obtained by using the densities of a constructed function of random variables, which is the stochastic representation of the conditional distribution of the quadratic discriminant function estimate. The application of the proposed methodology results in significant savings of computational time in the estimation of classification error over the traditional simulation and cross-validation methods. One of the main advantages of the proposed method is that it provides a direct estimation of the expected misclassification error at the time of feature selection, which provides an immediate assessment of the benefits of introducing an additional feature into an inspection/classification algorithm.

Fast and accurate jitter simulation technique for continuous-time modulators

A fast and accurate technique for modelling and simulation of clock jitter in continuous-time sigma-delta (ΣΔ) modulators is introduced. In addition to its high speed compared to the traditional jitter simulation method, the proposed technique is still continuous-time based, which is more convenient than discrete-time based jitter modelling suggested in other publications. The mathematical principle of the proposed technique, as well as simulations results, are presented and compared to other simulation techniques.

Variational integrators for almost-integrable systems

We construct several variational integrators—integrators based on a discrete variational principle—for systems with Lagrangians of the form L = LA + eLB, with \({\varepsilon \ll 1}\), where LA describes an integrable system. These integrators exploit that \({\varepsilon \ll 1}\) to increase their accuracy by constructing discrete Lagrangians based on the assumption that the integrator trajectory is close to that of the integrable system. Several of the integrators we present are equivalent to well-known symplectic integrators for the equivalent perturbed Hamiltonian systems, but their construction and error analysis is significantly simpler in the variational framework. One novel method we present, involving a weighted time-averaging of the perturbing terms, removes all errors from the integration at \({\fancyscript{O} {(\varepsilon)}}\). This last method is implicit, and involves evaluating a potentially expensive time-integral, but for some systems and some error tolerances it can significantly outperform traditional simulation methods.

Machining chatter simulation in multi-axis milling using graphical method

In this work, a computer graphics approach is developed for time-domain simulation of chatter in multi-axis milling. The new chatter simulation method is based on the local adaptive depth buffer method of Roth, Ismail, and Bedi [ Mechanistic modelling of the milling process using an adaptive depth buffer, CAD 35 (4) (2003) 1287–1303;Mechanistic modelling of the milling process using complex tool geometry, Journal of Advanced Manufacturing Technology 25 (1–2) (2005) 140–144] that was originally developed to calculate the cutting forces for a rigid tool. In the current work, the dynamic characteristics at the tool tip as well as the regeneration mechanism are accounted for. Implementation details of the proposed method are given. Limitations of the graphical method imposed by the pixel size in relationship to the vibration amplitude and frequency are discussed. The graphical chatter simulation approach is shown to agree with the traditional numerical simulation method. It is also experimentally verified in one dimension as well as simultaneous three-axis machining. In the three-axis test, the tool/workpiece engagement varied along the tool path.

Simulation-Based Technology for Rapid Assessment of Redevelopment Potential in Marginal Gas Fields—Technology Advances and Validation in Garden Plains Field, Western Canada Sedimentary Basin

SummaryIt is often difficult to quantify the redevelopment potential of marginal oil and gas fields because of a wide range of depositional environments, variability in reservoir properties, a large number of wells, and limited reservoir information. Evaluation of infill potential in these fields with traditional simulation methods is timeconsuming, labor-intensive, and frequently cost-prohibitive. Without adequate assessment technology, some unprofitable infill campaigns may be initiated, while other promising infill campaigns may be terminated prematurely because of disappointing early results.In this paper, we present a simulation-based regression technique to assess infill-drilling potential in marginal gas fields. With limited, basic reservoir information, this technique first estimates the spatial distribution of subsurface reservoir properties by rapid history matching of well production data. We implemented a sequential regression algorithm to estimate, from available flowrate measurements, not only the permeability distribution, but also the pore-volume distribution. Future production is forecasted and infill-drilling potential is determined using the estimated permeability and pore-volume distributions. Because the method uses an approximate reservoir description, it identifies regions of the field with promising infill potential rather than individual-infill-well locations.The proposed technique provides rapid, reliable, and cost-effective assessment of redevelopment potential in marginal gas fields. In this paper, we first validate our approach using synthetic reservoir data. We then apply the approach to the Second White Specks formation, Garden Plains field, Western Canada Sedimentary Basin. The prediction of infill potential in this gas field, which has more than 700 wells, demonstrates the power and utility of the proposed technique.

A Distributed Multi-Agent Framework for Simulating the Diffusion of Innovations

In this paper we report on the newly developed framework MADS (Multi-Agent Diffusion Simulation), designed for simulating the diffusion of innovations. Created for but not limited to the simulation of the diffusion of emergent technologies, MADS is both close to the diffusion theory and, by using a distributed agent infrastructure, performs data management and streamlines the simulation process. After presenting the framework, we show how it was applied to the simulation of the diffusion of fuel cell vehicles. Unlike the traditional simulation methods usually employed in this case, real consumer preferences are included and a sensitivity analysis is performed.

Simulation of turbulent combustion in DLR Scramjet

Turbulent combustion in a DLR (German Aerospace Center) Scramjet engine was simulated using the newly-proposed Partially Resolved Numerical Simulation (PRNS) procedure. The PRNS procedure uses temporal filtering to define large-scale turbulence, and the model developed to account for unresolved scales is grid independent. No problem about inner commutation error and inconsistencies will arise from the PRNS, while such issues are of concern in traditional Large Eddy Simulation (LES) methods. The mean results have good agreement with the experiment data and the flow structures with small scales are well resolved.

Pattern-Based Iterative Method for Extreme Large Power/Ground Analysis

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we present a novel pattern-based method to simulate large-scaled power/ground (P/G) grids. This method takes advantage of both traditional direct simulation methods and iterative simulation methods. The new method explores the geometry characteristics of regular P/G grids and translates topology similarity to submatrix regularity, which is called “pattern” in this paper. Such pattern structures can reduce the memory usage dramatically. Further, a new type of preconditioner is constructed to optimize the simulation process. Experimental results show that the proposed approach is about 5<formula formulatype="inline"><tex>$\times$</tex></formula> faster than the previous iterative methods with much lower memory, and is superior to the macro model-based hierarchical method on the tested large cases with pattern structures. </para>

ECAD – A Prototype Screen-based VR Solid Modeling Environment Incorporating Tangible Deformable Models

AbstractTwo shortcomings of the current generation of computer-aided design (CAD) software are (1) segregating the tasks of modeling and simulation, and (2) casting inherently 3D tasks, such as modeling and manipulation, into a 2D environment. The former is due to the fact that modeling is generally an interactive process whereas simulation often must be conducted off-line due to the computational cost of traditional simulation methods. The latter arises largely from the relative newness of 3D interface devices and the lack of software that takes good advantage of them. In this paper we present a screen-based VR modeling and simulation environment called ECAD (Enhanced CAD). ECAD is a proof-of-concept system that combines 6 DOF input, 3D visualization, haptic feedback, and a new real-time deformation simulation engine into a unified modeling and simulation environment. Real-time simulation of deformations provides the user with immediate tangible feedback regarding the behavior of the model, allowing for ...

Simulating deformations of MR brain images for validation of atlas-based segmentation and registration algorithms

Simulated deformations and images can act as the gold standard for evaluating various template-based image segmentation and registration algorithms. Traditional deformable simulation methods, such as the use of analytic deformation fields or the displacement of landmarks followed by some form of interpolation, are often unable to construct rich (complex) and/or realistic deformations of anatomical organs. This paper presents new methods aiming to automatically simulate realistic inter- and intra-individual deformations. The paper first describes a statistical approach to capturing inter-individual variability of high-deformation fields from a number of examples (training samples). In this approach, Wavelet–Packet Transform (WPT) of the training deformations and their Jacobians, in conjunction with a Markov random field (MRF) spatial regularization, are used to capture both coarse and fine characteristics of the training deformations in a statistical fashion. Simulated deformations can then be constructed by randomly sampling the resultant statistical distribution in an unconstrained or a landmark-constrained fashion. The paper also describes a model for generating tissue atrophy or growth in order to simulate intra-individual brain deformations. Several sets of simulated deformation fields and respective images are generated, which can be used in the future for systematic and extensive validation studies of automated atlas-based segmentation and deformable registration methods. The code and simulated data are available through our Web site.

Three-dimensional interactive Molecular Dynamics program for the study of defect dynamics in crystals

The study of crystal defects and the complex processes underlying their formation and time evolution has motivated the development of the program ALINE for interactive molecular dynamics experiments. This program couples a molecular dynamics code to a Graphical User Interface and runs on a UNIX-X11 Window System platform with the MOTIF library, which is contained in many standard Linux releases. ALINE is written in C, thus giving the user the possibility to modify the source code, and, at the same time, provides an effective and user-friendly framework for numerical experiments, in which the main parameters can be interactively varied and the system visualized in various ways. We illustrate the main features of the program through some examples of detection and dynamical tracking of point-defects, linear defects, and planar defects, such as stacking faults in lattice-mismatched heterostructures. Program summary Title of program: ALINE Catalogue identifier:ADYJ_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADYJ_v1_0 Program obtainable from: CPC Program Library, Queen University of Belfast, N. Ireland Computer for which the program is designed and others on which it has been tested: Computers:DEC ALPHA 300, Intel i386 compatible computers, G4 Apple Computers Installations:Laboratory of Computational Engineering, Helsinki University of Technology, Helsinki, Finland Operating systems under which the program has been tested:True64 UNIX, Linux-i386, Mac OS X 10.3 and 10.4 Programming language used:Standard C and MOTIF libraries Memory required to execute with typical data:6 Mbytes but may be larger depending on the system size No. of lines in distributed program, including test data, etc.:16 901 No. of bytes in distributed program, including test data, etc.:449 559 Distribution format:tar.gz Nature of physical problem:Some phenomena involving defects take place inside three-dimensional crystals at times which can be hardly predicted. For this reason they are difficult to detect and track even within numerical experiments, especially when one is interested in studying their dynamical properties and time evolution. Furthermore, traditional simulation methods require the storage of a huge amount of data which in turn may imply a long work for their analysis. Method of solution:Simplifications of the simulation work described above strongly depend also on the computer performance. It has now become possible to realize some of such simplifications thanks to the real possibility of using interactive programs. The solution proposed here is based on the development of an interactive graphical simulation program both for avoiding large storage of data and the subsequent elaboration and analysis as well as for visualizing and tracking many phenomena inside three-dimensional samples. However, the full computational power of traditional simulation programs may not be available in general in programs with graphical user interfaces, due to their interactive nature. Nevertheless interactive programs can still be very useful for detecting processes difficult to visualize, restricting the range or making a fine tuning of the parameters, and tailoring the faster programs toward precise targets. Restrictions on the complexity of the problem:The restrictions on the applicability of the program are related to the computer resources available. The graphical interface and interactivity demand computational resources that depend on the particular numerical simulation to be performed. To preserve a balance between speed and resources, the choice of the number of atoms to be simulated is critical. With an average current computer, simulations of systems with more than 10 5 atoms may not be easily feasible on an interactive scheme. Another restriction is related to the fact that the program was originally designed to simulate systems in the solid phase, so that problems in the simulation may occur if some particular physical quantities are computed beyond the melting point. Typical running time:It depends on the machine architecture, system size, and user needs. Unusual features of the program:In the program, besides the window in which the system is represented in real space, an additional graphical window presenting the real time distribution histogram for different physical variables (such as kinetic or potential energy) is included. Such tool is very interesting for making demonstrative numerical experiments for teaching purposes as well as for research, e.g., for detecting and tracking crystal defects. The program includes: an initial condition builder, an interactive display of the simulation, a set of tools which allow the user to filter through different physical quantities the information—either displayed in real time or printed in the output files—and to perform an efficient search of the interesting regions of parameter space.