Computational Field Simulation Research Articles

Optimization of a diffuser augmented kinetic turbine with the island model

Abstract An augmented kinetic turbine with a sectioned diffuser parameterized with thirty degrees of freedom is optimized using computational flow field simulations combined with the island model for parallelizing the optimization. The geometry and mesh generation is performed with an in-house design framework. The parallel optimization and the necessary database for migration are implemented in Python. For all runs an evolutionary optimization algorithm is used. Three different groups of runs with different initializations and migration strategies are investigated. The study shows good speedup values for a diverse initialization in combination with the database migration. Moreover, for several runs, a superior speedup value is observed. Additionally, the database migration handles homogeneous initializations better than commonly used strategies.

Temporal interference stimulation targets deep primate brain

Temporal interference (TI) stimulation, a novel non-invasive stimulation strategy, has recently been shown to modulate neural activity in deep brain regions of living mice. Yet, it is uncertain if this method is applicable to larger brains and whether the electric field produced under traditional safety currents can penetrate deep regions as observed in mice. Despite recent model-based simulation studies offering positive evidence at both macro- and micro-scale levels, the absence of electrophysiological data from actual brains hinders comprehensive understanding and potential application of TI. This study aims to directly measure the spatiotemporal properties of the interfered electric field in the rhesus monkey brain and to validate the effects of TI on the human brain. Two monkeys were involved in the measurement, with implantation of several stereo-electroencephalography (SEEG) depth electrodes. TI stimulation was applied to anesthetized monkeys using two pairs of surface electrodes at differing stimulation parameters. Model-based simulations were also conducted and subsequently compared with actual recordings. Additionally, TI stimulation was administered to patients with motor disorders to validate its effects on motor symptoms.Through the integration of computational electric field simulation with empirical measurements, it was determined that the temporally interfering electric fields in the deep central regions are capable of attaining a magnitude sufficient to induce a subthreshold modulation effect on neural signals. Additionally, an improvement in movement disorders was observed as a result of TI stimulation. This study is the first to systematically measure the TI electric field in living non-human primates, offering empirical evidence that TI holds promise as a more focal and precise method for modulating neural activities in deep regions of a large brain. This advancement paves the way for future applications of TI in treating neuropsychiatric disorders.

Design, Fabrication and Validation of a Precursor Pulsed Electromagnetic Field Device for Bone Fracture Repair.

Pulsed electromagnetic field (PEMF) stimulation has been utilized in the medical field since the early 20th century. A number of therapeutic devices have been developed for the treatment of bone fractures and other medical applications. Most of these devices are backed by limited quantitative evidence. In this paper we present the development of a PEMF device for the purposes of determining, through in vitro experimentation, the exposure parameters required to give the most optimal fracture repair. Following electromagnetic field characterization, the device was shown to match well with computational field simulations. The exposure system has been validated through adipose-derived stem cell viability studies with an exposure frequency of 5 Hz and an intensity of 1.1 mT, for a duration of seven days at 30 minutes per day. Under the specific field characteristics chosen, the fatty-tissue derived stem cell proliferation was not hindered and in fact was stimulated $( 0. 025 < P < 0.01)$ by the PEMF exposure. With continued experimentation of numerous exposure conditions at the cellular scale, it will be possible to quantitatively determine the optimal exposure conditions required to produce the most rapid fresh fracture repair. Following this, there is significant potential for development of an optimized wearable device suitable for enhancing repair of all types of bone fractures.

Impact of roof shape on air pressure, wind flow and indoor temperature of residential buildings

AbstractThe aim of this study is to investigate different roof shapes with respect to air flow and indoor temperature in order to find efficient roof shapes for residential buildings in Tehran, Iran. First, an analytical model is defined and then various roof types are modelled. Theoretical modelling is presented to assess the accuracy of the measurement procedures and the uncertainty of experimental modelling. Mathematical and computational field dynamics (CFD) modelling and simulation methods are applied; a κ-e standard model and finite difference discretisation technique are used to simulate the velocity and pressure path lines as well as the temperature. The results indicate that the energy performance of a domed roof is more efficient compared to flat, vaulted and pitched roofs. In the case of indoor temperature, a domed roof is about 8 K cooler. Also, the wind flow pattern around domed and pitched roofs is more complex; differences in the wind velocity and pressure are noticeable compared to the oth...

Multidisciplinary and multi-scale computational field simulations—Algorithms and applications

This paper describes the development and the validation of two computational fluid dynamics (CFD) frameworks for multidisciplinary and multi-scale simulations. The first framework is an overset grid topology with a six-degree of freedom rigid body dynamics library for both structured-grid and unstructured-grid approaches. This framework will enable the CFD flow solver to simulate the problems involving relative motions between multiple bodies such as the stage/store separation process, etc. The second framework is a hybrid scheme that integrates a direct simulation Monte-Carlo (DSMC) method for rarefied gas flows and a Navier–Stokes (NS) solver for continuum flows. The hybrid DSMC–NS numerical framework can greatly improve the computational efficiency for simulation of problems with disparate length scales or a wide range of Knudsen numbers. A density-based Navier–Stokes flow solver, HYB3D, and a pressure-based Navier–Stokes flow solver, FDNS, were employed in this study to demonstrate the capability, strength, and accuracy of these two frameworks. Numerical simulations of benchmark test cases were conducted as the preliminary evaluation for these two frameworks, and the numerical results are presented.

Automatic CAD model topology generation

AbstractComputer aided design (CAD) models often need to be processed due to the data translation issues and requirements of the downstream applications like computational field simulation, rapid prototyping, computer graphics, computational manufacturing, and real‐time rendering before they can be used. Automatic CAD model processing tools can significantly reduce the amount of time and cost associated with the manual processing. The topology generation algorithm, commonly known as CAD repairing/healing, is presented to detect commonly found geometrical and topological issues like cracks, gaps, overlaps, intersections, T‐connections, and no/invalid topology in the model, process them and build correct topological information. The present algorithm is based on the iterative vertex pair contraction and expansion operations called stitching and filling, respectively, to process the model accurately. Moreover, the topology generation algorithm can process manifold as well as non‐manifold models, which makes the procedure more general and flexible. In addition, a spatial data structure is used for searching and neighbour finding to process large models efficiently. In this way, the combination of generality, accuracy, and efficiency of this algorithm seems to be a significant improvement over existing techniques. Results are presented showing the effectiveness of the algorithm to process two‐ and three‐dimensional configurations. Copyright © 2006 John Wiley &amp; Sons, Ltd.

High fidelity field simulations using density and pressure based approaches

Density-based and pressure-based approaches in solving the Navier-Stokes equations for computational field simulations for compressible and incompressible flows have been presented. For the density...

3D hybrid mesh generation for reservoir simulation

AbstractA great challenge for flow simulators of new generation is to gain more accuracy at well proximity within complex geological structures. For this purpose, a new approach based on hybrid mesh modelling was proposed in 2D by Balaven et al. (Proceedings of the 7th International Conference on Numerical Grid Generation in Computational Field Simulations, Whistler, Canada, 2000; 407–416). In this hybrid mesh, the reservoir is described by a structured quadrilateral mesh and drainage areas around wells are represented by radial circular meshes. In order to generate a global conforming mesh, unstructured transition meshes constituted by convex polygonal elements satisfying finite volume properties are used to connect these two structured meshes. The hybrid mesh allows us to take full advantage of the simplicity and practical aspects of structured meshes, while complexity inherent to unstructured meshes is introduced only where strictly needed. This paper presents the 3D extension of the generation of such a hybrid mesh (ECCOMAS, Jyväskylä, Finland, 2004). The proposed method uses 3D power diagrams to generate the transition mesh. Due to the round‐off errors, this mesh is modified in order to ensure the conformity with the structured meshes. In addition, some criteria are introduced to measure the mesh quality, as well as an optimization procedure to remove or to expand small edges of the transition mesh under finite volume properties constraints. Numerical results are given to show the efficiency of the approach. Copyright © 2005 John Wiley &amp; Sons, Ltd.

High fidelity field simulations using density and pressure based approaches

Density-based and pressure-based approaches in solving the Navier–Stokes equations for computational field simulations for compressible and incompressible flows have been presented. For the density-based flow solver, a generalized grid based framework has been developed and employed to simulate the complex-geometry problems with ease. The integral form of the standard and artificial compressibility form of Navier–Stokes equations has been taken as the governing form for the density-based method. For the pressure-based flow solver, the differential form of the conservation equations in the curvilinear coordinates was solved with a non-staggered structure-grid topology. A predictor plus multi-corrector algorithm (which can handle the flow with a wide range of Mach numbers without using the artificial compressibility and the preconditioning method) is utilized in the pressure-based method. Also, the capability has been developed to model the gas-particle (liquid and/or solid) multi-phase flows in the Eulerian–LaGrangian particle-tracking framework. Though the strengths and weaknesses of these two methods have been well documented, there is yet an extensive study to compare these two methods in terms of their numerical accuracies, computational efficiencies, and limitations. In this paper, these two models are validated separately, and the results are presented. Comparisons of these two methods with various benchmark test cases will be assessed and addressed in the future.

On the Scalability of Dynamic Scheduling Scientific Applications with Adaptive Weighted Factoring

In heterogeneous environments, dynamic scheduling algorithms are a powerful tool towards performance improvement of scientific applications via load balancing. However, these scheduling techniques employ heuristics that require prior knowledge about workload via profiling resulting in higher overhead as problem sizes and number of processors increase. In addition, load imbalance may appear only at run-time, making profiling work tedious and sometimes even obsolete. Recently, the integration of dynamic loop scheduling algorithms into a number of scientific applications has been proven effective. This paper reports on performance improvements obtained by integrating the Adaptive Weighted Factoring, a recently proposed dynamic loop scheduling technique that addresses these concerns, into two scientific applications: computational field simulation on unstructured grids, and N-Body simulations. Reported experimental results confirm the benefits of using this methodology, and emphasize its high potential for future integration into other scientific applications that exhibit substantial performance degradation due to load imbalance.

Grid generation: Past, present, and future

The grid generation strategies employed in numerically solving nonlinear partial differential equations representative of complex physical phenomena involving complex geometry are discussed. A historical perspective of evolving distinct strategies and methodologies for static and dynamic grid generation in view of increased demand for Computational Field Simulations (CFS) is presented.

Efficiency Improvement of Unified Implicit Relaxation/Time Integration Algorithms

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Structure-significant representation of structured datasets

Numerical simulation of physical phenomena is an accepted way of scientific inquiry. However, the field is still evolving, with a profusion of new solution and grid generation techniques being continuously proposed. Concurrent and retrospective visualization are being used to validate the results. There is a need for representation schemes which allow access of structures in an increasing order of smoothness. We describe our methods on datasets obtained from curvilinear grids. Our target application required visualization of a computational simulation performed on a very remote supercomputer. Since no grid adaptation was performed, it was not deemed necessary to simplify or compress the grid. Inherent to the identification of significant structures is determining the location of the scale coherent structures and assigning saliency values to them. Scale coherent structures are obtained as a result of combining the coefficients of a wavelet transform across scales. The result of this operation is a correlation mask that delineates regions containing significant structures. A spatial subdivision is used to delineate regions of interest. The mask values in these subdivided regions are used as a measure of information content. Later, another wavelet transform is conducted within each subdivided region and the coefficients are sorted based on a perceptual function with bandpass characteristics. This allows for ranking of structures based on the order of significance, giving rise to an adaptive and embedded representation scheme. We demonstrate our methods on two datasets from computational field simulations. We show how our methods allow the ranked access of significant structures. We also compare our adaptive representation scheme with a fixed blocksize scheme.