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Computation, Volume 3, Issue 3 (September 2015) – 6 articles , Pages 336-508

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10533 KiB

Open AccessArticle

Applicability of URANS and DES Simulations of Flow Past Rectangular Cylinders and Bridge Sections

by Claudio Mannini

Computation 2015, 3(3), 479-508; https://doi.org/10.3390/computation3030479 - 18 Sep 2015

Cited by 12 | Viewed by 8357

Abstract

This paper discusses the results of computational fluid dynamics simulations carried out for rectangular cylinders with various side ratios of interest for many civil engineering structures. A bridge deck of common cross-section geometry was also considered. Unsteady Reynolds-averaged Navier–Stokes (URANS) equations were solved in conjunction with either an eddy viscosity or a linearized explicit algebraic Reynolds stress model. The analysis showed that for the case studies considered, the 2D URANS approach was able to give reasonable results if coupled with an advanced turbulence model and a suitable computational mesh. The simulations even reproduced, at least qualitatively, complex phenomena observed in the wind tunnel, such as Reynolds number effects for a sharp-edged geometry. The study focused both on stationary and harmonically oscillating bodies. For the latter, self-excited forces and flutter derivatives were calculated and compared to experimental data. In the particular case of a benchmark rectangular 5:1 cylinder, 3D detached eddy simulations were also carried out, highlighting the improvement in the accuracy of the results with respect to both 2D and 3D URANS calculations. All of the computations were performed with the Tau code, a non-commercial unstructured solver developed by the German Aerospace Center. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Civil Engineering)

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12920 KiB

Open AccessArticle

Towards Online Visualization and Interactive Monitoring of Real-Time CFD Simulations on Commodity Hardware

by Nils Koliha, Christian F. Janßen and Thomas Rung

Computation 2015, 3(3), 444-478; https://doi.org/10.3390/computation3030444 - 11 Sep 2015

Cited by 5 | Viewed by 7163

Abstract

Real-time rendering in the realm of computational fluid dynamics (CFD) in particular and scientific high performance computing (HPC) in general is a comparably young field of research, as the complexity of most problems with practical relevance is too high for a real-time numerical simulation. However, recent advances in HPC and the development of very efficient numerical techniques allow running first optimized numerical simulations in or near real-time, which in return requires integrated and optimized visualization techniques that do not affect performance. In this contribution, we present concepts, implementation details and several application examples of a minimally-invasive, efficient visualization tool for the interactive monitoring of 2D and 3D turbulent flow simulations on commodity hardware. The numerical simulations are conducted with ELBE, an efficient lattice Boltzmann environment based on NVIDIA CUDA (Compute Unified Device Architecture), which provides optimized numerical kernels for 2D and 3D computational fluid dynamics with fluid-structure interactions and turbulence. Full article

(This article belongs to the Section Computational Engineering)

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961 KiB

Open AccessArticle

Computational Modeling of Teaching and Learning through Application of Evolutionary Algorithms

by Richard Lamb and Joshua Premo

Computation 2015, 3(3), 427-443; https://doi.org/10.3390/computation3030427 - 2 Sep 2015

Cited by 10 | Viewed by 5692

Abstract

Within the mind, there are a myriad of ideas that make sense within the bounds of everyday experience, but are not reflective of how the world actually exists; this is particularly true in the domain of science. Classroom learning with teacher explanation are a bridge through which these naive understandings can be brought in line with scientific reality. The purpose of this paper is to examine how the application of a Multiobjective Evolutionary Algorithm (MOEA) can work in concert with an existing computational-model to effectively model critical-thinking in the science classroom. An evolutionary algorithm is an algorithm that iteratively optimizes machine learning based computational models. The research question is, does the application of an evolutionary algorithm provide a means to optimize the Student Task and Cognition Model (STAC-M) and does the optimized model sufficiently represent and predict teaching and learning outcomes in the science classroom? Within this computational study, the authors outline and simulate the effect of teaching on the ability of a “virtual” student to solve a Piagetian task. Using the Student Task and Cognition Model (STAC-M) a computational model of student cognitive processing in science class developed in 2013, the authors complete a computational experiment which examines the role of cognitive retraining on student learning. Comparison of the STAC-M and the STAC-M with inclusion of the Multiobjective Evolutionary Algorithm shows greater success in solving the Piagetian science-tasks post cognitive retraining with the Multiobjective Evolutionary Algorithm. This illustrates the potential uses of cognitive and neuropsychological computational modeling in educational research. The authors also outline the limitations and assumptions of computational modeling. Full article

(This article belongs to the Section Computational Biology)

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4871 KiB

Open AccessArticle

Numerical Simulations of Wave-Induced Flow Fields around Large-Diameter Surface-Piercing Vertical Circular Cylinder

by Giancarlo Alfonsi

Computation 2015, 3(3), 386-426; https://doi.org/10.3390/computation3030386 - 28 Aug 2015

Cited by 5 | Viewed by 8104

Abstract

A computational analysis is performed on the diffraction of water waves induced by large-diameter, surface-piercing, vertical circular cylinder. With reference to linear-wave cases, the phenomenon is preliminarly considered in terms of velocity potential, a simplified theoretical framework in which both hypotheses of inviscid fluid and irrotational flow are incorporated. Then, and as a first-approximation analysis, the Euler equations in primitive variables are considered (a framework in which the fluid is still handled as inviscid, but the field can be rotational). Finally, the real-fluid behavior is analyzed, by numerically integrating the full Navier-Stokes equations (viscous fluid and rotational field) in their velocity-pressure formulation, by following the approach of the Direct Numerical Simulation (DNS, no models are used for the fluctuating portion of the velocity field). For further investigation of the flow fields, the swirling-strength criterion for flow-structure extraction, and the Karhunen-Loève (KL) decomposition technique for the extraction of the most energetic flow modes respectively, are applied to the computed fields. It is found that remarkable differences exist between the wave-induced fields, as derived within the different computing frameworks tested. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Civil Engineering)

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6787 KiB

Open AccessArticle

Validation of the GPU-Accelerated CFD Solver ELBE for Free Surface Flow Problems in Civil and Environmental Engineering

by Christian F. Janßen, Dennis Mierke, Micha Überrück, Silke Gralher and Thomas Rung

Computation 2015, 3(3), 354-385; https://doi.org/10.3390/computation3030354 - 7 Jul 2015

Cited by 36 | Viewed by 8617

Abstract

This contribution is dedicated to demonstrating the high potential and manifold applications of state-of-the-art computational fluid dynamics (CFD) tools for free-surface flows in civil and environmental engineering. All simulations were performed with the academic research code ELBE (efficient lattice boltzmann environment, http://www.tuhh.de/elbe). The ELBE code follows the supercomputing-on-the-desktop paradigm and is especially designed for local supercomputing, without tedious accesses to supercomputers. ELBE uses graphics processing units (GPU) to accelerate the computations and can be used in a single GPU-equipped workstation of, e.g., a design engineer. The code has been successfully validated in very different fields, mostly related to naval architecture and mechanical engineering. In this contribution, we give an overview of past and present applications with practical relevance for civil engineers. The presented applications are grouped into three major categories: (i) tsunami simulations, considering wave propagation, wave runup, inundation and debris flows; (ii) dam break simulations; and (iii) numerical wave tanks for the calculation of hydrodynamic loads on fixed and moving bodies. This broad range of applications in combination with accurate numerical results and very competitive times to solution demonstrates that modern CFD tools in general, and the ELBE code in particular, can be a helpful design tool for civil and environmental engineers. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Civil Engineering)

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7381 KiB

Open AccessArticle

In Silico Comparison of the Hemicelluloses Xyloglucan and Glucuronoarabinoxylan in Protecting Cellulose from Degradation

by Indrakumar Vetharaniam, Martin Upsdell, William J. Kelly, Graeme T. Attwood, Christina D. Moon and Philip J. Harris

Computation 2015, 3(3), 336-353; https://doi.org/10.3390/computation3030336 - 6 Jul 2015

Viewed by 5328

Abstract

We used a previously developed simulation model of a plant cell wall and its enzymatic degradation to compare the abilities of two hemicelluloses, glucuronoarabinoxylan (GAX) and xyloglucan (XG), to protect cellulose microfibrils (CMFs) from attack by cellulose-degrading enzymes. Additionally, we investigated the effect of XG abundance on the degradation rate of CMFs in the presence of the same enzymes. Simulations were run using hypothetical cell-wall compositions in which the numbers and arrangement of CMFs and (1,3;1,4)-β-glucan were kept constant, but the proportions of GAX and XG were altered. Scenarios considered walls with low and equal proportions of either GAX or XG, and also low, medium and high proportions of XG in the absence of GAX. The rate of CMF degradation was much lower in walls with GAX than walls with XG, except for early in the simulation when the reverse held, suggesting that XGs were protecting CMFs by competitive inhibition. Increasing XG content reduced both the degradation rate of CMFs and the percent of XG degraded, indicating that activity of enzymes decreased with XG density despite XG being degradable. Glucose oligosaccharide breakdown products were analysed on the basis of the originating polysaccharide and their degree of polymerisation (DP). The presence of GAX as opposed to equal amounts of XG had some significant effects on the amount and profile of breakdown products from XG and CMFs. Full article

(This article belongs to the Section Computational Biology)

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