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• An embedded Finite Element framework for the resolution of strongly coupled Fluid–Structure Interaction problems. Application to volumetric and membrane-like structures

  R. Zorrilla, R. Rossi, R. Wüchner, E. Oñate

  Computer Methods in Applied Mechanics and Engineering (2020). Volume 368, pp. 113179

  
  

  Abstract

  This work presents a Fluid–Structure Interaction framework for the robust and efficient simulation of strongly coupled problems involving arbitrary large displacements and rotations. We focus on the application of the proposed tool to lightweight membrane-like structures. Nonetheless, all the techniques we present in this work can be applied to both volumetric and volumeless bodies. To achieve this, we rely on the use of embedded mesh methods in the fluid solver to conveniently handle the extremely large deflections and eventual topology changes of the structure. The coupling between the embedded fluid and mechanical solvers is based on an interface residual black-box strategy. We validate our proposal by solving reference benchmarking examples that consider both volumetric and volumeless geometries. Whenever it is possible, we also compare the embedded solution with the one obtained with our reference body fitted solver. Finally we present a real-life application of the presented embedded Fluid–Structure Interaction solver.

  Abstract
  This work presents a Fluid–Structure Interaction framework for the robust and efficient simulation of strongly coupled problems involving arbitrary large displacements [...]

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• PedPIV: Pedestrian Velocity Extraction From Particle Image Velocimetry

  M. Baqui, R. Lohner

  IEEE Transactions on Intelligent Transportation Systems (2019). Vol. 21 (2), pp. 580-589

  
  

  Abstract

  The analysis of velocities from high-density pedestrian events may provide more information on pedestrian flow dynamics. A framework based on particle image velocimetry (PIV)-a technique commonly used in experimental fluid dynamics-has been developed to evaluate the pedestrian velocities from high-density pedestrian events. The framework takes a sequence of two or more images from a regular closed-circuit television camera and obtains the flow properties (speed, direction) of the pedestrians. A detailed analysis has been done in both the qualitative and quantitative aspects of adapting PIV to pedestrian flow. An investigation through the use of the fundamental diagram and real-time extraction of crowd velocities is also presented and discussed. The proposed PIV-based framework enables on-the-spot analysis of pedestrian flow via velocity extraction in a reliable, automated manner.

  Abstract
  The analysis of velocities from high-density pedestrian events may provide more information on pedestrian flow dynamics. A framework based on particle image velocimetry (PIV)-a [...]

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• A Study of Dispersion, Vaporization, and Combustion of Burnable Liquids Surrounding Charges

  F. Togashi, J. Baum, O. Soto, R. Lohner, J. Bell

  (2019). 31st International Symposium on Shock Waves 2

  
  

  Abstract

  A complex numerical simulation where blast waves interacted with a liquid, burnable simulant inside a chamber was conducted. The liquid simulant was dispersed by a small high explosive (HE) charge and then impacted by the blast wave produced by a significantly larger HE charge. The physics of the problem required numerical tools that allowed for (1) coupling of compressible and near-incompressible (+VOF) solvers, (2) a dropletization model by liquid bulk dispersion, (3) droplet breakup and vaporization, (4) a chemical package for combustion, and (5) a particle update technique. The resulting numerical code successfully simulated the scenario, and the predicted pressure agreed excellently with the measured data.

  Abstract
  A complex numerical simulation where blast waves interacted with a liquid, burnable simulant inside a chamber was conducted. The liquid simulant was dispersed by a small high [...]

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• Towards overcoming the LES crisis

  R. Lohner

  Int. J. Computational Fluid Dynamics (2019). Vol. 33 (6), pp. 1-11

  
  

  Abstract

  Industrial large-eddy simulation (LES), i.e. overnight runs with O(109) degrees of freedom (DOFs) and O(107) timesteps, has been one of the top priorities of CFD research over the last two decades. Current network and solver timings indicate that the required target of 5 ms/timestep is within reach: some cumulant Lattice Boltzmann Method (LBM) codes are reporting speeds in this range using multi-GPU systems, while some Finite Difference Method (FDM) codes running on traditional CPUs are achieving speeds that are only a factor of 2–4 slower. This implies that the long wait may be coming to a close. During the last three decades, a number of promising approaches have been tried. Given that the majority of these were promoted as the ‘solution to LES’ or the ‘solution to turbulence’, the paper lists them under the label of ‘the false prophecies’. Furthermore, some of the assumptions that are always part of the scientific discovery process turned out to be incorrect. These are listed under the term 'the false assumptions'. From an informal survey conducted in January of 2018, it appears that simple Cartesian Finite Difference codes or, equivalently, Lattice Boltzmann codes may be the first to achieve industrial LES.

  Abstract
  Industrial large-eddy simulation (LES), i.e. overnight runs with O(109) degrees of freedom (DOFs) and O(107) timesteps, has been one of the top priorities of CFD research [...]

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• A Novel Framework for Automated Monitoring and Analysis of High Density Pedestrian Flow

  M. Baqui, M. Samad, R. Lohner

  Journal of Intelligent Transportation Systems (2019). Vol. 24 (4),

  
  

  Abstract

  Pedestrian traffic is an important subject of surveillance to ensure public safety and traffic management, which may benefit from intelligent and continuous analysis of pedestrian videos. State-of-the-art methods for intelligent pedestrian surveillance have a number of limitations in automating and deriving useful information of high-density pedestrian traffic (HDPT) using closed circuit television (CCTV) images. This work introduces an automatic and improved HDPT surveillance system by integrating and optimizing multiple computational steps to predict pedestrian distribution from input video frames. A fast and efficient particle image velocimetry (PIV) technique is proposed to yield pedestrian velocities. A machine learning regressor model, boosted Ferns, is used to improve pedestrian count and density estimation: an essential metric for HDPT analysis. A camera perspective model is proposed to improve the speed and position estimates of HDPT by projecting 2D image pixels to 3D world-coordinate data. All these functional improvements in HDPT velocity and displacement estimations are used as inputs to a sophisticated pedestrian flow evolution model, PEDFLOW to predict HDPT distribution at a future time point, which is a crucial information for pedestrian traffic management. The predicted and simulated HDPT properties (density, velocity) obtained using the proposed framework show low errors when compared to the ground truth data. The proposed framework is computationally efficient, suitable for multiple camera feeds with HDPT videos, and capable of rapidly analyzing and predicting flows of thousands of pedestrians. The paper shows one of the first steps towards fully integrated CCTV-based automated HDPT management system.

  Abstract
  Pedestrian traffic is an important subject of surveillance to ensure public safety and traffic management, which may benefit from intelligent and continuous analysis of pedestrian [...]

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• Empirical Evaluation of Crowds Using Automated Methods

  M. Baqui, M. Isenhour, R. Lohner

  (2019). Traffic and Granular Flow '17. TGF 2017. Springer, Cham

  
  

  Abstract

  This work presents a novel framework for automated monitoring of high density crowds from closed circuit television (CCTV) image data. The framework obtains pedestrian velocities from particle image velocimetry (PIV) technique and densities from a boosted ferns machine learning model. A pinhole camera based perspective correction scheme is employed to convert the 2D pixel coordinates into 3D metric coordinates. The framework is trained with and tested against real-world event data from the Hajj.

  Abstract
  This work presents a novel framework for automated monitoring of high density crowds from closed circuit television (CCTV) image data. The framework obtains pedestrian velocities [...]

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• Overnight Industrial LES for External Aerodynamics

  R. Lohner, C. Othmer, M. Mrosek, A. Figueroa, A. Degro

  (2020). Turbulent Flows VII

  
  

  Abstract

  This paper summarizes the efforts carried out over the last year to achieve overnight industrial Large-Eddy Simulation (LES) runs for external car aerodynamics. The solver employed is based on adaptive cartesian blocks, uses explicit timestepping to advance the Navier-Stokes equations describing mildly compressible flows, and scales well to tens of thousands of cores. The capabilities developed to date are tested on a Volkswagen Golf.

  Abstract
  This paper summarizes the efforts carried out over the last year to achieve overnight industrial Large-Eddy Simulation (LES) runs for external car aerodynamics. The solver [...]

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• Towards real-time monitoring of the Hajj

  M. Baqui, R. Lohner

  Collective Dynamics (2020). Vol. 5, pp. 394-402

  
  

  Abstract

  An automated approach to explore the fundamental properties of high-density pedestrian traffic is outlined. The framework operates on video or time lapse images captured from surveillance cameras. For pedestrian velocity extraction, the framework incorporates cross-correlation based Particle Image Velocimetry (PIV) techniques. For pedestrian density estimation, the framework relies on the Machine Learning technique of the Boosted Regression Trees. The information collected from images in pixel coordinates are transformed to world coordinates with a pin-hole camera based projective transformation technique. The framework has been tested with high density crowd images acquired during the Muslim religious event, the Hajj. Accuracy and performance of the framework are reported.

  Abstract
  An automated approach to explore the fundamental properties of high-density pedestrian traffic is outlined. The framework operates on video or time lapse images captured from [...]

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• Simple fault-tolerant computing for field solvers

  A. Degro, R. Lohner

  Int. J. Numer. Meth. Fluids (2020). Vol. 34 (1), pp. 1-14

  
  

  Abstract

  Fault-tolerant computing options based on the use of restart information stored on and off node and the use of reserve processes have been developed, implemented and tested in a large-scale, production field solver taken from the domain of computational fluid dynamics. The tests conducted to date have shown good results, with recovery rates approaching 100% under realistic node failure scenarios. Even though the computational overhead of the field solver is very low (explicit time-marching and finite differences), the fault-tolerant implementation adds a run-time penalty that is only in the range of 6–12%, depending on the spatial and temporal approximation used. The procedures developed are generally applicable, and could easily be ported to other code.

  Abstract
  Fault-tolerant computing options based on the use of restart information stored on and off node and the use of reserve processes have been developed, implemented and tested [...]

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• IberWQ: new simulation tool for 2D water quality modelling in rivers and shallow estuaries

  L. Cea, M. Bermudez, J. Puertas, E. Bladé, G. Corestein, E. Escolano, A. Conde, B. Bockelmann-Evans, R. Ahmadian

  Journal of hydroinformatics (2016). Vol. 18 (5), pp. 816-830

  
  

  Abstract

  The model computes the spatial and temporal evolution of several species and variables which are relevant for the evaluation of the environmental status of rivers and estuaries, including: Escherichia coli, dissolved oxygen, carbonaceous biochemical oxygen demand, organic nitrogen, ammoniacal nitrogen, nitrate–nitrite nitrogen, water temperature and salinity. A depth-averaged transport equation is solved for each variable with a mass conservative unstructured finite volume solver. IberWQ is fully coupled to the hydrodynamic module of the software Iber, a freeware simulation tool for solving the 2D shallow water equations. Both models are integrated in the same windows graphical environment, including several tools which allow the user to generate unstructured meshes adapted to the site topography, define spatially variable input parameters and visualize model outputs. We present four application examples to illustrate the possibilities of the software for the dynamic simulation of water quality in rivers and estuaries.

  Abstract
  The model computes the spatial and temporal evolution of several species and variables which are relevant for the evaluation of the environmental status of rivers and estuaries, [...]

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