Application of Ensemble Kalman Filter to Pedestrian Flow

We adopted the Ensemble Kalman Filter (EnKF) methodology in our computational simulation code for pedestrian flows. The EnKF, which is a type of data assimilation methodology, has been developed in the field of weather forecast where the atmospheric condition varies hour by hour. The EnKF estimates the parameters or boundary/initial conditions in the numerical model based on the updated measured data. We considered the EnKF a promising tool for the simulation of pedestrian flows, which are notoriously difficult to predict. In this study, two scenarios were conducted to confirm the usefulness of the EnKF. The first case was unidirectional pedestrian flow in straight corridors, and the second case was Mataf scenario at the Kaaba in Mecca. Needless to say, the second scenario was very challenging because of the number of pilgrims and the degrees of freedom. In each scenario, we conducted the numerical simulation using the original parameter set and then applied the EnKF to improve the accuracy of the simulation

Numerical simulation of H2/air detonation using unstructured mesh

To explore the capability of unstructured mesh to simulate detonation wave propagation phenomena, numerical simulation of H2/air detonation using unstructured mesh was conducted. The unstructured mesh has several adv- antages such as easy mesh adaptation and flexibility to the complicated configurations. To examine the resolution dependency of the unstructured mesh, several simulations varying the mesh size were conducted and compared with a computed result using a structured mesh. The results show that the unstructured mesh solution captures the detailed structure of detonation wave, as well as the structured mesh solution. To capture the detailed detonation cell structure, the unstructured mesh simulations required at least twice, ideally 5times the resolution of structured mesh solution

On the simulation of dropletization

Compressible and near-incompressible solvers, together with particle update techniques and chemistry packages are combined in order to compute complex multiphase flows that include dropletization, vaporization and subsquent combustion

On mesh-particle techniques

The treatment of dilute solid (or liquid) phases via Lagrangian particles within mesh-based gas-dynamics (or hydrodynamic) codes is common in computational fluid dynamics. While these techniques work very well for a large spectrum of physical parameters, in some cases, notably for very light or very heavy particles, numerical instabilities appear. The present paper examines ways of mitigating these instabilities, and summarizes important implementational issues

Numerical Simulation of Long-Duration Blast Wave Evolution in Confined Facilities

The objective of this research effort was to investigate the quasi-steady flow field produced by explosives in confined facilities. In this effort we modeled tests in which a high explosive (HE) cylindrical charge was hung in the center of a room and detonated. The HEs used for the tests were C-4 and AFX 757. While C-4 is just slightly under-oxidized and is typically modeled as an ideal explosive, AFX 757 includes a significant percentage of aluminum particles, so long-time afterburning and energy release must be considered. The Lawrence Livermore National Laboratory (LLNL)-produced thermo-chemical equilibrium algorithm, “Cheetah”, was used to estimate the remaining burnable detonation products. From these remaining species, the afterburning energy was computed and added to the flow field. Computations of the detonation and afterburn of two HEs in the confined multi-room facility were performed. The results demonstrate excellent agreement with available experimental data in terms of blast wave time of arrival, peak shock amplitude, reverberation, and total impulse (and hence, total energy release, via either the detonation or afterburn processes. KeywordsDetonation-Blast wave-EOS-After burning-CF

Role of reducing co-factors in catalytic reactions of 6-hydroxymellein synthase, a multifunctional polyketide biosynthetic enzyme in carrot cells

Abstract 6-Hydroxymellein (6HM) synthase, a multifunctional polyketide biosynthetic enzyme in carrot cells, is capable of catalyzing the acyl-CoA condensation and the ketoreduction in the presence of the nucleotide reducing co-factors. Although free CoA at high concentrations functioned as the activator of the NADPH-dependent 6HM formation, the compound exhibited an appreciable inhibitory activity toward the reaction mediated by NADH. CoA showed a potent inhibitory activity against substrate entry into the reaction center of the NADH-associated enzyme while, in the presence of NADPH, the compound slightly inhibited the formation of the acylated enzyme. The catalytic rate of the synthase was appreciably decreased when NADPH was replaced by the deuterium-labeled compound, however, the kH/kD value was markedly reduced if NADH and [D]NADH were employed as the reducing co-factors. These results suggest that the phosphate group attached to 2'-position of the adenosyl moiety of NADPH associated with the ketoreducing domain of 6HM synthase plays an important role in the regulation of the enzyme activity

Using ensemble Kalman filter to determine parameters for computational crowd dynamics simulations

It is of paramount importance to ensure safe and fast evacuation routes in cities in case of natural disasters, environmental accidents or acts of terrorism. The same applies to large-scale events such as concerts, sport events and religious pilgrimages as airports and to traffic hubs such as airports and train stations. The prediction of pedestrian is notoriously difficult because it varies depending on circumstances (age group, cultural characteristics, etc.). In this study, the Ensemble Kalman Filter (EnKF) data assimilation technique, which uses the updated observation data to improve the accuracy of the simulation, was applied to improve the accuracy of numerical simulations of pedestrian flow

Advances in FEFLO

This paper summarizes the major improvements and developments that have taken place during the last year for FEFLO, a general-purpose CFD code based on adaptive, unstructured grids. All aspects of a comprehensive simulation pipeline: pre-processing, gridding, field solvers and post-processing saw important advances, and are treated. The advent of machines with millions of cores focused a lot of the developments on distributed memory aspects of field solvers and multiphysics modules. Parallel grid generation, particles and flow, parallel interpolation, parallel domain splitting and repartitioning for multiphysics were all considered. Furthermore, timings on Xeon and AMD chips led to the realization that memory transfers play a considerable role as compared to floating point operations, something previous chip generations did not exhibit. This led to a thorough analysis of numerical algorithms with subsequent re-writing. This in-depth analysis determined that at present achievable speeds are limited by the communication between processors (MPI). Even as the number of cores/domains can increase to several hundred thousand, due to communication overheads the wall clock time it takes to update a flowfield is bounded. We expect that as more users get access to hundreds of thousands of cores and the domain size per core starts shrinking, they will also encounter this 'minimum timestep barrier'

The simulation of dust effects from fragmenting charges

Purpose - The purpose of this paper is to determine the reason for the discrepancy in estimated and observed damage caused by fragmenting charges in closed environments. Design/methodology/approach - A series of carefully conducted physical and numerical experiments was conducted. The results were analyzed and compared. Findings - The analysis shows that for fragmenting charges in closed environments, dust plays a far larger role than previously thought, leading to much lower pressures and damage. Research limitations/implications - In light of these findings, many assumptions and results for fragmenting charges in closed environments need to be reconsidered. Practical implications - This implies that for a far larger class of problems than previously estimated it is imperative to take into consideration dust production and its effect on the resulting pressures. Originality/value - This is the first time such a finding has been reported in this context.   &nbsp