When technology fails during simulation: Time for reflection?

2021 ◽  
Author(s):  
Catriona Neil ◽  
Daniel Slack ◽  
Jean Ker ◽  
Catherine Paton
Keyword(s):  
Simulation Time

Reduction of FDTD Simulation Time with Modal Methods

PIERS Online ◽  
2006 ◽  
Vol 2 (5) ◽  
pp. 510-513 ◽  
Author(s):  
Dmitry A. Gorodetsky ◽  
Philip A. Wilsey
Keyword(s):  
Fdtd Simulation ◽  
Simulation Time

scholarly journals Alternative Method to the Replication of Wind Effects into the Buildings Thermal Simulation

Buildings ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 237
Author(s):  
Aiman Albatayneh ◽  
Dariusz Alterman ◽  
Adrian Page ◽  
Behdad Moghtaderi
Keyword(s):  
Air Temperature ◽  
High Performance ◽  
Real Data ◽  
Wind Effect ◽  
Wind Effects ◽  
Energy Assessment ◽  
Wind Simulation ◽  
Brick Veneer ◽  
Equal Capacity ◽  
Simulation Time

To design energy-efficient buildings, energy assessment programs need to be developed for determining the inside air temperature, so that thermal comfort of the occupant can be sustained. The internal temperatures could be calculated through computational fluid dynamics (CFD) analysis; however, miniscule time steps (seconds and milliseconds) are used by a long-term simulation (i.e., weeks, months) that require excessive time for computing wind effects results even for high-performance personal computers. This paper examines a new method, wherein the wind effect surrounding the buildings is integrated with the external air temperature to facilitate wind simulation in building analysis over long periods. This was done with the help of an equivalent temperature (known as Tnatural), where the convection heat loss is produced in an equal capacity by this air temperature and by the built-in wind effects. Subsequently, this new external air temperature Tnatural can be used to calculate the internal air temperature. Upon inclusion of wind effects, above 90% of the results were found to be within 0–3 °C of the perceived temperatures compared to the real data (99% for insulated cavity brick (InsCB), 91% for cavity brick (CB), 93% for insulated reverse brick veneer (InsRBV) and 94% for insulated brick veneer (InsBV) modules). However, a decline of 83–88% was observed in the results after ignoring the wind effects. Hence, the presence of wind effects holds greater importance in correct simulation of the thermal performance of the modules. Moreover, the simulation time will expectedly reduce to below 1% of the original simulation time.

scholarly journals A Review on Combination of Ab Initio Molecular Dynamics and NMR Parameters Calculations

2021 ◽  
Vol 22 (9) ◽  
pp. 4378
Author(s):  
Anna Helena Mazurek ◽  
Łukasz Szeleszczuk ◽  
Dariusz Maciej Pisklak
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Small Amplitude ◽  
Ab Initio Molecular Dynamics ◽  
Quantum Mechanical ◽  
Time Step ◽  
Noticeable Effect ◽  
Nmr Parameters ◽  
Mechanical Methods ◽  
Simulation Time

This review focuses on a combination of ab initio molecular dynamics (aiMD) and NMR parameters calculations using quantum mechanical methods. The advantages of such an approach in comparison to the commonly applied computations for the structures optimized at 0 K are presented. This article was designed as a convenient overview of the applied parameters such as the aiMD type, DFT functional, time step, or total simulation time, as well as examples of previously studied systems. From the analysis of the published works describing the applications of such combinations, it was concluded that including fast, small-amplitude motions through aiMD has a noticeable effect on the accuracy of NMR parameters calculations.

scholarly journals Hydrogen Inter-Cage Hopping and Cage Occupancies inside Hydrogen Hydrate: Molecular-Dynamics Analysis

2020 ◽  
Vol 11 (1) ◽  
pp. 282
Author(s):  
Yogeshwaran Krishnan ◽  
Mohammad Reza Ghaani ◽  
Arnaud Desmedt ◽  
Niall J. English
Keyword(s):  
Molecular Dynamics ◽  
Energy Barrier ◽  
Guest Molecule ◽  
Arrhenius Equation ◽  
Dynamics Simulation ◽  
Type Ii ◽  
Large Cage ◽  
Guest Molecules ◽  
Simulation Time ◽  
Average Occupancy

The inter-cage hopping in a type II clathrate hydrate with different numbers of H2 and D2 molecules, from 1 to 4 molecules per large cage, was studied using a classical molecular dynamics simulation at temperatures of 80 to 240 K. We present the results for the diffusion of these guest molecules (H2 or D2) at all of the different occupations and temperatures, and we also calculated the activation energy as the energy barrier for the diffusion using the Arrhenius equation. The average occupancy number over the simulation time showed that the structures with double and triple large-cage H2 occupancy appeared to be the most stable, while the small cages remained with only one guest molecule. A Markov model was also calculated based on the number of transitions between the different cage types.

Numerical Simulation and Analysis of Compartment Fire in Subway Train

2012 ◽  
Vol 166-169 ◽  
pp. 2726-2730
Author(s):  
Bo Si Zhang ◽  
Shou Xiang Lu
Keyword(s):  
Numerical Simulation ◽  
Transport System ◽  
Fire Safety ◽  
Urban Transport ◽  
The Other ◽  
Compartment Fire ◽  
Fire Simulation ◽  
Subway Train ◽  
Simulation Time

Subway plays an important role in urban transport system. Fire as the major risk of the subway, is gaining increasing concern. In this study, fire simulation is performed to estimate fire safety of different compartments of the subway train. Result shows that the two compartments in the middle become dangerous at 150s and the compartments in the two ends are not safe at 300s approximately. The other two compartments are always safe during the simulation time.

Optimization of RANS Solver Simulation Setup for Propeller Open Water Performance Prediction

2015 ◽  
Author(s):  
Mohammed Islam ◽  
Fatima Jahra ◽  
Michael Doucet
Keyword(s):  
Domain Size ◽  
Open Water ◽  
Fractional Factorial ◽  
Navier Stokes ◽  
Calm Water ◽  
Simulation Results ◽  
Open Water Performance ◽  
Thrust And Torque ◽  
Simulation Time ◽  
Fixed Pitch

Mesh and domain optimization strategies for a RANS solver to accurately estimate the open water propulsive characteristics of fixed pitch propellers are proposed based on examining the effect of different mesh and computation domain parameters. The optimized mesh and domain size parameters were selected using Design of Experiments (DoE) methods enabling simulations to be carried out in a limited memory environment, and in a timely manner; without compromising the accuracy of results. A Reynolds-Averaged Navier Stokes solver is used to predict the propulsive performance of a fixed pitch propeller. The predicted thrust and torque for the propeller were compared to the corresponding measurements. A total of six meshing parameters were selected that could affect the computational results of propeller open water performance. A two-level fractional factorial design was used to screen out parameters that do not significantly contribute to explaining the dependent parameters: namely simulation time, propeller thrust and propeller torque. A total of 32 simulations were carried out only to find out that the selected six meshing parameters were significant in defining the response parameters. Optimum values of each of the input parameters were obtained for the DOE technique and additional simulations were run with those parameters. The simulation results were validated using open water experimental results of the same propeller. It was found that with the optimized meshing arrangement, the propeller opens simulation time was reduced by at least a factor of 6 as compared to the generally popular meshing arrangement. Also, the accuracy of propulsive characteristics was improved by up to 50% as compared to published simulation results. The methodologies presented in this paper can be similarly applied to other simulations such as calm water ship resistance, ship propulsion to systematically derive the optimized meshing arrangement for simulations with minimal simulation time and maximum accuracy. This investigation was carried out using STAR-CCM+, a commercial CFD package; however the findings can be applied to any RANS solver.

Simulation of blast waves with tailored explosive charges

1985 ◽  
Vol 158 ◽  
pp. 137-152
Author(s):  
M. Sanai ◽  
H. E. Lindberg ◽  
J. D. Colton
Keyword(s):  
Shock Tube ◽  
Charge Density ◽  
Cost Effective ◽  
Development Programme ◽  
Blast Waves ◽  
Charge Density Distribution ◽  
Test Conditions ◽  
Order Of Magnitude ◽  
Explosive Charges ◽  
Simulation Time

We have developed a compact and cost-effective shock tube to simulate the static and dynamic pressures of blast waves. The shock tube is open at both ends and is driven by high explosives distributed over a finite length of the tube near one end. The overall charge length is determined by the simulation time of interest, and the charge-density distribution is tailored to produce the pressure-waveform shape desired. For the shock tube to simulate a typical blast wave, the charge density must be highest at the charge front (closest to the test section) and gradually reduced towards the back. The resulting shock tube is an order of magnitude shorter than a conventional dynamic airblast simulator (DABS) in which concentrated explosives are used to drive the shock.Tailored charges designed using this method were built and tested in a simulation development programme sponsored by the U.S. Defense Nuclear Agency (DNA). The pressures measured for several charge distributions agreed very well with SRI's PUFF hydrocode computations and demonstrated the feasibility of the compact simulator under realistic test conditions.

LES and RANS Assessment of Rib Cooled Channel Related to SGT-800 Combustor Liner

2011 ◽  
Author(s):  
Daniel Lo¨rstad
Keyword(s):  
Pressure Drop ◽  
Cooling System ◽  
Large Temperature ◽  
Internal Cooling ◽  
Low Frequencies ◽  
System Pressure ◽  
Model Size ◽  
Periodic Boundaries ◽  
Combustor Liner ◽  
Simulation Time

The main parts of the annular combustor liner walls of the Siemens gas turbine SGT-800 are convectively cooled using rib turbulated cooling. Due to the serial system of cooling and combustion air there is a potential of further reduction of total combustor pressure drop by improvements of the cooling system. Apart from the rib cooling, also the cooling channel bypass entrance is related to a significant part of the total cooling system pressure drop. In this study, an investigation is performed for a rib cooled channel which is related to the considered combustor liner and where empirical correlations are available in order to evaluate the methodology used. The study includes an assessment of the Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) models available within commercial Computational Fluid Dynamics (CFD) codes and includes also an investigation of model size when using periodic boundaries for LES simulations. It is well known that a small geometrical distance in the direction of the periodic boundaries may have a strong effect on the flow field but is often neglected in practice in order to speed up LES calculations. Here the effect is assessed in order to show what size is required for accurate results, both for time averaged and transient results. In addition too small domains may be affected by spurious low frequencies originating from the periodic boundaries requiring additional simulation time for time converged statistics, but also the averages may be significantly affected. In addition the simulation period for time converged statistics is evaluated in order to show that larger model size in the periodic direction does not necessarily require longer practical simulation time, due to the fact that larger volumes may be used for the combined time and space averaging. The aim is to obtain practical guidelines for LES calculations for internal cooling flows. Then the study is extended step by step to investigate the importance due to high Reynolds number, variable fluid properties and large temperature gradients in order to cover the ranges and specifics required for SGT-800 engine conditions.

scholarly journals Optimal Design and Simulation Analysis of Spike Tooth Threshing Component Based on DEM

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1163
Author(s):  
Yajun Yu ◽  
Liangshan Li ◽  
Jiale Zhao ◽  
Xiangeng Wang ◽  
Jun Fu
Keyword(s):  
Optimal Design ◽  
Simulation Analysis ◽  
Process Analysis ◽  
Structural Parameters ◽  
Compressive Force ◽  
Microscopic Analysis ◽  
Analysis Software ◽  
Damage Rate ◽  
Tooth Type ◽  
Simulation Time

This paper takes a local drum-type corn thresher as an example. In order to make the threshing principle transform to the plate-tooth type, the width of the spike-tooth threshing component is increased gradually, and three threshing components of different shape and size are selected as the research objects. Based on the preliminary experimental research, the corn threshing process is simulation analyzed using the self-developed corn threshing process analysis software. The effects of the width of the threshing component on the corn ears threshing rate and kernel damage rate under different rates of drum rotation were studied from a macroscopic perspective. The results show that with the increase of drum rotation rate, both the corn ear threshing rate and kernel damage rate increase; with the increase of threshing component width, the threshing rate increases and the damage rate decreases; and when the component width is too large, the stacking between adjacent components has an impact on the threshing performance. The effects of threshing component width on the amount of kernel threshing and the total compressive force during the simulation time were investigated from microscopic perspective at different rates of drum rotation, and the results show that the microscopic analysis is consistent with the macroscopic analysis. Therefore, the optimization of the structural parameters and operating parameters of the threshing component was achieved. When the width of the threshing component was 25 mm and the roller speed was 187.50 rpm, the threshing performance was optimal, with a 98.04% corn ears threshing rate and a 2.56% kernel damage rate. This paper verifies the practical applicability of the corn threshing process analysis software and provides a reference for the optimal design of threshing devices.

Hormones Nanofiltration in Carbon Nanotubes and Boron Nitride Nanotubes Using Uniform External Electric Field Through Molecular Dynamics

2021 ◽  
Vol 21 (11) ◽  
pp. 5499-5509
Author(s):  
Rosely Maria dos Santos Cavaleiro ◽  
Tiago da Silva Arouche ◽  
Phelipe Seiichi Martins Tanoue ◽  
Tais Souza Sá Pereira ◽  
Raul Nunes de Carvalho Junior ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Molecular Dynamics ◽  
Boron Nitride ◽  
Electric Field ◽  
Field Potential ◽  
Boron Nitride Nanotubes ◽  
Attractive Potential ◽  
Water Molecules ◽  
Computer Simulation Study ◽  
Simulation Time

Hormones are a dangerous group of molecules that can cause harm to humans. This study based on classical molecular dynamics proposes the nanofiltration of wastewater contaminated by hormones from a computer simulation study, in which the water and the hormone were filtered in two single-walled nanotube compositions. The calculations were carried out by changing the intensities of the electric field that acted as a force exerting pressure on the filtration along the nanotube, in the simulation time of 100 ps. The hormones studied were estrone, estradiol, estriol, progesterone, ethinylestradiol, diethylbestrol, and levonorgestrel in carbon nanotubes (CNTs) and boron nitride (BNNTs). The most efficient nanofiltrations were for fields with low intensities in the order of 10-8 au and 10-7 au. The studied nanotubes can be used in membranes for nanofiltration in water treatment plants due to the evanescent field potential caused by the action of the electric field inside. Our data showed that the action of EF in conjunction with the van der Walls forces of the nanotubes is sufficient to generate the attractive potential. Evaluating the transport of water molecules in CNTs and BNNTs, under the influence of the electric field, a sequence of simulations with the same boundary conditions was carried out, seeking to know the percentage of water molecules filtered in the nanotubes.

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