A Test Case for Checking Computational Methods for Gas Flows with Discontinuities

1978 ◽  
pp. 100-114 ◽  
Author(s):  
V. V. Rusanov
Keyword(s):  
Computational Methods ◽  
Test Case ◽  
Gas Flows

scholarly journals Computational Methods for Calculating Multimodal Multiclass Traffic Network Equilibrium: Simulation Benchmark on a Large-Scale Test Case

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Mostafa Ameli ◽  
Jean-Patrick Lebacque ◽  
Ludovic Leclercq
Keyword(s):  
Computational Methods ◽  
Large Scale ◽  
Dynamic Traffic Assignment ◽  
Dynamic Network ◽  
Computation Time ◽  
Test Case ◽  
Network Equilibrium ◽  
Loading Mode ◽  
Network Loading ◽  
Metaheuristic Methods

This study reviews existing computational methods to calculate simulation-based dynamic network equilibrium. We consider a trip-based multimodal approach for the dynamic network loading. Mode and path choices are carried out at the same level; therefore, travel times depend on the travel path and the mode attributes of travelers. This study develops a multiclass model with several parameters per class. Two different categories of algorithms (heuristic and metaheuristic) are considered in order to solve the discrete dynamic traffic assignment (DTA) problem. Finally, we analyze the equilibrium in a large-scale multimodal DTA test case (Lyon 6th + Villeurbanne) in order to investigate the performance of different optimization approaches to solve trip-based DTA. The results show that, in a multimodal and heterogeneous setting, the metaheuristic methods provide better solutions than the heuristic methods in terms of optimality and computation time. These improvements are even more significant than in a homogeneous setting.

scholarly journals On the modelling of isothermal gas flows at the microscale

2008 ◽  
Vol 604 ◽  
pp. 235-261 ◽  
Author(s):  
DUNCAN A. LOCKERBY ◽  
JASON M. REESE
Keyword(s):  
Boundary Conditions ◽  
Constitutive Relations ◽  
Navier Stokes ◽  
Test Case ◽  
Gas Flows ◽  
Hydrodynamic Models ◽  
Slip Boundary ◽  
Knudsen Numbers ◽  
Isothermal Gas ◽  
Non Equilibrium

This paper makes two new propositions regarding the modelling of rarefied (non-equilibrium) isothermal gas flows at the microscale. The first is a new test case for benchmarking high-order, or extended, hydrodynamic models for these flows. This standing time-varying shear-wave problem does not require boundary conditions to be specified at a solid surface, so is useful for assessing whether fluid models can capture rarefaction effects in the bulk flow. We assess a number of different proposed extended hydrodynamic models, and we find the R13 equations perform the best in this case.Our second proposition is a simple technique for introducing non-equilibrium effects caused by the presence of solid surfaces into the computational fluid dynamics framework. By combining a new model for slip boundary conditions with a near-wall scaling of the Navier--Stokes constitutive relations, we obtain a model that is much more accurate at higher Knudsen numbers than the conventional second-order slip model. We show that this provides good results for combined Couette/Poiseuille flow, and that the model can predict the stress/strain-rate inversion that is evident from molecular simulations. The model's generality to non-planar geometries is demonstrated by examining low-speed flow around a micro-sphere. It shows a marked improvement over conventional predictions of the drag on the sphere, although there are some questions regarding its stability at the highest Knudsen numbers.

scholarly journals Multi-Objective Hydrodynamic Optimization of the DTMB 5415 for Resistance and Seakeeping

2015 ◽  
Author(s):  
Matteo Diez ◽  
Andrea Serani ◽  
Emilio F. Campana ◽  
Omer Goren ◽  
Kadir Sarioz ◽  
...  
Keyword(s):  
Computational Methods ◽  
Task Group ◽  
Test Case ◽  
Multi Objective Optimization ◽  
Hull Form ◽  
Multi Objective ◽  
Average Improvement ◽  
Hull Forms ◽  
Hydrodynamic Optimization

The paper presents recent research conducted within the NATO RTO Task Group AVT-204 “Assess the Ability to Optimize Hull Forms of Sea Vehicles for Best Performance in a Sea Environment.” The objective is the improvement of the hydrodynamic performances (resistance/powering requirements, seakeeping, etc.) of naval vessels, by integration of computational methods used to generate, evaluate, and optimize hull-form variants. Several optimization approaches are brought together and compared. A multi-objective optimization of the DTMB 5415 (specifically the MARIN variant 5415M) is used as a test case and results obtained so far using low-fidelity solvers show an average improvement for resistance and seakeeping performances of nearly 10 and 9%, respectively.

Multiscale Simulation of Internal Rarefied Gas Flows

2013 ◽  
Author(s):  
Duncan A. Lockerby ◽  
Alexander Patronis ◽  
Matthew K. Borg ◽  
Jason M. Reese
Keyword(s):  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Internal Flow ◽  
Multiscale Simulation ◽  
Full Scale ◽  
Test Case ◽  
Gas Flows ◽  
Computationally Efficient ◽  
Rarefied Gas Flows ◽  
Diverging Channel

This paper describes the development and application of a multiscale method for the efficient simulation of a large class of low-speed internal rarefied gas flows. The method is an extension of the hybrid atomistic-continuum approach recently proposed by Borg et al (2013) [J. Comp. Phys., 233, pp 400–413] for the simulation of micro/nano flows of high-aspect ratio. The extension is twofold: 1) a modification to accommodate fluid compressibility; and 2) implementation using a direct simulation Monte Carlo (DSMC) method for the treatment of dilute rarefied gas flows. The method is applied to a pair of internal-flow configurations: flow through a converging-diverging channel and eccentric cylindrical Couette flow. For validation/verification purposes, the multiscale simulation results are compared to those obtained from a full-scale DSMC simulation: very close agreement is obtained in all cases. The multiscale simulation is an order of magnitude more computationally efficient than the full-scale DSMC for the first test case, and two orders of magnitude more efficient for the second case.

In Situ Observation of Catalyzed Gasification of Graphite by Nickel

1981 ◽  
Vol 39 ◽  
pp. 76-77
Author(s):  
R. T. K. Baker ◽  
R. D. Sherwood
Keyword(s):  
Objective Lens ◽  
In Situ Observation ◽  
Gas Flows ◽  
Catalytic Gasification ◽  
Television Camera ◽  
Viewing Screen ◽  
Fuels And Chemicals ◽  
Gasification Of Carbon ◽  
Transmission Microscope

The catalytic gasification of carbon at high temperature by microscopic size metal particles is of fundamental importance to removal of coke deposits and conversion of refractory hydrocarbons into fuels and chemicals. The reaction of metal/carbon/gas systems can be observed by controlled atmosphere electron microscopy (CAEM) in an 100 KV conventional transmission microscope. In the JEOL gas reaction stage model AGl (Fig. 1) the specimen is positioned over a hole, 200μm diameter, in a platinum heater strip, and is interposed between two apertures, 75μm diameter. The control gas flows across the specimen and exits through these apertures into the specimen chamber. The gas is further confined by two apertures, one in the condenser and one in the objective lens pole pieces, and removed by an auxiliary vacuum pump. The reaction zone is <1 mm thick and is maintained at gas pressure up to 400 Torr and temperature up to 1300<C as measured by a Pt-Pt/Rh 13% thermocouple. Reaction events are observed and recorded on videotape by using a Philips phosphor-television camera located below a hole in the center of the viewing screen. The overall resolution is greater than 2.5 nm.

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