809 The effect of the size of the computational domain in the external stream

In order to determine the possibility of using the method of mathematical modeling for making long-term forecasts of channel deformations of trunk line underwater crossing (TLUC) through water obstacles, a methodology for performing and analyzing the results of mathematical modeling of channel deformations in the TLUC zone across the Kuban River is considered. Within the framework of the work, the following tasks were solved: 1) the format and composition of the initial data necessary for mathematical modeling were determined; 2) the procedure for assigning the boundaries of the computational domain of the model was considered, the computational domain was broken down into the computational grid, the zoning of the computational domain was performed by the value of the roughness coefficient; 3) the analysis of the results of modeling the water flow was carried out without taking the bottom deformations into account, as well as modeling the bottom deformations, the specifics of the verification and calibration calculations were determined to build a reliable mathematical model; 4) considered the possibility of using the method of mathematical modeling to check the stability of the bottom in the area of TLUC in the presence of man-made dumping or protective structure. It has been established that modeling the flow hydraulics and structure of currents, making short-term forecasts of local high-altitude reshaping of the bottom, determining the tendencies of erosion and accumulation of sediments upstream and downstream of protective structures are applicable for predicting channel deformations in the zone of the TLUC. In all these cases, it is mandatory to have materials from engineering-hydro-meteorological and engineering-geological surveys in an amount sufficient to compile a reliable mathematical model.

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Downscaled Finite Element Modeling of Metal Targets for Surface Roughness Level under Pulsed Laser Irradiation

Applied Sciences ◽

10.3390/app11031253 ◽

2021 ◽

Vol 11 (3) ◽

pp. 1253

Author(s):

Evaggelos Kaselouris ◽

Kyriaki Kosma ◽

Yannis Orphanos ◽

Alexandros Skoulakis ◽

Ioannis Fitilis ◽

...

Keyword(s):

Surface Roughness ◽

Finite Element ◽

Surface Acoustic Waves ◽

Pulsed Laser ◽

Multiscale Simulation ◽

Experimental Methodology ◽

Computational Domain ◽

Area Of Interest ◽

Depth Analysis ◽

Laser Solid Interactions

A three-dimensional, thermal-structural finite element model, originally developed for the study of laser–solid interactions and the generation and propagation of surface acoustic waves in the macroscopic level, was downscaled for the investigation of the surface roughness influence on pulsed laser–solid interactions. The dimensions of the computational domain were reduced to include the laser-heated area of interest. The initially flat surface was progressively downscaled to model the spatial roughness profile characteristics with increasing geometrical accuracy. Since we focused on the plastic and melting regimes, where structural changes occur in the submicrometer scale, the proposed downscaling approach allowed for their accurate positioning. Additionally, the multiscale simulation results were discussed in relation to experimental findings based on white light interferometry. The combination of this multiscale modeling approach with the experimental methodology presented in this study provides a multilevel scientific tool for an in-depth analysis of the influence of heat parameters on the surface roughness of solid materials and can be further extended to various laser–solid interaction applications.

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Effect of the Preheated Oxidizer Temperature on Soot Formation and Flame Structure in Turbulent Methane-Air Diffusion Flames at 1 and 3 atm: A CFD Investigation

Energies ◽

10.3390/en14123671 ◽

2021 ◽

Vol 14 (12) ◽

pp. 3671

Author(s):

Subrat Garnayak ◽

Subhankar Mohapatra ◽

Sukanta K. Dash ◽

Bok Jik Lee ◽

V. Mahendra Reddy

Keyword(s):

Mole Fraction ◽

Air Temperature ◽

Reaction Rate ◽

Volume Fraction ◽

Diffusion Flames ◽

Soot Formation ◽

Flame Structure ◽

Soot Volume Fraction ◽

Computational Domain ◽

Pressure Elevation

This article presents the results of computations on pilot-based turbulent methane/air co-flow diffusion flames under the influence of the preheated oxidizer temperature ranging from 293 to 723 K at two operating pressures of 1 and 3 atm. The focus is on investigating the soot formation and flame structure under the influence of both the preheated air and combustor pressure. The computations were conducted in a 2D axisymmetric computational domain by solving the Favre averaged governing equation using the finite volume-based CFD code Ansys Fluent 19.2. A steady laminar flamelet model in combination with GRI Mech 3.0 was considered for combustion modeling. A semi-empirical acetylene-based soot model proposed by Brookes and Moss was adopted to predict soot. A careful validation was initially carried out with the measurements by Brookes and Moss at 1 and 3 atm with the temperature of both fuel and air at 290 K before carrying out further simulation using preheated air. The results by the present computation demonstrated that the flame peak temperature increased with air temperature for both 1 and 3 atm, while it reduced with pressure elevation. The OH mole fraction, signifying reaction rate, increased with a rise in the oxidizer temperature at the two operating pressures of 1 and 3 atm. However, a reduced value of OH mole fraction was observed at 3 atm when compared with 1 atm. The soot volume fraction increased with air temperature as well as pressure. The reaction rate by soot surface growth, soot mass-nucleation, and soot-oxidation rate increased with an increase in both air temperature and pressure. Finally, the fuel consumption rate showed a decreasing trend with air temperature and an increasing trend with pressure elevation.

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Fully Coupled Large Eddy Simulation of Conjugate Heat Transfer in a Ribbed Channel with a 0.1 Blockage Ratio

Energies ◽

10.3390/en14082096 ◽

2021 ◽

Vol 14 (8) ◽

pp. 2096

Author(s):

Joon Ahn ◽

Jeong Chul Song ◽

Joon Sik Lee

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Conjugate Heat Transfer ◽

Heat Transfer Analysis ◽

Scale Model ◽

Computational Domain ◽

Blockage Ratio ◽

Ribbed Channel ◽

Large Eddy ◽

Cooling Passage

Large eddy simulations are performed to analyze the conjugate heat transfer of turbulent flow in a ribbed channel with a heat-conducting solid wall. An immersed boundary method (IBM) is used to determine the effect of heat transfer in the solid region on that in the fluid region in a unitary computational domain. To satisfy the continuity of the heat flux at the solid–fluid interface, effective conductivity is introduced. By applying the IBM, it is possible to fully couple the convection on the fluid side and the conduction inside the solid and use a dynamic subgrid scale model in a Cartesian grid. The blockage ratio (e/H) is set at 0.1, which is typical for gas turbine blades. Through conjugate heat transfer analysis, it is confirmed that the heat transfer peak in front of the rib occurs because of the impinging of the reattached flow and not the influence of the thermal boundary condition. When the rib turbulator acts as a fin, its efficiency and effectiveness are predicted to be 98.9% and 8.32, respectively. When considering conjugate heat transfer, the total heat transfer rate is reduced by 3% compared with that of the isothermal wall. The typical Biot number at the internal cooling passage of a gas turbine is <0.1, and the use of the rib height as the characteristic length better represents the heat transfer of the rib.

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An Online Generalized Multiscale Finite Element Method for Unsaturated Filtration Problem in Fractured Media

Mathematics ◽

10.3390/math9121382 ◽

2021 ◽

Vol 9 (12) ◽

pp. 1382

Author(s):

Denis Spiridonov ◽

Maria Vasilyeva ◽

Aleksei Tyrylgin ◽

Eric T. Chung

Keyword(s):

Finite Element Method ◽

Finite Element ◽

Model Reduction ◽

Basis Functions ◽

Computational Domain ◽

Filtration Problem ◽

Spectral Problems ◽

Multiscale Finite Element Method ◽

Multiscale Finite Element ◽

Element Method

In this paper, we present a multiscale model reduction technique for unsaturated filtration problem in fractured porous media using an Online Generalized Multiscale finite element method. The flow problem in unsaturated soils is described by the Richards equation. To approximate fractures we use the Discrete Fracture Model (DFM). Complex geometric features of the computational domain requires the construction of a fine grid that explicitly resolves the heterogeneities such as fractures. This approach leads to systems with a large number of unknowns, which require large computational costs. In order to develop a more efficient numerical scheme, we propose a model reduction procedure based on the Generalized Multiscale Finite element method (GMsFEM). The GMsFEM allows solving such problems on a very coarse grid using basis functions that can capture heterogeneities. In the GMsFEM, there are offline and online stages. In the offline stage, we construct snapshot spaces and solve local spectral problems to obtain multiscale basis functions. These spectral problems are defined in the snapshot space in each local domain. To improve the accuracy of the method, we add online basis functions in the online stage. The construction of the online basis functions is based on the local residuals. The use of online bases will allow us to get a significant improvement in the accuracy of the method. We present results with different number of offline and online multisacle basis functions. We compare all results with reference solution. Our results show that the proposed method is able to achieve high accuracy with a small computational cost.

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Design of Road-Side Barriers to Mitigate Air Pollution near Roads

Applied Sciences ◽

10.3390/app11052391 ◽

2021 ◽

Vol 11 (5) ◽

pp. 2391

Author(s):

Jose I. Huertas ◽

Javier E. Aguirre ◽

Omar D. Lopez Mejia ◽

Cristian H. Lopez

Keyword(s):

Fluid Dynamics ◽

Air Pollution ◽

Computational Fluid Dynamics ◽

Sulfur Hexafluoride ◽

Computational Domain ◽

Cfd Model ◽

Near Surface ◽

The Road ◽

Pollutant Concentrations ◽

Highly Correlated

The effects of using solid barriers on the dispersion of air pollutants emitted from the traffic of vehicles on roads located over flat areas were quantified, aiming to identify the geometry that maximizes the mitigation effect of air pollution near the road at the lowest barrier cost. Toward that end, a near road Computational Fluid Dynamics (NR-CFD) model that simulates the dispersion phenomena occurring in the near-surface atmosphere (<250 m high) in a small computational domain (<1 km long), via Computational Fluid Dynamics (CFD) was used. Results from the NR-CFD model were highly correlated (R2 > 0.96) with the sulfur hexafluoride (SF6) concentrations measured by the US-National Oceanic and Atmospheric Administration (US-NOAA) in 2008 downwind a line source emission, for the case of a 6m near road solid straight barrier and for the case without any barrier. Then, the effects of different geometries, sizes, and locations were considered. Results showed that, under all barrier configurations, the normalized pollutant concentrations downwind the barrier are highly correlated (R2 > 0.86) to the concentrations observed without barrier. The best cost-effective configuration was observed with a quarter-ellipse barrier geometry with a height equivalent to 15% of the road width and located at the road edge, where the pollutant concentrations were 76% lower than the ones observed without any barrier.

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Data-Informed Decomposition for Localized Uncertainty Quantification of Dynamical Systems

Vibration ◽

10.3390/vibration4010004 ◽

2020 ◽

Vol 4 (1) ◽

pp. 49-63

Author(s):

Waad Subber ◽

Sayan Ghosh ◽

Piyush Pandita ◽

Yiming Zhang ◽

Liping Wang

Keyword(s):

Dynamical Systems ◽

Computational Cost ◽

Three Dimensional ◽

Region Of Interest ◽

System Response ◽

Computational Domain ◽

User Interest ◽

Numerical Resolution ◽

Multi Scale ◽

Operation Conditions

Industrial dynamical systems often exhibit multi-scale responses due to material heterogeneity and complex operation conditions. The smallest length-scale of the systems dynamics controls the numerical resolution required to resolve the embedded physics. In practice however, high numerical resolution is only required in a confined region of the domain where fast dynamics or localized material variability is exhibited, whereas a coarser discretization can be sufficient in the rest majority of the domain. Partitioning the complex dynamical system into smaller easier-to-solve problems based on the localized dynamics and material variability can reduce the overall computational cost. The region of interest can be specified based on the localized features of the solution, user interest, and correlation length of the material properties. For problems where a region of interest is not evident, Bayesian inference can provide a feasible solution. In this work, we employ a Bayesian framework to update the prior knowledge of the localized region of interest using measurements of the system response. Once, the region of interest is identified, the localized uncertainty is propagate forward through the computational domain. We demonstrate our framework using numerical experiments on a three-dimensional elastodynamic problem.

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Optimising the computational domain size in CFD simulations of tall buildings

Heliyon ◽

10.1016/j.heliyon.2021.e06723 ◽

2021 ◽

Vol 7 (4) ◽

pp. e06723

Author(s):

Yousef Abu-Zidan ◽

Priyan Mendis ◽

Tharaka Gunawardena

Keyword(s):

Tall Buildings ◽

Domain Size ◽

Computational Domain ◽

Cfd Simulations

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Regional Downscaling of Copernicus ERA5 Wave Data for Coastal Engineering Activities and Operational Coastal Services

Water ◽

10.3390/w13060859 ◽

2021 ◽

Vol 13 (6) ◽

pp. 859

Author(s):

Giorgio Bellotti ◽

Leopoldo Franco ◽

Claudia Cecioni

Keyword(s):

Time Series ◽

National Level ◽

Wave Model ◽

Wave Climate ◽

Tyrrhenian Sea ◽

Computational Domain ◽

Multiple Wave ◽

Space Resolution ◽

Wave Data ◽

Fundamental Information

Hindcasted wind and wave data, available on a coarse resolution global grid (Copernicus ERA5 dataset), are downscaled by means of the numerical model SWAN (simulating waves in the nearshore) to produce time series of wave conditions at a high resolution along the Italian coasts in the central Tyrrhenian Sea. In order to achieve the proper spatial resolution along the coast, the finite element version of the model is used. Wave data time series at the ERA5 grid are used to specify boundary conditions for the wave model at the offshore sides of the computational domain. The wind field is fed to the model to account for local wave generation. The modeled sea states are compared against the multiple wave records available in the area, in order to calibrate and validate the model. The model results are in quite good agreement with direct measurements, both in terms of wave climate and wave extremes. The results show that using the present modeling chain, it is possible to build a reliable nearshore wave parameters database with high space resolution. Such a database, once prepared for coastal areas, possibly at the national level, can be of high value for many engineering activities related to coastal area management, and can be useful to provide fundamental information for the development of operational coastal services.

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Dynamical Downscaling of ERA5 Data on the North-Western Mediterranean Sea: From Atmosphere to High-Resolution Coastal Wave Climate

Journal of Marine Science and Engineering ◽

10.3390/jmse9020208 ◽

2021 ◽

Vol 9 (2) ◽

pp. 208

Author(s):

Valentina Vannucchi ◽

Stefano Taddei ◽

Valerio Capecchi ◽

Michele Bendoni ◽

Carlo Brandini

Keyword(s):

Mediterranean Sea ◽

Wind Wave ◽

Dynamical Downscaling ◽

Wave Climate ◽

Western Mediterranean ◽

Limited Area ◽

Computational Domain ◽

Wave Hindcast ◽

The North ◽

Western Mediterranean Sea

A 29-year wind/wave hindcast is produced over the Mediterranean Sea for the period 1990–2018. The dataset is obtained by downscaling the ERA5 global atmospheric reanalyses, which provide the initial and boundary conditions for a numerical chain based on limited-area weather and wave models: the BOLAM, MOLOCH and WaveWatch III (WW3) models. In the WW3 computational domain, an unstructured mesh is used. The variable resolutions reach up to 500 m along the coasts of the Ligurian and Tyrrhenian seas (Italy), the main objects of the study. The wind/wave hindcast is validated using observations from coastal weather stations and buoys. The wind validation provides velocity correlations between 0.45 and 0.76, while significant wave height correlations are much higher—between 0.89 and 0.96. The results are also compared to the original low-resolution ERA5 dataset, based on assimilated models. The comparison shows that the downscaling improves the hindcast reliability, particularly in the coastal regions, and especially with regard to wind and wave directions.

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