| 1. |
- Liefvendahl, Mattias, 1971, et al.
(författare)
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Wall-Modeled LES for Ship Hydrodynamics in Model Scale
- 2021
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Ingår i: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 65:1, s. 41-54
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Tidskriftsartikel (refereegranskat)abstract
- A complete approach for wall-modeled large-eddy simulation (WMLES) is demonstrated for the simulation of the flow around a bulk carrier in the model scale. Essential components of the method are an a-priori estimate of the thickness of the turbulent boundary layer (TBL) over the hull and to use an unstructured grid with the appropriate resolution relative to this thickness. Expressions from the literature for the scaling of the computational cost, in terms of the grid size, with Reynolds number, are adapted in this application. It is shown that WMLES is possible for model scale ship hydrodynamics, with similar to 10(8) grid cells, which is a gain of at least one order of magnitude as compared with wall-resolving LES. For the canonical case of a flat-plate TBL, the effects of wall model parameters and grid cell topology on the predictive accuracy of the method are investigated. For the flat-plate case, WMLES results are compared with results from direct numerical simulation, RANS (Reynolds-averaged Navier-Stokes), and semi-empirical formulas. For the bulk carrier flow, WMLES and RANS are compared, but further validation is needed to assess the predictive accuracy of the approach.
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| 2. |
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| 3. |
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| 4. |
- Bensow, Rickard, 1972, et al.
(författare)
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An acoustic analogy and scale-resolving flow simulation methodology for the prediction of propeller radiated noise
- 2016
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Ingår i: Symposium on Naval Hydrodynamics.
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Konferensbidrag (refereegranskat)abstract
- A methodology for the prediction of underwater radiated noise from ships is presented and applied to a configuration of a cavitating propeller, operating in behind condition. A scale resolved incompressible Large Eddy Simulation technique together with an acoustic analogy is em- ployed, with cavitation represented through a mixture assumption using a volume of fluid approach and explicit mass transfer modelling. The main configuration studied is the catamaran hull and propeller of a small research vessel in model scale. The hull and a complete geometrical model of the propeller is included, while the free surface is neglected in the simulation. Results of radiated noise from the complete configuration are presented and com- pared with experimental data. Further, as an intermediate step, the propeller alone on inclined shaft is studied for both cavitating and non-cavitating conditions.
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| 5. |
- Bensow, Rickard, 1972, et al.
(författare)
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Implicit and explicit subgrid modeling in LES applied to a marine propeller
- 2008
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Ingår i: 38th AIAA Fluid Dynamics Conference and Exhibit; Seattle, WA; United States; 23 June 2008 through 26 June 2008. - Reston, Virigina : American Institute of Aeronautics and Astronautics. - 9781563479427
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Konferensbidrag (refereegranskat)abstract
- The flow around a four-bladed marine propeller in homogeneous inflow and in non-cavitating conditions is investigated using Large Eddy Simulation, LES. Explicit, using a k-equation eddy viscosity model, and implicit subgrid modeling are compared for both the standard LES formulation as well as a mixed formulation containing the, so called, scale similarity term. A wall-modeled approach is used on a relatively coarse grid, containing 5.5 million cells, for the full propeller in order to mimic a future applied computation including the ship hull. The implicit modeling is of particular interest in cavitation simulation, where the interaction between an explicit subgrid model and the liquid-vapor interface may cause numerical and modeling problems. All simulations yield fairly similar results, although the implicit LES gives better prediction of the global performance of the propeller. The agreement with experimental data is good close to the propeller, but the simulated flow structures diffuses quickly at the present grid resolution.
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| 6. |
- Bensow, Rickard, 1972, et al.
(författare)
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Implicit and explicit subgrid modeling in LES applied to a marine propeller
- 2008
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Ingår i: 38th AIAA Fluid Dynamics Conference and Exhibit; Seattle, WA; United States; 23 June 2008 through 26 June 2008. - Reston, Virigina : American Institute of Aeronautics and Astronautics Inc.. - 9781563479427
-
Konferensbidrag (refereegranskat)abstract
- The flow around a four-bladed marine propeller in homogeneous inflow and in non-cavitating conditions is investigated using Large Eddy Simulation, LES. Explicit, using a k-equation eddy viscosity model, and implicit subgrid modeling are compared for both the standard LES formulation as well as a mixed formulation containing the, so called, scale similarity term. A wall-modeled approach is used on a relatively coarse grid, containing 5.5 million cells, for the full propeller in order to mimic a future applied computation including the ship hull. The implicit modeling is of particular interest in cavitation simulation, where the interaction between an explicit subgrid model and the liquid-vapor interface may cause numerical and modeling problems. All simulations yield fairly similar results, although the implicit LES gives better prediction of the global performance of the propeller. The agreement with experimental data is good close to the propeller, but the simulated flow structures diffuses quickly at the present grid resolution.
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| 7. |
- Bensow, Rickard, 1972, et al.
(författare)
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Large Eddy Simulation of Cavitating Propeller Flows
- 2008
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Ingår i: 27th Symposium on Naval Hydrodynamics.
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Konferensbidrag (refereegranskat)abstract
- This paper deals with the simulation of cavitating flowsbased on Large Eddy Simulation techniques, combinedwith a volume of fluid implementation to capture theinterface between liquid and vapor and a fairlysimplistic and ad hoc model for the mass transferbetween the phases. Two flows are considered: the firstis over a three dimensional hydrofoil, and the second is apropeller operating in an artificially generated wakefield. The cavitation over the hydrofoil displays a highlyunsteady flow including important cavitationmechanisms due to side-entrant and re-entrant jet, shearlayers and shed vorticity. Detailed experimental work isavailable, and partly revied in the paper, to validate thesimulations. The propeller cavitation displays, apartfrom internal jets, also the upstream desinence as theblade exits the wake flow. In both cases the simulationsgive qualitatively very promising results, reproducing allthe above mentioned mechanisms, although the cavityextent is slightly small. These results indicate that thetechniques used in this work, may, in a near future,make it possible to gain in understanding of theprocesses of erosive cavitation and even constitute apredictive tool for cavitation nuisance.
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| 8. |
- Bensow, Rickard, 1972, et al.
(författare)
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Large Eddy Simulations for Marine Flows
- 2007
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Ingår i: STG-Lectureday "CFD in Ship Design", Hamburg, Germany.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Bulik, M., et al.
(författare)
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Stochastic simulation for crashworthiness
- 2004
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Ingår i: Advances in Engineering Software. - : Elsevier Ltd. - 0965-9978 .- 1873-5339. ; 35:12, s. 791-803
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the M-Xplore extension of the Radioss software. The module contains facilities for the exploration of a parameterized finite element model design space. It supports facilities for interactive choice of variables and responses, definition of a sampling on a design space, automatic submission of the computations, and post-processing of the results. The computations are run automatically, either locally or in ASP-mode, i.e. as a client of a high-performance computing server. The software is described first in general, then we illustrate its exploration possibilities in terms of a model problem and a more typical application problem of crash simulation
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| 10. |
- Drikakis, D., et al.
(författare)
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Numerics for iles : Limiting algorithms
- 2007
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Large eddy simulation (LES) has emerged as the next-generation simulation tool for handling complex engineering, geophysical, astrophysical, and chemically reactive flows. As LES moves from being an academic tool to being a practical simulation strategy, the robustness of the LES solvers becomes a key issue to be concerned with, in conjunction with the classical and well-known issue of accuracy. For LES to be attractive for complex flows, the computational codes must be readily capable of handling complex geometries. Today, most LES codes use hexahedral elements; the grid-generation process is therefore cumbersome and time consuming. In the future, the use of unstructured grids, as used in Reynolds-averaged NavierâStokes (RANS) approaches, will also be necessary for LES. This will particularly challenge the development of high-order unstructured LES solvers. Because it does not require explicit filtering, Implicit LES (ILES) has some advantages over conventional LES; however, numerical requirements and issues are otherwise virtually the same for LES and ILES. In this chapterwe discuss an unstructured finite-volume methodology for both conventional LES and ILES, that is particularly suited for ILES. We believe that the next generation of practical computational fluid dynamics (CFD) models will involve structured and unstructured LES, using high-order flux-reconstruction algorithms and taking advantage of their built-in subgrid-scale (SGS) models. ILES based on functional reconstruction of the convective fluxes by use of high-resolution hybrid methods is the subject of this chapter. We use modified equation analysis (MEA) to show that the leading-order truncation error terms introduced by such methods provide implicit SGS models similar in form to those of conventional mixed SGS models.
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| 11. |
- Feymark, Andreas, 1984, et al.
(författare)
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Large Eddy Simulation of High Re Number Partially Separated Flow
- 2012
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Ingår i: 50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition. - Reston, Virigina : American Institute of Aeronautics and Astronautics. - 9781600869365
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Konferensbidrag (refereegranskat)abstract
- The predictive capability for Large Eddy Simulation (LES) for flows with unsteady separation at curved surfaces is investigated. LES with near wall modeling is applied and a range of subgrid models is evaluated for four different validation cases for which experimental flow measurement data is available. A novel model for the simulation of the effect of boundary layer tripping devices used in experiments is also proposed and evaluated. The validation focuses on the mean velocity distribution in the region of separation, as well as on the skin friction and the surface streamlines. The flow physics of separation for these four cases is illustrated and discussed in detail.
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| 12. |
- Feymark, Andreas, 1984, et al.
(författare)
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Large eddy simulation of high re number partially separated flow
- 2012
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Ingår i: 50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition. - Reston, Virigina : American Institute of Aeronautics and Astronautics Inc.. - 9781600869365
-
Konferensbidrag (refereegranskat)abstract
- The predictive capability for Large Eddy Simulation (LES) for flows with unsteady separation at curved surfaces is investigated. LES with near wall modeling is applied and a range of subgrid models is evaluated for four different validation cases for which experimental flow measurement data is available. A novel model for the simulation of the effect of boundary layer tripping devices used in experiments is also proposed and evaluated. The validation focuses on the mean velocity distribution in the region of separation, as well as on the skin friction and the surface streamlines. The flow physics of separation for these four cases is illustrated and discussed in detail.
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| 13. |
- Finnsgård, Christian, et al.
(författare)
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Ship power prediction with CFD in full scale
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report demonstrates the qualifications of RISE to carry out CFD for ship self-propulsion, thus predicting the delivered power. The procedures were fully developed at SSPA which became fully integrated into the Maritime Department of RISE by 2023-01-01. An outline is given of the best-practice guidelines used at SSPA/RISE and how they comply with the relevant ITTC recommendations for verification and analysis. In addition, an overview is given of previous validation studies performed for a wide range of ships, including comparison with both model-scale and full-scale data. Complete references are provided to reports and publications in which these SSPA studies and methods are described in detail.
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| 14. |
- Fureby, C., et al.
(författare)
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Incompressible wall-bounded flows
- 2007
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Almost all flows of practical interest are turbulent, and thus the simulation of turbulent flow and its diversity of flow characteristics remains one of the most challenging areas in the field of classical physics. In many situations the fluid can be considered incompressible; that is, its density is virtually constant in the frame of reference, moving locally with the fluid, but density gradients may be passively convected with the flow. Examples of such flows of engineering importance are as follows: external flows, such as those around cars, ships, buildings, chimneys, masts, and suspension bridges; and internal flows, such as those in intake manifolds, cooling and ventilation systems, combustion engines, and applications from the areas of biomedicine, the process industry, the food industry, and so on. In contrast to free flows (ideally considered as homogeneous and isotropic), wall-bounded flows are characterized by much less universal properties than free flows and are thus even more challenging to study. The main reason for this is that, as the Reynolds number increases, and the thickness of the viscous sublayer decreases, the number of grid points required to resolve the near-wall flow increases. The two basic ways of computing turbulent flows have traditionally been direct numerical simulation (DNS) and Reynolds-averaged NavierâStokes (RANS) modeling. In the former the time-dependent NavierâStokes equations (NSE) are solved numerically, essentially without approximations. In the latter, only time scales longer than those of the turbulent motion are computed, and the effect of the turbulent velocity fluctuations is modeled with a turbulence model.
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| 15. |
- Jalkanen, Jukka-Pekka, et al.
(författare)
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Modeling of ships as a source of underwater noise
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Shipping as a source of underwater noise is increasing. Underwater noise emission levels are seldom considered as a ship design parameter unless low vessel noise is specifically required, like in the case of warships and research vessels. Noise emissions are not regulated yet, but the awareness of possible impacts of noise on marine life is increasing. This paper describes the implementation of a noise source model for the Ship Traffic Emission Abatement Model (STEAM; Jalkanen et al. 2009; 2012; Johansson et al, 2017). The combination of vessel technical description and activity can be used to generate noise source maps which are based on actual ship traffic data. The generated noise source maps can ve used to describe the energy emitted as noise to the water, which facilitates regular annual updates of the noise emissions from ship traffic in the Baltic Sea area.
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| 16. |
- Jalkanen, J. P., et al.
(författare)
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Modelling of ships as a source of underwater noise
- 2018
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Ingår i: Ocean Science. - : Copernicus GmbH. - 1812-0792 .- 1812-0784. ; 14:6, s. 1373-1383
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a methodology is presented for modelling underwater noise emissions from ships based on realistic vessel activity in the Baltic Sea region. This paper combines the Wittekind noise source model with the Ship Traffic Emission Assessment Model (STEAM) in order to produce regular updates for underwater noise from ships. This approach allows the construction of noise source maps, but requires parameters which are not commonly available from commercial ship technical databases. For this reason, alternative methods were necessary to fill in the required information. Most of the parameters needed contain information that is available during the STEAM model runs, but features describing propeller cavitation are not easily recovered for the world fleet. Baltic Sea ship activity data were used to generate noise source maps for commercial shipping. Container ships were recognized as the most significant source of underwater noise, and the significant potential for an increase in their contribution to future noise emissions was identified.
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| 17. |
- Karasalo, I., et al.
(författare)
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Estimates of source spectra of ships from long term recordings in the Baltic sea
- 2017
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 4:JUN
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Karasalo, östberg, Sigray, Jalkanen, Johansson, Liefvendahl and Bensow. Estimates of the noise source spectra of ships based on long term measurements in the Baltic sea are presented. The measurement data were obtained by a hydrophone deployed near a major shipping lane south of the island öland. Data from over 2,000 close-by passages were recorded during a 3 month period from October to December 2014. For each passage, ship-to-hydrophone transmission loss (TL) spectra were computed by sound propagation modeling using 1. bathymetry data from the Baltic Sea Bathymetry Database (BSBD), 2. sound speed profiles from the HIROMB oceanographic model, 3. seabed parameters obtained by acoustic inversion of data from a calibrated source, and 4. AIS data providing information on each ship's position. These TL spectra were then subtracted from the received noise spectra to estimate the free field source level (SL) spectra for each passage. The SL were compared to predictions by some existing models of noise emission from ships. Input parameters to the models, including e.g., ship length, width, speed, displacement, and engine mass, were obtained from AIS (Automatic Identification System) data and the STEAM database of the Finnish Metereological Institute (FMI).
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| 18. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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A Validation Study of Full-Scale CFD Simulation for Sea Trial Performance Prediction of Ships
- 2023
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Ingår i: World Congress in Computational Mechanics and ECCOMAS Congress. - 2696-6999.
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Konferensbidrag (refereegranskat)abstract
- Shipping is a critical component of global trade but also accounts for a substantial portion of global greenhouse gas emissions. Recognising this issue, the International Maritime Organisation (IMO) has implemented new measures aimed at determining the energy efficiency of all ships and promoting continuous improvements, such as the Energy Efficiency Existing Ship Index (EEXI). As Computational Fluid Dynamics (CFD) can be used to calculate the EEXI value, RISE-SSPA1 and Flowtech have developed a CFD-based method for predicting full-scale ship performance with SHIPFLOW v7.0, which meets the new requirements of IMO. The method is validated through an extensive comparison study that examines the delivered power and propeller rotation rate between full-scale CFD predictions and high-quality sea trials using 14 common cargo ships of varying sizes and types. The comparison between the CFD predictions and 59 sea trials shows that both delivered power and RPM can be predicted with satisfactory accuracy, with an average comparison error of about 4% and 2%, respectively. The numerical methods used in this study differ significantly from the majority of the state-of-the-art CFD codes, highlighting their potential for future applications in ship performance prediction. Thorough validation with a large number of sea trials is essential to establish confidence in CFD-based ship performance prediction methods, which is crucial for the credibility of the EEXI framework and its potential to contribute to shipping decarbonisation.
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| 19. |
- Liefvendahl, Mattias, et al.
(författare)
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A study on algorithms for optimization of Latin hypercubes
- 2006
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Ingår i: Journal of Statistical Planning and Inference. - : Elsevier BV. - 0378-3758 .- 1873-1171. ; 136:9, s. 3231-3247
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Tidskriftsartikel (refereegranskat)abstract
- A crucial component in the statistical simulation of a computationally expensive model is a good design of experiments. In this paper we compare the efficiency of the columnwise-pairwise (CP) and genetic algorithms for the optimization of Latin hypercubes (LH) for the purpose of sampling in statistical investigations. The performed experiments indicate, among other results, that CP methods are most efficient for small and medium size LH, while an adopted genetic algorithm performs better for large LH. Two optimality criteria suggested in the literature are evaluated with respect to statistical properties and efficiency. The obtained results lead us to favor a criterion based on the physical analogy of minimization of forces between charged particles suggested in Audze and Eglais (1977. Problems Dyn. Strength 35, 104-107) over a ’maximin distance’ criterion from Johnson et al. (1990. J. Statist. Plann. Inference 26, 131-148).'
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| 20. |
- Liefvendahl, Mattias, et al.
(författare)
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Analytical and numerical investigation of the resolvent for plane Couette flow
- 2003
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Ingår i: SIAM Journal on Applied Mathematics. - 0036-1399 .- 1095-712X. ; 63:3, s. 801-817
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Tidskriftsartikel (refereegranskat)abstract
- We present new bounds for the solution of the resolvent equation for plane Couette flow. Both analytic methods and computation, using the Chebyshev tau spectral method, are used. The emphasis is on determining the Reynolds number-dependence of the estimates. The main result is the introduction of a weighted norm, which leads to optimal asymptotic behavior of the resolvent for large Reynolds numbers.
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| 21. |
- Liefvendahl, Mattias, et al.
(författare)
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Bounds for the threshold amplitude for plane couette flow
- 2002
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Ingår i: Journal of Nonlinear Mathematical Physics. - : Springer Science and Business Media LLC. - 1402-9251 .- 1776-0852. ; 9:3, s. 311-324
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Tidskriftsartikel (refereegranskat)abstract
- We prove nonlinear stability for finite amplitude perturbations of plane Couette flow. A bound of the solution of the resolvent equation in the unstable complex half-plane is used to estimate the solution of the full nonlinear problem. The result is a lower bound, including Reynolds number dependence, of the threshold amplitude below which all perturbations are stable. Our result is an improvement of the corresponding bound derived in [3].
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| 22. |
- Liefvendahl, Mattias, et al.
(författare)
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Computational methods for unsteady fluid force predictions using moving mesh large eddy simulations
- 2005
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Konferensbidrag (refereegranskat)abstract
- The flow around a stream-wise oscillating circular cylinder in a steady uniform flow is computed using large eddy simulations (LES). A finite volume method with capability to handle moving meshes is employed. The results are used for comparison with experiments for validation of the algorithms. Another goal of the investigation is to obtain information, complimentary to that of the experiments, about the process of vortex shedding, the structure of the flow in the wake and the relation between this and the forces acting on the cylinder.
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| 23. |
- Liefvendahl, Mattias, et al.
(författare)
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Deformation and regeneration of the computational grid for CFD with moving boundaries
- 2007
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Konferensbidrag (refereegranskat)abstract
- A general method for computational fluid dynamics with boundaries moving in any prescribed fashion, is presented. The method adapts the boundary fitted mesh to the changing spatial domain by deforming it and, when necessary due to grid quality requirements, regenerating it. Finite volumes are used for the discretisation of Navier-Stokes equations, the mesh is regenerated by the advancing front method and an elliptic differential equation, or an analytical expression, is used to compute the mesh motion. Results are presented for two model problems.
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| 24. |
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| 25. |
- Liefvendahl, Mattias, et al.
(författare)
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Grid generation for wall-modelled les of ship hydrodynamics in model scale
- 2017
-
Konferensbidrag (refereegranskat)abstract
- An unstructured grid generation approach for wall-modelled LES is proposed. The applicability of the approach is demonstrated for the simulation of the flow around an axisymmetric body, at Re-number 5.48·106, which is representable of model scale ship hydrodynamics. A numerical trip wire must be employed to induce resolved fluctuations in the simulated boundary layer. The predictive accuracy of the simulation technique is evaluated for the flow around the axisymmetric body, and for the computation of a turbulent boundary layer on a flat plate. For the flat plate, comparison is made with results from direct numerical simulation. For the axisymmetric body, results from wall-modelled LES, RANS and experimental measurements are compared.
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