| 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
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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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| 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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