Wageningen, Netherlands
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Eca L.,University of Lisbon | Hoekstra M.,Maritime Research Institute Netherlands | Vaz G.,Maritime Research Institute Netherlands
International Journal of Computational Fluid Dynamics | Year: 2012

This paper presents manufactured solutions (MS's) for code verification of incompressible flow solvers based on the Reynolds-averaged Navier-Stokes (RANS) equations. The proposed solutions mimic statistically steady, two-dimensional or three-dimensional near-wall turbulent flows in a simple domain (rectangle or rectangular box) at a given Reynolds number. The proposed analytical functions cover the mean flow quantities and the dependent variables of several eddy-viscosity turbulence models. Namely, the undamped eddy-viscosity of the Spalart and Allmaras and Menter one-equations models, √kL from the one (SKL) and two-equation (KSKL) models proposed by Menter, the turbulence kinetic energy and the turbulence frequency included in two-equation k - ω models. A basic flow field resembling a turbulent flat plate flow is constructed with the turbulence quantities defined from 'automatic wall functions' that are supposed to reproduce more or less the normal behaviour of these variables. Alternative flow fields are constructed superposing a perturbation flow field that creates a 'recirculation zone'. However, the near-wall solution of the basic flow is kept to avoid zero friction at the wall. Three-dimensional MS's are obtained from the blending of the basic two-dimensional MS's in the transverse direction. All flow fields satisfy mass conservation, i.e. mean velocity fields are divergence-free. The source functions required for the balancing of momentum and turbulence quantities transport equations and all the dependent variables and their derivatives are available in Fortran 90 modules. © 2012 Copyright Taylor and Francis Group, LLC.

Eca L.,University of Lisbon | Hoekstra M.,Maritime Research Institute Netherlands
Computers and Fluids | Year: 2011

This paper presents a study on the numerical requirements of including sand-grain wall roughness effects in the SST k-ω eddy-viscosity model. Three implementations are tried: two retain the direct application of the no-slip condition at the wall, the third is based on a wall function formulation. In the first two options the roughness effect is introduced via a change in wall boundary conditions, either for ω only or for k and ω. The two-dimensional flow along a finite flat plate is adopted to assess the numerical accuracy of the three approaches. The computed results are also compared with semi-empirical formula available in the open literature. It is demonstrated that sand-grain roughness effects can be simulated with acceptable numerical uncertainties with all three options, but the numerical settings to achieve that goal differ significantly. © 2010 Elsevier Ltd.

Eca L.,University of Lisbon | Hoekstra M.,Maritime Research Institute Netherlands
Journal of Computational Physics | Year: 2014

This paper offers a procedure for the estimation of the numerical uncertainty of any integral or local flow quantity as a result of a fluid flow computation; the procedure requires solutions on systematically refined grids. The error is estimated with power series expansions as a function of the typical cell size. These expansions, of which four types are used, are fitted to the data in the least-squares sense. The selection of the best error estimate is based on the standard deviation of the fits. The error estimate is converted into an uncertainty with a safety factor that depends on the observed order of grid convergence and on the standard deviation of the fit. For well-behaved data sets, i.e. monotonic convergence with the expected observed order of grid convergence and no scatter in the data, the method reduces to the well known Grid Convergence Index. Examples of application of the procedure are included. © 2014 Elsevier Inc.

Eca L.,University of Lisbon | Hoekstra M.,Maritime Research Institute Netherlands
International Journal for Numerical Methods in Fluids | Year: 2010

This paper presents for the simple flow over a flat plate the near-wall profiles of mean flow and turbulence quantities determined with seven eddy-viscosity turbulence models: the one-equation turbulence models of Menter and Spalart & Allmaras; the k-ω two-equation model proposed by Wilcox and its TNT, BSL √ and SST variants and the k - kL two-equation model. The results are obtained at several Reynolds numbers ranging from 107 to 2.5×109. Sets of nine geometrically similar Cartesian grids are adopted to demonstrate that the numerical uncertainty of the finest grid predictions is negligible. The profiles obtained numerically have relevance for the application of so-called 'wall function' boundary conditions. Such wall functions refer to assumptions about the flow in the viscous sublayer and the 'log law' region. It turns out that these assumptions are not always satisfied by our results, which are obtained by computing the flow with full near-wall resolution. In particular, the solution in the 'log-law' region is dependent on the turbulence model and on the Reynolds number, which is a disconcerting result for those who apply wall functions. © 2009 John Wiley & Sons, Ltd.

Mou J.M.,Wuhan University of Technology | Tak C.v.d.,Maritime Research Institute Netherlands | Ligteringen H.,Technical University of Delft
Ocean Engineering | Year: 2010

Due to high density of vessel traffic, busy waterways are water areas with high potential for collisions. The application of AIS makes it possible to investigate accurate and actual behavior of collision-involved ships, and benefits vessel traffic management and waterways design for these areas. As a case study, the authors focus on a Traffic Separation Scheme (TSS) off Rotterdam Port in Europe, and using AIS data, statistical analysis is made for collision involved ships. In order to identify the correlation of CPA, which is a key indicator for collision avoidance, with ship's size, speed, and course, linear regression models are developed. To assess risks, a dynamic method based on SAMSON is presented. © 2010 Elsevier Ltd. All rights reserved.

Make M.,Maritime Research Institute Netherlands Academy | Vaz G.,Maritime Research Institute Netherlands
Renewable Energy | Year: 2015

In this paper the flow over two (floating) wind turbines has been studied using RANS CFD calculations at model and full-scale Reynolds numbers conditions. The well-known NREL 5MW and MARIN designed turbines (MARIN Stock Wind Turbine or MSWT) have been analysed. The MSWT was designed to have the same thrust at model-scale as the NREL turbine at full-scale conditions. The thrust was the major driver since it is more important for the behaviour of the floating platform. Numerical sensitivity studies were done to minimize all possible uncertainties: domain size, iterative convergence, grid refinement, and turbulence model sensitivity was studied. Modern verification and validation procedures were used to assess those uncertainties and to perform a validation of the numerical results against experimental data coming from constant uniform inflow, fixed turbine experiments. Furthermore, the flow around the turbines and its performance, both for model and full-scale, have been scrutinised, compared, and insights into their behaviour and Reynolds/scale effects gained. A good agreement between the CFD results and the experimental data has been obtained, with low uncertainties for thrust but large uncertainties for power. The large Reynolds effects on the flow of these turbines have been also shown and explained. Finally, it has been confirmed that the MSWT performs as intended at model-scale conditions. © 2015 Elsevier Ltd.

Bos R.W.,Technical University of Delft | Bos R.W.,Maritime Research Institute Netherlands | Wikkerink J.,Maritime Research Institute Netherlands
Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015, Multibody Dynamics 2015 | Year: 2015

Multi-body simulations are widely used in a variety of research fields. In the maritime industry, for instance to predict the behaviour of a ship during side-by-side mooring, typically with few bodies. Recently an increased need from the industry is to expand those simulations to predict the behaviour or provide training for a floating structure in ice. Benchmarks are required to quantify the performance of the simulations. Benchmarks for bilateral constrains and friction exist, but for contact problems (unilateral constrains) they are absent, to the best of our knowledge. Therefore five new possible benchmarks are given, which can be used to test the accuracy of elastic friction-less collision response. Conservation of momentum is used to derive the analytical solution, which is usable for resolving multiple simultaneous collisions. A practical example of the use of these benchmarks is given.

Klaij C.M.,Maritime Research Institute Netherlands | Vuik C.,Technical University of Delft
International Journal for Numerical Methods in Fluids | Year: 2013

This paper contains a comparison of four SIMPLE-type methods used as solver and as preconditioner for the iterative solution of the (Reynolds-averaged) Navier-Stokes equations, discretized with a finite volume method for cell-centered, colocated variables on unstructured grids. A matrix-free implementation is presented, and special attention is given to the treatment of the stabilization matrix to maintain a compact stencil suitable for unstructured grids. We find SIMPLER preconditioning to be robust and efficient for academic test cases and industrial test cases. Compared with the classical SIMPLE solver, SIMPLER preconditioning reduces the number of nonlinear iterations by a factor 5-20 and the CPU time by a factor 2-5 depending on the case. The flow around a ship hull at Reynolds number 2E9, for example, on a grid with cell aspect ratio up to 1:1E6, can be computed in 3 instead of 15h. Copyright © 2012 John Wiley & Sons, Ltd. This paper contains a comparison of four SIMPLE-type methods used as solver and as preconditioner for the iterative solution of the (Reynolds-averaged) Navier-Stokes equations. We find SIMPLER preconditioning to be robust and efficient for academic and industrial test cases. The flow around a ship hull at Reynolds number 2E9, for example, on a grid with cell aspect ratio up to 1:1E6, can be computed in 3 instead of 15 h. © 2012 John Wiley & Sons, Ltd.

Abeil B.,Maritime Research Institute Netherlands
RINA, Royal Institution of Naval Architects - International Conference on Ship and Offshore Technology, ICSOT Indonesia 2012: Developments in Ship Design ad Construction | Year: 2012

The aim of the present paper is to provide a thorough overview of the most important seakeeping aspects related to survey vessels, in such a way that they can be integrated in future designs. The content of the paper is largely supported by recent hydrodynamic studies (numerical and experimental) performed at MARIN. The first part of the paper deals with the ship motions, with a particular attention given to roll and roll stabilisation. The following part elaborates on crew performance. Aspects such as seasickness, interruptions of activities from excessive motions or accelerations are thoroughly discussed. Thirdly, the operability of sounding equipment in a seaway is addressed. The paper provides a description of the risk of bubble sweep-down and emergence of the underwater equipment and the related consequences on sonar downtime and potential damage. The paper concludes on a discussion on the water motions inside a moonpool, both at zero speed and in transit, and on possible ways to reduce them.

Klaij C.M.,Maritime Research Institute Netherlands
Journal of Computational Physics | Year: 2015

Finite volume methods with co-located variables for incompressible flow suffer from spurious pressure oscillations unless a stabilization method is applied. Variations of the pressure-weighed interpolation (PWI) method are typically used for this purpose. But the PWI method does not only prevent spurious oscillations. Counter-intuitively, it also simplifies the approximation of the Schur complement (pressure matrix) which appears in iterative solution methods such as SIMPLE. © 2015 Elsevier Inc..

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