Maritime Research Institute Netherlands

Wageningen, Netherlands

Maritime Research Institute Netherlands

Wageningen, Netherlands

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News Article | July 14, 2017

The Netherlands is a fairly small country, so to support a growing population, the Dutch people have historically expanded out to sea. It's a remarkable feat of engineering how much land they've managed to reclaim by building dikes, but it might not be a sustainable solution nowadays. To update that tradition, the Maritime Research Institute Netherlands (MARIN) is testing the concept of an artificial floating island. MARIN's floating island is made up of large triangles that connect to each other in a modular fashion. Structurally, it works like the Italian Floating Piers and walkways we saw last year, but on a much bigger scale: MARIN says that floating islands built in this way could be as big as 5 km (3.1 miles) wide, and used for a variety of purposes. "As sea level rises, cities become overcrowded and more activities are carried out at sea, raising the dikes and reclaiming land from the seas are perhaps no longer an effective solution," says Olaf Waals, project manager of MARIN's floating islands. "An innovative alternative that fits with the Dutch maritime tradition is floating ports and cities." These new floating spaces could support offshore homes, public spaces, docks for the loading and unloading of ships, fishing and seaweed-harvesting facilities, and renewable energy systems like wind, solar, tidal or wave energy generators. But there are still plenty of questions surrounding the project's viability. The MARIN team is investigating the best ways to lock the triangles together and anchor the island to the seabed. Whether the undulations of the water will be too disruptive to the structures or people onboard, and how to minimize the environmental effects of the new islands are other issues that need to be addressed. To answer these questions, MARIN is running computer simulations and testing the idea with a scale model island made up of 87 triangles, in a facility it calls the Offshore Basin. This 40 x 40 m (131 x 131 ft) pool allows the team to simulate wind, waves and currents, and study how the island would handle these conditions in the real world. The team's tests, as well as computer images of what the end result might look like, can be seen in the video below.

News Article | July 16, 2017

Is it possible for ships to sail faster through rough water and keep the safety of the crew a priority? Lex Keuning, Associate Professor at the Technical University (TU) Delft, asked himself this question after he had broken both of his kneecaps in a speeding incident at sea. In cooperation with Jaap Gelling, Managing Director High-Speed Craft at Damen Shipyards Group*, Keuning introduced a new type of hull that could withstand more speed: the ‘axe bow’. During the lecture in the Maritime Museum in Rotterdam, Keuning and Gelling told the audience about this success story of naval engineering. Gelling started the lecture by emphasising the big difference between the automotive and shipbuilding industries: “As a result of large scale production since the twentieth century, the technology of cars has developed more rapidly than those of ships.” But there were some major innovations, like the axe bow. The two explained the audience how the special bow was developed. Lex Keuning pointed out the danger ships are exposed to when they speed in rough water: “The faster ships are sailing over waves, the stronger the movements of the ship become. When a ship hits a wave, the ship usually slows and accelerates again. During these movements, however, the G-forces on board also increase and can even endanger the crew.” In 1980, his knees collapsed due to a boost in G-forces during a ship speeding test. In this experiment, the crew experienced 6.5 G, which means that they had become six and half times heavier. For Keuning, this incident was a wake-up call – from now on the comfort and safety of the crew was the main focus of his research regarding the speed of ships. In Keuning’s further quest to safely expand the speed, he focused on the peak accelerations of ships and the subsequent reactions of the crew: “Peak accelerations appear when the vertical movement of a ship increases (positive) or decreases (negative) in a short amount of time. When the pounding of a ship becomes too heavy, the crew can only do one thing: reduce speed.” The choice to reduce speed is actually necessary to ensure the crew’s safety – that is how overwhelming the pound movements of ships can become. Keuning was the first to develop a mathematical method to estimate the vertical movements of ships. At the TU Delft, he analysed how he could reduce the pound movement of ships and in which way this affected the hull of the ship. Keuning concluded that the removal of flare, the minimisation of the V-shape of the bow and a deeper keel line sufficiently reduced the pound movement of a ship. However, because of the removal of flare and the minimisation of the V-shape, the bow loses a lot of ‘volume.’ This volume is nonetheless crucial to keep the front of the ship above the water. As a solution, Keuning added extra buoyancy. As a result, the shape of the bow became similar to an axe bow. Thus, the ‘axe bow’ was born. Gelling told the audience at the Maritime Museum in Rotterdam how he already knew Lex Keuning when he studied at the TU Delft, where Lex was a researcher. On a personal as well as a business level, there was a good connection between the two. At the beginning of this century, they worked together with the Royal Navy, Maritime Research Institute Netherlands (MARIN) and the US Coast Guard to investigate the axe bow as a new type of hull. Keuning’s earlier research was also confirmed by the outcome of these investigations. Due to the application of the axe bow, the number of peak accelerations was decreased by 80 per cent, and as a bonus, the axe bow also contributed to 10 to 20 per cent fuel use reduction. Since 2006, Damen Shipyards has been constructing ships with axe bows for the professional market. So far, Damen has sold over 150 different types of ships with the axe bow technology. Due to this success, the parties involved agreed to set aside a small part of the profit for collective research by the TU Delft and Damen. This success, however, also had a negative side. Just like in the automotive sector, ship builders copy each other’s technologies. As a result, there are ships in the waters of France, Australia and Bangladesh, to name a few, with hulls that look like bow axes even though they are not produced by Damen. Nevertheless, those are just lookalikes, since the special characteristic of the bow axe is located under the water level – and that technology is patented by Damen.

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.

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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