Maritime Research Institute Netherlands Research Articles

Numerical prediction for vertical dynamic anti-sinking performance of underwater vehicle

Computational fluid dynamics (CFD) simulations of an underwater vehicle (UV) during self-propulsion and dynamic anti-sinking maneuvers are presented. A generic submarine, Joubert BB2, was selected as the test model, which was modified by the Maritime Research Institute, Netherlands (MARIN). Different recovery maneuvers for improving the anti-sinking ability were performed when the UV bow cabin was broken. The overset mesh method was used to simulate the deflection of the rudder and stern planes, and a body-force propeller represented by an actuator disk incorporating predetermined propulsion properties provided the thrust and torque for self-propulsion. Extra vector forces of inflow water forces and recovery buoyancy forces were proposed to simulate the flooding of a bow cabin and recover buoyancy by emptying the ballast. Numerical simulations were performed for 20 different combinations of vertical anti-sinking maneuvers, including stern control surfaces, increasing ship speed, and emptying the ballast water. The pitch angle and depth characteristics of UV self-propelled motion were analyzed based on the pre-set anti-sinking criterions. The results indicated stern control surfaces combined with accelerating could effectively maintain the UV's depth and pitch angle, and discharge ballast water could always make it surface quickly. We hope that this study will provide ideas for further research on anti-sinking abilities.

Computational analysis of strut effects on a BB2 submarine at drift angle 0, 6, and 12°

Struts are attached to a submarine to maintain its submerged depth when conducting the model tests. While previous studies have mentioned that the attachment of the struts has a negligible effect on the performance of a submarine, it is difficult to find studies that clearly explain the effects of the struts. The present study examines the effect of struts with a circular cross-section on the resistance and propulsion performances of a submarine under both straight-ahead (β = 0°) and static-drift (β = 6° and 12°) conditions. For this analysis, the open-source computational fluid dynamics (CFD) toolkit OpenFOAM was utilized. A generic submarine Joubert BB2 was selected as a test model, which was modified by the Maritime Research Institute Netherlands (MARIN). Analyses of resistance were conducted in straight-ahead and static-drift conditions, and the flow characteristics such as pressure, velocity, vorticity, and turbulent kinetic energy were compared to identify differences caused by the struts on the BB2 submarine. The results showed that as the drift angle increased, the struts had a smaller effect on the submarine along the hull to the propeller plane. From the results, it was predicted that the effect of the struts should be considered during the design process for the submarine.

Identification of coupled response models for ship steering and roll motion using support vector machines

Based on the linearized equation of ship manoeuvring motion in 4 degrees of freedom, the coupled response models for ship steering and roll motion are derived. To verify the response models, part of the experimental data of 10°/10° zigzag test, performed with the DTMB 5415 model in the Maritime Research Institute Netherlands, is used to train the support vectors of the ε-support vector machines and least squares support vector machines, respectively; the manoeuvrability indexes in the response models are identified using the support vectors and the linear kernel function. 10°/10° and 20°/20° zigzag tests are predicted by using the identified manoeuvrability indexes. Good prediction ability and generalization performance of the obtained response models and the proposed identification method are demonstrated by comparing the prediction results with the experimental data.

Toward Improvement of Resistance Testing Reliability

. Periodically conducting a benchmark test with estimated uncertainty is important to improve the quality of resistance predictions and understand the influence of instrumentation, testing procedures and analysis techniques. The LHI-007 Ro-Ro Ferry ship model, made available by the Maritime Research Institute Netherlands (MARIN), was used for benchmark testing from 2010 to 2018 at the Indonesian Hydrodynamic Laboratory. Comparisons were made between filtering the resistance data with a low-pass filter and with a Kalman filter. This work shows how benchmark tests can be used to track test performance over a longer period and proposes techniques to improve the uncertainty in the resistance results.

Acoustic characterisation of towing tanks

Large water tanks known as towing tanks, wave basins and cavitation tunnels, are used to determine the performance of ships, boats and submarines at model-scale. They may also be used for noise measurements but suffer from the effects of reverberation, which makes it difficult to capture the free field conditions necessary for complete characterisation of the noise. This paper describes an adapted Image Source Model and its use to understand these reverberation effects. It extends the conventional Image Source Model by the use of spherical wave reflection coefficients at the tank boundaries, in addition to the inclusion of volumetric absorption. Validation of the Image Source Model is undertaken by comparison with published transfer function measurements made in the depressurized wave basin at the Maritime Research Institute Netherlands (MARIN). The relative contribution to the tank response from the direct field and free surface is examined. The tank response is found to vary with three frequency-scales (periodicities) resulting from interactions with the free surface and axial modes.

CFD Simulations and Experiments of a Submarine in Turn, Zigzag, and Surfacing Maneuvers

We present simulations and experiments of the generic submarine Joubert BB2 performing standard turn, zigzag, and surfacing maneuvers in calm water at depth. The free-sailing experiments, performed at Maritime Research Institute Netherlands (MARIN), are unique in that they present an open dataset for the community to benchmark maneuvering prediction methodologies. Computations were performed with explicitly gridded sailplanes, tail planes, and propellers using a dynamic overset technique. This study analyzes a 20-degree turning maneuver with vertical control commanding the stern planes and a 20/20 zigzag maneuver with vertical control commanding both sail and stern planes, both of them at a nominal speed of 10 knots, and a 20-degree rise maneuver with horizontal control at 12 knots. The results show that computational fluid dynamics can predict well motions and speeds for free-sailing conditions, but controller commands are harder to replicate. Computations of the rise maneuver with surfacing compare well with experiments, including a crashback maneuver to stop the submarine. Introduction Simulation of free-running submarine maneuvers is demanding in terms of computational fluid dynamics (CFD) capabilities and computational resources. Full 6-DoF motions, moving appendages, control algorithms, and scalable performance are some of the requirements to execute free-running maneuvering simulations. Open literature data for validation of submarine maneuvers are very limited and consist mostly of static conditions (see for instance rotating arm [Toxopeus et al. 2012] and static drift [Roddy 1990; Toxopeus 2008] data for Defense Advanced Research Projects Agency (DARPA) Suboff and static drift [Quick & Woodyatt 2014] for the Joubert hull form [Joubert 2006]). A new dataset has been recently made available to the research community for the generic submarine model BB2 (Overpelt et al. 2015), based on the Joubert hull form.

Numerical study on drag and lift coefficients of a marine riser at high Reynolds number using COMSOL multiphysics

Flow around a marine riser in water at the drag crisis regime was investigated using numerical modelling. In this regime, the drag coefficient drops off at a certain Reynolds number due to a change from laminar to turbulent flow. The aim is to investigate the capability of turbulence model to predict drag coefficient through COMSOL Multiphysics, a computational fluid dynamic (CFD) transient solver and compared against existing numerical models and experiment by Maritime Research Institute Netherlands (MARIN). Numerically, drag and lift forces depend on the point of separation from the cylinder in which different turbulence modelling will result in varying separation point and will lead to different vortex formation and the drag force. Reynolds Average Navier-Stokes (RANS) was employed using the k-ε and Menter’s Shear Stress Transport (SST) turbulence model in two-dimensional CFD simulation. Six Reynolds numbers, similar to the test case, were considered. It can be concluded that the standard k-ε turbulence model, can only provide a good approximation at high turbulence regime, which is Reynolds number of 3.15 × 105 and higher. While, SST turbulence model can provide a good approximation at subcritical regime which before the sudden drop of drag force regimes.

Linking Experimental and Numerical Wave Modelling

Experimental or numerical analysis of the response of ships and other floating structures starts with correct environmental modelling. The capabilities of numerical tools are rapidly expanding, but presently the evaluation of extreme events in waves (such as slamming, green water, air-gap exceedance) still requires a combination of experiments and different levels of numerical tools. The present paper describes recent efforts within the Maritime Research Institute Netherlands (MARIN) to improve experimental and numerical wave modelling and especially their combination. The ultimate objective is to be able to reproduce any wave condition from a basin or from sea in numerical tools and vice versa, including a sound treatment of basin effects, numerical effects and statistical variability. The aspects that are of importance in both types of wave modelling are first introduced, after which a number of examples of recent projects is discussed. It can be concluded that important steps were made towards linking experimental and numerical wave modelling, but there are some challenges common to all wave reproductions. Some future planned studies focussing on how to deal with them are discussed as well.

Maneuvering simulation of an X-plane submarine using computational fluid dynamics

X-plane submarines show better maneuverability as they have much longer span of control plane than that of cross plane submarines. In this study, captive model tests were conducted to evaluate the maneuverability of an X-plane submarine using Computational Fluid Dynamics (CFD) and a mathematical maneuvering model. For CFD analysis, SNUFOAM, CFD software specialized in naval hydrodynamics based on the open-source toolkit, OpenFOAM, was applied. A generic submarine Joubert BB2 was selected as a test model, which was modified by Maritime Research Institute Netherlands (MARIN). Captive model tests including propeller open water, resistance, self-propulsion, static drift, horizontal planar motion mechanism and vertical planar motion mechanism tests were carried out to obtain maneuvering coefficients of the submarine. Maneuvering simulations for turning circle tests were performed using the maneuvering coefficients obtained from the captive model tests. The simulated trajectory showed good agreement with that of free running model tests. From the results, it was proved that CFD simulations can be applicable to obtain reliable maneuvering coefficients for X-plane submarines.

Recent Developments in Computational Methods for the Analysis of Ducted Propellers in Open Water

This article presents an overview of the recent developments at Instituto Superior Técnico and Maritime Research Institute Netherlands in applying computational methods for the hydrodynamic analysis of ducted propellers. The developments focus on the propeller performance prediction in open water conditions using boundary element methods and Reynolds-averaged Navier-Stokes solvers. The article starts with an estimation of the numerical errors involved in both methods. Then, the different viscous mechanisms involved in the ducted propeller flow are discussed and numerical procedures for the potential flow solution proposed. Finally, the numerical predictions are compared with experimental measurements. 1. Introduction Ducted propellers have been widely used for marine applications. Nowadays, they may be found in tugs, trawlers, tankers, bulk ships, warships, and in dynamic positioning systems of offshore platforms or vessels. The duct may be classified as an accelerating or decelerating type. Accelerating ducts are often used to increase the efficiency and thrust of heavily loaded propellers. In the case of a decelerating duct, they are used to reduce the risk of cavitation and resulting noise. The complex interaction which occurs between the propeller and duct makes the hydrodynamic design of such systems a complicated task. For the selection of the numerical simulation tool, the designer has to choose between a simplified method that predicts the main features of the flow field around the ducted propeller, and a more complex tool that provides detailed information in problematic areas such as the gap region between propeller and duct inner surface. On the other hand, model tests in a towing tank or cavitation tunnel may be seen as an alternative, but they are usually expensive. Presently, the development of an accurate and cost-effective numerical method for the design and analysis of ducted propellers is still not complete.

OC5 Project Phase II: Validation of Global Loads of the DeepCwind Floating Semisubmersible Wind Turbine

This paper summarizes the findings from Phase II of the Offshore Code Comparison, Collaboration, Continued, with Correlation project. The project is run under the International Energy Agency Wind Research Task 30, and is focused on validating the tools used for modeling offshore wind systems through the comparison of simulated responses of select system designs to physical test data. Validation activities such as these lead to improvement of offshore wind modeling tools, which will enable the development of more innovative and cost-effective offshore wind designs.For Phase II of the project, numerical models of the DeepCwind floating semisubmersible wind system were validated using measurement data from a 1/50th-scale validation campaign performed at the Maritime Research Institute Netherlands offshore wave basin. Validation of the models was performed by comparing the calculated ultimate and fatigue loads for eight different wave-only and combined wind/wave test cases against the measured data, after calibration was performed using free-decay, wind-only, and wave-only tests. The results show a decent estimation of both the ultimate and fatigue loads for the simulated results, but with a fairly consistent underestimation in the tower and upwind mooring line loads that can be attributed to an underestimation of wave-excitation forces outside the linear wave-excitation region, and the presence of broadband frequency excitation in the experimental measurements from wind. Participant results showed varied agreement with the experimental measurements based on the modeling approach used. Modeling attributes that enabled better agreement included: the use of a dynamic mooring model; wave stretching, or some other hydrodynamic modeling approach that excites frequencies outside the linear wave region; nonlinear wave kinematics models; and unsteady aerodynamics models. Also, it was observed that a Morison-only hydrodynamic modeling approach could create excessive pitch excitation and resulting tower loads in some frequency bands.

On the use of time-domain simulation in the design of Remotely Operated Submergible Vehicles

Designing a Remotely Operated Vehicle (ROV) is a complicated task in which the design team deals with a considerable amount of uncertainty before the device is able to be tested at full scale. A way to cope with such uncertainty is to use simulation software to evaluate design concepts along the different levels of abstraction of the process. In this work, the use of aNySIM, the Maritime Research Institute Netherlands (MARIN) multibody time-domain simulation tool, as a part of the design process of an ROV is addressed. The simulation software is able to solve the equations of motion of the vehicle based on rigid body dynamics, including features such as hydrodynamics, hydrostatics, thrusters, thrust allocation, and PID control. Different simulation scenarios are proposed to evaluate different concept solutions to the design, including thruster parameters and distribution. The results are further used to select the concept solutions to be implemented in the final design.

Development of frequency-dependent ocean wave directional distributions

The paper discusses the development of a frequency dependent directional spread from an initial condition of frequency-independence. The study applies basin directional measurements from the Maritime Research Institute Netherlands (MARIN), simulated data from a nonlinear wave equation, and field measurements from the Ekofisk field. The basin experiments and numerical simulations are initialized with a JONSWAP spectrum with frequency-independent directional distributions. In both cases we observe the development of a strong frequency-dependence of the directional spread. The numerical simulations suggest that static nonlinear contributions to the surface elevation partially explain the behavior below the spectral peak in accordance with [1]. There are also dynamic nonlinear contributions on both sides of the spectral peak.

Hydrodynamic modelling for the remotely operated vehicle Visor3 using CFD

Abstract: This paper addresses the hydrodynamic modelling of an inspection-class remotely operated vehicle using a viscous-flow solver for the accurate prediction of manoeuvring coefficients needed for control purposes. The 6-DOF differential nonlinear equation of motion for the ROV visor3 is first described with emphasis on hydrodynamic terms. Then, the hydrodynamic model of the ROV is assembled from data obtained using the Virtual Captive Test (VCT) approach, where experiments such as the Planar Motion Mechanism (PMM) are simulated using CFD. In this work, the Maritime Research Institute Netherlands’ viscous flow solver ReFRESCO is used to solve the steady-state and unsteady Navier-Stokes equations for single-phase turbulent incompressible flow, using a detailed geometry of the ROV. Three scenarios are considered: steady-state computations of forces and moments for different values of inflow velocity’s direction, steady-state computations of forces and moments for circular manoeuvres in the XY plane, and unsteady computations of forces and moments for rotation around the XYZ axes. The computation of manoeuvring coefficients using CFD allows one to develop a preliminary mathematical model for control purposes when there are limitations for performing physical tests.

An experimental study on an auxiliary towing system for an FPSO using active thrusters

It is ideal to design the best hull shape for a floating production storage and offloading unit (FPSO) that meets all performance criteria from an engineering point of view. However, in reality, it is difficult to satisfy all the criteria at the same time. If one of the performances cannot meet the criteria, then additional equipment or systems are installed to improve that performance. In this paper, when an FPSO cannot meet the towing stability inherently, we attempt to establish a procedure for determining an auxiliary towing system. Firstly, various systems that can be applied to the FPSO are compared and reviewed to improve the towing stability of the FPSO. Among them, using three active thrusters was chosen as the auxiliary towing system. Improvement of towing stability was verified from a towing model test conducted at the Maritime Research Institute Netherlands (MARIN). However, thruster cavitation was raised as a key problem when using thrusters for a purpose for which they were not intended. A thruster cavitation model test was additionally performed to check the safety of the thrusters. Based on these results, a safe operating range under extreme condition was confirmed by observing the occurrence of thruster cavitation. The predicted maximum unit total thrust of each thruster was compared with the observed safe operating range. Finally, the effectiveness and safety of the auxiliary towing system was verified.

Calibration and validation of a spar-type floating offshore wind turbine model using the FAST dynamic simulation tool

High-quality computer simulations are required when designing floating wind turbines because of the complex dynamic responses that are inherent with a high number of degrees of freedom and variable metocean conditions. In 2007, the FAST wind turbine simulation tool, developed and maintained by the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL), was expanded to include capabilities that are suitable for modeling floating offshore wind turbines. In an effort to validate FAST and other offshore wind energy modeling tools, DOE funded the DeepCwind project that tested three prototype floating wind turbines at 1/50th scale in a wave basin, including a semisubmersible, a tension-leg platform, and a spar buoy. This paper describes the use of the results of the spar wave basin tests to calibrate and validate the FAST offshore floating simulation tool, and presents some initial results of simulated dynamic responses of the spar to several combinations of wind and sea states. Wave basin tests with the spar attached to a scale model of the NREL 5-megawatt reference wind turbine were performed at the Maritime Research Institute Netherlands under the DeepCwind project. This project included free-decay tests, tests with steady or turbulent wind and still water (both periodic and irregular waves with no wind), and combined wind/wave tests. The resulting data from the 1/50th model was scaled using Froude scaling to full size and used to calibrate and validate a full-size simulated model in FAST. Results of the model calibration and validation include successes, subtleties, and limitations of both wave basin testing and FAST modeling capabilities.

Variational space–time (dis)continuous Galerkin method for nonlinear free surface water waves

A new variational finite element method is developed for nonlinear free surface gravity water waves using the potential flow approximation. This method also handles waves generated by a wave maker. Its formulation stems from Miles' variational principle for water waves together with a finite element discretization that is continuous in space and discontinuous in time. One novel feature of this variational finite element approach is that the free surface evolution is variationally dependent on the mesh deformation vis-à-vis the mesh deformation being geometrically dependent on free surface evolution. Another key feature is the use of a variational (dis)continuous Galerkin finite element discretization in time. Moreover, in the absence of a wave maker, it is shown to be equivalent to the second order symplectic Störmer–Verlet time stepping scheme for the free-surface degrees of freedom. These key features add to the stability of the numerical method. Finally, the resulting numerical scheme is verified against nonlinear analytical solutions with long time simulations and validated against experimental measurements of driven wave solutions in a wave basin of the Maritime Research Institute Netherlands.

The effects of second-order hydrodynamics on a semisubmersible floating offshore wind turbine

The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of a floating system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the Maritime Research Institute Netherlands (MARIN) offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method was applied to the Offshore Code Comparison Collaboration Continuation OC4-DeepCwind semisubmersible platform, supporting the National Renewable Energy Laboratory's 5-MW baseline wind turbine. In this paper, the loads and response of the system caused by the second-order hydrodynamics are analysed and compared to the first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.

Evaluation of internal force superposition on a TLP for wind turbines

The offshore wind resources globally present a great opportunity for green power generation. Both types, fixed and floating foundations, will play a major role in utilizing these resources. The preliminary design of the floating system called GICON®-Tension Leg Platform (TLP) is meant to provide a solution for harnessing the power of offshore wind at water depths between 20 m and 350 m. In addition a design for water depth up to 700 m is currently under development. The research project is a joint development of private industry and academic institutions. The main partners are ESG GmbH and Technische Universität Freiberg. Currently ongoing research includes the comparison of calculated data with experimental data obtained by wave tank experiments with a scale model at the Maritime Research Institute Netherlands (MARIN) in June 2013. These tests have provided insights regarding the dynamic characteristics of the GICON®-TLP by analyzing the system's response to different load cases. Furthermore, the results of the scale model tests at MARIN have confirmed that a superposition of the internal forces for wind and wave loads can be assumed for the structural design. This can be traced back to the stiffness of the mooring line system and the innovative mooring line configuration.

Methodology for Wind/Wave Basin Testing of Floating Offshore Wind Turbines

Scale-model wave basin testing is often employed in the development and validation of large-scale offshore vessels and structures by the oil and gas, military, and marine industries. A basin-model test requires less time, resources, and risk than a full-scale test, while providing real and accurate data for numerical simulator validation. As the development of floating wind turbine technology progresses in order to capture the vast deep-water wind energy resource, it is clear that model testing will be essential for the economical and efficient advancement of this technology. However, the scale model testing of floating wind turbines requires accurate simulation of the wind and wave environments, structural flexibility, and wind turbine aerodynamics and thus requires a comprehensive scaling methodology. This paper presents a unified methodology for Froude scale model testing of floating wind turbines under combined wind and wave loading. First, an overview of the scaling relationships employed for the environment, floater, and wind turbine are presented. Afterward, a discussion is presented concerning suggested methods for manufacturing a high-quality, low-turbulence Froude scale wind environment in a wave basin to facilitate simultaneous application of wind and waves to the model. Subsequently, the difficulties of scaling the highly Reynolds number–dependent wind turbine aerodynamics is presented in addition to methods for tailoring the turbine and wind characteristics to best emulate the full-scale condition. Lastly, the scaling methodology is demonstrated using results from 1/50th-scale floating wind turbine testing performed at the Maritime Research Institute Netherlands (MARIN) Offshore Basin. The model test campaign investigated the response of the 126 -m rotor diameter National Renewable Energy Lab (NREL) horizontal axis wind turbine atop three floating platforms: a tension-leg platform, a spar-buoy, and a semisubmersible. The results highlight the methodology's strengths and weaknesses for simulating full-scale global response of floating wind turbine systems.