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Yacht Research Unit Kiel - Uncategorised

Uncategorised

  • Written by Kai Graf
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List of Publications

Boehm, C und Graf, K. RANS Based CFD Investigation of the Interference between two boats sailing upwind. Journal of Sailboat Technology 2016. http://www.sname.org/sailboattechnology/home.


Renzsch H, Graf K. FLYING SHAPE PREDICTION OF ASYMMETRIC SPINNAKERS – AN EXPERIMENTAL DATA SET FOR VALIDATION OF FSI-SIMULATIONS. International Journal of Small Craft Technology 2016;158.


Böhm C, Graf K. Advancements in free surface RANSE simulations for sailingyacht applications. J Ocean Engineering 2014;Vol. 90.


Graf K, van Hoeve, Adrian and Watin ,Simon. Comparison of full 3D-RANS simulations with 2D-RANS/lifting line method calculations for the flow analysis of rigid wings for high performance multihulls. J Ocean Engineering 2014;Vol. 90.


Graf K, Böhm C. Coupling of RANSE-CFD with VPP Methods: From the Numerical Tank to Virtual Boat Testing. International Journal of Small Craft Technology 2011;153.


Renzsch H, Graf K. Fluid Structure Interaction Simulation of Spinnakers – Getting Closer to Reality. International Journal of Small Craft Technology 2011;153.


Bertram V, Söding H, Graf K. PDSTRIP – A strip method for ship and yacht seakeeping. 9th Numerical Towing Tank Symposium Le Croisic, Nov 2006 2006.


Bertram V, Veelo B, Söding H, Graf K. Development of a Freely Available Strip Method for Seakeeping. Proc. 5th International Conference on Computer and IT Applications in the Maritime Industries 2006.

CONFERENCES

Graf K, Meyer J, Renzsch H, Preuß C. Investigation of modern sailing yachts using a new free-surface RANSE code. In: Cite de la Voile Eric Taberly and Naval Academy Research Institute. Innovation in high performance sailing yachts (INNOV'SAIL 2017): International conference, 28 June - 30 June 2017, Lorient, France: Lorient / France: Cite de la Voile Eric Taberly and Naval Academy Research Institute; 2017.


Meyer J, Graf K, Slavig T. A new adjustment-free damping method for free-surface waves in numerical simulations. In: ICNME. VII Intl. Conf. Computational Methods in Marine Engineering MARINE 2017; May 15-17, 2017: Nantes / France; 2017.


Graf K, Meyer J, Renzsch H. Prediction and optimization of aerodynamic and hydrodynamic forces and boat speed of foiling catamarans with a wing sail and a jib. In: Society of Naval and Marine Engineers (Hg.). The Twenty-Second Chesapeake Sailing Yacht Symposium: CSYS, March 18-19, 2016, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2016.


Meyer J, Renzsch H, Graf K, Slawig T. Advanced CFD-Simulations of free-surface flows around modern sailing yachts using a newly developed OpenFOAM solver. In: Society of Naval and Marine Engineers (Hg.). The Twenty-Second Chesapeake Sailing Yacht Symposium: CSYS, March 18-19, 2016, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2016.


Böhm C, Graf K. Advances in free surface RANSE simulations for sailing yacht applications. In: The Royal Institution of Naval Architects. Innovation in high performance sailing yachts (INNOV'SAIL 2013): International conference, 26 June - 28 June 2013, Lorient, France: The Royal Institution of Naval Architects. London: RINA; 2013.


Böhm C, Graf K, Meyer J, Brehm R, Duggen L. A Measurement System for Performance Monitoring on Small Sailing Dinghies. In: Society of Naval and Marine Engineers (Hg.). The Twenty-First Chesapeake Sailing Yacht Symposium: CSYS, March 15-16, 2013, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2013.


Graf K, Renzsch H. An experimental validation case for fluid-structure-interaction simulations of downwind sails. In: Society of Naval and Marine Engineers (Hg.). The Twenty-First Chesapeake Sailing Yacht Symposium: CSYS, March 15-16, 2013, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2013.


Graf K, Watin S, van Hoeve A. Comparison of full 3D-RANS simulations with 2D-RANS / lifting line method calculations for the flow analyis of rigid wings for high performance multihulls. In: The Royal Institution of Naval Architects. Innovation in high performance sailing yachts (INNOV'SAIL 2013): International conference, 26 June - 28 June 2013, Lorient, France: The Royal Institution of Naval Architects. London: RINA; 2013.


Böhm C, Graf K. RVPP: Sailing Yacht Performance Prediction fully integrated into a RANSE based flow code. In: Society of Naval and Marine Engineers (Hg.). The Twentieth Chesapeake Sailing Yacht Symposium: CSYS, March 18-19, 2011, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2011.


Mausolf J, Deparday J, Graf K. Photogrammetry Based Flying Shape Investigation of Downwind Sails in the Wind Tunnel and at Full Scale on a Sailing Yacht. In: Society of Naval and Marine Engineers (Hg.). The Twentieth Chesapeake Sailing Yacht Symposium: CSYS, March 18-19, 2011, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2011.
Böhm C, Graf K. Coupling of RANSE-CFD with VPP methods: From the Numerical Tank to Virtual Boat Testing. In: The Royal Institution of Naval Architects. Innovation in high performance sailing yachts (INNOV'SAIL 2010): International conference, 30 June - 1 July 2010, Lorient, France: The Royal Institution of Naval Architects. London: RINA; 2010.


Renzsch H, Graf K. Fluid Structure Interaction Simulation of Spinnakers – getting closer to reality. In: The Royal Institution of Naval Architects. Innovation in high performance sailing yachts (INNOV'SAIL 2010): International conference, 30 June - 1 July 2010, Lorient, France: The Royal Institution of Naval Architects. London: RINA; 2010.


Renzsch H, Graf K. Fluid Structure Interaction Simulation of Spinnakers – Towards Simulation Driven Sail Design. In: 21st International HISWA Symposium on Yacht Design and Yacht Construction: November 2010, Amsterdam RAI Convention Centre. Amsterdam, The Netherlands: Eurocongres; 2010.


Graf K, Böhm C, Renzsch H. CFD- and VPP-Challenges in the Design of the New AC90 Americas Cup Yacht. In: Society of Naval and Marine Engineers (Hg.). The Nienteenth Chesapeake Sailing Yacht Symposium: CSYS, March 2009, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2009.


Graf K, Müller O. Photogrammetric Investigation of the Flying Shape of Spinnakers in a Twisted Flow Wind Tunnel. In: Society of Naval and Marine Engineers (Hg.). The Nienteenth Chesapeake Sailing Yacht Symposium: CSYS, March 2009, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2009.


Böhm C, Graf K. Validation of RANSE Simulations of a Fully Appended ACC V5 Design using Towing Tank Data. In: The Royal Institution of Naval Architects. Innovation in high performance sailing yachts (INNOV'SAIL 2008): [international conference] ; 29 - 30 May, 2008, [Lorient, France ; papers]: The Royal Institution of Naval Architects. London: RINA; 2008.


Renzsch H, Müller O, Graf K. FLEXSAIL – A Fluid Structure Interaction Program for the Investigation of Spinnakers. In: The Royal Institution of Naval Architects. Innovation in high performance sailing yachts (INNOV'SAIL 2008): [international conference] ; 29 - 30 May, 2008, [Lorient, France ; papers]: The Royal Institution of Naval Architects. London: RINA; 2008.


Böhm C, Graf K. RANSE Calculations of Laminar-to-Turbulent Transition-Flow around Sailing Yacht Appendages. In: Society of Naval and Marine Engineers (Hg.). The Eighteenth Chesapeake Sailing Yacht Symposium: CSYS, March 2007, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2007.


Graf K, Pelz M, Bertram V, Söding H. Added resistance in seaways and its impact on yacht performance. In: Society of Naval and Marine Engineers (Hg.). The Eighteenth Chesapeake Sailing Yacht Symposium: CSYS, March 2007, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2007.


Graf K, Renzsch H. RANSE Investigations of Downwind Sails and Integration into Sailing Yacht Design Processes. In: High Performance Yacht Design Conference Auckland/NZ Januar 2006: HPYD: Royal Institution of Naval Architects. London: RINA; 2006.


Graf K, Böhm C. A New Velocity Prediction Method for Post-Processing of Towing Tank Test Results. In: Society of Naval and Marine Engineers (Hg.). The Seventeenth Chesapeake Sailing Yacht Symposium: CSYS, March 2005, Annapolis, Maryland, USA. [Jersey City, N.J.]: Society of Naval and Marine Engineers; 2005.

 

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Velocity prediction program

Sailing Yacht Velocity and Performance Prediction

Several VPPs and Performance prediction Tools are in daily use at YRU-Kiel

  • AVPP is a classical VPP with a full featured user Interface. It focusses on classical monohulls. The aerodynamic and hydrodynamic models to predict flow Forces can either be based on generic empirical estimates or on wind tunnel-, towing tank- or CFD-results. As such AVPP serves as a´n experimental post processor to asses sailing yacht Performance, for which hydro- and aerodynamic experiments have been carried out by YRU-Kiel
  • XVPP is an Excel-based VPP featuring the same aero- and hydrodynamic models as AVPP. It can easily be employed for variational studies of design alternatives or to assess changes the sail set, to the rig and to the main dimensions. XVPP is Freeware.
  • RVPP is a dynamic top-Level VPP embedded into a RANSE flow solver. It calculates flow Forces from solving the RANS equations and is coupled with a Motion solver to predict the bahavior of the yacht in six degrees of freedom.
  • Research VPPs and Performance prediction Tools: YRU-Kiel has developed some r&d-VPPs dedicated to multihulls, canting keel yachts and other unconventional yachts.

AVPP Velocity Prediction Program

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FLEXSAIL Fluid Structure

FLEXSAIL Fluid Structure Interaction

For the design of Spinnakers sail designers are often using design shapes and cloth selections evolved through experience instead of analysis. Unfortunately these design shapes often have little resemblance to the flying shape the sail assumes, making it difficult or impossible to design for a specific behaviour of the flow around the sail. There are two methods to investigate the flying shape apart of building and testing the full scale sail: model-testing in a wind-tunnel and simulation using fluid-structure-interaction.
Model-testing requires a suitable facility, captures the flow’s behaviour only to a limited extend due to scale effects and disregards the model to full-scale difference of the sailcloth’s structural behaviour. Opposed to that simulations are carried out at full scale Reynolds number and takes into account real sail cloth and its structural behaviour.

The Yacht Research Unit Kiel has developed a program that allows to calculate the flow around a spinnaker incorporating full-scale viscous flow effects as well as the full scale properties of the sailcloth considering orthotropy and orientation. This program, called FlexSail, is based on the commercial RANSE-code CFX11, using its extensive capabilities of flow modelling. The Finite Element module is linked to CFX using an interface provided by CFX giving complete two-way coupling. This means that the external loads on the sail as calculated by CFX are transmitted to the FE-code which calculates the deformations and feeds these
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back into the flow-code giving an adapted sail-surface shape. The FE-code allows isotropic as well as orthotropic materials with the latter being oriented within the sail according to the sail-designers panel layout. The structural data calculated by the flying shape enables the sail designer to orient the sail’s panels in accordance with the load lines and select the right sailclothes for the expected loads.

Validation studies carried out using the YRU-Kiel Twisted Flow Wind Tunnel showed good consistency of the calculated and measured data for the forces as well as the flying shapes.

 

 

 

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RANSE

Free Surface Calculations - Evaluation of boat performance in the Numerical towing tank

Hydrodynamic properties of sailing yachts are traditionally evaluated by conventional towing tank testing. However, progress has been made recently towards realizing a reliable numerical towing tank by using RANSE methods with free surface capabilities. Solving the RANS equation is a numerical method capable of taking into account effects like viscosity, turbulence and flow separation.
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In presence of a free surface an additional transport equation has to be introduced to capture the free surface interface and its deformation due to the investigated body’s wave pattern. Within the method used the free surface is calculated by using an interface-capturing scheme based on a Volume-of-Fluid (VOF) approach. One of the main problems in numerical simulation of free-floating bodies is that these bodies have to be allowed to trim sink dynamically to get reasonable results, whilst RANSE solvers usually use a rigid grid.

To cope with this problem, YRU-Kiel has developed a body motion module which allows to simulate the sailing yacht in free-floating condition taking into account any combination of hull weight and sail forces and balancing them with the flow forces resulting from the simulation.

The translation and rotation of the body is determined by integrating the equation of linear and angular momentum with an first order Euler approach which has been modified for numerical stability. The resulting displacement and rotation angle are returned to the RANSE code to deform the computational grid. The flow forces are then updated and the resulting forces again used to solve the rigid body equation. This iterative procedure is carried out until convergence is achieved.

Generally said this method generates the same type of results as can be derived from towing tank testing. Accuracy of results achieved from towing tank and RANSE simulation is on equal level. One of the main advantages of the RANSE-simulation is that it can be conducted in full scale.

This way the main disadvantage of towing tank testing is avoided: RANSE simulation can satisfy Reynolds' as well as Froude's rules of similarity simultaneously, relieving the results of any uncertainties arising from the model to full scale transformation. A further advantage is that RANSE simulation allows to use exact dyamic sailing forces and moments whilst in the towing tank this values can only be estimated. This further enhances the accuracy of the simulation.

RANSE simulations as described above are capable to supplement if not substitute towing tank testing. It’s numerous advantages recommend itself for extensive hull development programs carried out with professional sail sport as AC or VOR, but due to the steep increase in available computational power this tool is also of interest for projects with smaller budgets like Olympic, TP52 or Open 60 or similar campaigns.

 

 

 

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Twist Flow Wind Tunnel

Twist Flow Wind Tunnel

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General Purpose of the Wind Tunnel
YRU-Kiel has built a Twisted Flow Wind Tunnel (TFWT) for the investigation of sails for contemporary sailing yacht design. The TFWT mimics the shear flow a yacht encounters when sailing in natural wind boundary layer. It's primary purpose is being an investigation tool for the optimization of the shape of upwind and downwind sails.

The TFWT features adjustable shear flow of up to 10 m/s flow velocity, a model size of 1.8 m mast span, a highly accurate 6 DOF force balance and a photogrammetry equipment for the evaluation of the flying shape of the sails.

Yacht Model and Trimming Devices
The yacht model, which is fixed to the measurement table, consists of a base frame and a hull/deck model. The rig has a modular set up. The main dimensions of the rig (J, I, E, …) as well as the number of stays, spreaders and supports can be changed with minimal effort. The stepper servos of the winches are controlled by the measurement PC with the help of virtual instruments and control levers.

Shape Measurements and Photogrammetry
The wind tunnel is equipped with sail shape measurement techniques based on photogrammetry. The actual flying shape of the sail under optimum trim condition can be acquired simultaneously with flow force measurements.

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Coded Targets / NURBS surface generated from Coded Targets

Velocity, Twist Angle and Turbulence Intensity Profiles or the evaluation of flow velocity profiles in the measurement plane a 3D Dantec CTA is used. The CTA allows to measure the flow velocity profile in three dimensions.

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Contour plot of the impact of the twist vanes on the flow profil

Typical Results and VPP processing
In the context of the speed prognosis (in-house VPP) the wind tunnel driving and side force coefficients are converted into lift and drag coefficients to be integrated in our AVPP velocity prediction program. The velocity polar diagram is the ultimate measure for the merit of a sail design. It allows to compare different sail designs and provides valuable data for the handling of the sail, namely cross-over wind angles and wind speeds for sail changes.

 

 

 

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