scholarly journals An Improved Procedure for Strongly Coupled Prediction of Sailing Yacht Performance

2021 ◽  
Vol 6 (01) ◽  
pp. 133-150
Author(s):  
A. Persson ◽  
L. Larsson ◽  
C. Finnsgård
Keyword(s):  
Free Surface ◽  
Wind Speed ◽  
Control Algorithm ◽  
Body Motion ◽  
Force Model ◽  
Strongly Coupled ◽  
Performance Predictions ◽  
Correct Alignment ◽  
Sailing Yacht ◽  
Background Grid

Abstract In this paper, an improved procedure for strongly coupled prediction of sailing yacht performance is developed. The procedure uses 3D RANS CFD to compute the hydrodynamic forces. When coupled to a rigid body motion solver and a sail force model, along with a rudder control algorithm, this allows sailing yacht performance to be predicted within CFD software. The procedure provides improved convergence when compared to a previously published method. The grid motion scheme, partially using overset grid techniques, means that correct alignment between the free surface and the background grid is ensured even at large heel angles. The capabilities are demonstrated with performance predictions for the SYRF 14 m yacht, at one true wind speed, over a range of true wind angles, with up- and downwind sailsets. The results are compared to predictions from the ORC-VPP for a yacht with similar main particulars.

A Procedure for Encapsulation in Microchannel

2007 ◽  
Author(s):  
Y. F. Yap ◽  
J. C. Chai ◽  
N. T. Nguyen ◽  
T. N. Wong ◽  
L. Yobas
Keyword(s):  
Surface Force ◽  
High Viscosity ◽  
Moving Boundaries ◽  
Body Motion ◽  
Force Model ◽  
Governing Equations ◽  
Strongly Coupled ◽  
Carrier Fluid ◽  
Grid Approach ◽  
Three Phases

A fixed-grid approach for modeling the motion of a particle-encapsulated droplet carried by a pressure driven immiscible carrier fluid in a microchannel is presented. Three phases (the carrier fluid, the droplet and the particle), and two different moving boundaries (the droplet-carrier fluid and droplet-particle interfaces), are involved. This is a moving boundaries problem with the motion of the three phases strongly coupled. In the present article, the particle is assumed to be a fluid of high viscosity and constrained to move with rigid body motion. A combined formulation using one set of governing equations to treat the three phases is employed. The droplet-carrier fluid interface is represented and evolved using a level-set method with a mass correction scheme. Surface tension is modeled using the Continuum Surface Force model. An additional signed distance function is employed to define the droplet-particle interface. Its evolution is determined from the particle motion governed by the Newton-Euler equations. The governing equations are solved numerically using a Finite Volume method on a fixed Cartesian grid. For demonstration purpose, the flows of particle-encapsulated droplets through a constricted microchannel and through a microchannel system are presented.

Advanced CFD Simulations of free-surface flows around modern sailing yachts using a newly developed openFOAM solver

2016 ◽  
Author(s):  
Janek Meyer ◽  
Hannes Renzsch ◽  
Kai Graf ◽  
Thomas Slawig
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Breaking Waves ◽  
Free Surface Flows ◽  
Body Motion ◽  
Computational Time ◽  
Efficient Computation ◽  
Surface Flows ◽  
Scale Free ◽  
Wide Range

While plain vanilla OpenFOAM has strong capabilities with regards to quite a few typical CFD-tasks, some problems actually require additional bespoke solvers and numerics for efficient computation of high-quality results. One of the fields requiring these additions is the computation of large-scale free-surface flows as found e.g. in naval architecture. This holds especially for the flow around typical modern yacht hulls, often planing, sometimes with surface-piercing appendages. Particular challenges include, but are not limited to, breaking waves, sharpness of interface, numerical ventilation (aka streaking) and a wide range of flow phenomenon scales. A new OF-based application including newly implemented discretization schemes, gradient computation and rigid body motion computation is described. In the following the new code will be validated against published experimental data; the effect on accuracy, computational time and solver stability will be shown by comparison to standard OF-solvers (interFoam / interDyMFoam) and Star CCM+. The code’s capabilities to simulate complex “real-world” flows are shown on a well-known racing yacht design.

Centrifugal waves

1960 ◽  
Vol 7 (3) ◽  
pp. 340-352 ◽  
Author(s):  
O. M. Phillips
Keyword(s):  
Free Surface ◽  
Angular Velocity ◽  
Circular Cylinder ◽  
Rigid Body ◽  
Water Depth ◽  
Frequency Equation ◽  
Rigid Rotation ◽  
Body Motion ◽  
Small Perturbations ◽  
The Stability

When a hollow circular cylinder with its axis horizontal is partially filled with water and rotated rapidly about its axis, an almost rigid-body motion results with an interior free surface. The emotion is analysed assuming small perturbations to a rigid rotation, and a criterion is found for the stability of the motion. This is confirmed experimentally under varying conditions of water depth and angular velocity of the cylinder. The modes of oscillation (centrifugal waves) of the free surface are examined and a frequency equation deduced. Two particular modes are considered in detail, and satisfactory agreement is found with the frequencies observed.

scholarly journals Wind Speed and Direction Estimation from Wave Spectra using Deep Learning

2021 ◽  
Author(s):  
Haoyu Jiang
Keyword(s):  
Wind Speed ◽  
High Frequency ◽  
Deep Neural Networks ◽  
Fourier Coefficients ◽  
Ocean Wave ◽  
Wave Spectra ◽  
Strongly Coupled ◽  
Wave Measurements ◽  
Short Period ◽  
Wind Measurements

Abstract. High-frequency parts of ocean wave spectra are strongly coupled to the local wind. Measurements of ocean wave spectra can be used to estimate sea surface winds. In this study, two deep neural networks (DNNs) were used to estimate the wind speed and direction from the first five Fourier coefficients from buoys. The DNNs were trained by wind and wave measurements from more than 100 meteorological buoys during 2014–2018. It is found that the wave measurements can best represent the wind information ~1 h ago, because the wave spectra contain wind information a short period before. The overall root-mean-square error (RMSE) of estimated wind speed is ~1.1 m/s, and the RMSE of wind direction is ~14° when wind speed is 7~25 m/s. This model can not only be used for the wind estimation for compact wave buoys but also for the quality control of wind and wave measurements from meteorological buoys.

Development of a New Contact Angle Control Algorithm for Level-Set Method

2018 ◽  
Vol 141 (6) ◽  
Author(s):  
Mengnan Li ◽  
Kaiyue Zeng ◽  
Louis Wonnell ◽  
Igor A. Bolotnov
Keyword(s):  
Contact Angle ◽  
Control Algorithm ◽  
Force Model ◽  
Flat Plates ◽  
Flow Solver ◽  
Evaporation And Condensation ◽  
Condensation Algorithm ◽  
Current Contact ◽  
Mesh Resolution ◽  
Structured Meshes

A contact angle control algorithm is developed and implemented in the multiphase interface tracking flow solver—phasta. The subgrid force model is introduced to control the evolving contact angle. The contact angle force is applied when the current contact angle deviates from the desired value (or range of values) and decreases to zero when it reaches the desired value. The single bubble departure simulation and the capillary flat plates simulation are performed for verification purpose. The numerical results are compared with the analytical solution with good agreement. The mesh resolution sensitivity analysis and parametric study are conducted for both simulations. Coupled with the other existing capabilities in phasta like evaporation and condensation algorithm, the contact angle control algorithm will allow us to investigate the boiling phenomenon in various conditions with lower cost (by utilizing localized mesh refinement for bubble growth region) compared to uniformly refined structured meshes and in engineering geometries.

Mitigation of Biodynamic Response to Shock Loads Using Semi-Active Vertically Stroking Crew Seats

2010 ◽  
Author(s):  
Harinder J. Singh ◽  
Norman M. Wereley
Keyword(s):  
Human Body ◽  
Control Algorithm ◽  
Equations Of Motion ◽  
Comprehensive Analysis ◽  
Lumped Parameter Model ◽  
Force Model ◽  
Body Parts ◽  
Governing Equations ◽  
Lumped Parameter ◽  
Yield Force

This study addresses mitigation of biodynamic response due to an initial velocity impact of a vertically stroking crew seat using an adaptive magnetorheological energy absorber. Under consideration is a multiple degree-of-freedom detailed lumped parameter model of a human body falling with prescribed initial crash velocity (sink rate). The lumped parameter model of the human body consisted of four main parts: pelvis, upper torso, viscera and head. The governing equations of motion of a vertically stroking crew seat incorporating a human body were derived using parameters such as available damper stroke as well as MR yield force. The control algorithm for smooth landing of a rigid occupant was examined for compliant occupant and was modified accordingly. Four MR yield force models were analyzed to shape decelerations experienced by human body and an appropriate model was selected for comprehensive analysis. The simulated responses were analyzed with selected MR yield force model for a crew seat with an occupant corresponding to 90th percentile male at sink rates varying from 8 to 12 m/s. In addition, the mitigation of injuries to the human body parts due to load transmissions corresponding to crash velocities was also evaluated for the selected MR yield force model along with terminal conditions necessary for smooth landing.

Free-Surface Effects of Variations in Appendage Vertical Volume Distribution: Where does a Bulb not See the Free-Surface?

2011 ◽  
Author(s):  
Jonathan R. Binns ◽  
Robert Thompson ◽  
Paul A. Brandner ◽  
Leonard Imas
Keyword(s):  
Free Surface ◽  
Aspect Ratio ◽  
Wave Resistance ◽  
Volume Distribution ◽  
Drive Force ◽  
Centre Of Gravity ◽  
Numerical Predictions ◽  
Sailing Yacht ◽  
Hydrodynamic Effects ◽  
The Vertical Distribution

The vertical distribution of appendage volume for a sailing yacht is predominantly driven by the desire for the lowest possible centre of gravity due to the dependence of sail drive force on stability. This results in volume being pushed downwards regardless of hydrodynamic effects. The increase in aspect ratio of the appendages is also increased with greater draft, resulting in a higher efficiency as well as greater drive force. However, some modern designs have reached the limit of draft in terms of restricted access to ports, structural and rule limitations. To counter these restrictions it is not uncommon to incorporate lifting or swing keels to reduce draft at specified times. The effects on aspect ratio and stability are relatively easy to approximate for such a vertical shift in volume, the effects on the free surface are much more difficult to accurately predict. For this purpose some novel experiments using extreme shifts in vertical volume distribution have been performed and compared with numerical predictions. Limits on submergence beneath which appendages effectively “see” no wave resistance have been established based on numerical and experimental results.

Finite Element Analysis of Nonlinear Water Wave-Body Interaction: Computational Issues

2012 ◽  
Author(s):  
C. P. Vendhan ◽  
P. Sunny Kumar ◽  
P. Krishnankutty
Keyword(s):  
Finite Element ◽  
Free Surface ◽  
Water Waves ◽  
Water Wave ◽  
Large Body ◽  
Boundary Integral ◽  
Body Motion ◽  
Fe Model ◽  
Computational Domain ◽  
Hexahedral Elements

Design of floating structures exposed to water waves often requires nonlinear analysis because of high wave steepness and large body motion. In this context, Mixed Eulerian-Lagrangian (MEL) methods for nonlinear water wave problems based on the potential flow theory have been studied extensively. Here, the Laplace equation with Dirichlet boundary condition on the free surface is solved using the boundary integral method, and a time integration method is used to find the particle displacements and velocity potential on the free surface. Finite element methods based on the MEL formulation have been developed in the 90s. Several researchers have pursued this approach, addressing the various challenges thrown open, such as velocity computation, pressure computation on moving surfaces, remeshing of the computational domain, smoothing and imposition of radiation condition. Apart from these, the implementation of the FE model in particular involves several computational issues such as element property computation, solution of large banded matrix equations, and efficient organization of computer storage, all of which are crucial for the computational tool to become successful. A study of these aspects constitutes the primary focus of the present work. The authors have recently developed a 3-D FE model employing the MEL formulation, which has been applied to predict waves in a flume and basin. The fluid domain is discretized using 20-node hexahedral elements. The free surface equations are solved in the time domain employing the three-point Adams-Bashforth method. Validation of the numerical model and relative computation times for salient steps in the FE model are discussed in the paper.

Strongly Coupled Analysis of Fluid-Structure Interaction with Free Surface Flow

PAMM ◽  
2004 ◽  
Vol 4 (1) ◽  
pp. 338-339 ◽  
Author(s):  
Andreas Kölke ◽  
Elmar Walhorn ◽  
Björn Hübner ◽  
Dieter Dinkler
Keyword(s):  
Free Surface ◽  
Fluid Structure Interaction ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Coupled Analysis ◽  
Fluid Structure ◽  
Strongly Coupled ◽  
Structure Interaction

Systematic Study of the Hydrodynamic Forces on a Sailing Yacht Hull Using Parametric Design and CFD

2011 ◽  
Author(s):  
Lionel Huetz ◽  
Bertrand Alessandrini
Keyword(s):  
Wind Speed ◽  
Design Process ◽  
Parametric Design ◽  
Early Stage ◽  
Hydrodynamic Forces ◽  
Design Parameters ◽  
Shape Parameters ◽  
Prediction Program ◽  
The Matrix ◽  
Sailing Yacht

In order to predict the velocity and attitude of a sailing yacht travelling in a given wind speed and wind angle, the hydrodynamic problem and the aerodynamic problem need most of the time to be decoupled. Two matrices are built to characterize the hydrodynamic and the aerodynamic behavior separately. Then a Velocity Prediction Program (VPP) interpolates the matrices and finds the equilibrium between the forces acting on the hull and appendages on one side, and the forces acting on the sails on the other side. This gives the velocity and attitude of the yacht depending on the wind speed and wind angle. Two main approaches are currently used to build the hydrodynamic matrix. The first method is to build a reduced or a virtual model with the proper hull shape and test it in a towing tank or a Computational Fluid Dynamics (CFD) program. This approach can lead to a very precise estimation of the matrix for a given hull shape, but it is time consuming and gives no indication on other possible hull shapes. The second method is to build and test various hull shapes and use this database to build analytical formulas describing the evolution of the hydrodynamic forces depending on the speed and attitude, but also on the hull shape, via several “shape parameters”. During the early stage of design, numerous hulls are to be evaluated, and it is very valuable to understand the influence of the design parameters on hydrodynamic efficiency of the hull. Therefore, the second method should be much more efficient at this stage of the design process. The most used regressions have been provided by J.A. Keuning et al., based on the Delft Systematic Yacht Hull Series, [1], [2]. This work began in 1971; the sailing yacht hull shapes have changed a lot since then. The aim of the present work is to enhance these regressions, by using new shapes in the database and by adding new “shape parameters” to describe the hulls. A powerful loop driven by the commercial software ModeFrontier has been developed in order to build a database by means of CFD. Systematic morphing of the hull shapes, parallel computing, automatic meshing and automatic post-treatment will provide a large database in a relatively short time. The aim of the ongoing work is to improve the accuracy and sensitivity of the prediction of yacht hull performance during the early stages of the design process. The study will focus on flat water, steady predictions. The following results concern exclusively bare hulls, the interaction between the hull and its appendages will be treated separately.

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