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Keyword : simulation
Results 1 - 5 of 58
AVS: A Framework for Parametric Models Setting Dedicated to Simulation of Racing Multihull Behavior
Parametric models are good candidates for modeling the dynamic behavior of racing sailboats. A large number of different models have already been developed for boats. Each one has its specificity, and works with its own set of inputs/outputs. This paper presents the Advanced Vessel Simulation environment, a framework which allows the rapid programming of sailboat simulators by creating assembly of pre-existent and custom software components. The environment describes those different components, and generates the “glue” code allowing the communication between them during the simulation process. The goal of the AVS environment is to compare the accuracy and the performances of several parametric models. Different numerical criteria are implemented. They allow the comparison of several parametric models in given sailing points and weather conditions. The AVS environment is used to compare three parametric models of a racing foiling multihull, which have different levels of specific knowledge in their equations. It turns out that accuracy of models depends on the considered output data. AVS framework provides tools to find the best model to each output, and then to build a mixed model, adapted to the simulation needs.
Bayesian Strategies for Simulation-Based Optimisation and Response Surface Creation Using a Single Tool
Surrogate models are simplified models for the behaviour of a complex system, based on a limited number of operating points where the system behaviour is simulated accurately. In hydrofoil design for sailing yachts, surrogate models can be used both for automatic shape optimisation of the foil and for performance evaluation of the entire yacht in the context of a VPP, as a response surface. We present an adaptive method for the construction of surrogate models which can be used for both these objectives, with a simple change of parameters. A Gaussian process regression (GPR) is used for the data fitting, while the adaptive choice of sample points is based either on the GPR variance or on a combination with a cross-validation error estimation. A first test on analytical functions shows that the cross-validation approach is superior for response surface creation, while both adaptation methods are equally suited for shape optimisation. A second test on the shape optimisation of a two-dimensional hydrofoil indicates thatfor moderate immersion depths, the optimum shape is not sensible to the distance to the free surface.
Modal Analysis of Pressures on a Full-Scale Spinnaker
While sailing offwind, the trimmer typically adjusts the
downwind sail "on the verge of luffing", letting occasionally
the luff of the sail flapping. Due to the unsteadiness
of the spinnaker itself, maintaining the luff on the verge of
luffing needs continual adjustments. The propulsive force
generated by the offwind sail depends on this trimming and
is highly fluctuating. During a flapping sequence, the aerodynamic
load can fluctuate by 50% of the average load.
On a J/80 class yacht, we simultaneously measured timeresolved
pressures on the spinnaker, aerodynamic loads,
boat and wind data. Significant spatio-temporal patterns
are detected in the pressure distribution. In this paper we
present averages and main fluctuations of pressure distributions
and of load coefficients for different apparent wind angles
as well as a refined analysis of pressure fluctuations, using
the Proper Orthogonal Decomposition (POD) method.
POD shows that pressure fluctuations due to luffing of the
spinnaker can be well represented by only one proper mode
related to a unique spatial pressure pattern and a dynamic
behavior evolving with the Apparent Wind Angles. The
time evolution of this proper mode is highly correlated with
load fluctuations.
Moreover, POD can be employed to filter the measured pressures
more efficiently than basic filters. The reconstruction
using the first few modes allows to restrict to the most energetic
part of the signal and remove insignificant variations
and noises. This might be helpful for comparison with other
measurements and numerical simulations.
Towards a Νew Mathematical Model for Investigating Course Stability and Maneuvering Motions of Sailing Yachts
In order to create capability for analyzing course
instabilities of sailing yachts in waves, the authors are at an
advanced stage of development of a mathematical model
comprised of two major components: an aerodynamic,
focused on the calculation of the forces on the sails, taking
into account the variation of their shape under wind flow;
and a hydrodynamic one, handling the motion of the hull
with its appendages in water.
Regarding the first part, sails provide the aerodynamic
force necessary for propulsion. But being very thin, they
have their shape adapted according to the locally
developing pressures. Thus, the flying shape of a sail in real
sailing conditions differs from its design shape and it is
basically unknown. The authors have tackled the fluidstructure
interaction problem of the sails using a 3d
approach where the aerodynamic component of the model
involves the application of the steady form of the Lifting
Surface Theory, in order to obtain the force and moment
coefficients, while the deformed shape of each sail is
obtained using a relatively simple Shell Finite Element
formulation. The hydrodynamic part consists of modeling
hull reaction, hydrostatic and wave forces.
A Potential Flow Boundary Element Method is used to
calculate the Side Forces and Added Mass of the hull and
its appendages. The Side Forces are then incorporated into
an approximation method to calculate Hull Reaction terms.
The calculation of resistance is performed using a
formulation available in the literature. The wave excitation
is limited to the calculation of Froude - Krylov forces.
Numerical Simulations of a Surface Piercing A-Class Catamaran Hydrofoil and Comparison against Model Tests
Hydrofoil supported sailing vessels gained more and
more importance within the last years. Due to new
processes of manufacturing it is possible to build slender
section foils with low drag coefficients and heave stable
hydrofoil geometries are becoming possible to construct.
These surface piercing foils often tend to ventilate and
undergo cavitation at high speeds. The aim of this work is
to define a setup to calculate the hydrodynamic forces on
such foils with a RANS based CFD method and to
investigate whether the onset of ventilation and cavitation
can be predicted with sufficient accuracy...