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Keyword : performance prediction
Results 1 - 5 of 64
A Comparison of a RANS Based VPP to on the Water Sailing Performance
This paper compares performance predictions from a
Reynolds Averaged Navier Stokes (RANS) based Velocity
Prediction Program (VPP) to on the water testing of a J70.
The J70 has been outfitted with a system to determine sail
flying shapes, apparent wind conditions and performance
data. The on the water testing is conducted in both racing
and controlled sailing conditions. Data taken during racing
conditions is analyzed to determine optimal performance
envelopes while data taken in controlled conditions is used
to match exact sailing and VPP states. The data acquisition
system combines a number of standard marine sensors
including a sonic anemometer, a GPS, a digital compass, an
accelerometer and a gyroscope with custom sensors that
measure rudder and boom angles as well as a custom sail
shape acquisition system. The RANS based VPP developed
by Doyle CFD has three main components; an aerodynamic
force model, a hydrodynamic force model and an algorithm
to balance the forces. The force balance routine uses four
degrees of freedom; boat speed, yaw, heel and rudder angle
to balance the aerodynamic and hydrodynamic forces for a
given true wind speed and angle. The force models are
derived from RANS CFD data calculated using
OpenFOAM. The aerodynamic forces are calculated using
steady state RANS as a function of apparent wind angle,
apparent wind speed and sail flying shape. The VPP force
model is derived by fitting response surfaces to this data.
The aerodynamic CFD is run with sail flying shapes
recorded from on the water testing. Using accurate flying
shapes is critical for picking out slight aerodynamic
differences in sail and rig setup. The hydrodynamic CFD
data points are calculated using RANS Volume of Fluid
CFD (VOF) as a function of boat speed, rudder angle, yaw
angle, heel angle and displacement. Response surfaces are
generated from a 128 data point array of RANS VOF
simulations.
Fully Integrated Fluid-Structural Analysis for the Design and Performance Optimisation of Fibre Reinforced Sails
This paper presents an advanced and accurate integrated
system for the design and performance optimisation of
fibre reinforced sails, commonly named string sails,
developed by SMAR Azure. This integrated design system
allows sail designers not only to design sail shapes and the
reinforcing fibre paths, but also to validate the performance
of the flying sail shape and have accurate production
details including the overall sail weight, material used,
which means costs, and length of the fibre paths, which
means production time.
The SMAR Azure design and analysis method,
extensively validated and used to optimise several racing
and super-yacht sailing plans, includes a computationally
efficient structural analysis method coupled with a
modified vortex lattice method, with wake relaxation, to
enable a proper aeroelastic simulation of sails in upwind
conditions. The structural analysis method takes into
account the geometric non-linearity and wrinkling
behaviour of membrane structures, such as sails, the fibre
layout, the influence of battens, trimming loads and
interaction with rigging elements, e.g. luff sag calculation
on a headstay, in a timely manner.
Specifically, this paper presents an optimisation of a real
fibre reinforced membrane sailplan of an aluminium super
yacht, carried out in collaboration with Paolo Semeraro
(Banks Sails Europe). The optimisation process of the fibre
layouts led to a sensible reduction in maximum stress,
strain and displacement compared to the initial designs,
keeping the same fibre weight or slightly increasing it. The
results have been confirmed in the sailing tests, although no
exact measurements have been performed.
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.
The Influence of Sailor Position and Motion on the Performance Prediction of Racing Dinghies
The time-varying influence of a sailor’s position is
typically neglected in dinghy velocity prediction programs
(VPPs). When applied to the assessment of dinghy race
performance, the position and motions of the crew become
significant but are practically hard to measure as they
interact with the motions of the sailboat. As an initial stage
in developing a time accurate dinghy VPP this work
develops an on-water system capably of measuring the
applied hiking moment due to the sailor’s pose and
compares this with the resultant dinghy motion. The
sailor’s kinematics are captured using a network of inertial
motion sensors (IMS) synchronised to a video camera and
dinghy motion sensor. The hiking moment is analysed
using a ‘stick man’ body representation with the mass and
inertial terms associated with the main body segments
appropriately scaled for the representative sailor. The
accuracy of the pose captured is validated using laboratory
based pose measurements. The completed work will
provide a platform to model how sailor generated forces
interact with the sailboat to affect boat speed. This will be
used alongside realistic modelling of the wind and wave
loadings to extend an existing time-domain dynamic
velocity prediction program (DVPP). The results are
demonstrated using a single handed Laser and demonstrate
an acceptable level of accuracy.
Performance Assessment and Optimization of a C-Class Catamaran Hydrofoil Configuration
Recent breakthroughs in the America's Cup have put hydrofoil technology in the focus of high-performance sailing. This paper describes the performance assessment of two different centreboard hydrofoils designed for a C-class catamaran. Regarding the numerous design criteria resulting from sailing on hydrofoils, a reliable performance assessment tool helps to find the best compromise [1]. A Velocity Prediction Program (VPP) has been developed in order to facilitate the analysis of numerical simulation results obtained for appendages and the wing-sail in terms of speed potential of the C-Cat. The approach used to model the hydroand aerodynamic forces on the catamaran is described, along with the challenges peculiar to a VPP model for sailing on hydrofoils. Different optimization schemes for trimming the wing-sail and hydrofoil configurations are tested to obtain the theoretically most efficient trim settings and to evaluate the different hydrofoil designs. Using the developed VPP model, realistic velocity prediction can be carried out. The catamaran flying on hydrofoils sails at up to 2.8 times the true wind speed in many conditions. Records and observations made during the International C Class Cup (ICCC) of 2013 confirm the predicted performance of the modelled C-Cat. Some remaining challenges in velocity prediction of vessels equipped with hydrofoils are highlighted.