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Keyword : ship motion
Results 1 - 5 of 12
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.
Numerical Study of a Flexible Sail Plan: Effect of Pitching Decomposition and Adjustments
A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to har-monic pitching is presented to analyse the effects of motion simplifications and rigging adjustments on aerodynamic forces. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops. These hysteresis phenomena do not result from a simple phase shift between forces and motion. Plotting the hysteresis loops in the appropriate coordinate system enables the associated energy to be determined. This amount of exchanged energy is shown to increase almost linearly with the pitching reduced frequency and to increase almost quadratically with the pitching amplitude in the investigated ranges. The effect of reducing the real pitching motion to a simpler surge motion is investigated. Results show significant discrepancies on the aerodynamic forces amplitude and the hysteresis phenomenon between pitching and surge motion. However, the superposition assumption consisting in a decomposition of the surge into two translations normal and collinear to the apparent wind is verified. Then, simulations with different dock tunes and backstay loads highlight the importance of rig adjustments on the aerodynamic forces and the dynamic behaviour of a sail plan.
A simplified Method to Assess Acceleration loads on Sailing Yacht Masts
The behaviour of sailing boats in open sea is strictly related to their hydro and aerodynamic performances and to the wide range of loads acting on the hull and rigging system. Their evaluation could be done only by a careful seakeeping analysis with particular attention to the acceleration loads caused by hull motions which can create severe problems to mast and rigging up to extreme consequences such as dismasting. The main reasons of dismasting are related both to human errors and to the lack of load knowledge; as a matter of fact Classification Societies' Rules are quite poor about this subject and the structural design if often committed to the designer experience. The aim of this work is to investigate on the hull dynamic responses which mainly influence the mast and rigging loads with particular attention focused on the pitching behaviour of the vessel. With this goal in mind the seakeeping behaviour of a number of sailing yachts, different each other in sizes and typology, has been investigated. Despite the small size of the database, the achieved results allowed to formulate a preliminary simplified method to estimate the pitch Ratio Amplitude Operator (RAO), based only on the boat length. From the pitch RAO knowledge a very rough and quick formulation to evaluate the longitudinal acceleration in the mast centre of gravity has been obtained.
Numerical Investigation of the Unsteady Fluid Structure Interaction of a Yacht Sail Plan
This work presents simulation results of the dynamic Fluid Structure Interaction (FSI) of a J80 sail plan submitted to harmonic pitching motion. A dynamic FSI model dedicated to simulate the aero-elastic problem of yacht sails and rig has been developed, through an implicit coupling of a Vortex Lattice Method model (AVANTI) for the aerodynamics to a Finite Element Method model (ARA) for the structure dynamics. In this paper, both particular issues of aerodynamics unsteadiness and structural deformation are addressed. Results show that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. Oscillations of the aerodynamic coefficients exhibit phase shifts and hysteresis, increasing with the motion reduced frequency and amplitude, which denotes that unsteady conditions lead to aerodynamic equivalent damping and stiffening effects. Comparison of rigid versus deformable structures show that FSI increases the energy exchanged by the system and that aerodynamic forces are underestimated when the structure deformation is not considered. Concerning the dynamic loads in the rigging wires –analysed here only on forestay and backstay-, the structural and inertial effects are shown to dominate the aerodynamic effects. For the sails ropes –only main sheet studied here-, both structural and aerodynamic behaviours may play a significant role.
A 2D Smoothed Particle Hydrodynamics Theory for Calculating Slamming Loads on Ship Hull Sections
Current methods for assessing slamming of ships in head seas are generally based on constant-velocity wedge impact results for each hull section. A 2D Smoothed Particle Hydrodynamics (SPH) method is described for calculating slamming loads on realistic hull section shapes and impact velocity profiles. SPH is a particle-based method that is mesh-free and is therefore able to accurately simulate large free surface deformations such as jets and splashes, which are an important factor in slamming events. It is shown that large slamming pressures are predicted on wedge shaped hull sections and the concave part of flared monohull sections. Similarly, cross-deck slamming of catam aran hulls can produce large slamming pressures at the top of the arches. The nature of relative vertical velocity profiles during slam events is also discussed. Hull sections with varying velocity profiles are modelled using SPH to show the effect on slamming pressures as compared to the commonly used constant velocity profile.