Zyz sailing team started designing and manufacturing small sailing boats in 2008 to participate to Italian inter-university regattas called 1001velaCUP. During the first eight-year experience of the team, different boats have been launched, trying to optimize all different aspects that influence the final performance of a boat. R3 class rule adopted in this competition imposes geometrical and structural constrains to the design process: maximum length x beam of the boat is 4,60 x 2,10 m, while a minimum percentage weight for the hull constituted by 70% of plant-origin material is imposed.
The first pioneering attempt of the team was a small dinghy called Zyz. The design process used for Zyz was based mainly on hydrostatic analyses of the hull. Dimensioning of internal reinforcements didn’t follow a systematic study but came out from the team experience. A classic strip-planking technique was used to manufacture the entire boat. The result was definitely over-dimensioned and the boat, after the first regattas, was subjected to consistent modification.
The first experience given by Zyz, suggested to adopt a different approach for the design process. Expertise of the team members have then been addressed to implement a fully integrated simultaneous design approach using numerical analysis tools. A concurrent methodology was followed where Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) worked in parallel onto the parametric CAD model of the new boat. The easy integration with external parametric CAD (CREO 3.0 from PTC) and between Structural Mechanical and Fluid Dynamic packages convinces the team to adopt ANSYS Workbench and Fluent as numerical tools of the design process.
Starting from the typical shape of a skiff, under some preliminary assumptions in terms of total displacement, wind velocity and sailing conditions, an iterative procedure was adopted to obtain the final shape and structure of the new boat LED (acronym of Linen Epoxy Dinghy). Results of CFD in terms of pressures on sails, hull and appendages were used as input load conditions for FEM analyses. Concerning the hull, in order to evaluate the free surface effect, the Volume of Fluid (VOF) model has been applied with a high quality structured hexahedral mesh. At the same time, different sail plans and appendages have been investigated.
If aim of the CFD was to assess the best external shape of hull, sails and appendages, FEM was used to optimize the reinforcement configuration inside the hull. The first choice of the team was to develop a green-based material for the hull: a sandwich made of flax composite skins and cork core was designed and manufactured. Material selected for internal reinforcements was okoumè plywood. A realistic FEM model of the hull was obtained using the ANSYS Composite PrepPost (ACP) module. A symmetric angle-ply stacking sequence of the skin/core/skin material was implemented into the ACP module and used in ANSYS Mechanical for structural analysis. Preload conditions on mast and shrouds due to rigging have been added to loads coming from CFD results and static structural analyses were preliminarily launched. First results evidenced the location of the most stressed areas for hull panels and for reinforcements. Final configuration was decided and LED was manufactured with resin Infusion technique at the University of Palermo laboratories.
Then the team decided to plan an experimental setup with the double aim to validate preliminary results obtained with FEM and to install a real time monitoring system of the strain state of the boat. Single grid Electrical Resistance (ER) gauges and multiple grid rosettes have been installed in those areas where FEM results locate the critical values of deformations. Considering that the hull is a sandwich made of flax composite skins and an agglomerated cork core, for the determination of principal strain components on the internal skin, four three-grid rosettes have been applied plus a thermal compensator rosette. For the determination of maximum strains on internal transversal and longitudinal stiffeners made of okoumè plywood, four single-grid strain gages have been installed, plus a thermal compensator strain gage. Good agreement was noted between FEM and ER results for simple load condition simulated in laboratory.
A systematic use of numerical simulation tools from ANSYS has been here reported: in particular, Fluent for a complete determination of the fluid dynamics of hull, sails and appendages, ACP to realistically reproduce material characteristics of the green sandwich and ANSYS Mechanical to determine the strain state of the internal reinforcements. Final result was LED, a very light and stiff boat, able to successfully challenge in its sailing class.
EDITORS NOTE: This blog was co-authored by:
Antonio Mancuso is professor of Design and Methods in Industrial Engineering at the Università degli Studi di Palermo (Italy). He is the team principal of the university sailing team Zyz. His fields of interest are Design and Optimization methodologies, Sailing Yacht Design and numerical simulations.
Giuseppe Pitarresi is professor of Mechanics of Materials and Machine Design at the Università degli Studi di Palermo (Italy). He deals with materials characterisation within the sailing team Zyz. His main research fields comprise: Experimental Stress Analysis and Non-Destructive Evaluation and Mechanical Characterisation of Polymers and Polymer Matrix Composites.
Davide Tumino is assistant professor of Design and Methods in Industrial Engineering at the Università degli Studi di Enna Kore (Italy). He supports the sailing team Zyz on issues related to design and structural dimensioning. His fields of interest are Design and Optimization methodologies, Sailing Yacht Design and numerical simulations.