Maxsurf News August 2005

In this issue:

Multihull Design
Resistance Prediction
SHIPFLOW Interface
Optimisation
Enhanced Structural Definition
User Profile - VanDerHeijden Steelyachts

Formation Design Systems is pleased to announce the release of version 11.1 of Maxsurf. The product development program of enhancements and additions has continued at a rapid pace. All members of the Maxsurf subscription program will be sent Maxsurf version 11.1 over the coming weeks.

Multihull Design

The Maxsurf ship design and analysis software suite is widely used throughout the world by a large number of naval architects, shipyards and designers. In the latest release, Formation has focused on providing additional tools which will enable users to quickly prototype and optimise hull forms.

Following an increase in the number of multihulls being designed, Formation has added features that will assist in their design and analysis. Whilst it has always been possible to design and analyse stability characteristics of multihulls in Maxsurf, it has been more difficult to estimate the resistance of such vessels. This capability has now been achieved by adding theoretically based resistance prediction to the Maxsurf suite of applications.

Resistance Prediction

Hullspeed is the resistance prediction tool in the Maxsurf suite. It includes a comprehensive range of regression-based methods for a variety of monohull vessel types. In the latest version Formation has added a theoretical wave resistance method. This is suited to slender mono and multihull designs. The method is based on Michell’s method and is applicable to slender hull forms. Because the individual demihulls of catamarans (and other multihulls) are normally extremely slender, this method is ideally suited to the resistance prediction of those vessels.
 
Using the same theory, Hullspeed is able to predict the waves generated by mono and multihull vessels as shown below. This provides effective visualisation of results and also helps explain the analysis to the client.

SHIPFLOW Interface    

Computational Fluid Dynamics (CFD) has become a widely accepted tool for predicting ship resistance. For users requiring   sophisticated CFD calculations, Maxsurf's Hydrolink data exchange module now supports export to the SHIPFLOW file format. SHIPFLOW is a CFD package for computing ship resistance. It is produced by Flowtech International AB in Sweden (www.flowtech.se) and provides drag and lift calculations, optimised for ship forms. Hydrolink supports the definition of hull groups and the sections that define the shape within each group.
The group and section data are then exported in the SHIPFLOW file format. Formation was fortunate to have had the assistance of industry partner Force Technology (FT), Denmark (www.force.dk) during this development. This facility allows FT to quickly generate SHIPFLOW models from Maxsurf designs assisting in the optimising of hull lines and in particular the flow around bulbous bows.

Optimisation

The additional analysis tools and interfaces described above become even more powerful when coupled with the parametric transformation tool in Maxsurf. This enables the very rapid generation of a systematic series of hull forms from one parent hull. The systematic series can then be rapidly analysed in Hullspeed  and in Seakeeper for seakeeping performance.

Enhanced Structural Definition

Workshop, the Maxsurf suite’s structural modelling program, has had a very significant range of enhancements over the past few years. This continues in the version 11.1 release with the major addition being the ability to define both open frames and frames with varying web depth. A parametric design philosophy is maintained allowing concurrent design practices; i.e. the primary structure can be defined while the hullform is still undergoing final refinement. Once the hullform is completed, it is simply a matter of recalculating the frames and other structural elements in Workshop to take the modified hullform into account.

Another improvement is the way in which longitudinal stringer punch-outs in frames are stretched to take into account local hull shape. Instead of simply scaling the punch-outs, they are stretched so that circular arcs remain arcs (rather than becoming ellipses). This is important when the data is sent to NC cutting machines.

Finally, our focus on effectively linking design to production is continuing with this release of Workshop. Formation has again enhanced the link with ShipConstructor to provide production-ready frame data and accurate definition of hull stiffener locations.

The Workshop/ShipConstructor link is now being used by a range of shipyards involved in construction of naval vessels, high-speed ferries and tanker refits amongst others. The link helps improve communication between design and production teams by creating a unified 3D product model of the ship structure.

User Profile - VanDerHeijden Steelyachts 

VanDerHeijden Steelyachts is a small shipyard from the Netherlands specialising in the construction of luxury steel yachts. Founded in 1993, the yard has delivered over 200 yachts from a range of standard hull series designed by external designers. In recent years, an increasing number of prospective customers have been requesting custom design hulls, and so VDH made the decision to introduce an in-house design department and implement the Maxsurf suite for vessel design and ShipConstructor for vessel detailing. Not only does this enable the yard to sell into a bigger market, it also creates the opportunity to change over to more efficient building practices and increase product quality.

Maxsurf’s developable surface function is used to accurately model the hull so that it can be built from 100% developable plate. Workshop is used to develop the plate and calculate any regions where strain occurs. The plate parts are exported to ShipConstructor from where they are detailed and nested. The nests are then exported to NC files, which can be directly sent to the plasma cutting machine at VanDerHeijden. A high degree of developability of the hull plates allows VanDerHeijden to save cost on plate forming equipment and production resources. The Maxsurf/ShipConstructor combination helps them deliver highly accurate work packages to the shop floor, ready for assembly and with an absolute minimum of rework.

Recently VanDerHeijden started construction of a newly designed yacht with a flared bow. The plates in the bow region are divided up in such way that the strain in each of the plates is within the yard’s practical bending limits.

Maxsurf and ShipConstructor have allowed VanDerHeijden to completely review their building process; the existing practice was to start with the keel and hull plate and then, using a trial and error method, bend the transverse stiffeners and fit them to the hull plate. After introducing Maxsurf and ShipConstructor, VanDerHeijden is now able to reverse the building process; frames and longitudinals first, and then simply fold the hull plates along the framework. With this approach, parts no longer require any bending. This saves a significant amount of time and is made possible by highly accurate production information directly derived from the 3D model.