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| New net and surface rendering in v14 (Enlarge) |
Maxsurf News - December 2008
The naval architecture profession and the associated ship and boat building industries wax and wane from year to year. Recently most of our Maxsurf customers have experienced boom times as demand for new vessels across all sectors has been at an all time high. The world wide economic crisis in the latter part of this year will see things return to a more normal level. But regardless of whether business is rising or falling, one thing that doesn't change from year to year is our commitment to keep enhancing Maxsurf. Our goal is to ensure that each release adds features that improve its capability and productivity in your design office.
This year is no exception as we add more major enhancements to Maxsurf in version 14. All members of the Maxsurf subscription program will be sent Maxsurf version 14 over the coming weeks.
NURB Curves in Maxsurf
The major new feature in version 14 is the addition of capability to carry out curve based modelling in Maxsurf. This facility is useful for initial definition of key lines, to simplify trimming, and to facilitate data interchange with other surface modelling programs that also use curves extensively, like Rhino, Alias Studio and Catia.
Maxsurf's NURB surfaces ensure that hulls created using Maxsurf have a high degree of fairness. However it is often useful to use a master curve or curves as a starting point when creating a new design or when modifying surfaces in a design. The new NURB curve capability in Maxsurf 14 allows you to use curves to construct surfaces using the master curves to define the initial key geometry of your design.
Curve Creation
The curves can be created in two ways, either using the usual NURB control points, as used on surfaces, or using marker points. Curves created using control points behave in the same way as surface edges i.e. the end points lie on the curve and intermediate points influence curve shape but don't lie on the curve. Curves defined using marker points interpolate the curve through those data points. The first curve type prioritises curve fairness while the second prioritises matching the curve to existing known data points. Data points added are actually a special type of marker that retains a link to the curve. So if a marker that is linked to the curve is moved, the resulting curve shape will also adapt to the new position. Users familiar with Maxsurf will find the use of the control point curves is very similar to shaping with control points on surfaces.
Two other curve types that can be created with Maxsurf, that are a subset of the above two curve types, are linear curves (or polylines) and circles. The linear curves are simply a NURB curve with a stiffness of 2, while the circle is defined using a NURB curve of stiffness 6 and with its control point positions and control point weights set up to give a circular shape. Most geometric operations available for Maxsurf surfaces (i.e. flipping, moving, rotating) are also available for curves (see the Curve menu) and the functions available for manipulating control points on surfaces can also be used to manipulate control points on curves.
Trimming Surfaces with Curves
Up until now, Maxsurf's trimming capabilities have been based on using one surface to trim a piece out of another surface. With the version 14 curves, this dynamic trimming capability can be used to trim a portion of surface away using a curve projected on to the surface. This removes the need to have surfaces in the model just for trimming purposes and results in improved speed, a simpler model and more precise control over trimming.
The user has control over which surfaces a given curve will trim. This also simplifies the model, particularly when the projected curve intersects with multiple surfaces. For example, if you project a curve horizontally when working on a trimaran model, you can control whether the trimming curve affects the centre hull, outer hulls or both.
The trimming curves are projected on to the surface in the projection direction as defined in the curve's properties. The default projection direction of the curve depends on the view in which the curve was created. For example a curve created in the profile view will have a default projection direction of horizontal.
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| Hull trimming using one polyline and one circle trimming curve (Enlarge) |
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| Creating a surface using skinning over a curve group (Enlarge) |
Surface Skinning
A new Skin Surfaces command creates a surface by skinning it across a set of selected curves. When creating a skinned surface there is a balance between creating a surface with an exact fit (i.e. passes exactly through all the curves) and a fair surface (usually the fewer number of control points the fairer the surface). When creating the surface the fitting tolerance settings can be adjusted to obtain the desired surface fairness and accuracy of fit.
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| RIB collar created using a swept surface (Enlarge) |
Swept Surfaces
The Swept Surface command creates a surface
from two curves. The first curve selected is termed the “rail curve”
and the second curve the “section curve”. The new surface is created by
sweeping the section curve along the trajectory of the rail curve. A
swept surface is very useful for creating rounded edges, collars or
spray rails.
Patch Surface
The new Create 4 Sided Patch function can be used to make a surface patch within the boundary defined by four curves. The curves do not need to be compatible (i.e. do not need to share the same number of control points or stiffness) and do not need to be of the same type (i.e. control point curve or data point curve). This function is useful for a quick creation of a hull surface from four curves such as a transom curve, a deck edge curve, a bow curve and a keel curve.
New Drawing Functions
A range of new drawing functions have been added to support curve creation. These include new grid, drawing depth, axis indicator, and object snapping functions. The new concept of drawing depth gives you control over the depth at which curves are drawn. This is adaptive so that you can select objects in the model to dynamically move the drawing depth to the depth of the selected item.
Hydromax Enhancements
As well as the many new modelling functions in maxsurf, we are continuing to enhance our analysis modules, especially Hydromax's stability capabilities. Hydromax now supports calculation of maximum safe heeling angles for sailing vessels. These calculations are derived from the value of GZ at a critical heel angle, for example the angle of downflooding or angle of deck edge immersion. Once a GZ curve has been calculated, you can display the maximum safe heeling angle curves by selecting the graph type in the pull-down menu.
You can specify the critical condition that should not be exceeded due to a gust or squall. MCA requires downflooding point immersion be considered however you can include additional criteria if desired. You can also change the shape of the heeling arm curve, the gust ratio and the squall wind speeds.
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| New graphs of hydrostatic properties during large angle stability (Enlarge) |
Load Case Management
Load case management has also been
enhanced in Hydromax with the ability to create master groups of loads
and then cross reference these load groups in subsequent load cases.
The most obvious application of this would be to have a large list of
items in a Lightship load group and then reference that load group as a
single item in subsequent load cases.
You can also now copy and
paste weight information from the Workshop structural layout program
into the load cases in Hydromax. Some of the many other enhancements to
Hydromax include user defined tank levels at which free surface moments
should be applied, more control over data visibility, and new Limiting
KG options for damaged tanks containing liquid cargo.
Workshop
We continue to enhance Workshop to make it an ideal environment for laying out stringers and frames. The latest enhancement allows you to specify the properties of a frame location so that it is treated as a bulkhead. This automatically breaks stringers by a defined distance forward and aft of the frame and optionally prevents stringer cutout insertion in the bulkhead.
Project Profile - Designing Min of the Desert
It’s not everyday that you get asked to help design a reconstruction of a three-and-a-half thousand-year old ship, but this happened to FormSys’ senior naval architect Patrick Couser back in June 2006. A project, led and funded by French Production house Sombrero and Co (www.sombreroandco.fr) required the construction of such a vessel.
This project aimed to re-enact part of the fabled voyage of Queen Hatshepsut to the mythical land of Punt in a documentary that they were producing about the Pharaoh. Working in a team including Maritime Archeologist and Egyptologist Dr Cheryl Ward of Florida State University and Tom Vosmer, a shipwright with much experience in the construction of ancient ship replicas, FormSys’ Dr Patrick Couser worked to produce a design of a hypothetical reconstruction of an ancient Egyptian ship capable of navigating the Red Sea.
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| Bas-reliefs at Deir el Bahri; ships' timbers from Wadi Gerwasis and one of the Dashur boats (Enlarge) |
The design is based on three primary sources: iconic evidence from the
bas-reliefs at Hatshepsut’s funerary monument at Deir el Bahri which
depict the voyage to Punt; ships’ timbers found in excavations at Wadi
Gerwasis on the banks of the Red Sea; and the Dashur ships excavated in
the late 19th Century. The design was developed in Maxsurf where the
ability to use digital images of the bas-reliefs as background images
was invaluable. Since the bas-relief images only provided profile
views, the body-plan was based on a lines-plan lifted from the Dashur
boat at the Chicago museum that Cheryl Ward had previously documented.
The design was then analysed in Hydromax and Seakeeper to assess its
performance and ability to navigate the Red Sea, this led to some
subsequent modifications of the hull form to provide a more sea-going
vessel than the Dashur boat which would only have navigated the Nile
river.
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| Maxsurf model of the vessel (Enlarge) |
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| Hydromax analysis of Min's stability (Enlarge) |
Even Workshop was used to help define the positions of
the plank seams by tracing stringers along the hull. A NURBS IGES file,
exported from Maxsurf, was used make a scale-model in foam using a CNC
milling machine at Florida State University. This model was, in turn,
used to help determine the planking arrangement. The planking
arrangement was verified by Tom Vosmer by building another scale model
using hand-carved wooden planks before construction of the full-size
vessel.
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| Various stages of construction (Enlarge) |
The vessel was built at a shipyard in Rashid (Rosetta), a
port city near the mouth of the Nile, in Egypt. The timber used for the
construction was Oregon pine – similar in properties to, but more
readily available than, Lebanon cedar (the timber which would, most
likely, have been used in the original vessel). The thick timbers were
shaped by hand, the craftsmen creating three-dimensionally curved
planks which were joined using a mortise-and-tenon fastening system.
This was quite a challenge particularly for the 20+cm thick timbers
near the keel.
Construction of the hull, spars and sail was
completed in less than six months. Initial trials were performed in
late November 2008 on the Nile. These included assessment of the
effectiveness of the quarter-rudder steering oars (which proved to be
very effective under tow); and attempts to propel the vessel under oars
– with eight oars-men we were able to make some headway into a 10 knot
head-wind (the full complement of oarsmen is 26).
Further sailing
trials and a voyage on the Red Sea are planned for the Christmas/New
Year period 2008. The documentary is expected to be completed towards
the middle of 2009 and is to be shown in several countries around the
world.
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| Sea trials of the finished vessel (Enlarge) |
Maxsurf Subscription Program
The Maxsurf subscription program has been adopted by the majority of our users to ensure that they automatically receive any updates to Maxsurf as soon as they become available. The subscription program also makes you eligible to receive an unlimited amount of technical support via email, telephone or fax. When renewal time comes around, the subscription lets you pay one annual fee for all of the programs you own and will normally give you a major upgrade as well as any minor updates during the year. Upgrades are delivered on CD and minor updates are occasionally available for download from our web site.
