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Stefan Harries

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About Stefan Harries

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  1. Hi, Sometimes diagrams with important data are available only as graphics files (e.g. after scanning from a report or upon exporting from a pdf-file). CAESES / FRIENDSHIP-Framework can be quickly utilized to read off data from diagrams with high accuracy. To do so, import the graphics as an png-file within a "GL Picture Frame" (1st step). Upon setting the scales of abscissa (x-axis) and ordinate (y-axis) (2nd step) you can readily position a point in your diagram and get your x- and y-coordinates (3rd step). (You may want to use such a point to check the level of accuracy.) Furthermore, you can approximate a graph with a curve, say a B-spline curve (4th step) or interpolate it (5th step). Using the curve representation you can "inquire" the y-value for any given x-value (6th step). The attached fdb-project illustrates the work flow for an imaginary speed-power curve. In addition to using CAESES / FRIENDSHIP-Framework to extract data points from diagrams, you can follow the same approach to replicate a lines plan of a boat, yacht or ship, circumventing classic digitization. Offset data are thus produced effectively. Nice side effect is that you can adjust selected points, for instance to improve accuracy of lines remodeling and "repair" apparent outliers. Kind regards, Stefan ExampleDiagram.zip
  2. Hi, One of the famous hull forms found in literature is the so-called Wigley hull. It is mathematically defined, see attached formula, and used regularly for tests and validation work. By definition the Wigley hull is a (simple) fully parametric model with beam, draft and height as parameters to control the shape (often normalized by length). A realization of the Wigley hull via a MetaSurface that captures the mathematical formula is given in the attached CAESES project. In addition, some partially parametric modifications are shown, namely, Lackenby type swinging of sections that is realized via a DeltaShift. (Please note that a Generalized Lackenby variation would also be available but was not used here in order to keep the project light.) If you need the hull for your CFD validation work you can use the various exports for panels, offsets, STL, iges etc. More information about ship hull design can be found in the marine section of the CAESES website. Kind regards, Stefan standardWigley.fdb
  3. Hi, You may have asked yourself why you may actually need a parametric model? In other words: Why does a conventional CAD model not do? If you are interested in modeling geometry only once, i.e., if you are pretty sure you do not want to change the geometry later, say to adapt to a slightly different design task, well, then it might not be worth the effort to create a parametric model. So, you just produce your geometry in your CAD tool and be done with it. However, if you know that you will have to do variations it should quickly pay off to spend more time up front in order to come up with a model that is somewhat "intelligent." A parametric model is such a thing: You create relationships between various entities that make up your product. Usually, that leads to a certain hierarchy, i.e., some entities become dependent while others are free to change. The latter are the parameters that you want to vary, for instance within a CFD driven design process. They are often called free variables. A very simple dependency may be that some entities are multiples of others, for example B=0.5*L and H=B*L. Often, the relationship of entities is rather complex. Let us look at a slightly more complicated example (not too complicated though): From a plane sheet of paper you can fold a paper ship. Once you have selected your sheet of paper, for example a standard DIN A4, the size of your ship is set. The only free variable left is the beam of your ship. All vertices of your object are now defined by these two parameters, length and beam. If you do not want to tear your paper apart increasing or decreasing your beam will require your vertices to follow, they are dependent. Attached you can find a parametric model of such a ship as realized within CAESES / FRIENDSHIP-Framework. Essentially you get two main advantages from a parametric model: You will always get what you want (since you already put in your design rational you will not create anything that is not really of interest at this point in time)You will reduce the number of things you have to take care of when making changes (and this reduces the degrees of freedom of your system)Let us go back to the paper ship for a second: You could still just define all vertices conventionally in a CAD system. Consider the three vertices shown in the example, V0, V1 and V2. They fully define the shape since all other vertices are just mirrored. Together these vertices offer 3*3=9 coordinates for shape control. Taking advantage of symmetry conditions we can boil things down to 2*2=4 coordinates to be modified; V0 does actually not change at all, V1 can only move in the transversal plane y-z and V2 can only slide in the longitudinal plane x-z. The parametric model intrinsically takes care of this. The knowledge is built in. Consequently, you not only have fewer variables (typically one order of magnitude less) but also no danger of creating something that cannot be produced. In the paper ship model vertex V1 is moved along the circular path in the midship plane. Vertex V2 has to follow such that the distance between V2 and V0 as well as between V2 and V1 is maintained. This defines a circular path, too. Finding the correct corrdinates for V2 is done within an inner optimization (which also illustrates that things can be more complex than just B=0.5*L). Have fun, Stefan parametricPapership.fdb
  4. Hi, Suppose you have several educated guesses about the possible shape of your product but you are not sure which one of your shapes or which combination of these shapes will be the most suitable for a particular purpose. (Examples from naval architecture: Three different bulbous bows or two different stern configurations -- all look good and reasonable but what is the best mix?) One way to set up a parametric model (a partially parametric model to be more specific) is to use morphing, i.e., the smooth transition from one object to another by weighting. Suppose you have a cat and a dog. They look reasonably alike (two ears, two eyes, one snout etc.), meaning their topology is the same even though their geometry differ. If you set your weight to 100% cat and 0% dog, well, you get the cat. If you do it the other way round you would have the dog. Anything in-between, say 60% cat and 40% dog, makes an interesting mix, a cat-dog so to say. (No way to produce a donkey, not even by extrapolation.) Within CAESES / FRIENDSHIP-Framework you can build on this idea by utilizing one or several interspaceSurfaces. Assuming you have the same topology for your surfaces (matching orders and matching numbers of vertices when it comes to B-splines), you can interpolate between your shapes. Attached please find an example in which several surfaces are morphed. Cheers, Stefan surfaceMorphing.fdb
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