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Modify Form

modify-formOnce we have completed the creation of the mesh, we are in the main program screen WinTess3. At this point we need to look at a very important aspect:

What about the menu Calculate | Form finding (automatic)?

If it is marked with the symbol ✔, it means automatic Form finding is enabled when you modify any data and also in the initial stage. Therefore what we are going to see on the screen is not the mesh we trimmed, but the form generated by the program itself.

On the other hand if it is not marked with the symbol ✔, it means that you have not enabled automatic Form finding and therefore we have just the mesh on the screen which we have just trimmed. In this case, when we modify any data (node or bar), we will have to touch the button Run for the change to occur. We can also use the menu Calculate | Form finding (global) or the menu Calculate | Form finding (step by step), but those imply two mouse clicks instead of one. The first of the two menus is the most common as it is much faster. However, if the mesh has created with many nodes (more than appx. 1500), it is possible that, depending on the power of the computer that we use, the program may stall. In this case, it is better to use the second menu, although much slower, it does not lock up.

From here begins the process of adjustment or modification of the form. It follows the same manual process we would if we worked on a model of Lycra, latex or similar. We will be pulling or pushing the canvas, tensioning edges, etc. until we are happy with the shape of the membrane.

In the same way that we must cut a piece of suitable cloth for a physical model, it is very important that the trimmed mesh is as adaptable as possible to the shape that we wish to get. It is not valid to have an overly deformed mesh in order to get the desired shape. This is especially applicable to forms which are very complex and folded on themselves, in which we must be splitting a mesh that resembles the unfolded form, i.e. with total surface, not surface on projected on ground or in elevation.

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To achieve a shape like the figure, we start with a square mesh. In that screen, we fix two vertices on one side. Then we focus on the other side and lift the mid-point of that side. Then we bring the other two vertices together just where the mid-point, we just lift, was. In fact, it is the same we would have done if we had used a piece of Lycra for a model.

Modify nodes

One of the most typical ways of generating a form using a given mesh is to modify the coordinates of a given node. To do this, open the node edit window by clicking with the right button on a node in question. If we are in the Form finding, modifying the coordinates of a node makes is a fixed node (no need to mark it). This is so since it doesn’t make any sense to modify position of a node and leave it free.
If we are in other states of the program (analysis or patterning), modifying the coordinate of a node does not imply that the node becomes fixed.

If Form finding (automatic) is enabled, modifying the coordinates of a node will result in the new generated form. If not, we have to press the run button Run.

Modify bars
modify-barIn principle, the interior mesh bars must not be modified, since they are all the same and they simulate a homogeneous membrane. Typically, we change the edges, because in this way we obtain a membrane with a perimeter similar to what we were designing. To modify an edge, we click on a bar on edge. The window on the right appears.

We see that the bar type is boltrope which belongs to the edge called “Cable 2” (above the line on the right). This means that if we modify this bar, we will be modifying all the bars that belong to this cable. In fact, if we open the Grup dropdown and select Cable 2, we see all the bars of this cable are selected. However, it is not necessary to carry out this process.

Bar has a module E (t/m²) with a certain value. If we increase this value, the edge becomes more rigid and becomes straighter. On the contrary, if we reduce this value, edge becomes softer and its curvature increases. If we don’t have much experience, trial-error method is suitable to find the way. If we introduce a very high module (for example 1000), we observe how the edge becomes a straight line. Indeed this is one of the ways to have straight edges (although we will see later that it is not the most appropriate).

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In the previous figure, we see a membrane where an edge has been modified with a value of the module E that varies from 2 to 12 through the value 5, which is the default value of WinTess3 program. Anyway, it is interesting to note that when changing the stiffness of a border does not only change this edge but also the membrane. This is important, because if we go very finely by adjusting an edge and then the other, and so on, when we have finished with the last edge, we see that the first edge is out of adjustment

Although this is the most common, we don’t modify only the edges. In cases in which the membrane have valleys or ridges (which surely placement of a steel cable in them will involve), we can force these valleys or ridges by modifying the module E of interior bars. To do so please create a group of bars and modify all of them at the same time. In the following figures, we see an example of a form (axonometric and elevation) generated in this way.

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