If the tolerance limits are not met after reaching the maximum number of iterations, the program displays a warning message with the option to further use the intermediate result. Generally, the FF calculation should come to an end before reaching this limit while meeting all tolerance limits. To control the iteration process, there is a separate 'Form-Finding' tab in the Calculation Parameters dialog box. This shifting step is done iteratively using the URS method (Updated Reference Strategy, ) by Prof. You can counteract this reaction by fixing the surface stress vectors in the XY plane when using the projection method. It can happen that in the case of prestress vectors freely movable in space, the tangential vectors can contract to a point in the center, especially for rotationally symmetric models with conical shapes. In contrast, the projection method describes a surface stress vector which can move partially in space and is fixed to its XY coordinates.

The tension method describes a surface stress vector, which can move freely in space until it reaches the target position. The description of the surface stress on the membrane mesh elements can be defined in two ways. This process adopts the mesh geometry and surface stress/prestress from the initial input and shifts the location of the mesh elements until the surface stress on the FE element is in equilibrium with the boundary conditions. If the meshing process fails, the operation is ended directly before the calculation.Īfter a successful meshing, the program starts the FF process. From a program perspective, when initially entering the FF elements, you only have to make sure that all required connection nodes and lines are integrated into the surfaces/members and that the meshing process can generate a mesh for all the elements. It should be noted that the initial shape of the FF elements is irrelevant. Furthermore, the initial input requires a determination of surface stress value in the warp and weft direction of the membranes, including their application method (tension or projection), and the prestress level or sag dimension of the cable elements that should act according to the FF calculation.

The initial input provides the program with the information as to between which points a cable is enclosed, and between which line polygon a membrane is enclosed. Therefore, RFEM requires an initial input of the FF elements in the first instance. It is precisely the task of the FF process to find this position and fixate it. When defining a model of lightweight structures, you may realize that the geometric position of the membranes and ropes is unclear.

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