class RequirementsForSimulationTool "Requirements for Simulation Tools"
extends Modelica.Icons.Information;
annotation (
DocumentationClass = true,
Documentation(info = "<html>\n\n<p>\nThis library is designed in a fully object oriented way in order that\ncomponents can be connected together in every meaningful combination\n(e.g., direct connection of two springs or two inertias).\nAs a consequence, most models lead to a system of\ndifferential-algebraic equations of <strong>index 3</strong> (= constraint\nequations have to be differentiated twice in order to arrive at\na state space representation) and the Modelica translator or\nthe simulator has to cope with this system representation.\nAccording to our present knowledge, this requires that the\nModelica translator is able to symbolically differentiate equations\n(otherwise it is e.g., not possible to provide consistent initial\nconditions; even if consistent initial conditions are present, most\nnumerical DAE integrators can cope at most with index 2 DAEs).\n</p>\n<p>\nThe elements of this library can be connected together in an\narbitrary way. However, difficulties may occur, if the elements which can <strong>lock</strong> the\n<strong>relative motion</strong> between two flanges are connected <strong>rigidly</strong>\ntogether such that essentially the <strong>same relative motion</strong> can be locked.\nThe reason is\nthat the cut-torque in the locked phase is not uniquely defined if the\nelements are locked at the same time instant (i.e., there does not exist a\nunique solution) and some simulation systems may not be\nable to handle this situation, since this leads to a singularity during\nsimulation. Currently, this type of problem can occur with the\nCoulomb friction elements <strong>BearingFriction, Clutch, Brake, LossyGear</strong> when\nthe elements become stuck:\n</p>\n<p>\n<img src=\"modelica://Modelica/Resources/Images/Mechanics/Rotational/driveConnections3.png\" alt=\"driveConnections3\">\n</p>\n<p>\nIn the figure above two typical situations are shown: In the upper part of\nthe figure, the series connection of rigidly attached BearingFriction and\nClutch components are shown. This does not hurt, because the BearingFriction\nelement can lock the relative motion between the element and the housing,\nwhereas the clutch element can lock the relative motion between the two\nconnected flanges. Contrary, the drive train in the lower part of the figure\nmay give rise to simulation problems, because the BearingFriction element\nand the Brake element can lock the relative motion between a flange and\nthe housing and these flanges are rigidly connected together, i.e.,\nessentially the same relative motion can be locked. These difficulties\nmay be solved by either introducing a compliance between these flanges\nor by combining the BearingFriction and Brake element into\none component and resolving the ambiguity of the frictional torque in the\nstuck mode. A tool may handle this situation also <strong>automatically</strong>,\nby picking one solution of the infinitely many, e.g., the one where\nthe difference to the value of the previous time instant is as small\nas possible.\n</p>\n</html>"));
end RequirementsForSimulationTool;