{"id":166476,"date":"2023-03-17T13:11:57","date_gmt":"2023-03-17T13:11:57","guid":{"rendered":"\/knowledge\/forums\/topic\/model-with-nonlinear-contacts-not-converging-due-to-small-initial-rigid-body-motions-in-a-static-analysis-model-underconstrained\/"},"modified":"2023-07-31T12:31:53","modified_gmt":"2023-07-31T12:31:53","slug":"model-with-nonlinear-contacts-not-converging-due-to-small-initial-rigid-body-motions-in-a-static-analysis-model-underconstrained","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/model-with-nonlinear-contacts-not-converging-due-to-small-initial-rigid-body-motions-in-a-static-analysis-model-underconstrained\/","title":{"rendered":"Model with nonlinear Contacts not converging due to (small) initial Rigid Body Motions in a Static Analysis (model underconstrained)"},"content":{"rendered":"<p>In Static Analyses of Assemblies with nonlinear contacts (frictionless, frictional, rough), it easily happens that not all parts of the model are initially in well-defined contact with their neighboring components. Then, initially, free rigid body motions are possible, which lead to a singular (or very close to singular) Stiffness Matrix such that the resulting equation system cannot be solved for a unique solution. Accordingly, convergence problems are met from the very beginning. A typical example for this situation is, when a gap in a bearing shall be taken into account.   In these cases, it can be helpful to use the Quasi-Static solver option (TINTP,QUAS).  As this option uses backward Euler time-integration, it is indeed not part of a real STATIC solution algorithm but of a TRANSIENT one. Accordingly, it requires switching to the analysis type transient and usually is more computationally expensive than a simple static analysis (with nonlinear contacts).   ANSYS Help   https:\/\/ansyshelp.ansys.com\/account\/secured?returnurl=\/Views\/Secured\/corp\/v190\/ans_str\/Hlp_G_STR5_12.html  &#8220;For this option, the program uses backward Euler time-integration. The high numerical dissipation in this time-integration scheme can help to achieve convergence in some problems that are quasi-static in nature but fail to converge in a quasi-static analysis. &#8230; The automatic time incrementation does not try to maintain any minimum points per cycle, therefore allowing use of much larger time increments. &#8230; Applications that can benefit from using the QUAS option include:  &#8211; buckling dominated simulations  &#8211; models that may display temporary rigid body modes  &#8211; and simulations that have a snap-through event, causing instability.&#8221;  Nevertheless, in a &#8216;Static Structural&#8217; Analysis in Mechanical, it can be invoked by just a small command snippet with very few APDL commands.  Just insert a command snippet under the Static Structural branch  ANTYPE,TRANS! switch to analysis type transient TINPT,QUAS   ! switch to quasi-static solver option  and make sure that you choose a small enough time step as initial time step size (e.g. 0.0001 s).  Please also find a very simple example project attached, which contains a static and a transient analysis block. In each of them, the quasi-static solver option is invoked.  Finally, please note that Contact Stabilization can be an alternative to the procedure described above. ANSYS Help  https:\/\/ansyshelp.ansys.com\/account\/secured?returnurl=\/Views\/Secured\/corp\/v190\/ans_ctec\/Hlp_ctec_realkey.html  Chapter 3.9.15<\/p>\n<p>Attachments:<br \/>\n1. <a href=https:\/\/ansys13.ansys.com\/KnowledgeArticles\/Phase-1\/2058034\/2058034.zip>2058034.zip<\/a><\/p>\n","protected":false},"template":"","class_list":["post-166476","topic","type-topic","status-publish","hentry","topic-tag-4391","topic-tag-contact","topic-tag-mechanical","topic-tag-nonlinear-mechanics","topic-tag-structural-and-thermal","topic-tag-structural-mechanics"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_wp_page_template":["default"],"_bbp_last_active_time":["3\/15\/2023 20:20"],"_bbp_forum_id":["27795"],"_bbp_author_ip":["23.56.168.180"],"_btv_view_count":["3935"],"siebel_km_number":["2058034"],"product_version":["19"],"km_published_date":["2019-01-21T16:08:31.000Z"],"family":["Structural Mechanics"],"application_name":["Mechanical"]},"test":"solution"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics\/166476","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics\/166476\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/media?parent=166476"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}