{"id":355267,"date":"2024-03-04T20:42:23","date_gmt":"2024-03-04T20:42:23","guid":{"rendered":"\/forum\/forums\/topic\/nodal-difference-lines-that-shift-with-element-size\/"},"modified":"2024-03-04T20:42:23","modified_gmt":"2024-03-04T20:42:23","slug":"nodal-difference-lines-that-shift-with-element-size","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/nodal-difference-lines-that-shift-with-element-size\/","title":{"rendered":"Nodal difference lines that shift with element size"},"content":{"rendered":"<p>Hi,<\/p>\n<p>Currently I&#8217;m working on a simulation of a flexure system in ANSYS Mechanical.<\/p>\n<p>To give you some context, the complete flexure system is Illustrated:<\/p>\n<p><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/04-03-2024-1709584039-mceclip0.png\"><\/p>\n<p>It consists of three thin sheet flexures, all fixed to the world at the bottom and with an rigid plattorm on top. The system allows for a rotation around the Z axis as the flexures deform in their compliant direction. To simplify the system I&#8217;ve used the symmetry and came up with the resulting model (AB is still a flexure):<\/p>\n<p><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/04-03-2024-1709584068-mceclip1.png\"><\/p>\n<p>I&#8217;ve modeled this ANSYS Mechanical with these simulation parameters:<\/p>\n<ul>\n<li>large deflections ON<br \/>&#8211; Fixed boundary condition at the bottom<br \/>&#8211; remote displacement at the top: prescribed zrot (2.5 deg) free z displacement, fixed x displ, y displ, xrot, y rot<\/li>\n<\/ul>\n<p><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/04-03-2024-1709584114-mceclip2.png\"><\/p>\n<p>I&#8217;m interested in the stress gradient &amp; the maximum von mises stress of the flexure over a specified rotation like this:<\/p>\n<p><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/04-03-2024-1709584419-mceclip4.png\"> &nbsp;<\/p>\n<p>I&#8217;ve modeled the system with solid elements and have done a manual convergence study by measuring the averaged and unaveraged stress, while reducing the element size. There was quite a difference between the averaged\/unaveraged results so to dive a into this I&#8217;ve plotted the nodal differences. What i found was these lines of nodal differences at the outer edges of the flexure. And this line would shift with the element size.&nbsp;<\/p>\n<p><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/04-03-2024-1709584181-mceclip3.png\"><\/p>\n<p>So i found that this line of high nodal difference is always within the first row (top bottom) or column (left&amp; right side) of the elements. So as I move from a larger element to smaller the nodal differences shift. I.e. if i plot this at 2mm element size (width vs height) this line will be located 2mm from the top\/bottom or side. and if i plot this with a mesh that has 0.5mm element size (as in the picture) the nodal difference line is located at 0.5mm.&nbsp;<\/p>\n<p>Unfortunately this high nodal difference line lies really close to the location with maximum stress and therefore I can&#8217;t just ignore it.&nbsp;<\/p>\n<p>So my theory is that this has something to do with the harsh boundary conditions that are applied.&nbsp;<strong>As I&#8217;m still a student and I&#8217;m not that experienced with these simulation I was wondering about your point of view &amp; how you would deal with this problem.<\/strong> If you need any additional information, just let me know.<\/p>\n<p>I&#8217;ve also made the same model using shell elements.The shell elements have the same issue. I could just ignore the outer elements by scoping. S<span style=\"font-size: 14pt\">o as i reduce the element size I plot the stress results using a named selection that does not contain the outer edge of elements. For using shell elements i then obtain:<\/span><\/p>\n<ul>\n<li><img loading=\"lazy\" decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/04-03-2024-1709584535-mceclip5.png\" width=\"485\" height=\"364\"><\/li>\n<li>However when scoping with solids I was not able to achieve this yet, (maybe need to go even smaller..)&nbsp;<\/li>\n<li><img loading=\"lazy\" decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/04-03-2024-1709584619-mceclip6.png\" width=\"504\" height=\"378\"><\/li>\n<\/ul>\n","protected":false},"template":"","class_list":["post-355267","topic","type-topic","status-closed","hentry","topic-tag-mechanicalworkbench-1","topic-tag-convergence","topic-tag-nodal-difference-2"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["71229","88"],"_bbp_author_ip":["23.206.193.146"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["372"],"_bbp_topic_status":["unanswered"],"_bbp_topic_id":["355267"],"_bbp_forum_id":["27791"],"_bbp_engagement":["88","71229"],"_bbp_voice_count":["2"],"_bbp_reply_count":["1"],"_bbp_last_reply_id":["356334"],"_bbp_last_active_id":["356334"],"_bbp_last_active_time":["2024-03-11 11:52:41"]},"test":"tim-bomergmail-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/355267","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/355267\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=355267"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}