{"id":370911,"date":"2024-07-06T22:11:14","date_gmt":"2024-07-06T22:11:14","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/"},"modified":"2024-07-06T22:14:55","modified_gmt":"2024-07-06T22:14:55","slug":"370911","status":"publish","type":"reply","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/","title":{"rendered":"Reply To: Springs in modal analysis."},"content":{"rendered":"<p>&lt;p&gt;Hi Javat,&lt;\/p&gt;&lt;p&gt;Animate the first and second modes. What is the principal direction of movement?&nbsp; That is the direction where there is zero stiffness.&lt;\/p&gt;&lt;p&gt;To eliminate all rigid body motion, you need a minimum of stiffness in 6 directions, and that is only sufficient if the directions are not redundant.&lt;\/p&gt;&lt;p&gt;For example, if you have a frame that is attached to ground at 3 points, and ground is the X-Y plane with Z vertical, the first point can have stiffness in 3 directions (X, Y, Z).&nbsp; The second point must be separated from the first point along the X axis and needs stiffness in the Y and Z directions. &nbsp;The third point must be separated from the first point along the Y axis and needs stiffness in the Z direction. This is the minimum to avoid a zero frequency mode.&lt;\/p&gt;&lt;p&gt;You can have springs with stiffness in 3 directions on 3 or 4 attachment points, that is fine and may increase the frequencies of some modes.&lt;\/p&gt;&lt;p&gt;COMBIN14 is a 1D spring element, so to get stiffness in 3 directions, you need 3 springs. KEYOP(1) = 1 is for nonlinear damping. To get no rigid body modes, you would need 6 springs oriented in the correct directions as described above. If you wanted stiffness in 3 directions at 4 attachement points, you would need 12 COMBIN14 springs.&lt;\/p&gt;&lt;p&gt;Use one COMBIN250 at each attachment point which is a spring element that can have stiffness in 6 DOF (X, Y, Z, Rx, Ry, Rz).&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-370911","reply","type-reply","status-publish","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"Hi Javat,Animate the first and second modes. What is the principal direction of movement? That is the direction where there is zero stiffness.To eliminate all rigid body motion, you need a minimum of stiffness in 6 directions, and that is only sufficient if the directions are not redundant.For example, if you have a frame that\" \/>\n\t<meta name=\"robots\" content=\"max-image-preview:large\" \/>\n\t<link rel=\"canonical\" href=\"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/\" \/>\n\t<meta name=\"generator\" content=\"All in One SEO (AIOSEO) 4.9.10\" \/>\n\t\t<meta property=\"og:locale\" content=\"en_US\" \/>\n\t\t<meta property=\"og:site_name\" content=\"Ansys Learning Forum | Ansys Innovation Space\" \/>\n\t\t<meta property=\"og:type\" content=\"article\" \/>\n\t\t<meta property=\"og:title\" content=\"Reply To: Springs in modal analysis. | Ansys Learning Forum\" \/>\n\t\t<meta property=\"og:description\" content=\"Hi Javat,Animate the first and second modes. What is the principal direction of movement? That is the direction where there is zero stiffness.To eliminate all rigid body motion, you need a minimum of stiffness in 6 directions, and that is only sufficient if the directions are not redundant.For example, if you have a frame that\" \/>\n\t\t<meta property=\"og:url\" content=\"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/\" \/>\n\t\t<meta property=\"article:published_time\" content=\"2024-07-06T22:11:14+00:00\" \/>\n\t\t<meta property=\"article:modified_time\" content=\"2024-07-06T22:14:55+00:00\" \/>\n\t\t<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n\t\t<meta name=\"twitter:title\" content=\"Reply To: Springs in modal analysis. | Ansys Learning Forum\" \/>\n\t\t<meta name=\"twitter:description\" content=\"Hi Javat,Animate the first and second modes. What is the principal direction of movement? 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What is the principal direction of movement? 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That is the direction where there is zero stiffness.To eliminate all rigid body motion, you need a minimum of stiffness in 6 directions, and that is only sufficient if the directions are not redundant.For example, if you have a frame that","canonical_url":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"BreadcrumbList","@id":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/#breadcrumblist","itemListElement":[{"@type":"ListItem","@id":"https:\/\/innovationspace.ansys.com\/forum#listItem","position":1,"name":"Home","item":"https:\/\/innovationspace.ansys.com\/forum","nextItem":{"@type":"ListItem","@id":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/#listItem","name":"Reply To: Springs in modal analysis."}},{"@type":"ListItem","@id":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/#listItem","position":2,"name":"Reply To: Springs in modal analysis.","previousItem":{"@type":"ListItem","@id":"https:\/\/innovationspace.ansys.com\/forum#listItem","name":"Home"}}]},{"@type":"Organization","@id":"https:\/\/innovationspace.ansys.com\/forum\/#organization","name":"Ansys Learning Forum","description":"Ansys Innovation Space","url":"https:\/\/innovationspace.ansys.com\/forum\/"},{"@type":"WebPage","@id":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/#webpage","url":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/","name":"Reply To: Springs in modal analysis. | Ansys Learning Forum","description":"Hi Javat,Animate the first and second modes. What is the principal direction of movement? That is the direction where there is zero stiffness.To eliminate all rigid body motion, you need a minimum of stiffness in 6 directions, and that is only sufficient if the directions are not redundant.For example, if you have a frame that","inLanguage":"en-US","isPartOf":{"@id":"https:\/\/innovationspace.ansys.com\/forum\/#website"},"breadcrumb":{"@id":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/#breadcrumblist"},"datePublished":"2024-07-06T22:11:14+00:00","dateModified":"2024-07-06T22:14:55+00:00"},{"@type":"WebSite","@id":"https:\/\/innovationspace.ansys.com\/forum\/#website","url":"https:\/\/innovationspace.ansys.com\/forum\/","name":"Ansys Learning Forum","description":"Ansys Innovation Space","inLanguage":"en-US","publisher":{"@id":"https:\/\/innovationspace.ansys.com\/forum\/#organization"}}]},"og:locale":"en_US","og:site_name":"Ansys Learning Forum | Ansys Innovation Space","og:type":"article","og:title":"Reply To: Springs in modal analysis. | Ansys Learning Forum","og:description":"Hi Javat,Animate the first and second modes. What is the principal direction of movement? That is the direction where there is zero stiffness.To eliminate all rigid body motion, you need a minimum of stiffness in 6 directions, and that is only sufficient if the directions are not redundant.For example, if you have a frame that","og:url":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370911\/","article:published_time":"2024-07-06T22:11:14+00:00","article:modified_time":"2024-07-06T22:14:55+00:00","twitter:card":"summary_large_image","twitter:title":"Reply To: Springs in modal analysis. | Ansys Learning Forum","twitter:description":"Hi Javat,Animate the first and second modes. What is the principal direction of movement? 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