{"id":2146,"date":"2024-04-10T13:29:17","date_gmt":"2024-04-10T20:29:17","guid":{"rendered":"https:\/\/gantovnik.com\/bio-tips\/?p=2146"},"modified":"2024-04-10T13:29:17","modified_gmt":"2024-04-10T20:29:17","slug":"418-some-comments-about-exclude-command-in-linear-buckling-analysis-using-optistruct","status":"publish","type":"post","link":"https:\/\/gantovnik.com\/bio-tips\/2024\/04\/418-some-comments-about-exclude-command-in-linear-buckling-analysis-using-optistruct\/","title":{"rendered":"#418 Some comments about EXCLUDE command in Linear Buckling Analysis using OptiStruct"},"content":{"rendered":"

The EXCLUDE command can be used to select a set of elements to be excluded from a Linear Buckling Analysis.<\/p>\n

EXCLUDE = ESID
\n(ESID is Set identification number of an element set)<\/p>\n

    \n
  1. The excluded elements are only removed from the geometric stiffness matrix, resulting in a Buckling Analysis with elastic boundary conditions. This means that the excluded elements may still be showing movement in the buckling mode.<\/li>\n
  2. Extreme caution is advised when using the\u00a0EXCLUDE<\/span>\u00a0command. In general, excluding any region from buckling analysis can, and usually will, result in a higher, overestimated critical load calculation, which then may produce false overconfidence in a structure’s load bearing capacity. The excluded region will have no effect on the calculated critical load only if the excluded modes are geometrically separated from, or orthogonal to, the actual critical buckling mode.<\/li>\n
  3. A descriptive engineering explanation is as follows: Buckling Analysis by design seeks the weakest, least stable configuration of the structure. Excluding any region from this search can cause you to miss the actual critical buckling mode that involves the respective region and has the least load bearing capacity.<\/li>\n<\/ol>\n

     <\/p>\n","protected":false},"excerpt":{"rendered":"

    The EXCLUDE command can be used to select a set of elements to be excluded from a Linear Buckling Analysis. EXCLUDE = ESID (ESID is Set identification number of an element set) The excluded elements are only removed from the geometric stiffness matrix, resulting in a Buckling Analysis with elastic boundary conditions. This means that […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","_lmt_disableupdate":"yes","_lmt_disable":"","jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[24,28],"tags":[48],"class_list":["post-2146","post","type-post","status-publish","format-standard","hentry","category-hypermesh","category-optistruct","tag-buckling"],"modified_by":"gantovnik","jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p8bH0k-yC","jetpack_likes_enabled":true,"jetpack-related-posts":[{"id":539,"url":"https:\/\/gantovnik.com\/bio-tips\/2020\/05\/optistruct-can-i-use-buckling-constraints-on-a-topology-or-free-size-optimization\/","url_meta":{"origin":2146,"position":0},"title":"OptiStruct: Can I use buckling constraints on a topology or free-size optimization?","author":"gantovnik","date":"2020-05-09","format":false,"excerpt":"OptiStruct: Can I use buckling constraints on a topology or free-size optimization? There are several barriers for buckling constraints in topology optimization: Buckling constraints are conditional, similar to stress constraints (see Can I use stress constraints with topology or free-size optimization?). Structural instability does not exist when structural parts vanish.\u2026","rel":"","context":"In "HyperMesh"","block_context":{"text":"HyperMesh","link":"https:\/\/gantovnik.com\/bio-tips\/category\/hypermesh\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":481,"url":"https:\/\/gantovnik.com\/bio-tips\/2020\/03\/how-to-include-temperature-dependent-material-in-a-buckling-analysis\/","url_meta":{"origin":2146,"position":1},"title":"#70 How to include temperature-dependent material in a buckling analysis?","author":"gantovnik","date":"2020-03-04","format":false,"excerpt":"To include temperature-dependent material in a linear buckling analysis (SOL 105), the temp(load) case control command must be placed above the first subcase; otherwise, the temperature-dependent material properties will be ignored. As in all linear solutions, the material lookup is performed only once in a run.","rel":"","context":"In "nastran"","block_context":{"text":"nastran","link":"https:\/\/gantovnik.com\/bio-tips\/category\/nastran\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":637,"url":"https:\/\/gantovnik.com\/bio-tips\/2020\/09\/100-negative-eigenvalue-in-buckling-analysis\/","url_meta":{"origin":2146,"position":2},"title":"#100: Negative eigenvalue in buckling analysis","author":"gantovnik","date":"2020-09-25","format":false,"excerpt":"#100: Negative eigenvalue in buckling analysis In buckling analysis, a negative eigenvalue implies that the load that causes the structure to buckle is opposite to the direction of the applied load. A negative eigenvalue means that the critical load has a reversed direction compared to the applied load. Applying a\u2026","rel":"","context":"In "nastran"","block_context":{"text":"nastran","link":"https:\/\/gantovnik.com\/bio-tips\/category\/nastran\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":1023,"url":"https:\/\/gantovnik.com\/bio-tips\/2021\/10\/181-offset-for-pcomp\/","url_meta":{"origin":2146,"position":3},"title":"#181 Offset for PCOMP","author":"gantovnik","date":"2021-10-28","format":false,"excerpt":"#181 Offset for PCOMP For composites with offset (Z0 \u2260 0.5 * Thickness), the buckling results will not be correct. This is because the membrane-bending coupling resulting from the composite offset is not included in the differential stiffness matrix. Therefore, the preferred method of incorporating offset in buckling analysis is\u2026","rel":"","context":"In "composites"","block_context":{"text":"composites","link":"https:\/\/gantovnik.com\/bio-tips\/category\/composites\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":1558,"url":"https:\/\/gantovnik.com\/bio-tips\/2022\/09\/210-parametric-curve-in-3d-2-2-2-2-2-2-2-2-2-2-2-2-2-3-3-2-2-3-2\/","url_meta":{"origin":2146,"position":4},"title":"#301 Buckling Glossary","author":"gantovnik","date":"2022-09-13","format":false,"excerpt":"Asymmetric buckling: When the structure has asymmetric geometry it may undergo stable buckling for a positive displacement parameter and unstable buckling if this displacement parameter is negative. Bifurcation point: A point along a primary equilibrium path (or curve) intersected by a secondary path. Beyond this point, the primary equilibrium path\u2026","rel":"","context":"In "python"","block_context":{"text":"python","link":"https:\/\/gantovnik.com\/bio-tips\/category\/python\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":479,"url":"https:\/\/gantovnik.com\/bio-tips\/2020\/03\/what-does-a-negative-eigenvalue-in-a-buckling-analysis-mean\/","url_meta":{"origin":2146,"position":5},"title":"#69 What does a negative eigenvalue in a buckling analysis mean?","author":"gantovnik","date":"2020-03-04","format":false,"excerpt":"A negative eigenvalue in a buckling analysis may imply that the buckling load is in the opposite direction of the applied load. For example, for a simply supported beam, if a tensile axial load is applied to one end, then the eigenvalue will be negative. One the other hand, for\u2026","rel":"","context":"In "nastran"","block_context":{"text":"nastran","link":"https:\/\/gantovnik.com\/bio-tips\/category\/nastran\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"_links":{"self":[{"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/posts\/2146","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/comments?post=2146"}],"version-history":[{"count":1,"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/posts\/2146\/revisions"}],"predecessor-version":[{"id":2147,"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/posts\/2146\/revisions\/2147"}],"wp:attachment":[{"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/media?parent=2146"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/categories?post=2146"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gantovnik.com\/bio-tips\/wp-json\/wp\/v2\/tags?post=2146"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}