{"id":198709,"date":"2026-05-22T19:32:35","date_gmt":"2026-05-22T19:32:35","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/knowledge\/?post_type=topic&#038;p=198709"},"modified":"2026-05-22T19:36:18","modified_gmt":"2026-05-22T19:36:18","slug":"what-is-sph-adaptive-size-coarsening-and-how-does-it-work-in-ansys-freeflow","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/what-is-sph-adaptive-size-coarsening-and-how-does-it-work-in-ansys-freeflow\/","title":{"rendered":"What is SPH Adaptive size coarsening, and how does it work in Ansys FreeFlow?"},"content":{"rendered":"<h1  id=\"\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-198650 size-full\" src=\"https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2.png\" alt=\"\" width=\"1600\" height=\"200\" srcset=\"https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2.png 1600w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2-300x38.png 300w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2-1024x128.png 1024w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2-768x96.png 768w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2-1536x192.png 1536w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2-24x3.png 24w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2-36x5.png 36w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2026\/05\/Freeflow-FAQ-banner-v2-48x6.png 48w\" sizes=\"auto, (max-width: 1600px) 100vw, 1600px\" \/><\/h1>\n<h1  id=\"WHAT-IS-SPH-ADAPTIVE-SIZE-COARSENING-AND-HOW-DOES-IT-WORK-IN-ANSYS-FREEFLOW\"><strong>What is SPH Adaptive size coarsening, and how does it work in Ansys FreeFlow?<\/strong><\/h1>\n<p>Coarsening is the process of <strong>reducing SPH resolution<\/strong> when refined elements are no longer needed.<\/p>\n<div class=\"attachment\" style=\"background-color: #fedb8d;padding: 1%;font-weight: 300;height: auto!important;display: flex;border-radius: 15px;margin-bottom: 20px\">Without coarsening, the number of SPH elements would continuously increase, leading to excessive computational cost.<\/div>\n<p>Ansys FreeFlow applies <strong>automatic coarsening<\/strong> to maintain efficiency.<\/p>\n<ul>\n<li>Coarsening is performed <strong>every 5 solver iterations<\/strong> (fixed behavior)<\/li>\n<li>Instead of merging many elements at once, the solver <strong>merges SPH elements two by two<\/strong><\/li>\n<li>This gradual process avoids numerical instabilities and mass loss<\/li>\n<\/ul>\n<p>Two SPH elements are coarsened only if <strong>all three conditions below are satisfied<\/strong>:<\/p>\n<ol>\n<li><strong>Distance from geometry<\/strong><br \/>\nThe elements must be far enough from any geometry boundary:<\/p>\n<ul>\n<li>Distance &gt; Refinement Distance Factor \u00d7 Initial SPH Size<br \/>\nThis prevents instability near walls.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Refinement level compatibility<\/strong><br \/>\nEach SPH element tracks its refinement history.<\/p>\n<ul>\n<li>Coarsening occurs only if the combined refinement count is below the maximum allowed by the refinement level.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Distance between elements<\/strong><br \/>\nThe two elements must be close enough to each other:<\/p>\n<ul>\n<li>Their distance must be smaller than the average smoothing length<\/li>\n<li>The smoothing length is computed using the Kernel Distance Factor and the SPH element size.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<div class=\"packages-rocky\">\n<div class=\"additional-package-rocky col-md-5\">\n<p>Access more FAQs and Tips in the page:<\/p>\n<div><a class=\"download\" href=\"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/ansys-freeflow-faqs-and-tips\/\" target=\"_blank\" rel=\"noopener\">FreeFlow FAQs and Tips<\/a><\/div>\n<\/div>\n<\/div>\n<div>\n<h6 class=\"paragraph\" style=\"text-align: right\" align=\"right\" class=\"paragraph\" style=\"text-align: right\" align=\"right\"  id=\"ANSYS-FREEFLOW-SMOOTHED-PARTICLE-HYDRODYNAMICS-SPH-SIMULATION-SOFTWARE\"><span class=\"eop\"><span style=\"font-size: 16.0pt\"><em>Ansys FreeFlow\u2122 smoothed-particle hydrodynamics (SPH) simulation software<\/em> <\/span><\/span><\/h6>\n<p style=\"text-align: right\" xml:lang=\"EN-US\" align=\"right\"><strong><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-197810\" src=\"https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2025\/12\/author-foto.png\" alt=\"\" width=\"140\" height=\"143\" srcset=\"https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2025\/12\/author-foto.png 274w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2025\/12\/author-foto-24x24.png 24w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2025\/12\/author-foto-36x36.png 36w, https:\/\/innovationspace.ansys.com\/knowledge\/wp-content\/uploads\/sites\/4\/2025\/12\/author-foto-48x48.png 48w\" sizes=\"auto, (max-width: 140px) 100vw, 140px\" \/><\/strong><\/p>\n<h3 style=\"text-align: right\" style=\"text-align: right\"  id=\"JANAINA-OLIVEIRA\"><strong>Janaina Oliveira<\/strong><\/h3>\n<p style=\"text-align: right\"><em><strong>Technical\/Product Publications<\/strong><\/em><\/p>\n<\/div>\n","protected":false},"template":"","class_list":["post-198709","topic","type-topic","status-publish","hentry","topic-tag-ansys-freeflow","topic-tag-ansys-freeflow-faqs","topic-tag-coarsening","topic-tag-faqs","topic-tag-freeflow","topic-tag-freeflow-sph","topic-tag-sph","topic-tag-sph-adaptive-size","filter-by-application-ansys-freeflow","application-products-ansys-freeflow"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_edit_lock":["1779643520:17114"],"_edit_last":["17114"],"_aioseo_title":[null],"_aioseo_description":[null],"_aioseo_keywords":["a:0:{}"],"_aioseo_og_title":[null],"_aioseo_og_description":[null],"_aioseo_og_article_section":[""],"_aioseo_og_article_tags":["a:0:{}"],"_aioseo_twitter_title":[null],"_aioseo_twitter_description":[null],"application_name":[""],"_application_name":["field_64a80903c8e15"],"filter_by_optics_product":["Lumerical"],"_filter_by_optics_product":["field_64fb192ba3121"],"family":[""],"_family":["field_64a809229a857"],"siebel_km_number":[""],"_siebel_km_number":["field_63ecbffce60db"],"salesforce_km_number":[""],"_salesforce_km_number":["field_63ecc018e60dc"],"km_published_date":[""],"_km_published_date":["field_64c77704499dd"],"product_version":[""],"_product_version":["field_64c776cb4fd2e"],"_bbp_forum_id":["27796"],"_bbp_topic_id":["198709"],"_bbp_author_ip":["149.117.15.13"],"_bbp_last_reply_id":["0"],"_bbp_last_active_id":["198710"],"_bbp_last_active_time":["2026-05-22 19:32:35"],"_bbp_reply_count":["0"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["0"],"_btv_view_count":["75"],"_bbp_likes_count":["6"]},"test":"articlesansys-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics\/198709","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":2,"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics\/198709\/revisions"}],"predecessor-version":[{"id":198711,"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics\/198709\/revisions\/198711"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/media?parent=198709"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}