{"id":439671,"date":"2025-08-19T21:43:37","date_gmt":"2025-08-19T21:43:37","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/system-coupling-low-level-communication-error-4-write-error\/"},"modified":"2025-09-26T16:06:23","modified_gmt":"2025-09-26T16:06:23","slug":"system-coupling-low-level-communication-error-4-write-error","status":"answered","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/system-coupling-low-level-communication-error-4-write-error\/","title":{"rendered":"System Coupling \u201cLow-level communication error \u22124: Write error\u201d"},"content":{"rendered":"

<p data-start=”227″ data-end=”317″>I’m seeing repeat failures of Fluent–Mechanical coupling that don’t appear model-specific.<\/p><p data-start=”319″ data-end=”337″><strong data-start=”319″ data-end=”335″>Environments<\/strong><\/p><ul data-start=”338″ data-end=”500″><li data-start=”338″ data-end=”398″><p data-start=”340″ data-end=”398″><strong data-start=”340″ data-end=”360″>Local (Windows):<\/strong> Ansys 2025 R1 (v251) via Workbench.<\/p><\/li>\n

<li data-start=”399″ data-end=”500″><p data-start=”401″ data-end=”500″><strong data-start=”401″ data-end=”427″>Cluster (Linux\/SLURM):<\/strong> Ansys 2023 R1 (v231), single-node jobs, System Coupling shows Intel MPI.<\/p><\/li>\n<\/ul>\n

<p data-start=”502″ data-end=”516″><strong data-start=”502″ data-end=”514″>Symptoms<\/strong><\/p><ul data-start=”517″ data-end=”966″><li data-start=”517″ data-end=”709″><p data-start=”519″ data-end=”709″><strong data-start=”519″ data-end=”534″>Local v251:<\/strong> The stock <em data-start=”545″ data-end=”572″>Reed Valve FSI Simulation<\/em> tutorial (no edits) fails during initial participant connection; System Coupling reports that one participant exited during handshake.<\/p><\/li>\n

<li data-start=”710″ data-end=”966″><p data-start=”712″ data-end=”966″><strong data-start=”712″ data-end=”729″>Cluster v231:<\/strong> My minimal two-way FSI prototype launches and connects, Mechanical begins solving, then System Coupling aborts on the first data exchange with <strong data-start=”873″ data-end=”924″>“Low-level communication error −4: Write error”<\/strong> while making a remote call to <strong data-start=”955″ data-end=”965″>Fluent<\/strong>.<\/p><\/li>\n<\/ul>\n

<p data-start=”968″ data-end=”989″><strong data-start=”968″ data-end=”987″>What I’ve tried<\/strong><\/p><ul data-start=”990″ data-end=”1187″><li data-start=”990″ data-end=”1062″><p data-start=”992″ data-end=”1062″>Reproduced with both my prototype and the unmodified Ansys tutorial.<\/p><\/li>\n

<li data-start=”1063″ data-end=”1124″><p data-start=”1065″ data-end=”1124″>Multiple runs on both environments with the same outcome.<\/p><\/li>\n

<li data-start=”1125″ data-end=”1187″><p data-start=”1127″ data-end=”1187″>No custom MPI flags; default SC-assigned ports; single node.<\/p><\/li>\n<\/ul>\n

<p data-start=”1189″ data-end=”1198″><strong data-start=”1189″ data-end=”1196″>Ask<\/strong><\/p><ul data-start=”1199″ data-end=”1598″><li data-start=”1199″ data-end=”1274″><p data-start=”1201″ data-end=”1274″>Known causes\/fixes for <strong data-start=”1224″ data-end=”1250″>error −4 (Write error)<\/strong> when SC calls Fluent?<\/p><\/li>\n

<li data-start=”1275″ data-end=”1385″><p data-start=”1277″ data-end=”1385″>Recommended diagnostics (Fluent\/SC logging flags, environment variables) to pinpoint socket\/RPC shutdowns.<\/p><\/li>\n

<li data-start=”1386″ data-end=”1476″><p data-start=”1388″ data-end=”1476″>Any version-specific issues with v251\/v231 affecting SC ↔ Mechanical\/Fluent handshake?<\/p><\/li>\n

<li data-start=”1477″ data-end=”1598″><p data-start=”1479″ data-end=”1598″>MPI\/fabric or port\/hostname settings you recommend for single-node SC runs (e.g., loopback vs host IP, firewall notes)?<\/p><\/li>\n<\/ul>\n

<p data-start=”1600″ data-end=”1668″ data-is-last-node=”” data-is-only-node=””>I can upload the SC\/Fluent\/MAPDL logs (local and cluster) if needed.<\/p><p data-start=”1600″ data-end=”1668″ data-is-last-node=”” data-is-only-node=””>Thank you<\/p><\/p>\n","protected":false},"template":"","class_list":["post-439671","topic","type-topic","status-answered","hentry","topic-tag-2-way-coupled-fsi","topic-tag-2-way-fsi","topic-tag-fluent-mechanical","topic-tag-fsi","topic-tag-fsi-2-way-1","topic-tag-fsi-transient-2","topic-tag-system-coupling","topic-tag-system-coupling-error","topic-tag-system-coupling-transient-structural-fluid-flow-fluent-cfd-post-connector-1","topic-tag-systemcoupling","topic-tag-two-way-coupling","topic-tag-two-way-coupling-fluent-2","topic-tag-two-way-fsi-1"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27791"],"_bbp_topic_id":["439671"],"_bbp_subscription":["578579","805"],"_bbp_author_ip":["130.64.3.203"],"_bbp_last_reply_id":["440515"],"_bbp_last_active_id":["440515"],"_bbp_last_active_time":["2025-09-01 14:58:18"],"_bbp_reply_count":["10"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["2"],"_bbp_engagement":["578579","805"],"_btv_view_count":["487"],"_bbp_topic_status":["answered"]},"test":"kaeden-frestontufts-edu"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/439671","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":1,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/439671\/revisions"}],"predecessor-version":[{"id":442418,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/439671\/revisions\/442418"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=439671"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}