{"id":33428,"date":"2019-02-22T07:43:42","date_gmt":"2019-02-22T07:43:42","guid":{"rendered":"\/forum\/forums\/topic\/time-step-size-2\/"},"modified":"2019-02-22T07:43:42","modified_gmt":"2019-02-22T07:43:42","slug":"time-step-size-2","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/time-step-size-2\/","title":{"rendered":"Time Step Size"},"content":{"rendered":"<p>Hi,<\/p>\n<p><\/p>\n<p>For a transient simulation, we have to set the time step size in Run Calculation. This time step is based on the CFL-Number and the value of c depends on the type of solver used (explicit or implicit). The parameter are: u for the maximal velocity<strong> of the fluid<\/strong>, delta t the time step and delta x the minimal cell size.<\/p>\n<p><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/d652d665-7f9c-42a4-8f4c-a96d00d34316\/371c1748-f087-4ce7-b647-a9fc007db290_cfl.jpg?width=690&amp;upscale=false\" alt=\"\"><\/p>\n<p><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/d652d665-7f9c-42a4-8f4c-a96d00d34316\/3f34def8-1efb-4eaa-b943-a9fc007d0567_run-calculation.jpg?width=690&amp;upscale=false\" alt=\"\">&nbsp; <\/p>\n<p><\/p>\n<p>In order to Preview the Mesh Motion, we have to give a time step size too. Is this time step based on the CFL-Number too, in order to avoid the negative cells? The velocity u in this case is then the maximal velocity <strong>of the moving part.<\/strong><\/p>\n<p><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/d652d665-7f9c-42a4-8f4c-a96d00d34316\/c0b7b6bb-e257-45b7-8b6c-a9fc007bc083_mesh-motion.jpg?width=690&amp;upscale=false\" alt=\"\"><\/p>\n<p><\/p>\n<p>Is there then an physical time step and a numerical time step?<\/p>\n<p><\/p>\n<p>To obtain correct results and avoid negativ cells too, should I choose the minimal time step for the running the simulation or are the two times the same?<\/p>\n<p><\/p>\n<p>&nbsp;<\/p>\n<p><\/p>\n<p>Regards,<\/p>\n<p><\/p>\n<p>Maxime<\/p>\n","protected":false},"template":"","class_list":["post-33428","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_old_topic_id":["5600"],"_bbp_old_topic_author_name_id":["Anonymous"],"_bbp_old_is_topic_anonymous_id":["false"],"_bbp_old_closed_status_id":["publish"],"_bbp_author_ip":[null],"_bbp_old_sticky_status_id":["normal"],"_bbp_likes_count":["0","0","0","0","0"],"_btv_view_count":["2281"],"_bbp_subscription":["237203"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["33428"],"_bbp_forum_id":["27792"],"_bbp_engagement":["22555","159144"],"_bbp_voice_count":["2"],"_bbp_reply_count":["3"],"_bbp_last_reply_id":["78378"],"_bbp_last_active_id":["78378"],"_bbp_last_active_time":["2019-02-22 10:33:08"]},"test":"max4"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/33428","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\/33428\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=33428"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}