I am wondering if I understand the governing equation correctly ? I am wondering if I understand the governing equation correctly ? https://oss.deltares.nl/c/message_boards/find_thread?p_l_id=1806675&threadId=1077562 2019-09-19T02:26:29Z 2019-09-19T02:26:29Z I am wondering if I understand the governing equation correctly ? Peng Dai https://oss.deltares.nl/c/message_boards/find_message?p_l_id=1806675&messageId=1077561 2017-11-29T12:55:04Z 2016-11-24T15:59:16Z Dear:<br /><br />In D3D user manual (refer to the Version: 3.15), in the subsection 9.3.1 hydrodynamic equations, the continuity equation uses the depth-averaged velocity, i.e. capitalized U and V (eq.9.3). The momentum equation uses the layer horizontal velocity, i.e. lowercase u and v (eq. 9.7 &amp; eq. 9.8). I am a bit wondering how this set of equation can be coupled (see the snapshot below) since they use different velocities. There may be some tricks that I have not get yet. Can any one specify that?<br /><br /><br />Moreover, the continuity equation (eq. 9.3) is expressed in terms of depth-averaged velocity. However, the vertical velocity in the sigma-coordinate system is computed from the eq. 9.9 which is again a continuity equation but uses layer horizontal velocity. Can anyone specify how Delft3D-FLOW do when performing 2D and 3D modelling ?<br /><br /><br />Thanks in advance!<br /><br />Cheers, <br />Peng Peng Dai 2016-11-24T15:59:16Z