Grid resolution vs deep basin modelingGrid resolution vs deep basin modelinghttps://oss.deltares.nl/c/message_boards/find_thread?p_l_id=1806713&threadId=19143442021-04-17T01:27:24Z2021-04-17T01:27:24ZRE: Grid resolution vs deep basin modelingSoniaAllison SoniaAllisonhttps://oss.deltares.nl/c/message_boards/find_message?p_l_id=1806713&messageId=32417052020-08-31T05:39:19Z2020-08-29T04:33:18ZGreat post. It was much needed. Love your simplistic style of explanation. <img alt="emoticon" src="https://oss.deltares.nl/o/deltares-theme.war/images/emoticons/happy.gif" > <a href="https://www.tellpizzahut.online/">tellpizzahut</a><div class="lfr-code"><table><tbody><tr><td class="line-numbers" data-line-number="1"></td><td class="lines"><div class="line"><br /></div></td></tr></tbody></table></div>SoniaAllison SoniaAllison2020-08-29T04:33:18ZRE: Grid resolution vs deep basin modelingjohn smithhttps://oss.deltares.nl/c/message_boards/find_message?p_l_id=1806713&messageId=26110622019-10-02T10:40:49Z2019-10-02T10:40:49Z<div class="quote-title">Marina Amadori:</div><div class="quote"><div class="quote-content"><br /><p>Hi, </p><br /><p>I am working on stationary wind-induced velocity profile (Coriolis<br /> force neglected) in un-stratified box domains, constant turbulence<br /> model and no thermal fluxes. I am comparing the numerical<br /> results from boxes with different depths with the theoretical solution<br /> for the steady state (Heaps 1984). </p><br /><p>I verified that equilibrium is achieved (I am performing 60 days<br /> simulations) and I found good agreement for shallow boxes (H = 10 m,<br /> 30 m, 50 m, see Fig.v_res100m.png in the attachments). A mismatch<br /> between numerical and theoretical solution arises when I simulate deep<br /> boxes (H = 300 m, H = 500 m, always in Fig.v_res100m.png). </p><br /><p>As a first attempt I thought it was a time step problem and I reduced<br /> it to meet the conditions in Table 10.1 (FLOW manual) but I didn’t get<br /> any improvement.Then I tried changing the horizontal grid resolution<br /> and I got the results in Fig.v_allres.png (in the attachments), where<br /> I found that finer horizontal resolutions (DX = 20 m, 50 m, 100 m,<br /> square cells) lead to worse results. I got the best match with DX =<br /> 2000 m but still I am not there. What if I choose DX = 5000 m?</p><br /><p>Now, my questions are:</p><br /><p>1. Why are coarser resolutions giving better result?</p><br /><p>2. If the answer is the &quot;ADI accuracy&quot; in Table 10.1, why<br /> is reducing time step not providing any change in the solution?</p><br /><p>3. Is there a clear/formulated criterion for choosing the proper grid<br /> size according to the depth of the basin?</p><br /><p>4. How is it this criterion related to the choice of the background<br /> vertical eddy viscosity (I am modeling with constant turbulence model,<br /> nuz = 0.0373 m2/s)?</p><br /><p> </p><br /><p>Thank you!</p><br /><p>Marina<br /><br /> <br /><br /> <br /> </p></div></div>I also have this question, if someone has a solution, please tell mejohn smith2019-10-02T10:40:49ZRE: Grid resolution vs deep basin modelingRichard Measureshttps://oss.deltares.nl/c/message_boards/find_message?p_l_id=1806713&messageId=19188252018-08-13T00:04:32Z2018-08-13T00:04:32Z<p>Hi Marina,</p> <p>Interesting question - Well explained and I really like your graphs.</p> <p>Would you be able to give some more information about your vertical resolution e.g. how many layers do you have? Do you have the same number of layers when you increase the depth or do you have more vertical layers for the deeper models so the layer thickness is the same?</p> <p>I don't have a lot of experience with constant vertical eddy viscosity but from my experience calibrating constant horizontal eddy viscosity I expect it could be quite sensitive to vertical resolution (the selection of appropriate horizontal eddy viscosity is sensitive to horizontal resolution). I expect that thinner vertical layers would require a smaller eddy viscosity to get the same result?</p> <p>That doesn't help explain how horizontal resolution is influencing the vertical profile though! Have you checked to see if there are boundary effects propagating into your model horizontally? These could be affected by horizontal resolution and would be more significant for deeper domains. Maybe your horizontal eddy coefficient is too large for the models where you have a small cell size (I find the default horizontal eddy viscosity value is only suitable for very large cell sizes). As you are focused on vertical profiles I would try setting the horizontal eddy viscosity very small (but non-zero as that can cause weird instabilities) e.g. 0.001. Also you could try increasing the spatial size of the domain to see if that has any effect (i.e. reducing any horizontal boundary effect).</p> <p>Good luck, I look forward to finding out what the problem was when you do solve it!</p> <p>Cheers,</p> <p>Richard</p>Richard Measures2018-08-13T00:04:32ZGrid resolution vs deep basin modelingMarina Amadorihttps://oss.deltares.nl/c/message_boards/find_message?p_l_id=1806713&messageId=19143432018-08-07T18:52:39Z2018-08-07T18:52:39Z<p>Hi, </p> <p>I am working on stationary wind-induced velocity profile (Coriolis force neglected) in un-stratified box domains, constant turbulence model and no thermal fluxes. I am comparing the numerical results from boxes with different depths with the theoretical solution for the steady state (Heaps 1984). </p> <p>I verified that equilibrium is achieved (I am performing 60 days simulations) and I found good agreement for shallow boxes (H = 10 m, 30 m, 50 m, see Fig.v_res100m.png in the attachments). A mismatch between numerical and theoretical solution arises when I simulate deep boxes (H = 300 m, H = 500 m, always in Fig.v_res100m.png). </p> <p>As a first attempt I thought it was a time step problem and I reduced it to meet the conditions in Table 10.1 (FLOW manual) but I didn’t get any improvement.Then I tried changing the horizontal grid resolution and I got the results in Fig.v_allres.png (in the attachments), where I found that finer horizontal resolutions (DX = 20 m, 50 m, 100 m, square cells) lead to worse results. I got the best match with DX = 2000 m but still I am not there. What if I choose DX = 5000 m?</p> <p>Now, my questions are:</p> <p>1. Why are coarser resolutions giving better result?</p> <p>2. If the answer is the "ADI accuracy" in Table 10.1, why is reducing time step not providing any change in the solution?</p> <p>3. Is there a clear/formulated criterion for choosing the proper grid size according to the depth of the basin?</p> <p>4. How is it this criterion related to the choice of the background vertical eddy viscosity (I am modeling with constant turbulence model, nuz = 0.0373 m2/s)?</p> <p> </p> <p>Thank you!</p> <p>Marina<br /> <br /> <br /> </p>Marina Amadori2018-08-07T18:52:39Z