{"id":362928,"date":"2024-04-18T11:48:37","date_gmt":"2024-04-18T11:48:37","guid":{"rendered":"\/forum\/forums\/reply\/362928\/"},"modified":"2024-04-18T11:48:37","modified_gmt":"2024-04-18T11:48:37","slug":"362928","status":"publish","type":"reply","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/362928\/","title":{"rendered":"Reply To: Frequency Statistics Analysis – Ansys AQWA"},"content":{"rendered":"

<p>Hi Mike, Some updates for your reference. <br><br><\/p><div>Some Design Points Not Converged:<\/strong> I am using Nonlinear Roll Damping in my analysis. I am using the Bilge type as “Bilge Vortex Shedding and Bilge Keel Roll Damping”. I have noticed that when I use the actual bilge parameters, I get many design points that don’t converge. But as soon as I move bilge keel further away from the centerline, some design points gets converged. I see the warning as well that damping is less than 0.5% critical damping and adjusted automatically. However, I have a few questions as well regarding defining the bilge keel. <\/div><div> <\/div><div>1. What is the difference when we select bilge type as “Bilge Vortex Shedding Only” and “Bilge Vortex Shedding and Bilge Keel Roll Damping”? Does it mean for vortex shedding only, it only accounts for the eddy part of the damping and doesn’t consider the damping part due to pressure difference on the sides of the bilge keel?<\/div><div> <\/div><div>2. Bilge Radius: I am using the one at the midship section, is this the right approach?<\/div><div> <\/div><div>3. Depth To Bilge: When I use the depth to bilge till the point where the BK is attached to the hull i.e 5.85 m, I have more points that don’t converge, but when I use the “depth to the bilge” to the bottom corner of the bilge i.e 6.142 m, then the number of unconverged points is less. I assume as the damping increase, it is easily linearized by the solver. What is the right approach, which depth should be used bottom corner of the Bilge keel or the point where the BK is attached to the hull.<\/div><div> <\/div><div>4. Offset of Bilge from Central Line: What exactly is this distance from the centerline? To the center of the red cylinder that is formed and shown in the image or is this the distance to the point where the BK is attached to the hull?  I notice that this distance play an important role in linearization, the higher the distance, the more points converged.<\/div><div> <\/div><div>5. Bilge Keel Breadth: It is the bilge keel height that I am using.<\/div><div> <\/div><div>Below are the actual values from the vessel for the BK which gives less converged points with depth to bilge until the point attached to the hull and offset of Bilge from center line till the point bilge keel attached to the hull (12.201m). Looking at the images, this configuration seems to be realistic as we have on our vessels.<\/div><p><br><br><\/p><p>Below are the modified BK parameters which gave more converged points. Depth to bilge set to the bottom point of BK. Offset from center taken as 13.99 m (12.201 m + 1.798 m). Not a realistic scenario but gives only 2 unconverged points rather than 30 points. <br><\/p><p>Here is my outline tree, I don’t have any additional loads or non-linearities. Just the irregular wave spectrum is included. <\/p><p><\/p><p><\/p><p>Looking forward to your helpful response regarding the convergence issue. <\/p><\/p>\n","protected":false},"template":"","class_list":["post-362928","reply","type-reply","status-publish","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t