Dear Chengjiao, Thanks for your detailed tests and explanations. I used the IterativeStaticCond solver in parallel in my case and the jumps of lift force trace occured. I will test the “Xxt solver + StaticCond approach” you mentioned. Best wishes, Yong Wang On Mon, Aug 10, 2020 at 12:33 PM Chengjiao Ren <dlut_renchengjiao@163.com> wrote:
Dear all,
Same issue has been observed in the scenario of oscillatory flow (U=Um*sin(2*pi/T*t)) past a fixed cylinder at small KC=Um*T/D values, say, KC < 2, where the flow is symmetric along the streamwise direction. The attached figure shows an example of the time histories of lift coefficients (black lines) using different Global system solution schemes. The scaled freestream velocity is plotted as blue lines for reference. The drag & inertia coefficients and the overall flow fields wouldn’t be affected among those three cases.
As the flow is symmetric, the lift coefficients should be zero. The result using “Xxt solver + StaticCond approach” looks good, but the iterative solver doesn’t work, which actually amplifies the sudden jumps of lifts. Refinement of mesh distributions near the cylinder surface sometimes give worse results.
It seems the sudden jump of lift appears when there’s an oscillatory flow/oscillating cylinder exist in the system at small KC values (Yong’s case KC ~ 1 ). Since the Xxt solver is under development and it is quite slower than the iterative & direct solvers in Qusi-3D cases, I’m not sure if it is proper to use the Xxt solver.
P.S. All the simulations are simulated in parallel using 24 nodes. The version of Nektar++ is 4.4.1.
Kind regards,
Chengjiao
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任珵娇；Chengiiao Ren，
博士研究生；Ph.D Candidate，
建设工程学部；Faculty of Infrastructure Engineering，
大连理工大学； Dalian University of Technology，
大连，中国 116024；Dalian，CHINA 116024.
电话，Phone：86-18504285808，61-413077330
电子邮箱，Email：dlut_renchengjiao@163.com; chengjiao.ren@outlook.com;
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*From: *Yong Wang <yongwang.ttu@gmail.com> *Sent: *Tuesday, 11 August 2020 12:22 AM *To: *ybao <ybao@sjtu.edu.cn> *Cc: *nektar-users <nektar-users@imperial.ac.uk>; Lahooti, Mohsen <m.lahooti@imperial.ac.uk> *Subject: *Re: [Nektar-users] Jumps of lift force trace in simulation offorced vortex induced vibration
Hello,
Thanks Prof. Spencer for your referral.
Dear Yan, the drag and lift trace of my simulation is attached in this email. Thanks a lot for your help.
Best wishes,
Yong Wang
Ph.D. Student
National Wind Institute
Texas Tech University
Lubbock, Texas, US
On Mon, Aug 10, 2020 at 7:20 AM ybao <ybao@sjtu.edu.cn> wrote:
Dear Yong,
I can’t find the image attached! So could you send and let me have a look on the drag and lift trace of your simulations, thanks!
Cheers,
Yan
On 9 Aug 2020, at 18:50, Sherwin, Spencer J <s.sherwin@imperial.ac.uk> wrote:
Dear Yong,
I wonder if you might discuss this with Mohsen or Yan Bao who have most recently been using this version of the code.
Best regards,
Spencer.
Spencer Sherwin FREng, FRAeS Head of Aerodynamics Section, Director of Research Computing Service, Professor of Computational Fluid Mechanics, Department of Aeronautics, South Kensington Campus,
Imperial College London, SW7 2AZ, UK Phone: +44 (0)20 7594 5052
http://www.imperial.ac.uk/people/s.sherwin/
On 4 Aug 2020, at 15:55, Yong Wang <yongwang.ttu@gmail.com> wrote:
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Hello,
I am simulating forced vortex induced vibration by Nektar++ (latest version) and found jumps in the lift force trace as shown below. The jumps occur every 5 seconds, which is half of the period of the forced sinusoidal vibration (when displacement of the body is zero). The XML session file is also attached. I tried to find the reason from the formulation of additional body force due to the usage of inertial coordinate system fixed on the vibrating body, but can't explain these jumps. Do you have some ideas about this issue? Thanks a lot.
<drag_lift.png>
Best wishes,
Yong Wang
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