January 2022 - firedrake - imperial.ac.uk

Help with implementing steps in simulation
by Venketeswaran, Abhishek (FN) 01 Feb '22

01 Feb '22

Hi, I would like to prescribe a boundary condition for an initial time duration and then remove it for the remaining time duration. Commercial finite element solvers allow you to do this by specifying steps. I tried to implement it using the code below. This is giving nonsensical results at and after the time at which the BCs change. Can you please assist me in how I may implement this properly. I can share the full code if needed. m = rho*inner((u - 2.0 * u_n + u_nm1),v) / Constant(dt * dt) * dxlump k= inner(sigma(u_n),epsilon(v))*dx def collar_load(t,T,freq,amp=1.0): return amp*hanning(t,T)*stepfn(t,T)*np.sin(freq*t) # Define the loading as an expression depending on t t=0 collar_disp= Constant([0.0, 0.0, 0.0]) F = m+k a, r = lhs(F), rhs(F) zero = Constant((0.0, 0.0, 0.0)) # Dirichlet BC that is valid for the entire time duration bc1 = DirichletBC(V, zero, 11) # Collar BC that remains on till T_pulse bc2= DirichletBC(V, collar_disp, 21) # My attempt of defining two problems to mimic two simulation steps problem1 = LinearVariationalProblem(a, r, u_np1, bcs=[bc1,bc2], constant_jacobian=True) solver1 = LinearVariationalSolver(problem1, solver_parameters=params) problem2 = LinearVariationalProblem(a, r, u_np1, bcs=[bc1], constant_jacobian=True) solver2 = LinearVariationalSolver(problem2, solver_parameters=params) for i in range(len(time)): t = time[i] if (t<=T_pulse): solver1.solve() else: solver2.solve() u_nm1.assign(u_n) u_n.assign(u_np1) -- Abhishek Venketeswaran NETL Research Associate - ORISE National Energy Technology Laboratory Department of Energy abhishek.venketeswaran(a)netl.doe.gov Work: 412-386-4833 Mobile: 716-507-7890 www.netl.doe.gov<http://www.netl.doe.gov> [cid:97ebd409-8c9c-4361-9753-e4c626433151]

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Erroneous results for ultrasonic guided wave simulation with KMV elements
by Venketeswaran, Abhishek (FN) 28 Jan '22

28 Jan '22

Hi, The KMV discretized elastic wave solver seems to be doing something weird. I am essentially prescribing a sinusoidal impulse as displacement at a circumferential section for a short duration (150 microseconds). I have attached snapshots at 200 microseconds and 600 microseconds. Instead to the pulse traveling at group velocity, some random error is increasing near the loading section. I am not able to figure out what could be the problem. I have tried out different preconditioners while maintaining a direct "preonly" KSP iterations. Do you have any idea where I could be going wrong? -- Abhishek Venketeswaran NETL Research Associate - ORISE National Energy Technology Laboratory Department of Energy abhishek.venketeswaran(a)netl.doe.gov Work: 412-386-4833 Mobile: 716-507-7890 www.netl.doe.gov<http://www.netl.doe.gov> [cid:5c03a053-94d0-49c7-84af-375ffa90acbb]

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Elastic Wave Propagation in Pipe Simulation Failing
by Venketeswaran, Abhishek (FN) 21 Jan '22

21 Jan '22

Hi, I have spent considerable time trying to debug my code and am not able to find the bug in the code. I am essentially trying to simulate 3D elastic wave propagation in a pipe fixed on both ends and having an ultrasonic collar triggering ultrasonic impulse on a portion of the outer pipe segment. I would ideally like to use the KMV elements (similar to the spyro package). I generated a tetrahedral mesh of the pipe using GMsh and labeled the ends of the pipe using tag "1" and the collar segment as "2". Next I wrote the UFL expressions for 2nd order central difference for acceleration term and the elasticity as well as traction terms. The code runs but the displacement at certain nodes diverges to infinity and results in nonsensical results. I have tried multiple things including 1. specifying the collar load as displacement as well as traction 2. trying out KMV and CG element 3. trying out different KSP methods and preconditioners 4. Formulating the problem using semi-implicit HHT as well as second order explicit difference method 5. Ensuring the Gamma value of the tetrahedral mesh is atleast 0.2 I would really appreciate it if someone could help me out with this. -- Abhishek Venketeswaran NETL Research Associate - ORISE National Energy Technology Laboratory Department of Energy abhishek.venketeswaran(a)netl.doe.gov Work: 412-386-4833 Mobile: 716-507-7890 www.netl.doe.gov<http://www.netl.doe.gov> [cid:abfe3d17-ce71-45f1-8175-8e0cd802eaee]

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Apple silicon installation
by MUFANG YING 17 Jan '22

17 Jan '22

Hi, When I wanted to install the package on my M1 chip macbook, I found out that the installation is not that smooth since the home brew has some updates on the prefix. I was wondering if you could give me some advice on how to successfully install firedrake on M1 macbook. I would really appreciate any feedback. Thank you. Best, Mufang Ying

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another job
by Cotter, Colin J 13 Jan '22

13 Jan '22

Dear Firedrake friends, I've got another job advert out, this time for a 26 month postdoctoral contract. Please let me know offlist if you have any questions. https://www.imperial.ac.uk/jobs/description/NAT01069/research-associate-com… all the best ---cjc Professor Colin Cotter (he/him) Department of Mathematics 755, Huxley Building Imperial College London South Kensington Campus United Kingdom of Great Britain and Northern Ireland +44 2075943468

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