flapping device #170

ryancoe · 2020-09-08T19:34:30Z

Description

A bottom fixed flapping device (e.g., Oyster). I am leveraging gmsh for this, which is something that I've been wanting to do for some time (see #118).

Fixes #156

Checklist:

All new files contain the GPL header
[ ] If examples/RM3/optimization.m has been modified, the content / line
numbers in docs/user/optimization.rst are still valid or have been fixed

ryancoe · 2020-09-08T19:36:40Z

examples/Flapper/designDevice.m

+    zlim([-Inf, 0])
+    ylim([-10, 10])
+    xlim([-10, 10])
+


At this point, we need to create a file that NEMOH can use. It looks like one of the MATLAB tools that comes with NEMOH (https://github.com/LHEEA/Nemoh/blob/master/matlab%20routines/Mesh.m) may be able to do this for us.

This is already done by the NEMOH class. What we need is a gmsh equivalent of the AxiMesh class.

ryancoe · 2020-09-10T15:50:29Z

examples/Flapper/designDevice.m

+    % call gmsh to create the mesh and save as STL
+    geofn_2 = 'Flapper.stl';
+    meshscalefator = 1;
+    syscall_gmsh = sprintf('gmsh %s -clscale %f -1 -2 -o %s',...


Just remembered that (I think) NEMOH needs quads (four sided panels); just need to add the proper flags to the gmsh call: nschloe/pygmsh#331

I now believe NEMOH can work with either, but are specified in the mesh file as a four node panel with one repeated node.

ryancoe · 2020-09-16T17:43:01Z

examples/Flapper/designDevice.m

+    xlim([-10, 10])
+
+%     hydro = WecOptTool.solver("NEMOH", folder, meshes, w);
+    hydro = nan;


When writing the Nemoh.cal file for this flapping device, we will need to specify the degrees of freedom to look at pitch (not heave as with the WaveBot and RM3), see explanation here: https://lheea.ec-nantes.fr/valorisation/logiciels-et-brevets/nemoh-running.

... 1 ! Number of degrees of freedom 2 0. 1. 0. 0. 0. -7.5 ! Pitch about CG: 2 for rotation, followed by direction vector (axis and center of rotation) 1 ! Number of resulting generalised forces 2 0. 1. 0. 0. 0. -7.5 ! Moment force in y direction about CdG ....

Just a note here that we have been calculating all 6 degrees of freedom in all NEMOH simulations so far (since the repository was set up).

An example of a command line call to set parameters is also shown.

Add installation of the executable path, and checking Add MATLAB mesh file generation in Gmsh class. Needs to add file read.

H0R5E · 2020-09-25T15:56:22Z

So, I have Gmsh set up in a similar way to Aximesh now, and it produces similarly formatted meshes, as so:

Next job is to modify the NEMOH solver routine to allow different degrees of freedom to be simulated.

EDIT: Before that I need to add something to show the normals, to check that the node numbering is in the correct order.

ryancoe · 2020-10-01T14:59:52Z

You can look at the mesh normals in gmsh... this may be helpful -- you may be able to do a system call to do this.

ryancoe · 2020-10-01T15:07:41Z

Looks like the normals on one face are point in

Fix panel orientation for traditional model

Allows specific setting of degrees of freedom, rotation point, centre of gravity and water depth

* Uses half mesh. * Fixes issues with Mesh.cal writing. * Allows wave direction to be set (to 90 in this case).

ryancoe · 2020-10-15T14:54:54Z

examples/Flapper/simulateDevice.m

+    end
+
+    % Mass
+    mass = hydro.Vo * hydro.rho;


This needs to be the rotational inertia (I = r_cog^2 * m), where r_cog is the distance from the center of mass to the center of rotation

Additionally, we should allow m != Vo * rho - @ssolson has done this for #3

EDIT: I originally messed up the eq. for moment of inertia, corrected now

ryancoe · 2020-10-15T15:01:49Z

examples/Flapper/simulateDevice.m

+    myPerf.Fpto = -1 * myPerf.Zpto .* myPerf.u;
+
+    % power
+    myPerf.pow = 0.5 * myPerf.Fpto .* conj(myPerf.u);


we can check this against the theoretical limit... will point to a paper or Section of Falnes

sorry for the lag on this one... maximum absorbed power for a pitching device in a single frequency ("regular") wave is Pmax = J lambda / pi, where J is the wave power flux (units power/length), and lambda is the wave length.

Additionally, you can use Pmax = abs(Fe).^2 ./ (8*real(Zi)), where Fe is the excitation vector (units moment) and Zi is the impedance.

@ryancoe is Pmax invariant with the width of the flap?

H0R5E · 2020-11-04T16:40:34Z

So, the problem with NEMOH not calculating with depth < 10 was that the mesh generation was not being updated alongside the NEMOH config (the bottom centre of the flap is placed at (0, 0, -depth). Therefore, the flap was being placed below the seabed and NEMOH must not like that.

H0R5E · 2020-11-04T17:23:38Z

@ryancoe, do you think the issue could be where the excitation force is applied? ~~Where is NEMOH applying the forces, at the centre of mass? But then don't we have to do something about considering where the PTO acts?~~

EDIT: Actually, I am requesting the moment at the base of device. Perhaps this is the issue, wouldn't it be infinitely big at the point of rotation itself?

EDIT2: Tomorrow I will try requesting the forces not at the point of rotation and see what happens.

H0R5E · 2020-11-05T11:11:19Z

OK, I think that was a bit of a red herring, I am basically following the procedure here for setting up the case, where the calculation and rotation points are coincident.

From that page, I am struggling to interpret what "moment force along y axis" means. Is "moment force" the torque and does "along y axis" mean it is calculated at the origin? Do we need to scale it, perhaps?

EDIT: Yes, I think there is a good chance this is what is happening. I varied the depth of water for the same sized flap and got these results:

           AvgPow     |MaxPow|     PowTHD_dBc    MaxPos    MaxVel       MaxPTO  
           ______    __________    __________    ______    _______    __________

     -9    -26184    7.4173e+05       NaN        1.1274    0.67645    2.1156e+06
    -10    -30928    1.6164e+06       NaN        2.0519    1.2312     2.5756e+06
    -11    -35854    5.1083e+06       NaN        4.4137    2.6482     3.8308e+06

So, perhaps we should scale it to the z-value of the centre of mass?

EDIT 2: After scaling the torque to be applied at the centre of mass, I get the following results:

           AvgPow     |MaxPow|     PowTHD_dBc    MaxPos    MaxVel       MaxPTO  
           ______    __________    __________    ______    _______    __________

     -9    -2020.3     57232         NaN        0.31317    0.1879     5.8766e+05
    -10    -1933     1.0102e+05      NaN        0.51298    0.30779    6.4389e+05
    -11    -1852     2.6386e+05      NaN        1.0031     0.60186    8.7065e+05

It makes sense to me that the average power increases as the depth reduces, as linear waves are more powerful near the surface. I'm sort of surprised that all the other metrics reduce. These values seem more in the ballpark, at least.

ryancoe · 2020-11-24T17:30:13Z

We should confirm that they way we are setting up the problem and interpreting the results from NEMOH are consistent with what's been done here:

H0R5E · 2020-11-26T14:48:13Z

So, it looks like the measurements were taken at the origin for the WAMIT run for OSWC. So I guess that confirms that NEMOH is also outputting results measured at the origin (you can't set the equivalent WAMIT XFIELD value), although for some reason they were also measuring the values 0.5m off the body surface (in x) in WAMIT. They don't make any effort to translate these values into any power measurement, it's just a like for like comparison.

H0R5E · 2020-11-26T15:18:42Z

OK. so the power per wave front of a linear wave is:

$P=\frac{1}{32\pi}\rho g^{2} H^{2} T$

So, for $H=0.2$ and $T=10$ we get $P \approx 383 W$ . For a 10m width of device, that would be 3830W, so we're seeing a conversion ratio of 52% which doesn't seem too bad to me, given the device is 4m+ below the sea surface.

Add test

ryancoe · 2020-11-27T20:02:24Z

Can you find the capture width agains the limit for a pitching device (Falnes Sec. 6.4.2)?

H0R5E · 2020-11-30T13:34:56Z

There is equation 6.108, but I'm not sure what $h^\prime$ is. In the following paragraph it suggests that the absorption would be between 50 and 100% (salters duck is 80% apparently), but I guess that doesn't account for depth variation.

# Conflicts: # .travis.yml

Also skip Gmsh tests if not installed

H0R5E · 2021-01-12T14:12:33Z

Moved branches and reopened in #207

incomplete draft

1e3759c

ryancoe added enhancement New feature or request examples Tutorials and examples labels Sep 8, 2020

ryancoe commented Sep 8, 2020

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ryancoe commented Sep 10, 2020

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ryancoe commented Sep 16, 2020

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H0R5E added 7 commits September 24, 2020 12:00

Merge branch 'master' into flappingDevice

45b520f

Add example with rectangular panels

85725d0

An example of a command line call to set parameters is also shown.

Add a dummy function structure for the gmsh version of makeMesh

e6a8ba3

Add depth correction and centre

7ecadb7

Move depth correction to translate command

a3e7c16

Add Gmsh infrastructure

6270fdd

Add installation of the executable path, and checking Add MATLAB mesh file generation in Gmsh class. Needs to add file read.

Finish Gmsh mesh generation and demo in Flapper_caseA

99d142a

H0R5E added 10 commits October 5, 2020 12:58

Rename geo files for opencascade versus traditional model

3a26124

Fix panel orientation for traditional model

Merge branch 'master' into flappingDevice

bcc7085

Make the first value of getRegularFrequencies be dw

32abd25

Redesign NEMOH class makeMesh method input for greater control

04d6750

Allows specific setting of degrees of freedom, rotation point, centre of gravity and water depth

Extract results of forces in roll from NEMOH

a590235

Describe waterDepth option to NEMOH.getHydro

f7a96c0

Calculate power production using complex conjugate control

1a30e10

* Uses half mesh. * Fixes issues with Mesh.cal writing. * Allows wave direction to be set (to 90 in this case).

Update documentation

057f552

Remove unused template file

e59dd58

Minor update to docstring of makeMesh

51789a1

ryancoe commented Oct 15, 2020

View reviewed changes

Use moment of inertia rather than just mass.

3db6d2b

ryancoe mentioned this pull request Nov 3, 2020

only run Nemoh in relevant modes #195

Open

H0R5E added 3 commits November 5, 2020 11:46

Hack in some scaling to the "moment force"

3f6dca5

Move application of scaling to designDevice

a85a394

Minor change

f1885bb

Add P and PS controllers and change variable names to angular convention

b52f384

Add test

H0R5E marked this pull request as ready for review November 26, 2020 16:55

H0R5E added 9 commits November 26, 2020 17:37

Trigger build with gmsh

e8af81e

Merge branch 'master' into flappingDevice

3b8a133

Merge remote-tracking branch 'public/master' into flappingDevice

06ba4c9

Update travis file to download and install Gmsh

c26f1a0

Forgot the file extension

1d1825e

Add installation instructions to README and try Travis again

214729b

Update installation instructions in docs

c7bcae2

Remove unused geo file

0e8dc30

Make sure everything has license boilerplate

bc3de99

H0R5E mentioned this pull request Dec 1, 2020

Calculate standard error on PS results #203

Closed

3 tasks

H0R5E added 4 commits December 1, 2020 18:11

Add tests for Gmsh makeMesh and installExternal

2a7e78c

Merge branch 'master' into flappingDevice

5d4442d

# Conflicts: # .travis.yml

Fix bug I added to installExternal and harden tests.

4b42066

Also skip Gmsh tests if not installed

Fix simulateDevice docstrings for constraints

2c330e8

H0R5E mentioned this pull request Jan 12, 2021

Flapping device #207

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1 task

H0R5E closed this Jan 12, 2021

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flapping device #170

flapping device #170

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flapping device #170

flapping device #170

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