Latent Data on ROS 2

[andermi]

needs osrf/mbari_wec_utils#54

publish latent data (modeled but not directly measured) on ROS 2 including:

• power
• forces
• losses
• incoming wave heights (above water plane)
• miscellaneous

[andermi]

@hamilton8415 do you want hydraulic_motor_loss and relief_valve_loss to be in the latent data? If so, would you mind handling computing those?

[andermi]

Sample message:

header:
  stamp:
    sec: 87
    nanosec: 890000000
  frame_id: ''
inc_wave_heights:
- use_buoy_origin: true
  pose:
    position:
      x: 0.0
      y: 0.0
      z: -0.8808675951160896
    orientation:
      x: -0.003990554574864658
      y: -0.005342048959267687
      z: -2.131821184897409e-05
      w: 0.9999777685191985
upper_spring:
  force: -6947.903626699504
  temperature: 288.2707047344805
  heat_loss: 609.4042334225376
  piston_position: 0.6226419249097868
  piston_velocity: 0.07149783057808637
lower_spring:
  force: 14718.269494734053
  temperature: 281.33897617870065
  heat_loss: -2361.8917248091725
  piston_position: 0.6226419249097868
  piston_velocity: 0.07149783057808637
electro_hydraulic:
  inst_power: 67.36702579975064
  rpm: -744.3751840001763
  force: 2582.348884922011
  motor_drive_i2r_loss: 10.121847152709961
  motor_drive_switching_loss: 15.078186988830566
  motor_drive_friction_loss: 74.424560546875
  battery_i2r_loss: 0.3493275046348572
wave_body:
  buoyancy:
    force:
      x: 0.0
      y: 0.0
      z: 72255.24314572435
    torque:
      x: -7.3750446819340585
      y: -6515.153314486855
      z: 0.0
  radiation:
    force:
      x: 83.6086979953471
      y: -0.0885099768620667
      z: -450.4780387299854
    torque:
      x: 0.3131910732220865
      y: 284.4873501665259
      z: 0.0005220048689208334
  excitation:
    force:
      x: 324.9787072939932
      y: -7.905087287026117e-06
      z: -41644.46129943828
    torque:
      x: 4.082321707116394
      y: 4565.312364086205
      z: 0.03130321979768935
piston_friction_force: 857.4891528904318

[hamilton8415]

Great start, I'm catching up here and thought I'd start by brainstorming the items that I can think of, although I think you have most of this in here already, so in many cases my list here is already in the LatentData struct/msg. There are decisions to make about presenting forces, or instantaneous power losses. I think the latter may be more useful for many purposes, I'm not 100% sure... It would be really something to present a total power balance in real time, power in from the waves and out into all the losses (and hopefully the battery), but it's ambitious, a few items may be hard to compute. In any event, I can certainly take the electro-hydraulic and wave-body items to implement/check and will make a branch to work in...

Incident Waves

• Wave elevation and slope at specified points (done)

Free Surface Hydrodynamics (these force/moments are a little tricky b/c the coordinate system they are expressed in can be ambiguous)

• Wave Exciting Force/Powers
• Wave Exciting Moment/Powers
• Wave Radiation Force/Powers
• Wave Radiation Moment/Powers
• Buoyancy Force/Powers
• Buoyancy Moment/Powers

Hydrodynamic Drag Losses (This may be tricky or impossible b/c we are using an existing Gazebo plugin, so maybe skip for now)

• Surface buoy drag losses (instantaneous power in Watts)
• Heave Code drag losses (instantaneous power in Watts)
• PTO drag losses (instantaneous power in Watts)

Piston Behaviors

• Friction Losses (instantaneous Power in Watts)

ElectroHydraulic PTO

• motor drive i2R losses (instantaneous power in Watts)
• motor friction losses (instantaneous power in Watts)
• motor drive switching losses (instantaneous power in Watts)
• battery i2R losses (instantaneous power in Watts)
• Power in/out of battery storage (instantaneous power in Watts)
• Hydraulic motor losses (instantaneous power in Watts)
• Drive electronics hotel power (might be unmodelled at this point, very small... 2 Watts or so)
• Shaft torque
• differential hydraulic pressure
• mechanical/volumetric efficiencies

Tether (May be impossible to divine)

• Tether friction power loss

Air spring

• Heat loss (instantaneous power in watts)
• piston pos/vel
• force
• temperature
• mass of N2

[andermi]

@hamilton8415 edited your list with checkboxes

[andermi]

added mechanical/volumetric efficiencies

[andermi]

these force/moments are a little tricky b/c the coordinate system

I added them to latent_data in the same form as you apply the wrench
baseLink.AddWorldWrench(_ecm, w_FBp + w_FRp + w_FEp, w_MBp + w_MRp + w_MEp);

latent_data.wave_body.buoyant_force = w_FBp;
latent_data.wave_body.buoyant_moment = w_MBp;
latent_data.wave_body.radiation_force = w_FRp;
latent_data.wave_body.radiation_moment = w_MRp;
latent_data.wave_body.exciting_force = w_FEp;
latent_data.wave_body.exciting_moment = w_MEp;

[andermi]

We have a force/torque sensor at the universal joint between the buoy and the pto. It provides 6dof force/torque, but we are only using force.z to act as the load_cell. Do we want to report all the other values in latent_data?

[andermi]

we could also add more force/torque sensors anywhere we'd like for extra info

[hamilton8415]

Thanks, ros2 topic echo /latent_data now streaming data...

[andermi]

@hamilton8415 next step is power for WaveBodyInteractions?

[hamilton8415]

Yeah, I made branches to get started on that, but am still thinking about it some. We might not want to get too crazy, in that case there's energy coming and going from potential/kinetic energies, so things aren't going to line up so well as the quasi-static ehpto, so it'll be interesting maybe, but I'm not thinking we want to pursue an entire energy balance checking for the whole system, since we don't also have easy ways to incorporate viscous drag, etc. So basically, I think we should go ahead and include potentially interesting quantities throughout, and call it done. :)

[hamilton8415]

Progress.