Gantry System Build
3-axis servo-driven underwater oscillation platform — independent project
A custom 3-axis gantry designed and built to mount Nebula in the water tank and provide controlled oscillatory base excitation. This is a standalone lab infrastructure project, independent of both dissertation aims and the NREL contract. The gantry feeds directly into the Nebula EH on Bending Structure experiments.
Hardware Specs
AxesThree servo-driven axes (DYN4 drives)
ControllerGalil motion controller, interfaced via dSpace
Ball screw5.08 mm/rev leadscrew, 800 cts/rev → 1102 cts full 7 mm stroke
Z brake24V electromagnetic brake via Galil IO module pin 44
GUICustom oscilloscope-interface .exe (Desktop/dist folder)
Operation Notes
IPsGalil USB: 169.254.249.205 · Router: 192.168.202.220
HomingSet machine zero each session via ClearPath MSP software
TriggerGantry waits for dSpace digital trigger before moving (Galil code line 23)
MemoryCannot run >6 cycles at 0.5 Hz — memory overrun. Use ≥1.25 Hz for long runs.
Integration with Nebula EH experiments: The gantry provides the sinusoidal base excitation that drives bending of the HASEL structure in the energy harvesting on bending experiments. The gantry encoder signal is logged through dSpace alongside LDV, DIC, and HASEL voltage signals.
Underwater DIC — NREL Contract
Evaluating deformation measurement for NREL's wave flume — separate contract
A separate NREL contract (not a dissertation aim) to evaluate how to track the deformation of a flexible surging wave energy converter (flexWEC) inside NREL's wave flume (2.5 m wide, 1.3 m deep, 0.5–5 s period). The flume has viewing windows only on one side. We tested DIC with cameras outside the tank at multiple angles, and straight-on DIC as a proxy for underwater camera performance.
Snell's Law constraint: Light from water (n = 1.33) to air (n = 1) undergoes total internal reflection at θ_crit = arcsin(1/1.33) = 48.8°. Usable camera angles are less than 90° from the tank wall normal, but refraction heavily distorts images at large angles even well below critical.
Angle Test Results (24 mm wide-angle lens)
| Outside Angle θ | Internal Angle θ' (Snell) | Speckle Size | Outcome |
|---|---|---|---|
| 75° | 46° | 3–4 px (too small) | Cannot focus on speckles. Extreme distortion. |
| 45° | 32° | 5 px (marginal) | Very difficult to focus. Low contrast. |
| 37° ✓ | ~27° | — | Successful 4th-order VRO calibration. Poor data quality (large dropout patches during deformation). |
| 0° ✓✓ | 0° | 5–10 px (good) | Good calibration and tracking. Recommended baseline for underwater camera placement. |
Recommendation: Place DIC cameras underwater in the flume for a straight-on view. Cameras outside the tank achieve only marginal quality even at the shallowest feasible angles. NREL agreed to pursue underwater DIC housing.
DIC Setup Notes
VROVariable Ray Origin calibration (accounts for glass refraction)4th order
ApertureSmallest setting for maximum depth of fieldF22
Acq. rateImage acquisition rate25 fps
SubsetDIC correlation subset size (increased for robustness at shallow angle)41 px
SpeckleTarget speckle diameter in images5–10 px
Contract Timeline
Oct 2023Contract awarded by NREL
Jan 2024Angle tests completed — 37° best outside-tank option
Feb 2024Results reported to NREL → recommendation: underwater DIC
Summer 2024Specify underwater DIC system with NREL computational sciences group