Nonlinear Vibrations of Model PWR Fuel Assemblies: Part 2 — Interpretation of Results Using Bilinear Stiffness Model
Bibliographic record
Abstract
Abstract The experimental response of fuel rods with spacer grids was interpreted using a bilinear hysteresis model. Nonlinear experimental responses of two configurations of rods made out of Zirconium alloy tubes were considered in this paper: one configuration with a single beam and the second configuration with a cluster of beams (stacked in a 3 × 3 matrix formulation). These two configurations were designed to emulate part of the nuclear fuel assembly in Pressurized Water Reactors (PWR). Both configurations were supported by spacer girds at their extremities and were immersed in still water. Spacer grids are grid-like structures made out of thin Zirconium alloy sheets with 17 × 17 cells arranged in a square pattern. Spacer grids provide mechanical support and reduce flow-induced vibration of nuclear fuel rods. They also improve the heat transfer between nuclear fuel rods and the surrounding coolant. The spacer grids impose nonlinear boundary conditions to the beams at the contact points/surface. Specifically, spacer grids present bilinear hysteresis due to their inherent complexity. The bilinear hysteresis shown by spacer grids was measured in terms of force-displacement loops by testing rigid rod inserted in one of its cells. The rigid rod was then excited by external harmonic excitation with excitation frequencies ranging from 5 Hz to 50 Hz in steps of 5 Hz. The bilinear hysteresis model, first studied by Caughey, was modified to include viscous damping and was used to interpret the experimental results. The method of slowly varying parameters was used to solve the equation of motion. First, the measured force-displacement loops of spacer grids were fitted with the numerical model described in the current analysis. Good agreement between the model response and measured loops was found, and the identified parameters allowed the characterization of the nonlinear boundary conditions imposed by spacer grids. Finally, the nonlinear responses of the two configurations under study were interpreted using the bilinear hysteresis model. Excellent agreement between numerical and experimental results was obtained for both configurations.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".