Modal Analysis of Parabolic Trough Solar Collectors Based on Mode Participation Factors

• • Extraction of the first 15 modes yields a cumulative effective mass participation ratio of 91.20%, satisfying the ≥90% engineering threshold mandated by JGJ 3—2010 and GB/T 50011—2010; this truncation scheme exhibits numerical fluctuation below 0.10% across varying pitch angles, confirming its reliability for structural dynamic analysis of full-scale PTCs. • • Pitch angle variation produces negligible effects on modal parameters, with maximum natural frequency relative error of only 0.57% and essentially invariant mode shapes; this justifies simplifying the experimental object to the outermost purlin, reducing field test complexity without compromising data validity. • • Experimental modal parameters obtained via impulse hammer excitation on the outermost purlin show maximum natural frequency relative error of 3.86% compared to computational results, with highly similar mode shapes for corresponding orders; this level of agreement validates the finite element model's applicability for engineering design. • • Modes 4–7 were lost in experimental identification due to modal density and excitation limitations, yet the high-precision agreement of low-order modes (1–3 and 8–15) confirms that critical vibration characteristics are captured; this demonstrates that low-order modes dominate the dynamic response under field excitation conditions.