Structural safety assessment of a piston-type wavemaker under varying frequency and stroke conditions

Abstract

The structural behaviour of piston-type wave generators under repeated hydrodynamic and inertial loads is a critical design parameter for the safe and long-term operation of laboratory-scale wave flumes. This study develops a finite element-based structural design and safety assessment methodology for laboratory-scale pistontype wavemakers, validated through multi-step numerical analysis and FPGA-controlled experimental motion confirmation. The methodology is demonstrated on a piston-type wave generator fabricated from S235JR structural steel for a 23 m & times; 1 m & times; 1 m wave flume, operating at 1.00 Hz with a maximum stroke of +/- 400 mm for a target wave range of H = 0.02-0.10 m and T = 0.8-2.5 s. Structural integrity was assessed via static, modal, and time-dependent analyses in ANSYS 2024 R1, with a parametric study spanning three frequencies and eight stroke conditions. In the static analysis, the design safety factor was 5.02 and stress levels remained below the infinite-life fatigue limit. Modal analysis yielded a first natural frequency 51 times the operating frequency, confirming the absence of resonance risk. Transient analysis showed that inertial effects increased the maximum von Mises stress by 45.4% to 68.1 MPa, with FS = 3.45. Across the full parametric envelope, the safety factor ranged from 2.90 to 5.02, satisfying the minimum design requirement in all cases. Results were verified through a three-tier framework comprising analytical benchmarking against classical plate theory, numerical selfconsistency via mesh independence analysis, and operational confirmation of motion fidelity through FPGAbased position control experiments.