Pitch and Heave Tests and Uncertainty Assessment for a Surface Combatant in Regular Head Waves

Abstract

Towing-tank experiments of coupled pitch and heave motions are presented for a surface combatant advancing in regular head waves. The data include ballasting parameters, time histories, fast Fourier transform (FFT), Fourier series amplitudes, and pitch and heave transfer functions and phases for a range of speeds, wave steepnesses, and wave frequencies. The geometry is David Taylor Model Basin (DTMB) model 5512, which is a 1/46.6 scale geosim of DTMB model 5415 (DDG-51) with Lpp = 3.048 m. The experiments are performed in a 3.048 × 3.048 × 100 m towing tank equipped with a plunger-type wave maker. The test program is undertaken to provide a validation data set for unsteady Reynolds-averaged Navier-Stokes and other computational fluid dynamics (CFD) codes, including rigorous uncertainty assessment of the experimental results following standard procedures. Results indicate that the regular head waves are linear with second- and third-order magnitudes consistent with third-order Stokes waves. Pitch and heave responses and phases show expected trends for long and short wavelengths and are linear or Ak independent for all test conditions. Maximum response occurs for frequency of encounter equal to pitch and heave natural frequencies and Lpp / λ = 0.75. Under these conditions, an equation is derived that predicts the Froude number for maximum response as a function of ship geometrical coefficients.