Operational Experience With The New Harold E. Saunders Maneuvering And Seakeeping (MASK) Basin Directional Wavemaker

The Naval Surface Warfare Center, Carderock Division replaced their 21 pneumatic type wavemaker domes with a 216-paddle directional wavemaker in the fall of 2013. This wavemaker is capable of producing regular waves at oblique angles to the wave banks as well as long crested and short crested irregular model seas. Another powerful capability of the new system is the ability to preview the commanded waves in 3D virtual space on the computer screen. The new directional wavemaker facility has been in operation for four years. Mixtures of capabilities exceeding the original requirements as well as unforeseen problems were encountered. Based upon the operational experience gained in the last four years lessons learned are presented. Going from 21 domes to 216 individual paddles has adverse consequences on maintenance and reliability. That in and of itself is just a consequence of requiring a more complex machine to make more complex waves – not really good or bad. Despite the initial concerns this wavemaker has proven to be reliable, easily maintainable and when required, easily repairable.

Assessment of Hydrodynamic Tools for R/V Athena Model 5365 in Calm Water

Current structural design methods for high speed naval craft rely heavily on empirical methods. Though these methods have been employed reliably for a number of years, it is likely that an unknown level of conservatism exists in the prediction of impact loads. A better physical understanding of the dynamic response of high speed craft in seas would allow for increased structural optimization. The publicly releasable hull form Naval Surface Warfare Center Carderock Division (NSWCCD) Model 5365 (R/V Athena) was chosen to facilitate release of results to various computational teams. Model 5365 was tested in calm water, regular waves, and irregular waves. After reviewing data from the first test in 2014, it was determined that the model should be modified to enable towing from the longitudinal center of gravity. Model 5365 was then modified and re-tested using with added calm water speeds, and additional wave conditions. Calm water results from this test are presented with uncertainty analysis for resistance, heave, and trim.

Can Tests for Planing Craft Structural Design Accelerations Be Simplified?

A series of papers derived from ONR funded efforts to standardize high performance craft acceleration data have been authored by personnel at Naval Surface Warfare Center Carderock Division Det Norfolk Combatant Craft Division (CCD) in recent years. These papers proposed vertical acceleration data collection, analysis, and presentation approaches; noted the repeatability of a characteristic shape for individual acceleration events; characterized and compared impact types; and noted a relationship between the statistical value “average of the one-tenth highest vertical acceleration at the longitudinal center of gravity” and the equivalent static acceleration (ESG) for the half sine approximation of the single highest peak in a test dataset. When knowledge of this ESG relationship is coupled with standard structural design approaches, a provocative hypothesis follows, which may have substantial implications for model testing.

Maneuvering and Seakeeping Basin Wave Characterization Study

A series of experiments aimed at characterizing the wavefield generated by the new multi-directional wave making system in the Maneuvering and Seakeeping (MASK) Basin at the Naval Surface Warfare Center Carderock Division in West Bethesda, MD are described. These experiments were focused on the repeatability of phase resolved seaways, the spatial variability of wave parameters throughout the basin, and the stationarity of the wavefield over the span of 2 hours. Two different wave spectra were run repeatedly over a two week test window covering 21 discrete locations with one fixed array of sensors as a control. The results from the test show that when sampling at the same location and running the same wave condition, the phase resolved seaway exhibits a coherence of over 95% between 0.25 and 0.75 Hz. The spatial variability of the wave statistics proved to be within 5% of the average values throughout the tank, with a larger deviation over the 35ft deep trench section.

Experimental and Computational Characterization of a Large-Scale, Underwater Towed SPIV System

A new underwater Stereoscopic Particle Image Velocimetry (SPIV) Torpedo system was designed and constructed at the Naval Surface Warfare Center, Carderock Division for testing in the David Taylor Model Basin. The purpose of the work was to conduct a shakedown test of the new SPIV system to ensure it properly captured SPIV images, and successfully resolved both the in- and out-of-plane velocity fields. To test the system, SPIV measurements were taken on the free-stream flow in the basin and the canonical flow field produced by a circular cylinder at Reynolds numbers around 100,000. After successfully measuring the flow fields, cylinder results were compared to large eddy simulation results that were obtained using NavyFOAM.

Numerical Simulation of Short Duration Hydrodynamic Impact

Numerical simulations of wedge impact experiments, undertaken by the Naval Surface Warfare Center, Carderock Division, NSWCCD, and more recently by the United States Naval Academy, USNA, Hydromechanics Laboratory, were performed using the computational fluid dynamics code Numerical Flow Analysis, NFA, to assess its capabilities in simulating the short duration hydrodynamic loading associated with free-surface impact. NSWCCD performed experiments using drop heights of 15.24 cm (6 in) and 25.4 cm (10 in), while the Naval Academy used drop heights of: 7.94, 12.7, 15.88, 25.4, 31.75, 38.1, and 50.8 cm (3.125, 5.0, 6.25, 10.0, 12.5, 15.0, and 20.0 in), measured from the keel of the wedge to the calm water surface. Simulations and comparisons were made at heights of 15.24 cm (6 in) and 25.4 cm (10 in) with the NSWCCD data, and 12.5 inches for the USNA data providing for a detailed examination of NFA’s ability to simulate and predict short duration hydrodynamic impacts.