Carolyn Q. Judge

Empirical Methods for Predicting Lift and Heel Moment for a Heeled Planing Hull

Even in calm water, high-speed vessels can display unstable behaviors such as chine walking, sudden large heel, and porpoising. Large heel angle can result in the loss of transverse stability at high forward speed. When a planing craft begins to plane, the hydrodynamic lift forces raise the hull out of the water, reducing the underwater geometry. An experimental program at the U.S. Naval Academy has been designed to investigate the transverse stability of planing hulls. An experimental mechanism to force a planing hull model in heave and roll motion was designed and built. The first model tested was a wooden prismatic planing hull model with a constant deadrise of 20°, a beam of 1.48 ft (0.45 m), and a total length of 5 ft (1.52 m). The model was held at various heel and running draft positions while fixed in pitch, yaw, and sway. The tests were done at two model speeds, for one model displacement, five fixed heel angles, and five fixed running heave positions. The lift and sway forces, along with the heel moment, were measured and underwater photography was taken of the wetted surface. This article presents a set of equations based on empirical relationships for calculating the lift and heel moment for a prismatic planing hull at nonzero heel angles.

Comparisons Between Prediction and Experiment for Lift Force and Heel Moment for a Planing Hull

Even in calm water, high-speed vessels can display unstable behaviors such as chine walking, sudden large heel, and porpoising. Large heel results from the loss of transverse stability at high forward speed. When a planing craft begins to plane, the hydrodynamic lift forces raise the hull out of the water. The available righting moment resulting from the hydrostatic buoyancy is, therefore, reduced. As the righting moment resulting from hydrostatic buoyancy is reduced, the righting moment resulting from dynamic effects becomes important. These hydrodynamic righting effects are related to the hydrodynamic lift. This article explores the relationship between the hydrostatic lift and righting moment, the hydrodynamic lift and righting moment, and the total lift and heel-restoring moment of a planing craft operating at planing speeds. A series of tow tests using a prismatic hull with a constant deadrise of 20 measured the lift force and righting moment at various angles of heel and at various model velocities. The model was completely constrained in surge, sway, heave, roll, pitch, and yaw. The underwater volume is determined from the known hull configuration and the underwater photography of the keel and chine wetted lengths. The results presented include the total lift and righting moment with the hydrostatic and hydrodynamic contributions for various model speeds at two model displacements.

Measurement of Hydrodynamic Coefficients on a Planing Hull Using Forced Roll Oscillations

For planing hulls, dynamic lift reduces the submergence of the hull, allowing small motions to result in large changes in hydrodynamic forces and moments. This article explores various modeling assumptions associated with transverse plane dynamics in roll and the hydrodynamic forces in the planing regime. The significance of nonlinearities in the roll hydrodynamic forces for planing hulls was investigated with regard to roll amplitude, model speed, model displacement, and roll oscillation frequency. A wooden 20° deadrise prismatic planing hull was tested at steady roll angles and in dynamic roll at various roll amplitudes and frequencies. Two displacements, three model speeds, three roll amplitudes, and four roll oscillation frequencies were tested. The measured wetted lengths, roll-restoring coefficient, roll-added inertia coefficient, and roll-damping coefficient are presented. The roll-restoring moment is found to be nonlinear with roll amplitude, the added inertia coefficient shows some dependence on model speed, and the roll-damping coefficient shows some amplitude dependence.

Coupling of Heave and Roll for High-Speed Planing Hulls

For planing hulls, dynamic lift reduces the submergence of the hull, allowing small motions to result in large changes in hydrodynamic forces and moments. The dynamic lift forces acting on the bottom of a planing hull dominate the hydrodynamics and these lift forces are known to depend on speed and wetted surface. As a planing boat rolls the wetted surface changes, which affects the dynamic lift. A series of tests using a wooden prismatic planing hull model with a constant deadrise of 20 degrees were done at static heel and heave positions as well as oscillating heave conditions. This paper presents the results from these experiments, primarily looking at the hydrodynamic coefficients in heave as a function of heel angle and exploring the coupling between these motions for a prismatic high-speed planing hull.

A detailed assessment of numerical flow analysis (NFA) to predict the hydrodynamics of a deep-V planing hull

Over the past few years much progress has been made in Computational Fluid Dynamics (CFD) in its ability to accurately simulate the hydrodynamics associated with a deep-V monohull planing craft. This work has focused on not only predicting the hydrodynamic forces and moments, but also the complex multiphase free-surface flow field generated by a deep-V monohull planing boat at high Froude numbers. One of these state of the art CFD codes is Numerical Flow Analysis (NFA). NFA provides turnkey capabilities to model breaking waves around a ship, including both plunging and spilling breaking waves, the formation of spray and the entrainment of air. NFA uses a Cartesian-grid formulation with immersed body and volume-of-fluid methods. The focus of this paper is to describe and document a recent effort to assess NFA for the prediction of deep-V planing craft hydrodynamic forces and moments and evaluate how well it models the complex multiphase flows associated with high Froude number flows, specifically the formation of the spray sheet. This detailed validation effort was composed of three parts. The first part focused on assessing NFAs ability to predict pressures on the surface of a 10 degree deadrise wedge during impact with an undisturbed free surface. Detailed comparisons to pressure gauges are presented here for two different drop heights, 15.24 cm (6 in) and 25.4 cm (10 in). Results show NFA accurately predicted pressures during the slamming event. The second part examines NFAs ability to match sinkage, trim and resistance from Fridsmas experiments performed on constant deadrise planing hulls. Simulations were performed on two 20 degree deadrise hullforms of varying length to beam ratios (4 and 5) over a range of speed-length ratios (2, 3, 4, 5 and 6). Results show good agreement with experimentally measured values, as well as values calculated using Savitskys parametric equations. The final part of the validation study focused on assessing how well NFA was able to accurately model the complex multiphase flow associated with high Froude number flows, specifically the formation of the spray sheet. NFA simulations of a planing hull fixed at various angles of roll (0, 10, 20 and 30 degrees) were compared to experiments. Comparisons to underwater photographs illustrate NFAs ability to model the formation of the spray sheet and the free surface turbulence associated with planing boat hydrodynamics. Overall these three validation studies provide a detailed assessment on the current capabilities of NFA to predict the hydrodynamics of a deep-V planing hull.

Slamming Impacts of Hydrodynamically–Supported Craft

High–speed planing boats are subject to repeated slamming impacts, which can cause structural damage and discomfort or injury to passengers. The goal of this research is to study the fundamental physics of the water-impact of high–speed planing hulls and to measure the slamming loads and resulting motions of the craft upon re–entry into the water after becoming partially airborne. A set of towed scale–model experiments was conducted in calm water, regular waves and irregular waves to capture a sequence of individual impact events. Pressure measurements were taken on the bottom of the hull using both point sensors (PCB Piezotronics) and a pressure mapping system (Tekscan). The pressure signals from the pressure pads (providing both spatial and temporal resolution) and the point–pressure measurements (high temporal resolution) will be presented for individual slam events, allowing a deterministic approach to investigating high–speed planing craft wave slamming.© 2014 ASME

Turbulent boundary layer pressure fluctuations at large scales

The pressure fluctuations underneath a turbulent boundary are an important excitation source for noise and vibration for both aircraft and ships. This presentation describes experimental results from a new study of flat‐plate turbulent boundary layer pressure fluctuations in water at large scales and high Reynolds number. The experiments were performed at the U.S. Navy’s William B. Morgan Large Cavitation Channel in Memphis, TN on a polished flat plate 3.05 m wide, 12.8 m long, and 0.18 m thick. Flow velocity, skin friction, surface pressure, and plate acceleration measurements were made at multiple downstream locations at flow speeds ranging from 0.5 m/s to 19 m/s for a Reynolds number (based on downstream distance) range of several million to 200 million. Dynamic surface pressures were recorded with 16 flush mounted pressure transducers forming an L‐array with streamwise dimension of 0.264 m and cross‐stream dimension of 0.391 m. Measured 99% boundary‐layer thicknesses were typically of order 0.10 m. Re...

Hydrofoil near‐wake sound sources at high Reynolds number

An important hydroacoustic noise source from a fully submerged noncavitating hydrofoil is often the unsteady separated turbulent flow near its trailing edge. Here, hydroacoustic noise may be produced by boundary layer turbulence swept past and scattered from the foils trailing edge, and by coherent vortices formed in the foils near‐wake. Such vortices may generate an energetic tonal component that rises above the broadband trailing‐edge hydroacoustic noise. This presentation describes results of an experimental effort to identify and measure vortical flow features in the near‐wake of a two‐dimensional hydrofoil at chord‐based Reynolds numbers ranging from 0.5 to 60 million. The experiments were conducted at the U.S. Navy’s William B. Morgan Large Cavitation Channel with a test‐section‐spanning hydrofoil (2.1 m chord, 3.0 m span) at flow speeds from 0.25 to 18.3 m/s. Two trailing‐edge shapes were investigated, and foil‐internal accelerometers were used to monitor structural vibration. Velocity fluctuation ...

An Alternative Wing Sail Concept for Small Autonomous Sailing Craft

An alternative wing sail section shape was developed as a potential improvement to either a soft sail or the common NACA00XX section used on some small autonomous sailing craft. The prototype wing was developed as an evolution of a traditional square sail. Evaluation included wind tunnel and on-the-water tests followed by performance estimates from a Velocity Prediction Program. The test vessel was the 1.2 m long Version 2 MaxiMOOP. Advantages of the wing sail over the current voyaging soft sail design include: higher speeds in some conditions, increased durability, increased buoyancy in the case of capsizing, and easier implementation of control systems. Some potential theoretical advantage was found over the NACA0009.

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.Copyright