Diagnostic-Photographic Determination of Drag/Lift/Torque Coefficients of a High Speed Rigid Body in a Water Column

Bushnell

Journal of Defense Modeling & Simulation

et al. 2010

The falling of a Joint Direct Attack Munition (JDAM) through a water column was modeled using a six degrees of freedom model (called STRIKE35), which contains three components: hydrodynamics, semi-empirical determination of the drag/ lift/torque coefficients (depending on the Reynolds number and the angle of attack), and water surface characteristics.To validate and verify this model, three underwater bomb trajectory tests were conducted in the Naval Air Warfare Center, Weapons Division (NAWC/WD) in the middle of Indian Wells Valley, California. During the test, several JDAMs were dropped from an airplane into two frustum ponds with the same bottom diameter of approximately 30.5 m, different surface diameters (61 m, 79 m), and different depths (7.6 m, 12.1 m). High-speed digital cameras with light/pressure sensors, and a global positioning system were used to record the location and orientation of JDAMs. Model—data inter comparison shows the capability of STRIKE35, which may lead to a new approach (breaching technology) of sea mine clearance in very shallow water (water depth less than 12.2 m, i.e. 40 ft).

Section: Methodsmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Modeling of Underwater Bomb Trajectory for Mine Clearance

Bushnell

Journal of Defense Modeling & Simulation

et al. 2010

“…These coefficients depend on various physical processes such as water surface penetration, super-cavitation, and bubble dynamics. A diagnosticphotographic method has been developed [4] to get semi-empirical formulae for calculating the drag/lift/torque coefficients for underwater bombs with dependence on the Reynolds number (Re), angle of attack (α), and rotation rate along the bomb's major axis (Ω) [4], …”

Section: A 6-dof Model (Strike35)mentioning

confidence: 99%

Wave effect on the trajectory of a high-speed rigid body in a water column

WIT Transactions on Engineering Sciences

2010

Waves form when the water surface is disturbed, for example, by wind or gravitational forces. During such disturbances energy and momentum are transferred to the water mass and sea-state is changed. For shallow water regions, the bottom topography affects the waves dramatically. Waves may cause an evident slant of the ocean surface with a large inclination angle of about 55 o . When a high-speed rigid body strikes the wavy ocean surface, the random ocean slope largely affects its underwater trajectory. Identification of such an effect is a key point in the prediction of a fast moving rigid body in a water column. The probability density equation (PDF) of the ocean wave slopes was used to generate the stochastic surface slope. A 6-degree of freedom (DOF) model of a fast-moving rigid body is used with the stochastic sloping surface as its waterentry condition. The PDFs of the body location and orientation are obtained from results of 6-DOF model runs. From temporal change of these PDFs, the wave effect on the trajectory of a high-speed underwater rigid body has been identified.

“…Underwater bomb trajectory depends largely on the surface impact speed and angle. When the surface impact of high-speed rigid body such as scaled MK-84 warhead is normal or near normal to the flat water surface, four types of trajectories have been identified from experimental and numerical modeling results [4] depending the characteristics of the warheads: with tail section and four fins (Type-1), with tail section and two fins (Type-1I), with tail section and no fin (Type-1II), and with no tail section (Type-IV). Type-1 trajectories are quite stable downward without oscillation and tumbling no matter the water entry velocity is high or low.…”

Section: Introductionmentioning

confidence: 99%

Probability Density Function of Underwater Bomb Trajectory Deviation Due to Stochastic Ocean Surface Slope

Journal of Dynamic Systems, Measurement, and Control

2011

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