Wave resistance of an air-cushion vehicle in unsteady motion over an ice sheet

2008 ◽  
Vol 49 (1) ◽  
pp. 71-79 ◽  
Author(s):  
A. V. Pogorelova
Keyword(s):  
Ice Sheet ◽  
Unsteady Motion ◽  
Wave Resistance ◽  
Air Cushion ◽  
Air Cushion Vehicle

The Wave Resistance of an Air-Cushion Vehicle in Steady and Accelerated Motion

1972 ◽  
Vol 16 (04) ◽  
pp. 248-260 ◽  
Author(s):  
Lawrence J. Doctors ◽  
Som D. Sharma
Keyword(s):  
Steady Motion ◽  
Finite Depth ◽  
Unsteady Motion ◽  
Wave Resistance ◽  
Resistance Curve ◽  
Accelerated Motion ◽  
The Past ◽  
Air Cushion ◽  
Sharp Edges ◽  
Air Cushion Vehicle

This paper deals with the theoretical wave resistance of an air-cushion vehicle (ACV) traveling over water of uniform finite or infinite depth, in steady or unsteady motion. Referring first to steady motion, it is shown that the unrealistic oscillations in the wave resistance curve at low Froude numbers found by previous workers can be eliminated by using a smoothed-out pressure distribution rather than one with sharp edges studied exclusively in the past. The main result of unsteady motion calculations is that the peak wave resistance in shallow water, even in moderately accelerated motion, is appreciably less than the corresponding steady-state value. An interesting feature of unsteady motion is that besides wave resistance there is another mechanism transferring energy to the free surface, which is here called the dynamic sustention power. Contrary to intuition, the wave resistance in unsteady motion over finite depth sometimes becomes negative at supercritical Froude numbers before finally vanishing at infinite speed.

The Acceleration of an Air Cushion Vehicle Under the Action of a Propulsor

1973 ◽  
Vol 17 (02) ◽  
pp. 121-128
Author(s):  
Lawrence J. Doctors ◽  
Som D. Sharma
Keyword(s):  
Shallow Water ◽  
Aerodynamic Drag ◽  
Wave Resistance ◽  
Minor Effect ◽  
Critical Depth ◽  
Velocity Pattern ◽  
Air Cushion ◽  
Air Cushion Vehicle ◽  
A Minor ◽  
Adequate Power

This paper presents the solution for the motion of an air-cushion vehicle (ACV) starting from rest under the action of a propulsor of given thrust-speed characteristics. The wave resistance is based on linearized potential theory, while the aerodynamic drag components are assumed to be strictly quasi-steady. The problem is treated in two different ways: calculating the wave resistance in a truly unsteady manner, and on the simplified quasi-steady basis. The results show that the shape of the propeller characteristics has only a minor effect on the velocity pattern. However, the effect of overloading the ACV is shown to have crucial effects on its ability to surpass the critical depth hump. In this respect, the simpler quasi-steady calculations lead to unnecessarily pessimistic estimates of the acceleration margin. Under certain circumstances in relatively shallow water, the quasi-steady analysis would suggest that the ACV could not overcome the critical hump, while the more elaborate unsteady calculations show that it has indeed adequate power to reach its final cruising speed.

Hydrodynamic Power Radiated by a Heaving and Pitching Air-Cushion Vehicle

1978 ◽  
Vol 22 (02) ◽  
pp. 67-79 ◽  
Author(s):  
Lawrence J. Doctors
Keyword(s):  
Steady State ◽  
Critical Speed ◽  
Three Dimensional ◽  
Wave Resistance ◽  
Wave System ◽  
Two Dimensional ◽  
Similar Magnitude ◽  
Frequency Condition ◽  
Air Cushion ◽  
Air Cushion Vehicle

The harmonic heave and pitch motion of an air-cushion vehicle traveling at a constant speed over water is studied here, with a view to determining the power radiated by the surrounding wave system. The planform of the particular craft considered is compartmented into forward and aft subcushions, and the fluctuations of pressure in these are utilized to represent the effect of the vehicle on the water. The usual linearized incompressible potential flow theory is used. The calculations show that at typical Froude numbers and encounter frequencies, considerable power can be radiated in this manner, and it is generally of similar magnitude to the power required to overcome the usual steady-state wave resistance. Surprisingly, the singularity in the linear theory that occurs at the critical speed-frequency condition was found to be extremely localized and is therefore only significant in the case of a two-dimensional pressure band, or in the case of a three-dimensional pressure patch, at low Froude numbers.

Determination of Critical Speed in Ice Breaking by Air Cushion Vehicle

2011 ◽  
Vol 138-139 ◽  
pp. 529-533
Author(s):  
Chong Wang ◽  
Zhi Hong Zhang ◽  
Tao Miao ◽  
Jun Yao ◽  
Liao Yuan Zhang ◽  
...  
Keyword(s):  
Differential Equation ◽  
Wave Propagation ◽  
Phase Velocity ◽  
Group Velocity ◽  
Critical Speed ◽  
Ice Sheet ◽  
Air Cushion ◽  
Air Cushion Vehicle ◽  
Vibrating Plate

On the basis of the differential equation governing small flexure of thin elastic vibrating plate, the formula for calculating the phase velocity and group velocity of ice sheet wave propagation under the air cushion load is induced. The minimum of the phase velocity is the critical speed about ice breaking by air cushion vehicle (ACV). If ACV moves at the critical speed, the energy causing the deformation of ice sheet is concentrated constantly, thus the amplitude of the wave is enlarged enough to break the ice by resonance.

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