scholarly journals Dependence of wave parameters in broken ice on its cohesion in shallow water

2020 ◽  
Author(s):  
В.М. Козин
Keyword(s):  
Shallow Water ◽  
Pure Water ◽  
Wave Resistance ◽  
Hydraulic Structures ◽  
Technical Problems ◽  
Ice Jams ◽  
High Pressure Polyethylene ◽  
Broken Ice ◽  
Air Cushion ◽  
Crushed Ice

При решении таких ледотехнических задач, как измельчение крупно-битого льда для облегчения его пропуска через гидротехнические сооружения при весенних ледоходах, разрушение ледяных заторов и зажоров в условиях мелководья, где не могут работать ледоколы из-за их осадки и пр. находят применение амфибийные суда на воздушной подушке (СВП). В работе поставлена задача оценить влияние сплоченности битого льда на скорость и длину волн в битом льду, возбуждаемых СВП при их движении в условиях мелководья со скоростями, соответствующими возникновению максимального волнового сопротивления. С этой целью в опытовом бассейне были проведены соответствующие эксперименты с использованием искусственного битого льда, изготовленного из полиэтилена высокого давления, плотность и коэффициент трения которого были близки к естественному льду. Выполненные исследования позволяют разработать наиболее эффективные приемы маневрирования СВП в условиях битого льда различной сплоченности с целью его измельчения, т.е. уменьшения размеров обломков. На основании выполненных экспериментов и анализа известных теоретических зависимостей показано, что при определении таких важных параметров гравитационных волн, как их длина и скорость распространения, возбуждаемых судном в битом льду, могут быть использованы соответствующие зависимости из теории волн на чистой воде. When solving such ice-technical problems as crushing coarse-crushed ice to facilitate its passage through hydraulic structures during spring ice drifts, the destruction of ice jams and blockages in shallow water, where icebreakers cannot work due to precipitation, etc. amphibious vessels air cushion (SVP). The objective of the work is to assess the influence of the cohesion of broken ice on the speed and wavelength in broken ice excited by SVPs when they move in shallow water with speeds, corresponding to the occurrence of maximum wave resistance. For this purpose, corresponding experiments were carried out in the experimental pool using artificial beaten ice made of high pressure polyethylene, the density and friction coefficient of which were close to natural ice. The performed studies allow us to develop the most effective methods for maneuvering SVPs in the conditions of broken ice of various cohesion with the aim of crushing it, i.e. debris reduction. Based on the performed experiments and analysis of known theoretical dependences, it was shown that in determining important parameters of gravitational waves, such as their length and propagation velocity, excited by a vessel in broken ice, the corresponding dependences from the theory of waves in pure water can be used.

Waves and Wave Resistance for Air-Cushion Vehicles with Time-Dependent Cushion Pressures

1978 ◽  
Vol 22 (03) ◽  
pp. 170-177
Author(s):  
H. J. Haussling ◽  
R. T. Van Eseltine
Keyword(s):  
Shallow Water ◽  
Froude Number ◽  
Water Depth ◽  
Critical Frequency ◽  
Wave Resistance ◽  
Time Dependent ◽  
Length Ratio ◽  
Wave Patterns ◽  
Air Cushion ◽  
Air Cushion Vehicles

Wave patterns and wave resistance are computed for air-cushion vehicles with time-dependent cushion pressures moving at uniform speed over deep and shallow water. The effect of beam-to-length ratio, Froude number, and water depth on the resistance is investigated. The resistance is found to exhibit a distinctive behavior at a critical frequency. This behavior corresponds to a singularity in the resistance at the critical frequency. The importance of this behavior is found to diminish with decreasing beam-to-length ratio and increasing Froude number.

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.

Development of innovative monitoring technologies in the framework of InnovaMare Project

2021 ◽  
Author(s):  
Angelo Odetti ◽  
Federica Braga ◽  
Fabio Brunetti ◽  
Massimo Caccia ◽  
Simone Marini ◽  
...  
Keyword(s):  
Environmental Monitoring ◽  
Shallow Water ◽  
Adriatic Sea ◽  
Temporal Dynamics ◽  
Supervised Machine Learning ◽  
Detection Techniques ◽  
Cross Border ◽  
Wide Range ◽  
Air Cushion ◽  
The Cross

<p>The IT-HR InnovaMare project, led by the Croatian Chamber of Economy, puts together policy instruments and key players for development of innovative technologies for the sustainable development of the Adriatic Sea (https://www.italy-croatia.eu/web/innovamare). The project aims at enhancing the cross-border cooperation among research, public and private stakeholders through creation of a Digital Innovation Hub (DIH). The goal is to increase effectiveness of innovation in underwater robotics and sensors to achieve and maintain a healthy and productive Adriatic Sea, as one of the crucial and strategic societal challenges existing at the cross-border level. Within InnovaMare, CNR ISMAR and INM institutes and OGS, in cooperation with the University of Zagreb and other project partners, contribute to developing a solution to access and monitor extremely shallow water by means of portable, modular, reconfigurable and highly maneuverable robotic vehicles. The identified vehicle is SWAMP, an innovative highly modular catamaran ASV recently developed by CNR-INM. SWAMP is characterised by small size, low draft, new materials, azimuth propulsion system for shallow waters and modular WiFi-based hardware&software architecture. Two SWAMP vehicles will be enhanced with a series of kits, tools and sensors to perform a series of strategic actions in the environmental monitoring of the Venice Lagoon: <br>i) An air-cushion-system-kit will be designed and developed. The vehicle will become a side-wall air-cushion-vehicle with reduction of drag and increase in speed. This will also increase the payload with a reduction of draft. <br>ii) An intelligent winch kit with a communication cable for the management of underwater sensors and tools.<br>iii) A GPS-RTK kit for highly accurate positioning in the range of centimeters.<br>iv) An Autonomous programmable device for image acquisition and processing based on the Guard1 camera. This camera acquires images content and, by means of a supervised machine learning approach, recognises/classifies features such as fish, zooplankton, seabed, infrastructures. The system is conceived for autonomous monitoring activities extended in time in fixed or mobile platforms.<br>v) A Multibeam Echo-sounder (MBES) coupled with an IMU (for pitch-roll compensation). MBES data can be used, also coupled with Cameras Imagery, through image-detection techniques for reconstruction and comprehensive knowledge of underwater environment and infrastructures. Possible analyses in coastal areas are: seabed mapping also for cultural heritage, offshore structures and resources and monitoring of biodiversity, hydrocarbon, marine litter, pollution.<br>vi) An underwater Radiometer for multiple analysis: temporal dynamics of optical properties of water; temporal dynamics of water turbidity from water reflectance; submerged vegetation and water depth mapping in optically shallow water; produce reference data for validation of satellite data.<br>vii) Automatic Nutrient Analyzer for real-time nutrient monitoring. This sensor measures nitrate with high accuracy over a wide range of environmental conditions (including extremely turbid and high CDOM conditions), from blue-ocean nitraclines to storm runoff in rivers and streams. <br>The final result of this pilot action is the creation of an innovative prototype platform for sea environmental monitoring. This will be validated through the analysis of results and draw up of guidelines for the improvement of underwater conditions.</p>

Zero wave resistance for ships moving in shallow channels at supercritical speeds

1997 ◽  
Vol 335 ◽  
pp. 305-321 ◽  
Author(s):  
XUE-NONG CHEN ◽  
SOM DEO SHARMA
Keyword(s):  
Shallow Water ◽  
Water Channel ◽  
Wave Theory ◽  
Wave Pattern ◽  
Wave Resistance ◽  
Kp Equation ◽  
Nonlinear Case ◽  
Hull Form ◽  
Ship Waves ◽  
Shallow Channel

This paper deals with the wave pattern and wave resistance of a slender ship moving steadily at supercritical speed in a shallow water channel. Using, successively, linear and nonlinear shallow-water wave theory it is demonstrated that, if the hull form is adapted to speed and channel geometry according to certain rules, the ship waves can be made to form a localized pattern around the ship that moves at the same speed as the ship and at the same time the associated wave resistance can be made to vanish. In the nonlinear case, the zero-wave-resistance ship hull is derived from a KP equation solution of the oblique interaction of two identical solitons. This astonishing phenomenon may be called shallow-channel superconductivity.

An Experimental Crank Press

1950 ◽  
Vol 163 (1) ◽  
pp. 125-134 ◽  
Author(s):  
E. C. Seed ◽  
H. W. Swift
Keyword(s):  
Gear Wheel ◽  
Reduction Gear ◽  
Variable Speed ◽  
Technical Problems ◽  
Industrial Practice ◽  
Single Action ◽  
Shear Plate ◽  
The Press ◽  
Air Cushion ◽  
The University

An account is given of the technical problems which arose in the design of an experimental single-action, double-sided crank press of tie-rod construction which has been built for use in the deep-drawing researches carried out in the University of Sheffield. This press was required to have a specified capacity of 20 tons during the second half of the down-stroke and 50 tons during the last inch of the down-stroke. To cover the drawing speeds of industrial practice, a variable speed of 5–60 strokes per min. and a variable stroke of 3–10 inches were specified, and to maintain a close control over the speed, the slowdown at any speed over the whole range was limited to 10 per cent. An air cushion and also an automatic means for stopping the press at top dead centre after each stroke and for interrupting the stroke at any prescribed point in order to obtain partially drawn pressings for examination and measurement were incorporated. Speed variations are obtained through a transmission system consisting of a substantially fixed speed electric motor with a fixed gear to the flywheel, and a variable gearbox between the flywheel and the main gears of the press. It is shown that, from the functional points of view this is the most satisfactory system of power supply and transmission for a variable speed press. Two safety devices are embodied in the press: a shear plate in the ram to protect the crankshaft and a shearing pin in the first reduction gear wheel to protect the gearing. The design of these devices is described in an Appendix.

scholarly journals High order upwind scheme for modelling turbulent shallow water flow in hydraulic structures

PAMM ◽  
2007 ◽  
Vol 7 (1) ◽  
pp. 1100205-1100206
Author(s):  
María-Elena Vázquez-Cendón ◽  
Luis Cea
Keyword(s):  
Shallow Water ◽  
Water Flow ◽  
High Order ◽  
Upwind Scheme ◽  
Hydraulic Structures ◽  
Shallow Water Flow

Verification and Validation of URANS Wave Resistance for Air Cushion Vehicles, and Comparison With Linear Theory

2011 ◽  
Vol 55 (04) ◽  
pp. 249-267
Author(s):  
S. Bhushan ◽  
F. Stern ◽  
L. J. Doctors
Keyword(s):  
Experimental Data ◽  
Shallow Water ◽  
Froude Number ◽  
Linear Theory ◽  
Nonlinear Theory ◽  
Pressure Level ◽  
Sinkage And Trim ◽  
Air Cushion ◽  
Air Cushion Vehicles ◽  
Straight Ahead

Verification and validation of URANS wave-resistance predictions for straight-ahead and yawed air-cushion vehicles in calm deep and shallow water are performed. The nonlinear and linear theories are compared to explicate their trends for large cushion pressures, water depth, and cushion dimensions, and the nonlinear theory sinkage and trim trends are discussed. The grid-verification study shows monotonically converged solutions with averaged uncertainty of 4% and 10% for straight-ahead motion in deep and shallow water, respectively. URANS predictions agree with the experimental data to within 6% and 9% for straight-ahead deep and shallow water simulations, respectively. The smooth-edged cushion-pressure simulations predict lower resistance than the sharp-edged case, whereas no significant dependence is obtained for Reynolds number and turbulence modeling. URANS predicts attenuation in the resistance secondary hump as the cushion-pressure level increases. On the other hand, the linear theory does not account for the effect of cushion-pressure level. The linear and nonlinear theories compare within 4.5% for static cushion-pressure-to length ratios less than 0.025 and Froude number greater than 0.5 for both deep and shallow water. The nonlinear theory predicts the effect of water depth better than the linear theory, when compared with the experiments. Both the theories agree well in predicting the decrease in resistance with the decrease in cushion width. The nonlinear theory does not show unrealistically large resistance and side force for sharp-edged cushion pressure for yawed cases, as observed in the linear theory. However, both the theories compare well for the resistance and side-force predictions for the smooth-edged cushion pressure, where the results agree within 10% of the deep-water experimental data. The nonlinear theory predictions for the sinkage and trim are in good agreement with the experimental data, but sinkage is overpredicted and trim is underpredicted. URANS wave-elevation patterns display transverse and diverging waves, which compare well with the Kelvin waves for Froude number less than 0.6 and greater than 1.0, respectively. URANS predicts breaking waves for large cushion pressures for Froude number less than 0.6.

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