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Inhibition on porpoising instability of high-speed planing vessel by ventilated cavity
Highlights The ventilated cavities can inhibit porpoising instability of planing vessel. The disappearance of the porpoising instability is linked with the decrease in trim. The volume of displacement is believed to be the key for the inhibition effect.
Abstract Porpoising instability is a tough nut bewildering ocean academia for years. This study provides the first experiment found that the cavity formed by artificial ventilation can significantly inhibit the inherent porpoising instability of planing vessel under high/ultra-high forward speeds. Restricted by the occurrence of porpoising instability, a Froude number (volume of displacement based) upper limit of 5.91 is reached at the current conventional ship model calm water towing experiment. However, this instability phenomenon disappears when a cavity is formed at the bottom of ventilation ship model within all experimentally Froude number range (5.91−6.82). The inhibition effect can be tracked from the timing sequences value of trim. The decrease in trim value, to the degree below the threshold of porpoising instability, is responsible for the disappearance of this longitudinal instability. The enhancement in longitudinal stability is believed to be directly related to the increase in volume of displacement led by the cavity, which greatly reinforces the impact of hydrostatic lift in the vertical force balance. The strengthening of hydrostatic lift attenuates the influence of dynamic instability caused by fluid dynamic pressure. Therefore, if an external disturbance is given to the vessel, the disturbing moment around the center of rotation is weakened, which prevents the strong periodic alternation between inertial and restorative forces.
Inhibition on porpoising instability of high-speed planing vessel by ventilated cavity
Highlights The ventilated cavities can inhibit porpoising instability of planing vessel. The disappearance of the porpoising instability is linked with the decrease in trim. The volume of displacement is believed to be the key for the inhibition effect.
Abstract Porpoising instability is a tough nut bewildering ocean academia for years. This study provides the first experiment found that the cavity formed by artificial ventilation can significantly inhibit the inherent porpoising instability of planing vessel under high/ultra-high forward speeds. Restricted by the occurrence of porpoising instability, a Froude number (volume of displacement based) upper limit of 5.91 is reached at the current conventional ship model calm water towing experiment. However, this instability phenomenon disappears when a cavity is formed at the bottom of ventilation ship model within all experimentally Froude number range (5.91−6.82). The inhibition effect can be tracked from the timing sequences value of trim. The decrease in trim value, to the degree below the threshold of porpoising instability, is responsible for the disappearance of this longitudinal instability. The enhancement in longitudinal stability is believed to be directly related to the increase in volume of displacement led by the cavity, which greatly reinforces the impact of hydrostatic lift in the vertical force balance. The strengthening of hydrostatic lift attenuates the influence of dynamic instability caused by fluid dynamic pressure. Therefore, if an external disturbance is given to the vessel, the disturbing moment around the center of rotation is weakened, which prevents the strong periodic alternation between inertial and restorative forces.
Inhibition on porpoising instability of high-speed planing vessel by ventilated cavity
Wang, Luyao (author) / Qin, Shijie (author) / Fang, Hezhen (author) / Wu, Dazhuan (author) / Huang, Bin (author) / Wu, Rui (author)
Applied Ocean Research ; 111
2021-04-19
Article (Journal)
Electronic Resource
English
Porpoising instability , Ventilated cavity , Fluid–structure interaction , Ship hydrodynamics , <italic>Abbreviations: A<inf>ij</inf></italic> , Generalized added mass , <italic>B</italic> , Ship width , <italic>B<inf>ij</inf></italic> , Generalized damping coefficient , <italic>C<inf>∆</inf></italic> , Load coefficient , CCD , Charge coupled device , <italic>C<inf>ij</inf></italic> , Generalized restoring force coefficients , <italic>C<inf>L</inf></italic> , Lift coefficient , <italic>CL</italic> <inf>0</inf> , Lift coefficient with zero deadrise angle , <italic>CL<inf>β</inf></italic> , Lift coefficient with deadrise angle <italic>β</italic> , <italic>Cq</italic> , Gas entrainment coefficient , <italic>D</italic> , Buoyancy , <italic>D<inf>cavity</inf></italic> , Buoyancy from ventilated cavity , <italic>D<inf>ship</inf></italic> , Buoyancy from ship model , <italic>Fr<inf>B</inf></italic> , Froude number based on ship width , <italic>Fr<inf>∇</inf></italic> , Froude number based on volume of displacement , <italic>H</italic> , Average height of the step , <italic>I<inf>55</inf></italic> , Pitching moment of inertia , <italic>L</italic> , Ship length , <italic>L</italic> <inf>CG</inf> , Longitudinal distance of center gravity from transom , <italic>M</italic> , Mass of displacement , <italic>N</italic> , Average length of the gas chamber , <italic>∇</italic> , Volume of displacement , OSM , Original ship model , <italic>P</italic> , Time average value of pressure , <italic>P<inf>d</inf></italic> , Hydrodynamic lift , <italic>Q</italic> , Towing force , <italic>Qa</italic> , Ventilation rate , <italic>R</italic> <inf>f</inf> , Total drag , <italic>S</italic> , Area of the gas chamber , σ , Standard deviation , <italic>U</italic> , Towing velocity , VOF , Volume of fluid , VSM , Ventilation ship model , <italic>x<inf>i</inf></italic> , Instantaneous value of trim , <math xmlns="http://www.w3.org/1998/Math/MathML"><mover><mi>x</mi> <mo>¯</mo></mover></math> , Average value of trim , <italic><inf>Z</inf></italic> , Displacement of sinkage , <italic>β</italic> , Deadrise angle , Δ , Displacement , <italic>∆<inf>Fr</inf></italic> , Dynamic volume of displacement , <italic>ε</italic> , Proportion of hydrodynamic lift in total lift , <italic>λ<inf>w</inf></italic> , Mean wetted length-beam ratio , <italic>μ</italic> , Dynamic viscosity , <italic>ρ</italic> , Density of the fluid , <italic><inf>τ</inf></italic> , angle of pitch
Numerical prediction of ventilated planing flat plates for the design of Air Cavity Ships
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Numerical prediction of ventilated planing flat plates for the design of Air Cavity Ships
| Springer Verlag | 2018