UNSTEADY CHARACTERISTICS OF LIFT GENERATED BY SMALL UNDERWATER CONTROL FIN

2021 ◽  
Vol 158 (A1) ◽  
Author(s):  
M Yoshida ◽  
H Iwashita ◽  
M Kanda ◽  
H Kihara ◽  
T Kinoshita
Keyword(s):  
Frequency Domain ◽  
High Speed ◽  
Lift Coefficient ◽  
Phase Lag ◽  
Speed Reduction ◽  
Small Water ◽  
Theoretical Predictions ◽  
Large Amplitude Motions ◽  
Lift Curve ◽  
Unsteady Characteristics

Speed reduction or slamming must be restricted for a high-speed oceangoing vessel because of the requirement for punctuality and the high value of the cargo. Speed reduction and slamming are caused by large amplitude motions in waves. A promising ship form for such vessels is so-called “Resonance-Free SWATH (RFS)”, which has negative pitch and roll restoring moments due to the extraordinary small water plane area. As a consequence, the resonance peak is removed from the motion response. The attitude of the RFS with negative restoring moments is adjusted by four pairs of control fins attached to the fore and aft ends of the lower hulls. In previous studies, the steady value of the lift-curve slope is usually used in the motion equation of the frequency domain. However, when working in waves, the controlling fins are not working in a steady state and the lift coefficient is no longer a constant. In addition, there exists a phase lag between the change in the attack angle and the fin-generated lift. In the present study, theoretical predictions using a frequency-domain 3D-Rankine Panel Method, as well as experimental measurement, have been made to analyze the phenomena of the lift generation including the phase lag and the interference between fins, the lower hulls and the struts. The theoretical results agree well with the experimental results in spite of the potential theory being without viscosity. Next, the unsteady characteristics of fin-generated lift are expressed as the function of the encountering wave frequency. Then the effects of the fore fins, the lower hulls and struts on the lift curve-slope of the aft fins are discussed.

Lift Characteristics of Controlling Fins of Resonance-Free SWATH

2014 ◽  
Author(s):  
Go Oishi ◽  
Hidetsugu Iwashita ◽  
Masamitsu Kanda ◽  
Motoki Yoshida ◽  
Hajime Kihara ◽  
...  
Keyword(s):  
High Speed ◽  
Lift Coefficient ◽  
Ship Motions ◽  
Phase Lag ◽  
Sea State ◽  
Speed Reduction ◽  
Small Water ◽  
Additional Resistance ◽  
Lift Curve ◽  
Rough Sea

Speed reduction, additional resistance or slamming, which caused by the large ship motions, should be avoided for a high-speed oceangoing vessel, because of the delivery punctuality and high value of the cargo. A promising ship type for such the oceangoing vessel is the so-called “Resonance-Free SWATH (RFS)”. It has negative restoring moment due to the extraordinary small water plane area. As a consequence, the resonance peak is removed from the motion response. RFS is designed to cross 4,800 nautical miles of Pacific Ocean within 5 days punctually at a speed of 40 knots, with good seaworthiness such as no speed reduction or absolutely no slamming even when running in the rough sea of sea state 7 with significant wave height of 6–9 m. The attitude of RFS with negative restoring moment is adjusted by four pairs of controlling fins attached to the fore and aft ends of lower hulls. In the previous works, the quasi-steady values of lift-curve slope are usually adopted in the motion equations of frequency domain. However, when working in waves, the controlling fins are not in a steady state. The lift coefficient is no longer a constant. In addition, there exist a phase lag between the movement of attack angle and the fin-generated lift. The theoretical prediction and the experiment to analyze the phenomena of lift generation including the phase difference and the interaction among fins and lower hulls are carried out. The results show that the characteristics of fins depend on the encounter frequency. Then, the effect of lift characteristics of controlling fins on the RFS model is discussed. The results of theoretical estimation and experiment are discussed and it is observed that estimated results agree to some extent with experimental results.

SUPERIOR SEAWORTHINESS OF A RESONANCE-FREE FAST OCEANGOING SWATH

2021 ◽  
Vol 156 (A4) ◽  
Author(s):  
M Yoshida ◽  
H Kihara ◽  
H Iwashita ◽  
M Kanda ◽  
T Kinoshita
Keyword(s):  
High Speed ◽  
Time Lag ◽  
Ship Motions ◽  
Speed Reduction ◽  
Small Water ◽  
Motion Responses ◽  
Head Waves ◽  
Unsteady Characteristics ◽  
Hull Forms ◽  
Heave Motion

The speed reduction, additional resistance or slamming caused by the large amplitude ship motions, should be completely restricted for a large fast oceangoing ship because of the strict time-punctuality and the high value of the cargo. A “Resonance-Free SWATH (RFS)”, which has negative restoring moments due to the extremely small water plane area, is introduced to minimize the motion responses. A motion control system using small fins is necessary for the RFS, which has no stability during high speed cruising. Theoretical estimations and experiments to search for the optimum values of PD control gains have been performed. Unsteady characteristics of fin-generated lift such as the time lag and the interaction among the fins and lower hulls have been measured and they are taken into account in the motion equations. Then, experiments using the RFS model with controlling fins have been carried out to validate the theoretical estimation for the motion responses of the RFS in waves. The theoretical and experimental results agree well with each other. The motion responses of the RFS in regular and irregular head waves are compared with those of other hull forms, such as a mono-hull, an ordinary SWATH and a trimaran. The clear advantage of the RFS regarding the seaworthiness has been found. In summary, the heave motion response of the RFS is reduced to 1/60 and the pitch motion becomes1/8, compared with those of the existing mono-hull ship.

LOADING RESPONSE OF STERN TAB MOTION CONTROLS IN SHALLOW WATER

2021 ◽  
Vol 158 (A2) ◽  
Author(s):  
J Bell ◽  
J Lavroff ◽  
M R Davis
Keyword(s):  
Water Depth ◽  
Deep Water ◽  
High Speed ◽  
Lift Force ◽  
Lift Coefficient ◽  
Force Magnitude ◽  
Water Value ◽  
Ride Control ◽  
Lift Curve ◽  
Hydraulics Laboratory

The ride control systems of high-speed vessels frequently use active stern tabs for both motion control and maintenance of correct trim at various speeds and sea conditions. This paper investigates the effect of water depth on the lift force provided by stern mounted trim tabs, of the type fitted to INCAT high speed wave-piercer catamaran vehicle ferries and similar vessels. This investigation was carried out at model scale with the use of a test apparatus in a flume tank in the University of Tasmania hydraulics laboratory. The lift force magnitude and location were measured over a range of tab angles and flow depths. This was used to calculate the lift coefficient of the tab and asses the performance of the tab over the range of flow depths. It was found that the lift force increased and the force location progressed further forward of the hinge as flow depth decreased. The lift curve slope of the stern tab increased by a factor of over 3 relative to the deep water value when the water depth below the hull was approximately equal to the tab chord. The deep water lift curve slope appears to be approached only when the water depth exceeded 4 or more tab chord lengths. The centre of pressure of the lift force was more than two chord lengths ahead of the tab hinge, showing that most of the lift produced by the tab was under the hull rather than on the surface of the tab itself.

Finite-Element Analysis of the Magnetostatic Field of a Coaxial Magnetic Gear Device

2015 ◽  
Vol 764-765 ◽  
pp. 289-293
Author(s):  
Yi Chang Wu ◽  
Han Ting Hsu
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Magnetic Flux ◽  
High Speed ◽  
Field Analysis ◽  
Element Analysis ◽  
Magnetostatic Field ◽  
Speed Reduction ◽  
Dimensional Finite Element ◽  
Magnetic Gear

This paper presents the magnetostatic field analysis of a coaxial magnetic gear device proposed by Atallah and Howe. The structural configuration and speed reduction ratio of this magnetic gear device are introduced. The 2-dimensional finite-element analysis (2-D FEA), conducted by applying commercial FEA software Ansoft/Maxwell, is performed to evaluate the magnetostatic field distribution, especially for the magnetic flux densities within the outer air-gap. Once the number of steel pole-pieces equals the sum of the pole-pair numbers of the high-speed rotor and the low-speed rotor, the coaxial magnetic gear device possesses higher magnetic flux densities, thereby generating greater transmitted torque.

Prediction of Ball Motion in High-Speed Thrust-Loaded Ball Bearings

1976 ◽  
Vol 98 (3) ◽  
pp. 463-469 ◽  
Author(s):  
C. R. Gentle ◽  
R. J. Boness
Keyword(s):  
Computer Program ◽  
High Speed ◽  
Ball Bearing ◽  
Viscoelastic Behavior ◽  
Specific Situation ◽  
Fluid Models ◽  
Ball Bearings ◽  
Theoretical Predictions ◽  
Ball Motion

This paper describes the development of a computer program used to analyze completely the motion of a ball in a high-speed, thrust-loaded ball bearing. Particular emphasis is paid to the role of the lubricant in governing the forces and moments acting on each ball. Expressions for these forces due to the rolling and sliding of the ball are derived in the light of the latest fluid models, and estimates are also made of the cage forces applicable in this specific situation. It is found that only when lubricant viscoelastic behavior is considered do the theoretical predictions agree with existing experimental evidence.

Theoretical Prediction of Motions of High-Speed Planing Boats in Waves

1978 ◽  
Vol 22 (03) ◽  
pp. 140-169
Author(s):  
Milton Martin
Keyword(s):  
High Speed ◽  
Damping Ratio ◽  
Nonlinear Effects ◽  
Theoretical Method ◽  
Valuable Insight ◽  
Response Characteristics ◽  
Theoretical Predictions ◽  
Response Amplitude Operators ◽  
Phase Angles ◽  
Good Agreement

A theoretical method is derived for predicting the linearized response characteristics of constant deadrise high-speed planing boats in head and following waves. Comparisons of the theoretical predictions of the pitch and heave response amplitude operators and phase angles with existing experimental data show reasonably good agreement for a wide variety of conditions of interest. It appears that nonlinear effects are more severe at a speed to length ratio of 6 than of, say, 4 or less, principally because of the reduction of the damping ratio of the boat with increasing speed, and the consequent increase in motions in the vicinity of the resonant encounter frequency. However, it is concluded that the linear theory can provide a simple and fast means of determining the effect of various parameters such as trim angle, deadrise, loading, and speed on the damping, natural frequency, and linearized response in waves, and that this can furnish valuable insight into the actual boat dynamics, even though the accurate predictions of large motions and peak accelerations would require a nonlinear analysis.

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