LOW REYNOLDS NUMBER PERFORMANCE OF A MODEL SCALE T-FOIL

Submerged T-foils are an essential forward component of the ride control systems of high speed ferries. A model scale T-Foil for a 2.5m towing tank model of a 112m INCAT Tasmania high-speed wave-piercer catamaran has been tested for both static and dynamic lift performance. The tests were carried out using a closed-circuit water tunnel to investigate the lift and drag characteristics as well as frequency response of the T-Foil. The model T-Foil operates at a Reynolds number of approximately 105, has an aspect ratio of 3.6 and a planform which is strongly tapered from the inboard to outboard end. All of these factors, as well as strut and pivot interference, influence the steady lift curve slope ( of the model T-foil which was found to be 61% of the value for an ideal aerofoil with elliptic loading. The T-foil dynamic performance was limited primarily by the stepper motor drive system and connection linkage. At the frequency of maximum motion of the 2.5 m catamaran model (about 1.5Hz) the model T-foil has approximately 5% reduction of amplitude and 15 degrees of phase shift relative to the low frequency response. Only very small limitations arose due to the unsteady lift as predicted by the analysis of Theodorsen. It was concluded that the model scale T-foil performed adequately for application to simulation of a ride control system at model scale.

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Low Reynolds Number Performance of a Model Scale T-Foil

10.3940/rina.ijme.2015.a3.336 ◽

2015 ◽

Vol 157 (A3) ◽

pp. 175-188

Keyword(s):

Reynolds Number ◽

Frequency Response ◽

High Speed ◽

Dynamic Performance ◽

Low Frequency ◽

Model Scale ◽

Ride Control ◽

Lift Curve ◽

Lift And Drag ◽

Motor Drive System

"Submerged T-foils are an essential forward component of the ride control systems of high speed ferries. A model scale T-Foil for a 2.5m towing tank model of a 112m INCAT Tasmania high-speed wave-piercer catamaran has been tested for both static and dynamic lift performance. The tests were carried out using a closed-circuit water tunnel to investigate the lift and drag characteristics as well as frequency response of the T-Foil. The model T-Foil operates at a Reynolds number of approximately 105, has an aspect ratio of 3.6 and a planform which is strongly tapered from the inboard to outboard end. All of these factors, as well as strut and pivot interference, influence the steady lift curve slope of the model T-foil which was found to be 61% of the value for an ideal aerofoil with elliptic loading. The T-foil dynamic performance was limited primarily by the stepper motor drive system and connection linkage. At the frequency of maximum motion of the 2.5 m catamaran model (about 1.5Hz) the model T-foil has approximately 5% reduction of amplitude and 15 degrees of phase shift relative to the low frequency response. Only very small limitations arose due to the unsteady lift as predicted by the analysis of Theodorsen. It was concluded that the model scale T-foil performed adequately for application to simulation of a ride control system at model scale."

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An 850 nm SiGe/Si HPT with a 4.12 GHz maximum optical transition frequency and 0.805A/W responsivity

International Journal of Microwave and Wireless Technologies ◽

10.1017/s1759078715001531 ◽

2015 ◽

Vol 9 (1) ◽

pp. 17-24 ◽

Cited By ~ 5

Author(s):

Zerihun Gedeb Tegegne ◽

Carlos Viana ◽

Marc D. Rosales ◽

Julien Schiellein ◽

Jean-Luc Polleux ◽

...

Keyword(s):

Frequency Response ◽

Continuous Wave ◽

Optical Transition ◽

Near Field ◽

Dynamic Performance ◽

Low Frequency ◽

Bipolar Transistors ◽

Transition Frequency ◽

Optical Coupling ◽

Wave Measurements

A 10 × 10 μm2SiGe heterojunction bipolar photo-transistor (HPT) is fabricated using a commercial technological process of 80 GHz SiGe bipolar transistors (HBT). Its technology and structure are first briefly described. Its optimal opto-microwave dynamic performance is then analyzed versus voltage biasing conditions for opto-microwave continuous wave measurements. The optimal biasing points are then chosen in order to maximize the optical transition frequency (fTopt) and the opto-microwave responsivity of the HPT. An opto-microwave scanning near-field optical microscopy (OM-SNOM) is performed using these optimum bias conditions to localize the region of the SiGe HPT with highest frequency response. The OM-SNOM results are key to extract the optical coupling of the probe to the HPT (of 32.3%) and thus the absolute responsivity of the HPT. The effect of the substrate is also observed as it limits the extraction of the intrinsic HPT performance. A maximum optical transition frequency of 4.12 GHz and an absolute low frequency opto-microwave responsivity of 0.805A/W are extracted at 850 nm.

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An Experimental Investigation of Ride Control Algorithms for High-Speed Catamarans Part 1: Reduction of Ship Motions

Journal of Ship Research ◽

10.5957/jsr.2017.61.1.35 ◽

2017 ◽

Vol 61 (01) ◽

pp. 35-49

Author(s):

Javad AlaviMerh ◽

Jason Lavroff ◽

Michael R. Davis ◽

Damien S. Holloway ◽

Giles A. Thomas

Keyword(s):

Control System ◽

Motion Control ◽

High Speed ◽

Vertical Acceleration ◽

Pitch Control ◽

Model Scale ◽

Ride Control ◽

Control Feedback ◽

Control Surfaces ◽

Ride Control System

Ride control systems are essential for comfort and operability of high-speed ships, but it remains an open question what is the optimum ride control method. To investigate the motions of a 112-m high-speed catamaran fitted with a ride control system, a 2.5-m model was tested in a towing tank. The model active control system comprised two transom stern tabs and a central T-Foil beneath the bow. Six ideal motion control feedback algorithms were used to activate the model scale ride control system and surfaces in a closed-loop control system: heave control, local motion control, and pitch control, each in a linear and nonlinear version. The responses were compared with the responses with inactive control surfaces and with no control surfaces fitted. The model was tested in head seas at different wave heights and frequencies and the heave and pitch response amplitude operators (RAOs), response phase operators, and acceleration response were measured. It was found that the passive ride control system reduced the peak heave and pitch motions only slightly. The heave and pitch motions were more strongly reduced by their respective control feedback. This was most evident with nonlinear pitch control, which reduced the maximum pitch RAO by around 50% and the vertical acceleration near the bow by about 40% in 60-mm waves (2.69 m at full scale). These reductions were influenced favorably by phase shifts in the model scale system, which effectively contributed both stiffness and damping in the control action.

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LOADING RESPONSE OF STERN TAB MOTION CONTROLS IN SHALLOW WATER

The International Journal of Maritime Engineering ◽

10.5750/ijme.v158ia2.980 ◽

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.

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Forces Due to a Magnetic Dipole Near a Sliding Conductor: Applications to Magnetic Levitation and Bearings

Journal of Tribology ◽

10.1115/1.2927325 ◽

1994 ◽

Vol 116 (4) ◽

pp. 720-725 ◽

Cited By ~ 2

Author(s):

Michelle Simone ◽

John Tichy

Keyword(s):

Reynolds Number ◽

Magnetic Induction ◽

High Speed ◽

Eddy Currents ◽

Skin Depth ◽

Induction Vector ◽

Magnetic Induction Vector ◽

Drag Forces ◽

Conducting Body ◽

Lift And Drag

A conducting body moving with respect to a magnet experiences lift and drag forces from the eddy currents induced in the conductor. The force on the conductor is dependent on the relative velocity between the conductor and the magnet. In this study, we investigate the force dependence on magnetic Reynolds number, a dimensionless indicator of velocity. The Lorentz equation is used to predict the force on the conductor, given the spatial dependence of the eddy currents and magnetic induction vector inside the conductor. Maxwell’s equations, which govern the electromagnetic quantities, are reduced to a single convection-diffusion equation for the magnetic induction vector inside the conducting body. An integral solution which satisfies the governing equation and boundary conditions is used to obtain the eddy currents and magnetic field. For our model, both lift and drag forces increase sharply with Reynolds number, reach a maximum, and decrease with increasing Reynolds number to an asymptotic limit. We also find that skin depth, the depth to which the eddy currents decay inside the conductor, decreases with increasing Reynolds number. The relevance to magnetically supported high-speed vehicles and magnetic bearings is discussed.

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An Experimental Investigation of Ride Control Algorithms for High-Speed Catamarans Part 2: Mitigation of Wave Impact Loads

Journal of Ship Research ◽

10.5957/jsr.2017.61.2.51 ◽

2017 ◽

Vol 61 (02) ◽

pp. 51-63

Author(s):

Javad AlaviMehr ◽

Jason Lavroff ◽

Michael R. Davis ◽

Damien S. Holloway ◽

Giles A. Thomas

Keyword(s):

Control System ◽

High Speed ◽

Control Algorithms ◽

Impact Loads ◽

Wave Impact ◽

Pitch Control ◽

Model Scale ◽

Ride Control ◽

Control Feedback ◽

Ride Control System

High-speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112-m highspeed catamaran using a 2.5-m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T-Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model-scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112-m INCAT vessel, enabling isolation and measurement of a center bow force and bending moments at two cross sections along the demi-hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60-mm model-scale waves it significantly reduced the peak slam force by 90% and the average slam induced bending moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high-speed catamaran vessels.

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Pausing after clap reduces power required to fling wings apart at low Reynolds number

10.1101/2020.10.26.356386 ◽

2020 ◽

Author(s):

Vishwa T. Kasoju ◽

Arvind Santhanakrishnan

Keyword(s):

Reynolds Number ◽

Drag Coefficient ◽

High Speed ◽

Lift Coefficient ◽

Pause Duration ◽

Physical Models ◽

Power Coefficient ◽

Average Force ◽

Drag Forces ◽

Lift And Drag

AbstractThe smallest flying insects such as thrips (body length < 2 mm) are challenged with needing to move in air at chord-based Reynolds number (Rec) on the order of 10. Pronounced viscous dissipation at such low Rec requires considerable energetic expenditure for tiny insects to stay aloft. Free-flying thrips flap their densely bristled wings at large stroke amplitudes, bringing both wings in close proximity of each other at the end of upstroke (‘clap’) and moving their wings apart at the start of downstroke (‘fling’). From high-speed videos of free-flying thrips, we observed that their forewings remain clapped for approximately 10% of the wingbeat cycle before start of fling. We sought to examine if there are aerodynamic advantages associated with pausing wing motion after clap and before fling at Rec=10. A dynamically scaled robotic clap-and-fling platform was used to measure lift and drag forces generated by physical models of non-bristled (solid) and bristled wing pairs for pause times ranging between 0% to 41% of the cycle. In both solid and bristled wings, varying pause time showed no effect on average force coefficients generated within each half-stroke. This was supported by nearly identical time-variation of circulation of the leading and trailing edge vortices for different pause times. At smaller pause times, bristled wings showed larger reduction of cycle-averaged drag coefficient as compared to that of solid wings. For a given wing design (solid or bristled), the ratio of cycle-averaged lift coefficient to cycle-averaged drag coefficient was unchanged across different pause times. We observed 13.5% drop in cycle-averaged power coefficient and 3% drop in cycle-averaged lift coefficient when moving from 0% pause to 9% pause duration. Our results suggest that pausing at the end of clap can be beneficial for reducing the power required to fling, with a small reduction in lift.

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