Showing papers on "Rudder published in 1997"

Nonlinear vectorial backstepping design for global exponential tracking of marine vessels in the presence of actuator dynamics

Abstract: A nonlinear vectorial backstepping control law for commercial ships is derived by using the concept of vectorial backstepping. Vectorial backstepping is done in 3 steps corresponding to the state vectors of the ship dynamics, kinematics and actuator dynamics. Emphasis is placed on compensation of the actuator dynamics since the bandwidth of the propellers, thrusters and rudders often is close to the bandwidth of the ship dynamics. Global exponential tracking is proven by applying Lyapunov stability analysis. The case study is simultaneously global exponential tracking of the surge and sway positions (x,y) and the yaw angle /spl psi/ of a surface ship. This can only be done by applying nonlinear control theory due to the nonlinear structure of the kinematic equations, Coriolis and centripetal forces, and hydrodynamic damping forces.

Modular autonomous underwater vehicle system

Abstract: An autonomous underwater vehicle system for ocean science measurement and reconnaissance is about six feet long and 13 inches in diameter and includes various improvements which make turn-key, networkable, autonomous or tethered operation in aquatic environments possible. The improvements include a platform independent computer and I/O architecture which permits use of CISC or RISC CPUs and turn-key vehicle operation by persons unversed in computer programming, a floating launch and recovery frame which protects the vehicle and also provides for correct and safe vehicle assembly, an external battery charging port and high speed serial port with provision for optional control of the vehicle and data acquisition in real-time through connection of a lightweight electrically conducting tether, a four part hull assembly including an integrated strobe and antennae tower on the forward hull section which emerges from the water when the vehicle is at the surface, a modular, removable nose cone to carry sensors, and a motor mount which protects the main hull from flooding in the event of thruster failure, and flexible control surfaces with dive planes located on the forward hull and rudder fins on the stern hull section. These features are combined to produce a versatile and flexible platform for making oceanographic observations during complex behaviors executed by the vehicle and for providing duplex computer network connections when the vehicle is at the surface.

Autonomous Modal Identification of the Space Shuttle Tail Rudder

Abstract: Autonomous modal identification automates the calculation of natural vibration frequencies, damping, and mode shapes of a structure from experimental data. This technology complements damage detection techniques that use continuous or periodic monitoring of vibration characteristics. The approach shown in the paper incorporates the Eigensystem Realization Algorithm (ERA)as a data analysis engine and an autonomous supervisor to condense multiple estimates of modal parameters using ERA''s Consistent-Mode Indicator and correlation of mode shapes. The procedure was applied to free-decay responses of a Space Shuttle tail rudder and successfully identified the seven modes of the structure below 250 Hz. The final modal parameters are a condensed set of results for 87 individual ERA cases requiring approximately five minutes of CPU time on a DEC alpha computer.

Vertical Tail Buffeting Alleviation Using Piezoelectric Actuators - Some Results of the Actively Controlled Response Of Buffet-Affected Tails (ACROBAT) Program

Abstract: Buffet is an aeroelastic phenomenon associated with high performance aircraft especially those with twin vertical tails. In particular, for the F/A-18 aircraft at high angles of attack, vortices emanating from wing/fuselage leading edge extensions burst, immersing the vertical tails in their wake. The resulting buffet loads on the vertical tails are a concern from fatigue and inspection points of view. Recently, a 1/6-scale F-18 wind-tunnel model was tested in the Transonic Dynamics Tunnel at the NASA Langley Research Center as part of the Actively Controlled Response of Buffet Affected Tails (ACROBAT) Program to assess the use of active controls in reducing vertical tail buffeting. The starboard vertical tail was equipped with an active rudder and the port vertical tail was equiped with piezoelectric actuators. The tunnel conditions were atmospheric air at Mach 0.10. By using single-input-single-output control laws at gains well below the physical limits of the actuators, the power spectral density of the root strains at the frequency of the first bending mode of the vertical tail was reduced by as much as 60 percent up to angles of attack of 37 degrees. Root mean square (RMS) values of root strain were reduced by as much as 19 percent. The results herein illustrate that buffet alleviation of vertical tails can be accomplished using simple active control of the rudder or poezoelectric actuators. In fact, as demonstrated herein, a fixed gain single input single output control law that commands piezoelectric actuators may be active throughout the high angle-of-attack maneuver without requiring any changes during the maneuver. Future tests are mentioned for accentuating the international interest in this area of research.

Rudder assembly with a controlled boundary layer control for an aircraft

Abstract: The boundary layer flow along the surface of an aircraft rudder assembly is controlled by suction applied through perforations primarily installed in the leading edge of the rudder assembly. The control is such that a laminar flow is enforced or at least such that any turbulent flow is displaced so that it begins downstream of the rudder assembly leading edge. Suction air chambers are arranged along the leading edge inside a nose box of the rudder assembly and these boxes are connected through air ducts and a valve system to an exhaust fan. The valve system and the exhaust fan are controlled by a central processing unit providing a flow controller for the suction in response to control signals produced from rated values and sensed actual valves to provide a uniform distribution of the suction along the leading edge of the rudder assembly. The suction system may be switched over to a de-icing mode by blowing warm air out through the perforations in a controlled manner.

Flight direction control system for blimps

Abstract: A method and apparatus for controlling the flight direction of a blimp. The blimp includes an elongate fuselage for containing a lighter-than-air gas, a movable rudder located toward a tail end of the fuselage, and at least one propeller mounted on a side of the fuselage. The propeller is attached to the blimp by a connection that provides two axes of movement. The propeller connection can be rotated or pivoted (1) about a first axis which is a horizontal axis that is perpendicular to a direction of the longitudinal axis of the elongate fuselage, and/or (2) about a second axis which is a vertical axis that is perpendicular to the direction of the longitudinal axis of the fuselage.

A twisted rudder for reduced cavitation

Abstract: A rudder operating behind a propeller can experience large onset flow angles along the rudder span. At a given speed, the maximum rudder angle before cavitation is substantially higher in turning to one direction than to the opposite side. At high speeds, rudders can experience severe surface cavitation, even at zero degree rudder deflection angle. Observation from full-scale trials and dry dock inspection of a surface ship combatant show that rudder cavitation is a real problem in terms of ship operation and maintenance. It is shown in this paper that cavitation inception and erosion problems associated with the existing fleet rudders can be avoided or reduced by using the concept of a twisted rudder. A fleet rudder can be twisted along its span to align the incoming flow. The twisted rudder model has been designed, fabricated, and tested in the Navy's Large Cavitation Channel (LCC). Two-component Laser Doppler Velocimetry (LDV) was used to measure the field velocity and inflow angles in the propeller slipstream. A dynamometer and a series of pressure taps were used to measure rudder lift, drag and pressure distributions on the rudder surface. To evaluate the effect of twist angles on rudder performances, a full-scale rudder, designated the non-twisted rudder, has also been fabricated and tested back-to-back in the LCC with the twisted rudder for direct comparison. The advantages of using a twisted rudder to improve cavitation performance are presented in this paper.

Active Vertical Tail Buffeting Alleviation on a Twin-Tail Fighter Configuration in a Wind Tunnel

Abstract: A 1/6-scale F-18 wind-tunnel model was tested in the Transonic Dynamics Tunnel at the NASA Langley Research Center as part of the Actively Controlled Response of Buffet-Affected Tails (ACROBAT) program to assess the use of active controls in reducing vertical tail buffeting The starboard vertical tail was equipped with an active rudder and other aerodynamic devices, and the port vertical tail was equipped with piezoelectric actuators The tunnel conditions were atmospheric air at a dynamic pressure of 14 psf By using single-input-single-output control laws at gains well below the physical limits of the control effectors, the power spectral density of the root strains at the frequency reduced by as much as 60 percent up to angles of attack of 37 degrees Root mean square (RMS) values of root strain were reduced by as much as 19 percent Stability margins indicate that a constant gain setting in the control law may be used throughout the range of angle of attack tested

Robust control methodology applied to the design of a combined steering/stabiliser system for warships : Special section on marine control

Abstract: The consequences of roll motions in ship operations can seriously degrade the performance of mechanical and personnel effectiveness. To alleviate roll motions many ships are equipped with fin stabilisers. Rudders can also generate roll motions which can be harnessed to function in congress with the fins to accrue enhanced levels of stabilisation. An integrated rudder and fin stabilisation control strategy is proposed. Rudder roll controllers and autopilots are developed using the H∞ optimisation technique and their performance compared with the classical counterparts. Simulation studies are described that quantify the performance of the various controllers. The level of interaction present between the yaw and roll control loops is also examined. The study concludes that the overall performance of the H∞ RRS controller and autopilot is superior to that of the classical type. The level of interaction between the two loops can be suitably modified by varying the performance weighting functions. The study has concentrated on designing the controllers for frigates of the Royal Navy, however, the approach is suitable to present and future warship design.

Regularization Techniques for Real-Time Identification of Aircraft Parameters

Abstract: An algorithm for the identification of aircraft parameters in real-time during highly dynamic, nonlinear, maneuvers is presented. The system identification algorithm also identifies rapid changes in parameters, caused by failure and/or damage, for use in an adaptive reconfigurable control algorithm. This work is a continuation of the earlier work by the authors on regularizatio n modifed least squares identification, which is now applied to a nonlinear VISTA F-16 simulation. The previous two degree of freedom pitch axis parameter identification is expanded to include the lateral-directional axes for a total of five degrees of freedom. Identification results are presented for a strongly coupled stability axis roll maneuver where the aircraft undergoes rudder damage during the maneuver. The parameters are estimated closed

Robust control methodology applied to the design of a combined steering/stabiliser system for warships

Abstract: The consequences of roll motions in ship operations can seriously degrade the performance of mechanical and personnel effectiveness. To alleviate roll motions many ships are equipped with fin stabilisers. Rudders can also generate roll motions which can be harnessed to function in congress with the fins to accrue enhanced levels of stabilisation. An integrated rudder and fin stabilisation control strategy is proposed. Rudder roll controllers and autopilots are developed using the H∞ optimisation technique and their performance compared with the classical counterparts. Simulation studies are described that quantify the performance of the various controllers. The level of interaction present between the yaw and roll control loops is also examined. The study concludes that the overall performance of the H∞ RRS controller and autopilot is superior to that of the classical type. The level of interaction between the two loops can be suitably modified by varying the performance weighting functions. The study has concentrated on designing the controllers for frigates of the Royal Navy, however, the approach is suitable to present and future warship design.

Nonlinear rudder-roll damping of non-minimum phase ships using sliding mode control

Abstract: A non-minimum phase nonlinear ship model from rudder angle to roll angle is used to design a stable controller for simultaneous roll damping and course keeping. The controller is stable in presence of lst-order wave disturbances and modeling errors provided that the magnitude of the model errors and disturbances are known. Stability is proved using Lyapunov theory. The simulation results show excellent performance and robustness.

Semiglobal exponential output feedback control of ships

Abstract: This paper describes a semiglobal exponentially stable output feedback control law for automatic heading control of ships described by a nonlinear model. Only compass (yaw angle) feedback is used. The yaw rate signal is reconstructed by a linear observer. A wave filter is included in the observer to reduce wear and tear on the rudder servo due to first-order wave-induced disturbances. Integral action is included in the control law to compensate for wave drift (second-order wave disturbances), low-frequency wind, and current disturbances. The performance and robustness of the controller are demonstrated in a simulation study of two medium-sized ships.

Effects of ship hull and propeller on rudder Cavitation

Abstract: Ship trial observation and drydock inspection of a surface ship combatant show that rudder cavitation can be a real problem in terms of ship operation and maintenance. A project has been initiated by the Navy (a) to identify fleet rudder cavitation problem, (b) to investigate experimentally and numerically hull/propeller effects on rudder cavitation, and (c) to develop methods to incorporate propeller/rudder interaction into the future rudder design for cavitation improvement. Experiments were carried out at the Navy's Large Cavitation Channel (LCC) with a geosim model of a fleet rudder, propeller and ship hull of a surface combatant. Two-component Laser Doppler Velocimetry (LDV) was used to measure the field velocity and inflow angles in the propeller slip-stream. A dynamometer and pressure taps were used to measure rudder lift, drag and pressure distributions. Influence of the ship hull and propeller on rudder forces, pressure distribution, and cavitation performance are compared with numerical calculations. The resemblance between the model rudder cavitation pattern in the LCC and full-scale cavitation erosion pattern observed in the dry dock is discussed.

Autonomous craft controller system for landing craft air cushioned vehicle

Abstract: An autonomous craft controller system for automated control of operation of landing craft air-cushioned vehicle includes a command processor, a bow thruster controller, a prop pitch controller, and a rudder controller. The command processor receives and processes multiple inputs relating to vehicle heading, location and velocity and, in response thereto, produces multiple outputs relating to vehicle acceleration and vehicle heading, velocity and position error. The bow thruster controller receives and processes as inputs some of the multiple outputs from the command processor and, in response thereto, produces a bow thruster command output. The prop pitch controller receives and processes as inputs some of the multiple outputs from the command processor and, in response thereto, produces port and starboard prop pitch command outputs. The rudder controller receives and processes as inputs some of the outputs from the command processor and outputs from the prop pitch controller and, in response thereto, produces a rudder command output.

Active control of vertical fin buffeting with aerodynamic control surface and strain actuation

Abstract: In the present work a typical section aeroelastic model of a vertical fin is used to evaluate two different active control strategies to attenuate buffeting response at high angle of attack, namely the classic aerodynamic surface control approach using the rudder, and a new `smart' structures strain actuation approach. The three-degree-of-freedom typical section model including plunge, airfoil and flap rotation is augmented to incorporate the unsteady airloads due to motion, and an internal `buffet mode' to simulate the buffering excitation observed in wind tunnel tests of the fin at a given range of reduced frequencies. The two control strategies are studied using the Linear Quadratic Gaussian method of the Optimum Control Theory. Numerical results are presented in terms of Bode plots of the structure aeroelastic response, and root-loci of the aeroelastic modes at a representative flight condition.

Paddle wheel boat

Abstract: The vessel of this invention has a relatively uniform weight distribution throughout the length of the vessel which maintains a level trim under all operation conditions thereby maximizing the efficiency of the design and operation. This is, in part, accomplished by locating the engine and major transmission drive components inboard of the boat rather than outboard astern, and by locating the operator and the rudder assembly at the bow of the boat. Unique features of the invention include the propulsion and steering systems for a boat consisting of a paddle wheel, a power supply, a clutch, a gear reduction system to transfer and reverse power to the paddle wheel, an optional splash guard mounted between the stern of the boat and the paddle wheel, a frame to attach the propulsion members to the boat and a rudder assembly mounted to the bow of the boat. The paddle wheel can include blades to effect vertical lift secured to angled spokes at an angle radially, inclined or skewed to the axis of rotation of the paddle wheel rather than extending radially from the axis of rotation of the center hubs. The steering system includes the rudder assembly mounted at the bow of the boat and being formed and arranged to pivot freely about a horizontal axis in a vertical direction as well as having a rudder blade which pivots about a vertical axis.

Directional control for tailless aircraft using all moving wing tips

Abstract: This paper presents new information developed under a joint Wright Laboratory / Naval Air Warfare Center research effort investigating innovative aerodynamic control concepts for tailless fighters. This effort sponsored contracts with Lockheed Martin Tactical Aircraft Systems and Boeing Defense & Space Group to investigate several promising control concepts and develop aircraft level integration impacts for each concept. A control effector that has continued to show considerable promise is the all moving wing tip (AMT). Previous AMT investigations have looked at the effector as a roll control device. The current research focuses on the yaw control potential available when the tip is deflected trailing edge down. The effector exhibits excellent yaw control characteristics from low angles-of-attack (AOA) through very high AOA (70 deg) with little sensitivity to sideslip. A recent series of wind tunnel tests have indicated that skewing the pivot trunion aft resulted in increased yaw power due to favorable side forces created by the skewed surface. The balanced arrangement of the all moving surface is conducive to relatively low hinge moments at high speed when compared to more conventional drag rudders, providing a surface that can be used throughout the flight envelope.

Maneuvering Performance of a Ship with VecTwin Rudder System

Abstract: This paper is concerned with the maneuvering motion of a ship with VecTwin Rudder system. Firstly the forces on a couple of rudders and the interaction between both rudders steered with rudder angle are investigated analytically and experimentally. Secondly the free running model experiments are conducted for the turning, zig-zag and stopping maneuvers which are compared with the results simulated by mathematical model to describe the maneuvering motion. Finally an expression of force on VecTwin Rudder is proposed for the MMG model.

Propelling performance improving device for vessel

Abstract: PROBLEM TO BE SOLVED: To improve the propelling efficiency by forming a fin of a pair of fins in right and left, and projecting a front edge of the fin so as to coincide with a tip of a valve or a front edge of a rudder. SOLUTION: A pair of fins 5 in right and left, namely, a port fin 5a and a starboard fin 5b are arranged in both side of a rudder 3. This fin 5 is projected form the rudder 3 and a valve 4 symmetry or asymmetry in both boards of the center line 3c of the rudder 3 at a height of a propeller shaft core C, and set at an optimal fitting angle so as to generate the maximum propelling force, which fit a rear flow of a propeller. Futting angle is constantly set in the radial direction (without generating a torsion) so as to lower the manufacturing cost. In the fin 5, a front edge 5c of the fin is usually projected so as to coincide with a rudder front edge 3a, and has a sweep back angle at about 35 degree in consideration of the rudder angle. COPYRIGHT: (C)1999,JPO

Vertically adjustable stern mounted marine drive

Abstract: A stern mounted vertically adjustable propeller and rudder marine drive. The aft end of a propeller shaft, the propeller, the rudder and printle and a skeg are vertically moveable to adjust a boat's draft for use in the water and when trailering. A stern underwater slot in the boat hull and shaped to enhance water flow accommodates the propeller shaft which is driven by an inboard engine. As the propeller shaft passes through the hull slot it engages a flexible water seal mechanism which self adjusts or maintains itself in various up and downward positions; its pivotal point is common with the conterline pivotal point of a universal joint, which is attached to a drive shaft connected to the transmission of an inboard engine.

Prediction of Ship Manoeuvrability with a Flapped Rudder

Abstract: Recently, the powerful high-lift type rudder such as a flapped rudder is widely used in order to improve a steering quality or to achieve the reduction of labour cost in ship operations. For the prediction of manoeuvrability with these ships, it has been done by means of employing some empirical amplification factor in the calculation of rudder normal force. This procedure, however, makes some problems. The empirical amplification factor differs depending upon rudder angle especially when the flap angle is not proportional to the rudder angle. It is not also proper when a ship is swaying and yawing, as the inflow angle to the rudder changes depending on the ship motion, but the flap angle is kept unchanged. These facts may cause the mis-prediction of the manoeuvrability.In this paper, a mathematical model is proposed to predict the manoeuvrability for a flapped rudder equipped ship. It has been validated by free-running model tests. Based on the proposed mathematical model, the suitable flap angle is investigated by the numerical simulations. Then, it is found that the smaller flap angle is better for the stable ship in course-keeping, and that the larger flap angle for the unstable ship, though the maximum flap angle is the same in each other.

Dual hull watercraft

Abstract: In a dual-hull watercraft, a separate keel hull and sail hull are connected by a tie line. The sail hull comprises a sail and hull without a keel. The keel hull comprises a keel and hull or a submerged keel. The flexible tie line is coupled to the keel at or near the keel center of effort and is coupled to the sail at or near the center of sail effort. During operation, the sail and keel are configured to "toe in" relative to each other, maintaining tension in the tie line allowing the sail and keel to provide for the other's drag. The tie line allows for directional steering of the craft without a rudder, and for controlling the speed of the craft and the heel angles of the sail and keel hulls. Two gliders similarly connected can exploit wind velocity differences and are operable without updrafts.

Sailboat rudder having a monocoque structure

Abstract: A rudder for a sailboat or other vessel formed by a lightweight core having the combined shape of the blade and the stock of the rudder, and a fiber-reinforced resin skin enveloping the core and conforming thereto to create a monocoque structure in which the skin bears the major portion of the torsional and bending stresses to which the rudder is subjected when in use. The pre-cast foam-plastic core of the rudder is formed by a blade section and a stock section having a root received in a slot in the blade section, the stock section being wrapped with a layer of reinforcing fibers before being combined with the blade section. To produce the rudder, the pre-cast core is placed in the cavity of a mold lined with reinforcing fibers which wrap the core inserted therein. Then injected into the closed mold is a flowable resin which impregnates the fibers wrapping the core whereby when the resin cures, these fibers are bonded to and reinforce the resultant resin skin enveloping the rudder core to create a monocoque rudder structure of exceptional strength.

Hydrofoil assisted trimaran

Abstract: The present invention relates to the hydrofoil system of sailing-trimarans which provides the following arrangement of the hydrofoils. Inclined, retractable foil is placed in a head of each outrigger, onwards from the center of area of the sails and from the centre of gravity of a trimaran. Two additional hydrofoils are arranged one by one on the stern of each outrigger so as to let them be clear of the water, if the side wind pressure effecting on the sails is low. The third additional hydrofoil is arranged on the rudder in the stern of the central hull.

Servo control system for rudder of air plane

Abstract: PROBLEM TO BE SOLVED: To provide a controller, which can always obtain the stabilized control characteristic even in the case where the natural frequency of an object to be controlled is fluctuated in a certain range and of which installation is facilitated. SOLUTION: In this system, operation of a rudder of an air plane to be operated by an actuator is controlled by a controller 10 provided with a compensating unit 14 for outputting the operated variable so that a target value and a controlled variable of the rudder coincide with each other. The actuator and the rudder are regulated as an object to be controlled, which generate the fluctuation of' the natural frequency, and this system is also provided with a means a for treating the fluctuation of the object to be controlled in a predetermined range, which includes the natural frequency thereof, as the fluctuation of parameter of the equivalent mass and the rigidity of the rudder, and provided with a linear compensating unit 14 designed by the robust control method so as to obtain the robust stability even in the case where the object to be controlled is fluctuated within the predetermined range.

Two propeller, large angle propulsion arrangement for ship

Abstract: The utility model relates to a propulsion device for a ship with two propeller and large included angle. A propulsion and control system for a ship with two propeller and large included angle is put forward according to the situation that the existing propulsion and control system for a ship has big power loss, complex steering system, low handiness, etc. In the utility model, the power of a host machine is divided into two by a speed change bevel gear box and a turning bevel gear box; moreover, two propeller shafts are positioned to form an included angle of 70 DEG. The forward move, the backward move, the turning, etc. of a ship are determined by selecting one propeller to work or two propeller to work simultaneously. A rudder control system which is generally used in the present ship is canceled.