Showing papers on "Rudder published in 2008"

A unified seakeeping and maneuvering analysis of ships in regular waves

Abstract: The behavior of a ship in regular waves during maneuvering was studied by using a two-time scale model. The maneuvering analysis was based on Soding’s (Schiffstechnik 1982; 29:3–29) nonlinear slender-body theory generalized to account for heel. Forces and moments due to rudder, propeller, and viscous cross-flow follow from the state-of-the-art procedures. The developed unified theory of seakeeping and maneuvering was verified and validated for calm water by comparing it with experimental and calculated zigzag and circle maneuvers. Linear wave-induced motions and loads were determined by generalizing the Salvesen-Tuck-Faltinsen (Trans SNAME 1970; 78:250–287) strip theory. The mean second-order wave loads in incident regular deep water waves in oblique sea conditions were estimated by the potential flow theories of Faltinsen et al. (Proc 13th Symp Naval Hydrody 1980), Salvesen (Proc Intl Symp Dynam Mar Vehicl Struct Wave 1974), and Loukakis and Sclavounos (J Ship Res 1978; 22:1–19). The considered theories cover the whole range of important wavelengths. Comparisons between the different mean second-order wave load theories and available experimental data were carried out for different ship hull forms when the ship was advancing forward on a straight course. The mentioned methods have been incorporated into the maneuvering model. Their applicability from the perspective of the maneuvering ability of the selected types of ships was investigated in given wave environments. The wave conditions are valid for realistic maneuvering cases in open coastal areas. It was demonstrated that the incident waves may have an important influence on the maneuvering behavior of a ship. The added resistance, mean second-order transverse force, and yaw moment also play important roles.

$H_{2}$ and $H_{\infty}$ Designs for Diving and Course Control of an Autonomous Underwater Vehicle in Presence of Waves

Abstract: H 2 and H infin designs applied to the diving and course control of an autonomous underwater vehicle (AUV) considering the presence of wave disturbances are described. The six-degrees-of-freedom equations of motion of the vehicle are described as a linear model and divided into three noninteracting (or lightly interacting) subsystems for speed control, steering, and diving. This work is based on the slender form of the Naval Postgraduate School (NPS, Monterey, CA) AUV, considering that the subsystems can be controlled by means of two single-screw propellers, a rudder, port and starboard bow planes, and a stern plane. A model of the AUV dynamics is presented with the first- and the second-order wave force disturbances, i.e., the Froude-Kriloff and diffraction forces. An algorithm of nonlinear regression for the rationalization of the subsurface sea spectrum is provided in this case study. The obtained results are analyzed and evaluated in the frequency domain comparing the controllers performance considering or not the inclusion of the model of waves.

A ship motion simulation system

Abstract: In this article, efficient computational models for ship motions are presented. These models are used to simulate ship movements in real time. Compared with traditional approaches, our method possesses the ability to cope with different ship shapes, engines, and sea conditions without the loss of efficiency. Based on our models, we create a ship motion simulation system for both entertainment and educational applications. Our system assists users to learn the motions of a ship encountering waves, currents, and winds. Users can adjust engine powers, rudders, and other ship facilities via a graphical user interface to create their own ship models. They can also change the environment by altering wave frequencies, wave amplitudes, wave directions, currents, and winds. Therefore, numerous combinations of ships and the environment are generated and the learning becomes more amusing. In our system, a ship is treated as a rigid body floating on the sea surface. Its motions compose of 6 degrees of freedom: pitch, heave, roll, surge, sway, and yaw. These motions are divided into two categories. The first three movements are induced by sea waves, and the last three ones are caused by propellers, rudders, currents, and winds. Based on Newton’s laws and other basic physics motion models, we deduce algorithms to compute the magnitudes of the motions. Our methods can be carried out in real time and possess high fidelity. According to ship theory, the net effects of external forces on the ship hull depend on the ship shape. Therefore, the behaviors of the ship are influenced by its shape. To enhance our physics models, we classify ships into three basic types. They are flat ships, thin ships, and slender ships. Each type of ship is associated with some predefined parameters to specify their characteristics. Users can tune ship behaviors by varying the parameters even though they have only a little knowledge of ship theory.

URANS analysis of a broaching event in irregular quartering seas

Abstract: Ship motions in a high sea state can have adverse effects on controllability, cause loss of stability, and ultimately compromise the survivability of the ship. In a broaching event, the ship losses control, naturally turning broadside to the waves, causing a dangerous situation and possibly capsizing. Classical approaches to study broaching rely on costly experimental programs and/or time-domain potential or system-based simulation codes. In this paper the ability of Reynolds averaged Navier–Stokes (RANS) to simulate a broaching event in irregular waves is demonstrated, and the extensive information available is used to analyze the broaching process. The demonstration nature of this paper is stressed, as opposed to a validated study. Unsteady RANS (URANS) provides a model based on first principles to capture phenomena such as coupling between sway, yaw, and roll, roll damping, effects of complex waves on righting arm, rudders partially out of the water, etc. The computational fluid dynamics (CFD) method uses a single-phase level-set approach to model the free surface, and dynamic overset grids to resolve large-amplitude motions. Before evaluating irregular seas two regular wave cases are demonstrated, one causing broaching and one causing stable surf riding. A sea state 8 is imposed following an irregular Bretschneider spectrum, and an autopilot was implemented to control heading and speed with two different gains for the heading controller. It is concluded that the autopilot causes the ship to be in an adverse dynamic condition at the beginning of the broaching process, and thus is partially responsible for the occurrence of the broaching event.

Ground-Based Simulation of Complex Maneuvers of a Delta-Wing Aircraft

Abstract: In the process of aircraft development numerical approaches are gaining more and more importance. Not only steady flight conditions need to be modelled but also dynamic derivatives and last but not least realistic flight maneuvers. In particular in the case of delta-wing aircrafts a small change in the flight conditions can strongly influence the vortex dominated flow field about the wings and thus result in large changes of the aerodynamic loads. Numerical tools that are developed for predicting such behaviours need to be validated by experimental data. In order to obtain a data base for validation ground-based simulations of complex maneuvers of a model of the X-31 aircraft have been performed in the low-speed wind tunnel NWB of the German-Dutch Wind Tunnels DNW. In the wind tunnel tests a newly installed novel test rig with six degree of freedoms (DOF) was used for the first time for moving the model. Furthermore, the model was equipped with eight remotely controlled moving flaps. In this manner realistic flight maneuvers could be reproduced in a ground-based facility. Both, the specific technical equipment of the model and the novel six DOF test rig will be reviewed. Thereafter, experimental results obtained will be discussed and compared with numerical results. The X-31 is a single-engine, single-place cockpit, delta-wing aircraft. For control the aircraft had a small, forward-mounted canard; single vertical tail with conventional rudder, wing leading flaps and trailing-edge flaps (elevons). A fully equipped wind tunnel model of the X-31, the so-called X-31 remote-control model, was developed and built to a scale of about 1/7.25 at the German Aerospace Center DLR (cf. Fig. 1). The model is made from steel and carbon fiber reinforced plastic. Its control surfaces can be moved via a remote control system. The main part of the X-31 model is a wing-fuselage section including eight servo motors for changing the angles of canard, leading-edge inner and outer flaps, trailing-edge flaps and rudder. Dynamic surface pressures are measured by miniature piezo-resistive pressure sensors located at 60% and 70% chord length on the upper surface of the delta wing and on the leading edge flaps. Forces and moments are obtained by a 6-component strain gauge also included in the main part of the model. Data are transferred back and force between the model and the external data acquisition system by a 64-channel telemetric system. The transfer rate of the telemetric system is about 3 kHz. The novel configuration of the six DOF dynamic test rig used in the present tests for simulating real flight maneuvers was developed at DNW for its low-speed wind tunnel NWB located in Braunschweig and is called a “Model Positioning Mechanism” (MPM) hereafter. The MPM is based on the concept of a Stewart platform. This platform is linked to the wind tunnel fixed base by six constant-length struts that are connected to six carriages which can move along two parallel guiding rails so that the position and orientation of the platform is adjusted (cf. Fig. 1). The six carriages run independently of each other on the guiding rails thus allowing a displacement within all six degrees of freedom. Because each guiding rail is shared by three carriages, the design is simplified and has fewer components than conventional systems. The six linear motors used for moving the carriages allow accelerations up to 2.5 g. The workspace spans 1100 mm in the flow direction, 300 mm in the lateral direction and 500 mm in the heave direction. The range of pitching or rolling motions can be enlarged by an additional actuator on the MPM and a corresponding joint between the ventral sting and the internal balance. The accuracy of the system, for example, in pivoting angles is better than 0.005°. At the top of the sting the first eigenfrequency is above 20 Hz. The MPM allows for a payload of up to 5000 N. The complex three-dimensional motion of the model is controlled by an optical position tracking system. All measurements were performed in the open test section of the 2.85 X 3.20 m2 low speed atmospheric wind-tunnel NWB of DNW. The X-31 remote-control model was connected to the MPM by a belly sting (cf. Fig. 1). Already during the commissioning phase of the MPM complex maneuvers were successfully simulated. An example based on a real flight maneuver corresponding with steady-heading sideslip test points is shown in Fig. 2. On the left side, the variation in time of the angles of pitch, yaw and roll that were performed by the MPM and the corresponding motions of the flaps that were realized by the remotely controlled servo motors in the model, are shown. As an example, the coefficients of the lateral force and the rolling moment resulting from this maneuver are shown on the right side of Fig. 2. In the same manner many more scientific data have been gathered that are to be used for validating a numerical simulation framework that is under development at DLR for calculating a freely flying maneuvering combat aircraft. In the numerical approach a maneuver is realized by a time-accurate coupling of aerodynamics, structural mechanics and flight mechanics. Results of first numerical simulations will be compared with experimental data obtained under unsteady flow conditions. Thus, a ground-based simulation method has been successfully developed and tested that provides the possibility of simulating complex maneuvers in a subsonic facility.

Course Keeping Control of an Autonomous Boat using Low Cost Sensors

Abstract: This paper discusses the course keeping control problem for a small autonomous boat using low cost sensors. Comparing with full scale ships, a small boat is more sensitive to the environmental disturbances because of its small size and low inertia. The sensors available in the boat are a low cost GPS and a rate gyro while the commonly used compass in ship control is absent. The combined effect from disturbance, poor accuracy and significant delay in GPS measurement makes it a challenging task to achieve good performance. In this paper, we propose a simple dynamic model for the boat's horizontal motion. The model is based on the Nomoto's model and can be seen as an extension to it. The model describes the dynamics between rudder deflection and the boat's velocity vector angle while Nomoto's model reveals that between rudder deflection and the boat's yaw angle. With the proposed model there is no need for a yaw sensor for control if the boat's moving direction can be measured. GPS is a convenient device for that job. Based on the derived model, we apply mixed H2/H∞ control method to design the controller. It can guarantee the robust stability, and as the same time it can optimize the performance in the sense of H2 norm. The experimental data show that the proposed approach is proved to be effective and useful.

Mathematical model of single-propeller twin-rudder ship

Abstract: A mathematical model of a single-propeller twin-rudder ship has been developed from captive and free running model experiments. An open water rudder experiment was carried out to figure out the characteristics of the rudder. Captive experiments in a towing tank were carried out to figure out the performance of a single-propeller twin-rudder system on a large vessel. Interactions between the hull, propeller and twin rudders, including mutual interactions between the twin rudders, were expressed with several coefficients that were calculated from the experimental results at various ship speeds. In the analysis, the unique characteristics of a single-propeller twin-rudder ship, which affects rudder forces, were explained and formulated in the mathematical model. The captive model tests were conducted with zero ship’s yaw rate, so the interaction coefficients, which are influenced by the yaw rate, are determined from free running model experiments. Validation of the mathematical model of a single-propeller twin-rudder system for a blunt body ship is carried out with an independent set of free running experiments, which were not used for determining the interaction coefficients. The validated numerical model is used for carrying out simulations. Based on simulation results, some recommendations have been proposed for installing a single-propeller twin-rudder system.

A suggestion of gap flow control devices for the suppression of rudder cavitation

Abstract: This paper presents the numerical analysis of rudder cavitation in propeller slipstream and the development of a new rudder system aimed for lift augmentation and cavitation suppression. The new rudder system is equipped with cam devices which effectively close the gap between the horn/pintle and movable wing parts. A computational fluid dynamics code that solves the Reynolds-averaged Navier–Stokes equations is used to analyze the flow field of various rudder systems in propeller slipstream. The body force momentum source terms that mimic flow field behind a rotating propeller are added in the momentum equations to represent the influence of the propeller and its slipstream. For detailed explication of the new rudder system’s lift augmentation and cavitation suppression mechanism, three-dimensional flow analysis is carried out. Simulations clearly display the mechanism of the lift augmentation and cavitation suppression. The computational results suggest that the Reynolds-averaged Navier–Stokes-based computational fluid dynamics reproduces the flow field around a rudder in propeller slipstream and that the present concept for a cavitation suppressing rudder system is highly feasible and warrant further study for inclusion of the interaction with hull and mechanical design for manufacturing and operations.

Adaptive Compensation of Aircraft Actuation Failures Using an Engine Differential Model

Abstract: This paper investigates actuator failure compensation for aircraft flight control in a novel framework. A general failure compensation scheme for asymptotic tracking is developed based on a direct adaptive control approach. This control scheme is capable of utilizing the remaining control authority to achieve the desired performance in the presence of unknown and uncertain constant actuator failures occurring at unknown time instants. A nonlinear aircraft model that incorporates independently adjustable engine throttles and ailerons is employed and linearized to describe the aircraft's longitudinal and lateral motion. This model captures the key features of aircraft flight dynamics when in the engine differential mode. The proposed control scheme is applied to a transport aircraft model in the presence of three types of failures during operation: rudder failure, aileron failure, and engine malfunction. Simulation results are presented to assess the effectiveness of this adaptive failure compensation design.

Comparison of the mariner Schilling rudder and the mariner rudder for VLCCs in strong winds

Abstract: A simulation model of a very large crude carrier (VLCC) with either a mariner type Schilling rudder or a mariner rudder was developed from captive and free-running model tests. Kijima’s regression formula was used to predict the hydrodynamic hull forces on the VLCC. To simulate full-scale maneuvering at cruising speed, the constant torque operation of the main engine was assumed. Considering the higher normal lift force and maneuverability of the mariner type Schilling rudder as compared to the mariner rudder, the size of mariner type Schilling rudder is kept smaller as compared to mariner rudder. To compare the efficiency of the two types of rudder system, maneuvering simulations at constant engine torque and course-keeping simulations at various gusting wind speeds and encounter angles were carried out. Based on the simulation results, the two rudder types were compared from the viewpoint of maneuvering and fuel efficiency in windy conditions.

Adaptive Variable Structure Control of Aircraft with an Unknown High-Frequency Gain Matrix

Abstract: This paper presents nonlinear adaptive and sliding-mode flight control systems for the roll-coupled maneuvers of aircraft. It is assumed that the parameters of the aircraft, as well as its high-frequency gain matrix, are unknown. Based on a backstepping design approach, nonlinear control laws (an adaptive variable structure control law and an adaptive control law) for the trajectory control of the roll angle, angle of attack, and sideslip angle using the aileron, elevator, and rudder are derived. The decomposition of the high-frequency gain matrix is used for the derivation of singularity-free flight control laws. An additional advantage of the control laws lies in the choice of design parameters of matrix decomposition for shaping the response characteristics. In the closed-loop system, the roll angle, angle of attack, and sideslip angle trajectories asymptotically follow the reference output trajectories. Simulation results are presented that show that in the closed-loop system, simultaneous longitudinal and lateral maneuvers are precisely performed in spite of the uncertainties in the aircraft parameters using each control system.

Application of Topology Optimization and Manufacturing Simulations - A new trend in design of Aircraft components

Abstract: Structural optimization tools and computer simulations have gained the paramount importance in industrial applications as a result of innovative designs, reduced weight and cost effective products. Especially, in aircraft and automobile industries, topology optimization has become an integral part of the product design process. In this paper nonparametric topology optimization has been applied on a commercial aircraft vertical stabilizer component using ANSYS software. Suitable loads and constraints are applied on the initial design space of the component to accommodate for fin gust, rudder deflection, lateral gust, and other loads experienced by an aircraft during actual flight maneuvering. An integrated approach has also been developed to verify the structural performance and to overcome the problem of nonmanufacturable topology optimization results. Post machining distortions are also simulated by using element deactivation technique first by developing an initial residual stress field through Sequential Coupled Field analysis. CATIA is used to convert the optimized FE model into geometry based CAD model and then virtual machining is done. At the end topology assisted design model is compared with the actual part that is being manufactured for the aircraft. It is inferred that topology optimization results in a better and innovative product design with enhanced structural performance and stability.

Solar pilotless plane

Abstract: The invention relates to a solar unmanned aircraft. In order to overcome the problems of difficult flight control and bad stability of the flying wing solar unmanned aircrafts, the invention adopts the configuration of tip winglets(5) arranged at the outer segments of a large aspect-ratio high wing, a V shaped empennage and a wing(4); the wing(4) is connected with and a fuselage(7) through a bridge wing(3) and a controlling rudder(9) is arranged on the V shaped empennage(8) to realize the pitching and yawing control of the aircraft. Combining the characteristic of the high energy conversion efficiency of a flexible thin film solar battery, the invention lays the flexible thin film solar battery(6) on the wing(4). An engine and propeller propulsion system (1) adopts a haul-in-type, and an equipment cabin (2) is arranged at the front part of the fuselage(7). The solar unmanned aircraft improves the lift-drag ratio of the aerial vehicle, prolongs the operation time and effectively improves the horizontal and the vertical stabilities and maneuverability of the aircraft, thus relieving the problems of bad stability and bad maneuverability of the flying wing configuration.

Autonomous Underwater Vehicle Control in Presence of Waves

Abstract: In this paper, the 6 degrees of freedom equations of motion of an autonomous underwater vehicle (AUV) are described as a linear model and divided into three non-interacting (or lightly interacting) subsystems for speed control, steering and diving. In addition to the model of the AUV dynamics, the first and the second order wave force disturbances, i.e. the Froude-Kriloff and diffraction forces are introduced. Based on the principle of superposition it is possible to represent the AUV dynamics as the sum of low and high frequency motions. An algorithm of non-linear regression for the rationalization of the sub-surface sea spectrum is provided. Two different control designs, based on H2 and H∞ methodologies, were applied to the diving and course control of the vehicle considering the presence of the wave disturbances. The work is based on the slender form of the Naval Postgraduate School AUV, considering that the subsystems can be controlled by means of two single-screw propellers, a rudder, port and starboard bow planes and a stern plane. The wave effect on the corresponding motions of the underwater vehicle is analyzed and evaluated considering the AUV operating at different depths and different sea states using both controllers. The model presented here can be a useful simulation tool to predict the underwater vehicles behavior in different mission scenarios.

Simulation of the Incompressible Viscous Flow around Ducted Propellers with Rudders Using a RANSE Solver

Abstract: Within EU Project SUPERPROP, fishing vessels have been studied. Usually their propulsion units consist of ducted propellers in order to provide large thrust in trawling. Rudders may significantly influence the performance of ducted propellers especially if they are located at short distance from the duct. This paper summarizes some of the CFD calculations performed as the starting point for the development of a new propeller design for a reference fishing boat. The basic design performance particulars were obtained from the analysis of the existing conventional ducted propeller installed in the ship. The flow around the original propeller geometry and around one of the alternative designs is simulated using RANS code FINFLO. As a part of the project the rudder blockage effect has been investigated using a quasi-steady approach.

ADRC based ship tracking controller design and simulations

Abstract: Because of the strong non-linearity, uncertainty and typical underactuated properties, as well as the restraints of rudder, the design of ship tracking controller is yet a challenge work In this paper, the problem was investigated by utilizing the active disturbance rejection control (ADRC) method Firstly, the ADRC was introduced briefly and the characteristics of ship tracking motion were analyzed And the systempsilas nonlinear mathematical model with restraints and uncertainties was established Then the system was described as a series structure, and the tracking ADRC controller was designed based on a kind of three order polynomial trajectory planning algorithm At last, the simulations were performed The results show that the controller designed can achieve high precision on ship tracking control and has strong robustness to ship parameter perturbations and environment disturbances

Alleviation of Atmospheric Flow Disturbance Effects on Aircraft Response

Abstract: Since the air is the element of flying, air motion is an essential parameter in aeronautics. This paper gives an overview of the results of offline simulations, full flight simulator studies and results from in-flight simulation experiments to investigate the alleviation of atmospheric flow disturbance effects on aircraft response. The studies are part of the DLR project “Weather and Flying” aiming at the improvement of flight operation and safety in adverse weather conditions. Gusts and turbulence strongly affect the passenger comfort and the safety of aircraft. Another important air mass motion adversely affecting aircraft operation is wake vortex. This well known hazardous flow field is produced by aircraft themselves. Active control technology can be applied to alleviate these flow disturbance effects on aircraft motion in case of an encounter. DLR is developing the Integrated Ride and Loads Improvement System (IRLIS) to cope with the phenomena mentioned above. It can be shown that the aircraft response encountering natural and aircraftinduced (wake vortex) turbulence can be improved significantly by a feed-forward controller. Based on a forward-looking sensor, the controller generates aerodynamic surface deflections to counter the vertical accelerations generated by gusts as well as the roll response induced by lift variations along the wing span. For this investigation it is assumed that a LIDAR sensor is able to provide the necessary flow field information ahead of the a/c. In addition to the standard control surfaces (elevator, aileron and rudder) the a/c is supposed to be equipped with special flaps for independent direct lift control. Simulation results show a clear tendency that IRLIS can significantly improve the situation in adverse atmospheric flow fields.

Steering actuator for a steer-by-wire ship's control system and method for operating said steering actuator

Abstract: The invention relates to a steering actuator (1) for a ship's control system, designed as a linear electromechanical actuator and comprising an electric motor (2), a controller (11) that is connected to the electronic control unit of the ship's control system (ECU) via a CAN bus and an angle sensor (12) that is connected to the controller (11) for determining the angular position of the rudder (13). The electric motor (2) is designed as a vector-controlled brushless motor.

Differential tiller arms for marine vessels

Abstract: Advanced steering system designs for marine vessels which incorporate non-linear tiller arms for rudder control, designed for creating different turning radii for discrete rudders. Differential tiller anus are utilized to create distinct angular displacement of the separate rudders in turning maneuvers, which enhance control and maneuverability of the marine vessels.

Fixed point holding system for one-shaft one-rudder type bow thruster ship and fixed point holding method therefor

Abstract: PROBLEM TO BE SOLVED: To provide a fixed point holding system for one-shaft one-rudder type bow thruster ship having a tunnel type bow thruster and a fixed point holding method therefor, wherein the ship can be recovered to a slant rearward fixed point when the ship moves in a slant forward direction. SOLUTION: This fixed point holding method for one-shaft one-rudder type bow thruster ship having a tunnel type bow thruster is carried out in such a way that when the ship returns back to its target point placed at the rearward location of a hull or placed at a slant rearward location, the ship moves toward the target point in a lateral direction of the hull after the ship moves in the rearward direction of the hull and reaches up to a position where the target point occupies a front location as viewed from a right lateral side from the hull. COPYRIGHT: (C)2010,JPO&INPIT

Propulsion and steering arrangement

Abstract: A propulsion and steering arrangement for a vessel (40) comprises a screw propeller (2) and a rudder (10) arranged behind the propeller (2). A fairing (6) at a tail end of the propeller (2) and a bulb-shaped body (20) provided on a rudder blade (11) of the rudder (10) form a streamlined body which is continuous except for a narrow gap between the fairing (6) and the bulb-shaped body (20) to allow a swinging movement of the bulb-shaped body (20) relative to the fairing (6) when the rudder blade (11) is turned. A tail end of the rudder blade (11) is provided with a movable flap (12).

Numerical optimization of hull/propeller/rudder configurations

Abstract: The new framework of the global economy has stimulated and expanded the shipbuilding and shipping industry, especially in Asia in the twenty-first century. This induces urgent and high requirements on designing and building both conventional and new types of ships with high performance, such as high speed, manoeuvrability, seaworthiness and so on. Simultaneously, environmental concern and a constant increase in the price of fuels have put more pressure and demands on designers to minimize the energy consumption, maximize the protection of the marine environment and maximize the efficiency and economy of maritime operations. As the “heart” of a ship, the propulsion system has to be improved continuously to satisfy these requirements. Therefore, how to optimize the interaction between a ship’s hull, propeller and appendages, while minimizing the side effects of cavitation on the surface of propeller and rudder, plays an important role in improving ship performance and increasing the economy of ship operations. The work presented in this thesis is a research project at the Rolls-Royce University Technology Center (UTC) at Chalmers University of Technology. The objective of this project is to numerically simulate, analyze and automatically optimize the interaction between a ship hull, a propeller and a rudder. All the numerical calculations are carried out by the software SHIPFLOW, a RANS method-based code. The effect of the propeller is simulated by a lifting line method or a lifting surface method via body force. Two turbulence models, i.e. k-ω SST and EASM, are applied. Both gradient-based and genetic algorithm optimization methods are used in optimizations. In order to systematically investigate hull/propeller/rudder interaction and to verify and validate the numerical method, a series of computations are made for (1) a bare hull, (2) a propeller in open water, (3) a 3-D rudder in a free stream, (4) a hull/propeller combination, (5) a propeller-rudder combination in open water and (6) a hull/propeller/rudder combination. Problems with the lifting surface method are, however, identified when a rudder is added behind the propeller. The problem is resolved by adopting a lifting line method coupled with the RANS method. Among the different cases, three particularly interesting ones are optimized: (1) a single cavitating propeller in a given wake, (2) the hull/propeller configuration, and (3) the hull/propeller/rudder configuration. The project has yielded a validated numerical model for bare hull resistance, propulsive factors, open water propeller characteristics with or without rudder and hull/propeller/rudder configuration flows; a framework for automatic optimization and a design tool for cavitating and non-cavitating propellers. The main conclusion of this thesis is that coupling a RANS solver and a potential flow-based propeller model via body forces can yield a useful and practical tool for designing and optimizing hull/propeller/rudder configurations for both academic and industrial purposes.

Method for improving the ice-breaking properties of a water craft and a water craft constructed according to the method

Abstract: A method of providing a watercraft, especially an icebreaker or a cargo ship, tanker or similar transport vessel, with improved ice penetration characteristics and a watercraft manufactured according to the method, which watercraft has a hull (1) with a first end (2) and a second end (3) and which is equipped at said second end with a propulsion arrangement, which provides the main propulsive thrust of the watercraft, while the watercraft moves with either end ahead, and the steering of the watercraft, whereby said second end (3) of the watercraft is shaped and designed so that it, as such, has efficient ice penetration characteristics. Said propulsion arrangement is chosen so as to include at least three propulsion devices, at least the majority of which are rudder propeller devices (4) and which are arranged at least at two different distances from said second end (3) of the watercraft so that when the watercraft moves in ice or ice build-ups said second end (3) ahead, the propeller with one or more propulsion devices located near said second end (3) of the watercraft is arranged to break ice and the propeller with one or more propulsion devices located farther away from said second end (3) of the watercraft is arranged to remove disintegrated ice or ice chunks away from the ice build-up.

Mechanisms and methods for providing rudder control assist during symmetrical and asymmetrical thrust conditions

Abstract: Rudder assist mechanisms and methods are capable of being operably connected to an aircraft's rudder control system. The rudder assist mechanisms have over-the-center spring biasing functions so as to cause either substantially no spring force (i.e., when the linkage is over the spring-bias center) or substantially all spring force (i.e., when the linkage is left or right of the spring-bias center) to be exerted on the rudder control system. The rudder assist mechanism may include a control spring assembly, and a linkage assembly which operably connects the control spring assembly to the rudder control assembly. The linkage assembly is moveable between a null position wherein substantially no spring force of the control spring assembly is transferred to the rudder control system by the linkage assembly and right and left spring-biased positions wherein right and left spring forces of the control spring assembly are transferred to the rudder control system, respectively.

Rudder post for rudders for water vehicles

Abstract: The rudder post ( 40 ) for rudders for water vehicles has end sections ( 41, 42 ) made of a metallic material, in particular of wrought iron, and a mid post section ( 45 ) made of a nonmetallic material connected with the end sections so that the rudder post has a relatively low weight even for a very big length by maintaining a high flexural strength and torsion stiffness.