Transom Flaps Research Articles

Introducing a new flap form to reduce the transom waves using a 3-D numerical analysis

The present article introduces a new and innovative shape for the stern flap which modifies the flow of water underneath and around the transom stern. This is done in such a manner that the transom wave known as 'rooster tail' is reduced to a minimum, at different speeds. This hydrodynamic effect can be considered a radar signature reduction. Fuel consumption and resistance reduction are other advantages of the rooster tail reduction. To explore the effects of transom flap, a complete set of parametric studies is conducted and a three-dimensional numerical simulation of the transom stern flow, based on the FVM-VOF schemes in Ansys-CFX software, is presented. Three Froude numbers at four different trim angles are chosen and effects of transom flap on the rooster tail are probed in each case. Comparison of the numerical solutions with results of the existing empirical formula gives favourable agreement.

A computational tool for the design of ride control systems for fast planing vessels

An effective method to reduce the violent motion behaviour of fast planing vessels in waves may be found in the application of active control devices in conjunction with advanced motion control systems. This study aims to develop a computational tool for the design and optimization of these ride control systems for high speed planing monohulls. Hydrodynamic characteristics of both transom flaps and interceptors are determined by systematic series of model test experiments in the towing tank of the Laboratory of Ship Hydromechanics at the Delft University of Technology. Transom flap results at downward deflection angles are validated with formulations found in literature. In addition, experiments at up angle flap positions have been performed to increase the range of application for motion control purposes. The hydrodynamic performance of the interceptors and transom flaps are compared in order to determine their efficiency. The experimental data was implemented in a nonlinear time domain mathematical model that can predict the seakeeping behaviour of fast monohulls. Simulations demonstrate the improvement in motion behaviour of a fast planing vessel with a ride control system sailing in head waves. 2011 - IOS Press and the authors. All rights reserved.

Frequency Domain Study of Longitudinal Motion Attenuation of a Fast Ferry Using a T-Foil

Longitudinal, heave and pitch, motion of ships in response to encountered waves can be smoothed using moving submerged wings, like transom flaps or a T-foil under the bow. Recently a 3 DOF detailed model of the surge, pitch and heave motions of a fast ferry has been developed, in terms of a structure of twelve transfer functions. On the basis of this model the most effective control for motion attenuation using a T-foil has been determined in the frequency domain, both for unlimited or saturated action. The results have been obtained by point to point exploration and depict amplitude and phase profiles of the controller. This result is useful to orientate linear control design. A first preliminary linear controller is presented.

Feedback Stabilization of High-Speed Planing Vessels by a Controllable Transom Flap

This paper focuses on the mitigation of porpoising instability of high-speed planing vessels using controllable transom flap and dynamic feedback. A control oriented model that captures both steady-state and dynamic characteristics is presented and used to facilitate the model-based control design. A nonlinear controller is developed based on the feedback linearization method to achieve asymptotic stability of the planing boat, thus avoiding porpoising at high speeds. We first show that the full-state nonlinear dynamic model describing the ship motion is not feedback linearizable. A state transformation is then constructed to decompose the model into a linearizable subsystem and a nonlinear internal dynamic subsystem. A reduced order state feedback is shown next to stabilize the planing vessel motion around the equilibrium point. Analysis of the region of attraction is also performed to provide an assessment of the effective safe operating range around the equilibrium point.

A Preliminary Investigation Into Two Speed Operation of Ships

Some ship types, such as many surface warships, some motor yachts and some cruise ships are required to operate efficiently at two different speeds: low speed cruise; and high speed sprint. In the past, a single optimised hull form has been developed, with a balance between the different roles, based on the requirement set, and on the operations envisaged. In order to investigate the possibilities of reconfigurable hull and propulser configurations for the two speed regimes, a preliminary investigation was undertaken, based on a 90-100m Offshore Patrol Vessel (OPV). As a result of this work it has been shown that significant improvements in low speed powering performance, and hence range, for a monohull designed for high speed are possible by: 1. use of a retractable single screw thruster; 2. fitting waterjet inlet covers, and evacuating water from the inlet; 3. fitting an adjustable transom flap; and 4. making it possible to adjust the trim to trim by the bow. Larger improvements could be achieved if major changes to the stern shape are possible. The use of an adjustable bulbous bow has been shown to be of only marginal benefit, and is it is not recommended that this be considered further for this application. © 2006: Royal Institution of Naval Architects.

OVERVIEW OF A RESEARCH ON ACTUATORS CONTROL FOR BETTER SEAKEEPING IN FAST SHIPS

The paper is an overview of a research initiated seven years ago by three groups of three universities, under the auspices of a Spanish shipbuilder. The research aims to improve the seakeeping performances of fast ferries, by using moving appendages such transom flaps and T-foil. There is a problem of control design to move the actuators in adequate way, to counteract the effect of encountered waves. The research focuses on alleviation of seasickness. Several aspects have been covered along the research, motivating a long series of papers. The overview gives an ordered account of the main results, with the corresponding references. Main results concerning seasickness and navigation, prediction of seasickness during ship design, experimental modelling, control design and experimental verification, are presented.

VERTICAL PLANE MOTION OF HIGH SPEED PLANING VESSELS WITH CONTROLLABLE TRANSOM FLAPS: MODELING AND CONTROL

Hydrodynamics of porpoising instability in vertical-plane motions of high-speed planing vessels have been investigated for years. However, not much work has been published on dynamic control of vertical-plane motions of planing boats by controllable appendages. In this paper, effects of controllable transom flaps on heave/pitch motion characteristics of high-speed planing vessels are investigated. A control-oriented nonlinear model is derived first for the high-speed prismatic planing craft equipped with a controllable transom flap in the calm water. Then, effects of different static flap deflections on the ship's equilibrium running attitude and vertical-plane motion stability are analyzed. Analysis shows that porpoising cannot be avoided at high speeds by presetting static transom flap deflections through static feedforward control. An LQR feedback controller is designed to achieve local asymptotical stability.

Fast ships models for seakeeping improvement studies using flaps and T-foil

Fast ships are taking a relevant role with a clear interest for military purposes. Fast sea transportation encounters several problems to be solved. This article refers to the difficulties originated by brisk vertical motions. The waves encountered by fast ships induce such vertical motions, and this has negative effects: navigation risks, sea sickness, structural damages, and load displacement. It is also interesting for military uses to stabilize the ship when an aircraft is landing or when precision firing is required. By means of submerged actuators, it is possible to alleviate vertical motions. In this research, a pair of transom flaps and a T-foil near the bow are used to counteract the waves. These actuators must move with the maximum efficiency, taking into account the dynamical characteristics of the ship. As a consequence, there is a problem of automatic control design. To carry out this design, it is important to obtain mathematical models of all the aspects involved in the problem: the ship, the waves, the actuators, and the effect on crew and comfort. The aim of this paper is to present the development of these models and the use of them for problem analysis and control design.

Advances in the 6 DOF motions model of a fast ferry

In the present stage of our research on the use of moving submerged appendages for motions smoothing of a fast ferry, a 6 DOF motions mathematical model of the ship for control studies is under development. This model is needed from the very beginning of the next experimental research, because we are going to use an autonomous scaled physical model of the ship, and we need to design a basic course control. The actuators for motion smoothing of the fast ferry are two transom flaps, two lateral fins and a T-foil. These actuators must be considered by the 6DOF model. In a previous paper we discussed a first principles approach to build the mathematical control-oriented model, using data from a CFD program. On the basis of these principles, now we present new developments of the 6DOF model. In particular, we study the ship dynamic behaviour for heading angles of 180°, 150° and 90°. Some hints are obtained to predict how the model will change for other heading angles.

Autonomous fast ship physical model with actuators for 6DOF motion smoothing experiments

This paper describes a new experimental system that has been recently developed for a research on vertical motion alleviation of fast ferries. The case of a fast ferry with a pair of transom flaps, lateral fins and a T-foil is considered. All these actuators should be moved in the most effective way, and an appropriate control strategy must be obtained and tested. A scaled physical model of the fast ferry has been built, with moving actuators and a distributed monitoring and control system. The research considers 6DOF motion attenuation, for any ship's heading. For this scenario, an autonomous physical model, not to be towed, is required. The physical model includes two scaled waterjets, with the jet orientation under control. The ship has no rudder. Heading and motion alleviation control includes many sensors and actuators. As a good practical control solution, a distributed architecture based on the CANbus has been devised. There is a set of microcontrollers and an embedded PC as coordinator. The microcontrollers for the actuators simulate the time behaviour of hydraulic cylinders. The microcontrollers for sensors include signal conditioning functions. There is a digital radio communication with an off-shore monitoring system. The off-shore system can display the present and the recorded experiments with animated 3D graphics. The complete experimental platform can be used as an Internet laboratory. The system can be easily tailored for use in real ships.

A Research on Motion Smoothing of Fast Ferries

This paper is about a research on the use of active appendages to smooth the motions of fast ferries. According to BAZAN specifications, the research focused on a fast ferry with a T-foil and transom flaps. A collaboration of three research groups, with the experimental support of CEHIP AR was established to accomplish the objectives. The research was scheduled as two main steps. A first step of control-oriented modelling has successfully been achieved. The second step is dedicated to control design and experimental evaluation, seeking for the best solution. First experimental results confirm good expectations with the use of the active controlled appendages. This paper describes the main aspects of the research: the problem to be solved, the methodology and fulfilment of the research project, and the most relevant results obtained.

Control Code Generator Used for Control Experiments in Ship Scale Model

After a study of control design to get a good candidate for testing, it comes a step of experimental confirmation. The general objective of the research is to smooth the vertical motions of a fast ferry. A T-foil and transom flaps are added to a scaled down replica of the fast ferry. These appendages can move under control. So there is a control system installed on the replica, that moves the appendages using motors, and measures the main variables of the ship and actuators motions. This control system is based on an industrial PC with electronic interfaces for motors and sensors. The control algorithm obtained by the design, must be implemented as real-time control software, to be executed on the industrial PC. For a fast and easy translation from design to real-time application, a new software tool has been developed. This tool generates directly C++ code, easy to compile, from a graphical description of the control. With this tool, the experiments have been achieved in short time. During experiments, several non expected circumstances appear, but this was not a problem: the tool allows for an easy improvement of the original design. The paper describes the tool and its use during experiments.

A Simulation Tool for a Fast Ferry Control Design

The research considers a fast ferry with active appendages (actuators): a T-foil near the bow and transom flaps. The objective is to attenuate the ship's vertical motions. There is a problem of control design, to move the actuators in the most effective way. For an easy and safe control study, a simulation tool has been developed using MATLAB and SIMULINK: a modular architecture results where it is easy to integrate control strategies to be analysed. Simulated experiments can be run with the tool, to see the behaviour of the important variables: vertical motions of the ship, motions of the actuators, sea-sickness incidence, etc. The paper describes the simulation tool from a functional point of view, and explains some details of the main parts of its internal structure.

Experimental Study of Controlled Flaps and T-Foil for Comfort Improvement of a Fast Ferry

Fast ships can suffer important negative effects from vertical accelerations. The sea-sickness of passengers is related, in a cumulative form, to these accelerations. Our research deals with the alleviation of vertical accelerations, using appendages that can move under control to counteract each incident wave: a T-foil near the bow and transom flaps. After a long modelling work, involving experiments in a towing tank institution, the conditions for the study of control design have been established. First experimental confirmations of the efficacy of controlled appendages have been achieved. A well tuned P.D. has been tested, with very promising results. The paper begins with a short recapitulation of the previous research. Next, the paper focus on the experiments with a replica with appendages.

Pitch Stabilization for Surface Combatants

ABSTRACTPitching is one of the most damaging motions for a ship, and is the obvious choice after rolling for reduction to improve ship operability. Although SWATHs or bigger monohulls have greater operability, they are often costly. Therefore, some method of stabilizing pitch on existing combatant hulls should be found. Historical research has shown that devices such as transom flaps and bow fins are ineffective or undesirable, but canted rudders show some promise. Using criteria for ASW and mobility operations, a destroyer hull equipped with large canted rudders using rudder pitch stabilization (RPS) was modeled on seakeeping evaluation programs. Its motions and operability were compared with a baseline hull (no RPS) as well as a SWATH and a larger Seakeeping Monohull. RPS reduced pitch motions 30–40% and improved operability 6–11% over the baseline hull, making its seakeeping performance comparable to the SWATH and Seakeeping Monohull. The use of high‐lift devices can provide the same performance with reasonably sized rudders. We recommend a program to further develop pitch stabilization using high‐lift canted rudders, including development of high‐lift foil technology and small‐scale validation of the RPS concept.