Control of dynamic trim for planing vessels with interceptors in terms of comfort and minimum drag

Nowadays, interceptors are often used to decrease total resistance and enhance comfort by reducing dynamic trim for high-speed planing vessels. They can be controlled manually as well as automatically by using a suitable closed-loop control system. Thus, in the present study, an automatically controllable system is presented to minimize the total resistance by reducing the dynamic trim in calm water. To reach this aim, a mathematical model which can represent the 2 degree of freedom vertical motion of a prismatic planing vessel is presented. The coefficients used in the model are calculated by using the Savitsky method. The standard dynamic trim angle and the optimum ones in terms of resistance are calculated by using the same method. For control action, a linear full state feedback control strategy (linear quadratic regulator) is applied, and instantaneous blade heights are found considering the change in forward speed. Therefore, the control-oriented model is able to change the blade height to reach the optimum trim angle in terms of the total resistance of the vessel for different forward speeds and speed profiles. The results show that the designed linear quadratic regulator control strategy is successful for reference trim tracking problems

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

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

Performance Analysis and Prediction of High Speed Planing Craft

Merged with duplicate record 10026.1/2462 on 06.20.2017 by CS (TIS)A comprehensive and critical review of literature pertaining to the study of planing craft is given within this work. This study includes monohull design, analysis and performance prediction for flat water; many features of the planing characteristics, including dynamic stability, the use of stepped hullforms, re-entrant transoms and flow characteristics are detailed. Work on the rough water seakeeping analysis of planing craft is also given, and furthermore, literature pertaining to planing catamaran design and performance prediction, and on the ground effect is cited. Mathematical modelling approaches are discussed and it is explained that there is still much progress to be made in this area before accurate and reliable analytical prediction methods become available. The method of matched asymptotic expansions and also a proposed force-mathematical model are shown to be particularly suitable to the prediction of planing craft forces and moments, the first method being highly analytical and the latter requiring a semi-empirical approach to be adopted. A discussion is given of the physical phenomena responsible for the characteristics of planing craft and their interrelation. It is also discussed how modem craft are attaining higher and higher speeds, and a result of this is that the dynamic characteristics of the craft, including the flow conditions, are substantially different to those of more conventional craft. This modem very high speed regime of planing has been analysed and identified in this study under the new title of 'Alto-planing'. Further discussion of planing craft form and design concepts are persued, including details of the design of catamarans and more novel forms. A new computer-based prediction method is presented, which includes prediction methods for trim tabs and an aero foil. The ability of the program to allow the designer to vary given inputs of the hull data is explained, and a systematic variation of all the input characteristics is detailed. An optimisation procedure is offered and it is observed that this new prediction method can provide the designer with as much data as required for analysis of the form, a distinct advantage over current planing craft prediction software. Validation is undertaken by comparison with data from trials results, model test data and comparison with other prediction techniques. A discussion of current prediction methods is given. Finally, the aerodynamic characteristics of alto-planing craft are researched in detail, by means of a systematic series of model tests. Analysis of the results have extended the previous empirical limits and have furthermore segregated and quantified the components of the aerodynamic effects, including the aerodynamic resistance and the change in hydrodynamic running conditions due to the aerodynamic effects. An enhanced and novel prediction method is given, which is used to provide illustrative examples of the aerodynamic characteristics of alto-planing craft

Statistical Analysis of Wedge Effect on the Seakeeping of a Planing Hull in Irregular Waves at the Onset of the Planing Region

In the current paper, different experiments are conducted on a high speed planing craft in irregular waves, with and without a wedge. Performance and seakeeping aspects of these planing hulls in the form of trim, rise-up, and resistance in regular waves and heave, pitch, bow, and center of gravity (CG) acceleration in irregular waves are extracted in time series. Irregular waves represent sea state 3 with 12cm height and peak period of 1.66. A model length of 2.63m and 1:5 scale is considered and all data for irregular waves are scaled, as well. The deadrise angle is constant and is taken to be 24 degrees. The targeted experimental tests are conducted for four longitudinal Froude numbers of 1.0, 1.18, 1.37, and 1.57, which are all in the planing regime. The results are analyzed for the mean height of wave, significant wave height, RMS, and spectrum. The comprehensive study of wedges' effects is also presented which indicates that a wedge can decrease the motions and accelerations, exceedingly. Ultimately, the obtained results are compared against those by Fridsma (1971) and Soletic (2010) and it is demonstrated that motions and accelerations are indeed reduced

Enhanced SPH modeling of free-surface flows with large deformations

The subject of the present thesis is the development of a numerical solver to study the violent interaction of marine flows with rigid structures. Among the many numerical models available, the Smoothed Particle Hydrodynamics (SPH) has been chosen as it proved appropriate in dealing with violent free-surface flows. Due to its Lagrangian and meshless character it can naturally handle breaking waves and fragmentation that generally are not easily treated by standard methods. On the other hand, some consolidated features of mesh-based methods, such as the solid boundary treatment, still remain unsolved issues in the SPH context. In the present work a great part of the research activity has been devoted to tackle some of the bottlenecks of the method. Firstly, an enhanced SPH model, called delta-SPH, has been proposed. In this model, a proper numerical diffusive term has been added in the continuity equation in order to remove the spurious numerical noise in the pressure field which typically affects the weakly-compressible SPH models. Then, particular attention has been paid to the development of suitable techniques for the enforcement of the boundary conditions. As for the free-surface, a specific algorithm has been designed to detect free-surface particles and to define a related level-set function with two main targets: to allow the imposition of peculiar conditions on the free-surface and to analyse and visualize more easily the simulation outcome (especially in 3D cases). Concerning the solid boundary treatment, much effort has been spent to devise new techniques for handling generic body geometries with an adequate accuracy in both 2D and 3D problems. Two different techniques have been described: in the first one the standard ghost fluid method has been extended in order to treat complex solid geometries. Both free-slip and no-slip boundary conditions have been implemented, the latter being a quite complex matter in the SPH context. The proposed boundary treatment proved to be robust and accurate in evaluating local and global loads, though it is not easy to extend to generic 3D surfaces. The second technique has been adopted for these cases. Such a technique has been developed in the context of Riemann-SPH methods and in the present work is reformulated in the context of the standard SPH scheme. The method proved to be robust in treating complex 3D solid surfaces though less accurate than the former. Finally, an algorithm to correctly initialize the SPH simulation in the case of generic geometries has been described. It forces a resettlement of the fluid particles to achieve a regular and uniform spacing even in complex configurations. This pre-processing procedure avoids the generation of spurious currents due to local defects in the particle distribution at the beginning of the simulation. The delta-SPH model has been validated against several problems concerning fluid-structure interactions. Firstly, the capability of the solver in dealing with water impacts has been tested by simulating a jet impinging on a flat plate and a dam-break flow against a vertical wall. In this cases, the accuracy in the prediction of local loads and of the pressure field have been the main focus. Then, the viscous flow around a cylinder, in both steady and unsteady conditions, has been simulated comparing the results with reference solutions. Finally, the generation and propagation of 2D gravity waves has been simulated. Several regimes of propagation have been tested and the results compared against a potential flow solver. The developed numerical solver has been applied to several cases of free-surface flows striking rigid structures and to the problem of the generation and evolution of ship generated waves. In the former case, the robustness of the solver has been challenged by simulating 2D and 3D water impacts against complex solid surfaces. The numerical outcome have been compared with analytical solutions, experimental data and other numerical results and the limits of the model have been discussed. As for the ship generated waves, the problem has been firstly studied within the 2D+t approximation, focusing on the occurrence and features of the breaking bow waves. Then, a dedicated 3D SPH parallel solver has been developed to tackle the simulation of the entire ship in constant forward motion. This simulation is quite demanding in terms of complexities of the boundary geometry and computational resources required. The wave pattern obtained has been compared against experimental data and results from other numerical methods, showing in both the cases a fair and promising agreement

Vibration Control for a Coupled Pitch- roll Ship Model Via a Negative Cubic Velocity Feedback Control

One of the most essential ship reactions to waves is roll motion. Due to the intricacy of ship wave interactions and their sensitivity, predicting such a reaction is extremely challenging. Because vibration motion is an undesirable occurrence, it must be removed, decreased, or controlled. A coupled Pitch- roll ship model with negative cubic velocity feedback control subjected to parametric excitations is premeditated and solved in this paper. The method of multiple time scales is applied to scrutinize the response of the two modes of the system neighbouring the simultaneous sub-harmonic, and internal resonance situation. Besides, the steady-state solution is determined through the Rung-Kutta Method (RKM) of fourth order. Stability of the steady state solution near this resonance case is discussed and studied applying Lyapunov’s first indirect method and Routh- Hurwitz criterion. The influences of the different parameters on the steady state solution are reconnoitred and discussed. The controller effects on the stability are clarified. Simulation results are accomplished with the help of MATLAB and Maple software programs

Experimental Study of High-Speed Boats with Suspended Flaps for Reducing the Slamming Forces

This thesis consists of two parts. In the first part a small-scale high-speed monohull boat was fitted with a suspended flap under the bottom. The author tested shock absorbers for this boat, and worked on data analysis from a few initial test runs. The boat tests were performed during a few hours in a single day and the data are far too scarce to draw any conclusions. The second part of the thesis concerns multi-body numerical analysis of a suspension boat that consists of an airborne centerhull and four suspended sponsons. No simulations of boat dynamics in waves were performed. First, a brief overview of slamming problem and techniques used to reduce the vertical acceleration was conducted, full description of proposed mechanism and the instruments used to evaluate the boat behavior equipped with the mechanism, then boat testing and data analysis was illustrated. Second, advanced dynamic numerical model for the suspension boat with four sposons was developed

Investigations of Waterjet/Hull Interaction Effects

A waterjet propulsor operates in a different way than a conventional propeller. This makes it hard to use the same concepts for studying the thrust and powering of these systems. The net thrust of the propeller can be obtained by measuring the force transmitted through its shaft, but since there is not just a single contact point between the waterjet unit and the hull, the net thrust measurement cannot be easily accomplished for the waterjet unit. Instead another thrust force, which is simpler to measure, is defined to express the magnitude of the waterjet unit thrust. The new thrust definition is called the gross thrust and is obtained by the measurement of the momentum flux change through the waterjet control volume. In this thesis, it has been tried to find out the links between these two thrust forces. The original work fulfilled in this thesis can be divided in to two main parts. The first part is an introduction to an iterative algorithm for modelling the effect of the waterjet on the hull. The algorithm is called the Pressure Jump Method. This method is based on the fact that the resistance forces are balanced with the thrust force created by the head increase through the waterjet pump. In this thesis, the Pressure Jump Method is coupled with a potential flow solver capable of non-linear free-surface modelling but there is not any limitation for the method to be used in combination with, e.g., RANS solvers. Validation and verification of the Pressure Jump Method is accomplished by comparing the computational results with experimental data available from a test case. The second part of the thesis is dedicated to investigate the individual contribution of different parameters that may influence the thrust deduction of a waterjet-propelled craft. In this part the results obtained from the Pressure Jump Method along with some extra calculations are employed to find out the dominant parameters, which contribute to the thrust deduction

The Design and Development of a Recirculating Water Channel: A Critical Assessment

The thesis critically assesses the design, development and equipment of a recirculating water channel: the channel in the Department of Engineering at the University of Liverpool It is intended to provide a valuable reference manual for such facilities. The channel is a versatile item of equipment wliich can be used in four different configurations:- as a free surface water channel, including the ability to simulate shallow water and also to generate regular head waves; as a water tunnel; as a free surface cavitation channel or as a cavitation tunnel, with a minimum pressure of 1/30 atmosphere. Uie working section is 3.66m long, 1.4m wide and 0.84m deep with a maximum water speed of 5.7 m/s. The thesis includes: 1. A description of the water channel in its four configurations and earlier development of a jet injection system to overcome a velocity defect at the water surface. The flow velocity in tlie working section and methods of flow measurement are discussed together with new measurements of turbulence velocity and the time to reach equilibrium speed. The wavemaker has been shown to produce waves which are good approximations to a sinusoidal shape at low water speeds and can be maintained over a long period of time. At higher speeds it was found that the wave shape progressively degenerated; methods for improving the wave-maker are suggested. 2. The force measuring equipment is reviewed including a dynamometer for ship models and a miniature version for much smaller forces obtained on sea shells at low water speeds. 3. The principles of model testing are discussed together with a technique for measuring the actual wetted surface area in the case of fast ships. A new experimental and theoretical investigation into the effect of model size relative to the size of the working section is reported. 4. A final chapter reviews the design of the flume and all its equipment. Suggestions are made for further improvements suitable for a future water channel