A Lagrangian approach to nonlinear modeling of anti-roll tanks

This paper presents two novel nonlinear models of u-shaped anti-roll tanks for ships, and their linearizations. In addition, a third simplified nonlinear model is presented. The models are derived using Lagrangian mechanics. This formulation not only simplifies the modeling process, but also allows one to obtain models that satisfy energy-related physical properties. The proposed nonlinear models and their linearizations are validated using model-scale experimental data. Unlike other models in the literature, the nonlinear models in this paper are valid for large roll amplitudes. Even at moderate roll angles, the nonlinear models have three orders of magnitude lower mean square error relative to experimental data than the linear models.

Antispin thrust allocation for marine vessels

In extreme weather conditions, thrusters on ships and rigs may be subject to severe thrust losses caused by ventilation and in-and-out-of-water events. When a thruster ventilates, air is sucked down from the surface and into the propeller. In more severe cases, parts of or even the whole propeller can be out of the water. These losses vary rapidly with time and cause increased wear and tear in addition to reduced thruster performance. In this paper, a thrust allocation strategy is proposed to reduce the effects of thrust losses and to reduce the possibility of multiple ventilation events. This thrust allocation strategy is named antispin thrust allocation, based on the analogous behavior of antispin wheel control of cars. The proposed thrust allocation strategy is important for improving the life span of the propulsion system and the accuracy of positioning for vessels conducting station keeping in terms of dynamic positioning or thruster-assisted position mooring. Application of this strategy can result in an increase of operational time and, thus, increased profitability. The performance of the proposed allocation strategy is demonstrated with experiments on a model ship.

Nonlinear container ship model for the study of parametric roll resonance

Parametric roll is a critical phenomenon for ships, whose onset may cause roll oscillations up to +-40 degrees, leading to very dangerous situations and possibly capsizing. Container ships have been shown to be particularly prone to parametric roll resonance when they are sailing in moderate to heavy head seas. A Matlab/Simulink parametric roll benchmark model for a large container ship has been implemented and validated against a wide set of experimental data. The model is a part of a Matlab/Simulink Toolbox (MSS, 2007). The benchmark implements a 3rd-order nonlinear model where the dynamics of roll is strongly coupled with the heave and pitch dynamics. The implemented model has shown good accuracy in predicting the container ship motions, both in the vertical plane and in the transversal one. Parametric roll has been reproduced for all the data sets in which it happened, and the model provides realistic results which are in good agreement with the model tank experiments.

Analysis of ship roll gyrostabiliser control

The use of dedicated spinning wheels that generate gyroscopic forces for reducing the roll motion of ships was considered and tested over 100 years ago. These devices, known as gyrostabilisers, presented a remarkable performance, but they fell into disuse due to their relatively large size and, primarily, due to the inability of the control systems to maintain performance over an extended envelope of sea states and sailing conditions (speed and heading relative to the waves). To date, advances in materials, mechanical design, electrical drives, and computer control systems have resulted in a revitalized interest in gyro-stabilisers for ships. This paper revisits the modelling of the coupled vessel-gyrostabiliser and delves into the associated gyrostabiliser control design problem. It also describes design trade-offs and potential performance limitations. A simulation study based on a navy patrol vessel is presented.

Death on the front page : “Awesome things” and this thing called humanity

It has been called “the world’s worst recorded natural disaster,” and “the largest earthquake in 40 years,” galvanizing the largest global relief effort in history. For those of us involved in the discipline and/or the practice of communications, we realized that it presented a unique case study from a number of perspectives. Both the media and the public became so enraptured and enmeshed in the story of the tsunami of December 26, 2004, bringing to the fore a piece of geography and a peoples too rarely considered prior to the tragedy, that we felt compelled to examine the phenomenon. The overwhelming significance of this volume comes from its being a combination of both academic scholars and development practitioners in the field. Its poignancy becomes underscored from their wide-ranging perspectives, with 21 chapters representing some 14 different countries. Their realities provide not only credibility but also an unprecedented sensitivity to communication issues. Our approach here considers Tsunami 2004 from five communication perspectives: 1.) Interpersonal/ intercultural, 2.) Mass media, 3.) Telecommunications, 4.) Ethics, philanthropy, and development communication, and; 5.) Personal testimonies and observations. You will learn even more here about the theory and practice of disaster/crisis communication.

A loop cancellation based active damping solution for constant power instability in vehicular power systems

In recent years, electric propulsion systems have increasingly been used in land, sea and air vehicles. The vehicular power systems are usually loaded with tightly regulated power electronic converters which tend to draw constant power. Since the constant power loads (CPLs) impose negative incremental resistance characteristics on the feeder system, they pose a potential threat to the stability of vehicular power systems. This effect becomes more significant in the presence of distribution lines between source and load in large vehicular power systems such as electric ships and more electric aircrafts. System transients such as sudden drop of converter side loads or increase of constant power requirement can cause complete system instability. Most of the existing research work focuses on the modeling and stabilization of DC vehicular power systems with CPLs. Only a few solutions are proposed to stabilize AC vehicular power systems with non-negligible distribution lines and CPLs. Therefore, this paper proposes a novel loop cancellation technique to eliminate constant power instability in AC vehicular power systems with a theoretically unbounded system stability region. Analysis is carried out on system stability with the proposed method and simulation results are presented to validate its effectiveness.

What is the apparent angle of a Kelvin ship wave pattern?

While the half-angle which encloses a Kelvin ship wave pattern is commonly accepted to be 19.47 degrees, recent observations and calculations for sufficiently fast-moving ships suggest that the apparent wake angle decreases with ship speed. One explanation for this decrease in angle relies on the assumption that a ship cannot generate wavelengths much greater than its hull length. An alternative interpretation is that the wave pattern that is observed in practice is defined by the location of the highest peaks; for wakes created by sufficiently fast-moving objects, these highest peaks no longer lie on the outermost divergent waves, resulting in a smaller apparent angle. In this paper, we focus on the problems of free surface flow past a single submerged point source and past a submerged source doublet. In the linear version of these problems, we measure the apparent wake angle formed by the highest peaks, and observe the following three regimes: a small Froude number pattern, in which the divergent waves are not visible; standard wave patterns for which the maximum peaks occur on the outermost divergent waves; and a third regime in which the highest peaks form a V-shape with an angle much less than the Kelvin angle. For nonlinear flows, we demonstrate that nonlinearity has the effect of increasing the apparent wake angle so that some highly nonlinear solutions have apparent wake angles that are greater than Kelvin's angle. For large Froude numbers, the effect on apparent wake angle can be more dramatic, with the possibility of strong nonlinearity shifting the wave pattern from the third regime to the second. We expect our nonlinear results will translate to other more complicated flow configurations, such as flow due to a steadily moving closed body such as a submarine.

Take a journey to saga country, Reykjavik, Iceland

A travel article about a journey to Reykholt in Western Iceland, once the farm of saga author Snorri Sturluson. A TRIP back into snowbound Iceland's past in search of a famed warrior-poet throws up some old memories and fresh revelations for Kari Gislason "The fish must sing." An odd idea, I know - one uttered by a merchant in a novel by Halldor Laxness. But it said no more than what every Icelander since the settlement had known. If you were going to live on the edge of the world, it paid to do something to remind the rest of the world you were still here...

Advances in gyro-stabilisation of vessel roll motion

The use of gyro-dynamic forces to counteract the wave-induced roll motion of marine vessels in a seaway was proposed over 100 years ago. These early systems showed a remarkable performance, reporting roll reductions of up to 95% in some sailing conditions. Despite this success, further developments were not pursued since the systems were unable to provide acceptable performance over an extended envelope of sailing and environmental conditions, and the invention of fin roll stabilisers provided a satisfactory alternative. This has been attributed to simplistic controls, heavy drive systems, and large structural mass required to withstand the loads given the low strength materials available at the time. Today, advances in material strength, bearings, motor technology and mechanical design methods, together with powerful signal processing algorithms, has resulted in a revitalized interest in gyro-stabilisers for ships. Advanced control systems have enabled optimisation of restoring torques across a range of wave environments and sailing conditions through adaptive control system design. All of these improvements have resulted in increased spinning speed, lower mass, and dramatically increased stabilising performance. This brief paper provides an overview of recent developments in the design and control of gyro-stabilisers of ship roll motion. In particular, the novel Halcyon Gyro-Stabilisers are introduced, and their performance is illustrated based on a simulation case study for a naval patrol vessel. Given the growing national and global interest in small combatants and patrol vessels, modem gyro-stabilisers may offer a significant technological contribution to the age old problem of comfort and mission operability on small ships, especially at loiter speeds.

A novel manoeuvering model based on low-aspect-ratio lift theory and Lagrangian mechanics

This paper proposes a physically motivated reappraisal of manoeuvring models for ships and presents a new model developed from first principles by application of low aspect-ratio aerodynamic theory and Lagrangian mechanics. The coefficients of the model are shown to be related to physical processes, and validation is presented using the results from a planar motion mechanism dataset.

Prevention of Pollution of the Marine Environment from Vessels : The Potential and Limits of the International Maritime Organisation

--Critically discusses the role of International Maritime Organization (IMO) in the protection of the marine environment --Presents a clear, updated, concise and critical overview of the IMO marine environmental legal instruments --A fresh outlook on the north-south tensions in the IMO marine environmental discourses --Critically examines the principle of common but differentiated responsibilities in the context of IMO This book examines the role of The International Maritime Organization (IMO) in the prevention and control of pollution of the marine environment from vessels with a particular reference to the current north-south tensions regarding the strategy for combating climate change in the maritime sector as well as the prevention of marine pollution from the ship-breaking industry. The IMO, a United Nations specialized agency, has been entrusted with the duty to provide machinery for cooperation among governments for the prevention and control of pollution of the marine environment from vessels. The organization is responsible for drafting legal instruments as well as for facilitating technical cooperation for the protection of the marine environment. Although IMO legal instruments are mainly targeted at the prevention of pollution of the marine environment from vessels, there is a trend towards a liberal interpretation of this, and the organization has expanded its work to areas like shipbreaking, which is essentially a land-based industry.

Design and control of MIRA: A lightweight climbing robot for ship inspection

The inspection of marine vessels is currently performed manually. Inspectors use tools (e.g. cameras and devices for non-destructive testing) to detect damaged areas, cracks, and corrosion in large cargo holds, tanks, and other parts of a ship. Due to the size and complex geometry of most ships, ship inspection is time-consuming and expensive. The EU-funded project INCASS develops concepts for a marine inspection robotic assistant system to improve and automate ship inspections. In this paper, we introduce our magnetic wall–climbing robot: Marine Inspection Robotic Assistant (MIRA). This semiautonomous lightweight system is able to climb a vessels steel frame to deliver on-line visual inspection data. In addition, we describe the design of the robot and its building subsystems as well as its hardware and software components.

Crossing international boundaries through doctoral partnerships: Learnings from a Chinese-Australian forum

International forums for doctoral students offer a fertile context for developing strategic partner-ships between higher education institutions, as well as for building the intercultural capacity of early career academics. However, there is limited research investigating the benefits of international doctoral forum partnerships. This paper presents learnings from a recent international doctoral forum held in Beijing, China and attended by doctoral students and academics from Beijing Normal University (China) and Queensland University of Technology (Australia). Drawing on qualitative case study method and a model of boundary crossing mechanisms, we identify the beneficial outcomes of the forum. We describe how the forum arose from a strong ongoing partnership between the Education Faculties of Beijing Normal University and Queensland University of Technology. We then identify how, at the institutional and individual level, international doctoral forum participants can be challenged and benefit in four areas: collaboration, intercultural capacity, academic enhancement and program development. Implications for engaging successfully in international doctoral forum partnerships are also discussed.

Control of Ship Roll Motion

The undesirable effects of roll motion of ships (rocking about the longitudinal axis) became noticeable in the mid-nineteenth century when significant changes were introduced to the design of ships as a result of sails being replaced by steam engines and the arrangement being changed from broad to narrow hulls. The combination of these changes led to lower transverse stability (lower restoring moment for a given angle of roll) with the consequence of larger roll motion. The increase in roll motion and its effect on cargo and human performance lead to the development several control devices that aimed at reducing and controlling roll motion. The control devices most commonly used today are fin stabilizers, rudder, anti-roll tanks, and gyrostabilizers. The use of different types of actuators for control of ship roll motion has been amply demonstrated for over 100 years. Performance, however, can still fall short of expectations because of difficulties associated with control system design, which have proven to be far from trivial due to fundamental performance limitations and large variations of the spectral characteristics of wave-induced roll motion. This short article provides an overview of the fundamentals of control design for ship roll motion reduction. The overview is limited to the most common control devices.

Flow of metal in a wedge-shaped cavity

The wedge shape is a fairly common cross-section found in many non-axisymmetric components used in machines, aircraft, ships and automobiles. If such components are forged between two mutually inclined dies the metal displaced by the dies flows into the converging as well as into the diverging channels created by the inclined dies. The extent of each type of flow (convergent/divergent) depends on the die—material interface friction and the included die angle. Given the initial cross-section, the length as well as the exact geometry of the forged cross-section are therefore uniquely determined by these parameters. In this paper a simple stress analysis is used to predict changes in the geometry of a wedge undergoing compression between inclined platens. The flow in directions normal to the cross-section is assumed to be negligible. Experiments carried out using wedge-shaped lead billets show that, knowing the interface friction and as long as the deformation is not too large, the dimensional changes in the wedge can be predicted with reasonable accuracy. The predicted flow behaviour of metal for a wide range of die angles and interface friction is presented: these characteristics can be used by the die designer to choose the die lubricant (only) if the die angle is specified and to choose both of these parameters if there is no restriction on the exact die angle. The present work shows that the length of a wedge undergoing compression is highly sensitive to die—material interface friction. Thus in a situation where the top and bottom dies are inclined to each other, a wedge made of the material to be forged could be put between the dies and then compressed, whereupon the length of the compressed wedge — given the degree of compression — affords an estimate of the die—material interface friction.