This paper presents insight into the structure of TFfuel, the Transport Factor component related to the weight of fuel needed to meet a ship's endurance requirement. TFfuel is shown to be dependent on the required range and the specific fuel consumption rate of the machinery while being independent of installed power and speed. The effect of operating ships at less than full-load displacement to increase fuel efficiency is illustrated. The results are compatible with Transport Factor analyses that assess transport properties of ship types of interest for high-speed sealift such as displacement and semi-displacement monohulls and multihulls.
RMS Titanic collided with an iceberg and sank on the morning of April 15, 1912. Testimony at hearings on both sides of the Atlantic included conflicting stories of the ship breaking in two or sinking whole. The discovery of the wreck in 1985 confirmed that the ship did break near the surface. Recent evidence and analysis indicates that the initial point of hull failure was at or near the double bottom and the ship effectively broke bottom up.
Ships and offshore structures are frequently subject to various types of actions and action effects during service that may range from the routine to the extreme or accidental. The oceanic environmental phenomena to which such structures may be exposed include freak/rogue waves, impact pressure actions (arising from sloshing, slamming, and green water), collisions, grounding, dropped objects, fire, and explosions. All of these phenomena have highly nonlinear structural consequences that result in geometric and material nonlinearities. Although the identification of both the actions and their effects is equally important in terms of structural design and strength assessments, this paper focuses on the action effects associated with nonlinear structural mechanics and the subsequent analysis of limit states and risk assessment and management. Future trends and further R&D requirements are also addressed. This paper does not offer a literature survey, but rather discusses some of the important issues that relate to nonlinear structural mechanics and analysis.
A design and optimization procedure developed and used for a propeller installed on a twin-semitunnel-hull ship navigating in very shallow and icy water under heavy load conditions is presented. The base propeller for this vessel was first determined using classic design routines under open-water condition with existing model test data. In the optimization process, a panel method code (PROPELLA) was used to vary the pitch values and distributions and take into account the inflow wake distribution, tunnel gap, and cavitation effects. The optimized propeller was able to improve a ship speed of 0.02 knots higher than the desired speed and 0.06 knots higher than the classic B-series propeller. The analysis of the effect of inflow wake, hull tunnel, cavitation, and blade rake angle on propulsive performance is the focus of this paper.
This paper presents the experimental measurement of lift and drag as well as the determination of the onset of cavitation on rudders with leading-edge protuberances (tubercles) that are operating at low to moderate Reynolds Numbers in water. The leading-edge shape used for the rudders in this study is derived from our earlier work concerning the analysis of the leading-edge morphology found on the pectoral flippers of humpback whales. While humpback whales do not swim at speeds that induce cavitation, engineered control surfaces based on this bio-inspired control surface modification might operate in cavitation conditions. This point motivates our present work to investigate the onset of cavitation on small aspect ratio rudders with tubercles. Our findings are that (i) the presence of leading-edge tubercles accelerates the onset of cavitation, (ii) the tubercles can modify the location of the onset of cavitation, (iii) the tubercle geometry has an influence on the rudder's hydrodynamic performance, (iv) for the lower Reynolds Numbers considered in this paper, the tubercles decrease lift and increase drag for angles of attack between 15 and 22 deg, (v) for angles above 22 deg, rudders with tubercles generate more lift than smooth rudders, and (vi) for the higher Reynolds Numbers investigated, the difference in performance between the smooth and tubercled rudders diminishes, suggesting the existence of a critical Reynolds Number for a given tubercle geometry beyond which tubercles have no significant effect on hydrodynamic performance.
A novel procedure for the assessment of propulsion shafting torsional vibration key responses is proposed in this paper. The procedure is based on the response surface methodology applied to a set of system responses compiled over a selected design space. Design space of 1250 design points comprising the shafting stiffness, propeller, turning wheel and tuning wheel mass moments of inertia coordinates has been employed to build the first torsional natural frequency, crankshaft peak vibration torque and shafting peak vibration torque quadratic polynomial approximations. Statistical evaluation performed on a full test set of 2500 design points showed that the mean relative errors of 0.14% for natural frequency, 2.93% for crankshaft peak vibration torque and 0.41% for shafting peak vibration torque were achieved. Good agreement between the assessed and actual torsional responses stresses the importance and utility of the proposed metamodels for the propulsion shafting preliminary design purposes. An example application based on the 114, 000 dwt tanker propulsion shafting is also provided.
Results of an extensive series of model tests that define the longitudinal surface wake profiles aft of prismatic hulls having deadrise angles of 10º, 20º and 30º are presented. Empirical equations are developed that quantitatively define these profiles and are in a form that can be easily applied by designers of stepped planing hulls. These equations are applicable for an expected range of variations in trim angle, speed coefficient, and loading coefficient typical for these hulls. A brief introduction to the concept and to the hydrodynamic advantages of stepped planing hulls is presented to orient the reader as to the importance of wake data in their design. Examples are presented that illustrate the application of these wake data for stepped planing hulls with wetted forebody chine to achieve maximum hydrodynamic lift/drag ratios. Finally experimental results are presented that illustrate the potential resistance penalty associated with the operation of chines dry forebodies where the stagnation line crosses the step.
Formal Safety Assessment (FSA) is the premier scientific method that is currently being used for the analysis of maritime safety and for the formulation of related regulatory policy. This paper conducts a critical review of the FSA methodology and proposes ways to improve it. All steps of the FSA approach are looked at, and possible pitfalls or other deficiencies are identified. Then proposals are made to alleviate such deficiencies, with a view to achieve a more transparent and objective approach. The results of this paper may be useful if a revision of the FSA guidelines is contemplated along these lines. Recent International Maritime Organizations (IMO) developments are also described.
In this paper a nonlinear thrust controller for fixed pitch marine propellers with torque loss estimation and an antispin strategy is presented. The controller, designed to operate in the four-quadrant plane composed by the shaft speed and the vessel speed, is a combination of a thrust controller developed for calm/moderate sea states and an anti-spin strategy to reduce power peaks and wear-and-tear in extreme sea conditions. The thrust controller aims at producing the demanded thrust independently from the propeller losses. The anti-spin algorithm lowers the shaft speed once large torque losses are detected and increases the shaft speed to normal when the loss situation is considered over. The torque losses are estimated with a nonlinear observer. The performance of the proposed controller is validated by experiments carried out in a towing tank.
Shipboard bilges can be a sink and reservoir for a range of substances other than oil and water, i.e., particles, chemicals, biological activity, any of which alone or in combination can cause an oily water separator (OWS) and related bilge water treatment systems to fail. Borrowing from the data processing / computation industry we conclude "garbage in, garbage out." To assist the operator in properly identifying contaminants and troubleshooting occurring OWS systems failures, members of SNAME's Technical and Research Committee panel EC-3 (Oily Waste Water and Bilge-water) developed a diagnostic guide "A Guide to Diagnosing Contaminants in Oily Bilgewater to Maintain, Operate and Troubleshoot Bilgewater Treatment Systems." This Guide provides a foundation for the development of bilge water contaminant identification skills along with diagnostic and bilge water treatment systems troubleshooting techniques to prevent and remedy many hypes of oily bilgewater system failures.
Most imminent faults in gas turbines often emanate from the rotor shaft of the engine. Some of these faults that could lead to catastrophe include misalignment, imbalance, crack, and eccentricity. These defects are equally likely to lead to unscheduled downtime resulting in large economic losses to equipment owners. It is against this backdrop that the rotor shaft of a gas turbine system was isolated and used for this dynamic model to reduce downtime. A method of dynamic modeling was used to consider how the aforementioned faults could be addressed at the design stage of the gas turbine engine. Modeling and simulation of the faults were carried out, and the obtained results compared favorably with what theory suggests. It was observed that cracking, as the most prominent rotor shaft fault, could manifest even at a turbine speed of 7,264 rpm (0.18 m for 0.8776 mm/s vibration velocity amplitude). Artificial neural networks (ANN) were then used to validate and link the results together, which also confirmed the authenticity of the work. Also, a Visual Basic program was used in the course of the various simulations adopted for the modeling, with faults being randomized every 3000 ms, and outputs were easily displayed on desktop computer screen. The work therefore showed how an ANN could be integrated into the monitoring of gas turbine rotor shaft defects. In its totality, the monitoring technique metamorphosed into the development of a software code-named "The MICE" for monitoring essential performance parameters in gas turbine operations.
The equations of motion for the coupled dynamics of a long flexible life raft and fast rescue craft in an irregular ocean wave are formulated in two dimensions using the methods of Kane and Levinson (Dynamics: Theory and Applications, McGraw Hill Inc., 1985). The flexible raft is modeled as spring connected lumped masses, and it is assumed that the motion normal to the wave surface is small and can be neglected; that is, the bodies move along the propagating wave profile. The wave forces are applied using Morison's equation for bodies in accelerated flow. Wind loads are similarly modeled using drag coefficients. The equations are solved numerically using the Runge-Kutta routine "ode45" of MATLAB. The numerical model provides guidelines for predicting the tow loads and motions in severe sea states.
This paper presents a summary of an investigation into the effects of hull flexibility when deriving an equivalent service factor for a single passage of a Great Lakes Bulk Carrier from the Canadian Great Lakes to China. induced bending moment predicted using traditional three-dimensional rigid body hydrodynamic methods is augmented due to the effects of springing and whipping by including allowances based on two-dimensional hydroelasticity predictions across a range of headings and sea states. The analysis results are correlated with full scale measurements that are available for this ship. By combining the long term "rigid body" wave-bending moment with the effects of hydroelasticity, a suitable service factor is derived for a Great Lakes Bulk Carrier traveling from the Canadian Great Lakes to China via the Suez Canal.
The finite element (FE) method is suitable as a numerical tool in the numerical analysis of, for example, ship collision scenarios. It is feasible to simulate and compare different collision scenarios by parameter variations. The objective with this investigation was to establish a reliable and robust FIE modeling procedure for ship-ship collision simulations, using the commercial FE software Abacus/Explicit, by means of parameter sensitivity and experimental analyses. Four types of experiments are presented that have supported the development of the FIE models and simulations with sufficient information for representation of material characteristics and for validation of models: (i) uniaxial tensile tests, (ii) friction tests, (iii) bulb impact with a steel-sheet test and, finally (iv) a bull) impact with a side-shell ship structure. The outcome of the parameter study after calibration against test results was two validated FE models: one of the bulb-sheet test and one of the bulb-structure test.
The aim of the paper is to calculate hull-girder reliability of chemical tanker according to the reliability model proposed by International Maritime Organization (IMO). The probability of hull-girder failure is calculated using a first-order reliability method for two operational profiles-one typical for oil tanker and the other one modified in order to reflect differences between oil tanker and chemical tanker. The evaluation of the wave-induced load effects that occur during long-term operation of the ship in the seaway is carried out in accordance with International Association of Classification Societies (IACS) recommended procedure. The stillwater loads are defined on the basis of a statistical analysis of loading conditions from the loading manual. The ultimate collapse bending moment of the midship cross section, which is used as the basis for the reliability formulation, is evaluated by progressive collapse analysis and by single-step procedure. The reliability analysis is performed for "as-built" ship and for "corroded" ship according to corrosion deduction thickness from new Common Structural Rules for double-hull oil tankers. It is shown that hull-girder failure probability of "as-built" chemical tanker is well above the upper reliability bound proposed by IMO, while the "corroded" ship is slightly unconservative since the reliability index is lower than IMO lower reliability bound.
Waterline parabolization or addition of side bulbs about the ship's midbody can significantly reduce the wave-making resistance of a vessel [Calisal, S. M., Goren, O., and Danisman, D. B., 2002 Resistance reduction by increased beam for displacement-type ships, Journal of Ship Research, 46, 3, 208–213]. These side bulbs are designed to create a wave pattern that interacts with the ship wave system of the hull at the desired speed range. This concept was first successfully tested on a coaster tanker and then extended to the UBC series hull, a series typical of Canadian West Coast fishing vessels. Systematic tow tank experiments revealed that while parabolization decreases the total resistance, the form factor suffered an increase. An integral boundary layer solver and a 2D RANS solver both showed that the increase in viscous resistance was mainly caused by an increase in form drag or viscous pressure drag. The parabolization concept was subsequently extended to a high-speed NPL trimaran to determine whether resistance reduction using parabolic side bulbs could be achieved for a very slender multihull vessel. A Rankine source panel method was used to predict the wave-making characteristics of the trimaran, and an integral boundary layer solver and a RANS solver were used to calculate the viscous drag. A parametric study, varying the size and location of bulbs, was first performed on the center hull to design the side bulb. The study was then extended to the trimaran to evaluate the additional wave interactions caused by the outriggers. Experimental model tests validated the numerically predicted wave interactions, as well as the change in viscous drag. Based on the numerical work, a modified NPL trimaran hull form was designed that reduced the total resistance of the vessel by up to 6% in the design speed range and providing critical additional engine or accommodation space.
This paper presents the results of experiments to measure flow velocities around the hull of an escort tug model operating at a yaw angle of 45 deg using particle image velocimetry (PIV). The paper describes the setup, calibration, and operation of the PIV system and the analysis of the results, including an estimate of the experimental uncertainty. Flow vectors are given within planes normal to the direction of motion of the tug. One plane was on the upstream side of the hull, and the other plane was on the downstream side of the hull. The downstream measurements were made with and without a low aspect ratio fin, typical of many modern escort tug designs. The results showed that the fin, when fitted, created a large vortex under the hull of the tug. Smaller features of the flow, such as the separation of the flow at the upstream and downstream bilge corners were also defined. The intention of these experiments was to create a data set that can be used to validate computational fluid dynamics (CFD) predictions of flow vectors around an escort tug at a large yaw angle.
The aim of the present study was to predict propeller performance during propeller-ice interaction. Total loads acting on a propeller blade during propeller-ice interaction were assumed to consist of three major components: separable hydrodynamic loads, inseparable hydrodynamic loads, and ice milling loads. A panel method and an empirical formula were used for the hydrodynamic load calculations and the ice contact load calculations, respectively. This empirical model was implemented into a numerical panel code. The numerical prediction model for the ice loads including the detailed implementation is described, and the results are compared with experimental results.
The purpose of this paper is to consider a practical way to estimate the cost of oil spills from ships within the framework of establishing environmental risk evaluation criteria in International Maritime Organization (IMO). Regression analysis between the cost of oil spills and the weight of oil spilled (oil spill weight) was carried out using historical oil spill data from tankers reported by International Oil Pollution Compensation (IOPC) Funds. A nonlinear regression formula between the cost of oil spills and the oil spill weight is estimated from the historical data, and a critical value of cost to avert one tonne of spilled oil (CATScr) is obtained. CATScr obtained by the present study is compared with that obtained by previous work. This study shows that the cost of oil spills estimated by the present regression formula is in fairly good agreement with the mean value obtained from historical data while the CATScr gives relatively larger costs and shows the upper bound of the cost of oil spills.
