The Breakup of Titanic: A Progress Report From the Marine Forensics Panel (SD-7)

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.

Some Recent Advances and Future Trends in Nonlinear Structural Mechanics for Ships and Offshore Structures

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.

On the Nature of the Transport Factor Component TF fuel

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.

Surface Wave Contours Associated with the Forebody Wake of Stepped Planing Hulls

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.

Regression-Based Assessment of Shafting Torsional Vibration Key Responses

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.

Design Study of a Heavily Loaded Ice Class Propeller Using an Advance Panel Method

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.

Lift, Drag, and Cavitation Onset On Rudders With Leading-edge Tubercles

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.

Gap Effect on Performance of Podded Propulsors in Straight-Ahead and Azimuthing Conditions

This paper presents results of an experimental study on the effect of gap distance on propulsive characteristics of puller and pusher podded propulsors in straight-ahead and static azimuthing open-water conditions. The gap distance is the axial distance between the rotating (propeller) and stationary (pod) parts of a podded propulsor. The propeller thrust and torque, unit forces, and moments in the three-coordinate directions of a model podded unit were measured using a custom-designed pod dynamometer in various operating conditions. The model propulsor was tested at the gap distances of 0.3%, 1%, and 2% of propeller diameter for a range of advance coefficients combined with the range of static azimuthing angles from +20_ to 20_ with a 10_ increment. The tests were conducted both in puller and pusher configurations in the same loading and azimuthing conditions. In the puller configuration, the gap distance did not have any noticeable effect on propeller torque in straight course condition, but had an effect in azimuthing conditions. The propeller thrust and efficiency were also influenced by the change of gap distance, and the effects were more pronounced at high azimuthing angles and high advance coefficients. For pusher configuration, however, the gap distance did not affect the propeller performance characteristics in straight-ahead and azimuthing conditions. Both in straight course and azimuthing conditions, the unit thrust and efficiency were not influenced by the gap distance in either puller or pusher configurations. The gap distance had a noticeable effect on unit transverse force and steering moment both in puller and pusher configurations, and both in straight course

Hull-Girder Reliability of a Chemical Tanker

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.

A Four-Quadrant Thrust Controller for Marine Propellers with Loss Estimation and Anti-Spin: Theory and Experiments

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.