Small Waterplane Area Research Articles

A generalised collaborative optimisation method and its combination with kriging metamodels for engineering design

In this paper, a generalised collaborative optimisation (GCO) method is proposed in the field of multidisciplinary design optimisation (MDO). In this method, the concept of generalised multidisciplinary variables is put forward and summarised as four types to provide more comprehensive interdisciplinary compatibility constraints than traditional collaborative optimisation. The linear normalisation method is adopted in GCO to remove inconsistencies caused by the range discrepancies between design variables. The effectiveness of GCO is demonstrated by its successful application in the design of a gear reducer. Furthermore, to undertake the computational and organisational challenges in MDO, an effective approach combining kriging and GCO (KGCO) is presented. In this approach, kriging metamodels are employed to reduce the computational cost by replacing expensive simulation and analysis codes. System-level compatibility constraints are approximated by kriging metamodels to remove the non-smoothness of the original quadratic constraint forms. The feasibility and computing efficiency of the KGCO approach are illustrated by solving the gear reducer design problem. Through its innovative and successful application in the design of a small waterplane area twin hull ship, it is further demonstrated that the KGCO approach is a feasible and efficient design methodology in support of the design of engineering products.

Concept design and hydrodynamic optimization of an innovative SWATH USV by CFD methods

The paper presents the main characteristics of an innovative platform which has been conceived and designed to extend the operational capabilities of current unmanned surface vehicles in terms of platform stability in waves and of powering requirement at a relatively high speed. The main idea which rules the project is the realization of a small autonomous surface unit (about 6 m in length) capable of undertaking several tasks in the marine environment even with moderate rough sea conditions. The designed vessel has the ability to locate, recover, and launch other members of the autonomous fleet (like AUVs or other underwater devices) and at the same time could carry out a surveillance service of the surrounding areas. To manage these tasks, the vehicle is designed to provide a fairly good autonomy which is needed to face intermediate-range missions (100 nautical miles). The choice of a small waterplane area twin hull (SWATH) form has been motivated by its excellent properties of seakeeping qualities, combined with a non-conventional low resistance underwater hull shape, currently under patenting process, which is able to reduce to a minimum the resistance of the vessel especially at higher speeds. To obtain the most efficient profile of the underwater bodies, a systematic optimization with an automatic procedure based on a parametric definition of the geometry, a state-of-the-art computational fluid dynamics (CFD) flow solver, and a differential evolution global minimization algorithm have been created and used. As expected, all the final CFD computations on the best design have demonstrated the superior efficiency of the developed unconventional SWATH technology with respect to different alternatives of current hull typologies.

Some lessons from a design

This study describes results of a collaboration from the design work on a new type of ship. A passenger ship with a small water-plane area was designed but without a deep understanding between the designers and the consultant. The main differences between the two options for the ship were the wet deck structure, the vertical clearance, the number of shafts, the number and placement of motion mitigation foils, and the possibilities for other forms of motion mitigation. Various consequences, such as displacement (empty and full), the propulsive coefficient, and the seaworthiness, are the result of various technical decisions. The failure of the design was attributed to the lack of discussion and collaboration.

Considerations of a horizontal axis tidal turbine

This paper considers the performance of a horizontal axis tidal turbine, at two sites off the Welsh coast of the UK, one in the Severn estuary and the second off Anglesey. Acoustic Doppler current profiler surveys were performed to investigate local velocity profiles. A small water plane area twin hull (Swath) bathymetric survey established the local bathymetry of the area. Energy extraction from a three-bladed 10 m diameter turbine was studied using a quasi-static computational fluid dynamics model and velocity profile data from the acoustic Doppler current profiler surveys. The acoustic Doppler current profiler data were rescaled allowing further insight to the attenuation of power density through the water column at a higher tidal velocity. The velocity profile has a significant effect on power attenuation reducing the extracted power to 30–40% of peak power. The turbine performance calculation is highly dependent on the velocity used; the velocity should be monitored around five turbine diameters upstream, at the depth of its axis of rotation. The axial load on the turbine peaks at the freewheeling velocity dropping to 88% at peak power. It is suggested that the velocity at the Severn estuary site is, unlike the Anglesey site, unlikely to provide a suitable level of power to be viable.

Multi-hulls: new options and scientific developments

The widespread development of multi-hull ships began in the second half of the twentieth century, and today many hundreds of such ships of various designs are being built. This intensive development can be explained by the characteristics of various multi-hull ships. Any multi-hull ship type differs both from mono-hulls and from other multi-hull types because of their individual characteristics. The main characteristics of multi-hull ships are examined briefly here. Their larger deck area relative to mono-hull ships means that they are more economical for most types of ‘volume’ cargoes including passengers, cars and other wheeled vehicles, light containers, laboratories, weapons, aircraft and helicopters and so on. Similarly, in comparison with their mono-hull counterparts, multi-hulls are safer because of their larger and more simply achieved transverse stability and bigger above-water volumes. The larger permissible aspect ratio of these hulls also makes them more energy efficient at higher speeds. All multi-hull ships are, in general, more seaworthy than their mono-hull counterparts, and ships with small water-plane area (SWA ships) have the best performance characteristics with regard to seakeeping. The strength specificity of multi-hulls is the leading role in determining transverse loads and the need for avoiding wet bottom slamming. Despite their applied significant advantages, the author believes that the main characteristics of multi-hull ships can be further improved. A general picture of his proposals is given below: • New level feature: Super-fast, triple-hulled vessels with sufficient airborne unloading capacity – for the doubling of achievable speeds in smooth water and relatively small wave conditions. • New level feature: New shape for fast ships with SWA – for higher speeds in waves. • New level feature: Special options for container-carriers (for transatlantic routes or for island service by gas-carrying containers) – for small-draft harbours with no reduction in seaworthiness. • New level feature: Twin-hull escort tugs – for 10 times greater transverse stability, i.e. sufficiently less likelihood of being over-heeled by the tow rope. • New service feature: Outrigger SWA carrier for unmanned aircraft – for minimal displacement and sufficient seaworthiness. • New service feature: Outrigger SWA passenger liners with one to two helicopters – to avoid entry into harbours. • New safety feature: Inexpensive modernisation of existing small- and medium-sized passenger ferries through the addition of outriggers without docking the ship

Ｒｅｓｏｎａｎｃｅ−Ｆｒｅｅ ＳＷＡＴＨ の波浪中運動性能

A "Resonance-Free SWATH (RFS)" as the oceangoing large fast ship has the negative restoring moments, which leads to resonance-free in the motion responses, because of the extraordinary small water plane area. The RFS is designed to cross 4,800 nautical miles of Pacific Ocean in 5 days punctually at a high speed of 40 knots, with the good seaworthiness such as no speed reduction or absolutely no slamming even in the rough sea. To verify the seaworthiness of the RFS, experiments in model basin and theoretical predictions are carried out to examine the lowest limit of motion responses in waves. The results in regular and irregular head waves are compared with those of various hull forms, such as mono-hull, ordinary SWATH or trimaran. The predominance of the RFS regarding seaworthiness will be pointed out in the conclusion. For example, by using PD control action, heave motion responses of the RFS is reduced to about 1/40 compared with those of mono-hull or trimaran, and pitch motion responses of the RFS become about 1/8.

Slow-speed ships with small water-plane area: methods of development

Nowadays there are a few ships built or designed with a small water-plane area (SWA) and low (absolute) speed. Some general methods of such ship development are described with an example of a Chinese-designed research SWA ship. Initially a work definition of slow speed is proposed and then some of the specificities of slow-speed SWA ships are discussed. The main methods of such ship development are: ship type selection; optimal hull structure; high enough tensile steel application; hull structure selection by calculations; measure of viscosity resistance decreasing; and method of motion mitigation. These topics are examined briefly. This paper discusses the initial ship option, estimated characteristics, and two alternative options.

SeaWASP: A Small Waterplane Area Twin Hull Autonomous Platform for Shallow Water Mapping

AbstractStudents with Santa Clara University (SCU) and the Monterey Bay Aquarium Research Institute (MBARI) are developing an innovative platform for shallow water bathymetry. Bathymetry data is used to analyze the geography, ecosystem, and health of marine habitats. Current methods for shallow water measurements typically involve large manned vessels that are costly to operate and that may pose a danger to themselves and the environment in shallow, semi-navigable waters. Small vessels, however, are prone to disturbances by shallow water waves, tides, and currents, thereby requiring more instrumentation and computation to accurately process bathymetric data. The SCU/MBARI autonomous surface vessel, SeaWASP, is designed to operate safely and stably in waters as shallow as 1 m without significant manned support in order to produce cost-effective and high-quality bathymetric maps.The SeaWASP design introduces several key design innovations in order to provide high-quality maps with a platform that is safe, stable, and inexpensive. A small waterplane area twin hull (SWATH) design features a submerged dual hull, a small waterplane area, and a high mass-to-damping ratio, thereby making the craft less prone to disturbances. Precision sensing, autonomous control, and platform-level configuration planning and control algorithms are used to navigate the boat along desirable trajectories in support of efficient map generation and to implement low-cost unpiloted operations. Bathymetry is measured with multibeam sonar in concert with Doppler Velocity Logger and GPS sensors.The vessel has been operated successfully in several open water test environments, including Elkhorn Slough, Steven’s Creek Reservoir, and Lake Tahoe, all in California. It is currently in the final stages of integration and test for its first major science mission at Orcas Island, San Juan Islands, WA, in 2009. Final deployment will be at the National Oceanographic and Atmospheric Administration's (NOAA’s) Kasitsna Bay Laboratory in Alaska as one element of a multi-system remote observatory.SeaWASP has been developed in partnership with SCU, MBARI, the University of Alaska‐Fairbanks, and NOAA’s West Coast and Polar Regions Undersea Research Center.

Ｒｅｓｏｎａｎｃｅ−Ｆｒｅｅ ＳＷＡＴＨ の概念設計と耐航性能

A "Resonance-Free SWATH (RFS)" ship is introduced as an example of the oceangoing large fast ship. Because of the extraordinary small water plane area, the restoring moments of the RFS are negative, which leads to resonance-free in the motion responses. The RFS is designed to cross 4,800 nautical miles of Pacific Ocean in 5 days punctually at a high speed of 40 knots, with the good seaworthiness such as no speed reduction or absolutely no slamming even in the rough sea. To verify the seaworthiness of the RFS, experiments in towing tank and theoretical calculations based on the strip theory are carried out to examine hydrodynamic forces and motion responses in waves. The results are compared with those of various hull forms, i.e. mono-hull, ordinary SWATH and trimaran. The predominance of the RFS regarding seaworthiness will be pointed out in the conclusion.

Ｒｅｓｏｎａｎｃｅ−Ｆｒｅｅ ＳＷＡＴＨの運動応答解析

The paper describes the computational method for motion responses on a Resonance-Free SWATH (RFS), which has extremely small water-plane area and it leads to the feature close to the resonance-free in the motion responses.Theoretical calculations based on the strip theory are carried out and compared with experimental results in regular head waves. The influence of forward speed on lift due to hydrofoils and lower hulls are large and numerically modeled well. Hydrodynamic interaction between twin hulls is well computed through the introduction of a practical manner.

An example of a triple-hull SWA ship of ultimate longitudinal shift (hull structure mass estimation)

As it was shown by, for example, V. Dubrovsky, Ships & Offshore Structures, 1(3) (2006), pp. 185–189, the favourable interaction of wave systems of hull with small water-plane area can ensure decreasing of residual resistance coefficient of three interacted hulls (in a comparison with three single hulls) in a defined scope of Froude numbers by a hull length (in general, Fn = 0.4–0.7). But the corresponding longitudinal shift of the bow ship hull relative to side hulls is big enough. Big shift (longitudinal clearance) means the growth of metal-structure mass and the corresponding growth of ship displacement. This article shows an example of a triple-hull small-water plane ship (‘tricore’, in terms of V. Dubrovsky, A. Lyakhovitsky, ISBN 0-9644311-2-2, Backbone Publishing Co., USA, 2001, p. 495), for a demonstration of hull-structure mass role and methods of its decreasing. The concept design of the tricore was carried out, for the initial data of two catamaran options were conceptually designed previously by various design bureaus.

Three identical hulls: Ultimate options for longitudinal shift

Any three hulls, independent of a hull shape, can have smaller relative residual resistance than two as they may result in sufficient favorable interaction with the hull-generated wave systems. Some of the ship types are defined in order to compare the power requirements. Specificity of hull structure is important for ultimate options of triple-hull ships. Two groups of ships are compared, one with small water-plane area and the other with conventional hulls. Main dimensions and power requirements are shown. If a twin-hull ship failed to achieve Froude numbers due to “bad” region, triple-hull ship with the same displacement can have higher Froude numbers at 10–25% achievable speed or smaller Froude numbers at 2–2.5 times power requirements. The results can be improved further after determining the weight of triple-hull structure.

Technical noteConcept consideration of all-weather feeder ships with small waterplane area

Small Waterplane Area Twin Hull (SWATH) is a promising concept for all-weather feeder vessels because of its high seaworthiness at relatively small dimensions. Basic description, main design steps, and achievable characteristics of SWATH performing as Ro-Ro and container carrier are presented. Economic estimation suggests that operational cost of SWATH feeder does not exceed that of traditional ships, while SWATH can provide reliable service in practically all-weather conditions.

Triple-hull ships with small water-plane area: Towing test results and some full-scale comparisons

A small water-plane area (SWA) ship consists of an above-water platform and one or more hulls, which include an underwater gondola and thin strut(s) crossing the freewater surface. Applications of the SWA concept ensure very high seaworthiness, but their relatively large wetted areas provide the motivation for finding methods for reducing wave resistance. The main characteristic of triple-hull ships with identical hulls is the strong interaction between wave systems generated by individual hulls. This provides an opportunity to find configurations with favorable wave system interactions, which is the main reason of interest in triple-hull SWA ships. In this study, the model series of triple-hull SWA ships with the hull aspect ratio 9, 15, and 24 was tested in a towing tank. The effect of the triple-hull SWA configuration was determined by comparing these test results with those of twin-hull SWA ship models. Based on the tests, the effective power of some 1,000-tonne ships was predicted. Triple-hull ships were shown to be advantageous in a certain range of relative speeds. Generally, this advantage decreased with an increase in the hull's aspect ratio.

Small waterplane area ship models: Re-analysis of test results based on scale effect and form drag

The first systematic model series of hulls with small waterplane area (both single hulls and twin-hulls) was designed and tested in Krylov Shipbuilding Research Institute in the middle of the 1980's. The series was intended to cover a broad range of Froude numbers, hull aspect ratios, design drafts, and spacing between hulls. In the present paper, these test results are re-analyzed by accounting for the scale effect in the form drag, obtained from the comparison with test data of larger out-of-series models. Illustrative results are also given for the influence of the cross-section hull shape, strut configuration, and shifted hulls on the residual resistance and for dynamic trim and draft. Some data are compared with those of the later series tests of twin-hull models with small waterplane area carried out in HSVA, Germany. Factors influencing the residual resistance of ships of this type are discussed.

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The underwater acoustic noise of five representative whale-watching boats used in the waters of west Maui was measured in order to study the effects of boat noise on humpback whales. The first set of measurements were performed on 9 and 10 March, close to the peak of the whale season. The ambient noise was relatively high with the major contribution from many chorusing humpback whales. Measurements of boat sounds were contaminated by this high ambient background noise. A second set of measurements was performed on 28 and 29 April, towards the end of the humpback whale season. In both sets of measurements, two of the boats were inflatables with outboard engines, two were larger coastal boats with twin inboard diesel engines and the fifth was a small water plane area twin hull (SWATH) ship with inter-island cruise capabilities. The inflatable boats with outboard engines produced very complex sounds with many bands of tonal-like components. The boats with inboard engines produced less intense sounds with fewer tonal bands. One-third octave band measurements of ambient noise measured on 9 March indicated a maximum sound pressure level of about 123 dB re 1 μPa at 315 Hz. The maximum sound pressure level of 127 dB at 315 Hz was measured for the SWATH ship. One of the boats with outboard engines produced sounds between 2 and 4 kHz that were about 8–10 dB greater than the level of background humpback whale sounds at the peak of the whale season. We concluded that it is unlikely that the levels of sounds produced by the boats in our study would have any grave effects on the auditory system of humpback whales.

First‐year performance assessment of SWATH Research Ship

The first small waterplane area twin hull (SWATH) design ship in the U.S. academic research vessel fleet, the R/V Kilo Moana (Figure 1), entered service in September 2002. The ship, whose home port is in Honolulu, has been operating with diverse groups of oceanographers on board. Before the ship became operational, the University National Oceanographic Laboratory System Fleet Improvement Committee (UNOLS‐ FIC) decided that it was important to gather fair and representative impressions of the vessel's performance from the first scientists on board. Science mission requirements developed over the past year by UNOLS have all indicated that sea‐keeping is a very high priority: oceano graphers wanted to work comfortably at higher sea states. Just about the only way to achieve this is by using the SWATH design rather than the mono‐hull.

Optimal setpoint chasing in dynamic positioning of deep‐water drilling and intervention vessels

Conventional controller designs for dynamic positioning of ships and floating marine structures have so far been based on the principle on automatic positioning in the horizontal-plane about desired position and heading co-ordinates defined by the operator. A three degrees-of-freedom multivariable controller either of linear or nonlinear type, normally with feedback signals from surge, sway and yaw position and velocities, has been regarded as adequate for the control objective. For floating structures with small waterplane area such as semi-submersibles, feedback from roll and pitch angular rotation velocity may also be included to avoid thrust-induced roll and pitch motions that are caused by the hydrodynamic and the geometrical couplings between the horizontal and vertical planes. However, for certain marine operations this control philosophy may not be the most appropriate approach ensuring safety and cost effectiveness. For drilling and work-over operations the main positioning objective is to minimize the bending stresses along the riser and the riser angle magnitudes at the well head on the subsea structure, and at the top joint as well. A positioning control strategy solely based on manual setting of the desired position co-ordinates may not be the most optimal solution for these applications. In this paper a new hybrid dynamic positioning controller, that also accounts for riser angle offsets and bending stresses is proposed. It is shown that a significant reduction in riser angle magnitude can be achieved. Simulations with a drilling semi-submersible demonstrate the effect of the proposed control strategy. Copyright © 2001 John Wiley & Sons, Ltd.

Optimal setpoint chasing in dynamic positioning of deep‐water drilling and intervention vessels

AbstractConventional controller designs for dynamic positioning of ships and floating marine structures have so far been based on the principle on automatic positioning in the horizontal‐plane about desired position and heading co‐ordinates defined by the operator. A three degrees‐of‐freedom multivariable controller either of linear or nonlinear type, normally with feedback signals from surge, sway and yaw position and velocities, has been regarded as adequate for the control objective. For floating structures with small waterplane area such as semi‐submersibles, feedback from roll and pitch angular rotation velocity may also be included to avoid thrust‐induced roll and pitch motions that are caused by the hydrodynamic and the geometrical couplings between the horizontal and vertical planes. However, for certain marine operations this control philosophy may not be the most appropriate approach ensuring safety and cost effectiveness. For drilling and work‐over operations the main positioning objective is to minimize the bending stresses along the riser and the riser angle magnitudes at the well head on the subsea structure, and at the top joint as well. A positioning control strategy solely based on manual setting of the desired position co‐ordinates may not be the most optimal solution for these applications. In this paper a new hybrid dynamic positioning controller, that also accounts for riser angle offsets and bending stresses is proposed. It is shown that a significant reduction in riser angle magnitude can be achieved. Simulations with a drilling semi‐submersible demonstrate the effect of the proposed control strategy. Copyright © 2001 John Wiley & Sons, Ltd.

Complex Comparison of Seakeeping: Method and Example

A method of seakeeping comparison, proposed originally by author in 1978, offers the possibility of taking into account all limitations of speed in waves and other ship characteristics, including motion amplitudes, accelerations at any point, slamming, deck wetness and bending moments for every type of ship. General characteristics of seakeeping are presented as one number for needed sea or for average conditions of the world's oceans. An example of the comparison is presented for two small-sized ships: a catamaran and a twin-hulled ship of small waterplane area (SWATH). Results of systematic calculations for naval ships in the North Atlantic are also presented.