Small Waterplane Area Twin Hull Research Articles

The Low-Noise Optimization of a SWATH Ship’s Structures Based on the Three-Dimensional Sono-Elasticity of Ships

Basic equations and numerical methods are presented for the three-dimensional sono-elasticity theory of ships in shallow sea Pekeris acoustic waveguide environment. The corresponding software three-dimensional hydroelastic analysis of floating and traveling structures-Acoustic developed based on this theory is used for low-noise optimization design of the strut structures of a 1500-ton small waterplane area twin hull (SWATH) ship. When the SWATH ship was moored in waves and laying down instruments for ocean survey, it was observed that the waves continuously beat the vertical side walls of the struts, resulting in structural vibration and acoustic radiation in the frequency band below 100 Hz. This is a new phenomenon that the hydroelastic response of a local structure disturbs ocean survey performance. This phenomenon is not good for the performance of underwater acoustic equipment because it increases the background noise in the vicinity of the SWATH ship. This problem needs a low-cost and feasible solution. The mechanism of this phenomenon is first discussed by means of a sono-elastic analysis. After a series of low-noise design calculations for the strut structures, a design of optimal acoustic performance is obtained with only a small increase in the structure weight. Some suggestions on engineering design for solving such problems are also put forward. 1. Introduction The theory of fluid-structure interaction has been widely applied in various engineering practices, including improvement of ship's seakeeping performance and structural safety, ship vibration and noise control, and enhancement of underwater acoustic stealthiness. In the late 1970s of the twentieth century, hydroelasticity of ships was established as one new branch of ship's fluid-structure coupling dynamics (Bishop & Price 1979). In the early 1980s, by combining the three-dimensional potential flow theory of ship motions with the three-dimensional structural dynamics, three-dimensional hydroelasticity was established by Wu (1984) and Bishop et al. (1986) to deal with the dynamic response of arbitrarily shaped three-dimensional deformable body under internal and external loads. Hereafter, the theory was developed continuously into two main subbranches: one is the three-dimensional hydroelasticity with respect to wave-induced dynamic responses of structures in the incompressible fluid field (Wu 1984; Bishop et al. 1986; Wu et al. 1997; Tian & Wu 2006; Kim et al. 2009; Wu & Cui 2009) and the other deals with the acoustic effect in the compressible fluid field (Zhou et al. 2010; Zou et al. 2013; Zou 2014), the latter of which is also called the three-dimensional sono-elasticity of ships.

Intact stability and seakeeping characteristics of autonomous surface vehicle (asv) using swath hullform to support bathymetry survey activities on the coastal area

The information is an important thing to search a new resource. In this decade, with leading-edge technology is easier to find any information about our earth. Thus, that is must be explored by the ships. The exploration works usually take a long time, and for convenience, the unmanned technology is much promised. In this research, we focused on the autonomous surface vehicle for bathymetry survey. To design the ASV, we must consider the reliability, efficiency, and safety. To reach those three components, the analysis of resistance, stability and wave response are necessary. Therefore, the hull form design is focused on Small Waterplane Area Twin Hull (SWATH) hull form. According to the numerical analysis, the proposed SWATH hull form of ASV is suitable for bathymetry activities. It can be proved by the stability performance which the maximum value of GZ is at 26.40. The resistance calculation result is indicated that the drag of coefficient of this hull form is about 0.013.

A space mapping method based on Gaussian process model for variable fidelity metamodeling

Computational simulation models with different fidelities are usually available in the design of engineering products for obtaining the quantity of interest (QOI). To integrate and fully exploit variable fidelity information, a space mapping based variable-fidelity metamodeling (VFM) approach is developed in this work. Firstly, a Gaussian process (GP) model is constructed for the low-fidelity (LF) model. Secondly, a variable-fidelity metamodel is constructed by taking the predicted information from this GP model as a prior-knowledge of the QOI and directly mapped into the outputs space of the high-fidelity (HF) model. This space mapping process is performed by constructing another GP model. A mathematic example is first adopted for illustrating how the proposed approach works under different sample sizes and sample noises. Then, the proposed approach is applied to two real-life cases, modeling of the maximum stress for the structure of a Small Waterplane Area Twin Hull (SWATH) catamaran and predicting weld geometry in fiber laser keyhole welding, to illustrate its ability in support of complex engineering design.

DYNAMIC STABILITY OF FOILBORNE HYDROFOIL/SWATH WITH ANHEDRAL FOIL CONFIGURATION

The hybrid hydrofoil/SWATH (Small Waterplane Area Twin Hull) designed and patented by Stefano Brizzolara, is a novel vehicle that is optimized to operate in both a high-speed foilborne mode and a displacement mode. The deployable hydrofoils on the vehicle take on a unique four surface piercing anhedral foil configuration. This foilborne design had previously undergone only preliminary assessment of stability characteristics. A six degree of freedom model of the foilborne vehicle dynamics is introduced as a framework to study vehicle stability and maneuvering. Stability criteria derived from multiple linearized models of the vehicle dynamics are compared to the six degree of freedom results in both the vertical and horizontal planes. Foil configuration design criteria are developed for pitch equilibrium, pitch stability, and directional stability.

Ultimate strength analysis of a SWATH ship subjected to transverse loads

When SWATH (Small Waterplane Area Twin Hull) ship hulls are exposed to horizontal extreme wave loads, the transverse ultimate strength is critical due to large stress concentrations in the narrow struts and haunches. In this paper, an experiment has been performed to examine the ultimate strength of a one-eighth scaled SWATH ship model subjected to transverse loads. The experimental results are compared with finite element simulations. The structural model, scaled from an actual SWATH ship, is designed with scaling laws and linear static analyses performed by the MSC.Nastran finite element solver. The procedure to design and manufacture the complex structural model is given. The actual ship and its scaled model are analysed numerically to achieve the consistency of the maximum stress and the stress distribution in their corresponding finite element models. The experimentally obtained force-displacement response and shape of the deformation show good agreement with the simulations performed by the implicit MSC.Marc nonlinear finite element solver. The maximum stresses are mainly concentrated around the hull haunches, and the stress distributions at the ship ultimate collapse are presented. The ultimate strength of the actual SWATH ship is evaluated according to scaling laws, and the ship safety margin is analysed. Moreover, the effects of hydrodynamic wave pressure distributions on the ship ultimate strength are investigated.

Modeling and simulation of five DOF motions for SWATH ships

To develop marine simulators of Small Waterplane Area Twin Hull (SWATH) ships and gain a better understanding of the maneuverability of the SWATH, a mathematical model with five Degree of Freedom (DOF) for SWATH has been established, in which the surge, sway, yaw, roll and pitch motions are all considered. The characteristics of the SWATH ship form and the hydrodynamic interaction among the twin bodies, twin propellers and twin rudders are taken into consideration on the basis of the three DOF maneuvering mathematical model. To verify the effectiveness of the modeling and ensure the use of the model in marine handling simulators, a detailed model is tentatively established on the basis of empirical formulas. Based on the acquired results, tests were performed to simulate the steady turning and zigzag motions of the ship. The results are in accordance with regular pattern and trend of motion of SWATH ships. This verifies the effectiveness of the mathematical model of the turning movement.

A new shock factor of SWATH catamaran subjected to underwater explosion

In order to measure the extreme degree of the impact environment on a SWATH (small waterplane area twin hull) catamaran subjected to an underwater explosion, this work defines a new type of shock factor based on shock wave energy. This new shock factor is used as a parameter to describe the response from this kind of ship, and it is divided into two categories according to characteristics of the SWATH catamaran structure. This research used finite element software to simulate and calculate the response of SWATH catamaran subjected to an underwater explosion. The validity of this new shock factor is proved in three categories, including total kinetic energy, total strain energy and shock spectrum. The results show that the responses of the SWATH catamaran structure are similar when the new shock factor is equal, and it is also appropriate for situations involving short explosive distances.

Numerical investigation on seakeeping performance of SWATH with Three Dimensional Translating-pulsating Source Green Function

The seakeeping performance of Small Waterplane Area Twin Hull (SWATH) was investigated by the boundary element method based on the Three Dimensional Translating-pulsating Source Green Function (3DTP). Some factors that differ from conventional monohull ships, but may have great influence on SWATH were included in the equations of motion, namely the hydrodynamic interaction between the twin hulls, the viscous damping and the effect of stabilizing fins. Numerical simulations have been carried out to predict the wave loads and motions of several SWATH vehicles. The present method has been validated by comparison with both the strip theory formulation (STF) method and the experiment. The result indicates that the predictions of heave responses from both numerical methods agrees well with that of the experiment at different forward speed, while the discrepancies between numerical methods and the experiment are much more pronounced at pitch motions. Generally, the motions are better predicted by the present method based on 3DTP than by the STF method, particularly for pitch motion.

A modified BLISCO method and its combination with variable fidelity metamodel for engineering design

Purpose – The purpose of this paper is to present a modified bi-level integrated system collaborative optimization (BLISCO) to avoid the non-separability of the original BLISCO. Besides, to mitigate the computational burden caused by expensive simulation codes and employ both efficiently simplified and expensively detailed information in multidisciplinary design optimization (MDO), an effective framework combining variable fidelity metamodels (VFM) and modified BLISCO (MBLISCO) (VFM-MBLISCO) is proposed. Design/methodology/approach – The concept of the quasi-separable MDO problems is introduced to limit range of applicability about the BLISCO method and then based on the quasi-separable MDO form, the modification of BLISCO method without any derivatives is presented to solve the problems of BLISCO. Besides, an effective framework combining VFM-MBLISCO is presented. Findings – One mathematical problem conforms to the quasi-separable MDO form is tested and the overall results illustrate the feasibility and robustness of the MBLISCO. The design of a Small Waterplane Area Twin Hull catamaran demonstrates that the proposed VFM-MBLISCO framework is a feasible and efficient design methodology in support of design of engineering products. Practical implications – The proposed approach exhibits great capability for MDO problems with tremendous computational costs. Originality/value – A MBLISCO is proposed which can avoid the non-separability of the original BLISCO and an effective framework combining VFM-MBLISCO is presented to efficiently integrate the different fidelities information in MDO.

The numerical simulation of a towing cylinder based on immersed body boundary method

An immersed body boundary method is adopted to track the motions of a towing cylinder, and a homogenous multiphase Eulerian-Eulerian fluid approach is used to capture the free surface. The Reynolds average Navier-Stockes (RANS) solver is applied to all gird nodes to deal with different velocities of the nodes that are in the body boundary, near the boundary and out of the boundary and their effect on the fluid. The towing cylinder resistance at different submerged depths in the tank is presented. The simulation results are compared with the experimental data, and the method is verified and validated. Finally, the hydrodynamic characters of the cylinder are discussed further. The numerical and experimental results show that at high speeds, the deeper the cylinder submerges, the lower resistance it suffers. The resistance coefficient trough is obtained at Froude number in the range of 0.3 < Fr < 0.4. These phenomena can provide some suggestions on the small waterplane area twin hull (SWATH) design.

SWATH- A new concept for the Safety and Security at Sea

SWATH means Small Waterplane Area Twin Hull and is guarantor for excellent sea keeping behaviour.The basis of this ship type was born in the 1960’s and 70’s when semi-submersible vessels were introduced to the offshore market. Naval architects developed these vessels further and it was used as navy test craft, pilot tender, yachts, passenger boats etc.The German Shipyard Abeking &amp; Rasmussen has more than 100 year of experience in innovative ships and designs. Since 1999 more than 20 SWATH vessels like pilot tender, pilot station vessel, explorer yacht, wind park maintenance tender, offshore patrol vessels and a hydrographical research vessel were built.This paper should give an insight to the SWATH technology and the implementation in the market. Different applications and ideas will be shown. Whatever you need - a navy ship, a workboat, a multipurpose platform a ferry or a yacht – there are many possibilities.

Numerical and experimental studies on hydrodynamic performance of a small-waterplane-area-twin-hull (SWATH) vehicle with inclined struts

A small-waterplane-area-twin-hull (SWATH) vehicle with inclined struts was investigated by numerical and experimental methods. Seakeeping performance was studied firstly based on the STF (Salvesen, N., Tuck, E. O. and Faltinsen, O. M. (1970). Ship motions and sea loads. Transactions–Society of Naval Architects and Marine Engineers. No. 78:250–287) strip theory. Results show that the inclined struts demonstrates improved seakeeping performances by comparison with a vertical-strut SWATH and an NPL (National Physical Laboratory) catamaran. 3D numerical simulations adopting an RANS method and model tests in the towing tank were carried out both in calm water and in regular waves. Numerical simulations have been validated by comparison with laborotary tests. As negative added resistance has been observed both in the model tests and in the numerical simulations, it can be concluded that the inclined struts, which could make use of wave energy, can give rise to a reduction of power required in waves.

Determination of the wind heeling moment for the small waterplane area twin hull ship

Determination of the wind heeling moment for the small waterplane area twin hull ship

A new methodology for multi-objective multidisciplinary design optimization problems based on game theory

The design of engineering systems often involves multiple disciplines and competing objectives, which requires coordination, information exchange and share amongst the disciplines. However, in practical design environments, designers have to make decisions in isolation due to organization barriers, time schedules and geographical constraints. This paper will propose a new approach for the multi-objective multidisciplinary design optimization (MDO) problems in non-cooperative environments based on gene expression programming (GEP) and Nash equilibrium in the game theory. In this approach, the GEP method is used as a surrogate to construct the approximate rational reaction sets (RRSs) in the Nash model. The effectiveness of the proposed method is demonstrated by the design of a thin-walled pressure vessel and the hull form parameter design of a small waterplane area twin hull (SWATH) ship. The results show that this approach can fully explore and provide the explicit functional relationship between the strategy of an isolated player and the control variables of the other players, thus able to obtain a better Nash equilibrium solution.

Characterization and System Identification of an Unmanned Amphibious Tracked Vehicle

Experimental testing of an unmanned amphibious tracked vehicle on dry sand, in the surfzone and in water, has been performed to explore its maneuvering and performance characteristics for the planned future development of an automatic control system. The 2.69-m-long, 295-kg concept vehicle utilizes a small waterplane area twin hull (SWATH) configuration with integrated crawler tracks and twin propellers for propulsion. Maximum traversable incline tests on dry sand reveal that the vehicle has a drawbar pull (DP) of about 1000 N (about one third of its weight) and can operate on slopes of 15 ° briefly and 10 ° for extended periods of time. Maneuvering tests were performed on flat, dry sand, as well as into and out of a surfzone at a beach site with inclines ranging from about 3 ° to 6 ° . In each of the tests, the track forces, speed over ground, and both linear and rotational accelerations were measured. Also recorded were environmental conditions, such as wind speed, significant waveheight/period, and ground slope. The tests reveal that the vehicle has a maximum straight-line flat ground speed of about 2 m/s, a minimum flat ground turning radius of 2.4 m, an in-water minimum turning radius of 1.9 m, and a maximum straight-line waterborne speed of 1.2 m/s. It is also shown that system identification applied to the data recorded from the flat ground and waterborne maneuvering tests can be used to find a linear, parametric state-space model for the vehicle that adequately reproduces its motion. Land-to-sea transition tests in two different seas of one-third significant waveheights of 8 and 28 cm (both measured at a distance of 6 m from the mean waterline on the beach) show that the vehicle exhibits substantial track slip as it traverses into the surfzone and its weight becomes increasingly supported by the displacement of its hulls. The tractive force model developed by Wong (Theory of Ground Vehicles, New York, NY, USA: Wiley, 2001) is modified to account for the reduction in track-supported vehicle weight as the vehicle becomes waterborne. It is shown that this adapted model captures the main physical features of the measured track forces. The waveheights and periods recorded during surfzone transition tests are used to examine the seakeeping properties of the vehicle. It is found that the vehicle's natural frequency of roll is near the dominant wave frequencies measured. A Froude-Krylov strip theory simulation shows that the wave forces acting on the vehicle in 28-cm waves may be slightly larger than the force measured on each track when the DUKW-Ling is crossing the transition zone between the beach and surfzone and should not be ignored in modeling and simulation studies.

Underwater image bidirectional matching for localization based on SIFT

For the purpose of identifying the stern of the SWATH (Small Waterplane Area Twin Hull) availably and perfecting the detection technique of the SWATH ship’s performance, this paper presents a novel bidirectional image registration strategy and mosaicing technique based on the scale invariant feature transform (SIFT) algorithm. The proposed method can help us observe the stern with a great visual angle for analyzing the performance of the control fins of the SWATH. SIFT is one of the most effective local features of the scale, rotation and illumination invariant. However, there are a few false match rates in this algorithm. In terms of underwater machine vision, only by acquiring an accurate match rate can we find an underwater robot rapidly and identify the location of the object. Therefore, firstly, the selection of the match ratio principle is put forward in this paper; secondly, some advantages of the bidirectional registration algorithm are concluded by analyzing the characteristics of the unidirectional matching method. Finally, an automatic underwater image splicing method is proposed on the basis of fixed dimension, and then the edge of the image’s overlapping section is merged by the principal components analysis algorithm. The experimental results achieve a better registration and smooth mosaicing effect, demonstrating that the proposed method is effective.

Mathematical model of small water-plane area twin-hull and application in marine simulator

Small water-plane area twin-hull (SWATH) has drawn the attention of many researchers due to its good sea-keeping ability. In this paper, MMG’s idea of separation was used to perform SWATH movement modeling and simulation; respectively the forces and moment of SWATH were divided into bare hull, propeller, rudder at the fluid hydrodynamics, etc. Wake coefficient at the propellers which reduces thrust coefficient, and rudder mutual interference forces among the hull and propeller, for the calculation of SWATH, were all considered. The fourth-order Runge-Kutta method of integration was used by solving differential equations, in order to get SWATH’s movement states. As an example, a turning test at full speed and full starboard rudder of ‘Seagull’ craft is shown. The simulation results show the SWATH’s regular pattern and trend of motion. It verifies the correctness of the mathematical model of the turning movement. The SWATH’s mathematical model is applied to marine simulator in order to train the pilots or seamen, or safety assessment for ocean engineering project. Lastly, the full mission navigation simulating system (FMNSS) was determined to be a successful virtual reality technology application sample in the field of navigation simulation.

Historical perspective on the structural design of special ships and the evolution of structural design methods

Recent decades of ship design and construction have produced numerous examples of innovative and special-purpose hull forms, structures, speeds, size and complexity. These include progressively larger container ships, ultra-large crude carriers and cruise vessels, liquefied natural gas (LNG) carriers, high-speed catamarans, small-waterplane-area twin-hull (SWATH) vessels, trimarans and others. The geometries, structural topologies and materials required for these vessels did not fit well with traditional design methods and procedures, rooted in empirical approaches. Instead, these ships and their structures required some form of direct analysis or first-principles approach, which by its nature is computer based. The ship design and design approval community responded to this new set of requirements by developing and implementing new procedures, new methods and new technologies to adequately address the need for first principles in the design. This design methodology innovation in turn placed new and significant demands on the state of the design software environment under which the new methods and procedures were being developed. This paper traces some of the innovative ship types that have evolved over recent decades and the associated computer-based structural design technology evolution during this time. In particular, the innovations of Professor Owen Hughes in establishing a first-principles approach to ship structural design, documenting the theoretical basis for this approach in the textbook Ship Structural Design: A Rationally-Based, Computer-Aided, Optimization Approach, and developing the MAESTRO computer-based implementation of the methodology are presented

Determination of the main characteristics of the small waterplane area twin hull ships at the initial stage of design

Abstract The basic selecting peculiarities of the optimal project characteristics of the small waterplane area twin hull ships compared to conventional ships are considered. The description of the mathematical model and the ship operating model is given. The choice of the optimization method is justified.

Field operation of a robotic small waterplane area twin hull boat for shallow‐water bathymetric characterization

AbstractAn innovative robotic boat has been developed for performing bathymetric mapping of very shallow coastal, estuarine, and inland waters. The boat uses a small waterplane area twin hull design to provide natural platform stability for a multibeam sonar payload, and a navigation system automatically guides the boat in a “lawn‐mowing” pattern to map a region of interest. Developed in stages over five years as part of a low‐cost student design program, the boat is now operational and is being used to generate science‐quality maps for scientific and civil use; it is also being used as a testbed for evaluating the platform for other types of scientific missions and for demonstrating advanced control techniques. This paper reviews the student‐based development process, describes the design of the boat, presents results from field operations, and reviews plans for future extensions to the system. © 2012 Wiley Periodicals, Inc.